Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3685 insertions, 0 deletions

diff --git a/dom/script/ScriptLoader.cpp b/dom/script/ScriptLoader.cpp
new file mode 100644
index 0000000000..219d2d1650
--- /dev/null
+++ b/dom/script/ScriptLoader.cpp
@@ -0,0 +1,3685 @@
+/* -*- 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/. */
+
+#include "ScriptLoader.h"
+#include "ScriptLoadHandler.h"
+#include "ScriptTrace.h"
+#include "ModuleLoader.h"
+
+#include "nsIChildChannel.h"
+#include "zlib.h"
+
+#include "prsystem.h"
+#include "jsapi.h"
+#include "jsfriendapi.h"
+#include "js/Array.h"  // JS::GetArrayLength
+#include "js/CompilationAndEvaluation.h"
+#include "js/ContextOptions.h"        // JS::ContextOptionsRef
+#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "js/loader/ScriptLoadRequest.h"
+#include "ScriptCompression.h"
+#include "js/loader/LoadedScript.h"
+#include "js/loader/ModuleLoadRequest.h"
+#include "js/MemoryFunctions.h"
+#include "js/Modules.h"
+#include "js/OffThreadScriptCompilation.h"
+#include "js/PropertyAndElement.h"  // JS_DefineProperty
+#include "js/Realm.h"
+#include "js/SourceText.h"
+#include "js/Transcoding.h"
+#include "js/Utility.h"
+#include "xpcpublic.h"
+#include "GeckoProfiler.h"
+#include "nsContentSecurityManager.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsIContent.h"
+#include "nsJSUtils.h"
+#include "mozilla/dom/AutoEntryScript.h"
+#include "mozilla/dom/DocGroup.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/JSExecutionContext.h"
+#include "mozilla/dom/ScriptDecoding.h"  // mozilla::dom::ScriptDecoding
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/SRILogHelper.h"
+#include "mozilla/dom/WindowContext.h"
+#include "mozilla/net/UrlClassifierFeatureFactory.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/StaticPrefs_javascript.h"
+#include "mozilla/StaticPrefs_network.h"
+#include "nsAboutProtocolUtils.h"
+#include "nsGkAtoms.h"
+#include "nsNetUtil.h"
+#include "nsGlobalWindowInner.h"
+#include "nsIScriptGlobalObject.h"
+#include "nsIScriptContext.h"
+#include "nsIPrincipal.h"
+#include "nsJSPrincipals.h"
+#include "nsContentPolicyUtils.h"
+#include "nsIClassifiedChannel.h"
+#include "nsIHttpChannel.h"
+#include "nsIHttpChannelInternal.h"
+#include "nsIClassOfService.h"
+#include "nsICacheInfoChannel.h"
+#include "nsITimedChannel.h"
+#include "nsIScriptElement.h"
+#include "nsISupportsPriority.h"
+#include "nsIDocShell.h"
+#include "nsContentUtils.h"
+#include "nsUnicharUtils.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 "nsMimeTypes.h"
+#include "mozilla/ConsoleReportCollector.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/LoadInfo.h"
+#include "ReferrerInfo.h"
+
+#include "mozilla/AsyncEventDispatcher.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/Utf8.h"  // mozilla::Utf8Unit
+#include "nsIScriptError.h"
+#include "nsIAsyncOutputStream.h"
+
+using JS::SourceText;
+using namespace JS::loader;
+
+using mozilla::Telemetry::LABELS_DOM_SCRIPT_PRELOAD_RESULT;
+
+namespace mozilla::dom {
+
+LazyLogModule ScriptLoader::gCspPRLog("CSP");
+LazyLogModule ScriptLoader::gScriptLoaderLog("ScriptLoader");
+
+#undef LOG
+#define LOG(args) \
+  MOZ_LOG(ScriptLoader::gScriptLoaderLog, mozilla::LogLevel::Debug, args)
+
+#define LOG_ENABLED() \
+  MOZ_LOG_TEST(ScriptLoader::gScriptLoaderLog, mozilla::LogLevel::Debug)
+
+// Alternate Data MIME type used by the ScriptLoader to register that we want to
+// store bytecode without reading it.
+static constexpr auto kNullMimeType = "javascript/null"_ns;
+
+/////////////////////////////////////////////////////////////
+// AsyncCompileShutdownObserver
+/////////////////////////////////////////////////////////////
+
+NS_IMPL_ISUPPORTS(AsyncCompileShutdownObserver, nsIObserver)
+
+void AsyncCompileShutdownObserver::OnShutdown() {
+  if (mScriptLoader) {
+    mScriptLoader->Destroy();
+    MOZ_ASSERT(!mScriptLoader);
+  }
+}
+
+void AsyncCompileShutdownObserver::Unregister() {
+  if (mScriptLoader) {
+    mScriptLoader = nullptr;
+    nsContentUtils::UnregisterShutdownObserver(this);
+  }
+}
+
+NS_IMETHODIMP
+AsyncCompileShutdownObserver::Observe(nsISupports* aSubject, const char* aTopic,
+                                      const char16_t* aData) {
+  OnShutdown();
+  return NS_OK;
+}
+
+//////////////////////////////////////////////////////////////
+// ScriptLoader::PreloadInfo
+//////////////////////////////////////////////////////////////
+
+inline void ImplCycleCollectionUnlink(ScriptLoader::PreloadInfo& aField) {
+  ImplCycleCollectionUnlink(aField.mRequest);
+}
+
+inline void ImplCycleCollectionTraverse(
+    nsCycleCollectionTraversalCallback& aCallback,
+    ScriptLoader::PreloadInfo& aField, const char* aName, uint32_t aFlags = 0) {
+  ImplCycleCollectionTraverse(aCallback, aField.mRequest, aName, aFlags);
+}
+
+//////////////////////////////////////////////////////////////
+// ScriptLoader
+//////////////////////////////////////////////////////////////
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(ScriptLoader)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION(ScriptLoader, mNonAsyncExternalScriptInsertedRequests,
+                         mLoadingAsyncRequests, mLoadedAsyncRequests,
+                         mOffThreadCompilingRequests, mDeferRequests,
+                         mXSLTRequests, mParserBlockingRequest,
+                         mBytecodeEncodingQueue, mPreloads,
+                         mPendingChildLoaders, mModuleLoader,
+                         mWebExtModuleLoaders, mShadowRealmModuleLoaders)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(ScriptLoader)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(ScriptLoader)
+
+ScriptLoader::ScriptLoader(Document* aDocument)
+    : mDocument(aDocument),
+      mParserBlockingBlockerCount(0),
+      mBlockerCount(0),
+      mNumberOfProcessors(0),
+      mTotalFullParseSize(0),
+      mPhysicalSizeOfMemory(-1),
+      mEnabled(true),
+      mDeferEnabled(false),
+      mSpeculativeOMTParsingEnabled(false),
+      mDeferCheckpointReached(false),
+      mBlockingDOMContentLoaded(false),
+      mLoadEventFired(false),
+      mGiveUpEncoding(false),
+      mReporter(new ConsoleReportCollector()) {
+  LOG(("ScriptLoader::ScriptLoader %p", this));
+
+  mSpeculativeOMTParsingEnabled = StaticPrefs::
+      dom_script_loader_external_scripts_speculative_omt_parse_enabled();
+
+  mShutdownObserver = new AsyncCompileShutdownObserver(this);
+  nsContentUtils::RegisterShutdownObserver(mShutdownObserver);
+}
+
+ScriptLoader::~ScriptLoader() {
+  LOG(("ScriptLoader::~ScriptLoader %p", this));
+
+  mObservers.Clear();
+
+  if (mParserBlockingRequest) {
+    FireScriptAvailable(NS_ERROR_ABORT, mParserBlockingRequest);
+  }
+
+  for (ScriptLoadRequest* req = mXSLTRequests.getFirst(); req;
+       req = req->getNext()) {
+    FireScriptAvailable(NS_ERROR_ABORT, req);
+  }
+
+  for (ScriptLoadRequest* req = mDeferRequests.getFirst(); req;
+       req = req->getNext()) {
+    FireScriptAvailable(NS_ERROR_ABORT, req);
+  }
+
+  for (ScriptLoadRequest* req = mLoadingAsyncRequests.getFirst(); req;
+       req = req->getNext()) {
+    FireScriptAvailable(NS_ERROR_ABORT, req);
+  }
+
+  for (ScriptLoadRequest* req = mLoadedAsyncRequests.getFirst(); req;
+       req = req->getNext()) {
+    FireScriptAvailable(NS_ERROR_ABORT, req);
+  }
+
+  for (ScriptLoadRequest* req =
+           mNonAsyncExternalScriptInsertedRequests.getFirst();
+       req; req = req->getNext()) {
+    FireScriptAvailable(NS_ERROR_ABORT, req);
+  }
+
+  // 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();
+  }
+
+  for (size_t i = 0; i < mPreloads.Length(); i++) {
+    AccumulateCategorical(LABELS_DOM_SCRIPT_PRELOAD_RESULT::NotUsed);
+  }
+
+  if (mShutdownObserver) {
+    mShutdownObserver->Unregister();
+    mShutdownObserver = nullptr;
+  }
+
+  mModuleLoader = nullptr;
+}
+
+void ScriptLoader::SetGlobalObject(nsIGlobalObject* aGlobalObject) {
+  if (!aGlobalObject) {
+    // The document is being detached.
+    CancelAndClearScriptLoadRequests();
+    return;
+  }
+
+  MOZ_ASSERT(!HasPendingRequests());
+
+  if (!mModuleLoader) {
+    // The module loader is associated with a global object, so don't create it
+    // until we have a global set.
+    mModuleLoader = new ModuleLoader(this, aGlobalObject, ModuleLoader::Normal);
+  }
+
+  MOZ_ASSERT(mModuleLoader->GetGlobalObject() == aGlobalObject);
+  MOZ_ASSERT(aGlobalObject->GetModuleLoader(dom::danger::GetJSContext()) ==
+             mModuleLoader);
+}
+
+void ScriptLoader::RegisterContentScriptModuleLoader(ModuleLoader* aLoader) {
+  MOZ_ASSERT(aLoader);
+  MOZ_ASSERT(aLoader->GetScriptLoader() == this);
+
+  mWebExtModuleLoaders.AppendElement(aLoader);
+}
+
+void ScriptLoader::RegisterShadowRealmModuleLoader(ModuleLoader* aLoader) {
+  MOZ_ASSERT(aLoader);
+  MOZ_ASSERT(aLoader->GetScriptLoader() == this);
+
+  mShadowRealmModuleLoaders.AppendElement(aLoader);
+}
+
+// Collect telemtry data about the cache information, and the kind of source
+// which are being loaded, and where it is being loaded from.
+static void CollectScriptTelemetry(ScriptLoadRequest* aRequest) {
+  using namespace mozilla::Telemetry;
+
+  MOZ_ASSERT(aRequest->IsFetching());
+
+  // Skip this function if we are not running telemetry.
+  if (!CanRecordExtended()) {
+    return;
+  }
+
+  // Report the script kind.
+  if (aRequest->IsModuleRequest()) {
+    AccumulateCategorical(LABELS_DOM_SCRIPT_KIND::ModuleScript);
+  } else {
+    AccumulateCategorical(LABELS_DOM_SCRIPT_KIND::ClassicScript);
+  }
+
+  // Report the type of source. This is used to monitor the status of the
+  // JavaScript Start-up Bytecode Cache, with the expectation of an almost zero
+  // source-fallback and alternate-data being roughtly equal to source loads.
+  if (aRequest->mFetchSourceOnly) {
+    if (aRequest->GetScriptLoadContext()->mIsInline) {
+      AccumulateCategorical(LABELS_DOM_SCRIPT_LOADING_SOURCE::Inline);
+    } else if (aRequest->IsTextSource()) {
+      AccumulateCategorical(LABELS_DOM_SCRIPT_LOADING_SOURCE::SourceFallback);
+    }
+  } else {
+    if (aRequest->IsTextSource()) {
+      AccumulateCategorical(LABELS_DOM_SCRIPT_LOADING_SOURCE::Source);
+    } else if (aRequest->IsBytecode()) {
+      AccumulateCategorical(LABELS_DOM_SCRIPT_LOADING_SOURCE::AltData);
+    }
+  }
+}
+
+// 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(ScriptKind kind, nsIContent* aScriptElement) {
+  if (kind != ScriptKind::eClassic) {
+    return false;
+  }
+
+  if (!aScriptElement->IsHTMLElement()) {
+    return false;
+  }
+
+  nsAutoString forAttr, eventAttr;
+  if (!aScriptElement->AsElement()->GetAttr(kNameSpaceID_None, nsGkAtoms::_for,
+                                            forAttr) ||
+      !aScriptElement->AsElement()->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, u"onload"_ns,
+                        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;
+}
+
+nsContentPolicyType ScriptLoadRequestToContentPolicyType(
+    ScriptLoadRequest* aRequest) {
+  if (aRequest->GetScriptLoadContext()->IsPreload()) {
+    return aRequest->IsModuleRequest()
+               ? nsIContentPolicy::TYPE_INTERNAL_MODULE_PRELOAD
+               : nsIContentPolicy::TYPE_INTERNAL_SCRIPT_PRELOAD;
+  }
+
+  return aRequest->IsModuleRequest() ? nsIContentPolicy::TYPE_INTERNAL_MODULE
+                                     : nsIContentPolicy::TYPE_INTERNAL_SCRIPT;
+}
+
+nsresult ScriptLoader::CheckContentPolicy(Document* aDocument,
+                                          nsISupports* aContext,
+                                          const nsAString& aType,
+                                          ScriptLoadRequest* aRequest) {
+  nsContentPolicyType contentPolicyType =
+      ScriptLoadRequestToContentPolicyType(aRequest);
+
+  nsCOMPtr<nsINode> requestingNode = do_QueryInterface(aContext);
+  nsCOMPtr<nsILoadInfo> secCheckLoadInfo = new net::LoadInfo(
+      aDocument->NodePrincipal(),  // loading principal
+      aDocument->NodePrincipal(),  // triggering principal
+      requestingNode, nsILoadInfo::SEC_ONLY_FOR_EXPLICIT_CONTENTSEC_CHECK,
+      contentPolicyType);
+
+  // snapshot the nonce at load start time for performing CSP checks
+  if (contentPolicyType == nsIContentPolicy::TYPE_INTERNAL_SCRIPT ||
+      contentPolicyType == nsIContentPolicy::TYPE_INTERNAL_MODULE) {
+    nsCOMPtr<nsINode> node = do_QueryInterface(aContext);
+    if (node) {
+      nsString* cspNonce =
+          static_cast<nsString*>(node->GetProperty(nsGkAtoms::nonce));
+      if (cspNonce) {
+        secCheckLoadInfo->SetCspNonce(*cspNonce);
+      }
+    }
+  }
+
+  int16_t shouldLoad = nsIContentPolicy::ACCEPT;
+  nsresult rv = NS_CheckContentLoadPolicy(
+      aRequest->mURI, secCheckLoadInfo, NS_LossyConvertUTF16toASCII(aType),
+      &shouldLoad, nsContentUtils::GetContentPolicy());
+  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;
+}
+
+/* static */
+bool ScriptLoader::IsAboutPageLoadingChromeURI(ScriptLoadRequest* aRequest,
+                                               Document* aDocument) {
+  // if the uri to be loaded is not of scheme chrome:, there is nothing to do.
+  if (!aRequest->mURI->SchemeIs("chrome")) {
+    return false;
+  }
+
+  // we can either get here with a regular contentPrincipal or with a
+  // NullPrincipal in case we are showing an error page in a sandboxed iframe.
+  // In either case if the about: page is linkable from content, there is
+  // nothing to do.
+  uint32_t aboutModuleFlags = 0;
+  nsresult rv = NS_OK;
+
+  nsCOMPtr<nsIPrincipal> triggeringPrincipal = aRequest->TriggeringPrincipal();
+  if (triggeringPrincipal->GetIsContentPrincipal()) {
+    if (!triggeringPrincipal->SchemeIs("about")) {
+      return false;
+    }
+    rv = triggeringPrincipal->GetAboutModuleFlags(&aboutModuleFlags);
+    NS_ENSURE_SUCCESS(rv, false);
+  } else if (triggeringPrincipal->GetIsNullPrincipal()) {
+    nsCOMPtr<nsIURI> docURI = aDocument->GetDocumentURI();
+    if (!docURI->SchemeIs("about")) {
+      return false;
+    }
+
+    nsCOMPtr<nsIAboutModule> aboutModule;
+    rv = NS_GetAboutModule(docURI, getter_AddRefs(aboutModule));
+    if (NS_FAILED(rv) || !aboutModule) {
+      return false;
+    }
+    rv = aboutModule->GetURIFlags(docURI, &aboutModuleFlags);
+    NS_ENSURE_SUCCESS(rv, false);
+  } else {
+    return false;
+  }
+
+  if (aboutModuleFlags & nsIAboutModule::MAKE_LINKABLE) {
+    return false;
+  }
+
+  // seems like an about page wants to load a chrome URI.
