Add m-esr52 at 52.6.0

1 files changed, 3016 insertions, 0 deletions

diff --git a/dom/base/nsScriptLoader.cpp b/dom/base/nsScriptLoader.cpp
new file mode 100644
index 000000000..6c732db6c
--- /dev/null
+++ b/dom/base/nsScriptLoader.cpp
@@ -0,0 +1,3016 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+/*
+ * A class that handles loading and evaluation of <script> elements.
+ */
+
+#include "nsScriptLoader.h"
+
+#include "prsystem.h"
+#include "jsapi.h"
+#include "jsfriendapi.h"
+#include "xpcpublic.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsIContent.h"
+#include "nsJSUtils.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/SRILogHelper.h"
+#include "nsGkAtoms.h"
+#include "nsNetUtil.h"
+#include "nsIScriptGlobalObject.h"
+#include "nsIScriptContext.h"
+#include "nsIScriptSecurityManager.h"
+#include "nsIPrincipal.h"
+#include "nsJSPrincipals.h"
+#include "nsContentPolicyUtils.h"
+#include "nsIHttpChannel.h"
+#include "nsIHttpChannelInternal.h"
+#include "nsIClassOfService.h"
+#include "nsITimedChannel.h"
+#include "nsIScriptElement.h"
+#include "nsIDOMHTMLScriptElement.h"
+#include "nsIDocShell.h"
+#include "nsContentUtils.h"
+#include "nsUnicharUtils.h"
+#include "nsAutoPtr.h"
+#include "nsIXPConnect.h"
+#include "nsError.h"
+#include "nsThreadUtils.h"
+#include "nsDocShellCID.h"
+#include "nsIContentSecurityPolicy.h"
+#include "mozilla/Logging.h"
+#include "nsCRT.h"
+#include "nsContentCreatorFunctions.h"
+#include "nsProxyRelease.h"
+#include "nsSandboxFlags.h"
+#include "nsContentTypeParser.h"
+#include "nsINetworkPredictor.h"
+#include "ImportManager.h"
+#include "mozilla/dom/EncodingUtils.h"
+#include "mozilla/ConsoleReportCollector.h"
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Unused.h"
+#include "nsIScriptError.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+using JS::SourceBufferHolder;
+
+static LazyLogModule gCspPRLog("CSP");
+
+void
+ImplCycleCollectionUnlink(nsScriptLoadRequestList& aField);
+
+void
+ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
+                            nsScriptLoadRequestList& aField,
+                            const char* aName,
+                            uint32_t aFlags = 0);
+
+//////////////////////////////////////////////////////////////
+// nsScriptLoadRequest
+//////////////////////////////////////////////////////////////
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsScriptLoadRequest)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION_0(nsScriptLoadRequest)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(nsScriptLoadRequest)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(nsScriptLoadRequest)
+
+nsScriptLoadRequest::~nsScriptLoadRequest()
+{
+  js_free(mScriptTextBuf);
+
+  // We should always clean up any off-thread script parsing resources.
+  MOZ_ASSERT(!mOffThreadToken);
+
+  // But play it safe in release builds and try to clean them up here
+  // as a fail safe.
+  MaybeCancelOffThreadScript();
+}
+
+void
+nsScriptLoadRequest::SetReady()
+{
+  MOZ_ASSERT(mProgress != Progress::Ready);
+  mProgress = Progress::Ready;
+}
+
+void
+nsScriptLoadRequest::Cancel()
+{
+  MaybeCancelOffThreadScript();
+  mIsCanceled = true;
+}
+
+void
+nsScriptLoadRequest::MaybeCancelOffThreadScript()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!mOffThreadToken) {
+    return;
+  }
+
+  JSContext* cx = danger::GetJSContext();
+  JS::CancelOffThreadScript(cx, mOffThreadToken);
+  mOffThreadToken = nullptr;
+}
+
+//////////////////////////////////////////////////////////////
+// nsModuleLoadRequest
+//////////////////////////////////////////////////////////////
+
+// A load request for a module, created for every top level module script and
+// every module import.  Load request can share an nsModuleScript if there are
+// multiple imports of the same module.
+
+class nsModuleLoadRequest final : public nsScriptLoadRequest
+{
+  ~nsModuleLoadRequest() {}
+
+  nsModuleLoadRequest(const nsModuleLoadRequest& aOther) = delete;
+  nsModuleLoadRequest(nsModuleLoadRequest&& aOther) = delete;
+
+public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(nsModuleLoadRequest, nsScriptLoadRequest)
+
+  nsModuleLoadRequest(nsIScriptElement* aElement,
+                      uint32_t aVersion,
+                      CORSMode aCORSMode,
+                      const SRIMetadata& aIntegrity,
+                      nsScriptLoader* aLoader);
+
+  bool IsTopLevel() const {
+    return mIsTopLevel;
+  }
+
+  void SetReady() override;
+  void Cancel() override;
+
+  void ModuleLoaded();
+  void DependenciesLoaded();
+  void LoadFailed();
+
+  // Is this a request for a top level module script or an import?
+  bool mIsTopLevel;
+
+  // The base URL used for resolving relative module imports.
+  nsCOMPtr<nsIURI> mBaseURL;
+
+  // Pointer to the script loader, used to trigger actions when the module load
+  // finishes.
+  RefPtr<nsScriptLoader> mLoader;
+
+  // The importing module, or nullptr for top level module scripts.  Used to
+  // implement the ancestor list checked when fetching module dependencies.
+  RefPtr<nsModuleLoadRequest> mParent;
+
+  // Set to a module script object after a successful load or nullptr on
+  // failure.
+  RefPtr<nsModuleScript> mModuleScript;
+
+  // A promise that is completed on successful load of this module and all of
+  // its dependencies, indicating that the module is ready for instantiation and
+  // evaluation.
+  MozPromiseHolder<GenericPromise> mReady;
+
+  // Array of imported modules.
+  nsTArray<RefPtr<nsModuleLoadRequest>> mImports;
+};
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(nsModuleLoadRequest)
+NS_INTERFACE_MAP_END_INHERITING(nsScriptLoadRequest)
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(nsModuleLoadRequest, nsScriptLoadRequest,
+                                   mBaseURL,
+                                   mLoader,
+                                   mParent,
+                                   mModuleScript,
+                                   mImports)
+
+NS_IMPL_ADDREF_INHERITED(nsModuleLoadRequest, nsScriptLoadRequest)
+NS_IMPL_RELEASE_INHERITED(nsModuleLoadRequest, nsScriptLoadRequest)
+
+nsModuleLoadRequest::nsModuleLoadRequest(nsIScriptElement* aElement,
+                                         uint32_t aVersion,
+                                         CORSMode aCORSMode,
+                                         const SRIMetadata &aIntegrity,
+                                         nsScriptLoader* aLoader)
+  : nsScriptLoadRequest(nsScriptKind::Module,
+                        aElement,
+                        aVersion,
+                        aCORSMode,
+                        aIntegrity),
+    mIsTopLevel(true),
+    mLoader(aLoader)
+{}
+
+inline nsModuleLoadRequest*
+nsScriptLoadRequest::AsModuleRequest()
+{
+  MOZ_ASSERT(IsModuleRequest());
+  return static_cast<nsModuleLoadRequest*>(this);
+}
+
+void nsModuleLoadRequest::Cancel()
+{
+  nsScriptLoadRequest::Cancel();
+  mModuleScript = nullptr;
+  mProgress = nsScriptLoadRequest::Progress::Ready;
+  for (size_t i = 0; i < mImports.Length(); i++) {
+    mImports[i]->Cancel();
+  }
+  mReady.RejectIfExists(NS_ERROR_FAILURE, __func__);
+}
+
+void
+nsModuleLoadRequest::SetReady()
+{
+#ifdef DEBUG
+  for (size_t i = 0; i < mImports.Length(); i++) {
+    MOZ_ASSERT(mImports[i]->IsReadyToRun());
+  }
+#endif
+
+  nsScriptLoadRequest::SetReady();
+  mReady.ResolveIfExists(true, __func__);
+}
+
+void
+nsModuleLoadRequest::ModuleLoaded()
+{
+  // A module that was found to be marked as fetching in the module map has now
+  // been loaded.
+
+  mModuleScript = mLoader->GetFetchedModule(mURI);
+  mLoader->StartFetchingModuleDependencies(this);
+}
+
+void
+nsModuleLoadRequest::DependenciesLoaded()
+{
+  // The module and all of its dependencies have been successfully fetched and
+  // compiled.
+
+  if (!mLoader->InstantiateModuleTree(this)) {
+    LoadFailed();
+    return;
+  }
+
+  SetReady();
+  mLoader->ProcessLoadedModuleTree(this);
+  mLoader = nullptr;
+  mParent = nullptr;
+}
+
+void
+nsModuleLoadRequest::LoadFailed()
+{
+  Cancel();
+  mLoader->ProcessLoadedModuleTree(this);
+  mLoader = nullptr;
+  mParent = nullptr;
+}
+
+//////////////////////////////////////////////////////////////
+// nsModuleScript
+//////////////////////////////////////////////////////////////
+
+// A single module script.  May be used to satisfy multiple load requests.
+
+class nsModuleScript final : public nsISupports
+{
+  enum InstantiationState {
+    Uninstantiated,
+    Instantiated,
+    Errored
+  };
+
+  RefPtr<nsScriptLoader> mLoader;
+  nsCOMPtr<nsIURI> mBaseURL;
+  JS::Heap<JSObject*> mModuleRecord;
+  JS::Heap<JS::Value> mException;
+  InstantiationState mInstantiationState;
+
+  ~nsModuleScript();
+
+public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(nsModuleScript)
+
+  nsModuleScript(nsScriptLoader* aLoader,
+                 nsIURI* aBaseURL,
+                 JS::Handle<JSObject*> aModuleRecord);
+
+  nsScriptLoader* Loader() const { return mLoader; }
+  JSObject* ModuleRecord() const { return mModuleRecord; }
+  JS::Value Exception() const { return mException; }
+  nsIURI* BaseURL() const { return mBaseURL; }
+
+  void SetInstantiationResult(JS::Handle<JS::Value> aMaybeException);
+  bool IsUninstantiated() const {
+    return mInstantiationState == Uninstantiated;
+  }
+  bool IsInstantiated() const {
+    return mInstantiationState == Instantiated;
+  }
+  bool InstantiationFailed() const {
+    return mInstantiationState == Errored;
+  }
+
+  void UnlinkModuleRecord();
+};
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsModuleScript)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(nsModuleScript)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsModuleScript)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mLoader)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mBaseURL)
+  tmp->UnlinkModuleRecord();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsModuleScript)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mLoader)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(nsModuleScript)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mModuleRecord)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mException)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(nsModuleScript)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(nsModuleScript)
+
+nsModuleScript::nsModuleScript(nsScriptLoader *aLoader, nsIURI* aBaseURL,
+                               JS::Handle<JSObject*> aModuleRecord)
+ : mLoader(aLoader),
+   mBaseURL(aBaseURL),
+   mModuleRecord(aModuleRecord),
+   mInstantiationState(Uninstantiated)
+{
+  MOZ_ASSERT(mLoader);
+  MOZ_ASSERT(mBaseURL);
+  MOZ_ASSERT(mModuleRecord);
+  MOZ_ASSERT(mException.isUndefined());
+
+  // Make module's host defined field point to this module script object.
+  // This is cleared in the UnlinkModuleRecord().
+  JS::SetModuleHostDefinedField(mModuleRecord, JS::PrivateValue(this));
+  HoldJSObjects(this);
+}
+
+void
+nsModuleScript::UnlinkModuleRecord()
+{
+  // Remove module's back reference to this object request if present.
+  if (mModuleRecord) {
+    MOZ_ASSERT(JS::GetModuleHostDefinedField(mModuleRecord).toPrivate() ==
+               this);
+    JS::SetModuleHostDefinedField(mModuleRecord, JS::UndefinedValue());
+  }
+  mModuleRecord = nullptr;
+  mException.setUndefined();
+}
+
+nsModuleScript::~nsModuleScript()
+{
+  if (mModuleRecord) {
+    // The object may be destroyed without being unlinked first.
+    UnlinkModuleRecord();
+  }
+  DropJSObjects(this);
+}
+
+void
+nsModuleScript::SetInstantiationResult(JS::Handle<JS::Value> aMaybeException)
+{
+  MOZ_ASSERT(mInstantiationState == Uninstantiated);
+  MOZ_ASSERT(mModuleRecord);
+  MOZ_ASSERT(mException.isUndefined());
+
+  if (aMaybeException.isUndefined()) {
+    mInstantiationState = Instantiated;
+  } else {
+    mModuleRecord = nullptr;
+    mException = aMaybeException;
+    mInstantiationState = Errored;
+  }
+}
+
+//////////////////////////////////////////////////////////////
+
+// nsScriptLoadRequestList
+//////////////////////////////////////////////////////////////
+
+nsScriptLoadRequestList::~nsScriptLoadRequestList()
+{
+  Clear();
+}
+
+void
+nsScriptLoadRequestList::Clear()
+{
+  while (!isEmpty()) {
+    RefPtr<nsScriptLoadRequest> first = StealFirst();
+    first->Cancel();
+    // And just let it go out of scope and die.
