Merge pull request #1278 from MoonchildProductions/js-modules

Partial solution for JS modules

36 files changed, 353 insertions, 254 deletions

diff --git a/dom/base/nsGkAtomList.h b/dom/base/nsGkAtomList.h
index 8fefa0e02f..73a3a02b1f 100644
--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -665,6 +665,7 @@ GK_ATOM(noembed, "noembed")
 GK_ATOM(noframes, "noframes")
 GK_ATOM(nohref, "nohref")
 GK_ATOM(noisolation, "noisolation")
+GK_ATOM(nomodule, "nomodule")
 GK_ATOM(nonce, "nonce")
 GK_ATOM(none, "none")
 GK_ATOM(noresize, "noresize")
diff --git a/dom/base/nsScriptLoader.cpp b/dom/base/nsScriptLoader.cpp
index 1e23d6c5ff..3ac00142dc 100644
--- a/dom/base/nsScriptLoader.cpp
+++ b/dom/base/nsScriptLoader.cpp
@@ -654,6 +654,19 @@ nsScriptLoader::CheckContentPolicy(nsIDocument* aDocument,
 }
 
 bool
+nsScriptLoader::ModuleScriptsEnabled()
+{
+  static bool sEnabledForContent = false;
+  static bool sCachedPref = false;
+  if (!sCachedPref) {
+    sCachedPref = true;
+    Preferences::AddBoolVarCache(&sEnabledForContent, "dom.moduleScripts.enabled", false);
+  }
+
+  return nsContentUtils::IsChromeDoc(mDocument) || sEnabledForContent;
+}
+
+bool
 nsScriptLoader::ModuleMapContainsModule(nsModuleLoadRequest *aRequest) const
 {
   // Returns whether we have fetched, or are currently fetching, a module script
@@ -1230,15 +1243,27 @@ nsScriptLoader::StartLoad(nsScriptLoadRequest *aRequest, const nsAString &aType,
   nsCOMPtr<nsIInterfaceRequestor> prompter(do_QueryInterface(docshell));
 
   nsSecurityFlags securityFlags;
-  // TODO: the spec currently gives module scripts different CORS behaviour to
-  // classic scripts.
-  securityFlags = aRequest->mCORSMode == CORS_NONE
-    ? nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_IS_NULL
-    : nsILoadInfo::SEC_REQUIRE_CORS_DATA_INHERITS;
-  if (aRequest->mCORSMode == CORS_ANONYMOUS) {
-    securityFlags |= nsILoadInfo::SEC_COOKIES_SAME_ORIGIN;
-  } else if (aRequest->mCORSMode == CORS_USE_CREDENTIALS) {
-    securityFlags |= nsILoadInfo::SEC_COOKIES_INCLUDE;
+  if (aRequest->IsModuleRequest()) {
+    // According to the spec, module scripts have different behaviour to classic
+    // scripts and always use CORS.
+    securityFlags = nsILoadInfo::SEC_REQUIRE_CORS_DATA_INHERITS;
+    if (aRequest->mCORSMode == CORS_NONE) {
+      securityFlags |= nsILoadInfo::SEC_COOKIES_OMIT;
+    } else if (aRequest->mCORSMode == CORS_ANONYMOUS) {
+      securityFlags |= nsILoadInfo::SEC_COOKIES_SAME_ORIGIN;
+    } else {
+      MOZ_ASSERT(aRequest->mCORSMode == CORS_USE_CREDENTIALS);
+      securityFlags |= nsILoadInfo::SEC_COOKIES_INCLUDE;
+    }
+  } else {
+    securityFlags = aRequest->mCORSMode == CORS_NONE
+      ? nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_IS_NULL
+      : nsILoadInfo::SEC_REQUIRE_CORS_DATA_INHERITS;
+    if (aRequest->mCORSMode == CORS_ANONYMOUS) {
+      securityFlags |= nsILoadInfo::SEC_COOKIES_SAME_ORIGIN;
+    } else if (aRequest->mCORSMode == CORS_USE_CREDENTIALS) {
+      securityFlags |= nsILoadInfo::SEC_COOKIES_INCLUDE;
+    }
   }
   securityFlags |= nsILoadInfo::SEC_ALLOW_CHROME;
 
@@ -1434,7 +1459,7 @@ nsScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
 
   nsCOMPtr<nsIContent> scriptContent = do_QueryInterface(aElement);
 
-  // Step 12. Check that the script is not an eventhandler
+  // Step 13. Check that the script is not an eventhandler
   if (IsScriptEventHandler(scriptContent)) {
     return false;
   }
@@ -1448,8 +1473,7 @@ nsScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
 
   nsScriptKind scriptKind = nsScriptKind::Classic;
   if (!type.IsEmpty()) {
-    // Support type="module" only for chrome documents.
-    if (nsContentUtils::IsChromeDoc(mDocument) && type.LowerCaseEqualsASCII("module")) {
+    if (ModuleScriptsEnabled() && type.LowerCaseEqualsASCII("module")) {
       scriptKind = nsScriptKind::Module;
     } else {
       NS_ENSURE_TRUE(ParseTypeAttribute(type, &version), false);
@@ -1469,7 +1493,18 @@ nsScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
     }
   }
 
-  // Step 14. in the HTML5 spec
+  // "In modern user agents that support module scripts, the script element with
+  // the nomodule attribute will be ignored".
+  // "The nomodule attribute must not be specified on module scripts (and will
+  // be ignored if it is)."
+  if (ModuleScriptsEnabled() &&
+      scriptKind == nsScriptKind::Classic &&
+      scriptContent->IsHTMLElement() &&
+      scriptContent->HasAttr(kNameSpaceID_None, nsGkAtoms::nomodule)) {
+    return false;
+  }
+
+  // Step 15. and later in the HTML5 spec
   nsresult rv = NS_OK;
   RefPtr<nsScriptLoadRequest> request;
   if (aElement->GetScriptExternal()) {
@@ -1577,7 +1612,7 @@ nsScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
       }
       return false;
     }
-    if (!aElement->GetParserCreated() && !request->IsModuleRequest()) {
+    if (!aElement->GetParserCreated()) {
       // Violate the HTML5 spec in order to make LABjs and the "order" plug-in
       // for RequireJS work with their Gecko-sniffed code path. See
       // http://lists.w3.org/Archives/Public/public-html/2010Oct/0088.html
@@ -2768,7 +2803,7 @@ nsScriptLoader::PreloadURI(nsIURI *aURI, const nsAString &aCharset,
   }
 