+  return true;
+}
+
+nsIURI* ScriptLoader::GetBaseURI() const {
+  MOZ_ASSERT(mDocument);
+  return mDocument->GetDocBaseURI();
+}
+
+class ScriptRequestProcessor : public Runnable {
+ private:
+  RefPtr<ScriptLoader> mLoader;
+  RefPtr<ScriptLoadRequest> mRequest;
+
+ public:
+  ScriptRequestProcessor(ScriptLoader* aLoader, ScriptLoadRequest* aRequest)
+      : Runnable("dom::ScriptRequestProcessor"),
+        mLoader(aLoader),
+        mRequest(aRequest) {}
+  NS_IMETHOD Run() override { return mLoader->ProcessRequest(mRequest); }
+};
+
+void ScriptLoader::RunScriptWhenSafe(ScriptLoadRequest* aRequest) {
+  auto* runnable = new ScriptRequestProcessor(this, aRequest);
+  nsContentUtils::AddScriptRunner(runnable);
+}
+
+nsresult ScriptLoader::RestartLoad(ScriptLoadRequest* aRequest) {
+  MOZ_ASSERT(aRequest->IsBytecode());
+  aRequest->mScriptBytecode.clearAndFree();
+  TRACE_FOR_TEST(aRequest->GetScriptLoadContext()->GetScriptElement(),
+                 "scriptloader_fallback");
+
+  // Notify preload restart so that we can register this preload request again.
+  aRequest->GetScriptLoadContext()->NotifyRestart(mDocument);
+
+  // Start a new channel from which we explicitly request to stream the source
+  // instead of the bytecode.
+  aRequest->mFetchSourceOnly = true;
+  nsresult rv;
+  if (aRequest->IsModuleRequest()) {
+    rv = aRequest->AsModuleRequest()->RestartModuleLoad();
+  } else {
+    rv = StartLoad(aRequest, 0, Nothing());
+  }
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // Close the current channel and this ScriptLoadHandler as we created a new
+  // one for the same request.
+  return NS_BINDING_RETARGETED;
+}
+
+nsresult ScriptLoader::StartLoad(
+    ScriptLoadRequest* aRequest, uint64_t aEarlyHintPreloaderId,
+    const Maybe<nsAutoString>& aCharsetForPreload) {
+  if (aRequest->IsModuleRequest()) {
+    return aRequest->AsModuleRequest()->StartModuleLoad();
+  }
+
+  return StartClassicLoad(aRequest, aEarlyHintPreloaderId, aCharsetForPreload);
+}
+
+nsresult ScriptLoader::StartClassicLoad(
+    ScriptLoadRequest* aRequest, uint64_t aEarlyHintPreloaderId,
+    const Maybe<nsAutoString>& aCharsetForPreload) {
+  MOZ_ASSERT(aRequest->IsFetching());
+  NS_ENSURE_TRUE(mDocument, NS_ERROR_NULL_POINTER);
+  aRequest->SetUnknownDataType();
+
+  // If this document is sandboxed without 'allow-scripts', abort.
+  if (mDocument->HasScriptsBlockedBySandbox()) {
+    return NS_OK;
+  }
+
+  if (LOG_ENABLED()) {
+    nsAutoCString url;
+    aRequest->mURI->GetAsciiSpec(url);
+    LOG(("ScriptLoadRequest (%p): Start Classic Load (url = %s)", aRequest,
+         url.get()));
+  }
+
+  nsSecurityFlags securityFlags =
+      nsContentSecurityManager::ComputeSecurityFlags(
+          aRequest->CORSMode(), nsContentSecurityManager::CORSSecurityMapping::
+                                    CORS_NONE_MAPS_TO_DISABLED_CORS_CHECKS);
+
+  securityFlags |= nsILoadInfo::SEC_ALLOW_CHROME;
+
+  nsresult rv = StartLoadInternal(aRequest, securityFlags,
+                                  aEarlyHintPreloaderId, aCharsetForPreload);
+
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+static bool IsWebExtensionRequest(ScriptLoadRequest* aRequest) {
+  if (!aRequest->IsModuleRequest()) {
+    return false;
+  }
+
+  ModuleLoader* loader =
+      ModuleLoader::From(aRequest->AsModuleRequest()->mLoader);
+  return loader->GetKind() == ModuleLoader::WebExtension;
+}
+
+nsresult ScriptLoader::StartLoadInternal(
+    ScriptLoadRequest* aRequest, nsSecurityFlags securityFlags,
+    uint64_t aEarlyHintPreloaderId,
+    const Maybe<nsAutoString>& aCharsetForPreload) {
+  nsContentPolicyType contentPolicyType =
+      ScriptLoadRequestToContentPolicyType(aRequest);
+  nsCOMPtr<nsINode> context;
+  if (aRequest->GetScriptLoadContext()->GetScriptElement()) {
+    context =
+        do_QueryInterface(aRequest->GetScriptLoadContext()->GetScriptElement());
+  } else {
+    context = mDocument;
+  }
+
+  nsCOMPtr<nsILoadGroup> loadGroup = mDocument->GetDocumentLoadGroup();
+  nsCOMPtr<nsPIDOMWindowOuter> window = mDocument->GetWindow();
+  NS_ENSURE_TRUE(window, NS_ERROR_NULL_POINTER);
+  nsIDocShell* docshell = window->GetDocShell();
+  nsCOMPtr<nsIInterfaceRequestor> prompter(do_QueryInterface(docshell));
+
+  nsCOMPtr<nsIChannel> channel;
+  nsresult rv = NS_NewChannelWithTriggeringPrincipal(
+      getter_AddRefs(channel), aRequest->mURI, context,
+      aRequest->TriggeringPrincipal(), securityFlags, contentPolicyType,
+      nullptr,  // aPerformanceStorage
+      loadGroup, prompter);
+
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (aEarlyHintPreloaderId) {
+    nsCOMPtr<nsIHttpChannelInternal> channelInternal =
+        do_QueryInterface(channel);
+    NS_ENSURE_TRUE(channelInternal != nullptr, NS_ERROR_FAILURE);
+
+    rv = channelInternal->SetEarlyHintPreloaderId(aEarlyHintPreloaderId);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  // snapshot the nonce at load start time for performing CSP checks
+  if (contentPolicyType == nsIContentPolicy::TYPE_INTERNAL_SCRIPT ||
+      contentPolicyType == nsIContentPolicy::TYPE_INTERNAL_MODULE) {
+    if (context) {
+      nsString* cspNonce =
+          static_cast<nsString*>(context->GetProperty(nsGkAtoms::nonce));
+      if (cspNonce) {
+        nsCOMPtr<nsILoadInfo> loadInfo = channel->LoadInfo();
+        loadInfo->SetCspNonce(*cspNonce);
+      }
+    }
+  }
+
+  nsCOMPtr<nsIScriptGlobalObject> scriptGlobal = GetScriptGlobalObject();
+  if (!scriptGlobal) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // To avoid decoding issues, the build-id is part of the bytecode MIME type
+  // constant.
+  aRequest->mCacheInfo = nullptr;
+  nsCOMPtr<nsICacheInfoChannel> cic(do_QueryInterface(channel));
+  if (cic && StaticPrefs::dom_script_loader_bytecode_cache_enabled()) {
+    MOZ_ASSERT(!IsWebExtensionRequest(aRequest),
+               "Can not bytecode cache WebExt code");
+    if (!aRequest->mFetchSourceOnly) {
+      // Inform the HTTP cache that we prefer to have information coming from
+      // the bytecode cache instead of the sources, if such entry is already
+      // registered.
+      LOG(("ScriptLoadRequest (%p): Maybe request bytecode", aRequest));
+      cic->PreferAlternativeDataType(
+          BytecodeMimeTypeFor(aRequest), ""_ns,
+          nsICacheInfoChannel::PreferredAlternativeDataDeliveryType::ASYNC);
+    } else {
+      // If we are explicitly loading from the sources, such as after a
+      // restarted request, we might still want to save the bytecode after.
+      //
+      // The following tell the cache to look for an alternative data type which
+      // does not exist, such that we can later save the bytecode with a
+      // different alternative data type.
+      LOG(("ScriptLoadRequest (%p): Request saving bytecode later", aRequest));
+      cic->PreferAlternativeDataType(
+          kNullMimeType, ""_ns,
+          nsICacheInfoChannel::PreferredAlternativeDataDeliveryType::ASYNC);
+    }
+  }
+
+  LOG(("ScriptLoadRequest (%p): mode=%u tracking=%d", aRequest,
+       unsigned(aRequest->GetScriptLoadContext()->mScriptMode),
+       aRequest->GetScriptLoadContext()->IsTracking()));
+
+  if (aRequest->GetScriptLoadContext()->IsLinkPreloadScript()) {
+    // This is <link rel="preload" as="script"> or <link rel="modulepreload">
+    // initiated speculative load, put it to the group that is not blocked by
+    // leaders and doesn't block follower at the same time. Giving it a much
+    // higher priority will make this request be processed ahead of other
+    // Unblocked requests, but with the same weight as Leaders. This will make
+    // us behave similar way for both http2 and http1.
+    ScriptLoadContext::PrioritizeAsPreload(channel);
+    ScriptLoadContext::AddLoadBackgroundFlag(channel);
+  } else if (nsCOMPtr<nsIClassOfService> cos = do_QueryInterface(channel)) {
+    if (aRequest->GetScriptLoadContext()->mScriptFromHead &&
+        aRequest->GetScriptLoadContext()->IsBlockingScript()) {
+      // synchronous head scripts block loading of most other non js/css
+      // content such as images, Leader implicitely disallows tailing
+      cos->AddClassFlags(nsIClassOfService::Leader);
+    } else if (aRequest->GetScriptLoadContext()->IsDeferredScript() &&
+               !StaticPrefs::network_http_tailing_enabled()) {
+      // Bug 1395525 and the !StaticPrefs::network_http_tailing_enabled() bit:
+      // We want to make sure that turing tailing off by the pref makes the
+      // browser behave exactly the same way as before landing the tailing
+      // patch.
+
+      // head/body deferred scripts are blocked by leaders but are not
+      // allowed tailing because they block DOMContentLoaded
+      cos->AddClassFlags(nsIClassOfService::TailForbidden);
+    } else {
+      // other scripts (=body sync or head/body async) are neither blocked
+      // nor prioritized
+      cos->AddClassFlags(nsIClassOfService::Unblocked);
+
+      if (aRequest->GetScriptLoadContext()->IsAsyncScript()) {
+        // async scripts are allowed tailing, since those and only those
+        // don't block DOMContentLoaded; this flag doesn't enforce tailing,
+        // just overweights the Unblocked flag when the channel is found
+        // to be a thrird-party tracker and thus set the Tail flag to engage
+        // tailing.
+        cos->AddClassFlags(nsIClassOfService::TailAllowed);
+      }
+    }
+  }
+
+  nsCOMPtr<nsIHttpChannel> httpChannel(do_QueryInterface(channel));
+  if (httpChannel) {
+    // HTTP content negotation has little value in this context.
+    nsAutoCString acceptTypes("*/*");
+    rv = httpChannel->SetRequestHeader("Accept"_ns, acceptTypes, false);
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+    nsCOMPtr<nsIReferrerInfo> referrerInfo =
+        new ReferrerInfo(aRequest->mReferrer, aRequest->ReferrerPolicy());
+    rv = httpChannel->SetReferrerInfoWithoutClone(referrerInfo);
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+    nsCOMPtr<nsIHttpChannelInternal> internalChannel(
+        do_QueryInterface(httpChannel));
+    if (internalChannel) {
+      rv = internalChannel->SetIntegrityMetadata(
+          aRequest->mIntegrity.GetIntegrityString());
+      MOZ_ASSERT(NS_SUCCEEDED(rv));
+    }
+
+    nsAutoString hintCharset;
+    if (!aRequest->GetScriptLoadContext()->IsPreload() &&
+        aRequest->GetScriptLoadContext()->GetScriptElement()) {
+      aRequest->GetScriptLoadContext()->GetScriptElement()->GetScriptCharset(
+          hintCharset);
+    } else if (aCharsetForPreload.isSome()) {
+      hintCharset = aCharsetForPreload.ref();
+    }
+
+    rv = httpChannel->SetClassicScriptHintCharset(hintCharset);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  mozilla::net::PredictorLearn(
+      aRequest->mURI, mDocument->GetDocumentURI(),
+      nsINetworkPredictor::LEARN_LOAD_SUBRESOURCE,
+      mDocument->NodePrincipal()->OriginAttributesRef());
+
+  // Set the initiator type
+  nsCOMPtr<nsITimedChannel> timedChannel(do_QueryInterface(httpChannel));
+  if (timedChannel) {
+    if (aEarlyHintPreloaderId) {
+      timedChannel->SetInitiatorType(u"early-hints"_ns);
+    } else if (aRequest->GetScriptLoadContext()->IsLinkPreloadScript()) {
+      timedChannel->SetInitiatorType(u"link"_ns);
+    } else {
+      timedChannel->SetInitiatorType(u"script"_ns);
+    }
+  }
+
+  UniquePtr<mozilla::dom::SRICheckDataVerifier> sriDataVerifier;
+  if (!aRequest->mIntegrity.IsEmpty()) {
+    nsAutoCString sourceUri;
+    if (mDocument->GetDocumentURI()) {
+      mDocument->GetDocumentURI()->GetAsciiSpec(sourceUri);
+    }
+    sriDataVerifier = MakeUnique<SRICheckDataVerifier>(aRequest->mIntegrity,
+                                                       sourceUri, mReporter);
+  }
+
+  RefPtr<ScriptLoadHandler> handler =
+      new ScriptLoadHandler(this, aRequest, std::move(sriDataVerifier));
+
+  nsCOMPtr<nsIIncrementalStreamLoader> loader;
+  rv = NS_NewIncrementalStreamLoader(getter_AddRefs(loader), handler);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  auto key = PreloadHashKey::CreateAsScript(
+      aRequest->mURI, aRequest->CORSMode(), aRequest->mKind);
+  aRequest->GetScriptLoadContext()->NotifyOpen(
+      key, channel, mDocument,
+      aRequest->GetScriptLoadContext()->IsLinkPreloadScript(),
+      aRequest->IsModuleRequest());
+
+  if (aEarlyHintPreloaderId) {
+    nsCOMPtr<nsIHttpChannelInternal> channelInternal =
+        do_QueryInterface(channel);
+    NS_ENSURE_TRUE(channelInternal != nullptr, NS_ERROR_FAILURE);
+
+    rv = channelInternal->SetEarlyHintPreloaderId(aEarlyHintPreloaderId);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  rv = channel->AsyncOpen(loader);
+
+  if (NS_FAILED(rv)) {
+    // Make sure to inform any <link preload> tags about failure to load the
+    // resource.
+    aRequest->GetScriptLoadContext()->NotifyStart(channel);
+    aRequest->GetScriptLoadContext()->NotifyStop(rv);
+  }
+
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+bool ScriptLoader::PreloadURIComparator::Equals(const PreloadInfo& aPi,
+                                                nsIURI* const& aURI) const {
+  bool same;
+  return NS_SUCCEEDED(aPi.mRequest->mURI->Equals(aURI, &same)) && same;
+}
+
+static bool CSPAllowsInlineScript(nsIScriptElement* aElement,
+                                  Document* aDocument) {
+  nsCOMPtr<nsIContentSecurityPolicy> csp = aDocument->GetCsp();
+  if (!csp) {
+    // no CSP --> allow
+    return true;
+  }
+
+  // query the nonce
+  nsCOMPtr<Element> scriptContent = do_QueryInterface(aElement);
+  nsAutoString nonce;
+  if (scriptContent) {
+    nsString* cspNonce =
+        static_cast<nsString*>(scriptContent->GetProperty(nsGkAtoms::nonce));
+    if (cspNonce) {
+      nonce = *cspNonce;
+    }
+  }
+
+  bool parserCreated =
+      aElement->GetParserCreated() != mozilla::dom::NOT_FROM_PARSER;
+
+  bool allowInlineScript = false;
+  nsresult rv = csp->GetAllowsInline(
+      nsIContentSecurityPolicy::SCRIPT_SRC_ELEM_DIRECTIVE,
+      false /* aHasUnsafeHash */, nonce, parserCreated, scriptContent,
+      nullptr /* nsICSPEventListener */, u""_ns,
+      aElement->GetScriptLineNumber(), aElement->GetScriptColumnNumber(),
+      &allowInlineScript);
+  return NS_SUCCEEDED(rv) && allowInlineScript;
+}
+
+already_AddRefed<ScriptLoadRequest> ScriptLoader::CreateLoadRequest(
+    ScriptKind aKind, nsIURI* aURI, nsIScriptElement* aElement,
+    nsIPrincipal* aTriggeringPrincipal, CORSMode aCORSMode,
+    const SRIMetadata& aIntegrity, ReferrerPolicy aReferrerPolicy) {
+  nsIURI* referrer = mDocument->GetDocumentURIAsReferrer();
+  nsCOMPtr<Element> domElement = do_QueryInterface(aElement);
+  RefPtr<ScriptFetchOptions> fetchOptions = new ScriptFetchOptions(
+      aCORSMode, aReferrerPolicy, aTriggeringPrincipal, domElement);
+  RefPtr<ScriptLoadContext> context = new ScriptLoadContext();
+
+  if (aKind == ScriptKind::eClassic || aKind == ScriptKind::eImportMap) {
+    RefPtr<ScriptLoadRequest> aRequest = new ScriptLoadRequest(
+        aKind, aURI, fetchOptions, aIntegrity, referrer, context);
+
+    return aRequest.forget();
+  }
+
+  MOZ_ASSERT(aKind == ScriptKind::eModule);
+  RefPtr<ModuleLoadRequest> aRequest = ModuleLoader::CreateTopLevel(
+      aURI, fetchOptions, aIntegrity, referrer, this, context);
+  return aRequest.forget();
+}
+
+bool ScriptLoader::ProcessScriptElement(nsIScriptElement* aElement,
+                                        const nsAutoString& aTypeAttr) {
+  // 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);
+
+  ScriptKind scriptKind;
+  if (aElement->GetScriptIsModule()) {
+    scriptKind = ScriptKind::eModule;
+  } else if (aElement->GetScriptIsImportMap()) {
+    scriptKind = ScriptKind::eImportMap;
+  } else {
+    scriptKind = ScriptKind::eClassic;
+  }
+
+  // Step 13. Check that the script is not an eventhandler
+  if (IsScriptEventHandler(scriptKind, scriptContent)) {
+    return false;
+  }
+
+  // "In modern user agents that support module scripts, the script element with
+  // the nomodule attribute will be ignored".
