Adding upstream version 115.8.0esr.upstream/115.8.0esr

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

164 files changed, 39634 insertions, 0 deletions

diff --git a/xpcom/base/AppShutdown.cpp b/xpcom/base/AppShutdown.cpp
new file mode 100644
index 0000000000..c68dedef31
--- /dev/null
+++ b/xpcom/base/AppShutdown.cpp
@@ -0,0 +1,469 @@
+/* -*- 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 "ShutdownPhase.h"
+#ifdef XP_WIN
+#  include <windows.h>
+#  include "mozilla/PreXULSkeletonUI.h"
+#else
+#  include <unistd.h>
+#endif
+
+#include "ProfilerControl.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/CmdLineAndEnvUtils.h"
+#include "mozilla/PoisonIOInterposer.h"
+#include "mozilla/Printf.h"
+#include "mozilla/scache/StartupCache.h"
+#include "mozilla/SpinEventLoopUntil.h"
+#include "mozilla/StartupTimeline.h"
+#include "mozilla/StaticPrefs_toolkit.h"
+#include "mozilla/LateWriteChecks.h"
+#include "mozilla/Services.h"
+#include "nsAppDirectoryServiceDefs.h"
+#include "nsAppRunner.h"
+#include "nsDirectoryServiceUtils.h"
+#include "nsExceptionHandler.h"
+#include "nsICertStorage.h"
+#include "nsThreadUtils.h"
+
+#include "AppShutdown.h"
+
+// TODO: understand why on Android we cannot include this and if we should
+#ifndef ANDROID
+#  include "nsTerminator.h"
+#endif
+#include "prenv.h"
+
+#ifdef MOZ_BACKGROUNDTASKS
+#  include "mozilla/BackgroundTasks.h"
+#endif
+
+namespace mozilla {
+
+const char* sPhaseObserverKeys[] = {
+    nullptr,                            // NotInShutdown
+    "quit-application",                 // AppShutdownConfirmed
+    "profile-change-net-teardown",      // AppShutdownNetTeardown
+    "profile-change-teardown",          // AppShutdownTeardown
+    "profile-before-change",            // AppShutdown
+    "profile-before-change-qm",         // AppShutdownQM
+    "profile-before-change-telemetry",  // AppShutdownTelemetry
+    "xpcom-will-shutdown",              // XPCOMWillShutdown
+    "xpcom-shutdown",                   // XPCOMShutdown
+    "xpcom-shutdown-threads",           // XPCOMShutdownThreads
+    nullptr,                            // XPCOMShutdownFinal
+    nullptr                             // CCPostLastCycleCollection
+};
+
+static_assert(sizeof(sPhaseObserverKeys) / sizeof(sPhaseObserverKeys[0]) ==
+              (size_t)ShutdownPhase::ShutdownPhase_Length);
+
+const char* sPhaseReadableNames[] = {"NotInShutdown",
+                                     "AppShutdownConfirmed",
+                                     "AppShutdownNetTeardown",
+                                     "AppShutdownTeardown",
+                                     "AppShutdown",
+                                     "AppShutdownQM",
+                                     "AppShutdownTelemetry",
+                                     "XPCOMWillShutdown",
+                                     "XPCOMShutdown",
+                                     "XPCOMShutdownThreads",
+                                     "XPCOMShutdownFinal",
+                                     "CCPostLastCycleCollection"};
+
+static_assert(sizeof(sPhaseReadableNames) / sizeof(sPhaseReadableNames[0]) ==
+              (size_t)ShutdownPhase::ShutdownPhase_Length);
+
+#ifndef ANDROID
+static nsTerminator* sTerminator = nullptr;
+#endif
+
+static ShutdownPhase sFastShutdownPhase = ShutdownPhase::NotInShutdown;
+static ShutdownPhase sLateWriteChecksPhase = ShutdownPhase::NotInShutdown;
+static AppShutdownMode sShutdownMode = AppShutdownMode::Normal;
+static Atomic<ShutdownPhase> sCurrentShutdownPhase(
+    ShutdownPhase::NotInShutdown);
+static int sExitCode = 0;
+
+// These environment variable strings are all deliberately copied and leaked
+// due to requirements of PR_SetEnv and similar.
+static char* sSavedXulAppFile = nullptr;
+#ifdef XP_WIN
+static wchar_t* sSavedProfDEnvVar = nullptr;
+static wchar_t* sSavedProfLDEnvVar = nullptr;
+#else
+static char* sSavedProfDEnvVar = nullptr;
+static char* sSavedProfLDEnvVar = nullptr;
+#endif
+
+ShutdownPhase GetShutdownPhaseFromPrefValue(int32_t aPrefValue) {
+  switch (aPrefValue) {
+    case 1:
+      return ShutdownPhase::CCPostLastCycleCollection;
+    case 2:
+      return ShutdownPhase::XPCOMShutdownThreads;
+    case 3:
+      return ShutdownPhase::XPCOMShutdown;
+      // NOTE: the remaining values from the ShutdownPhase enum will be added
+      // when we're at least reasonably confident that the world won't come
+      // crashing down if we do a fast shutdown at that point.
+  }
+  return ShutdownPhase::NotInShutdown;
+}
+
+ShutdownPhase AppShutdown::GetCurrentShutdownPhase() {
+  return sCurrentShutdownPhase;
+}
+
+bool AppShutdown::IsInOrBeyond(ShutdownPhase aPhase) {
+  return (sCurrentShutdownPhase >= aPhase);
+}
+
+int AppShutdown::GetExitCode() { return sExitCode; }
+
+void AppShutdown::SaveEnvVarsForPotentialRestart() {
+  const char* s = PR_GetEnv("XUL_APP_FILE");
+  if (s) {
+    sSavedXulAppFile = Smprintf("%s=%s", "XUL_APP_FILE", s).release();
+    MOZ_LSAN_INTENTIONALLY_LEAK_OBJECT(sSavedXulAppFile);
+  }
+}
+
+const char* AppShutdown::GetObserverKey(ShutdownPhase aPhase) {
+  return sPhaseObserverKeys[static_cast<std::underlying_type_t<ShutdownPhase>>(
+      aPhase)];
+}
+
+const char* AppShutdown::GetShutdownPhaseName(ShutdownPhase aPhase) {
+  return sPhaseReadableNames[static_cast<std::underlying_type_t<ShutdownPhase>>(
+      aPhase)];
+}
+
+void AppShutdown::MaybeDoRestart() {
+  if (sShutdownMode == AppShutdownMode::Restart) {
+    StopLateWriteChecks();
+
+    // Since we'll be launching our child while we're still alive, make sure
+    // we've unlocked the profile first, otherwise the child could hit its
+    // profile lock check before we've exited and thus released our lock.
+    UnlockProfile();
+
+    if (sSavedXulAppFile) {
+      PR_SetEnv(sSavedXulAppFile);
+    }
+
+#ifdef XP_WIN
+    if (sSavedProfDEnvVar && !EnvHasValue("XRE_PROFILE_PATH")) {
+      SetEnvironmentVariableW(L"XRE_PROFILE_PATH", sSavedProfDEnvVar);
+    }
+    if (sSavedProfLDEnvVar && !EnvHasValue("XRE_PROFILE_LOCAL_PATH")) {
+      SetEnvironmentVariableW(L"XRE_PROFILE_LOCAL_PATH", sSavedProfLDEnvVar);
+    }
+    Unused << NotePreXULSkeletonUIRestarting();
+#else
+    if (sSavedProfDEnvVar && !EnvHasValue("XRE_PROFILE_PATH")) {
+      PR_SetEnv(sSavedProfDEnvVar);
+    }
+    if (sSavedProfLDEnvVar && !EnvHasValue("XRE_PROFILE_LOCAL_PATH")) {
+      PR_SetEnv(sSavedProfLDEnvVar);
+    }
+#endif
+
+    LaunchChild(true);
+  }
+}
+
+#ifdef XP_WIN
+wchar_t* CopyPathIntoNewWCString(nsIFile* aFile) {
+  wchar_t* result = nullptr;
+  nsAutoString resStr;
+  aFile->GetPath(resStr);
+  if (resStr.Length() > 0) {
+    result = (wchar_t*)malloc((resStr.Length() + 1) * sizeof(wchar_t));
+    if (result) {
+      wcscpy(result, resStr.get());
+      result[resStr.Length()] = 0;
+    }
+  }
+
+  return result;
+}
+#endif
+
+void AppShutdown::Init(AppShutdownMode aMode, int aExitCode,
+                       AppShutdownReason aReason) {
+  if (sShutdownMode == AppShutdownMode::Normal) {
+    sShutdownMode = aMode;
+  }
+  AppShutdown::AnnotateShutdownReason(aReason);
+
+  sExitCode = aExitCode;
+
+#ifndef ANDROID
+  sTerminator = new nsTerminator();
+#endif
+
+  // Late-write checks needs to find the profile directory, so it has to
+  // be initialized before services::Shutdown or (because of
+  // xpcshell tests replacing the service) modules being unloaded.
+  InitLateWriteChecks();
+
+  int32_t fastShutdownPref = StaticPrefs::toolkit_shutdown_fastShutdownStage();
+  sFastShutdownPhase = GetShutdownPhaseFromPrefValue(fastShutdownPref);
+  int32_t lateWriteChecksPref =
+      StaticPrefs::toolkit_shutdown_lateWriteChecksStage();
+  sLateWriteChecksPhase = GetShutdownPhaseFromPrefValue(lateWriteChecksPref);
+
+  // Very early shutdowns can happen before the startup cache is even
+  // initialized; don't bother initializing it during shutdown.
+  if (auto* cache = scache::StartupCache::GetSingletonNoInit()) {
+    cache->MaybeInitShutdownWrite();
+  }
+}
+
+void AppShutdown::MaybeFastShutdown(ShutdownPhase aPhase) {
+  // For writes which we want to ensure are recorded, we don't want to trip
+  // the late write checking code. Anything that writes to disk and which
+  // we don't want to skip should be listed out explicitly in this section.
+  if (aPhase == sFastShutdownPhase || aPhase == sLateWriteChecksPhase) {
+    if (auto* cache = scache::StartupCache::GetSingletonNoInit()) {
+      cache->EnsureShutdownWriteComplete();
+    }
+
+    nsresult rv;
+    nsCOMPtr<nsICertStorage> certStorage =
+        do_GetService("@mozilla.org/security/certstorage;1", &rv);
+    if (NS_SUCCEEDED(rv)) {
+      SpinEventLoopUntil("AppShutdown::MaybeFastShutdown"_ns, [&]() {
+        int32_t remainingOps;
+        nsresult rv = certStorage->GetRemainingOperationCount(&remainingOps);
+        NS_ASSERTION(NS_SUCCEEDED(rv),
+                     "nsICertStorage::getRemainingOperationCount failed during "
+                     "shutdown");
+        return NS_FAILED(rv) || remainingOps <= 0;
+      });
+    }
+  }
+  if (aPhase == sFastShutdownPhase) {
+    StopLateWriteChecks();
+    RecordShutdownEndTimeStamp();
+    MaybeDoRestart();
+
+    profiler_shutdown(IsFastShutdown::Yes);
+
+    DoImmediateExit(sExitCode);
+  } else if (aPhase == sLateWriteChecksPhase) {
+#ifdef XP_MACOSX
+    OnlyReportDirtyWrites();
+#endif /* XP_MACOSX */
+    BeginLateWriteChecks();
+  }
+}
+
+void AppShutdown::OnShutdownConfirmed() {
+  // If we're restarting, we need to save environment variables correctly
+  // while everything is still alive to do so.
+  if (sShutdownMode == AppShutdownMode::Restart) {
+    nsCOMPtr<nsIFile> profD;
+    nsCOMPtr<nsIFile> profLD;
+    NS_GetSpecialDirectory(NS_APP_USER_PROFILE_50_DIR, getter_AddRefs(profD));
+    NS_GetSpecialDirectory(NS_APP_USER_PROFILE_LOCAL_50_DIR,
+                           getter_AddRefs(profLD));
+#ifdef XP_WIN
+    sSavedProfDEnvVar = CopyPathIntoNewWCString(profD);
+    sSavedProfLDEnvVar = CopyPathIntoNewWCString(profLD);
+#else
+    nsAutoCString profDStr;
+    profD->GetNativePath(profDStr);
+    sSavedProfDEnvVar =
+        Smprintf("XRE_PROFILE_PATH=%s", profDStr.get()).release();
+    nsAutoCString profLDStr;
+    profLD->GetNativePath(profLDStr);
+    sSavedProfLDEnvVar =
+        Smprintf("XRE_PROFILE_LOCAL_PATH=%s", profLDStr.get()).release();
+#endif
+    MOZ_LSAN_INTENTIONALLY_LEAK_OBJECT(sSavedProfDEnvVar);
+    MOZ_LSAN_INTENTIONALLY_LEAK_OBJECT(sSavedProfLDEnvVar);
+  }
+}
+
+void AppShutdown::DoImmediateExit(int aExitCode) {
+#ifdef XP_WIN
+  HANDLE process = ::GetCurrentProcess();
+  if (::TerminateProcess(process, aExitCode)) {
+    ::WaitForSingleObject(process, INFINITE);
+  }
+  MOZ_CRASH("TerminateProcess failed.");
+#else
+  _exit(aExitCode);
+#endif
+}
+
+bool AppShutdown::IsRestarting() {
+  return sShutdownMode == AppShutdownMode::Restart;
+}
+
+void AppShutdown::AnnotateShutdownReason(AppShutdownReason aReason) {
+  auto key = CrashReporter::Annotation::ShutdownReason;
+  nsCString reasonStr;
+  switch (aReason) {
+    case AppShutdownReason::AppClose:
+      reasonStr = "AppClose"_ns;
+      break;
+    case AppShutdownReason::AppRestart:
+      reasonStr = "AppRestart"_ns;
+      break;
+    case AppShutdownReason::OSForceClose:
+      reasonStr = "OSForceClose"_ns;
+      break;
+    case AppShutdownReason::OSSessionEnd:
+      reasonStr = "OSSessionEnd"_ns;
+      break;
+    case AppShutdownReason::OSShutdown:
+      reasonStr = "OSShutdown"_ns;
+      break;
+    case AppShutdownReason::WinUnexpectedMozQuit:
+      reasonStr = "WinUnexpectedMozQuit"_ns;
+      break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("We should know the given reason for shutdown.");
+      reasonStr = "Unknown"_ns;
+      break;
+  }
+  CrashReporter::AnnotateCrashReport(key, reasonStr);
+}
+
+#ifdef DEBUG
+static bool sNotifyingShutdownObservers = false;
+static bool sAdvancingShutdownPhase = false;
+
+bool AppShutdown::IsNoOrLegalShutdownTopic(const char* aTopic) {
+  if (!XRE_IsParentProcess()) {
+    // Until we know what to do with AppShutdown for child processes,
+    // we ignore them for now. See bug 1697745.
+    return true;
+  }
+  ShutdownPhase phase = GetShutdownPhaseFromTopic(aTopic);
+  return phase == ShutdownPhase::NotInShutdown ||
+         (sNotifyingShutdownObservers && phase == sCurrentShutdownPhase);
+}
+#endif
+
+void AppShutdown::AdvanceShutdownPhaseInternal(
+    ShutdownPhase aPhase, bool doNotify, const char16_t* aNotificationData,
+    const nsCOMPtr<nsISupports>& aNotificationSubject) {
+  AssertIsOnMainThread();
+#ifdef DEBUG
+  // Prevent us from re-entrance
+  MOZ_ASSERT(!sAdvancingShutdownPhase);
+  sAdvancingShutdownPhase = true;
+  auto exit = MakeScopeExit([] { sAdvancingShutdownPhase = false; });
+#endif
+
+  // We ensure that we can move only forward. We cannot
+  // MOZ_ASSERT here as there are some tests that fire
+  // notifications out of shutdown order.
+  // See for example test_sss_sanitizeOnShutdown.js
+  if (sCurrentShutdownPhase >= aPhase) {
+    return;
+  }
+
+  nsCOMPtr<nsIThread> thread = do_GetCurrentThread();
+
+  // AppShutdownConfirmed is special in some ways as
+  // - we can be called on top of a nested event loop (and it is the phase for
+  //   which SpinEventLoopUntilOrQuit breaks, so we want to return soon)
+  // - we can be called from a sync marionette function that wants immediate
+  //   feedback, too
+  // - in general, AppShutdownConfirmed will fire the "quit-application"
+  //   notification which in turn will cause an event to be dispatched that
+  //   runs all the rest of our shutdown sequence which we do not want to be
+  //   processed on top of the running event.
+  // Thus we never do any NS_ProcessPendingEvents for it.
+  bool mayProcessPending = (aPhase > ShutdownPhase::AppShutdownConfirmed);
+
+  // Give runnables dispatched between two calls to AdvanceShutdownPhase
+  // a chance to run before actually advancing the phase. As we excluded
+  // AppShutdownConfirmed above we can be sure that the processing is
+  // covered by the terminator's timer of the previous phase during normal
+  // shutdown (except out-of-order calls from some test).
+  // Note that this affects only main thread runnables, such that the correct
+  // way of ensuring shutdown processing remains to have an async shutdown
+  // blocker.
+  if (mayProcessPending && thread) {
+    NS_ProcessPendingEvents(thread);
+  }
+
+  // From now on any IsInOrBeyond checks will find the new phase set.
+  sCurrentShutdownPhase = aPhase;
+
+#ifndef ANDROID
+  if (sTerminator) {
+    sTerminator->AdvancePhase(aPhase);
+  }
+#endif
+
+  AppShutdown::MaybeFastShutdown(aPhase);
+
+  // This will null out the gathered pointers for this phase synchronously.
+  // Note that we keep the old order here to avoid breakage, so be aware that
+  // the notifications fired below will find these already cleared in case
+  // you expected the opposite.
+  mozilla::KillClearOnShutdown(aPhase);
+
+  // Empty our MT event queue to process any side effects thereof.
+  if (mayProcessPending && thread) {
+    NS_ProcessPendingEvents(thread);
+  }
+
+  if (doNotify) {
+    const char* aTopic = AppShutdown::GetObserverKey(aPhase);
+    if (aTopic) {
+      nsCOMPtr<nsIObserverService> obsService =
+          mozilla::services::GetObserverService();
+      if (obsService) {
+#ifdef DEBUG
+        sNotifyingShutdownObservers = true;
+        auto reset = MakeScopeExit([] { sNotifyingShutdownObservers = false; });
+#endif
+        obsService->NotifyObservers(aNotificationSubject, aTopic,
+                                    aNotificationData);
+        // Empty our MT event queue again after the notification has finished
+        if (mayProcessPending && thread) {
+          NS_ProcessPendingEvents(thread);
+        }
+      }
+    }
+  }
+}
+
+/**
+ * XXX: Before tackling bug 1697745 we need the
+ * possibility to advance the phase without notification
+ * in the content process.
+ */
+void AppShutdown::AdvanceShutdownPhaseWithoutNotify(ShutdownPhase aPhase) {
+  AdvanceShutdownPhaseInternal(aPhase, /* doNotify */ false, nullptr, nullptr);
+}
+
+void AppShutdown::AdvanceShutdownPhase(
+    ShutdownPhase aPhase, const char16_t* aNotificationData,
+    const nsCOMPtr<nsISupports>& aNotificationSubject) {
+  AdvanceShutdownPhaseInternal(aPhase, /* doNotify */ true, aNotificationData,
+                               aNotificationSubject);
+}
+
+ShutdownPhase AppShutdown::GetShutdownPhaseFromTopic(const char* aTopic) {
+  for (size_t i = 0; i < ArrayLength(sPhaseObserverKeys); ++i) {
+    if (sPhaseObserverKeys[i] && !strcmp(sPhaseObserverKeys[i], aTopic)) {
+      return static_cast<ShutdownPhase>(i);
+    }
+  }
+  return ShutdownPhase::NotInShutdown;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/AppShutdown.h b/xpcom/base/AppShutdown.h
new file mode 100644
index 0000000000..6056338900
--- /dev/null
+++ b/xpcom/base/AppShutdown.h
@@ -0,0 +1,152 @@
+/* -*- 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/. */
+
+#ifndef AppShutdown_h
+#define AppShutdown_h
+
+#include <type_traits>
+#include "nsCOMPtr.h"
+#include "nsISupports.h"
+#include "ShutdownPhase.h"
+
+namespace mozilla {
+
+enum class AppShutdownMode {
+  Normal,
+  Restart,
+};
+
+enum class AppShutdownReason {
+  // No reason.
+  Unknown,
+  // Normal application shutdown.
+  AppClose,
+  // The application wants to restart.
+  AppRestart,
+  // The OS is force closing us.
+  OSForceClose,
+  // The user is logging off from the OS session, the system may stay alive.
+  OSSessionEnd,
+  // The system is shutting down (and maybe restarting).
+  OSShutdown,
+  // We unexpectedly received MOZ_WM_APP_QUIT, see bug 1827807.
+  WinUnexpectedMozQuit,
+};
+
+class AppShutdown {
+ public:
+  static ShutdownPhase GetCurrentShutdownPhase();
+  static bool IsInOrBeyond(ShutdownPhase aPhase);
+
+  /**
+   * Returns the current exit code that the process will be terminated with.
+   */
+  static int GetExitCode();
+
+  /**
+   * Save environment variables that we might need if the app initiates a
+   * restart later in its lifecycle.
+   */
+  static void SaveEnvVarsForPotentialRestart();
+
+  /**
+   * Init the shutdown with the requested shutdown mode, exit code and optional
+   * a reason (if missing it will be derived from aMode).
+   */
+  static void Init(AppShutdownMode aMode, int aExitCode,
+                   AppShutdownReason aReason);
+
+  /**
+   * Confirm that we are in fact going to be shutting down.
+   */
+  static void OnShutdownConfirmed();
+
+  /**
+   * If we've attempted to initiate a restart, this call will set up the
+   * necessary environment variables and launch the new process.
+   */
+  static void MaybeDoRestart();
+
+  /**
+   * The _exit() call is not a safe way to terminate your own process on
+   * Windows, because _exit runs DLL detach callbacks which run static
+   * destructors for xul.dll.
+   *
+   * This method terminates the current process without those issues.
+   *
+   * Optionally a custom exit code can be supplied.
+   */
+  static void DoImmediateExit(int aExitCode = 0);
+
+  /**
+   * True if the application is currently attempting to shut down in order to
+   * restart.
+   */
+  static bool IsRestarting();
+
+  /**
+   * Wrapper for shutdown notifications that informs the terminator before
+   * we notify other observers. Calls MaybeFastShutdown.
+   */
+  static void AdvanceShutdownPhase(
+      ShutdownPhase aPhase, const char16_t* aNotificationData = nullptr,
+      const nsCOMPtr<nsISupports>& aNotificationSubject =
+          nsCOMPtr<nsISupports>(nullptr));
+
+  /**
+   * XXX: Before tackling bug 1697745 we need the
+   * possibility to advance the phase without notification
+   * in the content process.
+   */
+  static void AdvanceShutdownPhaseWithoutNotify(ShutdownPhase aPhase);
+
+  /**
+   * Map shutdown phase to observer key
+   */
+  static const char* GetObserverKey(ShutdownPhase aPhase);
+
+  /**
+   * Map shutdown phase to readable name
+   */
+  static const char* GetShutdownPhaseName(ShutdownPhase aPhase);
+
+  /**
+   * Map observer topic key to shutdown phase
+   */
+  static ShutdownPhase GetShutdownPhaseFromTopic(const char* aTopic);
+
+#ifdef DEBUG
+  /**
+   * Check, if we are allowed to send a shutdown notification.
+   * Shutdown specific topics are only allowed during calls to
+   * AdvanceShutdownPhase itself.
+   */
+  static bool IsNoOrLegalShutdownTopic(const char* aTopic);
+#endif
+
+ private:
+  /**
+   * Set the shutdown reason annotation.
+   */
+  static void AnnotateShutdownReason(AppShutdownReason aReason);
+
+  /**
+   * This will perform a fast shutdown via _exit(0) or similar if the user's
+   * prefs are configured to do so at this phase.
+   */
+  static void MaybeFastShutdown(ShutdownPhase aPhase);
+
+  /**
+   * Internal helper function, uses MaybeFastShutdown.
+   */
+  static void AdvanceShutdownPhaseInternal(
+      ShutdownPhase aPhase, bool doNotify, const char16_t* aNotificationData,
+      const nsCOMPtr<nsISupports>& aNotificationSubject);
+};
+
+}  // namespace mozilla
+
+#endif  // AppShutdown_h
diff --git a/xpcom/base/AutoRestore.h b/xpcom/base/AutoRestore.h
new file mode 100644
index 0000000000..fc585da14b
--- /dev/null
+++ b/xpcom/base/AutoRestore.h
@@ -0,0 +1,42 @@
+/* -*- 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/. */
+
+/* functions for restoring saved values at the end of a C++ scope */
+
+#ifndef mozilla_AutoRestore_h_
+#define mozilla_AutoRestore_h_
+
+#include "mozilla/Attributes.h"  // MOZ_STACK_CLASS
+
+namespace mozilla {
+
+/**
+ * Save the current value of a variable and restore it when the object
+ * goes out of scope.  For example:
+ *   {
+ *     AutoRestore<bool> savePainting(mIsPainting);
+ *     mIsPainting = true;
+ *
+ *     // ... your code here ...
+ *
+ *     // mIsPainting is reset to its old value at the end of this block
+ *   }
+ */
+template <class T>
+class MOZ_RAII AutoRestore {
+ private:
+  T& mLocation;
+  T mValue;
+
+ public:
+  explicit AutoRestore(T& aValue) : mLocation(aValue), mValue(aValue) {}
+  ~AutoRestore() { mLocation = mValue; }
+  T SavedValue() const { return mValue; }
+};
+
+}  // namespace mozilla
+
+#endif /* !defined(mozilla_AutoRestore_h_) */
diff --git a/xpcom/base/AvailableMemoryTracker.cpp b/xpcom/base/AvailableMemoryTracker.cpp
new file mode 100644
index 0000000000..5e75f26ac6
--- /dev/null
+++ b/xpcom/base/AvailableMemoryTracker.cpp
@@ -0,0 +1,194 @@
+/* -*- 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 "mozilla/AvailableMemoryTracker.h"
+
+#if defined(XP_WIN)
+#  include "mozilla/WindowsVersion.h"
+#  include "nsIMemoryReporter.h"
+#endif
+
+#include "nsIObserver.h"
+#include "nsIObserverService.h"
+#include "nsIRunnable.h"
+#include "nsISupports.h"
+#include "nsThreadUtils.h"
+#include "nsXULAppAPI.h"
+
+#include "mozilla/Mutex.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/Services.h"
+
+#if defined(MOZ_MEMORY)
+#  include "mozmemory.h"
+#endif  // MOZ_MEMORY
+
+using namespace mozilla;
+
+Atomic<uint32_t, MemoryOrdering::Relaxed> sNumLowPhysicalMemEvents;
+
+namespace {
+
+#if defined(XP_WIN)
+
+#  if (NTDDI_VERSION < NTDDI_WINBLUE) || \
+      (NTDDI_VERSION == NTDDI_WINBLUE && !defined(WINBLUE_KBSPRING14))
+// Definitions for heap optimization that require the Windows SDK to target the
+// Windows 8.1 Update
+static const HEAP_INFORMATION_CLASS HeapOptimizeResources =
+    static_cast<HEAP_INFORMATION_CLASS>(3);
+
+static const DWORD HEAP_OPTIMIZE_RESOURCES_CURRENT_VERSION = 1;
+
+typedef struct _HEAP_OPTIMIZE_RESOURCES_INFORMATION {
+  DWORD Version;
+  DWORD Flags;
+} HEAP_OPTIMIZE_RESOURCES_INFORMATION, *PHEAP_OPTIMIZE_RESOURCES_INFORMATION;
+#  endif
+
+static int64_t LowMemoryEventsPhysicalDistinguishedAmount() {
+  return sNumLowPhysicalMemEvents;
+}
+
+class LowEventsReporter final : public nsIMemoryReporter {
+  ~LowEventsReporter() {}
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    // clang-format off
+    MOZ_COLLECT_REPORT(
+      "low-memory-events/physical", KIND_OTHER, UNITS_COUNT_CUMULATIVE,
+      LowMemoryEventsPhysicalDistinguishedAmount(),
+"Number of low-physical-memory events fired since startup. We fire such an "
+"event when a windows low memory resource notification is signaled. The "
+"machine will start to page if it runs out of physical memory.  This may "
+"cause it to run slowly, but it shouldn't cause it to crash.");
+    // clang-format on
+
+    return NS_OK;
+  }
+};
+
+NS_IMPL_ISUPPORTS(LowEventsReporter, nsIMemoryReporter)
+
+#endif  // defined(XP_WIN)
+
+/**
+ * This runnable is executed in response to a memory-pressure event; we spin
+ * the event-loop when receiving the memory-pressure event in the hope that
+ * other observers will synchronously free some memory that we'll be able to
+ * purge here.
+ */
+class nsJemallocFreeDirtyPagesRunnable final : public Runnable {
+  ~nsJemallocFreeDirtyPagesRunnable() = default;
+
+#if defined(XP_WIN)
+  void OptimizeSystemHeap();
+#endif
+
+ public:
+  NS_DECL_NSIRUNNABLE
+
+  nsJemallocFreeDirtyPagesRunnable()
+      : Runnable("nsJemallocFreeDirtyPagesRunnable") {}
+};
+
+NS_IMETHODIMP
+nsJemallocFreeDirtyPagesRunnable::Run() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+#if defined(MOZ_MEMORY)
+  jemalloc_free_dirty_pages();
+#endif
+
+#if defined(XP_WIN)
+  OptimizeSystemHeap();
+#endif
+
+  return NS_OK;
+}
+
+#if defined(XP_WIN)
+void nsJemallocFreeDirtyPagesRunnable::OptimizeSystemHeap() {
+  // HeapSetInformation exists prior to Windows 8.1, but the
+  // HeapOptimizeResources information class does not.
+  if (IsWin8Point1OrLater()) {
+    HEAP_OPTIMIZE_RESOURCES_INFORMATION heapOptInfo = {
+        HEAP_OPTIMIZE_RESOURCES_CURRENT_VERSION};
+
+    ::HeapSetInformation(nullptr, HeapOptimizeResources, &heapOptInfo,
+                         sizeof(heapOptInfo));
+  }
+}
+#endif  // defined(XP_WIN)
+
+/**
+ * The memory pressure watcher is used for listening to memory-pressure events
+ * and reacting upon them. We use one instance per process currently only for
+ * cleaning up dirty unused pages held by jemalloc.
+ */
+class nsMemoryPressureWatcher final : public nsIObserver {
+  ~nsMemoryPressureWatcher() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  void Init();
+};
+
+NS_IMPL_ISUPPORTS(nsMemoryPressureWatcher, nsIObserver)
+
+/**
+ * Initialize and subscribe to the memory-pressure events. We subscribe to the
+ * observer service in this method and not in the constructor because we need
+ * to hold a strong reference to 'this' before calling the observer service.
+ */
+void nsMemoryPressureWatcher::Init() {
+  nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+
+  if (os) {
+    os->AddObserver(this, "memory-pressure", /* ownsWeak */ false);
+  }
+}
+
+/**
+ * Reacts to all types of memory-pressure events, launches a runnable to
+ * free dirty pages held by jemalloc.
+ */
+NS_IMETHODIMP
+nsMemoryPressureWatcher::Observe(nsISupports* aSubject, const char* aTopic,
+                                 const char16_t* aData) {
+  MOZ_ASSERT(!strcmp(aTopic, "memory-pressure"), "Unknown topic");
+
+  nsCOMPtr<nsIRunnable> runnable = new nsJemallocFreeDirtyPagesRunnable();
+
+  NS_DispatchToMainThread(runnable);
+
+  return NS_OK;
+}
+
+}  // namespace
+
+namespace mozilla {
+namespace AvailableMemoryTracker {
+
+void Init() {
+  // The watchers are held alive by the observer service.
+  RefPtr<nsMemoryPressureWatcher> watcher = new nsMemoryPressureWatcher();
+  watcher->Init();
+
+#if defined(XP_WIN)
+  RegisterLowMemoryEventsPhysicalDistinguishedAmount(
+      LowMemoryEventsPhysicalDistinguishedAmount);
+#endif  // defined(XP_WIN)
+}
+
+}  // namespace AvailableMemoryTracker
+}  // namespace mozilla
diff --git a/xpcom/base/AvailableMemoryTracker.h b/xpcom/base/AvailableMemoryTracker.h
new file mode 100644
index 0000000000..3d2a048cb3
--- /dev/null
+++ b/xpcom/base/AvailableMemoryTracker.h
@@ -0,0 +1,25 @@
+/* -*- 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/. */
+
+#ifndef mozilla_AvailableMemoryTracker_h
+#define mozilla_AvailableMemoryTracker_h
+
+namespace mozilla {
+namespace AvailableMemoryTracker {
+
+// The AvailableMemoryTracker launches a memory pressure watcher on all
+// platforms to react to low-memory situations and on Windows it implements
+// the full functionality used to monitor how much memory is available.
+//
+// Init() requires the observer service to be already available so cannot be
+// called too early during initialization.
+
+void Init();
+
+}  // namespace AvailableMemoryTracker
+}  // namespace mozilla
+
+#endif  // ifndef mozilla_AvailableMemoryTracker_h
diff --git a/xpcom/base/AvailableMemoryWatcher.cpp b/xpcom/base/AvailableMemoryWatcher.cpp
new file mode 100644
index 0000000000..44e0f7d220
--- /dev/null
+++ b/xpcom/base/AvailableMemoryWatcher.cpp
@@ -0,0 +1,180 @@
+/* -*- 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 "AvailableMemoryWatcher.h"
+
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/Telemetry.h"
+#include "nsExceptionHandler.h"
+#include "nsMemoryPressure.h"
+#include "nsXULAppAPI.h"
+
+namespace mozilla {
+
+// Use this class as the initial value of
+// nsAvailableMemoryWatcherBase::mCallback until RegisterCallback() is called
+// so that nsAvailableMemoryWatcherBase does not have to check if its callback
+// object is valid or not.
+class NullTabUnloader final : public nsITabUnloader {
+  ~NullTabUnloader() = default;
+
+ public:
+  NullTabUnloader() = default;
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSITABUNLOADER
+};
+
+NS_IMPL_ISUPPORTS(NullTabUnloader, nsITabUnloader)
+
+NS_IMETHODIMP NullTabUnloader::UnloadTabAsync() {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+StaticRefPtr<nsAvailableMemoryWatcherBase>
+    nsAvailableMemoryWatcherBase::sSingleton;
+
+/*static*/
+already_AddRefed<nsAvailableMemoryWatcherBase>
+nsAvailableMemoryWatcherBase::GetSingleton() {
+  if (!sSingleton) {
+    sSingleton = CreateAvailableMemoryWatcher();
+    ClearOnShutdown(&sSingleton);
+  }
+
+  return do_AddRef(sSingleton);
+}
+
+NS_IMPL_ISUPPORTS(nsAvailableMemoryWatcherBase, nsIAvailableMemoryWatcherBase);
+
+nsAvailableMemoryWatcherBase::nsAvailableMemoryWatcherBase()
+    : mNumOfTabUnloading(0),
+      mNumOfMemoryPressure(0),
+      mTabUnloader(new NullTabUnloader),
+      mInteracting(false) {
+  MOZ_ASSERT(XRE_IsParentProcess(),
+             "Watching memory only in the main process.");
+}
+
+const char* const nsAvailableMemoryWatcherBase::kObserverTopics[] = {
+    // Use this shutdown phase to make sure the instance is destroyed in GTest
+    "xpcom-shutdown",
+    "user-interaction-active",
+    "user-interaction-inactive",
+};
+
+nsresult nsAvailableMemoryWatcherBase::Init() {
+  MOZ_ASSERT(NS_IsMainThread(),
+             "nsAvailableMemoryWatcherBase needs to be initialized "
+             "in the main thread.");
+
+  if (mObserverSvc) {
+    return NS_ERROR_ALREADY_INITIALIZED;
+  }
+
+  mObserverSvc = services::GetObserverService();
+  MOZ_ASSERT(mObserverSvc);
+
+  for (auto topic : kObserverTopics) {
+    nsresult rv = mObserverSvc->AddObserver(this, topic,
+                                            /* ownsWeak */ false);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  return NS_OK;
+}
+
+void nsAvailableMemoryWatcherBase::Shutdown() {
+  for (auto topic : kObserverTopics) {
+    mObserverSvc->RemoveObserver(this, topic);
+  }
+}
+
+NS_IMETHODIMP
+nsAvailableMemoryWatcherBase::Observe(nsISupports* aSubject, const char* aTopic,
+                                      const char16_t* aData) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (strcmp(aTopic, "xpcom-shutdown") == 0) {
+    Shutdown();
+  } else if (strcmp(aTopic, "user-interaction-inactive") == 0) {
+    mInteracting = false;
+#ifdef MOZ_CRASHREPORTER
+    CrashReporter::SetInactiveStateStart();
+#endif
+  } else if (strcmp(aTopic, "user-interaction-active") == 0) {
+    mInteracting = true;
+#ifdef MOZ_CRASHREPORTER
+    CrashReporter::ClearInactiveStateStart();
+#endif
+  }
+  return NS_OK;
+}
+
+nsresult nsAvailableMemoryWatcherBase::RegisterTabUnloader(
+    nsITabUnloader* aTabUnloader) {
+  mTabUnloader = aTabUnloader;
+  return NS_OK;
+}
+
+nsresult nsAvailableMemoryWatcherBase::OnUnloadAttemptCompleted(
+    nsresult aResult) {
+  switch (aResult) {
+    // A tab was unloaded successfully.
+    case NS_OK:
+      ++mNumOfTabUnloading;
+      break;
+
+    // There was no unloadable tab.
+    case NS_ERROR_NOT_AVAILABLE:
+      ++mNumOfMemoryPressure;
+      NS_NotifyOfEventualMemoryPressure(MemoryPressureState::LowMemory);
+      break;
+
+    // There was a pending task to unload a tab.
+    case NS_ERROR_ABORT:
+      break;
+
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unexpected aResult");
+      break;
+  }
+  return NS_OK;
+}
+
+void nsAvailableMemoryWatcherBase::UpdateLowMemoryTimeStamp() {
+  if (mLowMemoryStart.IsNull()) {
+    mLowMemoryStart = TimeStamp::NowLoRes();
+  }
+}
+
+void nsAvailableMemoryWatcherBase::RecordTelemetryEventOnHighMemory() {
+  Telemetry::SetEventRecordingEnabled("memory_watcher"_ns, true);
+  Telemetry::RecordEvent(
+      Telemetry::EventID::Memory_watcher_OnHighMemory_Stats,
+      Some(nsPrintfCString(
+          "%u,%u,%f", mNumOfTabUnloading, mNumOfMemoryPressure,
+          (TimeStamp::NowLoRes() - mLowMemoryStart).ToSeconds())),
+      Nothing());
+  mNumOfTabUnloading = mNumOfMemoryPressure = 0;
+  mLowMemoryStart = TimeStamp();
+}
+
+// Define the fallback method for a platform for which a platform-specific
+// CreateAvailableMemoryWatcher() is not defined.
+#if defined(ANDROID) || \
+    !defined(XP_WIN) && !defined(XP_DARWIN) && !defined(XP_LINUX)
+already_AddRefed<nsAvailableMemoryWatcherBase> CreateAvailableMemoryWatcher() {
+  RefPtr instance(new nsAvailableMemoryWatcherBase);
+  return do_AddRef(instance);
+}
+#endif
+
+}  // namespace mozilla
diff --git a/xpcom/base/AvailableMemoryWatcher.h b/xpcom/base/AvailableMemoryWatcher.h
new file mode 100644
index 0000000000..0468ad0fa3
--- /dev/null
+++ b/xpcom/base/AvailableMemoryWatcher.h
@@ -0,0 +1,68 @@
+/* -*- 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/. */
+
+#ifndef mozilla_AvailableMemoryWatcher_h
+#define mozilla_AvailableMemoryWatcher_h
+
+#include "mozilla/ipc/CrashReporterHost.h"
+#include "mozilla/UniquePtr.h"
+#include "MemoryPressureLevelMac.h"
+#include "nsCOMPtr.h"
+#include "nsIAvailableMemoryWatcherBase.h"
+#include "nsIObserver.h"
+#include "nsIObserverService.h"
+
+namespace mozilla {
+
+// This class implements a platform-independent part to watch the system's
+// memory situation and invoke the registered callbacks when we detect
+// a low-memory situation or a high-memory situation.
+// The actual logic to monitor the memory status is implemented in a subclass
+// of nsAvailableMemoryWatcherBase per platform.
+class nsAvailableMemoryWatcherBase : public nsIAvailableMemoryWatcherBase,
+                                     public nsIObserver {
+  static StaticRefPtr<nsAvailableMemoryWatcherBase> sSingleton;
+  static const char* const kObserverTopics[];
+
+  TimeStamp mLowMemoryStart;
+
+ protected:
+  uint32_t mNumOfTabUnloading;
+  uint32_t mNumOfMemoryPressure;
+
+  nsCOMPtr<nsITabUnloader> mTabUnloader;
+  nsCOMPtr<nsIObserverService> mObserverSvc;
+  // Do not change this value off the main thread.
+  bool mInteracting;
+
+  virtual ~nsAvailableMemoryWatcherBase() = default;
+  virtual nsresult Init();
+  void Shutdown();
+  void UpdateLowMemoryTimeStamp();
+  void RecordTelemetryEventOnHighMemory();
+
+ public:
+  static already_AddRefed<nsAvailableMemoryWatcherBase> GetSingleton();
+
+  nsAvailableMemoryWatcherBase();
+
+#if defined(XP_DARWIN)
+  virtual void OnMemoryPressureChanged(MacMemoryPressureLevel aNewLevel){};
+  virtual void AddChildAnnotations(
+      const UniquePtr<ipc::CrashReporterHost>& aCrashReporter){};
+#endif
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIAVAILABLEMEMORYWATCHERBASE
+  NS_DECL_NSIOBSERVER
+};
+
+// Method to create a platform-specific object
+already_AddRefed<nsAvailableMemoryWatcherBase> CreateAvailableMemoryWatcher();
+
+}  // namespace mozilla
+
+#endif  // ifndef mozilla_AvailableMemoryWatcher_h
diff --git a/xpcom/base/AvailableMemoryWatcherLinux.cpp b/xpcom/base/AvailableMemoryWatcherLinux.cpp
new file mode 100644
index 0000000000..d2be46c84d
--- /dev/null
+++ b/xpcom/base/AvailableMemoryWatcherLinux.cpp
@@ -0,0 +1,290 @@
+/* -*- 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 "AvailableMemoryWatcher.h"
+#include "AvailableMemoryWatcherUtils.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPrefs_browser.h"
+#include "mozilla/Unused.h"
+#include "nsAppRunner.h"
+#include "nsIObserverService.h"
+#include "nsISupports.h"
+#include "nsITimer.h"
+#include "nsIThread.h"
+#include "nsMemoryPressure.h"
+
+namespace mozilla {
+
+// Linux has no native low memory detection. This class creates a timer that
+// polls for low memory and sends a low memory notification if it notices a
+// memory pressure event.
+class nsAvailableMemoryWatcher final : public nsITimerCallback,
+                                       public nsINamed,
+                                       public nsAvailableMemoryWatcherBase {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_NSITIMERCALLBACK
+  NS_DECL_NSIOBSERVER
+  NS_DECL_NSINAMED
+
+  nsresult Init() override;
+  nsAvailableMemoryWatcher();
+
+  void HandleLowMemory();
+  void MaybeHandleHighMemory();
+
+ private:
+  ~nsAvailableMemoryWatcher() = default;
+  void StartPolling(const MutexAutoLock&);
+  void StopPolling(const MutexAutoLock&);
+  void ShutDown();
+  void UpdateCrashAnnotation(const MutexAutoLock&);
+  static bool IsMemoryLow();
+
+  nsCOMPtr<nsITimer> mTimer MOZ_GUARDED_BY(mMutex);
+  nsCOMPtr<nsIThread> mThread MOZ_GUARDED_BY(mMutex);
+
+  bool mPolling MOZ_GUARDED_BY(mMutex);
+  bool mUnderMemoryPressure MOZ_GUARDED_BY(mMutex);
+
+  // We might tell polling to start/stop from our polling thread
+  // or from the main thread during ::Observe().
+  Mutex mMutex;
+
+  // Polling interval to check for low memory. In high memory scenarios,
+  // default to 5000 ms between each check.
+  static const uint32_t kHighMemoryPollingIntervalMS = 5000;
+
+  // Polling interval to check for low memory. Default to 1000 ms between each
+  // check. Use this interval when memory is low,
+  static const uint32_t kLowMemoryPollingIntervalMS = 1000;
+};
+
+// A modern version of linux should keep memory information in the
+// /proc/meminfo path.
+static const char* kMeminfoPath = "/proc/meminfo";
+
+nsAvailableMemoryWatcher::nsAvailableMemoryWatcher()
+    : mPolling(false),
+      mUnderMemoryPressure(false),
+      mMutex("Memory Poller mutex") {}
+
+nsresult nsAvailableMemoryWatcher::Init() {
+  nsresult rv = nsAvailableMemoryWatcherBase::Init();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  MutexAutoLock lock(mMutex);
+  mTimer = NS_NewTimer();
+  nsCOMPtr<nsIThread> thread;
+  // We have to make our own thread here instead of using the background pool,
+  // because some low memory scenarios can cause the background pool to fill.
+  rv = NS_NewNamedThread("MemoryPoller", getter_AddRefs(thread));
+  if (NS_FAILED(rv)) {
+    NS_WARNING("Couldn't make a thread for nsAvailableMemoryWatcher.");
+    // In this scenario we can't poll for low memory, since we can't dispatch
+    // to our memory watcher thread.
+    return rv;
+  }
+  mThread = thread;
+
+  // Set the crash annotation to its initial state.
+  UpdateCrashAnnotation(lock);
+
+  StartPolling(lock);
+
+  return NS_OK;
+}
+
+already_AddRefed<nsAvailableMemoryWatcherBase> CreateAvailableMemoryWatcher() {
+  RefPtr watcher(new nsAvailableMemoryWatcher);
+
+  if (NS_FAILED(watcher->Init())) {
+    return do_AddRef(new nsAvailableMemoryWatcherBase);
+  }
+
+  return watcher.forget();
+}
+
+NS_IMPL_ISUPPORTS_INHERITED(nsAvailableMemoryWatcher,
+                            nsAvailableMemoryWatcherBase, nsITimerCallback,
+                            nsIObserver, nsINamed);
+
+void nsAvailableMemoryWatcher::StopPolling(const MutexAutoLock&)
+    MOZ_REQUIRES(mMutex) {
+  if (mPolling && mTimer) {
+    // stop dispatching memory checks to the thread.
+    mTimer->Cancel();
+    mPolling = false;
+  }
+}
+
+// Check /proc/meminfo for low memory. Largely C method for reading
+// /proc/meminfo.
+/* static */
+bool nsAvailableMemoryWatcher::IsMemoryLow() {
+  MemoryInfo memInfo{0, 0};
+  bool aResult = false;
+
+  nsresult rv = ReadMemoryFile(kMeminfoPath, memInfo);
+
+  if (NS_FAILED(rv) || memInfo.memAvailable == 0) {
+    // If memAvailable cannot be found, then we are using an older system.
+    // We can't accurately poll on this.
+    return aResult;
+  }
+  unsigned long memoryAsPercentage =
+      (memInfo.memAvailable * 100) / memInfo.memTotal;
+
+  if (memoryAsPercentage <=
+          StaticPrefs::browser_low_commit_space_threshold_percent() ||
+      memInfo.memAvailable <
+          StaticPrefs::browser_low_commit_space_threshold_mb() * 1024) {
+    aResult = true;
+  }
+
+  return aResult;
+}
+
+void nsAvailableMemoryWatcher::ShutDown() {
+  nsCOMPtr<nsIThread> thread;
+  {
+    MutexAutoLock lock(mMutex);
+    if (mTimer) {
+      mTimer->Cancel();
+      mTimer = nullptr;
+    }
+    thread = mThread.forget();
+  }
+  // thread->Shutdown() spins a nested event loop while waiting for the thread
+  // to end. But the thread might execute some previously dispatched event that
+  // wants to lock our mutex, too, before arriving at the shutdown event.
+  if (thread) {
+    thread->Shutdown();
+  }
+}
+
+// We will use this to poll for low memory.
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::Notify(nsITimer* aTimer) {
+  MutexAutoLock lock(mMutex);
+  if (!mThread) {
+    // If we've made it this far and there's no  |mThread|,
+    // we might have failed to dispatch it for some reason.
+    MOZ_ASSERT(mThread);
+    return NS_ERROR_FAILURE;
+  }
+  nsresult rv = mThread->Dispatch(
+      NS_NewRunnableFunction("MemoryPoller", [self = RefPtr{this}]() {
+        if (self->IsMemoryLow()) {
+          self->HandleLowMemory();
+        } else {
+          self->MaybeHandleHighMemory();
+        }
+      }));
+
+  if NS_FAILED (rv) {
+    NS_WARNING("Cannot dispatch memory polling event.");
+  }
+  return NS_OK;
+}
+
+void nsAvailableMemoryWatcher::HandleLowMemory() {
+  MutexAutoLock lock(mMutex);
+  if (!mTimer) {
+    // We have been shut down from outside while in flight.
+    return;
+  }
+  if (!mUnderMemoryPressure) {
+    mUnderMemoryPressure = true;
+    UpdateCrashAnnotation(lock);
+    // Poll more frequently under memory pressure.
+    StartPolling(lock);
+  }
+  UpdateLowMemoryTimeStamp();
+  // We handle low memory offthread, but we want to unload
+  // tabs only from the main thread, so we will dispatch this
+  // back to the main thread.
+  NS_DispatchToMainThread(NS_NewRunnableFunction(
+      "nsAvailableMemoryWatcher::OnLowMemory",
+      [self = RefPtr{this}]() { self->mTabUnloader->UnloadTabAsync(); }));
+}
+
+void nsAvailableMemoryWatcher::UpdateCrashAnnotation(const MutexAutoLock&)
+    MOZ_REQUIRES(mMutex) {
+  CrashReporter::AnnotateCrashReport(
+      CrashReporter::Annotation::LinuxUnderMemoryPressure,
+      mUnderMemoryPressure);
+}
+
+// If memory is not low, we may need to dispatch an
+// event for it if we have been under memory pressure.
+// We can also adjust our polling interval.
+void nsAvailableMemoryWatcher::MaybeHandleHighMemory() {
+  MutexAutoLock lock(mMutex);
+  if (!mTimer) {
+    // We have been shut down from outside while in flight.
+    return;
+  }
+  if (mUnderMemoryPressure) {
+    RecordTelemetryEventOnHighMemory();
+    NS_NotifyOfEventualMemoryPressure(MemoryPressureState::NoPressure);
+    mUnderMemoryPressure = false;
+    UpdateCrashAnnotation(lock);
+  }
+  StartPolling(lock);
+}
+
+// When we change the polling interval, we will need to restart the timer
+// on the new interval.
+void nsAvailableMemoryWatcher::StartPolling(const MutexAutoLock& aLock)
+    MOZ_REQUIRES(mMutex) {
+  uint32_t pollingInterval = mUnderMemoryPressure
+                                 ? kLowMemoryPollingIntervalMS
+                                 : kHighMemoryPollingIntervalMS;
+  if (!mPolling) {
+    // Restart the timer with the new interval if it has stopped.