+  }
+}
+
+#ifdef DEBUG
+bool
+nsScriptLoadRequestList::Contains(nsScriptLoadRequest* aElem) const
+{
+  for (const nsScriptLoadRequest* req = getFirst();
+       req; req = req->getNext()) {
+    if (req == aElem) {
+      return true;
+    }
+  }
+
+  return false;
+}
+#endif // DEBUG
+
+inline void
+ImplCycleCollectionUnlink(nsScriptLoadRequestList& aField)
+{
+  while (!aField.isEmpty()) {
+    RefPtr<nsScriptLoadRequest> first = aField.StealFirst();
+  }
+}
+
+inline void
+ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
+                            nsScriptLoadRequestList& aField,
+                            const char* aName,
+                            uint32_t aFlags)
+{
+  for (nsScriptLoadRequest* request = aField.getFirst();
+       request; request = request->getNext())
+  {
+    CycleCollectionNoteChild(aCallback, request, aName, aFlags);
+  }
+}
+
+//////////////////////////////////////////////////////////////
+// nsScriptLoader::PreloadInfo
+//////////////////////////////////////////////////////////////
+
+inline void
+ImplCycleCollectionUnlink(nsScriptLoader::PreloadInfo& aField)
+{
+  ImplCycleCollectionUnlink(aField.mRequest);
+}
+
+inline void
+ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
+                            nsScriptLoader::PreloadInfo& aField,
+                            const char* aName,
+                            uint32_t aFlags = 0)
+{
+  ImplCycleCollectionTraverse(aCallback, aField.mRequest, aName, aFlags);
+}
+
+//////////////////////////////////////////////////////////////
+// nsScriptLoader
+//////////////////////////////////////////////////////////////
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsScriptLoader)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION(nsScriptLoader,
+                         mNonAsyncExternalScriptInsertedRequests,
+                         mLoadingAsyncRequests,
+                         mLoadedAsyncRequests,
+                         mDeferRequests,
+                         mXSLTRequests,
+                         mParserBlockingRequest,
+                         mPreloads,
+                         mPendingChildLoaders,
+                         mFetchedModules)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(nsScriptLoader)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(nsScriptLoader)
+
+nsScriptLoader::nsScriptLoader(nsIDocument *aDocument)
+  : mDocument(aDocument),
+    mParserBlockingBlockerCount(0),
+    mBlockerCount(0),
+    mNumberOfProcessors(0),
+    mEnabled(true),
+    mDeferEnabled(false),
+    mDocumentParsingDone(false),
+    mBlockingDOMContentLoaded(false),
+    mReporter(new ConsoleReportCollector())
+{
+}
+
+nsScriptLoader::~nsScriptLoader()
+{
+  mObservers.Clear();
+
+  if (mParserBlockingRequest) {
+    mParserBlockingRequest->FireScriptAvailable(NS_ERROR_ABORT);
+  }
+
+  for (nsScriptLoadRequest* req = mXSLTRequests.getFirst(); req;
+       req = req->getNext()) {
+    req->FireScriptAvailable(NS_ERROR_ABORT);
+  }
+
+  for (nsScriptLoadRequest* req = mDeferRequests.getFirst(); req;
+       req = req->getNext()) {
+    req->FireScriptAvailable(NS_ERROR_ABORT);
+  }
+
+  for (nsScriptLoadRequest* req = mLoadingAsyncRequests.getFirst(); req;
+       req = req->getNext()) {
+    req->FireScriptAvailable(NS_ERROR_ABORT);
+  }
+
+  for (nsScriptLoadRequest* req = mLoadedAsyncRequests.getFirst(); req;
+       req = req->getNext()) {
+    req->FireScriptAvailable(NS_ERROR_ABORT);
+  }
+
+  for(nsScriptLoadRequest* req = mNonAsyncExternalScriptInsertedRequests.getFirst();
+      req;
+      req = req->getNext()) {
+    req->FireScriptAvailable(NS_ERROR_ABORT);
+  }
+
+  // Unblock the kids, in case any of them moved to a different document
+  // subtree in the meantime and therefore aren't actually going away.
+  for (uint32_t j = 0; j < mPendingChildLoaders.Length(); ++j) {
+    mPendingChildLoaders[j]->RemoveParserBlockingScriptExecutionBlocker();
+  }
+}
+
+// Helper method for checking if the script element is an event-handler
+// This means that it has both a for-attribute and a event-attribute.
+// Also, if the for-attribute has a value that matches "\s*window\s*",
+// and the event-attribute matches "\s*onload([ \(].*)?" then it isn't an
+// eventhandler. (both matches are case insensitive).
+// This is how IE seems to filter out a window's onload handler from a
+// <script for=... event=...> element.
+
+static bool
+IsScriptEventHandler(nsIContent* aScriptElement)
+{
+  if (!aScriptElement->IsHTMLElement()) {
+    return false;
+  }
+
+  nsAutoString forAttr, eventAttr;
+  if (!aScriptElement->GetAttr(kNameSpaceID_None, nsGkAtoms::_for, forAttr) ||
+      !aScriptElement->GetAttr(kNameSpaceID_None, nsGkAtoms::event, eventAttr)) {
+    return false;
+  }
+
+  const nsAString& for_str =
+    nsContentUtils::TrimWhitespace<nsCRT::IsAsciiSpace>(forAttr);
+  if (!for_str.LowerCaseEqualsLiteral("window")) {
+    return true;
+  }
+
+  // We found for="window", now check for event="onload".
+  const nsAString& event_str =
+    nsContentUtils::TrimWhitespace<nsCRT::IsAsciiSpace>(eventAttr, false);
+  if (!StringBeginsWith(event_str, NS_LITERAL_STRING("onload"),
+                        nsCaseInsensitiveStringComparator())) {
+    // It ain't "onload.*".
+
+    return true;
+  }
+
+  nsAutoString::const_iterator start, end;
+  event_str.BeginReading(start);
+  event_str.EndReading(end);
+
+  start.advance(6); // advance past "onload"
+
+  if (start != end && *start != '(' && *start != ' ') {
+    // We got onload followed by something other than space or
+    // '('. Not good enough.
+
+    return true;
+  }
+
+  return false;
+}
+
+nsresult
+nsScriptLoader::CheckContentPolicy(nsIDocument* aDocument,
+                                   nsISupports *aContext,
+                                   nsIURI *aURI,
+                                   const nsAString &aType,
+                                   bool aIsPreLoad)
+{
+  nsContentPolicyType contentPolicyType = aIsPreLoad
+                                          ? nsIContentPolicy::TYPE_INTERNAL_SCRIPT_PRELOAD
+                                          : nsIContentPolicy::TYPE_INTERNAL_SCRIPT;
+
+  int16_t shouldLoad = nsIContentPolicy::ACCEPT;
+  nsresult rv = NS_CheckContentLoadPolicy(contentPolicyType,
+                                          aURI,
+                                          aDocument->NodePrincipal(),
+                                          aContext,
+                                          NS_LossyConvertUTF16toASCII(aType),
+                                          nullptr,    //extra
+                                          &shouldLoad,
+                                          nsContentUtils::GetContentPolicy(),
+                                          nsContentUtils::GetSecurityManager());
+  if (NS_FAILED(rv) || NS_CP_REJECTED(shouldLoad)) {
+    if (NS_FAILED(rv) || shouldLoad != nsIContentPolicy::REJECT_TYPE) {
+      return NS_ERROR_CONTENT_BLOCKED;
+    }
+    return NS_ERROR_CONTENT_BLOCKED_SHOW_ALT;
+  }
+
+  return NS_OK;
+}
+
+bool
+nsScriptLoader::ModuleMapContainsModule(nsModuleLoadRequest *aRequest) const
+{
+  // Returns whether we have fetched, or are currently fetching, a module script
+  // for the request's URL.
+  return mFetchingModules.Contains(aRequest->mURI) ||
+         mFetchedModules.Contains(aRequest->mURI);
+}
+
+bool
+nsScriptLoader::IsFetchingModule(nsModuleLoadRequest *aRequest) const
+{
+  bool fetching = mFetchingModules.Contains(aRequest->mURI);
+  MOZ_ASSERT_IF(fetching, !mFetchedModules.Contains(aRequest->mURI));
+  return fetching;
+}
+
+void
+nsScriptLoader::SetModuleFetchStarted(nsModuleLoadRequest *aRequest)
+{
+  // Update the module map to indicate that a module is currently being fetched.
+
+  MOZ_ASSERT(aRequest->IsLoading());
+  MOZ_ASSERT(!ModuleMapContainsModule(aRequest));
+  mFetchingModules.Put(aRequest->mURI, nullptr);
+}
+
+void
+nsScriptLoader::SetModuleFetchFinishedAndResumeWaitingRequests(nsModuleLoadRequest *aRequest,
+                                                               nsresult aResult)
+{
+  // Update module map with the result of fetching a single module script.  The
+  // module script pointer is nullptr on error.
+
+  MOZ_ASSERT(!aRequest->IsReadyToRun());
+
+  RefPtr<GenericPromise::Private> promise;
+  MOZ_ALWAYS_TRUE(mFetchingModules.Get(aRequest->mURI, getter_AddRefs(promise)));
+  mFetchingModules.Remove(aRequest->mURI);
+
+  RefPtr<nsModuleScript> ms(aRequest->mModuleScript);
+  MOZ_ASSERT(NS_SUCCEEDED(aResult) == (ms != nullptr));
+  mFetchedModules.Put(aRequest->mURI, ms);
+
+  if (promise) {
+    if (ms) {
+      promise->Resolve(true, __func__);
+    } else {
+      promise->Reject(aResult, __func__);
+    }
+  }
+}
+
+RefPtr<GenericPromise>
+nsScriptLoader::WaitForModuleFetch(nsModuleLoadRequest *aRequest)
+{
+  MOZ_ASSERT(ModuleMapContainsModule(aRequest));
+
+  RefPtr<GenericPromise::Private> promise;
+  if (mFetchingModules.Get(aRequest->mURI, getter_AddRefs(promise))) {
+    if (!promise) {
+      promise = new GenericPromise::Private(__func__);
+      mFetchingModules.Put(aRequest->mURI, promise);
+    }
+    return promise;
+  }
+
+  RefPtr<nsModuleScript> ms;
+  MOZ_ALWAYS_TRUE(mFetchedModules.Get(aRequest->mURI, getter_AddRefs(ms)));
+  if (!ms) {
+    return GenericPromise::CreateAndReject(NS_ERROR_FAILURE, __func__);
+  }
+
+  return GenericPromise::CreateAndResolve(true, __func__);
+}
+
+nsModuleScript*
+nsScriptLoader::GetFetchedModule(nsIURI* aURL) const
+{
+  bool found;
+  nsModuleScript* ms = mFetchedModules.GetWeak(aURL, &found);
+  MOZ_ASSERT(found);
+  return ms;
+}
+
+nsresult
+nsScriptLoader::ProcessFetchedModuleSource(nsModuleLoadRequest* aRequest)
+{
+  MOZ_ASSERT(!aRequest->mModuleScript);
+
+  nsresult rv = CreateModuleScript(aRequest);
+  SetModuleFetchFinishedAndResumeWaitingRequests(aRequest, rv);
+
+  free(aRequest->mScriptTextBuf);
+  aRequest->mScriptTextBuf = nullptr;
+  aRequest->mScriptTextLength = 0;
+
+  if (NS_SUCCEEDED(rv)) {
+    StartFetchingModuleDependencies(aRequest);
+  }
+
+  return rv;
+}
+
+nsresult
+nsScriptLoader::CreateModuleScript(nsModuleLoadRequest* aRequest)
+{
+  MOZ_ASSERT(!aRequest->mModuleScript);
+  MOZ_ASSERT(aRequest->mBaseURL);
+
+  nsCOMPtr<nsIScriptGlobalObject> globalObject = GetScriptGlobalObject();
+  if (!globalObject) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsIScriptContext> context = globalObject->GetScriptContext();
+  if (!context) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAutoMicroTask mt;
+  AutoEntryScript aes(globalObject, "CompileModule", true);
+
+  bool oldProcessingScriptTag = context->GetProcessingScriptTag();
+  context->SetProcessingScriptTag(true);
+
+  nsresult rv;
+  {
+    // Update our current script.
+    AutoCurrentScriptUpdater scriptUpdater(this, aRequest->mElement);
+    Maybe<AutoCurrentScriptUpdater> masterScriptUpdater;
+    nsCOMPtr<nsIDocument> master = mDocument->MasterDocument();
+    if (master != mDocument) {
+      masterScriptUpdater.emplace(master->ScriptLoader(),
+                                  aRequest->mElement);
+    }
+
+    JSContext* cx = aes.cx();
+    JS::Rooted<JSObject*> module(cx);
+
+    if (aRequest->mWasCompiledOMT) {
+      module = JS::FinishOffThreadModule(cx, aRequest->mOffThreadToken);
+      aRequest->mOffThreadToken = nullptr;
+      rv = module ? NS_OK : NS_ERROR_FAILURE;
+    } else {
+      JS::Rooted<JSObject*> global(cx, globalObject->GetGlobalJSObject());
+
+      JS::CompileOptions options(cx);
+      rv = FillCompileOptionsForRequest(aes, aRequest, global, &options);
+
+      if (NS_SUCCEEDED(rv)) {
+        nsAutoString inlineData;
+        SourceBufferHolder srcBuf = GetScriptSource(aRequest, inlineData);
+        rv = nsJSUtils::CompileModule(cx, srcBuf, global, options, &module);
+      }
+    }
+    MOZ_ASSERT(NS_SUCCEEDED(rv) == (module != nullptr));
+    if (module) {
+      aRequest->mModuleScript =
+        new nsModuleScript(this, aRequest->mBaseURL, module);
+    }
+  }
+
+  context->SetProcessingScriptTag(oldProcessingScriptTag);
+
+  return rv;
+}
+
+static bool
+ThrowTypeError(JSContext* aCx, nsModuleScript* aScript,
+               const nsString& aMessage)
+{
+  JS::Rooted<JSObject*> module(aCx, aScript->ModuleRecord());
+  JS::Rooted<JSScript*> script(aCx, JS::GetModuleScript(aCx, module));
+  JS::Rooted<JSString*> filename(aCx);
+  filename = JS_NewStringCopyZ(aCx, JS_GetScriptFilename(script));
+  if (!filename) {
+    return false;
+  }
+
+  JS::Rooted<JSString*> message(aCx, JS_NewUCStringCopyZ(aCx, aMessage.get()));
+  if (!message) {
+    return false;
+  }
+
+  JS::Rooted<JS::Value> error(aCx);
+  if (!JS::CreateError(aCx, JSEXN_TYPEERR, nullptr, filename, 0, 0, nullptr,
+                       message, &error)) {
+    return false;
+  }
+
+  JS_SetPendingException(aCx, error);
+  return false;
+}
+
+static bool
+HandleResolveFailure(JSContext* aCx, nsModuleScript* aScript,
+                     const nsAString& aSpecifier)
+{
+  // TODO: How can we get the line number of the failed import?