+  // "The nomodule attribute must not be specified on module scripts (and will
+  // be ignored if it is)."
+  if (mDocument->ModuleScriptsEnabled() && scriptKind == ScriptKind::eClassic &&
+      scriptContent->IsHTMLElement() &&
+      scriptContent->AsElement()->HasAttr(kNameSpaceID_None,
+                                          nsGkAtoms::nomodule)) {
+    return false;
+  }
+
+  // Step 15. and later in the HTML5 spec
+  if (aElement->GetScriptExternal()) {
+    return ProcessExternalScript(aElement, scriptKind, aTypeAttr,
+                                 scriptContent);
+  }
+
+  return ProcessInlineScript(aElement, scriptKind);
+}
+
+bool ScriptLoader::ProcessExternalScript(nsIScriptElement* aElement,
+                                         ScriptKind aScriptKind,
+                                         const nsAutoString& aTypeAttr,
+                                         nsIContent* aScriptContent) {
+  LOG(("ScriptLoader (%p): Process external script for element %p", this,
+       aElement));
+
+  // https://html.spec.whatwg.org/multipage/scripting.html#prepare-the-script-element
+  // Step 30.1. If el's type is "importmap", then queue an element task on the
+  // DOM manipulation task source given el to fire an event named error at el,
+  // and return.
+  if (aScriptKind == ScriptKind::eImportMap) {
+    NS_DispatchToCurrentThread(
+        NewRunnableMethod("nsIScriptElement::FireErrorEvent", aElement,
+                          &nsIScriptElement::FireErrorEvent));
+    nsContentUtils::ReportToConsole(
+        nsIScriptError::warningFlag, "Script Loader"_ns, mDocument,
+        nsContentUtils::eDOM_PROPERTIES, "ImportMapExternalNotSupported");
+    return false;
+  }
+
+  nsCOMPtr<nsIURI> scriptURI = aElement->GetScriptURI();
+  if (!scriptURI) {
+    // Asynchronously report the failure to create a URI object
+    NS_DispatchToCurrentThread(
+        NewRunnableMethod("nsIScriptElement::FireErrorEvent", aElement,
+                          &nsIScriptElement::FireErrorEvent));
+    return false;
+  }
+
+  SRIMetadata sriMetadata;
+  {
+    nsAutoString integrity;
+    aScriptContent->AsElement()->GetAttr(kNameSpaceID_None,
+                                         nsGkAtoms::integrity, integrity);
+    GetSRIMetadata(integrity, &sriMetadata);
+  }
+
+  RefPtr<ScriptLoadRequest> request =
+      LookupPreloadRequest(aElement, aScriptKind, sriMetadata);
+
+  if (request &&
+      NS_FAILED(CheckContentPolicy(mDocument, aElement, aTypeAttr, request))) {
+    LOG(("ScriptLoader (%p): content policy check failed for preload", this));
+
+    // 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();
+    AccumulateCategorical(LABELS_DOM_SCRIPT_PRELOAD_RESULT::RejectedByPolicy);
+    return false;
+  }
+
+  if (request) {
+    // Use the preload request.
+
+    LOG(("ScriptLoadRequest (%p): Using preload request", request.get()));
+
+    // https://html.spec.whatwg.org/multipage/webappapis.html#fetch-a-module-script-tree
+    // Step 1. Disallow further import maps given settings object.
+    if (request->IsModuleRequest()) {
+      LOG(("ScriptLoadRequest (%p): Disallow further import maps.",
+           request.get()));
+      mModuleLoader->DisallowImportMaps();
+    }
+
+    // It's possible these attributes changed since we started the preload so
+    // update them here.
+    request->GetScriptLoadContext()->SetScriptMode(
+        aElement->GetScriptDeferred(), aElement->GetScriptAsync(), false);
+
+    // The request will be added to another list or set as
+    // mParserBlockingRequest below.
+    if (request->GetScriptLoadContext()->mInCompilingList) {
+      mOffThreadCompilingRequests.Remove(request);
+      request->GetScriptLoadContext()->mInCompilingList = false;
+    }
+
+    AccumulateCategorical(LABELS_DOM_SCRIPT_PRELOAD_RESULT::Used);
+  } else {
+    // No usable preload found.
+
+    nsCOMPtr<nsIPrincipal> principal =
+        aElement->GetScriptURITriggeringPrincipal();
+    if (!principal) {
+      principal = aScriptContent->NodePrincipal();
+    }
+
+    CORSMode ourCORSMode = aElement->GetCORSMode();
+    ReferrerPolicy referrerPolicy = GetReferrerPolicy(aElement);
+
+    request = CreateLoadRequest(aScriptKind, scriptURI, aElement, principal,
+                                ourCORSMode, sriMetadata, referrerPolicy);
+    request->GetScriptLoadContext()->mIsInline = false;
+    request->GetScriptLoadContext()->SetScriptMode(
+        aElement->GetScriptDeferred(), aElement->GetScriptAsync(), false);
+    // keep request->GetScriptLoadContext()->mScriptFromHead to false so we
+    // don't treat non preloaded scripts as blockers for full page load. See bug
+    // 792438.
+
+    LOG(("ScriptLoadRequest (%p): Created request for external script",
+         request.get()));
+
+    nsresult rv = StartLoad(request, 0, Nothing());
+    if (NS_FAILED(rv)) {
+      ReportErrorToConsole(request, rv);
+
+      // Asynchronously report the load failure
+      nsCOMPtr<nsIRunnable> runnable =
+          NewRunnableMethod("nsIScriptElement::FireErrorEvent", aElement,
+                            &nsIScriptElement::FireErrorEvent);
+      if (mDocument) {
+        mDocument->Dispatch(TaskCategory::Other, runnable.forget());
+      } else {
+        NS_DispatchToCurrentThread(runnable);
+      }
+      return false;
+    }
+  }
+
+  // We should still be in loading stage of script unless we're loading a
+  // module or speculatively off-main-thread parsing a script.
+  NS_ASSERTION(SpeculativeOMTParsingEnabled() ||
+                   !request->GetScriptLoadContext()->CompileStarted() ||
+                   request->IsModuleRequest(),
+               "Request should not yet be in compiling stage.");
+
+  if (request->GetScriptLoadContext()->IsAsyncScript()) {
+    AddAsyncRequest(request);
+    if (request->IsReadyToRun()) {
+      // 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();
+    }
+    return false;
+  }
+  if (!aElement->GetParserCreated()) {
+    // Violate the HTML5 spec in order to make LABjs and the "order" plug-in
+    // for RequireJS work with their Gecko-sniffed code path. See
+    // http://lists.w3.org/Archives/Public/public-html/2010Oct/0088.html
+    request->GetScriptLoadContext()->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 (request->GetScriptLoadContext()->IsDeferredScript()) {
+    // 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->GetScriptLoadContext()->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;
+}
+
+bool ScriptLoader::ProcessInlineScript(nsIScriptElement* aElement,
+                                       ScriptKind aScriptKind) {
+  // 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;
+  }
+
+  // Check if adding an import map script is allowed. If not, we bail out
+  // early to prevent creating a load request.
+  if (aScriptKind == ScriptKind::eImportMap) {
+    // https://html.spec.whatwg.org/multipage/scripting.html#prepare-the-script-element
+    // Step 31.2 type is "importmap":
+    //   Step 1. If el's relevant global object's import maps allowed is false,
+    //   then queue an element task on the DOM manipulation task source given el
+    //   to fire an event named error at el, and return.
+    if (!mModuleLoader->IsImportMapAllowed()) {
+      NS_WARNING("ScriptLoader: import maps allowed is false.");
+      const char* msg = mModuleLoader->HasImportMapRegistered()
+                            ? "ImportMapNotAllowedMultiple"
+                            : "ImportMapNotAllowedAfterModuleLoad";
+      nsContentUtils::ReportToConsole(nsIScriptError::warningFlag,
+                                      "Script Loader"_ns, mDocument,
+                                      nsContentUtils::eDOM_PROPERTIES, msg);
+      NS_DispatchToCurrentThread(
+          NewRunnableMethod("nsIScriptElement::FireErrorEvent", aElement,
+                            &nsIScriptElement::FireErrorEvent));
+      return false;
+    }
+  }
+
+  // Inline classic scripts ignore their CORS mode and are always CORS_NONE.
+  CORSMode corsMode = CORS_NONE;
+  if (aScriptKind == ScriptKind::eModule) {
+    corsMode = aElement->GetCORSMode();
+  }
+
+  ReferrerPolicy referrerPolicy = GetReferrerPolicy(aElement);
+  RefPtr<ScriptLoadRequest> request =
+      CreateLoadRequest(aScriptKind, mDocument->GetDocumentURI(), aElement,
+                        mDocument->NodePrincipal(), corsMode,
+                        SRIMetadata(),  // SRI doesn't apply
+                        referrerPolicy);
+  request->GetScriptLoadContext()->mIsInline = true;
+  request->GetScriptLoadContext()->mLineNo = aElement->GetScriptLineNumber();
+  request->GetScriptLoadContext()->mColumnNo =
+      aElement->GetScriptColumnNumber();
+  request->mFetchSourceOnly = true;
+  request->SetTextSource();
+  TRACE_FOR_TEST_BOOL(request->GetScriptLoadContext()->GetScriptElement(),
+                      "scriptloader_load_source");
+  CollectScriptTelemetry(request);
+
+  // Only the 'async' attribute is heeded on an inline module script and
+  // inline classic scripts ignore both these attributes.
+  MOZ_ASSERT(!aElement->GetScriptDeferred());
+  MOZ_ASSERT_IF(!request->IsModuleRequest(), !aElement->GetScriptAsync());
+  request->GetScriptLoadContext()->SetScriptMode(
+      false, aElement->GetScriptAsync(), false);
+
+  LOG(("ScriptLoadRequest (%p): Created request for inline script",
+       request.get()));
+
+  request->mBaseURL = mDocument->GetDocBaseURI();
+
+  if (request->IsModuleRequest()) {
+    // https://html.spec.whatwg.org/multipage/webappapis.html#fetch-an-inline-module-script-graph
+    // Step 1. Disallow further import maps given settings object.
+    mModuleLoader->DisallowImportMaps();
+
+    ModuleLoadRequest* modReq = request->AsModuleRequest();
+    if (aElement->GetParserCreated() != NOT_FROM_PARSER) {
+      if (aElement->GetScriptAsync()) {
+        AddAsyncRequest(modReq);
+      } else {
+        AddDeferRequest(modReq);
+      }
+    }
+
+    // This calls OnFetchComplete directly since there's no need to start
+    // fetching an inline script.
+    nsresult rv = modReq->OnFetchComplete(NS_OK);
+    if (NS_FAILED(rv)) {
+      ReportErrorToConsole(modReq, rv);
+      HandleLoadError(modReq, rv);
+    }
+
+    return false;
+  }
+
+  if (request->IsImportMapRequest()) {
+    // https://html.spec.whatwg.org/multipage/scripting.html#prepare-the-script-element
+    // Step 31.2 type is "importmap":
+    //   Impl note: Step 1 is done above before creating a ScriptLoadRequest.
+    MOZ_ASSERT(mModuleLoader->IsImportMapAllowed());
+
+    //   Step 2. Set el's relevant global object's import maps allowed to false.
+    mModuleLoader->DisallowImportMaps();
+
+    //   Step 3. Let result be the result of creating an import map parse result
+    //   given source text and base URL.
+    UniquePtr<ImportMap> importMap = mModuleLoader->ParseImportMap(request);
+    if (!importMap) {
+      // If parsing import maps fails, the exception will be reported in
+      // ModuleLoaderBase::ParseImportMap, and the registration of the import
+      // map will bail out early.
+      return false;
+    }
+
+    // TODO: Bug 1781758: Move RegisterImportMap into EvaluateScriptElement.
+    //
+    // https://html.spec.whatwg.org/multipage/scripting.html#execute-the-script-element
+    // The spec defines 'register an import map' should be done in
+    // 'execute the script element', because inside 'execute the script element'
+    // it will perform a 'preparation-time document check'.
+    // However, as import maps could be only inline scripts by now, the
+    // 'preparation-time document check' will never fail for import maps.
+    // So we simply call 'register an import map' here.
+    mModuleLoader->RegisterImportMap(std::move(importMap));
+    return false;
+  }
+
+  request->mState = ScriptLoadRequest::State::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?");
+    RunScriptWhenSafe(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;
+}
+
+ScriptLoadRequest* ScriptLoader::LookupPreloadRequest(
+    nsIScriptElement* aElement, ScriptKind aScriptKind,
+    const SRIMetadata& aSRIMetadata) {
+  MOZ_ASSERT(aElement);
+
+  nsTArray<PreloadInfo>::index_type i =
+      mPreloads.IndexOf(aElement->GetScriptURI(), 0, PreloadURIComparator());
+  if (i == nsTArray<PreloadInfo>::NoIndex) {
+    return nullptr;
+  }
+  RefPtr<ScriptLoadRequest> request = mPreloads[i].mRequest;
+  if (aScriptKind != request->mKind) {
+    return nullptr;
+  }
+
+  // Found preloaded request. Note that a script-inserted script can steal a
+  // preload!
+  request->GetScriptLoadContext()->SetIsLoadRequest(aElement);
+
+  if (request->GetScriptLoadContext()->mWasCompiledOMT &&
+      !request->IsModuleRequest()) {
+    request->SetReady();
+  }
+
+  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);
+
+  // Bug 1832361: charset and crossorigin attributes shouldn't affect matching
+  // of module scripts and modulepreload
+  if (!request->IsModuleRequest() &&
+      (!elementCharset.Equals(preloadCharset) ||
+       aElement->GetCORSMode() != request->CORSMode())) {
+    // Drop the preload.
+    request->Cancel();
+    AccumulateCategorical(LABELS_DOM_SCRIPT_PRELOAD_RESULT::RequestMismatch);
+    return nullptr;
+  }
+
+  if (!aSRIMetadata.CanTrustBeDelegatedTo(request->mIntegrity)) {
+    // Don't cancel link preload requests, we want to deliver onload according
+    // the result of the load, cancellation would unexpectedly lead to error
+    // notification.
+    if (!request->GetScriptLoadContext()->IsLinkPreloadScript()) {
+      request->Cancel();
+    }
+    return nullptr;
+  }
+
+  // Report any errors that we skipped while preloading.
+  ReportPreloadErrorsToConsole(request);
+
+  // This makes sure the pending preload (if exists) for this resource is
+  // properly marked as used and thus not notified in the console as unused.
+  request->GetScriptLoadContext()->NotifyUsage(mDocument);
+  // A used preload must no longer be found in the Document's hash table.  Any
+  // <link preload> tag after the <script> tag will start a new request, that
+  // can be satisfied from a different cache, but not from the preload cache.
+  request->GetScriptLoadContext()->RemoveSelf(mDocument);
+
+  return request;
+}
+
+void ScriptLoader::GetSRIMetadata(const nsAString& aIntegrityAttr,
+                                  SRIMetadata* aMetadataOut) {
+  MOZ_ASSERT(aMetadataOut->IsEmpty());
+
+  if (aIntegrityAttr.IsEmpty()) {
+    return;
+  }
+
+  MOZ_LOG(SRILogHelper::GetSriLog(), mozilla::LogLevel::Debug,
+          ("ScriptLoader::GetSRIMetadata, integrity=%s",
+           NS_ConvertUTF16toUTF8(aIntegrityAttr).get()));
+
+  nsAutoCString sourceUri;
+  if (mDocument->GetDocumentURI()) {
+    mDocument->GetDocumentURI()->GetAsciiSpec(sourceUri);
+  }
+  SRICheck::IntegrityMetadata(aIntegrityAttr, sourceUri, mReporter,
+                              aMetadataOut);
+}
+
+ReferrerPolicy ScriptLoader::GetReferrerPolicy(nsIScriptElement* aElement) {
+  ReferrerPolicy scriptReferrerPolicy = aElement->GetReferrerPolicy();
+  if (scriptReferrerPolicy != ReferrerPolicy::_empty) {
+    return scriptReferrerPolicy;
+  }
+  return mDocument->GetReferrerPolicy();
+}
+
+void ScriptLoader::CancelAndClearScriptLoadRequests() {
+  // Cancel all requests that have not been executed and remove them.