   // TODO: Preload module scripts.
-  if (nsContentUtils::IsChromeDoc(mDocument) && aType.LowerCaseEqualsASCII("module")) {
+  if (ModuleScriptsEnabled() && aType.LowerCaseEqualsASCII("module")) {
     return;
   }
 
diff --git a/dom/base/nsScriptLoader.h b/dom/base/nsScriptLoader.h
index d30a58441e..a00239be5f 100644
--- a/dom/base/nsScriptLoader.h
+++ b/dom/base/nsScriptLoader.h
@@ -568,6 +568,8 @@ private:
   JS::SourceBufferHolder GetScriptSource(nsScriptLoadRequest* aRequest,
                                          nsAutoString& inlineData);
 
+  bool ModuleScriptsEnabled();
+
   void SetModuleFetchStarted(nsModuleLoadRequest *aRequest);
   void SetModuleFetchFinishedAndResumeWaitingRequests(nsModuleLoadRequest *aRequest,
                                                       nsresult aResult);
diff --git a/dom/html/HTMLScriptElement.cpp b/dom/html/HTMLScriptElement.cpp
index 94d09c12c1..095b9b77de 100644
--- a/dom/html/HTMLScriptElement.cpp
+++ b/dom/html/HTMLScriptElement.cpp
@@ -218,6 +218,18 @@ HTMLScriptElement::SetAsync(bool aValue, ErrorResult& rv)
   SetHTMLBoolAttr(nsGkAtoms::async, aValue, rv);
 }
 
+bool
+HTMLScriptElement::NoModule()
+{
+  return GetBoolAttr(nsGkAtoms::nomodule);
+}
+
+void
+HTMLScriptElement::SetNoModule(bool aValue, ErrorResult& aRv)
+{
+  SetHTMLBoolAttr(nsGkAtoms::nomodule, aValue, aRv);
+}
+
 nsresult
 HTMLScriptElement::AfterSetAttr(int32_t aNamespaceID, nsIAtom* aName,
                                 const nsAttrValue* aValue, bool aNotify)
diff --git a/dom/html/HTMLScriptElement.h b/dom/html/HTMLScriptElement.h
index 00628bd6d3..19ceb414f9 100644
--- a/dom/html/HTMLScriptElement.h
+++ b/dom/html/HTMLScriptElement.h
@@ -89,6 +89,8 @@ public:
   }
   bool Async();
   void SetAsync(bool aValue, ErrorResult& rv);
+  bool NoModule();
+  void SetNoModule(bool aValue, ErrorResult& rv);
 
 protected:
   virtual ~HTMLScriptElement();
diff --git a/dom/html/test/file_script_module.html b/dom/html/test/file_script_module.html
new file mode 100644
index 0000000000..78c4992654
--- /dev/null
+++ b/dom/html/test/file_script_module.html
@@ -0,0 +1,42 @@
+<html>
+<body>
+  <script>
+// Helper methods.
+function ok(a, msg) {
+  parent.postMessage({ check: !!a, msg }, "*")
+}
+
+function is(a, b, msg) {
+  ok(a === b, msg);
+}
+
+function finish() {
+  parent.postMessage({ done: true }, "*");
+}
+  </script>
+
+  <script id="a" nomodule>42</script>
+  <script id="b">42</script>
+  <script>
+// Let's test the behavior of nomodule attribute and noModule getter/setter.
+var a = document.getElementById("a");
+is(a.noModule, true, "HTMLScriptElement with nomodule attribute has noModule set to true");
+a.removeAttribute("nomodule");
+is(a.noModule, false, "HTMLScriptElement without nomodule attribute has noModule set to false");
+a.noModule = true;
+ok(a.hasAttribute('nomodule'), "HTMLScriptElement.noModule = true add the nomodule attribute");
+
+var b = document.getElementById("b");
+is(b.noModule, false, "HTMLScriptElement without nomodule attribute has noModule set to false");
+b.noModule = true;
+ok(b.hasAttribute('nomodule'), "HTMLScriptElement.noModule = true add the nomodule attribute");
+  </script>
+
+  <script>var foo = 42;</script>
+  <script nomodule>foo = 43;</script>
+  <script>
+is(foo, 42, "nomodule HTMLScriptElements should not be executed in modern browsers");
+finish();
+  </script>
+</body>
+</html>
diff --git a/dom/html/test/file_script_nomodule.html b/dom/html/test/file_script_nomodule.html
new file mode 100644
index 0000000000..303edb90bb
--- /dev/null
+++ b/dom/html/test/file_script_nomodule.html
@@ -0,0 +1,32 @@
+<html>
+<body>
+  <script>
+// Helper methods.
+function ok(a, msg) {
+  parent.postMessage({ check: !!a, msg }, "*")
+}
+
+function is(a, b, msg) {
+  ok(a === b, msg);
+}
+
+function finish() {
+  parent.postMessage({ done: true }, "*");
+}
+  </script>
+
+  <script id="a" nomodule>42</script>
+  <script>
+// Let's test the behavior of nomodule attribute and noModule getter/setter.
+var a = document.getElementById("a");
+ok(!("noModule" in a), "When modules are disabled HTMLScriptElement.noModule is not defined");
+  </script>
+
+  <script>var foo = 42;</script>
+  <script nomodule>foo = 43;</script>
+  <script>
+is(foo, 43, "nomodule attribute is ignored when modules are disabled");
+finish();
+  </script>
+</body>
+</html>
diff --git a/dom/html/test/mochitest.ini b/dom/html/test/mochitest.ini
index f619be5df6..b9da7def8e 100644
--- a/dom/html/test/mochitest.ini
+++ b/dom/html/test/mochitest.ini
@@ -605,3 +605,7 @@ skip-if = os == "android" # up/down arrow keys not supported on android
 [test_bug1295719_event_sequence_for_number_keys.html]
 [test_bug1310865.html]
 [test_bug1315146.html]
+[test_script_module.html]
+support-files =
+  file_script_module.html
+  file_script_nomodule.html
\ No newline at end of file
diff --git a/dom/html/test/test_script_module.html b/dom/html/test/test_script_module.html
new file mode 100644
index 0000000000..4878bb379f
--- /dev/null
+++ b/dom/html/test/test_script_module.html
@@ -0,0 +1,56 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for HTMLScriptElement with nomodule attribute</title>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+
+<body>
+  <script>
+onmessage = (e) => {
+  if ("done" in e.data) {
+    next();
+  } else if ("check" in e.data) {
+    ok(e.data.check, e.data.msg);
+  } else {
+    ok(false, "Unknown message");
+  }
+}
+
+var tests = [
+  function() {
+    SpecialPowers.pushPrefEnv({"set":[["dom.moduleScripts.enabled", true]]})
+    .then(() => {
+      var ifr = document.createElement('iframe');
+      ifr.src = "file_script_module.html";
+      document.body.appendChild(ifr);
+    });
+  },
+
+  function() {
+    SpecialPowers.pushPrefEnv({"set":[["dom.moduleScripts.enabled", false]]})
+    .then(() => {
+      var ifr = document.createElement('iframe');
+      ifr.src = "file_script_nomodule.html";
+      document.body.appendChild(ifr);
+    });
+  },
+];
+
+SimpleTest.waitForExplicitFinish();
+next();
+
+function next() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+
+  var test = tests.shift();
+  test();
+}
+  </script>
+
+</body>
+</html>
diff --git a/dom/webidl/HTMLScriptElement.webidl b/dom/webidl/HTMLScriptElement.webidl
index 377056366d..5b64c42d7c 100644
--- a/dom/webidl/HTMLScriptElement.webidl
+++ b/dom/webidl/HTMLScriptElement.webidl
@@ -13,6 +13,8 @@ interface HTMLScriptElement : HTMLElement {
   attribute DOMString src;
   [SetterThrows]
   attribute DOMString type;
+  [SetterThrows, Pref="dom.moduleScripts.enabled"]
+  attribute boolean noModule;
   [SetterThrows]
   attribute DOMString charset;
   [SetterThrows]
diff --git a/js/src/builtin/Iterator.js b/js/src/builtin/Iterator.js
index 735eec7a06..e25b761561 100644
--- a/js/src/builtin/Iterator.js
+++ b/js/src/builtin/Iterator.js
@@ -84,44 +84,3 @@ function LegacyIteratorShim() {
 function LegacyGeneratorIteratorShim() {
     return NewLegacyIterator(ToObject(this), LegacyGeneratorIterator);
 }
-
-// 7.4.8 CreateListIterator()
-function CreateListIterator(array) {
-    let iterator = NewListIterator();
-    UnsafeSetReservedSlot(iterator, ITERATOR_SLOT_TARGET, array);
-    UnsafeSetReservedSlot(iterator, ITERATOR_SLOT_NEXT_INDEX, 0);
-
-    // 7.4.8.1 ListIterator next()
-    // The spec requires that we use a new next function per iterator object.
-    let next = function() {
-        if (!IsObject(this) || !IsListIterator(this))
-            return callFunction(CallListIteratorMethodIfWrapped, this, "ListIteratorNext");
-
-        if (ActiveFunction() !== UnsafeGetReservedSlot(this, ITERATOR_SLOT_NEXT_METHOD))
-            ThrowTypeError(JSMSG_INCOMPATIBLE_METHOD, "next", "method", ToString(this));
-
-        let array = UnsafeGetObjectFromReservedSlot(this, ITERATOR_SLOT_TARGET);
-        let index = UnsafeGetReservedSlot(this, ITERATOR_SLOT_NEXT_INDEX);
-
-        if (index >= ToLength(array.length)) {
-            UnsafeSetReservedSlot(this, ITERATOR_SLOT_NEXT_INDEX, 1/0);
-            return { value: undefined, done: true };
-        }
-
-        UnsafeSetReservedSlot(this, ITERATOR_SLOT_NEXT_INDEX, index + 1);
-        return { value: array[index], done: false };
-    };
-
-    UnsafeSetReservedSlot(iterator, ITERATOR_SLOT_NEXT_METHOD, next);
-    iterator.next = next;
-
-    iterator[std_iterator] = ListIteratorIdentity;
-    return iterator;
-}
-
-function ListIteratorIdentity() {
-    if (!IsObject(this) || !IsListIterator(this))
-        return callFunction(CallListIteratorMethodIfWrapped, this, "ListIteratorIdentity");
-
-    return this;
-}
diff --git a/js/src/builtin/Module.js b/js/src/builtin/Module.js
index 7b70a7fe8b..5c3d5e1479 100644
--- a/js/src/builtin/Module.js
+++ b/js/src/builtin/Module.js
@@ -65,12 +65,12 @@ function ModuleGetExportedNames(exportStarSet = [])
     return exportedNames;
 }
 