+    // For testing, use a small polling interval.
+    if (NS_SUCCEEDED(
+            mTimer->InitWithCallback(this, gIsGtest ? 10 : pollingInterval,
+                                     nsITimer::TYPE_REPEATING_SLACK))) {
+      mPolling = true;
+    }
+  } else {
+    mTimer->SetDelay(gIsGtest ? 10 : pollingInterval);
+  }
+}
+
+// Observe events for shutting down and starting/stopping the timer.
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::Observe(nsISupports* aSubject, const char* aTopic,
+                                  const char16_t* aData) {
+  nsresult rv = nsAvailableMemoryWatcherBase::Observe(aSubject, aTopic, aData);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (strcmp(aTopic, "xpcom-shutdown") == 0) {
+    ShutDown();
+  } else {
+    MutexAutoLock lock(mMutex);
+    if (mTimer) {
+      if (strcmp(aTopic, "user-interaction-active") == 0) {
+        StartPolling(lock);
+      } else if (strcmp(aTopic, "user-interaction-inactive") == 0) {
+        StopPolling(lock);
+      }
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsAvailableMemoryWatcher::GetName(nsACString& aName) {
+  aName.AssignLiteral("nsAvailableMemoryWatcher");
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/AvailableMemoryWatcherMac.cpp b/xpcom/base/AvailableMemoryWatcherMac.cpp
new file mode 100644
index 0000000000..452b32a149
--- /dev/null
+++ b/xpcom/base/AvailableMemoryWatcherMac.cpp
@@ -0,0 +1,625 @@
+/* -*- 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 <sys/sysctl.h>
+#include <sys/types.h>
+#include <time.h>
+
+#include "AvailableMemoryWatcher.h"
+#include "Logging.h"
+#include "mozilla/Preferences.h"
+#include "nsICrashReporter.h"
+#include "nsISupports.h"
+#include "nsITimer.h"
+#include "nsMemoryPressure.h"
+#include "nsPrintfCString.h"
+
+#define MP_LOG(...) MOZ_LOG(gMPLog, mozilla::LogLevel::Debug, (__VA_ARGS__))
+static mozilla::LazyLogModule gMPLog("MemoryPressure");
+
+namespace mozilla {
+
+/*
+ * The Mac AvailableMemoryWatcher works as follows. When the OS memory pressure
+ * level changes on macOS, nsAvailableMemoryWatcher::OnMemoryPressureChanged()
+ * is called with the new memory pressure level. The level is represented in
+ * Gecko by a MacMemoryPressureLevel instance and represents the states of
+ * normal, warning, or critical which correspond to the native levels. When the
+ * browser launches, the initial level is determined using a sysctl. Which
+ * actions are taken in the browser in response to memory pressure, and the
+ * level (warning or critical) which trigger the reponse is configurable with
+ * prefs to make it easier to perform experiments to study how the response
+ * affects the user experience.
+ *
+ * By default, the browser responds by attempting to reduce memory use when the
+ * OS transitions to the critical level and while it stays in the critical
+ * level. i.e., "critical" OS memory pressure is the default threshold for the
+ * low memory response. Setting pref "browser.lowMemoryResponseOnWarn" to true
+ * changes the memory response to occur at the "warning" level which is less
+ * severe than "critical". When entering the critical level, we begin polling
+ * the memory pressure level every 'n' milliseconds (specified via the pref
+ * "browser.lowMemoryPollingIntervalMS"). Each time the poller wakes up and
+ * finds the OS still under memory pressure, the low memory response is
+ * executed.
+ *
+ * By default, the memory pressure response is, in order, to
+ *   1) call nsITabUnloader::UnloadTabAsync(),
+ *   2) if no tabs could be unloaded, issue a Gecko
+ *      MemoryPressureState::LowMemory notification.
+ * The response can be changed via the pref "browser.lowMemoryResponseMask" to
+ * limit the actions to only tab unloading or Gecko memory pressure
+ * notifications.
+ *
+ * Polling occurs on the main thread because, at each polling interval, we
+ * call into the tab unloader which requires being on the main thread.
+ * Polling only occurs while under OS memory pressure at the critical (by
+ * default) level.
+ */
+class nsAvailableMemoryWatcher final : public nsITimerCallback,
+                                       public nsINamed,
+                                       public nsAvailableMemoryWatcherBase {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_NSIOBSERVER
+  NS_DECL_NSITIMERCALLBACK
+  NS_DECL_NSINAMED
+
+  nsAvailableMemoryWatcher();
+  nsresult Init() override;
+
+  void OnMemoryPressureChanged(MacMemoryPressureLevel aLevel) override;
+  void AddChildAnnotations(
+      const UniquePtr<ipc::CrashReporterHost>& aCrashReporter) override;
+
+ private:
+  ~nsAvailableMemoryWatcher(){};
+
+  void OnMemoryPressureChangedInternal(MacMemoryPressureLevel aNewLevel,
+                                       bool aIsInitialLevel);
+
+  // Override OnUnloadAttemptCompleted() so that we can control whether
+  // or not a Gecko memory-pressure event is sent after a tab unload attempt.
+  // This method is called externally by the tab unloader after a tab unload
+  // attempt. It is used internally when tab unloading is disabled in
+  // mResponseMask.
+  nsresult OnUnloadAttemptCompleted(nsresult aResult) override;
+
+  void OnShutdown();
+  void OnPrefChange();
+
+  void InitParentAnnotations();
+  void UpdateParentAnnotations();
+
+  void AddParentAnnotation(CrashReporter::Annotation aAnnotation,
+                           nsAutoCString aString) {
+    CrashReporter::AnnotateCrashReport(aAnnotation, aString);
+  }
+  void AddParentAnnotation(CrashReporter::Annotation aAnnotation,
+                           uint32_t aData) {
+    CrashReporter::AnnotateCrashReport(aAnnotation, aData);
+  }
+
+  void LowMemoryResponse();
+  void StartPolling();
+  void StopPolling();
+  void RestartPolling();
+  inline bool IsPolling() { return mTimer; }
+
+  void ReadSysctls();
+
+  // This enum represents the allowed values for the pref that controls
+  // the low memory response - "browser.lowMemoryResponseMask". Specifically,
+  // whether or not we unload tabs and/or issue the Gecko "memory-pressure"
+  // internal notification. For tab unloading, the pref
+  // "browser.tabs.unloadOnLowMemory" must also be set.
+  enum ResponseMask {
+    eNone = 0x0,
+    eTabUnload = 0x1,
+    eInternalMemoryPressure = 0x2,
+    eAll = 0x3,
+  };
+  static constexpr char kResponseMask[] = "browser.lowMemoryResponseMask";
+  static const uint32_t kResponseMaskDefault;
+  static const uint32_t kResponseMaskMax;
+
+  // Pref for controlling how often we wake up during an OS memory pressure
+  // time period. At each wakeup, we unload tabs and issue the Gecko
+  // "memory-pressure" internal notification. When not under OS memory pressure,
+  // polling is disabled.
+  static constexpr char kPollingIntervalMS[] =
+      "browser.lowMemoryPollingIntervalMS";
+  static const uint32_t kPollingIntervalMaxMS;
+  static const uint32_t kPollingIntervalMinMS;
+  static const uint32_t kPollingIntervalDefaultMS;
+
+  static constexpr char kResponseOnWarn[] = "browser.lowMemoryResponseOnWarn";
+  static const bool kResponseLevelOnWarnDefault = false;
+
+  // Init has been called.
+  bool mInitialized;
+
+  // The memory pressure reported to the application by macOS.
+  MacMemoryPressureLevel mLevel;
+
+  // The OS memory pressure level that triggers the response.
+  MacMemoryPressureLevel mResponseLevel;
+
+  // The value of the kern.memorystatus_vm_pressure_level sysctl. The OS
+  // notifies the application when the memory pressure level changes,
+  // but the sysctl value can be read at any time. Unofficially, the sysctl
+  // value corresponds to the OS memory pressure level with 4=>critical,
+  // 2=>warning, and 1=>normal (values from kernel event.h file).
+  uint32_t mLevelSysctl;
+  static const int kSysctlLevelNormal = 0x1;
+  static const int kSysctlLevelWarning = 0x2;
+  static const int kSysctlLevelCritical = 0x4;
+
+  // The value of the kern.memorystatus_level sysctl. Unofficially,
+  // this is the percentage of available memory. (Also readable
+  // via the undocumented memorystatus_get_level syscall.)
+  int mAvailMemSysctl;
+
+  // The string representation of `mLevel`. i.e., normal, warning, or critical.
+  // Set to "unset" until a memory pressure change is reported to the process
+  // by the OS.
+  nsAutoCString mLevelStr;
+
+  // Timestamps for memory pressure level changes. Specifically, the Unix
+  // time in string form. Saved as Unix time to allow comparisons with
+  // the crash time.
+  nsAutoCString mNormalTimeStr;
+  nsAutoCString mWarningTimeStr;
+  nsAutoCString mCriticalTimeStr;
+
+  nsCOMPtr<nsITimer> mTimer;  // non-null indicates the timer is active
+
+  // Saved pref values.
+  uint32_t mPollingInterval;
+  uint32_t mResponseMask;
+};
+
+const uint32_t nsAvailableMemoryWatcher::kResponseMaskDefault =
+    ResponseMask::eAll;
+const uint32_t nsAvailableMemoryWatcher::kResponseMaskMax = ResponseMask::eAll;
+
+// 10 seconds
+const uint32_t nsAvailableMemoryWatcher::kPollingIntervalDefaultMS = 10'000;
+// 10 minutes
+const uint32_t nsAvailableMemoryWatcher::kPollingIntervalMaxMS = 600'000;
+// 100 milliseconds
+const uint32_t nsAvailableMemoryWatcher::kPollingIntervalMinMS = 100;
+
+NS_IMPL_ISUPPORTS_INHERITED(nsAvailableMemoryWatcher,
+                            nsAvailableMemoryWatcherBase, nsIObserver,
+                            nsITimerCallback, nsINamed)
+
+nsAvailableMemoryWatcher::nsAvailableMemoryWatcher()
+    : mInitialized(false),
+      mLevel(MacMemoryPressureLevel::Value::eUnset),
+      mResponseLevel(MacMemoryPressureLevel::Value::eCritical),
+      mLevelSysctl(0xFFFFFFFF),
+      mAvailMemSysctl(-1),
+      mLevelStr("Unset"),
+      mNormalTimeStr("Unset"),
+      mWarningTimeStr("Unset"),
+      mCriticalTimeStr("Unset"),
+      mPollingInterval(0),
+      mResponseMask(ResponseMask::eAll) {}
+
+nsresult nsAvailableMemoryWatcher::Init() {
+  nsresult rv = nsAvailableMemoryWatcherBase::Init();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // Users of nsAvailableMemoryWatcher should use
+  // nsAvailableMemoryWatcherBase::GetSingleton() and not call Init directly.
+  MOZ_ASSERT(!mInitialized);
+  if (mInitialized) {
+    return NS_ERROR_ALREADY_INITIALIZED;
+  }
+
+  // Read polling frequency pref
+  mPollingInterval =
+      Preferences::GetUint(kPollingIntervalMS, kPollingIntervalDefaultMS);
+  mPollingInterval = std::clamp(mPollingInterval, kPollingIntervalMinMS,
+                                kPollingIntervalMaxMS);
+
+  // Read response bitmask pref which (along with the main tab unloading
+  // preference) controls whether or not tab unloading and Gecko (internal)
+  // memory pressure notifications will be sent. The main tab unloading
+  // preference must also be enabled for tab unloading to occur.
+  mResponseMask = Preferences::GetUint(kResponseMask, kResponseMaskDefault);
+  if (mResponseMask > kResponseMaskMax) {
+    mResponseMask = kResponseMaskMax;
+  }
+
+  // Read response level pref
+  if (Preferences::GetBool(kResponseOnWarn, kResponseLevelOnWarnDefault)) {
+    mResponseLevel = MacMemoryPressureLevel::Value::eWarning;
+  } else {
+    mResponseLevel = MacMemoryPressureLevel::Value::eCritical;
+  }
+
+  ReadSysctls();
+  MP_LOG("Initial memory pressure sysctl: %d", mLevelSysctl);
+  MP_LOG("Initial available memory sysctl: %d", mAvailMemSysctl);
+
+  // Set the initial state of all annotations for parent crash reports.
+  // Content process crash reports are set when a crash occurs and
+  // AddChildAnnotations() is called.
+  CrashReporter::AnnotateCrashReport(
+      CrashReporter::Annotation::MacMemoryPressure, mLevelStr);
+  CrashReporter::AnnotateCrashReport(
+      CrashReporter::Annotation::MacMemoryPressureNormalTime, mNormalTimeStr);
+  CrashReporter::AnnotateCrashReport(
+      CrashReporter::Annotation::MacMemoryPressureWarningTime, mWarningTimeStr);
+  CrashReporter::AnnotateCrashReport(
+      CrashReporter::Annotation::MacMemoryPressureCriticalTime,
+      mCriticalTimeStr);
+  CrashReporter::AnnotateCrashReport(
+      CrashReporter::Annotation::MacMemoryPressureSysctl, mLevelSysctl);
+  CrashReporter::AnnotateCrashReport(
+      CrashReporter::Annotation::MacAvailableMemorySysctl, mAvailMemSysctl);
+
+  // To support running experiments, handle pref
+  // changes without requiring a browser restart.
+  rv = Preferences::AddStrongObserver(this, kResponseMask);
+  if (NS_FAILED(rv)) {
+    NS_WARNING(
+        nsPrintfCString("Failed to add %s observer", kResponseMask).get());
+  }
+  rv = Preferences::AddStrongObserver(this, kPollingIntervalMS);
+  if (NS_FAILED(rv)) {
+    NS_WARNING(
+        nsPrintfCString("Failed to add %s observer", kPollingIntervalMS).get());
+  }
+  rv = Preferences::AddStrongObserver(this, kResponseOnWarn);
+  if (NS_FAILED(rv)) {
+    NS_WARNING(
+        nsPrintfCString("Failed to add %s observer", kResponseOnWarn).get());
+  }
+
+  // Use the memory pressure sysctl to initialize our memory pressure state.
+  MacMemoryPressureLevel initialLevel;
+  switch (mLevelSysctl) {
+    case kSysctlLevelNormal:
+      initialLevel = MacMemoryPressureLevel::Value::eNormal;
+      break;
+    case kSysctlLevelWarning:
+      initialLevel = MacMemoryPressureLevel::Value::eWarning;
+      break;
+    case kSysctlLevelCritical:
+      initialLevel = MacMemoryPressureLevel::Value::eCritical;
+      break;
+    default:
+      initialLevel = MacMemoryPressureLevel::Value::eUnexpected;
+  }
+
+  OnMemoryPressureChangedInternal(initialLevel, /* aIsInitialLevel */ true);
+  mInitialized = true;
+  return NS_OK;
+}
+
+already_AddRefed<nsAvailableMemoryWatcherBase> CreateAvailableMemoryWatcher() {
+  // Users of nsAvailableMemoryWatcher should use
+  // nsAvailableMemoryWatcherBase::GetSingleton().
+  RefPtr watcher(new nsAvailableMemoryWatcher());
+  watcher->Init();
+  return watcher.forget();
+}
+
+// Update the memory pressure level, level change timestamps, and sysctl
+// level crash report annotations.
+void nsAvailableMemoryWatcher::UpdateParentAnnotations() {
+  // Generate a string representation of the current Unix time.
+  time_t timeChanged = time(NULL);
+  nsAutoCString timeChangedString;
+  timeChangedString =
+      nsPrintfCString("%" PRIu64, static_cast<uint64_t>(timeChanged));
+
+  nsAutoCString pressureLevelString;
+  Maybe<CrashReporter::Annotation> pressureLevelKey;
+
+  switch (mLevel.GetValue()) {
+    case MacMemoryPressureLevel::Value::eNormal:
+      mNormalTimeStr = timeChangedString;
+      pressureLevelString = "Normal";
+      pressureLevelKey.emplace(
+          CrashReporter::Annotation::MacMemoryPressureNormalTime);
+      break;
+    case MacMemoryPressureLevel::Value::eWarning:
+      mWarningTimeStr = timeChangedString;
+      pressureLevelString = "Warning";
+      pressureLevelKey.emplace(
+          CrashReporter::Annotation::MacMemoryPressureWarningTime);
+      break;
+    case MacMemoryPressureLevel::Value::eCritical:
+      mCriticalTimeStr = timeChangedString;
+      pressureLevelString = "Critical";
+      pressureLevelKey.emplace(
+          CrashReporter::Annotation::MacMemoryPressureCriticalTime);
+      break;
+    default:
+      pressureLevelString = "Unexpected";
+      break;
+  }
+
+  // Save the current memory pressure level.
+  AddParentAnnotation(CrashReporter::Annotation::MacMemoryPressure,
+                      pressureLevelString);
+
+  // Save the time we transitioned to the current memory pressure level.
+  if (pressureLevelKey.isSome()) {
+    AddParentAnnotation(pressureLevelKey.value(), timeChangedString);
+  }
+
+  AddParentAnnotation(CrashReporter::Annotation::MacMemoryPressureSysctl,
+                      mLevelSysctl);
+  AddParentAnnotation(CrashReporter::Annotation::MacAvailableMemorySysctl,
+                      mAvailMemSysctl);
+}
+
+void nsAvailableMemoryWatcher::ReadSysctls() {
+  // Pressure level
+  uint32_t level;
+  size_t size = sizeof(level);
+  if (sysctlbyname("kern.memorystatus_vm_pressure_level", &level, &size, NULL,
+                   0) == -1) {
+    MP_LOG("Failure reading memory pressure sysctl");
+  }
+  mLevelSysctl = level;
+
+  // Available memory percent
+  int availPercent;
+  size = sizeof(availPercent);
+  if (sysctlbyname("kern.memorystatus_level", &availPercent, &size, NULL, 0) ==
+      -1) {
+    MP_LOG("Failure reading available memory level");
+  }
+  mAvailMemSysctl = availPercent;
+}
+
+/* virtual */
+void nsAvailableMemoryWatcher::OnMemoryPressureChanged(
+    MacMemoryPressureLevel aNewLevel) {
+  MOZ_ASSERT(mInitialized);
+  OnMemoryPressureChangedInternal(aNewLevel, /* aIsInitialLevel */ false);
+}
+
+void nsAvailableMemoryWatcher::OnMemoryPressureChangedInternal(
+    MacMemoryPressureLevel aNewLevel, bool aIsInitialLevel) {
+  MOZ_ASSERT(mInitialized || aIsInitialLevel);
+  MP_LOG("MemoryPressureChange: existing level: %s, new level: %s",
+         mLevel.ToString(), aNewLevel.ToString());
+
+  // If 'aNewLevel' is not one of normal, warning, or critical, ASSERT
+  // here so we can debug this scenario. For non-debug builds, ignore
+  // the unexpected value which will be logged in crash reports.
+  MOZ_ASSERT(aNewLevel.IsNormal() || aNewLevel.IsWarningOrAbove());
+
+  if (mLevel == aNewLevel) {
+    return;
+  }
+
+  // Start the memory pressure response if the new level is high enough
+  // and the existing level was not.
+  if ((mLevel < mResponseLevel) && (aNewLevel >= mResponseLevel)) {
+    UpdateLowMemoryTimeStamp();
+    LowMemoryResponse();
+    if (mResponseMask) {
+      StartPolling();
+    }
+  }
+
+  // End the memory pressure reponse if the new level is not high enough.
+  if ((mLevel >= mResponseLevel) && (aNewLevel < mResponseLevel)) {
+    RecordTelemetryEventOnHighMemory();
+    StopPolling();
+    MP_LOG("Issuing MemoryPressureState::NoPressure");
+    NS_NotifyOfMemoryPressure(MemoryPressureState::NoPressure);
+  }
+
+  mLevel = aNewLevel;
+
+  if (!aIsInitialLevel) {
+    // Sysctls are already read by ::Init().
+    ReadSysctls();
+    MP_LOG("level sysctl: %d, available memory: %d percent", mLevelSysctl,
+           mAvailMemSysctl);
+  }
+  UpdateParentAnnotations();
+}
+
+/* virtual */
+// Add all annotations to the provided crash reporter instance.
+void nsAvailableMemoryWatcher::AddChildAnnotations(
+    const UniquePtr<ipc::CrashReporterHost>& aCrashReporter) {
+  aCrashReporter->AddAnnotation(CrashReporter::Annotation::MacMemoryPressure,
+                                mLevelStr);
+  aCrashReporter->AddAnnotation(
+      CrashReporter::Annotation::MacMemoryPressureNormalTime, mNormalTimeStr);
+  aCrashReporter->AddAnnotation(
+      CrashReporter::Annotation::MacMemoryPressureWarningTime, mWarningTimeStr);
+  aCrashReporter->AddAnnotation(
+      CrashReporter::Annotation::MacMemoryPressureCriticalTime,
+      mCriticalTimeStr);
+  aCrashReporter->AddAnnotation(
+      CrashReporter::Annotation::MacMemoryPressureSysctl, mLevelSysctl);
+  aCrashReporter->AddAnnotation(
+      CrashReporter::Annotation::MacAvailableMemorySysctl, mAvailMemSysctl);
+}
+
+void nsAvailableMemoryWatcher::LowMemoryResponse() {
+  if (mResponseMask & ResponseMask::eTabUnload) {
+    MP_LOG("Attempting tab unload");
+    mTabUnloader->UnloadTabAsync();
+  } else {
+    // Re-use OnUnloadAttemptCompleted() to issue the internal
+    // memory pressure event.
+    OnUnloadAttemptCompleted(NS_ERROR_NOT_AVAILABLE);
+  }
+}
+
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::Notify(nsITimer* aTimer) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(mLevel >= mResponseLevel);
+  LowMemoryResponse();
+  return NS_OK;
+}
+
+// Override OnUnloadAttemptCompleted() so that we can issue Gecko memory
+// pressure notifications only if eInternalMemoryPressure is set in
+// mResponseMask. When called from the tab unloader, an |aResult| value of
+// NS_OK indicates the tab unloader successfully unloaded a tab.
+// NS_ERROR_NOT_AVAILABLE indicates the tab unloader did not unload any tabs.
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::OnUnloadAttemptCompleted(nsresult aResult) {
+  switch (aResult) {
+    // A tab was unloaded successfully.
+    case NS_OK:
+      MP_LOG("Tab unloaded");
+      ++mNumOfTabUnloading;
+      break;
+
+    // Either the tab unloader found no unloadable tabs OR we've been called
+    // locally to explicitly issue the internal memory pressure event because
+    // tab unloading is disabled in |mResponseMask|. In either case, attempt
+    // to reduce memory use using the internal memory pressure notification.
+    case NS_ERROR_NOT_AVAILABLE:
+      if (mResponseMask & ResponseMask::eInternalMemoryPressure) {
+        ++mNumOfMemoryPressure;
+        MP_LOG("Tab not unloaded");
+        MP_LOG("Issuing MemoryPressureState::LowMemory");
+        NS_NotifyOfEventualMemoryPressure(MemoryPressureState::LowMemory);
+      }
+      break;
+
+    // There was a pending task to unload a tab.
+    case NS_ERROR_ABORT:
+      break;
+
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unexpected aResult");
+      break;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::Observe(nsISupports* aSubject, const char* aTopic,
+                                  const char16_t* aData) {
+  nsresult rv = nsAvailableMemoryWatcherBase::Observe(aSubject, aTopic, aData);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (strcmp(aTopic, "xpcom-shutdown") == 0) {
+    OnShutdown();
+  } else if (strcmp(aTopic, NS_PREFBRANCH_PREFCHANGE_TOPIC_ID) == 0) {
+    OnPrefChange();
+  }
+  return NS_OK;
+}
+
+void nsAvailableMemoryWatcher::OnShutdown() {
+  StopPolling();
+  Preferences::RemoveObserver(this, kResponseMask);
+  Preferences::RemoveObserver(this, kPollingIntervalMS);
+}
+
+void nsAvailableMemoryWatcher::OnPrefChange() {
+  MP_LOG("OnPrefChange()");
+  // Handle the polling interval changing.
+  uint32_t pollingInterval = Preferences::GetUint(kPollingIntervalMS);
+  if (pollingInterval != mPollingInterval) {
+    mPollingInterval = std::clamp(pollingInterval, kPollingIntervalMinMS,
+                                  kPollingIntervalMaxMS);
+    RestartPolling();
+  }
+
+  // Handle the response mask changing.
+  uint32_t responseMask = Preferences::GetUint(kResponseMask);
+  if (mResponseMask != responseMask) {
+    mResponseMask = std::min(responseMask, kResponseMaskMax);
+
+    // Do we need to turn on polling?
+    if (mResponseMask && (mLevel >= mResponseLevel) && !IsPolling()) {
+      StartPolling();
+    }
+
+    // Do we need to turn off polling?
+    if (!mResponseMask && IsPolling()) {
+      StopPolling();
+    }
+  }
+
+  // Handle the response level changing.
+  MacMemoryPressureLevel newResponseLevel;
+  if (Preferences::GetBool(kResponseOnWarn, kResponseLevelOnWarnDefault)) {
+    newResponseLevel = MacMemoryPressureLevel::Value::eWarning;
+  } else {
+    newResponseLevel = MacMemoryPressureLevel::Value::eCritical;
+  }
+  if (newResponseLevel == mResponseLevel) {
+    return;
+  }
+
+  // Do we need to turn on polling?
+  if (mResponseMask && (newResponseLevel <= mLevel)) {
+    UpdateLowMemoryTimeStamp();
+    LowMemoryResponse();
+    StartPolling();
+  }
+
+  // Do we need to turn off polling?
+  if (IsPolling() && (newResponseLevel > mLevel)) {
+    RecordTelemetryEventOnHighMemory();
+    StopPolling();
+    MP_LOG("Issuing MemoryPressureState::NoPressure");
+    NS_NotifyOfMemoryPressure(MemoryPressureState::NoPressure);
+  }
+  mResponseLevel = newResponseLevel;
+}
+
+void nsAvailableMemoryWatcher::StartPolling() {
+  MOZ_ASSERT(NS_IsMainThread());
+  if (!mTimer) {
+    MP_LOG("Starting poller");
+    mTimer = NS_NewTimer();
+    if (mTimer) {
+      mTimer->InitWithCallback(this, mPollingInterval,
+                               nsITimer::TYPE_REPEATING_SLACK);
+    }
+  }
+}
+
+void nsAvailableMemoryWatcher::StopPolling() {
+  MOZ_ASSERT(NS_IsMainThread());
+  if (mTimer) {
+    MP_LOG("Pausing poller");
+    mTimer->Cancel();
+    mTimer = nullptr;
+  }
+}
+
+void nsAvailableMemoryWatcher::RestartPolling() {
+  if (IsPolling()) {
+    StopPolling();
+    StartPolling();
+  } else {
+    MOZ_ASSERT(!mTimer);
+  }
+}
+
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::GetName(nsACString& aName) {
+  aName.AssignLiteral("nsAvailableMemoryWatcher");
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/AvailableMemoryWatcherUtils.h b/xpcom/base/AvailableMemoryWatcherUtils.h
new file mode 100644
index 0000000000..2d70fe5fd0
--- /dev/null
+++ b/xpcom/base/AvailableMemoryWatcherUtils.h
@@ -0,0 +1,56 @@
+/* -*- 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/. */
+
+#ifndef mozilla_AvailableMemoryWatcherUtils_h
+#define mozilla_AvailableMemoryWatcherUtils_h
+
+#include "mozilla/Attributes.h"
+#include "nsISupportsUtils.h"  // For nsresult
+
+namespace mozilla {
+
+struct MemoryInfo {
+  unsigned long memTotal;
+  unsigned long memAvailable;
+};
+// Check /proc/meminfo for low memory. Largely C method for reading
+// /proc/meminfo.
+MOZ_MAYBE_UNUSED
+static nsresult ReadMemoryFile(const char* meminfoPath, MemoryInfo& aResult) {
+  FILE* fd;
+  if ((fd = fopen(meminfoPath, "r")) == nullptr) {
+    // Meminfo somehow unreachable
+    return NS_ERROR_FAILURE;
+  }
+
+  char buff[128];
+
+  /* The first few lines of meminfo look something like this:
+   * MemTotal:       65663448 kB
+   * MemFree:        57368112 kB
+   * MemAvailable:   61852700 kB
+   * We mostly care about the available versus the total. We calculate our
+   * memory thresholds using this, and when memory drops below 5% we consider
+   * this to be a memory pressure event. In practice these lines aren't
+   * necessarily in order, but we can simply search for MemTotal
+   * and MemAvailable.
+   */
+  char namebuffer[20];
+  while ((fgets(buff, sizeof(buff), fd)) != nullptr) {
+    if (strstr(buff, "MemTotal:")) {
+      sscanf(buff, "%s %lu ", namebuffer, &aResult.memTotal);
+    }
+    if (strstr(buff, "MemAvailable:")) {
+      sscanf(buff, "%s %lu ", namebuffer, &aResult.memAvailable);
+    }
+  }
+  fclose(fd);
+  return NS_OK;
+}
+
+}  // namespace mozilla
+
+#endif  // ifndef mozilla_AvailableMemoryWatcherUtils_h
diff --git a/xpcom/base/AvailableMemoryWatcherWin.cpp b/xpcom/base/AvailableMemoryWatcherWin.cpp
new file mode 100644
index 0000000000..42e590e93a
--- /dev/null
+++ b/xpcom/base/AvailableMemoryWatcherWin.cpp
@@ -0,0 +1,407 @@
+/* -*- 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 "AvailableMemoryWatcher.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPrefs_browser.h"
+#include "nsAppRunner.h"
+#include "nsExceptionHandler.h"
+#include "nsICrashReporter.h"
+#include "nsIObserver.h"
+#include "nsISupports.h"
+#include "nsITimer.h"
+#include "nsMemoryPressure.h"
+#include "nsServiceManagerUtils.h"
+#include "nsWindowsHelpers.h"
+
+#include <memoryapi.h>
+
+extern mozilla::Atomic<uint32_t, mozilla::MemoryOrdering::Relaxed>
+    sNumLowPhysicalMemEvents;
+
+namespace mozilla {
+
+// This class is used to monitor low memory events delivered by Windows via
+// memory resource notification objects. When we enter a low memory scenario
+// the LowMemoryCallback() is invoked by Windows. This initial call triggers
+// an nsITimer that polls to see when the low memory condition has been lifted.
+// When it has, we'll stop polling and start waiting for the next
+// LowMemoryCallback(). Meanwhile, the polling may be stopped and restarted by
+// user-interaction events from the observer service.
+class nsAvailableMemoryWatcher final : public nsITimerCallback,
+                                       public nsINamed,
+                                       public nsAvailableMemoryWatcherBase {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_NSIOBSERVER
+  NS_DECL_NSITIMERCALLBACK
+  NS_DECL_NSINAMED
+
+  nsAvailableMemoryWatcher();
+  nsresult Init() override;
+
+ private:
+  static VOID CALLBACK LowMemoryCallback(PVOID aContext, BOOLEAN aIsTimer);
+  static void RecordLowMemoryEvent();
+  static bool IsCommitSpaceLow();
+
+  ~nsAvailableMemoryWatcher();
+  bool RegisterMemoryResourceHandler(const MutexAutoLock& aLock)
+      MOZ_REQUIRES(mMutex);
+  void UnregisterMemoryResourceHandler(const MutexAutoLock&)
+      MOZ_REQUIRES(mMutex);
+  void MaybeSaveMemoryReport(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void Shutdown(const MutexAutoLock& aLock) MOZ_REQUIRES(mMutex);
+  bool ListenForLowMemory(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void OnLowMemory(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void OnHighMemory(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void StartPollingIfUserInteracting(const MutexAutoLock& aLock)
+      MOZ_REQUIRES(mMutex);
+  void StopPolling(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void StopPollingIfUserIdle(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void OnUserInteracting(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+
+  // The publicly available methods (::Observe() and ::Notify()) are called on
+  // the main thread while the ::LowMemoryCallback() method is called by an
+  // external thread. All functions called from those must acquire a lock on
+  // this mutex before accessing the object's fields to prevent races.
+  Mutex mMutex;
+  nsCOMPtr<nsITimer> mTimer MOZ_GUARDED_BY(mMutex);
+  nsAutoHandle mLowMemoryHandle MOZ_GUARDED_BY(mMutex);
+  HANDLE mWaitHandle MOZ_GUARDED_BY(mMutex);
+  bool mPolling MOZ_GUARDED_BY(mMutex);
+
+  // Indicates whether to start a timer when user interaction is notified.
+  // This flag is needed because the low-memory callback may be triggered when
+  // the user is inactive and we want to delay-start the timer.
+  bool mNeedToRestartTimerOnUserInteracting MOZ_GUARDED_BY(mMutex);
+  // Indicate that the available commit space is low.  The timer handler needs
+  // this flag because it is triggered by the low physical memory regardless
+  // of the available commit space.
+  bool mUnderMemoryPressure MOZ_GUARDED_BY(mMutex);
+
+  bool mSavedReport MOZ_GUARDED_BY(mMutex);
+  bool mIsShutdown MOZ_GUARDED_BY(mMutex);
+
+  // Members below this line are used only in the main thread.
+  // No lock is needed.
+
+  // Don't fire a low-memory notification more often than this interval.
+  uint32_t mPollingInterval;
+};
+
+NS_IMPL_ISUPPORTS_INHERITED(nsAvailableMemoryWatcher,
+                            nsAvailableMemoryWatcherBase, nsIObserver,
+                            nsITimerCallback, nsINamed)
+
+nsAvailableMemoryWatcher::nsAvailableMemoryWatcher()
+    : mMutex("low memory callback mutex"),
+      mWaitHandle(nullptr),
+      mPolling(false),
+      mNeedToRestartTimerOnUserInteracting(false),
+      mUnderMemoryPressure(false),
+      mSavedReport(false),
+      mIsShutdown(false),
+      mPollingInterval(0) {}
+
+nsresult nsAvailableMemoryWatcher::Init() {
+  nsresult rv = nsAvailableMemoryWatcherBase::Init();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  MutexAutoLock lock(mMutex);
+  mTimer = NS_NewTimer();
+  if (!mTimer) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  // Use a very short interval for GTest to verify the timer's behavior.
+  mPollingInterval = gIsGtest ? 10 : 10000;
+
+  if (!RegisterMemoryResourceHandler(lock)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+nsAvailableMemoryWatcher::~nsAvailableMemoryWatcher() {
+  // These handles should have been released during the shutdown phase.
+  MOZ_ASSERT(!mLowMemoryHandle);
+  MOZ_ASSERT(!mWaitHandle);
+}
+
+// static
+VOID CALLBACK nsAvailableMemoryWatcher::LowMemoryCallback(PVOID aContext,
+                                                          BOOLEAN aIsTimer) {
+  if (aIsTimer) {
+    return;
+  }
+
+  // The |watcher| was addref'ed when we registered the wait handle in
+  // ListenForLowMemory().  It is decremented when exiting the function,
+  // so please make sure we unregister the wait handle after this line.
+  RefPtr<nsAvailableMemoryWatcher> watcher =
+      already_AddRefed<nsAvailableMemoryWatcher>(
+          static_cast<nsAvailableMemoryWatcher*>(aContext));
+
+  MutexAutoLock lock(watcher->mMutex);
+  if (watcher->mIsShutdown) {
+    // mWaitHandle should have been unregistered during shutdown
+    MOZ_ASSERT(!watcher->mWaitHandle);
+    return;
+  }
+
+  ::UnregisterWait(watcher->mWaitHandle);
+  watcher->mWaitHandle = nullptr;
+
+  // On Windows, memory allocations fails when the available commit space is
+  // not sufficient.  It's possible that this callback function is invoked
+  // but there is still commit space enough for the application to continue
+  // to run.  In such a case, there is no strong need to trigger the memory
+  // pressure event.  So we trigger the event only when the available commit
+  // space is low.
+  if (IsCommitSpaceLow()) {
+    watcher->OnLowMemory(lock);
+  } else {
+    // Since we have unregistered the callback, we need to start a timer to
+    // continue watching memory.
+    watcher->StartPollingIfUserInteracting(lock);
+  }
+}
+
+// static
+void nsAvailableMemoryWatcher::RecordLowMemoryEvent() {
+  sNumLowPhysicalMemEvents++;
+  CrashReporter::AnnotateCrashReport(
+      CrashReporter::Annotation::LowPhysicalMemoryEvents,
+      sNumLowPhysicalMemEvents);
+}
+
+bool nsAvailableMemoryWatcher::RegisterMemoryResourceHandler(
+    const MutexAutoLock& aLock) {
+  mLowMemoryHandle.own(
+      ::CreateMemoryResourceNotification(LowMemoryResourceNotification));
+
+  if (!mLowMemoryHandle) {
+    return false;
+  }
+
+  return ListenForLowMemory(aLock);
+}
+
+void nsAvailableMemoryWatcher::UnregisterMemoryResourceHandler(
+    const MutexAutoLock&) {
+  if (mWaitHandle) {
+    bool res = ::UnregisterWait(mWaitHandle);
+    if (res || ::GetLastError() != ERROR_IO_PENDING) {
+      // We decrement the refcount only when we're sure the LowMemoryCallback()
+      // callback won't be invoked, otherwise the callback will do it
+      this->Release();
+    }
+    mWaitHandle = nullptr;
+  }
+
+  mLowMemoryHandle.reset();
+}
+
+void nsAvailableMemoryWatcher::Shutdown(const MutexAutoLock& aLock) {
+  mIsShutdown = true;
+  mNeedToRestartTimerOnUserInteracting = false;
+
+  if (mTimer) {
+    mTimer->Cancel();
+    mTimer = nullptr;
+  }
+
+  UnregisterMemoryResourceHandler(aLock);
+}
+
+bool nsAvailableMemoryWatcher::ListenForLowMemory(const MutexAutoLock&) {
+  if (mLowMemoryHandle && !mWaitHandle) {
+    // We're giving ownership of this object to the LowMemoryCallback(). We
+    // increment the count here so that the object is kept alive until the
+    // callback decrements it.
+    this->AddRef();
+    bool res = ::RegisterWaitForSingleObject(
+        &mWaitHandle, mLowMemoryHandle, LowMemoryCallback, this, INFINITE,
+        WT_EXECUTEDEFAULT | WT_EXECUTEONLYONCE);
+    if (!res) {
+      // We couldn't register the callback, decrement the count
+      this->Release();
+    }
+    // Once we register the wait handle, we no longer need to start
+    // the timer because we can continue watching memory via callback.
+    mNeedToRestartTimerOnUserInteracting = false;
+    return res;
+  }
+
+  return false;
+}
+
+void nsAvailableMemoryWatcher::MaybeSaveMemoryReport(const MutexAutoLock&) {
+  if (mSavedReport) {
+    return;
+  }
+
+  if (nsCOMPtr<nsICrashReporter> cr =
+          do_GetService("@mozilla.org/toolkit/crash-reporter;1")) {
+    mSavedReport = NS_SUCCEEDED(cr->SaveMemoryReport());
+  }
+}
+
+void nsAvailableMemoryWatcher::OnLowMemory(const MutexAutoLock& aLock) {
+  mUnderMemoryPressure = true;
+  RecordLowMemoryEvent();
+
+  if (NS_IsMainThread()) {
+    MaybeSaveMemoryReport(aLock);
+    UpdateLowMemoryTimeStamp();
+    {
+      // Don't invoke UnloadTabAsync() with the lock to avoid deadlock
+      // because nsAvailableMemoryWatcher::Notify may be invoked while
+      // running the method.
+      MutexAutoUnlock unlock(mMutex);
+      mTabUnloader->UnloadTabAsync();
+    }
+  } else {
+    // SaveMemoryReport and mTabUnloader needs to be run in the main thread
+    // (See nsMemoryReporterManager::GetReportsForThisProcessExtended)
+    NS_DispatchToMainThread(NS_NewRunnableFunction(
+        "nsAvailableMemoryWatcher::OnLowMemory", [self = RefPtr{this}]() {
+          {
+            MutexAutoLock lock(self->mMutex);
+            self->MaybeSaveMemoryReport(lock);
+            self->UpdateLowMemoryTimeStamp();
+          }
+          self->mTabUnloader->UnloadTabAsync();
+        }));
+  }
+
+  StartPollingIfUserInteracting(aLock);
+}
+
+void nsAvailableMemoryWatcher::OnHighMemory(const MutexAutoLock& aLock) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (mUnderMemoryPressure) {
+    RecordTelemetryEventOnHighMemory();
+    NS_NotifyOfEventualMemoryPressure(MemoryPressureState::NoPressure);
+  }
+
+  mUnderMemoryPressure = false;
+  mSavedReport = false;  // Will save a new report if memory gets low again
+  StopPolling(aLock);
+  ListenForLowMemory(aLock);
+}
+
+// static
+bool nsAvailableMemoryWatcher::IsCommitSpaceLow() {
+  // Other options to get the available page file size:
+  //   - GetPerformanceInfo
+  //     Too slow, don't use it.
+  //   - PdhCollectQueryData and PdhGetRawCounterValue
+  //     Faster than GetPerformanceInfo, but slower than GlobalMemoryStatusEx.
+  //   - NtQuerySystemInformation(SystemMemoryUsageInformation)
+  //     Faster than GlobalMemoryStatusEx, but undocumented.
+  MEMORYSTATUSEX memStatus = {sizeof(memStatus)};
+  if (!::GlobalMemoryStatusEx(&memStatus)) {
+    return false;
+  }
+
+  constexpr size_t kBytesPerMB = 1024 * 1024;
+  return (memStatus.ullAvailPageFile / kBytesPerMB) <
+         StaticPrefs::browser_low_commit_space_threshold_mb();
+}
+
+void nsAvailableMemoryWatcher::StartPollingIfUserInteracting(
+    const MutexAutoLock&) {
+  // When the user is inactive, we mark the flag to delay-start
+  // the timer when the user becomes active later.
+  mNeedToRestartTimerOnUserInteracting = true;
+
+  if (mInteracting && !mPolling) {
+    if (NS_SUCCEEDED(mTimer->InitWithCallback(
+            this, mPollingInterval, nsITimer::TYPE_REPEATING_SLACK))) {
+      mPolling = true;
+    }
+  }
+}
+
+void nsAvailableMemoryWatcher::StopPolling(const MutexAutoLock&) {
+  mTimer->Cancel();
+  mPolling = false;
+}
+
+void nsAvailableMemoryWatcher::StopPollingIfUserIdle(
+    const MutexAutoLock& aLock) {
+  if (!mInteracting) {
+    StopPolling(aLock);
+  }
+}
+
+void nsAvailableMemoryWatcher::OnUserInteracting(const MutexAutoLock& aLock) {
+  if (mNeedToRestartTimerOnUserInteracting) {
+    StartPollingIfUserInteracting(aLock);
+  }
+}
+
+// Timer callback, polls the low memory resource notification to detect when
+// we've freed enough memory or if we have to send more memory pressure events.
+// Polling stops automatically when the user is not interacting with the UI.
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::Notify(nsITimer* aTimer) {
+  MutexAutoLock lock(mMutex);
+  StopPollingIfUserIdle(lock);
+
+  if (IsCommitSpaceLow()) {
+    OnLowMemory(lock);
+  } else {
+    OnHighMemory(lock);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::GetName(nsACString& aName) {
+  aName.AssignLiteral("nsAvailableMemoryWatcher");
+  return NS_OK;
+}
+
+// Observer service callback, used to stop the polling timer when the user
+// stops interacting with Firefox and resuming it when they interact again.
+// Also used to shut down the service if the application is quitting.
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::Observe(nsISupports* aSubject, const char* aTopic,
+                                  const char16_t* aData) {
+  nsresult rv = nsAvailableMemoryWatcherBase::Observe(aSubject, aTopic, aData);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  MutexAutoLock lock(mMutex);
+
+  if (strcmp(aTopic, "xpcom-shutdown") == 0) {
+    Shutdown(lock);
+  } else if (strcmp(aTopic, "user-interaction-active") == 0) {
+    OnUserInteracting(lock);
+  }
+
+  return NS_OK;
+}
+
+already_AddRefed<nsAvailableMemoryWatcherBase> CreateAvailableMemoryWatcher() {
+  RefPtr watcher(new nsAvailableMemoryWatcher);
+  if (NS_FAILED(watcher->Init())) {
+    return do_AddRef(new nsAvailableMemoryWatcherBase);  // fallback
+  }
+  return watcher.forget();
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/ClearOnShutdown.cpp b/xpcom/base/ClearOnShutdown.cpp
new file mode 100644
index 0000000000..700785736d
--- /dev/null
+++ b/xpcom/base/ClearOnShutdown.cpp
@@ -0,0 +1,63 @@
+/* -*- 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 "mozilla/ClearOnShutdown.h"
+
+namespace mozilla {
+namespace ClearOnShutdown_Internal {
+
+Array<StaticAutoPtr<ShutdownList>,
+      static_cast<size_t>(ShutdownPhase::ShutdownPhase_Length)>
+    sShutdownObservers;
+ShutdownPhase sCurrentClearOnShutdownPhase = ShutdownPhase::NotInShutdown;
+
+void InsertIntoShutdownList(ShutdownObserver* aObserver, ShutdownPhase aPhase) {
+  // Adding a ClearOnShutdown for a "past" phase is an error.
+  if (PastShutdownPhase(aPhase)) {
+    MOZ_ASSERT(false, "ClearOnShutdown for phase that already was cleared");
+    aObserver->Shutdown();
+    delete aObserver;
+    return;
+  }
+
+  if (!(sShutdownObservers[static_cast<size_t>(aPhase)])) {
+    sShutdownObservers[static_cast<size_t>(aPhase)] = new ShutdownList();
+  }
+  sShutdownObservers[static_cast<size_t>(aPhase)]->insertBack(aObserver);
+}
+
+}  // namespace ClearOnShutdown_Internal
+
+// Called by AdvanceShutdownPhase each time we switch a phase. Will null out
+// pointers added by ClearOnShutdown for all phases up to and including aPhase.
+void KillClearOnShutdown(ShutdownPhase aPhase) {
+  using namespace ClearOnShutdown_Internal;
+
+  MOZ_ASSERT(NS_IsMainThread());
+  // Shutdown only goes one direction...
+  MOZ_ASSERT(!PastShutdownPhase(aPhase));
+
+  // Set the phase before notifying observers to make sure that they can't run
+  // any code which isn't allowed to run after the start of this phase.
+  sCurrentClearOnShutdownPhase = aPhase;
+
+  // It's impossible to add an entry for a "past" phase; this is blocked in
+  // ClearOnShutdown, but clear them out anyways in case there are phases
+  // that weren't passed to KillClearOnShutdown.
+  for (size_t phase = static_cast<size_t>(ShutdownPhase::First);
+       phase <= static_cast<size_t>(aPhase); phase++) {
+    if (sShutdownObservers[static_cast<size_t>(phase)]) {
+      while (ShutdownObserver* observer =
+                 sShutdownObservers[static_cast<size_t>(phase)]->popLast()) {
+        observer->Shutdown();
+        delete observer;
+      }
+      sShutdownObservers[static_cast<size_t>(phase)] = nullptr;
+    }
+  }
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/ClearOnShutdown.h b/xpcom/base/ClearOnShutdown.h
new file mode 100644
index 0000000000..f927e3334a
--- /dev/null
+++ b/xpcom/base/ClearOnShutdown.h
@@ -0,0 +1,147 @@
+/* -*- 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/. */
+
+#ifndef mozilla_ClearOnShutdown_h
+#define mozilla_ClearOnShutdown_h
+
+#include "mozilla/LinkedList.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/Array.h"
+#include "ShutdownPhase.h"
+#include "MainThreadUtils.h"
+
+#include <functional>
+
+/*
+ * This header exports two public methods in the mozilla namespace:
+ *
+ *   template<class SmartPtr>
+ *   void ClearOnShutdown(SmartPtr *aPtr,
+ * aPhase=ShutdownPhase::XPCOMShutdownFinal)
+ *
+ * This function takes a pointer to a smart pointer and nulls the smart pointer
+ * on shutdown (and a particular phase of shutdown as needed).  If a phase
+ * is specified, the ptr will be cleared at the start of that phase.  Also,
+ * if a phase has already occurred when ClearOnShutdown() is called it will
+ * cause a MOZ_ASSERT.  In case a phase is not explicitly cleared we will
+ * clear it on the next phase that occurs.
+ *
+ * This is useful if you have a global smart pointer object which you don't
+ * want to "leak" on shutdown.
+ *
+ * Although ClearOnShutdown will work with any smart pointer (i.e., nsCOMPtr,
+ * RefPtr, StaticRefPtr, and StaticAutoPtr), you probably want to
+ * use it only with StaticRefPtr and StaticAutoPtr.  There is no way to undo a
+ * call to ClearOnShutdown, so you can call it only on smart pointers which you
+ * know will live until the program shuts down.  In practice, these are likely
+ * global variables, which should be Static{Ref,Auto}Ptr.
+ *
+ *   template <typename CallableT>
+ *   void RunOnShutdown(CallableT&& aCallable,
+ *                      aPhase = ShutdownPhase::XPCOMShutdownFinal)
+ *
+ * This function takes a callable and executes it upon shutdown at the start of
+ * the specified phase. If the phase has already occurred when RunOnShutdown()
+ * is called, it will cause a MOZ_ASSERT. In case a phase is not explicitly
+ * cleared, we will clear it on the next phase that occurs.
+ *
+ * ClearOnShutdown and RunOnShutdown are both currently main-thread only because
+ * we don't want to accidentally free an object from a different thread than the
+ * one it was created on.
+ */
+
+namespace mozilla {
+
+namespace ClearOnShutdown_Internal {
+
+class ShutdownObserver : public LinkedListElement<ShutdownObserver> {
+ public:
+  virtual void Shutdown() = 0;
+  virtual ~ShutdownObserver() = default;
+};
+
+template <class SmartPtr>
+class PointerClearer : public ShutdownObserver {
+ public:
+  explicit PointerClearer(SmartPtr* aPtr) : mPtr(aPtr) {}
+
+  virtual void Shutdown() override {
+    if (mPtr) {
+      *mPtr = nullptr;
+    }
+  }
+
+ private:
+  SmartPtr* mPtr;
+};
+
+class FunctionInvoker : public ShutdownObserver {
+ public:
+  template <typename CallableT>
+  explicit FunctionInvoker(CallableT&& aCallable)
+      : mCallable(std::forward<CallableT>(aCallable)) {}
+
+  virtual void Shutdown() override {
+    if (!mCallable) {
+      return;
+    }
+
+    mCallable();
+  }
+
+ private:
+  std::function<void()> mCallable;
+};
+
+void InsertIntoShutdownList(ShutdownObserver* aShutdownObserver,
+                            ShutdownPhase aPhase);
+
+typedef LinkedList<ShutdownObserver> ShutdownList;
+extern Array<StaticAutoPtr<ShutdownList>,
+             static_cast<size_t>(ShutdownPhase::ShutdownPhase_Length)>
+    sShutdownObservers;
+extern ShutdownPhase sCurrentClearOnShutdownPhase;
+
+}  // namespace ClearOnShutdown_Internal
+
+template <class SmartPtr>
+inline void ClearOnShutdown(
+    SmartPtr* aPtr, ShutdownPhase aPhase = ShutdownPhase::XPCOMShutdownFinal) {
+  using namespace ClearOnShutdown_Internal;
+
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aPhase != ShutdownPhase::ShutdownPhase_Length);
+
+  InsertIntoShutdownList(new PointerClearer<SmartPtr>(aPtr), aPhase);
+}
+
+template <typename CallableT>
+inline void RunOnShutdown(
+    CallableT&& aCallable,
+    ShutdownPhase aPhase = ShutdownPhase::XPCOMShutdownFinal) {
+  using namespace ClearOnShutdown_Internal;
+
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aPhase != ShutdownPhase::ShutdownPhase_Length);
+
+  InsertIntoShutdownList(
+      new FunctionInvoker(std::forward<CallableT>(aCallable)), aPhase);
+}
+
+inline bool PastShutdownPhase(ShutdownPhase aPhase) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  return size_t(ClearOnShutdown_Internal::sCurrentClearOnShutdownPhase) >=
+         size_t(aPhase);
+}
+
+// Called by AdvanceShutdownPhase each time we switch a phase. Will null out
+// pointers added by ClearOnShutdown for all phases up to and including aPhase.
