Revert "Add Basilisk"

This reverts commit e72ef92b5bdc43cd2584198e2e54e951b70299e8.

1 files changed, 0 insertions, 4929 deletions

diff --git a/application/basilisk/components/sessionstore/SessionStore.jsm b/application/basilisk/components/sessionstore/SessionStore.jsm
deleted file mode 100644
index c583d534d2..0000000000
--- a/application/basilisk/components/sessionstore/SessionStore.jsm
+++ /dev/null
@@ -1,4929 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this file,
- * You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-"use strict";
-
-this.EXPORTED_SYMBOLS = ["SessionStore"];
-
-const Cu = Components.utils;
-const Cc = Components.classes;
-const Ci = Components.interfaces;
-const Cr = Components.results;
-
-// Current version of the format used by Session Restore.
-const FORMAT_VERSION = 1;
-
-const TAB_STATE_NEEDS_RESTORE = 1;
-const TAB_STATE_RESTORING = 2;
-const TAB_STATE_WILL_RESTORE = 3;
-
-// A new window has just been restored. At this stage, tabs are generally
-// not restored.
-const NOTIFY_SINGLE_WINDOW_RESTORED = "sessionstore-single-window-restored";
-const NOTIFY_WINDOWS_RESTORED = "sessionstore-windows-restored";
-const NOTIFY_BROWSER_STATE_RESTORED = "sessionstore-browser-state-restored";
-const NOTIFY_LAST_SESSION_CLEARED = "sessionstore-last-session-cleared";
-const NOTIFY_RESTORING_ON_STARTUP = "sessionstore-restoring-on-startup";
-const NOTIFY_INITIATING_MANUAL_RESTORE = "sessionstore-initiating-manual-restore";
-const NOTIFY_CLOSED_OBJECTS_CHANGED = "sessionstore-closed-objects-changed";
-
-const NOTIFY_TAB_RESTORED = "sessionstore-debug-tab-restored"; // WARNING: debug-only
-
-// Maximum number of tabs to restore simultaneously. Previously controlled by
-// the browser.sessionstore.max_concurrent_tabs pref.
-const MAX_CONCURRENT_TAB_RESTORES = 3;
-
-// Amount (in CSS px) by which we allow window edges to be off-screen
-// when restoring a window, before we override the saved position to
-// pull the window back within the available screen area.
-const SCREEN_EDGE_SLOP = 8;
-
-// global notifications observed
-const OBSERVING = [
-  "browser-window-before-show", "domwindowclosed",
-  "quit-application-granted", "browser-lastwindow-close-granted",
-  "quit-application", "browser:purge-session-history",
-  "browser:purge-domain-data",
-  "idle-daily",
-];
-
-// XUL Window properties to (re)store
-// Restored in restoreDimensions()
-const WINDOW_ATTRIBUTES = ["width", "height", "screenX", "screenY", "sizemode"];
-
-// Hideable window features to (re)store
-// Restored in restoreWindowFeatures()
-const WINDOW_HIDEABLE_FEATURES = [
-  "menubar", "toolbar", "locationbar", "personalbar", "statusbar", "scrollbars"
-];
-
-// Messages that will be received via the Frame Message Manager.
-const MESSAGES = [
-  // The content script sends us data that has been invalidated and needs to
-  // be saved to disk.
-  "SessionStore:update",
-
-  // The restoreHistory code has run. This is a good time to run SSTabRestoring.
-  "SessionStore:restoreHistoryComplete",
-
-  // The load for the restoring tab has begun. We update the URL bar at this
-  // time; if we did it before, the load would overwrite it.
-  "SessionStore:restoreTabContentStarted",
-
-  // All network loads for a restoring tab are done, so we should
-  // consider restoring another tab in the queue. The document has
-  // been restored, and forms have been filled. We trigger
-  // SSTabRestored at this time.
-  "SessionStore:restoreTabContentComplete",
-
-  // A crashed tab was revived by navigating to a different page. Remove its
-  // browser from the list of crashed browsers to stop ignoring its messages.
-  "SessionStore:crashedTabRevived",
-
-  // The content script encountered an error.
-  "SessionStore:error",
-];
-
-// The list of messages we accept from <xul:browser>s that have no tab
-// assigned, or whose windows have gone away. Those are for example the
-// ones that preload about:newtab pages, or from browsers where the window
-// has just been closed.
-const NOTAB_MESSAGES = new Set([
-  // For a description see above.
-  "SessionStore:crashedTabRevived",
-
-  // For a description see above.
-  "SessionStore:update",
-
-  // For a description see above.
-  "SessionStore:error",
-]);
-
-// The list of messages we accept without an "epoch" parameter.
-// See getCurrentEpoch() and friends to find out what an "epoch" is.
-const NOEPOCH_MESSAGES = new Set([
-  // For a description see above.
-  "SessionStore:crashedTabRevived",
-
-  // For a description see above.
-  "SessionStore:error",
-]);
-
-// The list of messages we want to receive even during the short period after a
-// frame has been removed from the DOM and before its frame script has finished
-// unloading.
-const CLOSED_MESSAGES = new Set([
-  // For a description see above.
-  "SessionStore:crashedTabRevived",
-
-  // For a description see above.
-  "SessionStore:update",
-
-  // For a description see above.
-  "SessionStore:error",
-]);
-
-// These are tab events that we listen to.
-const TAB_EVENTS = [
-  "TabOpen", "TabBrowserInserted", "TabClose", "TabSelect", "TabShow", "TabHide", "TabPinned",
-  "TabUnpinned"
-];
-
-const NS_XUL = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
-
-Cu.import("resource://gre/modules/PrivateBrowsingUtils.jsm", this);
-Cu.import("resource://gre/modules/Promise.jsm", this);
-Cu.import("resource://gre/modules/Services.jsm", this);
-Cu.import("resource://gre/modules/Task.jsm", this);
-Cu.import("resource://gre/modules/TelemetryStopwatch.jsm", this);
-Cu.import("resource://gre/modules/TelemetryTimestamps.jsm", this);
-Cu.import("resource://gre/modules/Timer.jsm", this);
-Cu.import("resource://gre/modules/XPCOMUtils.jsm", this);
-Cu.import("resource://gre/modules/debug.js", this);
-Cu.import("resource://gre/modules/osfile.jsm", this);
-
-XPCOMUtils.defineLazyServiceGetter(this, "gSessionStartup",
-  "@mozilla.org/browser/sessionstartup;1", "nsISessionStartup");
-XPCOMUtils.defineLazyServiceGetter(this, "gScreenManager",
-  "@mozilla.org/gfx/screenmanager;1", "nsIScreenManager");
-XPCOMUtils.defineLazyServiceGetter(this, "Telemetry",
-  "@mozilla.org/base/telemetry;1", "nsITelemetry");
-XPCOMUtils.defineLazyModuleGetter(this, "console",
-  "resource://gre/modules/Console.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "RecentWindow",
-  "resource:///modules/RecentWindow.jsm");
-
-XPCOMUtils.defineLazyModuleGetter(this, "GlobalState",
-  "resource:///modules/sessionstore/GlobalState.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "PrivacyFilter",
-  "resource:///modules/sessionstore/PrivacyFilter.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "RunState",
-  "resource:///modules/sessionstore/RunState.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "ScratchpadManager",
-  "resource://devtools/client/scratchpad/scratchpad-manager.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "SessionSaver",
-  "resource:///modules/sessionstore/SessionSaver.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "SessionCookies",
-  "resource:///modules/sessionstore/SessionCookies.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "SessionFile",
-  "resource:///modules/sessionstore/SessionFile.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "setTimeout",
-  "resource://gre/modules/Timer.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "TabAttributes",
-  "resource:///modules/sessionstore/TabAttributes.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "TabCrashHandler",
-  "resource:///modules/ContentCrashHandlers.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "TabState",
-  "resource:///modules/sessionstore/TabState.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "TabStateCache",
-  "resource:///modules/sessionstore/TabStateCache.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "TabStateFlusher",
-  "resource:///modules/sessionstore/TabStateFlusher.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "Utils",
-  "resource://gre/modules/sessionstore/Utils.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "ViewSourceBrowser",
-  "resource://gre/modules/ViewSourceBrowser.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "AsyncShutdown",
-  "resource://gre/modules/AsyncShutdown.jsm");
-
-Object.defineProperty(this, "HUDService", {
-  get: function HUDService_getter() {
-    let devtools = Cu.import("resource://devtools/shared/Loader.jsm", {}).devtools;
-    return devtools.require("devtools/client/webconsole/hudservice").HUDService;
-  },
-  configurable: true,
-  enumerable: true
-});
-
-/**
- * |true| if we are in debug mode, |false| otherwise.
- * Debug mode is controlled by preference browser.sessionstore.debug
- */
-var gDebuggingEnabled = false;
-function debug(aMsg) {
-  if (gDebuggingEnabled) {
-    aMsg = ("SessionStore: " + aMsg).replace(/\S{80}/g, "$&\n");
-    Services.console.logStringMessage(aMsg);
-  }
-}
-
-this.SessionStore = {
-  get promiseInitialized() {
-    return SessionStoreInternal.promiseInitialized;
-  },
-
-  get canRestoreLastSession() {
-    return SessionStoreInternal.canRestoreLastSession;
-  },
-
-  set canRestoreLastSession(val) {
-    SessionStoreInternal.canRestoreLastSession = val;
-  },
-
-  get lastClosedObjectType() {
-    return SessionStoreInternal.lastClosedObjectType;
-  },
-
-  init: function ss_init() {
-    SessionStoreInternal.init();
-  },
-
-  getBrowserState: function ss_getBrowserState() {
-    return SessionStoreInternal.getBrowserState();
-  },
-
-  setBrowserState: function ss_setBrowserState(aState) {
-    SessionStoreInternal.setBrowserState(aState);
-  },
-
-  getWindowState: function ss_getWindowState(aWindow) {
-    return SessionStoreInternal.getWindowState(aWindow);
-  },
-
-  setWindowState: function ss_setWindowState(aWindow, aState, aOverwrite) {
-    SessionStoreInternal.setWindowState(aWindow, aState, aOverwrite);
-  },
-
-  getTabState: function ss_getTabState(aTab) {
-    return SessionStoreInternal.getTabState(aTab);
-  },
-
-  setTabState: function ss_setTabState(aTab, aState) {
-    SessionStoreInternal.setTabState(aTab, aState);
-  },
-
-  duplicateTab: function ss_duplicateTab(aWindow, aTab, aDelta = 0, aRestoreImmediately = true) {
-    return SessionStoreInternal.duplicateTab(aWindow, aTab, aDelta, aRestoreImmediately);
-  },
-
-  getClosedTabCount: function ss_getClosedTabCount(aWindow) {
-    return SessionStoreInternal.getClosedTabCount(aWindow);
-  },
-
-  getClosedTabData: function ss_getClosedTabData(aWindow, aAsString = true) {
-    return SessionStoreInternal.getClosedTabData(aWindow, aAsString);
-  },
-
-  undoCloseTab: function ss_undoCloseTab(aWindow, aIndex) {
-    return SessionStoreInternal.undoCloseTab(aWindow, aIndex);
-  },
-
-  forgetClosedTab: function ss_forgetClosedTab(aWindow, aIndex) {
-    return SessionStoreInternal.forgetClosedTab(aWindow, aIndex);
-  },
-
-  getClosedWindowCount: function ss_getClosedWindowCount() {
-    return SessionStoreInternal.getClosedWindowCount();
-  },
-
-  getClosedWindowData: function ss_getClosedWindowData(aAsString = true) {
-    return SessionStoreInternal.getClosedWindowData(aAsString);
-  },
-
-  undoCloseWindow: function ss_undoCloseWindow(aIndex) {
-    return SessionStoreInternal.undoCloseWindow(aIndex);
-  },
-
-  forgetClosedWindow: function ss_forgetClosedWindow(aIndex) {
-    return SessionStoreInternal.forgetClosedWindow(aIndex);
-  },
-
-  getWindowValue: function ss_getWindowValue(aWindow, aKey) {
-    return SessionStoreInternal.getWindowValue(aWindow, aKey);
-  },
-
-  setWindowValue: function ss_setWindowValue(aWindow, aKey, aStringValue) {
-    SessionStoreInternal.setWindowValue(aWindow, aKey, aStringValue);
-  },
-
-  deleteWindowValue: function ss_deleteWindowValue(aWindow, aKey) {
-    SessionStoreInternal.deleteWindowValue(aWindow, aKey);
-  },
-
-  getTabValue: function ss_getTabValue(aTab, aKey) {
-    return SessionStoreInternal.getTabValue(aTab, aKey);
-  },
-
-  setTabValue: function ss_setTabValue(aTab, aKey, aStringValue) {
-    SessionStoreInternal.setTabValue(aTab, aKey, aStringValue);
-  },
-
-  deleteTabValue: function ss_deleteTabValue(aTab, aKey) {
-    SessionStoreInternal.deleteTabValue(aTab, aKey);
-  },
-
-  getGlobalValue: function ss_getGlobalValue(aKey) {
-    return SessionStoreInternal.getGlobalValue(aKey);
-  },
-
-  setGlobalValue: function ss_setGlobalValue(aKey, aStringValue) {
-    SessionStoreInternal.setGlobalValue(aKey, aStringValue);
-  },
-
-  deleteGlobalValue: function ss_deleteGlobalValue(aKey) {
-    SessionStoreInternal.deleteGlobalValue(aKey);
-  },
-
-  persistTabAttribute: function ss_persistTabAttribute(aName) {
-    SessionStoreInternal.persistTabAttribute(aName);
-  },
-
-  restoreLastSession: function ss_restoreLastSession() {
-    SessionStoreInternal.restoreLastSession();
-  },
-
-  getCurrentState: function (aUpdateAll) {
-    return SessionStoreInternal.getCurrentState(aUpdateAll);
-  },
-
-  reviveCrashedTab(aTab) {
-    return SessionStoreInternal.reviveCrashedTab(aTab);
-  },
-
-  reviveAllCrashedTabs() {
-    return SessionStoreInternal.reviveAllCrashedTabs();
-  },
-
-  navigateAndRestore(tab, loadArguments, historyIndex) {
-    return SessionStoreInternal.navigateAndRestore(tab, loadArguments, historyIndex);
-  },
-
-  getSessionHistory(tab, updatedCallback) {
-    return SessionStoreInternal.getSessionHistory(tab, updatedCallback);
-  },
-
-  undoCloseById(aClosedId) {
-    return SessionStoreInternal.undoCloseById(aClosedId);
-  },
-
-  /**
-   * Determines whether the passed version number is compatible with
-   * the current version number of the SessionStore.
-   *
-   * @param version The format and version of the file, as an array, e.g.
-   * ["sessionrestore", 1]
-   */
-  isFormatVersionCompatible(version) {
-    if (!version) {
-      return false;
-    }
-    if (!Array.isArray(version)) {
-      // Improper format.
-      return false;
-    }
-    if (version[0] != "sessionrestore") {
-      // Not a Session Restore file.
-      return false;
-    }
-    let number = Number.parseFloat(version[1]);
-    if (Number.isNaN(number)) {
-      return false;
-    }
-    return number <= FORMAT_VERSION;
-  },
-
-  /**
-   * Filters out not worth-saving tabs from a given browser state object.
-   *
-   * @param aState (object)
-   *        The browser state for which we remove worth-saving tabs.
-   *        The given object will be modified.
-   */
-  keepOnlyWorthSavingTabs: function (aState) {
-    for (let i = aState.windows.length - 1; i >= 0; i--) {
-      let win = aState.windows[i];
-      for (let j = win.tabs.length - 1; j >= 0; j--) {
-        let tab = win.tabs[j];
-        if (!SessionStoreInternal._shouldSaveTab(tab)) {
-          win.tabs.splice(j, 1);
-          if (win.selected > j) {
-            win.selected--;
-          }
-        }
-      }
-      if (!win.tabs.length) {
-        aState.windows.splice(i, 1);
-        if (aState.selectedWindow > i) {
-          aState.selectedWindow--;
-        }
-      }
-    }
-  },
-};
-
-// Freeze the SessionStore object. We don't want anyone to modify it.
-Object.freeze(SessionStore);
-
-var SessionStoreInternal = {
-  QueryInterface: XPCOMUtils.generateQI([
-    Ci.nsIDOMEventListener,
-    Ci.nsIObserver,
-    Ci.nsISupportsWeakReference
-  ]),
-
-  _globalState: new GlobalState(),
-
-  // A counter to be used to generate a unique ID for each closed tab or window.
-  _nextClosedId: 0,
-
-  // During the initial restore and setBrowserState calls tracks the number of
-  // windows yet to be restored
-  _restoreCount: -1,
-
-  // For each <browser> element, records the current epoch.
-  _browserEpochs: new WeakMap(),
-
-  // Any browsers that fires the oop-browser-crashed event gets stored in
-  // here - that way we know which browsers to ignore messages from (until
-  // they get restored).
-  _crashedBrowsers: new WeakSet(),
-
-  // A map (xul:browser -> nsIFrameLoader) that maps a browser to the last
-  // associated frameLoader we heard about.
-  _lastKnownFrameLoader: new WeakMap(),
-
-  // A map (xul:browser -> object) that maps a browser associated with a
-  // recently closed tab to all its necessary state information we need to
-  // properly handle final update message.
-  _closedTabs: new WeakMap(),
-
-  // A map (xul:browser -> object) that maps a browser associated with a
-  // recently closed tab due to a window closure to the tab state information
-  // that is being stored in _closedWindows for that tab.
-  _closedWindowTabs: new WeakMap(),
-
-  // A set of window data that has the potential to be saved in the _closedWindows
-  // array for the session. We will remove window data from this set whenever
-  // forgetClosedWindow is called for the window, or when session history is
-  // purged, so that we don't accidentally save that data after the flush has
-  // completed. Closed tabs use a more complicated mechanism for this particular
-  // problem. When forgetClosedTab is called, the browser is removed from the
-  // _closedTabs map, so its data is not recorded. In the purge history case,
-  // the closedTabs array per window is overwritten so that once the flush is
-  // complete, the tab would only ever add itself to an array that SessionStore
-  // no longer cares about. Bug 1230636 has been filed to make the tab case
-  // work more like the window case, which is more explicit, and easier to
-  // reason about.
-  _saveableClosedWindowData: new WeakSet(),
-
-  // A map (xul:browser -> object) that maps a browser that is switching
-  // remoteness via navigateAndRestore, to the loadArguments that were
-  // most recently passed when calling navigateAndRestore.
-  _remotenessChangingBrowsers: new WeakMap(),
-
-  // whether a setBrowserState call is in progress
-  _browserSetState: false,
-
-  // time in milliseconds when the session was started (saved across sessions),
-  // defaults to now if no session was restored or timestamp doesn't exist
-  _sessionStartTime: Date.now(),
-
-  // states for all currently opened windows
-  _windows: {},
-
-  // counter for creating unique window IDs
-  _nextWindowID: 0,
-
-  // states for all recently closed windows
-  _closedWindows: [],
-
-  // collection of session states yet to be restored
-  _statesToRestore: {},
-
-  // counts the number of crashes since the last clean start
-  _recentCrashes: 0,
-
-  // whether the last window was closed and should be restored
-  _restoreLastWindow: false,
-
-  // number of tabs currently restoring
-  _tabsRestoringCount: 0,
-
-  // When starting Firefox with a single private window, this is the place
-  // where we keep the session we actually wanted to restore in case the user
-  // decides to later open a non-private window as well.
-  _deferredInitialState: null,
-
-  // Keeps track of whether a notification needs to be sent that closed objects have changed.
-  _closedObjectsChanged: false,
-
-  // A promise resolved once initialization is complete
-  _deferredInitialized: (function () {
-    let deferred = {};
-
-    deferred.promise = new Promise((resolve, reject) => {
-      deferred.resolve = resolve;
-      deferred.reject = reject;
-    });
-
-    return deferred;
-  })(),
-
-  // Whether session has been initialized
-  _sessionInitialized: false,
-
-  // Promise that is resolved when we're ready to initialize
-  // and restore the session.
-  _promiseReadyForInitialization: null,
-
-  // Keep busy state counters per window.
-  _windowBusyStates: new WeakMap(),
-
-  /**
-   * A promise fulfilled once initialization is complete.
-   */
-  get promiseInitialized() {
-    return this._deferredInitialized.promise;
-  },
-
-  get canRestoreLastSession() {
-    return LastSession.canRestore;
-  },
-
-  set canRestoreLastSession(val) {
-    // Cheat a bit; only allow false.
-    if (!val) {
-      LastSession.clear();
-    }
-  },
-
-  /**
-   * Returns a string describing the last closed object, either "tab" or "window".
-   *
-   * This was added to support the sessions.restore WebExtensions API.
-   */
-  get lastClosedObjectType() {
-    if (this._closedWindows.length) {
-      // Since there are closed windows, we need to check if there's a closed tab
-      // in one of the currently open windows that was closed after the
-      // last-closed window.
-      let tabTimestamps = [];
-      let windowsEnum = Services.wm.getEnumerator("navigator:browser");
-      while (windowsEnum.hasMoreElements()) {
-        let window = windowsEnum.getNext();
-        let windowState = this._windows[window.__SSi];
-        if (windowState && windowState._closedTabs[0]) {
-          tabTimestamps.push(windowState._closedTabs[0].closedAt);
-        }
-      }
-      if (!tabTimestamps.length ||
-          (tabTimestamps.sort((a, b) => b - a)[0] < this._closedWindows[0].closedAt)) {
-        return "window";
-      }
-    }
-    return "tab";
-  },
-
-  /**
-   * Initialize the sessionstore service.
-   */
-  init: function () {
-    if (this._initialized) {
-      throw new Error("SessionStore.init() must only be called once!");
-    }
-
-    TelemetryTimestamps.add("sessionRestoreInitialized");
-    OBSERVING.forEach(function(aTopic) {
-      Services.obs.addObserver(this, aTopic, true);
-    }, this);
-
-    this._initPrefs();
-    this._initialized = true;
-  },
-
-  /**
-   * Initialize the session using the state provided by SessionStartup
-   */
-  initSession: function () {
-    TelemetryStopwatch.start("FX_SESSION_RESTORE_STARTUP_INIT_SESSION_MS");
-    let state;
-    let ss = gSessionStartup;
-
-    if (ss.doRestore() ||
-        ss.sessionType == Ci.nsISessionStartup.DEFER_SESSION) {
-      state = ss.state;
-    }
-
-    if (state) {
-      try {
-        // If we're doing a DEFERRED session, then we want to pull pinned tabs
-        // out so they can be restored.