+
+  if (mParserBlockingRequest) {
+    mParserBlockingRequest->Cancel();
+    mParserBlockingRequest = nullptr;
+  }
+
+  mDeferRequests.CancelRequestsAndClear();
+  mLoadingAsyncRequests.CancelRequestsAndClear();
+  mLoadedAsyncRequests.CancelRequestsAndClear();
+  mNonAsyncExternalScriptInsertedRequests.CancelRequestsAndClear();
+  mXSLTRequests.CancelRequestsAndClear();
+  mOffThreadCompilingRequests.CancelRequestsAndClear();
+
+  if (mModuleLoader) {
+    mModuleLoader->CancelAndClearDynamicImports();
+  }
+
+  for (ModuleLoader* loader : mWebExtModuleLoaders) {
+    loader->CancelAndClearDynamicImports();
+  }
+
+  for (ModuleLoader* loader : mShadowRealmModuleLoaders) {
+    loader->CancelAndClearDynamicImports();
+  }
+
+  for (size_t i = 0; i < mPreloads.Length(); i++) {
+    mPreloads[i].mRequest->Cancel();
+  }
+  mPreloads.Clear();
+}
+
+nsresult ScriptLoader::CompileOffThreadOrProcessRequest(
+    ScriptLoadRequest* aRequest) {
+  NS_ASSERTION(nsContentUtils::IsSafeToRunScript(),
+               "Processing requests when running scripts is unsafe.");
+
+  if (!aRequest->GetScriptLoadContext()->mOffThreadToken &&
+      !aRequest->GetScriptLoadContext()->CompileStarted()) {
+    bool couldCompile = false;
+    nsresult rv = AttemptOffThreadScriptCompile(aRequest, &couldCompile);
+    if (NS_FAILED(rv)) {
+      HandleLoadError(aRequest, rv);
+      return rv;
+    }
+
+    if (couldCompile) {
+      return NS_OK;
+    }
+  }
+
+  return ProcessRequest(aRequest);
+}
+
+namespace {
+
+class OffThreadCompilationCompleteRunnable : public Runnable {
+  nsMainThreadPtrHandle<ScriptLoadRequest> mRequest;
+  nsMainThreadPtrHandle<ScriptLoader> mLoader;
+  nsCOMPtr<nsISerialEventTarget> mEventTarget;
+  JS::OffThreadToken* mToken;
+  TimeStamp mStartTime;
+  TimeStamp mStopTime;
+
+ public:
+  OffThreadCompilationCompleteRunnable(ScriptLoadRequest* aRequest,
+                                       ScriptLoader* aLoader)
+      : Runnable("dom::OffThreadCompilationCompleteRunnable"),
+        mRequest(
+            new nsMainThreadPtrHolder<ScriptLoadRequest>("mRequest", aRequest)),
+        mLoader(new nsMainThreadPtrHolder<ScriptLoader>("mLoader", aLoader)),
+        mToken(nullptr) {
+    MOZ_ASSERT(NS_IsMainThread());
+    if (DocGroup* docGroup = aLoader->GetDocGroup()) {
+      mEventTarget = docGroup->EventTargetFor(TaskCategory::Other);
+    }
+  }
+
+  void RecordStartTime() { mStartTime = TimeStamp::Now(); }
+  void RecordStopTime() { mStopTime = TimeStamp::Now(); }
+
+  void SetToken(JS::OffThreadToken* aToken) {
+    MOZ_ASSERT(aToken && !mToken);
+    mToken = aToken;
+  }
+
+  static void Dispatch(
+      already_AddRefed<OffThreadCompilationCompleteRunnable>&& aSelf) {
+    RefPtr<OffThreadCompilationCompleteRunnable> self = aSelf;
+    nsCOMPtr<nsISerialEventTarget> eventTarget = self->mEventTarget;
+    eventTarget->Dispatch(self.forget());
+  }
+
+  NS_DECL_NSIRUNNABLE
+};
+
+} /* anonymous namespace */
+
+nsresult ScriptLoader::AttemptOffThreadScriptCompile(
+    ScriptLoadRequest* aRequest, bool* aCouldCompileOut) {
+  // If speculative parsing is enabled, the request may not be ready to run if
+  // the element is not yet available.
+  MOZ_ASSERT_IF(!SpeculativeOMTParsingEnabled() && !aRequest->IsModuleRequest(),
+                aRequest->IsReadyToRun());
+  MOZ_ASSERT(!aRequest->GetScriptLoadContext()->mWasCompiledOMT);
+  MOZ_ASSERT(aCouldCompileOut && !*aCouldCompileOut);
+
+  // Don't off-thread compile inline scripts.
+  if (aRequest->GetScriptLoadContext()->mIsInline) {
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIGlobalObject> globalObject = GetGlobalForRequest(aRequest);
+  if (!globalObject) {
+    return NS_ERROR_FAILURE;
+  }
+
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(globalObject)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  JSContext* cx = jsapi.cx();
+  JS::CompileOptions options(cx);
+
+  // Introduction script will actually be computed and set when the script is
+  // collected from offthread
+  JS::Rooted<JSScript*> dummyIntroductionScript(cx);
+  nsresult rv = FillCompileOptionsForRequest(cx, aRequest, &options,
+                                             &dummyIntroductionScript);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (aRequest->IsTextSource()) {
+    if (!JS::CanCompileOffThread(cx, options, aRequest->ScriptTextLength())) {
+      TRACE_FOR_TEST(aRequest->GetScriptLoadContext()->GetScriptElement(),
+                     "scriptloader_main_thread_compile");
+      return NS_OK;
+    }
+  } else {
+    MOZ_ASSERT(aRequest->IsBytecode());
+
+    size_t length =
+        aRequest->mScriptBytecode.length() - aRequest->mBytecodeOffset;
+    JS::DecodeOptions decodeOptions(options);
+    if (!JS::CanDecodeOffThread(cx, decodeOptions, length)) {
+      return NS_OK;
+    }
+  }
+
+  RefPtr<OffThreadCompilationCompleteRunnable> runnable =
+      new OffThreadCompilationCompleteRunnable(aRequest, this);
+
+  // Emulate dispatch. CompileOffThreadModule will call
+  // OffThreadCompilationCompleteCallback were we will emulate run.
+  LogRunnable::LogDispatch(runnable);
+
+  runnable->RecordStartTime();
+
+  JS::OffThreadToken* token = nullptr;
+  rv = StartOffThreadCompilation(cx, aRequest, options, runnable, &token);
+  NS_ENSURE_SUCCESS(rv, rv);
+  MOZ_ASSERT(token);
+
+  aRequest->GetScriptLoadContext()->mOffThreadToken = token;
+  aRequest->GetScriptLoadContext()->mRunnable = runnable;
+
+  aRequest->GetScriptLoadContext()->BlockOnload(mDocument);
+
+  // Once the compilation is finished, a callback will dispatch the runnable to
+  // the main thread to call ScriptLoader::ProcessOffThreadRequest for the
+  // request.
+  aRequest->mState = ScriptLoadRequest::State::Compiling;
+
+  // Requests that are not tracked elsewhere are added to a list while they are
+  // being compiled off-thread, so we can cancel the compilation later if
+  // necessary.
+  //
+  // Non-top-level modules not tracked because these are cancelled from their
+  // importing module.
+  if (aRequest->IsTopLevel() && !aRequest->isInList()) {
+    mOffThreadCompilingRequests.AppendElement(aRequest);
+    aRequest->GetScriptLoadContext()->mInCompilingList = true;
+  }
+
+  *aCouldCompileOut = true;
+
+  return NS_OK;
+}
+
+static inline nsresult CompileResultForToken(void* aToken) {
+  return aToken ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+}
+
+nsresult ScriptLoader::StartOffThreadCompilation(
+    JSContext* aCx, ScriptLoadRequest* aRequest, JS::CompileOptions& aOptions,
+    Runnable* aRunnable, JS::OffThreadToken** aTokenOut) {
+  const JS::OffThreadCompileCallback callback =
+      OffThreadCompilationCompleteCallback;
+
+  if (aRequest->IsBytecode()) {
+    JS::DecodeOptions decodeOptions(aOptions);
+    *aTokenOut = JS::DecodeStencilOffThread(
+        aCx, decodeOptions, aRequest->mScriptBytecode,
+        aRequest->mBytecodeOffset, callback, aRunnable);
+    return CompileResultForToken(*aTokenOut);
+  }
+
+  MaybeSourceText maybeSource;
+  nsresult rv = aRequest->GetScriptSource(aCx, &maybeSource);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (aRequest->IsModuleRequest()) {
+    auto compile = [&](auto& source) {
+      return JS::CompileModuleToStencilOffThread(aCx, aOptions, source,
+                                                 callback, aRunnable);
+    };
+
+    MOZ_ASSERT(!maybeSource.empty());
+    *aTokenOut = maybeSource.mapNonEmpty(compile);
+    return CompileResultForToken(*aTokenOut);
+  }
+
+  if (ShouldApplyDelazifyStrategy(aRequest)) {
+    ApplyDelazifyStrategy(&aOptions);
+    mTotalFullParseSize +=
+        aRequest->ScriptTextLength() > 0
+            ? static_cast<uint32_t>(aRequest->ScriptTextLength())
+            : 0;
+
+    LOG(
+        ("ScriptLoadRequest (%p): non-on-demand-only Parsing Enabled for "
+         "url=%s mTotalFullParseSize=%u",
+         aRequest, aRequest->mURI->GetSpecOrDefault().get(),
+         mTotalFullParseSize));
+  }
+
+  if (StaticPrefs::dom_expose_test_interfaces()) {
+    switch (aOptions.eagerDelazificationStrategy()) {
+      case JS::DelazificationOption::OnDemandOnly:
+        TRACE_FOR_TEST(aRequest->GetScriptLoadContext()->GetScriptElement(),
+                       "delazification_on_demand_only");
+        break;
+      case JS::DelazificationOption::CheckConcurrentWithOnDemand:
+      case JS::DelazificationOption::ConcurrentDepthFirst:
+        TRACE_FOR_TEST(aRequest->GetScriptLoadContext()->GetScriptElement(),
+                       "delazification_concurrent_depth_first");
+        break;
+      case JS::DelazificationOption::ConcurrentLargeFirst:
+        TRACE_FOR_TEST(aRequest->GetScriptLoadContext()->GetScriptElement(),
+                       "delazification_concurrent_large_first");
+        break;
+      case JS::DelazificationOption::ParseEverythingEagerly:
+        TRACE_FOR_TEST(aRequest->GetScriptLoadContext()->GetScriptElement(),
+                       "delazification_parse_everything_eagerly");
+        break;
+    }
+  }
+
+  auto compile = [&](auto& source) {
+    return JS::CompileToStencilOffThread(aCx, aOptions, source, callback,
+                                         aRunnable);
+  };
+
+  MOZ_ASSERT(!maybeSource.empty());
+  *aTokenOut = maybeSource.mapNonEmpty(compile);
+  return CompileResultForToken(*aTokenOut);
+}
+
+void ScriptLoader::OffThreadCompilationCompleteCallback(
+    JS::OffThreadToken* aToken, void* aCallbackData) {
+  RefPtr<OffThreadCompilationCompleteRunnable> aRunnable =
+      static_cast<OffThreadCompilationCompleteRunnable*>(aCallbackData);
+
+  LogRunnable::Run run(aRunnable);
+
+  aRunnable->RecordStopTime();
+  aRunnable->SetToken(aToken);
+
+  OffThreadCompilationCompleteRunnable::Dispatch(aRunnable.forget());
+}
+
+NS_IMETHODIMP
+OffThreadCompilationCompleteRunnable::Run() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  RefPtr<ScriptLoadContext> context = mRequest->GetScriptLoadContext();
+  MOZ_ASSERT_IF(context->mRunnable, context->mRunnable == this);
+  MOZ_ASSERT_IF(context->mOffThreadToken, context->mOffThreadToken == mToken);
+
+  // Clear the pointer to the runnable. The final reference will be released
+  // when this method returns.
+  context->mRunnable = nullptr;
+
+  if (!context->mOffThreadToken) {
+    // Request has been cancelled by MaybeCancelOffThreadScript.
+    return NS_OK;
+  }
+
+  if (profiler_is_active()) {
+    ProfilerString8View scriptSourceString;
+    if (mRequest->IsTextSource()) {
+      scriptSourceString = "ScriptCompileOffThread";
+    } else {
+      MOZ_ASSERT(mRequest->IsBytecode());
+      scriptSourceString = "BytecodeDecodeOffThread";
+    }
+
+    nsAutoCString profilerLabelString;
+    mRequest->GetScriptLoadContext()->GetProfilerLabel(profilerLabelString);
+    PROFILER_MARKER_TEXT(scriptSourceString, JS,
+                         MarkerTiming::Interval(mStartTime, mStopTime),
+                         profilerLabelString);
+  }
+
+  nsresult rv = mLoader->ProcessOffThreadRequest(mRequest);
+
+  mRequest = nullptr;
+  mLoader = nullptr;
+  return rv;
+}
+
+nsresult ScriptLoader::ProcessOffThreadRequest(ScriptLoadRequest* aRequest) {
+  MOZ_ASSERT(aRequest->IsCompiling());
+  MOZ_ASSERT(!aRequest->GetScriptLoadContext()->mWasCompiledOMT);
+
+  if (aRequest->IsCanceled()) {
+    return NS_OK;
+  }
+
+  aRequest->GetScriptLoadContext()->mWasCompiledOMT = true;
+
+  if (aRequest->GetScriptLoadContext()->mInCompilingList) {
+    mOffThreadCompilingRequests.Remove(aRequest);
+    aRequest->GetScriptLoadContext()->mInCompilingList = false;
+  }
+
+  if (aRequest->IsModuleRequest()) {
+    MOZ_ASSERT(aRequest->GetScriptLoadContext()->mOffThreadToken);
+    ModuleLoadRequest* request = aRequest->AsModuleRequest();
+    return request->OnFetchComplete(NS_OK);
+  }
+
+  // Element may not be ready yet if speculatively compiling, so process the
+  // request in ProcessPendingRequests when it is available.
+  MOZ_ASSERT_IF(!SpeculativeOMTParsingEnabled(),
+                aRequest->GetScriptLoadContext()->GetScriptElement());
+  if (!aRequest->GetScriptLoadContext()->GetScriptElement()) {
+    // Unblock onload here in case this request never gets executed.
+    aRequest->GetScriptLoadContext()->MaybeUnblockOnload();
+    return NS_OK;
+  }
+
+  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);
+    ContinueParserAsync(aRequest);
+    return NS_OK;
+  }
+
+  // Async scripts and blocking scripts can be executed right away.
+  if ((aRequest->GetScriptLoadContext()->IsAsyncScript() ||
+       aRequest->GetScriptLoadContext()->IsBlockingScript()) &&
+      !aRequest->isInList()) {
+    return ProcessRequest(aRequest);
+  }
+
+  // Process other scripts in the proper order.
+  ProcessPendingRequests();
+  return NS_OK;
+}
+
+nsresult ScriptLoader::ProcessRequest(ScriptLoadRequest* aRequest) {
+  LOG(("ScriptLoadRequest (%p): Process request", 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);
+
+  auto unblockOnload = MakeScopeExit(
+      [&] { aRequest->GetScriptLoadContext()->MaybeUnblockOnload(); });
+
+  if (aRequest->IsModuleRequest()) {
+    ModuleLoadRequest* request = aRequest->AsModuleRequest();
+    if (request->IsDynamicImport()) {
+      request->ProcessDynamicImport();
+      return NS_OK;
+    }
+
+    if (request->mModuleScript) {
+      if (!request->InstantiateModuleGraph()) {
+        request->mModuleScript = nullptr;
+      }
+    }
+
+    if (!request->mModuleScript) {
+      // There was an error fetching a module script.  Nothing to do here.
+      LOG(("ScriptLoadRequest (%p):   Error loading request, firing error",
+           aRequest));
+      FireScriptAvailable(NS_ERROR_FAILURE, aRequest);
+      return NS_OK;
+    }
+  }
+
+  nsCOMPtr<nsINode> scriptElem =
+      do_QueryInterface(aRequest->GetScriptLoadContext()->GetScriptElement());
+
+  nsCOMPtr<Document> doc;
+  if (!aRequest->GetScriptLoadContext()->mIsInline ||
+      aRequest->IsModuleRequest()) {
+    doc = scriptElem->OwnerDoc();
+  }
+
+  nsCOMPtr<nsIScriptElement> oldParserInsertedScript;
+  uint32_t parserCreated = aRequest->GetScriptLoadContext()->GetParserCreated();
+  if (parserCreated) {
+    oldParserInsertedScript = mCurrentParserInsertedScript;
+    mCurrentParserInsertedScript =
+        aRequest->GetScriptLoadContext()->GetScriptElement();
+  }
+
+  aRequest->GetScriptLoadContext()->GetScriptElement()->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.
+
+  {
+    // Try to perform a microtask checkpoint
+    nsAutoMicroTask mt;
+  }
+
+  nsPIDOMWindowInner* pwin = mDocument->GetInnerWindow();
+  bool runScript = !!pwin;
+  if (runScript) {
+    nsContentUtils::DispatchTrustedEvent(
+        scriptElem->OwnerDoc(), scriptElem, u"beforescriptexecute"_ns,
+        CanBubble::eYes, Cancelable::eYes, &runScript);
+  }
+
+  // Inner window could have gone away after firing beforescriptexecute
+  pwin = mDocument->GetInnerWindow();
+  if (!pwin) {
+    runScript = false;
+  }
+
+  nsresult rv = NS_OK;
+  if (runScript) {
+    if (doc) {
+      doc->IncrementIgnoreDestructiveWritesCounter();
+    }
+    rv = EvaluateScriptElement(aRequest);
+    if (doc) {
+      doc->DecrementIgnoreDestructiveWritesCounter();
+    }
+
+    nsContentUtils::DispatchTrustedEvent(scriptElem->OwnerDoc(), scriptElem,
+                                         u"afterscriptexecute"_ns,
+                                         CanBubble::eYes, Cancelable::eNo);
+  }
+
+  FireScriptEvaluated(rv, aRequest);
+
+  aRequest->GetScriptLoadContext()->GetScriptElement()->EndEvaluating();
+
+  if (parserCreated) {
+    mCurrentParserInsertedScript = oldParserInsertedScript;
+  }
+
+  if (aRequest->GetScriptLoadContext()->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->GetScriptLoadContext()->MaybeCancelOffThreadScript();
+  }
+
+  // Free any source data, but keep the bytecode content as we might have to
+  // save it later.