+void KillClearOnShutdown(ShutdownPhase aPhase);
+
+}  // namespace mozilla
+
+#endif
diff --git a/xpcom/base/CodeAddressService.h b/xpcom/base/CodeAddressService.h
new file mode 100644
index 0000000000..821bf2c73c
--- /dev/null
+++ b/xpcom/base/CodeAddressService.h
@@ -0,0 +1,250 @@
+/* -*- 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/. */
+
+#ifndef CodeAddressService_h__
+#define CodeAddressService_h__
+
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include "mozilla/AllocPolicy.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/HashFunctions.h"
+#include "mozilla/HashTable.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/StackWalk.h"
+
+namespace mozilla {
+
+namespace detail {
+
+template <class AllocPolicy>
+class CodeAddressServiceAllocPolicy : public AllocPolicy {
+ public:
+  char* strdup_(const char* aStr) {
+    char* s = AllocPolicy::template pod_malloc<char>(strlen(aStr) + 1);
+    if (!s) {
+      MOZ_CRASH("CodeAddressService OOM");
+    }
+    strcpy(s, aStr);
+    return s;
+  }
+};
+
+// Default implementation of DescribeCodeAddressLock.
+struct DefaultDescribeCodeAddressLock {
+  static void Unlock() {}
+  static void Lock() {}
+  // Because CodeAddressService asserts that IsLocked() is true, returning true
+  // here is a sensible default when there is no relevant lock.
+  static bool IsLocked() { return true; }
+};
+
+}  // namespace detail
+
+// This class is used to print details about code locations.
+//
+// |AllocPolicy_| must adhere to the description in mfbt/AllocPolicy.h.
+//
+// |DescribeCodeAddressLock| is needed when the callers may be holding a lock
+// used by MozDescribeCodeAddress.  |DescribeCodeAddressLock| must implement
+// static methods IsLocked(), Unlock() and Lock().
+template <class AllocPolicy_ = MallocAllocPolicy,
+          class DescribeCodeAddressLock =
+              detail::DefaultDescribeCodeAddressLock>
+class CodeAddressService
+    : private detail::CodeAddressServiceAllocPolicy<AllocPolicy_> {
+ protected:
+  // GetLocation() is the key function in this class.  It's basically a wrapper
+  // around MozDescribeCodeAddress.
+  //
+  // However, MozDescribeCodeAddress is very slow on some platforms, and we
+  // have lots of repeated (i.e. same PC) calls to it.  So we do some caching
+  // of results.  Each cached result includes two strings (|mFunction| and
+  // |mLibrary|), so we also optimize them for space in the following ways.
+  //
+  // - The number of distinct library names is small, e.g. a few dozen.  There
+  //   is lots of repetition, especially of libxul.  So we intern them in their
+  //   own table, which saves space over duplicating them for each cache entry.
+  //
+  // - The number of distinct function names is much higher, so we duplicate
+  //   them in each cache entry.  That's more space-efficient than interning
+  //   because entries containing single-occurrence function names are quickly
+  //   overwritten, and their copies released.  In addition, empty function
+  //   names are common, so we use nullptr to represent them compactly.
+
+  using AllocPolicy = detail::CodeAddressServiceAllocPolicy<AllocPolicy_>;
+  using StringHashSet = HashSet<const char*, CStringHasher, AllocPolicy>;
+
+  StringHashSet mLibraryStrings;
+
+  struct Entry : private AllocPolicy {
+    const void* mPc;
+    char* mFunction;       // owned by the Entry;  may be null
+    const char* mLibrary;  // owned by mLibraryStrings;  never null
+                           //   in a non-empty entry is in use
+    ptrdiff_t mLOffset;
+    char* mFileName;  // owned by the Entry; may be null
+    uint32_t mLineNo : 31;
+    uint32_t mInUse : 1;  // is the entry used?
+
+    Entry()
+        : mPc(0),
+          mFunction(nullptr),
+          mLibrary(nullptr),
+          mLOffset(0),
+          mFileName(nullptr),
+          mLineNo(0),
+          mInUse(0) {}
+
+    ~Entry() {
+      // We don't free mLibrary because it's externally owned.
+      AllocPolicy::free_(mFunction);
+      AllocPolicy::free_(mFileName);
+    }
+
+    void Replace(const void* aPc, const char* aFunction, const char* aLibrary,
+                 ptrdiff_t aLOffset, const char* aFileName,
+                 unsigned long aLineNo) {
+      mPc = aPc;
+
+      // Convert "" to nullptr.  Otherwise, make a copy of the name.
+      AllocPolicy::free_(mFunction);
+      mFunction = !aFunction[0] ? nullptr : AllocPolicy::strdup_(aFunction);
+      AllocPolicy::free_(mFileName);
+      mFileName = !aFileName[0] ? nullptr : AllocPolicy::strdup_(aFileName);
+
+      mLibrary = aLibrary;
+      mLOffset = aLOffset;
+      mLineNo = aLineNo;
+
+      mInUse = 1;
+    }
+
+    size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
+      // Don't measure mLibrary because it's externally owned.
+      size_t n = 0;
+      n += aMallocSizeOf(mFunction);
+      n += aMallocSizeOf(mFileName);
+      return n;
+    }
+  };
+
+  const char* InternLibraryString(const char* aString) {
+    auto p = mLibraryStrings.lookupForAdd(aString);
+    if (p) {
+      return *p;
+    }
+
+    const char* newString = AllocPolicy::strdup_(aString);
+    if (!mLibraryStrings.add(p, newString)) {
+      MOZ_CRASH("CodeAddressService OOM");
+    }
+    return newString;
+  }
+
+  Entry& GetEntry(const void* aPc) {
+    MOZ_ASSERT(DescribeCodeAddressLock::IsLocked());
+
+    uint32_t index = HashGeneric(aPc) & kMask;
+    MOZ_ASSERT(index < kNumEntries);
+    Entry& entry = mEntries[index];
+
+    if (!entry.mInUse || entry.mPc != aPc) {
+      mNumCacheMisses++;
+
+      // MozDescribeCodeAddress can (on Linux) acquire a lock inside
+      // the shared library loader.  Another thread might call malloc
+      // while holding that lock (when loading a shared library).  So
+      // we have to exit the lock around this call.  For details, see
+      // https://bugzilla.mozilla.org/show_bug.cgi?id=363334#c3
+      MozCodeAddressDetails details;
+      {
+        DescribeCodeAddressLock::Unlock();
+        (void)MozDescribeCodeAddress(const_cast<void*>(aPc), &details);
+        DescribeCodeAddressLock::Lock();
+      }
+
+      const char* library = InternLibraryString(details.library);
+      entry.Replace(aPc, details.function, library, details.loffset,
+                    details.filename, details.lineno);
+
+    } else {
+      mNumCacheHits++;
+    }
+
+    MOZ_ASSERT(entry.mPc == aPc);
+
+    return entry;
+  }
+
+  // A direct-mapped cache.  When doing dmd::Analyze() just after starting
+  // desktop Firefox (which is similar to analyzing after a longer-running
+  // session, thanks to the limit on how many records we print), a cache with
+  // 2^24 entries (which approximates an infinite-entry cache) has a ~91% hit
+  // rate.  A cache with 2^12 entries has a ~83% hit rate, and takes up ~85 KiB
+  // (on 32-bit platforms) or ~150 KiB (on 64-bit platforms).
+  static const size_t kNumEntries = 1 << 12;
+  static const size_t kMask = kNumEntries - 1;
+  Entry mEntries[kNumEntries];
+
+  size_t mNumCacheHits;
+  size_t mNumCacheMisses;
+
+ public:
+  CodeAddressService()
+      : mLibraryStrings(64), mEntries(), mNumCacheHits(0), mNumCacheMisses(0) {}
+
+  ~CodeAddressService() {
+    for (auto iter = mLibraryStrings.iter(); !iter.done(); iter.next()) {
+      AllocPolicy::free_(const_cast<char*>(iter.get()));
+    }
+  }
+
+  // Returns the minimum number of characters necessary to format the frame
+  // information, without the terminating null. The buffer will be truncated
+  // if the returned value is greater than aBufLen-1.
+  int GetLocation(uint32_t aFrameNumber, const void* aPc, char* aBuf,
+                  size_t aBufLen) {
+    Entry& entry = GetEntry(aPc);
+    return MozFormatCodeAddress(aBuf, aBufLen, aFrameNumber, entry.mPc,
+                                entry.mFunction, entry.mLibrary, entry.mLOffset,
+                                entry.mFileName, entry.mLineNo);
+  }
+
+  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
+    size_t n = aMallocSizeOf(this);
+    for (uint32_t i = 0; i < kNumEntries; i++) {
+      n += mEntries[i].SizeOfExcludingThis(aMallocSizeOf);
+    }
+
+    n += mLibraryStrings.shallowSizeOfExcludingThis(aMallocSizeOf);
+    for (auto iter = mLibraryStrings.iter(); !iter.done(); iter.next()) {
+      n += aMallocSizeOf(iter.get());
+    }
+
+    return n;
+  }
+
+  size_t CacheCapacity() const { return kNumEntries; }
+
+  size_t CacheCount() const {
+    size_t n = 0;
+    for (size_t i = 0; i < kNumEntries; i++) {
+      if (mEntries[i].mInUse) {
+        n++;
+      }
+    }
+    return n;
+  }
+
+  size_t NumCacheHits() const { return mNumCacheHits; }
+  size_t NumCacheMisses() const { return mNumCacheMisses; }
+};
+
+}  // namespace mozilla
+
+#endif  // CodeAddressService_h__
diff --git a/xpcom/base/CountingAllocatorBase.h b/xpcom/base/CountingAllocatorBase.h
new file mode 100644
index 0000000000..02d74f3223
--- /dev/null
+++ b/xpcom/base/CountingAllocatorBase.h
@@ -0,0 +1,158 @@
+/* -*- 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/. */
+
+#ifndef CountingAllocatorBase_h
+#define CountingAllocatorBase_h
+
+#include <cstdlib>
+#include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/mozalloc.h"
+#include "nsIMemoryReporter.h"
+
+namespace mozilla {
+
+// This CRTP class handles several details of wrapping allocators and should
+// be preferred to manually counting with MOZ_DEFINE_MALLOC_SIZE_OF_ON_ALLOC
+// and MOZ_DEFINE_MALLOC_SIZE_OF_ON_FREE.  The typical use is in a memory
+// reporter for a particular third party library:
+//
+//   class MyMemoryReporter : public CountingAllocatorBase<MyMemoryReporter>
+//   {
+//     ...
+//     NS_IMETHOD
+//     CollectReports(nsIHandleReportCallback* aHandleReport,
+//                    nsISupports* aData, bool aAnonymize) override
+//     {
+//        MOZ_COLLECT_REPORT(
+//          "explicit/path/to/somewhere", KIND_HEAP, UNITS_BYTES,
+//          MemoryAllocated(),
+//          "A description of what we are reporting.");
+//
+//        return NS_OK;
+//     }
+//   };
+//
+//   ...somewhere later in the code...
+//   SetThirdPartyMemoryFunctions(MyMemoryReporter::CountingAlloc,
+//                                MyMemoryReporter::CountingFree);
+template <typename T>
+class CountingAllocatorBase {
+ public:
+  CountingAllocatorBase() {
+#ifdef DEBUG
+    // There must be only one instance of this class, due to |sAmount| being
+    // static.
+    static bool hasRun = false;
+    MOZ_ASSERT(!hasRun);
+    hasRun = true;
+#endif
+  }
+
+  static size_t MemoryAllocated() { return sAmount; }
+
+  static void* CountingMalloc(size_t size) {
+    void* p = malloc(size);
+    sAmount += MallocSizeOfOnAlloc(p);
+    return p;
+  }
+
+  static void* CountingCalloc(size_t nmemb, size_t size) {
+    void* p = calloc(nmemb, size);
+    sAmount += MallocSizeOfOnAlloc(p);
+    return p;
+  }
+
+  static void* CountingRealloc(void* p, size_t size) {
+    size_t oldsize = MallocSizeOfOnFree(p);
+    void* pnew = realloc(p, size);
+    if (pnew) {
+      size_t newsize = MallocSizeOfOnAlloc(pnew);
+      sAmount += newsize - oldsize;
+    } else if (size == 0) {
+      // We asked for a 0-sized (re)allocation of some existing pointer
+      // and received NULL in return.  0-sized allocations are permitted
+      // to either return NULL or to allocate a unique object per call (!).
+      // For a malloc implementation that chooses the second strategy,
+      // that allocation may fail (unlikely, but possible).
+      //
+      // Given a NULL return value and an allocation size of 0, then, we
+      // don't know if that means the original pointer was freed or if
+      // the allocation of the unique object failed.  If the original
+      // pointer was freed, then we have nothing to do here.  If the
+      // allocation of the unique object failed, the original pointer is
+      // still valid and we ought to undo the decrement from above.
+      // However, we have no way of knowing how the underlying realloc
+      // implementation is behaving.  Assuming that the original pointer
+      // was freed is the safest course of action.  We do, however, need
+      // to note that we freed memory.
+      sAmount -= oldsize;
+    } else {
+      // realloc failed.  The amount allocated hasn't changed.
+    }
+    return pnew;
+  }
+
+  // Some library code expects that realloc(x, 0) will free x, which is not
+  // the behavior of the version of jemalloc we're using, so this wrapped
+  // version of realloc is needed.
+  static void* CountingFreeingRealloc(void* p, size_t size) {
+    if (size == 0) {
+      CountingFree(p);
+      return nullptr;
+    }
+    return CountingRealloc(p, size);
+  }
+
+  static void CountingFree(void* p) {
+    sAmount -= MallocSizeOfOnFree(p);
+    free(p);
+  }
+
+  // Infallible-allocation wrappers for the counting malloc/calloc/realloc
+  // functions, for clients that don't safely handle allocation failures
+  // themselves.
+  static void* InfallibleCountingMalloc(size_t size) {
+    void* p = moz_xmalloc(size);
+    sAmount += MallocSizeOfOnAlloc(p);
+    return p;
+  }
+
+  static void* InfallibleCountingCalloc(size_t nmemb, size_t size) {
+    void* p = moz_xcalloc(nmemb, size);
+    sAmount += MallocSizeOfOnAlloc(p);
+    return p;
+  }
+
+  static void* InfallibleCountingRealloc(void* p, size_t size) {
+    size_t oldsize = MallocSizeOfOnFree(p);
+    void* pnew = moz_xrealloc(p, size);
+    if (pnew) {
+      size_t newsize = MallocSizeOfOnAlloc(pnew);
+      sAmount += newsize - oldsize;
+    } else if (size == 0) {
+      // See comment in CountingRealloc above.
+      sAmount -= oldsize;
+    } else {
+      // realloc failed.  The amount allocated hasn't changed.
+    }
+    return pnew;
+  }
+
+ private:
+  // |sAmount| can be (implicitly) accessed by multiple threads, so it
+  // must be thread-safe. It may be written during GC, so accesses are not
+  // recorded.
+  typedef Atomic<size_t, SequentiallyConsistent> AmountType;
+  static inline AmountType sAmount{0};
+
+  MOZ_DEFINE_MALLOC_SIZE_OF_ON_ALLOC(MallocSizeOfOnAlloc)
+  MOZ_DEFINE_MALLOC_SIZE_OF_ON_FREE(MallocSizeOfOnFree)
+};
+
+}  // namespace mozilla
+
+#endif  // CountingAllocatorBase_h
diff --git a/xpcom/base/CycleCollectedJSContext.cpp b/xpcom/base/CycleCollectedJSContext.cpp
new file mode 100644
index 0000000000..9e2f89a5b4
--- /dev/null
+++ b/xpcom/base/CycleCollectedJSContext.cpp
@@ -0,0 +1,928 @@
+/* -*- 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 "mozilla/CycleCollectedJSContext.h"
+
+#include <algorithm>
+#include <utility>
+
+#include "js/Debug.h"
+#include "js/GCAPI.h"
+#include "js/Utility.h"
+#include "jsapi.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/AsyncEventDispatcher.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/CycleCollectedJSRuntime.h"
+#include "mozilla/DebuggerOnGCRunnable.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/ProfilerMarkers.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/TimelineConsumers.h"
+#include "mozilla/TimelineMarker.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/DOMException.h"
+#include "mozilla/dom/DOMJSClass.h"
+#include "mozilla/dom/FinalizationRegistryBinding.h"
+#include "mozilla/dom/ProfileTimelineMarkerBinding.h"
+#include "mozilla/dom/PromiseBinding.h"
+#include "mozilla/dom/PromiseDebugging.h"
+#include "mozilla/dom/PromiseRejectionEvent.h"
+#include "mozilla/dom/PromiseRejectionEventBinding.h"
+#include "mozilla/dom/RootedDictionary.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/UserActivation.h"
+#include "nsContentUtils.h"
+#include "nsCycleCollectionNoteRootCallback.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsCycleCollector.h"
+#include "nsDOMJSUtils.h"
+#include "nsDOMMutationObserver.h"
+#include "nsJSUtils.h"
+#include "nsPIDOMWindow.h"
+#include "nsStringBuffer.h"
+#include "nsThread.h"
+#include "nsThreadUtils.h"
+#include "nsWrapperCache.h"
+#include "xpcpublic.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+namespace mozilla {
+
+CycleCollectedJSContext::CycleCollectedJSContext()
+    : mRuntime(nullptr),
+      mJSContext(nullptr),
+      mDoingStableStates(false),
+      mTargetedMicroTaskRecursionDepth(0),
+      mMicroTaskLevel(0),
+      mSuppressionGeneration(0),
+      mDebuggerRecursionDepth(0),
+      mMicroTaskRecursionDepth(0),
+      mFinalizationRegistryCleanup(this) {
+  MOZ_COUNT_CTOR(CycleCollectedJSContext);
+
+  nsCOMPtr<nsIThread> thread = do_GetCurrentThread();
+  mOwningThread = thread.forget().downcast<nsThread>().take();
+  MOZ_RELEASE_ASSERT(mOwningThread);
+}
+
+CycleCollectedJSContext::~CycleCollectedJSContext() {
+  MOZ_COUNT_DTOR(CycleCollectedJSContext);
+  // If the allocation failed, here we are.
+  if (!mJSContext) {
+    return;
+  }
+
+  JS::SetHostCleanupFinalizationRegistryCallback(mJSContext, nullptr, nullptr);
+
+  JS_SetContextPrivate(mJSContext, nullptr);
+
+  mRuntime->SetContext(nullptr);
+  mRuntime->Shutdown(mJSContext);
+
+  // Last chance to process any events.
+  CleanupIDBTransactions(mBaseRecursionDepth);
+  MOZ_ASSERT(mPendingIDBTransactions.IsEmpty());
+
+  ProcessStableStateQueue();
+  MOZ_ASSERT(mStableStateEvents.IsEmpty());
+
+  // Clear mPendingException first, since it might be cycle collected.
+  mPendingException = nullptr;
+
+  MOZ_ASSERT(mDebuggerMicroTaskQueue.empty());
+  MOZ_ASSERT(mPendingMicroTaskRunnables.empty());
+
+  mUncaughtRejections.reset();
+  mConsumedRejections.reset();
+
+  mAboutToBeNotifiedRejectedPromises.Clear();
+  mPendingUnhandledRejections.Clear();
+
+  mFinalizationRegistryCleanup.Destroy();
+
+  JS_DestroyContext(mJSContext);
+  mJSContext = nullptr;
+
+  nsCycleCollector_forgetJSContext();
+
+  mozilla::dom::DestroyScriptSettings();
+
+  mOwningThread->SetScriptObserver(nullptr);
+  NS_RELEASE(mOwningThread);
+
+  delete mRuntime;
+  mRuntime = nullptr;
+}
+
+nsresult CycleCollectedJSContext::Initialize(JSRuntime* aParentRuntime,
+                                             uint32_t aMaxBytes) {
+  MOZ_ASSERT(!mJSContext);
+
+  mozilla::dom::InitScriptSettings();
+  mJSContext = JS_NewContext(aMaxBytes, aParentRuntime);
+  if (!mJSContext) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  mRuntime = CreateRuntime(mJSContext);
+  mRuntime->SetContext(this);
+
+  mOwningThread->SetScriptObserver(this);
+  // The main thread has a base recursion depth of 0, workers of 1.
+  mBaseRecursionDepth = RecursionDepth();
+
+  NS_GetCurrentThread()->SetCanInvokeJS(true);
+
+  JS::SetJobQueue(mJSContext, this);
+  JS::SetPromiseRejectionTrackerCallback(mJSContext,
+                                         PromiseRejectionTrackerCallback, this);
+  mUncaughtRejections.init(mJSContext,
+                           JS::GCVector<JSObject*, 0, js::SystemAllocPolicy>(
+                               js::SystemAllocPolicy()));
+  mConsumedRejections.init(mJSContext,
+                           JS::GCVector<JSObject*, 0, js::SystemAllocPolicy>(
+                               js::SystemAllocPolicy()));
+
+  mFinalizationRegistryCleanup.Init();
+
+  // Cast to PerThreadAtomCache for dom::GetAtomCache(JSContext*).
+  JS_SetContextPrivate(mJSContext, static_cast<PerThreadAtomCache*>(this));
+
+  nsCycleCollector_registerJSContext(this);
+
+  return NS_OK;
+}
+
+/* static */
+CycleCollectedJSContext* CycleCollectedJSContext::GetFor(JSContext* aCx) {
+  // Cast from void* matching JS_SetContextPrivate.
+  auto atomCache = static_cast<PerThreadAtomCache*>(JS_GetContextPrivate(aCx));
+  // Down cast.
+  return static_cast<CycleCollectedJSContext*>(atomCache);
+}
+
+size_t CycleCollectedJSContext::SizeOfExcludingThis(
+    MallocSizeOf aMallocSizeOf) const {
+  return 0;
+}
+
+class PromiseJobRunnable final : public MicroTaskRunnable {
+ public:
+  PromiseJobRunnable(JS::HandleObject aPromise, JS::HandleObject aCallback,
+                     JS::HandleObject aCallbackGlobal,
+                     JS::HandleObject aAllocationSite,
+                     nsIGlobalObject* aIncumbentGlobal)
+      : mCallback(new PromiseJobCallback(aCallback, aCallbackGlobal,
+                                         aAllocationSite, aIncumbentGlobal)),
+        mPropagateUserInputEventHandling(false) {
+    MOZ_ASSERT(js::IsFunctionObject(aCallback));
+
+    if (aPromise) {
+      JS::PromiseUserInputEventHandlingState state =
+          JS::GetPromiseUserInputEventHandlingState(aPromise);
+      mPropagateUserInputEventHandling =
+          state ==
+          JS::PromiseUserInputEventHandlingState::HadUserInteractionAtCreation;
+    }
+  }
+
+  virtual ~PromiseJobRunnable() = default;
+
+ protected:
+  MOZ_CAN_RUN_SCRIPT
+  virtual void Run(AutoSlowOperation& aAso) override {
+    JSObject* callback = mCallback->CallbackPreserveColor();
+    nsIGlobalObject* global = callback ? xpc::NativeGlobal(callback) : nullptr;
+    if (global && !global->IsDying()) {
+      // Propagate the user input event handling bit if needed.
+      nsCOMPtr<nsPIDOMWindowInner> win = do_QueryInterface(global);
+      RefPtr<Document> doc;
+      if (win) {
+        doc = win->GetExtantDoc();
+      }
+      AutoHandlingUserInputStatePusher userInpStatePusher(
+          mPropagateUserInputEventHandling);
+
+      mCallback->Call("promise callback");
+      aAso.CheckForInterrupt();
+    }
+    // Now that mCallback is no longer needed, clear any pointers it contains to
+    // JS GC things. This removes any storebuffer entries associated with those
+    // pointers, which can cause problems by taking up memory and by triggering
+    // minor GCs. This otherwise would not happen until the next minor GC or
+    // cycle collection.
+    mCallback->Reset();
+  }
+
+  virtual bool Suppressed() override {
+    JSObject* callback = mCallback->CallbackPreserveColor();
+    nsIGlobalObject* global = callback ? xpc::NativeGlobal(callback) : nullptr;
+    return global && global->IsInSyncOperation();
+  }
+
+ private:
+  const RefPtr<PromiseJobCallback> mCallback;
+  bool mPropagateUserInputEventHandling;
+};
+
+JSObject* CycleCollectedJSContext::getIncumbentGlobal(JSContext* aCx) {
+  nsIGlobalObject* global = mozilla::dom::GetIncumbentGlobal();
+  if (global) {
+    return global->GetGlobalJSObject();
+  }
+  return nullptr;
+}
+
+bool CycleCollectedJSContext::enqueuePromiseJob(
+    JSContext* aCx, JS::HandleObject aPromise, JS::HandleObject aJob,
+    JS::HandleObject aAllocationSite, JS::HandleObject aIncumbentGlobal) {
+  MOZ_ASSERT(aCx == Context());
+  MOZ_ASSERT(Get() == this);
+
+  nsIGlobalObject* global = nullptr;
+  if (aIncumbentGlobal) {
+    global = xpc::NativeGlobal(aIncumbentGlobal);
+  }
+  JS::RootedObject jobGlobal(aCx, JS::CurrentGlobalOrNull(aCx));
+  RefPtr<PromiseJobRunnable> runnable = new PromiseJobRunnable(
+      aPromise, aJob, jobGlobal, aAllocationSite, global);
+  DispatchToMicroTask(runnable.forget());
+  return true;
+}
+
+// Used only by the SpiderMonkey Debugger API, and even then only via
+// JS::AutoDebuggerJobQueueInterruption, to ensure that the debuggee's queue is
+// not affected; see comments in js/public/Promise.h.
+void CycleCollectedJSContext::runJobs(JSContext* aCx) {
+  MOZ_ASSERT(aCx == Context());
+  MOZ_ASSERT(Get() == this);
+  PerformMicroTaskCheckPoint();
+}
+
+bool CycleCollectedJSContext::empty() const {
+  // This is our override of JS::JobQueue::empty. Since that interface is only
+  // concerned with the ordinary microtask queue, not the debugger microtask
+  // queue, we only report on the former.
+  return mPendingMicroTaskRunnables.empty();
+}
+
+// Preserve a debuggee's microtask queue while it is interrupted by the
+// debugger. See the comments for JS::AutoDebuggerJobQueueInterruption.
+class CycleCollectedJSContext::SavedMicroTaskQueue
+    : public JS::JobQueue::SavedJobQueue {
+ public:
+  explicit SavedMicroTaskQueue(CycleCollectedJSContext* ccjs) : ccjs(ccjs) {
+    ccjs->mDebuggerRecursionDepth++;
+    ccjs->mPendingMicroTaskRunnables.swap(mQueue);
+  }
+
+  ~SavedMicroTaskQueue() {
+    // The JS Debugger attempts to maintain the invariant that microtasks which
+    // occur durring debugger operation are completely flushed from the task
+    // queue before returning control to the debuggee, in order to avoid
+    // micro-tasks generated during debugging from interfering with regular
+    // operation.
+    //
+    // While the vast majority of microtasks can be reliably flushed,
+    // synchronous operations (see nsAutoSyncOperation) such as printing and
+    // alert diaglogs suppress the execution of some microtasks.
+    //
+    // When PerformMicroTaskCheckpoint is run while microtasks are suppressed,
+    // any suppressed microtasks are gathered into a new SuppressedMicroTasks
+    // runnable, which is enqueued on exit from PerformMicroTaskCheckpoint. As a
+    // result, AutoDebuggerJobQueueInterruption::runJobs is not able to
+    // correctly guarantee that the microtask queue is totally empty in the
+    // presence of sync operations.
+    //
+    // Previous versions of this code release-asserted that the queue was empty,
+    // causing user observable crashes (Bug 1849675). To avoid this, we instead
+    // choose to move suspended microtasks from the SavedMicroTaskQueue to the
+    // main microtask queue in this destructor. This means that jobs enqueued
+    // during synchnronous events under debugger control may produce events
+    // which run outside the debugger, but this is viewed as strictly
+    // preferrable to crashing.
+    MOZ_RELEASE_ASSERT(ccjs->mPendingMicroTaskRunnables.size() <= 1);
+    MOZ_RELEASE_ASSERT(ccjs->mDebuggerRecursionDepth);
+    RefPtr<MicroTaskRunnable> maybeSuppressedTasks;
+
+    // Handle the case where there is a SuppressedMicroTask still in the queue.
+    if (!ccjs->mPendingMicroTaskRunnables.empty()) {
+      maybeSuppressedTasks = ccjs->mPendingMicroTaskRunnables.front();
+      ccjs->mPendingMicroTaskRunnables.pop_front();
+    }
+
+    MOZ_RELEASE_ASSERT(ccjs->mPendingMicroTaskRunnables.empty());
+    ccjs->mDebuggerRecursionDepth--;
+    ccjs->mPendingMicroTaskRunnables.swap(mQueue);
+
+    // Re-enqueue the suppressed task now that we've put the original microtask
+    // queue back.
+    if (maybeSuppressedTasks) {
+      ccjs->mPendingMicroTaskRunnables.push_back(maybeSuppressedTasks);
+    }
+  }
+
+ private:
+  CycleCollectedJSContext* ccjs;
+  std::deque<RefPtr<MicroTaskRunnable>> mQueue;
+};
+
+js::UniquePtr<JS::JobQueue::SavedJobQueue>
+CycleCollectedJSContext::saveJobQueue(JSContext* cx) {
+  auto saved = js::MakeUnique<SavedMicroTaskQueue>(this);
+  if (!saved) {
+    // When MakeUnique's allocation fails, the SavedMicroTaskQueue constructor
+    // is never called, so mPendingMicroTaskRunnables is still initialized.
+    JS_ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  return saved;
+}
+
+/* static */
+void CycleCollectedJSContext::PromiseRejectionTrackerCallback(
+    JSContext* aCx, bool aMutedErrors, JS::HandleObject aPromise,
+    JS::PromiseRejectionHandlingState state, void* aData) {
+  CycleCollectedJSContext* self = static_cast<CycleCollectedJSContext*>(aData);
+
+  MOZ_ASSERT(aCx == self->Context());
+  MOZ_ASSERT(Get() == self);
+
+  // TODO: Bug 1549351 - Promise rejection event should not be sent for
+  // cross-origin scripts
+
+  PromiseArray& aboutToBeNotified = self->mAboutToBeNotifiedRejectedPromises;
+  PromiseHashtable& unhandled = self->mPendingUnhandledRejections;
+  uint64_t promiseID = JS::GetPromiseID(aPromise);
+
+  if (state == JS::PromiseRejectionHandlingState::Unhandled) {
+    PromiseDebugging::AddUncaughtRejection(aPromise);
+    if (!aMutedErrors) {
+      RefPtr<Promise> promise =
+          Promise::CreateFromExisting(xpc::NativeGlobal(aPromise), aPromise);
+      aboutToBeNotified.AppendElement(promise);
+      unhandled.InsertOrUpdate(promiseID, std::move(promise));
+    }
+  } else {
+    PromiseDebugging::AddConsumedRejection(aPromise);
+    for (size_t i = 0; i < aboutToBeNotified.Length(); i++) {
+      if (aboutToBeNotified[i] &&
+          aboutToBeNotified[i]->PromiseObj() == aPromise) {
+        // To avoid large amounts of memmoves, we don't shrink the vector
+        // here. Instead, we filter out nullptrs when iterating over the
+        // vector later.
+        aboutToBeNotified[i] = nullptr;
+        DebugOnly<bool> isFound = unhandled.Remove(promiseID);
+        MOZ_ASSERT(isFound);
+        return;
+      }
+    }
+    RefPtr<Promise> promise;
+    unhandled.Remove(promiseID, getter_AddRefs(promise));
+    if (!promise && !aMutedErrors) {
+      nsIGlobalObject* global = xpc::NativeGlobal(aPromise);
+      if (nsCOMPtr<EventTarget> owner = do_QueryInterface(global)) {
+        RootedDictionary<PromiseRejectionEventInit> init(aCx);
+        init.mPromise = Promise::CreateFromExisting(global, aPromise);
+        init.mReason = JS::GetPromiseResult(aPromise);
+
+        RefPtr<PromiseRejectionEvent> event =
+            PromiseRejectionEvent::Constructor(owner, u"rejectionhandled"_ns,
+                                               init);
+
+        RefPtr<AsyncEventDispatcher> asyncDispatcher =
+            new AsyncEventDispatcher(owner, event);
+        asyncDispatcher->PostDOMEvent();
+      }
+    }
+  }
+}
+
+already_AddRefed<Exception> CycleCollectedJSContext::GetPendingException()
+    const {
+  MOZ_ASSERT(mJSContext);
+
+  nsCOMPtr<Exception> out = mPendingException;
+  return out.forget();
+}
+
+void CycleCollectedJSContext::SetPendingException(Exception* aException) {
+  MOZ_ASSERT(mJSContext);
+  mPendingException = aException;
+}
+
+std::deque<RefPtr<MicroTaskRunnable>>&
+CycleCollectedJSContext::GetMicroTaskQueue() {
+  MOZ_ASSERT(mJSContext);
+  return mPendingMicroTaskRunnables;
+}
+
+std::deque<RefPtr<MicroTaskRunnable>>&
+CycleCollectedJSContext::GetDebuggerMicroTaskQueue() {
+  MOZ_ASSERT(mJSContext);
+  return mDebuggerMicroTaskQueue;
+}
+
+void CycleCollectedJSContext::ProcessStableStateQueue() {
+  MOZ_ASSERT(mJSContext);
+  MOZ_RELEASE_ASSERT(!mDoingStableStates);
+  mDoingStableStates = true;
+
+  // When run, one event can add another event to the mStableStateEvents, as
+  // such you can't use iterators here.
+  for (uint32_t i = 0; i < mStableStateEvents.Length(); ++i) {
+    nsCOMPtr<nsIRunnable> event = std::move(mStableStateEvents[i]);
+    event->Run();
+  }
+
+  mStableStateEvents.Clear();
+  mDoingStableStates = false;
+}
+
+void CycleCollectedJSContext::CleanupIDBTransactions(uint32_t aRecursionDepth) {
+  MOZ_ASSERT(mJSContext);
+  MOZ_RELEASE_ASSERT(!mDoingStableStates);
+  mDoingStableStates = true;
+
+  nsTArray<PendingIDBTransactionData> localQueue =
+      std::move(mPendingIDBTransactions);
+
+  localQueue.RemoveLastElements(
+      localQueue.end() -
+      std::remove_if(localQueue.begin(), localQueue.end(),
+                     [aRecursionDepth](PendingIDBTransactionData& data) {
+                       if (data.mRecursionDepth != aRecursionDepth) {
+                         return false;
+                       }
+
+                       {
+                         nsCOMPtr<nsIRunnable> transaction =
+                             std::move(data.mTransaction);
+                         transaction->Run();
+                       }
+
+                       return true;
+                     }));
+
+  // If mPendingIDBTransactions has events in it now, they were added from
+  // something we called, so they belong at the end of the queue.
+  localQueue.AppendElements(std::move(mPendingIDBTransactions));
+  mPendingIDBTransactions = std::move(localQueue);
+  mDoingStableStates = false;
+}
+
+void CycleCollectedJSContext::BeforeProcessTask(bool aMightBlock) {
+  // If ProcessNextEvent was called during a microtask callback, we
+  // must process any pending microtasks before blocking in the event loop,
+  // otherwise we may deadlock until an event enters the queue later.
+  if (aMightBlock && PerformMicroTaskCheckPoint()) {
+    // If any microtask was processed, we post a dummy event in order to
+    // force the ProcessNextEvent call not to block.  This is required
+    // to support nested event loops implemented using a pattern like
+    // "while (condition) thread.processNextEvent(true)", in case the
+    // condition is triggered here by a Promise "then" callback.
+    NS_DispatchToMainThread(new Runnable("BeforeProcessTask"));
+  }
+}
+
+void CycleCollectedJSContext::AfterProcessTask(uint32_t aRecursionDepth) {
+  MOZ_ASSERT(mJSContext);
+
+  // See HTML 6.1.4.2 Processing model
+
+  // Step 4.1: Execute microtasks.
+  PerformMicroTaskCheckPoint();
+
+  // Step 4.2 Execute any events that were waiting for a stable state.
+  ProcessStableStateQueue();
+
+  // This should be a fast test so that it won't affect the next task
+  // processing.
+  MaybePokeGC();
+}
+
+void CycleCollectedJSContext::AfterProcessMicrotasks() {
+  MOZ_ASSERT(mJSContext);
+  // Notify unhandled promise rejections:
+  // https://html.spec.whatwg.org/multipage/webappapis.html#notify-about-rejected-promises
+  if (mAboutToBeNotifiedRejectedPromises.Length()) {
+    RefPtr<NotifyUnhandledRejections> runnable = new NotifyUnhandledRejections(
+        std::move(mAboutToBeNotifiedRejectedPromises));
+    NS_DispatchToCurrentThread(runnable);
+  }
+  // Cleanup Indexed Database transactions:
+  // https://html.spec.whatwg.org/multipage/webappapis.html#perform-a-microtask-checkpoint
+  CleanupIDBTransactions(RecursionDepth());
+
+  // Clear kept alive objects in JS WeakRef.
+  // https://whatpr.org/html/4571/webappapis.html#perform-a-microtask-checkpoint
+  //
+  // ECMAScript implementations are expected to call ClearKeptObjects when a
+  // synchronous sequence of ECMAScript execution completes.
+  //
+  // https://tc39.es/proposal-weakrefs/#sec-clear-kept-objects
+  JS::ClearKeptObjects(mJSContext);
+}
+
+void CycleCollectedJSContext::MaybePokeGC() {
+  // Worker-compatible check to see if we want to do an idle-time minor
+  // GC.
+  class IdleTimeGCTaskRunnable : public mozilla::IdleRunnable {
+   public:
+    using mozilla::IdleRunnable::IdleRunnable;
+
+   public:
+    IdleTimeGCTaskRunnable() : IdleRunnable("IdleTimeGCTask") {}
+
+    NS_IMETHOD Run() override {
+      CycleCollectedJSRuntime* ccrt = CycleCollectedJSRuntime::Get();
+      if (ccrt) {
+        ccrt->RunIdleTimeGCTask();
+      }
+      return NS_OK;
+    }
+  };
+
+  if (Runtime()->IsIdleGCTaskNeeded()) {
+    nsCOMPtr<nsIRunnable> gc_task = new IdleTimeGCTaskRunnable();
+    NS_DispatchToCurrentThreadQueue(gc_task.forget(), EventQueuePriority::Idle);
+    Runtime()->SetPendingIdleGCTask();
+  }
+}
+
+uint32_t CycleCollectedJSContext::RecursionDepth() const {
+  // Debugger interruptions are included in the recursion depth so that debugger
+  // microtask checkpoints do not run IDB transactions which were initiated
+  // before the interruption.
+  return mOwningThread->RecursionDepth() + mDebuggerRecursionDepth;
+}
+
+void CycleCollectedJSContext::RunInStableState(
+    already_AddRefed<nsIRunnable>&& aRunnable) {
+  MOZ_ASSERT(mJSContext);
+  mStableStateEvents.AppendElement(std::move(aRunnable));
+}
+
+void CycleCollectedJSContext::AddPendingIDBTransaction(
+    already_AddRefed<nsIRunnable>&& aTransaction) {
+  MOZ_ASSERT(mJSContext);
+
+  PendingIDBTransactionData data;
+  data.mTransaction = aTransaction;
+
+  MOZ_ASSERT(mOwningThread);
+  data.mRecursionDepth = RecursionDepth();
+
+  // There must be an event running to get here.
+#ifndef MOZ_WIDGET_COCOA
+  MOZ_ASSERT(data.mRecursionDepth > mBaseRecursionDepth);
+#else
+  // XXX bug 1261143
+  // Recursion depth should be greater than mBaseRecursionDepth,
+  // or the runnable will stay in the queue forever.
+  if (data.mRecursionDepth <= mBaseRecursionDepth) {
+    data.mRecursionDepth = mBaseRecursionDepth + 1;
+  }
+#endif
+
+  mPendingIDBTransactions.AppendElement(std::move(data));
+}
+
+void CycleCollectedJSContext::DispatchToMicroTask(
+    already_AddRefed<MicroTaskRunnable> aRunnable) {
+  RefPtr<MicroTaskRunnable> runnable(aRunnable);
+
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(runnable);
+
+  JS::JobQueueMayNotBeEmpty(Context());
+
+  LogMicroTaskRunnable::LogDispatch(runnable.get());
+  mPendingMicroTaskRunnables.push_back(std::move(runnable));
+}
+
+class AsyncMutationHandler final : public mozilla::Runnable {
+ public:
+  AsyncMutationHandler() : mozilla::Runnable("AsyncMutationHandler") {}
+
+  // MOZ_CAN_RUN_SCRIPT_BOUNDARY until Runnable::Run is MOZ_CAN_RUN_SCRIPT.  See
+  // bug 1535398.
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  NS_IMETHOD Run() override {
+    CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
+    if (ccjs) {
+      ccjs->PerformMicroTaskCheckPoint();
+    }
+    return NS_OK;
+  }
+};
+
+SuppressedMicroTasks::SuppressedMicroTasks(CycleCollectedJSContext* aContext)
+    : mContext(aContext),
+      mSuppressionGeneration(aContext->mSuppressionGeneration) {}
+
+bool SuppressedMicroTasks::Suppressed() {
+  if (mSuppressionGeneration == mContext->mSuppressionGeneration) {
+    return true;
+  }
+
+  for (std::deque<RefPtr<MicroTaskRunnable>>::reverse_iterator it =
+           mSuppressedMicroTaskRunnables.rbegin();
+       it != mSuppressedMicroTaskRunnables.rend(); ++it) {
+    mContext->GetMicroTaskQueue().push_front(*it);
+  }
+  mContext->mSuppressedMicroTasks = nullptr;
+
+  return false;
+}
+
+bool CycleCollectedJSContext::PerformMicroTaskCheckPoint(bool aForce) {
+  if (mPendingMicroTaskRunnables.empty() && mDebuggerMicroTaskQueue.empty()) {
+    AfterProcessMicrotasks();
+    // Nothing to do, return early.
+    return false;
+  }
+
+  uint32_t currentDepth = RecursionDepth();
+  if (mMicroTaskRecursionDepth >= currentDepth && !aForce) {
+    // We are already executing microtasks for the current recursion depth.
+    return false;
+  }
+
+  if (mTargetedMicroTaskRecursionDepth != 0 &&
+      mTargetedMicroTaskRecursionDepth + mDebuggerRecursionDepth !=
+          currentDepth) {
+    return false;
+  }
+
+  if (NS_IsMainThread() && !nsContentUtils::IsSafeToRunScript()) {
+    // Special case for main thread where DOM mutations may happen when
+    // it is not safe to run scripts.
+    nsContentUtils::AddScriptRunner(new AsyncMutationHandler());
+    return false;
+  }
+
+  mozilla::AutoRestore<uint32_t> restore(mMicroTaskRecursionDepth);
+  MOZ_ASSERT(aForce ? currentDepth == 0 : currentDepth > 0);
+  mMicroTaskRecursionDepth = currentDepth;
+
+  AUTO_PROFILER_TRACING_MARKER("JS", "Perform microtasks", JS);
+
+  bool didProcess = false;
+  AutoSlowOperation aso;
+
+  for (;;) {
+    RefPtr<MicroTaskRunnable> runnable;
+    if (!mDebuggerMicroTaskQueue.empty()) {
+      runnable = std::move(mDebuggerMicroTaskQueue.front());
+      mDebuggerMicroTaskQueue.pop_front();
+    } else if (!mPendingMicroTaskRunnables.empty()) {
+      runnable = std::move(mPendingMicroTaskRunnables.front());
+      mPendingMicroTaskRunnables.pop_front();
+    } else {
+      break;
+    }
+
+    if (runnable->Suppressed()) {
+      // Microtasks in worker shall never be suppressed.
+      // Otherwise, mPendingMicroTaskRunnables will be replaced later with
+      // all suppressed tasks in mDebuggerMicroTaskQueue unexpectedly.
+      MOZ_ASSERT(NS_IsMainThread());
+      JS::JobQueueMayNotBeEmpty(Context());
+      if (runnable != mSuppressedMicroTasks) {
+        if (!mSuppressedMicroTasks) {
+          mSuppressedMicroTasks = new SuppressedMicroTasks(this);
+        }
+        mSuppressedMicroTasks->mSuppressedMicroTaskRunnables.push_back(
+            runnable);
+      }
+    } else {
+      if (mPendingMicroTaskRunnables.empty() &&
+          mDebuggerMicroTaskQueue.empty() && !mSuppressedMicroTasks) {
+        JS::JobQueueIsEmpty(Context());
+      }
+      didProcess = true;
+
+      LogMicroTaskRunnable::Run log(runnable.get());
+      runnable->Run(aso);
+      runnable = nullptr;
+    }
+  }
+
+  // Put back the suppressed microtasks so that they will be run later.
+  // Note, it is possible that we end up keeping these suppressed tasks around
+  // for some time, but no longer than spinning the event loop nestedly
+  // (sync XHR, alert, etc.)
+  if (mSuppressedMicroTasks) {
+    mPendingMicroTaskRunnables.push_back(mSuppressedMicroTasks);
+  }
+
+  AfterProcessMicrotasks();
+
+  return didProcess;
+}
+
+void CycleCollectedJSContext::PerformDebuggerMicroTaskCheckpoint() {
+  // Don't do normal microtask handling checks here, since whoever is calling
+  // this method is supposed to know what they are doing.
+
+  AutoSlowOperation aso;
+  for (;;) {
+    // For a debugger microtask checkpoint, we always use the debugger microtask
+    // queue.
+    std::deque<RefPtr<MicroTaskRunnable>>* microtaskQueue =
+        &GetDebuggerMicroTaskQueue();
+
+    if (microtaskQueue->empty()) {
+      break;
+    }
+
+    RefPtr<MicroTaskRunnable> runnable = std::move(microtaskQueue->front());
+    MOZ_ASSERT(runnable);
+
+    LogMicroTaskRunnable::Run log(runnable.get());
+
+    // This function can re-enter, so we remove the element before calling.
+    microtaskQueue->pop_front();
+
+    if (mPendingMicroTaskRunnables.empty() && mDebuggerMicroTaskQueue.empty()) {
+      JS::JobQueueIsEmpty(Context());
+    }
+    runnable->Run(aso);
+    runnable = nullptr;
+  }
+
+  AfterProcessMicrotasks();
+}
+
+NS_IMETHODIMP CycleCollectedJSContext::NotifyUnhandledRejections::Run() {
+  for (size_t i = 0; i < mUnhandledRejections.Length(); ++i) {
+    CycleCollectedJSContext* cccx = CycleCollectedJSContext::Get();
+    NS_ENSURE_STATE(cccx);
+
+    RefPtr<Promise>& promise = mUnhandledRejections[i];
+    if (!promise) {
+      continue;
+    }
+
+    JS::RootingContext* cx = cccx->RootingCx();
+    JS::RootedObject promiseObj(cx, promise->PromiseObj());
+    MOZ_ASSERT(JS::IsPromiseObject(promiseObj));
+
+    // Only fire unhandledrejection if the promise is still not handled;
+    uint64_t promiseID = JS::GetPromiseID(promiseObj);
+    if (!JS::GetPromiseIsHandled(promiseObj)) {
+      if (nsCOMPtr<EventTarget> target =
+              do_QueryInterface(promise->GetParentObject())) {
+        RootedDictionary<PromiseRejectionEventInit> init(cx);
+        init.mPromise = promise;
+        init.mReason = JS::GetPromiseResult(promiseObj);
+        init.mCancelable = true;
+
+        RefPtr<PromiseRejectionEvent> event =
+            PromiseRejectionEvent::Constructor(target, u"unhandledrejection"_ns,
+                                               init);
+        // We don't use the result of dispatching event here to check whether to
+        // report the Promise to console.
+        target->DispatchEvent(*event);
+      }
+    }
+
+    cccx = CycleCollectedJSContext::Get();
+    NS_ENSURE_STATE(cccx);
+    if (!JS::GetPromiseIsHandled(promiseObj)) {
+      DebugOnly<bool> isFound =
+          cccx->mPendingUnhandledRejections.Remove(promiseID);
+      MOZ_ASSERT(isFound);
+    }
+
+    // If a rejected promise is being handled in "unhandledrejection" event
+    // handler, it should be removed from the table in
+    // PromiseRejectionTrackerCallback.
+    MOZ_ASSERT(!cccx->mPendingUnhandledRejections.Lookup(promiseID));
+  }
+  return NS_OK;
+}
+
+nsresult CycleCollectedJSContext::NotifyUnhandledRejections::Cancel() {
+  CycleCollectedJSContext* cccx = CycleCollectedJSContext::Get();
+  NS_ENSURE_STATE(cccx);
+
+  for (size_t i = 0; i < mUnhandledRejections.Length(); ++i) {
+    RefPtr<Promise>& promise = mUnhandledRejections[i];
+    if (!promise) {
+      continue;
+    }
+
+    JS::RootedObject promiseObj(cccx->RootingCx(), promise->PromiseObj());
+    cccx->mPendingUnhandledRejections.Remove(JS::GetPromiseID(promiseObj));
+  }
+  return NS_OK;
+}
+
+class FinalizationRegistryCleanup::CleanupRunnable
+    : public DiscardableRunnable {
+ public:
+  explicit CleanupRunnable(FinalizationRegistryCleanup* aCleanupWork)
+      : DiscardableRunnable("CleanupRunnable"), mCleanupWork(aCleanupWork) {}
+
+  // MOZ_CAN_RUN_SCRIPT_BOUNDARY until Runnable::Run is MOZ_CAN_RUN_SCRIPT.  See
+  // bug 1535398.
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  NS_IMETHOD Run() override {
+    mCleanupWork->DoCleanup();
+    return NS_OK;
+  }
+
+ private:
+  FinalizationRegistryCleanup* mCleanupWork;
+};
+
+FinalizationRegistryCleanup::FinalizationRegistryCleanup(
+    CycleCollectedJSContext* aContext)
+    : mContext(aContext) {}
+
+void FinalizationRegistryCleanup::Destroy() {
+  // This must happen before the CycleCollectedJSContext destructor calls
+  // JS_DestroyContext().
