Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 2227 insertions, 0 deletions

diff --git a/js/xpconnect/loader/mozJSModuleLoader.cpp b/js/xpconnect/loader/mozJSModuleLoader.cpp
new file mode 100644
index 0000000000..f20306f0a0
--- /dev/null
+++ b/js/xpconnect/loader/mozJSModuleLoader.cpp
@@ -0,0 +1,2227 @@
+/* -*- 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 "ScriptLoadRequest.h"
+#include "mozilla/Assertions.h"  // MOZ_ASSERT, MOZ_ASSERT_IF
+#include "mozilla/Attributes.h"
+#include "mozilla/ArrayUtils.h"  // mozilla::ArrayLength
+#include "mozilla/RefPtr.h"      // RefPtr, mozilla::StaticRefPtr
+#include "mozilla/Utf8.h"        // mozilla::Utf8Unit
+
+#include <cstdarg>
+
+#include "mozilla/Logging.h"
+#include "mozilla/dom/RequestBinding.h"
+#ifdef ANDROID
+#  include <android/log.h>
+#endif
+#ifdef XP_WIN
+#  include <windows.h>
+#endif
+
+#include "jsapi.h"
+#include "js/Array.h"  // JS::GetArrayLength, JS::IsArrayObject
+#include "js/CharacterEncoding.h"
+#include "js/CompilationAndEvaluation.h"
+#include "js/CompileOptions.h"         // JS::CompileOptions
+#include "js/ErrorReport.h"            // JS_ReportErrorUTF8, JSErrorReport
+#include "js/Exception.h"              // JS_ErrorFromException
+#include "js/friend/JSMEnvironment.h"  // JS::ExecuteInJSMEnvironment, JS::GetJSMEnvironmentOfScriptedCaller, JS::NewJSMEnvironment
+#include "js/friend/ErrorMessages.h"   // JSMSG_*
+#include "js/loader/ModuleLoadRequest.h"
+#include "js/Object.h"  // JS::GetCompartment
+#include "js/Printf.h"
+#include "js/PropertyAndElement.h"  // JS_DefineFunctions, JS_DefineProperty, JS_Enumerate, JS_GetElement, JS_GetProperty, JS_GetPropertyById, JS_HasOwnProperty, JS_HasOwnPropertyById, JS_SetProperty, JS_SetPropertyById
+#include "js/PropertySpec.h"
+#include "js/SourceText.h"  // JS::SourceText
+#include "nsCOMPtr.h"
+#include "nsDirectoryServiceDefs.h"
+#include "nsDirectoryServiceUtils.h"
+#include "nsIFile.h"
+#include "mozJSModuleLoader.h"
+#include "mozJSLoaderUtils.h"
+#include "nsIFileURL.h"
+#include "nsIJARURI.h"
+#include "nsIChannel.h"
+#include "nsIStreamListener.h"
+#include "nsNetUtil.h"
+#include "nsJSUtils.h"
+#include "xpcprivate.h"
+#include "xpcpublic.h"
+#include "nsContentUtils.h"
+#include "nsXULAppAPI.h"
+#include "WrapperFactory.h"
+#include "JSMEnvironmentProxy.h"
+#include "ModuleEnvironmentProxy.h"
+#include "JSServices.h"
+
+#include "mozilla/scache/StartupCache.h"
+#include "mozilla/scache/StartupCacheUtils.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/MacroForEach.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/ProfilerMarkers.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/ScriptPreloader.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/Try.h"
+#include "mozilla/dom/AutoEntryScript.h"
+#include "mozilla/dom/ReferrerPolicyBinding.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/WorkerCommon.h"  // dom::GetWorkerPrivateFromContext
+#include "mozilla/dom/WorkerPrivate.h"  // dom::WorkerPrivate, dom::AutoSyncLoopHolder
+#include "mozilla/dom/WorkerRunnable.h"  // dom::MainThreadStopSyncLoopRunnable
+#include "mozilla/Unused.h"
+
+using namespace mozilla;
+using namespace mozilla::scache;
+using namespace mozilla::loader;
+using namespace xpc;
+using namespace JS;
+
+#define JS_CACHE_PREFIX(aScopeType, aCompilationTarget) \
+  "jsloader/" aScopeType "/" aCompilationTarget
+
+/**
+ * Buffer sizes for serialization and deserialization of scripts.
+ * FIXME: bug #411579 (tune this macro!) Last updated: Jan 2008
+ */
+#define XPC_SERIALIZATION_BUFFER_SIZE (64 * 1024)
+#define XPC_DESERIALIZATION_BUFFER_SIZE (12 * 8192)
+
+// MOZ_LOG=JSModuleLoader:5
+static LazyLogModule gJSCLLog("JSModuleLoader");
+
+#define LOG(args) MOZ_LOG(gJSCLLog, mozilla::LogLevel::Debug, args)
+
+// Components.utils.import error messages
+#define ERROR_SCOPE_OBJ "%s - Second argument must be an object."
+#define ERROR_NO_TARGET_OBJECT "%s - Couldn't find target object for import."
+#define ERROR_NOT_PRESENT "%s - EXPORTED_SYMBOLS is not present."
+#define ERROR_NOT_AN_ARRAY "%s - EXPORTED_SYMBOLS is not an array."
+#define ERROR_GETTING_ARRAY_LENGTH \
+  "%s - Error getting array length of EXPORTED_SYMBOLS."
+#define ERROR_ARRAY_ELEMENT "%s - EXPORTED_SYMBOLS[%d] is not a string."
+#define ERROR_GETTING_SYMBOL "%s - Could not get symbol '%s'."
+#define ERROR_SETTING_SYMBOL "%s - Could not set symbol '%s' on target object."
+#define ERROR_UNINITIALIZED_SYMBOL \
+  "%s - Symbol '%s' accessed before initialization. Cyclic import?"
+
+static constexpr char JSM_Suffix[] = ".jsm";
+static constexpr size_t JSM_SuffixLength = mozilla::ArrayLength(JSM_Suffix) - 1;
+static constexpr char JSM_JS_Suffix[] = ".jsm.js";
+static constexpr size_t JSM_JS_SuffixLength =
+    mozilla::ArrayLength(JSM_JS_Suffix) - 1;
+static constexpr char JS_Suffix[] = ".js";
+static constexpr size_t JS_SuffixLength = mozilla::ArrayLength(JS_Suffix) - 1;
+static constexpr char MJS_Suffix[] = ".sys.mjs";
+static constexpr size_t MJS_SuffixLength = mozilla::ArrayLength(MJS_Suffix) - 1;
+
+static bool IsJSM(const nsACString& aLocation) {
+  if (aLocation.Length() < JSM_SuffixLength) {
+    return false;
+  }
+  const auto ext = Substring(aLocation, aLocation.Length() - JSM_SuffixLength);
+  return ext == JSM_Suffix;
+}
+
+static bool IsJS(const nsACString& aLocation) {
+  if (aLocation.Length() < JS_SuffixLength) {
+    return false;
+  }
+  const auto ext = Substring(aLocation, aLocation.Length() - JS_SuffixLength);
+  return ext == JS_Suffix;
+}
+
+static bool IsJSM_JS(const nsACString& aLocation) {
+  if (aLocation.Length() < JSM_JS_SuffixLength) {
+    return false;
+  }
+  const auto ext =
+      Substring(aLocation, aLocation.Length() - JSM_JS_SuffixLength);
+  return ext == JSM_JS_Suffix;
+}
+
+static bool IsMJS(const nsACString& aLocation) {
+  if (aLocation.Length() < MJS_SuffixLength) {
+    return false;
+  }
+  const auto ext = Substring(aLocation, aLocation.Length() - MJS_SuffixLength);
+  return ext == MJS_Suffix;
+}
+
+static void MJSToJSM(const nsACString& aLocation, nsAutoCString& aOut) {
+  MOZ_ASSERT(IsMJS(aLocation));
+  aOut = Substring(aLocation, 0, aLocation.Length() - MJS_SuffixLength);
+  aOut += JSM_Suffix;
+}
+
+static bool TryToMJS(const nsACString& aLocation, nsAutoCString& aOut) {
+  if (IsJSM(aLocation)) {
+    aOut = Substring(aLocation, 0, aLocation.Length() - JSM_SuffixLength);
+    aOut += MJS_Suffix;
+    return true;
+  }
+
+  if (IsJSM_JS(aLocation)) {
+    aOut = Substring(aLocation, 0, aLocation.Length() - JSM_JS_SuffixLength);
+    aOut += MJS_Suffix;
+    return true;
+  }
+
+  if (IsJS(aLocation)) {
+    aOut = Substring(aLocation, 0, aLocation.Length() - JS_SuffixLength);
+    aOut += MJS_Suffix;
+    return true;
+  }
+
+  return false;
+}
+
+static bool Dump(JSContext* cx, unsigned argc, Value* vp) {
+  if (!nsJSUtils::DumpEnabled()) {
+    return true;
+  }
+
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  if (args.length() == 0) {
+    return true;
+  }
+
+  RootedString str(cx, JS::ToString(cx, args[0]));
+  if (!str) {
+    return false;
+  }
+
+  JS::UniqueChars utf8str = JS_EncodeStringToUTF8(cx, str);
+  if (!utf8str) {
+    return false;
+  }
+
+  MOZ_LOG(nsContentUtils::DOMDumpLog(), mozilla::LogLevel::Debug,
+          ("[Backstage.Dump] %s", utf8str.get()));
+#ifdef ANDROID
+  __android_log_print(ANDROID_LOG_INFO, "Gecko", "%s", utf8str.get());
+#endif
+#ifdef XP_WIN
+  if (IsDebuggerPresent()) {
+    nsAutoJSString wstr;
+    if (!wstr.init(cx, str)) {
+      return false;
+    }
+    OutputDebugStringW(wstr.get());
+  }
+#endif
+  fputs(utf8str.get(), stdout);
+  fflush(stdout);
+  return true;
+}
+
+static bool Debug(JSContext* cx, unsigned argc, Value* vp) {
+#ifdef DEBUG
+  return Dump(cx, argc, vp);
+#else
+  return true;
+#endif
+}
+
+static const JSFunctionSpec gGlobalFun[] = {
+    JS_FN("dump", Dump, 1, 0), JS_FN("debug", Debug, 1, 0),
+    JS_FN("atob", Atob, 1, 0), JS_FN("btoa", Btoa, 1, 0), JS_FS_END};
+
+class MOZ_STACK_CLASS JSCLContextHelper {
+ public:
+  explicit JSCLContextHelper(JSContext* aCx);
+  ~JSCLContextHelper();
+
+  void reportErrorAfterPop(UniqueChars&& buf);
+
+ private:
+  JSContext* mContext;
+  UniqueChars mBuf;
+
+  // prevent copying and assignment
+  JSCLContextHelper(const JSCLContextHelper&) = delete;
+  const JSCLContextHelper& operator=(const JSCLContextHelper&) = delete;
+};
+
+static nsresult MOZ_FORMAT_PRINTF(2, 3)
+    ReportOnCallerUTF8(JSContext* callerContext, const char* format, ...) {
+  if (!callerContext) {
+    return NS_ERROR_FAILURE;
+  }
+
+  va_list ap;
+  va_start(ap, format);
+
+  UniqueChars buf = JS_vsmprintf(format, ap);
+  if (!buf) {
+    va_end(ap);
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  JS_ReportErrorUTF8(callerContext, "%s", buf.get());
+
+  va_end(ap);
+  return NS_OK;
+}
+
+NS_IMPL_ISUPPORTS(mozJSModuleLoader, nsIMemoryReporter)
+
+mozJSModuleLoader::mozJSModuleLoader()
+    : mImports(16),
+      mInProgressImports(16),
+      mFallbackImports(16),
+#ifdef STARTUP_RECORDER_ENABLED
+      mImportStacks(16),
+#endif
+      mLocations(16),
+      mInitialized(false),
+      mLoaderGlobal(dom::RootingCx()),
+      mServicesObj(dom::RootingCx()) {
+}
+
+#define ENSURE_DEP(name)          \
+  {                               \
+    nsresult rv = Ensure##name(); \
+    NS_ENSURE_SUCCESS(rv, rv);    \
+  }
+#define ENSURE_DEPS(...) MOZ_FOR_EACH(ENSURE_DEP, (), (__VA_ARGS__));
+#define BEGIN_ENSURE(self, ...) \
+  {                             \
+    if (m##self) return NS_OK;  \
+    ENSURE_DEPS(__VA_ARGS__);   \
+  }
+
+class MOZ_STACK_CLASS ModuleLoaderInfo {
+ public:
+  explicit ModuleLoaderInfo(const nsACString& aLocation,
+                            SkipCheckForBrokenURLOrZeroSized aSkipCheck =
+                                SkipCheckForBrokenURLOrZeroSized::No)
+      : mLocation(&aLocation), mIsModule(false), mSkipCheck(aSkipCheck) {}
+  explicit ModuleLoaderInfo(JS::loader::ModuleLoadRequest* aRequest)
+      : mLocation(nullptr),
+        mURI(aRequest->mURI),
+        mIsModule(true),
+        mSkipCheck(aRequest->GetSyncLoadContext()->mSkipCheck) {}
+
+  SkipCheckForBrokenURLOrZeroSized getSkipCheckForBrokenURLOrZeroSized() const {
+    return mSkipCheck;
+  }
+
+  void resetChannelWithCheckForBrokenURLOrZeroSized() {
+    MOZ_ASSERT(mSkipCheck == SkipCheckForBrokenURLOrZeroSized::Yes);
+    mSkipCheck = SkipCheckForBrokenURLOrZeroSized::No;
+    mScriptChannel = nullptr;
+  }
+
+  nsIIOService* IOService() {
+    MOZ_ASSERT(mIOService);
+    return mIOService;
+  }
+  nsresult EnsureIOService() {
+    if (mIOService) {
+      return NS_OK;
+    }
+    nsresult rv;
+    mIOService = do_GetIOService(&rv);
+    return rv;
+  }
+
+  nsIURI* URI() {
+    MOZ_ASSERT(mURI);
+    return mURI;
+  }
+  nsresult EnsureURI() {
+    BEGIN_ENSURE(URI, IOService);
+    MOZ_ASSERT(mLocation);
+    return mIOService->NewURI(*mLocation, nullptr, nullptr,
+                              getter_AddRefs(mURI));
+  }
+
+  nsIChannel* ScriptChannel() {
+    MOZ_ASSERT(mScriptChannel);
+    return mScriptChannel;
+  }
+  nsresult EnsureScriptChannel() {
+    BEGIN_ENSURE(ScriptChannel, IOService, URI);
+
+    // Skip check for missing URL when handling JSM-to-ESM fallback.
+    return NS_NewChannel(
+        getter_AddRefs(mScriptChannel), mURI,
+        nsContentUtils::GetSystemPrincipal(),
+        nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_SEC_CONTEXT_IS_NULL,
+        nsIContentPolicy::TYPE_SCRIPT,
+        /* aCookieJarSettings = */ nullptr,
+        /* aPerformanceStorage = */ nullptr,
+        /* aLoadGroup = */ nullptr, /* aCallbacks = */ nullptr,
+        nsIRequest::LOAD_NORMAL, mIOService, /* aSandboxFlags = */ 0,
+        mSkipCheck == SkipCheckForBrokenURLOrZeroSized::Yes);
+  }
+
+  nsIURI* ResolvedURI() {
+    MOZ_ASSERT(mResolvedURI);
+    return mResolvedURI;
+  }
+  nsresult EnsureResolvedURI() {
+    BEGIN_ENSURE(ResolvedURI, URI);
+    return ResolveURI(mURI, getter_AddRefs(mResolvedURI));
+  }
+
+  const nsACString& Key() {
+    MOZ_ASSERT(mLocation);
+    return *mLocation;
+  }
+
+  [[nodiscard]] nsresult GetLocation(nsCString& aLocation) {
+    nsresult rv = EnsureURI();
+    NS_ENSURE_SUCCESS(rv, rv);
+    return mURI->GetSpec(aLocation);
+  }
+
+  bool IsModule() const { return mIsModule; }
+
+ private:
+  const nsACString* mLocation;
+  nsCOMPtr<nsIIOService> mIOService;
+  nsCOMPtr<nsIURI> mURI;
+  nsCOMPtr<nsIChannel> mScriptChannel;
+  nsCOMPtr<nsIURI> mResolvedURI;
+  const bool mIsModule;
+  SkipCheckForBrokenURLOrZeroSized mSkipCheck;
+};
+
+template <typename... Args>
+static nsresult ReportOnCallerUTF8(JSCLContextHelper& helper,
+                                   const char* format, ModuleLoaderInfo& info,
+                                   Args... args) {
+  nsCString location;
+  MOZ_TRY(info.GetLocation(location));
+
+  UniqueChars buf = JS_smprintf(format, location.get(), args...);
+  if (!buf) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  helper.reportErrorAfterPop(std::move(buf));
+  return NS_ERROR_FAILURE;
+}
+
+#undef BEGIN_ENSURE
+#undef ENSURE_DEPS
+#undef ENSURE_DEP
+
+mozJSModuleLoader::~mozJSModuleLoader() {
+  MOZ_ASSERT(!mInitialized,
+             "UnloadModules() was not explicitly called before cleaning up "
+             "mozJSModuleLoader");
+
+  if (mInitialized) {
+    UnloadModules();
+  }
+}
+
+StaticRefPtr<mozJSModuleLoader> mozJSModuleLoader::sSelf;
+StaticRefPtr<mozJSModuleLoader> mozJSModuleLoader::sDevToolsLoader;
+
+void mozJSModuleLoader::FindTargetObject(JSContext* aCx,
+                                         MutableHandleObject aTargetObject) {
+  aTargetObject.set(JS::GetJSMEnvironmentOfScriptedCaller(aCx));
+
+  // The above could fail if the scripted caller is not a JSM (it could be a DOM
+  // scope, for instance).
+  //
+  // If the target object was not in the JSM shared global, return the global
+  // instead. This is needed when calling the subscript loader within a frame
+  // script, since it the FrameScript NSVO will have been found.
+  if (!aTargetObject ||
+      !IsLoaderGlobal(JS::GetNonCCWObjectGlobal(aTargetObject))) {
+    aTargetObject.set(JS::GetScriptedCallerGlobal(aCx));
+
+    // Return nullptr if the scripted caller is in a different compartment.
+    if (JS::GetCompartment(aTargetObject) != js::GetContextCompartment(aCx)) {
+      aTargetObject.set(nullptr);
+    }
+  }
+}
+
+void mozJSModuleLoader::InitStatics() {
+  MOZ_ASSERT(!sSelf);
+  sSelf = new mozJSModuleLoader();
+  RegisterWeakMemoryReporter(sSelf);
+  NonSharedGlobalSyncModuleLoaderScope::InitStatics();
+}
+
+void mozJSModuleLoader::UnloadLoaders() {
+  if (sSelf) {
+    sSelf->Unload();
+  }
+  if (sDevToolsLoader) {
+    sDevToolsLoader->Unload();
+  }
+}
+
+void mozJSModuleLoader::Unload() {
+  UnloadModules();
+
+  if (mModuleLoader) {
+    mModuleLoader->Shutdown();
+    mModuleLoader = nullptr;
+  }
+}
+
+void mozJSModuleLoader::ShutdownLoaders() {
+  MOZ_ASSERT(sSelf);
+  UnregisterWeakMemoryReporter(sSelf);
+  sSelf = nullptr;
+
+  if (sDevToolsLoader) {
+    UnregisterWeakMemoryReporter(sDevToolsLoader);
+    sDevToolsLoader = nullptr;
+  }
+}
+
+mozJSModuleLoader* mozJSModuleLoader::GetOrCreateDevToolsLoader() {
+  if (sDevToolsLoader) {
+    return sDevToolsLoader;
+  }
+  sDevToolsLoader = new mozJSModuleLoader();
+  RegisterWeakMemoryReporter(sDevToolsLoader);
+  return sDevToolsLoader;
+}
+
+void mozJSModuleLoader::InitSyncModuleLoaderForGlobal(
+    nsIGlobalObject* aGlobal) {
+  MOZ_ASSERT(!mLoaderGlobal);
+  MOZ_ASSERT(!mModuleLoader);
+
+  RefPtr<SyncScriptLoader> scriptLoader = new SyncScriptLoader;
+  mModuleLoader = new SyncModuleLoader(scriptLoader, aGlobal);
+  mLoaderGlobal = aGlobal->GetGlobalJSObject();
+}
+
+void mozJSModuleLoader::DisconnectSyncModuleLoaderFromGlobal() {
+  MOZ_ASSERT(mLoaderGlobal);
+  MOZ_ASSERT(mModuleLoader);
+
+  mLoaderGlobal = nullptr;
+  Unload();
+}
+
+/* static */
+bool mozJSModuleLoader::IsSharedSystemGlobal(nsIGlobalObject* aGlobal) {
+  return sSelf->IsLoaderGlobal(aGlobal->GetGlobalJSObject());
+}
+
+/* static */
+bool mozJSModuleLoader::IsDevToolsLoaderGlobal(nsIGlobalObject* aGlobal) {
+  return sDevToolsLoader &&
+         sDevToolsLoader->IsLoaderGlobal(aGlobal->GetGlobalJSObject());
+}
+
+// This requires that the keys be strings and the values be pointers.