-        if (ss.sessionType == Ci.nsISessionStartup.DEFER_SESSION) {
-          let [iniState, remainingState] = this._prepDataForDeferredRestore(state);
-          // If we have a iniState with windows, that means that we have windows
-          // with app tabs to restore.
-          if (iniState.windows.length)
-            state = iniState;
-          else
-            state = null;
-
-          if (remainingState.windows.length) {
-            LastSession.setState(remainingState);
-          }
-        }
-        else {
-          // Get the last deferred session in case the user still wants to
-          // restore it
-          LastSession.setState(state.lastSessionState);
-
-          if (ss.previousSessionCrashed) {
-            this._recentCrashes = (state.session &&
-                                   state.session.recentCrashes || 0) + 1;
-
-            if (this._needsRestorePage(state, this._recentCrashes)) {
-              // replace the crashed session with a restore-page-only session
-              let url = "about:sessionrestore";
-              let formdata = {id: {sessionData: state}, url};
-              let entry = {url, triggeringPrincipal_base64: Utils.SERIALIZED_SYSTEMPRINCIPAL };
-              state = { windows: [{ tabs: [{ entries: [entry], formdata }] }] };
-            } else if (this._hasSingleTabWithURL(state.windows,
-                                                 "about:welcomeback")) {
-              // On a single about:welcomeback URL that crashed, replace about:welcomeback
-              // with about:sessionrestore, to make clear to the user that we crashed.
-              state.windows[0].tabs[0].entries[0].url = "about:sessionrestore";
-              state.windows[0].tabs[0].entries[0].triggeringPrincipal_base64 = Utils.SERIALIZED_SYSTEMPRINCIPAL;
-            }
-          }
-
-          // Update the session start time using the restored session state.
-          this._updateSessionStartTime(state);
-
-          // make sure that at least the first window doesn't have anything hidden
-          delete state.windows[0].hidden;
-          // Since nothing is hidden in the first window, it cannot be a popup
-          delete state.windows[0].isPopup;
-          // We don't want to minimize and then open a window at startup.
-          if (state.windows[0].sizemode == "minimized")
-            state.windows[0].sizemode = "normal";
-          // clear any lastSessionWindowID attributes since those don't matter
-          // during normal restore
-          state.windows.forEach(function(aWindow) {
-            delete aWindow.__lastSessionWindowID;
-          });
-        }
-      }
-      catch (ex) { debug("The session file is invalid: " + ex); }
-    }
-
-    // at this point, we've as good as resumed the session, so we can
-    // clear the resume_session_once flag, if it's set
-    if (!RunState.isQuitting &&
-        this._prefBranch.getBoolPref("sessionstore.resume_session_once"))
-      this._prefBranch.setBoolPref("sessionstore.resume_session_once", false);
-
-    TelemetryStopwatch.finish("FX_SESSION_RESTORE_STARTUP_INIT_SESSION_MS");
-    return state;
-  },
-
-  _initPrefs : function() {
-    this._prefBranch = Services.prefs.getBranch("browser.");
-
-    gDebuggingEnabled = this._prefBranch.getBoolPref("sessionstore.debug");
-
-    Services.prefs.addObserver("browser.sessionstore.debug", () => {
-      gDebuggingEnabled = this._prefBranch.getBoolPref("sessionstore.debug");
-    }, false);
-
-    this._max_tabs_undo = this._prefBranch.getIntPref("sessionstore.max_tabs_undo");
-    this._prefBranch.addObserver("sessionstore.max_tabs_undo", this, true);
-
-    this._max_windows_undo = this._prefBranch.getIntPref("sessionstore.max_windows_undo");
-    this._prefBranch.addObserver("sessionstore.max_windows_undo", this, true);
-  },
-
-  /**
-   * Called on application shutdown, after notifications:
-   * quit-application-granted, quit-application
-   */
-  _uninit: function ssi_uninit() {
-    if (!this._initialized) {
-      throw new Error("SessionStore is not initialized.");
-    }
-
-    // Prepare to close the session file and write the last state.
-    RunState.setClosing();
-
-    // save all data for session resuming
-    if (this._sessionInitialized) {
-      SessionSaver.run();
-    }
-
-    // clear out priority queue in case it's still holding refs
-    TabRestoreQueue.reset();
-
-    // Make sure to cancel pending saves.
-    SessionSaver.cancel();
-  },
-
-  /**
-   * Handle notifications
-   */
-  observe: function ssi_observe(aSubject, aTopic, aData) {
-    switch (aTopic) {
-      case "browser-window-before-show": // catch new windows
-        this.onBeforeBrowserWindowShown(aSubject);
-        break;
-      case "domwindowclosed": // catch closed windows
-        this.onClose(aSubject).then(() => {
-          this._notifyOfClosedObjectsChange();
-        });
-        break;
-      case "quit-application-granted":
-        let syncShutdown = aData == "syncShutdown";
-        this.onQuitApplicationGranted(syncShutdown);
-        break;
-      case "browser-lastwindow-close-granted":
-        this.onLastWindowCloseGranted();
-        break;
-      case "quit-application":
-        this.onQuitApplication(aData);
-        break;
-      case "browser:purge-session-history": // catch sanitization
-        this.onPurgeSessionHistory();
-        this._notifyOfClosedObjectsChange();
-        break;
-      case "browser:purge-domain-data":
-        this.onPurgeDomainData(aData);
-        this._notifyOfClosedObjectsChange();
-        break;
-      case "nsPref:changed": // catch pref changes
-        this.onPrefChange(aData);
-        this._notifyOfClosedObjectsChange();
-        break;
-      case "idle-daily":
-        this.onIdleDaily();
-        this._notifyOfClosedObjectsChange();
-        break;
-    }
-  },
-
-  /**
-   * This method handles incoming messages sent by the session store content
-   * script via the Frame Message Manager or Parent Process Message Manager,
-   * and thus enables communication with OOP tabs.
-   */
-  receiveMessage(aMessage) {
-    // If we got here, that means we're dealing with a frame message
-    // manager message, so the target will be a <xul:browser>.
-    var browser = aMessage.target;
-    let win = browser.ownerGlobal;
-    let tab = win ? win.gBrowser.getTabForBrowser(browser) : null;
-
-    // Ensure we receive only specific messages from <xul:browser>s that
-    // have no tab or window assigned, e.g. the ones that preload
-    // about:newtab pages, or windows that have closed.
-    if (!tab && !NOTAB_MESSAGES.has(aMessage.name)) {
-      throw new Error(`received unexpected message '${aMessage.name}' ` +
-                      `from a browser that has no tab or window`);
-    }
-
-    let data = aMessage.data || {};
-    let hasEpoch = data.hasOwnProperty("epoch");
-
-    // Most messages sent by frame scripts require to pass an epoch.
-    if (!hasEpoch && !NOEPOCH_MESSAGES.has(aMessage.name)) {
-      throw new Error(`received message '${aMessage.name}' without an epoch`);
-    }
-
-    // Ignore messages from previous epochs.
-    if (hasEpoch && !this.isCurrentEpoch(browser, data.epoch)) {
-      return;
-    }
-
-    switch (aMessage.name) {
-      case "SessionStore:update":
-        // |browser.frameLoader| might be empty if the browser was already
-        // destroyed and its tab removed. In that case we still have the last
-        // frameLoader we know about to compare.
-        let frameLoader = browser.frameLoader ||
-                          this._lastKnownFrameLoader.get(browser.permanentKey);
-
-        // If the message isn't targeting the latest frameLoader discard it.
-        if (frameLoader != aMessage.targetFrameLoader) {
-          return;
-        }
-
-        if (aMessage.data.isFinal) {
-          // If this the final message we need to resolve all pending flush
-          // requests for the given browser as they might have been sent too
-          // late and will never respond. If they have been sent shortly after
-          // switching a browser's remoteness there isn't too much data to skip.
-          TabStateFlusher.resolveAll(browser);
-        } else if (aMessage.data.flushID) {
-          // This is an update kicked off by an async flush request. Notify the
-          // TabStateFlusher so that it can finish the request and notify its
-          // consumer that's waiting for the flush to be done.
-          TabStateFlusher.resolve(browser, aMessage.data.flushID);
-        }
-
-        // Ignore messages from <browser> elements that have crashed
-        // and not yet been revived.
-        if (this._crashedBrowsers.has(browser.permanentKey)) {
-          return;
-        }
-
-        // Record telemetry measurements done in the child and update the tab's
-        // cached state. Mark the window as dirty and trigger a delayed write.
-        this.recordTelemetry(aMessage.data.telemetry);
-        TabState.update(browser, aMessage.data);
-        this.saveStateDelayed(win);
-
-        // Handle any updates sent by the child after the tab was closed. This
-        // might be the final update as sent by the "unload" handler but also
-        // any async update message that was sent before the child unloaded.
-        if (this._closedTabs.has(browser.permanentKey)) {
-          let {closedTabs, tabData} = this._closedTabs.get(browser.permanentKey);
-
-          // Update the closed tab's state. This will be reflected in its
-          // window's list of closed tabs as that refers to the same object.
-          TabState.copyFromCache(browser, tabData.state);
-
-          // Is this the tab's final message?
-          if (aMessage.data.isFinal) {
-            // We expect no further updates.
-            this._closedTabs.delete(browser.permanentKey);
-            // The tab state no longer needs this reference.
-            delete tabData.permanentKey;
-
-            // Determine whether the tab state is worth saving.
-            let shouldSave = this._shouldSaveTabState(tabData.state);
-            let index = closedTabs.indexOf(tabData);
-
-            if (shouldSave && index == -1) {
-              // If the tab state is worth saving and we didn't push it onto
-              // the list of closed tabs when it was closed (because we deemed
-              // the state not worth saving) then add it to the window's list
-              // of closed tabs now.
-              this.saveClosedTabData(closedTabs, tabData);
-            } else if (!shouldSave && index > -1) {
-              // Remove from the list of closed tabs. The update messages sent
-              // after the tab was closed changed enough state so that we no
-              // longer consider its data interesting enough to keep around.
-              this.removeClosedTabData(closedTabs, index);
-            }
-          }
-        }
-        break;
-      case "SessionStore:restoreHistoryComplete":
-        // Notify the tabbrowser that the tab chrome has been restored.
-        let tabData = TabState.collect(tab);
-
-        // wall-paper fix for bug 439675: make sure that the URL to be loaded
-        // is always visible in the address bar if no other value is present
-        let activePageData = tabData.entries[tabData.index - 1] || null;
-        let uri = activePageData ? activePageData.url || null : null;
-        // NB: we won't set initial URIs (about:home, about:newtab, etc.) here
-        // because their load will not normally trigger a location bar clearing
-        // when they finish loading (to avoid race conditions where we then
-        // clear user input instead), so we shouldn't set them here either.
-        // They also don't fall under the issues in bug 439675 where user input
-        // needs to be preserved if the load doesn't succeed.
-        // We also don't do this for remoteness updates, where it should not
-        // be necessary.
-        if (!browser.userTypedValue && uri && !data.isRemotenessUpdate &&
-            !win.gInitialPages.includes(uri)) {
-          browser.userTypedValue = uri;
-        }
-
-        // If the page has a title, set it.
-        if (activePageData) {
-          if (activePageData.title) {
-            tab.label = activePageData.title;
-          } else if (activePageData.url != "about:blank") {
-            tab.label = activePageData.url;
-          }
-        } else if (tab.hasAttribute("customizemode")) {
-          win.gCustomizeMode.setTab(tab);
-        }
-
-        // Restore the tab icon.
-        if ("image" in tabData) {
-          // Use the serialized contentPrincipal with the new icon load.
-          let loadingPrincipal = Utils.deserializePrincipal(tabData.iconLoadingPrincipal);
-          win.gBrowser.setIcon(tab, tabData.image, loadingPrincipal);
-          TabStateCache.update(browser, { image: null, iconLoadingPrincipal: null });
-        }
-
-        let event = win.document.createEvent("Events");
-        event.initEvent("SSTabRestoring", true, false);
-        tab.dispatchEvent(event);
-        break;
-      case "SessionStore:restoreTabContentStarted":
-        if (browser.__SS_restoreState == TAB_STATE_NEEDS_RESTORE) {
-          // If a load not initiated by sessionstore was started in a
-          // previously pending tab. Mark the tab as no longer pending.
-          this.markTabAsRestoring(tab);
-        } else if (!data.isRemotenessUpdate) {
-          // If the user was typing into the URL bar when we crashed, but hadn't hit
-          // enter yet, then we just need to write that value to the URL bar without
-          // loading anything. This must happen after the load, as the load will clear
-          // userTypedValue.
-          let tabData = TabState.collect(tab);
-          if (tabData.userTypedValue && !tabData.userTypedClear && !browser.userTypedValue) {
-            browser.userTypedValue = tabData.userTypedValue;
-            win.URLBarSetURI();
-          }
-
-          // Remove state we don't need any longer.
-          TabStateCache.update(browser, {
-            userTypedValue: null, userTypedClear: null
-          });
-        }
-        break;
-      case "SessionStore:restoreTabContentComplete":
-        // This callback is used exclusively by tests that want to
-        // monitor the progress of network loads.
-        if (gDebuggingEnabled) {
-          Services.obs.notifyObservers(browser, NOTIFY_TAB_RESTORED, null);
-        }
-
-        SessionStoreInternal._resetLocalTabRestoringState(tab);
-        SessionStoreInternal.restoreNextTab();
-
-        this._sendTabRestoredNotification(tab, data.isRemotenessUpdate);
-        break;
-      case "SessionStore:crashedTabRevived":
-        // The browser was revived by navigating to a different page
-        // manually, so we remove it from the ignored browser set.
-        this._crashedBrowsers.delete(browser.permanentKey);
-        break;
-      case "SessionStore:error":
-        this.reportInternalError(data);
-        TabStateFlusher.resolveAll(browser, false, "Received error from the content process");
-        break;
-      default:
-        throw new Error(`received unknown message '${aMessage.name}'`);
-        break;
-    }
-  },
-
-  /**
-   * Record telemetry measurements stored in an object.
-   * @param telemetry
-   *        {histogramID: value, ...} An object mapping histogramIDs to the
-   *        value to be recorded for that ID,
-   */
-  recordTelemetry: function (telemetry) {
-    for (let histogramId in telemetry){
-      Telemetry.getHistogramById(histogramId).add(telemetry[histogramId]);
-    }
-  },
-
-  /* ........ Window Event Handlers .............. */
-
-  /**
-   * Implement nsIDOMEventListener for handling various window and tab events
-   */
-  handleEvent: function ssi_handleEvent(aEvent) {
-    let win = aEvent.currentTarget.ownerGlobal;
-    let target = aEvent.originalTarget;
-    switch (aEvent.type) {
-      case "TabOpen":
-        this.onTabAdd(win);
-        break;
-      case "TabBrowserInserted":
-        this.onTabBrowserInserted(win, target);
-        break;
-      case "TabClose":
-        // `adoptedBy` will be set if the tab was closed because it is being
-        // moved to a new window.
-        if (!aEvent.detail.adoptedBy)
-          this.onTabClose(win, target);
-        this.onTabRemove(win, target);
-        this._notifyOfClosedObjectsChange();
-        break;
-      case "TabSelect":
-        this.onTabSelect(win);
-        break;
-      case "TabShow":
-        this.onTabShow(win, target);
-        break;
-      case "TabHide":
-        this.onTabHide(win, target);
-        break;
-      case "TabPinned":
-      case "TabUnpinned":
-      case "SwapDocShells":
-        this.saveStateDelayed(win);
-        break;
-      case "oop-browser-crashed":
-        this.onBrowserCrashed(target);
-        break;
-      case "XULFrameLoaderCreated":
-        if (target.namespaceURI == NS_XUL &&
-            target.localName == "browser" &&
-            target.frameLoader &&
-            target.permanentKey) {
-          this._lastKnownFrameLoader.set(target.permanentKey, target.frameLoader);
-          this.resetEpoch(target);
-        }
-        break;
-      case "BrowserWillChangeProcess":
-        let promise = TabStateFlusher.flush(target);
-        target.frameLoader.addProcessChangeBlockingPromise(promise);
-        break;
-      case "BrowserChangedProcess":
-        let newEpoch = 1 + Math.max(this.getCurrentEpoch(target),
-                                    this.getCurrentEpoch(aEvent.otherBrowser));
-        this.setCurrentEpoch(target, newEpoch);
-        target.messageManager.sendAsyncMessage("SessionStore:becomeActiveProcess", {
-          epoch: newEpoch
-        });
-        break;
-      default:
-        throw new Error(`unhandled event ${aEvent.type}?`);
-    }
-    this._clearRestoringWindows();
-  },
-
-  /**
-   * Generate a unique window identifier
-   * @return string
-   *         A unique string to identify a window
-   */
-  _generateWindowID: function ssi_generateWindowID() {
-    return "window" + (this._nextWindowID++);
-  },
-
-  /**
-   * Registers and tracks a given window.
-   *
-   * @param aWindow
-   *        Window reference
-   */
-  onLoad(aWindow) {
-    // return if window has already been initialized
-    if (aWindow && aWindow.__SSi && this._windows[aWindow.__SSi])
-      return;
-
-    // ignore windows opened while shutting down
-    if (RunState.isQuitting)
-      return;
-
-    // Assign the window a unique identifier we can use to reference
-    // internal data about the window.
-    aWindow.__SSi = this._generateWindowID();
-
-    let mm = aWindow.getGroupMessageManager("browsers");
-    MESSAGES.forEach(msg => {
-      let listenWhenClosed = CLOSED_MESSAGES.has(msg);
-      mm.addMessageListener(msg, this, listenWhenClosed);
-    });
-
-    // Load the frame script after registering listeners.
-    mm.loadFrameScript("chrome://browser/content/content-sessionStore.js", true);
-
-    // and create its data object
-    this._windows[aWindow.__SSi] = { tabs: [], selected: 0, _closedTabs: [], busy: false };
-
-    if (PrivateBrowsingUtils.isWindowPrivate(aWindow))
-      this._windows[aWindow.__SSi].isPrivate = true;
-    if (!this._isWindowLoaded(aWindow))
-      this._windows[aWindow.__SSi]._restoring = true;
-    if (!aWindow.toolbar.visible)
-      this._windows[aWindow.__SSi].isPopup = true;
-
-    let tabbrowser = aWindow.gBrowser;
-
-    // add tab change listeners to all already existing tabs
-    for (let i = 0; i < tabbrowser.tabs.length; i++) {
-      this.onTabBrowserInserted(aWindow, tabbrowser.tabs[i]);
-    }
-    // notification of tab add/remove/selection/show/hide
-    TAB_EVENTS.forEach(function(aEvent) {
-      tabbrowser.tabContainer.addEventListener(aEvent, this, true);
-    }, this);
-
-    // Keep track of a browser's latest frameLoader.
-    aWindow.gBrowser.addEventListener("XULFrameLoaderCreated", this);
-    aWindow.gBrowser.addEventListener("BrowserChangedProcess", this);
-    aWindow.gBrowser.addEventListener("BrowserWillChangeProcess", this);
-  },
-
-  /**
-   * Initializes a given window.
-   *
-   * Windows are registered as soon as they are created but we need to wait for
-   * the session file to load, and the initial window's delayed startup to
-   * finish before initializing a window, i.e. restoring data into it.
-   *
-   * @param aWindow
-   *        Window reference
-   * @param aInitialState
-   *        The initial state to be loaded after startup (optional)
-   */
-  initializeWindow(aWindow, aInitialState = null) {
-    let isPrivateWindow = PrivateBrowsingUtils.isWindowPrivate(aWindow);
-
-    // perform additional initialization when the first window is loading
-    if (RunState.isStopped) {
-      RunState.setRunning();
-
-      // restore a crashed session resp. resume the last session if requested
-      if (aInitialState) {
-        // Don't write to disk right after startup. Set the last time we wrote
-        // to disk to NOW() to enforce a full interval before the next write.
-        SessionSaver.updateLastSaveTime();
-
-        if (isPrivateWindow) {
-          // We're starting with a single private window. Save the state we
-          // actually wanted to restore so that we can do it later in case
-          // the user opens another, non-private window.
-          this._deferredInitialState = gSessionStartup.state;
-
-          // Nothing to restore now, notify observers things are complete.
-          Services.obs.notifyObservers(null, NOTIFY_WINDOWS_RESTORED, "");
-        } else {
-          TelemetryTimestamps.add("sessionRestoreRestoring");
-          this._restoreCount = aInitialState.windows ? aInitialState.windows.length : 0;
-
-          // global data must be restored before restoreWindow is called so that
-          // it happens before observers are notified
-          this._globalState.setFromState(aInitialState);
-
-          let overwrite = this._isCmdLineEmpty(aWindow, aInitialState);
-          let options = {firstWindow: true, overwriteTabs: overwrite};
-          this.restoreWindows(aWindow, aInitialState, options);
-        }
-      }
-      else {
-        // Nothing to restore, notify observers things are complete.
-        Services.obs.notifyObservers(null, NOTIFY_WINDOWS_RESTORED, "");
-      }
-    }
-    // this window was opened by _openWindowWithState
-    else if (!this._isWindowLoaded(aWindow)) {
-      let state = this._statesToRestore[aWindow.__SS_restoreID];
-      let options = {overwriteTabs: true, isFollowUp: state.windows.length == 1};
-      this.restoreWindow(aWindow, state.windows[0], options);
-    }
-    // The user opened another, non-private window after starting up with
-    // a single private one. Let's restore the session we actually wanted to
-    // restore at startup.
-    else if (this._deferredInitialState && !isPrivateWindow &&
-             aWindow.toolbar.visible) {
-
-      // global data must be restored before restoreWindow is called so that
-      // it happens before observers are notified
-      this._globalState.setFromState(this._deferredInitialState);
-
-      this._restoreCount = this._deferredInitialState.windows ?
-        this._deferredInitialState.windows.length : 0;
-      this.restoreWindows(aWindow, this._deferredInitialState, {firstWindow: true});
-      this._deferredInitialState = null;
-    }
-    else if (this._restoreLastWindow && aWindow.toolbar.visible &&
-             this._closedWindows.length && !isPrivateWindow) {
-
-      // default to the most-recently closed window
-      // don't use popup windows
-      let closedWindowState = null;
-      let closedWindowIndex;
-      for (let i = 0; i < this._closedWindows.length; i++) {
-        // Take the first non-popup, point our object at it, and break out.