+  mCallbacks.reset();
+}
+
+void FinalizationRegistryCleanup::Init() {
+  JSContext* cx = mContext->Context();
+  mCallbacks.init(cx);
+  JS::SetHostCleanupFinalizationRegistryCallback(cx, QueueCallback, this);
+}
+
+/* static */
+void FinalizationRegistryCleanup::QueueCallback(JSFunction* aDoCleanup,
+                                                JSObject* aIncumbentGlobal,
+                                                void* aData) {
+  FinalizationRegistryCleanup* cleanup =
+      static_cast<FinalizationRegistryCleanup*>(aData);
+  cleanup->QueueCallback(aDoCleanup, aIncumbentGlobal);
+}
+
+void FinalizationRegistryCleanup::QueueCallback(JSFunction* aDoCleanup,
+                                                JSObject* aIncumbentGlobal) {
+  bool firstCallback = mCallbacks.empty();
+
+  MOZ_ALWAYS_TRUE(mCallbacks.append(Callback{aDoCleanup, aIncumbentGlobal}));
+
+  if (firstCallback) {
+    RefPtr<CleanupRunnable> cleanup = new CleanupRunnable(this);
+    NS_DispatchToCurrentThread(cleanup.forget());
+  }
+}
+
+void FinalizationRegistryCleanup::DoCleanup() {
+  if (mCallbacks.empty()) {
+    return;
+  }
+
+  JS::RootingContext* cx = mContext->RootingCx();
+
+  JS::Rooted<CallbackVector> callbacks(cx);
+  std::swap(callbacks.get(), mCallbacks.get());
+
+  for (const Callback& callback : callbacks) {
+    JS::ExposeObjectToActiveJS(
+        JS_GetFunctionObject(callback.mCallbackFunction));
+    JS::ExposeObjectToActiveJS(callback.mIncumbentGlobal);
+
+    JS::RootedObject functionObj(
+        cx, JS_GetFunctionObject(callback.mCallbackFunction));
+    JS::RootedObject globalObj(cx, JS::GetNonCCWObjectGlobal(functionObj));
+
+    nsIGlobalObject* incumbentGlobal =
+        xpc::NativeGlobal(callback.mIncumbentGlobal);
+    if (!incumbentGlobal) {
+      continue;
+    }
+
+    RefPtr<FinalizationRegistryCleanupCallback> cleanupCallback(
+        new FinalizationRegistryCleanupCallback(functionObj, globalObj, nullptr,
+                                                incumbentGlobal));
+
+    nsIGlobalObject* global =
+        xpc::NativeGlobal(cleanupCallback->CallbackPreserveColor());
+    if (global) {
+      cleanupCallback->Call("FinalizationRegistryCleanup::DoCleanup");
+    }
+  }
+}
+
+void FinalizationRegistryCleanup::Callback::trace(JSTracer* trc) {
+  JS::TraceRoot(trc, &mCallbackFunction, "mCallbackFunction");
+  JS::TraceRoot(trc, &mIncumbentGlobal, "mIncumbentGlobal");
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/CycleCollectedJSContext.h b/xpcom/base/CycleCollectedJSContext.h
new file mode 100644
index 0000000000..bbe47a57a5
--- /dev/null
+++ b/xpcom/base/CycleCollectedJSContext.h
@@ -0,0 +1,396 @@
+/* -*- 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/. */
+
+#ifndef mozilla_CycleCollectedJSContext_h
+#define mozilla_CycleCollectedJSContext_h
+
+#include <deque>
+
+#include "mozilla/Attributes.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/dom/AtomList.h"
+#include "mozilla/dom/Promise.h"
+#include "js/GCVector.h"
+#include "js/Promise.h"
+
+#include "nsCOMPtr.h"
+#include "nsRefPtrHashtable.h"
+#include "nsTArray.h"
+
+class nsCycleCollectionNoteRootCallback;
+class nsIRunnable;
+class nsThread;
+
+namespace mozilla {
+class AutoSlowOperation;
+
+class CycleCollectedJSContext;
+class CycleCollectedJSRuntime;
+
+namespace dom {
+class Exception;
+class WorkerJSContext;
+class WorkletJSContext;
+}  // namespace dom
+
+// Contains various stats about the cycle collection.
+struct CycleCollectorResults {
+  CycleCollectorResults() {
+    // Initialize here so when we increment mNumSlices the first time we're
+    // not using uninitialized memory.
+    Init();
+  }
+
+  void Init() {
+    mForcedGC = false;
+    mSuspectedAtCCStart = 0;
+    mMergedZones = false;
+    mAnyManual = false;
+    mVisitedRefCounted = 0;
+    mVisitedGCed = 0;
+    mFreedRefCounted = 0;
+    mFreedGCed = 0;
+    mFreedJSZones = 0;
+    mNumSlices = 1;
+    // mNumSlices is initialized to one, because we call Init() after the
+    // per-slice increment of mNumSlices has already occurred.
+  }
+
+  bool mForcedGC;
+  bool mMergedZones;
+  // mAnyManual is true if any slice was manually triggered, and at shutdown.
+  bool mAnyManual;
+  uint32_t mSuspectedAtCCStart;
+  uint32_t mVisitedRefCounted;
+  uint32_t mVisitedGCed;
+  uint32_t mFreedRefCounted;
+  uint32_t mFreedGCed;
+  uint32_t mFreedJSZones;
+  uint32_t mNumSlices;
+};
+
+class MicroTaskRunnable {
+ public:
+  MicroTaskRunnable() = default;
+  NS_INLINE_DECL_REFCOUNTING(MicroTaskRunnable)
+  MOZ_CAN_RUN_SCRIPT virtual void Run(AutoSlowOperation& aAso) = 0;
+  virtual bool Suppressed() { return false; }
+
+ protected:
+  virtual ~MicroTaskRunnable() = default;
+};
+
+// Store the suppressed mictotasks in another microtask so that operations
+// for the microtask queue as a whole keep working.
+class SuppressedMicroTasks : public MicroTaskRunnable {
+ public:
+  explicit SuppressedMicroTasks(CycleCollectedJSContext* aContext);
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY void Run(AutoSlowOperation& aAso) final {}
+  virtual bool Suppressed();
+
+  CycleCollectedJSContext* mContext;
+  uint64_t mSuppressionGeneration;
+  std::deque<RefPtr<MicroTaskRunnable>> mSuppressedMicroTaskRunnables;
+};
+
+// Support for JS FinalizationRegistry objects, which allow a JS callback to be
+// registered that is called when objects die.
+//
+// We keep a vector of functions that call back into the JS engine along
+// with their associated incumbent globals, one per FinalizationRegistry object
+// that has pending cleanup work. These are run in their own task.
+class FinalizationRegistryCleanup {
+ public:
+  explicit FinalizationRegistryCleanup(CycleCollectedJSContext* aContext);
+  void Init();
+  void Destroy();
+  void QueueCallback(JSFunction* aDoCleanup, JSObject* aIncumbentGlobal);
+  MOZ_CAN_RUN_SCRIPT void DoCleanup();
+
+ private:
+  static void QueueCallback(JSFunction* aDoCleanup, JSObject* aIncumbentGlobal,
+                            void* aData);
+
+  class CleanupRunnable;
+
+  struct Callback {
+    JSFunction* mCallbackFunction;
+    JSObject* mIncumbentGlobal;
+    void trace(JSTracer* trc);
+  };
+
+  // This object is part of CycleCollectedJSContext, so it's safe to have a raw
+  // pointer to its containing context here.
+  CycleCollectedJSContext* mContext;
+
+  using CallbackVector = JS::GCVector<Callback, 0, InfallibleAllocPolicy>;
+  JS::PersistentRooted<CallbackVector> mCallbacks;
+};
+
+class CycleCollectedJSContext : dom::PerThreadAtomCache, private JS::JobQueue {
+  friend class CycleCollectedJSRuntime;
+  friend class SuppressedMicroTasks;
+
+ protected:
+  CycleCollectedJSContext();
+  virtual ~CycleCollectedJSContext();
+
+  MOZ_IS_CLASS_INIT
+  nsresult Initialize(JSRuntime* aParentRuntime, uint32_t aMaxBytes);
+
+  virtual CycleCollectedJSRuntime* CreateRuntime(JSContext* aCx) = 0;
+
+  size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
+
+ private:
+  static void PromiseRejectionTrackerCallback(
+      JSContext* aCx, bool aMutedErrors, JS::Handle<JSObject*> aPromise,
+      JS::PromiseRejectionHandlingState state, void* aData);
+
+  void AfterProcessMicrotasks();
+
+ public:
+  void ProcessStableStateQueue();
+
+ private:
+  void CleanupIDBTransactions(uint32_t aRecursionDepth);
+
+ public:
+  virtual dom::WorkerJSContext* GetAsWorkerJSContext() { return nullptr; }
+  virtual dom::WorkletJSContext* GetAsWorkletJSContext() { return nullptr; }
+
+  CycleCollectedJSRuntime* Runtime() const {
+    MOZ_ASSERT(mRuntime);
+    return mRuntime;
+  }
+
+  already_AddRefed<dom::Exception> GetPendingException() const;
+  void SetPendingException(dom::Exception* aException);
+
+  std::deque<RefPtr<MicroTaskRunnable>>& GetMicroTaskQueue();
+  std::deque<RefPtr<MicroTaskRunnable>>& GetDebuggerMicroTaskQueue();
+
+  JSContext* Context() const {
+    MOZ_ASSERT(mJSContext);
+    return mJSContext;
+  }
+
+  JS::RootingContext* RootingCx() const {
+    MOZ_ASSERT(mJSContext);
+    return JS::RootingContext::get(mJSContext);
+  }
+
+  void SetTargetedMicroTaskRecursionDepth(uint32_t aDepth) {
+    mTargetedMicroTaskRecursionDepth = aDepth;
+  }
+
+  void UpdateMicroTaskSuppressionGeneration() { ++mSuppressionGeneration; }
+
+ protected:
+  JSContext* MaybeContext() const { return mJSContext; }
+
+ public:
+  // nsThread entrypoints
+  //
+  // MOZ_CAN_RUN_SCRIPT_BOUNDARY so we don't need to annotate
+  // nsThread::ProcessNextEvent and all its callers MOZ_CAN_RUN_SCRIPT for now.
+  // But we really should!
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  virtual void BeforeProcessTask(bool aMightBlock);
+  // MOZ_CAN_RUN_SCRIPT_BOUNDARY so we don't need to annotate
+  // nsThread::ProcessNextEvent and all its callers MOZ_CAN_RUN_SCRIPT for now.
+  // But we really should!
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  virtual void AfterProcessTask(uint32_t aRecursionDepth);
+
+  // Check whether any eager thresholds have been reached, which would mean
+  // an idle GC task (minor or major) would be useful.
+  virtual void MaybePokeGC();
+
+  uint32_t RecursionDepth() const;
+
+  // Run in stable state (call through nsContentUtils)
+  void RunInStableState(already_AddRefed<nsIRunnable>&& aRunnable);
+
+  void AddPendingIDBTransaction(already_AddRefed<nsIRunnable>&& aTransaction);
+
+  // Get the CycleCollectedJSContext for a JSContext.
+  // Returns null only if Initialize() has not completed on or during
+  // destruction of the CycleCollectedJSContext.
+  static CycleCollectedJSContext* GetFor(JSContext* aCx);
+
+  // Get the current thread's CycleCollectedJSContext.  Returns null if there
+  // isn't one.
+  static CycleCollectedJSContext* Get();
+
+  // Queue an async microtask to the current main or worker thread.
+  virtual void DispatchToMicroTask(
+      already_AddRefed<MicroTaskRunnable> aRunnable);
+
+  // Call EnterMicroTask when you're entering JS execution.
+  // Usually the best way to do this is to use nsAutoMicroTask.
+  void EnterMicroTask() { ++mMicroTaskLevel; }
+
+  MOZ_CAN_RUN_SCRIPT
+  void LeaveMicroTask() {
+    if (--mMicroTaskLevel == 0) {
+      PerformMicroTaskCheckPoint();
+    }
+  }
+
+  uint32_t MicroTaskLevel() const { return mMicroTaskLevel; }
+
+  void SetMicroTaskLevel(uint32_t aLevel) { mMicroTaskLevel = aLevel; }
+
+  MOZ_CAN_RUN_SCRIPT
+  bool PerformMicroTaskCheckPoint(bool aForce = false);
+
+  MOZ_CAN_RUN_SCRIPT
+  void PerformDebuggerMicroTaskCheckpoint();
+
+  bool IsInStableOrMetaStableState() const { return mDoingStableStates; }
+
+  // Storage for watching rejected promises waiting for some client to
+  // consume their rejection.
+  // Promises in this list have been rejected in the last turn of the
+  // event loop without the rejection being handled.
+  // Note that this can contain nullptrs in place of promises removed because
+  // they're consumed before it'd be reported.
+  JS::PersistentRooted<JS::GCVector<JSObject*, 0, js::SystemAllocPolicy>>
+      mUncaughtRejections;
+
+  // Promises in this list have previously been reported as rejected
+  // (because they were in the above list), but the rejection was handled
+  // in the last turn of the event loop.
+  JS::PersistentRooted<JS::GCVector<JSObject*, 0, js::SystemAllocPolicy>>
+      mConsumedRejections;
+  nsTArray<nsCOMPtr<nsISupports /* UncaughtRejectionObserver */>>
+      mUncaughtRejectionObservers;
+
+  virtual bool IsSystemCaller() const = 0;
+
+  // Unused on main thread.  Used by AutoJSAPI on Worker and Worklet threads.
+  virtual void ReportError(JSErrorReport* aReport,
+                           JS::ConstUTF8CharsZ aToStringResult) {
+    MOZ_ASSERT_UNREACHABLE("Not supported");
+  }
+
+ private:
+  // JS::JobQueue implementation: see js/public/Promise.h.
+  // SpiderMonkey uses some of these methods to enqueue promise resolution jobs.
+  // Others protect the debuggee microtask queue from the debugger's
+  // interruptions; see the comments on JS::AutoDebuggerJobQueueInterruption for
+  // details.
+  JSObject* getIncumbentGlobal(JSContext* cx) override;
+  bool enqueuePromiseJob(JSContext* cx, JS::Handle<JSObject*> promise,
+                         JS::Handle<JSObject*> job,
+                         JS::Handle<JSObject*> allocationSite,
+                         JS::Handle<JSObject*> incumbentGlobal) override;
+  // MOZ_CAN_RUN_SCRIPT_BOUNDARY for now so we don't have to change SpiderMonkey
+  // headers.  The caller presumably knows this can run script (like everything
+  // in SpiderMonkey!) and will deal.
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void runJobs(JSContext* cx) override;
+  bool empty() const override;
+  class SavedMicroTaskQueue;
+  js::UniquePtr<SavedJobQueue> saveJobQueue(JSContext*) override;
+
+ private:
+  CycleCollectedJSRuntime* mRuntime;
+
+  JSContext* mJSContext;
+
+  nsCOMPtr<dom::Exception> mPendingException;
+  nsThread* mOwningThread;  // Manual refcounting to avoid include hell.
+
+  struct PendingIDBTransactionData {
+    nsCOMPtr<nsIRunnable> mTransaction;
+    uint32_t mRecursionDepth;
+  };
+
+  nsTArray<nsCOMPtr<nsIRunnable>> mStableStateEvents;
+  nsTArray<PendingIDBTransactionData> mPendingIDBTransactions;
+  uint32_t mBaseRecursionDepth;
+  bool mDoingStableStates;
+
+  // If set to none 0, microtasks will be processed only when recursion depth
+  // is the set value.
+  uint32_t mTargetedMicroTaskRecursionDepth;
+
+  uint32_t mMicroTaskLevel;
+
+  std::deque<RefPtr<MicroTaskRunnable>> mPendingMicroTaskRunnables;
+  std::deque<RefPtr<MicroTaskRunnable>> mDebuggerMicroTaskQueue;
+  RefPtr<SuppressedMicroTasks> mSuppressedMicroTasks;
+  uint64_t mSuppressionGeneration;
+
+  // How many times the debugger has interrupted execution, possibly creating
+  // microtask checkpoints in places that they would not normally occur.
+  uint32_t mDebuggerRecursionDepth;
+
+  uint32_t mMicroTaskRecursionDepth;
+
+  // This implements about-to-be-notified rejected promises list in the spec.
+  // https://html.spec.whatwg.org/multipage/webappapis.html#about-to-be-notified-rejected-promises-list
+  typedef nsTArray<RefPtr<dom::Promise>> PromiseArray;
+  PromiseArray mAboutToBeNotifiedRejectedPromises;
+
+  // This is for the "outstanding rejected promises weak set" in the spec,
+  // https://html.spec.whatwg.org/multipage/webappapis.html#outstanding-rejected-promises-weak-set
+  // We use different data structure and opposite logic here to achieve the same
+  // effect. Basically this is used for tracking the rejected promise that does
+  // NOT need firing a rejectionhandled event. We will check the table to see if
+  // firing rejectionhandled event is required when a rejected promise is being
+  // handled.
+  //
+  // The rejected promise will be stored in the table if
+  // - it is unhandled, and
+  // - The unhandledrejection is not yet fired.
+  //
+  // And be removed when
+  // - it is handled, or
+  // - A unhandledrejection is fired and it isn't being handled in event
+  // handler.
+  typedef nsRefPtrHashtable<nsUint64HashKey, dom::Promise> PromiseHashtable;
+  PromiseHashtable mPendingUnhandledRejections;
+
+  class NotifyUnhandledRejections final : public CancelableRunnable {
+   public:
+    explicit NotifyUnhandledRejections(PromiseArray&& aPromises)
+        : CancelableRunnable("NotifyUnhandledRejections"),
+          mUnhandledRejections(std::move(aPromises)) {}
+
+    NS_IMETHOD Run() final;
+
+    nsresult Cancel() final;
+
+   private:
+    PromiseArray mUnhandledRejections;
+  };
+
+  FinalizationRegistryCleanup mFinalizationRegistryCleanup;
+};
+
+class MOZ_STACK_CLASS nsAutoMicroTask {
+ public:
+  nsAutoMicroTask() {
+    CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
+    if (ccjs) {
+      ccjs->EnterMicroTask();
+    }
+  }
+  MOZ_CAN_RUN_SCRIPT ~nsAutoMicroTask() {
+    CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
+    if (ccjs) {
+      ccjs->LeaveMicroTask();
+    }
+  }
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_CycleCollectedJSContext_h
diff --git a/xpcom/base/CycleCollectedJSRuntime.cpp b/xpcom/base/CycleCollectedJSRuntime.cpp
new file mode 100644
index 0000000000..4e2557f51e
--- /dev/null
+++ b/xpcom/base/CycleCollectedJSRuntime.cpp
@@ -0,0 +1,2075 @@
+/* -*- 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/. */
+
+// We're dividing JS objects into 3 categories:
+//
+// 1. "real" roots, held by the JS engine itself or rooted through the root
+//    and lock JS APIs. Roots from this category are considered black in the
+//    cycle collector, any cycle they participate in is uncollectable.
+//
+// 2. certain roots held by C++ objects that are guaranteed to be alive.
+//    Roots from this category are considered black in the cycle collector,
+//    and any cycle they participate in is uncollectable. These roots are
+//    traced from TraceNativeBlackRoots.
+//
+// 3. all other roots held by C++ objects that participate in cycle collection,
+//    held by us (see TraceNativeGrayRoots). Roots from this category are
+//    considered grey in the cycle collector; whether or not they are collected
+//    depends on the objects that hold them.
+//
+// Note that if a root is in multiple categories the fact that it is in
+// category 1 or 2 that takes precedence, so it will be considered black.
+//
+// During garbage collection we switch to an additional mark color (gray) when
+// tracing inside TraceNativeGrayRoots. This allows us to walk those roots later
+// on and add all objects reachable only from them to the cycle collector.
+//
+// Phases:
+//
+// 1. marking of the roots in category 1 by having the JS GC do its marking
+// 2. marking of the roots in category 2 by having the JS GC call us back
+//    (via JS_SetExtraGCRootsTracer) and running TraceNativeBlackRoots
+// 3. marking of the roots in category 3 by
+//    TraceNativeGrayRootsInCollectingZones using an additional color (gray).
+// 4. end of GC, GC can sweep its heap
+//
+// At some later point, when the cycle collector runs:
+//
+// 5. walk gray objects and add them to the cycle collector, cycle collect
+//
+// JS objects that are part of cycles the cycle collector breaks will be
+// collected by the next JS GC.
+//
+// If WantAllTraces() is false the cycle collector will not traverse roots
+// from category 1 or any JS objects held by them. Any JS objects they hold
+// will already be marked by the JS GC and will thus be colored black
+// themselves. Any C++ objects they hold will have a missing (untraversed)
+// edge from the JS object to the C++ object and so it will be marked black
+// too. This decreases the number of objects that the cycle collector has to
+// deal with.
+// To improve debugging, if WantAllTraces() is true all JS objects are
+// traversed.
+
+#include "mozilla/CycleCollectedJSRuntime.h"
+
+#include <algorithm>
+#include <utility>
+
+#include "js/Debug.h"
+#include "js/RealmOptions.h"
+#include "js/friend/DumpFunctions.h"  // js::DumpHeap
+#include "js/GCAPI.h"
+#include "js/HeapAPI.h"
+#include "js/Object.h"  // JS::GetClass, JS::GetCompartment, JS::GetPrivate
+#include "js/PropertyAndElement.h"  // JS_DefineProperty
+#include "js/Warnings.h"            // JS::SetWarningReporter
+#include "js/ShadowRealmCallbacks.h"
+#include "js/SliceBudget.h"
+#include "jsfriendapi.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/DebuggerOnGCRunnable.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/PerfStats.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/ProfilerMarkers.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/StaticPrefs_javascript.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/TimelineConsumers.h"
+#include "mozilla/TimelineMarker.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/AutoEntryScript.h"
+#include "mozilla/dom/DOMJSClass.h"
+#include "mozilla/dom/JSExecutionManager.h"
+#include "mozilla/dom/ProfileTimelineMarkerBinding.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/PromiseBinding.h"
+#include "mozilla/dom/PromiseDebugging.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/ShadowRealmGlobalScope.h"
+#include "mozilla/dom/RegisterShadowRealmBindings.h"
+#include "nsContentUtils.h"
+#include "nsCycleCollectionNoteRootCallback.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsCycleCollector.h"
+#include "nsDOMJSUtils.h"
+#include "nsExceptionHandler.h"
+#include "nsJSUtils.h"
+#include "nsStringBuffer.h"
+#include "nsWrapperCache.h"
+#include "prenv.h"
+
+#if defined(XP_MACOSX)
+#  include "nsMacUtilsImpl.h"
+#endif
+
+#include "nsThread.h"
+#include "nsThreadUtils.h"
+#include "xpcpublic.h"
+
+#ifdef NIGHTLY_BUILD
+// For performance reasons, we make the JS Dev Error Interceptor a Nightly-only
+// feature.
+#  define MOZ_JS_DEV_ERROR_INTERCEPTOR = 1
+#endif  // NIGHTLY_BUILD
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+namespace mozilla {
+
+struct DeferredFinalizeFunctionHolder {
+  DeferredFinalizeFunction run;
+  void* data;
+};
+
+class IncrementalFinalizeRunnable : public DiscardableRunnable {
+  typedef AutoTArray<DeferredFinalizeFunctionHolder, 16> DeferredFinalizeArray;
+  typedef CycleCollectedJSRuntime::DeferredFinalizerTable
+      DeferredFinalizerTable;
+
+  CycleCollectedJSRuntime* mRuntime;
+  DeferredFinalizeArray mDeferredFinalizeFunctions;
+  uint32_t mFinalizeFunctionToRun;
+  bool mReleasing;
+
+  static const PRTime SliceMillis = 5; /* ms */
+
+ public:
+  IncrementalFinalizeRunnable(CycleCollectedJSRuntime* aRt,
+                              DeferredFinalizerTable& aFinalizerTable);
+  virtual ~IncrementalFinalizeRunnable();
+
+  void ReleaseNow(bool aLimited);
+
+  NS_DECL_NSIRUNNABLE
+};
+
+}  // namespace mozilla
+
+struct NoteWeakMapChildrenTracer : public JS::CallbackTracer {
+  NoteWeakMapChildrenTracer(JSRuntime* aRt,
+                            nsCycleCollectionNoteRootCallback& aCb)
+      : JS::CallbackTracer(aRt, JS::TracerKind::Callback),
+        mCb(aCb),
+        mTracedAny(false),
+        mMap(nullptr),
+        mKey(nullptr),
+        mKeyDelegate(nullptr) {}
+  void onChild(JS::GCCellPtr aThing, const char* name) override;
+  nsCycleCollectionNoteRootCallback& mCb;
+  bool mTracedAny;
+  JSObject* mMap;
+  JS::GCCellPtr mKey;
+  JSObject* mKeyDelegate;
+};
+
+void NoteWeakMapChildrenTracer::onChild(JS::GCCellPtr aThing,
+                                        const char* name) {
+  if (aThing.is<JSString>()) {
+    return;
+  }
+
+  if (!JS::GCThingIsMarkedGrayInCC(aThing) && !mCb.WantAllTraces()) {
+    return;
+  }
+
+  if (JS::IsCCTraceKind(aThing.kind())) {
+    mCb.NoteWeakMapping(mMap, mKey, mKeyDelegate, aThing);
+    mTracedAny = true;
+  } else {
+    JS::TraceChildren(this, aThing);
+  }
+}
+
+struct NoteWeakMapsTracer : public js::WeakMapTracer {
+  NoteWeakMapsTracer(JSRuntime* aRt, nsCycleCollectionNoteRootCallback& aCccb)
+      : js::WeakMapTracer(aRt), mCb(aCccb), mChildTracer(aRt, aCccb) {}
+  void trace(JSObject* aMap, JS::GCCellPtr aKey, JS::GCCellPtr aValue) override;
+  nsCycleCollectionNoteRootCallback& mCb;
+  NoteWeakMapChildrenTracer mChildTracer;
+};
+
+void NoteWeakMapsTracer::trace(JSObject* aMap, JS::GCCellPtr aKey,
+                               JS::GCCellPtr aValue) {
+  // If nothing that could be held alive by this entry is marked gray, return.
+  if ((!aKey || !JS::GCThingIsMarkedGrayInCC(aKey)) &&
+      MOZ_LIKELY(!mCb.WantAllTraces())) {
+    if (!aValue || !JS::GCThingIsMarkedGrayInCC(aValue) ||
+        aValue.is<JSString>()) {
+      return;
+    }
+  }
+
+  // The cycle collector can only properly reason about weak maps if it can
+  // reason about the liveness of their keys, which in turn requires that
+  // the key can be represented in the cycle collector graph.  All existing
+  // uses of weak maps use either objects or scripts as keys, which are okay.
+  MOZ_ASSERT(JS::IsCCTraceKind(aKey.kind()));
+
+  // As an emergency fallback for non-debug builds, if the key is not
+  // representable in the cycle collector graph, we treat it as marked.  This
+  // can cause leaks, but is preferable to ignoring the binding, which could
+  // cause the cycle collector to free live objects.
+  if (!JS::IsCCTraceKind(aKey.kind())) {
+    aKey = nullptr;
+  }
+
+  JSObject* kdelegate = nullptr;
+  if (aKey.is<JSObject>()) {
+    kdelegate = js::UncheckedUnwrapWithoutExpose(&aKey.as<JSObject>());
+  }
+
+  if (JS::IsCCTraceKind(aValue.kind())) {
+    mCb.NoteWeakMapping(aMap, aKey, kdelegate, aValue);
+  } else {
+    mChildTracer.mTracedAny = false;
+    mChildTracer.mMap = aMap;
+    mChildTracer.mKey = aKey;
+    mChildTracer.mKeyDelegate = kdelegate;
+
+    if (!aValue.is<JSString>()) {
+      JS::TraceChildren(&mChildTracer, aValue);
+    }
+
+    // The delegate could hold alive the key, so report something to the CC
+    // if we haven't already.
+    if (!mChildTracer.mTracedAny && aKey && JS::GCThingIsMarkedGrayInCC(aKey) &&
+        kdelegate) {
+      mCb.NoteWeakMapping(aMap, aKey, kdelegate, nullptr);
+    }
+  }
+}
+
+// Report whether the key or value of a weak mapping entry are gray but need to
+// be marked black.
+static void ShouldWeakMappingEntryBeBlack(JSObject* aMap, JS::GCCellPtr aKey,
+                                          JS::GCCellPtr aValue,
+                                          bool* aKeyShouldBeBlack,
+                                          bool* aValueShouldBeBlack) {
+  *aKeyShouldBeBlack = false;
+  *aValueShouldBeBlack = false;
+
+  // If nothing that could be held alive by this entry is marked gray, return.
+  bool keyMightNeedMarking = aKey && JS::GCThingIsMarkedGrayInCC(aKey);
+  bool valueMightNeedMarking = aValue && JS::GCThingIsMarkedGrayInCC(aValue) &&
+                               aValue.kind() != JS::TraceKind::String;
+  if (!keyMightNeedMarking && !valueMightNeedMarking) {
+    return;
+  }
+
+  if (!JS::IsCCTraceKind(aKey.kind())) {
+    aKey = nullptr;
+  }
+
+  if (keyMightNeedMarking && aKey.is<JSObject>()) {
+    JSObject* kdelegate =
+        js::UncheckedUnwrapWithoutExpose(&aKey.as<JSObject>());
+    if (kdelegate && !JS::ObjectIsMarkedGray(kdelegate) &&
+        (!aMap || !JS::ObjectIsMarkedGray(aMap))) {
+      *aKeyShouldBeBlack = true;
+    }
+  }
+
+  if (aValue && JS::GCThingIsMarkedGrayInCC(aValue) &&
+      (!aKey || !JS::GCThingIsMarkedGrayInCC(aKey)) &&
+      (!aMap || !JS::ObjectIsMarkedGray(aMap)) &&
+      aValue.kind() != JS::TraceKind::Shape) {
+    *aValueShouldBeBlack = true;
+  }
+}
+
+struct FixWeakMappingGrayBitsTracer : public js::WeakMapTracer {
+  explicit FixWeakMappingGrayBitsTracer(JSRuntime* aRt)
+      : js::WeakMapTracer(aRt) {}
+
+  void FixAll() {
+    do {
+      mAnyMarked = false;
+      js::TraceWeakMaps(this);
+    } while (mAnyMarked);
+  }
+
+  void trace(JSObject* aMap, JS::GCCellPtr aKey,
+             JS::GCCellPtr aValue) override {
+    bool keyShouldBeBlack;
+    bool valueShouldBeBlack;
+    ShouldWeakMappingEntryBeBlack(aMap, aKey, aValue, &keyShouldBeBlack,
+                                  &valueShouldBeBlack);
+    if (keyShouldBeBlack && JS::UnmarkGrayGCThingRecursively(aKey)) {
+      mAnyMarked = true;
+    }
+
+    if (valueShouldBeBlack && JS::UnmarkGrayGCThingRecursively(aValue)) {
+      mAnyMarked = true;
+    }
+  }
+
+  MOZ_INIT_OUTSIDE_CTOR bool mAnyMarked;
+};
+
+#ifdef DEBUG
+// Check whether weak maps are marked correctly according to the logic above.
+struct CheckWeakMappingGrayBitsTracer : public js::WeakMapTracer {
+  explicit CheckWeakMappingGrayBitsTracer(JSRuntime* aRt)
+      : js::WeakMapTracer(aRt), mFailed(false) {}
+
+  static bool Check(JSRuntime* aRt) {
+    CheckWeakMappingGrayBitsTracer tracer(aRt);
+    js::TraceWeakMaps(&tracer);
+    return !tracer.mFailed;
+  }
+
+  void trace(JSObject* aMap, JS::GCCellPtr aKey,
+             JS::GCCellPtr aValue) override {
+    bool keyShouldBeBlack;
+    bool valueShouldBeBlack;
+    ShouldWeakMappingEntryBeBlack(aMap, aKey, aValue, &keyShouldBeBlack,
+                                  &valueShouldBeBlack);
+
+    if (keyShouldBeBlack) {
+      fprintf(stderr, "Weak mapping key %p of map %p should be black\n",
+              aKey.asCell(), aMap);
+      mFailed = true;
+    }
+
+    if (valueShouldBeBlack) {
+      fprintf(stderr, "Weak mapping value %p of map %p should be black\n",
+              aValue.asCell(), aMap);
+      mFailed = true;
+    }
+  }
+
+  bool mFailed;
+};
+#endif  // DEBUG
+
+static void CheckParticipatesInCycleCollection(JS::GCCellPtr aThing,
+                                               const char* aName,
+                                               void* aClosure) {
+  bool* cycleCollectionEnabled = static_cast<bool*>(aClosure);
+
+  if (*cycleCollectionEnabled) {
+    return;
+  }
+
+  if (JS::IsCCTraceKind(aThing.kind()) && JS::GCThingIsMarkedGrayInCC(aThing)) {
+    *cycleCollectionEnabled = true;
+  }
+}
+
+NS_IMETHODIMP
+JSGCThingParticipant::TraverseNative(void* aPtr,
+                                     nsCycleCollectionTraversalCallback& aCb) {
+  auto runtime = reinterpret_cast<CycleCollectedJSRuntime*>(
+      reinterpret_cast<char*>(this) -
+      offsetof(CycleCollectedJSRuntime, mGCThingCycleCollectorGlobal));
+
+  JS::GCCellPtr cellPtr(aPtr, JS::GCThingTraceKind(aPtr));
+  runtime->TraverseGCThing(CycleCollectedJSRuntime::TRAVERSE_FULL, cellPtr,
+                           aCb);
+  return NS_OK;
+}
+
+// NB: This is only used to initialize the participant in
+// CycleCollectedJSRuntime. It should never be used directly.
+static JSGCThingParticipant sGCThingCycleCollectorGlobal;
+
+NS_IMETHODIMP
+JSZoneParticipant::TraverseNative(void* aPtr,
+                                  nsCycleCollectionTraversalCallback& aCb) {
+  auto runtime = reinterpret_cast<CycleCollectedJSRuntime*>(
+      reinterpret_cast<char*>(this) -
+      offsetof(CycleCollectedJSRuntime, mJSZoneCycleCollectorGlobal));
+
+  MOZ_ASSERT(!aCb.WantAllTraces());
+  JS::Zone* zone = static_cast<JS::Zone*>(aPtr);
+
+  runtime->TraverseZone(zone, aCb);
+  return NS_OK;
+}
+
+struct TraversalTracer : public JS::CallbackTracer {
+  TraversalTracer(JSRuntime* aRt, nsCycleCollectionTraversalCallback& aCb)
+      : JS::CallbackTracer(aRt, JS::TracerKind::Callback,
+                           JS::TraceOptions(JS::WeakMapTraceAction::Skip,
+                                            JS::WeakEdgeTraceAction::Trace)),
+        mCb(aCb) {}
+  void onChild(JS::GCCellPtr aThing, const char* name) override;
+  nsCycleCollectionTraversalCallback& mCb;
+};
+
+void TraversalTracer::onChild(JS::GCCellPtr aThing, const char* name) {
+  // Checking strings and symbols for being gray is rather slow, and we don't
+  // need either of them for the cycle collector.
+  if (aThing.is<JSString>() || aThing.is<JS::Symbol>()) {
+    return;
+  }
+
+  // Don't traverse non-gray objects, unless we want all traces.
+  if (!JS::GCThingIsMarkedGrayInCC(aThing) && !mCb.WantAllTraces()) {
+    return;
+  }
+
+  /*
+   * This function needs to be careful to avoid stack overflow. Normally, when
+   * IsCCTraceKind is true, the recursion terminates immediately as we just add
+   * |thing| to the CC graph. So overflow is only possible when there are long
+   * or cyclic chains of non-IsCCTraceKind GC things. Places where this can
+   * occur use special APIs to handle such chains iteratively.
+   */
+  if (JS::IsCCTraceKind(aThing.kind())) {
+    if (MOZ_UNLIKELY(mCb.WantDebugInfo())) {
+      char buffer[200];
+      context().getEdgeName(name, buffer, sizeof(buffer));
+      mCb.NoteNextEdgeName(buffer);
+    }
+    mCb.NoteJSChild(aThing);
+    return;
+  }
+
+  // Allow re-use of this tracer inside trace callback.
+  JS::AutoClearTracingContext actc(this);
+
+  if (aThing.is<js::Shape>()) {
+    // The maximum depth of traversal when tracing a Shape is unbounded, due to
+    // the parent pointers on the shape.
+    JS_TraceShapeCycleCollectorChildren(this, aThing);
+  } else {
+    JS::TraceChildren(this, aThing);
+  }
+}
+
+/*
+ * The cycle collection participant for a Zone is intended to produce the same
+ * results as if all of the gray GCthings in a zone were merged into a single
+ * node, except for self-edges. This avoids the overhead of representing all of
+ * the GCthings in the zone in the cycle collector graph, which should be much
+ * faster if many of the GCthings in the zone are gray.
+ *
+ * Zone merging should not always be used, because it is a conservative
+ * approximation of the true cycle collector graph that can incorrectly identify
+ * some garbage objects as being live. For instance, consider two cycles that
+ * pass through a zone, where one is garbage and the other is live. If we merge
+ * the entire zone, the cycle collector will think that both are alive.
+ *
+ * We don't have to worry about losing track of a garbage cycle, because any
+ * such garbage cycle incorrectly identified as live must contain at least one
+ * C++ to JS edge, and XPConnect will always add the C++ object to the CC graph.
+ * (This is in contrast to pure C++ garbage cycles, which must always be
+ * properly identified, because we clear the purple buffer during every CC,
+ * which may contain the last reference to a garbage cycle.)
+ */
+
+// NB: This is only used to initialize the participant in
+// CycleCollectedJSRuntime. It should never be used directly.
+static const JSZoneParticipant sJSZoneCycleCollectorGlobal;
+
+static void JSObjectsTenuredCb(JSContext* aContext, void* aData) {
+  static_cast<CycleCollectedJSRuntime*>(aData)->JSObjectsTenured();
+}
+
+static void MozCrashWarningReporter(JSContext*, JSErrorReport*) {
+  MOZ_CRASH("Why is someone touching JSAPI without an AutoJSAPI?");
+}
+
+JSHolderMap::Entry::Entry() : Entry(nullptr, nullptr, nullptr) {}
+
+JSHolderMap::Entry::Entry(void* aHolder, nsScriptObjectTracer* aTracer,
+                          JS::Zone* aZone)
+    : mHolder(aHolder),
+      mTracer(aTracer)
+#ifdef DEBUG
+      ,
+      mZone(aZone)
+#endif
+{
+}
+
+void JSHolderMap::EntryVectorIter::Settle() {
+  if (Done()) {
+    return;
+  }
+
+  Entry* entry = &mIter.Get();
+
+  // If the entry has been cleared, remove it and shrink the vector.
+  if (!entry->mHolder && !mHolderMap.RemoveEntry(mVector, entry)) {
+    // We removed the last entry, so reset the iterator to an empty one.
+    mIter = EntryVector().Iter();
+    MOZ_ASSERT(Done());
+  }
+}
+
+JSHolderMap::Iter::Iter(JSHolderMap& aMap, WhichHolders aWhich)
+    : mHolderMap(aMap), mIter(aMap, aMap.mAnyZoneJSHolders) {
+  MOZ_RELEASE_ASSERT(!mHolderMap.mHasIterator);
+  mHolderMap.mHasIterator = true;
+
+  // Populate vector of zones to iterate after the any-zone holders.
+  for (auto i = aMap.mPerZoneJSHolders.iter(); !i.done(); i.next()) {
+    JS::Zone* zone = i.get().key();
+    if (aWhich == AllHolders || JS::NeedGrayRootsForZone(i.get().key())) {
+      MOZ_ALWAYS_TRUE(mZones.append(zone));
+    }
+  }
+
+  Settle();
+}
+
+void JSHolderMap::Iter::Settle() {
+  while (mIter.Done()) {
+    if (mZone && mIter.Vector().IsEmpty()) {
+      mHolderMap.mPerZoneJSHolders.remove(mZone);
+    }
+
+    mZone = nullptr;
+    if (mZones.empty()) {
+      break;
+    }
+
+    mZone = mZones.popCopy();
+    EntryVector& vector = *mHolderMap.mPerZoneJSHolders.lookup(mZone)->value();
+    new (&mIter) EntryVectorIter(mHolderMap, vector);
+  }
+}
+
+void JSHolderMap::Iter::UpdateForRemovals() {
+  mIter.Settle();
+  Settle();
+}
+
+JSHolderMap::JSHolderMap() : mJSHolderMap(256) {}
+
+bool JSHolderMap::RemoveEntry(EntryVector& aJSHolders, Entry* aEntry) {
+  MOZ_ASSERT(aEntry);
+  MOZ_ASSERT(!aEntry->mHolder);
+
+  // Remove all dead entries from the end of the vector.
+  while (!aJSHolders.GetLast().mHolder && &aJSHolders.GetLast() != aEntry) {
+    aJSHolders.PopLast();
+  }
+
+  // Swap the element we want to remove with the last one and update the hash
+  // table.
+  Entry* lastEntry = &aJSHolders.GetLast();
+  if (aEntry != lastEntry) {
+    MOZ_ASSERT(lastEntry->mHolder);
+    *aEntry = *lastEntry;
+    MOZ_ASSERT(mJSHolderMap.has(aEntry->mHolder));
+    MOZ_ALWAYS_TRUE(mJSHolderMap.put(aEntry->mHolder, aEntry));
+  }
+
+  aJSHolders.PopLast();
+
+  // Return whether aEntry is still in the vector.
+  return aEntry != lastEntry;
+}
+
+bool JSHolderMap::Has(void* aHolder) const { return mJSHolderMap.has(aHolder); }
+
+nsScriptObjectTracer* JSHolderMap::Get(void* aHolder) const {
+  auto ptr = mJSHolderMap.lookup(aHolder);
+  if (!ptr) {
+    return nullptr;
+  }
+
+  Entry* entry = ptr->value();
+  MOZ_ASSERT(entry->mHolder == aHolder);
+  return entry->mTracer;
+}
+
+nsScriptObjectTracer* JSHolderMap::Extract(void* aHolder) {
+  MOZ_ASSERT(aHolder);
+
+  auto ptr = mJSHolderMap.lookup(aHolder);
+  if (!ptr) {
+    return nullptr;
+  }
+
+  Entry* entry = ptr->value();
+  MOZ_ASSERT(entry->mHolder == aHolder);
+  nsScriptObjectTracer* tracer = entry->mTracer;
+
+  // Clear the entry's contents. It will be removed the next time iteration
+  // visits this entry.
+  *entry = Entry();
+
+  mJSHolderMap.remove(ptr);
+
+  return tracer;
+}
+
+void JSHolderMap::Put(void* aHolder, nsScriptObjectTracer* aTracer,
+                      JS::Zone* aZone) {
+  MOZ_ASSERT(aHolder);
+  MOZ_ASSERT(aTracer);
+
+  // Don't associate multi-zone holders with a zone, even if one is supplied.
+  if (!aTracer->IsSingleZoneJSHolder()) {
+    aZone = nullptr;
+  }
+
+  auto ptr = mJSHolderMap.lookupForAdd(aHolder);
+  if (ptr) {
+    Entry* entry = ptr->value();
+#ifdef DEBUG
+    MOZ_ASSERT(entry->mHolder == aHolder);
+    MOZ_ASSERT(entry->mTracer == aTracer,
+               "Don't call HoldJSObjects in superclass ctors");
+    if (aZone) {
+      if (entry->mZone) {
+        MOZ_ASSERT(entry->mZone == aZone);
+      } else {
+        entry->mZone = aZone;
+      }
+    }
+#endif
+    entry->mTracer = aTracer;
+    return;
+  }
+
+  EntryVector* vector = &mAnyZoneJSHolders;
+  if (aZone) {
+    auto ptr = mPerZoneJSHolders.lookupForAdd(aZone);
+    if (!ptr) {
+      MOZ_ALWAYS_TRUE(
+          mPerZoneJSHolders.add(ptr, aZone, MakeUnique<EntryVector>()));
+    }
+    vector = ptr->value().get();
+  }
+
+  vector->InfallibleAppend(Entry{aHolder, aTracer, aZone});
+  MOZ_ALWAYS_TRUE(mJSHolderMap.add(ptr, aHolder, &vector->GetLast()));
+}
+
+size_t JSHolderMap::SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
+  size_t n = 0;
+
+  // We're deliberately not measuring anything hanging off the entries in
+  // mJSHolders.
+  n += mJSHolderMap.shallowSizeOfExcludingThis(aMallocSizeOf);
+  n += mAnyZoneJSHolders.SizeOfExcludingThis(aMallocSizeOf);
+  n += mPerZoneJSHolders.shallowSizeOfExcludingThis(aMallocSizeOf);
+  for (auto i = mPerZoneJSHolders.iter(); !i.done(); i.next()) {
+    n += i.get().value()->SizeOfExcludingThis(aMallocSizeOf);
+  }
+
+  return n;
+}
+
+static bool InitializeShadowRealm(JSContext* aCx,
+                                  JS::Handle<JSObject*> aGlobal) {
+  MOZ_ASSERT(StaticPrefs::javascript_options_experimental_shadow_realms());
+
+  JSAutoRealm ar(aCx, aGlobal);
+  return dom::RegisterShadowRealmBindings(aCx, aGlobal);
+}
+
+CycleCollectedJSRuntime::CycleCollectedJSRuntime(JSContext* aCx)
+    : mContext(nullptr),
+      mGCThingCycleCollectorGlobal(sGCThingCycleCollectorGlobal),
+      mJSZoneCycleCollectorGlobal(sJSZoneCycleCollectorGlobal),
+      mJSRuntime(JS_GetRuntime(aCx)),
+      mHasPendingIdleGCTask(false),
+      mPrevGCSliceCallback(nullptr),
+      mPrevGCNurseryCollectionCallback(nullptr),
+      mOutOfMemoryState(OOMState::OK),
+      mLargeAllocationFailureState(OOMState::OK)
+#ifdef DEBUG
+      ,
+      mShutdownCalled(false)
+#endif
+{
+  MOZ_COUNT_CTOR(CycleCollectedJSRuntime);
+  MOZ_ASSERT(aCx);
+  MOZ_ASSERT(mJSRuntime);
+
+#if defined(XP_MACOSX)
+  if (!XRE_IsParentProcess()) {
+    nsMacUtilsImpl::EnableTCSMIfAvailable();
+  }
+#endif
+
+  if (!JS_AddExtraGCRootsTracer(aCx, TraceBlackJS, this)) {
+    MOZ_CRASH("JS_AddExtraGCRootsTracer failed");
+  }
+  JS_SetGrayGCRootsTracer(aCx, TraceGrayJS, this);
+  JS_SetGCCallback(aCx, GCCallback, this);
+  mPrevGCSliceCallback = JS::SetGCSliceCallback(aCx, GCSliceCallback);
+
+  if (NS_IsMainThread()) {
+    // We would like to support all threads here, but the way timeline consumers
+    // are set up currently, you can either add a marker for one specific
+    // docshell, or for every consumer globally. We would like to add a marker
+    // for every consumer observing anything on this thread, but that is not
+    // currently possible. For now, add global markers only when we are on the
+    // main thread, since the UI for this tracing data only displays data
+    // relevant to the main-thread.
+    mPrevGCNurseryCollectionCallback =
+        JS::SetGCNurseryCollectionCallback(aCx, GCNurseryCollectionCallback);
+  }
+
+  JS_SetObjectsTenuredCallback(aCx, JSObjectsTenuredCb, this);
+  JS::SetOutOfMemoryCallback(aCx, OutOfMemoryCallback, this);
+  JS::SetWaitCallback(mJSRuntime, BeforeWaitCallback, AfterWaitCallback,
+                      sizeof(dom::AutoYieldJSThreadExecution));
+  JS::SetWarningReporter(aCx, MozCrashWarningReporter);
+  JS::SetShadowRealmInitializeGlobalCallback(aCx, InitializeShadowRealm);
+  JS::SetShadowRealmGlobalCreationCallback(aCx, dom::NewShadowRealmGlobal);
+
+  js::AutoEnterOOMUnsafeRegion::setAnnotateOOMAllocationSizeCallback(
+      CrashReporter::AnnotateOOMAllocationSize);
+
+  static js::DOMCallbacks DOMcallbacks = {InstanceClassHasProtoAtDepth};
+  SetDOMCallbacks(aCx, &DOMcallbacks);
+  js::SetScriptEnvironmentPreparer(aCx, &mEnvironmentPreparer);
+
+  JS::dbg::SetDebuggerMallocSizeOf(aCx, moz_malloc_size_of);
+
+#ifdef MOZ_JS_DEV_ERROR_INTERCEPTOR
+  JS_SetErrorInterceptorCallback(mJSRuntime, &mErrorInterceptor);
+#endif  // MOZ_JS_DEV_ERROR_INTERCEPTOR
+
+  JS_SetDestroyZoneCallback(aCx, OnZoneDestroyed);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+class JSLeakTracer : public JS::CallbackTracer {
+ public:
+  explicit JSLeakTracer(JSRuntime* aRuntime)
+      : JS::CallbackTracer(aRuntime, JS::TracerKind::Callback,
+                           JS::WeakMapTraceAction::TraceKeysAndValues) {}
+
+ private:
+  void onChild(JS::GCCellPtr thing, const char* name) override {
+    const char* kindName = JS::GCTraceKindToAscii(thing.kind());
+    size_t size = JS::GCTraceKindSize(thing.kind());
+    MOZ_LOG_CTOR(thing.asCell(), kindName, size);
+  }
+};
+#endif
+
+void CycleCollectedJSRuntime::Shutdown(JSContext* cx) {
+#ifdef MOZ_JS_DEV_ERROR_INTERCEPTOR
+  mErrorInterceptor.Shutdown(mJSRuntime);
+#endif  // MOZ_JS_DEV_ERROR_INTERCEPTOR
+
+  // There should not be any roots left to trace at this point. Ensure any that
+  // remain are flagged as leaks.
+#ifdef NS_BUILD_REFCNT_LOGGING
+  JSLeakTracer tracer(Runtime());
+  TraceNativeBlackRoots(&tracer);
+  TraceAllNativeGrayRoots(&tracer);
+#endif
+
+#ifdef DEBUG
+  mShutdownCalled = true;
+#endif
+
+  JS_SetDestroyZoneCallback(cx, nullptr);
+}
+
+CycleCollectedJSRuntime::~CycleCollectedJSRuntime() {
+  MOZ_COUNT_DTOR(CycleCollectedJSRuntime);
+  MOZ_ASSERT(!mDeferredFinalizerTable.Count());
+  MOZ_ASSERT(!mFinalizeRunnable);
+  MOZ_ASSERT(mShutdownCalled);
+}
+
+void CycleCollectedJSRuntime::SetContext(CycleCollectedJSContext* aContext) {
+  MOZ_ASSERT(!mContext || !aContext, "Don't replace the context!");
+  mContext = aContext;
+}
+
+size_t CycleCollectedJSRuntime::SizeOfExcludingThis(
+    MallocSizeOf aMallocSizeOf) const {
+  return mJSHolders.SizeOfExcludingThis(aMallocSizeOf);
+}
+
+void CycleCollectedJSRuntime::UnmarkSkippableJSHolders() {
+  for (JSHolderMap::Iter entry(mJSHolders); !entry.Done(); entry.Next()) {
+    entry->mTracer->CanSkip(entry->mHolder, true);
+  }
+}
+
+void CycleCollectedJSRuntime::DescribeGCThing(
+    bool aIsMarked, JS::GCCellPtr aThing,
+    nsCycleCollectionTraversalCallback& aCb) const {
+  if (!aCb.WantDebugInfo()) {
+    aCb.DescribeGCedNode(aIsMarked, "JS Object");
+    return;
+  }
+
+  char name[72];
+  uint64_t compartmentAddress = 0;
+  if (aThing.is<JSObject>()) {
+    JSObject* obj = &aThing.as<JSObject>();
+    compartmentAddress = (uint64_t)JS::GetCompartment(obj);
+    const JSClass* clasp = JS::GetClass(obj);
+
+    // Give the subclass a chance to do something
+    if (DescribeCustomObjects(obj, clasp, name)) {
+      // Nothing else to do!