+template <class Key, class Data, class UserData, class Converter>
+static size_t SizeOfTableExcludingThis(
+    const nsBaseHashtable<Key, Data, UserData, Converter>& aTable,
+    MallocSizeOf aMallocSizeOf) {
+  size_t n = aTable.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  for (const auto& entry : aTable) {
+    n += entry.GetKey().SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+    n += entry.GetData()->SizeOfIncludingThis(aMallocSizeOf);
+  }
+  return n;
+}
+
+#ifdef STARTUP_RECORDER_ENABLED
+template <class Key, class Data, class UserData, class Converter>
+static size_t SizeOfStringTableExcludingThis(
+    const nsBaseHashtable<Key, Data, UserData, Converter>& aTable,
+    MallocSizeOf aMallocSizeOf) {
+  size_t n = aTable.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  for (const auto& entry : aTable) {
+    n += entry.GetKey().SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+    n += entry.GetData().SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+  }
+  return n;
+}
+#endif
+
+size_t mozJSModuleLoader::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) {
+  size_t n = aMallocSizeOf(this);
+  n += SizeOfTableExcludingThis(mImports, aMallocSizeOf);
+  n += mLocations.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  n += SizeOfTableExcludingThis(mInProgressImports, aMallocSizeOf);
+  n += SizeOfTableExcludingThis(mFallbackImports, aMallocSizeOf);
+#ifdef STARTUP_RECORDER_ENABLED
+  n += SizeOfStringTableExcludingThis(mImportStacks, aMallocSizeOf);
+#endif
+  return n;
+}
+
+// Memory report paths are split on '/', with each module displayed as a
+// separate layer of a visual tree. Any slashes which are meant to belong to a
+// particular path module, rather than be used to build a hierarchy, therefore
+// need to be replaced with backslashes, which are displayed as slashes in the
+// UI.
+//
+// If `aAnonymize` is true, this function also attempts to translate any file:
+// URLs to replace the path of the GRE directory with a placeholder containing
+// no private information, and strips all other file: URIs of everything upto
+// their last `/`.
+static nsAutoCString MangleURL(const char* aURL, bool aAnonymize) {
+  nsAutoCString url(aURL);
+
+  if (aAnonymize) {
+    static nsCString greDirURI;
+    if (greDirURI.IsEmpty()) {
+      nsCOMPtr<nsIFile> file;
+      Unused << NS_GetSpecialDirectory(NS_GRE_DIR, getter_AddRefs(file));
+      if (file) {
+        nsCOMPtr<nsIURI> uri;
+        NS_NewFileURI(getter_AddRefs(uri), file);
+        if (uri) {
+          uri->GetSpec(greDirURI);
+          RunOnShutdown([&]() { greDirURI.Truncate(0); });
+        }
+      }
+    }
+
+    url.ReplaceSubstring(greDirURI, "<GREDir>/"_ns);
+
+    if (FindInReadable("file:"_ns, url)) {
+      if (StringBeginsWith(url, "jar:file:"_ns)) {
+        int32_t idx = url.RFindChar('!');
+        url = "jar:file://<anonymized>!"_ns + Substring(url, idx);
+      } else {
+        int32_t idx = url.RFindChar('/');
+        url = "file://<anonymized>/"_ns + Substring(url, idx);
+      }
+    }
+  }
+
+  url.ReplaceChar('/', '\\');
+  return url;
+}
+
+NS_IMETHODIMP
+mozJSModuleLoader::CollectReports(nsIHandleReportCallback* aHandleReport,
+                                  nsISupports* aData, bool aAnonymize) {
+  for (const auto& entry : mImports.Values()) {
+    nsAutoCString path("js-module-loader/modules/");
+    path.Append(MangleURL(entry->location, aAnonymize));
+
+    aHandleReport->Callback(""_ns, path, KIND_NONHEAP, UNITS_COUNT, 1,
+                            "Loaded JS modules"_ns, aData);
+  }
+
+  return NS_OK;
+}
+
+void mozJSModuleLoader::CreateLoaderGlobal(JSContext* aCx,
+                                           const nsACString& aLocation,
+                                           MutableHandleObject aGlobal) {
+  auto backstagePass = MakeRefPtr<BackstagePass>();
+  RealmOptions options;
+  auto& creationOptions = options.creationOptions();
+
+  creationOptions.setFreezeBuiltins(true).setNewCompartmentInSystemZone();
+  if (IsDevToolsLoader()) {
+    creationOptions.setInvisibleToDebugger(true);
+  }
+  xpc::SetPrefableRealmOptions(options);
+
+  // Defer firing OnNewGlobalObject until after the __URI__ property has
+  // been defined so the JS debugger can tell what module the global is
+  // for
+  RootedObject global(aCx);
+
+#ifdef DEBUG
+  // See mozJSModuleLoader::DefineJSServices.
+  mIsInitializingLoaderGlobal = true;
+#endif
+  nsresult rv = xpc::InitClassesWithNewWrappedGlobal(
+      aCx, static_cast<nsIGlobalObject*>(backstagePass),
+      nsContentUtils::GetSystemPrincipal(), xpc::DONT_FIRE_ONNEWGLOBALHOOK,
+      options, &global);
+#ifdef DEBUG
+  mIsInitializingLoaderGlobal = false;
+#endif
+  NS_ENSURE_SUCCESS_VOID(rv);
+
+  NS_ENSURE_TRUE_VOID(global);
+
+  backstagePass->SetGlobalObject(global);
+
+  JSAutoRealm ar(aCx, global);
+  if (!JS_DefineFunctions(aCx, global, gGlobalFun)) {
+    return;
+  }
+
+  if (!CreateJSServices(aCx)) {
+    return;
+  }
+
+  if (!DefineJSServices(aCx, global)) {
+    return;
+  }
+
+  // Set the location information for the new global, so that tools like
+  // about:memory may use that information
+  xpc::SetLocationForGlobal(global, aLocation);
+
+  MOZ_ASSERT(!mModuleLoader);
+  RefPtr<SyncScriptLoader> scriptLoader = new SyncScriptLoader;
+  mModuleLoader = new SyncModuleLoader(scriptLoader, backstagePass);
+  backstagePass->InitModuleLoader(mModuleLoader);
+
+  aGlobal.set(global);
+}
+
+JSObject* mozJSModuleLoader::GetSharedGlobal(JSContext* aCx) {
+  if (!mLoaderGlobal) {
+    JS::RootedObject globalObj(aCx);
+
+    CreateLoaderGlobal(
+        aCx, IsDevToolsLoader() ? "DevTools global"_ns : "shared JSM global"_ns,
+        &globalObj);
+
+    // If we fail to create a module global this early, we're not going to
+    // get very far, so just bail out now.
+    MOZ_RELEASE_ASSERT(globalObj);
+    mLoaderGlobal = globalObj;
+
+    // AutoEntryScript required to invoke debugger hook, which is a
+    // Gecko-specific concept at present.
+    dom::AutoEntryScript aes(globalObj, "module loader report global");
+    JS_FireOnNewGlobalObject(aes.cx(), globalObj);
+  }
+
+  return mLoaderGlobal;
+}
+
+// Read script file on the main thread and pass it back to worker.
+class ScriptReaderRunnable final : public nsIRunnable,
+                                   public nsINamed,
+                                   public nsIStreamListener {
+ public:
+  ScriptReaderRunnable(dom::WorkerPrivate* aWorkerPrivate,
+                       nsIEventTarget* aSyncLoopTarget,
+                       const nsCString& aLocation)
+      : mLocation(aLocation),
+        mRv(NS_ERROR_FAILURE),
+        mWorkerPrivate(aWorkerPrivate),
+        mSyncLoopTarget(aSyncLoopTarget) {}
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  nsCString& Data() { return mData; }
+
+  nsresult Result() const { return mRv; }
+
+  // nsIRunnable
+
+  NS_IMETHOD
+  Run() override {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    nsresult rv = StartReadScriptFromLocation();
+    if (NS_FAILED(rv)) {
+      OnComplete(rv);
+    }
+
+    return NS_OK;
+  }
+
+  // nsINamed
+
+  NS_IMETHOD
+  GetName(nsACString& aName) override {
+    aName.AssignLiteral("ScriptReaderRunnable");
+    return NS_OK;
+  }
+
+  // nsIStreamListener
+
+  NS_IMETHOD OnDataAvailable(nsIRequest* aRequest, nsIInputStream* aInputStream,
+                             uint64_t aOffset, uint32_t aCount) override {
+    uint32_t read = 0;
+    return aInputStream->ReadSegments(AppendSegmentToData, this, aCount, &read);
+  }
+
+  // nsIRequestObserver
+
+  NS_IMETHOD OnStartRequest(nsIRequest* aRequest) override { return NS_OK; }
+
+  NS_IMETHOD OnStopRequest(nsIRequest* aRequest,
+                           nsresult aStatusCode) override {
+    OnComplete(aStatusCode);
+    return NS_OK;
+  }
+
+ private:
+  ~ScriptReaderRunnable() = default;
+
+  static nsresult AppendSegmentToData(nsIInputStream* aInputStream,
+                                      void* aClosure, const char* aRawSegment,
+                                      uint32_t aToOffset, uint32_t aCount,
+                                      uint32_t* outWrittenCount) {
+    auto* self = static_cast<ScriptReaderRunnable*>(aClosure);
+    self->mData.Append(aRawSegment, aCount);
+    *outWrittenCount = aCount;
+    return NS_OK;
+  }
+
+  void OnComplete(nsresult aRv) {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    mRv = aRv;
+
+    RefPtr<dom::MainThreadStopSyncLoopRunnable> runnable =
+        new dom::MainThreadStopSyncLoopRunnable(
+            mWorkerPrivate, std::move(mSyncLoopTarget), mRv);
+    MOZ_ALWAYS_TRUE(runnable->Dispatch());
+
+    mWorkerPrivate = nullptr;
+    mSyncLoopTarget = nullptr;
+  }
+
+  nsresult StartReadScriptFromLocation() {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    ModuleLoaderInfo info(mLocation);
+    nsresult rv = info.EnsureScriptChannel();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    return info.ScriptChannel()->AsyncOpen(this);
+  }
+
+ private:
+  nsAutoCString mLocation;
+  nsCString mData;
+  nsresult mRv;
+
+  // This pointer is guaranteed to be alive until OnComplete, given
+  // the worker thread is synchronously waiting with AutoSyncLoopHolder::Run
+  // until the corresponding WorkerPrivate::StopSyncLoop is called by
+  // MainThreadStopSyncLoopRunnable, which is dispatched from OnComplete.