-        if (!this._closedWindows[i].isPopup) {
-          closedWindowState = this._closedWindows[i];
-          closedWindowIndex = i;
-          break;
-        }
-      }
-
-      if (closedWindowState) {
-        let newWindowState;
-#ifdef XP_MACOSX
-        let isMacOS = true;
-#else
-        let isMacOS = false;
-#endif
-        if (isMacOS || !this._doResumeSession()) {
-          // We want to split the window up into pinned tabs and unpinned tabs.
-          // Pinned tabs should be restored. If there are any remaining tabs,
-          // they should be added back to _closedWindows.
-          // We'll cheat a little bit and reuse _prepDataForDeferredRestore
-          // even though it wasn't built exactly for this.
-          let [appTabsState, normalTabsState] =
-            this._prepDataForDeferredRestore({ windows: [closedWindowState] });
-
-          // These are our pinned tabs, which we should restore
-          if (appTabsState.windows.length) {
-            newWindowState = appTabsState.windows[0];
-            delete newWindowState.__lastSessionWindowID;
-          }
-
-          // In case there were no unpinned tabs, remove the window from _closedWindows
-          if (!normalTabsState.windows.length) {
-            this._removeClosedWindow(closedWindowIndex);
-          }
-          // Or update _closedWindows with the modified state
-          else {
-            delete normalTabsState.windows[0].__lastSessionWindowID;
-            this._closedWindows[closedWindowIndex] = normalTabsState.windows[0];
-          }
-        }
-        else {
-          // If we're just restoring the window, make sure it gets removed from
-          // _closedWindows.
-          this._removeClosedWindow(closedWindowIndex);
-          newWindowState = closedWindowState;
-          delete newWindowState.hidden;
-        }
-
-        if (newWindowState) {
-          // Ensure that the window state isn't hidden
-          this._restoreCount = 1;
-          let state = { windows: [newWindowState] };
-          let options = {overwriteTabs: this._isCmdLineEmpty(aWindow, state)};
-          this.restoreWindow(aWindow, newWindowState, options);
-        }
-      }
-      // we actually restored the session just now.
-      this._prefBranch.setBoolPref("sessionstore.resume_session_once", false);
-    }
-    if (this._restoreLastWindow && aWindow.toolbar.visible) {
-      // always reset (if not a popup window)
-      // we don't want to restore a window directly after, for example,
-      // undoCloseWindow was executed.
-      this._restoreLastWindow = false;
-    }
-  },
-
-  /**
-   * Called right before a new browser window is shown.
-   * @param aWindow
-   *        Window reference
-   */
-  onBeforeBrowserWindowShown: function (aWindow) {
-    // Register the window.
-    this.onLoad(aWindow);
-
-    // Just call initializeWindow() directly if we're initialized already.
-    if (this._sessionInitialized) {
-      this.initializeWindow(aWindow);
-      return;
-    }
-
-    // The very first window that is opened creates a promise that is then
-    // re-used by all subsequent windows. The promise will be used to tell
-    // when we're ready for initialization.
-    if (!this._promiseReadyForInitialization) {
-      // Wait for the given window's delayed startup to be finished.
-      let promise = new Promise(resolve => {
-        Services.obs.addObserver(function obs(subject, topic) {
-          if (aWindow == subject) {
-            Services.obs.removeObserver(obs, topic);
-            resolve();
-          }
-        }, "browser-delayed-startup-finished", false);
-      });
-
-      // We are ready for initialization as soon as the session file has been
-      // read from disk and the initial window's delayed startup has finished.
-      this._promiseReadyForInitialization =
-        Promise.all([promise, gSessionStartup.onceInitialized]);
-    }
-
-    // We can't call this.onLoad since initialization
-    // hasn't completed, so we'll wait until it is done.
-    // Even if additional windows are opened and wait
-    // for initialization as well, the first opened
-    // window should execute first, and this.onLoad
-    // will be called with the initialState.
-    this._promiseReadyForInitialization.then(() => {
-      if (aWindow.closed) {
-        return;
-      }
-
-      if (this._sessionInitialized) {
-        this.initializeWindow(aWindow);
-      } else {
-        let initialState = this.initSession();
-        this._sessionInitialized = true;
-
-        if (initialState) {
-          Services.obs.notifyObservers(null, NOTIFY_RESTORING_ON_STARTUP, "");
-        }
-        TelemetryStopwatch.start("FX_SESSION_RESTORE_STARTUP_ONLOAD_INITIAL_WINDOW_MS");
-        this.initializeWindow(aWindow, initialState);
-        TelemetryStopwatch.finish("FX_SESSION_RESTORE_STARTUP_ONLOAD_INITIAL_WINDOW_MS");
-
-        // Let everyone know we're done.
-        this._deferredInitialized.resolve();
-      }
-    }, console.error);
-  },
-
-  /**
-   * On window close...
-   * - remove event listeners from tabs
-   * - save all window data
-   * @param aWindow
-   *        Window reference
-   *
-   * @returns a Promise
-   */
-  onClose: function ssi_onClose(aWindow) {
-    let completionPromise = Promise.resolve();
-    // this window was about to be restored - conserve its original data, if any
-    let isFullyLoaded = this._isWindowLoaded(aWindow);
-    if (!isFullyLoaded) {
-      if (!aWindow.__SSi) {
-        aWindow.__SSi = this._generateWindowID();
-      }
-
-      this._windows[aWindow.__SSi] = this._statesToRestore[aWindow.__SS_restoreID];
-      delete this._statesToRestore[aWindow.__SS_restoreID];
-      delete aWindow.__SS_restoreID;
-    }
-
-    // ignore windows not tracked by SessionStore
-    if (!aWindow.__SSi || !this._windows[aWindow.__SSi]) {
-      return completionPromise;
-    }
-
-    // notify that the session store will stop tracking this window so that
-    // extensions can store any data about this window in session store before
-    // that's not possible anymore
-    let event = aWindow.document.createEvent("Events");
-    event.initEvent("SSWindowClosing", true, false);
-    aWindow.dispatchEvent(event);
-
-    if (this.windowToFocus && this.windowToFocus == aWindow) {
-      delete this.windowToFocus;
-    }
-
-    var tabbrowser = aWindow.gBrowser;
-
-    let browsers = Array.from(tabbrowser.browsers);
-
-    TAB_EVENTS.forEach(function(aEvent) {
-      tabbrowser.tabContainer.removeEventListener(aEvent, this, true);
-    }, this);
-
-    aWindow.gBrowser.removeEventListener("XULFrameLoaderCreated", this);
-    aWindow.gBrowser.removeEventListener("BrowserChangedProcess", this);
-    aWindow.gBrowser.removeEventListener("BrowserWillChangeProcess", this);
-
-    let winData = this._windows[aWindow.__SSi];
-
-    // Collect window data only when *not* closed during shutdown.
-    if (RunState.isRunning) {
-      // Grab the most recent window data. The tab data will be updated
-      // once we finish flushing all of the messages from the tabs.
-      let tabMap = this._collectWindowData(aWindow);
-
-      for (let [tab, tabData] of tabMap) {
-        let permanentKey = tab.linkedBrowser.permanentKey;
-        this._closedWindowTabs.set(permanentKey, tabData);
-      }
-
-      if (isFullyLoaded) {
-        winData.title = tabbrowser.selectedBrowser.contentTitle || tabbrowser.selectedTab.label;
-        winData.title = this._replaceLoadingTitle(winData.title, tabbrowser,
-                                                  tabbrowser.selectedTab);
-        SessionCookies.update([winData]);
-      }
-
-#ifndef XP_MACOSX
-      // Until we decide otherwise elsewhere, this window is part of a series
-      // of closing windows to quit.
-      winData._shouldRestore = true;
-#endif
-
-      // Store the window's close date to figure out when each individual tab
-      // was closed. This timestamp should allow re-arranging data based on how
-      // recently something was closed.
-      winData.closedAt = Date.now();
-
-      // we don't want to save the busy state
-      delete winData.busy;
-
-      // When closing windows one after the other until Firefox quits, we
-      // will move those closed in series back to the "open windows" bucket
-      // before writing to disk. If however there is only a single window
-      // with tabs we deem not worth saving then we might end up with a
-      // random closed or even a pop-up window re-opened. To prevent that
-      // we explicitly allow saving an "empty" window state.
-      let isLastWindow =
-        Object.keys(this._windows).length == 1 &&
-        !this._closedWindows.some(win => win._shouldRestore || false);
-
-      // clear this window from the list, since it has definitely been closed.
-      delete this._windows[aWindow.__SSi];
-
-      // This window has the potential to be saved in the _closedWindows
-      // array (maybeSaveClosedWindows gets the final call on that).
-      this._saveableClosedWindowData.add(winData);
-
-      // Now we have to figure out if this window is worth saving in the _closedWindows
-      // Object.
-      //
-      // We're about to flush the tabs from this window, but it's possible that we
-      // might never hear back from the content process(es) in time before the user
-      // chooses to restore the closed window. So we do the following:
-      //
-      // 1) Use the tab state cache to determine synchronously if the window is
-      //    worth stashing in _closedWindows.
-      // 2) Flush the window.
-      // 3) When the flush is complete, revisit our decision to store the window
-      //    in _closedWindows, and add/remove as necessary.
-      if (!winData.isPrivate) {
-        // Remove any open private tabs the window may contain.
-        PrivacyFilter.filterPrivateTabs(winData);
-        this.maybeSaveClosedWindow(winData, isLastWindow);
-      }
-
-      completionPromise = TabStateFlusher.flushWindow(aWindow).then(() => {
-        // At this point, aWindow is closed! You should probably not try to
-        // access any DOM elements from aWindow within this callback unless
-        // you're holding on to them in the closure.
-
-        for (let browser of browsers) {
-          if (this._closedWindowTabs.has(browser.permanentKey)) {
-            let tabData = this._closedWindowTabs.get(browser.permanentKey);
-            TabState.copyFromCache(browser, tabData);
-            this._closedWindowTabs.delete(browser.permanentKey);
-          }
-        }
-
-        // Save non-private windows if they have at
-        // least one saveable tab or are the last window.
-        if (!winData.isPrivate) {
-          // It's possible that a tab switched its privacy state at some point
-          // before our flush, so we need to filter again.
-          PrivacyFilter.filterPrivateTabs(winData);
-          this.maybeSaveClosedWindow(winData, isLastWindow);
-        }
-
-        // Update the tabs data now that we've got the most
-        // recent information.
-        this.cleanUpWindow(aWindow, winData, browsers);
-
-        // save the state without this window to disk
-        this.saveStateDelayed();
-      });
-    } else {
-      this.cleanUpWindow(aWindow, winData, browsers);
-    }
-
-    for (let i = 0; i < tabbrowser.tabs.length; i++) {
-      this.onTabRemove(aWindow, tabbrowser.tabs[i], true);
-    }
-
-    return completionPromise;
-  },
-
-  /**
-   * Clean up the message listeners on a window that has finally
-   * gone away. Call this once you're sure you don't want to hear
-   * from any of this windows tabs from here forward.
-   *
-   * @param aWindow
-   *        The browser window we're cleaning up.
-   * @param winData
-   *        The data for the window that we should hold in the
-   *        DyingWindowCache in case anybody is still holding a
-   *        reference to it.
-   */
-  cleanUpWindow(aWindow, winData, browsers) {
-    // Any leftover TabStateFlusher Promises need to be resolved now,
-    // since we're about to remove the message listeners.
-    for (let browser of browsers) {
-      TabStateFlusher.resolveAll(browser);
-    }
-
-    // Cache the window state until it is completely gone.
-    DyingWindowCache.set(aWindow, winData);
-
-    let mm = aWindow.getGroupMessageManager("browsers");
-    MESSAGES.forEach(msg => mm.removeMessageListener(msg, this));
-
-    this._saveableClosedWindowData.delete(winData);
-    delete aWindow.__SSi;
-  },
-
-  /**
-   * Decides whether or not a closed window should be put into the
-   * _closedWindows Object. This might be called multiple times per
-   * window, and will do the right thing of moving the window data
-   * in or out of _closedWindows if the winData indicates that our
-   * need for saving it has changed.
-   *
-   * @param winData
-   *        The data for the closed window that we might save.
-   * @param isLastWindow
-   *        Whether or not the window being closed is the last
-   *        browser window. Callers of this function should pass
-   *        in the value of SessionStoreInternal.atLastWindow for
-   *        this argument, and pass in the same value if they happen
-   *        to call this method again asynchronously (for example, after
-   *        a window flush).
-   */
-  maybeSaveClosedWindow(winData, isLastWindow) {
-    // Make sure SessionStore is still running, and make sure that we
-    // haven't chosen to forget this window.
-    if (RunState.isRunning && this._saveableClosedWindowData.has(winData)) {
-      // Determine whether the window has any tabs worth saving.
-      let hasSaveableTabs = winData.tabs.some(this._shouldSaveTabState);
-
-      // Note that we might already have this window stored in
-      // _closedWindows from a previous call to this function.
-      let winIndex = this._closedWindows.indexOf(winData);
-      let alreadyStored = (winIndex != -1);
-      let shouldStore = (hasSaveableTabs || isLastWindow);
-
-      if (shouldStore && !alreadyStored) {
-        let index = this._closedWindows.findIndex(win => {
-          return win.closedAt < winData.closedAt;
-        });
-
-        // If we found no tab closed before our
-        // tab then just append it to the list.
-        if (index == -1) {
-          index = this._closedWindows.length;
-        }
-
-        // About to save the closed window, add a unique ID.
-        winData.closedId = this._nextClosedId++;
-
-        // Insert tabData at the right position.
-        this._closedWindows.splice(index, 0, winData);
-        this._capClosedWindows();
-        this._closedObjectsChanged = true;
-      } else if (!shouldStore && alreadyStored) {
-        this._removeClosedWindow(winIndex);
-      }
-    }
-  },
-
-  /**
-   * On quit application granted
-   */
-  onQuitApplicationGranted: function ssi_onQuitApplicationGranted(syncShutdown=false) {
-    // Collect an initial snapshot of window data before we do the flush
-    this._forEachBrowserWindow((win) => {
-      this._collectWindowData(win);
-    });
-
-    // Now add an AsyncShutdown blocker that'll spin the event loop
-    // until the windows have all been flushed.
-
-    // This progress object will track the state of async window flushing
-    // and will help us debug things that go wrong with our AsyncShutdown
-    // blocker.
-    let progress = { total: -1, current: -1 };
-
-    // We're going down! Switch state so that we treat closing windows and
-    // tabs correctly.
-    RunState.setQuitting();
-
-    if (!syncShutdown) {
-      // We've got some time to shut down, so let's do this properly.
-      // To prevent blocker from breaking the 60 sec limit(which will cause a
-      // crash) of async shutdown during flushing all windows, we resolve the
-      // promise passed to blocker once:
-      // 1. the flushing exceed 50 sec, or
-      // 2. 'oop-frameloader-crashed' or 'ipc:content-shutdown' is observed.
-      // Thus, Firefox still can open the last session on next startup.
-      AsyncShutdown.quitApplicationGranted.addBlocker(
-        "SessionStore: flushing all windows",
-        () => {
-          var promises = [];
-          promises.push(this.flushAllWindowsAsync(progress));
-          promises.push(this.looseTimer(50000));
-
-          var promiseOFC = new Promise(resolve => {
-            Services.obs.addObserver(function obs(subject, topic) {
-              Services.obs.removeObserver(obs, topic);
-              resolve();
-            }, "oop-frameloader-crashed", false);
-          });
-          promises.push(promiseOFC);
-
-          var promiseICS = new Promise(resolve => {
-            Services.obs.addObserver(function obs(subject, topic) {
-              Services.obs.removeObserver(obs, topic);
-              resolve();
-            }, "ipc:content-shutdown", false);
-          });
-          promises.push(promiseICS);
-
-          return Promise.race(promises);
-        },
-        () => progress);
-    } else {
-      // We have to shut down NOW, which means we only get to save whatever
-      // we already had cached.
-    }
-  },
-
-  /**
-   * An async Task that iterates all open browser windows and flushes
-   * any outstanding messages from their tabs. This will also close
-   * all of the currently open windows while we wait for the flushes
-   * to complete.
-   *
-   * @param progress (Object)
-   *        Optional progress object that will be updated as async
-   *        window flushing progresses. flushAllWindowsSync will
-   *        write to the following properties:
-   *
-   *        total (int):
-   *          The total number of windows to be flushed.
-   *        current (int):
-   *          The current window that we're waiting for a flush on.
-   *
-   * @return Promise
-   */
-  flushAllWindowsAsync: Task.async(function*(progress={}) {
-    let windowPromises = new Map();
-    // We collect flush promises and close each window immediately so that
-    // the user can't start changing any window state while we're waiting
-    // for the flushes to finish.
-    this._forEachBrowserWindow((win) => {
-      windowPromises.set(win, TabStateFlusher.flushWindow(win));
-
-      // We have to wait for these messages to come up from
-      // each window and each browser. In the meantime, hide
-      // the windows to improve perceived shutdown speed.
-      let baseWin = win.QueryInterface(Ci.nsIInterfaceRequestor)
-                       .getInterface(Ci.nsIDocShell)
-                       .QueryInterface(Ci.nsIDocShellTreeItem)
-                       .treeOwner
-                       .QueryInterface(Ci.nsIBaseWindow);
-      baseWin.visibility = false;
-    });
-
-    progress.total = windowPromises.size;
-    progress.current = 0;
-
-    // We'll iterate through the Promise array, yielding each one, so as to
-    // provide useful progress information to AsyncShutdown.
-    for (let [win, promise] of windowPromises) {
-      yield promise;
-      this._collectWindowData(win);
-      progress.current++;
-    };
-
-    // We must cache this because _getMostRecentBrowserWindow will always
-    // return null by the time quit-application occurs.
-    var activeWindow = this._getMostRecentBrowserWindow();
-    if (activeWindow)
-      this.activeWindowSSiCache = activeWindow.__SSi || "";
-    DirtyWindows.clear();
-  }),
-
-  /**
-   * On last browser window close
-   */
-  onLastWindowCloseGranted: function ssi_onLastWindowCloseGranted() {
-    // last browser window is quitting.
-    // remember to restore the last window when another browser window is opened
-    // do not account for pref(resume_session_once) at this point, as it might be
-    // set by another observer getting this notice after us
-    this._restoreLastWindow = true;
-  },
-
-  /**
-   * On quitting application
-   * @param aData
-   *        String type of quitting
-   */
-  onQuitApplication: function ssi_onQuitApplication(aData) {
-    if (aData == "restart") {
-      this._prefBranch.setBoolPref("sessionstore.resume_session_once", true);
-      // The browser:purge-session-history notification fires after the
-      // quit-application notification so unregister the
-      // browser:purge-session-history notification to prevent clearing
-      // session data on disk on a restart.  It is also unnecessary to
-      // perform any other sanitization processing on a restart as the
-      // browser is about to exit anyway.
-      Services.obs.removeObserver(this, "browser:purge-session-history");
-    }
-
-    if (aData != "restart") {
-      // Throw away the previous session on shutdown
-      LastSession.clear();
-    }
-
-    this._uninit();
-  },
-
-  /**
-   * On purge of session history
-   */
-  onPurgeSessionHistory: function ssi_onPurgeSessionHistory() {
-    SessionFile.wipe();
-    // If the browser is shutting down, simply return after clearing the
-    // session data on disk as this notification fires after the
-    // quit-application notification so the browser is about to exit.
-    if (RunState.isQuitting)
-      return;
-    LastSession.clear();
-
-    let openWindows = {};
-    // Collect open windows.
-    this._forEachBrowserWindow(({__SSi: id}) => openWindows[id] = true);
-
-    // also clear all data about closed tabs and windows
-    for (let ix in this._windows) {
-      if (ix in openWindows) {
-        if (this._windows[ix]._closedTabs.length) {
-          this._windows[ix]._closedTabs = [];
-          this._closedObjectsChanged = true;
-        }
-      } else {
-        delete this._windows[ix];
-      }
-    }
-    // also clear all data about closed windows
-    if (this._closedWindows.length) {
-      this._closedWindows = [];
-      this._closedObjectsChanged = true;
-    }
-    // give the tabbrowsers a chance to clear their histories first
-    var win = this._getMostRecentBrowserWindow();
-    if (win) {
-      win.setTimeout(() => SessionSaver.run(), 0);
-    } else if (RunState.isRunning) {
-      SessionSaver.run();
-    }
-
-    this._clearRestoringWindows();
-    this._saveableClosedWindowData = new WeakSet();
-  },
-
-  /**
-   * On purge of domain data
-   * @param aData
-   *        String domain data
-   */
-  onPurgeDomainData: function ssi_onPurgeDomainData(aData) {
-    // does a session history entry contain a url for the given domain?