+
+  nsAutoString message(NS_LITERAL_STRING("Error resolving module specifier: "));
+  message.Append(aSpecifier);
+
+  return ThrowTypeError(aCx, aScript, message);
+}
+
+static bool
+HandleModuleNotFound(JSContext* aCx, nsModuleScript* aScript,
+                     const nsAString& aSpecifier)
+{
+  // TODO: How can we get the line number of the failed import?
+
+  nsAutoString message(NS_LITERAL_STRING("Resolved module not found in map: "));
+  message.Append(aSpecifier);
+
+  return ThrowTypeError(aCx, aScript, message);
+}
+
+static already_AddRefed<nsIURI>
+ResolveModuleSpecifier(nsModuleScript* aScript,
+                       const nsAString& aSpecifier)
+{
+  // The following module specifiers are allowed by the spec:
+  //  - a valid absolute URL
+  //  - a valid relative URL that starts with "/", "./" or "../"
+  //
+  // Bareword module specifiers are currently disallowed as these may be given
+  // special meanings in the future.
+
+  nsCOMPtr<nsIURI> uri;
+  nsresult rv = NS_NewURI(getter_AddRefs(uri), aSpecifier);
+  if (NS_SUCCEEDED(rv)) {
+    return uri.forget();
+  }
+
+  if (rv != NS_ERROR_MALFORMED_URI) {
+    return nullptr;
+  }
+
+  if (!StringBeginsWith(aSpecifier, NS_LITERAL_STRING("/")) &&
+      !StringBeginsWith(aSpecifier, NS_LITERAL_STRING("./")) &&
+      !StringBeginsWith(aSpecifier, NS_LITERAL_STRING("../"))) {
+    return nullptr;
+  }
+
+  rv = NS_NewURI(getter_AddRefs(uri), aSpecifier, nullptr, aScript->BaseURL());
+  if (NS_SUCCEEDED(rv)) {
+    return uri.forget();
+  }
+
+  return nullptr;
+}
+
+static nsresult
+RequestedModuleIsInAncestorList(nsModuleLoadRequest* aRequest, nsIURI* aURL, bool* aResult)
+{
+  const size_t ImportDepthLimit = 100;
+
+  *aResult = false;
+  size_t depth = 0;
+  while (aRequest) {
+    if (depth++ == ImportDepthLimit) {
+      return NS_ERROR_FAILURE;
+    }
+
+    bool equal;
+    nsresult rv = aURL->Equals(aRequest->mURI, &equal);
+    NS_ENSURE_SUCCESS(rv, rv);
+    if (equal) {
+      *aResult = true;
+      return NS_OK;
+    }
+
+    aRequest = aRequest->mParent;
+  }
+
+  return NS_OK;
+}
+
+static nsresult
+ResolveRequestedModules(nsModuleLoadRequest* aRequest, nsCOMArray<nsIURI> &aUrls)
+{
+  nsModuleScript* ms = aRequest->mModuleScript;
+
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(ms->ModuleRecord())) {
+    return NS_ERROR_FAILURE;
+  }
+
+  JSContext* cx = jsapi.cx();
+  JS::Rooted<JSObject*> moduleRecord(cx, ms->ModuleRecord());
+  JS::Rooted<JSObject*> specifiers(cx, JS::GetRequestedModules(cx, moduleRecord));
+
+  uint32_t length;
+  if (!JS_GetArrayLength(cx, specifiers, &length)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  JS::Rooted<JS::Value> val(cx);
+  for (uint32_t i = 0; i < length; i++) {
+    if (!JS_GetElement(cx, specifiers, i, &val)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    nsAutoJSString specifier;
+    if (!specifier.init(cx, val)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    // Let url be the result of resolving a module specifier given module script and requested.
+    nsModuleScript* ms = aRequest->mModuleScript;
+    nsCOMPtr<nsIURI> uri = ResolveModuleSpecifier(ms, specifier);
+    if (!uri) {
+      HandleResolveFailure(cx, ms, specifier);
+      return NS_ERROR_FAILURE;
+    }
+
+    bool isAncestor;
+    nsresult rv = RequestedModuleIsInAncestorList(aRequest, uri, &isAncestor);
+    NS_ENSURE_SUCCESS(rv, rv);
+    if (!isAncestor) {
+      aUrls.AppendElement(uri.forget());
+    }
+  }
+
+  return NS_OK;
+}
+
+void
+nsScriptLoader::StartFetchingModuleDependencies(nsModuleLoadRequest* aRequest)
+{
+  MOZ_ASSERT(aRequest->mModuleScript);
+  MOZ_ASSERT(!aRequest->IsReadyToRun());
+  aRequest->mProgress = nsModuleLoadRequest::Progress::FetchingImports;
+
+  nsCOMArray<nsIURI> urls;
+  nsresult rv = ResolveRequestedModules(aRequest, urls);
+  if (NS_FAILED(rv)) {
+    aRequest->LoadFailed();
+    return;
+  }
+
+  if (urls.Length() == 0) {
+    // There are no descendents to load so this request is ready.
+    aRequest->DependenciesLoaded();
+    return;
+  }
+
+  // For each url in urls, fetch a module script tree given url, module script's
+  // CORS setting, and module script's settings object.
+  nsTArray<RefPtr<GenericPromise>> importsReady;
+  for (size_t i = 0; i < urls.Length(); i++) {
+    RefPtr<GenericPromise> childReady =
+      StartFetchingModuleAndDependencies(aRequest, urls[i]);
+    importsReady.AppendElement(childReady);
+  }
+
+  // Wait for all imports to become ready.
+  RefPtr<GenericPromise::AllPromiseType> allReady =
+    GenericPromise::All(AbstractThread::GetCurrent(), importsReady);
+  allReady->Then(AbstractThread::GetCurrent(), __func__, aRequest,
+                 &nsModuleLoadRequest::DependenciesLoaded,
+                 &nsModuleLoadRequest::LoadFailed);
+}
+
+RefPtr<GenericPromise>
+nsScriptLoader::StartFetchingModuleAndDependencies(nsModuleLoadRequest* aRequest,
+                                                   nsIURI* aURI)
+{
+  MOZ_ASSERT(aURI);
+
+  RefPtr<nsModuleLoadRequest> childRequest =
+    new nsModuleLoadRequest(aRequest->mElement, aRequest->mJSVersion,
+                            aRequest->mCORSMode, aRequest->mIntegrity, this);
+
+  childRequest->mIsTopLevel = false;
+  childRequest->mURI = aURI;
+  childRequest->mIsInline = false;
+  childRequest->mReferrerPolicy = aRequest->mReferrerPolicy;
+  childRequest->mParent = aRequest;
+
+  RefPtr<GenericPromise> ready = childRequest->mReady.Ensure(__func__);
+
+  nsresult rv = StartLoad(childRequest, NS_LITERAL_STRING("module"), false);
+  if (NS_FAILED(rv)) {
+    childRequest->mReady.Reject(rv, __func__);
+    return ready;
+  }
+
+  aRequest->mImports.AppendElement(childRequest);
+  return ready;
+}
+
+bool
+HostResolveImportedModule(JSContext* aCx, unsigned argc, JS::Value* vp)
+{
+  MOZ_ASSERT(argc == 2);
+  JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+  JS::Rooted<JSObject*> module(aCx, &args[0].toObject());
+  JS::Rooted<JSString*> specifier(aCx, args[1].toString());
+
+  // Let referencing module script be referencingModule.[[HostDefined]].
+  JS::Value value = JS::GetModuleHostDefinedField(module);
+  auto script = static_cast<nsModuleScript*>(value.toPrivate());
+  MOZ_ASSERT(script->ModuleRecord() == module);
+
+  // Let url be the result of resolving a module specifier given referencing
+  // module script and specifier. If the result is failure, throw a TypeError
+  // exception and abort these steps.
+  nsAutoJSString string;
+  if (!string.init(aCx, specifier)) {
+    return false;
+  }
+
+  nsCOMPtr<nsIURI> uri = ResolveModuleSpecifier(script, string);
+  if (!uri) {
+    return HandleResolveFailure(aCx, script, string);
+  }
+
+  // Let resolved module script be the value of the entry in module map whose
+  // key is url. If no such entry exists, throw a TypeError exception and abort
+  // these steps.
+  nsModuleScript* ms = script->Loader()->GetFetchedModule(uri);
+  if (!ms) {
+    return HandleModuleNotFound(aCx, script, string);
+  }
+
+  if (ms->InstantiationFailed()) {
+    JS::Rooted<JS::Value> exception(aCx, ms->Exception());
+    JS_SetPendingException(aCx, exception);
+    return false;
+  }
+
+  *vp = JS::ObjectValue(*ms->ModuleRecord());
+  return true;
+}
+
+static nsresult
+EnsureModuleResolveHook(JSContext* aCx)
+{
+  if (JS::GetModuleResolveHook(aCx)) {
+    return NS_OK;
+  }
+
+  JS::Rooted<JSFunction*> func(aCx);
+  func = JS_NewFunction(aCx, HostResolveImportedModule, 2, 0,
+                        "HostResolveImportedModule");
+  if (!func) {
+    return NS_ERROR_FAILURE;
+  }
+
+  JS::SetModuleResolveHook(aCx, func);
+  return NS_OK;
+}
+
+void
+nsScriptLoader::ProcessLoadedModuleTree(nsModuleLoadRequest* aRequest)
+{
+  if (aRequest->IsTopLevel()) {
+    MaybeMoveToLoadedList(aRequest);
+    ProcessPendingRequests();
+  }
+
+  if (aRequest->mWasCompiledOMT) {
+    mDocument->UnblockOnload(false);
+  }
+}
+
+bool
+nsScriptLoader::InstantiateModuleTree(nsModuleLoadRequest* aRequest)
+{
+  // Perform eager instantiation of the loaded module tree.
+
+  MOZ_ASSERT(aRequest);
+
+  nsModuleScript* ms = aRequest->mModuleScript;
+  MOZ_ASSERT(ms);
+  if (!ms->ModuleRecord()) {
+    return false;
+  }
+
+  AutoJSAPI jsapi;
+  if (NS_WARN_IF(!jsapi.Init(ms->ModuleRecord()))) {
+    return false;
+  }
+
+  nsresult rv = EnsureModuleResolveHook(jsapi.cx());
+  NS_ENSURE_SUCCESS(rv, false);
+
+  JS::Rooted<JSObject*> module(jsapi.cx(), ms->ModuleRecord());
+  bool ok = NS_SUCCEEDED(nsJSUtils::ModuleDeclarationInstantiation(jsapi.cx(), module));
+
+  JS::RootedValue exception(jsapi.cx());
+  if (!ok) {
+    MOZ_ASSERT(jsapi.HasException());
+    if (!jsapi.StealException(&exception)) {
+      return false;
+    }
+    MOZ_ASSERT(!exception.isUndefined());
+  }
+
+  // Mark this module and any uninstantiated dependencies found via depth-first
+  // search as instantiated and record any error.
+
+  mozilla::Vector<nsModuleLoadRequest*, 1> requests;
+  if (!requests.append(aRequest)) {
+    return false;
+  }
+
+  while (!requests.empty()) {
+    nsModuleLoadRequest* request = requests.popCopy();
+    nsModuleScript* ms = request->mModuleScript;
+    if (!ms->IsUninstantiated()) {
+      continue;
+    }
+
+    ms->SetInstantiationResult(exception);
+
+    for (auto import : request->mImports) {
+      if (import->mModuleScript->IsUninstantiated() &&
+          !requests.append(import))
+      {
+        return false;
+      }
+    }
+  }
+
+  return true;
+}
+
+nsresult
+nsScriptLoader::StartLoad(nsScriptLoadRequest *aRequest, const nsAString &aType,
+                          bool aScriptFromHead)
+{
+  MOZ_ASSERT(aRequest->IsLoading());
+  NS_ENSURE_TRUE(mDocument, NS_ERROR_NULL_POINTER);
+
+  // If this document is sandboxed without 'allow-scripts', abort.
+  if (mDocument->HasScriptsBlockedBySandbox()) {
+    return NS_OK;
+  }
+
+  if (aRequest->IsModuleRequest()) {
+    // Check whether the module has been fetched or is currently being fetched,
+    // and if so wait for it.
+    nsModuleLoadRequest* request = aRequest->AsModuleRequest();
+    if (ModuleMapContainsModule(request)) {
+      WaitForModuleFetch(request)
+        ->Then(AbstractThread::GetCurrent(), __func__, request,
+               &nsModuleLoadRequest::ModuleLoaded,
+               &nsModuleLoadRequest::LoadFailed);
+      return NS_OK;
+    }
+
+    // Otherwise put the URL in the module map and mark it as fetching.
+    SetModuleFetchStarted(request);
+  }
+
+  nsContentPolicyType contentPolicyType = aRequest->IsPreload()
+                                          ? nsIContentPolicy::TYPE_INTERNAL_SCRIPT_PRELOAD
+                                          : nsIContentPolicy::TYPE_INTERNAL_SCRIPT;
+  nsCOMPtr<nsINode> context;
+  if (aRequest->mElement) {
+    context = do_QueryInterface(aRequest->mElement);
+  }
+  else {
+    context = mDocument;
+  }
+
+  nsCOMPtr<nsILoadGroup> loadGroup = mDocument->GetDocumentLoadGroup();
+  nsCOMPtr<nsPIDOMWindowOuter> window = mDocument->MasterDocument()->GetWindow();
+  NS_ENSURE_TRUE(window, NS_ERROR_NULL_POINTER);
+  nsIDocShell *docshell = window->GetDocShell();
+  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;
+  }
+  securityFlags |= nsILoadInfo::SEC_ALLOW_CHROME;
+
+  nsCOMPtr<nsIChannel> channel;
+  nsresult rv = NS_NewChannel(getter_AddRefs(channel),
+                              aRequest->mURI,
+                              context,
+                              securityFlags,
+                              contentPolicyType,
+                              loadGroup,
+                              prompter,
+                              nsIRequest::LOAD_NORMAL |
+                              nsIChannel::LOAD_CLASSIFY_URI);
+
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsIScriptElement *script = aRequest->mElement;
+  nsCOMPtr<nsIClassOfService> cos(do_QueryInterface(channel));
+
+  if (cos) {
+    if (aScriptFromHead &&
+        !(script && (script->GetScriptAsync() || script->GetScriptDeferred()))) {
+      // synchronous head scripts block lading of most other non js/css
+      // content such as images
+      cos->AddClassFlags(nsIClassOfService::Leader);
+    } else if (!(script && script->GetScriptDeferred())) {
+      // other scripts are neither blocked nor prioritized unless marked deferred
+      cos->AddClassFlags(nsIClassOfService::Unblocked);
+    }
+  }
+
+  nsCOMPtr<nsIHttpChannel> httpChannel(do_QueryInterface(channel));
+  if (httpChannel) {
+    // HTTP content negotation has little value in this context.