-// 15.2.1.16.3 ResolveExport(exportName, resolveSet, exportStarSet)
-function ModuleResolveExport(exportName, resolveSet = [], exportStarSet = [])
+// 15.2.1.16.3 ResolveExport(exportName, resolveSet)
+function ModuleResolveExport(exportName, resolveSet = [])
 {
     if (!IsObject(this) || !IsModule(this)) {
         return callFunction(CallModuleMethodIfWrapped, this, exportName, resolveSet,
-                            exportStarSet, "ModuleResolveExport");
+                            "ModuleResolveExport");
     }
 
     // Step 1
@@ -100,38 +100,29 @@ function ModuleResolveExport(exportName, resolveSet = [], exportStarSet = [])
         let e = indirectExportEntries[i];
         if (exportName === e.exportName) {
             let importedModule = CallModuleResolveHook(module, e.moduleRequest,
-                                                       MODULE_STATE_INSTANTIATED);
-            let indirectResolution = callFunction(importedModule.resolveExport, importedModule,
-                                                  e.importName, resolveSet, exportStarSet);
-            if (indirectResolution !== null)
-                return indirectResolution;
+                                                       MODULE_STATE_PARSED);
+            return callFunction(importedModule.resolveExport, importedModule, e.importName,
+                                resolveSet);
         }
     }
 
     // Step 6
     if (exportName === "default") {
         // A default export cannot be provided by an export *.
-        ThrowSyntaxError(JSMSG_BAD_DEFAULT_EXPORT);
+        return null;
     }
 
     // Step 7
-    if (callFunction(ArrayIncludes, exportStarSet, module))
-        return null;
-
-    // Step 8
-    _DefineDataProperty(exportStarSet, exportStarSet.length, module);
-
-    // Step 9
     let starResolution = null;
 
-    // Step 10
+    // Step 8
     let starExportEntries = module.starExportEntries;
     for (let i = 0; i < starExportEntries.length; i++) {
         let e = starExportEntries[i];
         let importedModule = CallModuleResolveHook(module, e.moduleRequest,
-                                                   MODULE_STATE_INSTANTIATED);
+                                                   MODULE_STATE_PARSED);
         let resolution = callFunction(importedModule.resolveExport, importedModule,
-                                      exportName, resolveSet, exportStarSet);
+                                      exportName, resolveSet);
         if (resolution === "ambiguous")
             return resolution;
 
@@ -148,6 +139,7 @@ function ModuleResolveExport(exportName, resolveSet = [], exportStarSet = [])
         }
     }
 