-    function containsDomain(aEntry) {
-      if (Utils.hasRootDomain(aEntry.url, aData)) {
-        return true;
-      }
-      return aEntry.children && aEntry.children.some(containsDomain, this);
-    }
-    // remove all closed tabs containing a reference to the given domain
-    for (let ix in this._windows) {
-      let closedTabs = this._windows[ix]._closedTabs;
-      for (let i = closedTabs.length - 1; i >= 0; i--) {
-        if (closedTabs[i].state.entries.some(containsDomain, this)) {
-          closedTabs.splice(i, 1);
-          this._closedObjectsChanged = true;
-        }
-      }
-    }
-    // remove all open & closed tabs containing a reference to the given
-    // domain in closed windows
-    for (let ix = this._closedWindows.length - 1; ix >= 0; ix--) {
-      let closedTabs = this._closedWindows[ix]._closedTabs;
-      let openTabs = this._closedWindows[ix].tabs;
-      let openTabCount = openTabs.length;
-      for (let i = closedTabs.length - 1; i >= 0; i--)
-        if (closedTabs[i].state.entries.some(containsDomain, this))
-          closedTabs.splice(i, 1);
-      for (let j = openTabs.length - 1; j >= 0; j--) {
-        if (openTabs[j].entries.some(containsDomain, this)) {
-          openTabs.splice(j, 1);
-          if (this._closedWindows[ix].selected > j)
-            this._closedWindows[ix].selected--;
-        }
-      }
-      if (openTabs.length == 0) {
-        this._closedWindows.splice(ix, 1);
-      }
-      else if (openTabs.length != openTabCount) {
-        // Adjust the window's title if we removed an open tab
-        let selectedTab = openTabs[this._closedWindows[ix].selected - 1];
-        // some duplication from restoreHistory - make sure we get the correct title
-        let activeIndex = (selectedTab.index || selectedTab.entries.length) - 1;
-        if (activeIndex >= selectedTab.entries.length)
-          activeIndex = selectedTab.entries.length - 1;
-        this._closedWindows[ix].title = selectedTab.entries[activeIndex].title;
-      }
-    }
-
-    if (RunState.isRunning) {
-      SessionSaver.run();
-    }
-
-    this._clearRestoringWindows();
-  },
-
-  /**
-   * On preference change
-   * @param aData
-   *        String preference changed
-   */
-  onPrefChange: function ssi_onPrefChange(aData) {
-    switch (aData) {
-      // if the user decreases the max number of closed tabs they want
-      // preserved update our internal states to match that max
-      case "sessionstore.max_tabs_undo":
-        this._max_tabs_undo = this._prefBranch.getIntPref("sessionstore.max_tabs_undo");
-        for (let ix in this._windows) {
-          if (this._windows[ix]._closedTabs.length > this._max_tabs_undo) {
-            this._windows[ix]._closedTabs.splice(this._max_tabs_undo, this._windows[ix]._closedTabs.length);
-            this._closedObjectsChanged = true;
-          }
-        }
-        break;
-      case "sessionstore.max_windows_undo":
-        this._max_windows_undo = this._prefBranch.getIntPref("sessionstore.max_windows_undo");
-        this._capClosedWindows();
-        break;
-    }
-  },
-
-  /**
-   * save state when new tab is added
-   * @param aWindow
-   *        Window reference
-   */
-  onTabAdd: function ssi_onTabAdd(aWindow) {
-    this.saveStateDelayed(aWindow);
-  },
-
-  /**
-   * set up listeners for a new tab
-   * @param aWindow
-   *        Window reference
-   * @param aTab
-   *        Tab reference
-   */
-  onTabBrowserInserted: function ssi_onTabBrowserInserted(aWindow, aTab) {
-    let browser = aTab.linkedBrowser;
-    browser.addEventListener("SwapDocShells", this);
-    browser.addEventListener("oop-browser-crashed", this);
-
-    if (browser.frameLoader) {
-      this._lastKnownFrameLoader.set(browser.permanentKey, browser.frameLoader);
-    }
-  },
-
-  /**
-   * remove listeners for a tab
-   * @param aWindow
-   *        Window reference
-   * @param aTab
-   *        Tab reference
-   * @param aNoNotification
-   *        bool Do not save state if we're updating an existing tab
-   */
-  onTabRemove: function ssi_onTabRemove(aWindow, aTab, aNoNotification) {
-    let browser = aTab.linkedBrowser;
-    browser.removeEventListener("SwapDocShells", this);
-    browser.removeEventListener("oop-browser-crashed", this);
-
-    // If this tab was in the middle of restoring or still needs to be restored,
-    // we need to reset that state. If the tab was restoring, we will attempt to
-    // restore the next tab.
-    let previousState = browser.__SS_restoreState;
-    if (previousState) {
-      this._resetTabRestoringState(aTab);
-      if (previousState == TAB_STATE_RESTORING)
-        this.restoreNextTab();
-    }
-
-    if (!aNoNotification) {
-      this.saveStateDelayed(aWindow);
-    }
-  },
-
-  /**
-   * When a tab closes, collect its properties
-   * @param aWindow
-   *        Window reference
-   * @param aTab
-   *        Tab reference
-   */
-  onTabClose: function ssi_onTabClose(aWindow, aTab) {
-    // notify the tabbrowser that the tab state will be retrieved for the last time
-    // (so that extension authors can easily set data on soon-to-be-closed tabs)
-    var event = aWindow.document.createEvent("Events");
-    event.initEvent("SSTabClosing", true, false);
-    aTab.dispatchEvent(event);
-
-    // don't update our internal state if we don't have to
-    if (this._max_tabs_undo == 0) {
-      return;
-    }
-
-    // Get the latest data for this tab (generally, from the cache)
-    let tabState = TabState.collect(aTab);
-
-    // Don't save private tabs
-    let isPrivateWindow = PrivateBrowsingUtils.isWindowPrivate(aWindow);
-    if (!isPrivateWindow && tabState.isPrivate) {
-      return;
-    }
-
-    // Store closed-tab data for undo.
-    let tabbrowser = aWindow.gBrowser;
-    let tabTitle = this._replaceLoadingTitle(aTab.label, tabbrowser, aTab);
-    let {permanentKey} = aTab.linkedBrowser;
-
-    let tabData = {
-      permanentKey,
-      state: tabState,
-      title: tabTitle,
-      image: tabbrowser.getIcon(aTab),
-      iconLoadingPrincipal: Utils.serializePrincipal(aTab.linkedBrowser.contentPrincipal),
-      pos: aTab._tPos,
-      closedAt: Date.now()
-    };
-
-    let closedTabs = this._windows[aWindow.__SSi]._closedTabs;
-
-    // Determine whether the tab contains any information worth saving. Note
-    // that there might be pending state changes queued in the child that
-    // didn't reach the parent yet. If a tab is emptied before closing then we
-    // might still remove it from the list of closed tabs later.
-    if (this._shouldSaveTabState(tabState)) {
-      // Save the tab state, for now. We might push a valid tab out
-      // of the list but those cases should be extremely rare and
-      // do probably never occur when using the browser normally.
-      // (Tests or add-ons might do weird things though.)
-      this.saveClosedTabData(closedTabs, tabData);
-    }
-
-    // Remember the closed tab to properly handle any last updates included in
-    // the final "update" message sent by the frame script's unload handler.
-    this._closedTabs.set(permanentKey, {closedTabs, tabData});
-  },
-
-  /**
-   * Insert a given |tabData| object into the list of |closedTabs|. We will
-   * determine the right insertion point based on the .closedAt properties of
-   * all tabs already in the list. The list will be truncated to contain a
-   * maximum of |this._max_tabs_undo| entries.
-   *
-   * @param closedTabs (array)
-   *        The list of closed tabs for a window.
-   * @param tabData (object)
-   *        The tabData to be inserted.
-   */
-  saveClosedTabData(closedTabs, tabData) {
-    // Find the index of the first tab in the list
-    // of closed tabs that was closed before our tab.
-    let index = closedTabs.findIndex(tab => {
-      return tab.closedAt < tabData.closedAt;
-    });
-
-    // If we found no tab closed before our
-    // tab then just append it to the list.
-    if (index == -1) {
-      index = closedTabs.length;
-    }
-
-    // About to save the closed tab, add a unique ID.
-    tabData.closedId = this._nextClosedId++;
-
-    // Insert tabData at the right position.
-    closedTabs.splice(index, 0, tabData);
-    this._closedObjectsChanged = true;
-
-    // Truncate the list of closed tabs, if needed.
-    if (closedTabs.length > this._max_tabs_undo) {
-      closedTabs.splice(this._max_tabs_undo, closedTabs.length);
-    }
-  },
-
-  /**
-   * Remove the closed tab data at |index| from the list of |closedTabs|. If
-   * the tab's final message is still pending we will simply discard it when
-   * it arrives so that the tab doesn't reappear in the list.
-   *
-   * @param closedTabs (array)
-   *        The list of closed tabs for a window.
-   * @param index (uint)
-   *        The index of the tab to remove.
-   */
-  removeClosedTabData(closedTabs, index) {
-    // Remove the given index from the list.
-    let [closedTab] = closedTabs.splice(index, 1);
-    this._closedObjectsChanged = true;
-
-    // If the closed tab's state still has a .permanentKey property then we
-    // haven't seen its final update message yet. Remove it from the map of
-    // closed tabs so that we will simply discard its last messages and will
-    // not add it back to the list of closed tabs again.
-    if (closedTab.permanentKey) {
-      this._closedTabs.delete(closedTab.permanentKey);
-      this._closedWindowTabs.delete(closedTab.permanentKey);
-      delete closedTab.permanentKey;
-    }
-
-    return closedTab;
-  },
-
-  /**
-   * When a tab is selected, save session data
-   * @param aWindow
-   *        Window reference
-   */
-  onTabSelect: function ssi_onTabSelect(aWindow) {
-    if (RunState.isRunning) {
-      this._windows[aWindow.__SSi].selected = aWindow.gBrowser.tabContainer.selectedIndex;
-
-      let tab = aWindow.gBrowser.selectedTab;
-      let browser = tab.linkedBrowser;
-
-      if (browser.__SS_restoreState &&
-          browser.__SS_restoreState == TAB_STATE_NEEDS_RESTORE) {
-        // If __SS_restoreState is still on the browser and it is
-        // TAB_STATE_NEEDS_RESTORE, then then we haven't restored
-        // this tab yet.
-        //
-        // It's possible that this tab was recently revived, and that
-        // we've deferred showing the tab crashed page for it (if the
-        // tab crashed in the background). If so, we need to re-enter
-        // the crashed state, since we'll be showing the tab crashed
-        // page.
-        if (TabCrashHandler.willShowCrashedTab(browser)) {
-          this.enterCrashedState(browser);
-        } else {
-          this.restoreTabContent(tab);
-        }
-      }
-    }
-  },
-
-  onTabShow: function ssi_onTabShow(aWindow, aTab) {
-    // If the tab hasn't been restored yet, move it into the right bucket
-    if (aTab.linkedBrowser.__SS_restoreState &&
-        aTab.linkedBrowser.__SS_restoreState == TAB_STATE_NEEDS_RESTORE) {
-      TabRestoreQueue.hiddenToVisible(aTab);
-
-      // let's kick off tab restoration again to ensure this tab gets restored
-      // with "restore_hidden_tabs" == false (now that it has become visible)
-      this.restoreNextTab();
-    }
-
-    // Default delay of 2 seconds gives enough time to catch multiple TabShow
-    // events. This used to be due to changing groups in 'tab groups'. We
-    // might be able to get rid of this now?
-    this.saveStateDelayed(aWindow);
-  },
-
-  onTabHide: function ssi_onTabHide(aWindow, aTab) {
-    // If the tab hasn't been restored yet, move it into the right bucket
-    if (aTab.linkedBrowser.__SS_restoreState &&
-        aTab.linkedBrowser.__SS_restoreState == TAB_STATE_NEEDS_RESTORE) {
-      TabRestoreQueue.visibleToHidden(aTab);
-    }
-
-    // Default delay of 2 seconds gives enough time to catch multiple TabHide
-    // events. This used to be due to changing groups in 'tab groups'. We
-    // might be able to get rid of this now?
-    this.saveStateDelayed(aWindow);
-  },
-
-  /**
-   * Handler for the event that is fired when a <xul:browser> crashes.
-   *
-   * @param aWindow
-   *        The window that the crashed browser belongs to.
-   * @param aBrowser
-   *        The <xul:browser> that is now in the crashed state.
-   */
-  onBrowserCrashed: function(aBrowser) {
-    NS_ASSERT(aBrowser.isRemoteBrowser,
-              "Only remote browsers should be able to crash");
-
-    this.enterCrashedState(aBrowser);
-    // The browser crashed so we might never receive flush responses.
-    // Resolve all pending flush requests for the crashed browser.
-    TabStateFlusher.resolveAll(aBrowser);
-  },
-
-  /**
-   * Called when a browser is showing or is about to show the tab
-   * crashed page. This method causes SessionStore to ignore the
-   * tab until it's restored.
-   *
-   * @param browser
-   *        The <xul:browser> that is about to show the crashed page.
-   */
-  enterCrashedState(browser) {
-    this._crashedBrowsers.add(browser.permanentKey);
-
-    let win = browser.ownerGlobal;
-
-    // If we hadn't yet restored, or were still in the midst of
-    // restoring this browser at the time of the crash, we need
-    // to reset its state so that we can try to restore it again
-    // when the user revives the tab from the crash.
-    if (browser.__SS_restoreState) {
-      let tab = win.gBrowser.getTabForBrowser(browser);
-      this._resetLocalTabRestoringState(tab);
-    }
-  },
-
-  // Clean up data that has been closed a long time ago.
-  // Do not reschedule a save. This will wait for the next regular
-  // save.
-  onIdleDaily: function() {
-    // Remove old closed windows
-    this._cleanupOldData([this._closedWindows]);
-
-    // Remove closed tabs of closed windows
-    this._cleanupOldData(this._closedWindows.map((winData) => winData._closedTabs));
-
-    // Remove closed tabs of open windows
-    this._cleanupOldData(Object.keys(this._windows).map((key) => this._windows[key]._closedTabs));
-
-    this._notifyOfClosedObjectsChange();
-  },
-
-  // Remove "old" data from an array
-  _cleanupOldData: function(targets) {
-    const TIME_TO_LIVE = this._prefBranch.getIntPref("sessionstore.cleanup.forget_closed_after");
-    const now = Date.now();
-
-    for (let array of targets) {
-      for (let i = array.length - 1; i >= 0; --i)  {
-        let data = array[i];
-        // Make sure that we have a timestamp to tell us when the target
-        // has been closed. If we don't have a timestamp, default to a
-        // safe timestamp: just now.
-        data.closedAt = data.closedAt || now;
-        if (now - data.closedAt > TIME_TO_LIVE) {
-          array.splice(i, 1);
-          this._closedObjectsChanged = true;
-        }
-      }
-    }
-  },
-
-  /* ........ nsISessionStore API .............. */
-
-  getBrowserState: function ssi_getBrowserState() {
-    let state = this.getCurrentState();
-
-    // Don't include the last session state in getBrowserState().
-    delete state.lastSessionState;
-
-    // Don't include any deferred initial state.
-    delete state.deferredInitialState;
-
-    return JSON.stringify(state);
-  },
-
-  setBrowserState: function ssi_setBrowserState(aState) {
-    this._handleClosedWindows();
-
-    try {
-      var state = JSON.parse(aState);
-    }
-    catch (ex) { /* invalid state object - don't restore anything */ }
-    if (!state) {
-      throw Components.Exception("Invalid state string: not JSON", Cr.NS_ERROR_INVALID_ARG);
-    }
-    if (!state.windows) {
-      throw Components.Exception("No windows", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    this._browserSetState = true;
-
-    // Make sure the priority queue is emptied out
-    this._resetRestoringState();
-
-    var window = this._getMostRecentBrowserWindow();
-    if (!window) {
-      this._restoreCount = 1;
-      this._openWindowWithState(state);
-      return;
-    }
-
-    // close all other browser windows
-    this._forEachBrowserWindow(function(aWindow) {
-      if (aWindow != window) {
-        aWindow.close();
-        this.onClose(aWindow);
-      }
-    });
-
-    // make sure closed window data isn't kept
-    if (this._closedWindows.length) {
-      this._closedWindows = [];
-      this._closedObjectsChanged = true;
-    }
-
-    // determine how many windows are meant to be restored
-    this._restoreCount = state.windows ? state.windows.length : 0;
-
-    // global data must be restored before restoreWindow is called so that
-    // it happens before observers are notified
-    this._globalState.setFromState(state);
-
-    // restore to the given state
-    this.restoreWindows(window, state, {overwriteTabs: true});
-
-    // Notify of changes to closed objects.
-    this._notifyOfClosedObjectsChange();
-  },
-
-  getWindowState: function ssi_getWindowState(aWindow) {
-    if ("__SSi" in aWindow) {
-      return JSON.stringify(this._getWindowState(aWindow));
-    }
-
-    if (DyingWindowCache.has(aWindow)) {
-      let data = DyingWindowCache.get(aWindow);
-      return JSON.stringify({ windows: [data] });
-    }
-
-    throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
-  },
-
-  setWindowState: function ssi_setWindowState(aWindow, aState, aOverwrite) {
-    if (!aWindow.__SSi) {
-      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    this.restoreWindows(aWindow, aState, {overwriteTabs: aOverwrite});
-
-    // Notify of changes to closed objects.
-    this._notifyOfClosedObjectsChange();
-  },
-
-  getTabState: function ssi_getTabState(aTab) {
-    if (!aTab.ownerGlobal.__SSi) {
-      throw Components.Exception("Default view is not tracked", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    let tabState = TabState.collect(aTab);
-
-    return JSON.stringify(tabState);
-  },
-
-  setTabState(aTab, aState) {
-    // Remove the tab state from the cache.
-    // Note that we cannot simply replace the contents of the cache
-    // as |aState| can be an incomplete state that will be completed
-    // by |restoreTabs|.
-    let tabState = JSON.parse(aState);
-    if (!tabState) {
-      throw Components.Exception("Invalid state string: not JSON", Cr.NS_ERROR_INVALID_ARG);
-    }
-    if (typeof tabState != "object") {
-      throw Components.Exception("Not an object", Cr.NS_ERROR_INVALID_ARG);
-    }
-    if (!("entries" in tabState)) {
-      throw Components.Exception("Invalid state object: no entries", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    let window = aTab.ownerGlobal;
-    if (!("__SSi" in window)) {
-      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    if (aTab.linkedBrowser.__SS_restoreState) {
-      this._resetTabRestoringState(aTab);
-    }
-
-    this.restoreTab(aTab, tabState);
-
-    // Notify of changes to closed objects.
-    this._notifyOfClosedObjectsChange();
-  },
-
-  duplicateTab: function ssi_duplicateTab(aWindow, aTab, aDelta = 0, aRestoreImmediately = true) {
-    if (!aTab.ownerGlobal.__SSi) {
-      throw Components.Exception("Default view is not tracked", Cr.NS_ERROR_INVALID_ARG);
-    }
-    if (!aWindow.gBrowser) {
-      throw Components.Exception("Invalid window object: no gBrowser", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    // Create a new tab.
-    let userContextId = aTab.getAttribute("usercontextid");
-    let newTab = aTab == aWindow.gBrowser.selectedTab ?
-      aWindow.gBrowser.addTab(null, {relatedToCurrent: true, ownerTab: aTab, userContextId}) :
-      aWindow.gBrowser.addTab(null, {userContextId});
-
-    // Set tab title to "Connecting..." and start the throbber to pretend we're
-    // doing something while actually waiting for data from the frame script.
-    aWindow.gBrowser.setTabTitleLoading(newTab);
-    newTab.setAttribute("busy", "true");
-
-    // Collect state before flushing.
-    let tabState = TabState.clone(aTab);
-
-    // Flush to get the latest tab state to duplicate.
-    let browser = aTab.linkedBrowser;
-    TabStateFlusher.flush(browser).then(() => {
-      // The new tab might have been closed in the meantime.
-      if (newTab.closing || !newTab.linkedBrowser) {
-        return;
-      }
-
-      let window = newTab.ownerGlobal;
-
-      // The tab or its window might be gone.
-      if (!window || !window.__SSi) {
-        return;
-      }
-
-      // Update state with flushed data. We can't use TabState.clone() here as
-      // the tab to duplicate may have already been closed. In that case we
-      // only have access to the <xul:browser>.
-      let options = {includePrivateData: true};
-      TabState.copyFromCache(browser, tabState, options);
-
-      tabState.index += aDelta;
-      tabState.index = Math.max(1, Math.min(tabState.index, tabState.entries.length));
-      tabState.pinned = false;
-
-      // Restore the state into the new tab.
-      this.restoreTab(newTab, tabState, {
-        restoreImmediately: aRestoreImmediately
-      });
-    });
-
-    return newTab;
-  },
-
-  getClosedTabCount: function ssi_getClosedTabCount(aWindow) {
-    if ("__SSi" in aWindow) {
-      return this._windows[aWindow.__SSi]._closedTabs.length;
-    }
-
-    if (!DyingWindowCache.has(aWindow)) {
-      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    return DyingWindowCache.get(aWindow)._closedTabs.length;
-  },
-
-  getClosedTabData: function ssi_getClosedTabData(aWindow, aAsString = true) {
-    if ("__SSi" in aWindow) {
-      return aAsString ?
-        JSON.stringify(this._windows[aWindow.__SSi]._closedTabs) :
-        Cu.cloneInto(this._windows[aWindow.__SSi]._closedTabs, {});
-    }
-
-    if (!DyingWindowCache.has(aWindow)) {
-      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    let data = DyingWindowCache.get(aWindow);
-    return aAsString ? JSON.stringify(data._closedTabs) : Cu.cloneInto(data._closedTabs, {});
-  },
-
-  undoCloseTab: function ssi_undoCloseTab(aWindow, aIndex) {
-    if (!aWindow.__SSi) {
-      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    var closedTabs = this._windows[aWindow.__SSi]._closedTabs;
-
-    // default to the most-recently closed tab
-    aIndex = aIndex || 0;
-    if (!(aIndex in closedTabs)) {
-      throw Components.Exception("Invalid index: not in the closed tabs", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    // fetch the data of closed tab, while removing it from the array
-    let {state, pos} = this.removeClosedTabData(closedTabs, aIndex);
-
-    // create a new tab
-    let tabbrowser = aWindow.gBrowser;
-    let tab = tabbrowser.selectedTab = tabbrowser.addTab(null, state);
-
-    // restore tab content
-    this.restoreTab(tab, state);
-
-    // restore the tab's position
-    tabbrowser.moveTabTo(tab, pos);
-
-    // focus the tab's content area (bug 342432)
-    tab.linkedBrowser.focus();
-
-    // Notify of changes to closed objects.
-    this._notifyOfClosedObjectsChange();
-
-    return tab;
-  },
-
-  forgetClosedTab: function ssi_forgetClosedTab(aWindow, aIndex) {
-    if (!aWindow.__SSi) {
-      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    var closedTabs = this._windows[aWindow.__SSi]._closedTabs;
-
-    // default to the most-recently closed tab
-    aIndex = aIndex || 0;
-    if (!(aIndex in closedTabs)) {
-      throw Components.Exception("Invalid index: not in the closed tabs", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    // remove closed tab from the array
-    this.removeClosedTabData(closedTabs, aIndex);
-
-    // Notify of changes to closed objects.
-    this._notifyOfClosedObjectsChange();
-  },
-
-  getClosedWindowCount: function ssi_getClosedWindowCount() {
-    return this._closedWindows.length;
-  },
-
-  getClosedWindowData: function ssi_getClosedWindowData(aAsString = true) {
-    return aAsString ? JSON.stringify(this._closedWindows) : Cu.cloneInto(this._closedWindows, {});
-  },
-
-  undoCloseWindow: function ssi_undoCloseWindow(aIndex) {
-    if (!(aIndex in this._closedWindows)) {
-      throw Components.Exception("Invalid index: not in the closed windows", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    // reopen the window
-    let state = { windows: this._removeClosedWindow(aIndex) };
-    delete state.windows[0].closedAt; // Window is now open.