+    httpChannel->SetRequestHeader(NS_LITERAL_CSTRING("Accept"),
+                                  NS_LITERAL_CSTRING("*/*"),
+                                  false);
+    httpChannel->SetReferrerWithPolicy(mDocument->GetDocumentURI(),
+                                       aRequest->mReferrerPolicy);
+
+    nsCOMPtr<nsIHttpChannelInternal> internalChannel(do_QueryInterface(httpChannel));
+    if (internalChannel) {
+      internalChannel->SetIntegrityMetadata(aRequest->mIntegrity.GetIntegrityString());
+    }
+  }
+
+  nsCOMPtr<nsILoadContext> loadContext(do_QueryInterface(docshell));
+  mozilla::net::PredictorLearn(aRequest->mURI, mDocument->GetDocumentURI(),
+      nsINetworkPredictor::LEARN_LOAD_SUBRESOURCE, loadContext);
+
+  // Set the initiator type
+  nsCOMPtr<nsITimedChannel> timedChannel(do_QueryInterface(httpChannel));
+  if (timedChannel) {
+    timedChannel->SetInitiatorType(NS_LITERAL_STRING("script"));
+  }
+
+  nsAutoPtr<mozilla::dom::SRICheckDataVerifier> sriDataVerifier;
+  if (!aRequest->mIntegrity.IsEmpty()) {
+    nsAutoCString sourceUri;
+    if (mDocument->GetDocumentURI()) {
+      mDocument->GetDocumentURI()->GetAsciiSpec(sourceUri);
+    }
+    sriDataVerifier = new SRICheckDataVerifier(aRequest->mIntegrity, sourceUri,
+                                               mReporter);
+  }
+
+  RefPtr<nsScriptLoadHandler> handler =
+      new nsScriptLoadHandler(this, aRequest, sriDataVerifier.forget());
+
+  nsCOMPtr<nsIIncrementalStreamLoader> loader;
+  rv = NS_NewIncrementalStreamLoader(getter_AddRefs(loader), handler);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return channel->AsyncOpen2(loader);
+}
+
+bool
+nsScriptLoader::PreloadURIComparator::Equals(const PreloadInfo &aPi,
+                                             nsIURI * const &aURI) const
+{
+  bool same;
+  return NS_SUCCEEDED(aPi.mRequest->mURI->Equals(aURI, &same)) &&
+         same;
+}
+
+class nsScriptRequestProcessor : public Runnable
+{
+private:
+  RefPtr<nsScriptLoader> mLoader;
+  RefPtr<nsScriptLoadRequest> mRequest;
+public:
+  nsScriptRequestProcessor(nsScriptLoader* aLoader,
+                           nsScriptLoadRequest* aRequest)
+    : mLoader(aLoader)
+    , mRequest(aRequest)
+  {}
+  NS_IMETHOD Run() override
+  {
+    return mLoader->ProcessRequest(mRequest);
+  }
+};
+
+static inline bool
+ParseTypeAttribute(const nsAString& aType, JSVersion* aVersion)
+{
+  MOZ_ASSERT(!aType.IsEmpty());
+  MOZ_ASSERT(aVersion);
+  MOZ_ASSERT(*aVersion == JSVERSION_DEFAULT);
+
+  nsContentTypeParser parser(aType);
+
+  nsAutoString mimeType;
+  nsresult rv = parser.GetType(mimeType);
+  NS_ENSURE_SUCCESS(rv, false);
+
+  if (!nsContentUtils::IsJavascriptMIMEType(mimeType)) {
+    return false;
+  }
+
+  // Get the version string, and ensure the language supports it.
+  nsAutoString versionName;
+  rv = parser.GetParameter("version", versionName);
+
+  if (NS_SUCCEEDED(rv)) {
+    *aVersion = nsContentUtils::ParseJavascriptVersion(versionName);
+  } else if (rv != NS_ERROR_INVALID_ARG) {
+    return false;
+  }
+
+  return true;
+}
+
+static bool
+CSPAllowsInlineScript(nsIScriptElement *aElement, nsIDocument *aDocument)
+{
+  nsCOMPtr<nsIContentSecurityPolicy> csp;
+  // Note: For imports NodePrincipal and the principal of the master are
+  // the same.
+  nsresult rv = aDocument->NodePrincipal()->GetCsp(getter_AddRefs(csp));
+  NS_ENSURE_SUCCESS(rv, false);
+
+  if (!csp) {
+    // no CSP --> allow
+    return true;
+  }
+
+  // query the nonce
+  nsCOMPtr<nsIContent> scriptContent = do_QueryInterface(aElement);
+  nsAutoString nonce;
+  scriptContent->GetAttr(kNameSpaceID_None, nsGkAtoms::nonce, nonce);
+  bool parserCreated = aElement->GetParserCreated() != mozilla::dom::NOT_FROM_PARSER;
+
+  // query the scripttext
+  nsAutoString scriptText;
+  aElement->GetScriptText(scriptText);
+
+  bool allowInlineScript = false;
+  rv = csp->GetAllowsInline(nsIContentPolicy::TYPE_SCRIPT,
+                            nonce, parserCreated, scriptText,
+                            aElement->GetScriptLineNumber(),
+                            &allowInlineScript);
+  return allowInlineScript;
+}
+
+nsScriptLoadRequest*
+nsScriptLoader::CreateLoadRequest(nsScriptKind aKind,
+                                  nsIScriptElement* aElement,
+                                  uint32_t aVersion, CORSMode aCORSMode,
+                                  const SRIMetadata &aIntegrity)
+{
+  if (aKind == nsScriptKind::Classic) {
+    return new nsScriptLoadRequest(aKind, aElement, aVersion, aCORSMode,
+                                   aIntegrity);
+  }
+
+  MOZ_ASSERT(aKind == nsScriptKind::Module);
+  return new nsModuleLoadRequest(aElement, aVersion, aCORSMode, aIntegrity,
+                                 this);
+}
+
+bool
+nsScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
+{
+  // We need a document to evaluate scripts.
+  NS_ENSURE_TRUE(mDocument, false);
+
+  // Check to see if scripts has been turned off.
+  if (!mEnabled || !mDocument->IsScriptEnabled()) {
+    return false;
+  }
+
+  NS_ASSERTION(!aElement->IsMalformed(), "Executing malformed script");
+
+  nsCOMPtr<nsIContent> scriptContent = do_QueryInterface(aElement);
+
+  // Step 12. Check that the script is not an eventhandler
+  if (IsScriptEventHandler(scriptContent)) {
+    return false;
+  }
+
+  JSVersion version = JSVERSION_DEFAULT;
+
+  // Check the type attribute to determine language and version.
+  // If type exists, it trumps the deprecated 'language='
+  nsAutoString type;
+  bool hasType = aElement->GetScriptType(type);
+
+  nsScriptKind scriptKind = nsScriptKind::Classic;
+  if (!type.IsEmpty()) {
+    // Support type="module" only for chrome documents.
+    if (nsContentUtils::IsChromeDoc(mDocument) && type.LowerCaseEqualsASCII("module")) {
+      scriptKind = nsScriptKind::Module;
+    } else {
+      NS_ENSURE_TRUE(ParseTypeAttribute(type, &version), false);
+    }
+  } else if (!hasType) {
+    // no 'type=' element
+    // "language" is a deprecated attribute of HTML, so we check it only for
+    // HTML script elements.
+    if (scriptContent->IsHTMLElement()) {
+      nsAutoString language;
+      scriptContent->GetAttr(kNameSpaceID_None, nsGkAtoms::language, language);
+      if (!language.IsEmpty()) {
+        if (!nsContentUtils::IsJavaScriptLanguage(language)) {
+          return false;
+        }
+      }
+    }
+  }
+
+  // Step 14. in the HTML5 spec
+  nsresult rv = NS_OK;
+  RefPtr<nsScriptLoadRequest> request;
+  if (aElement->GetScriptExternal()) {
+    // external script
+    nsCOMPtr<nsIURI> scriptURI = aElement->GetScriptURI();
+    if (!scriptURI) {
+      // Asynchronously report the failure to create a URI object
+      NS_DispatchToCurrentThread(
+        NewRunnableMethod(aElement,
+                          &nsIScriptElement::FireErrorEvent));
+      return false;
+    }
+
+    // Double-check that the preload matches what we're asked to load now.
+    mozilla::net::ReferrerPolicy ourRefPolicy = mDocument->GetReferrerPolicy();
+    CORSMode ourCORSMode = aElement->GetCORSMode();
+    nsTArray<PreloadInfo>::index_type i =
+      mPreloads.IndexOf(scriptURI.get(), 0, PreloadURIComparator());
+    if (i != nsTArray<PreloadInfo>::NoIndex) {
+      // preloaded
+      // note that a script-inserted script can steal a preload!
+      request = mPreloads[i].mRequest;
+      request->mElement = aElement;
+      nsString preloadCharset(mPreloads[i].mCharset);
+      mPreloads.RemoveElementAt(i);
+
+      // Double-check that the charset the preload used is the same as
+      // the charset we have now.
+      nsAutoString elementCharset;
+      aElement->GetScriptCharset(elementCharset);
+      if (elementCharset.Equals(preloadCharset) &&
+          ourCORSMode == request->mCORSMode &&
+          ourRefPolicy == request->mReferrerPolicy &&
+          scriptKind == request->mKind) {
+        rv = CheckContentPolicy(mDocument, aElement, request->mURI, type, false);
+        if (NS_FAILED(rv)) {
+          // probably plans have changed; even though the preload was allowed seems
+          // like the actual load is not; let's cancel the preload request.
+          request->Cancel();
+          return false;
+        }
+      } else {
+        // Drop the preload
+        request = nullptr;
+      }
+    }
+
+    if (!request) {
+      // no usable preload
+
+      SRIMetadata sriMetadata;
+      {
+        nsAutoString integrity;
+        scriptContent->GetAttr(kNameSpaceID_None, nsGkAtoms::integrity,
+                               integrity);
+        if (!integrity.IsEmpty()) {
+          MOZ_LOG(SRILogHelper::GetSriLog(), mozilla::LogLevel::Debug,
+                 ("nsScriptLoader::ProcessScriptElement, integrity=%s",
+                  NS_ConvertUTF16toUTF8(integrity).get()));
+          nsAutoCString sourceUri;
+          if (mDocument->GetDocumentURI()) {
+            mDocument->GetDocumentURI()->GetAsciiSpec(sourceUri);
+          }
+          SRICheck::IntegrityMetadata(integrity, sourceUri, mReporter,
+                                      &sriMetadata);
+        }
+      }
+
+      request = CreateLoadRequest(scriptKind, aElement, version, ourCORSMode,
+                                  sriMetadata);
+      request->mURI = scriptURI;
+      request->mIsInline = false;
+      request->mReferrerPolicy = ourRefPolicy;
+
+      // set aScriptFromHead to false so we don't treat non preloaded scripts as
+      // blockers for full page load. See bug 792438.
+      rv = StartLoad(request, type, false);
+      if (NS_FAILED(rv)) {
+        // Asynchronously report the load failure
+        NS_DispatchToCurrentThread(
+          NewRunnableMethod(aElement,
+                            &nsIScriptElement::FireErrorEvent));
+        return false;
+      }
+    }
+
+    // Should still be in loading stage of script.
+    NS_ASSERTION(!request->InCompilingStage(),
+                 "Request should not yet be in compiling stage.");
+
+    request->mJSVersion = version;
+
+    if (aElement->GetScriptAsync()) {
+      request->mIsAsync = true;
+      if (request->IsReadyToRun()) {
+        mLoadedAsyncRequests.AppendElement(request);
+        // The script is available already. Run it ASAP when the event
+        // loop gets a chance to spin.
+
+        // KVKV TODO: Instead of processing immediately, try off-thread-parsing
+        // it and only schedule a pending ProcessRequest if that fails.
+        ProcessPendingRequestsAsync();
+      } else {
+        mLoadingAsyncRequests.AppendElement(request);
+      }
+      return false;
+    }
+    if (!aElement->GetParserCreated() && !request->IsModuleRequest()) {
+      // 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
+      request->mIsNonAsyncScriptInserted = true;
+      mNonAsyncExternalScriptInsertedRequests.AppendElement(request);
+      if (request->IsReadyToRun()) {
+        // The script is available already. Run it ASAP when the event
+        // loop gets a chance to spin.
+        ProcessPendingRequestsAsync();
+      }
+      return false;
+    }
+    // we now have a parser-inserted request that may or may not be still
+    // loading
+    if (aElement->GetScriptDeferred() || request->IsModuleRequest()) {
+      // We don't want to run this yet.
+      // If we come here, the script is a parser-created script and it has
+      // the defer attribute but not the async attribute. Since a
+      // a parser-inserted script is being run, we came here by the parser
+      // running the script, which means the parser is still alive and the
+      // parse is ongoing.