+    // Step 9
     return starResolution;
 }
 
@@ -213,8 +205,8 @@ function GetModuleEnvironment(module)
 
 function RecordInstantationFailure(module)
 {
-    // Set the module's environment slot to 'null' to indicate a failed module
-    // instantiation.
+    // Set the module's state to 'failed' to indicate a failed module
+    // instantiation and reset the environment slot to 'undefined'.
     assert(IsModule(module), "Non-module passed to RecordInstantationFailure");
     SetModuleState(module, MODULE_STATE_FAILED);
     UnsafeSetReservedSlot(module, MODULE_OBJECT_ENVIRONMENT_SLOT, undefined);
@@ -275,11 +267,13 @@ function ModuleDeclarationInstantiation()
                     ThrowSyntaxError(JSMSG_MISSING_IMPORT, imp.importName);
                 if (resolution === "ambiguous")
                     ThrowSyntaxError(JSMSG_AMBIGUOUS_IMPORT, imp.importName);
+                if (resolution.module.state < MODULE_STATE_INSTANTIATED)
+                    ThrowInternalError(JSMSG_BAD_MODULE_STATE);
                 CreateImportBinding(env, imp.localName, resolution.module, resolution.bindingName);
             }
         }
 
-        // Step 16.iv
+        // Step 17.a.iii
         InstantiateModuleFunctionDeclarations(module);
     } catch (e) {
         RecordInstantationFailure(module);
@@ -318,11 +312,3 @@ function ModuleEvaluation()
     return EvaluateModule(module);
 }
 _SetCanonicalName(ModuleEvaluation, "ModuleEvaluation");
-
-function ModuleNamespaceEnumerate()
-{
-    if (!IsObject(this) || !IsModuleNamespace(this))
-        return callFunction(CallModuleMethodIfWrapped, this, "ModuleNamespaceEnumerate");
-
-    return CreateListIterator(ModuleNamespaceExports(this));
-}
diff --git a/js/src/builtin/ModuleObject.cpp b/js/src/builtin/ModuleObject.cpp
index 798ef46e11..575bab0b0c 100644
--- a/js/src/builtin/ModuleObject.cpp
+++ b/js/src/builtin/ModuleObject.cpp
@@ -147,7 +147,7 @@ DEFINE_GETTER_FUNCTIONS(ExportEntryObject, moduleRequest, ModuleRequestSlot)
 DEFINE_GETTER_FUNCTIONS(ExportEntryObject, importName, ImportNameSlot)
 DEFINE_GETTER_FUNCTIONS(ExportEntryObject, localName, LocalNameSlot)
 
-DEFINE_ATOM_ACCESSOR_METHOD(ExportEntryObject, exportName)
+DEFINE_ATOM_OR_NULL_ACCESSOR_METHOD(ExportEntryObject, exportName)
 DEFINE_ATOM_OR_NULL_ACCESSOR_METHOD(ExportEntryObject, moduleRequest)
 DEFINE_ATOM_OR_NULL_ACCESSOR_METHOD(ExportEntryObject, importName)
 DEFINE_ATOM_OR_NULL_ACCESSOR_METHOD(ExportEntryObject, localName)
@@ -289,14 +289,6 @@ ModuleNamespaceObject::create(JSContext* cx, HandleModuleObject module)
     if (!object)
         return nullptr;
 
-    RootedId funName(cx, INTERNED_STRING_TO_JSID(cx, cx->names().Symbol_iterator_fun));
-    RootedFunction enumerateFun(cx);
-    enumerateFun = JS::GetSelfHostedFunction(cx, "ModuleNamespaceEnumerate", funName, 0);
-    if (!enumerateFun)
-        return nullptr;
-
-    SetProxyExtra(object, ProxyHandler::EnumerateFunctionSlot, ObjectValue(*enumerateFun));
-
     return &object->as<ModuleNamespaceObject>();
 }
 
@@ -338,14 +330,9 @@ ModuleNamespaceObject::addBinding(JSContext* cx, HandleAtom exportedName,
 const char ModuleNamespaceObject::ProxyHandler::family = 0;
 
 ModuleNamespaceObject::ProxyHandler::ProxyHandler()
-  : BaseProxyHandler(&family, true)
+  : BaseProxyHandler(&family, false)
 {}
 
-JS::Value ModuleNamespaceObject::ProxyHandler::getEnumerateFunction(HandleObject proxy) const
-{
-    return GetProxyExtra(proxy, EnumerateFunctionSlot);
-}
-
 bool
 ModuleNamespaceObject::ProxyHandler::getPrototype(JSContext* cx, HandleObject proxy,
                                                   MutableHandleObject protop) const
@@ -358,6 +345,8 @@ bool
 ModuleNamespaceObject::ProxyHandler::setPrototype(JSContext* cx, HandleObject proxy,
                                                   HandleObject proto, ObjectOpResult& result) const
 {
+    if (!proto)
+        return result.succeed();
     return result.failCantSetProto();
 }
 
@@ -402,21 +391,12 @@ ModuleNamespaceObject::ProxyHandler::getOwnPropertyDescriptor(JSContext* cx, Han
     Rooted<ModuleNamespaceObject*> ns(cx, &proxy->as<ModuleNamespaceObject>());
     if (JSID_IS_SYMBOL(id)) {
         Rooted<JS::Symbol*> symbol(cx, JSID_TO_SYMBOL(id));
-        if (symbol == cx->wellKnownSymbols().iterator) {
-            RootedValue enumerateFun(cx, getEnumerateFunction(proxy));
-            desc.object().set(proxy);
-            desc.setConfigurable(false);
-            desc.setEnumerable(false);
-            desc.setValue(enumerateFun);
-            return true;
-        }
-
         if (symbol == cx->wellKnownSymbols().toStringTag) {
             RootedValue value(cx, StringValue(cx->names().Module));
             desc.object().set(proxy);
             desc.setWritable(false);
             desc.setEnumerable(false);
-            desc.setConfigurable(true);
+            desc.setConfigurable(false);
             desc.setValue(value);
             return true;
         }
@@ -458,8 +438,8 @@ ModuleNamespaceObject::ProxyHandler::has(JSContext* cx, HandleObject proxy, Hand
     Rooted<ModuleNamespaceObject*> ns(cx, &proxy->as<ModuleNamespaceObject>());
     if (JSID_IS_SYMBOL(id)) {
         Rooted<JS::Symbol*> symbol(cx, JSID_TO_SYMBOL(id));
-        return symbol == cx->wellKnownSymbols().iterator ||
-               symbol == cx->wellKnownSymbols().toStringTag;
+        *bp = symbol == cx->wellKnownSymbols().toStringTag;
+        return true;
     }
 
     *bp = ns->bindings().has(id);
@@ -473,23 +453,21 @@ ModuleNamespaceObject::ProxyHandler::get(JSContext* cx, HandleObject proxy, Hand
     Rooted<ModuleNamespaceObject*> ns(cx, &proxy->as<ModuleNamespaceObject>());
     if (JSID_IS_SYMBOL(id)) {
         Rooted<JS::Symbol*> symbol(cx, JSID_TO_SYMBOL(id));
-        if (symbol == cx->wellKnownSymbols().iterator) {
-            vp.set(getEnumerateFunction(proxy));
-            return true;
-        }
-
         if (symbol == cx->wellKnownSymbols().toStringTag) {
             vp.setString(cx->names().Module);
             return true;
         }
 