+  dom::WorkerPrivate* mWorkerPrivate;
+
+  nsCOMPtr<nsIEventTarget> mSyncLoopTarget;
+};
+
+NS_IMPL_ISUPPORTS(ScriptReaderRunnable, nsIRunnable, nsINamed,
+                  nsIStreamListener)
+
+/* static */
+nsresult mozJSModuleLoader::ReadScriptOnMainThread(JSContext* aCx,
+                                                   const nsCString& aLocation,
+                                                   nsCString& aData) {
+  dom::WorkerPrivate* workerPrivate = dom::GetWorkerPrivateFromContext(aCx);
+  MOZ_ASSERT(workerPrivate);
+
+  dom::AutoSyncLoopHolder syncLoop(workerPrivate, dom::WorkerStatus::Canceling);
+  nsCOMPtr<nsISerialEventTarget> syncLoopTarget =
+      syncLoop.GetSerialEventTarget();
+  if (!syncLoopTarget) {
+    return NS_ERROR_DOM_INVALID_STATE_ERR;
+  }
+
+  RefPtr<ScriptReaderRunnable> runnable =
+      new ScriptReaderRunnable(workerPrivate, syncLoopTarget, aLocation);
+
+  if (NS_FAILED(NS_DispatchToMainThread(runnable))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  syncLoop.Run();
+
+  if (NS_FAILED(runnable->Result())) {
+    return runnable->Result();
+  }
+
+  aData = std::move(runnable->Data());
+
+  return NS_OK;
+}
+
+/* static */
+nsresult mozJSModuleLoader::LoadSingleModuleScriptOnWorker(
+    SyncModuleLoader* aModuleLoader, JSContext* aCx,
+    JS::loader::ModuleLoadRequest* aRequest, MutableHandleScript aScriptOut) {
+  nsAutoCString location;
+  nsresult rv = aRequest->mURI->GetSpec(location);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCString data;
+  rv = ReadScriptOnMainThread(aCx, location, data);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  CompileOptions options(aCx);
+  ScriptPreloader::FillCompileOptionsForCachedStencil(options);
+  options.setFileAndLine(location.BeginReading(), 1);
+  SetModuleOptions(options);
+
+  JS::SourceText<mozilla::Utf8Unit> srcBuf;
+  if (!srcBuf.init(aCx, data.get(), data.Length(),
+                   JS::SourceOwnership::Borrowed)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  RefPtr<JS::Stencil> stencil =
+      CompileStencil(aCx, options, srcBuf, /* aIsModule = */ true);
+  if (!stencil) {
+    return NS_ERROR_FAILURE;
+  }
+
+  aScriptOut.set(InstantiateStencil(aCx, stencil, /* aIsModule = */ true));
+
+  return NS_OK;
+}
+
+/* static */
+nsresult mozJSModuleLoader::LoadSingleModuleScript(
+    SyncModuleLoader* aModuleLoader, JSContext* aCx,
+    JS::loader::ModuleLoadRequest* aRequest, MutableHandleScript aScriptOut) {
+  AUTO_PROFILER_MARKER_TEXT(
+      "ChromeUtils.importESModule static import", JS,
+      MarkerOptions(MarkerStack::Capture(),
+                    MarkerInnerWindowIdFromJSContext(aCx)),
+      nsContentUtils::TruncatedURLForDisplay(aRequest->mURI));
+
+  if (!NS_IsMainThread()) {
+    return LoadSingleModuleScriptOnWorker(aModuleLoader, aCx, aRequest,
+                                          aScriptOut);
+  }
+
+  ModuleLoaderInfo info(aRequest);
+  nsresult rv = info.EnsureResolvedURI();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIFile> sourceFile;
+  rv = GetSourceFile(info.ResolvedURI(), getter_AddRefs(sourceFile));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  bool realFile = LocationIsRealFile(aRequest->mURI);
+
+  RootedScript script(aCx);
+  rv = GetScriptForLocation(aCx, info, sourceFile, realFile, aScriptOut);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+#ifdef STARTUP_RECORDER_ENABLED
+  if (aModuleLoader == sSelf->mModuleLoader) {
+    sSelf->RecordImportStack(aCx, aRequest);
+  } else if (sDevToolsLoader &&
+             aModuleLoader == sDevToolsLoader->mModuleLoader) {
+    sDevToolsLoader->RecordImportStack(aCx, aRequest);
+  } else {
+    // NOTE: Do not record import stack for non-shared globals, given the
+    //       loader is associated with the global only while importing.
+  }
+#endif
+
+  return NS_OK;
+}
+
+/* static */
+nsresult mozJSModuleLoader::GetSourceFile(nsIURI* aResolvedURI,
+                                          nsIFile** aSourceFileOut) {
+  // Get the JAR if there is one.
+  nsCOMPtr<nsIJARURI> jarURI;
+  nsresult rv = NS_OK;
+  jarURI = do_QueryInterface(aResolvedURI, &rv);
+  nsCOMPtr<nsIFileURL> baseFileURL;
+  if (NS_SUCCEEDED(rv)) {
+    nsCOMPtr<nsIURI> baseURI;
+    while (jarURI) {
+      jarURI->GetJARFile(getter_AddRefs(baseURI));
+      jarURI = do_QueryInterface(baseURI, &rv);
+    }
+    baseFileURL = do_QueryInterface(baseURI, &rv);
+    NS_ENSURE_SUCCESS(rv, rv);
+  } else {
+    baseFileURL = do_QueryInterface(aResolvedURI, &rv);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  return baseFileURL->GetFile(aSourceFileOut);
+}
+
+/* static */
+bool mozJSModuleLoader::LocationIsRealFile(nsIURI* aURI) {
+  // We need to be extra careful checking for URIs pointing to files.
+  // EnsureFile may not always get called, especially on resource URIs so we
+  // need to call GetFile to make sure this is a valid file.
+  nsresult rv = NS_OK;
+  nsCOMPtr<nsIFileURL> fileURL = do_QueryInterface(aURI, &rv);
+  nsCOMPtr<nsIFile> testFile;
+  if (NS_SUCCEEDED(rv)) {
+    fileURL->GetFile(getter_AddRefs(testFile));
+  }
+
+  return bool(testFile);
+}
+
+JSObject* mozJSModuleLoader::PrepareObjectForLocation(JSContext* aCx,
+                                                      nsIFile* aModuleFile,
+                                                      nsIURI* aURI,
+                                                      bool aRealFile) {
+  RootedObject globalObj(aCx, GetSharedGlobal(aCx));
+  NS_ENSURE_TRUE(globalObj, nullptr);
+  JSAutoRealm ar(aCx, globalObj);
+
+  // |thisObj| is the object we set properties on for a particular .jsm.
+  RootedObject thisObj(aCx, JS::NewJSMEnvironment(aCx));
+  NS_ENSURE_TRUE(thisObj, nullptr);
+
+  if (aRealFile) {
+    if (XRE_IsParentProcess()) {
+      RootedObject locationObj(aCx);
+
+      nsresult rv = nsXPConnect::XPConnect()->WrapNative(
+          aCx, thisObj, aModuleFile, NS_GET_IID(nsIFile),
+          locationObj.address());
+      NS_ENSURE_SUCCESS(rv, nullptr);
+      NS_ENSURE_TRUE(locationObj, nullptr);
+
+      if (!JS_DefineProperty(aCx, thisObj, "__LOCATION__", locationObj, 0)) {
+        return nullptr;
+      }
+    }
+  }
+
+  // Expose the URI from which the script was imported through a special
+  // variable that we insert into the JSM.
+  nsAutoCString nativePath;
+  NS_ENSURE_SUCCESS(aURI->GetSpec(nativePath), nullptr);
+
+  RootedString exposedUri(
+      aCx, JS_NewStringCopyN(aCx, nativePath.get(), nativePath.Length()));
+  NS_ENSURE_TRUE(exposedUri, nullptr);
+
+  if (!JS_DefineProperty(aCx, thisObj, "__URI__", exposedUri, 0)) {
+    return nullptr;
+  }
+
+  return thisObj;
+}
+
+static mozilla::Result<nsCString, nsresult> ReadScript(
+    ModuleLoaderInfo& aInfo) {
+  MOZ_TRY(aInfo.EnsureScriptChannel());
+
+  nsCOMPtr<nsIInputStream> scriptStream;
+  MOZ_TRY(aInfo.ScriptChannel()->Open(getter_AddRefs(scriptStream)));
+
+  uint64_t len64;
+  uint32_t bytesRead;
+
+  MOZ_TRY(scriptStream->Available(&len64));
+  NS_ENSURE_TRUE(len64 < UINT32_MAX, Err(NS_ERROR_FILE_TOO_BIG));
+  NS_ENSURE_TRUE(len64, Err(NS_ERROR_FAILURE));
+  uint32_t len = (uint32_t)len64;
+
+  /* malloc an internal buf the size of the file */
+  nsCString str;
+  if (!str.SetLength(len, fallible)) {
+    return Err(NS_ERROR_OUT_OF_MEMORY);
+  }
+
+  /* read the file in one swoop */
+  MOZ_TRY(scriptStream->Read(str.BeginWriting(), len, &bytesRead));
+  if (bytesRead != len) {
+    return Err(NS_BASE_STREAM_OSERROR);
+  }
+
+  return std::move(str);
+}
+
+nsresult mozJSModuleLoader::ObjectForLocation(
+    ModuleLoaderInfo& aInfo, nsIFile* aModuleFile, MutableHandleObject aObject,
+    MutableHandleScript aTableScript, char** aLocation,
+    bool aPropagateExceptions, MutableHandleValue aException) {
+  MOZ_ASSERT(NS_IsMainThread(), "Must be on main thread.");
+
+  dom::AutoJSAPI jsapi;
+  jsapi.Init();
+  JSContext* cx = jsapi.cx();
+
+  nsresult rv = aInfo.EnsureURI();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  bool realFile = LocationIsRealFile(aInfo.URI());
+
+  RootedObject obj(
+      cx, PrepareObjectForLocation(cx, aModuleFile, aInfo.URI(), realFile));
+  NS_ENSURE_TRUE(obj, NS_ERROR_FAILURE);
+  MOZ_ASSERT(!JS_IsGlobalObject(obj));
+
+  JSAutoRealm ar(cx, obj);
+
+  RootedScript script(cx);
+  rv = GetScriptForLocation(cx, aInfo, aModuleFile, realFile, &script,
+                            aLocation);
+  if (NS_FAILED(rv)) {
+    // Propagate the exception, if one exists. Also, don't leave the stale
+    // exception on this context.
+    if (aPropagateExceptions && jsapi.HasException()) {
+      if (!jsapi.StealException(aException)) {
+        return NS_ERROR_OUT_OF_MEMORY;
+      }
+    }
+
+    return rv;
+  }
+
+  // Assign aObject here so that it's available to recursive imports.
+  // See bug 384168.
+  aObject.set(obj);
+
+  aTableScript.set(script);
+
+  {  // Scope for AutoEntryScript
+    AutoAllowLegacyScriptExecution exemption;
+
+    // We're going to run script via JS_ExecuteScript, so we need an
+    // AutoEntryScript. This is Gecko-specific and not in any spec.