+      NS_ASSERTION(mDocument->GetCurrentContentSink() ||
+                   aElement->GetParserCreated() == FROM_PARSER_XSLT,
+          "Non-XSLT Defer script on a document without an active parser; bug 592366.");
+      AddDeferRequest(request);
+      return false;
+    }
+
+    if (aElement->GetParserCreated() == FROM_PARSER_XSLT) {
+      // Need to maintain order for XSLT-inserted scripts
+      NS_ASSERTION(!mParserBlockingRequest,
+          "Parser-blocking scripts and XSLT scripts in the same doc!");
+      request->mIsXSLT = true;
+      mXSLTRequests.AppendElement(request);
+      if (request->IsReadyToRun()) {
+        // The script is available already. Run it ASAP when the event
+        // loop gets a chance to spin.
+        ProcessPendingRequestsAsync();
+      }
+      return true;
+    }
+
+    if (request->IsReadyToRun() && ReadyToExecuteParserBlockingScripts()) {
+      // The request has already been loaded and there are no pending style
+      // sheets. If the script comes from the network stream, cheat for
+      // performance reasons and avoid a trip through the event loop.
+      if (aElement->GetParserCreated() == FROM_PARSER_NETWORK) {
+        return ProcessRequest(request) == NS_ERROR_HTMLPARSER_BLOCK;
+      }
+      // Otherwise, we've got a document.written script, make a trip through
+      // the event loop to hide the preload effects from the scripts on the
+      // Web page.
+      NS_ASSERTION(!mParserBlockingRequest,
+          "There can be only one parser-blocking script at a time");
+      NS_ASSERTION(mXSLTRequests.isEmpty(),
+          "Parser-blocking scripts and XSLT scripts in the same doc!");
+      mParserBlockingRequest = request;
+      ProcessPendingRequestsAsync();
+      return true;
+    }
+
+    // The script hasn't loaded yet or there's a style sheet blocking it.
+    // The script will be run when it loads or the style sheet loads.
+    NS_ASSERTION(!mParserBlockingRequest,
+        "There can be only one parser-blocking script at a time");
+    NS_ASSERTION(mXSLTRequests.isEmpty(),
+        "Parser-blocking scripts and XSLT scripts in the same doc!");
+    mParserBlockingRequest = request;
+    return true;
+  }
+
+  // inline script
+  // Is this document sandboxed without 'allow-scripts'?
+  if (mDocument->HasScriptsBlockedBySandbox()) {
+    return false;
+  }
+
+  // Does CSP allow this inline script to run?
+  if (!CSPAllowsInlineScript(aElement, mDocument)) {
+    return false;
+  }
+
+  // Inline scripts ignore ther CORS mode and are always CORS_NONE
+  request = CreateLoadRequest(scriptKind, aElement, version, CORS_NONE,
+                              SRIMetadata()); // SRI doesn't apply
+  request->mJSVersion = version;
+  request->mIsInline = true;
+  request->mURI = mDocument->GetDocumentURI();
+  request->mLineNo = aElement->GetScriptLineNumber();
+
+  if (request->IsModuleRequest()) {
+    nsModuleLoadRequest* modReq = request->AsModuleRequest();
+    modReq->mBaseURL = mDocument->GetDocBaseURI();
+    rv = CreateModuleScript(modReq);
+    NS_ENSURE_SUCCESS(rv, false);
+    StartFetchingModuleDependencies(modReq);
+    if (aElement->GetScriptAsync()) {
+      mLoadingAsyncRequests.AppendElement(request);
+    } else {
+      AddDeferRequest(request);
+    }
+    return false;
+  }
+  request->mProgress = nsScriptLoadRequest::Progress::Ready;
+  if (aElement->GetParserCreated() == FROM_PARSER_XSLT &&
+      (!ReadyToExecuteParserBlockingScripts() || !mXSLTRequests.isEmpty())) {
+    // Need to maintain order for XSLT-inserted scripts
+    NS_ASSERTION(!mParserBlockingRequest,
+        "Parser-blocking scripts and XSLT scripts in the same doc!");
+    mXSLTRequests.AppendElement(request);
+    return true;
+  }
+  if (aElement->GetParserCreated() == NOT_FROM_PARSER) {
+    NS_ASSERTION(!nsContentUtils::IsSafeToRunScript(),
+        "A script-inserted script is inserted without an update batch?");
+    nsContentUtils::AddScriptRunner(new nsScriptRequestProcessor(this,
+                                                                 request));
+    return false;
+  }
+  if (aElement->GetParserCreated() == FROM_PARSER_NETWORK &&
+      !ReadyToExecuteParserBlockingScripts()) {
+    NS_ASSERTION(!mParserBlockingRequest,
+        "There can be only one parser-blocking script at a time");
+    mParserBlockingRequest = request;
+    NS_ASSERTION(mXSLTRequests.isEmpty(),
+        "Parser-blocking scripts and XSLT scripts in the same doc!");
+    return true;
+  }
+  // We now have a document.written inline script or we have an inline script
+  // from the network but there is no style sheet that is blocking scripts.
+  // Don't check for style sheets blocking scripts in the document.write
+  // case to avoid style sheet network activity affecting when
+  // document.write returns. It's not really necessary to do this if
+  // there's no document.write currently on the call stack. However,
+  // this way matches IE more closely than checking if document.write
+  // is on the call stack.
+  NS_ASSERTION(nsContentUtils::IsSafeToRunScript(),
+      "Not safe to run a parser-inserted script?");
+  return ProcessRequest(request) == NS_ERROR_HTMLPARSER_BLOCK;
+}
+
+namespace {
+
+class NotifyOffThreadScriptLoadCompletedRunnable : public Runnable
+{
+  RefPtr<nsScriptLoadRequest> mRequest;
+  RefPtr<nsScriptLoader> mLoader;
+  void *mToken;
+
+public:
+  NotifyOffThreadScriptLoadCompletedRunnable(nsScriptLoadRequest* aRequest,
+                                             nsScriptLoader* aLoader)
+    : mRequest(aRequest), mLoader(aLoader), mToken(nullptr)
+  {}
+
+  virtual ~NotifyOffThreadScriptLoadCompletedRunnable();
+
+  void SetToken(void* aToken) {
+    MOZ_ASSERT(aToken && !mToken);
+    mToken = aToken;
+  }
+
+  NS_DECL_NSIRUNNABLE
+};
+
+} /* anonymous namespace */
+
+nsresult
+nsScriptLoader::ProcessOffThreadRequest(nsScriptLoadRequest* aRequest)
+{
+  MOZ_ASSERT(aRequest->mProgress == nsScriptLoadRequest::Progress::Compiling);
+  MOZ_ASSERT(!aRequest->mWasCompiledOMT);
+
+  aRequest->mWasCompiledOMT = true;
+
+  if (aRequest->IsModuleRequest()) {
+    MOZ_ASSERT(aRequest->mOffThreadToken);
+    nsModuleLoadRequest* request = aRequest->AsModuleRequest();
+    nsresult rv = ProcessFetchedModuleSource(request);
+    if (NS_FAILED(rv)) {
+      request->LoadFailed();
+    }
+    return rv;
+  }
+
+  aRequest->SetReady();
+
+  if (aRequest == mParserBlockingRequest) {
+    if (!ReadyToExecuteParserBlockingScripts()) {
+      // If not ready to execute scripts, schedule an async call to
+      // ProcessPendingRequests to handle it.
+      ProcessPendingRequestsAsync();
+      return NS_OK;
+    }
+
+    // Same logic as in top of ProcessPendingRequests.
+    mParserBlockingRequest = nullptr;
+    UnblockParser(aRequest);
+    ProcessRequest(aRequest);
+    mDocument->UnblockOnload(false);
+    ContinueParserAsync(aRequest);
+    return NS_OK;
+  }
+
+  nsresult rv = ProcessRequest(aRequest);
+  mDocument->UnblockOnload(false);
+  return rv;
+}
+
+NotifyOffThreadScriptLoadCompletedRunnable::~NotifyOffThreadScriptLoadCompletedRunnable()
+{
+  if (MOZ_UNLIKELY(mRequest || mLoader) && !NS_IsMainThread()) {
+    NS_ReleaseOnMainThread(mRequest.forget());
+    NS_ReleaseOnMainThread(mLoader.forget());
+  }
+}
+
+NS_IMETHODIMP
+NotifyOffThreadScriptLoadCompletedRunnable::Run()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
+  // We want these to be dropped on the main thread, once we return from this
+  // function.
+  RefPtr<nsScriptLoadRequest> request = mRequest.forget();
+  RefPtr<nsScriptLoader> loader = mLoader.forget();
+
+  request->mOffThreadToken = mToken;
+  nsresult rv = loader->ProcessOffThreadRequest(request);
+
+  return rv;
+}
+
+static void
+OffThreadScriptLoaderCallback(void *aToken, void *aCallbackData)
+{
+  RefPtr<NotifyOffThreadScriptLoadCompletedRunnable> aRunnable =
+    dont_AddRef(static_cast<NotifyOffThreadScriptLoadCompletedRunnable*>(aCallbackData));
+  aRunnable->SetToken(aToken);
+  NS_DispatchToMainThread(aRunnable);
+}
+
+nsresult
+nsScriptLoader::AttemptAsyncScriptCompile(nsScriptLoadRequest* aRequest)
+{
+  MOZ_ASSERT_IF(!aRequest->IsModuleRequest(), aRequest->IsReadyToRun());
+  MOZ_ASSERT(!aRequest->mWasCompiledOMT);
+
+  // Don't off-thread compile inline scripts.
+  if (aRequest->mIsInline) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsIScriptGlobalObject> globalObject = GetScriptGlobalObject();
+  if (!globalObject) {
+    return NS_ERROR_FAILURE;
+  }
+
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(globalObject)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  JSContext* cx = jsapi.cx();
+  JS::Rooted<JSObject*> global(cx, globalObject->GetGlobalJSObject());
+  JS::CompileOptions options(cx);
+
+  nsresult rv = FillCompileOptionsForRequest(jsapi, aRequest, global, &options);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (!JS::CanCompileOffThread(cx, options, aRequest->mScriptTextLength)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  RefPtr<NotifyOffThreadScriptLoadCompletedRunnable> runnable =
+    new NotifyOffThreadScriptLoadCompletedRunnable(aRequest, this);
+
+  if (aRequest->IsModuleRequest()) {
+    if (!JS::CompileOffThreadModule(cx, options,
+                                    aRequest->mScriptTextBuf, aRequest->mScriptTextLength,
+                                    OffThreadScriptLoaderCallback,
+                                    static_cast<void*>(runnable))) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  } else {
+    if (!JS::CompileOffThread(cx, options,
+                              aRequest->mScriptTextBuf, aRequest->mScriptTextLength,
+                              OffThreadScriptLoaderCallback,
+                              static_cast<void*>(runnable))) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  }
+
+  mDocument->BlockOnload();
+  aRequest->mProgress = nsScriptLoadRequest::Progress::Compiling;
+
+  Unused << runnable.forget();
+  return NS_OK;
+}
+
+nsresult
+nsScriptLoader::CompileOffThreadOrProcessRequest(nsScriptLoadRequest* aRequest)
+{
+  NS_ASSERTION(nsContentUtils::IsSafeToRunScript(),
+               "Processing requests when running scripts is unsafe.");
+  NS_ASSERTION(!aRequest->mOffThreadToken,
+               "Candidate for off-thread compile is already parsed off-thread");
+  NS_ASSERTION(!aRequest->InCompilingStage(),
+               "Candidate for off-thread compile is already in compiling stage.");
+
+  nsresult rv = AttemptAsyncScriptCompile(aRequest);
+  if (NS_SUCCEEDED(rv)) {
+    return rv;
+  }
+
+  return ProcessRequest(aRequest);
+}
+
+SourceBufferHolder
+nsScriptLoader::GetScriptSource(nsScriptLoadRequest* aRequest, nsAutoString& inlineData)
+{
+  // Return a SourceBufferHolder object holding the script's source text.
+  // |inlineData| is used to hold the text for inline objects.
+
+  // If there's no script text, we try to get it from the element
+  if (aRequest->mIsInline) {
+    // XXX This is inefficient - GetText makes multiple
+    // copies.
+    aRequest->mElement->GetScriptText(inlineData);
+    return SourceBufferHolder(inlineData.get(),
+                              inlineData.Length(),
+                              SourceBufferHolder::NoOwnership);
+  }
+
+  return SourceBufferHolder(aRequest->mScriptTextBuf,
+                            aRequest->mScriptTextLength,
+                            SourceBufferHolder::NoOwnership);
+}
+
+nsresult
+nsScriptLoader::ProcessRequest(nsScriptLoadRequest* aRequest)
+{
+  NS_ASSERTION(nsContentUtils::IsSafeToRunScript(),
+               "Processing requests when running scripts is unsafe.");
+  NS_ASSERTION(aRequest->IsReadyToRun(),
+               "Processing a request that is not ready to run.");
+
+  NS_ENSURE_ARG(aRequest);
+
+  if (aRequest->IsModuleRequest() &&
+      !aRequest->AsModuleRequest()->mModuleScript)
+  {
+    // There was an error parsing a module script.  Nothing to do here.
+    FireScriptAvailable(NS_ERROR_FAILURE, aRequest);
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsINode> scriptElem = do_QueryInterface(aRequest->mElement);
+
+  nsCOMPtr<nsIDocument> doc;
+  if (!aRequest->mIsInline) {
+    doc = scriptElem->OwnerDoc();
+  }
+
+  nsCOMPtr<nsIScriptElement> oldParserInsertedScript;
+  uint32_t parserCreated = aRequest->mElement->GetParserCreated();
+  if (parserCreated) {
+    oldParserInsertedScript = mCurrentParserInsertedScript;
+    mCurrentParserInsertedScript = aRequest->mElement;
+  }
+
+  aRequest->mElement->BeginEvaluating();
+
+  FireScriptAvailable(NS_OK, aRequest);
+
+  // The window may have gone away by this point, in which case there's no point
+  // in trying to run the script.