+    } else if (js::IsFunctionObject(obj)) {
+      JSFunction* fun = JS_GetObjectFunction(obj);
+      JSString* str = JS_GetFunctionDisplayId(fun);
+      if (str) {
+        JSLinearString* linear = JS_ASSERT_STRING_IS_LINEAR(str);
+        nsAutoString chars;
+        AssignJSLinearString(chars, linear);
+        NS_ConvertUTF16toUTF8 fname(chars);
+        SprintfLiteral(name, "JS Object (Function - %s)", fname.get());
+      } else {
+        SprintfLiteral(name, "JS Object (Function)");
+      }
+    } else {
+      SprintfLiteral(name, "JS Object (%s)", clasp->name);
+    }
+  } else {
+    SprintfLiteral(name, "%s", JS::GCTraceKindToAscii(aThing.kind()));
+  }
+
+  // Disable printing global for objects while we figure out ObjShrink fallout.
+  aCb.DescribeGCedNode(aIsMarked, name, compartmentAddress);
+}
+
+void CycleCollectedJSRuntime::NoteGCThingJSChildren(
+    JS::GCCellPtr aThing, nsCycleCollectionTraversalCallback& aCb) const {
+  TraversalTracer trc(mJSRuntime, aCb);
+  JS::TraceChildren(&trc, aThing);
+}
+
+void CycleCollectedJSRuntime::NoteGCThingXPCOMChildren(
+    const JSClass* aClasp, JSObject* aObj,
+    nsCycleCollectionTraversalCallback& aCb) const {
+  MOZ_ASSERT(aClasp);
+  MOZ_ASSERT(aClasp == JS::GetClass(aObj));
+
+  JS::Rooted<JSObject*> obj(RootingCx(), aObj);
+
+  if (NoteCustomGCThingXPCOMChildren(aClasp, obj, aCb)) {
+    // Nothing else to do!
+    return;
+  }
+
+  // XXX This test does seem fragile, we should probably allowlist classes
+  //     that do hold a strong reference, but that might not be possible.
+  if (aClasp->slot0IsISupports()) {
+    NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "JS::GetObjectISupports(obj)");
+    aCb.NoteXPCOMChild(JS::GetObjectISupports<nsISupports>(obj));
+    return;
+  }
+
+  const DOMJSClass* domClass = GetDOMClass(aClasp);
+  if (domClass) {
+    NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "UnwrapDOMObject(obj)");
+    // It's possible that our object is an unforgeable holder object, in
+    // which case it doesn't actually have a C++ DOM object associated with
+    // it.  Use UnwrapPossiblyNotInitializedDOMObject, which produces null in
+    // that case, since NoteXPCOMChild/NoteNativeChild are null-safe.
+    if (domClass->mDOMObjectIsISupports) {
+      aCb.NoteXPCOMChild(
+          UnwrapPossiblyNotInitializedDOMObject<nsISupports>(obj));
+    } else if (domClass->mParticipant) {
+      aCb.NoteNativeChild(UnwrapPossiblyNotInitializedDOMObject<void>(obj),
+                          domClass->mParticipant);
+    }
+    return;
+  }
+
+  if (IsRemoteObjectProxy(obj)) {
+    auto handler =
+        static_cast<const RemoteObjectProxyBase*>(js::GetProxyHandler(obj));
+    return handler->NoteChildren(obj, aCb);
+  }
+
+  JS::Value value = js::MaybeGetScriptPrivate(obj);
+  if (!value.isUndefined()) {
+    aCb.NoteXPCOMChild(static_cast<nsISupports*>(value.toPrivate()));
+  }
+}
+
+void CycleCollectedJSRuntime::TraverseGCThing(
+    TraverseSelect aTs, JS::GCCellPtr aThing,
+    nsCycleCollectionTraversalCallback& aCb) {
+  bool isMarkedGray = JS::GCThingIsMarkedGrayInCC(aThing);
+
+  if (aTs == TRAVERSE_FULL) {
+    DescribeGCThing(!isMarkedGray, aThing, aCb);
+  }
+
+  // If this object is alive, then all of its children are alive. For JS
+  // objects, the black-gray invariant ensures the children are also marked
+  // black. For C++ objects, the ref count from this object will keep them
+  // alive. Thus we don't need to trace our children, unless we are debugging
+  // using WantAllTraces.
+  if (!isMarkedGray && !aCb.WantAllTraces()) {
+    return;
+  }
+
+  if (aTs == TRAVERSE_FULL) {
+    NoteGCThingJSChildren(aThing, aCb);
+  }
+
+  if (aThing.is<JSObject>()) {
+    JSObject* obj = &aThing.as<JSObject>();
+    NoteGCThingXPCOMChildren(JS::GetClass(obj), obj, aCb);
+  }
+}
+
+struct TraverseObjectShimClosure {
+  nsCycleCollectionTraversalCallback& cb;
+  CycleCollectedJSRuntime* self;
+};
+
+void CycleCollectedJSRuntime::TraverseZone(
+    JS::Zone* aZone, nsCycleCollectionTraversalCallback& aCb) {
+  /*
+   * We treat the zone as being gray. We handle non-gray GCthings in the
+   * zone by not reporting their children to the CC. The black-gray invariant
+   * ensures that any JS children will also be non-gray, and thus don't need to
+   * be added to the graph. For C++ children, not representing the edge from the
+   * non-gray JS GCthings to the C++ object will keep the child alive.
+   *
+   * We don't allow zone merging in a WantAllTraces CC, because then these
+   * assumptions don't hold.
+   */
+  aCb.DescribeGCedNode(false, "JS Zone");
+
+  /*
+   * Every JS child of everything in the zone is either in the zone
+   * or is a cross-compartment wrapper. In the former case, we don't need to
+   * represent these edges in the CC graph because JS objects are not ref
+   * counted. In the latter case, the JS engine keeps a map of these wrappers,
+   * which we iterate over. Edges between compartments in the same zone will add
+   * unnecessary loop edges to the graph (bug 842137).
+   */
+  TraversalTracer trc(mJSRuntime, aCb);
+  js::TraceGrayWrapperTargets(&trc, aZone);
+
+  /*
+   * To find C++ children of things in the zone, we scan every JS Object in
+   * the zone. Only JS Objects can have C++ children.
+   */
+  TraverseObjectShimClosure closure = {aCb, this};
+  js::IterateGrayObjects(aZone, TraverseObjectShim, &closure);
+}
+
+/* static */
+void CycleCollectedJSRuntime::TraverseObjectShim(
+    void* aData, JS::GCCellPtr aThing, const JS::AutoRequireNoGC& nogc) {
+  TraverseObjectShimClosure* closure =
+      static_cast<TraverseObjectShimClosure*>(aData);
+
+  MOZ_ASSERT(aThing.is<JSObject>());
+  closure->self->TraverseGCThing(CycleCollectedJSRuntime::TRAVERSE_CPP, aThing,
+                                 closure->cb);
+}
+
+void CycleCollectedJSRuntime::TraverseNativeRoots(
+    nsCycleCollectionNoteRootCallback& aCb) {
+  // NB: This is here just to preserve the existing XPConnect order. I doubt it
+  // would hurt to do this after the JS holders.
+  TraverseAdditionalNativeRoots(aCb);
+
+  for (JSHolderMap::Iter entry(mJSHolders); !entry.Done(); entry.Next()) {
+    void* holder = entry->mHolder;
+    nsScriptObjectTracer* tracer = entry->mTracer;
+
+    bool noteRoot = false;
+    if (MOZ_UNLIKELY(aCb.WantAllTraces())) {
+      noteRoot = true;
+    } else {
+      tracer->Trace(holder,
+                    TraceCallbackFunc(CheckParticipatesInCycleCollection),
+                    &noteRoot);
+    }
+
+    if (noteRoot) {
+      aCb.NoteNativeRoot(holder, tracer);
+    }
+  }
+}
+
+/* static */
+void CycleCollectedJSRuntime::TraceBlackJS(JSTracer* aTracer, void* aData) {
+  CycleCollectedJSRuntime* self = static_cast<CycleCollectedJSRuntime*>(aData);
+
+  self->TraceNativeBlackRoots(aTracer);
+}
+
+/* static */
+bool CycleCollectedJSRuntime::TraceGrayJS(JSTracer* aTracer,
+                                          js::SliceBudget& budget,
+                                          void* aData) {
+  CycleCollectedJSRuntime* self = static_cast<CycleCollectedJSRuntime*>(aData);
+
+  // Mark these roots as gray so the CC can walk them later.
+
+  JSHolderMap::WhichHolders which = JSHolderMap::AllHolders;
+
+  // Only trace holders in collecting zones when marking, except if we are
+  // collecting the atoms zone since any holder may point into that zone.
+  if (aTracer->isMarkingTracer() &&
+      !JS::AtomsZoneIsCollecting(self->Runtime())) {
+    which = JSHolderMap::HoldersRequiredForGrayMarking;
+  }
+
+  return self->TraceNativeGrayRoots(aTracer, which, budget);
+}
+
+/* static */
+void CycleCollectedJSRuntime::GCCallback(JSContext* aContext,
+                                         JSGCStatus aStatus,
+                                         JS::GCReason aReason, void* aData) {
+  CycleCollectedJSRuntime* self = static_cast<CycleCollectedJSRuntime*>(aData);
+
+  MOZ_ASSERT(CycleCollectedJSContext::Get()->Context() == aContext);
+  MOZ_ASSERT(CycleCollectedJSContext::Get()->Runtime() == self);
+
+  self->OnGC(aContext, aStatus, aReason);
+}
+
+/* static */
+void CycleCollectedJSRuntime::GCSliceCallback(JSContext* aContext,
+                                              JS::GCProgress aProgress,
+                                              const JS::GCDescription& aDesc) {
+  CycleCollectedJSRuntime* self = CycleCollectedJSRuntime::Get();
+  MOZ_ASSERT(CycleCollectedJSContext::Get()->Context() == aContext);
+
+  if (profiler_thread_is_being_profiled_for_markers()) {
+    if (aProgress == JS::GC_CYCLE_END) {
+      struct GCMajorMarker {
+        static constexpr mozilla::Span<const char> MarkerTypeName() {
+          return mozilla::MakeStringSpan("GCMajor");
+        }
+        static void StreamJSONMarkerData(
+            mozilla::baseprofiler::SpliceableJSONWriter& aWriter,
+            const mozilla::ProfilerString8View& aTimingJSON) {
+          if (aTimingJSON.Length() != 0) {
+            aWriter.SplicedJSONProperty("timings", aTimingJSON);
+          } else {
+            aWriter.NullProperty("timings");
+          }
+        }
+        static mozilla::MarkerSchema MarkerTypeDisplay() {
+          using MS = mozilla::MarkerSchema;
+          MS schema{MS::Location::MarkerChart, MS::Location::MarkerTable,
+                    MS::Location::TimelineMemory};
+          schema.AddStaticLabelValue(
+              "Description",
+              "Summary data for an entire major GC, encompassing a set of "
+              "incremental slices. The main thread is not blocked for the "
+              "entire major GC interval, only for the individual slices.");
+          // No display instructions here, there is special handling in the
+          // front-end.
+          return schema;
+        }
+      };
+
+      profiler_add_marker("GCMajor", baseprofiler::category::GCCC,
+                          MarkerTiming::Interval(aDesc.startTime(aContext),
+                                                 aDesc.endTime(aContext)),
+                          GCMajorMarker{},
+                          ProfilerString8View::WrapNullTerminatedString(
+                              aDesc.formatJSONProfiler(aContext).get()));
+    } else if (aProgress == JS::GC_SLICE_END) {
+      struct GCSliceMarker {
+        static constexpr mozilla::Span<const char> MarkerTypeName() {
+          return mozilla::MakeStringSpan("GCSlice");
+        }
+        static void StreamJSONMarkerData(
+            mozilla::baseprofiler::SpliceableJSONWriter& aWriter,
+            const mozilla::ProfilerString8View& aTimingJSON) {
+          if (aTimingJSON.Length() != 0) {
+            aWriter.SplicedJSONProperty("timings", aTimingJSON);
+          } else {
+            aWriter.NullProperty("timings");
+          }
+        }
+        static mozilla::MarkerSchema MarkerTypeDisplay() {
+          using MS = mozilla::MarkerSchema;
+          MS schema{MS::Location::MarkerChart, MS::Location::MarkerTable,
+                    MS::Location::TimelineMemory};
+          schema.AddStaticLabelValue(
+              "Description",
+              "One slice of an incremental garbage collection (GC). The main "
+              "thread is blocked during this time.");
+          // No display instructions here, there is special handling in the
+          // front-end.
+          return schema;
+        }
+      };
+
+      profiler_add_marker("GCSlice", baseprofiler::category::GCCC,
+                          MarkerTiming::Interval(aDesc.lastSliceStart(aContext),
+                                                 aDesc.lastSliceEnd(aContext)),
+                          GCSliceMarker{},
+                          ProfilerString8View::WrapNullTerminatedString(
+                              aDesc.sliceToJSONProfiler(aContext).get()));
+    }
+  }
+
+  if (aProgress == JS::GC_CYCLE_END &&
+      JS::dbg::FireOnGarbageCollectionHookRequired(aContext)) {
+    JS::GCReason reason = aDesc.reason_;
+    Unused << NS_WARN_IF(
+        NS_FAILED(DebuggerOnGCRunnable::Enqueue(aContext, aDesc)) &&
+        reason != JS::GCReason::SHUTDOWN_CC &&
+        reason != JS::GCReason::DESTROY_RUNTIME &&
+        reason != JS::GCReason::XPCONNECT_SHUTDOWN);
+  }
+
+  if (self->mPrevGCSliceCallback) {
+    self->mPrevGCSliceCallback(aContext, aProgress, aDesc);
+  }
+}
+
+class MinorGCMarker : public TimelineMarker {
+ private:
+  JS::GCReason mReason;
+
+ public:
+  MinorGCMarker(MarkerTracingType aTracingType, JS::GCReason aReason)
+      : TimelineMarker("MinorGC", aTracingType, MarkerStackRequest::NO_STACK),
+        mReason(aReason) {
+    MOZ_ASSERT(aTracingType == MarkerTracingType::START ||
+               aTracingType == MarkerTracingType::END);
+  }
+
+  MinorGCMarker(JS::GCNurseryProgress aProgress, JS::GCReason aReason)
+      : TimelineMarker(
+            "MinorGC",
+            aProgress == JS::GCNurseryProgress::GC_NURSERY_COLLECTION_START
+                ? MarkerTracingType::START
+                : MarkerTracingType::END,
+            MarkerStackRequest::NO_STACK),
+        mReason(aReason) {}
+
+  virtual void AddDetails(JSContext* aCx,
+                          dom::ProfileTimelineMarker& aMarker) override {
+    TimelineMarker::AddDetails(aCx, aMarker);
+
+    if (GetTracingType() == MarkerTracingType::START) {
+      auto reason = JS::ExplainGCReason(mReason);
+      aMarker.mCauseName.Construct(NS_ConvertUTF8toUTF16(reason));
+    }
+  }
+
+  virtual UniquePtr<AbstractTimelineMarker> Clone() override {
+    auto clone = MakeUnique<MinorGCMarker>(GetTracingType(), mReason);
+    clone->SetCustomTime(GetTime());
+    return UniquePtr<AbstractTimelineMarker>(std::move(clone));
+  }
+};
+
+/* static */
+void CycleCollectedJSRuntime::GCNurseryCollectionCallback(
+    JSContext* aContext, JS::GCNurseryProgress aProgress,
+    JS::GCReason aReason) {
+  CycleCollectedJSRuntime* self = CycleCollectedJSRuntime::Get();
+  MOZ_ASSERT(CycleCollectedJSContext::Get()->Context() == aContext);
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!TimelineConsumers::IsEmpty()) {
+    UniquePtr<AbstractTimelineMarker> abstractMarker(
+        MakeUnique<MinorGCMarker>(aProgress, aReason));
+    TimelineConsumers::AddMarkerForAllObservedDocShells(abstractMarker);
+  }
+
+  TimeStamp now = TimeStamp::Now();
+  if (aProgress == JS::GCNurseryProgress::GC_NURSERY_COLLECTION_START) {
+    self->mLatestNurseryCollectionStart = now;
+  } else if (aProgress == JS::GCNurseryProgress::GC_NURSERY_COLLECTION_END) {
+    PerfStats::RecordMeasurement(PerfStats::Metric::MinorGC,
+                                 now - self->mLatestNurseryCollectionStart);
+  }
+
+  if (aProgress == JS::GCNurseryProgress::GC_NURSERY_COLLECTION_END &&
+      profiler_thread_is_being_profiled_for_markers()) {
+    struct GCMinorMarker {
+      static constexpr mozilla::Span<const char> MarkerTypeName() {
+        return mozilla::MakeStringSpan("GCMinor");
+      }
+      static void StreamJSONMarkerData(
+          mozilla::baseprofiler::SpliceableJSONWriter& aWriter,
+          const mozilla::ProfilerString8View& aTimingJSON) {
+        if (aTimingJSON.Length() != 0) {
+          aWriter.SplicedJSONProperty("nursery", aTimingJSON);
+        } else {
+          aWriter.NullProperty("nursery");
+        }
+      }
+      static mozilla::MarkerSchema MarkerTypeDisplay() {
+        using MS = mozilla::MarkerSchema;
+        MS schema{MS::Location::MarkerChart, MS::Location::MarkerTable,
+                  MS::Location::TimelineMemory};
+        schema.AddStaticLabelValue(
+            "Description",
+            "A minor GC (aka nursery collection) to clear out the buffer used "
+            "for recent allocations and move surviving data to the tenured "
+            "(long-lived) heap.");
+        // No display instructions here, there is special handling in the
+        // front-end.
+        return schema;
+      }
+    };
+
+    profiler_add_marker(
+        "GCMinor", baseprofiler::category::GCCC,
+        MarkerTiming::Interval(self->mLatestNurseryCollectionStart, now),
+        GCMinorMarker{},
+        ProfilerString8View::WrapNullTerminatedString(
+            JS::MinorGcToJSON(aContext).get()));
+  }
+
+  if (self->mPrevGCNurseryCollectionCallback) {
+    self->mPrevGCNurseryCollectionCallback(aContext, aProgress, aReason);
+  }
+}
+
+/* static */
+void CycleCollectedJSRuntime::OutOfMemoryCallback(JSContext* aContext,
+                                                  void* aData) {
+  CycleCollectedJSRuntime* self = static_cast<CycleCollectedJSRuntime*>(aData);
+
+  MOZ_ASSERT(CycleCollectedJSContext::Get()->Context() == aContext);
+  MOZ_ASSERT(CycleCollectedJSContext::Get()->Runtime() == self);
+
+  self->OnOutOfMemory();
+}
+
+/* static */
+void* CycleCollectedJSRuntime::BeforeWaitCallback(uint8_t* aMemory) {
+  MOZ_ASSERT(aMemory);
+
+  // aMemory is stack allocated memory to contain our RAII object. This allows
+  // for us to avoid allocations on the heap during this callback.
+  return new (aMemory) dom::AutoYieldJSThreadExecution;
+}
+
+/* static */
+void CycleCollectedJSRuntime::AfterWaitCallback(void* aCookie) {
+  MOZ_ASSERT(aCookie);
+  static_cast<dom::AutoYieldJSThreadExecution*>(aCookie)
+      ->~AutoYieldJSThreadExecution();
+}
+
+struct JsGcTracer : public TraceCallbacks {
+  virtual void Trace(JS::Heap<JS::Value>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JS::Heap<jsid>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JS::Heap<JSObject*>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(nsWrapperCache* aPtr, const char* aName,
+                     void* aClosure) const override {
+    aPtr->TraceWrapper(static_cast<JSTracer*>(aClosure), aName);
+  }
+  virtual void Trace(JS::TenuredHeap<JSObject*>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JS::Heap<JSString*>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JS::Heap<JSScript*>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JS::Heap<JSFunction*>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+};
+
+void mozilla::TraceScriptHolder(nsISupports* aHolder, JSTracer* aTracer) {
+  nsXPCOMCycleCollectionParticipant* participant = nullptr;
+  CallQueryInterface(aHolder, &participant);
+  participant->Trace(aHolder, JsGcTracer(), aTracer);
+}
+
+#if defined(NIGHTLY_BUILD) || defined(MOZ_DEV_EDITION) || defined(DEBUG)
+#  define CHECK_SINGLE_ZONE_JS_HOLDERS
+#endif
+
+#ifdef CHECK_SINGLE_ZONE_JS_HOLDERS
+
+// A tracer that checks that a JS holder only holds JS GC things in a single
+// JS::Zone.
+struct CheckZoneTracer : public TraceCallbacks {
+  const char* mClassName;
+  mutable JS::Zone* mZone;
+
+  explicit CheckZoneTracer(const char* aClassName, JS::Zone* aZone = nullptr)
+      : mClassName(aClassName), mZone(aZone) {}
+
+  void checkZone(JS::Zone* aZone, const char* aName) const {
+    if (JS::IsAtomsZone(aZone)) {
+      // Any holder may contain pointers into the atoms zone.
+      return;
+    }
+
+    if (!mZone) {
+      mZone = aZone;
+      return;
+    }
+
+    if (aZone == mZone) {
+      return;
+    }
+
+    // Most JS holders only contain pointers to GC things in a single zone. We
+    // group holders by referent zone where possible, allowing us to improve GC
+    // performance by only tracing holders for zones that are being collected.
+    //
+    // Additionally, pointers from any holder into the atoms zone are allowed
+    // since all holders are traced when we collect the atoms zone.
+    //
+    // If you added a holder that has pointers into multiple zones do not
+    // use NS_IMPL_CYCLE_COLLECTION_SINGLE_ZONE_SCRIPT_HOLDER_CLASS.
+    MOZ_CRASH_UNSAFE_PRINTF(
+        "JS holder %s contains pointers to GC things in more than one zone ("
+        "found in %s)\n",
+        mClassName, aName);
+  }
+
+  virtual void Trace(JS::Heap<JS::Value>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JS::Value value = aPtr->unbarrieredGet();
+    if (value.isGCThing()) {
+      checkZone(JS::GetGCThingZone(value.toGCCellPtr()), aName);
+    }
+  }
+  virtual void Trace(JS::Heap<jsid>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    jsid id = aPtr->unbarrieredGet();
+    if (id.isGCThing()) {
+      MOZ_ASSERT(JS::IsAtomsZone(JS::GetTenuredGCThingZone(id.toGCCellPtr())));
+    }
+  }
+  virtual void Trace(JS::Heap<JSObject*>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JSObject* obj = aPtr->unbarrieredGet();
+    if (obj) {
+      checkZone(js::GetObjectZoneFromAnyThread(obj), aName);
+    }
+  }
+  virtual void Trace(nsWrapperCache* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JSObject* obj = aPtr->GetWrapperPreserveColor();
+    if (obj) {
+      checkZone(js::GetObjectZoneFromAnyThread(obj), aName);
+    }
+  }
+  virtual void Trace(JS::TenuredHeap<JSObject*>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JSObject* obj = aPtr->unbarrieredGetPtr();
+    if (obj) {
+      checkZone(js::GetObjectZoneFromAnyThread(obj), aName);
+    }
+  }
+  virtual void Trace(JS::Heap<JSString*>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JSString* str = aPtr->unbarrieredGet();
+    if (str) {
+      checkZone(JS::GetStringZone(str), aName);
+    }
+  }
+  virtual void Trace(JS::Heap<JSScript*>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JSScript* script = aPtr->unbarrieredGet();
+    if (script) {
+      checkZone(JS::GetTenuredGCThingZone(JS::GCCellPtr(script)), aName);
+    }
+  }
+  virtual void Trace(JS::Heap<JSFunction*>* aPtr, const char* aName,
+                     void* aClosure) const override {
+    JSFunction* fun = aPtr->unbarrieredGet();
+    if (fun) {
+      checkZone(js::GetObjectZoneFromAnyThread(JS_GetFunctionObject(fun)),
+                aName);
+    }
+  }
+};
+
+static inline void CheckHolderIsSingleZone(
+    void* aHolder, nsCycleCollectionParticipant* aParticipant,
+    JS::Zone* aZone) {
+  CheckZoneTracer tracer(aParticipant->ClassName(), aZone);
+  aParticipant->Trace(aHolder, tracer, nullptr);
+}
+
+#endif
+
+static inline bool ShouldCheckSingleZoneHolders() {
+#if defined(DEBUG)
+  return true;
+#elif defined(NIGHTLY_BUILD) || defined(MOZ_DEV_EDITION)
+  // Don't check every time to avoid performance impact.
+  return rand() % 256 == 0;
+#else
+  return false;
+#endif
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+void CycleCollectedJSRuntime::TraceAllNativeGrayRoots(JSTracer* aTracer) {
+  MOZ_RELEASE_ASSERT(mHolderIter.isNothing());
+  js::SliceBudget budget = js::SliceBudget::unlimited();
+  MOZ_ALWAYS_TRUE(
+      TraceNativeGrayRoots(aTracer, JSHolderMap::AllHolders, budget));
+}
+#endif
+
+bool CycleCollectedJSRuntime::TraceNativeGrayRoots(
+    JSTracer* aTracer, JSHolderMap::WhichHolders aWhich,
+    js::SliceBudget& aBudget) {
+  if (!mHolderIter) {
+    // NB: This is here just to preserve the existing XPConnect order. I doubt
+    // it would hurt to do this after the JS holders.
+    TraceAdditionalNativeGrayRoots(aTracer);
+
+    mHolderIter.emplace(mJSHolders, aWhich);
+    aBudget.stepAndForceCheck();
+  } else {
+    // Holders may have been removed between slices, so we may need to update
+    // the iterator.
+    mHolderIter->UpdateForRemovals();
+  }
+
+  bool finished = TraceJSHolders(aTracer, *mHolderIter, aBudget);
+  if (finished) {
+    mHolderIter.reset();
+  }
+
+  return finished;
+}
+
+bool CycleCollectedJSRuntime::TraceJSHolders(JSTracer* aTracer,
+                                             JSHolderMap::Iter& aIter,
+                                             js::SliceBudget& aBudget) {
+  bool checkSingleZoneHolders = ShouldCheckSingleZoneHolders();
+
+  while (!aIter.Done() && !aBudget.isOverBudget()) {
+    void* holder = aIter->mHolder;
+    nsScriptObjectTracer* tracer = aIter->mTracer;
+
+#ifdef CHECK_SINGLE_ZONE_JS_HOLDERS
+    if (checkSingleZoneHolders && tracer->IsSingleZoneJSHolder()) {
+      CheckHolderIsSingleZone(holder, tracer, aIter.Zone());
+    }
+#else
+    Unused << checkSingleZoneHolders;
+#endif
+
+    tracer->Trace(holder, JsGcTracer(), aTracer);
+
+    aIter.Next();
+    aBudget.step();
+  }
+
+  return aIter.Done();
+}
+
+void CycleCollectedJSRuntime::AddJSHolder(void* aHolder,
+                                          nsScriptObjectTracer* aTracer,
+                                          JS::Zone* aZone) {
+  mJSHolders.Put(aHolder, aTracer, aZone);
+}
+
+struct ClearJSHolder : public TraceCallbacks {
+  virtual void Trace(JS::Heap<JS::Value>* aPtr, const char*,
+                     void*) const override {
+    aPtr->setUndefined();
+  }
+
+  virtual void Trace(JS::Heap<jsid>* aPtr, const char*, void*) const override {
+    *aPtr = JS::PropertyKey::Void();
+  }
+
+  virtual void Trace(JS::Heap<JSObject*>* aPtr, const char*,
+                     void*) const override {
+    *aPtr = nullptr;
+  }
+
+  virtual void Trace(nsWrapperCache* aPtr, const char* aName,
+                     void* aClosure) const override {
+    aPtr->ClearWrapper();
+  }
+
+  virtual void Trace(JS::TenuredHeap<JSObject*>* aPtr, const char*,
+                     void*) const override {
+    *aPtr = nullptr;
+  }
+
+  virtual void Trace(JS::Heap<JSString*>* aPtr, const char*,
+                     void*) const override {
+    *aPtr = nullptr;
+  }
+
+  virtual void Trace(JS::Heap<JSScript*>* aPtr, const char*,
+                     void*) const override {
+    *aPtr = nullptr;
+  }
+
+  virtual void Trace(JS::Heap<JSFunction*>* aPtr, const char*,
+                     void*) const override {
+    *aPtr = nullptr;
+  }
+};
+
+void CycleCollectedJSRuntime::RemoveJSHolder(void* aHolder) {
+  nsScriptObjectTracer* tracer = mJSHolders.Extract(aHolder);
+  if (tracer) {
+    // Bug 1531951: The analysis can't see through the virtual call but we know
+    // that the ClearJSHolder tracer will never GC.
+    JS::AutoSuppressGCAnalysis nogc;
+    tracer->Trace(aHolder, ClearJSHolder(), nullptr);
+  }
+}
+
+#ifdef DEBUG
+static void AssertNoGcThing(JS::GCCellPtr aGCThing, const char* aName,
+                            void* aClosure) {
+  MOZ_ASSERT(!aGCThing);
+}
+
+void CycleCollectedJSRuntime::AssertNoObjectsToTrace(void* aPossibleJSHolder) {
+  nsScriptObjectTracer* tracer = mJSHolders.Get(aPossibleJSHolder);
+  if (tracer) {
+    tracer->Trace(aPossibleJSHolder, TraceCallbackFunc(AssertNoGcThing),
+                  nullptr);
+  }
+}
+#endif
+
+nsCycleCollectionParticipant* CycleCollectedJSRuntime::GCThingParticipant() {
+  return &mGCThingCycleCollectorGlobal;
+}
+
+nsCycleCollectionParticipant* CycleCollectedJSRuntime::ZoneParticipant() {
+  return &mJSZoneCycleCollectorGlobal;
+}
+
+nsresult CycleCollectedJSRuntime::TraverseRoots(
+    nsCycleCollectionNoteRootCallback& aCb) {
+  TraverseNativeRoots(aCb);
+
+  NoteWeakMapsTracer trc(mJSRuntime, aCb);
+  js::TraceWeakMaps(&trc);
+
+  return NS_OK;
+}
+
+bool CycleCollectedJSRuntime::UsefulToMergeZones() const { return false; }
+
+void CycleCollectedJSRuntime::FixWeakMappingGrayBits() const {
+  MOZ_ASSERT(!JS::IsIncrementalGCInProgress(mJSRuntime),
+             "Don't call FixWeakMappingGrayBits during a GC.");
+  FixWeakMappingGrayBitsTracer fixer(mJSRuntime);
+  fixer.FixAll();
+}
+
+void CycleCollectedJSRuntime::CheckGrayBits() const {
+  MOZ_ASSERT(!JS::IsIncrementalGCInProgress(mJSRuntime),
+             "Don't call CheckGrayBits during a GC.");
+
+#ifndef ANDROID
+  // Bug 1346874 - The gray state check is expensive. Android tests are already
+  // slow enough that this check can easily push them over the threshold to a
+  // timeout.
+
+  MOZ_ASSERT(js::CheckGrayMarkingState(mJSRuntime));
+  MOZ_ASSERT(CheckWeakMappingGrayBitsTracer::Check(mJSRuntime));
+#endif
+}
+
+bool CycleCollectedJSRuntime::AreGCGrayBitsValid() const {
+  return js::AreGCGrayBitsValid(mJSRuntime);
+}
+
+void CycleCollectedJSRuntime::GarbageCollect(JS::GCOptions aOptions,
+                                             JS::GCReason aReason) const {
+  JSContext* cx = CycleCollectedJSContext::Get()->Context();
+  JS::PrepareForFullGC(cx);
+  JS::NonIncrementalGC(cx, aOptions, aReason);
+}
+
+void CycleCollectedJSRuntime::JSObjectsTenured() {
+  JSContext* cx = CycleCollectedJSContext::Get()->Context();
+  for (auto iter = mNurseryObjects.Iter(); !iter.Done(); iter.Next()) {
+    nsWrapperCache* cache = iter.Get();
+    JSObject* wrapper = cache->GetWrapperMaybeDead();
+    MOZ_DIAGNOSTIC_ASSERT(wrapper);
+    if (!JS::ObjectIsTenured(wrapper)) {
+      MOZ_ASSERT(!cache->PreservingWrapper());
+      js::gc::FinalizeDeadNurseryObject(cx, wrapper);
+    }
+  }
+
+  mNurseryObjects.Clear();
+}
+
+void CycleCollectedJSRuntime::NurseryWrapperAdded(nsWrapperCache* aCache) {
+  MOZ_ASSERT(aCache);
+  MOZ_ASSERT(aCache->GetWrapperMaybeDead());
+  MOZ_ASSERT(!JS::ObjectIsTenured(aCache->GetWrapperMaybeDead()));
+  mNurseryObjects.InfallibleAppend(aCache);
+}
+
+void CycleCollectedJSRuntime::DeferredFinalize(
+    DeferredFinalizeAppendFunction aAppendFunc, DeferredFinalizeFunction aFunc,
+    void* aThing) {
+  // Tell the analysis that the function pointers will not GC.
+  JS::AutoSuppressGCAnalysis suppress;
+  mDeferredFinalizerTable.WithEntryHandle(aFunc, [&](auto&& entry) {
+    if (entry) {
+      aAppendFunc(entry.Data(), aThing);
+    } else {
+      entry.Insert(aAppendFunc(nullptr, aThing));
+    }
+  });
+}
+
+void CycleCollectedJSRuntime::DeferredFinalize(nsISupports* aSupports) {
+  typedef DeferredFinalizerImpl<nsISupports> Impl;
+  DeferredFinalize(Impl::AppendDeferredFinalizePointer, Impl::DeferredFinalize,
+                   aSupports);
+}
+
+void CycleCollectedJSRuntime::DumpJSHeap(FILE* aFile) {
+  JSContext* cx = CycleCollectedJSContext::Get()->Context();
+
+  mozilla::MallocSizeOf mallocSizeOf =
+      PR_GetEnv("MOZ_GC_LOG_SIZE") ? moz_malloc_size_of : nullptr;
+  js::DumpHeap(cx, aFile, js::CollectNurseryBeforeDump, mallocSizeOf);
+}
+
+IncrementalFinalizeRunnable::IncrementalFinalizeRunnable(
+    CycleCollectedJSRuntime* aRt, DeferredFinalizerTable& aFinalizers)
+    : DiscardableRunnable("IncrementalFinalizeRunnable"),
+      mRuntime(aRt),
+      mFinalizeFunctionToRun(0),
+      mReleasing(false) {
+  for (auto iter = aFinalizers.Iter(); !iter.Done(); iter.Next()) {
+    DeferredFinalizeFunction& function = iter.Key();
+    void*& data = iter.Data();
+
+    DeferredFinalizeFunctionHolder* holder =
+        mDeferredFinalizeFunctions.AppendElement();
+    holder->run = function;
+    holder->data = data;
+
+    iter.Remove();
+  }
+  MOZ_ASSERT(mDeferredFinalizeFunctions.Length());
+}
+
+IncrementalFinalizeRunnable::~IncrementalFinalizeRunnable() {
+  MOZ_ASSERT(!mDeferredFinalizeFunctions.Length());
+  MOZ_ASSERT(!mRuntime);
+}
+
+void IncrementalFinalizeRunnable::ReleaseNow(bool aLimited) {
+  if (mReleasing) {
+    NS_WARNING("Re-entering ReleaseNow");
+    return;
+  }
+  {
+    AUTO_PROFILER_LABEL("IncrementalFinalizeRunnable::ReleaseNow",
+                        GCCC_Finalize);
+
+    mozilla::AutoRestore<bool> ar(mReleasing);
+    mReleasing = true;
+    MOZ_ASSERT(mDeferredFinalizeFunctions.Length() != 0,
+               "We should have at least ReleaseSliceNow to run");
+    MOZ_ASSERT(mFinalizeFunctionToRun < mDeferredFinalizeFunctions.Length(),
+               "No more finalizers to run?");
+
+    TimeDuration sliceTime = TimeDuration::FromMilliseconds(SliceMillis);
+    TimeStamp started = aLimited ? TimeStamp::Now() : TimeStamp();
+    bool timeout = false;
+    do {
+      const DeferredFinalizeFunctionHolder& function =
+          mDeferredFinalizeFunctions[mFinalizeFunctionToRun];
+      if (aLimited) {
+        bool done = false;
+        while (!timeout && !done) {
+          /*
+           * We don't want to read the clock too often, so we try to
+           * release slices of 100 items.
+           */
+          done = function.run(100, function.data);
+          timeout = TimeStamp::Now() - started >= sliceTime;
+        }
+        if (done) {
+          ++mFinalizeFunctionToRun;
+        }
+        if (timeout) {
+          break;
+        }
+      } else {
+        while (!function.run(UINT32_MAX, function.data))
+          ;
+        ++mFinalizeFunctionToRun;
+      }
+    } while (mFinalizeFunctionToRun < mDeferredFinalizeFunctions.Length());
+  }
+
+  if (mFinalizeFunctionToRun == mDeferredFinalizeFunctions.Length()) {
+    MOZ_ASSERT(mRuntime->mFinalizeRunnable == this);
+    mDeferredFinalizeFunctions.Clear();
+    CycleCollectedJSRuntime* runtime = mRuntime;
+    mRuntime = nullptr;
+    // NB: This may delete this!
+    runtime->mFinalizeRunnable = nullptr;
+  }
+}
+
+NS_IMETHODIMP
+IncrementalFinalizeRunnable::Run() {
+  if (!mDeferredFinalizeFunctions.Length()) {
+    /* These items were already processed synchronously in JSGC_END. */
+    MOZ_ASSERT(!mRuntime);
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(mRuntime->mFinalizeRunnable == this);
+  TimeStamp start = TimeStamp::Now();
+  ReleaseNow(true);
+
+  if (mDeferredFinalizeFunctions.Length()) {
+    nsresult rv = NS_DispatchToCurrentThread(this);
+    if (NS_FAILED(rv)) {
+      ReleaseNow(false);
+    }
+  } else {
+    MOZ_ASSERT(!mRuntime);
+  }
+
+  uint32_t duration = (uint32_t)((TimeStamp::Now() - start).ToMilliseconds());
+  Telemetry::Accumulate(Telemetry::DEFERRED_FINALIZE_ASYNC, duration);
+
+  return NS_OK;
+}
+
+void CycleCollectedJSRuntime::FinalizeDeferredThings(
+    DeferredFinalizeType aType) {
+  // If mFinalizeRunnable isn't null, we didn't finalize everything from the
+  // previous GC.
+  if (mFinalizeRunnable) {
+    if (aType == FinalizeLater) {
+      // We need to defer all finalization until we return to the event loop,
+      // so leave things alone. Any new objects to be finalized from the current
+      // GC will be handled by the existing mFinalizeRunnable.
+      return;
+    }
+    MOZ_ASSERT(aType == FinalizeIncrementally || aType == FinalizeNow);
+    // If we're finalizing incrementally, we don't want finalizers to build up,
+    // so try to finish them off now.
+    // If we're finalizing synchronously, also go ahead and clear them out,
+    // so we make sure as much as possible is freed.
+    mFinalizeRunnable->ReleaseNow(false);
+    if (mFinalizeRunnable) {
+      // If we re-entered ReleaseNow, we couldn't delete mFinalizeRunnable and
+      // we need to just continue processing it.
+      return;
+    }
+  }
+
+  // If there's nothing to finalize, don't create a new runnable.
+  if (mDeferredFinalizerTable.Count() == 0) {
+    return;
+  }
+
+  mFinalizeRunnable =
+      new IncrementalFinalizeRunnable(this, mDeferredFinalizerTable);
+
+  // Everything should be gone now.
+  MOZ_ASSERT(mDeferredFinalizerTable.Count() == 0);
+
+  if (aType == FinalizeNow) {
+    mFinalizeRunnable->ReleaseNow(false);
+    MOZ_ASSERT(!mFinalizeRunnable);
+  } else {
+    MOZ_ASSERT(aType == FinalizeIncrementally || aType == FinalizeLater);
+    NS_DispatchToCurrentThreadQueue(do_AddRef(mFinalizeRunnable), 2500,
+                                    EventQueuePriority::Idle);
+  }
+}
+
+const char* CycleCollectedJSRuntime::OOMStateToString(
+    const OOMState aOomState) const {
+  switch (aOomState) {
+    case OOMState::OK:
+      return "OK";
+    case OOMState::Reporting:
+      return "Reporting";
+    case OOMState::Reported:
+      return "Reported";
+    case OOMState::Recovered:
+      return "Recovered";
+    default:
+      MOZ_ASSERT_UNREACHABLE("OOMState holds an invalid value");
+      return "Unknown";
+  }
+}
+
+bool CycleCollectedJSRuntime::OOMReported() {
+  return mOutOfMemoryState == OOMState::Reported;
+}
+
+void CycleCollectedJSRuntime::AnnotateAndSetOutOfMemory(OOMState* aStatePtr,
+                                                        OOMState aNewState) {
+  *aStatePtr = aNewState;
+  CrashReporter::Annotation annotation =
+      (aStatePtr == &mOutOfMemoryState)
+          ? CrashReporter::Annotation::JSOutOfMemory
+          : CrashReporter::Annotation::JSLargeAllocationFailure;
+
+  CrashReporter::AnnotateCrashReport(
+      annotation, nsDependentCString(OOMStateToString(aNewState)));
+}
+
+void CycleCollectedJSRuntime::OnGC(JSContext* aContext, JSGCStatus aStatus,
+                                   JS::GCReason aReason) {
+  switch (aStatus) {
+    case JSGC_BEGIN:
+      MOZ_RELEASE_ASSERT(mHolderIter.isNothing());
+      nsCycleCollector_prepareForGarbageCollection();
+      PrepareWaitingZonesForGC();
+      break;
+    case JSGC_END: {
+      MOZ_RELEASE_ASSERT(mHolderIter.isNothing());
+      if (mOutOfMemoryState == OOMState::Reported) {
+        AnnotateAndSetOutOfMemory(&mOutOfMemoryState, OOMState::Recovered);
+      }
+      if (mLargeAllocationFailureState == OOMState::Reported) {
+        AnnotateAndSetOutOfMemory(&mLargeAllocationFailureState,
+                                  OOMState::Recovered);
+      }
+
+      DeferredFinalizeType finalizeType;
+      if (JS_IsExceptionPending(aContext)) {
+        // There is a pending exception. The finalizers are not set up to run
+        // in that state, so don't run the finalizer until we've returned to the
+        // event loop.
+        finalizeType = FinalizeLater;
+      } else if (JS::InternalGCReason(aReason)) {
+        if (aReason == JS::GCReason::DESTROY_RUNTIME) {
+          // We're shutting down, so we need to destroy things immediately.
+          finalizeType = FinalizeNow;
+        } else {
+          // We may be in the middle of running some code that the JIT has
+          // assumed can't have certain kinds of side effects. Finalizers can do
+          // all sorts of things, such as run JS, so we want to run them later,
+          // after we've returned to the event loop.
+          finalizeType = FinalizeLater;
+        }
+      } else if (JS::WasIncrementalGC(mJSRuntime)) {
+        // The GC was incremental, so we probably care about pauses. Try to
+        // break up finalization, but it is okay if we do some now.
+        finalizeType = FinalizeIncrementally;
+      } else {
+        // If we're running a synchronous GC, we probably want to free things as
+        // quickly as possible. This can happen during testing or if memory is
+        // low.
+        finalizeType = FinalizeNow;
+      }
+      FinalizeDeferredThings(finalizeType);
+
+      break;
+    }
+    default:
+      MOZ_CRASH();
+  }
+
+  CustomGCCallback(aStatus);
+}
+
+void CycleCollectedJSRuntime::OnOutOfMemory() {
+  AnnotateAndSetOutOfMemory(&mOutOfMemoryState, OOMState::Reporting);
+  CustomOutOfMemoryCallback();
+  AnnotateAndSetOutOfMemory(&mOutOfMemoryState, OOMState::Reported);
+}
+
+void CycleCollectedJSRuntime::SetLargeAllocationFailure(OOMState aNewState) {
+  AnnotateAndSetOutOfMemory(&mLargeAllocationFailureState, aNewState);
+}
+
+void CycleCollectedJSRuntime::PrepareWaitingZonesForGC() {
+  JSContext* cx = CycleCollectedJSContext::Get()->Context();
+  if (mZonesWaitingForGC.Count() == 0) {
+    JS::PrepareForFullGC(cx);
+  } else {
+    for (const auto& key : mZonesWaitingForGC) {
+      JS::PrepareZoneForGC(cx, key);
+    }
+    mZonesWaitingForGC.Clear();
+  }
+}
+
+/* static */
+void CycleCollectedJSRuntime::OnZoneDestroyed(JS::GCContext* aGcx,
+                                              JS::Zone* aZone) {
+  // Remove the zone from the set of zones waiting for GC, if present. This can
+  // happen if a zone is added to the set during an incremental GC in which it
+  // is later destroyed.
+  CycleCollectedJSRuntime* runtime = Get();
+  runtime->mZonesWaitingForGC.Remove(aZone);
+}
+
+void CycleCollectedJSRuntime::EnvironmentPreparer::invoke(
+    JS::HandleObject global, js::ScriptEnvironmentPreparer::Closure& closure) {
+  MOZ_ASSERT(JS_IsGlobalObject(global));
+  nsIGlobalObject* nativeGlobal = xpc::NativeGlobal(global);
+
+  // Not much we can do if we simply don't have a usable global here...
+  NS_ENSURE_TRUE_VOID(nativeGlobal && nativeGlobal->HasJSGlobal());
+
+  AutoEntryScript aes(nativeGlobal, "JS-engine-initiated execution");
+
+  MOZ_ASSERT(!JS_IsExceptionPending(aes.cx()));
+
+  DebugOnly<bool> ok = closure(aes.cx());
+
+  MOZ_ASSERT_IF(ok, !JS_IsExceptionPending(aes.cx()));
+
+  // The AutoEntryScript will check for JS_IsExceptionPending on the
+  // JSContext and report it as needed as it comes off the stack.
+}
+
+/* static */
+CycleCollectedJSRuntime* CycleCollectedJSRuntime::Get() {
+  auto context = CycleCollectedJSContext::Get();
+  if (context) {
+    return context->Runtime();
+  }
+  return nullptr;
+}
+
+#ifdef MOZ_JS_DEV_ERROR_INTERCEPTOR
+
+namespace js {
+extern void DumpValue(const JS::Value& val);
+}
+
+void CycleCollectedJSRuntime::ErrorInterceptor::Shutdown(JSRuntime* rt) {
+  JS_SetErrorInterceptorCallback(rt, nullptr);
+  mThrownError.reset();
+}
+
+/* virtual */
+void CycleCollectedJSRuntime::ErrorInterceptor::interceptError(
+    JSContext* cx, JS::HandleValue exn) {
+  if (mThrownError) {
+    // We already have an error, we don't need anything more.
+    return;
+  }
+
+  if (!nsContentUtils::ThreadsafeIsSystemCaller(cx)) {
+    // We are only interested in chrome code.
+    return;
+  }
+
+  const auto type = JS_GetErrorType(exn);
+  if (!type) {
+    // This is not one of the primitive error types.
+    return;
+  }
+
+  switch (*type) {
+    case JSExnType::JSEXN_REFERENCEERR:
+    case JSExnType::JSEXN_SYNTAXERR:
+      break;
+    default:
+      // Not one of the errors we are interested in.
+      // Note that we are not interested in instances of `TypeError`
+      // for the time being, as DOM (ab)uses this constructor to represent
+      // all sorts of errors that are not even remotely related to type
+      // errors (e.g. some network errors).
+      // If we ever have a mechanism to differentiate between DOM-thrown
+      // and SpiderMonkey-thrown instances of `TypeError`, we should
+      // consider watching for `TypeError` here.
+      return;
+  }
+
+  // Now copy the details of the exception locally.
+  // While copying the details of an exception could be expensive, in most runs,
+  // this will be done at most once during the execution of the process, so the
+  // total cost should be reasonable.
+
+  ErrorDetails details;
+  details.mType = *type;
+  // If `exn` isn't an exception object, `ExtractErrorValues` could end up
+  // calling `toString()`, which could in turn end up throwing an error. While
+  // this should work, we want to avoid that complex use case. Fortunately, we
+  // have already checked above that `exn` is an exception object, so nothing
+  // such should happen.
+  nsContentUtils::ExtractErrorValues(cx, exn, details.mFilename, &details.mLine,
+                                     &details.mColumn, details.mMessage);
+
+  JS::UniqueChars buf =
+      JS::FormatStackDump(cx, /* showArgs = */ false, /* showLocals = */ false,
+                          /* showThisProps = */ false);
+  CopyUTF8toUTF16(mozilla::MakeStringSpan(buf.get()), details.mStack);
+
+  mThrownError.emplace(std::move(details));
+}
+
+void CycleCollectedJSRuntime::ClearRecentDevError() {
+  mErrorInterceptor.mThrownError.reset();
+}
+
+bool CycleCollectedJSRuntime::GetRecentDevError(
+    JSContext* cx, JS::MutableHandle<JS::Value> error) {
+  if (!mErrorInterceptor.mThrownError) {
+    return true;
+  }
+
+  // Create a copy of the exception.
+  JS::RootedObject obj(cx, JS_NewPlainObject(cx));
+  if (!obj) {
+    return false;
+  }
+
+  JS::RootedValue message(cx);
+  JS::RootedValue filename(cx);
+  JS::RootedValue stack(cx);
+  if (!ToJSValue(cx, mErrorInterceptor.mThrownError->mMessage, &message) ||
+      !ToJSValue(cx, mErrorInterceptor.mThrownError->mFilename, &filename) ||
+      !ToJSValue(cx, mErrorInterceptor.mThrownError->mStack, &stack)) {
+    return false;
+  }
+
+  // Build the object.
+  const auto FLAGS = JSPROP_READONLY | JSPROP_ENUMERATE | JSPROP_PERMANENT;
+  if (!JS_DefineProperty(cx, obj, "message", message, FLAGS) ||
+      !JS_DefineProperty(cx, obj, "fileName", filename, FLAGS) ||
+      !JS_DefineProperty(cx, obj, "lineNumber",
+                         mErrorInterceptor.mThrownError->mLine, FLAGS) ||
+      !JS_DefineProperty(cx, obj, "stack", stack, FLAGS)) {
+    return false;
+  }
+
+  // Pass the result.