-        return false;
+        vp.setUndefined();
+        return true;
     }
 
     ModuleEnvironmentObject* env;
     Shape* shape;
-    if (!ns->bindings().lookup(id, &env, &shape))
-        return false;
+    if (!ns->bindings().lookup(id, &env, &shape)) {
+        vp.setUndefined();
+        return true;
+    }
 
     RootedValue value(cx, env->getSlot(shape->slot()));
     if (value.isMagic(JS_UNINITIALIZED_LEXICAL)) {
@@ -526,7 +504,7 @@ ModuleNamespaceObject::ProxyHandler::ownPropertyKeys(JSContext* cx, HandleObject
     Rooted<ModuleNamespaceObject*> ns(cx, &proxy->as<ModuleNamespaceObject>());
     RootedObject exports(cx, &ns->exports());
     uint32_t count;
-    if (!GetLengthProperty(cx, exports, &count) || !props.reserve(props.length() + count))
+    if (!GetLengthProperty(cx, exports, &count) || !props.reserve(props.length() + count + 1))
         return false;
 
     Rooted<ValueVector> names(cx, ValueVector(cx));
@@ -536,6 +514,8 @@ ModuleNamespaceObject::ProxyHandler::ownPropertyKeys(JSContext* cx, HandleObject
     for (uint32_t i = 0; i < count; i++)
         props.infallibleAppend(AtomToId(&names[i].toString()->asAtom()));
 
+    props.infallibleAppend(SYMBOL_TO_JSID(cx->wellKnownSymbols().toStringTag));
+
     return true;
 }
 
@@ -1014,7 +994,7 @@ GlobalObject::initModuleProto(JSContext* cx, Handle<GlobalObject*> global)
 
     static const JSFunctionSpec protoFunctions[] = {
         JS_SELF_HOSTED_FN("getExportedNames", "ModuleGetExportedNames", 1, 0),
-        JS_SELF_HOSTED_FN("resolveExport", "ModuleResolveExport", 3, 0),
+        JS_SELF_HOSTED_FN("resolveExport", "ModuleResolveExport", 2, 0),
         JS_SELF_HOSTED_FN("declarationInstantiation", "ModuleDeclarationInstantiation", 0, 0),
         JS_SELF_HOSTED_FN("evaluation", "ModuleEvaluation", 0, 0),
         JS_FS_END
@@ -1164,6 +1144,13 @@ ModuleBuilder::processExport(frontend::ParseNode* pn)
     bool isDefault = pn->getKind() == PNK_EXPORT_DEFAULT;
     ParseNode* kid = isDefault ? pn->pn_left : pn->pn_kid;
 
+    if (isDefault && pn->pn_right) {
+        // This is an export default containing an expression.
+        RootedAtom localName(cx_, cx_->names().starDefaultStar);
+        RootedAtom exportName(cx_, cx_->names().default_);
+        return appendExportEntry(exportName, localName);
+    }
+
     switch (kid->getKind()) {
       case PNK_EXPORT_SPEC_LIST:
         MOZ_ASSERT(!isDefault);
@@ -1177,53 +1164,46 @@ ModuleBuilder::processExport(frontend::ParseNode* pn)
         break;
 
       case PNK_CLASS: {
-          const ClassNode& cls = kid->as<ClassNode>();
-          MOZ_ASSERT(cls.names());
-          RootedAtom localName(cx_, cls.names()->innerBinding()->pn_atom);
-          RootedAtom exportName(cx_, isDefault ? cx_->names().default_ : localName.get());
-          if (!appendExportEntry(exportName, localName))
-              return false;
-          break;
+        const ClassNode& cls = kid->as<ClassNode>();
+        MOZ_ASSERT(cls.names());
+        RootedAtom localName(cx_, cls.names()->innerBinding()->pn_atom);
+        RootedAtom exportName(cx_, isDefault ? cx_->names().default_ : localName.get());
+        if (!appendExportEntry(exportName, localName))
+            return false;
+        break;
       }
 
       case PNK_VAR:
       case PNK_CONST:
       case PNK_LET: {
-          MOZ_ASSERT(kid->isArity(PN_LIST));
-          for (ParseNode* var = kid->pn_head; var; var = var->pn_next) {
-              if (var->isKind(PNK_ASSIGN))
-                  var = var->pn_left;
-              MOZ_ASSERT(var->isKind(PNK_NAME));
-              RootedAtom localName(cx_, var->pn_atom);
-              RootedAtom exportName(cx_, isDefault ? cx_->names().default_ : localName.get());
-              if (!appendExportEntry(exportName, localName))
-                  return false;
-          }
-          break;
+        MOZ_ASSERT(kid->isArity(PN_LIST));
+        for (ParseNode* var = kid->pn_head; var; var = var->pn_next) {
+            if (var->isKind(PNK_ASSIGN))
+                var = var->pn_left;
+            MOZ_ASSERT(var->isKind(PNK_NAME));
+            RootedAtom localName(cx_, var->pn_atom);
+            RootedAtom exportName(cx_, isDefault ? cx_->names().default_ : localName.get());
+            if (!appendExportEntry(exportName, localName))
+                return false;
+        }
+        break;
       }
 
       case PNK_FUNCTION: {
-          RootedFunction func(cx_, kid->pn_funbox->function());
-          if (!func->isArrow()) {
-              RootedAtom localName(cx_, func->explicitName());
-              RootedAtom exportName(cx_, isDefault ? cx_->names().default_ : localName.get());
-              MOZ_ASSERT_IF(isDefault, localName);
-              if (!appendExportEntry(exportName, localName))
-                  return false;
-              break;
-          }
-      }
-
-      MOZ_FALLTHROUGH; // Arrow functions are handled below.
-
-      default:
-        MOZ_ASSERT(isDefault);
-        RootedAtom localName(cx_, cx_->names().starDefaultStar);
-        RootedAtom exportName(cx_, cx_->names().default_);
+        RootedFunction func(cx_, kid->pn_funbox->function());
+        MOZ_ASSERT(!func->isArrow());
+        RootedAtom localName(cx_, func->explicitName());
+        RootedAtom exportName(cx_, isDefault ? cx_->names().default_ : localName.get());
+        MOZ_ASSERT_IF(isDefault, localName);
         if (!appendExportEntry(exportName, localName))
             return false;
         break;
+      }
+
+      default:
+        MOZ_CRASH("Unexpected parse node");
     }
+
     return true;
 }
 
diff --git a/js/src/builtin/ModuleObject.h b/js/src/builtin/ModuleObject.h
index e83520ebe6..22db762ac6 100644
--- a/js/src/builtin/ModuleObject.h
+++ b/js/src/builtin/ModuleObject.h
@@ -142,15 +142,8 @@ class ModuleNamespaceObject : public ProxyObject
   private:
     struct ProxyHandler : public BaseProxyHandler
     {
-        enum
-        {
-            EnumerateFunctionSlot = 0
-        };
-
         ProxyHandler();
 