+    dom::AutoEntryScript aes(CurrentGlobalOrNull(cx),
+                             "module loader load module");
+    JSContext* aescx = aes.cx();
+
+    bool executeOk = false;
+    if (JS_IsGlobalObject(obj)) {
+      JS::RootedValue rval(cx);
+      executeOk = JS_ExecuteScript(aescx, script, &rval);
+    } else {
+      executeOk = JS::ExecuteInJSMEnvironment(aescx, script, obj);
+    }
+
+    if (!executeOk) {
+      if (aPropagateExceptions && aes.HasException()) {
+        // Ignore return value because we're returning an error code
+        // anyway.
+        Unused << aes.StealException(aException);
+      }
+      aObject.set(nullptr);
+      aTableScript.set(nullptr);
+      return NS_ERROR_FAILURE;
+    }
+  }
+
+  return rv;
+}
+
+/* static */
+void mozJSModuleLoader::SetModuleOptions(CompileOptions& aOptions) {
+  aOptions.setModule();
+
+  // Top level await is not supported in synchronously loaded modules.
+  aOptions.topLevelAwait = false;
+
+  // Make all top-level `vars` available in `ModuleEnvironmentObject`.
+  aOptions.deoptimizeModuleGlobalVars = true;
+}
+
+/* static */
+nsresult mozJSModuleLoader::GetScriptForLocation(
+    JSContext* aCx, ModuleLoaderInfo& aInfo, nsIFile* aModuleFile,
+    bool aUseMemMap, MutableHandleScript aScriptOut, char** aLocationOut) {
+  // JS compilation errors are returned via an exception on the context.
+  MOZ_ASSERT(!JS_IsExceptionPending(aCx));
+
+  aScriptOut.set(nullptr);
+
+  nsAutoCString nativePath;
+  nsresult rv = aInfo.URI()->GetSpec(nativePath);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Before compiling the script, first check to see if we have it in
+  // the preloader cache or the startupcache.  Note: as a rule, preloader cache
+  // errors and startupcache errors are not fatal to loading the script, since
+  // we can always slow-load.
+
+  bool storeIntoStartupCache = false;
+  StartupCache* cache = StartupCache::GetSingleton();
+
+  aInfo.EnsureResolvedURI();
+
+  nsAutoCString cachePath;
+  if (aInfo.IsModule()) {
+    rv = PathifyURI(JS_CACHE_PREFIX("non-syntactic", "module"),
+                    aInfo.ResolvedURI(), cachePath);
+  } else {
+    rv = PathifyURI(JS_CACHE_PREFIX("non-syntactic", "script"),
+                    aInfo.ResolvedURI(), cachePath);
+  }
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  JS::DecodeOptions decodeOptions;
+  ScriptPreloader::FillDecodeOptionsForCachedStencil(decodeOptions);
+
+  RefPtr<JS::Stencil> stencil =
+      ScriptPreloader::GetSingleton().GetCachedStencil(aCx, decodeOptions,
+                                                       cachePath);
+
+  if (!stencil && cache) {
+    ReadCachedStencil(cache, cachePath, aCx, decodeOptions,
+                      getter_AddRefs(stencil));
+    if (!stencil) {
+      JS_ClearPendingException(aCx);
+
+      storeIntoStartupCache = true;
+    }
+  }
+
+  if (stencil) {
+    LOG(("Successfully loaded %s from cache\n", nativePath.get()));
+  } else {
+    // The script wasn't in the cache , so compile it now.
+    LOG(("Slow loading %s\n", nativePath.get()));
+
+    CompileOptions options(aCx);
+    ScriptPreloader::FillCompileOptionsForCachedStencil(options);
+    options.setFileAndLine(nativePath.get(), 1);
+    if (aInfo.IsModule()) {
+      SetModuleOptions(options);
+    } else {
+      options.setForceStrictMode();
+      options.setNonSyntacticScope(true);
+    }
+
+    // If we can no longer write to caches, we should stop using lazy sources
+    // and instead let normal syntax parsing occur. This can occur in content
+    // processes after the ScriptPreloader is flushed where we can read but no
+    // longer write.
+    if (!storeIntoStartupCache && !ScriptPreloader::GetSingleton().Active()) {
+      options.setSourceIsLazy(false);
+    }
+
+    if (aUseMemMap) {
+      AutoMemMap map;
+      MOZ_TRY(map.init(aModuleFile));
+
+      // Note: exceptions will get handled further down;
+      // don't early return for them here.
+      auto buf = map.get<char>();
+
+      JS::SourceText<mozilla::Utf8Unit> srcBuf;
+      if (srcBuf.init(aCx, buf.get(), map.size(),
+                      JS::SourceOwnership::Borrowed)) {
+        stencil = CompileStencil(aCx, options, srcBuf, aInfo.IsModule());
+      }
+    } else {
+      nsCString str;
+      MOZ_TRY_VAR(str, ReadScript(aInfo));
+
+      JS::SourceText<mozilla::Utf8Unit> srcBuf;
+      if (srcBuf.init(aCx, str.get(), str.Length(),
+                      JS::SourceOwnership::Borrowed)) {
+        stencil = CompileStencil(aCx, options, srcBuf, aInfo.IsModule());
+      }
+    }
+
+#ifdef DEBUG
+    // The above shouldn't touch any options for instantiation.
+    JS::InstantiateOptions instantiateOptions(options);
+    instantiateOptions.assertDefault();
+#endif
+
+    if (!stencil) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+
+  aScriptOut.set(InstantiateStencil(aCx, stencil, aInfo.IsModule()));
+  if (!aScriptOut) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // ScriptPreloader::NoteScript needs to be called unconditionally, to
+  // reflect the usage into the next session's cache.
+  ScriptPreloader::GetSingleton().NoteStencil(nativePath, cachePath, stencil);
+
+  // Write to startup cache only when we didn't have any cache for the script
+  // and compiled it.
+  if (storeIntoStartupCache) {
+    MOZ_ASSERT(stencil);
+
+    // We successfully compiled the script, so cache it.
+    rv = WriteCachedStencil(cache, cachePath, aCx, stencil);
+
+    // Don't treat failure to write as fatal, since we might be working
+    // with a read-only cache.
+    if (NS_SUCCEEDED(rv)) {
+      LOG(("Successfully wrote to cache\n"));
+    } else {
+      LOG(("Failed to write to cache\n"));
+    }
+  }
+
+  /* Owned by ModuleEntry. Freed when we remove from the table. */
+  if (aLocationOut) {
+    *aLocationOut = ToNewCString(nativePath, mozilla::fallible);
+    if (!*aLocationOut) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  }
+
+  return NS_OK;
+}
+
+void mozJSModuleLoader::UnloadModules() {
+  mInitialized = false;
+
+  if (mLoaderGlobal) {
+    MOZ_ASSERT(JS_HasExtensibleLexicalEnvironment(mLoaderGlobal));
+    JS::RootedObject lexicalEnv(dom::RootingCx(),
+                                JS_ExtensibleLexicalEnvironment(mLoaderGlobal));
+    JS_SetAllNonReservedSlotsToUndefined(lexicalEnv);
+    JS_SetAllNonReservedSlotsToUndefined(mLoaderGlobal);
+    mLoaderGlobal = nullptr;
+  }
+  mServicesObj = nullptr;
+
+#ifdef STARTUP_RECORDER_ENABLED
+  mImportStacks.Clear();
+#endif
+  mFallbackImports.Clear();
+  mInProgressImports.Clear();
+  mImports.Clear();
+  mLocations.Clear();
+}
+
+/* static */
+already_AddRefed<Stencil> mozJSModuleLoader::CompileStencil(
+    JSContext* aCx, const JS::CompileOptions& aOptions,
+    JS::SourceText<mozilla::Utf8Unit>& aSource, bool aIsModule) {
+  if (aIsModule) {
+    return CompileModuleScriptToStencil(aCx, aOptions, aSource);
+  }
+
+  return CompileGlobalScriptToStencil(aCx, aOptions, aSource);
+}
+
+/* static */
+JSScript* mozJSModuleLoader::InstantiateStencil(JSContext* aCx,
+                                                JS::Stencil* aStencil,
+                                                bool aIsModule) {
+  JS::InstantiateOptions instantiateOptions;
+
+  if (aIsModule) {
+    RootedObject module(aCx);
+    module = JS::InstantiateModuleStencil(aCx, instantiateOptions, aStencil);
+    if (!module) {
+      return nullptr;
+    }
+
+    return JS::GetModuleScript(module);
+  }
+
+  return JS::InstantiateGlobalStencil(aCx, instantiateOptions, aStencil);
+}
+
+nsresult mozJSModuleLoader::ImportInto(const nsACString& registryLocation,
+                                       HandleValue targetValArg, JSContext* cx,
+                                       uint8_t optionalArgc,
+                                       MutableHandleValue retval) {
+  MOZ_ASSERT(nsContentUtils::IsCallerChrome());
+
+  RootedValue targetVal(cx, targetValArg);
+  RootedObject targetObject(cx, nullptr);
+
+  if (optionalArgc) {
+    // The caller passed in the optional second argument. Get it.
+    if (targetVal.isObject()) {
+      // If we're passing in something like a content DOM window, chances
+      // are the caller expects the properties to end up on the object
+      // proper and not on the Xray holder. This is dubious, but can be used
+      // during testing. Given that dumb callers can already leak JSMs into
+      // content by passing a raw content JS object (where Xrays aren't
+      // possible), we aim for consistency here. Waive xray.
+      if (WrapperFactory::IsXrayWrapper(&targetVal.toObject()) &&
+          !WrapperFactory::WaiveXrayAndWrap(cx, &targetVal)) {
+        return NS_ERROR_FAILURE;
+      }
+      targetObject = &targetVal.toObject();
+    } else if (!targetVal.isNull()) {
+      // If targetVal isNull(), we actually want to leave targetObject null.
+      // Not doing so breaks |make package|.