+  error.setObject(*obj);
+  return true;
+}
+#endif  // MOZ_JS_DEV_ERROR_INTERCEPTOR
+
+#undef MOZ_JS_DEV_ERROR_INTERCEPTOR
diff --git a/xpcom/base/CycleCollectedJSRuntime.h b/xpcom/base/CycleCollectedJSRuntime.h
new file mode 100644
index 0000000000..7008fadb28
--- /dev/null
+++ b/xpcom/base/CycleCollectedJSRuntime.h
@@ -0,0 +1,528 @@
+/* -*- 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/. */
+
+#ifndef mozilla_CycleCollectedJSRuntime_h
+#define mozilla_CycleCollectedJSRuntime_h
+
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/DeferredFinalize.h"
+#include "mozilla/HashTable.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/SegmentedVector.h"
+#include "jsapi.h"
+#include "jsfriendapi.h"
+#include "js/TypeDecls.h"
+
+#include "nsCycleCollectionParticipant.h"
+#include "nsTHashMap.h"
+#include "nsHashKeys.h"
+#include "nsStringFwd.h"
+#include "nsTHashSet.h"
+
+class nsCycleCollectionNoteRootCallback;
+class nsIException;
+class nsWrapperCache;
+
+namespace mozilla {
+
+class JSGCThingParticipant : public nsCycleCollectionParticipant {
+ public:
+  constexpr JSGCThingParticipant() : nsCycleCollectionParticipant(false) {}
+
+  NS_IMETHOD_(void) Root(void*) override {
+    MOZ_ASSERT(false, "Don't call Root on GC things");
+  }
+
+  NS_IMETHOD_(void) Unlink(void*) override {
+    MOZ_ASSERT(false, "Don't call Unlink on GC things, as they may be dead");
+  }
+
+  NS_IMETHOD_(void) Unroot(void*) override {
+    MOZ_ASSERT(false, "Don't call Unroot on GC things, as they may be dead");
+  }
+
+  NS_IMETHOD_(void) DeleteCycleCollectable(void* aPtr) override {
+    MOZ_ASSERT(false, "Can't directly delete a cycle collectable GC thing");
+  }
+
+  NS_IMETHOD TraverseNative(void* aPtr,
+                            nsCycleCollectionTraversalCallback& aCb) override;
+
+  NS_DECL_CYCLE_COLLECTION_CLASS_NAME_METHOD(JSGCThingParticipant)
+};
+
+class JSZoneParticipant : public nsCycleCollectionParticipant {
+ public:
+  constexpr JSZoneParticipant() : nsCycleCollectionParticipant(false) {}
+
+  NS_IMETHOD_(void) Root(void*) override {
+    MOZ_ASSERT(false, "Don't call Root on GC things");
+  }
+
+  NS_IMETHOD_(void) Unlink(void*) override {
+    MOZ_ASSERT(false, "Don't call Unlink on GC things, as they may be dead");
+  }
+
+  NS_IMETHOD_(void) Unroot(void*) override {
+    MOZ_ASSERT(false, "Don't call Unroot on GC things, as they may be dead");
+  }
+
+  NS_IMETHOD_(void) DeleteCycleCollectable(void*) override {
+    MOZ_ASSERT(false, "Can't directly delete a cycle collectable GC thing");
+  }
+
+  NS_IMETHOD TraverseNative(void* aPtr,
+                            nsCycleCollectionTraversalCallback& aCb) override;
+
+  NS_DECL_CYCLE_COLLECTION_CLASS_NAME_METHOD(JSZoneParticipant)
+};
+
+class IncrementalFinalizeRunnable;
+
+// A map from JS holders to tracer objects, where the values are stored in
+// SegmentedVector to speed up iteration.
+class JSHolderMap {
+ public:
+  enum WhichHolders { AllHolders, HoldersRequiredForGrayMarking };
+
+  class Iter;
+
+  JSHolderMap();
+  ~JSHolderMap() { MOZ_RELEASE_ASSERT(!mHasIterator); }
+
+  bool Has(void* aHolder) const;
+  nsScriptObjectTracer* Get(void* aHolder) const;
+  nsScriptObjectTracer* Extract(void* aHolder);
+  void Put(void* aHolder, nsScriptObjectTracer* aTracer, JS::Zone* aZone);
+
+  size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const;
+
+ private:
+  struct Entry {
+    void* mHolder;
+    nsScriptObjectTracer* mTracer;
+#ifdef DEBUG
+    JS::Zone* mZone;
+#endif
+
+    Entry();
+    Entry(void* aHolder, nsScriptObjectTracer* aTracer, JS::Zone* aZone);
+  };
+
+  using EntryMap = mozilla::HashMap<void*, Entry*, DefaultHasher<void*>,
+                                    InfallibleAllocPolicy>;
+
+  using EntryVector = SegmentedVector<Entry, 256, InfallibleAllocPolicy>;
+
+  using EntryVectorMap =
+      mozilla::HashMap<JS::Zone*, UniquePtr<EntryVector>,
+                       DefaultHasher<JS::Zone*>, InfallibleAllocPolicy>;
+
+  class EntryVectorIter;
+
+  bool RemoveEntry(EntryVector& aJSHolders, Entry* aEntry);
+
+  // A map from a holder pointer to a pointer to an entry in a vector.
+  EntryMap mJSHolderMap;
+
+  // A vector of holders not associated with a particular zone or that can
+  // contain pointers to GC things in more than one zone.
+  EntryVector mAnyZoneJSHolders;
+
+  // A map from a zone to a vector of holders that only contain pointers to GC
+  // things in that zone.
+  //
+  // Currently this will only contain wrapper cache wrappers since these are the
+  // only holders to pass a zone parameter through to AddJSHolder.
+  EntryVectorMap mPerZoneJSHolders;
+
+  // Iterators can mutate the element vectors by removing stale elements. Allow
+  // at most one to exist at a time.
+  bool mHasIterator = false;
+};
+
+// An iterator over an EntryVector that skips over removed entries and removes
+// them from the map.
+class JSHolderMap::EntryVectorIter {
+ public:
+  EntryVectorIter(JSHolderMap& aMap, EntryVector& aVector)
+      : mHolderMap(aMap), mVector(aVector), mIter(aVector.Iter()) {
+    Settle();
+  }
+
+  const EntryVector& Vector() const { return mVector; }
+
+  bool Done() const { return mIter.Done(); }
+  const Entry& Get() const { return mIter.Get(); }
+  void Next() {
+    mIter.Next();
+    Settle();
+  }
+
+  operator const Entry*() const { return &Get(); }
+  const Entry* operator->() const { return &Get(); }
+
+ private:
+  void Settle();
+  friend class JSHolderMap::Iter;
+
+  JSHolderMap& mHolderMap;
+  EntryVector& mVector;
+  EntryVector::IterImpl mIter;
+};
+
+class JSHolderMap::Iter {
+ public:
+  explicit Iter(JSHolderMap& aMap, WhichHolders aWhich = AllHolders);
+
+  ~Iter() {
+    MOZ_RELEASE_ASSERT(mHolderMap.mHasIterator);
+    mHolderMap.mHasIterator = false;
+  }
+
+  bool Done() const { return mIter.Done(); }
+  const Entry& Get() const { return mIter.Get(); }
+  void Next() {
+    mIter.Next();
+    Settle();
+  }
+
+  // If the holders have been removed from the map while the iterator is live,
+  // then the iterator may point to a removed entry. Update the iterator to make
+  // sure it points to a valid entry or is done.
+  void UpdateForRemovals();
+
+  operator const Entry*() const { return &Get(); }
+  const Entry* operator->() const { return &Get(); }
+
+  JS::Zone* Zone() const { return mZone; }
+
+ private:
+  void Settle();
+
+  JSHolderMap& mHolderMap;
+  Vector<JS::Zone*, 1, InfallibleAllocPolicy> mZones;
+  JS::Zone* mZone = nullptr;
+  EntryVectorIter mIter;
+};
+
+class CycleCollectedJSRuntime {
+  friend class JSGCThingParticipant;
+  friend class JSZoneParticipant;
+  friend class IncrementalFinalizeRunnable;
+  friend class CycleCollectedJSContext;
+
+ protected:
+  CycleCollectedJSRuntime(JSContext* aMainContext);
+  virtual ~CycleCollectedJSRuntime();
+
+  virtual void Shutdown(JSContext* cx);
+
+  size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
+  void UnmarkSkippableJSHolders();
+
+  virtual void TraverseAdditionalNativeRoots(
+      nsCycleCollectionNoteRootCallback& aCb) {}
+  virtual void TraceAdditionalNativeGrayRoots(JSTracer* aTracer) {}
+
+  virtual void CustomGCCallback(JSGCStatus aStatus) {}
+  virtual void CustomOutOfMemoryCallback() {}
+
+  CycleCollectedJSContext* GetContext() { return mContext; }
+
+ private:
+  void DescribeGCThing(bool aIsMarked, JS::GCCellPtr aThing,
+                       nsCycleCollectionTraversalCallback& aCb) const;
+
+  virtual bool DescribeCustomObjects(JSObject* aObject, const JSClass* aClasp,
+                                     char (&aName)[72]) const {
+    return false;  // We did nothing.
+  }
+
+  void NoteGCThingJSChildren(JS::GCCellPtr aThing,
+                             nsCycleCollectionTraversalCallback& aCb) const;
+
+  void NoteGCThingXPCOMChildren(const JSClass* aClasp, JSObject* aObj,
+                                nsCycleCollectionTraversalCallback& aCb) const;
+
+  virtual bool NoteCustomGCThingXPCOMChildren(
+      const JSClass* aClasp, JSObject* aObj,
+      nsCycleCollectionTraversalCallback& aCb) const {
+    return false;  // We did nothing.
+  }
+
+  enum TraverseSelect { TRAVERSE_CPP, TRAVERSE_FULL };
+
+  void TraverseGCThing(TraverseSelect aTs, JS::GCCellPtr aThing,
+                       nsCycleCollectionTraversalCallback& aCb);
+
+  void TraverseZone(JS::Zone* aZone, nsCycleCollectionTraversalCallback& aCb);
+
+  static void TraverseObjectShim(void* aData, JS::GCCellPtr aThing,
+                                 const JS::AutoRequireNoGC& nogc);
+
+  void TraverseNativeRoots(nsCycleCollectionNoteRootCallback& aCb);
+
+  static void TraceBlackJS(JSTracer* aTracer, void* aData);
+
+  // Trace gray JS roots until budget is exceeded and return whether we
+  // finished.
+  static bool TraceGrayJS(JSTracer* aTracer, js::SliceBudget& budget,
+                          void* aData);
+
+  static void GCCallback(JSContext* aContext, JSGCStatus aStatus,
+                         JS::GCReason aReason, void* aData);
+  static void GCSliceCallback(JSContext* aContext, JS::GCProgress aProgress,
+                              const JS::GCDescription& aDesc);
+  static void GCNurseryCollectionCallback(JSContext* aContext,
+                                          JS::GCNurseryProgress aProgress,
+                                          JS::GCReason aReason);
+  static void OutOfMemoryCallback(JSContext* aContext, void* aData);
+
+  static bool ContextCallback(JSContext* aCx, unsigned aOperation, void* aData);
+
+  static void* BeforeWaitCallback(uint8_t* aMemory);
+  static void AfterWaitCallback(void* aCookie);
+
+  virtual void TraceNativeBlackRoots(JSTracer* aTracer){};
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+  void TraceAllNativeGrayRoots(JSTracer* aTracer);
+#endif
+
+  bool TraceNativeGrayRoots(JSTracer* aTracer, JSHolderMap::WhichHolders aWhich,
+                            js::SliceBudget& aBudget);
+  bool TraceJSHolders(JSTracer* aTracer, JSHolderMap::Iter& aIter,
+                      js::SliceBudget& aBudget);
+
+ public:
+  enum DeferredFinalizeType {
+    // Never finalize immediately, because it would be unsafe.
+    FinalizeLater,
+    // Finalize later if we can, but it is okay to do it immediately.
+    FinalizeIncrementally,
+    // Finalize immediately, for shutdown or testing purposes.
+    FinalizeNow,
+  };
+
+  void FinalizeDeferredThings(DeferredFinalizeType aType);
+
+  virtual void PrepareForForgetSkippable() = 0;
+  virtual void BeginCycleCollectionCallback(mozilla::CCReason aReason) = 0;
+  virtual void EndCycleCollectionCallback(CycleCollectorResults& aResults) = 0;
+  virtual void DispatchDeferredDeletion(bool aContinuation,
+                                        bool aPurge = false) = 0;
+
+  // Two conditions, JSOutOfMemory and JSLargeAllocationFailure, are noted in
+  // crash reports. Here are the values that can appear in the reports:
+  enum class OOMState : uint32_t {
+    // The condition has never happened. No entry appears in the crash report.
+    OK,
+
+    // We are currently reporting the given condition.
+    //
+    // Suppose a crash report contains "JSLargeAllocationFailure:
+    // Reporting". This means we crashed while executing memory-pressure
+    // observers, trying to shake loose some memory. The large allocation in
+    // question did not return null: it is still on the stack. Had we not
+    // crashed, it would have been retried.
+    Reporting,
+
+    // The condition has been reported since the last GC.
+    //
+    // If a crash report contains "JSOutOfMemory: Reported", that means a small
+    // allocation failed, and then we crashed, probably due to buggy
+    // error-handling code that ran after allocation returned null.
+    //
+    // This contrasts with "Reporting" which means that no error-handling code
+    // had executed yet.
+    Reported,
+
+    // The condition has happened, but a GC cycle ended since then.
+    //
+    // GC is taken as a proxy for "we've been banging on the heap a good bit
+    // now and haven't crashed; the OOM was probably handled correctly".
+    Recovered
+  };
+
+  const char* OOMStateToString(const OOMState aOomState) const;
+
+  // Returns true if OOM was reported and a new successful GC cycle hasn't
+  // occurred since.
+  bool OOMReported();
+
+  void SetLargeAllocationFailure(OOMState aNewState);
+
+  void AnnotateAndSetOutOfMemory(OOMState* aStatePtr, OOMState aNewState);
+  void OnGC(JSContext* aContext, JSGCStatus aStatus, JS::GCReason aReason);
+  void OnOutOfMemory();
+  void OnLargeAllocationFailure();
+
+  JSRuntime* Runtime() { return mJSRuntime; }
+  const JSRuntime* Runtime() const { return mJSRuntime; }
+
+  bool HasPendingIdleGCTask() const {
+    // Idle GC task associates with JSRuntime.
+    MOZ_ASSERT_IF(mHasPendingIdleGCTask, Runtime());
+    return mHasPendingIdleGCTask;
+  }
+  void SetPendingIdleGCTask() {
+    // Idle GC task associates with JSRuntime.
+    MOZ_ASSERT(Runtime());
+    mHasPendingIdleGCTask = true;
+  }
+  void ClearPendingIdleGCTask() { mHasPendingIdleGCTask = false; }
+
+  void RunIdleTimeGCTask() {
+    if (HasPendingIdleGCTask()) {
+      JS::MaybeRunNurseryCollection(Runtime(),
+                                    JS::GCReason::EAGER_NURSERY_COLLECTION);
+      ClearPendingIdleGCTask();
+    }
+  }
+
+  bool IsIdleGCTaskNeeded() {
+    return !HasPendingIdleGCTask() && Runtime() &&
+           JS::WantEagerMinorGC(Runtime()) != JS::GCReason::NO_REASON;
+  }
+
+ public:
+  void AddJSHolder(void* aHolder, nsScriptObjectTracer* aTracer,
+                   JS::Zone* aZone);
+  void RemoveJSHolder(void* aHolder);
+#ifdef DEBUG
+  void AssertNoObjectsToTrace(void* aPossibleJSHolder);
+#endif
+
+  nsCycleCollectionParticipant* GCThingParticipant();
+  nsCycleCollectionParticipant* ZoneParticipant();
+
+  nsresult TraverseRoots(nsCycleCollectionNoteRootCallback& aCb);
+  virtual bool UsefulToMergeZones() const;
+  void FixWeakMappingGrayBits() const;
+  void CheckGrayBits() const;
+  bool AreGCGrayBitsValid() const;
+  void GarbageCollect(JS::GCOptions options, JS::GCReason aReason) const;
+
+  // This needs to be an nsWrapperCache, not a JSObject, because we need to know
+  // when our object gets moved.  But we can't trace it (and hence update our
+  // storage), because we do not want to keep it alive.  nsWrapperCache handles
+  // this for us via its "object moved" handling.
+  void NurseryWrapperAdded(nsWrapperCache* aCache);
+  void JSObjectsTenured();
+
+  void DeferredFinalize(DeferredFinalizeAppendFunction aAppendFunc,
+                        DeferredFinalizeFunction aFunc, void* aThing);
+  void DeferredFinalize(nsISupports* aSupports);
+
+  void DumpJSHeap(FILE* aFile);
+
+  // Add aZone to the set of zones waiting for a GC.
+  void AddZoneWaitingForGC(JS::Zone* aZone) {
+    mZonesWaitingForGC.Insert(aZone);
+  }
+
+  static void OnZoneDestroyed(JS::GCContext* aGcx, JS::Zone* aZone);
+
+  // Prepare any zones for GC that have been passed to AddZoneWaitingForGC()
+  // since the last GC or since the last call to PrepareWaitingZonesForGC(),
+  // whichever was most recent. If there were no such zones, prepare for a
+  // full GC.
+  void PrepareWaitingZonesForGC();
+
+  // Get the current thread's CycleCollectedJSRuntime.  Returns null if there
+  // isn't one.
+  static CycleCollectedJSRuntime* Get();
+
+  void SetContext(CycleCollectedJSContext* aContext);
+
+#ifdef NIGHTLY_BUILD
+  bool GetRecentDevError(JSContext* aContext,
+                         JS::MutableHandle<JS::Value> aError);
+  void ClearRecentDevError();
+#endif  // defined(NIGHTLY_BUILD)
+
+ private:
+  CycleCollectedJSContext* mContext;
+
+  JSGCThingParticipant mGCThingCycleCollectorGlobal;
+
+  JSZoneParticipant mJSZoneCycleCollectorGlobal;
+
+  JSRuntime* mJSRuntime;
+  bool mHasPendingIdleGCTask;
+
+  JS::GCSliceCallback mPrevGCSliceCallback;
+  JS::GCNurseryCollectionCallback mPrevGCNurseryCollectionCallback;
+
+  mozilla::TimeStamp mLatestNurseryCollectionStart;
+
+  JSHolderMap mJSHolders;
+  Maybe<JSHolderMap::Iter> mHolderIter;
+
+  typedef nsTHashMap<nsFuncPtrHashKey<DeferredFinalizeFunction>, void*>
+      DeferredFinalizerTable;
+  DeferredFinalizerTable mDeferredFinalizerTable;
+
+  RefPtr<IncrementalFinalizeRunnable> mFinalizeRunnable;
+
+  OOMState mOutOfMemoryState;
+  OOMState mLargeAllocationFailureState;
+
+  static const size_t kSegmentSize = 512;
+  SegmentedVector<nsWrapperCache*, kSegmentSize, InfallibleAllocPolicy>
+      mNurseryObjects;
+
+  nsTHashSet<JS::Zone*> mZonesWaitingForGC;
+
+  struct EnvironmentPreparer : public js::ScriptEnvironmentPreparer {
+    void invoke(JS::Handle<JSObject*> global, Closure& closure) override;
+  };
+  EnvironmentPreparer mEnvironmentPreparer;
+
+#ifdef DEBUG
+  bool mShutdownCalled;
+#endif
+
+#ifdef NIGHTLY_BUILD
+  // Implementation of the error interceptor.
+  // Built on nightly only to avoid any possible performance impact on release
+
+  struct ErrorInterceptor final : public JSErrorInterceptor {
+    virtual void interceptError(JSContext* cx,
+                                JS::Handle<JS::Value> exn) override;
+    void Shutdown(JSRuntime* rt);
+
+    // Copy of the details of the exception.
+    // We store this rather than the exception itself to avoid dealing with
+    // complicated garbage-collection scenarios, e.g. a JSContext being killed
+    // while we still hold onto an exception thrown from it.
+    struct ErrorDetails {
+      nsString mFilename;
+      nsString mMessage;
+      nsString mStack;
+      JSExnType mType;
+      uint32_t mLine;
+      uint32_t mColumn;
+    };
+
+    // If we have encountered at least one developer error,
+    // the first error we have encountered. Otherwise, or
+    // if we have reset since the latest error, `None`.
+    Maybe<ErrorDetails> mThrownError;
+  };
+  ErrorInterceptor mErrorInterceptor;
+
+#endif  // defined(NIGHTLY_BUILD)
+};
+
+void TraceScriptHolder(nsISupports* aHolder, JSTracer* aTracer);
+
+}  // namespace mozilla
+
+#endif  // mozilla_CycleCollectedJSRuntime_h
diff --git a/xpcom/base/Debug.cpp b/xpcom/base/Debug.cpp
new file mode 100644
index 0000000000..7e2a4c1d10
--- /dev/null
+++ b/xpcom/base/Debug.cpp
@@ -0,0 +1,21 @@
+/* -*- 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 "mozilla/Debug.h"
+
+#ifdef XP_WIN
+#  include <windows.h>
+#endif
+
+#ifdef XP_WIN
+
+void mozilla::PrintToDebugger(const char* aStr) {
+  if (::IsDebuggerPresent()) {
+    ::OutputDebugStringA(aStr);
+  }
+}
+
+#endif
diff --git a/xpcom/base/Debug.h b/xpcom/base/Debug.h
new file mode 100644
index 0000000000..1d6eaaf9a4
--- /dev/null
+++ b/xpcom/base/Debug.h
@@ -0,0 +1,21 @@
+/* -*- 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/. */
+
+#ifndef mozilla_Debug_h__
+#define mozilla_Debug_h__
+
+namespace mozilla {
+
+#ifdef XP_WIN
+
+// Print aStr to a debugger if the debugger is attached.
+void PrintToDebugger(const char* aStr);
+
+#endif
+
+}  // namespace mozilla
+
+#endif  // mozilla_Debug_h__
diff --git a/xpcom/base/DebuggerOnGCRunnable.cpp b/xpcom/base/DebuggerOnGCRunnable.cpp
new file mode 100644
index 0000000000..bcb13b3226
--- /dev/null
+++ b/xpcom/base/DebuggerOnGCRunnable.cpp
@@ -0,0 +1,51 @@
+/* -*- 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 "mozilla/DebuggerOnGCRunnable.h"
+
+#include <utility>
+
+#include "js/Debug.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/SchedulerGroup.h"
+
+namespace mozilla {
+
+/* static */
+nsresult DebuggerOnGCRunnable::Enqueue(JSContext* aCx,
+                                       const JS::GCDescription& aDesc) {
+  auto gcEvent = aDesc.toGCEvent(aCx);
+  if (!gcEvent) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  RefPtr<DebuggerOnGCRunnable> runOnGC =
+      new DebuggerOnGCRunnable(std::move(gcEvent));
+  if (NS_IsMainThread()) {
+    return SchedulerGroup::Dispatch(TaskCategory::GarbageCollection,
+                                    runOnGC.forget());
+  } else {
+    return NS_DispatchToCurrentThread(runOnGC);
+  }
+}
+
+NS_IMETHODIMP
+DebuggerOnGCRunnable::Run() {
+  dom::AutoJSAPI jsapi;
+  jsapi.Init();
+  if (!JS::dbg::FireOnGarbageCollectionHook(jsapi.cx(), std::move(mGCData))) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  return NS_OK;
+}
+
+nsresult DebuggerOnGCRunnable::Cancel() {
+  mGCData = nullptr;
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/DebuggerOnGCRunnable.h b/xpcom/base/DebuggerOnGCRunnable.h
new file mode 100644
index 0000000000..93ac48b56c
--- /dev/null
+++ b/xpcom/base/DebuggerOnGCRunnable.h
@@ -0,0 +1,35 @@
+/* -*- 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/. */
+
+#ifndef mozilla_DebuggerOnGCRunnable_h
+#define mozilla_DebuggerOnGCRunnable_h
+
+#include <utility>
+
+#include "js/GCAPI.h"
+#include "mozilla/UniquePtr.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla {
+
+// Runnable to fire the SpiderMonkey Debugger API's onGarbageCollection hook.
+class DebuggerOnGCRunnable : public CancelableRunnable {
+  JS::dbg::GarbageCollectionEvent::Ptr mGCData;
+
+  explicit DebuggerOnGCRunnable(JS::dbg::GarbageCollectionEvent::Ptr&& aGCData)
+      : CancelableRunnable("DebuggerOnGCRunnable"),
+        mGCData(std::move(aGCData)) {}
+
+ public:
+  static nsresult Enqueue(JSContext* aCx, const JS::GCDescription& aDesc);
+
+  NS_DECL_NSIRUNNABLE
+  nsresult Cancel() override;
+};
+
+}  // namespace mozilla
+
+#endif  // ifdef mozilla_dom_DebuggerOnGCRunnable_h
diff --git a/xpcom/base/DeferredFinalize.cpp b/xpcom/base/DeferredFinalize.cpp
new file mode 100644
index 0000000000..aea034dbf3
--- /dev/null
+++ b/xpcom/base/DeferredFinalize.cpp
@@ -0,0 +1,23 @@
+/* -*- 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 "mozilla/DeferredFinalize.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/CycleCollectedJSRuntime.h"
+
+void mozilla::DeferredFinalize(nsISupports* aSupports) {
+  CycleCollectedJSRuntime* rt = CycleCollectedJSRuntime::Get();
+  MOZ_ASSERT(rt, "Should have a CycleCollectedJSRuntime by now");
+  rt->DeferredFinalize(aSupports);
+}
+
+void mozilla::DeferredFinalize(DeferredFinalizeAppendFunction aAppendFunc,
+                               DeferredFinalizeFunction aFunc, void* aThing) {
+  CycleCollectedJSRuntime* rt = CycleCollectedJSRuntime::Get();
+  MOZ_ASSERT(rt, "Should have a CycleCollectedJSRuntime by now");
+  rt->DeferredFinalize(aAppendFunc, aFunc, aThing);
+}
diff --git a/xpcom/base/DeferredFinalize.h b/xpcom/base/DeferredFinalize.h
new file mode 100644
index 0000000000..8b0e7e28be
--- /dev/null
+++ b/xpcom/base/DeferredFinalize.h
@@ -0,0 +1,35 @@
+/* -*- 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/. */
+
+#ifndef mozilla_DeferredFinalize_h
+#define mozilla_DeferredFinalize_h
+
+#include <cstdint>
+#include "mozilla/Attributes.h"
+
+class nsISupports;
+
+namespace mozilla {
+
+// Called back from DeferredFinalize.  Should add 'thing' to the array of smart
+// pointers in 'pointers', creating the array if 'pointers' is null, and return
+// the array.
+typedef void* (*DeferredFinalizeAppendFunction)(void* aPointers, void* aThing);
+
+// Called to finalize a number of objects. Slice is the number of objects to
+// finalize. The return value indicates whether it finalized all objects in the
+// buffer. If it returns true, the function will not be called again, so the
+// function should free aData.
+typedef bool (*DeferredFinalizeFunction)(uint32_t aSlice, void* aData);
+
+void DeferredFinalize(DeferredFinalizeAppendFunction aAppendFunc,
+                      DeferredFinalizeFunction aFunc, void* aThing);
+
+MOZ_NEVER_INLINE void DeferredFinalize(nsISupports* aSupports);
+
+}  // namespace mozilla
+
+#endif  // mozilla_DeferredFinalize_h
diff --git a/xpcom/base/EnumeratedArrayCycleCollection.h b/xpcom/base/EnumeratedArrayCycleCollection.h
new file mode 100644
index 0000000000..465d4cf38a
--- /dev/null
+++ b/xpcom/base/EnumeratedArrayCycleCollection.h
@@ -0,0 +1,32 @@
+/* -*- 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/. */
+
+#ifndef EnumeratedArrayCycleCollection_h_
+#define EnumeratedArrayCycleCollection_h_
+
+#include "mozilla/EnumeratedArray.h"
+#include "nsCycleCollectionTraversalCallback.h"
+
+template <typename IndexType, IndexType SizeAsEnumValue, typename ValueType>
+inline void ImplCycleCollectionUnlink(
+    mozilla::EnumeratedArray<IndexType, SizeAsEnumValue, ValueType>& aField) {
+  for (size_t i = 0; i < size_t(SizeAsEnumValue); ++i) {
+    aField[IndexType(i)] = nullptr;
+  }
+}
+
+template <typename IndexType, IndexType SizeAsEnumValue, typename ValueType>
+inline void ImplCycleCollectionTraverse(
+    nsCycleCollectionTraversalCallback& aCallback,
+    mozilla::EnumeratedArray<IndexType, SizeAsEnumValue, ValueType>& aField,
+    const char* aName, uint32_t aFlags = 0) {
+  aFlags |= CycleCollectionEdgeNameArrayFlag;
+  for (size_t i = 0; i < size_t(SizeAsEnumValue); ++i) {
+    ImplCycleCollectionTraverse(aCallback, aField[IndexType(i)], aName, aFlags);
+  }
+}
+
+#endif  // EnumeratedArrayCycleCollection_h_
diff --git a/xpcom/base/ErrorList.py b/xpcom/base/ErrorList.py
new file mode 100755
index 0000000000..68059c8898
--- /dev/null
+++ b/xpcom/base/ErrorList.py
@@ -0,0 +1,1406 @@
+#!/usr/bin/env python
+from collections import OrderedDict
+
+
+class Mod:
+    """
+    A nserror module. When used with a `with` statement, binds the itself to
+    Mod.active.
+    """
+
+    active = None
+
+    def __init__(self, num):
+        self.num = num
+
+    def __enter__(self):
+        Mod.active = self
+
+    def __exit__(self, _type, _value, _traceback):
+        Mod.active = None
+
+
+modules = OrderedDict()
+
+# To add error code to your module, you need to do the following:
+#
+# 1) Add a module offset code.  Add yours to the bottom of the list
+# right below this comment, adding 1.
+#
+# 2) In your module, define a header file which uses one of the
+# NE_ERROR_GENERATExxxxxx macros.  Some examples below:
+#
+#    #define NS_ERROR_MYMODULE_MYERROR1 \
+#        NS_ERROR_GENERATE(NS_ERROR_SEVERITY_ERROR,NS_ERROR_MODULE_MYMODULE,1)
+#    #define NS_ERROR_MYMODULE_MYERROR2 NS_ERROR_GENERATE_SUCCESS(NS_ERROR_MODULE_MYMODULE,2)
+#    #define NS_ERROR_MYMODULE_MYERROR3 NS_ERROR_GENERATE_FAILURE(NS_ERROR_MODULE_MYMODULE,3)
+
+# @name Standard Module Offset Code. Each Module should identify a unique number
+#       and then all errors associated with that module become offsets from the
+#       base associated with that module id. There are 16 bits of code bits for
+#       each module.
+
+modules["XPCOM"] = Mod(1)
+modules["BASE"] = Mod(2)
+modules["GFX"] = Mod(3)
+modules["WIDGET"] = Mod(4)
+modules["CALENDAR"] = Mod(5)
+modules["NETWORK"] = Mod(6)
+modules["PLUGINS"] = Mod(7)
+modules["LAYOUT"] = Mod(8)
+modules["HTMLPARSER"] = Mod(9)
+modules["RDF"] = Mod(10)
+modules["UCONV"] = Mod(11)
+modules["REG"] = Mod(12)
+modules["FILES"] = Mod(13)
+modules["DOM"] = Mod(14)
+modules["IMGLIB"] = Mod(15)
+modules["MAILNEWS"] = Mod(16)
+modules["EDITOR"] = Mod(17)
+modules["XPCONNECT"] = Mod(18)
+modules["PROFILE"] = Mod(19)
+modules["LDAP"] = Mod(20)
+modules["SECURITY"] = Mod(21)
+modules["DOM_XPATH"] = Mod(22)
+# Mod(23) used to be NS_ERROR_MODULE_DOM_RANGE (see bug 711047)
+modules["URILOADER"] = Mod(24)
+modules["CONTENT"] = Mod(25)
+modules["PYXPCOM"] = Mod(26)
+modules["XSLT"] = Mod(27)
+modules["IPC"] = Mod(28)
+modules["SVG"] = Mod(29)
+modules["STORAGE"] = Mod(30)
+modules["SCHEMA"] = Mod(31)
+modules["DOM_FILE"] = Mod(32)
+modules["DOM_INDEXEDDB"] = Mod(33)
+modules["DOM_FILEHANDLE"] = Mod(34)
+modules["SIGNED_JAR"] = Mod(35)
+modules["DOM_FILESYSTEM"] = Mod(36)
+modules["DOM_BLUETOOTH"] = Mod(37)
+modules["SIGNED_APP"] = Mod(38)
+modules["DOM_ANIM"] = Mod(39)
+modules["DOM_PUSH"] = Mod(40)
+modules["DOM_MEDIA"] = Mod(41)
+modules["URL_CLASSIFIER"] = Mod(42)
+# ErrorResult gets its own module to reduce the chance of someone accidentally
+# defining an error code matching one of the ErrorResult ones.
+modules["ERRORRESULT"] = Mod(43)
+# Win32 system error codes, which are not mapped to a specific other value,
+# see Bug 1686041.
+modules["WIN32"] = Mod(44)
+
+# NS_ERROR_MODULE_GENERAL should be used by modules that do not
+# care if return code values overlap. Callers of methods that
+# return such codes should be aware that they are not
+# globally unique. Implementors should be careful about blindly
+# returning codes from other modules that might also use
+# the generic base.
+modules["GENERAL"] = Mod(51)
+
+MODULE_BASE_OFFSET = 0x45
+
+NS_ERROR_SEVERITY_SUCCESS = 0
+NS_ERROR_SEVERITY_ERROR = 1
+
+
+def SUCCESS_OR_FAILURE(sev, module, code):
+    return (sev << 31) | ((module + MODULE_BASE_OFFSET) << 16) | code
+
+
+def FAILURE(code):
+    return SUCCESS_OR_FAILURE(NS_ERROR_SEVERITY_ERROR, Mod.active.num, code)
+
+
+def SUCCESS(code):
+    return SUCCESS_OR_FAILURE(NS_ERROR_SEVERITY_SUCCESS, Mod.active.num, code)
+
+
+# Errors is an ordered dictionary, so that we can recover the order in which
+# they were defined. This is important for determining which name is the
+# canonical name for an error code.
+errors = OrderedDict()
+
+# Standard "it worked" return value
+errors["NS_OK"] = 0
+
+# =======================================================================
+# Core errors, not part of any modules
+# =======================================================================
+errors["NS_ERROR_BASE"] = 0xC1F30000
+# Returned when an instance is not initialized
+errors["NS_ERROR_NOT_INITIALIZED"] = errors["NS_ERROR_BASE"] + 1
+# Returned when an instance is already initialized
+errors["NS_ERROR_ALREADY_INITIALIZED"] = errors["NS_ERROR_BASE"] + 2
+# Returned by a not implemented function
+errors["NS_ERROR_NOT_IMPLEMENTED"] = 0x80004001
+# Returned when a given interface is not supported.
+errors["NS_NOINTERFACE"] = 0x80004002
+errors["NS_ERROR_NO_INTERFACE"] = errors["NS_NOINTERFACE"]
+# Returned when a function aborts
+errors["NS_ERROR_ABORT"] = 0x80004004
+# Returned when a function fails
+errors["NS_ERROR_FAILURE"] = 0x80004005
+# Returned when an unexpected error occurs
+errors["NS_ERROR_UNEXPECTED"] = 0x8000FFFF
+# Returned when a memory allocation fails
+errors["NS_ERROR_OUT_OF_MEMORY"] = 0x8007000E
+# Returned when an illegal value is passed
+errors["NS_ERROR_ILLEGAL_VALUE"] = 0x80070057
+errors["NS_ERROR_INVALID_ARG"] = errors["NS_ERROR_ILLEGAL_VALUE"]
+errors["NS_ERROR_INVALID_POINTER"] = errors["NS_ERROR_INVALID_ARG"]
+errors["NS_ERROR_NULL_POINTER"] = errors["NS_ERROR_INVALID_ARG"]
+# Returned when an operation can't complete due to an unavailable resource
+errors["NS_ERROR_NOT_AVAILABLE"] = 0x80040111
+# Returned when a class is not registered
+errors["NS_ERROR_FACTORY_NOT_REGISTERED"] = 0x80040154
+# Returned when a class cannot be registered, but may be tried again later
+errors["NS_ERROR_FACTORY_REGISTER_AGAIN"] = 0x80040155
+# Returned when a dynamically loaded factory couldn't be found
+errors["NS_ERROR_FACTORY_NOT_LOADED"] = 0x800401F8
+# Returned when a factory doesn't support signatures
+errors["NS_ERROR_FACTORY_NO_SIGNATURE_SUPPORT"] = errors["NS_ERROR_BASE"] + 0x101
+# Returned when a factory already is registered
+errors["NS_ERROR_FACTORY_EXISTS"] = errors["NS_ERROR_BASE"] + 0x100
+
+
+# =======================================================================
+# 1: NS_ERROR_MODULE_XPCOM
+# =======================================================================
+with modules["XPCOM"]:
+    # Result codes used by nsIVariant
+    errors["NS_ERROR_CANNOT_CONVERT_DATA"] = FAILURE(1)
+    errors["NS_ERROR_OBJECT_IS_IMMUTABLE"] = FAILURE(2)
+    errors["NS_ERROR_LOSS_OF_SIGNIFICANT_DATA"] = FAILURE(3)
+    # Result code used by nsIThreadManager
+    errors["NS_ERROR_NOT_SAME_THREAD"] = FAILURE(4)
+    # Various operations are not permitted during XPCOM shutdown and will fail
+    # with this exception.
+    errors["NS_ERROR_ILLEGAL_DURING_SHUTDOWN"] = FAILURE(30)
+    errors["NS_ERROR_SERVICE_NOT_AVAILABLE"] = FAILURE(22)
+
+    errors["NS_SUCCESS_LOSS_OF_INSIGNIFICANT_DATA"] = SUCCESS(1)
+    # Used by nsCycleCollectionParticipant
+    errors["NS_SUCCESS_INTERRUPTED_TRAVERSE"] = SUCCESS(2)
+
+# =======================================================================
+# 2: NS_ERROR_MODULE_BASE
+# =======================================================================
+with modules["BASE"]:
+    # I/O Errors
+
+    #  Stream closed
+    errors["NS_BASE_STREAM_CLOSED"] = FAILURE(2)
+    #  Error from the operating system
+    errors["NS_BASE_STREAM_OSERROR"] = FAILURE(3)
+    #  Illegal arguments
+    errors["NS_BASE_STREAM_ILLEGAL_ARGS"] = FAILURE(4)
+    #  For unichar streams
+    errors["NS_BASE_STREAM_NO_CONVERTER"] = FAILURE(5)
+    #  For unichar streams
+    errors["NS_BASE_STREAM_BAD_CONVERSION"] = FAILURE(6)
+    errors["NS_BASE_STREAM_WOULD_BLOCK"] = FAILURE(7)
+
+
+# =======================================================================
+# 3: NS_ERROR_MODULE_GFX
+# =======================================================================
+with modules["GFX"]:
+    # no printer available (e.g. cannot find _any_ printer)
+    errors["NS_ERROR_GFX_PRINTER_NO_PRINTER_AVAILABLE"] = FAILURE(1)
+    # _specified_ (by name) printer not found
+    errors["NS_ERROR_GFX_PRINTER_NAME_NOT_FOUND"] = FAILURE(2)
+    # print-to-file: could not open output file
+    errors["NS_ERROR_GFX_PRINTER_COULD_NOT_OPEN_FILE"] = FAILURE(3)
+    # print: starting document
+    errors["NS_ERROR_GFX_PRINTER_STARTDOC"] = FAILURE(4)
+    # print: ending document
+    errors["NS_ERROR_GFX_PRINTER_ENDDOC"] = FAILURE(5)
+    # print: starting page
+    errors["NS_ERROR_GFX_PRINTER_STARTPAGE"] = FAILURE(6)
+    # The document is still being loaded
+    errors["NS_ERROR_GFX_PRINTER_DOC_IS_BUSY"] = FAILURE(7)
+
+    # Font cmap is strangely structured - avoid this font!
+    errors["NS_ERROR_GFX_CMAP_MALFORMED"] = FAILURE(51)
+
+
+# =======================================================================
+# 4:  NS_ERROR_MODULE_WIDGET
+# =======================================================================
+with modules["WIDGET"]:
+    # Used by:
+    #   - nsIWidget::NotifyIME()
+    # Returned when the notification or the event is handled and it's consumed
+    # by somebody.
+    errors["NS_SUCCESS_EVENT_CONSUMED"] = SUCCESS(1)
+
+
+# =======================================================================
+# 6: NS_ERROR_MODULE_NETWORK
+# =======================================================================
+with modules["NETWORK"]:
+    # General async request error codes:
+    #
+    # These error codes are commonly passed through callback methods to indicate
+    # the status of some requested async request.
+    #
+    # For example, see nsIRequestObserver::onStopRequest.
+
+    # The async request completed successfully.
+    errors["NS_BINDING_SUCCEEDED"] = errors["NS_OK"]
+
+    # The async request failed for some unknown reason.
+    errors["NS_BINDING_FAILED"] = FAILURE(1)
+    # The async request failed because it was aborted by some user action.
+    errors["NS_BINDING_ABORTED"] = FAILURE(2)
+    # The async request has been "redirected" to a different async request.
+    # (e.g., an HTTP redirect occurred).
+    #
+    # This error code is used with load groups to notify the load group observer
+    # when a request in the load group is redirected to another request.
+    errors["NS_BINDING_REDIRECTED"] = FAILURE(3)
+    # The async request has been "retargeted" to a different "handler."
+    #
+    # This error code is used with load groups to notify the load group observer
+    # when a request in the load group is removed from the load group and added
+    # to a different load group.
+    errors["NS_BINDING_RETARGETED"] = FAILURE(4)
+
+    # Miscellaneous error codes: These errors are not typically passed via
+    # onStopRequest.
+
+    # The URI is malformed.
+    errors["NS_ERROR_MALFORMED_URI"] = FAILURE(10)
+    # The requested action could not be completed while the object is busy.
+    # Implementations of nsIChannel::asyncOpen will commonly return this error
+    # if the channel has already been opened (and has not yet been closed).
+    errors["NS_ERROR_IN_PROGRESS"] = FAILURE(15)
+    # Returned from nsIChannel::asyncOpen to indicate that OnDataAvailable will
+    # not be called because there is no content available.  This is used by
+    # helper app style protocols (e.g., mailto).  XXX perhaps this should be a
+    # success code.
+    errors["NS_ERROR_NO_CONTENT"] = FAILURE(17)
+    # The URI scheme corresponds to an unknown protocol handler.
+    errors["NS_ERROR_UNKNOWN_PROTOCOL"] = FAILURE(18)
+    # The content encoding of the source document was incorrect, for example
+    # returning a plain HTML document advertised as Content-Encoding: gzip
+    errors["NS_ERROR_INVALID_CONTENT_ENCODING"] = FAILURE(27)
+    # A transport level corruption was found in the source document. for example
+    # a document with a calculated checksum that does not match the Content-MD5
+    # http header.
+    errors["NS_ERROR_CORRUPTED_CONTENT"] = FAILURE(29)
+    # A content signature verification failed for some reason. This can be either
+    # an actual verification error, or any other error that led to the fact that
+    # a content signature that was expected couldn't be verified.
+    errors["NS_ERROR_INVALID_SIGNATURE"] = FAILURE(58)
+    # While parsing for the first component of a header field using syntax as in
+    # Content-Disposition or Content-Type, the first component was found to be
+    # empty, such as in: Content-Disposition: ; filename=foo
+    errors["NS_ERROR_FIRST_HEADER_FIELD_COMPONENT_EMPTY"] = FAILURE(34)
+    # Returned from nsIChannel::asyncOpen when trying to open the channel again
+    # (reopening is not supported).
+    errors["NS_ERROR_ALREADY_OPENED"] = FAILURE(73)
+
+    # Connectivity error codes:
+
+    # The connection is already established.  XXX unused - consider removing.
+    errors["NS_ERROR_ALREADY_CONNECTED"] = FAILURE(11)
+    # The connection does not exist.  XXX unused - consider removing.
+    errors["NS_ERROR_NOT_CONNECTED"] = FAILURE(12)
+    # The connection attempt failed, for example, because no server was
+    # listening at specified host:port.
+    errors["NS_ERROR_CONNECTION_REFUSED"] = FAILURE(13)
+    # The connection was lost due to a timeout error.
+    errors["NS_ERROR_NET_TIMEOUT"] = FAILURE(14)
+    # The requested action could not be completed while the networking library
+    # is in the offline state.
+    errors["NS_ERROR_OFFLINE"] = FAILURE(16)
+    # The requested action was prohibited because it would have caused the
+    # networking library to establish a connection to an unsafe or otherwise
+    # banned port.
+    errors["NS_ERROR_PORT_ACCESS_NOT_ALLOWED"] = FAILURE(19)
+    # The connection was established, but no data was ever received.
+    errors["NS_ERROR_NET_RESET"] = FAILURE(20)
+    # The connection was established, but the data transfer was interrupted.
+    errors["NS_ERROR_NET_INTERRUPT"] = FAILURE(71)
+    # The connection attempt to a proxy failed.
+    errors["NS_ERROR_PROXY_CONNECTION_REFUSED"] = FAILURE(72)
+    # A transfer was only partially done when it completed.
+    errors["NS_ERROR_NET_PARTIAL_TRANSFER"] = FAILURE(76)
+    # HTTP/2 detected invalid TLS configuration
+    errors["NS_ERROR_NET_INADEQUATE_SECURITY"] = FAILURE(82)
+    # HTTP/2 sent a GOAWAY
+    errors["NS_ERROR_NET_HTTP2_SENT_GOAWAY"] = FAILURE(83)
+    # HTTP/3 protocol internal error
+    errors["NS_ERROR_NET_HTTP3_PROTOCOL_ERROR"] = FAILURE(84)
+    # A timeout error code that can be used to cancel requests.
+    errors["NS_ERROR_NET_TIMEOUT_EXTERNAL"] = FAILURE(85)
+    # An error related to HTTPS-only mode
+    errors["NS_ERROR_HTTPS_ONLY"] = FAILURE(86)
+    # A WebSocket connection is failed.
+    errors["NS_ERROR_WEBSOCKET_CONNECTION_REFUSED"] = FAILURE(87)
+    # A connection to a non local address is refused because
+    # xpc::AreNonLocalConnectionsDisabled() returns true.
+    errors["NS_ERROR_NON_LOCAL_CONNECTION_REFUSED"] = FAILURE(88)
+    # Connection to a sts host without a hsts header.
+    errors["NS_ERROR_BAD_HSTS_CERT"] = FAILURE(89)
+
+    # XXX really need to better rationalize these error codes.  are consumers of
+    # necko really expected to know how to discern the meaning of these??
+    # This request is not resumable, but it was tried to resume it, or to
+    # request resume-specific data.
+    errors["NS_ERROR_NOT_RESUMABLE"] = FAILURE(25)
+    # The request failed as a result of a detected redirection loop.
+    errors["NS_ERROR_REDIRECT_LOOP"] = FAILURE(31)
+    # It was attempted to resume the request, but the entity has changed in the
+    # meantime.
+    errors["NS_ERROR_ENTITY_CHANGED"] = FAILURE(32)
+    # The request failed because the content type returned by the server was not
+    # a type expected by the channel (for nested channels such as the JAR
+    # channel).
+    errors["NS_ERROR_UNSAFE_CONTENT_TYPE"] = FAILURE(74)
+    # The request resulted in an error page being displayed.
+    errors["NS_ERROR_LOAD_SHOWED_ERRORPAGE"] = FAILURE(77)
+    # The request occurred in docshell that lacks a treeowner, so it is
+    # probably in the process of being torn down.
+    errors["NS_ERROR_DOCSHELL_DYING"] = FAILURE(78)
+
+    # DNS specific error codes:
+
+    # The lookup of a hostname failed.  This generally refers to the hostname
+    # from the URL being loaded.
+    errors["NS_ERROR_UNKNOWN_HOST"] = FAILURE(30)
+    # A low or medium priority DNS lookup failed because the pending queue was
+    # already full. High priorty (the default) always makes room
+    errors["NS_ERROR_DNS_LOOKUP_QUEUE_FULL"] = FAILURE(33)
+    # The lookup of a proxy hostname failed.  If a channel is configured to
+    # speak to a proxy server, then it will generate this error if the proxy
+    # hostname cannot be resolved.
+    errors["NS_ERROR_UNKNOWN_PROXY_HOST"] = FAILURE(42)
+    # This DNS error will occur when the resolver uses the Extended DNS Error
+    # option to indicate an error code for which we should not fall back to the
+    # default DNS resolver. This means the DNS failure is definitive.
+    errors["NS_ERROR_DEFINITIVE_UNKNOWN_HOST"] = FAILURE(43)
+
+    # Socket specific error codes:
+
+    # The specified socket type does not exist.
+    errors["NS_ERROR_UNKNOWN_SOCKET_TYPE"] = FAILURE(51)
+    # The specified socket type could not be created.
+    errors["NS_ERROR_SOCKET_CREATE_FAILED"] = FAILURE(52)
+    # The operating system doesn't support the given type of address.
+    errors["NS_ERROR_SOCKET_ADDRESS_NOT_SUPPORTED"] = FAILURE(53)
+    # The address to which we tried to bind the socket was busy.
+    errors["NS_ERROR_SOCKET_ADDRESS_IN_USE"] = FAILURE(54)
+
+    # Cache specific error codes:
+    errors["NS_ERROR_CACHE_KEY_NOT_FOUND"] = FAILURE(61)
+    errors["NS_ERROR_CACHE_DATA_IS_STREAM"] = FAILURE(62)
+    errors["NS_ERROR_CACHE_DATA_IS_NOT_STREAM"] = FAILURE(63)
+    errors["NS_ERROR_CACHE_WAIT_FOR_VALIDATION"] = FAILURE(64)
+    errors["NS_ERROR_CACHE_ENTRY_DOOMED"] = FAILURE(65)
+    errors["NS_ERROR_CACHE_READ_ACCESS_DENIED"] = FAILURE(66)
+    errors["NS_ERROR_CACHE_WRITE_ACCESS_DENIED"] = FAILURE(67)
+    errors["NS_ERROR_CACHE_IN_USE"] = FAILURE(68)
+    # Error passed through onStopRequest if the document could not be fetched
+    # from the cache.
+    errors["NS_ERROR_DOCUMENT_NOT_CACHED"] = FAILURE(70)
+
+    # Effective TLD Service specific error codes:
+
+    # The requested number of domain levels exceeds those present in the host
+    # string.
+    errors["NS_ERROR_INSUFFICIENT_DOMAIN_LEVELS"] = FAILURE(80)
+    # The host string is an IP address.
+    errors["NS_ERROR_HOST_IS_IP_ADDRESS"] = FAILURE(81)
+
+    # StreamLoader specific result codes:
+
+    # Result code returned by nsIStreamLoaderObserver to indicate that the
+    # observer is taking over responsibility for the data buffer, and the loader
+    # should NOT free it.
+    errors["NS_SUCCESS_ADOPTED_DATA"] = SUCCESS(90)
+
+    # This success code may be returned by nsIAuthModule::getNextToken to
+    # indicate that the authentication is finished and thus there's no need
+    # to call getNextToken again.
+    errors["NS_SUCCESS_AUTH_FINISHED"] = SUCCESS(40)
+
+    # These are really not "results", they're statuses, used by nsITransport and
+    # friends.  This is abuse of nsresult, but we'll put up with it for now.