-        JS::Value getEnumerateFunction(HandleObject proxy) const;
-
         bool getOwnPropertyDescriptor(JSContext* cx, HandleObject proxy, HandleId id,
                                       MutableHandle<PropertyDescriptor> desc) const override;
         bool defineProperty(JSContext* cx, HandleObject proxy, HandleId id,
diff --git a/js/src/builtin/SelfHostingDefines.h b/js/src/builtin/SelfHostingDefines.h
index b57c172691..d676270a14 100644
--- a/js/src/builtin/SelfHostingDefines.h
+++ b/js/src/builtin/SelfHostingDefines.h
@@ -71,8 +71,6 @@
 // Used for list, i.e. Array and String, iterators.
 #define ITERATOR_SLOT_NEXT_INDEX 1
 #define ITERATOR_SLOT_ITEM_KIND 2
-// Used for ListIterator.
-#define ITERATOR_SLOT_NEXT_METHOD 2
 
 #define ITEM_KIND_KEY 0
 #define ITEM_KIND_VALUE 1
diff --git a/js/src/jit-test/modules/empty.js b/js/src/jit-test/modules/empty.js
new file mode 100644
index 0000000000..bd9ec079d8
--- /dev/null
+++ b/js/src/jit-test/modules/empty.js
@@ -0,0 +1 @@
+// Intentionally empty.
diff --git a/js/src/jit-test/modules/export-circular-nonexisting-binding-1.js b/js/src/jit-test/modules/export-circular-nonexisting-binding-1.js
new file mode 100644
index 0000000000..2b91b6a284
--- /dev/null
+++ b/js/src/jit-test/modules/export-circular-nonexisting-binding-1.js
@@ -0,0 +1,4 @@
+import "export-circular-nonexisting-binding-2.js";
+
+export* from "empty.js";
+export {x} from "empty.js";
diff --git a/js/src/jit-test/modules/export-circular-nonexisting-binding-2.js b/js/src/jit-test/modules/export-circular-nonexisting-binding-2.js
new file mode 100644
index 0000000000..ba7dcc1b48
--- /dev/null
+++ b/js/src/jit-test/modules/export-circular-nonexisting-binding-2.js
@@ -0,0 +1 @@
+export {x} from "export-circular-nonexisting-binding-1.js";
diff --git a/js/src/jit-test/modules/export-star-circular-1.js b/js/src/jit-test/modules/export-star-circular-1.js
new file mode 100644
index 0000000000..9a0771b024
--- /dev/null
+++ b/js/src/jit-test/modules/export-star-circular-1.js
@@ -0,0 +1 @@
+export* from "export-star-circular-2.js";
diff --git a/js/src/jit-test/modules/export-star-circular-2.js b/js/src/jit-test/modules/export-star-circular-2.js
new file mode 100644
index 0000000000..b273d9cefa
--- /dev/null
+++ b/js/src/jit-test/modules/export-star-circular-2.js
@@ -0,0 +1,3 @@
+export {y as x} from "export-star-circular-1.js";
+
+export var y = "pass";
diff --git a/js/src/jit-test/tests/basic/bug1220766.js b/js/src/jit-test/tests/basic/bug1220766.js
deleted file mode 100644
index fca11eafe6..0000000000
--- a/js/src/jit-test/tests/basic/bug1220766.js
+++ /dev/null
@@ -1,3 +0,0 @@
-iter = getSelfHostedValue("CreateListIterator")([]);
-iter.next();
-iter.next();
diff --git a/js/src/jit-test/tests/modules/bug-1320993.js b/js/src/jit-test/tests/modules/bug-1320993.js
new file mode 100644
index 0000000000..bece5731a3
--- /dev/null
+++ b/js/src/jit-test/tests/modules/bug-1320993.js
@@ -0,0 +1,2 @@
+parseModule("export default (class {})");
+parseModule("export default (class A {})");
diff --git a/js/src/jit-test/tests/modules/export-circular-nonexisting-binding.js b/js/src/jit-test/tests/modules/export-circular-nonexisting-binding.js
new file mode 100644
index 0000000000..387c7c369a
--- /dev/null
+++ b/js/src/jit-test/tests/modules/export-circular-nonexisting-binding.js
@@ -0,0 +1,3 @@
+// |jit-test| module; error:SyntaxError
+
+import "export-circular-nonexisting-binding-1.js";
diff --git a/js/src/jit-test/tests/modules/export-star-cannot-rescue-missing-export.js b/js/src/jit-test/tests/modules/export-star-cannot-rescue-missing-export.js
new file mode 100644
index 0000000000..f87829d89b
--- /dev/null
+++ b/js/src/jit-test/tests/modules/export-star-cannot-rescue-missing-export.js
@@ -0,0 +1,4 @@
+// |jit-test| module; error:SyntaxError
+
+export { a } from "empty.js";
+export* from "module1.js";
diff --git a/js/src/jit-test/tests/modules/export-star-circular-dependencies.js b/js/src/jit-test/tests/modules/export-star-circular-dependencies.js
new file mode 100644
index 0000000000..9aa612f087
--- /dev/null
+++ b/js/src/jit-test/tests/modules/export-star-circular-dependencies.js
@@ -0,0 +1,6 @@
+// |jit-test| module
+
+import { x, y } from "export-star-circular-1.js";
+
+assertEq(x, "pass");
+assertEq(y, "pass");
diff --git a/js/src/jit-test/tests/modules/import-namespace.js b/js/src/jit-test/tests/modules/import-namespace.js
index f44d4568aa..0287f7a60e 100644
--- a/js/src/jit-test/tests/modules/import-namespace.js
+++ b/js/src/jit-test/tests/modules/import-namespace.js
@@ -19,9 +19,19 @@ function testHasNames(names, expected) {
     });
 }
 