+      return ReportOnCallerUTF8(cx, ERROR_SCOPE_OBJ,
+                                PromiseFlatCString(registryLocation).get());
+    }
+  } else {
+    FindTargetObject(cx, &targetObject);
+    if (!targetObject) {
+      return ReportOnCallerUTF8(cx, ERROR_NO_TARGET_OBJECT,
+                                PromiseFlatCString(registryLocation).get());
+    }
+  }
+
+  js::AssertSameCompartment(cx, targetObject);
+
+  RootedObject global(cx);
+  nsresult rv = ImportInto(registryLocation, targetObject, cx, &global);
+
+  if (global) {
+    if (!JS_WrapObject(cx, &global)) {
+      NS_ERROR("can't wrap return value");
+      return NS_ERROR_FAILURE;
+    }
+
+    retval.setObject(*global);
+  }
+  return rv;
+}
+
+nsresult mozJSModuleLoader::IsModuleLoaded(const nsACString& aLocation,
+                                           bool* retval) {
+  MOZ_ASSERT(nsContentUtils::IsCallerChrome());
+
+  mInitialized = true;
+  ModuleLoaderInfo info(aLocation);
+  if (mImports.Get(info.Key())) {
+    *retval = true;
+    return NS_OK;
+  }
+
+  if (mModuleLoader) {
+    nsAutoCString mjsLocation;
+    if (!TryToMJS(aLocation, mjsLocation)) {
+      *retval = false;
+      return NS_OK;
+    }
+
+    ModuleLoaderInfo mjsInfo(mjsLocation);
+
+    nsresult rv = mjsInfo.EnsureURI();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (mModuleLoader->IsModuleFetched(mjsInfo.URI())) {
+      *retval = true;
+      return NS_OK;
+    }
+  }
+
+  *retval = false;
+  return NS_OK;
+}
+
+nsresult mozJSModuleLoader::IsJSModuleLoaded(const nsACString& aLocation,
+                                             bool* retval) {
+  MOZ_ASSERT(nsContentUtils::IsCallerChrome());
+
+  mInitialized = true;
+  ModuleLoaderInfo info(aLocation);
+  if (mImports.Get(info.Key())) {
+    *retval = true;
+    return NS_OK;
+  }
+
+  *retval = false;
+  return NS_OK;
+}
+
+nsresult mozJSModuleLoader::IsESModuleLoaded(const nsACString& aLocation,
+                                             bool* retval) {
+  MOZ_ASSERT(nsContentUtils::IsCallerChrome());
+
+  mInitialized = true;
+  ModuleLoaderInfo info(aLocation);
+
+  nsresult rv = info.EnsureURI();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (mModuleLoader->IsModuleFetched(info.URI())) {
+    *retval = true;
+    return NS_OK;
+  }
+
+  *retval = false;
+  return NS_OK;
+}
+
+void mozJSModuleLoader::GetLoadedModules(nsTArray<nsCString>& aLoadedModules) {
+  aLoadedModules.SetCapacity(mImports.Count());
+  for (const auto& data : mImports.Values()) {
+    aLoadedModules.AppendElement(data->location);
+  }
+}
+
+nsresult mozJSModuleLoader::GetLoadedESModules(
+    nsTArray<nsCString>& aLoadedModules) {
+  return mModuleLoader->GetFetchedModuleURLs(aLoadedModules);
+}
+
+nsresult mozJSModuleLoader::GetLoadedJSAndESModules(
+    nsTArray<nsCString>& aLoadedModules) {
+  GetLoadedModules(aLoadedModules);
+
+  nsTArray<nsCString> modules;
+  nsresult rv = GetLoadedESModules(modules);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  for (const auto& location : modules) {
+    if (IsMJS(location)) {
+      nsAutoCString jsmLocation;
+      // NOTE: Unconditionally convert to *.jsm.  This doesn't cover *.js case
+      //       but given `Cu.loadedModules` is rarely used for system modules,
+      //       this won't cause much compat issue.
+      MJSToJSM(location, jsmLocation);
+      aLoadedModules.AppendElement(jsmLocation);
+    }
+  }
+
+  return NS_OK;
+}
+
+#ifdef STARTUP_RECORDER_ENABLED
+void mozJSModuleLoader::RecordImportStack(JSContext* aCx,
+                                          const nsACString& aLocation) {
+  if (!Preferences::GetBool("browser.startup.record", false)) {
+    return;
+  }
+
+  mImportStacks.InsertOrUpdate(
+      aLocation, xpc_PrintJSStack(aCx, false, false, false).get());
+}
+
+void mozJSModuleLoader::RecordImportStack(
+    JSContext* aCx, JS::loader::ModuleLoadRequest* aRequest) {
+  if (!Preferences::GetBool("browser.startup.record", false)) {
+    return;
+  }
+
+  nsAutoCString location;
+  nsresult rv = aRequest->mURI->GetSpec(location);
+  if (NS_FAILED(rv)) {
+    return;
+  }
+
+  auto recordJSStackOnly = [&]() {
+    mImportStacks.InsertOrUpdate(
+        location, xpc_PrintJSStack(aCx, false, false, false).get());
+  };
+
+  if (aRequest->IsTopLevel()) {
+    recordJSStackOnly();
+    return;
+  }
+
+  nsAutoCString importerSpec;
+  rv = aRequest->mReferrer->GetSpec(importerSpec);
+  if (NS_FAILED(rv)) {
+    recordJSStackOnly();
+    return;
+  }
+
+  ModuleLoaderInfo importerInfo(importerSpec);
+  auto importerStack = mImportStacks.Lookup(importerInfo.Key());
+  if (!importerStack) {
+    // The importer's stack is not collected, possibly due to OOM.
+    recordJSStackOnly();
+    return;
+  }
+
+  nsAutoCString stack;
+
+  stack += "* import [\"";
+  stack += importerSpec;
+  stack += "\"]\n";
+  stack += *importerStack;
+
+  mImportStacks.InsertOrUpdate(location, stack);
+}
+#endif
+
+nsresult mozJSModuleLoader::GetModuleImportStack(const nsACString& aLocation,
+                                                 nsACString& retval) {
+#ifdef STARTUP_RECORDER_ENABLED
+  MOZ_ASSERT(nsContentUtils::IsCallerChrome());
+
+  // When querying the DevTools loader, it may not be initialized yet
+  if (!mInitialized) {
+    return NS_ERROR_FAILURE;
+  }
+
+  ModuleLoaderInfo info(aLocation);
+  auto str = mImportStacks.Lookup(info.Key());
+  if (!str) {
+    return NS_ERROR_FAILURE;
+  }
+
+  retval = *str;
+  return NS_OK;
+#else
+  return NS_ERROR_NOT_IMPLEMENTED;
+#endif
+}
+
+nsresult mozJSModuleLoader::ImportInto(const nsACString& aLocation,
+                                       HandleObject targetObj, JSContext* cx,
+                                       MutableHandleObject vp) {
+  vp.set(nullptr);
+
+  JS::RootedObject exports(cx);
+  MOZ_TRY(Import(cx, aLocation, vp, &exports, !targetObj));
+
+  if (targetObj) {
+    JS::Rooted<JS::IdVector> ids(cx, JS::IdVector(cx));
+    if (!JS_Enumerate(cx, exports, &ids)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    JS::RootedValue value(cx);
+    JS::RootedId id(cx);
+    for (jsid idVal : ids) {
+      id = idVal;
+      if (!JS_GetPropertyById(cx, exports, id, &value) ||
+          !JS_SetPropertyById(cx, targetObj, id, value)) {
+        return NS_ERROR_FAILURE;
+      }
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult mozJSModuleLoader::ExtractExports(JSContext* aCx,
+                                           ModuleLoaderInfo& aInfo,
+                                           ModuleEntry* aMod,
+                                           JS::MutableHandleObject aExports) {
+  // cxhelper must be created before jsapi, so that jsapi is destroyed and
+  // pops any context it has pushed before we report to the caller context.
+  JSCLContextHelper cxhelper(aCx);
+
+  // Even though we are calling JS_SetPropertyById on targetObj, we want
+  // to ensure that we never run script here, so we use an AutoJSAPI and
+  // not an AutoEntryScript.
+  dom::AutoJSAPI jsapi;
+  jsapi.Init();
+  JSContext* cx = jsapi.cx();
+  JSAutoRealm ar(cx, aMod->obj);
+
+  RootedValue symbols(cx);
+  {
+    RootedObject obj(
+        cx, ResolveModuleObjectProperty(cx, aMod->obj, "EXPORTED_SYMBOLS"));
+    if (!obj || !JS_GetProperty(cx, obj, "EXPORTED_SYMBOLS", &symbols)) {
+      return ReportOnCallerUTF8(cxhelper, ERROR_NOT_PRESENT, aInfo);
+    }
+  }
+
+  bool isArray;
+  if (!JS::IsArrayObject(cx, symbols, &isArray)) {
+    return NS_ERROR_FAILURE;
+  }
+  if (!isArray) {
+    return ReportOnCallerUTF8(cxhelper, ERROR_NOT_AN_ARRAY, aInfo);
+  }
+
+  RootedObject symbolsObj(cx, &symbols.toObject());
+
+  // Iterate over symbols array, installing symbols on targetObj:
+
+  uint32_t symbolCount = 0;
+  if (!JS::GetArrayLength(cx, symbolsObj, &symbolCount)) {
+    return ReportOnCallerUTF8(cxhelper, ERROR_GETTING_ARRAY_LENGTH, aInfo);
+  }
+
+#ifdef DEBUG
+  nsAutoCString logBuffer;
+#endif
+
+  aExports.set(JS_NewPlainObject(cx));
+  if (!aExports) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  bool missing = false;
+
+  RootedValue value(cx);
+  RootedId symbolId(cx);
+  RootedObject symbolHolder(cx);
+  for (uint32_t i = 0; i < symbolCount; ++i) {
+    if (!JS_GetElement(cx, symbolsObj, i, &value) || !value.isString() ||
+        !JS_ValueToId(cx, value, &symbolId)) {
+      return ReportOnCallerUTF8(cxhelper, ERROR_ARRAY_ELEMENT, aInfo, i);
+    }
+
+    symbolHolder = ResolveModuleObjectPropertyById(cx, aMod->obj, symbolId);
+    if (!symbolHolder ||
+        !JS_GetPropertyById(cx, symbolHolder, symbolId, &value)) {
+      RootedString symbolStr(cx, symbolId.toString());
+      JS::UniqueChars bytes = JS_EncodeStringToUTF8(cx, symbolStr);
+      if (!bytes) {
+        return NS_ERROR_FAILURE;
+      }
+      return ReportOnCallerUTF8(cxhelper, ERROR_GETTING_SYMBOL, aInfo,
+                                bytes.get());
+    }
+
+    // It's possible |value| is the uninitialized lexical MagicValue when
+    // there's a cyclic import: const obj = ChromeUtils.import("parent.jsm").