-
-    let window = this._openWindowWithState(state);
-    this.windowToFocus = window;
-
-    // Notify of changes to closed objects.
-    this._notifyOfClosedObjectsChange();
-
-    return window;
-  },
-
-  forgetClosedWindow: function ssi_forgetClosedWindow(aIndex) {
-    // default to the most-recently closed window
-    aIndex = aIndex || 0;
-    if (!(aIndex in this._closedWindows)) {
-      throw Components.Exception("Invalid index: not in the closed windows", Cr.NS_ERROR_INVALID_ARG);
-    }
-
-    // remove closed window from the array
-    let winData = this._closedWindows[aIndex];
-    this._removeClosedWindow(aIndex);
-    this._saveableClosedWindowData.delete(winData);
-
-    // Notify of changes to closed objects.
-    this._notifyOfClosedObjectsChange();
-  },
-
-  getWindowValue: function ssi_getWindowValue(aWindow, aKey) {
-    if ("__SSi" in aWindow) {
-      var data = this._windows[aWindow.__SSi].extData || {};
-      return data[aKey] || "";
-    }
-
-    if (DyingWindowCache.has(aWindow)) {
-      let data = DyingWindowCache.get(aWindow).extData || {};
-      return data[aKey] || "";
-    }
-
-    throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
-  },
-
-  setWindowValue: function ssi_setWindowValue(aWindow, aKey, aStringValue) {
-    if (typeof aStringValue != "string") {
-      throw new TypeError("setWindowValue only accepts string values");
-    }
-
-    if (!("__SSi" in aWindow)) {
-      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
-    }
-    if (!this._windows[aWindow.__SSi].extData) {
-      this._windows[aWindow.__SSi].extData = {};
-    }
-    this._windows[aWindow.__SSi].extData[aKey] = aStringValue;
-    this.saveStateDelayed(aWindow);
-  },
-
-  deleteWindowValue: function ssi_deleteWindowValue(aWindow, aKey) {
-    if (aWindow.__SSi && this._windows[aWindow.__SSi].extData &&
-        this._windows[aWindow.__SSi].extData[aKey])
-      delete this._windows[aWindow.__SSi].extData[aKey];
-    this.saveStateDelayed(aWindow);
-  },
-
-  getTabValue: function ssi_getTabValue(aTab, aKey) {
-    return (aTab.__SS_extdata || {})[aKey] || "";
-  },
-
-  setTabValue: function ssi_setTabValue(aTab, aKey, aStringValue) {
-    if (typeof aStringValue != "string") {
-      throw new TypeError("setTabValue only accepts string values");
-    }
-
-    // If the tab hasn't been restored, then set the data there, otherwise we
-    // could lose newly added data.
-    if (!aTab.__SS_extdata) {
-      aTab.__SS_extdata = {};
-    }
-
-    aTab.__SS_extdata[aKey] = aStringValue;
-    this.saveStateDelayed(aTab.ownerGlobal);
-  },
-
-  deleteTabValue: function ssi_deleteTabValue(aTab, aKey) {
-    if (aTab.__SS_extdata && aKey in aTab.__SS_extdata) {
-      delete aTab.__SS_extdata[aKey];
-      this.saveStateDelayed(aTab.ownerGlobal);
-    }
-  },
-
-  getGlobalValue: function ssi_getGlobalValue(aKey) {
-    return this._globalState.get(aKey);
-  },
-
-  setGlobalValue: function ssi_setGlobalValue(aKey, aStringValue) {
-    if (typeof aStringValue != "string") {
-      throw new TypeError("setGlobalValue only accepts string values");
-    }
-
-    this._globalState.set(aKey, aStringValue);
-    this.saveStateDelayed();
-  },
-
-  deleteGlobalValue: function ssi_deleteGlobalValue(aKey) {
-    this._globalState.delete(aKey);
-    this.saveStateDelayed();
-  },
-
-  persistTabAttribute: function ssi_persistTabAttribute(aName) {
-    if (TabAttributes.persist(aName)) {
-      this.saveStateDelayed();
-    }
-  },
-
-
-  /**
-   * Undoes the closing of a tab or window which corresponds
-   * to the closedId passed in.
-   *
-   * @param aClosedId
-   *        The closedId of the tab or window
-   *
-   * @returns a tab or window object
-   */
-  undoCloseById(aClosedId) {
-    // Check for a window first.
-    for (let i = 0, l = this._closedWindows.length; i < l; i++) {
-      if (this._closedWindows[i].closedId == aClosedId) {
-        return this.undoCloseWindow(i);
-      }
-    }
-
-    // Check for a tab.
-    let windowsEnum = Services.wm.getEnumerator("navigator:browser");
-    while (windowsEnum.hasMoreElements()) {
-      let window = windowsEnum.getNext();
-      let windowState = this._windows[window.__SSi];
-      if (windowState) {
-        for (let j = 0, l = windowState._closedTabs.length; j < l; j++) {
-          if (windowState._closedTabs[j].closedId == aClosedId) {
-            return this.undoCloseTab(window, j);
-          }
-        }
-      }
-    }
-
-    // Neither a tab nor a window was found, return undefined and let the caller decide what to do about it.
-    return undefined;
-  },
-
-  /**
-   * Restores the session state stored in LastSession. This will attempt
-   * to merge data into the current session. If a window was opened at startup
-   * with pinned tab(s), then the remaining data from the previous session for
-   * that window will be opened into that window. Otherwise new windows will
-   * be opened.
-   */
-  restoreLastSession: function ssi_restoreLastSession() {
-    // Use the public getter since it also checks PB mode
-    if (!this.canRestoreLastSession) {
-      throw Components.Exception("Last session can not be restored");
-    }
-
-    Services.obs.notifyObservers(null, NOTIFY_INITIATING_MANUAL_RESTORE, "");
-
-    // First collect each window with its id...
-    let windows = {};
-    this._forEachBrowserWindow(function(aWindow) {
-      if (aWindow.__SS_lastSessionWindowID)
-        windows[aWindow.__SS_lastSessionWindowID] = aWindow;
-    });
-
-    let lastSessionState = LastSession.getState();
-
-    // This shouldn't ever be the case...
-    if (!lastSessionState.windows.length) {
-      throw Components.Exception("lastSessionState has no windows", Cr.NS_ERROR_UNEXPECTED);
-    }
-
-    // We're technically doing a restore, so set things up so we send the
-    // notification when we're done. We want to send "sessionstore-browser-state-restored".
-    this._restoreCount = lastSessionState.windows.length;
-    this._browserSetState = true;
-
-    // We want to re-use the last opened window instead of opening a new one in
-    // the case where it's "empty" and not associated with a window in the session.
-    // We will do more processing via _prepWindowToRestoreInto if we need to use
-    // the lastWindow.
-    let lastWindow = this._getMostRecentBrowserWindow();
-    let canUseLastWindow = lastWindow &&
-                           !lastWindow.__SS_lastSessionWindowID;
-
-    // global data must be restored before restoreWindow is called so that
-    // it happens before observers are notified
-    this._globalState.setFromState(lastSessionState);
-
-    // Restore into windows or open new ones as needed.
-    for (let i = 0; i < lastSessionState.windows.length; i++) {
-      let winState = lastSessionState.windows[i];
-      let lastSessionWindowID = winState.__lastSessionWindowID;
-      // delete lastSessionWindowID so we don't add that to the window again
-      delete winState.__lastSessionWindowID;
-
-      // See if we can use an open window. First try one that is associated with
-      // the state we're trying to restore and then fallback to the last selected
-      // window.
-      let windowToUse = windows[lastSessionWindowID];
-      if (!windowToUse && canUseLastWindow) {
-        windowToUse = lastWindow;
-        canUseLastWindow = false;
-      }
-
-      let [canUseWindow, canOverwriteTabs] = this._prepWindowToRestoreInto(windowToUse);
-
-      // If there's a window already open that we can restore into, use that
-      if (canUseWindow) {
-        // Since we're not overwriting existing tabs, we want to merge _closedTabs,
-        // putting existing ones first. Then make sure we're respecting the max pref.
-        if (winState._closedTabs && winState._closedTabs.length) {
-          let curWinState = this._windows[windowToUse.__SSi];
-          curWinState._closedTabs = curWinState._closedTabs.concat(winState._closedTabs);
-          curWinState._closedTabs.splice(this._max_tabs_undo, curWinState._closedTabs.length);
-        }
-
-        // Restore into that window - pretend it's a followup since we'll already
-        // have a focused window.
-        //XXXzpao This is going to merge extData together (taking what was in
-        //        winState over what is in the window already.
-        let options = {overwriteTabs: canOverwriteTabs, isFollowUp: true};
-        this.restoreWindow(windowToUse, winState, options);
-      }
-      else {
-        this._openWindowWithState({ windows: [winState] });
-      }
-    }
-
-    // Merge closed windows from this session with ones from last session
-    if (lastSessionState._closedWindows) {
-      this._closedWindows = this._closedWindows.concat(lastSessionState._closedWindows);
-      this._capClosedWindows();
-      this._closedObjectsChanged = true;
-    }
-
-    // Scratchpad
-    if (lastSessionState.scratchpads) {
-      ScratchpadManager.restoreSession(lastSessionState.scratchpads);
-    }
-
-    // The Browser Console
-    if (lastSessionState.browserConsole) {
-      HUDService.restoreBrowserConsoleSession();
-    }
-
-    // Set data that persists between sessions
-    this._recentCrashes = lastSessionState.session &&
-                          lastSessionState.session.recentCrashes || 0;
-
-    // Update the session start time using the restored session state.
-    this._updateSessionStartTime(lastSessionState);
-
-    LastSession.clear();
-
-    // Notify of changes to closed objects.
-    this._notifyOfClosedObjectsChange();
-  },
-
-  /**
-   * Revive a crashed tab and restore its state from before it crashed.
-   *
-   * @param aTab
-   *        A <xul:tab> linked to a crashed browser. This is a no-op if the
-   *        browser hasn't actually crashed, or is not associated with a tab.
-   *        This function will also throw if the browser happens to be remote.
-   */
-  reviveCrashedTab(aTab) {
-    if (!aTab) {
-      throw new Error("SessionStore.reviveCrashedTab expected a tab, but got null.");
-    }
-
-    let browser = aTab.linkedBrowser;
-    if (!this._crashedBrowsers.has(browser.permanentKey)) {
-      return;
-    }
-
-    // Sanity check - the browser to be revived should not be remote
-    // at this point.
-    if (browser.isRemoteBrowser) {
-      throw new Error("SessionStore.reviveCrashedTab: " +
-                      "Somehow a crashed browser is still remote.")
-    }
-
-    // We put the browser at about:blank in case the user is
-    // restoring tabs on demand. This way, the user won't see
-    // a flash of the about:tabcrashed page after selecting
-    // the revived tab.
-    aTab.removeAttribute("crashed");
-    browser.loadURI("about:blank", null, null);
-
-    let data = TabState.collect(aTab);
-    this.restoreTab(aTab, data, {
-      forceOnDemand: true,
-    });
-  },
-
-  /**
-   * Revive all crashed tabs and reset the crashed tabs count to 0.
-   */
-  reviveAllCrashedTabs() {
-    let windowsEnum = Services.wm.getEnumerator("navigator:browser");
-    while (windowsEnum.hasMoreElements()) {
-      let window = windowsEnum.getNext();
-      for (let tab of window.gBrowser.tabs) {
-        this.reviveCrashedTab(tab);
-      }
-    }
-  },
-
-  /**
-   * Navigate the given |tab| by first collecting its current state and then
-   * either changing only the index of the currently shown history entry,
-   * or restoring the exact same state again and passing the new URL to load
-   * in |loadArguments|. Use this method to seamlessly switch between pages
-   * loaded in the parent and pages loaded in the child process.
-   *
-   * This method might be called multiple times before it has finished
-   * flushing the browser tab. If that occurs, the loadArguments from
-   * the most recent call to navigateAndRestore will be used once the
-   * flush has finished.
-   */
-  navigateAndRestore(tab, loadArguments, historyIndex) {
-    let window = tab.ownerGlobal;
-    NS_ASSERT(window.__SSi, "tab's window must be tracked");
-    let browser = tab.linkedBrowser;
-
-    // Were we already waiting for a flush from a previous call to
-    // navigateAndRestore on this tab?
-    let alreadyRestoring =
-      this._remotenessChangingBrowsers.has(browser.permanentKey);
-
-    // Stash the most recent loadArguments in this WeakMap so that
-    // we know to use it when the TabStateFlusher.flush resolves.
-    this._remotenessChangingBrowsers.set(browser.permanentKey, loadArguments);
-
-    if (alreadyRestoring) {
-      // This tab was already being restored to run in the
-      // correct process. We're done here.
-      return;
-    }
-
-    // Set tab title to "Connecting..." and start the throbber to pretend we're
-    // doing something while actually waiting for data from the frame script.
-    window.gBrowser.setTabTitleLoading(tab);
-    tab.setAttribute("busy", "true");
-
-    // Flush to get the latest tab state.
-    TabStateFlusher.flush(browser).then(() => {
-      // loadArguments might have been overwritten by multiple calls
-      // to navigateAndRestore while we waited for the tab to flush,
-      // so we use the most recently stored one.
-      let recentLoadArguments =
-        this._remotenessChangingBrowsers.get(browser.permanentKey);
-      this._remotenessChangingBrowsers.delete(browser.permanentKey);
-
-      // The tab might have been closed/gone in the meantime.
-      if (tab.closing || !tab.linkedBrowser) {
-        return;
-      }
-
-      let window = tab.ownerGlobal;
-
-      // The tab or its window might be gone.
-      if (!window || !window.__SSi || window.closed) {
-        return;
-      }
-
-      let tabState = TabState.clone(tab);
-      let options = {
-        restoreImmediately: true,
-        // We want to make sure that this information is passed to restoreTab
-        // whether or not a historyIndex is passed in. Thus, we extract it from
-        // the loadArguments.
-        reloadInFreshProcess: !!recentLoadArguments.reloadInFreshProcess,
-      };
-
-      if (historyIndex >= 0) {
-        tabState.index = historyIndex + 1;
-        tabState.index = Math.max(1, Math.min(tabState.index, tabState.entries.length));
-      } else {
-        options.loadArguments = recentLoadArguments;
-      }
-
-      // Need to reset restoring tabs.
-      if (tab.linkedBrowser.__SS_restoreState) {
-        this._resetLocalTabRestoringState(tab);
-      }
-
-      // Restore the state into the tab.
-      this.restoreTab(tab, tabState, options);
-    });
-
-    tab.linkedBrowser.__SS_restoreState = TAB_STATE_WILL_RESTORE;
-
-    // Notify of changes to closed objects.
-    this._notifyOfClosedObjectsChange();
-  },
-
-  /**
-   * Retrieves the latest session history information for a tab. The cached data
-   * is returned immediately, but a callback may be provided that supplies
-   * up-to-date data when or if it is available. The callback is passed a single
-   * argument with data in the same format as the return value.
-   *
-   * @param tab tab to retrieve the session history for
-   * @param updatedCallback function to call with updated data as the single argument
-   * @returns a object containing 'index' specifying the current index, and an
-   * array 'entries' containing an object for each history item.
-   */
-  getSessionHistory(tab, updatedCallback) {
-    if (updatedCallback) {
-      TabStateFlusher.flush(tab.linkedBrowser).then(() => {
-        let sessionHistory = this.getSessionHistory(tab);
-        if (sessionHistory) {
-          updatedCallback(sessionHistory);
-        }
-      });
-    }
-
-    // Don't continue if the tab was closed before TabStateFlusher.flush resolves.
-    if (tab.linkedBrowser) {
-      let tabState = TabState.collect(tab);
-      return { index: tabState.index - 1, entries: tabState.entries }
-    }
-  },
-
-  /**
-   * See if aWindow is usable for use when restoring a previous session via
-   * restoreLastSession. If usable, prepare it for use.
-   *
-   * @param aWindow
-   *        the window to inspect & prepare
-   * @returns [canUseWindow, canOverwriteTabs]
-   *          canUseWindow: can the window be used to restore into
-   *          canOverwriteTabs: all of the current tabs are home pages and we
-   *                            can overwrite them
-   */
-  _prepWindowToRestoreInto: function ssi_prepWindowToRestoreInto(aWindow) {
-    if (!aWindow)
-      return [false, false];
-
-    // We might be able to overwrite the existing tabs instead of just adding
-    // the previous session's tabs to the end. This will be set if possible.
-    let canOverwriteTabs = false;
-
-    // Look at the open tabs in comparison to home pages. If all the tabs are
-    // home pages then we'll end up overwriting all of them. Otherwise we'll
-    // just close the tabs that match home pages. Tabs with the about:blank
-    // URI will always be overwritten.
-    let homePages = ["about:blank"];
-    let removableTabs = [];
-    let tabbrowser = aWindow.gBrowser;
-    let normalTabsLen = tabbrowser.tabs.length - tabbrowser._numPinnedTabs;
-    let startupPref = this._prefBranch.getIntPref("startup.page");
-    if (startupPref == 1)
-      homePages = homePages.concat(aWindow.gHomeButton.getHomePage().split("|"));
-
-    for (let i = tabbrowser._numPinnedTabs; i < tabbrowser.tabs.length; i++) {
-      let tab = tabbrowser.tabs[i];
-      if (homePages.indexOf(tab.linkedBrowser.currentURI.spec) != -1) {
-        removableTabs.push(tab);
-      }
-    }
-
-    if (tabbrowser.tabs.length == removableTabs.length) {
-      canOverwriteTabs = true;
-    }
-    else {
-      // If we're not overwriting all of the tabs, then close the home tabs.
-      for (let i = removableTabs.length - 1; i >= 0; i--) {
-        tabbrowser.removeTab(removableTabs.pop(), { animate: false });
-      }
-    }
-
-    return [true, canOverwriteTabs];
-  },
-
-  /* ........ Saving Functionality .............. */
-
-  /**
-   * Store window dimensions, visibility, sidebar
-   * @param aWindow
-   *        Window reference
-   */
-  _updateWindowFeatures: function ssi_updateWindowFeatures(aWindow) {
-    var winData = this._windows[aWindow.__SSi];
-
-    WINDOW_ATTRIBUTES.forEach(function(aAttr) {
-      winData[aAttr] = this._getWindowDimension(aWindow, aAttr);
-    }, this);
-
-    var hidden = WINDOW_HIDEABLE_FEATURES.filter(function(aItem) {
-      return aWindow[aItem] && !aWindow[aItem].visible;
-    });
-    if (hidden.length != 0)
-      winData.hidden = hidden.join(",");
-    else if (winData.hidden)
-      delete winData.hidden;
-
-    var sidebar = aWindow.document.getElementById("sidebar-box").getAttribute("sidebarcommand");
-    if (sidebar)
-      winData.sidebar = sidebar;
-    else if (winData.sidebar)
-      delete winData.sidebar;
-  },
-
-  /**
-   * gather session data as object
-   * @param aUpdateAll
-   *        Bool update all windows
-   * @returns object
-   */
-  getCurrentState: function (aUpdateAll) {
-    this._handleClosedWindows().then(() => {
-      this._notifyOfClosedObjectsChange();
-    });
-
-    var activeWindow = this._getMostRecentBrowserWindow();
-
-    TelemetryStopwatch.start("FX_SESSION_RESTORE_COLLECT_ALL_WINDOWS_DATA_MS");
-    if (RunState.isRunning) {
-      // update the data for all windows with activities since the last save operation
-      this._forEachBrowserWindow(function(aWindow) {
-        if (!this._isWindowLoaded(aWindow)) // window data is still in _statesToRestore
-          return;
-        if (aUpdateAll || DirtyWindows.has(aWindow) || aWindow == activeWindow) {
-          this._collectWindowData(aWindow);
-        }
-        else { // always update the window features (whose change alone never triggers a save operation)
-          this._updateWindowFeatures(aWindow);
-        }
-      });
-      DirtyWindows.clear();
-    }
-    TelemetryStopwatch.finish("FX_SESSION_RESTORE_COLLECT_ALL_WINDOWS_DATA_MS");
-
-    // An array that at the end will hold all current window data.
-    var total = [];
-    // The ids of all windows contained in 'total' in the same order.
-    var ids = [];
-    // The number of window that are _not_ popups.
-    var nonPopupCount = 0;
-    var ix;
-
-    // collect the data for all windows
-    for (ix in this._windows) {
-      if (this._windows[ix]._restoring) // window data is still in _statesToRestore
-        continue;
-      total.push(this._windows[ix]);
-      ids.push(ix);
-      if (!this._windows[ix].isPopup)
-        nonPopupCount++;
-    }
-
-    TelemetryStopwatch.start("FX_SESSION_RESTORE_COLLECT_COOKIES_MS");
-    SessionCookies.update(total);
-    TelemetryStopwatch.finish("FX_SESSION_RESTORE_COLLECT_COOKIES_MS");
-
-    // collect the data for all windows yet to be restored
-    for (ix in this._statesToRestore) {
-      for (let winData of this._statesToRestore[ix].windows) {
-        total.push(winData);
-        if (!winData.isPopup)
-          nonPopupCount++;
-      }
-    }
-
-    // shallow copy this._closedWindows to preserve current state
-    let lastClosedWindowsCopy = this._closedWindows.slice();
-
-#ifndef XP_MACOSX
-    // If no non-popup browser window remains open, return the state of the last
-    // closed window(s). We only want to do this when we're actually "ending"
-    // the session.
-    //XXXzpao We should do this for _restoreLastWindow == true, but that has
-    //        its own check for popups. c.f. bug 597619
-    if (nonPopupCount == 0 && lastClosedWindowsCopy.length > 0 &&
-        RunState.isQuitting) {
-      // prepend the last non-popup browser window, so that if the user loads more tabs
-      // at startup we don't accidentally add them to a popup window
-      do {
-        total.unshift(lastClosedWindowsCopy.shift())
-      } while (total[0].isPopup && lastClosedWindowsCopy.length > 0)
-    }
-#endif
-
-    if (activeWindow) {
-      this.activeWindowSSiCache = activeWindow.__SSi || "";
-    }
-    ix = ids.indexOf(this.activeWindowSSiCache);
-    // We don't want to restore focus to a minimized window or a window which had all its
-    // tabs stripped out (doesn't exist).