+  aRequest->ClearScriptSource();
+  if (aRequest->IsBytecode()) {
+    // We received bytecode as input, thus we were decoding, and we will not be
+    // encoding the bytecode once more. We can safely clear the content of this
+    // buffer.
+    aRequest->mScriptBytecode.clearAndFree();
+  }
+
+  return rv;
+}
+
+void ScriptLoader::FireScriptAvailable(nsresult aResult,
+                                       ScriptLoadRequest* aRequest) {
+  for (int32_t i = 0; i < mObservers.Count(); i++) {
+    nsCOMPtr<nsIScriptLoaderObserver> obs = mObservers[i];
+    obs->ScriptAvailable(
+        aResult, aRequest->GetScriptLoadContext()->GetScriptElement(),
+        aRequest->GetScriptLoadContext()->mIsInline, aRequest->mURI,
+        aRequest->GetScriptLoadContext()->mLineNo);
+  }
+
+  bool isInlineClassicScript = aRequest->GetScriptLoadContext()->mIsInline &&
+                               !aRequest->IsModuleRequest();
+  RefPtr<nsIScriptElement> scriptElement =
+      aRequest->GetScriptLoadContext()->GetScriptElement();
+  scriptElement->ScriptAvailable(aResult, scriptElement, isInlineClassicScript,
+                                 aRequest->mURI,
+                                 aRequest->GetScriptLoadContext()->mLineNo);
+}
+
+// TODO: Convert this to MOZ_CAN_RUN_SCRIPT (bug 1415230)
+MOZ_CAN_RUN_SCRIPT_BOUNDARY void ScriptLoader::FireScriptEvaluated(
+    nsresult aResult, ScriptLoadRequest* aRequest) {
+  for (int32_t i = 0; i < mObservers.Count(); i++) {
+    nsCOMPtr<nsIScriptLoaderObserver> obs = mObservers[i];
+    RefPtr<nsIScriptElement> scriptElement =
+        aRequest->GetScriptLoadContext()->GetScriptElement();
+    obs->ScriptEvaluated(aResult, scriptElement,
+                         aRequest->GetScriptLoadContext()->mIsInline);
+  }
+
+  RefPtr<nsIScriptElement> scriptElement =
+      aRequest->GetScriptLoadContext()->GetScriptElement();
+  scriptElement->ScriptEvaluated(aResult, scriptElement,
+                                 aRequest->GetScriptLoadContext()->mIsInline);
+}
+
+already_AddRefed<nsIGlobalObject> ScriptLoader::GetGlobalForRequest(
+    ScriptLoadRequest* aRequest) {
+  if (aRequest->IsModuleRequest()) {
+    ModuleLoader* loader =
+        ModuleLoader::From(aRequest->AsModuleRequest()->mLoader);
+    nsCOMPtr<nsIGlobalObject> global = loader->GetGlobalObject();
+    return global.forget();
+  }
+
+  return GetScriptGlobalObject();
+}
+
+already_AddRefed<nsIScriptGlobalObject> ScriptLoader::GetScriptGlobalObject() {
+  if (!mDocument) {
+    return nullptr;
+  }
+
+  nsPIDOMWindowInner* pwin = mDocument->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 ScriptLoader::FillCompileOptionsForRequest(
+    JSContext* aCx, ScriptLoadRequest* aRequest, JS::CompileOptions* aOptions,
+    JS::MutableHandle<JSScript*> aIntroductionScript) {
+  // 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 = aRequest->mURI->GetSpec(aRequest->mURL);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (mDocument) {
+    mDocument->NoteScriptTrackingStatus(
+        aRequest->mURL, aRequest->GetScriptLoadContext()->IsTracking());
+  }
+
+  const char* introductionType;
+  if (aRequest->IsModuleRequest() &&
+      !aRequest->AsModuleRequest()->IsTopLevel()) {
+    introductionType = "importedModule";
+  } else if (!aRequest->GetScriptLoadContext()->mIsInline) {
+    introductionType = "srcScript";
+  } else if (aRequest->GetScriptLoadContext()->GetParserCreated() ==
+             FROM_PARSER_NETWORK) {
+    introductionType = "inlineScript";
+  } else {
+    introductionType = "injectedScript";
+  }
+  aOptions->setIntroductionInfoToCaller(aCx, introductionType,
+                                        aIntroductionScript);
+  aOptions->setFileAndLine(aRequest->mURL.get(),
+                           aRequest->GetScriptLoadContext()->mLineNo);
+  // The column is only relevant for inline scripts in order for SpiderMonkey to
+  // properly compute offsets relatively to the script position within the HTML
+  // file. injectedScript are not concerned and are always considered to start
+  // at column 0.
+  if (aRequest->GetScriptLoadContext()->mIsInline &&
+      aRequest->GetScriptLoadContext()->GetParserCreated() ==
+          FROM_PARSER_NETWORK) {
+    aOptions->setColumn(aRequest->GetScriptLoadContext()->mColumnNo);
+  }
+  aOptions->setIsRunOnce(true);
+  aOptions->setNoScriptRval(true);
+  if (aRequest->mSourceMapURL) {
+    aOptions->setSourceMapURL(aRequest->mSourceMapURL->get());
+  }
+  if (aRequest->mOriginPrincipal) {
+    nsCOMPtr<nsIGlobalObject> globalObject = GetGlobalForRequest(aRequest);
+    nsIPrincipal* scriptPrin = globalObject->PrincipalOrNull();
+    MOZ_ASSERT(scriptPrin);
+    bool subsumes = scriptPrin->Subsumes(aRequest->mOriginPrincipal);
+    aOptions->setMutedErrors(!subsumes);
+  }
+
+  if (aRequest->IsModuleRequest()) {
+    aOptions->setHideScriptFromDebugger(true);
+  }
+
+  aOptions->setDeferDebugMetadata(true);
+
+  aOptions->borrowBuffer = true;
+
+  aOptions->allocateInstantiationStorage = true;
+
+  return NS_OK;
+}
+
+/* static */
+bool ScriptLoader::ShouldCacheBytecode(ScriptLoadRequest* aRequest) {
+  using mozilla::TimeDuration;
+  using mozilla::TimeStamp;
+
+  // We need the nsICacheInfoChannel to exist to be able to open the alternate
+  // data output stream. This pointer would only be non-null if the bytecode was
+  // activated at the time the channel got created in StartLoad.
+  if (!aRequest->mCacheInfo) {
+    LOG(("ScriptLoadRequest (%p): Cannot cache anything (cacheInfo = %p)",
+         aRequest, aRequest->mCacheInfo.get()));
+    return false;
+  }
+
+  // Look at the preference to know which strategy (parameters) should be used
+  // when the bytecode cache is enabled.
+  int32_t strategy = StaticPrefs::dom_script_loader_bytecode_cache_strategy();
+
+  // List of parameters used by the strategies.
+  bool hasSourceLengthMin = false;
+  bool hasFetchCountMin = false;
+  size_t sourceLengthMin = 100;
+  uint32_t fetchCountMin = 4;
+
+  LOG(("ScriptLoadRequest (%p): Bytecode-cache: strategy = %d.", aRequest,
+       strategy));
+  switch (strategy) {
+    case -2: {
+      // Reader mode, keep requesting alternate data but no longer save it.
+      LOG(("ScriptLoadRequest (%p): Bytecode-cache: Encoding disabled.",
+           aRequest));
+      return false;
+    }
+    case -1: {
+      // Eager mode, skip heuristics!
+      hasSourceLengthMin = false;
+      hasFetchCountMin = false;
+      break;
+    }
+    default:
+    case 0: {
+      hasSourceLengthMin = true;
+      hasFetchCountMin = true;
+      sourceLengthMin = 1024;
+      // If we were to optimize only for speed, without considering the impact
+      // on memory, we should set this threshold to 2. (Bug 900784 comment 120)
+      fetchCountMin = 4;
+      break;
+    }
+  }
+
+  // If the script is too small/large, do not attempt at creating a bytecode
+  // cache for this script, as the overhead of parsing it might not be worth the
+  // effort.
+  if (hasSourceLengthMin) {
+    size_t sourceLength;
+    size_t minLength;
+    MOZ_ASSERT(aRequest->IsTextSource());
+    sourceLength = aRequest->mScriptTextLength;
+    minLength = sourceLengthMin;
+    if (sourceLength < minLength) {
+      LOG(("ScriptLoadRequest (%p): Bytecode-cache: Script is too small.",
+           aRequest));
+      return false;
+    }
+  }
+
+  // Check that we loaded the cache entry a few times before attempting any
+  // bytecode-cache optimization, such that we do not waste time on entry which
+  // are going to be dropped soon.
+  if (hasFetchCountMin) {
+    uint32_t fetchCount = 0;
+    if (NS_FAILED(aRequest->mCacheInfo->GetCacheTokenFetchCount(&fetchCount))) {
+      LOG(("ScriptLoadRequest (%p): Bytecode-cache: Cannot get fetchCount.",
+           aRequest));
+      return false;
+    }
+    LOG(("ScriptLoadRequest (%p): Bytecode-cache: fetchCount = %d.", aRequest,
+         fetchCount));
+    if (fetchCount < fetchCountMin) {
+      return false;
+    }
+  }
+
+  LOG(("ScriptLoadRequest (%p): Bytecode-cache: Trigger encoding.", aRequest));
+  return true;
+}
+
+class MOZ_RAII AutoSetProcessingScriptTag {
+  nsCOMPtr<nsIScriptContext> mContext;
+  bool mOldTag;
+
+ public:
+  explicit AutoSetProcessingScriptTag(nsIScriptContext* aContext)
+      : mContext(aContext), mOldTag(mContext->GetProcessingScriptTag()) {
+    mContext->SetProcessingScriptTag(true);
+  }
+
+  ~AutoSetProcessingScriptTag() { mContext->SetProcessingScriptTag(mOldTag); }
+};
+
+static nsresult ExecuteCompiledScript(JSContext* aCx, JSExecutionContext& aExec,
+                                      ClassicScript* aLoaderScript) {
+  JS::Rooted<JSScript*> script(aCx, aExec.GetScript());
+  if (!script) {
+    // Compilation succeeds without producing a script if scripting is
+    // disabled for the global.
+    return NS_OK;
+  }
+
+  if (JS::GetScriptPrivate(script).isUndefined()) {
+    aLoaderScript->AssociateWithScript(script);
+  }
+
+  return aExec.ExecScript();
+}
+
+nsresult ScriptLoader::EvaluateScriptElement(ScriptLoadRequest* aRequest) {
+  using namespace mozilla::Telemetry;
+  MOZ_ASSERT(aRequest->IsReadyToRun());
+
+  // We need a document to evaluate scripts.
+  if (!mDocument) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsIContent> scriptContent(
+      do_QueryInterface(aRequest->GetScriptLoadContext()->GetScriptElement()));
+  MOZ_ASSERT(scriptContent);
+  Document* ownerDoc = scriptContent->OwnerDoc();
+  if (ownerDoc != mDocument) {
+    // Willful violation of HTML5 as of 2010-12-01
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsIGlobalObject> globalObject;
+  nsCOMPtr<nsIScriptContext> context;
+  if (!IsWebExtensionRequest(aRequest)) {
+    // Otherwise we have to ensure that there is a nsIScriptContext.
+    nsCOMPtr<nsIScriptGlobalObject> scriptGlobal = GetScriptGlobalObject();
+    if (!scriptGlobal) {
+      return NS_ERROR_FAILURE;
+    }
+
+    MOZ_ASSERT_IF(
+        aRequest->IsModuleRequest(),
+        aRequest->AsModuleRequest()->GetGlobalObject() == scriptGlobal);
+
+    // 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.
+    context = scriptGlobal->GetScriptContext();
+    if (!context) {
+      return NS_ERROR_FAILURE;
+    }
+
+    globalObject = scriptGlobal;
+  }
+
+  // Update our current script.
+  // This must be destroyed after destroying nsAutoMicroTask, see:
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=1620505#c4
+  nsIScriptElement* currentScript =
+      aRequest->IsModuleRequest()
+          ? nullptr
+          : aRequest->GetScriptLoadContext()->GetScriptElement();
+  AutoCurrentScriptUpdater scriptUpdater(this, currentScript);
+
+  Maybe<AutoSetProcessingScriptTag> setProcessingScriptTag;
+  if (context) {
+    setProcessingScriptTag.emplace(context);
+  }
+
+  // https://wicg.github.io/import-maps/#integration-script-type
+  // Switch on the script's type for scriptElement:
+  // "importmap"
+  //    Assert: Never reached.
+  MOZ_ASSERT(!aRequest->IsImportMapRequest());
+
+  if (aRequest->IsModuleRequest()) {
+    return aRequest->AsModuleRequest()->EvaluateModule();
+  }
+
+  return EvaluateScript(globalObject, aRequest);
+}
+
+nsresult ScriptLoader::CompileOrDecodeClassicScript(
+    JSContext* aCx, JSExecutionContext& aExec, ScriptLoadRequest* aRequest) {
+  nsAutoCString profilerLabelString;
+  aRequest->GetScriptLoadContext()->GetProfilerLabel(profilerLabelString);
+
+  nsresult rv;
+  if (aRequest->IsBytecode()) {
+    if (aRequest->GetScriptLoadContext()->mOffThreadToken) {
+      LOG(("ScriptLoadRequest (%p): Decode Bytecode & Join and Execute",
+           aRequest));
+      rv = aExec.JoinOffThread(
+          &aRequest->GetScriptLoadContext()->mOffThreadToken);
+    } else {
+      LOG(("ScriptLoadRequest (%p): Decode Bytecode and Execute", aRequest));
+      AUTO_PROFILER_MARKER_TEXT("BytecodeDecodeMainThread", JS,
+                                MarkerInnerWindowIdFromJSContext(aCx),
+                                profilerLabelString);
+
+      rv = aExec.Decode(aRequest->mScriptBytecode, aRequest->mBytecodeOffset);
+    }
+
+    // We do not expect to be saving anything when we already have some
+    // bytecode.
+    MOZ_ASSERT(!aRequest->mCacheInfo);
+    return rv;
+  }
+
+  MOZ_ASSERT(aRequest->IsSource());
+  bool encodeBytecode = ShouldCacheBytecode(aRequest);
+  aExec.SetEncodeBytecode(encodeBytecode);
+
+  if (aRequest->GetScriptLoadContext()->mOffThreadToken) {
+    // Off-main-thread parsing.
+    LOG(
+        ("ScriptLoadRequest (%p): Join (off-thread parsing) and "
+         "Execute",
+         aRequest));
+    MOZ_ASSERT(aRequest->IsTextSource());
+    rv =
+        aExec.JoinOffThread(&aRequest->GetScriptLoadContext()->mOffThreadToken);
+  } else {
+    // Main thread parsing (inline and small scripts)
+    LOG(("ScriptLoadRequest (%p): Compile And Exec", aRequest));
+    MOZ_ASSERT(aRequest->IsTextSource());
+    MaybeSourceText maybeSource;
+    rv = aRequest->GetScriptSource(aCx, &maybeSource);
+    if (NS_SUCCEEDED(rv)) {
+      AUTO_PROFILER_MARKER_TEXT("ScriptCompileMainThread", JS,
+                                MarkerInnerWindowIdFromJSContext(aCx),
+                                profilerLabelString);
+
+      auto compile = [&](auto& source) { return aExec.Compile(source); };
+
+      MOZ_ASSERT(!maybeSource.empty());
+      TimeStamp startTime = TimeStamp::Now();
+      rv = maybeSource.mapNonEmpty(compile);
+      mMainThreadParseTime += TimeStamp::Now() - startTime;
+    }
+  }
+  return rv;
+}
+
+/* static */
+nsCString& ScriptLoader::BytecodeMimeTypeFor(ScriptLoadRequest* aRequest) {
+  if (aRequest->IsModuleRequest()) {
+    return nsContentUtils::JSModuleBytecodeMimeType();
+  }
+  return nsContentUtils::JSScriptBytecodeMimeType();
+}
+
+void ScriptLoader::MaybePrepareForBytecodeEncodingBeforeExecute(
+    ScriptLoadRequest* aRequest, JS::Handle<JSScript*> aScript) {
+  if (!ShouldCacheBytecode(aRequest)) {
+    return;
+  }
+
+  aRequest->MarkForBytecodeEncoding(aScript);
+}
+
+nsresult ScriptLoader::MaybePrepareForBytecodeEncodingAfterExecute(
+    ScriptLoadRequest* aRequest, nsresult aRv) {
+  if (aRequest->IsMarkedForBytecodeEncoding()) {
+    TRACE_FOR_TEST(aRequest->GetScriptLoadContext()->GetScriptElement(),
+                   "scriptloader_encode");
+    // NOTE: This assertion will fail once we start encoding more data after the
+    //       first encode.
+    MOZ_ASSERT(aRequest->mBytecodeOffset == aRequest->mScriptBytecode.length());
+    RegisterForBytecodeEncoding(aRequest);
+    MOZ_ASSERT(IsAlreadyHandledForBytecodeEncodingPreparation(aRequest));
+
+    return aRv;
+  }
+
+  LOG(("ScriptLoadRequest (%p): Bytecode-cache: disabled (rv = %X)", aRequest,
+       unsigned(aRv)));
+  TRACE_FOR_TEST_NONE(aRequest->GetScriptLoadContext()->GetScriptElement(),
+                      "scriptloader_no_encode");
+  aRequest->mCacheInfo = nullptr;
+  MOZ_ASSERT(IsAlreadyHandledForBytecodeEncodingPreparation(aRequest));
+
+  return aRv;
+}
+
+bool ScriptLoader::IsAlreadyHandledForBytecodeEncodingPreparation(
+    ScriptLoadRequest* aRequest) {
+  return aRequest->isInList() || !aRequest->mCacheInfo;
+}
+
+void ScriptLoader::MaybePrepareModuleForBytecodeEncodingBeforeExecute(
+    JSContext* aCx, ModuleLoadRequest* aRequest) {
+  {
+    ModuleScript* moduleScript = aRequest->mModuleScript;
+    JS::Rooted<JSObject*> module(aCx, moduleScript->ModuleRecord());
+
+    if (aRequest->IsMarkedForBytecodeEncoding()) {
+      // This module is imported multiple times, and already marked.