+    if (value.isMagic(JS_UNINITIALIZED_LEXICAL)) {
+      RootedString symbolStr(cx, symbolId.toString());
+      JS::UniqueChars bytes = JS_EncodeStringToUTF8(cx, symbolStr);
+      if (!bytes) {
+        return NS_ERROR_FAILURE;
+      }
+      return ReportOnCallerUTF8(cxhelper, ERROR_UNINITIALIZED_SYMBOL, aInfo,
+                                bytes.get());
+    }
+
+    if (value.isUndefined()) {
+      missing = true;
+    }
+
+    if (!JS_SetPropertyById(cx, aExports, symbolId, value)) {
+      RootedString symbolStr(cx, symbolId.toString());
+      JS::UniqueChars bytes = JS_EncodeStringToUTF8(cx, symbolStr);
+      if (!bytes) {
+        return NS_ERROR_FAILURE;
+      }
+      return ReportOnCallerUTF8(cxhelper, ERROR_GETTING_SYMBOL, aInfo,
+                                bytes.get());
+    }
+#ifdef DEBUG
+    if (i == 0) {
+      logBuffer.AssignLiteral("Installing symbols [ ");
+    }
+    JS::UniqueChars bytes = JS_EncodeStringToLatin1(cx, symbolId.toString());
+    if (!!bytes) {
+      logBuffer.Append(bytes.get());
+    }
+    logBuffer.Append(' ');
+    if (i == symbolCount - 1) {
+      nsCString location;
+      MOZ_TRY(aInfo.GetLocation(location));
+      LOG(("%s] from %s\n", logBuffer.get(), location.get()));
+    }
+#endif
+  }
+
+  // Don't cache the exports object if any of its exported symbols are
+  // missing. If the module hasn't finished loading yet, they may be
+  // defined the next time we try to import it.
+  if (!missing) {
+    aMod->exports = aExports;
+  }
+  return NS_OK;
+}
+
+/* static */
+bool mozJSModuleLoader::IsTrustedScheme(nsIURI* aURI) {
+  return aURI->SchemeIs("resource") || aURI->SchemeIs("chrome");
+}
+
+nsresult mozJSModuleLoader::Import(JSContext* aCx, const nsACString& aLocation,
+                                   JS::MutableHandleObject aModuleGlobal,
+                                   JS::MutableHandleObject aModuleExports,
+                                   bool aIgnoreExports) {
+  mInitialized = true;
+
+  AUTO_PROFILER_MARKER_TEXT(
+      "ChromeUtils.import", JS,
+      MarkerOptions(MarkerStack::Capture(),
+                    MarkerInnerWindowIdFromJSContext(aCx)),
+      Substring(aLocation, 0, std::min(size_t(128), aLocation.Length())));
+
+  // The JSM may already be ESM-ified, and in that case the load is expected
+  // to fail.  Suppress the error message, the crash, and also the telemetry
+  // event for the failure.
+  //
+  // If this load fails, it will be redirected to `.sys.mjs` URL
+  // in TryFallbackToImportESModule, and if the redirect also fails,
+  // the load is performed again below, with the check enabled.
+  ModuleLoaderInfo info(aLocation, SkipCheckForBrokenURLOrZeroSized::Yes);
+
+  nsresult rv;
+  ModuleEntry* mod;
+  UniquePtr<ModuleEntry> newEntry;
+  if (!mImports.Get(info.Key(), &mod) &&
+      !mInProgressImports.Get(info.Key(), &mod)) {
+    // We're trying to import a new JSM, but we're late in shutdown and this
+    // will likely not succeed and might even crash, so fail here.
+    if (PastShutdownPhase(ShutdownPhase::XPCOMShutdownFinal)) {
+      return NS_ERROR_ILLEGAL_DURING_SHUTDOWN;
+    }
+
+    // If we've hit file-not-found and fallback was successful,
+    // return the cached data.
+    bool aFound;
+    rv = TryCachedFallbackToImportESModule(
+        aCx, aLocation, aModuleGlobal, aModuleExports, aIgnoreExports, &aFound);
+    NS_ENSURE_SUCCESS(rv, rv);
+    if (aFound) {
+      return NS_OK;
+    }
+
+    newEntry = MakeUnique<ModuleEntry>(RootingContext::get(aCx));
+
+    // Note: This implies EnsureURI().
+    MOZ_TRY(info.EnsureResolvedURI());
+
+    // Reject imports from untrusted sources.
+    if (!IsTrustedScheme(info.URI())) {
+      return NS_ERROR_DOM_SECURITY_ERR;
+    }
+
+    nsCOMPtr<nsIFile> sourceFile;
+    rv = GetSourceFile(info.ResolvedURI(), getter_AddRefs(sourceFile));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = info.ResolvedURI()->GetSpec(newEntry->resolvedURL);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCString* existingPath;
+    if (mLocations.Get(newEntry->resolvedURL, &existingPath) &&
+        *existingPath != info.Key()) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    mLocations.InsertOrUpdate(newEntry->resolvedURL,
+                              MakeUnique<nsCString>(info.Key()));
+
+    RootedValue exception(aCx);
+    {
+      mInProgressImports.InsertOrUpdate(info.Key(), newEntry.get());
+      auto cleanup =
+          MakeScopeExit([&]() { mInProgressImports.Remove(info.Key()); });
+
+      rv = ObjectForLocation(info, sourceFile, &newEntry->obj,
+                             &newEntry->thisObjectKey, &newEntry->location,
+                             true, &exception);
+    }
+
+    if (NS_FAILED(rv)) {
+      mLocations.Remove(newEntry->resolvedURL);
+      if (!exception.isUndefined()) {
+        // An exception was thrown during compilation. Propagate it
+        // out to our caller so they can report it.
+        bool isModuleSyntaxError = false;
+
+        if (exception.isObject()) {
+          JS::Rooted<JSObject*> exceptionObj(aCx, &exception.toObject());
+          JSAutoRealm ar(aCx, exceptionObj);
+          JSErrorReport* report = JS_ErrorFromException(aCx, exceptionObj);
+          if (report) {
+            switch (report->errorNumber) {
+              case JSMSG_IMPORT_DECL_AT_TOP_LEVEL:
+              case JSMSG_EXPORT_DECL_AT_TOP_LEVEL:
+                // If the exception is related to module syntax, it's most
+                // likely because of misuse of API.
+                // Provide better error message.
+                isModuleSyntaxError = true;
+
+                JS_ReportErrorUTF8(aCx,
+                                   "ChromeUtils.import is called against "
+                                   "an ES module script (%s).  Please use "
+                                   "ChromeUtils.importESModule instead "
+                                   "(SyntaxError: %s)",
+                                   aLocation.BeginReading(),
+                                   report->message().c_str());
+                break;
+              default:
+                break;
+            }
+          }
+        }
+
+        if (!isModuleSyntaxError) {
+          if (!JS_WrapValue(aCx, &exception)) {
+            return NS_ERROR_OUT_OF_MEMORY;
+          }
+          JS_SetPendingException(aCx, exception);
+        }
+
+        return NS_ERROR_FAILURE;
+      }
+
+      if (rv == NS_ERROR_FILE_NOT_FOUND || rv == NS_ERROR_FILE_ACCESS_DENIED) {
+        // NS_ERROR_FILE_ACCESS_DENIED happens if the access is blocked by
+        // sandbox.
+        rv = TryFallbackToImportESModule(aCx, aLocation, aModuleGlobal,
+                                         aModuleExports, aIgnoreExports);
+
+        if (rv == NS_ERROR_FILE_NOT_FOUND ||
+            rv == NS_ERROR_FILE_ACCESS_DENIED) {
+          // Both JSM and ESM are not found, with the check inside necko
+          // skipped (See EnsureScriptChannel and mSkipCheck).
+          //
+          // Perform the load again with the check enabled, so that
+          // logging, crash-on-autonation, and telemetry event happen.
+          if (NS_SUCCEEDED(info.EnsureURI()) &&
+              !LocationIsRealFile(info.URI())) {
+            info.resetChannelWithCheckForBrokenURLOrZeroSized();
+            (void)ReadScript(info);
+          }
+        }
+
+        return rv;
+      }
+
+      // Something failed, but we don't know what it is, guess.
+      return NS_ERROR_FILE_NOT_FOUND;
+    }
+
+#ifdef STARTUP_RECORDER_ENABLED
+    RecordImportStack(aCx, aLocation);
+#endif
+
+    mod = newEntry.get();
+  }
+
+  MOZ_ASSERT(mod->obj, "Import table contains entry with no object");
+  JS::RootedObject globalProxy(aCx);
+  {
+    JSAutoRealm ar(aCx, mod->obj);
+
+    globalProxy = CreateJSMEnvironmentProxy(aCx, mod->obj);
+    if (!globalProxy) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+  if (!JS_WrapObject(aCx, &globalProxy)) {
+    return NS_ERROR_FAILURE;
+  }
+  aModuleGlobal.set(globalProxy);
+
+  JS::RootedObject exports(aCx, mod->exports);
+  if (!exports && !aIgnoreExports) {
+    MOZ_TRY(ExtractExports(aCx, info, mod, &exports));
+  }
+
+  if (exports && !JS_WrapObject(aCx, &exports)) {
+    mLocations.Remove(newEntry->resolvedURL);
+    return NS_ERROR_FAILURE;
+  }
+  aModuleExports.set(exports);
+
+  // Cache this module for later
+  if (newEntry) {
+    mImports.InsertOrUpdate(info.Key(), std::move(newEntry));
+  }
+
+  return NS_OK;
+}
+
+nsresult mozJSModuleLoader::TryFallbackToImportESModule(
+    JSContext* aCx, const nsACString& aLocation,
+    JS::MutableHandleObject aModuleGlobal,
+    JS::MutableHandleObject aModuleExports, bool aIgnoreExports) {
+  nsAutoCString mjsLocation;
+  if (!TryToMJS(aLocation, mjsLocation)) {
+    return NS_ERROR_FILE_NOT_FOUND;
+  }
+
+  JS::RootedObject moduleNamespace(aCx);
+  // The fallback can fail if the URL was not for ESMified JSM.  Suppress the
+  // error message, the crash, and also the telemetry event for the failure.
+  nsresult rv = ImportESModule(aCx, mjsLocation, &moduleNamespace,
+                               SkipCheckForBrokenURLOrZeroSized::Yes);
+  if (rv == NS_ERROR_FILE_NOT_FOUND || rv == NS_ERROR_FILE_ACCESS_DENIED) {
+    // The error for ESModule shouldn't be exposed if the file does not exist,
+    // or the access is blocked by sandbox.
+    if (JS_IsExceptionPending(aCx)) {
+      JS_ClearPendingException(aCx);
+    }
+  }
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  JS::RootedObject globalProxy(aCx);
+  {
+    JSAutoRealm ar(aCx, moduleNamespace);
+
+    JS::RootedObject moduleObject(
+        aCx, JS::GetModuleForNamespace(aCx, moduleNamespace));
+    if (!moduleObject) {
+      return NS_ERROR_FAILURE;
+    }
+
+    globalProxy = CreateModuleEnvironmentProxy(aCx, moduleObject);
+    if (!globalProxy) {
+      return NS_ERROR_FAILURE;
+    }
+
+    // Cache the redirect to use in subsequent imports.