+  nsCOMPtr<nsIDocument> master = mDocument->MasterDocument();
+  {
+    // Try to perform a microtask checkpoint
+    nsAutoMicroTask mt;
+  }
+
+  nsPIDOMWindowInner *pwin = master->GetInnerWindow();
+  bool runScript = !!pwin;
+  if (runScript) {
+    nsContentUtils::DispatchTrustedEvent(scriptElem->OwnerDoc(),
+                                         scriptElem,
+                                         NS_LITERAL_STRING("beforescriptexecute"),
+                                         true, true, &runScript);
+  }
+
+  // Inner window could have gone away after firing beforescriptexecute
+  pwin = master->GetInnerWindow();
+  if (!pwin) {
+    runScript = false;
+  }
+
+  nsresult rv = NS_OK;
+  if (runScript) {
+    if (doc) {
+      doc->BeginEvaluatingExternalScript();
+    }
+    rv = EvaluateScript(aRequest);
+    if (doc) {
+      doc->EndEvaluatingExternalScript();
+    }
+
+    nsContentUtils::DispatchTrustedEvent(scriptElem->OwnerDoc(),
+                                         scriptElem,
+                                         NS_LITERAL_STRING("afterscriptexecute"),
+                                         true, false);
+  }
+
+  FireScriptEvaluated(rv, aRequest);
+
+  aRequest->mElement->EndEvaluating();
+
+  if (parserCreated) {
+    mCurrentParserInsertedScript = oldParserInsertedScript;
+  }
+
+  if (aRequest->mOffThreadToken) {
+    // The request was parsed off-main-thread, but the result of the off
+    // thread parse was not actually needed to process the request
+    // (disappearing window, some other error, ...). Finish the
+    // request to avoid leaks in the JS engine.
+    MOZ_ASSERT(!aRequest->IsModuleRequest());
+    aRequest->MaybeCancelOffThreadScript();
+  }
+
+  // Free any source data.
+  free(aRequest->mScriptTextBuf);
+  aRequest->mScriptTextBuf = nullptr;
+  aRequest->mScriptTextLength = 0;
+
+  return rv;
+}
+
+void
+nsScriptLoader::FireScriptAvailable(nsresult aResult,
+                                    nsScriptLoadRequest* aRequest)
+{
+  for (int32_t i = 0; i < mObservers.Count(); i++) {
+    nsCOMPtr<nsIScriptLoaderObserver> obs = mObservers[i];
+    obs->ScriptAvailable(aResult, aRequest->mElement,
+                         aRequest->mIsInline, aRequest->mURI,
+                         aRequest->mLineNo);
+  }
+
+  aRequest->FireScriptAvailable(aResult);
+}
+
+void
+nsScriptLoader::FireScriptEvaluated(nsresult aResult,
+                                    nsScriptLoadRequest* aRequest)
+{
+  for (int32_t i = 0; i < mObservers.Count(); i++) {
+    nsCOMPtr<nsIScriptLoaderObserver> obs = mObservers[i];
+    obs->ScriptEvaluated(aResult, aRequest->mElement,
+                         aRequest->mIsInline);
+  }
+
+  aRequest->FireScriptEvaluated(aResult);
+}
+
+already_AddRefed<nsIScriptGlobalObject>
+nsScriptLoader::GetScriptGlobalObject()
+{
+  nsCOMPtr<nsIDocument> master = mDocument->MasterDocument();
+  nsPIDOMWindowInner *pwin = master->GetInnerWindow();
+  if (!pwin) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIScriptGlobalObject> globalObject = do_QueryInterface(pwin);
+  NS_ASSERTION(globalObject, "windows must be global objects");
+
+  // and make sure we are setup for this type of script.
+  nsresult rv = globalObject->EnsureScriptEnvironment();
+  if (NS_FAILED(rv)) {
+    return nullptr;
+  }
+
+  return globalObject.forget();
+}
+
+nsresult
+nsScriptLoader::FillCompileOptionsForRequest(const AutoJSAPI&jsapi,
+                                             nsScriptLoadRequest* aRequest,
+                                             JS::Handle<JSObject*> aScopeChain,
+                                             JS::CompileOptions* aOptions)
+{
+  // It's very important to use aRequest->mURI, not the final URI of the channel
+  // aRequest ended up getting script data from, as the script filename.
+  nsresult rv;
+  nsContentUtils::GetWrapperSafeScriptFilename(mDocument, aRequest->mURI,
+                                               aRequest->mURL, &rv);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  bool isScriptElement = !aRequest->IsModuleRequest() ||
+                         aRequest->AsModuleRequest()->IsTopLevel();
+  aOptions->setIntroductionType(isScriptElement ? "scriptElement"
+                                                : "importedModule");
+  aOptions->setFileAndLine(aRequest->mURL.get(), aRequest->mLineNo);
+  aOptions->setVersion(JSVersion(aRequest->mJSVersion));
+  aOptions->setIsRunOnce(true);
+  // We only need the setNoScriptRval bit when compiling off-thread here, since
+  // otherwise nsJSUtils::EvaluateString will set it up for us.
+  aOptions->setNoScriptRval(true);
+  if (aRequest->mHasSourceMapURL) {
+    aOptions->setSourceMapURL(aRequest->mSourceMapURL.get());
+  }
+  if (aRequest->mOriginPrincipal) {
+    nsIPrincipal* scriptPrin = nsContentUtils::ObjectPrincipal(aScopeChain);
+    bool subsumes = scriptPrin->Subsumes(aRequest->mOriginPrincipal);
+    aOptions->setMutedErrors(!subsumes);
+  }
+
+  JSContext* cx = jsapi.cx();
+  JS::Rooted<JS::Value> elementVal(cx);
+  MOZ_ASSERT(aRequest->mElement);
+  if (NS_SUCCEEDED(nsContentUtils::WrapNative(cx, aRequest->mElement,
+                                              &elementVal,
+                                              /* aAllowWrapping = */ true))) {
+    MOZ_ASSERT(elementVal.isObject());
+    aOptions->setElement(&elementVal.toObject());
+  }
+
+  return NS_OK;
+}
+
+nsresult
+nsScriptLoader::EvaluateScript(nsScriptLoadRequest* aRequest)
+{
+  // We need a document to evaluate scripts.
+  if (!mDocument) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsIContent> scriptContent(do_QueryInterface(aRequest->mElement));
+  nsIDocument* ownerDoc = scriptContent->OwnerDoc();
+  if (ownerDoc != mDocument) {
+    // Willful violation of HTML5 as of 2010-12-01
+    return NS_ERROR_FAILURE;
+  }
+
+  // Get the script-type to be used by this element.
+  NS_ASSERTION(scriptContent, "no content - what is default script-type?");
+
+  nsCOMPtr<nsIScriptGlobalObject> globalObject = GetScriptGlobalObject();
+  if (!globalObject) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Make sure context is a strong reference since we access it after
+  // we've executed a script, which may cause all other references to
+  // the context to go away.
+  nsCOMPtr<nsIScriptContext> context = globalObject->GetScriptContext();
+  if (!context) {
+    return NS_ERROR_FAILURE;
+  }
+
+  JSVersion version = JSVersion(aRequest->mJSVersion);
+  if (version == JSVERSION_UNKNOWN) {
+    return NS_OK;
+  }
+
+  // New script entry point required, due to the "Create a script" sub-step of
+  // http://www.whatwg.org/specs/web-apps/current-work/#execute-the-script-block
+  nsAutoMicroTask mt;
+  AutoEntryScript aes(globalObject, "<script> element", true);
+  JS::Rooted<JSObject*> global(aes.cx(),
+                               globalObject->GetGlobalJSObject());
+
+  bool oldProcessingScriptTag = context->GetProcessingScriptTag();
+  context->SetProcessingScriptTag(true);
+  nsresult rv;
+  {
+    // Update our current script.
+    AutoCurrentScriptUpdater scriptUpdater(this, aRequest->mElement);
+    Maybe<AutoCurrentScriptUpdater> masterScriptUpdater;
+    nsCOMPtr<nsIDocument> master = mDocument->MasterDocument();
+    if (master != mDocument) {
+      // If this script belongs to an import document, it will be
+      // executed in the context of the master document. During the
+      // execution currentScript of the master should refer to this
+      // script. So let's update the mCurrentScript of the ScriptLoader
+      // of the master document too.
+      masterScriptUpdater.emplace(master->ScriptLoader(),
+                                  aRequest->mElement);
+    }
+
+    if (aRequest->IsModuleRequest()) {
+      nsModuleLoadRequest* request = aRequest->AsModuleRequest();
+      MOZ_ASSERT(request->mModuleScript);
+      MOZ_ASSERT(!request->mOffThreadToken);
+      nsModuleScript* ms = request->mModuleScript;
+      MOZ_ASSERT(!ms->IsUninstantiated());
+      if (ms->InstantiationFailed()) {
+        JS::Rooted<JS::Value> exception(aes.cx(), ms->Exception());
+        JS_SetPendingException(aes.cx(), exception);
+        rv = NS_ERROR_FAILURE;
+      } else {
+        JS::Rooted<JSObject*> module(aes.cx(), ms->ModuleRecord());
+        MOZ_ASSERT(module);
+        rv = nsJSUtils::ModuleEvaluation(aes.cx(), module);
+      }
+    } else {
+      JS::CompileOptions options(aes.cx());
+      rv = FillCompileOptionsForRequest(aes, aRequest, global, &options);
+
+      if (NS_SUCCEEDED(rv)) {
+        nsAutoString inlineData;
+        SourceBufferHolder srcBuf = GetScriptSource(aRequest, inlineData);
+        rv = nsJSUtils::EvaluateString(aes.cx(), srcBuf, global, options,
+                                       aRequest->OffThreadTokenPtr());
+      }
+    }
+  }
+
+  context->SetProcessingScriptTag(oldProcessingScriptTag);
+  return rv;
+}
+
+void
+nsScriptLoader::ProcessPendingRequestsAsync()
+{
+  if (mParserBlockingRequest ||
+      !mXSLTRequests.isEmpty() ||
+      !mLoadedAsyncRequests.isEmpty() ||
+      !mNonAsyncExternalScriptInsertedRequests.isEmpty() ||
+      !mDeferRequests.isEmpty() ||
+      !mPendingChildLoaders.IsEmpty()) {
+    NS_DispatchToCurrentThread(NewRunnableMethod(this,
+                                                 &nsScriptLoader::ProcessPendingRequests));
+  }
+}
+
+void
+nsScriptLoader::ProcessPendingRequests()
+{
+  RefPtr<nsScriptLoadRequest> request;
+
+  if (mParserBlockingRequest &&
+      mParserBlockingRequest->IsReadyToRun() &&
+      ReadyToExecuteParserBlockingScripts()) {
+    request.swap(mParserBlockingRequest);
+    UnblockParser(request);
+    ProcessRequest(request);
+    if (request->mWasCompiledOMT) {
+      mDocument->UnblockOnload(false);
+    }
+    ContinueParserAsync(request);
+  }
+
+  while (ReadyToExecuteParserBlockingScripts() &&
+         !mXSLTRequests.isEmpty() &&
+         mXSLTRequests.getFirst()->IsReadyToRun()) {
+    request = mXSLTRequests.StealFirst();
+    ProcessRequest(request);
+  }
+
+  while (ReadyToExecuteScripts() && !mLoadedAsyncRequests.isEmpty()) {
+    request = mLoadedAsyncRequests.StealFirst();
+    if (request->IsModuleRequest()) {
+      ProcessRequest(request);
+    } else {
+      CompileOffThreadOrProcessRequest(request);
+    }
+  }
+
+  while (ReadyToExecuteScripts() &&
+         !mNonAsyncExternalScriptInsertedRequests.isEmpty() &&
+         mNonAsyncExternalScriptInsertedRequests.getFirst()->IsReadyToRun()) {
+    // Violate the HTML5 spec and execute these in the insertion order 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
+    request = mNonAsyncExternalScriptInsertedRequests.StealFirst();
+    ProcessRequest(request);
+  }
+
+  if (mDocumentParsingDone && mXSLTRequests.isEmpty()) {
+    while (ReadyToExecuteScripts() &&
+           !mDeferRequests.isEmpty() &&
+           mDeferRequests.getFirst()->IsReadyToRun()) {
+      request = mDeferRequests.StealFirst();
+      ProcessRequest(request);
+    }
+  }
+
+  while (!mPendingChildLoaders.IsEmpty() &&
+         ReadyToExecuteParserBlockingScripts()) {
+    RefPtr<nsScriptLoader> child = mPendingChildLoaders[0];
+    mPendingChildLoaders.RemoveElementAt(0);
+    child->RemoveParserBlockingScriptExecutionBlocker();
+  }
+
+  if (mDocumentParsingDone && mDocument && !mParserBlockingRequest &&
+      mNonAsyncExternalScriptInsertedRequests.isEmpty() &&
+      mXSLTRequests.isEmpty() && mDeferRequests.isEmpty() &&
+      MaybeRemovedDeferRequests()) {
+    return ProcessPendingRequests();
+  }
+
+  if (mDocumentParsingDone && mDocument &&
+      !mParserBlockingRequest && mLoadingAsyncRequests.isEmpty() &&
+      mLoadedAsyncRequests.isEmpty() &&
+      mNonAsyncExternalScriptInsertedRequests.isEmpty() &&
+      mXSLTRequests.isEmpty() && mDeferRequests.isEmpty()) {
+    // No more pending scripts; time to unblock onload.
+    // OK to unblock onload synchronously here, since callers must be
+    // prepared for the world changing anyway.
+    mDocumentParsingDone = false;
+    mDocument->UnblockOnload(true);
+  }
+}
+
+bool
+nsScriptLoader::ReadyToExecuteParserBlockingScripts()
+{
+  // Make sure the SelfReadyToExecuteParserBlockingScripts check is first, so
+  // that we don't block twice on an ancestor.