-    if (ix != -1 && total[ix] && total[ix].sizemode == "minimized")
-      ix = -1;
-
-    let session = {
-      lastUpdate: Date.now(),
-      startTime: this._sessionStartTime,
-      recentCrashes: this._recentCrashes
-    };
-
-    let state = {
-      version: ["sessionrestore", FORMAT_VERSION],
-      windows: total,
-      selectedWindow: ix + 1,
-      _closedWindows: lastClosedWindowsCopy,
-      session: session,
-      global: this._globalState.getState()
-    };
-
-    // Scratchpad
-    if (Cu.isModuleLoaded("resource://devtools/client/scratchpad/scratchpad-manager.jsm")) {
-      // get open Scratchpad window states too
-      let scratchpads = ScratchpadManager.getSessionState();
-      if (scratchpads && scratchpads.length) {
-        state.scratchpads = scratchpads;
-      }
-    }
-
-    // The Browser Console
-    state.browserConsole = HUDService.getBrowserConsoleSessionState();
-
-    // Persist the last session if we deferred restoring it
-    if (LastSession.canRestore) {
-      state.lastSessionState = LastSession.getState();
-    }
-
-    // If we were called by the SessionSaver and started with only a private
-    // window we want to pass the deferred initial state to not lose the
-    // previous session.
-    if (this._deferredInitialState) {
-      state.deferredInitialState = this._deferredInitialState;
-    }
-
-    return state;
-  },
-
-  /**
-   * serialize session data for a window
-   * @param aWindow
-   *        Window reference
-   * @returns string
-   */
-  _getWindowState: function ssi_getWindowState(aWindow) {
-    if (!this._isWindowLoaded(aWindow))
-      return this._statesToRestore[aWindow.__SS_restoreID];
-
-    if (RunState.isRunning) {
-      this._collectWindowData(aWindow);
-    }
-
-    let windows = [this._windows[aWindow.__SSi]];
-    SessionCookies.update(windows);
-
-    return { windows: windows };
-  },
-
-  /**
-   * Gathers data about a window and its tabs, and updates its
-   * entry in this._windows.
-   *
-   * @param aWindow
-   *        Window references.
-   * @returns a Map mapping the browser tabs from aWindow to the tab
-   *          entry that was put into the window data in this._windows.
-   */
-  _collectWindowData: function ssi_collectWindowData(aWindow) {
-    let tabMap = new Map();
-
-    if (!this._isWindowLoaded(aWindow))
-      return tabMap;
-
-    let tabbrowser = aWindow.gBrowser;
-    let tabs = tabbrowser.tabs;
-    let winData = this._windows[aWindow.__SSi];
-    let tabsData = winData.tabs = [];
-
-    // update the internal state data for this window
-    for (let tab of tabs) {
-      let tabData = TabState.collect(tab);
-      tabMap.set(tab, tabData);
-      tabsData.push(tabData);
-    }
-    winData.selected = tabbrowser.mTabBox.selectedIndex + 1;
-
-    this._updateWindowFeatures(aWindow);
-
-    // Make sure we keep __SS_lastSessionWindowID around for cases like entering
-    // or leaving PB mode.
-    if (aWindow.__SS_lastSessionWindowID)
-      this._windows[aWindow.__SSi].__lastSessionWindowID =
-        aWindow.__SS_lastSessionWindowID;
-
-    DirtyWindows.remove(aWindow);
-    return tabMap;
-  },
-
-  /* ........ Restoring Functionality .............. */
-
-  /**
-   * restore features to a single window
-   * @param aWindow
-   *        Window reference to the window to use for restoration
-   * @param winData
-   *        JS object
-   * @param aOptions
-   *        {overwriteTabs: true} to overwrite existing tabs w/ new ones
-   *        {isFollowUp: true} if this is not the restoration of the 1st window
-   *        {firstWindow: true} if this is the first non-private window we're
-   *                            restoring in this session, that might open an
-   *                            external link as well
-   */
-  restoreWindow: function ssi_restoreWindow(aWindow, winData, aOptions = {}) {
-    let overwriteTabs = aOptions && aOptions.overwriteTabs;
-    let isFollowUp = aOptions && aOptions.isFollowUp;
-    let firstWindow = aOptions && aOptions.firstWindow;
-
-    if (isFollowUp) {
-      this.windowToFocus = aWindow;
-    }
-
-    // initialize window if necessary
-    if (aWindow && (!aWindow.__SSi || !this._windows[aWindow.__SSi]))
-      this.onLoad(aWindow);
-
-    TelemetryStopwatch.start("FX_SESSION_RESTORE_RESTORE_WINDOW_MS");
-
-    // We're not returning from this before we end up calling restoreTabs
-    // for this window, so make sure we send the SSWindowStateBusy event.
-    this._setWindowStateBusy(aWindow);
-
-    if (!winData.tabs) {
-      winData.tabs = [];
-    }
-
-    // don't restore a single blank tab when we've had an external
-    // URL passed in for loading at startup (cf. bug 357419)
-    else if (firstWindow && !overwriteTabs && winData.tabs.length == 1 &&
-             (!winData.tabs[0].entries || winData.tabs[0].entries.length == 0)) {
-      winData.tabs = [];
-    }
-
-    var tabbrowser = aWindow.gBrowser;
-    var openTabCount = overwriteTabs ? tabbrowser.browsers.length : -1;
-    var newTabCount = winData.tabs.length;
-    var tabs = [];
-
-    // disable smooth scrolling while adding, moving, removing and selecting tabs
-    var tabstrip = tabbrowser.tabContainer.mTabstrip;
-    var smoothScroll = tabstrip.smoothScroll;
-    tabstrip.smoothScroll = false;
-
-    // unpin all tabs to ensure they are not reordered in the next loop
-    if (overwriteTabs) {
-      for (let t = tabbrowser._numPinnedTabs - 1; t > -1; t--)
-        tabbrowser.unpinTab(tabbrowser.tabs[t]);
-    }
-
-    // We need to keep track of the initially open tabs so that they
-    // can be moved to the end of the restored tabs.
-    let initialTabs = [];
-    if (!overwriteTabs && firstWindow) {
-      initialTabs = Array.slice(tabbrowser.tabs);
-    }
-
-    // make sure that the selected tab won't be closed in order to
-    // prevent unnecessary flickering
-    if (overwriteTabs && tabbrowser.selectedTab._tPos >= newTabCount)
-      tabbrowser.moveTabTo(tabbrowser.selectedTab, newTabCount - 1);
-
-    let numVisibleTabs = 0;
-
-    for (var t = 0; t < newTabCount; t++) {
-      // When trying to restore into existing tab, we also take the userContextId
-      // into account if present.
-      let userContextId = winData.tabs[t].userContextId;
-      let reuseExisting = t < openTabCount &&
-                          (tabbrowser.tabs[t].getAttribute("usercontextid") == (userContextId || ""));
-      // If the tab is pinned, then we'll be loading it right away, and
-      // there's no need to cause a remoteness flip by loading it initially
-      // non-remote.
-      let forceNotRemote = !winData.tabs[t].pinned;
-      let tab = reuseExisting ? tabbrowser.tabs[t] :
-                                tabbrowser.addTab("about:blank",
-                                                  {skipAnimation: true,
-                                                   forceNotRemote,
-                                                   userContextId});
-
-      // If we inserted a new tab because the userContextId didn't match with the
-      // open tab, even though `t < openTabCount`, we need to remove that open tab
-      // and put the newly added tab in its place.
-      if (!reuseExisting && t < openTabCount) {
-        tabbrowser.removeTab(tabbrowser.tabs[t]);
-        tabbrowser.moveTabTo(tab, t);
-      }
-
-      tabs.push(tab);
-
-      if (winData.tabs[t].pinned)
-        tabbrowser.pinTab(tabs[t]);
-
-      if (winData.tabs[t].hidden) {
-        tabbrowser.hideTab(tabs[t]);
-      }
-      else {
-        tabbrowser.showTab(tabs[t]);
-        numVisibleTabs++;
-      }
-
-      if (!!winData.tabs[t].muted != tabs[t].linkedBrowser.audioMuted) {
-        tabs[t].toggleMuteAudio(winData.tabs[t].muteReason);
-      }
-    }
-
-    if (!overwriteTabs && firstWindow) {
-      // Move the originally open tabs to the end
-      let endPosition = tabbrowser.tabs.length - 1;
-      for (let i = 0; i < initialTabs.length; i++) {
-        tabbrowser.moveTabTo(initialTabs[i], endPosition);
-      }
-    }
-
-    // if all tabs to be restored are hidden, make the first one visible
-    if (!numVisibleTabs && winData.tabs.length) {
-      winData.tabs[0].hidden = false;
-      tabbrowser.showTab(tabs[0]);
-    }
-
-    // If overwriting tabs, we want to reset each tab's "restoring" state. Since
-    // we're overwriting those tabs, they should no longer be restoring. The
-    // tabs will be rebuilt and marked if they need to be restored after loading
-    // state (in restoreTabs).
-    if (overwriteTabs) {
-      for (let i = 0; i < tabbrowser.tabs.length; i++) {
-        let tab = tabbrowser.tabs[i];
-        if (tabbrowser.browsers[i].__SS_restoreState)
-          this._resetTabRestoringState(tab);
-      }
-    }
-
-    // We want to correlate the window with data from the last session, so
-    // assign another id if we have one. Otherwise clear so we don't do
-    // anything with it.
-    delete aWindow.__SS_lastSessionWindowID;
-    if (winData.__lastSessionWindowID)
-      aWindow.__SS_lastSessionWindowID = winData.__lastSessionWindowID;
-
-    // when overwriting tabs, remove all superflous ones
-    if (overwriteTabs && newTabCount < openTabCount) {
-      Array.slice(tabbrowser.tabs, newTabCount, openTabCount)
-           .forEach(tabbrowser.removeTab, tabbrowser);
-    }
-
-    if (overwriteTabs) {
-      this.restoreWindowFeatures(aWindow, winData);
-      delete this._windows[aWindow.__SSi].extData;
-    }
-    if (winData.cookies) {
-      SessionCookies.restore(winData.cookies);
-    }
-    if (winData.extData) {
-      if (!this._windows[aWindow.__SSi].extData) {
-        this._windows[aWindow.__SSi].extData = {};
-      }
-      for (var key in winData.extData) {
-        this._windows[aWindow.__SSi].extData[key] = winData.extData[key];
-      }
-    }
-
-    let newClosedTabsData = winData._closedTabs || [];
-
-    if (overwriteTabs || firstWindow) {
-      // Overwrite existing closed tabs data when overwriteTabs=true
-      // or we're the first window to be restored.
-      this._windows[aWindow.__SSi]._closedTabs = newClosedTabsData;
-    } else if (this._max_tabs_undo > 0) {
-      // If we merge tabs, we also want to merge closed tabs data. We'll assume
-      // the restored tabs were closed more recently and append the current list
-      // of closed tabs to the new one...
-      newClosedTabsData =
-        newClosedTabsData.concat(this._windows[aWindow.__SSi]._closedTabs);
-
-      // ... and make sure that we don't exceed the max number of closed tabs
-      // we can restore.
-      this._windows[aWindow.__SSi]._closedTabs =
-        newClosedTabsData.slice(0, this._max_tabs_undo);
-    }
-
-    // Restore tabs, if any.
-    if (winData.tabs.length) {
-      this.restoreTabs(aWindow, tabs, winData.tabs,
-        (overwriteTabs ? (parseInt(winData.selected || "1")) : 0));
-    }
-
-    // set smoothScroll back to the original value
-    tabstrip.smoothScroll = smoothScroll;
-
-    TelemetryStopwatch.finish("FX_SESSION_RESTORE_RESTORE_WINDOW_MS");
-
-    this._setWindowStateReady(aWindow);
-
-    this._sendWindowRestoredNotification(aWindow);
-
-    Services.obs.notifyObservers(aWindow, NOTIFY_SINGLE_WINDOW_RESTORED, "");
-
-    this._sendRestoreCompletedNotifications();
-  },
-
-  /**
-   * Restore multiple windows using the provided state.
-   * @param aWindow
-   *        Window reference to the first window to use for restoration.
-   *        Additionally required windows will be opened.
-   * @param aState
-   *        JS object or JSON string
-   * @param aOptions
-   *        {overwriteTabs: true} to overwrite existing tabs w/ new ones
-   *        {isFollowUp: true} if this is not the restoration of the 1st window
-   *        {firstWindow: true} if this is the first non-private window we're
-   *                            restoring in this session, that might open an
-   *                            external link as well
-   */
-  restoreWindows: function ssi_restoreWindows(aWindow, aState, aOptions = {}) {
-    let isFollowUp = aOptions && aOptions.isFollowUp;
-
-    if (isFollowUp) {
-      this.windowToFocus = aWindow;
-    }
-
-    // initialize window if necessary
-    if (aWindow && (!aWindow.__SSi || !this._windows[aWindow.__SSi]))
-      this.onLoad(aWindow);
-
-    let root;
-    try {
-      root = (typeof aState == "string") ? JSON.parse(aState) : aState;
-    }
-    catch (ex) { // invalid state object - don't restore anything
-      debug(ex);
-      this._sendRestoreCompletedNotifications();
-      return;
-    }
-
-    // Restore closed windows if any.
-    if (root._closedWindows) {
-      this._closedWindows = root._closedWindows;
-      this._closedObjectsChanged = true;
-    }
-
-    // We're done here if there are no windows.
-    if (!root.windows || !root.windows.length) {
-      this._sendRestoreCompletedNotifications();
-      return;
-    }
-
-    if (!root.selectedWindow || root.selectedWindow > root.windows.length) {
-      root.selectedWindow = 0;
-    }
-
-    // open new windows for all further window entries of a multi-window session
-    // (unless they don't contain any tab data)
-    let winData;
-    for (var w = 1; w < root.windows.length; w++) {
-      winData = root.windows[w];
-      if (winData && winData.tabs && winData.tabs[0]) {
-        var window = this._openWindowWithState({ windows: [winData] });
-        if (w == root.selectedWindow - 1) {
-          this.windowToFocus = window;
-        }
-      }
-    }
-
-    this.restoreWindow(aWindow, root.windows[0], aOptions);
-
-    // Scratchpad
-    if (aState.scratchpads) {
-      ScratchpadManager.restoreSession(aState.scratchpads);
-    }
-
-    // The Browser Console
-    if (aState.browserConsole) {
-      HUDService.restoreBrowserConsoleSession();
-    }
-  },
-
-  /**
-   * Manage history restoration for a window
-   * @param aWindow
-   *        Window to restore the tabs into
-   * @param aTabs
-   *        Array of tab references
-   * @param aTabData
-   *        Array of tab data
-   * @param aSelectTab
-   *        Index of the tab to select. This is a 1-based index where "1"
-   *        indicates the first tab should be selected, and "0" indicates that
-   *        the currently selected tab will not be changed.
-   */
-  restoreTabs(aWindow, aTabs, aTabData, aSelectTab) {
-    var tabbrowser = aWindow.gBrowser;
-
-    if (!this._isWindowLoaded(aWindow)) {
-      // from now on, the data will come from the actual window
-      delete this._statesToRestore[aWindow.__SS_restoreID];
-      delete aWindow.__SS_restoreID;
-      delete this._windows[aWindow.__SSi]._restoring;
-    }
-
-    let numTabsToRestore = aTabs.length;
-    let numTabsInWindow = tabbrowser.tabs.length;
-    let tabsDataArray = this._windows[aWindow.__SSi].tabs;
-
-    // Update the window state in case we shut down without being notified.
-    // Individual tab states will be taken care of by restoreTab() below.
-    if (numTabsInWindow == numTabsToRestore) {
-      // Remove all previous tab data.
-      tabsDataArray.length = 0;
-    } else {
-      // Remove all previous tab data except tabs that should not be overriden.
-      tabsDataArray.splice(numTabsInWindow - numTabsToRestore);
-    }
-
-    // Let the tab data array have the right number of slots.
-    tabsDataArray.length = numTabsInWindow;
-
-    // If provided, set the selected tab.
-    if (aSelectTab > 0 && aSelectTab <= aTabs.length) {
-      tabbrowser.selectedTab = aTabs[aSelectTab - 1];
-
-      // Update the window state in case we shut down without being notified.
-      this._windows[aWindow.__SSi].selected = aSelectTab;
-    }
-
-    // Restore all tabs.
-    for (let t = 0; t < aTabs.length; t++) {
-      this.restoreTab(aTabs[t], aTabData[t]);
-    }
-  },
-
-  // Restores the given tab state for a given tab.
-  restoreTab(tab, tabData, options = {}) {
-    NS_ASSERT(!tab.linkedBrowser.__SS_restoreState,
-              "must reset tab before calling restoreTab()");
-
-    let restoreImmediately = options.restoreImmediately;
-    let loadArguments = options.loadArguments;
-    let browser = tab.linkedBrowser;
-    let window = tab.ownerGlobal;
-    let tabbrowser = window.gBrowser;
-    let forceOnDemand = options.forceOnDemand;
-    let reloadInFreshProcess = options.reloadInFreshProcess;
-
-    let willRestoreImmediately = restoreImmediately ||
-                                 tabbrowser.selectedBrowser == browser ||
-                                 loadArguments;
-
-    if (!willRestoreImmediately && !forceOnDemand) {
-      TabRestoreQueue.add(tab);
-    }
-
-    this._maybeUpdateBrowserRemoteness({ tabbrowser, tab,
-                                         willRestoreImmediately });
-
-    // Increase the busy state counter before modifying the tab.
-    this._setWindowStateBusy(window);
-
-    // It's important to set the window state to dirty so that
-    // we collect their data for the first time when saving state.
-    DirtyWindows.add(window);
-
-    // In case we didn't collect/receive data for any tabs yet we'll have to
-    // fill the array with at least empty tabData objects until |_tPos| or
-    // we'll end up with |null| entries.
-    for (let otherTab of Array.slice(tabbrowser.tabs, 0, tab._tPos)) {
-      let emptyState = {entries: [], lastAccessed: otherTab.lastAccessed};
-      this._windows[window.__SSi].tabs.push(emptyState);
-    }
-
-    // Update the tab state in case we shut down without being notified.
-    this._windows[window.__SSi].tabs[tab._tPos] = tabData;
-
-    // Prepare the tab so that it can be properly restored. We'll pin/unpin
-    // and show/hide tabs as necessary. We'll also attach a copy of the tab's
-    // data in case we close it before it's been restored.
-    if (tabData.pinned) {
-      tabbrowser.pinTab(tab);
-    } else {
-      tabbrowser.unpinTab(tab);
-    }
-
-    if (tabData.hidden) {
-      tabbrowser.hideTab(tab);
-    } else {
-      tabbrowser.showTab(tab);
-    }
-
-    if (!!tabData.muted != browser.audioMuted) {
-      tab.toggleMuteAudio(tabData.muteReason);
-    }
-
-    if (tabData.lastAccessed) {
-      tab.updateLastAccessed(tabData.lastAccessed);
-    }
-
-    if ("attributes" in tabData) {
-      // Ensure that we persist tab attributes restored from previous sessions.
-      Object.keys(tabData.attributes).forEach(a => TabAttributes.persist(a));
-    }
-
-    if (!tabData.entries) {
-      tabData.entries = [];
-    }
-    if (tabData.extData) {
-      tab.__SS_extdata = Cu.cloneInto(tabData.extData, {});
-    } else {
-      delete tab.__SS_extdata;
-    }
-
-    // Tab is now open.
-    delete tabData.closedAt;
-
-    // Ensure the index is in bounds.
-    let activeIndex = (tabData.index || tabData.entries.length) - 1;
-    activeIndex = Math.min(activeIndex, tabData.entries.length - 1);
-    activeIndex = Math.max(activeIndex, 0);
-
-    // Save the index in case we updated it above.
-    tabData.index = activeIndex + 1;
-
-    // Start a new epoch to discard all frame script messages relating to a
-    // previous epoch. All async messages that are still on their way to chrome
-    // will be ignored and don't override any tab data set when restoring.
-    let epoch = this.startNextEpoch(browser);
-
-    // keep the data around to prevent dataloss in case
-    // a tab gets closed before it's been properly restored
-    browser.__SS_restoreState = TAB_STATE_NEEDS_RESTORE;
-    browser.setAttribute("pending", "true");
-    tab.setAttribute("pending", "true");
-
-    // If we're restoring this tab, it certainly shouldn't be in
-    // the ignored set anymore.
-    this._crashedBrowsers.delete(browser.permanentKey);
-
-    // Update the persistent tab state cache with |tabData| information.
-    TabStateCache.update(browser, {
-      // NOTE: Copy the entries array shallowly, so as to not screw with the
-      // original tabData's history when getting history updates.
-      history: {entries: [...tabData.entries], index: tabData.index},
-      scroll: tabData.scroll || null,
-      storage: tabData.storage || null,
-      formdata: tabData.formdata || null,
-      disallow: tabData.disallow || null,
-      pageStyle: tabData.pageStyle || null,
-
-      // This information is only needed until the tab has finished restoring.
-      // When that's done it will be removed from the cache and we always
-      // collect it in TabState._collectBaseTabData().
-      image: tabData.image || "",
-      iconLoadingPrincipal: tabData.iconLoadingPrincipal || null,
-      userTypedValue: tabData.userTypedValue || "",
-      userTypedClear: tabData.userTypedClear || 0
-    });
-
-    browser.messageManager.sendAsyncMessage("SessionStore:restoreHistory",
-                                            {tabData: tabData, epoch: epoch, loadArguments});
-
-    // Restore tab attributes.
-    if ("attributes" in tabData) {
-      TabAttributes.set(tab, tabData.attributes);
-    }
-
-    // This could cause us to ignore MAX_CONCURRENT_TAB_RESTORES a bit, but
-    // it ensures each window will have its selected tab loaded.
-    if (willRestoreImmediately) {
-      this.restoreTabContent(tab, loadArguments, reloadInFreshProcess);
-    } else if (!forceOnDemand) {
-      this.restoreNextTab();
-    }
-
-    // Decrease the busy state counter after we're done.
-    this._setWindowStateReady(window);
-  },
-
-  /**
-   * Kicks off restoring the given tab.