+function testEqualArrays(actual, expected) {
+	assertEq(Array.isArray(actual), true);
+	assertEq(Array.isArray(expected), true);
+    assertEq(actual.length, expected.length);
+    for (let i = 0; i < expected.length; i++) {
+    	assertEq(actual[i], expected[i]);
+    }
+}
+
 let a = moduleRepo['a'] = parseModule(
-    `export var a = 1;
-     export var b = 2;`
+    `// Reflection methods should return these exports alphabetically sorted.
+     export var b = 2;
+     export var a = 1;`
 );
 
 let b = moduleRepo['b'] = parseModule(
@@ -35,11 +45,16 @@ b.evaluation();
 testHasNames(getModuleEnvironmentNames(b), ["ns", "x"]);
 let ns = getModuleEnvironmentValue(b, "ns");
 testHasNames(Object.keys(ns), ["a", "b"]);
+assertEq(ns.a, 1);
+assertEq(ns.b, 2);
+assertEq(ns.c, undefined);
 assertEq(getModuleEnvironmentValue(b, "x"), 3);
 
 // Test module namespace internal methods as defined in 9.4.6
 assertEq(Object.getPrototypeOf(ns), null);
-assertThrowsInstanceOf(() => Object.setPrototypeOf(ns, null), TypeError);
+assertEq(Reflect.setPrototypeOf(ns, null), true);
+assertEq(Reflect.setPrototypeOf(ns, Object.prototype), false);
+assertThrowsInstanceOf(() => Object.setPrototypeOf(ns, {}), TypeError);
 assertThrowsInstanceOf(function() { ns.foo = 1; }, TypeError);
 assertEq(Object.isExtensible(ns), false);
 Object.preventExtensions(ns);
@@ -59,29 +74,15 @@ desc = Object.getOwnPropertyDescriptor(ns, Symbol.toStringTag);
 assertEq(desc.value, "Module");
 assertEq(desc.writable, false);
 assertEq(desc.enumerable, false);
-assertEq(desc.configurable, true);
+assertEq(desc.configurable, false);
 assertEq(typeof desc.get, "undefined");
 assertEq(typeof desc.set, "undefined");
 assertEq(Object.prototype.toString.call(ns), "[object Module]");
 
-// Test @@iterator method.
-let iteratorFun = ns[Symbol.iterator];
-assertEq(iteratorFun.name, "[Symbol.iterator]");
-
-let iterator = ns[Symbol.iterator]();
-assertEq(iterator[Symbol.iterator](), iterator);
-assertIteratorNext(iterator, "a");
-assertIteratorNext(iterator, "b");
-assertIteratorDone(iterator);
-
-// The iterator's next method can only be called on the object it was originally
-// associated with.
-iterator = ns[Symbol.iterator]();
-let iterator2 = ns[Symbol.iterator]();
-assertThrowsInstanceOf(() => iterator.next.call({}), TypeError);
-assertThrowsInstanceOf(() => iterator.next.call(iterator2), TypeError);
-assertEq(iterator.next.call(iterator).value, "a");
-assertEq(iterator2.next.call(iterator2).value, "a");
+// Test [[OwnPropertyKeys]] internal method.
+testEqualArrays(Reflect.ownKeys(ns), ["a", "b", Symbol.toStringTag]);
+testEqualArrays(Object.getOwnPropertyNames(ns), ["a", "b"]);
+testEqualArrays(Object.getOwnPropertySymbols(ns), [Symbol.toStringTag]);
 
 // Test cyclic namespace import and access in module evaluation.
 let c = moduleRepo['c'] =
diff --git a/js/src/jit/InlinableNatives.h b/js/src/jit/InlinableNatives.h
index 1d0506f743..9c864515d0 100644
--- a/js/src/jit/InlinableNatives.h
+++ b/js/src/jit/InlinableNatives.h
@@ -119,7 +119,6 @@
     _(IntrinsicGuardToArrayIterator) \
     _(IntrinsicGuardToMapIterator)  \
     _(IntrinsicGuardToSetIterator)  \
-    _(IntrinsicIsListIterator)      \
     _(IntrinsicGuardToStringIterator) \
                                     \
     _(IntrinsicGuardToMapObject)    \
diff --git a/js/src/jit/MCallOptimize.cpp b/js/src/jit/MCallOptimize.cpp
index 5eee30e497..2363545300 100644
--- a/js/src/jit/MCallOptimize.cpp
+++ b/js/src/jit/MCallOptimize.cpp
@@ -285,8 +285,6 @@ IonBuilder::inlineNativeCall(CallInfo& callInfo, JSFunction* target)
         return inlineGuardToClass(callInfo, &SetIteratorObject::class_);
       case InlinableNative::IntrinsicGuardToStringIterator:
         return inlineGuardToClass(callInfo, &StringIteratorObject::class_);
-      case InlinableNative::IntrinsicIsListIterator:
-        return inlineHasClass(callInfo, &ListIteratorObject::class_);
       case InlinableNative::IntrinsicDefineDataProperty:
         return inlineDefineDataProperty(callInfo);
       case InlinableNative::IntrinsicObjectHasPrototype:
diff --git a/js/src/jsiter.cpp b/js/src/jsiter.cpp
index 749e15d27d..3e222ca6fb 100644
--- a/js/src/jsiter.cpp
+++ b/js/src/jsiter.cpp
@@ -1135,18 +1135,6 @@ static const JSFunctionSpec string_iterator_methods[] = {
     JS_FS_END
 };
 
-enum {
-    ListIteratorSlotIteratedObject,
-    ListIteratorSlotNextIndex,
-    ListIteratorSlotNextMethod,
-    ListIteratorSlotCount
-};
-
-const Class ListIteratorObject::class_ = {
-    "List Iterator",
-    JSCLASS_HAS_RESERVED_SLOTS(ListIteratorSlotCount)
-};
-
 JSObject*
 js::ValueToIterator(JSContext* cx, unsigned flags, HandleValue vp)
 {
diff --git a/js/src/jsiter.h b/js/src/jsiter.h
index f11f09b550..a3035ddd0f 100644
--- a/js/src/jsiter.h
+++ b/js/src/jsiter.h
@@ -151,12 +151,6 @@ class StringIteratorObject : public JSObject
     static const Class class_;
 };
 