+      return;
+    }
+
+    if (ShouldCacheBytecode(aRequest)) {
+      aRequest->MarkModuleForBytecodeEncoding();
+    }
+  }
+
+  for (ModuleLoadRequest* childRequest : aRequest->mImports) {
+    MaybePrepareModuleForBytecodeEncodingBeforeExecute(aCx, childRequest);
+  }
+}
+
+nsresult ScriptLoader::MaybePrepareModuleForBytecodeEncodingAfterExecute(
+    ModuleLoadRequest* aRequest, nsresult aRv) {
+  if (IsAlreadyHandledForBytecodeEncodingPreparation(aRequest)) {
+    // This module is imported multiple times and already handled.
+    return aRv;
+  }
+
+  aRv = MaybePrepareForBytecodeEncodingAfterExecute(aRequest, aRv);
+
+  for (ModuleLoadRequest* childRequest : aRequest->mImports) {
+    aRv = MaybePrepareModuleForBytecodeEncodingAfterExecute(childRequest, aRv);
+  }
+
+  return aRv;
+}
+
+nsresult ScriptLoader::EvaluateScript(nsIGlobalObject* aGlobalObject,
+                                      ScriptLoadRequest* aRequest) {
+  nsAutoMicroTask mt;
+  AutoEntryScript aes(aGlobalObject, "EvaluateScript", true);
+  JSContext* cx = aes.cx();
+
+  nsAutoCString profilerLabelString;
+  aRequest->GetScriptLoadContext()->GetProfilerLabel(profilerLabelString);
+
+  // Create a ClassicScript object and associate it with the JSScript.
+  RefPtr<ClassicScript> classicScript =
+      new ClassicScript(aRequest->mFetchOptions, aRequest->mBaseURL);
+  JS::Rooted<JS::Value> classicScriptValue(cx, JS::PrivateValue(classicScript));
+
+  JS::CompileOptions options(cx);
+  JS::Rooted<JSScript*> introductionScript(cx);
+  nsresult rv =
+      FillCompileOptionsForRequest(cx, aRequest, &options, &introductionScript);
+
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  TRACE_FOR_TEST(aRequest->GetScriptLoadContext()->GetScriptElement(),
+                 "scriptloader_execute");
+  JS::Rooted<JSObject*> global(cx, aGlobalObject->GetGlobalJSObject());
+  JSExecutionContext exec(cx, global, options, classicScriptValue,
+                          introductionScript);
+
+  rv = CompileOrDecodeClassicScript(cx, exec, aRequest);
+
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // TODO (yulia): rewrite this section. rv can be a failing pattern other than
+  // NS_OK which will pass the NS_FAILED check above. If we call exec.GetScript
+  // in that case, it will crash.
+  if (rv == NS_OK) {
+    JS::Rooted<JSScript*> script(cx, exec.GetScript());
+    MaybePrepareForBytecodeEncodingBeforeExecute(aRequest, script);
+
+    {
+      LOG(("ScriptLoadRequest (%p): Evaluate Script", aRequest));
+      AUTO_PROFILER_MARKER_TEXT("ScriptExecution", JS,
+                                MarkerInnerWindowIdFromJSContext(cx),
+                                profilerLabelString);
+
+      rv = ExecuteCompiledScript(cx, exec, classicScript);
+    }
+  }
+
+  // This must be called also for compilation failure case, in order to
+  // dispatch test-only event.
+  rv = MaybePrepareForBytecodeEncodingAfterExecute(aRequest, rv);
+
+  // Even if we are not saving the bytecode of the current script, we have
+  // to trigger the encoding of the bytecode, as the current script can
+  // call functions of a script for which we are recording the bytecode.
+  LOG(("ScriptLoadRequest (%p): ScriptLoader = %p", aRequest, this));
+  MaybeTriggerBytecodeEncoding();
+
+  return rv;
+}
+
+/* static */
+LoadedScript* ScriptLoader::GetActiveScript(JSContext* aCx) {
+  JS::Value value = JS::GetScriptedCallerPrivate(aCx);
+  if (value.isUndefined()) {
+    return nullptr;
+  }
+
+  return static_cast<LoadedScript*>(value.toPrivate());
+}
+
+void ScriptLoader::RegisterForBytecodeEncoding(ScriptLoadRequest* aRequest) {
+  MOZ_ASSERT(aRequest->mCacheInfo);
+  MOZ_ASSERT(aRequest->IsMarkedForBytecodeEncoding());
+  MOZ_DIAGNOSTIC_ASSERT(!aRequest->isInList());
+  mBytecodeEncodingQueue.AppendElement(aRequest);
+}
+
+void ScriptLoader::LoadEventFired() {
+  mLoadEventFired = true;
+  MaybeTriggerBytecodeEncoding();
+
+  if (!mMainThreadParseTime.IsZero()) {
+    Telemetry::Accumulate(
+        Telemetry::JS_PAGELOAD_PARSE_MS,
+        static_cast<uint32_t>(mMainThreadParseTime.ToMilliseconds()));
+  }
+}
+
+void ScriptLoader::Destroy() {
+  if (mShutdownObserver) {
+    mShutdownObserver->Unregister();
+    mShutdownObserver = nullptr;
+  }
+
+  CancelAndClearScriptLoadRequests();
+  GiveUpBytecodeEncoding();
+}
+
+void ScriptLoader::MaybeTriggerBytecodeEncoding() {
+  // If we already gave up, ensure that we are not going to enqueue any script,
+  // and that we finalize them properly.
+  if (mGiveUpEncoding) {
+    LOG(("ScriptLoader (%p): Keep giving-up bytecode encoding.", this));
+    GiveUpBytecodeEncoding();
+    return;
+  }
+
+  // We wait for the load event to be fired before saving the bytecode of
+  // any script to the cache. It is quite common to have load event
+  // listeners trigger more JavaScript execution, that we want to save as
+  // part of this start-up bytecode cache.
+  if (!mLoadEventFired) {
+    LOG(("ScriptLoader (%p): Wait for the load-end event to fire.", this));
+    return;
+  }
+
+  // No need to fire any event if there is no bytecode to be saved.
+  if (mBytecodeEncodingQueue.isEmpty()) {
+    LOG(("ScriptLoader (%p): No script in queue to be encoded.", this));
+    return;
+  }
+
+  // Wait until all scripts are loaded before saving the bytecode, such that
+  // we capture most of the intialization of the page.
+  if (HasPendingRequests()) {
+    LOG(("ScriptLoader (%p): Wait for other pending request to finish.", this));
+    return;
+  }
+
+  // Create a new runnable dedicated to encoding the content of the bytecode of
+  // all enqueued scripts when the document is idle. In case of failure, we
+  // give-up on encoding the bytecode.
+  nsCOMPtr<nsIRunnable> encoder = NewRunnableMethod(
+      "ScriptLoader::EncodeBytecode", this, &ScriptLoader::EncodeBytecode);
+  if (NS_FAILED(NS_DispatchToCurrentThreadQueue(encoder.forget(),
+                                                EventQueuePriority::Idle))) {
+    GiveUpBytecodeEncoding();
+    return;
+  }
+
+  LOG(("ScriptLoader (%p): Schedule bytecode encoding.", this));
+}
+
+void ScriptLoader::EncodeBytecode() {
+  LOG(("ScriptLoader (%p): Start bytecode encoding.", this));
+
+  // If any script got added in the previous loop cycle, wait until all
+  // remaining script executions are completed, such that we capture most of
+  // the initialization.
+  if (HasPendingRequests()) {
+    return;
+  }
+
+  // Should not be encoding modules at all.
+  nsCOMPtr<nsIScriptGlobalObject> globalObject = GetScriptGlobalObject();
+  if (!globalObject) {
+    GiveUpBytecodeEncoding();
+    return;
+  }
+
+  nsCOMPtr<nsIScriptContext> context = globalObject->GetScriptContext();
+  if (!context) {
+    GiveUpBytecodeEncoding();
+    return;
+  }
+
+  AutoEntryScript aes(globalObject, "encode bytecode", true);
+  RefPtr<ScriptLoadRequest> request;
+  while (!mBytecodeEncodingQueue.isEmpty()) {
+    request = mBytecodeEncodingQueue.StealFirst();
+    MOZ_ASSERT(!IsWebExtensionRequest(request),
+               "Bytecode for web extension content scrips is not cached");
+    EncodeRequestBytecode(aes.cx(), request);
+    request->mScriptBytecode.clearAndFree();
+    request->DropBytecodeCacheReferences();
+  }
+}
+
+void ScriptLoader::EncodeRequestBytecode(JSContext* aCx,
+                                         ScriptLoadRequest* aRequest) {
+  using namespace mozilla::Telemetry;
+  nsresult rv = NS_OK;
+  MOZ_ASSERT(aRequest->mCacheInfo);
+  auto bytecodeFailed = mozilla::MakeScopeExit([&]() {
+    TRACE_FOR_TEST_NONE(aRequest->GetScriptLoadContext()->GetScriptElement(),
+                        "scriptloader_bytecode_failed");
+  });
+
+  bool result;
+  if (aRequest->IsModuleRequest()) {
+    ModuleScript* moduleScript = aRequest->AsModuleRequest()->mModuleScript;
+    JS::Rooted<JSObject*> module(aCx, moduleScript->ModuleRecord());
+    result =
+        JS::FinishIncrementalEncoding(aCx, module, aRequest->mScriptBytecode);
+  } else {
+    JS::Rooted<JSScript*> script(aCx, aRequest->mScriptForBytecodeEncoding);
+    result =
+        JS::FinishIncrementalEncoding(aCx, script, aRequest->mScriptBytecode);
+  }
+  if (!result) {
+    // Encoding can be aborted for non-supported syntax (e.g. asm.js), or
+    // any other internal error.
+    // We don't care the error and just give up encoding.
+    JS_ClearPendingException(aCx);
+
+    LOG(("ScriptLoadRequest (%p): Cannot serialize bytecode", aRequest));
+    return;
+  }
+
+  Vector<uint8_t> compressedBytecode;
+  // TODO probably need to move this to a helper thread
+  if (!ScriptBytecodeCompress(aRequest->mScriptBytecode,
+                              aRequest->mBytecodeOffset, compressedBytecode)) {
+    return;
+  }
+
+  if (compressedBytecode.length() >= UINT32_MAX) {
+    LOG(
+        ("ScriptLoadRequest (%p): Bytecode cache is too large to be decoded "
+         "correctly.",
+         aRequest));
+    return;
+  }
+
+  // Open the output stream to the cache entry alternate data storage. This
+  // might fail if the stream is already open by another request, in which
+  // case, we just ignore the current one.
+  nsCOMPtr<nsIAsyncOutputStream> output;
+  rv = aRequest->mCacheInfo->OpenAlternativeOutputStream(
+      BytecodeMimeTypeFor(aRequest),
+      static_cast<int64_t>(compressedBytecode.length()),
+      getter_AddRefs(output));
+  if (NS_FAILED(rv)) {
+    LOG(
+        ("ScriptLoadRequest (%p): Cannot open bytecode cache (rv = %X, output "
+         "= %p)",
+         aRequest, unsigned(rv), output.get()));
+    return;
+  }
+  MOZ_ASSERT(output);
+
+  auto closeOutStream = mozilla::MakeScopeExit([&]() {
+    rv = output->CloseWithStatus(rv);
+    LOG(("ScriptLoadRequest (%p): Closing (rv = %X)", aRequest, unsigned(rv)));
+  });
+
+  uint32_t n;
+  rv = output->Write(reinterpret_cast<char*>(compressedBytecode.begin()),
+                     compressedBytecode.length(), &n);
+  LOG(
+      ("ScriptLoadRequest (%p): Write bytecode cache (rv = %X, length = %u, "
+       "written = %u)",
+       aRequest, unsigned(rv), unsigned(compressedBytecode.length()), n));
+  if (NS_FAILED(rv)) {
+    return;
+  }
+
+  MOZ_RELEASE_ASSERT(compressedBytecode.length() == n);
+
+  bytecodeFailed.release();
+  TRACE_FOR_TEST_NONE(aRequest->GetScriptLoadContext()->GetScriptElement(),
+                      "scriptloader_bytecode_saved");
+}
+
+void ScriptLoader::GiveUpBytecodeEncoding() {
+  // If the document went away prematurely, we still want to set this, in order
+  // to avoid queuing more scripts.
+  mGiveUpEncoding = true;
+
+  // Ideally we prefer to properly end the incremental encoder, such that we
+  // would not keep a large buffer around.  If we cannot, we fallback on the
+  // removal of all request from the current list and these large buffers would
+  // be removed at the same time as the source object.
+  nsCOMPtr<nsIScriptGlobalObject> globalObject = GetScriptGlobalObject();
+  AutoAllowLegacyScriptExecution exemption;
+  Maybe<AutoEntryScript> aes;
+
+  if (globalObject) {
+    nsCOMPtr<nsIScriptContext> context = globalObject->GetScriptContext();
+    if (context) {
+      aes.emplace(globalObject, "give-up bytecode encoding", true);
+    }
+  }
+
+  while (!mBytecodeEncodingQueue.isEmpty()) {
+    RefPtr<ScriptLoadRequest> request = mBytecodeEncodingQueue.StealFirst();
+    LOG(("ScriptLoadRequest (%p): Cannot serialize bytecode", request.get()));
+    TRACE_FOR_TEST_NONE(request->GetScriptLoadContext()->GetScriptElement(),
+                        "scriptloader_bytecode_failed");
+    MOZ_ASSERT(!IsWebExtensionRequest(request));
+
+    if (aes.isSome()) {
+      if (request->IsModuleRequest()) {
+        ModuleScript* moduleScript = request->AsModuleRequest()->mModuleScript;
+        JS::Rooted<JSObject*> module(aes->cx(), moduleScript->ModuleRecord());
+        JS::AbortIncrementalEncoding(module);
+      } else {
+        JS::Rooted<JSScript*> script(aes->cx(),
+                                     request->mScriptForBytecodeEncoding);
+        JS::AbortIncrementalEncoding(script);
+      }
+    }
+
+    request->mScriptBytecode.clearAndFree();
+    request->DropBytecodeCacheReferences();
+  }
+}
+
+bool ScriptLoader::HasPendingRequests() const {
+  return mParserBlockingRequest || !mXSLTRequests.isEmpty() ||
+         !mLoadedAsyncRequests.isEmpty() ||
+         !mNonAsyncExternalScriptInsertedRequests.isEmpty() ||
+         !mDeferRequests.isEmpty() || HasPendingDynamicImports() ||
+         !mPendingChildLoaders.IsEmpty();
+  // mOffThreadCompilingRequests are already being processed.
+}
+
+bool ScriptLoader::HasPendingDynamicImports() const {
+  if (mModuleLoader && mModuleLoader->HasPendingDynamicImports()) {
+    return true;
+  }
+
+  for (ModuleLoader* loader : mWebExtModuleLoaders) {
+    if (loader->HasPendingDynamicImports()) {
+      return true;
+    }
+  }
+
+  for (ModuleLoader* loader : mShadowRealmModuleLoaders) {
+    if (loader->HasPendingDynamicImports()) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+void ScriptLoader::ProcessPendingRequestsAsync() {
+  if (HasPendingRequests()) {
+    nsCOMPtr<nsIRunnable> task =
+        NewRunnableMethod("dom::ScriptLoader::ProcessPendingRequests", this,
+                          &ScriptLoader::ProcessPendingRequests);
+    if (mDocument) {
+      mDocument->Dispatch(TaskCategory::Other, task.forget());
+    } else {
+      NS_DispatchToCurrentThread(task.forget());
+    }
+  }
+}
+
+void ScriptLoader::ProcessPendingRequests() {
+  RefPtr<ScriptLoadRequest> request;
+
+  if (mParserBlockingRequest && mParserBlockingRequest->IsReadyToRun() &&
+      ReadyToExecuteParserBlockingScripts()) {
+    request.swap(mParserBlockingRequest);
+    UnblockParser(request);
+    ProcessRequest(request);
+    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 (mDeferCheckpointReached && mXSLTRequests.isEmpty()) {
+    while (ReadyToExecuteScripts() && !mDeferRequests.isEmpty() &&
+           mDeferRequests.getFirst()->IsReadyToRun()) {
+      request = mDeferRequests.StealFirst();
+      ProcessRequest(request);
+    }
+  }
+
+  while (!mPendingChildLoaders.IsEmpty() &&
+         ReadyToExecuteParserBlockingScripts()) {
+    RefPtr<ScriptLoader> child = mPendingChildLoaders[0];
+    mPendingChildLoaders.RemoveElementAt(0);
+    child->RemoveParserBlockingScriptExecutionBlocker();
+  }
+
+  if (mDeferCheckpointReached && mDocument && !mParserBlockingRequest &&
+      mNonAsyncExternalScriptInsertedRequests.isEmpty() &&
+      mXSLTRequests.isEmpty() && mDeferRequests.isEmpty() &&
+      MaybeRemovedDeferRequests()) {
+    return ProcessPendingRequests();
+  }
+
+  if (mDeferCheckpointReached && 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.