+    # nsITransport
+    errors["NS_NET_STATUS_READING"] = SUCCESS(8)
+    errors["NS_NET_STATUS_WRITING"] = SUCCESS(9)
+
+    # nsISocketTransport
+    errors["NS_NET_STATUS_RESOLVING_HOST"] = SUCCESS(3)
+    errors["NS_NET_STATUS_RESOLVED_HOST"] = SUCCESS(11)
+    errors["NS_NET_STATUS_CONNECTING_TO"] = SUCCESS(7)
+    errors["NS_NET_STATUS_CONNECTED_TO"] = SUCCESS(4)
+    errors["NS_NET_STATUS_TLS_HANDSHAKE_STARTING"] = SUCCESS(12)
+    errors["NS_NET_STATUS_TLS_HANDSHAKE_ENDED"] = SUCCESS(13)
+    errors["NS_NET_STATUS_SENDING_TO"] = SUCCESS(5)
+    errors["NS_NET_STATUS_WAITING_FOR"] = SUCCESS(10)
+    errors["NS_NET_STATUS_RECEIVING_FROM"] = SUCCESS(6)
+
+    # nsIInterceptedChannel
+    # Generic error for non-specific failures during service worker interception
+    errors["NS_ERROR_INTERCEPTION_FAILED"] = FAILURE(100)
+
+    errors["NS_ERROR_WEBTRANSPORT_CODE_BASE"] = FAILURE(200)
+    errors["NS_ERROR_WEBTRANSPORT_CODE_END"] = (
+        errors["NS_ERROR_WEBTRANSPORT_CODE_BASE"] + 255
+    )
+
+    # All Http proxy CONNECT response codes
+    errors["NS_ERROR_PROXY_CODE_BASE"] = FAILURE(1000)
+    # Redirection 3xx
+    errors["NS_ERROR_PROXY_MULTIPLE_CHOICES"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 300
+    errors["NS_ERROR_PROXY_MOVED_PERMANENTLY"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 301
+    )
+    errors["NS_ERROR_PROXY_FOUND"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 302
+    errors["NS_ERROR_PROXY_SEE_OTHER"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 303
+    errors["NS_ERROR_PROXY_NOT_MODIFIED"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 304
+    errors["NS_ERROR_PROXY_TEMPORARY_REDIRECT"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 307
+    )
+    errors["NS_ERROR_PROXY_PERMANENT_REDIRECT"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 308
+    )
+
+    # Client error 4xx
+    errors["NS_ERROR_PROXY_BAD_REQUEST"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 400
+    errors["NS_ERROR_PROXY_UNAUTHORIZED"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 401
+    errors["NS_ERROR_PROXY_PAYMENT_REQUIRED"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 402
+    errors["NS_ERROR_PROXY_FORBIDDEN"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 403
+    errors["NS_ERROR_PROXY_NOT_FOUND"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 404
+    errors["NS_ERROR_PROXY_METHOD_NOT_ALLOWED"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 405
+    )
+    errors["NS_ERROR_PROXY_NOT_ACCEPTABLE"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 406
+    # The proxy requires authentication; used when we can't easily propagate 407s.
+    errors["NS_ERROR_PROXY_AUTHENTICATION_FAILED"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 407
+    )
+    errors["NS_ERROR_PROXY_REQUEST_TIMEOUT"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 408
+    errors["NS_ERROR_PROXY_CONFLICT"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 409
+    errors["NS_ERROR_PROXY_GONE"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 410
+    errors["NS_ERROR_PROXY_LENGTH_REQUIRED"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 411
+    errors["NS_ERROR_PROXY_PRECONDITION_FAILED"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 412
+    )
+    errors["NS_ERROR_PROXY_REQUEST_ENTITY_TOO_LARGE"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 413
+    )
+    errors["NS_ERROR_PROXY_REQUEST_URI_TOO_LONG"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 414
+    )
+    errors["NS_ERROR_PROXY_UNSUPPORTED_MEDIA_TYPE"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 415
+    )
+    errors["NS_ERROR_PROXY_REQUESTED_RANGE_NOT_SATISFIABLE"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 416
+    )
+    errors["NS_ERROR_PROXY_EXPECTATION_FAILED"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 417
+    )
+    errors["NS_ERROR_PROXY_MISDIRECTED_REQUEST"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 421
+    )
+    errors["NS_ERROR_PROXY_TOO_EARLY"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 425
+    errors["NS_ERROR_PROXY_UPGRADE_REQUIRED"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 426
+    errors["NS_ERROR_PROXY_PRECONDITION_REQUIRED"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 428
+    )
+    # Indicates that we have sent too many requests in a given amount of time.
+    errors["NS_ERROR_PROXY_TOO_MANY_REQUESTS"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 429
+    )
+    errors["NS_ERROR_PROXY_REQUEST_HEADER_FIELDS_TOO_LARGE"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 431
+    )
+    errors["NS_ERROR_PROXY_UNAVAILABLE_FOR_LEGAL_REASONS"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 451
+    )
+
+    # Server error 5xx
+    errors["NS_ERROR_PROXY_INTERNAL_SERVER_ERROR"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 500
+    )
+    errors["NS_ERROR_PROXY_NOT_IMPLEMENTED"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 501
+    errors["NS_ERROR_PROXY_BAD_GATEWAY"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 502
+    errors["NS_ERROR_PROXY_SERVICE_UNAVAILABLE"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 503
+    )
+    # The proxy did get any response from the remote server in time.
+    errors["NS_ERROR_PROXY_GATEWAY_TIMEOUT"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 504
+    errors["NS_ERROR_PROXY_VERSION_NOT_SUPPORTED"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 505
+    )
+    errors["NS_ERROR_PROXY_VARIANT_ALSO_NEGOTIATES"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 506
+    )
+    errors["NS_ERROR_PROXY_NOT_EXTENDED"] = errors["NS_ERROR_PROXY_CODE_BASE"] + 510
+    errors["NS_ERROR_PROXY_NETWORK_AUTHENTICATION_REQUIRED"] = (
+        errors["NS_ERROR_PROXY_CODE_BASE"] + 511
+    )
+
+# =======================================================================
+# 7: NS_ERROR_MODULE_PLUGINS
+# =======================================================================
+with modules["PLUGINS"]:
+    errors["NS_ERROR_PLUGINS_PLUGINSNOTCHANGED"] = FAILURE(1000)
+    errors["NS_ERROR_PLUGIN_DISABLED"] = FAILURE(1001)
+    errors["NS_ERROR_PLUGIN_BLOCKLISTED"] = FAILURE(1002)
+    errors["NS_ERROR_PLUGIN_TIME_RANGE_NOT_SUPPORTED"] = FAILURE(1003)
+    errors["NS_ERROR_PLUGIN_CLICKTOPLAY"] = FAILURE(1004)
+
+
+# =======================================================================
+# 8: NS_ERROR_MODULE_LAYOUT
+# =======================================================================
+with modules["LAYOUT"]:
+    # Return code for SheetLoadData::VerifySheetReadyToParse
+    errors["NS_OK_PARSE_SHEET"] = SUCCESS(1)
+
+
+# =======================================================================
+# 9: NS_ERROR_MODULE_HTMLPARSER
+# =======================================================================
+with modules["HTMLPARSER"]:
+    errors["NS_ERROR_HTMLPARSER_CONTINUE"] = errors["NS_OK"]
+
+    errors["NS_ERROR_HTMLPARSER_EOF"] = FAILURE(1000)
+    errors["NS_ERROR_HTMLPARSER_UNKNOWN"] = FAILURE(1001)
+    errors["NS_ERROR_HTMLPARSER_CANTPROPAGATE"] = FAILURE(1002)
+    errors["NS_ERROR_HTMLPARSER_CONTEXTMISMATCH"] = FAILURE(1003)
+    errors["NS_ERROR_HTMLPARSER_BADFILENAME"] = FAILURE(1004)
+    errors["NS_ERROR_HTMLPARSER_BADURL"] = FAILURE(1005)
+    errors["NS_ERROR_HTMLPARSER_INVALIDPARSERCONTEXT"] = FAILURE(1006)
+    errors["NS_ERROR_HTMLPARSER_INTERRUPTED"] = FAILURE(1007)
+    errors["NS_ERROR_HTMLPARSER_BLOCK"] = FAILURE(1008)
+    errors["NS_ERROR_HTMLPARSER_BADTOKENIZER"] = FAILURE(1009)
+    errors["NS_ERROR_HTMLPARSER_BADATTRIBUTE"] = FAILURE(1010)
+    errors["NS_ERROR_HTMLPARSER_UNRESOLVEDDTD"] = FAILURE(1011)
+    errors["NS_ERROR_HTMLPARSER_MISPLACEDTABLECONTENT"] = FAILURE(1012)
+    errors["NS_ERROR_HTMLPARSER_BADDTD"] = FAILURE(1013)
+    errors["NS_ERROR_HTMLPARSER_BADCONTEXT"] = FAILURE(1014)
+    errors["NS_ERROR_HTMLPARSER_STOPPARSING"] = FAILURE(1015)
+    errors["NS_ERROR_HTMLPARSER_UNTERMINATEDSTRINGLITERAL"] = FAILURE(1016)
+    errors["NS_ERROR_HTMLPARSER_HIERARCHYTOODEEP"] = FAILURE(1017)
+    errors["NS_ERROR_HTMLPARSER_FAKE_ENDTAG"] = FAILURE(1018)
+    errors["NS_ERROR_HTMLPARSER_INVALID_COMMENT"] = FAILURE(1019)
+
+
+# =======================================================================
+# 10: NS_ERROR_MODULE_RDF
+# =======================================================================
+with modules["RDF"]:
+    # Returned from nsIRDFDataSource::Assert() and Unassert() if the assertion
+    # (or unassertion was accepted by the datasource
+    errors["NS_RDF_ASSERTION_ACCEPTED"] = errors["NS_OK"]
+    # Returned from nsIRDFDataSource::GetSource() and GetTarget() if the
+    # source/target has no value
+    errors["NS_RDF_NO_VALUE"] = SUCCESS(2)
+    # Returned from nsIRDFDataSource::Assert() and Unassert() if the assertion
+    # (or unassertion) was rejected by the datasource; i.e., the datasource was
+    # not willing to record the statement.
+    errors["NS_RDF_ASSERTION_REJECTED"] = SUCCESS(3)
+    # Return this from rdfITripleVisitor to stop cycling
+    errors["NS_RDF_STOP_VISIT"] = SUCCESS(4)
+
+
+# =======================================================================
+# 11: NS_ERROR_MODULE_UCONV
+# =======================================================================
+with modules["UCONV"]:
+    errors["NS_ERROR_UCONV_NOCONV"] = FAILURE(1)
+    errors["NS_ERROR_UDEC_ILLEGALINPUT"] = FAILURE(14)
+
+    errors["NS_OK_HAD_REPLACEMENTS"] = SUCCESS(3)
+    errors["NS_OK_UDEC_MOREINPUT"] = SUCCESS(12)
+    errors["NS_OK_UDEC_MOREOUTPUT"] = SUCCESS(13)
+    errors["NS_OK_UENC_MOREOUTPUT"] = SUCCESS(34)
+    errors["NS_ERROR_UENC_NOMAPPING"] = SUCCESS(35)
+
+    # BEGIN DEPRECATED
+    errors["NS_ERROR_ILLEGAL_INPUT"] = errors["NS_ERROR_UDEC_ILLEGALINPUT"]
+    # END DEPRECATED
+
+
+# =======================================================================
+# 13: NS_ERROR_MODULE_FILES
+# =======================================================================
+with modules["FILES"]:
+    errors["NS_ERROR_FILE_UNRECOGNIZED_PATH"] = FAILURE(1)
+    errors["NS_ERROR_FILE_UNRESOLVABLE_SYMLINK"] = FAILURE(2)
+    errors["NS_ERROR_FILE_EXECUTION_FAILED"] = FAILURE(3)
+    errors["NS_ERROR_FILE_UNKNOWN_TYPE"] = FAILURE(4)
+    errors["NS_ERROR_FILE_DESTINATION_NOT_DIR"] = FAILURE(5)
+    errors["NS_ERROR_FILE_COPY_OR_MOVE_FAILED"] = FAILURE(7)
+    errors["NS_ERROR_FILE_ALREADY_EXISTS"] = FAILURE(8)
+    errors["NS_ERROR_FILE_INVALID_PATH"] = FAILURE(9)
+    errors["NS_ERROR_FILE_CORRUPTED"] = FAILURE(11)
+    errors["NS_ERROR_FILE_NOT_DIRECTORY"] = FAILURE(12)
+    errors["NS_ERROR_FILE_IS_DIRECTORY"] = FAILURE(13)
+    errors["NS_ERROR_FILE_IS_LOCKED"] = FAILURE(14)
+    errors["NS_ERROR_FILE_TOO_BIG"] = FAILURE(15)
+    errors["NS_ERROR_FILE_NO_DEVICE_SPACE"] = FAILURE(16)
+    errors["NS_ERROR_FILE_NAME_TOO_LONG"] = FAILURE(17)
+    errors["NS_ERROR_FILE_NOT_FOUND"] = FAILURE(18)
+    errors["NS_ERROR_FILE_READ_ONLY"] = FAILURE(19)
+    errors["NS_ERROR_FILE_DIR_NOT_EMPTY"] = FAILURE(20)
+    errors["NS_ERROR_FILE_ACCESS_DENIED"] = FAILURE(21)
+    errors["NS_ERROR_FILE_FS_CORRUPTED"] = FAILURE(22)
+    errors["NS_ERROR_FILE_DEVICE_FAILURE"] = FAILURE(23)
+    errors["NS_ERROR_FILE_DEVICE_TEMPORARY_FAILURE"] = FAILURE(24)
+    errors["NS_ERROR_FILE_INVALID_HANDLE"] = FAILURE(25)
+
+    errors["NS_SUCCESS_FILE_DIRECTORY_EMPTY"] = SUCCESS(1)
+    # Result codes used by nsIDirectoryServiceProvider2
+    errors["NS_SUCCESS_AGGREGATE_RESULT"] = SUCCESS(2)
+
+
+# =======================================================================
+# 14: NS_ERROR_MODULE_DOM
+# =======================================================================
+with modules["DOM"]:
+    # XXX If you add a new DOM error code, also add an error string to
+    # dom/base/domerr.msg
+
+    # Standard DOM error codes: http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html
+    errors["NS_ERROR_DOM_INDEX_SIZE_ERR"] = FAILURE(1)
+    errors["NS_ERROR_DOM_HIERARCHY_REQUEST_ERR"] = FAILURE(3)
+    errors["NS_ERROR_DOM_WRONG_DOCUMENT_ERR"] = FAILURE(4)
+    errors["NS_ERROR_DOM_INVALID_CHARACTER_ERR"] = FAILURE(5)
+    errors["NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR"] = FAILURE(7)
+    errors["NS_ERROR_DOM_NOT_FOUND_ERR"] = FAILURE(8)
+    errors["NS_ERROR_DOM_NOT_SUPPORTED_ERR"] = FAILURE(9)
+    errors["NS_ERROR_DOM_INUSE_ATTRIBUTE_ERR"] = FAILURE(10)
+    errors["NS_ERROR_DOM_INVALID_STATE_ERR"] = FAILURE(11)
+    errors["NS_ERROR_DOM_SYNTAX_ERR"] = FAILURE(12)
+    errors["NS_ERROR_DOM_INVALID_MODIFICATION_ERR"] = FAILURE(13)
+    errors["NS_ERROR_DOM_NAMESPACE_ERR"] = FAILURE(14)
+    errors["NS_ERROR_DOM_INVALID_ACCESS_ERR"] = FAILURE(15)
+    errors["NS_ERROR_DOM_TYPE_MISMATCH_ERR"] = FAILURE(17)
+    errors["NS_ERROR_DOM_SECURITY_ERR"] = FAILURE(18)
+    errors["NS_ERROR_DOM_NETWORK_ERR"] = FAILURE(19)
+    errors["NS_ERROR_DOM_ABORT_ERR"] = FAILURE(20)
+    errors["NS_ERROR_DOM_URL_MISMATCH_ERR"] = FAILURE(21)
+    errors["NS_ERROR_DOM_QUOTA_EXCEEDED_ERR"] = FAILURE(22)
+    errors["NS_ERROR_DOM_TIMEOUT_ERR"] = FAILURE(23)
+    errors["NS_ERROR_DOM_INVALID_NODE_TYPE_ERR"] = FAILURE(24)
+    errors["NS_ERROR_DOM_DATA_CLONE_ERR"] = FAILURE(25)
+    # StringEncoding API errors from http://wiki.whatwg.org/wiki/StringEncoding
+    errors["NS_ERROR_DOM_ENCODING_NOT_SUPPORTED_ERR"] = FAILURE(28)
+    # WebCrypto API errors from http://www.w3.org/TR/WebCryptoAPI/
+    errors["NS_ERROR_DOM_UNKNOWN_ERR"] = FAILURE(30)
+    errors["NS_ERROR_DOM_DATA_ERR"] = FAILURE(31)
+    errors["NS_ERROR_DOM_OPERATION_ERR"] = FAILURE(32)
+    # https://heycam.github.io/webidl/#notallowederror
+    errors["NS_ERROR_DOM_NOT_ALLOWED_ERR"] = FAILURE(33)
+    # DOM error codes defined by us
+    errors["NS_ERROR_DOM_WRONG_TYPE_ERR"] = FAILURE(1002)
+    errors["NS_ERROR_DOM_NOT_NUMBER_ERR"] = FAILURE(1005)
+    errors["NS_ERROR_DOM_PROP_ACCESS_DENIED"] = FAILURE(1010)
+    errors["NS_ERROR_DOM_XPCONNECT_ACCESS_DENIED"] = FAILURE(1011)
+    errors["NS_ERROR_DOM_BAD_URI"] = FAILURE(1012)
+    errors["NS_ERROR_DOM_RETVAL_UNDEFINED"] = FAILURE(1013)
+
+    # A way to represent uncatchable exceptions
+    errors["NS_ERROR_UNCATCHABLE_EXCEPTION"] = FAILURE(1015)
+
+    errors["NS_ERROR_DOM_MALFORMED_URI"] = FAILURE(1016)
+    errors["NS_ERROR_DOM_INVALID_HEADER_NAME"] = FAILURE(1017)
+
+    errors["NS_ERROR_DOM_INVALID_STATE_XHR_HAS_INVALID_CONTEXT"] = FAILURE(1018)
+
+    # When manipulating the bytecode cache with the JS API, some transcoding
+    # errors, such as a different bytecode format can cause failures of the
+    # decoding process.
+    errors["NS_ERROR_DOM_JS_DECODING_ERROR"] = FAILURE(1026)
+
+    # Image decode errors.
+    errors["NS_ERROR_DOM_IMAGE_INACTIVE_DOCUMENT"] = FAILURE(1027)
+    errors["NS_ERROR_DOM_IMAGE_INVALID_REQUEST"] = FAILURE(1028)
+    errors["NS_ERROR_DOM_IMAGE_BROKEN"] = FAILURE(1029)
+
+    # Used to indicate that a resource with the Cross-Origin-Resource-Policy
+    # response header set failed the origin check.
+    # https://fetch.spec.whatwg.org/#cross-origin-resource-policy-header
+    errors["NS_ERROR_DOM_CORP_FAILED"] = FAILURE(1036)
+
+    # Used to indicate that a URI may not be loaded into a cross-origin
+    # context.
+    errors["NS_ERROR_DOM_BAD_CROSS_ORIGIN_URI"] = FAILURE(1037)
+
+    # The request failed because there are too many recursive iframes or
+    # objects being loaded.
+    errors["NS_ERROR_RECURSIVE_DOCUMENT_LOAD"] = FAILURE(1038)
+
+    # WebExtension content script may not load this URL.
+    errors["NS_ERROR_DOM_WEBEXT_CONTENT_SCRIPT_URI"] = FAILURE(1039)
+
+    # Used to indicate that a resource load was blocked because of the
+    # Cross-Origin-Embedder-Policy response header.
+    # https://html.spec.whatwg.org/multipage/origin.html#coep
+    errors["NS_ERROR_DOM_COEP_FAILED"] = FAILURE(1040)
+
+    # Used to indicate that a resource load was blocked because of the
+    # Cross-Origin-Opener-Policy response header.
+    # https://html.spec.whatwg.org/multipage/origin.html#cross-origin-opener-policies
+    errors["NS_ERROR_DOM_COOP_FAILED"] = FAILURE(1041)
+
+    # May be used to indicate when e.g. setting a property value didn't
+    # actually change the value, like for obj.foo = "bar"; obj.foo = "bar";
+    # the second assignment throws NS_SUCCESS_DOM_NO_OPERATION.
+    errors["NS_SUCCESS_DOM_NO_OPERATION"] = SUCCESS(1)
+
+    # A success code that indicates that evaluating a string of JS went
+    # just fine except it threw an exception. Only for legacy use by
+    # nsJSUtils.
+    errors["NS_SUCCESS_DOM_SCRIPT_EVALUATION_THREW"] = SUCCESS(2)
+
+    # A success code that indicates that evaluating a string of JS went
+    # just fine except it was killed by an uncatchable exception.
+    # Only for legacy use by nsJSUtils.
+    errors["NS_SUCCESS_DOM_SCRIPT_EVALUATION_THREW_UNCATCHABLE"] = SUCCESS(3)
+
+
+# =======================================================================
+# 15: NS_ERROR_MODULE_IMGLIB
+# =======================================================================
+with modules["IMGLIB"]:
+    errors["NS_IMAGELIB_ERROR_FAILURE"] = FAILURE(5)
+    errors["NS_IMAGELIB_ERROR_NO_DECODER"] = FAILURE(6)
+    errors["NS_IMAGELIB_ERROR_NOT_FINISHED"] = FAILURE(7)
+    errors["NS_IMAGELIB_ERROR_NO_ENCODER"] = FAILURE(9)
+
+
+# =======================================================================
+# 17: NS_ERROR_MODULE_EDITOR
+# =======================================================================
+with modules["EDITOR"]:
+    errors["NS_ERROR_EDITOR_DESTROYED"] = FAILURE(1)
+
+    # An error code that indicates that the DOM tree has been modified by
+    # web app or add-on while the editor modifying the tree.  However,
+    # this shouldn't be exposed to the web because the result should've
+    # been expected by the web app.
+    errors["NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE"] = FAILURE(2)
+
+    # An error code that indicates that the edit action canceled by
+    # clipboard event listener or beforeinput event listener.  Note that
+    # don't make this as a success code since it's not check with NS_FAILED()
+    # and may keep handling the operation unexpectedly.
+    errors["NS_ERROR_EDITOR_ACTION_CANCELED"] = FAILURE(3)
+
+    # An error code that indicates that there is no editable selection ranges.
+    # E.g., Selection has no range, caret is in non-editable element,
+    # non-collapsed range crosses editing host boundaries.
+    errors["NS_ERROR_EDITOR_NO_EDITABLE_RANGE"] = FAILURE(4)
+
+    errors["NS_SUCCESS_EDITOR_ELEMENT_NOT_FOUND"] = SUCCESS(1)
+    errors["NS_SUCCESS_EDITOR_FOUND_TARGET"] = SUCCESS(2)
+
+    # If most callers ignore error except serious error (like
+    # NS_ERROR_EDITOR_DESTROYED), this success code is useful.  E.g. such
+    # callers can do:
+    # nsresult rv = Foo();
+    # if (MOZ_UNLIKELY(NS_FAILED(rv))) {
+    #   NS_WARNING("Foo() failed");
+    #   return rv;
+    # }
+    # NS_WARNING_ASSERTION(
+    #   rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+    #   "Foo() failed, but ignored");
+    errors["NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR"] = SUCCESS(3)
+
+
+# =======================================================================
+# 18: NS_ERROR_MODULE_XPCONNECT
+# =======================================================================
+with modules["XPCONNECT"]:
+    errors["NS_ERROR_XPC_NOT_ENOUGH_ARGS"] = FAILURE(1)
+    errors["NS_ERROR_XPC_NEED_OUT_OBJECT"] = FAILURE(2)
+    errors["NS_ERROR_XPC_CANT_SET_OUT_VAL"] = FAILURE(3)
+    errors["NS_ERROR_XPC_NATIVE_RETURNED_FAILURE"] = FAILURE(4)
+    errors["NS_ERROR_XPC_CANT_GET_INTERFACE_INFO"] = FAILURE(5)
+    errors["NS_ERROR_XPC_CANT_GET_PARAM_IFACE_INFO"] = FAILURE(6)
+    errors["NS_ERROR_XPC_CANT_GET_METHOD_INFO"] = FAILURE(7)
+    errors["NS_ERROR_XPC_UNEXPECTED"] = FAILURE(8)
+    errors["NS_ERROR_XPC_BAD_CONVERT_JS"] = FAILURE(9)
+    errors["NS_ERROR_XPC_BAD_CONVERT_NATIVE"] = FAILURE(10)
+    errors["NS_ERROR_XPC_BAD_CONVERT_JS_NULL_REF"] = FAILURE(11)
+    errors["NS_ERROR_XPC_BAD_OP_ON_WN_PROTO"] = FAILURE(12)
+    errors["NS_ERROR_XPC_CANT_CONVERT_WN_TO_FUN"] = FAILURE(13)
+    errors["NS_ERROR_XPC_CANT_DEFINE_PROP_ON_WN"] = FAILURE(14)
+    errors["NS_ERROR_XPC_CANT_WATCH_WN_STATIC"] = FAILURE(15)
+    errors["NS_ERROR_XPC_CANT_EXPORT_WN_STATIC"] = FAILURE(16)
+    errors["NS_ERROR_XPC_SCRIPTABLE_CALL_FAILED"] = FAILURE(17)
+    errors["NS_ERROR_XPC_SCRIPTABLE_CTOR_FAILED"] = FAILURE(18)
+    errors["NS_ERROR_XPC_CANT_CALL_WO_SCRIPTABLE"] = FAILURE(19)
+    errors["NS_ERROR_XPC_CANT_CTOR_WO_SCRIPTABLE"] = FAILURE(20)
+    errors["NS_ERROR_XPC_CI_RETURNED_FAILURE"] = FAILURE(21)
+    errors["NS_ERROR_XPC_GS_RETURNED_FAILURE"] = FAILURE(22)
+    errors["NS_ERROR_XPC_BAD_CID"] = FAILURE(23)
+    errors["NS_ERROR_XPC_BAD_IID"] = FAILURE(24)
+    errors["NS_ERROR_XPC_CANT_CREATE_WN"] = FAILURE(25)
+    errors["NS_ERROR_XPC_JS_THREW_EXCEPTION"] = FAILURE(26)
+    errors["NS_ERROR_XPC_JS_THREW_NATIVE_OBJECT"] = FAILURE(27)
+    errors["NS_ERROR_XPC_JS_THREW_JS_OBJECT"] = FAILURE(28)
+    errors["NS_ERROR_XPC_JS_THREW_NULL"] = FAILURE(29)
+    errors["NS_ERROR_XPC_JS_THREW_STRING"] = FAILURE(30)
+    errors["NS_ERROR_XPC_JS_THREW_NUMBER"] = FAILURE(31)
+    errors["NS_ERROR_XPC_JAVASCRIPT_ERROR"] = FAILURE(32)
+    errors["NS_ERROR_XPC_JAVASCRIPT_ERROR_WITH_DETAILS"] = FAILURE(33)
+    errors["NS_ERROR_XPC_CANT_CONVERT_PRIMITIVE_TO_ARRAY"] = FAILURE(34)
+    errors["NS_ERROR_XPC_CANT_CONVERT_OBJECT_TO_ARRAY"] = FAILURE(35)
+    errors["NS_ERROR_XPC_NOT_ENOUGH_ELEMENTS_IN_ARRAY"] = FAILURE(36)
+    errors["NS_ERROR_XPC_CANT_GET_ARRAY_INFO"] = FAILURE(37)
+    errors["NS_ERROR_XPC_NOT_ENOUGH_CHARS_IN_STRING"] = FAILURE(38)
+    errors["NS_ERROR_XPC_SECURITY_MANAGER_VETO"] = FAILURE(39)
+    errors["NS_ERROR_XPC_INTERFACE_NOT_SCRIPTABLE"] = FAILURE(40)
+    errors["NS_ERROR_XPC_INTERFACE_NOT_FROM_NSISUPPORTS"] = FAILURE(41)
+    errors["NS_ERROR_XPC_CANT_SET_READ_ONLY_CONSTANT"] = FAILURE(43)
+    errors["NS_ERROR_XPC_CANT_SET_READ_ONLY_ATTRIBUTE"] = FAILURE(44)
+    errors["NS_ERROR_XPC_CANT_SET_READ_ONLY_METHOD"] = FAILURE(45)
+    errors["NS_ERROR_XPC_CANT_ADD_PROP_TO_WRAPPED_NATIVE"] = FAILURE(46)
+    errors["NS_ERROR_XPC_CALL_TO_SCRIPTABLE_FAILED"] = FAILURE(47)
+    errors["NS_ERROR_XPC_JSOBJECT_HAS_NO_FUNCTION_NAMED"] = FAILURE(48)
+    errors["NS_ERROR_XPC_BAD_ID_STRING"] = FAILURE(49)
+    errors["NS_ERROR_XPC_BAD_INITIALIZER_NAME"] = FAILURE(50)
+    errors["NS_ERROR_XPC_HAS_BEEN_SHUTDOWN"] = FAILURE(51)
+    errors["NS_ERROR_XPC_CANT_MODIFY_PROP_ON_WN"] = FAILURE(52)
+    errors["NS_ERROR_XPC_BAD_CONVERT_JS_ZERO_ISNOT_NULL"] = FAILURE(53)
+    # any new errors here should have an associated entry added in xpc.msg
+
+
+# =======================================================================
+# 19: NS_ERROR_MODULE_PROFILE
+# =======================================================================
+with modules["PROFILE"]:
+    errors["NS_ERROR_LAUNCHED_CHILD_PROCESS"] = FAILURE(200)
+    errors["NS_ERROR_SHOW_PROFILE_MANAGER"] = FAILURE(201)
+    errors["NS_ERROR_DATABASE_CHANGED"] = FAILURE(202)
+
+
+# =======================================================================
+# 21: NS_ERROR_MODULE_SECURITY
+# =======================================================================
+with modules["SECURITY"]:
+    # Error code for XFO
+    errors["NS_ERROR_XFO_VIOLATION"] = FAILURE(96)
+
+    # Error code for CSP
+    errors["NS_ERROR_CSP_NAVIGATE_TO_VIOLATION"] = FAILURE(97)
+    errors["NS_ERROR_CSP_FORM_ACTION_VIOLATION"] = FAILURE(98)
+    errors["NS_ERROR_CSP_FRAME_ANCESTOR_VIOLATION"] = FAILURE(99)
+
+    # Error code for Sub-Resource Integrity
+    errors["NS_ERROR_SRI_CORRUPT"] = FAILURE(200)
+    errors["NS_ERROR_SRI_NOT_ELIGIBLE"] = FAILURE(201)
+    errors["NS_ERROR_SRI_UNEXPECTED_HASH_TYPE"] = FAILURE(202)
+    errors["NS_ERROR_SRI_IMPORT"] = FAILURE(203)
+
+    # CMS specific nsresult error codes.  Note: the numbers used here correspond
+    # to the values in nsICMSMessageErrors.idl.
+    errors["NS_ERROR_CMS_VERIFY_NOT_SIGNED"] = FAILURE(1024)
+    errors["NS_ERROR_CMS_VERIFY_NO_CONTENT_INFO"] = FAILURE(1025)
+    errors["NS_ERROR_CMS_VERIFY_BAD_DIGEST"] = FAILURE(1026)
+    errors["NS_ERROR_CMS_VERIFY_NOCERT"] = FAILURE(1028)
+    errors["NS_ERROR_CMS_VERIFY_UNTRUSTED"] = FAILURE(1029)
+    errors["NS_ERROR_CMS_VERIFY_ERROR_UNVERIFIED"] = FAILURE(1031)
+    errors["NS_ERROR_CMS_VERIFY_ERROR_PROCESSING"] = FAILURE(1032)
+    errors["NS_ERROR_CMS_VERIFY_BAD_SIGNATURE"] = FAILURE(1033)
+    errors["NS_ERROR_CMS_VERIFY_DIGEST_MISMATCH"] = FAILURE(1034)
+    errors["NS_ERROR_CMS_VERIFY_UNKNOWN_ALGO"] = FAILURE(1035)
+    errors["NS_ERROR_CMS_VERIFY_UNSUPPORTED_ALGO"] = FAILURE(1036)
+    errors["NS_ERROR_CMS_VERIFY_MALFORMED_SIGNATURE"] = FAILURE(1037)
+    errors["NS_ERROR_CMS_VERIFY_HEADER_MISMATCH"] = FAILURE(1038)
+    errors["NS_ERROR_CMS_VERIFY_NOT_YET_ATTEMPTED"] = FAILURE(1039)
+    errors["NS_ERROR_CMS_VERIFY_CERT_WITHOUT_ADDRESS"] = FAILURE(1040)
+    errors["NS_ERROR_CMS_ENCRYPT_NO_BULK_ALG"] = FAILURE(1056)
+    errors["NS_ERROR_CMS_ENCRYPT_INCOMPLETE"] = FAILURE(1057)
+
+
+# =======================================================================
+# 24: NS_ERROR_MODULE_URILOADER
+# =======================================================================
+with modules["URILOADER"]:
+    errors["NS_ERROR_WONT_HANDLE_CONTENT"] = FAILURE(1)
+    # The load has been cancelled because it was found on a malware or phishing
+    # list.
+    errors["NS_ERROR_MALWARE_URI"] = FAILURE(30)
+    errors["NS_ERROR_PHISHING_URI"] = FAILURE(31)
+    errors["NS_ERROR_TRACKING_URI"] = FAILURE(34)
+    errors["NS_ERROR_UNWANTED_URI"] = FAILURE(35)
+    errors["NS_ERROR_BLOCKED_URI"] = FAILURE(37)
+    errors["NS_ERROR_HARMFUL_URI"] = FAILURE(38)
+    errors["NS_ERROR_FINGERPRINTING_URI"] = FAILURE(41)
+    errors["NS_ERROR_CRYPTOMINING_URI"] = FAILURE(42)
+    errors["NS_ERROR_SOCIALTRACKING_URI"] = FAILURE(43)
+    errors["NS_ERROR_EMAILTRACKING_URI"] = FAILURE(44)
+    # Used when "Save Link As..." doesn't see the headers quickly enough to
+    # choose a filename.  See nsContextMenu.js.
+    errors["NS_ERROR_SAVE_LINK_AS_TIMEOUT"] = FAILURE(32)
+    # Used when the data from a channel has already been parsed and cached so it
+    # doesn't need to be reparsed from the original source.
+    errors["NS_ERROR_PARSED_DATA_CACHED"] = FAILURE(33)
+
+    # When browser.tabs.documentchannel.parent-controlled pref and SHIP
+    # are enabled and a load gets cancelled due to another one
+    # starting, the error is NS_BINDING_CANCELLED_OLD_LOAD.
+    errors["NS_BINDING_CANCELLED_OLD_LOAD"] = FAILURE(39)
+
+
+# =======================================================================
+# 25: NS_ERROR_MODULE_CONTENT
+# =======================================================================
+with modules["CONTENT"]:
+    # Error codes for content policy blocking
+    errors["NS_ERROR_CONTENT_BLOCKED"] = FAILURE(6)
+    errors["NS_ERROR_CONTENT_BLOCKED_SHOW_ALT"] = FAILURE(7)
+    # Success variations of content policy blocking
+    errors["NS_PROPTABLE_PROP_NOT_THERE"] = FAILURE(10)
+    # Error code for when the content process crashed
+    errors["NS_ERROR_CONTENT_CRASHED"] = FAILURE(16)
+    # Error code for when a subframe process crashed
+    errors["NS_ERROR_FRAME_CRASHED"] = FAILURE(14)
+    # Error code for when the content process had a different buildID than the
+    # parent
+    errors["NS_ERROR_BUILDID_MISMATCH"] = FAILURE(17)
+
+    errors["NS_PROPTABLE_PROP_OVERWRITTEN"] = SUCCESS(11)
+    # Error codes for FindBroadcaster in XULBroadcastManager.cpp
+    errors["NS_FINDBROADCASTER_NOT_FOUND"] = SUCCESS(12)
+    errors["NS_FINDBROADCASTER_FOUND"] = SUCCESS(13)
+
+
+# =======================================================================
+# 27: NS_ERROR_MODULE_XSLT
+# =======================================================================
+with modules["XSLT"]:
+    errors["NS_ERROR_XPATH_INVALID_ARG"] = errors["NS_ERROR_INVALID_ARG"]
+
+    errors["NS_ERROR_XSLT_PARSE_FAILURE"] = FAILURE(1)
+    errors["NS_ERROR_XPATH_PARSE_FAILURE"] = FAILURE(2)
+    errors["NS_ERROR_XSLT_ALREADY_SET"] = FAILURE(3)
+    errors["NS_ERROR_XSLT_EXECUTION_FAILURE"] = FAILURE(4)
+    errors["NS_ERROR_XPATH_UNKNOWN_FUNCTION"] = FAILURE(5)
+    errors["NS_ERROR_XSLT_BAD_RECURSION"] = FAILURE(6)
+    errors["NS_ERROR_XSLT_BAD_VALUE"] = FAILURE(7)
+    errors["NS_ERROR_XSLT_NODESET_EXPECTED"] = FAILURE(8)
+    errors["NS_ERROR_XSLT_ABORTED"] = FAILURE(9)
+    errors["NS_ERROR_XSLT_NETWORK_ERROR"] = FAILURE(10)
+    errors["NS_ERROR_XSLT_WRONG_MIME_TYPE"] = FAILURE(11)
+    errors["NS_ERROR_XSLT_LOAD_RECURSION"] = FAILURE(12)
+    errors["NS_ERROR_XPATH_BAD_ARGUMENT_COUNT"] = FAILURE(13)
+    errors["NS_ERROR_XPATH_BAD_EXTENSION_FUNCTION"] = FAILURE(14)
+    errors["NS_ERROR_XPATH_PAREN_EXPECTED"] = FAILURE(15)
+    errors["NS_ERROR_XPATH_INVALID_AXIS"] = FAILURE(16)
+    errors["NS_ERROR_XPATH_NO_NODE_TYPE_TEST"] = FAILURE(17)
+    errors["NS_ERROR_XPATH_BRACKET_EXPECTED"] = FAILURE(18)
+    errors["NS_ERROR_XPATH_INVALID_VAR_NAME"] = FAILURE(19)
+    errors["NS_ERROR_XPATH_UNEXPECTED_END"] = FAILURE(20)
+    errors["NS_ERROR_XPATH_OPERATOR_EXPECTED"] = FAILURE(21)
+    errors["NS_ERROR_XPATH_UNCLOSED_LITERAL"] = FAILURE(22)
+    errors["NS_ERROR_XPATH_BAD_COLON"] = FAILURE(23)
+    errors["NS_ERROR_XPATH_BAD_BANG"] = FAILURE(24)
+    errors["NS_ERROR_XPATH_ILLEGAL_CHAR"] = FAILURE(25)
+    errors["NS_ERROR_XPATH_BINARY_EXPECTED"] = FAILURE(26)
+    errors["NS_ERROR_XSLT_LOAD_BLOCKED_ERROR"] = FAILURE(27)
+    errors["NS_ERROR_XPATH_INVALID_EXPRESSION_EVALUATED"] = FAILURE(28)
+    errors["NS_ERROR_XPATH_UNBALANCED_CURLY_BRACE"] = FAILURE(29)
+    errors["NS_ERROR_XSLT_BAD_NODE_NAME"] = FAILURE(30)
+    errors["NS_ERROR_XSLT_VAR_ALREADY_SET"] = FAILURE(31)
+    errors["NS_ERROR_XSLT_CALL_TO_KEY_NOT_ALLOWED"] = FAILURE(32)
+
+    errors["NS_XSLT_GET_NEW_HANDLER"] = SUCCESS(1)
+
+
+# =======================================================================
+# 28: NS_ERROR_MODULE_IPC
+# =======================================================================
+with modules["IPC"]:
+    # Initial creation of a Transport object failed internally for unknown reasons.
+    errors["NS_ERROR_TRANSPORT_INIT"] = FAILURE(1)
+    # Generic error related to duplicating handle failures.
+    errors["NS_ERROR_DUPLICATE_HANDLE"] = FAILURE(2)
+    # Bridging: failure trying to open the connection to the parent
+    errors["NS_ERROR_BRIDGE_OPEN_PARENT"] = FAILURE(3)
+    # Bridging: failure trying to open the connection to the child
+    errors["NS_ERROR_BRIDGE_OPEN_CHILD"] = FAILURE(4)
+
+
+# =======================================================================
+# 30: NS_ERROR_MODULE_STORAGE
+# =======================================================================
+with modules["STORAGE"]:
+    # To add additional errors to Storage, please append entries to the bottom
+    # of the list in the following format:
+    #   NS_ERROR_STORAGE_YOUR_ERR,  FAILURE(n)
+    # where n is the next unique positive integer.  You must also add an entry
+    # to js/xpconnect/src/xpc.msg under the code block beginning with the
+    # comment 'storage related codes (from mozStorage.h)', in the following
+    # format: 'XPC_MSG_DEF(NS_ERROR_STORAGE_YOUR_ERR, "brief description of your
+    # error")'
+    errors["NS_ERROR_STORAGE_BUSY"] = FAILURE(1)
+    errors["NS_ERROR_STORAGE_IOERR"] = FAILURE(2)
+    errors["NS_ERROR_STORAGE_CONSTRAINT"] = FAILURE(3)
+
+
+# =======================================================================
+# 32: NS_ERROR_MODULE_DOM_FILE
+# =======================================================================
+with modules["DOM_FILE"]:
+    errors["NS_ERROR_DOM_FILE_NOT_FOUND_ERR"] = FAILURE(0)
+    errors["NS_ERROR_DOM_FILE_NOT_READABLE_ERR"] = FAILURE(1)
+
+
+# =======================================================================
+# 33: NS_ERROR_MODULE_DOM_INDEXEDDB
+# =======================================================================
+with modules["DOM_INDEXEDDB"]:
+    # IndexedDB error codes http://dvcs.w3.org/hg/IndexedDB/raw-file/tip/Overview.html
+    errors["NS_ERROR_DOM_INDEXEDDB_UNKNOWN_ERR"] = FAILURE(1)
+    errors["NS_ERROR_DOM_INDEXEDDB_NOT_FOUND_ERR"] = FAILURE(3)
+    errors["NS_ERROR_DOM_INDEXEDDB_CONSTRAINT_ERR"] = FAILURE(4)
+    errors["NS_ERROR_DOM_INDEXEDDB_DATA_ERR"] = FAILURE(5)
+    errors["NS_ERROR_DOM_INDEXEDDB_NOT_ALLOWED_ERR"] = FAILURE(6)
+    errors["NS_ERROR_DOM_INDEXEDDB_TRANSACTION_INACTIVE_ERR"] = FAILURE(7)
+    errors["NS_ERROR_DOM_INDEXEDDB_ABORT_ERR"] = FAILURE(8)
+    errors["NS_ERROR_DOM_INDEXEDDB_READ_ONLY_ERR"] = FAILURE(9)
+    errors["NS_ERROR_DOM_INDEXEDDB_QUOTA_ERR"] = FAILURE(11)
+    errors["NS_ERROR_DOM_INDEXEDDB_VERSION_ERR"] = FAILURE(12)
+    errors["NS_ERROR_DOM_INDEXEDDB_KEY_ERR"] = FAILURE(1002)
+    errors["NS_ERROR_DOM_INDEXEDDB_RENAME_OBJECT_STORE_ERR"] = FAILURE(1003)
+    errors["NS_ERROR_DOM_INDEXEDDB_RENAME_INDEX_ERR"] = FAILURE(1004)
+
+
+# =======================================================================
+# 34: NS_ERROR_MODULE_DOM_FILEHANDLE
+# =======================================================================
+with modules["DOM_FILEHANDLE"]:
+    errors["NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR"] = FAILURE(1)
+    errors["NS_ERROR_DOM_FILEHANDLE_NOT_ALLOWED_ERR"] = FAILURE(2)
+    errors["NS_ERROR_DOM_FILEHANDLE_INACTIVE_ERR"] = FAILURE(3)
+    errors["NS_ERROR_DOM_FILEHANDLE_ABORT_ERR"] = FAILURE(4)
+    errors["NS_ERROR_DOM_FILEHANDLE_READ_ONLY_ERR"] = FAILURE(5)
+    errors["NS_ERROR_DOM_FILEHANDLE_QUOTA_ERR"] = FAILURE(6)
+
+
+# =======================================================================
+# 35: NS_ERROR_MODULE_SIGNED_JAR
+# =======================================================================
+with modules["SIGNED_JAR"]:
+    errors["NS_ERROR_SIGNED_JAR_NOT_SIGNED"] = FAILURE(1)
+    errors["NS_ERROR_SIGNED_JAR_MODIFIED_ENTRY"] = FAILURE(2)
+    errors["NS_ERROR_SIGNED_JAR_UNSIGNED_ENTRY"] = FAILURE(3)
+    errors["NS_ERROR_SIGNED_JAR_ENTRY_MISSING"] = FAILURE(4)
+    errors["NS_ERROR_SIGNED_JAR_WRONG_SIGNATURE"] = FAILURE(5)
+    errors["NS_ERROR_SIGNED_JAR_ENTRY_TOO_LARGE"] = FAILURE(6)
+    errors["NS_ERROR_SIGNED_JAR_ENTRY_INVALID"] = FAILURE(7)
+    errors["NS_ERROR_SIGNED_JAR_MANIFEST_INVALID"] = FAILURE(8)
+
+
+# =======================================================================
+# 36: NS_ERROR_MODULE_DOM_FILESYSTEM
+# =======================================================================
+with modules["DOM_FILESYSTEM"]:
+    errors["NS_ERROR_DOM_FILESYSTEM_INVALID_PATH_ERR"] = FAILURE(1)
+    errors["NS_ERROR_DOM_FILESYSTEM_INVALID_MODIFICATION_ERR"] = FAILURE(2)
+    errors["NS_ERROR_DOM_FILESYSTEM_NO_MODIFICATION_ALLOWED_ERR"] = FAILURE(3)
+    errors["NS_ERROR_DOM_FILESYSTEM_PATH_EXISTS_ERR"] = FAILURE(4)
+    errors["NS_ERROR_DOM_FILESYSTEM_TYPE_MISMATCH_ERR"] = FAILURE(5)
+    errors["NS_ERROR_DOM_FILESYSTEM_UNKNOWN_ERR"] = FAILURE(6)
+
+
+# =======================================================================
+# 38: NS_ERROR_MODULE_SIGNED_APP
+# =======================================================================
+with modules["SIGNED_APP"]:
+    errors["NS_ERROR_SIGNED_APP_MANIFEST_INVALID"] = FAILURE(1)
+
+
+# =======================================================================
+# 40: NS_ERROR_MODULE_DOM_PUSH
+# =======================================================================
+with modules["DOM_PUSH"]:
+    errors["NS_ERROR_DOM_PUSH_DENIED_ERR"] = FAILURE(2)
+    errors["NS_ERROR_DOM_PUSH_ABORT_ERR"] = FAILURE(3)
+    errors["NS_ERROR_DOM_PUSH_SERVICE_UNREACHABLE"] = FAILURE(4)
+    errors["NS_ERROR_DOM_PUSH_INVALID_KEY_ERR"] = FAILURE(5)
+    errors["NS_ERROR_DOM_PUSH_MISMATCHED_KEY_ERR"] = FAILURE(6)
+
+
+# =======================================================================
+# 41: NS_ERROR_MODULE_DOM_MEDIA
+# =======================================================================
+with modules["DOM_MEDIA"]:
+    # HTMLMediaElement API errors from
+    # https://html.spec.whatwg.org/multipage/embedded-content.html#media-elements
+    errors["NS_ERROR_DOM_MEDIA_ABORT_ERR"] = FAILURE(1)
+    errors["NS_ERROR_DOM_MEDIA_NOT_ALLOWED_ERR"] = FAILURE(2)
+    errors["NS_ERROR_DOM_MEDIA_NOT_SUPPORTED_ERR"] = FAILURE(3)
+
+    # HTMLMediaElement internal decoding error
+    errors["NS_ERROR_DOM_MEDIA_DECODE_ERR"] = FAILURE(4)
+    errors["NS_ERROR_DOM_MEDIA_FATAL_ERR"] = FAILURE(5)
+    errors["NS_ERROR_DOM_MEDIA_METADATA_ERR"] = FAILURE(6)
+    errors["NS_ERROR_DOM_MEDIA_OVERFLOW_ERR"] = FAILURE(7)
+    errors["NS_ERROR_DOM_MEDIA_END_OF_STREAM"] = FAILURE(8)
+    errors["NS_ERROR_DOM_MEDIA_WAITING_FOR_DATA"] = FAILURE(9)
+    errors["NS_ERROR_DOM_MEDIA_CANCELED"] = FAILURE(10)
+    errors["NS_ERROR_DOM_MEDIA_MEDIASINK_ERR"] = FAILURE(11)
+    errors["NS_ERROR_DOM_MEDIA_DEMUXER_ERR"] = FAILURE(12)
+    errors["NS_ERROR_DOM_MEDIA_CDM_ERR"] = FAILURE(13)
+    errors["NS_ERROR_DOM_MEDIA_NEED_NEW_DECODER"] = FAILURE(14)
+    errors["NS_ERROR_DOM_MEDIA_INITIALIZING_DECODER"] = FAILURE(15)
+    errors["NS_ERROR_DOM_MEDIA_REMOTE_DECODER_CRASHED_RDD_OR_GPU_ERR"] = FAILURE(16)
+    errors["NS_ERROR_DOM_MEDIA_REMOTE_DECODER_CRASHED_UTILITY_ERR"] = FAILURE(17)
+    errors["NS_ERROR_DOM_MEDIA_REMOTE_DECODER_CRASHED_MF_CDM_ERR"] = FAILURE(18)
+
+    # QuotaExceededError specializations
+    errors["NS_ERROR_DOM_MEDIA_KEY_QUOTA_EXCEEDED_ERR"] = FAILURE(30)
+    errors["NS_ERROR_DOM_MEDIA_SOURCE_MAX_BUFFER_QUOTA_EXCEEDED_ERR"] = FAILURE(31)
+    errors["NS_ERROR_DOM_MEDIA_SOURCE_FULL_BUFFER_QUOTA_EXCEEDED_ERR"] = FAILURE(32)
+
+    # Internal CDM error
+    errors["NS_ERROR_DOM_MEDIA_CDM_NO_SESSION_ERR"] = FAILURE(50)
+    errors["NS_ERROR_DOM_MEDIA_CDM_SESSION_OPERATION_ERR"] = FAILURE(51)
+
+    # Internal platform-related errors
+    errors["NS_ERROR_DOM_MEDIA_CUBEB_INITIALIZATION_ERR"] = FAILURE(101)
+    errors["NS_ERROR_DOM_MEDIA_EXTERNAL_ENGINE_NOT_SUPPORTED_ERR"] = FAILURE(102)
+    errors["NS_ERROR_DOM_MEDIA_CDM_PROXY_NOT_SUPPORTED_ERR"] = FAILURE(103)
+
+# =======================================================================
+# 42: NS_ERROR_MODULE_URL_CLASSIFIER
+# =======================================================================
+with modules["URL_CLASSIFIER"]:
+    # Errors during list updates
+    errors["NS_ERROR_UC_UPDATE_UNKNOWN"] = FAILURE(1)
+    errors["NS_ERROR_UC_UPDATE_DUPLICATE_PREFIX"] = FAILURE(2)
+    errors["NS_ERROR_UC_UPDATE_INFINITE_LOOP"] = FAILURE(3)
+    errors["NS_ERROR_UC_UPDATE_WRONG_REMOVAL_INDICES"] = FAILURE(4)
+    errors["NS_ERROR_UC_UPDATE_CHECKSUM_MISMATCH"] = FAILURE(5)
+    errors["NS_ERROR_UC_UPDATE_MISSING_CHECKSUM"] = FAILURE(6)
+    errors["NS_ERROR_UC_UPDATE_SHUTDOWNING"] = FAILURE(7)
+    errors["NS_ERROR_UC_UPDATE_TABLE_NOT_FOUND"] = FAILURE(8)
+    errors["NS_ERROR_UC_UPDATE_BUILD_PREFIX_FAILURE"] = FAILURE(9)
+    errors["NS_ERROR_UC_UPDATE_FAIL_TO_WRITE_DISK"] = FAILURE(10)
+    errors["NS_ERROR_UC_UPDATE_UNEXPECTED_VERSION"] = FAILURE(11)
+
+    # Specific errors while parsing pver2/pver4 responses
+    errors["NS_ERROR_UC_PARSER_MISSING_PARAM"] = FAILURE(12)
+    errors["NS_ERROR_UC_PARSER_DECODE_FAILURE"] = FAILURE(13)
+    errors["NS_ERROR_UC_PARSER_UNKNOWN_THREAT"] = FAILURE(14)
+    errors["NS_ERROR_UC_PARSER_MISSING_VALUE"] = FAILURE(15)
+
+
+# =======================================================================
+# 43: NS_ERROR_MODULE_ERRORRESULT
+# =======================================================================
+with modules["ERRORRESULT"]:
+    # Represents a JS Value being thrown as an exception.