-class ListIteratorObject : public JSObject
-{
-  public:
-    static const Class class_;
-};
-
 bool
 GetIterator(JSContext* cx, HandleObject obj, unsigned flags, MutableHandleObject objp);
 
diff --git a/js/src/vm/EnvironmentObject.cpp b/js/src/vm/EnvironmentObject.cpp
index 3680c5b7b4..c95bb0597a 100644
--- a/js/src/vm/EnvironmentObject.cpp
+++ b/js/src/vm/EnvironmentObject.cpp
@@ -490,7 +490,7 @@ ModuleEnvironmentObject::createImportBinding(JSContext* cx, HandleAtom importNam
 {
     RootedId importNameId(cx, AtomToId(importName));
     RootedId localNameId(cx, AtomToId(localName));
-    RootedModuleEnvironmentObject env(cx, module->environment());
+    RootedModuleEnvironmentObject env(cx, &module->initialEnvironment());
     if (!importBindings().putNew(cx, importNameId, env, localNameId)) {
         ReportOutOfMemory(cx);
         return false;
diff --git a/js/src/vm/SelfHosting.cpp b/js/src/vm/SelfHosting.cpp
index 792a00490c..82d2cde642 100644
--- a/js/src/vm/SelfHosting.cpp
+++ b/js/src/vm/SelfHosting.cpp
@@ -857,37 +857,6 @@ intrinsic_NewStringIterator(JSContext* cx, unsigned argc, Value* vp)
 }
 
 static bool
-intrinsic_NewListIterator(JSContext* cx, unsigned argc, Value* vp)
-{
-    CallArgs args = CallArgsFromVp(argc, vp);
-    MOZ_ASSERT(args.length() == 0);
-
-    RootedObject proto(cx, GlobalObject::getOrCreateIteratorPrototype(cx, cx->global()));
-    if (!proto)
-        return false;
-
-    RootedObject iterator(cx);
-    iterator = NewObjectWithGivenProto(cx, &ListIteratorObject::class_, proto);
-    if (!iterator)
-        return false;
-
-    args.rval().setObject(*iterator);
-    return true;
-}
-
-static bool
-intrinsic_ActiveFunction(JSContext* cx, unsigned argc, Value* vp)
-{
-    CallArgs args = CallArgsFromVp(argc, vp);
-    MOZ_ASSERT(args.length() == 0);
-
-    ScriptFrameIter iter(cx);
-    MOZ_ASSERT(iter.isFunctionFrame());
-    args.rval().setObject(*iter.callee(cx));
-    return true;
-}
-
-static bool
 intrinsic_SetCanonicalName(JSContext* cx, unsigned argc, Value* vp)
 {
     CallArgs args = CallArgsFromVp(argc, vp);
@@ -2290,11 +2259,6 @@ static const JSFunctionSpec intrinsic_functions[] = {
     JS_FN("CallArrayIteratorMethodIfWrapped",
           CallNonGenericSelfhostedMethod<Is<ArrayIteratorObject>>,      2,0),
 
-    JS_FN("NewListIterator",         intrinsic_NewListIterator,         0,0),
-    JS_FN("CallListIteratorMethodIfWrapped",
-          CallNonGenericSelfhostedMethod<Is<ListIteratorObject>>,       2,0),
-    JS_FN("ActiveFunction",          intrinsic_ActiveFunction,          0,0),
-
     JS_FN("_SetCanonicalName",       intrinsic_SetCanonicalName,        2,0),
 
     JS_INLINABLE_FN("GuardToArrayIterator",
@@ -2309,9 +2273,6 @@ static const JSFunctionSpec intrinsic_functions[] = {
     JS_INLINABLE_FN("GuardToStringIterator",
                     intrinsic_GuardToBuiltin<StringIteratorObject>, 1,0,
                     IntrinsicGuardToStringIterator),
-    JS_INLINABLE_FN("IsListIterator",
-                    intrinsic_IsInstanceOfBuiltin<ListIteratorObject>,  1,0,
-                    IntrinsicIsListIterator),
 
     JS_FN("_CreateMapIterationResultPair", intrinsic_CreateMapIterationResultPair, 0, 0),
     JS_INLINABLE_FN("_GetNextMapEntryForIterator", intrinsic_GetNextMapEntryForIterator, 2,0,
@@ -2533,7 +2494,6 @@ static const JSFunctionSpec intrinsic_functions[] = {
           intrinsic_InstantiateModuleFunctionDeclarations, 1, 0),
     JS_FN("SetModuleState", intrinsic_SetModuleState, 1, 0),
     JS_FN("EvaluateModule", intrinsic_EvaluateModule, 1, 0),
-    JS_FN("IsModuleNamespace", intrinsic_IsInstanceOfBuiltin<ModuleNamespaceObject>, 1, 0),
     JS_FN("NewModuleNamespace", intrinsic_NewModuleNamespace, 2, 0),
     JS_FN("AddModuleNamespaceBinding", intrinsic_AddModuleNamespaceBinding, 4, 0),
     JS_FN("ModuleNamespaceExports", intrinsic_ModuleNamespaceExports, 1, 0),
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 2e3d2aecfd..61a2ef1b54 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -5486,3 +5486,7 @@ pref("dom.storageManager.enabled", false);
 // >0 = suppress further prompts after the user has canceled the dialog n times
 // See application preferences for appropriate defaults.
 pref("prompts.authentication_dialog_abuse_limit", 0);
+
+// Whether module scripts (<script type="module">) are enabled for content.
+pref("dom.moduleScripts.enabled", false);
+
diff --git a/testing/web-platform/mozilla/meta/html/semantics/scripting-1/the-script-element/create-module-script.html.ini b/testing/web-platform/mozilla/meta/html/semantics/scripting-1/the-script-element/create-module-script.html.ini
new file mode 100644
index 0000000000..007349f1aa
--- /dev/null
+++ b/testing/web-platform/mozilla/meta/html/semantics/scripting-1/the-script-element/create-module-script.html.ini
@@ -0,0 +1,2 @@
+[create-module-script.html]
+  prefs: [dom.moduleScripts.enabled:true]
diff --git a/testing/web-platform/mozilla/tests/html/semantics/scripting-1/the-script-element/create-module-script.html b/testing/web-platform/mozilla/tests/html/semantics/scripting-1/the-script-element/create-module-script.html
new file mode 100644
index 0000000000..44337a0217
--- /dev/null
+++ b/testing/web-platform/mozilla/tests/html/semantics/scripting-1/the-script-element/create-module-script.html
@@ -0,0 +1,25 @@
+<!doctype html>
+<meta charset=utf-8>
+<title>Insert non-async module script</title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<script>
+  var test = async_test("Create module script")
+  var moduleRan = false;
+  function loadModule() {
+    var script = document.createElement("script");
+    script.onerror = function() {
+      test.step(() => assert_unreached("Should not get an error"));
+      test.done();
+    };
+    script.onload = function() {
+      test.step(() => assert_equals(moduleRan, true));
+      test.done();
+    };
+    script.type = "module";
+    script.src = "support/module.js";
+    script.async = false;
+    document.documentElement.appendChild(script);
+  }
+</script>
+<body onload='loadModule()'></body>
diff --git a/testing/web-platform/mozilla/tests/html/semantics/scripting-1/the-script-element/support/module.js b/testing/web-platform/mozilla/tests/html/semantics/scripting-1/the-script-element/support/module.js
new file mode 100644
index 0000000000..e4d6289d59
--- /dev/null
+++ b/testing/web-platform/mozilla/tests/html/semantics/scripting-1/the-script-element/support/module.js
@@ -0,0 +1,2 @@
+export default 42;
+moduleRan = true;