+    mDeferCheckpointReached = false;
+    mDocument->UnblockOnload(true);
+  }
+}
+
+bool ScriptLoader::ReadyToExecuteParserBlockingScripts() {
+  // Make sure the SelfReadyToExecuteParserBlockingScripts check is first, so
+  // that we don't block twice on an ancestor.
+  if (!SelfReadyToExecuteParserBlockingScripts()) {
+    return false;
+  }
+
+  if (mDocument && mDocument->GetWindowContext()) {
+    for (WindowContext* wc =
+             mDocument->GetWindowContext()->GetParentWindowContext();
+         wc; wc = wc->GetParentWindowContext()) {
+      if (Document* doc = wc->GetDocument()) {
+        ScriptLoader* ancestor = doc->ScriptLoader();
+        if (!ancestor->SelfReadyToExecuteParserBlockingScripts() &&
+            ancestor->AddPendingChildLoader(this)) {
+          AddParserBlockingScriptExecutionBlocker();
+          return false;
+        }
+      }
+    }
+  }
+
+  return true;
+}
+
+template <typename Unit>
+static nsresult ConvertToUnicode(nsIChannel* aChannel, const uint8_t* aData,
+                                 uint32_t aLength,
+                                 const nsAString& aHintCharset,
+                                 Document* aDocument, Unit*& aBufOut,
+                                 size_t& aLengthOut) {
+  if (!aLength) {
+    aBufOut = nullptr;
+    aLengthOut = 0;
+    return NS_OK;
+  }
+
+  auto data = Span(aData, aLength);
+
+  // 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
+
+  UniquePtr<Decoder> unicodeDecoder;
+
+  const Encoding* encoding;
+  std::tie(encoding, std::ignore) = Encoding::ForBOM(data);
+  if (encoding) {
+    unicodeDecoder = encoding->NewDecoderWithBOMRemoval();
+  }
+
+  if (!unicodeDecoder && aChannel) {
+    nsAutoCString label;
+    if (NS_SUCCEEDED(aChannel->GetContentCharset(label)) &&
+        (encoding = Encoding::ForLabel(label))) {
+      unicodeDecoder = encoding->NewDecoderWithoutBOMHandling();
+    }
+  }
+
+  if (!unicodeDecoder && (encoding = Encoding::ForLabel(aHintCharset))) {
+    unicodeDecoder = encoding->NewDecoderWithoutBOMHandling();
+  }
+
+  if (!unicodeDecoder && aDocument) {
+    unicodeDecoder =
+        aDocument->GetDocumentCharacterSet()->NewDecoderWithoutBOMHandling();
+  }
+
+  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.
+    unicodeDecoder = WINDOWS_1252_ENCODING->NewDecoderWithoutBOMHandling();
+  }
+
+  auto signalOOM = mozilla::MakeScopeExit([&aBufOut, &aLengthOut]() {
+    aBufOut = nullptr;
+    aLengthOut = 0;
+  });
+
+  CheckedInt<size_t> bufferLength =
+      ScriptDecoding<Unit>::MaxBufferLength(unicodeDecoder, aLength);
+  if (!bufferLength.isValid()) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  CheckedInt<size_t> bufferByteSize = bufferLength * sizeof(Unit);
+  if (!bufferByteSize.isValid()) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  aBufOut = static_cast<Unit*>(js_malloc(bufferByteSize.value()));
+  if (!aBufOut) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  signalOOM.release();
+  aLengthOut = ScriptDecoding<Unit>::DecodeInto(
+      unicodeDecoder, data, Span(aBufOut, bufferLength.value()),
+      /* aEndOfSource = */ true);
+  return NS_OK;
+}
+
+/* static */
+nsresult ScriptLoader::ConvertToUTF16(nsIChannel* aChannel,
+                                      const uint8_t* aData, uint32_t aLength,
+                                      const nsAString& aHintCharset,
+                                      Document* aDocument, char16_t*& aBufOut,
+                                      size_t& aLengthOut) {
+  return ConvertToUnicode(aChannel, aData, aLength, aHintCharset, aDocument,
+                          aBufOut, aLengthOut);
+}
+
+/* static */
+nsresult ScriptLoader::ConvertToUTF8(nsIChannel* aChannel, const uint8_t* aData,
+                                     uint32_t aLength,
+                                     const nsAString& aHintCharset,
+                                     Document* aDocument, Utf8Unit*& aBufOut,
+                                     size_t& aLengthOut) {
+  return ConvertToUnicode(aChannel, aData, aLength, aHintCharset, aDocument,
+                          aBufOut, aLengthOut);
+}
+
+nsresult ScriptLoader::OnStreamComplete(
+    nsIIncrementalStreamLoader* aLoader, ScriptLoadRequest* aRequest,
+    nsresult aChannelStatus, nsresult aSRIStatus,
+    SRICheckDataVerifier* aSRIDataVerifier) {
+  NS_ASSERTION(aRequest, "null request in stream complete handler");
+  NS_ENSURE_TRUE(aRequest, NS_ERROR_FAILURE);
+
+  nsresult rv = VerifySRI(aRequest, aLoader, aSRIStatus, aSRIDataVerifier);
+
+  if (NS_SUCCEEDED(rv)) {
+    // If we are loading from source, save the computed SRI hash or a dummy SRI
+    // hash in case we are going to save the bytecode of this script in the
+    // cache.
+    if (aRequest->IsSource()) {
+      uint32_t sriLength = 0;
+      rv = SaveSRIHash(aRequest, aSRIDataVerifier, &sriLength);
+      MOZ_ASSERT_IF(NS_SUCCEEDED(rv),
+                    aRequest->mScriptBytecode.length() == sriLength);
+
+      aRequest->mBytecodeOffset = JS::AlignTranscodingBytecodeOffset(sriLength);
+      if (aRequest->mBytecodeOffset != sriLength) {
+        // We need extra padding after SRI hash.
+        if (!aRequest->mScriptBytecode.resize(aRequest->mBytecodeOffset)) {
+          return NS_ERROR_OUT_OF_MEMORY;
+        }
+      }
+    }
+
+    if (NS_SUCCEEDED(rv)) {
+      rv = PrepareLoadedRequest(aRequest, aLoader, aChannelStatus);
+    }
+
+    if (NS_FAILED(rv)) {
+      ReportErrorToConsole(aRequest, rv);
+    }
+  }
+
+  if (NS_FAILED(rv)) {
+    // When loading bytecode, we verify the SRI hash. If it does not match the
+    // one from the document we restart the load, forcing us to load the source
+    // instead. If this happens do not remove the current request from script
+    // loader's data structures or fire any events.
+    if (aChannelStatus != NS_BINDING_RETARGETED) {
+      HandleLoadError(aRequest, rv);
+    }
+  }
+
+  // Process our request and/or any pending ones
+  ProcessPendingRequests();
+
+  return rv;
+}
+
+nsresult ScriptLoader::VerifySRI(ScriptLoadRequest* aRequest,
+                                 nsIIncrementalStreamLoader* aLoader,
+                                 nsresult aSRIStatus,
+                                 SRICheckDataVerifier* aSRIDataVerifier) const {
+  nsCOMPtr<nsIRequest> channelRequest;
+  aLoader->GetRequest(getter_AddRefs(channelRequest));
+  nsCOMPtr<nsIChannel> channel;
+  channel = do_QueryInterface(channelRequest);
+
+  nsresult rv = NS_OK;
+  if (!aRequest->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(aRequest->mIntegrity, channel, sourceUri,
+                                  mReporter);
+    if (channelRequest) {
+      mReporter->FlushReportsToConsole(
+          nsContentUtils::GetInnerWindowID(channelRequest));
+    } else {
+      mReporter->FlushConsoleReports(mDocument);
+    }
+    if (NS_FAILED(rv)) {
+      rv = NS_ERROR_SRI_CORRUPT;
+    }
+  }
+
+  return rv;
+}
+
+nsresult ScriptLoader::SaveSRIHash(ScriptLoadRequest* aRequest,
+                                   SRICheckDataVerifier* aSRIDataVerifier,
+                                   uint32_t* sriLength) const {
+  MOZ_ASSERT(aRequest->IsSource());
+  MOZ_ASSERT(aRequest->mScriptBytecode.empty());
+
+  uint32_t len;
+
+  // If the integrity metadata does not correspond to a valid hash function,
+  // IsComplete would be false.
+  if (!aRequest->mIntegrity.IsEmpty() && aSRIDataVerifier->IsComplete()) {
+    MOZ_ASSERT(aRequest->mScriptBytecode.length() == 0);
+
+    // Encode the SRI computed hash.
+    len = aSRIDataVerifier->DataSummaryLength();
+
+    if (!aRequest->mScriptBytecode.resize(len)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    DebugOnly<nsresult> res = aSRIDataVerifier->ExportDataSummary(
+        len, aRequest->mScriptBytecode.begin());
+    MOZ_ASSERT(NS_SUCCEEDED(res));
+  } else {
+    MOZ_ASSERT(aRequest->mScriptBytecode.length() == 0);
+
+    // Encode a dummy SRI hash.
+    len = SRICheckDataVerifier::EmptyDataSummaryLength();
+
+    if (!aRequest->mScriptBytecode.resize(len)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    DebugOnly<nsresult> res = SRICheckDataVerifier::ExportEmptyDataSummary(
+        len, aRequest->mScriptBytecode.begin());
+    MOZ_ASSERT(NS_SUCCEEDED(res));
+  }
+
+  // Verify that the exported and predicted length correspond.
+  DebugOnly<uint32_t> srilen{};
+  MOZ_ASSERT(NS_SUCCEEDED(SRICheckDataVerifier::DataSummaryLength(
+      len, aRequest->mScriptBytecode.begin(), &srilen)));
+  MOZ_ASSERT(srilen == len);
+
+  *sriLength = len;
+
+  return NS_OK;
+}
+
+void ScriptLoader::ReportErrorToConsole(ScriptLoadRequest* aRequest,
+                                        nsresult aResult) const {
+  MOZ_ASSERT(aRequest);
+
+  if (aRequest->GetScriptLoadContext()->IsPreload()) {
+    // Skip reporting errors in preload requests. If the request is actually
+    // used then we will report the error in ReportPreloadErrorsToConsole below.
+    aRequest->GetScriptLoadContext()->mUnreportedPreloadError = aResult;
+    return;
+  }
+
+  bool isScript = !aRequest->IsModuleRequest();
+  const char* message;
+  if (aResult == NS_ERROR_MALFORMED_URI) {
+    message = isScript ? "ScriptSourceMalformed" : "ModuleSourceMalformed";
+  } else if (aResult == NS_ERROR_DOM_BAD_URI) {
+    message = isScript ? "ScriptSourceNotAllowed" : "ModuleSourceNotAllowed";
+  } else if (aResult == NS_ERROR_DOM_WEBEXT_CONTENT_SCRIPT_URI) {
+    MOZ_ASSERT(!isScript);
+    message = "WebExtContentScriptModuleSourceNotAllowed";
+  } else if (net::UrlClassifierFeatureFactory::IsClassifierBlockingErrorCode(
+                 aResult)) {
+    // Blocking classifier error codes already show their own console messages.
+    return;
+  } else {
+    message = isScript ? "ScriptSourceLoadFailed" : "ModuleSourceLoadFailed";
+  }
+
+  AutoTArray<nsString, 1> params;
+  CopyUTF8toUTF16(aRequest->mURI->GetSpecOrDefault(), *params.AppendElement());
+
+  nsIScriptElement* element =
+      aRequest->GetScriptLoadContext()->GetScriptElement();
+  uint32_t lineNo = element ? element->GetScriptLineNumber() : 0;
+  uint32_t columnNo = element ? element->GetScriptColumnNumber() : 0;
+
+  nsContentUtils::ReportToConsole(nsIScriptError::warningFlag,
+                                  "Script Loader"_ns, mDocument,
+                                  nsContentUtils::eDOM_PROPERTIES, message,
+                                  params, nullptr, u""_ns, lineNo, columnNo);
+}
+
+void ScriptLoader::ReportWarningToConsole(
+    ScriptLoadRequest* aRequest, const char* aMessageName,
+    const nsTArray<nsString>& aParams) const {
+  nsIScriptElement* element =
+      aRequest->GetScriptLoadContext()->GetScriptElement();
+  uint32_t lineNo = element ? element->GetScriptLineNumber() : 0;
+  uint32_t columnNo = element ? element->GetScriptColumnNumber() : 0;
+  nsContentUtils::ReportToConsole(nsIScriptError::warningFlag,
+                                  "Script Loader"_ns, mDocument,
+                                  nsContentUtils::eDOM_PROPERTIES, aMessageName,
+                                  aParams, nullptr, u""_ns, lineNo, columnNo);
+}
+
+void ScriptLoader::ReportPreloadErrorsToConsole(ScriptLoadRequest* aRequest) {
+  if (NS_FAILED(aRequest->GetScriptLoadContext()->mUnreportedPreloadError)) {
+    ReportErrorToConsole(
+        aRequest, aRequest->GetScriptLoadContext()->mUnreportedPreloadError);
+    aRequest->GetScriptLoadContext()->mUnreportedPreloadError = NS_OK;
+  }
+
+  if (aRequest->IsModuleRequest()) {
+    for (const auto& childRequest : aRequest->AsModuleRequest()->mImports) {
+      ReportPreloadErrorsToConsole(childRequest);
+    }
+  }
+}
+
+void ScriptLoader::HandleLoadError(ScriptLoadRequest* aRequest,
+                                   nsresult aResult) {
+  /*
+   * Handle script not loading error because source was an tracking URL (or
+   * fingerprinting, cryptomining, etc).
+   * We make a note of this script node by including it in a dedicated
+   * array of blocked tracking nodes under its parent document.
+   */
+  if (net::UrlClassifierFeatureFactory::IsClassifierBlockingErrorCode(
+          aResult)) {
+    nsCOMPtr<nsIContent> cont =
+        do_QueryInterface(aRequest->GetScriptLoadContext()->GetScriptElement());
+    mDocument->AddBlockedNodeByClassifier(cont);
+  }
+
+  if (aRequest->IsModuleRequest()) {
+    MOZ_ASSERT(!aRequest->GetScriptLoadContext()->mIsInline);
+    aRequest->AsModuleRequest()->OnFetchComplete(aResult);
+  }
+
+  if (aRequest->GetScriptLoadContext()->mInDeferList) {
+    MOZ_ASSERT_IF(aRequest->IsModuleRequest(),
+                  aRequest->AsModuleRequest()->IsTopLevel());
+    if (aRequest->isInList()) {
+      RefPtr<ScriptLoadRequest> req = mDeferRequests.Steal(aRequest);
+      FireScriptAvailable(aResult, req);
+    }
+  } else if (aRequest->GetScriptLoadContext()->mInAsyncList) {
+    MOZ_ASSERT_IF(aRequest->IsModuleRequest(),
+                  aRequest->AsModuleRequest()->IsTopLevel());
+    if (aRequest->isInList()) {
+      RefPtr<ScriptLoadRequest> req = mLoadingAsyncRequests.Steal(aRequest);
+      FireScriptAvailable(aResult, req);
+    }
+  } else if (aRequest->GetScriptLoadContext()->mIsNonAsyncScriptInserted) {
+    if (aRequest->isInList()) {
+      RefPtr<ScriptLoadRequest> req =
+          mNonAsyncExternalScriptInsertedRequests.Steal(aRequest);
+      FireScriptAvailable(aResult, req);
+    }
+  } else if (aRequest->GetScriptLoadContext()->mIsXSLT) {
+    if (aRequest->isInList()) {
+      RefPtr<ScriptLoadRequest> req = mXSLTRequests.Steal(aRequest);
+      FireScriptAvailable(aResult, req);
+    }
+  } else if (aRequest->GetScriptLoadContext()->IsPreload()) {
+    if (aRequest->IsModuleRequest()) {
+      aRequest->Cancel();
+    }
+    if (aRequest->IsTopLevel()) {
+      // Request may already have been removed by
+      // CancelAndClearScriptLoadRequests.
+      mPreloads.RemoveElement(aRequest, PreloadRequestComparator());
+    }
+    MOZ_ASSERT(!aRequest->isInList());
+    AccumulateCategorical(LABELS_DOM_SCRIPT_PRELOAD_RESULT::LoadError);
+  } else if (aRequest->IsModuleRequest()) {
+    ModuleLoadRequest* modReq = aRequest->AsModuleRequest();
+    if (modReq->IsDynamicImport()) {
+      MOZ_ASSERT(modReq->IsTopLevel());
+      if (aRequest->isInList()) {
+        modReq->CancelDynamicImport(aResult);
+      }
+    } else {
+      MOZ_ASSERT(!modReq->IsTopLevel());
+      MOZ_ASSERT(!modReq->isInList());
+      modReq->Cancel();
+      // The error is handled for the top level module.
+    }
+  } else if (mParserBlockingRequest == aRequest) {
+    MOZ_ASSERT(!aRequest->isInList());
+    mParserBlockingRequest = nullptr;
+    UnblockParser(aRequest);
+
+    // Ensure that we treat aRequest->GetScriptLoadContext()->GetScriptElement()
+    // as our current parser-inserted script while firing onerror on it.
+    MOZ_ASSERT(aRequest->GetScriptLoadContext()
+                   ->GetScriptElement()
+                   ->GetParserCreated());
+    nsCOMPtr<nsIScriptElement> oldParserInsertedScript =
+        mCurrentParserInsertedScript;
+    mCurrentParserInsertedScript =
+        aRequest->GetScriptLoadContext()->GetScriptElement();
+    FireScriptAvailable(aResult, aRequest);
+    ContinueParserAsync(aRequest);
+    mCurrentParserInsertedScript = oldParserInsertedScript;
+  } else {
+    // This happens for blocking requests cancelled by ParsingComplete().