+  if (!SelfReadyToExecuteParserBlockingScripts()) {
+    return false;
+  }
+
+  for (nsIDocument* doc = mDocument; doc; doc = doc->GetParentDocument()) {
+    nsScriptLoader* ancestor = doc->ScriptLoader();
+    if (!ancestor->SelfReadyToExecuteParserBlockingScripts() &&
+        ancestor->AddPendingChildLoader(this)) {
+      AddParserBlockingScriptExecutionBlocker();
+      return false;
+    }
+  }
+
+  if (mDocument && !mDocument->IsMasterDocument()) {
+    RefPtr<ImportManager> im = mDocument->ImportManager();
+    RefPtr<ImportLoader> loader = im->Find(mDocument);
+    MOZ_ASSERT(loader, "How can we have an import document without a loader?");
+
+    // The referring link that counts in the execution order calculation
+    // (in spec: flagged as branch)
+    nsCOMPtr<nsINode> referrer = loader->GetMainReferrer();
+    MOZ_ASSERT(referrer, "There has to be a main referring link for each imports");
+
+    // Import documents are blocked by their import predecessors. We need to
+    // wait with script execution until all the predecessors are done.
+    // Technically it means we have to wait for the last one to finish,
+    // which is the neares one to us in the order.
+    RefPtr<ImportLoader> lastPred = im->GetNearestPredecessor(referrer);
+    if (!lastPred) {
+      // If there is no predecessor we can run.
+      return true;
+    }
+
+    nsCOMPtr<nsIDocument> doc = lastPred->GetDocument();
+    if (lastPred->IsBlocking() || !doc ||
+        !doc->ScriptLoader()->SelfReadyToExecuteParserBlockingScripts()) {
+      // Document has not been created yet or it was created but not ready.
+      // Either case we are blocked by it. The ImportLoader will take care
+      // of blocking us, and adding the pending child loader to the blocking
+      // ScriptLoader when it's possible (at this point the blocking loader
+      // might not have created the document/ScriptLoader)
+      lastPred->AddBlockedScriptLoader(this);
+      // As more imports are parsed, this can change, let's cache what we
+      // blocked, so it can be later updated if needed (see: ImportLoader::Updater).
+      loader->SetBlockingPredecessor(lastPred);
+      return false;
+    }
+  }
+
+  return true;
+}
+
+/* static */ nsresult
+nsScriptLoader::ConvertToUTF16(nsIChannel* aChannel, const uint8_t* aData,
+                               uint32_t aLength, const nsAString& aHintCharset,
+                               nsIDocument* aDocument,
+                               char16_t*& aBufOut, size_t& aLengthOut)
+{
+  if (!aLength) {
+    aBufOut = nullptr;
+    aLengthOut = 0;
+    return NS_OK;
+  }
+
+  // The encoding info precedence is as follows from high to low:
+  // The BOM
+  // HTTP Content-Type (if name recognized)
+  // charset attribute (if name recognized)
+  // The encoding of the document
+
+  nsAutoCString charset;
+
+  nsCOMPtr<nsIUnicodeDecoder> unicodeDecoder;
+
+  if (nsContentUtils::CheckForBOM(aData, aLength, charset)) {
+    // charset is now one of "UTF-16BE", "UTF-16BE" or "UTF-8".  Those decoder
+    // will take care of swallowing the BOM.
+    unicodeDecoder = EncodingUtils::DecoderForEncoding(charset);
+  }
+
+  if (!unicodeDecoder &&
+      aChannel &&
+      NS_SUCCEEDED(aChannel->GetContentCharset(charset)) &&
+      EncodingUtils::FindEncodingForLabel(charset, charset)) {
+    unicodeDecoder = EncodingUtils::DecoderForEncoding(charset);
+  }
+
+  if (!unicodeDecoder &&
+      EncodingUtils::FindEncodingForLabel(aHintCharset, charset)) {
+    unicodeDecoder = EncodingUtils::DecoderForEncoding(charset);
+  }
+
+  if (!unicodeDecoder && aDocument) {
+    charset = aDocument->GetDocumentCharacterSet();
+    unicodeDecoder = EncodingUtils::DecoderForEncoding(charset);
+  }
+
+  if (!unicodeDecoder) {
+    // Curiously, there are various callers that don't pass aDocument. The
+    // fallback in the old code was ISO-8859-1, which behaved like
+    // windows-1252. Saying windows-1252 for clarity and for compliance
+    // with the Encoding Standard.
+    unicodeDecoder = EncodingUtils::DecoderForEncoding("windows-1252");
+  }
+
+  int32_t unicodeLength = 0;
+
+  nsresult rv =
+    unicodeDecoder->GetMaxLength(reinterpret_cast<const char*>(aData),
+                                 aLength, &unicodeLength);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  aBufOut = static_cast<char16_t*>(js_malloc(unicodeLength * sizeof(char16_t)));
+  if (!aBufOut) {
+    aLengthOut = 0;
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  aLengthOut = unicodeLength;
+
+  rv = unicodeDecoder->Convert(reinterpret_cast<const char*>(aData),
+                               (int32_t *) &aLength, aBufOut,
+                               &unicodeLength);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+  aLengthOut = unicodeLength;
+  if (NS_FAILED(rv)) {
+    js_free(aBufOut);
+    aBufOut = nullptr;
+    aLengthOut = 0;
+  }
+  return rv;
+}
+
+nsresult
+nsScriptLoader::OnStreamComplete(nsIIncrementalStreamLoader* aLoader,
+                                 nsISupports* aContext,
+                                 nsresult aChannelStatus,
+                                 nsresult aSRIStatus,
+                                 mozilla::Vector<char16_t> &aString,
+                                 mozilla::dom::SRICheckDataVerifier* aSRIDataVerifier)
+{
+  nsScriptLoadRequest* request = static_cast<nsScriptLoadRequest*>(aContext);
+  NS_ASSERTION(request, "null request in stream complete handler");
+  NS_ENSURE_TRUE(request, NS_ERROR_FAILURE);
+
+  nsCOMPtr<nsIRequest> channelRequest;
+  aLoader->GetRequest(getter_AddRefs(channelRequest));
+  nsCOMPtr<nsIChannel> channel;
+  channel = do_QueryInterface(channelRequest);
+
+  nsresult rv = NS_OK;
+  if (!request->mIntegrity.IsEmpty() &&
+      NS_SUCCEEDED((rv = aSRIStatus))) {
+    MOZ_ASSERT(aSRIDataVerifier);
+    MOZ_ASSERT(mReporter);
+
+    nsAutoCString sourceUri;
+    if (mDocument && mDocument->GetDocumentURI()) {
+      mDocument->GetDocumentURI()->GetAsciiSpec(sourceUri);
+    }
+    rv = aSRIDataVerifier->Verify(request->mIntegrity, channel, sourceUri,
+                                  mReporter);
+    mReporter->FlushConsoleReports(mDocument);
+    if (NS_FAILED(rv)) {
+      rv = NS_ERROR_SRI_CORRUPT;
+    }
+  } else {
+    nsCOMPtr<nsILoadInfo> loadInfo = channel->GetLoadInfo();
+
+    if (loadInfo->GetEnforceSRI()) {
+      MOZ_LOG(SRILogHelper::GetSriLog(), mozilla::LogLevel::Debug,
+             ("nsScriptLoader::OnStreamComplete, required SRI not found"));
+      nsCOMPtr<nsIContentSecurityPolicy> csp;
+      loadInfo->LoadingPrincipal()->GetCsp(getter_AddRefs(csp));
+      nsAutoCString violationURISpec;
+      mDocument->GetDocumentURI()->GetAsciiSpec(violationURISpec);
+      uint32_t lineNo = request->mElement ? request->mElement->GetScriptLineNumber() : 0;
+      csp->LogViolationDetails(
+        nsIContentSecurityPolicy::VIOLATION_TYPE_REQUIRE_SRI_FOR_SCRIPT,
+        NS_ConvertUTF8toUTF16(violationURISpec),
+        EmptyString(), lineNo, EmptyString(), EmptyString());
+      rv = NS_ERROR_SRI_CORRUPT;
+    }
+  }
+
+  if (NS_SUCCEEDED(rv)) {
+    rv = PrepareLoadedRequest(request, aLoader, aChannelStatus, aString);
+  }
+
+  if (NS_FAILED(rv)) {
+    /*
+     * Handle script not loading error because source was a tracking URL.
+     * We make a note of this script node by including it in a dedicated
+     * array of blocked tracking nodes under its parent document.
+     */
+    if (rv == NS_ERROR_TRACKING_URI) {
+      nsCOMPtr<nsIContent> cont = do_QueryInterface(request->mElement);
+      mDocument->AddBlockedTrackingNode(cont);
+    }
+
+    if (request->mIsDefer) {
+      MOZ_ASSERT_IF(request->IsModuleRequest(),
+                    request->AsModuleRequest()->IsTopLevel());
+      if (request->isInList()) {
+        RefPtr<nsScriptLoadRequest> req = mDeferRequests.Steal(request);
+        FireScriptAvailable(rv, req);
+      }
+    } else if (request->mIsAsync) {
+      MOZ_ASSERT_IF(request->IsModuleRequest(),
+                    request->AsModuleRequest()->IsTopLevel());
+      if (request->isInList()) {
+        RefPtr<nsScriptLoadRequest> req = mLoadingAsyncRequests.Steal(request);
+        FireScriptAvailable(rv, req);
+      }
+    } else if (request->mIsNonAsyncScriptInserted) {
+      if (request->isInList()) {
+        RefPtr<nsScriptLoadRequest> req =
+          mNonAsyncExternalScriptInsertedRequests.Steal(request);
+        FireScriptAvailable(rv, req);
+      }
+    } else if (request->mIsXSLT) {
+      if (request->isInList()) {
+        RefPtr<nsScriptLoadRequest> req = mXSLTRequests.Steal(request);
+        FireScriptAvailable(rv, req);
+      }
+    } else if (request->IsModuleRequest()) {
+      nsModuleLoadRequest* modReq = request->AsModuleRequest();
+      MOZ_ASSERT(!modReq->IsTopLevel());
+      MOZ_ASSERT(!modReq->isInList());
+      modReq->Cancel();
+      FireScriptAvailable(rv, request);
+    } else if (mParserBlockingRequest == request) {
+      MOZ_ASSERT(!request->isInList());
+      mParserBlockingRequest = nullptr;
+      UnblockParser(request);
+
+      // Ensure that we treat request->mElement as our current parser-inserted
+      // script while firing onerror on it.
+      MOZ_ASSERT(request->mElement->GetParserCreated());
+      nsCOMPtr<nsIScriptElement> oldParserInsertedScript =
+        mCurrentParserInsertedScript;
+      mCurrentParserInsertedScript = request->mElement;
+      FireScriptAvailable(rv, request);
+      ContinueParserAsync(request);
+      mCurrentParserInsertedScript = oldParserInsertedScript;
+    } else {
+      mPreloads.RemoveElement(request, PreloadRequestComparator());
+    }
+  }
+
+  // Process our request and/or any pending ones
+  ProcessPendingRequests();
+
+  return NS_OK;
+}
+
+void
+nsScriptLoader::UnblockParser(nsScriptLoadRequest* aParserBlockingRequest)
+{
+  aParserBlockingRequest->mElement->UnblockParser();
+}
+
+void
+nsScriptLoader::ContinueParserAsync(nsScriptLoadRequest* aParserBlockingRequest)
+{
+  aParserBlockingRequest->mElement->ContinueParserAsync();
+}
+
+uint32_t
+nsScriptLoader::NumberOfProcessors()
+{
+  if (mNumberOfProcessors > 0)
+    return mNumberOfProcessors;
+
+  int32_t numProcs = PR_GetNumberOfProcessors();
+  if (numProcs > 0)
+    mNumberOfProcessors = numProcs;
+  return mNumberOfProcessors;
+}
+
+void
+nsScriptLoader::MaybeMoveToLoadedList(nsScriptLoadRequest* aRequest)
+{
+  MOZ_ASSERT(aRequest->IsReadyToRun());
+
+  // If it's async, move it to the loaded list.  aRequest->mIsAsync really
+  // _should_ be in a list, but the consequences if it's not are bad enough we
+  // want to avoid trying to move it if it's not.
+  if (aRequest->mIsAsync) {
+    MOZ_ASSERT(aRequest->isInList());
+    if (aRequest->isInList()) {
+      RefPtr<nsScriptLoadRequest> req = mLoadingAsyncRequests.Steal(aRequest);
+      mLoadedAsyncRequests.AppendElement(req);
+    }
+  }
+}
+
+nsresult
+nsScriptLoader::PrepareLoadedRequest(nsScriptLoadRequest* aRequest,
+                                     nsIIncrementalStreamLoader* aLoader,
+                                     nsresult aStatus,
+                                     mozilla::Vector<char16_t> &aString)
+{
+  if (NS_FAILED(aStatus)) {
+    return aStatus;
+  }
+
+  if (aRequest->IsCanceled()) {
+    return NS_BINDING_ABORTED;
+  }
+
+  // If we don't have a document, then we need to abort further
+  // evaluation.
+  if (!mDocument) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  // If the load returned an error page, then we need to abort
+  nsCOMPtr<nsIRequest> req;
+  nsresult rv = aLoader->GetRequest(getter_AddRefs(req));
+  NS_ASSERTION(req, "StreamLoader's request went away prematurely");
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(req);
+  if (httpChannel) {
+    bool requestSucceeded;
+    rv = httpChannel->GetRequestSucceeded(&requestSucceeded);
+    if (NS_SUCCEEDED(rv) && !requestSucceeded) {
+      return NS_ERROR_NOT_AVAILABLE;
+    }
+
+    nsAutoCString sourceMapURL;
+    rv = httpChannel->GetResponseHeader(NS_LITERAL_CSTRING("X-SourceMap"), sourceMapURL);
+    if (NS_SUCCEEDED(rv)) {
+      aRequest->mHasSourceMapURL = true;
+      aRequest->mSourceMapURL = NS_ConvertUTF8toUTF16(sourceMapURL);
+    }
+  }
+
+  nsCOMPtr<nsIChannel> channel = do_QueryInterface(req);
+  // If this load was subject to a CORS check; don't flag it with a
+  // separate origin principal, so that it will treat our document's
+  // principal as the origin principal
+  if (aRequest->mCORSMode == CORS_NONE) {
+    rv = nsContentUtils::GetSecurityManager()->
+      GetChannelResultPrincipal(channel, getter_AddRefs(aRequest->mOriginPrincipal));
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  if (!aString.empty()) {
+    aRequest->mScriptTextLength = aString.length();
+    aRequest->mScriptTextBuf = aString.extractOrCopyRawBuffer();
+  }
+
+  // This assertion could fire errorously if we ran out of memory when
+  // inserting the request in the array. However it's an unlikely case
+  // so if you see this assertion it is likely something else that is
+  // wrong, especially if you see it more than once.