-   *
-   * @param aTab
-   *        the tab to restore
-   * @param aLoadArguments
-   *        optional load arguments used for loadURI()
-   * @param aReloadInFreshProcess
-   *        true if we want to reload into a fresh process
-   */
-  restoreTabContent: function (aTab, aLoadArguments = null, aReloadInFreshProcess = false) {
-    if (aTab.hasAttribute("customizemode") && !aLoadArguments) {
-      return;
-    }
-
-    let browser = aTab.linkedBrowser;
-    let window = aTab.ownerGlobal;
-    let tabbrowser = window.gBrowser;
-    let tabData = TabState.clone(aTab);
-    let activeIndex = tabData.index - 1;
-    let activePageData = tabData.entries[activeIndex] || null;
-    let uri = activePageData ? activePageData.url || null : null;
-    if (aLoadArguments) {
-      uri = aLoadArguments.uri;
-      if (aLoadArguments.userContextId) {
-        browser.setAttribute("usercontextid", aLoadArguments.userContextId);
-      }
-    }
-
-    // We have to mark this tab as restoring first, otherwise
-    // the "pending" attribute will be applied to the linked
-    // browser, which removes it from the display list. We cannot
-    // flip the remoteness of any browser that is not being displayed.
-    this.markTabAsRestoring(aTab);
-
-    // We need a new frameloader either if we are reloading into a fresh
-    // process, or we have a browser with a grouped session history (as we don't
-    // support restoring into browsers with grouped session histories directly).
-    let newFrameloader =
-      aReloadInFreshProcess || !!browser.frameLoader.groupedSHistory;
-    let isRemotenessUpdate =
-      tabbrowser.updateBrowserRemotenessByURL(browser, uri, {
-        freshProcess: aReloadInFreshProcess,
-        newFrameloader: newFrameloader,
-      });
-
-    if (isRemotenessUpdate) {
-      // We updated the remoteness, so we need to send the history down again.
-      //
-      // Start a new epoch to discard all frame script messages relating to a
-      // previous epoch. All async messages that are still on their way to chrome
-      // will be ignored and don't override any tab data set when restoring.
-      let epoch = this.startNextEpoch(browser);
-
-      browser.messageManager.sendAsyncMessage("SessionStore:restoreHistory", {
-        tabData: tabData,
-        epoch: epoch,
-        loadArguments: aLoadArguments,
-        isRemotenessUpdate,
-      });
-
-    }
-
-    // If the restored browser wants to show view source content, start up a
-    // view source browser that will load the required frame script.
-    if (uri && ViewSourceBrowser.isViewSource(uri)) {
-      new ViewSourceBrowser(browser);
-    }
-
-    browser.messageManager.sendAsyncMessage("SessionStore:restoreTabContent",
-      {loadArguments: aLoadArguments, isRemotenessUpdate});
-  },
-
-  /**
-   * Marks a given pending tab as restoring.
-   *
-   * @param aTab
-   *        the pending tab to mark as restoring
-   */
-  markTabAsRestoring(aTab) {
-    let browser = aTab.linkedBrowser;
-    if (browser.__SS_restoreState != TAB_STATE_NEEDS_RESTORE) {
-      throw new Error("Given tab is not pending.");
-    }
-
-    // Make sure that this tab is removed from the priority queue.
-    TabRestoreQueue.remove(aTab);
-
-    // Increase our internal count.
-    this._tabsRestoringCount++;
-
-    // Set this tab's state to restoring
-    browser.__SS_restoreState = TAB_STATE_RESTORING;
-    browser.removeAttribute("pending");
-    aTab.removeAttribute("pending");
-  },
-
-  /**
-   * This _attempts_ to restore the next available tab. If the restore fails,
-   * then we will attempt the next one.
-   * There are conditions where this won't do anything:
-   *   if we're in the process of quitting
-   *   if there are no tabs to restore
-   *   if we have already reached the limit for number of tabs to restore
-   */
-  restoreNextTab: function ssi_restoreNextTab() {
-    // If we call in here while quitting, we don't actually want to do anything
-    if (RunState.isQuitting)
-      return;
-
-    // Don't exceed the maximum number of concurrent tab restores.
-    if (this._tabsRestoringCount >= MAX_CONCURRENT_TAB_RESTORES)
-      return;
-
-    let tab = TabRestoreQueue.shift();
-    if (tab) {
-      this.restoreTabContent(tab);
-    }
-  },
-
-  /**
-   * Restore visibility and dimension features to a window
-   * @param aWindow
-   *        Window reference
-   * @param aWinData
-   *        Object containing session data for the window
-   */
-  restoreWindowFeatures: function ssi_restoreWindowFeatures(aWindow, aWinData) {
-    var hidden = (aWinData.hidden)?aWinData.hidden.split(","):[];
-    WINDOW_HIDEABLE_FEATURES.forEach(function(aItem) {
-      aWindow[aItem].visible = hidden.indexOf(aItem) == -1;
-    });
-
-    if (aWinData.isPopup) {
-      this._windows[aWindow.__SSi].isPopup = true;
-      if (aWindow.gURLBar) {
-        aWindow.gURLBar.readOnly = true;
-        aWindow.gURLBar.setAttribute("enablehistory", "false");
-      }
-    }
-    else {
-      delete this._windows[aWindow.__SSi].isPopup;
-      if (aWindow.gURLBar) {
-        aWindow.gURLBar.readOnly = false;
-        aWindow.gURLBar.setAttribute("enablehistory", "true");
-      }
-    }
-
-    var _this = this;
-    aWindow.setTimeout(function() {
-      _this.restoreDimensions.apply(_this, [aWindow,
-        +(aWinData.width || 0),
-        +(aWinData.height || 0),
-        "screenX" in aWinData ? +aWinData.screenX : NaN,
-        "screenY" in aWinData ? +aWinData.screenY : NaN,
-        aWinData.sizemode || "", aWinData.sidebar || ""]);
-    }, 0);
-  },
-
-  /**
-   * Restore a window's dimensions
-   * @param aWidth
-   *        Window width
-   * @param aHeight
-   *        Window height
-   * @param aLeft
-   *        Window left
-   * @param aTop
-   *        Window top
-   * @param aSizeMode
-   *        Window size mode (eg: maximized)
-   * @param aSidebar
-   *        Sidebar command
-   */
-  restoreDimensions: function ssi_restoreDimensions(aWindow, aWidth, aHeight, aLeft, aTop, aSizeMode, aSidebar) {
-    var win = aWindow;
-    var _this = this;
-    function win_(aName) { return _this._getWindowDimension(win, aName); }
-
-    // find available space on the screen where this window is being placed
-    let screen = gScreenManager.screenForRect(aLeft, aTop, aWidth, aHeight);
-    if (screen) {
-      let screenLeft = {}, screenTop = {}, screenWidth = {}, screenHeight = {};
-      screen.GetAvailRectDisplayPix(screenLeft, screenTop, screenWidth, screenHeight);
-      // screenX/Y are based on the origin of the screen's desktop-pixel coordinate space
-      let screenLeftCss = screenLeft.value;
-      let screenTopCss = screenTop.value;
-      // convert screen's device pixel dimensions to CSS px dimensions
-      screen.GetAvailRect(screenLeft, screenTop, screenWidth, screenHeight);
-      let cssToDevScale = screen.defaultCSSScaleFactor;
-      let screenRightCss = screenLeftCss + screenWidth.value / cssToDevScale;
-      let screenBottomCss = screenTopCss + screenHeight.value / cssToDevScale;
-
-      // Pull the window within the screen's bounds (allowing a little slop
-      // for windows that may be deliberately placed with their border off-screen
-      // as when Win10 "snaps" a window to the left/right edge -- bug 1276516).
-      // First, ensure the left edge is large enough...
-      if (aLeft < screenLeftCss - SCREEN_EDGE_SLOP) {
-        aLeft = screenLeftCss;
-      }
-      // Then check the resulting right edge, and reduce it if necessary.
-      let right = aLeft + aWidth;
-      if (right > screenRightCss + SCREEN_EDGE_SLOP) {
-        right = screenRightCss;
-        // See if we can move the left edge leftwards to maintain width.
-        if (aLeft > screenLeftCss) {
-          aLeft = Math.max(right - aWidth, screenLeftCss);
-        }
-      }
-      // Finally, update aWidth to account for the adjusted left and right edges.
-      aWidth = right - aLeft;
-
-      // And do the same in the vertical dimension.
-      if (aTop < screenTopCss - SCREEN_EDGE_SLOP) {
-        aTop = screenTopCss;
-      }
-      let bottom = aTop + aHeight;
-      if (bottom > screenBottomCss + SCREEN_EDGE_SLOP) {
-        bottom = screenBottomCss;
-        if (aTop > screenTopCss) {
-          aTop = Math.max(bottom - aHeight, screenTopCss);
-        }
-      }
-      aHeight = bottom - aTop;
-    }
-
-    // only modify those aspects which aren't correct yet
-    if (!isNaN(aLeft) && !isNaN(aTop) && (aLeft != win_("screenX") || aTop != win_("screenY"))) {
-      aWindow.moveTo(aLeft, aTop);
-    }
-    if (aWidth && aHeight && (aWidth != win_("width") || aHeight != win_("height"))) {
-      // Don't resize the window if it's currently maximized and we would
-      // maximize it again shortly after.
-      if (aSizeMode != "maximized" || win_("sizemode") != "maximized") {
-        aWindow.resizeTo(aWidth, aHeight);
-      }
-    }
-    if (aSizeMode && win_("sizemode") != aSizeMode)
-    {
-      switch (aSizeMode)
-      {
-      case "maximized":
-        aWindow.maximize();
-        break;
-      case "minimized":
-        aWindow.minimize();
-        break;
-      case "normal":
-        aWindow.restore();
-        break;
-      }
-    }
-    var sidebar = aWindow.document.getElementById("sidebar-box");
-    if (sidebar.getAttribute("sidebarcommand") != aSidebar) {
-      aWindow.SidebarUI.show(aSidebar);
-    }
-    // since resizing/moving a window brings it to the foreground,
-    // we might want to re-focus the last focused window
-    if (this.windowToFocus) {
-      this.windowToFocus.focus();
-    }
-  },
-
-  /* ........ Disk Access .............. */
-
-  /**
-   * Save the current session state to disk, after a delay.
-   *
-   * @param aWindow (optional)
-   *        Will mark the given window as dirty so that we will recollect its
-   *        data before we start writing.
-   */
-  saveStateDelayed: function (aWindow = null) {
-    if (aWindow) {
-      DirtyWindows.add(aWindow);
-    }
-
-    SessionSaver.runDelayed();
-  },
-
-  /* ........ Auxiliary Functions .............. */
-
-  /**
-   * Remove a closed window from the list of closed windows and indicate that
-   * the change should be notified.
-   *
-   * @param index
-   *        The index of the window in this._closedWindows.
-   *
-   * @returns Array of closed windows.
-   */
-  _removeClosedWindow(index) {
-    let windows = this._closedWindows.splice(index, 1);
-    this._closedObjectsChanged = true;
-    return windows;
-  },
-
-  /**
-   * Notifies observers that the list of closed tabs and/or windows has changed.
-   * Waits a tick to allow SessionStorage a chance to register the change.
-   */
-  _notifyOfClosedObjectsChange() {
-    if (!this._closedObjectsChanged) {
-      return;
-    }
-    this._closedObjectsChanged = false;
-    setTimeout(() => {
-      Services.obs.notifyObservers(null, NOTIFY_CLOSED_OBJECTS_CHANGED, null);
-    }, 0);
-  },
-
-  /**
-   * Determines whether or not a tab that is being restored needs
-   * to have its remoteness flipped first.
-   *
-   * @param (object) with the following properties:
-   *
-   *        tabbrowser (<xul:tabbrowser>):
-   *          The tabbrowser that the browser belongs to.
-   *
-   *        tab (<xul:tab>):
-   *          The tab being restored
-   *
-   *        willRestoreImmediately (bool):
-   *          true if the tab is going to have its content
-   *          restored immediately by the caller.
-   *
-   */
-  _maybeUpdateBrowserRemoteness({ tabbrowser, tab,
-                                  willRestoreImmediately }) {
-    // If the browser we're attempting to restore happens to be
-    // remote, we need to flip it back to non-remote if it's going
-    // to go into the pending background tab state. This is to make
-    // sure that a background tab can't crash if it hasn't yet
-    // been restored.
-    //
-    // Normally, when a window is restored, the tabs that SessionStore
-    // inserts are non-remote - but the initial browser is, by default,
-    // remote, so this check and flip covers this case. The other case
-    // is when window state is overwriting the state of an existing
-    // window with some remote tabs.
-    let browser = tab.linkedBrowser;
-
-    // There are two ways that a tab might start restoring its content
-    // very soon - either the caller is going to restore the content
-    // immediately, or the TabRestoreQueue is set up so that the tab
-    // content is going to be restored in the very near future. In
-    // either case, we don't want to flip remoteness, since the browser
-    // will soon be loading content.
-    let willRestore = willRestoreImmediately ||
-                      TabRestoreQueue.willRestoreSoon(tab);
-
-    if (browser.isRemoteBrowser && !willRestore) {
-      tabbrowser.updateBrowserRemoteness(browser, false);
-    }
-  },
-
-  /**
-   * Update the session start time and send a telemetry measurement
-   * for the number of days elapsed since the session was started.
-   *
-   * @param state
-   *        The session state.
-   */
-  _updateSessionStartTime: function ssi_updateSessionStartTime(state) {
-    // Attempt to load the session start time from the session state
-    if (state.session && state.session.startTime) {
-      this._sessionStartTime = state.session.startTime;
-    }
-  },
-
-  /**
-   * call a callback for all currently opened browser windows
-   * (might miss the most recent one)
-   * @param aFunc
-   *        Callback each window is passed to
-   */
-  _forEachBrowserWindow: function ssi_forEachBrowserWindow(aFunc) {
-    var windowsEnum = Services.wm.getEnumerator("navigator:browser");
-
-    while (windowsEnum.hasMoreElements()) {
-      var window = windowsEnum.getNext();
-      if (window.__SSi && !window.closed) {
-        aFunc.call(this, window);
-      }
-    }
-  },
-
-  /**
-   * Returns most recent window
-   * @returns Window reference
-   */
-  _getMostRecentBrowserWindow: function ssi_getMostRecentBrowserWindow() {
-    return RecentWindow.getMostRecentBrowserWindow({ allowPopups: true });
-  },
-
-  /**
-   * Calls onClose for windows that are determined to be closed but aren't
-   * destroyed yet, which would otherwise cause getBrowserState and
-   * setBrowserState to treat them as open windows.
-   */
-  _handleClosedWindows: function ssi_handleClosedWindows() {
-    var windowsEnum = Services.wm.getEnumerator("navigator:browser");
-
-    let promises = [];
-    while (windowsEnum.hasMoreElements()) {
-      var window = windowsEnum.getNext();
-      if (window.closed) {
-        promises.push(this.onClose(window));
-      }
-    }
-    return Promise.all(promises);
-  },
-
-  /**
-   * open a new browser window for a given session state
-   * called when restoring a multi-window session
-   * @param aState
-   *        Object containing session data
-   */
-  _openWindowWithState: function ssi_openWindowWithState(aState) {
-    var argString = Cc["@mozilla.org/supports-string;1"].
-                    createInstance(Ci.nsISupportsString);
-    argString.data = "";
-
-    // Build feature string
-    let features = "chrome,dialog=no,macsuppressanimation,all";
-    let winState = aState.windows[0];
-    WINDOW_ATTRIBUTES.forEach(function(aFeature) {
-      // Use !isNaN as an easy way to ignore sizemode and check for numbers
-      if (aFeature in winState && !isNaN(winState[aFeature]))
-        features += "," + aFeature + "=" + winState[aFeature];
-    });
-
-    if (winState.isPrivate) {
-      features += ",private";
-    }
-
-    var window =
-      Services.ww.openWindow(null, this._prefBranch.getCharPref("chromeURL"),
-                             "_blank", features, argString);
-
-    do {
-      var ID = "window" + Math.random();
-    } while (ID in this._statesToRestore);
-    this._statesToRestore[(window.__SS_restoreID = ID)] = aState;
-
-    return window;
-  },
-
-  /**
-   * Whether or not to resume session, if not recovering from a crash.
-   * @returns bool
-   */
-  _doResumeSession: function ssi_doResumeSession() {
-    return this._prefBranch.getIntPref("startup.page") == 3 ||
-           this._prefBranch.getBoolPref("sessionstore.resume_session_once");
-  },
-
-  /**
-   * whether the user wants to load any other page at startup
-   * (except the homepage) - needed for determining whether to overwrite the current tabs
-   * C.f.: nsBrowserContentHandler's defaultArgs implementation.
-   * @returns bool
-   */
-  _isCmdLineEmpty: function ssi_isCmdLineEmpty(aWindow, aState) {
-    var pinnedOnly = aState.windows &&
-                     aState.windows.every(win =>
-                       win.tabs.every(tab => tab.pinned));
-
-    let hasFirstArgument = aWindow.arguments && aWindow.arguments[0];
-    if (!pinnedOnly) {
-      let defaultArgs = Cc["@mozilla.org/browser/clh;1"].
-                        getService(Ci.nsIBrowserHandler).defaultArgs;
-      if (aWindow.arguments &&
-          aWindow.arguments[0] &&
-          aWindow.arguments[0] == defaultArgs)
-        hasFirstArgument = false;
-    }
-
-    return !hasFirstArgument;
-  },
-
-  /**
-   * on popup windows, the XULWindow's attributes seem not to be set correctly
-   * we use thus JSDOMWindow attributes for sizemode and normal window attributes
-   * (and hope for reasonable values when maximized/minimized - since then
-   * outerWidth/outerHeight aren't the dimensions of the restored window)
-   * @param aWindow
-   *        Window reference
-   * @param aAttribute
-   *        String sizemode | width | height | other window attribute
-   * @returns string
-   */
-  _getWindowDimension: function ssi_getWindowDimension(aWindow, aAttribute) {
-    if (aAttribute == "sizemode") {
-      switch (aWindow.windowState) {
-      case aWindow.STATE_FULLSCREEN:
-      case aWindow.STATE_MAXIMIZED:
-        return "maximized";
-      case aWindow.STATE_MINIMIZED:
-        return "minimized";
-      default:
-        return "normal";
-      }
-    }
-
-    var dimension;
-    switch (aAttribute) {
-    case "width":
-      dimension = aWindow.outerWidth;
-      break;
-    case "height":
-      dimension = aWindow.outerHeight;
-      break;
-    default:
-      dimension = aAttribute in aWindow ? aWindow[aAttribute] : "";
-      break;
-    }
-
-    if (aWindow.windowState == aWindow.STATE_NORMAL) {
-      return dimension;
-    }
-    return aWindow.document.documentElement.getAttribute(aAttribute) || dimension;
-  },
-
-  /**
-   * @param aState is a session state
-   * @param aRecentCrashes is the number of consecutive crashes
-   * @returns whether a restore page will be needed for the session state
-   */
-  _needsRestorePage: function ssi_needsRestorePage(aState, aRecentCrashes) {
-    const SIX_HOURS_IN_MS = 6 * 60 * 60 * 1000;
-
-    // don't display the page when there's nothing to restore
-    let winData = aState.windows || null;
-    if (!winData || winData.length == 0)
-      return false;
-
-    // don't wrap a single about:sessionrestore page
-    if (this._hasSingleTabWithURL(winData, "about:sessionrestore") ||
-        this._hasSingleTabWithURL(winData, "about:welcomeback")) {
-      return false;
-    }
-
-    // don't automatically restore in Safe Mode
-    if (Services.appinfo.inSafeMode)
-      return true;
-
-    let max_resumed_crashes =
-      this._prefBranch.getIntPref("sessionstore.max_resumed_crashes");
-    let sessionAge = aState.session && aState.session.lastUpdate &&
-                     (Date.now() - aState.session.lastUpdate);
-
-    return max_resumed_crashes != -1 &&
-           (aRecentCrashes > max_resumed_crashes ||
-            sessionAge && sessionAge >= SIX_HOURS_IN_MS);
-  },
-
-  /**
-   * @param aWinData is the set of windows in session state
-   * @param aURL is the single URL we're looking for
-   * @returns whether the window data contains only the single URL passed
-   */
-  _hasSingleTabWithURL: function(aWinData, aURL) {
-    if (aWinData &&
-        aWinData.length == 1 &&
-        aWinData[0].tabs &&
-        aWinData[0].tabs.length == 1 &&
-        aWinData[0].tabs[0].entries &&
-        aWinData[0].tabs[0].entries.length == 1) {
-      return aURL == aWinData[0].tabs[0].entries[0].url;
-    }
-    return false;
-  },
-
-  /**
-   * Determine if the tab state we're passed is something we should save. This
-   * is used when closing a tab or closing a window with a single tab
-   *
-   * @param aTabState
-   *        The current tab state
-   * @returns boolean
-   */
-  _shouldSaveTabState: function ssi_shouldSaveTabState(aTabState) {
-    // If the tab has only a transient about: history entry, no other
-    // session history, and no userTypedValue, then we don't actually want to
-    // store this tab's data.
-    return aTabState.entries.length &&
-           !(aTabState.entries.length == 1 &&
-                (aTabState.entries[0].url == "about:blank" ||
-                 aTabState.entries[0].url == "about:newtab" ||
-                 aTabState.entries[0].url == "about:printpreview" ||
-                 aTabState.entries[0].url == "about:privatebrowsing") &&
-                 !aTabState.userTypedValue);
-  },
-
-  /**
-   * Determine if the tab state we're passed is something we should keep to be
-   * reopened at session restore. This is used when we are saving the current
-   * session state to disk. This method is very similar to _shouldSaveTabState,
-   * however, "about:blank" and "about:newtab" tabs will still be saved to disk.
-   *
-   * @param aTabState
-   *        The current tab state
-   * @returns boolean
-   */
-  _shouldSaveTab: function ssi_shouldSaveTab(aTabState) {
-    // If the tab has one of the following transient about: history entry,
-    // then we don't actually want to write this tab's data to disk.
-    return aTabState.userTypedValue ||
-           (aTabState.entries.length &&
-            !(aTabState.entries[0].url == "about:printpreview" ||
-              aTabState.entries[0].url == "about:privatebrowsing"));
-  },
-
-  /**
-   * This is going to take a state as provided at startup (via
-   * nsISessionStartup.state) and split it into 2 parts. The first part
-   * (defaultState) will be a state that should still be restored at startup,
-   * while the second part (state) is a state that should be saved for later.
-   * defaultState will be comprised of windows with only pinned tabs, extracted
-   * from state. It will contain the cookies that go along with the history
-   * entries in those tabs. It will also contain window position information.