+    // Ignore cancellation status for link-preload requests, as cancellation can
+    // be omitted for them when SRI is stronger on consumer tags.
+    MOZ_ASSERT(aRequest->IsCanceled() ||
+               aRequest->GetScriptLoadContext()->IsLinkPreloadScript());
+    MOZ_ASSERT(!aRequest->isInList());
+  }
+}
+
+void ScriptLoader::UnblockParser(ScriptLoadRequest* aParserBlockingRequest) {
+  aParserBlockingRequest->GetScriptLoadContext()
+      ->GetScriptElement()
+      ->UnblockParser();
+}
+
+void ScriptLoader::ContinueParserAsync(
+    ScriptLoadRequest* aParserBlockingRequest) {
+  aParserBlockingRequest->GetScriptLoadContext()
+      ->GetScriptElement()
+      ->ContinueParserAsync();
+}
+
+uint32_t ScriptLoader::NumberOfProcessors() {
+  if (mNumberOfProcessors > 0) {
+    return mNumberOfProcessors;
+  }
+
+  int32_t numProcs = PR_GetNumberOfProcessors();
+  if (numProcs > 0) {
+    mNumberOfProcessors = numProcs;
+  }
+  return mNumberOfProcessors;
+}
+
+int32_t ScriptLoader::PhysicalSizeOfMemoryInGB() {
+  // 0 is a valid result from PR_GetPhysicalMemorySize() which
+  // means a failure occured.
+  if (mPhysicalSizeOfMemory >= 0) {
+    return mPhysicalSizeOfMemory;
+  }
+
+  // Save the size in GB.
+  mPhysicalSizeOfMemory =
+      static_cast<int32_t>(PR_GetPhysicalMemorySize() >> 30);
+  return mPhysicalSizeOfMemory;
+}
+
+static bool IsInternalURIScheme(nsIURI* uri) {
+  return uri->SchemeIs("moz-extension") || uri->SchemeIs("resource") ||
+         uri->SchemeIs("chrome");
+}
+
+bool ScriptLoader::ShouldApplyDelazifyStrategy(ScriptLoadRequest* aRequest) {
+  // Full parse everything if negative.
+  if (StaticPrefs::dom_script_loader_delazification_max_size() < 0) {
+    return true;
+  }
+
+  // Be conservative on machines with 2GB or less of memory.
+  if (PhysicalSizeOfMemoryInGB() <=
+      StaticPrefs::dom_script_loader_delazification_min_mem()) {
+    return false;
+  }
+
+  uint32_t max_size = static_cast<uint32_t>(
+      StaticPrefs::dom_script_loader_delazification_max_size());
+  uint32_t script_size =
+      aRequest->ScriptTextLength() > 0
+          ? static_cast<uint32_t>(aRequest->ScriptTextLength())
+          : 0;
+
+  if (mTotalFullParseSize + script_size < max_size) {
+    return true;
+  }
+
+  if (LOG_ENABLED()) {
+    nsCString url = aRequest->mURI->GetSpecOrDefault();
+    LOG(
+        ("ScriptLoadRequest (%p): non-on-demand-only Parsing Disabled for (%s) "
+         "with size=%u because mTotalFullParseSize=%u would exceed max_size=%u",
+         aRequest, url.get(), script_size, mTotalFullParseSize, max_size));
+  }
+
+  return false;
+}
+
+void ScriptLoader::ApplyDelazifyStrategy(JS::CompileOptions* aOptions) {
+  JS::DelazificationOption strategy =
+      JS::DelazificationOption::ParseEverythingEagerly;
+  uint32_t strategyIndex =
+      StaticPrefs::dom_script_loader_delazification_strategy();
+
+  // Assert that all enumerated values of DelazificationOption are dense between
+  // OnDemandOnly and ParseEverythingEagerly.
+#ifdef DEBUG
+  uint32_t count = 0;
+  uint32_t mask = 0;
+#  define _COUNT_ENTRIES(Name) count++;
+#  define _MASK_ENTRIES(Name) \
+    mask |= 1 << uint32_t(JS::DelazificationOption::Name);
+
+  FOREACH_DELAZIFICATION_STRATEGY(_COUNT_ENTRIES);
+  MOZ_ASSERT(count == uint32_t(strategy) + 1);
+  FOREACH_DELAZIFICATION_STRATEGY(_MASK_ENTRIES);
+  MOZ_ASSERT(((mask + 1) & mask) == 0);
+#  undef _COUNT_ENTRIES
+#  undef _MASK_ENTRIES
+#endif
+
+  // Any strategy index larger than ParseEverythingEagerly would default to
+  // ParseEverythingEagerly.
+  if (strategyIndex <= uint32_t(strategy)) {
+    strategy = JS::DelazificationOption(uint8_t(strategyIndex));
+  }
+
+  aOptions->setEagerDelazificationStrategy(strategy);
+}
+
+bool ScriptLoader::ShouldCompileOffThread(ScriptLoadRequest* aRequest) {
+  if (NumberOfProcessors() <= 1) {
+    return false;
+  }
+  if (aRequest == mParserBlockingRequest) {
+    return true;
+  }
+  if (SpeculativeOMTParsingEnabled()) {
+    // Processing non async inserted scripts too early can potentially delay the
+    // load event from firing so focus on other scripts instead.
+    if (aRequest->GetScriptLoadContext()->mIsNonAsyncScriptInserted &&
+        !StaticPrefs::
+            dom_script_loader_external_scripts_speculate_non_parser_inserted_enabled()) {
+      return false;
+    }
+
+    // Async and link preload scripts do not need to be parsed right away.
+    if (aRequest->GetScriptLoadContext()->IsAsyncScript() &&
+        !StaticPrefs::
+            dom_script_loader_external_scripts_speculate_async_enabled()) {
+      return false;
+    }
+
+    if (aRequest->GetScriptLoadContext()->IsLinkPreloadScript() &&
+        !StaticPrefs::
+            dom_script_loader_external_scripts_speculate_link_preload_enabled()) {
+      return false;
+    }
+
+    return true;
+  }
+  return false;
+}
+
+nsresult ScriptLoader::PrepareLoadedRequest(ScriptLoadRequest* aRequest,
+                                            nsIIncrementalStreamLoader* aLoader,
+                                            nsresult aStatus) {
+  if (NS_FAILED(aStatus)) {
+    return aStatus;
+  }
+
+  if (aRequest->IsCanceled()) {
+    return NS_BINDING_ABORTED;
+  }
+  MOZ_ASSERT(aRequest->IsFetching());
+  CollectScriptTelemetry(aRequest);
+
+  // 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;
+    if (nsContentUtils::GetSourceMapURL(httpChannel, sourceMapURL)) {
+      aRequest->mSourceMapURL = Some(NS_ConvertUTF8toUTF16(sourceMapURL));
+    }
+
+    nsCOMPtr<nsIClassifiedChannel> classifiedChannel = do_QueryInterface(req);
+    MOZ_ASSERT(classifiedChannel);
+    if (classifiedChannel &&
+        classifiedChannel->IsThirdPartyTrackingResource()) {
+      aRequest->GetScriptLoadContext()->SetIsTracking();
+    }
+  }
+
+  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.  Module loads always use CORS.
+  if (!aRequest->IsModuleRequest() && aRequest->CORSMode() == CORS_NONE) {
+    rv = nsContentUtils::GetSecurityManager()->GetChannelResultPrincipal(
+        channel, getter_AddRefs(aRequest->mOriginPrincipal));
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  // 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()->IsRegisteredDynamicImport() ||
+                     !aRequest->AsModuleRequest()->IsTopLevel())) ||
+                   mPreloads.Contains(aRequest, PreloadRequestComparator()) ||
+                   mParserBlockingRequest == aRequest,
+               "aRequest should be pending!");
+
+  nsCOMPtr<nsIURI> uri;
+  rv = channel->GetOriginalURI(getter_AddRefs(uri));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Fixup moz-extension: and resource: URIs, because the channel URI will
+  // point to file:, which won't be allowed to load.
+  if (uri && IsInternalURIScheme(uri)) {
+    aRequest->mBaseURL = uri;
+  } else {
+    channel->GetURI(getter_AddRefs(aRequest->mBaseURL));
+  }
+
+  if (aRequest->IsModuleRequest()) {
+    ModuleLoadRequest* 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;
+    }
+
+    // Attempt to compile off main thread.
+    bool couldCompile = false;
+    rv = AttemptOffThreadScriptCompile(request, &couldCompile);
+    NS_ENSURE_SUCCESS(rv, rv);
+    if (couldCompile) {
+      return NS_OK;
+    }
+
+    // Otherwise compile it right away and start fetching descendents.
+    return request->OnFetchComplete(NS_OK);
+  }
+
+  // The script is now loaded and ready to run.
+  aRequest->SetReady();
+
+  // If speculative parsing is enabled attempt to compile all
+  // external scripts off-main-thread.  Otherwise, only omt compile scripts
+  // blocking the parser.
+  if (ShouldCompileOffThread(aRequest)) {
+    MOZ_ASSERT(!aRequest->IsModuleRequest());
+    bool couldCompile = false;
+    nsresult rv = AttemptOffThreadScriptCompile(aRequest, &couldCompile);
+    NS_ENSURE_SUCCESS(rv, rv);
+    if (couldCompile) {
+      MOZ_ASSERT(aRequest->mState == ScriptLoadRequest::State::Compiling,
+                 "Request should be off-thread compiling now.");
+      return NS_OK;
+    }
+
+    // If off-thread compile was rejected, continue with regular processing.
+  }
+
+  MaybeMoveToLoadedList(aRequest);
+
+  return NS_OK;
+}
+
+void ScriptLoader::DeferCheckpointReached() {
+  if (mDeferEnabled) {
+    // Have to check because we apparently get ParsingComplete
+    // without BeginDeferringScripts in some cases
+    mDeferCheckpointReached = true;
+  }
+
+  mDeferEnabled = false;
+  ProcessPendingRequests();
+}
+
+void ScriptLoader::ParsingComplete(bool aTerminated) {
+  if (aTerminated) {
+    CancelAndClearScriptLoadRequests();
+
+    // Have to call this even if aTerminated so we'll correctly unblock onload.
+    DeferCheckpointReached();
+  }
+}
+
+void ScriptLoader::PreloadURI(nsIURI* aURI, const nsAString& aCharset,
+                              const nsAString& aType,
+                              const nsAString& aCrossOrigin,
+                              const nsAString& aIntegrity, bool aScriptFromHead,
+                              bool aAsync, bool aDefer, bool aNoModule,
+                              bool aLinkPreload,
+                              const ReferrerPolicy aReferrerPolicy,
+                              uint64_t aEarlyHintPreloaderId) {
+  NS_ENSURE_TRUE_VOID(mDocument);
+  // Check to see if scripts has been turned off.
+  if (!mEnabled || !mDocument->IsScriptEnabled()) {
+    return;
+  }
+
+  ScriptKind scriptKind = ScriptKind::eClassic;
+
+  if (mDocument->ModuleScriptsEnabled()) {
+    // Don't load nomodule scripts.
+    if (aNoModule) {
+      return;
+    }
+
+    static const char kASCIIWhitespace[] = "\t\n\f\r ";
+
+    nsAutoString type(aType);
+    type.Trim(kASCIIWhitespace);
+    if (type.LowerCaseEqualsASCII("module")) {
+      scriptKind = ScriptKind::eModule;
+    }
+  }
+
+  if (scriptKind == ScriptKind::eClassic && !aType.IsEmpty() &&
+      !nsContentUtils::IsJavascriptMIMEType(aType)) {
+    // Unknown type.  Don't load it.
+    return;
+  }
+
+  SRIMetadata sriMetadata;
+  GetSRIMetadata(aIntegrity, &sriMetadata);
+
+  RefPtr<ScriptLoadRequest> request = CreateLoadRequest(
+      scriptKind, aURI, nullptr, mDocument->NodePrincipal(),
+      Element::StringToCORSMode(aCrossOrigin), sriMetadata, aReferrerPolicy);
+  request->GetScriptLoadContext()->mIsInline = false;
+  request->GetScriptLoadContext()->mScriptFromHead = aScriptFromHead;
+  request->GetScriptLoadContext()->SetScriptMode(aDefer, aAsync, aLinkPreload);
+  request->GetScriptLoadContext()->SetIsPreloadRequest();
+
+  if (LOG_ENABLED()) {
+    nsAutoCString url;
+    aURI->GetAsciiSpec(url);
+    LOG(("ScriptLoadRequest (%p): Created preload request for %s",
+         request.get(), url.get()));
+  }
+
+  nsAutoString charset(aCharset);
+  nsresult rv = StartLoad(request, aEarlyHintPreloaderId, Some(charset));
+  if (NS_FAILED(rv)) {
+    return;
+  }
+
+  PreloadInfo* pi = mPreloads.AppendElement();
+  pi->mRequest = request;
+  pi->mCharset = aCharset;
+}
+
+void ScriptLoader::AddDeferRequest(ScriptLoadRequest* aRequest) {
+  MOZ_ASSERT(aRequest->GetScriptLoadContext()->IsDeferredScript());
+  MOZ_ASSERT(!aRequest->GetScriptLoadContext()->mInDeferList &&
+             !aRequest->GetScriptLoadContext()->mInAsyncList);
+  MOZ_ASSERT(!aRequest->GetScriptLoadContext()->mInCompilingList);
+
+  aRequest->GetScriptLoadContext()->mInDeferList = true;
+  mDeferRequests.AppendElement(aRequest);
+  if (mDeferEnabled && aRequest == mDeferRequests.getFirst() && mDocument &&
+      !mBlockingDOMContentLoaded) {
+    MOZ_ASSERT(mDocument->GetReadyStateEnum() == Document::READYSTATE_LOADING);
+    mBlockingDOMContentLoaded = true;
+    mDocument->BlockDOMContentLoaded();
+  }
+}
+
+void ScriptLoader::AddAsyncRequest(ScriptLoadRequest* aRequest) {
+  MOZ_ASSERT(aRequest->GetScriptLoadContext()->IsAsyncScript());
+  MOZ_ASSERT(!aRequest->GetScriptLoadContext()->mInDeferList &&
+             !aRequest->GetScriptLoadContext()->mInAsyncList);
+  MOZ_ASSERT(!aRequest->GetScriptLoadContext()->mInCompilingList);
+
+  aRequest->GetScriptLoadContext()->mInAsyncList = true;
+  if (aRequest->IsReadyToRun()) {
+    mLoadedAsyncRequests.AppendElement(aRequest);
+  } else {
+    mLoadingAsyncRequests.AppendElement(aRequest);
+  }
+}
+
+void ScriptLoader::MaybeMoveToLoadedList(ScriptLoadRequest* aRequest) {
+  MOZ_ASSERT(aRequest->IsReadyToRun());
+  MOZ_ASSERT(aRequest->IsTopLevel());
+
+  // If it's async, move it to the loaded list.
+  // aRequest->GetScriptLoadContext()->mInAsyncList 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->GetScriptLoadContext()->mInAsyncList) {
+    MOZ_ASSERT(aRequest->isInList());
+    if (aRequest->isInList()) {
+      RefPtr<ScriptLoadRequest> req = mLoadingAsyncRequests.Steal(aRequest);
+      mLoadedAsyncRequests.AppendElement(req);
+    }
+  } else if (aRequest->IsModuleRequest() &&
+             aRequest->AsModuleRequest()->IsDynamicImport()) {
+    // Process dynamic imports with async scripts.
+    MOZ_ASSERT(!aRequest->isInList());
+    mLoadedAsyncRequests.AppendElement(aRequest);
+  }
+}
+
+bool ScriptLoader::MaybeRemovedDeferRequests() {
+  if (mDeferRequests.isEmpty() && mDocument && mBlockingDOMContentLoaded) {
+    mBlockingDOMContentLoaded = false;
+    mDocument->UnblockDOMContentLoaded();
+    return true;
+  }
+  return false;
+}
+
+DocGroup* ScriptLoader::GetDocGroup() const { return mDocument->GetDocGroup(); }
+
+void ScriptLoader::BeginDeferringScripts() {
+  mDeferEnabled = true;
+  if (mDeferCheckpointReached) {
+    // We already completed a parse and were just waiting for some async
+    // scripts to load (and were already blocking the load event waiting for
+    // that to happen), when document.open() happened and now we're doing a
+    // new parse.  We shouldn't block the load event again, but _should_ reset
+    // mDeferCheckpointReached to false.  It'll get set to true again when the
+    // DeferCheckpointReached call that corresponds to this
+    // BeginDeferringScripts call happens (on document.close()), since we just
+    // set mDeferEnabled to true.
+    mDeferCheckpointReached = false;
+  } else {
+    if (mDocument) {
+      mDocument->BlockOnload();
+    }
+  }
+}
+
+nsAutoScriptLoaderDisabler::nsAutoScriptLoaderDisabler(Document* aDoc) {
+  mLoader = aDoc->ScriptLoader();
+  mWasEnabled = mLoader->GetEnabled();
+  if (mWasEnabled) {
+    mLoader->SetEnabled(false);
+  }
+}
+
+nsAutoScriptLoaderDisabler::~nsAutoScriptLoaderDisabler() {
+  if (mWasEnabled) {
+    mLoader->SetEnabled(true);
+  }
+}
+
+#undef TRACE_FOR_TEST
+#undef TRACE_FOR_TEST_BOOL
+#undef TRACE_FOR_TEST_NONE
+
+#undef LOG
+
+}  // namespace mozilla::dom