+    ModuleLoaderInfo info(aLocation);
+    auto newEntry = MakeUnique<FallbackModuleEntry>(RootingContext::get(aCx));
+    newEntry->globalProxy = globalProxy;
+    newEntry->moduleNamespace = moduleNamespace;
+    mFallbackImports.InsertOrUpdate(info.Key(), std::move(newEntry));
+  }
+
+  if (!JS_WrapObject(aCx, &globalProxy)) {
+    return NS_ERROR_FAILURE;
+  }
+  aModuleGlobal.set(globalProxy);
+
+  if (!aIgnoreExports) {
+    JS::RootedObject exports(aCx, moduleNamespace);
+    if (!JS_WrapObject(aCx, &exports)) {
+      return NS_ERROR_FAILURE;
+    }
+    aModuleExports.set(exports);
+  }
+
+  return NS_OK;
+}
+
+nsresult mozJSModuleLoader::TryCachedFallbackToImportESModule(
+    JSContext* aCx, const nsACString& aLocation,
+    JS::MutableHandleObject aModuleGlobal,
+    JS::MutableHandleObject aModuleExports, bool aIgnoreExports, bool* aFound) {
+  ModuleLoaderInfo info(aLocation);
+  FallbackModuleEntry* fallbackMod;
+  if (!mFallbackImports.Get(info.Key(), &fallbackMod)) {
+    *aFound = false;
+    return NS_OK;
+  }
+
+  JS::RootedObject globalProxy(aCx, fallbackMod->globalProxy);
+  if (!JS_WrapObject(aCx, &globalProxy)) {
+    return NS_ERROR_FAILURE;
+  }
+  aModuleGlobal.set(globalProxy);
+
+  if (!aIgnoreExports) {
+    JS::RootedObject exports(aCx, fallbackMod->moduleNamespace);
+    if (!JS_WrapObject(aCx, &exports)) {
+      return NS_ERROR_FAILURE;
+    }
+    aModuleExports.set(exports);
+  }
+
+  *aFound = true;
+  return NS_OK;
+}
+
+nsresult mozJSModuleLoader::ImportESModule(
+    JSContext* aCx, const nsACString& aLocation,
+    JS::MutableHandleObject aModuleNamespace,
+    SkipCheckForBrokenURLOrZeroSized
+        aSkipCheck /* = SkipCheckForBrokenURLOrZeroSized::No */) {
+  using namespace JS::loader;
+
+  mInitialized = true;
+
+  // Called from ChromeUtils::ImportESModule.
+  nsCString str(aLocation);
+
+  AUTO_PROFILER_MARKER_TEXT(
+      "ChromeUtils.importESModule", JS,
+      MarkerOptions(MarkerStack::Capture(),
+                    MarkerInnerWindowIdFromJSContext(aCx)),
+      Substring(aLocation, 0, std::min(size_t(128), aLocation.Length())));
+
+  RootedObject globalObj(aCx, GetSharedGlobal(aCx));
+  NS_ENSURE_TRUE(globalObj, NS_ERROR_FAILURE);
+  MOZ_ASSERT_IF(NS_IsMainThread(),
+                xpc::Scriptability::Get(globalObj).Allowed());
+
+  // The module loader should be instantiated when fetching the shared global
+  MOZ_ASSERT(mModuleLoader);
+
+  JSAutoRealm ar(aCx, globalObj);
+
+  nsCOMPtr<nsIURI> uri;
+  nsresult rv = NS_NewURI(getter_AddRefs(uri), aLocation);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIPrincipal> principal =
+      mModuleLoader->GetGlobalObject()->PrincipalOrNull();
+  MOZ_ASSERT(principal);
+
+  RefPtr<ScriptFetchOptions> options = new ScriptFetchOptions(
+      CORS_NONE, /* aNonce = */ u""_ns, dom::RequestPriority::Auto,
+      ParserMetadata::NotParserInserted, principal);
+
+  RefPtr<SyncLoadContext> context = new SyncLoadContext();
+  context->mSkipCheck = aSkipCheck;
+
+  RefPtr<VisitedURLSet> visitedSet =
+      ModuleLoadRequest::NewVisitedSetForTopLevelImport(uri);
+
+  RefPtr<ModuleLoadRequest> request = new ModuleLoadRequest(
+      uri, dom::ReferrerPolicy::No_referrer, options, dom::SRIMetadata(),
+      /* aReferrer = */ nullptr, context,
+      /* aIsTopLevel = */ true,
+      /* aIsDynamicImport = */ false, mModuleLoader, visitedSet, nullptr);
+
+  request->NoCacheEntryFound();
+
+  rv = request->StartModuleLoad();
+  if (NS_FAILED(rv)) {
+    mModuleLoader->MaybeReportLoadError(aCx);
+    return rv;
+  }
+
+  rv = mModuleLoader->ProcessRequests();
+  if (NS_FAILED(rv)) {
+    mModuleLoader->MaybeReportLoadError(aCx);
+    return rv;
+  }
+
+  MOZ_ASSERT(request->IsFinished());
+  if (!request->mModuleScript) {
+    mModuleLoader->MaybeReportLoadError(aCx);
+    return NS_ERROR_FAILURE;
+  }
+
+  // All modules are loaded. MaybeReportLoadError isn't necessary from here.
+
+  if (!request->InstantiateModuleGraph()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  rv = mModuleLoader->EvaluateModuleInContext(aCx, request,
+                                              JS::ThrowModuleErrorsSync);
+  NS_ENSURE_SUCCESS(rv, rv);
+  if (JS_IsExceptionPending(aCx)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  RefPtr<ModuleScript> moduleScript = request->mModuleScript;
+  JS::Rooted<JSObject*> module(aCx, moduleScript->ModuleRecord());
+  aModuleNamespace.set(JS::GetModuleNamespace(aCx, module));
+
+  return NS_OK;
+}
+
+nsresult mozJSModuleLoader::Unload(const nsACString& aLocation) {
+  if (!mInitialized) {
+    return NS_OK;
+  }
+
+  ModuleLoaderInfo info(aLocation);
+
+  ModuleEntry* mod;
+  if (mImports.Get(info.Key(), &mod)) {
+    mLocations.Remove(mod->resolvedURL);
+    mImports.Remove(info.Key());
+  }
+
+  // If this is the last module to be unloaded, we will leak mLoaderGlobal
+  // until UnloadModules is called. So be it.
+
+  return NS_OK;
+}
+
+bool mozJSModuleLoader::CreateJSServices(JSContext* aCx) {
+  JSObject* services = NewJSServices(aCx);
+  if (!services) {
+    return false;
+  }
+
+  mServicesObj = services;
+  return true;
+}
+
+bool mozJSModuleLoader::DefineJSServices(JSContext* aCx,
+                                         JS::Handle<JSObject*> aGlobal) {
+  if (!mServicesObj) {
+    // This function is called whenever creating a new global that needs
+    // `Services`, including the loader's shared global.
+    //
+    // This function is no-op if it's called during creating the loader's
+    // shared global.
+    //
+    // See also  CreateAndDefineJSServices.
+    MOZ_ASSERT(!mLoaderGlobal);
+    MOZ_ASSERT(mIsInitializingLoaderGlobal);
+    return true;
+  }
+
+  JS::Rooted<JS::Value> services(aCx, ObjectValue(*mServicesObj));
+  if (!JS_WrapValue(aCx, &services)) {
+    return false;
+  }
+
+  JS::Rooted<JS::PropertyKey> servicesId(
+      aCx, XPCJSContext::Get()->GetStringID(XPCJSContext::IDX_SERVICES));
+  return JS_DefinePropertyById(aCx, aGlobal, servicesId, services, 0);
+}
+
+size_t mozJSModuleLoader::ModuleEntry::SizeOfIncludingThis(
+    MallocSizeOf aMallocSizeOf) const {
+  size_t n = aMallocSizeOf(this);
+  n += aMallocSizeOf(location);
+
+  return n;
+}
+
+//----------------------------------------------------------------------
+
+/* static */
+MOZ_THREAD_LOCAL(mozJSModuleLoader*)
+NonSharedGlobalSyncModuleLoaderScope::sTlsActiveLoader;
+
+void NonSharedGlobalSyncModuleLoaderScope::InitStatics() {
+  sTlsActiveLoader.infallibleInit();
+}
+
+NonSharedGlobalSyncModuleLoaderScope::NonSharedGlobalSyncModuleLoaderScope(
+    JSContext* aCx, nsIGlobalObject* aGlobal) {
+  MOZ_ASSERT_IF(NS_IsMainThread(),
+                !mozJSModuleLoader::IsSharedSystemGlobal(aGlobal));
+  MOZ_ASSERT_IF(NS_IsMainThread(),
+                !mozJSModuleLoader::IsDevToolsLoaderGlobal(aGlobal));
+
+  mAsyncModuleLoader = aGlobal->GetModuleLoader(aCx);
+  MOZ_ASSERT(mAsyncModuleLoader,
+             "The consumer should guarantee the global returns non-null module "
+             "loader");
+
+  mLoader = new mozJSModuleLoader();
+  RegisterWeakMemoryReporter(mLoader);
+  mLoader->InitSyncModuleLoaderForGlobal(aGlobal);
+
+  mAsyncModuleLoader->CopyModulesTo(mLoader->mModuleLoader);
+
+  mMaybeOverride.emplace(mAsyncModuleLoader, mLoader->mModuleLoader);
+
+  MOZ_ASSERT(!sTlsActiveLoader.get());
+  sTlsActiveLoader.set(mLoader);
+}
+
+NonSharedGlobalSyncModuleLoaderScope::~NonSharedGlobalSyncModuleLoaderScope() {
+  MOZ_ASSERT(sTlsActiveLoader.get() == mLoader);
+  sTlsActiveLoader.set(nullptr);
+
+  mLoader->DisconnectSyncModuleLoaderFromGlobal();
+  UnregisterWeakMemoryReporter(mLoader);
+}
+
+void NonSharedGlobalSyncModuleLoaderScope::Finish() {
+  mLoader->mModuleLoader->MoveModulesTo(mAsyncModuleLoader);
+}
+
+/* static */
+bool NonSharedGlobalSyncModuleLoaderScope::IsActive() {
+  return !!sTlsActiveLoader.get();
+}
+
+/*static */
+mozJSModuleLoader* NonSharedGlobalSyncModuleLoaderScope::ActiveLoader() {
+  return sTlsActiveLoader.get();
+}
+
+//----------------------------------------------------------------------
+
+JSCLContextHelper::JSCLContextHelper(JSContext* aCx)
+    : mContext(aCx), mBuf(nullptr) {}
+
+JSCLContextHelper::~JSCLContextHelper() {
+  if (mBuf) {
+    JS_ReportErrorUTF8(mContext, "%s", mBuf.get());
+  }
+}
+
+void JSCLContextHelper::reportErrorAfterPop(UniqueChars&& buf) {
+  MOZ_ASSERT(!mBuf, "Already called reportErrorAfterPop");
+  mBuf = std::move(buf);
+}