-   *
-   * defaultState will be restored at startup. state will be passed into
-   * LastSession and will be kept in case the user explicitly wants
-   * to restore the previous session (publicly exposed as restoreLastSession).
-   *
-   * @param state
-   *        The state, presumably from nsISessionStartup.state
-   * @returns [defaultState, state]
-   */
-  _prepDataForDeferredRestore: function ssi_prepDataForDeferredRestore(state) {
-    // Make sure that we don't modify the global state as provided by
-    // nsSessionStartup.state.
-    state = Cu.cloneInto(state, {});
-
-    let defaultState = { windows: [], selectedWindow: 1 };
-
-    state.selectedWindow = state.selectedWindow || 1;
-
-    // Look at each window, remove pinned tabs, adjust selectedindex,
-    // remove window if necessary.
-    for (let wIndex = 0; wIndex < state.windows.length;) {
-      let window = state.windows[wIndex];
-      window.selected = window.selected || 1;
-      // We're going to put the state of the window into this object
-      let pinnedWindowState = { tabs: [], cookies: []};
-      for (let tIndex = 0; tIndex < window.tabs.length;) {
-        if (window.tabs[tIndex].pinned) {
-          // Adjust window.selected
-          if (tIndex + 1 < window.selected)
-            window.selected -= 1;
-          else if (tIndex + 1 == window.selected)
-            pinnedWindowState.selected = pinnedWindowState.tabs.length + 2;
-            // + 2 because the tab isn't actually in the array yet
-
-          // Now add the pinned tab to our window
-          pinnedWindowState.tabs =
-            pinnedWindowState.tabs.concat(window.tabs.splice(tIndex, 1));
-          // We don't want to increment tIndex here.
-          continue;
-        }
-        tIndex++;
-      }
-
-      // At this point the window in the state object has been modified (or not)
-      // We want to build the rest of this new window object if we have pinnedTabs.
-      if (pinnedWindowState.tabs.length) {
-        // First get the other attributes off the window
-        WINDOW_ATTRIBUTES.forEach(function(attr) {
-          if (attr in window) {
-            pinnedWindowState[attr] = window[attr];
-            delete window[attr];
-          }
-        });
-        // We're just copying position data into the pinned window.
-        // Not copying over:
-        // - _closedTabs
-        // - extData
-        // - isPopup
-        // - hidden
-
-        // Assign a unique ID to correlate the window to be opened with the
-        // remaining data
-        window.__lastSessionWindowID = pinnedWindowState.__lastSessionWindowID
-                                     = "" + Date.now() + Math.random();
-
-        // Extract the cookies that belong with each pinned tab
-        this._splitCookiesFromWindow(window, pinnedWindowState);
-
-        // Actually add this window to our defaultState
-        defaultState.windows.push(pinnedWindowState);
-        // Remove the window from the state if it doesn't have any tabs
-        if (!window.tabs.length) {
-          if (wIndex + 1 <= state.selectedWindow)
-            state.selectedWindow -= 1;
-          else if (wIndex + 1 == state.selectedWindow)
-            defaultState.selectedIndex = defaultState.windows.length + 1;
-
-          state.windows.splice(wIndex, 1);
-          // We don't want to increment wIndex here.
-          continue;
-        }
-
-
-      }
-      wIndex++;
-    }
-
-    return [defaultState, state];
-  },
-
-  /**
-   * Splits out the cookies from aWinState into aTargetWinState based on the
-   * tabs that are in aTargetWinState.
-   * This alters the state of aWinState and aTargetWinState.
-   */
-  _splitCookiesFromWindow:
-    function ssi_splitCookiesFromWindow(aWinState, aTargetWinState) {
-    if (!aWinState.cookies || !aWinState.cookies.length)
-      return;
-
-    // Get the hosts for history entries in aTargetWinState
-    let cookieHosts = SessionCookies.getHostsForWindow(aTargetWinState);
-
-    // By creating a regex we reduce overhead and there is only one loop pass
-    // through either array (cookieHosts and aWinState.cookies).
-    let hosts = Object.keys(cookieHosts).join("|").replace(/\./g, "\\.");
-    // If we don't actually have any hosts, then we don't want to do anything.
-    if (!hosts.length)
-      return;
-    let cookieRegex = new RegExp(".*(" + hosts + ")");
-    for (let cIndex = 0; cIndex < aWinState.cookies.length;) {
-      if (cookieRegex.test(aWinState.cookies[cIndex].host)) {
-        aTargetWinState.cookies =
-          aTargetWinState.cookies.concat(aWinState.cookies.splice(cIndex, 1));
-        continue;
-      }
-      cIndex++;
-    }
-  },
-
-  _sendRestoreCompletedNotifications: function ssi_sendRestoreCompletedNotifications() {
-    // not all windows restored, yet
-    if (this._restoreCount > 1) {
-      this._restoreCount--;
-      return;
-    }
-
-    // observers were already notified
-    if (this._restoreCount == -1)
-      return;
-
-    // This was the last window restored at startup, notify observers.
-    Services.obs.notifyObservers(null,
-      this._browserSetState ? NOTIFY_BROWSER_STATE_RESTORED : NOTIFY_WINDOWS_RESTORED,
-      "");
-
-    this._browserSetState = false;
-    this._restoreCount = -1;
-  },
-
-   /**
-   * Set the given window's busy state
-   * @param aWindow the window
-   * @param aValue the window's busy state
-   */
-  _setWindowStateBusyValue:
-    function ssi_changeWindowStateBusyValue(aWindow, aValue) {
-
-    this._windows[aWindow.__SSi].busy = aValue;
-
-    // Keep the to-be-restored state in sync because that is returned by
-    // getWindowState() as long as the window isn't loaded, yet.
-    if (!this._isWindowLoaded(aWindow)) {
-      let stateToRestore = this._statesToRestore[aWindow.__SS_restoreID].windows[0];
-      stateToRestore.busy = aValue;
-    }
-  },
-
-  /**
-   * Set the given window's state to 'not busy'.
-   * @param aWindow the window
-   */
-  _setWindowStateReady: function ssi_setWindowStateReady(aWindow) {
-    let newCount = (this._windowBusyStates.get(aWindow) || 0) - 1;
-    if (newCount < 0) {
-      throw new Error("Invalid window busy state (less than zero).");
-    }
-    this._windowBusyStates.set(aWindow, newCount);
-
-    if (newCount == 0) {
-      this._setWindowStateBusyValue(aWindow, false);
-      this._sendWindowStateEvent(aWindow, "Ready");
-    }
-  },
-
-  /**
-   * Set the given window's state to 'busy'.
-   * @param aWindow the window
-   */
-  _setWindowStateBusy: function ssi_setWindowStateBusy(aWindow) {
-    let newCount = (this._windowBusyStates.get(aWindow) || 0) + 1;
-    this._windowBusyStates.set(aWindow, newCount);
-
-    if (newCount == 1) {
-      this._setWindowStateBusyValue(aWindow, true);
-      this._sendWindowStateEvent(aWindow, "Busy");
-    }
-  },
-
-  /**
-   * Dispatch an SSWindowState_____ event for the given window.
-   * @param aWindow the window
-   * @param aType the type of event, SSWindowState will be prepended to this string
-   */
-  _sendWindowStateEvent: function ssi_sendWindowStateEvent(aWindow, aType) {
-    let event = aWindow.document.createEvent("Events");
-    event.initEvent("SSWindowState" + aType, true, false);
-    aWindow.dispatchEvent(event);
-  },
-
-  /**
-   * Dispatch the SSWindowRestored event for the given window.
-   * @param aWindow
-   *        The window which has been restored
-   */
-  _sendWindowRestoredNotification(aWindow) {
-    let event = aWindow.document.createEvent("Events");
-    event.initEvent("SSWindowRestored", true, false);
-    aWindow.dispatchEvent(event);
-  },
-
-  /**
-   * Dispatch the SSTabRestored event for the given tab.
-   * @param aTab
-   *        The tab which has been restored
-   * @param aIsRemotenessUpdate
-   *        True if this tab was restored due to flip from running from
-   *        out-of-main-process to in-main-process or vice-versa.
-   */
-  _sendTabRestoredNotification(aTab, aIsRemotenessUpdate) {
-    let event = aTab.ownerDocument.createEvent("CustomEvent");
-    event.initCustomEvent("SSTabRestored", true, false, {
-      isRemotenessUpdate: aIsRemotenessUpdate,
-    });
-    aTab.dispatchEvent(event);
-  },
-
-  /**
-   * @param aWindow
-   *        Window reference
-   * @returns whether this window's data is still cached in _statesToRestore
-   *          because it's not fully loaded yet
-   */
-  _isWindowLoaded: function ssi_isWindowLoaded(aWindow) {
-    return !aWindow.__SS_restoreID;
-  },
-
-  /**
-   * Replace "Loading..." with the tab label (with minimal side-effects)
-   * @param aString is the string the title is stored in
-   * @param aTabbrowser is a tabbrowser object, containing aTab
-   * @param aTab is the tab whose title we're updating & using
-   *
-   * @returns aString that has been updated with the new title
-   */
-  _replaceLoadingTitle : function ssi_replaceLoadingTitle(aString, aTabbrowser, aTab) {
-    if (aString == aTabbrowser.mStringBundle.getString("tabs.connecting")) {
-      aTabbrowser.setTabTitle(aTab);
-      [aString, aTab.label] = [aTab.label, aString];
-    }
-    return aString;
-  },
-
-  /**
-   * Resize this._closedWindows to the value of the pref, except in the case
-   * where we don't have any non-popup windows on Windows and Linux. Then we must
-   * resize such that we have at least one non-popup window.
-   */
-  _capClosedWindows : function ssi_capClosedWindows() {
-    if (this._closedWindows.length <= this._max_windows_undo)
-      return;
-    let spliceTo = this._max_windows_undo;
-#ifndef XP_MACOSX
-    let normalWindowIndex = 0;
-    // try to find a non-popup window in this._closedWindows
-    while (normalWindowIndex < this._closedWindows.length &&
-           !!this._closedWindows[normalWindowIndex].isPopup)
-      normalWindowIndex++;
-    if (normalWindowIndex >= this._max_windows_undo)
-      spliceTo = normalWindowIndex + 1;
-#endif
-    if (spliceTo < this._closedWindows.length) {
-      this._closedWindows.splice(spliceTo, this._closedWindows.length);
-      this._closedObjectsChanged = true;
-    }
-  },
-
-  /**
-   * Clears the set of windows that are "resurrected" before writing to disk to
-   * make closing windows one after the other until shutdown work as expected.
-   *
-   * This function should only be called when we are sure that there has been
-   * a user action that indicates the browser is actively being used and all
-   * windows that have been closed before are not part of a series of closing
-   * windows.
-   */
-  _clearRestoringWindows: function ssi_clearRestoringWindows() {
-    for (let i = 0; i < this._closedWindows.length; i++) {
-      delete this._closedWindows[i]._shouldRestore;
-    }
-  },
-
-  /**
-   * Reset state to prepare for a new session state to be restored.
-   */
-  _resetRestoringState: function ssi_initRestoringState() {
-    TabRestoreQueue.reset();
-    this._tabsRestoringCount = 0;
-  },
-
-  /**
-   * Reset the restoring state for a particular tab. This will be called when
-   * removing a tab or when a tab needs to be reset (it's being overwritten).
-   *
-   * @param aTab
-   *        The tab that will be "reset"
-   */
-  _resetLocalTabRestoringState: function (aTab) {
-    NS_ASSERT(aTab.linkedBrowser.__SS_restoreState,
-              "given tab is not restoring");
-
-    let browser = aTab.linkedBrowser;
-
-    // Keep the tab's previous state for later in this method
-    let previousState = browser.__SS_restoreState;
-
-    // The browser is no longer in any sort of restoring state.
-    delete browser.__SS_restoreState;
-
-    aTab.removeAttribute("pending");
-    browser.removeAttribute("pending");
-
-    if (previousState == TAB_STATE_RESTORING) {
-      if (this._tabsRestoringCount)
-        this._tabsRestoringCount--;
-    } else if (previousState == TAB_STATE_NEEDS_RESTORE) {
-      // Make sure that the tab is removed from the list of tabs to restore.
-      // Again, this is normally done in restoreTabContent, but that isn't being called
-      // for this tab.
-      TabRestoreQueue.remove(aTab);
-    }
-  },
-
-  _resetTabRestoringState: function (tab) {
-    NS_ASSERT(tab.linkedBrowser.__SS_restoreState,
-              "given tab is not restoring");
-
-    let browser = tab.linkedBrowser;
-    browser.messageManager.sendAsyncMessage("SessionStore:resetRestore", {});
-    this._resetLocalTabRestoringState(tab);
-  },
-
-  /**
-   * Each fresh tab starts out with epoch=0. This function can be used to
-   * start a next epoch by incrementing the current value. It will enables us
-   * to ignore stale messages sent from previous epochs. The function returns
-   * the new epoch ID for the given |browser|.
-   */
-  startNextEpoch(browser) {
-    let next = this.getCurrentEpoch(browser) + 1;
-    this._browserEpochs.set(browser.permanentKey, next);
-    return next;
-  },
-
-  /**
-   * Manually set the epoch to a given value.
-   */
-  setCurrentEpoch(aBrowser, aEpoch) {
-    this._browserEpochs.set(aBrowser.permanentKey, aEpoch);
-    return aEpoch;
-  },
-
-  /**
-   * Returns the current epoch for the given <browser>. If we haven't assigned
-   * a new epoch this will default to zero for new tabs.
-   */
-  getCurrentEpoch(browser) {
-    return this._browserEpochs.get(browser.permanentKey) || 0;
-  },
-
-  /**
-   * Each time a <browser> element is restored, we increment its "epoch". To
-   * check if a message from content-sessionStore.js is out of date, we can
-   * compare the epoch received with the message to the <browser> element's
-   * epoch. This function does that, and returns true if |epoch| is up-to-date
-   * with respect to |browser|.
-   */
-  isCurrentEpoch: function (browser, epoch) {
-    return this.getCurrentEpoch(browser) == epoch;
-  },
-
-  /**
-   * Resets the epoch for a given <browser>. We need to this every time we
-   * receive a hint that a new docShell has been loaded into the browser as
-   * the frame script starts out with epoch=0.
-   */
-  resetEpoch(browser) {
-    this._browserEpochs.delete(browser.permanentKey);
-  },
-
-  /**
-   * Handle an error report from a content process.
-   */
-  reportInternalError(data) {
-    // For the moment, we only report errors through Telemetry.
-    if (data.telemetry) {
-      for (let key of Object.keys(data.telemetry)) {
-        let histogram = Telemetry.getHistogramById(key);
-        histogram.add(data.telemetry[key]);
-      }
-    }
-  },
-
-  /**
-   * Countdown for a given duration, skipping beats if the computer is too busy,
-   * sleeping or otherwise unavailable.
-   *
-   * @param {number} delay An approximate delay to wait in milliseconds (rounded
-   * up to the closest second).
-   *
-   * @return Promise
-   */
-  looseTimer(delay) {
-    let DELAY_BEAT = 1000;
-    let timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
-    let beats = Math.ceil(delay / DELAY_BEAT);
-    let promise =  new Promise(resolve => {
-      timer.initWithCallback(function() {
-        if (beats <= 0) {
-          resolve();
-        }
-        --beats;
-      }, DELAY_BEAT, Ci.nsITimer.TYPE_REPEATING_PRECISE_CAN_SKIP);
-    });
-    // Ensure that the timer is both canceled once we are done with it
-    // and not garbage-collected until then.
-    promise.then(() => timer.cancel(), () => timer.cancel());
-    return promise;
-  }
-};
-
-/**
- * Priority queue that keeps track of a list of tabs to restore and returns
- * the tab we should restore next, based on priority rules. We decide between
- * pinned, visible and hidden tabs in that and FIFO order. Hidden tabs are only
- * restored with restore_hidden_tabs=true.
- */
-var TabRestoreQueue = {
-  // The separate buckets used to store tabs.
-  tabs: {priority: [], visible: [], hidden: []},
-
-  // Preferences used by the TabRestoreQueue to determine which tabs
-  // are restored automatically and which tabs will be on-demand.
-  prefs: {
-    // Lazy getter that returns whether tabs are restored on demand.
-    get restoreOnDemand() {
-      let updateValue = () => {
-        let value = Services.prefs.getBoolPref(PREF);
-        let definition = {value: value, configurable: true};
-        Object.defineProperty(this, "restoreOnDemand", definition);
-        return value;
-      }
-
-      const PREF = "browser.sessionstore.restore_on_demand";
-      Services.prefs.addObserver(PREF, updateValue, false);
-      return updateValue();
-    },
-
-    // Lazy getter that returns whether pinned tabs are restored on demand.
-    get restorePinnedTabsOnDemand() {
-      let updateValue = () => {
-        let value = Services.prefs.getBoolPref(PREF);
-        let definition = {value: value, configurable: true};
-        Object.defineProperty(this, "restorePinnedTabsOnDemand", definition);
-        return value;
-      }
-
-      const PREF = "browser.sessionstore.restore_pinned_tabs_on_demand";
-      Services.prefs.addObserver(PREF, updateValue, false);
-      return updateValue();
-    },
-
-    // Lazy getter that returns whether we should restore hidden tabs.
-    get restoreHiddenTabs() {
-      let updateValue = () => {
-        let value = Services.prefs.getBoolPref(PREF);
-        let definition = {value: value, configurable: true};
-        Object.defineProperty(this, "restoreHiddenTabs", definition);
-        return value;
-      }
-
-      const PREF = "browser.sessionstore.restore_hidden_tabs";
-      Services.prefs.addObserver(PREF, updateValue, false);
-      return updateValue();
-    }
-  },
-
-  // Resets the queue and removes all tabs.
-  reset: function () {
-    this.tabs = {priority: [], visible: [], hidden: []};
-  },
-
-  // Adds a tab to the queue and determines its priority bucket.
-  add: function (tab) {
-    let {priority, hidden, visible} = this.tabs;
-
-    if (tab.pinned) {
-      priority.push(tab);
-    } else if (tab.hidden) {
-      hidden.push(tab);
-    } else {
-      visible.push(tab);
-    }
-  },
-
-  // Removes a given tab from the queue, if it's in there.
-  remove: function (tab) {
-    let {priority, hidden, visible} = this.tabs;
-
-    // We'll always check priority first since we don't
-    // have an indicator if a tab will be there or not.
-    let set = priority;
-    let index = set.indexOf(tab);
-
-    if (index == -1) {
-      set = tab.hidden ? hidden : visible;
-      index = set.indexOf(tab);
-    }
-
-    if (index > -1) {
-      set.splice(index, 1);
-    }
-  },
-
-  // Returns and removes the tab with the highest priority.
-  shift: function () {
-    let set;
-    let {priority, hidden, visible} = this.tabs;
-
-    let {restoreOnDemand, restorePinnedTabsOnDemand} = this.prefs;
-    let restorePinned = !(restoreOnDemand && restorePinnedTabsOnDemand);
-    if (restorePinned && priority.length) {
-      set = priority;
-    } else if (!restoreOnDemand) {
-      if (visible.length) {
-        set = visible;
-      } else if (this.prefs.restoreHiddenTabs && hidden.length) {
-        set = hidden;
-      }
-    }
-
-    return set && set.shift();
-  },
-
-  // Moves a given tab from the 'hidden' to the 'visible' bucket.
-  hiddenToVisible: function (tab) {
-    let {hidden, visible} = this.tabs;
-    let index = hidden.indexOf(tab);
-
-    if (index > -1) {
-      hidden.splice(index, 1);
-      visible.push(tab);
-    }
-  },
-
-  // Moves a given tab from the 'visible' to the 'hidden' bucket.
-  visibleToHidden: function (tab) {
-    let {visible, hidden} = this.tabs;
-    let index = visible.indexOf(tab);
-
-    if (index > -1) {
-      visible.splice(index, 1);
-      hidden.push(tab);
-    }
-  },
-
-  /**
-   * Returns true if the passed tab is in one of the sets that we're
-   * restoring content in automatically.
-   *
-   * @param tab (<xul:tab>)
-   *        The tab to check
-   * @returns bool
-   */
-  willRestoreSoon: function (tab) {
-    let { priority, hidden, visible } = this.tabs;
-    let { restoreOnDemand, restorePinnedTabsOnDemand,
-          restoreHiddenTabs } = this.prefs;
-    let restorePinned = !(restoreOnDemand && restorePinnedTabsOnDemand);
-    let candidateSet = [];
-
-    if (restorePinned && priority.length)
-      candidateSet.push(...priority);
-
-    if (!restoreOnDemand) {
-      if (visible.length)
-        candidateSet.push(...visible);
-
-      if (restoreHiddenTabs && hidden.length)
-        candidateSet.push(...hidden);
-    }
-
-    return candidateSet.indexOf(tab) > -1;
-  },
-};
-
-// A map storing a closed window's state data until it goes aways (is GC'ed).
-// This ensures that API clients can still read (but not write) states of
-// windows they still hold a reference to but we don't.
-var DyingWindowCache = {
-  _data: new WeakMap(),
-
-  has: function (window) {
-    return this._data.has(window);
-  },
-
-  get: function (window) {
-    return this._data.get(window);
-  },
-
-  set: function (window, data) {
-    this._data.set(window, data);
-  },
-
-  remove: function (window) {
-    this._data.delete(window);
-  }
-};
-
-// A weak set of dirty windows. We use it to determine which windows we need to
-// recollect data for when getCurrentState() is called.
-var DirtyWindows = {
-  _data: new WeakMap(),
-
-  has: function (window) {
-    return this._data.has(window);
-  },
-
-  add: function (window) {
-    return this._data.set(window, true);
-  },
-
-  remove: function (window) {
-    this._data.delete(window);
-  },
-
-  clear: function (window) {
-    this._data = new WeakMap();
-  }
-};
-
-// The state from the previous session (after restoring pinned tabs). This
-// state is persisted and passed through to the next session during an app
-// restart to make the third party add-on warning not trash the deferred
-// session
-var LastSession = {
-  _state: null,
-
-  get canRestore() {
-    return !!this._state;
-  },
-
-  getState: function () {
-    return this._state;
-  },
-
-  setState: function (state) {
-    this._state = state;
-  },
-
-  clear: function () {
-    if (this._state) {
-      this._state = null;
-      Services.obs.notifyObservers(null, NOTIFY_LAST_SESSION_CLEARED, null);
-    }
-  }
-};