+  NS_ASSERTION(mDeferRequests.Contains(aRequest) ||
+               mLoadingAsyncRequests.Contains(aRequest) ||
+               mNonAsyncExternalScriptInsertedRequests.Contains(aRequest) ||
+               mXSLTRequests.Contains(aRequest)  ||
+               (aRequest->IsModuleRequest() &&
+                !aRequest->AsModuleRequest()->IsTopLevel() &&
+                !aRequest->isInList()) ||
+               mPreloads.Contains(aRequest, PreloadRequestComparator()) ||
+               mParserBlockingRequest,
+               "aRequest should be pending!");
+
+  if (aRequest->IsModuleRequest()) {
+    nsModuleLoadRequest* request = aRequest->AsModuleRequest();
+
+    // When loading a module, only responses with a JavaScript MIME type are
+    // acceptable.
+    nsAutoCString mimeType;
+    channel->GetContentType(mimeType);
+    NS_ConvertUTF8toUTF16 typeString(mimeType);
+    if (!nsContentUtils::IsJavascriptMIMEType(typeString)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    channel->GetURI(getter_AddRefs(request->mBaseURL));
+
+    // Attempt to compile off main thread.
+    rv = AttemptAsyncScriptCompile(request);
+    if (NS_SUCCEEDED(rv)) {
+      return rv;
+    }
+
+    // Otherwise compile it right away and start fetching descendents.
+    return ProcessFetchedModuleSource(request);
+  }
+
+  // The script is now loaded and ready to run.
+  aRequest->SetReady();
+
+  // If this is currently blocking the parser, attempt to compile it off-main-thread.
+  if (aRequest == mParserBlockingRequest && (NumberOfProcessors() > 1)) {
+    MOZ_ASSERT(!aRequest->IsModuleRequest());
+    nsresult rv = AttemptAsyncScriptCompile(aRequest);
+    if (rv == NS_OK) {
+      MOZ_ASSERT(aRequest->mProgress == nsScriptLoadRequest::Progress::Compiling,
+                 "Request should be off-thread compiling now.");
+      return NS_OK;
+    }
+
+    // If off-thread compile errored, return the error.
+    if (rv != NS_ERROR_FAILURE) {
+      return rv;
+    }
+
+    // If off-thread compile was rejected, continue with regular processing.
+  }
+
+  MaybeMoveToLoadedList(aRequest);
+
+  return NS_OK;
+}
+
+void
+nsScriptLoader::ParsingComplete(bool aTerminated)
+{
+  if (mDeferEnabled) {
+    // Have to check because we apparently get ParsingComplete
+    // without BeginDeferringScripts in some cases
+    mDocumentParsingDone = true;
+  }
+  mDeferEnabled = false;
+  if (aTerminated) {
+    mDeferRequests.Clear();
+    mLoadingAsyncRequests.Clear();
+    mLoadedAsyncRequests.Clear();
+    mNonAsyncExternalScriptInsertedRequests.Clear();
+    mXSLTRequests.Clear();
+    if (mParserBlockingRequest) {
+      mParserBlockingRequest->Cancel();
+      mParserBlockingRequest = nullptr;
+    }
+  }
+
+  // Have to call this even if aTerminated so we'll correctly unblock
+  // onload and all.
+  ProcessPendingRequests();
+}
+
+void
+nsScriptLoader::PreloadURI(nsIURI *aURI, const nsAString &aCharset,
+                           const nsAString &aType,
+                           const nsAString &aCrossOrigin,
+                           const nsAString& aIntegrity,
+                           bool aScriptFromHead,
+                           const mozilla::net::ReferrerPolicy aReferrerPolicy)
+{
+  NS_ENSURE_TRUE_VOID(mDocument);
+  // Check to see if scripts has been turned off.
+  if (!mEnabled || !mDocument->IsScriptEnabled()) {
+    return;
+  }
+
+  // TODO: Preload module scripts.
+  if (nsContentUtils::IsChromeDoc(mDocument) && aType.LowerCaseEqualsASCII("module")) {
+    return;
+  }
+
+  SRIMetadata sriMetadata;
+  if (!aIntegrity.IsEmpty()) {
+    MOZ_LOG(SRILogHelper::GetSriLog(), mozilla::LogLevel::Debug,
+           ("nsScriptLoader::PreloadURI, integrity=%s",
+            NS_ConvertUTF16toUTF8(aIntegrity).get()));
+    nsAutoCString sourceUri;
+    if (mDocument->GetDocumentURI()) {
+      mDocument->GetDocumentURI()->GetAsciiSpec(sourceUri);
+    }
+    SRICheck::IntegrityMetadata(aIntegrity, sourceUri, mReporter, &sriMetadata);
+  }
+
+  RefPtr<nsScriptLoadRequest> request =
+    CreateLoadRequest(nsScriptKind::Classic, nullptr, 0,
+                      Element::StringToCORSMode(aCrossOrigin), sriMetadata);
+  request->mURI = aURI;
+  request->mIsInline = false;
+  request->mReferrerPolicy = aReferrerPolicy;
+
+  nsresult rv = StartLoad(request, aType, aScriptFromHead);
+  if (NS_FAILED(rv)) {
+    return;
+  }
+
+  PreloadInfo *pi = mPreloads.AppendElement();
+  pi->mRequest = request;
+  pi->mCharset = aCharset;
+}
+
+void
+nsScriptLoader::AddDeferRequest(nsScriptLoadRequest* aRequest)
+{
+  aRequest->mIsDefer = true;
+  mDeferRequests.AppendElement(aRequest);
+  if (mDeferEnabled && aRequest == mDeferRequests.getFirst() &&
+      mDocument && !mBlockingDOMContentLoaded) {
+    MOZ_ASSERT(mDocument->GetReadyStateEnum() == nsIDocument::READYSTATE_LOADING);
+    mBlockingDOMContentLoaded = true;
+    mDocument->BlockDOMContentLoaded();
+  }
+}
+
+bool
+nsScriptLoader::MaybeRemovedDeferRequests()
+{
+  if (mDeferRequests.isEmpty() && mDocument &&
+      mBlockingDOMContentLoaded) {
+    mBlockingDOMContentLoaded = false;
+    mDocument->UnblockDOMContentLoaded();
+    return true;
+  }
+  return false;
+}
+
+//////////////////////////////////////////////////////////////
+// nsScriptLoadHandler
+//////////////////////////////////////////////////////////////
+
+nsScriptLoadHandler::nsScriptLoadHandler(nsScriptLoader *aScriptLoader,
+                                         nsScriptLoadRequest *aRequest,
+                                         mozilla::dom::SRICheckDataVerifier *aSRIDataVerifier)
+  : mScriptLoader(aScriptLoader),
+    mRequest(aRequest),
+    mSRIDataVerifier(aSRIDataVerifier),
+    mSRIStatus(NS_OK),
+    mDecoder(),
+    mBuffer()
+{}
+
+nsScriptLoadHandler::~nsScriptLoadHandler()
+{}
+
+NS_IMPL_ISUPPORTS(nsScriptLoadHandler, nsIIncrementalStreamLoaderObserver)
+
+NS_IMETHODIMP
+nsScriptLoadHandler::OnIncrementalData(nsIIncrementalStreamLoader* aLoader,
+                                       nsISupports* aContext,
+                                       uint32_t aDataLength,
+                                       const uint8_t* aData,
+                                       uint32_t *aConsumedLength)
+{
+  if (mRequest->IsCanceled()) {
+    // If request cancelled, ignore any incoming data.
+    *aConsumedLength = aDataLength;
+    return NS_OK;
+  }
+
+  if (!EnsureDecoder(aLoader, aData, aDataLength,
+                     /* aEndOfStream = */ false)) {
+    return NS_OK;
+  }
+
+  // Below we will/shall consume entire data chunk.
+  *aConsumedLength = aDataLength;
+
+  // Decoder has already been initialized. -- trying to decode all loaded bytes.
+  nsresult rv = TryDecodeRawData(aData, aDataLength,
+                                 /* aEndOfStream = */ false);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // If SRI is required for this load, appending new bytes to the hash.
+  if (mSRIDataVerifier && NS_SUCCEEDED(mSRIStatus)) {
+    mSRIStatus = mSRIDataVerifier->Update(aDataLength, aData);
+  }
+
+  return rv;
+}
+
+nsresult
+nsScriptLoadHandler::TryDecodeRawData(const uint8_t* aData,
+                                      uint32_t aDataLength,
+                                      bool aEndOfStream)
+{
+  int32_t srcLen = aDataLength;
+  const char* src = reinterpret_cast<const char *>(aData);
+  int32_t dstLen;
+  nsresult rv =
+    mDecoder->GetMaxLength(src, srcLen, &dstLen);
+
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  uint32_t haveRead = mBuffer.length();
+
+  CheckedInt<uint32_t> capacity = haveRead;
+  capacity += dstLen;
+
+  if (!capacity.isValid() || !mBuffer.reserve(capacity.value())) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  rv = mDecoder->Convert(src,
+                      &srcLen,
+                      mBuffer.begin() + haveRead,
+                      &dstLen);
+
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  haveRead += dstLen;
+  MOZ_ASSERT(haveRead <= capacity.value(), "mDecoder produced more data than expected");
+  MOZ_ALWAYS_TRUE(mBuffer.resizeUninitialized(haveRead));
+
+  return NS_OK;
+}
+
+bool
+nsScriptLoadHandler::EnsureDecoder(nsIIncrementalStreamLoader *aLoader,
+                                   const uint8_t* aData,
+                                   uint32_t aDataLength,
+                                   bool aEndOfStream)
+{
+  // Check if decoder has already been created.
+  if (mDecoder) {
+    return true;
+  }
+
+  nsAutoCString charset;
+
+  // JavaScript modules are always UTF-8.
+  if (mRequest->IsModuleRequest()) {
+    charset = "UTF-8";
+    mDecoder = EncodingUtils::DecoderForEncoding(charset);
+    return true;
+  }
+
+  // Determine if BOM check should be done.  This occurs either
+  // if end-of-stream has been reached, or at least 3 bytes have
+  // been read from input.
+  if (!aEndOfStream && (aDataLength < 3)) {
+    return false;
+  }
+
+  // Do BOM detection.
+  if (nsContentUtils::CheckForBOM(aData, aDataLength, charset)) {
+    mDecoder = EncodingUtils::DecoderForEncoding(charset);
+    return true;
+  }
+
+  // BOM detection failed, check content stream for charset.
+  nsCOMPtr<nsIRequest> req;
+  nsresult rv = aLoader->GetRequest(getter_AddRefs(req));
+  NS_ASSERTION(req, "StreamLoader's request went away prematurely");
+  NS_ENSURE_SUCCESS(rv, false);
+
+  nsCOMPtr<nsIChannel> channel = do_QueryInterface(req);
+
+  if (channel &&
+      NS_SUCCEEDED(channel->GetContentCharset(charset)) &&
+      EncodingUtils::FindEncodingForLabel(charset, charset)) {
+    mDecoder = EncodingUtils::DecoderForEncoding(charset);
+    return true;
+  }
+
+  // Check the hint charset from the script element or preload
+  // request.
+  nsAutoString hintCharset;
+  if (!mRequest->IsPreload()) {
+    mRequest->mElement->GetScriptCharset(hintCharset);
+  } else {
+    nsTArray<nsScriptLoader::PreloadInfo>::index_type i =
+      mScriptLoader->mPreloads.IndexOf(mRequest, 0,
+            nsScriptLoader::PreloadRequestComparator());
+
+    NS_ASSERTION(i != mScriptLoader->mPreloads.NoIndex,
+                 "Incorrect preload bookkeeping");
+    hintCharset = mScriptLoader->mPreloads[i].mCharset;
+  }
+
+  if (EncodingUtils::FindEncodingForLabel(hintCharset, charset)) {
+    mDecoder = EncodingUtils::DecoderForEncoding(charset);
+    return true;
+  }
+
+  // Get the charset from the charset of the document.
+  if (mScriptLoader->mDocument) {
+    charset = mScriptLoader->mDocument->GetDocumentCharacterSet();
+    mDecoder = EncodingUtils::DecoderForEncoding(charset);
+    return true;
+  }
+
+  // Curiously, there are various callers that don't pass aDocument. The
+  // fallback in the old code was ISO-8859-1, which behaved like
+  // windows-1252. Saying windows-1252 for clarity and for compliance
+  // with the Encoding Standard.
+  charset = "windows-1252";
+  mDecoder = EncodingUtils::DecoderForEncoding(charset);
+  return true;
+}
+
+NS_IMETHODIMP
+nsScriptLoadHandler::OnStreamComplete(nsIIncrementalStreamLoader* aLoader,
+                                      nsISupports* aContext,
+                                      nsresult aStatus,
+                                      uint32_t aDataLength,
+                                      const uint8_t* aData)
+{
+  if (!mRequest->IsCanceled()) {
+    DebugOnly<bool> encoderSet =
+      EnsureDecoder(aLoader, aData, aDataLength, /* aEndOfStream = */ true);
+    MOZ_ASSERT(encoderSet);
+    DebugOnly<nsresult> rv = TryDecodeRawData(aData, aDataLength,
+                                              /* aEndOfStream = */ true);
+
+    // If SRI is required for this load, appending new bytes to the hash.
+    if (mSRIDataVerifier && NS_SUCCEEDED(mSRIStatus)) {
+      mSRIStatus = mSRIDataVerifier->Update(aDataLength, aData);
+    }
+  }
+
+  // we have to mediate and use mRequest.
+  return mScriptLoader->OnStreamComplete(aLoader, mRequest, aStatus, mSRIStatus,
+                                         mBuffer, mSRIDataVerifier);
+}