+    errors["NS_ERROR_INTERNAL_ERRORRESULT_JS_EXCEPTION"] = FAILURE(1)
+    # Used to indicate that we want to throw a DOMException.
+    errors["NS_ERROR_INTERNAL_ERRORRESULT_DOMEXCEPTION"] = FAILURE(2)
+    # Used to indicate that an exception is already pending on the JSContext.
+    errors["NS_ERROR_INTERNAL_ERRORRESULT_EXCEPTION_ON_JSCONTEXT"] = FAILURE(3)
+    # Used to indicate that we want to throw a TypeError.
+    errors["NS_ERROR_INTERNAL_ERRORRESULT_TYPEERROR"] = FAILURE(4)
+    # Used to indicate that we want to throw a RangeError.
+    errors["NS_ERROR_INTERNAL_ERRORRESULT_RANGEERROR"] = FAILURE(5)
+
+
+# =======================================================================
+# 51: NS_ERROR_MODULE_GENERAL
+# =======================================================================
+with modules["GENERAL"]:
+    # Error code used internally by the incremental downloader to cancel the
+    # network channel when the download is already complete.
+    errors["NS_ERROR_DOWNLOAD_COMPLETE"] = FAILURE(1)
+    # Error code used internally by the incremental downloader to cancel the
+    # network channel when the response to a range request is 200 instead of
+    # 206.
+    errors["NS_ERROR_DOWNLOAD_NOT_PARTIAL"] = FAILURE(2)
+    errors["NS_ERROR_UNORM_MOREOUTPUT"] = FAILURE(33)
+
+    errors["NS_ERROR_DOCSHELL_REQUEST_REJECTED"] = FAILURE(1001)
+    # This is needed for displaying an error message when navigation is
+    # attempted on a document when printing The value arbitrary as long as it
+    # doesn't conflict with any of the other values in the errors in
+    # DisplayLoadError
+    errors["NS_ERROR_DOCUMENT_IS_PRINTMODE"] = FAILURE(2001)
+
+    errors["NS_SUCCESS_DONT_FIXUP"] = SUCCESS(1)
+    # This success code may be returned by nsIAppStartup::Run to indicate that
+    # the application should be restarted.  This condition corresponds to the
+    # case in which nsIAppStartup::Quit was called with the eRestart flag.
+    errors["NS_SUCCESS_RESTART_APP"] = SUCCESS(1)
+
+    # a11y
+    # raised when current pivot's position is needed but it's not in the tree
+    errors["NS_ERROR_NOT_IN_TREE"] = FAILURE(38)
+
+    # see nsTextEquivUtils
+    errors["NS_OK_NO_NAME_CLAUSE_HANDLED"] = SUCCESS(34)
+
+    # Error code used to indicate that functionality has been blocked by the
+    # Policy Manager
+    errors["NS_ERROR_BLOCKED_BY_POLICY"] = FAILURE(3)
+
+
+# ============================================================================
+# Write out the resulting module declarations to C++ and rust files
+# ============================================================================
+
+
+def error_list_h(output):
+    output.write(
+        """
+/* THIS FILE IS GENERATED BY ErrorList.py - DO NOT EDIT */
+
+#ifndef ErrorList_h__
+#define ErrorList_h__
+
+#include <stdint.h>
+
+"""
+    )
+
+    output.write("#define NS_ERROR_MODULE_BASE_OFFSET {}\n".format(MODULE_BASE_OFFSET))
+
+    for mod, val in modules.items():
+        output.write("#define NS_ERROR_MODULE_{} {}\n".format(mod, val.num))
+
+    items = []
+    for error, val in errors.items():
+        items.append("  {} = 0x{:X}".format(error, val))
+    output.write(
+        """
+enum class nsresult : uint32_t
+{{
+{}
+}};
+
+""".format(
+            ",\n".join(items)
+        )
+    )
+
+    items = []
+    for error, val in errors.items():
+        items.append("  {0} = nsresult::{0}".format(error))
+
+    output.write(
+        """
+const nsresult
+{}
+;
+
+#endif // ErrorList_h__
+""".format(
+            ",\n".join(items)
+        )
+    )
+
+
+def error_names_internal_h(output):
+    """Generate ErrorNamesInternal.h, which is a header file declaring one
+    function, const char* GetErrorNameInternal(nsresult). This method is not
+    intended to be used by consumer code, which should instead call
+    GetErrorName in ErrorNames.h."""
+
+    output.write(
+        """
+/* THIS FILE IS GENERATED BY ErrorList.py - DO NOT EDIT */
+
+#ifndef ErrorNamesInternal_h__
+#define ErrorNamesInternal_h__
+
+#include "ErrorNames.h"
+
+namespace {
+
+const char*
+GetErrorNameInternal(nsresult rv)
+{
+  switch (rv) {
+"""
+    )
+
+    # NOTE: Making sure we don't write out duplicate values is important as
+    # we're using a switch statement to implement this.
+    seen = set()
+    for error, val in errors.items():
+        if val not in seen:
+            output.write('  case nsresult::{0}: return "{0}";\n'.format(error))
+        seen.add(val)
+
+    output.write(
+        """
+  default: return nullptr;
+  }
+} // GetErrorNameInternal
+
+} // namespace
+
+#endif // ErrorNamesInternal_h__
+"""
+    )
+
+
+def error_list_rs(output):
+    output.write(
+        """
+/* THIS FILE IS GENERATED BY ErrorList.py - DO NOT EDIT */
+
+use super::nsresult;
+
+"""
+    )
+
+    output.write(
+        "pub const NS_ERROR_MODULE_BASE_OFFSET: nsresult = nsresult({});\n".format(
+            MODULE_BASE_OFFSET
+        )
+    )
+
+    for mod, val in modules.items():
+        output.write(
+            "pub const NS_ERROR_MODULE_{}: nsresult = nsresult({});\n".format(
+                mod, val.num
+            )
+        )
+
+    for error, val in errors.items():
+        output.write("pub const {}: nsresult = nsresult(0x{:X});\n".format(error, val))
+
+
+def gen_jinja(output, input_filename):
+    # This is used to generate Java code for error lists, and can be expanded to
+    # other required contexts in the future if desired.
+    import os
+
+    from jinja2 import Environment, FileSystemLoader, StrictUndefined
+
+    # FileSystemLoader requires the path to the directory containing templates,
+    # not the file name of the template itself.
+    (path, leaf) = os.path.split(input_filename)
+    env = Environment(
+        loader=FileSystemLoader(path, encoding="utf-8"),
+        undefined=StrictUndefined,
+    )
+    tpl = env.get_template(leaf)
+
+    context = {
+        "MODULE_BASE_OFFSET": MODULE_BASE_OFFSET,
+        "modules": ((mod, val.num) for mod, val in modules.items()),
+        "errors": errors.items(),
+    }
+
+    tpl.stream(context).dump(output, encoding="utf-8")
diff --git a/xpcom/base/ErrorNames.cpp b/xpcom/base/ErrorNames.cpp
new file mode 100644
index 0000000000..42401aa860
--- /dev/null
+++ b/xpcom/base/ErrorNames.cpp
@@ -0,0 +1,78 @@
+/* -*- 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 "mozilla/ArrayUtils.h"
+#include "mozilla/ErrorNames.h"
+#include "nsString.h"
+#include "prerror.h"
+#include "MainThreadUtils.h"
+
+// Get the GetErrorNameInternal method
+#include "ErrorNamesInternal.h"
+
+namespace mozilla {
+
+const char* GetStaticErrorName(nsresult rv) { return GetErrorNameInternal(rv); }
+
+void GetErrorName(nsresult rv, nsACString& name) {
+  if (const char* errorName = GetErrorNameInternal(rv)) {
+    name.AssignASCII(errorName);
+    return;
+  }
+
+  bool isSecurityError = NS_ERROR_GET_MODULE(rv) == NS_ERROR_MODULE_SECURITY;
+
+  // NS_ERROR_MODULE_SECURITY is the only module that is "allowed" to
+  // synthesize nsresult error codes that are not listed in ErrorList.h. (The
+  // NS_ERROR_MODULE_SECURITY error codes are synthesized from NSPR error
+  // codes.)
+  MOZ_ASSERT(isSecurityError);
+
+  if (NS_SUCCEEDED(rv)) {
+    name.AssignLiteral("NS_ERROR_GENERATE_SUCCESS(");
+  } else {
+    name.AssignLiteral("NS_ERROR_GENERATE_FAILURE(");
+  }
+
+  if (isSecurityError) {
+    name.AppendLiteral("NS_ERROR_MODULE_SECURITY");
+  } else {
+    // This should never happen given the assertion above, so we don't bother
+    // trying to print a symbolic name for the module here.
+    name.AppendInt(NS_ERROR_GET_MODULE(rv));
+  }
+
+  name.AppendLiteral(", ");
+
+  const char* nsprName = nullptr;
+  if (isSecurityError && NS_IsMainThread()) {
+    // Invert the logic from NSSErrorsService::GetXPCOMFromNSSError
+    PRErrorCode nsprCode = -1 * static_cast<PRErrorCode>(NS_ERROR_GET_CODE(rv));
+    nsprName = PR_ErrorToName(nsprCode);
+
+    // All NSPR error codes defined by NSPR or NSS should have a name mapping.
+    MOZ_ASSERT(nsprName);
+  }
+
+  if (nsprName) {
+    name.AppendASCII(nsprName);
+  } else {
+    name.AppendInt(NS_ERROR_GET_CODE(rv));
+  }
+
+  name.AppendLiteral(")");
+}
+
+}  // namespace mozilla
+
+extern "C" {
+
+// This is an extern "C" binding for the GetErrorName method which is used by
+// the nsresult rust bindings in xpcom/rust/nserror.
+void Gecko_GetErrorName(nsresult aRv, nsACString& aName) {
+  mozilla::GetErrorName(aRv, aName);
+}
+}
diff --git a/xpcom/base/ErrorNames.h b/xpcom/base/ErrorNames.h
new file mode 100644
index 0000000000..d209cc492b
--- /dev/null
+++ b/xpcom/base/ErrorNames.h
@@ -0,0 +1,29 @@
+/* -*- 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/. */
+
+#ifndef mozilla_ErrorNames_h
+#define mozilla_ErrorNames_h
+
+#include "nsError.h"
+#include "nsStringFwd.h"
+
+namespace mozilla {
+
+// Maps the given nsresult to its symbolic name. For example,
+// GetErrorName(NS_OK, name) will result in name == "NS_OK".
+// When the symbolic name is unknown, name will be of the form
+// "NS_ERROR_GENERATE_SUCCESS(<module>, <code>)" or
+// "NS_ERROR_GENERATE_FAILURE(<module>, <code>)".
+void GetErrorName(nsresult rv, nsACString& name);
+
+// Same as GetErrorName, except that only nsresult values with statically
+// known symbolic names are handled. For all other values, nullptr is
+// returned.
+const char* GetStaticErrorName(nsresult rv);
+
+}  // namespace mozilla
+
+#endif  // mozilla_ErrorNames_h
diff --git a/xpcom/base/GkRustUtils.cpp b/xpcom/base/GkRustUtils.cpp
new file mode 100644
index 0000000000..00d32e6f65
--- /dev/null
+++ b/xpcom/base/GkRustUtils.cpp
@@ -0,0 +1,16 @@
+/* -*- 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 "gk_rust_utils_ffi_generated.h"
+#include "GkRustUtils.h"
+
+using namespace mozilla;
+
+/* static */
+bool GkRustUtils::ParseSemVer(const nsACString& aVersion, uint64_t& aOutMajor,
+                              uint64_t& aOutMinor, uint64_t& aOutPatch) {
+  return GkRustUtils_ParseSemVer(&aVersion, &aOutMajor, &aOutMinor, &aOutPatch);
+}
diff --git a/xpcom/base/GkRustUtils.h b/xpcom/base/GkRustUtils.h
new file mode 100644
index 0000000000..b7f8c3b99c
--- /dev/null
+++ b/xpcom/base/GkRustUtils.h
@@ -0,0 +1,18 @@
+/* -*- 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/. */
+
+#ifndef __mozilla_GkRustUtils_h
+#define __mozilla_GkRustUtils_h
+
+#include "nsString.h"
+
+class GkRustUtils {
+ public:
+  static bool ParseSemVer(const nsACString& aVersion, uint64_t& aOutMajor,
+                          uint64_t& aOutMinor, uint64_t& aOutPatch);
+};
+
+#endif
diff --git a/xpcom/base/HoldDropJSObjects.cpp b/xpcom/base/HoldDropJSObjects.cpp
new file mode 100644
index 0000000000..2b3a810d89
--- /dev/null
+++ b/xpcom/base/HoldDropJSObjects.cpp
@@ -0,0 +1,53 @@
+/* -*- 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 "mozilla/HoldDropJSObjects.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/CycleCollectedJSRuntime.h"
+
+namespace mozilla {
+namespace cyclecollector {
+
+void HoldJSObjectsImpl(void* aHolder, nsScriptObjectTracer* aTracer,
+                       JS::Zone* aZone) {
+  CycleCollectedJSRuntime* rt = CycleCollectedJSRuntime::Get();
+  MOZ_ASSERT(rt, "Should have a CycleCollectedJSRuntime by now");
+  rt->AddJSHolder(aHolder, aTracer, aZone);
+}
+
+void HoldJSObjectsImpl(nsISupports* aHolder) {
+  nsXPCOMCycleCollectionParticipant* participant = nullptr;
+  CallQueryInterface(aHolder, &participant);
+  MOZ_ASSERT(participant, "Failed to QI to nsXPCOMCycleCollectionParticipant!");
+  MOZ_ASSERT(
+      participant->CheckForRightISupports(aHolder),
+      "The result of QIing a JS holder should be the same as ToSupports");
+
+  HoldJSObjectsImpl(aHolder, participant);
+}
+
+void DropJSObjectsImpl(void* aHolder) {
+  CycleCollectedJSRuntime* rt = CycleCollectedJSRuntime::Get();
+  MOZ_ASSERT(rt, "Should have a CycleCollectedJSRuntime by now");
+  rt->RemoveJSHolder(aHolder);
+}
+
+void DropJSObjectsImpl(nsISupports* aHolder) {
+#ifdef DEBUG
+  nsXPCOMCycleCollectionParticipant* participant = nullptr;
+  CallQueryInterface(aHolder, &participant);
+  MOZ_ASSERT(participant, "Failed to QI to nsXPCOMCycleCollectionParticipant!");
+  MOZ_ASSERT(
+      participant->CheckForRightISupports(aHolder),
+      "The result of QIing a JS holder should be the same as ToSupports");
+#endif
+  DropJSObjectsImpl(static_cast<void*>(aHolder));
+}
+
+}  // namespace cyclecollector
+
+}  // namespace mozilla
diff --git a/xpcom/base/HoldDropJSObjects.h b/xpcom/base/HoldDropJSObjects.h
new file mode 100644
index 0000000000..e01590208f
--- /dev/null
+++ b/xpcom/base/HoldDropJSObjects.h
@@ -0,0 +1,84 @@
+/* -*- 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/. */
+
+#ifndef mozilla_HoldDropJSObjects_h
+#define mozilla_HoldDropJSObjects_h
+
+#include <type_traits>
+#include "nsCycleCollectionNoteChild.h"
+
+class nsISupports;
+class nsScriptObjectTracer;
+class nsCycleCollectionParticipant;
+
+namespace JS {
+class Zone;
+}
+
+// Only HoldJSObjects and DropJSObjects should be called directly.
+
+namespace mozilla {
+namespace cyclecollector {
+
+void HoldJSObjectsImpl(void* aHolder, nsScriptObjectTracer* aTracer,
+                       JS::Zone* aZone = nullptr);
+void HoldJSObjectsImpl(nsISupports* aHolder);
+void DropJSObjectsImpl(void* aHolder);
+void DropJSObjectsImpl(nsISupports* aHolder);
+
+}  // namespace cyclecollector
+
+template <class T, bool isISupports = std::is_base_of<nsISupports, T>::value,
+          typename P = typename T::NS_CYCLE_COLLECTION_INNERCLASS>
+struct HoldDropJSObjectsHelper {
+  static void Hold(T* aHolder) {
+    cyclecollector::HoldJSObjectsImpl(aHolder,
+                                      NS_CYCLE_COLLECTION_PARTICIPANT(T));
+  }
+  static void Drop(T* aHolder) { cyclecollector::DropJSObjectsImpl(aHolder); }
+};
+
+template <class T>
+struct HoldDropJSObjectsHelper<T, true> {
+  static void Hold(T* aHolder) {
+    cyclecollector::HoldJSObjectsImpl(ToSupports(aHolder));
+  }
+  static void Drop(T* aHolder) {
+    cyclecollector::DropJSObjectsImpl(ToSupports(aHolder));
+  }
+};
+
+/**
+  Classes that hold strong references to JS GC things such as `JSObjects` and
+  `JS::Values` (e.g. `JS::Heap<JSObject*> mFoo;`) must use these, generally by
+  calling `HoldJSObjects(this)` and `DropJSObjects(this)` in the ctor and dtor
+  respectively.
+
+  For classes that are wrapper cached and hold no other strong references to JS
+  GC things, there's no need to call these; it will be taken care of
+  automatically by nsWrapperCache.
+**/
+template <class T>
+void HoldJSObjects(T* aHolder) {
+  static_assert(!std::is_base_of<nsCycleCollectionParticipant, T>::value,
+                "Don't call this on the CC participant but on the object that "
+                "it's for (in an Unlink implementation it's usually stored in "
+                "a variable named 'tmp').");
+  HoldDropJSObjectsHelper<T>::Hold(aHolder);
+}
+
+template <class T>
+void DropJSObjects(T* aHolder) {
+  static_assert(!std::is_base_of<nsCycleCollectionParticipant, T>::value,
+                "Don't call this on the CC participant but on the object that "
+                "it's for (in an Unlink implementation it's usually stored in "
+                "a variable named 'tmp').");
+  HoldDropJSObjectsHelper<T>::Drop(aHolder);
+}
+
+}  // namespace mozilla
+
+#endif  // mozilla_HoldDropJSObjects_h
diff --git a/xpcom/base/IntentionalCrash.h b/xpcom/base/IntentionalCrash.h
new file mode 100644
index 0000000000..3ee751f7c7
--- /dev/null
+++ b/xpcom/base/IntentionalCrash.h
@@ -0,0 +1,71 @@
+/* -*- 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/. */
+
+#ifndef mozilla_IntentionalCrash_h
+#define mozilla_IntentionalCrash_h
+
+#include <string>
+#include <sstream>
+#include <stdlib.h>
+#include <stdio.h>
+
+#ifdef XP_WIN
+#  include <process.h>
+#  define getpid _getpid
+#else
+#  include <unistd.h>
+#endif
+
+namespace mozilla {
+
+inline void NoteIntentionalCrash(const char* aProcessType, uint32_t aPid = 0) {
+// In opt builds we don't actually have the leak checking enabled, and the
+// sandbox doesn't allow writing to this path, so we just disable this
+// function's behaviour.
+#ifdef MOZ_DEBUG
+  char* f = getenv("XPCOM_MEM_BLOAT_LOG");
+  if (!f) {
+    return;
+  }
+
+  fprintf(stderr, "XPCOM_MEM_BLOAT_LOG: %s\n", f);
+
+  uint32_t processPid = aPid == 0 ? getpid() : aPid;
+
+  std::ostringstream bloatName;
+  std::string processType(aProcessType);
+  if (!processType.compare("default")) {
+    bloatName << f;
+  } else {
+    std::string bloatLog(f);
+
+    bool hasExt = false;
+    if (bloatLog.size() >= 4 &&
+        bloatLog.compare(bloatLog.size() - 4, 4, ".log", 4) == 0) {
+      hasExt = true;
+      bloatLog.erase(bloatLog.size() - 4, 4);
+    }
+
+    bloatName << bloatLog << "_" << processType << "_pid" << processPid;
+    if (hasExt) {
+      bloatName << ".log";
+    }
+  }
+
+  fprintf(stderr, "Writing to log: %s\n", bloatName.str().c_str());
+
+  FILE* processfd = fopen(bloatName.str().c_str(), "a");
+  if (processfd) {
+    fprintf(processfd, "\n==> process %d will purposefully crash\n",
+            processPid);
+    fclose(processfd);
+  }
+#endif
+}
+
+}  // namespace mozilla
+
+#endif  // mozilla_IntentionalCrash_h
diff --git a/xpcom/base/JSONStringWriteFuncs.h b/xpcom/base/JSONStringWriteFuncs.h
new file mode 100644
index 0000000000..65b688788c
--- /dev/null
+++ b/xpcom/base/JSONStringWriteFuncs.h
@@ -0,0 +1,52 @@
+/* -*- 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/. */
+
+#ifndef JSONSTRINGWRITEFUNCS_H
+#define JSONSTRINGWRITEFUNCS_H
+
+#include "mozilla/JSONWriter.h"
+#include "nsString.h"
+
+#include <type_traits>
+
+namespace mozilla {
+
+// JSONWriteFunc that writes to an owned string.
+template <typename StringType>
+class JSONStringWriteFunc final : public JSONWriteFunc {
+  static_assert(
+      !std::is_reference_v<StringType>,
+      "Use JSONStringRefWriteFunc instead to write to a referenced string");
+
+ public:
+  JSONStringWriteFunc() = default;
+
+  void Write(const Span<const char>& aStr) final { mString.Append(aStr); }
+
+  const StringType& StringCRef() const { return mString; }
+
+  StringType&& StringRRef() && { return std::move(mString); }
+
+ private:
+  StringType mString;
+};
+
+// JSONWriteFunc that writes to a given nsACString reference.
+class JSONStringRefWriteFunc final : public JSONWriteFunc {
+ public:
+  MOZ_IMPLICIT JSONStringRefWriteFunc(nsACString& aString) : mString(aString) {}
+
+  void Write(const Span<const char>& aStr) final { mString.Append(aStr); }
+
+  const nsACString& StringCRef() const { return mString; }
+
+ private:
+  nsACString& mString;
+};
+
+}  // namespace mozilla
+
+#endif  // JSONSTRINGWRITEFUNCS_H
diff --git a/xpcom/base/JSObjectHolder.cpp b/xpcom/base/JSObjectHolder.cpp
new file mode 100644
index 0000000000..5bcc3cabbf
--- /dev/null
+++ b/xpcom/base/JSObjectHolder.cpp
@@ -0,0 +1,9 @@
+/* -*- 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 "JSObjectHolder.h"
+
+NS_IMPL_ISUPPORTS(mozilla::JSObjectHolder, nsISupports)
diff --git a/xpcom/base/JSObjectHolder.h b/xpcom/base/JSObjectHolder.h
new file mode 100644
index 0000000000..d64d41e479
--- /dev/null
+++ b/xpcom/base/JSObjectHolder.h
@@ -0,0 +1,42 @@
+/* -*- 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/. */
+
+#ifndef mozilla_JSObjectHolder_h
+#define mozilla_JSObjectHolder_h
+
+#include "js/RootingAPI.h"
+#include "nsISupportsImpl.h"
+
+namespace mozilla {
+
+// This class is useful when something on one thread needs to keep alive
+// a JS Object from another thread. If they are both on the same thread, the
+// owning class should instead be made a cycle collected SCRIPT_HOLDER class.
+// This object should only be AddRefed and Released on the same thread as
+// mJSObject.
+//
+// Note that this keeps alive the JS object until it goes away, so be sure not
+// to create cycles that keep alive the holder.
+//
+// JSObjectHolder is ISupports to make it usable with
+// NS_ReleaseOnMainThread.
+class JSObjectHolder final : public nsISupports {
+ public:
+  JSObjectHolder(JSContext* aCx, JSObject* aObject) : mJSObject(aCx, aObject) {}
+
+  NS_DECL_ISUPPORTS
+
+  JSObject* GetJSObject() { return mJSObject; }
+
+ private:
+  ~JSObjectHolder() = default;
+
+  JS::PersistentRooted<JSObject*> mJSObject;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_JSObjectHolder_h
diff --git a/xpcom/base/LogCommandLineHandler.cpp b/xpcom/base/LogCommandLineHandler.cpp
new file mode 100644
index 0000000000..26e78670e9
--- /dev/null
+++ b/xpcom/base/LogCommandLineHandler.cpp
@@ -0,0 +1,90 @@
+/* -*- 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 "LogCommandLineHandler.h"
+
+#include "mozilla/Tokenizer.h"
+#include "nsDebug.h"
+
+namespace mozilla {
+
+void LoggingHandleCommandLineArgs(
+    int argc, char const* const* argv,
+    std::function<void(nsACString const&)> const& consumer) {
+  // Keeps the name of a pending env var (MOZ_LOG or MOZ_LOG_FILE) that
+  // we expect to get a value for in the next iterated arg.
+  // Used for the `-MOZ_LOG <modules>` form of argument.
+  nsAutoCString env;
+
+  auto const names = {"MOZ_LOG"_ns, "MOZ_LOG_FILE"_ns};
+
+  for (int arg = 1; arg < argc; ++arg) {
+    Tokenizer p(argv[arg]);
+
+    if (!env.IsEmpty() && p.CheckChar('-')) {
+      NS_WARNING(
+          "Expects value after -MOZ_LOG(_FILE) argument, but another argument "
+          "found");
+
+      // We only expect values for the pending env var, start over
+      p.Rollback();
+      env.Truncate();
+    }
+
+    if (env.IsEmpty()) {
+      if (!p.CheckChar('-')) {
+        continue;
+      }
+      // We accept `-MOZ_LOG` as well as `--MOZ_LOG`.
+      Unused << p.CheckChar('-');
+
+      for (auto const& name : names) {
+        if (!p.CheckWord(name)) {
+          continue;
+        }
+
+        env.Assign(name);
+        env.Append('=');
+        break;
+      }
+
+      if (env.IsEmpty()) {
+        // An unknonwn argument, ignore.
+        continue;
+      }
+
+      // We accept `-MOZ_LOG <modules>` as well as `-MOZ_LOG=<modules>`.
+
+      if (p.CheckEOF()) {
+        // We have a lone `-MOZ_LOG` arg, the next arg is expected to be
+        // the value, |env| is now prepared as `MOZ_LOG=`.
+        continue;
+      }
+
+      if (!p.CheckChar('=')) {
+        // There is a character after the arg name and it's not '=',
+        // ignore this argument.
+        NS_WARNING("-MOZ_LOG(_FILE) argument not in a proper form");
+
+        env.Truncate();
+        continue;
+      }
+    }
+
+    // This can be non-empty from previous iteration or in this iteration.
+    if (!env.IsEmpty()) {
+      nsDependentCSubstring value;
+      Unused << p.ReadUntil(Tokenizer::Token::EndOfFile(), value);
+      env.Append(value);
+
+      consumer(env);
+
+      env.Truncate();
+    }
+  }
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/LogCommandLineHandler.h b/xpcom/base/LogCommandLineHandler.h
new file mode 100644
index 0000000000..ef945d7980
--- /dev/null
+++ b/xpcom/base/LogCommandLineHandler.h
@@ -0,0 +1,49 @@
+/* -*- 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/. */
+
+#ifndef LogCommandLineHandler_h
+#define LogCommandLineHandler_h
+
+#include <functional>
+#include "nsString.h"
+
+namespace mozilla {
+
+/**
+ * A helper function parsing provided command line arguments and handling two
+ * specific args:
+ *
+ * -MOZ_LOG=modulelist
+ * -MOZ_LOG_FILE=file/path
+ *
+ * both expecting an argument, and corresponding to the same-name environment
+ * variables we use for logging setup.
+ *
+ * When an argument is found in the proper form, the consumer callback is called
+ * with a string in a follwing form, note that we do this for every occurence,
+ * and not just at the end of the parsing:
+ *
+ * "MOZ_LOG=modulelist" or "MOZ_LOG_FILE=file/path"
+ *
+ * All the following forms of arguments of the application are possible:
+ *
+ * --MOZ_LOG modulelist
+ * -MOZ_LOG modulelist
+ * --MOZ_LOG=modulelist
+ * -MOZ_LOG=modulelist
+ *
+ * The motivation for a separte function and not implementing a command line
+ * handler interface is that we need to process this very early during the
+ * application startup.  Command line handlers are proccessed way later
+ * after logging has already been set up.
+ */
+void LoggingHandleCommandLineArgs(
+    int argc, char const* const* argv,
+    std::function<void(nsACString const&)> const& consumer);
+
+}  // namespace mozilla
+
+#endif
diff --git a/xpcom/base/LogModulePrefWatcher.cpp b/xpcom/base/LogModulePrefWatcher.cpp
new file mode 100644
index 0000000000..bd06660533
--- /dev/null
+++ b/xpcom/base/LogModulePrefWatcher.cpp
@@ -0,0 +1,164 @@
+/* -*- 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 "LogModulePrefWatcher.h"
+
+#include "mozilla/Logging.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Services.h"
+#include "nsIObserverService.h"
+#include "nsString.h"
+#include "nsXULAppAPI.h"
+#include "base/process_util.h"
+
+static const char kLoggingPrefPrefix[] = "logging.";
+static const char kLoggingConfigPrefPrefix[] = "logging.config";
+static const int kLoggingConfigPrefixLen = sizeof(kLoggingConfigPrefPrefix) - 1;
+static const char kLoggingPrefClearOnStartup[] =
+    "logging.config.clear_on_startup";
+static const char kLoggingPrefLogFile[] = "logging.config.LOG_FILE";
+static const char kLoggingPrefAddTimestamp[] = "logging.config.add_timestamp";
+static const char kLoggingPrefSync[] = "logging.config.sync";
+static const char kLoggingPrefStacks[] = "logging.config.profilerstacks";
+
+namespace mozilla {
+
+NS_IMPL_ISUPPORTS(LogModulePrefWatcher, nsIObserver)
+
+/**
+ * Resets all the preferences in the logging. branch
+ * This is needed because we may crash while logging, and this would cause us
+ * to log after restarting as well.
+ *
+ * If logging after restart is desired, set the logging.config.clear_on_startup
+ * pref to false, or use the MOZ_LOG_FILE and MOZ_LOG_MODULES env vars.
+ */
+static void ResetExistingPrefs() {
+  nsTArray<nsCString> names;
+  nsresult rv =
+      Preferences::GetRootBranch()->GetChildList(kLoggingPrefPrefix, names);
+  if (NS_SUCCEEDED(rv)) {
+    for (auto& name : names) {
+      // Clearing the pref will cause it to reload, thus resetting the log level
+      Preferences::ClearUser(name.get());
+    }
+  }
+}
+
+/**
+ * Loads the log level from the given pref and updates the corresponding
+ * LogModule.
+ */
+static void LoadPrefValue(const char* aName) {
+  LogLevel logLevel = LogLevel::Disabled;
+
+  nsresult rv;
+  int32_t prefLevel = 0;
+  nsAutoCString prefValue;
+
+  if (strncmp(aName, kLoggingConfigPrefPrefix, kLoggingConfigPrefixLen) == 0) {
+    nsAutoCString prefName(aName);
+
+    if (prefName.EqualsLiteral(kLoggingPrefLogFile)) {
+      rv = Preferences::GetCString(aName, prefValue);
+      // The pref was reset. Clear the user file.
+      if (NS_FAILED(rv) || prefValue.IsEmpty()) {
+        LogModule::SetLogFile(nullptr);
+        return;
+      }
+
+      // If the pref value doesn't have a PID placeholder, append it to the end.
+      if (!strstr(prefValue.get(), MOZ_LOG_PID_TOKEN)) {
+        prefValue.AppendLiteral(MOZ_LOG_PID_TOKEN);
+      }
+
+      LogModule::SetLogFile(prefValue.BeginReading());
+    } else if (prefName.EqualsLiteral(kLoggingPrefAddTimestamp)) {
+      bool addTimestamp = Preferences::GetBool(aName, false);
+      LogModule::SetAddTimestamp(addTimestamp);
+    } else if (prefName.EqualsLiteral(kLoggingPrefSync)) {
+      bool sync = Preferences::GetBool(aName, false);
+      LogModule::SetIsSync(sync);
+    } else if (prefName.EqualsLiteral(kLoggingPrefStacks)) {
+      bool captureStacks = Preferences::GetBool(aName, false);
+      LogModule::SetCaptureStacks(captureStacks);
+    }
+    return;
+  }
+
+  if (Preferences::GetInt(aName, &prefLevel) == NS_OK) {
+    logLevel = ToLogLevel(prefLevel);
+  } else if (Preferences::GetCString(aName, prefValue) == NS_OK) {
+    if (prefValue.LowerCaseEqualsLiteral("error")) {
+      logLevel = LogLevel::Error;
+    } else if (prefValue.LowerCaseEqualsLiteral("warning")) {
+      logLevel = LogLevel::Warning;
+    } else if (prefValue.LowerCaseEqualsLiteral("info")) {
+      logLevel = LogLevel::Info;
+    } else if (prefValue.LowerCaseEqualsLiteral("debug")) {
+      logLevel = LogLevel::Debug;
+    } else if (prefValue.LowerCaseEqualsLiteral("verbose")) {
+      logLevel = LogLevel::Verbose;
+    }
+  }
+
+  const char* moduleName = aName + strlen(kLoggingPrefPrefix);
+  LogModule::Get(moduleName)->SetLevel(logLevel);
+}
+
+static void LoadExistingPrefs() {
+  nsIPrefBranch* root = Preferences::GetRootBranch();
+  if (!root) {
+    return;
+  }
+
+  nsTArray<nsCString> names;
+  nsresult rv = root->GetChildList(kLoggingPrefPrefix, names);
+  if (NS_SUCCEEDED(rv)) {
+    for (auto& name : names) {
+      LoadPrefValue(name.get());
+    }
+  }
+}
+
+LogModulePrefWatcher::LogModulePrefWatcher() = default;
+
+void LogModulePrefWatcher::RegisterPrefWatcher() {
+  RefPtr<LogModulePrefWatcher> prefWatcher = new LogModulePrefWatcher();
+  Preferences::AddStrongObserver(prefWatcher, kLoggingPrefPrefix);
+
+  nsCOMPtr<nsIObserverService> observerService =
+      mozilla::services::GetObserverService();
+  if (observerService && XRE_IsParentProcess()) {
+    observerService->AddObserver(prefWatcher,
+                                 "browser-delayed-startup-finished", false);
+  }
+
+  LoadExistingPrefs();
+}
+
+NS_IMETHODIMP
+LogModulePrefWatcher::Observe(nsISupports* aSubject, const char* aTopic,
+                              const char16_t* aData) {
+  if (strcmp(NS_PREFBRANCH_PREFCHANGE_TOPIC_ID, aTopic) == 0) {
+    NS_LossyConvertUTF16toASCII prefName(aData);
+    LoadPrefValue(prefName.get());
+  } else if (strcmp("browser-delayed-startup-finished", aTopic) == 0) {
+    bool clear = Preferences::GetBool(kLoggingPrefClearOnStartup, true);
+    if (clear) {
+      ResetExistingPrefs();
+    }
+    nsCOMPtr<nsIObserverService> observerService =
+        mozilla::services::GetObserverService();
+    if (observerService) {
+      observerService->RemoveObserver(this, "browser-delayed-startup-finished");
+    }
+  }
+
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/LogModulePrefWatcher.h b/xpcom/base/LogModulePrefWatcher.h
new file mode 100644
index 0000000000..92a2a3d5b7
--- /dev/null
+++ b/xpcom/base/LogModulePrefWatcher.h
@@ -0,0 +1,39 @@
+/* -*- 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/. */
+
+#ifndef LogModulePrefWatcher_h
+#define LogModulePrefWatcher_h
+
+#include "nsIObserver.h"
+
+namespace mozilla {
+
+/**
+ * Watches for changes to "logging.*" prefs and then updates the appropriate
+ * LogModule's log level. Both the integer and string versions of the LogLevel
+ * enum are supported.
+ *
+ * For example setting the pref "logging.Foo" to "Verbose" will set the
+ * LogModule for "Foo" to the LogLevel::Verbose level. Setting "logging.Bar" to
+ * 4 would set the LogModule for "Bar" to the LogLevel::Debug level.
+ */
+class LogModulePrefWatcher : public nsIObserver {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  /**
+   * Starts observing logging pref changes.
+   */
+  static void RegisterPrefWatcher();
+
+ private:
+  LogModulePrefWatcher();
+  virtual ~LogModulePrefWatcher() = default;
+};
+}  // namespace mozilla
+
+#endif  // LogModulePrefWatcher_h
diff --git a/xpcom/base/Logging.cpp b/xpcom/base/Logging.cpp
new file mode 100644
index 0000000000..44f74686a9
--- /dev/null
+++ b/xpcom/base/Logging.cpp
@@ -0,0 +1,912 @@
+/* -*- 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 "mozilla/Logging.h"
+
+#include <algorithm>
+
+#include "base/process_util.h"
+#include "GeckoProfiler.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/FileUtils.h"
+#include "mozilla/LateWriteChecks.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/Printf.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/UniquePtrExtensions.h"
+#include "MainThreadUtils.h"
+#include "nsClassHashtable.h"
+#include "nsDebug.h"
+#include "nsDebugImpl.h"
+#include "nsPrintfCString.h"
+#include "NSPRLogModulesParser.h"
+#include "nsXULAppAPI.h"
+#include "LogCommandLineHandler.h"
+
+#include "prenv.h"
+#ifdef XP_WIN
+#  include <fcntl.h>
+#  include <process.h>
+#else
+#  include <sys/stat.h>  // for umask()
+#  include <sys/types.h>
+#  include <unistd.h>
+#endif
+
+// NB: Amount determined by performing a typical browsing session and finding
+//     the maximum number of modules instantiated, and padding up to the next
+//     power of 2.
+const uint32_t kInitialModuleCount = 256;
+// When rotate option is added to the modules list, this is the hardcoded
+// number of files we create and rotate.  When there is rotate:40,
+// we will keep four files per process, each limited to 10MB.  Sum is 40MB,
+// the given limit.
+//
+// (Note: When this is changed to be >= 10, SandboxBroker::LaunchApp must add
+// another rule to allow logfile.?? be written by content processes.)
+const uint32_t kRotateFilesNumber = 4;
+
+namespace mozilla {
+
+namespace detail {
+
+void log_print(const LogModule* aModule, LogLevel aLevel, const char* aFmt,
+               ...) {
+  va_list ap;
+  va_start(ap, aFmt);
+  aModule->Printv(aLevel, aFmt, ap);
+  va_end(ap);
+}
+
+void log_print(const LogModule* aModule, LogLevel aLevel, TimeStamp* aStart,
+               const char* aFmt, ...) {
+  va_list ap;
+  va_start(ap, aFmt);
+  aModule->Printv(aLevel, aStart, aFmt, ap);
+  va_end(ap);
+}
+
+}  // namespace detail
+
+LogLevel ToLogLevel(int32_t aLevel) {
+  aLevel = std::min(aLevel, static_cast<int32_t>(LogLevel::Verbose));
+  aLevel = std::max(aLevel, static_cast<int32_t>(LogLevel::Disabled));
+  return static_cast<LogLevel>(aLevel);
+}
+
+static const char* ToLogStr(LogLevel aLevel) {
+  switch (aLevel) {
+    case LogLevel::Error:
+      return "E";
+    case LogLevel::Warning:
+      return "W";
+    case LogLevel::Info:
+      return "I";
+    case LogLevel::Debug:
+      return "D";
+    case LogLevel::Verbose:
+      return "V";
+    case LogLevel::Disabled:
+    default:
+      MOZ_CRASH("Invalid log level.");
+      return "";
+  }
+}
+
+namespace detail {
+
+/**
+ * A helper class providing reference counting for FILE*.
+ * It encapsulates the following:
+ *  - the FILE handle
+ *  - the order number it was created for when rotating (actual path)
+ *  - number of active references
+ */
+class LogFile {
+  FILE* mFile;
+  uint32_t mFileNum;
+
+ public:
+  LogFile(FILE* aFile, uint32_t aFileNum)
+      : mFile(aFile), mFileNum(aFileNum), mNextToRelease(nullptr) {}
+
+  ~LogFile() {
+    fclose(mFile);
+    delete mNextToRelease;
+  }
+
+  FILE* File() const { return mFile; }
+  uint32_t Num() const { return mFileNum; }
+
+  LogFile* mNextToRelease;
+};
+
+static const char* ExpandLogFileName(const char* aFilename,
+                                     char (&buffer)[2048]) {
+  MOZ_ASSERT(aFilename);
+  static const char kPIDToken[] = MOZ_LOG_PID_TOKEN;
+  static const char kMOZLOGExt[] = MOZ_LOG_FILE_EXTENSION;
+
+  bool hasMozLogExtension = StringEndsWith(nsDependentCString(aFilename),
+                                           nsLiteralCString(kMOZLOGExt));
+
+  const char* pidTokenPtr = strstr(aFilename, kPIDToken);
+  if (pidTokenPtr &&
+      SprintfLiteral(buffer, "%.*s%s%" PRIPID "%s%s",
+                     static_cast<int>(pidTokenPtr - aFilename), aFilename,
+                     XRE_IsParentProcess() ? "-main." : "-child.",
+                     base::GetCurrentProcId(), pidTokenPtr + strlen(kPIDToken),
+                     hasMozLogExtension ? "" : kMOZLOGExt) > 0) {
+    return buffer;
+  }
+
+  if (!hasMozLogExtension &&
+      SprintfLiteral(buffer, "%s%s", aFilename, kMOZLOGExt) > 0) {
+    return buffer;
+  }
+
+  return aFilename;
+}
+
+// Drop initial lines from the given file until it is less than or equal to the
+// given size.
+//
+// For simplicity and to reduce memory consumption, lines longer than the given
+// long line size may be broken.
+//
+// This function uses `mkstemp` and `rename` on POSIX systems and `_mktemp_s`
+// and `ReplaceFileA` on Win32 systems.  `ReplaceFileA` was introduced in
+// Windows 7 so it's available.
+bool LimitFileToLessThanSize(const char* aFilename, uint32_t aSize,
+                             uint16_t aLongLineSize = 16384) {
+  // `tempFilename` will be further updated below.
+  char tempFilename[2048];
+  SprintfLiteral(tempFilename, "%s.tempXXXXXX", aFilename);
+
+  bool failedToWrite = false;
+
+  {  // Scope `file` and `temp`, so that they are definitely closed.
+    ScopedCloseFile file(fopen(aFilename, "rb"));
+    if (!file) {
+      return false;
+    }
+
+    if (fseek(file, 0, SEEK_END)) {
+      // If we can't seek for some reason, better to just not limit the log at
+      // all and hope to sort out large logs upon further analysis.
+      return false;
+    }
+
+    // `ftell` returns a positive `long`, which might be more than 32 bits.
+    uint64_t fileSize = static_cast<uint64_t>(ftell(file));
+
+    if (fileSize <= aSize) {
+      return true;
+    }
+
+    uint64_t minBytesToDrop = fileSize - aSize;
+    uint64_t numBytesDropped = 0;
+
+    if (fseek(file, 0, SEEK_SET)) {
+      // Same as above: if we can't seek, hope for the best.
+      return false;
+    }
+
+    ScopedCloseFile temp;
+
+#if defined(OS_WIN)
+    // This approach was cribbed from
+    // https://searchfox.org/mozilla-central/rev/868935867c6241e1302e64cf9be8f56db0fd0d1c/xpcom/build/LateWriteChecks.cpp#158.
+    HANDLE hFile;
+    do {
+      // mkstemp isn't supported so keep trying until we get a file.
+      _mktemp_s(tempFilename, strlen(tempFilename) + 1);
+      hFile = CreateFileA(tempFilename, GENERIC_WRITE, 0, nullptr, CREATE_NEW,
+                          FILE_ATTRIBUTE_NORMAL, nullptr);
+    } while (GetLastError() == ERROR_FILE_EXISTS);
+
+    if (hFile == INVALID_HANDLE_VALUE) {
+      NS_WARNING("INVALID_HANDLE_VALUE");
+      return false;
+    }
+
+    int fd = _open_osfhandle((intptr_t)hFile, _O_APPEND);
+    if (fd == -1) {
+      NS_WARNING("_open_osfhandle failed!");
+      return false;
+    }
+
+    temp.reset(_fdopen(fd, "ab"));
+#elif defined(OS_POSIX)
+
+    // Coverity would prefer us to set a secure umask before using `mkstemp`.
+    // However, the umask is process-wide, so setting it may lead to difficult
+    // to debug complications; and it is fine for this particular short-lived
+    // temporary file to be insecure.
+    //
+    // coverity[SECURE_TEMP : FALSE]
+    int fd = mkstemp(tempFilename);
+    if (fd == -1) {
+      NS_WARNING("mkstemp failed!");
+      return false;
+    }
+    temp.reset(fdopen(fd, "ab"));
+#else
+#  error Do not know how to open named temporary file
+#endif
+
+    if (!temp) {
+      NS_WARNING(nsPrintfCString("could not open named temporary file %s",
+                                 tempFilename)
+                     .get());
+      return false;
+    }
+
+    // `fgets` always null terminates.  If the line is too long, it won't
+    // include a trailing '\n' but will be null-terminated.
+    UniquePtr<char[]> line = MakeUnique<char[]>(aLongLineSize + 1);
+    while (fgets(line.get(), aLongLineSize + 1, file)) {
+      if (numBytesDropped >= minBytesToDrop) {
+        if (fputs(line.get(), temp) < 0) {
+          NS_WARNING(
+              nsPrintfCString("fputs failed: ferror %d\n", ferror(temp)).get());
+          failedToWrite = true;
+          break;
+        }
+      } else {
+        // Binary mode avoids platform-specific wrinkles with text streams.  In
+        // particular, on Windows, `\r\n` gets read as `\n` (and the reverse
+        // when writing), complicating this calculation.
+        numBytesDropped += strlen(line.get());
+      }
+    }
+  }
+
+  // At this point, `file` and `temp` are closed, so we can remove and rename.
+  if (failedToWrite) {
+    remove(tempFilename);
+    return false;
+  }
+
+#if defined(OS_WIN)
+  if (!::ReplaceFileA(aFilename, tempFilename, nullptr, 0, 0, 0)) {
+    NS_WARNING(
+        nsPrintfCString("ReplaceFileA failed: %lu\n", GetLastError()).get());
+    return false;
+  }
+#elif defined(OS_POSIX)
+  if (rename(tempFilename, aFilename)) {
+    NS_WARNING(
+        nsPrintfCString("rename failed: %s (%d)\n", strerror(errno), errno)
+            .get());
+    return false;
+  }
+#else
+#  error Do not know how to atomically replace file
+#endif
+
+  return true;
+}
+
+}  // namespace detail
+
+namespace {
+// Helper method that initializes an empty va_list to be empty.
+void empty_va(va_list* va, ...) {
+  va_start(*va, va);
+  va_end(*va);
+}
+}  // namespace
+
+class LogModuleManager {
+ public:
+  LogModuleManager()
+      : mModulesLock("logmodules"),
+        mModules(kInitialModuleCount),
+#ifdef DEBUG
+        mLoggingModuleRegistered(0),
+#endif
+        mPrintEntryCount(0),
+        mOutFile(nullptr),
+        mToReleaseFile(nullptr),
+        mOutFileNum(0),
+        mOutFilePath(strdup("")),
+        mMainThread(PR_GetCurrentThread()),
+        mSetFromEnv(false),
+        mAddTimestamp(false),
+        mCaptureProfilerStack(false),
+        mIsRaw(false),
+        mIsSync(false),
+        mRotate(0),
+        mInitialized(false) {
+  }
+
+  ~LogModuleManager() {
+    detail::LogFile* logFile = mOutFile.exchange(nullptr);
+    delete logFile;
+  }
+
+  /**
+   * Loads config from command line args or env vars if present, in
+   * this specific order of priority.
+   *
+   * Notes:
+   *
+   * 1) This function is only intended to be called once per session.
+   * 2) None of the functions used in Init should rely on logging.
+   */
+  void Init(int argc, char* argv[]) {
+    MOZ_DIAGNOSTIC_ASSERT(!mInitialized);
+    mInitialized = true;
+
+    LoggingHandleCommandLineArgs(argc, static_cast<char const* const*>(argv),
+                                 [](nsACString const& env) {
+                                   // We deliberately set/rewrite the
+                                   // environment variables so that when child
+                                   // processes are spawned w/o passing the
+                                   // arguments they still inherit the logging
+                                   // settings as well as sandboxing can be
+                                   // correctly set. Scripts can pass
+                                   // -MOZ_LOG=$MOZ_LOG,modules as an argument
+                                   // to merge existing settings, if required.
+
+                                   // PR_SetEnv takes ownership of the string.
+                                   PR_SetEnv(ToNewCString(env));
+                                 });
+
+    bool shouldAppend = false;
+    bool addTimestamp = false;
+    bool isSync = false;
+    bool isRaw = false;
+    bool captureStacks = false;
+    int32_t rotate = 0;
+    int32_t maxSize = 0;
+    bool prependHeader = false;
+    const char* modules = PR_GetEnv("MOZ_LOG");
+    if (!modules || !modules[0]) {
+      modules = PR_GetEnv("MOZ_LOG_MODULES");
+      if (modules) {
+        NS_WARNING(
+            "MOZ_LOG_MODULES is deprecated."
+            "\nPlease use MOZ_LOG instead.");
+      }
+    }
+    if (!modules || !modules[0]) {
+      modules = PR_GetEnv("NSPR_LOG_MODULES");
+      if (modules) {
+        NS_WARNING(
+            "NSPR_LOG_MODULES is deprecated."
+            "\nPlease use MOZ_LOG instead.");
+      }
+    }
+
+    // Need to capture `this` since `sLogModuleManager` is not set until after
+    // initialization is complete.
+    NSPRLogModulesParser(
+        modules,
+        [this, &shouldAppend, &addTimestamp, &isSync, &isRaw, &rotate, &maxSize,
+         &prependHeader, &captureStacks](const char* aName, LogLevel aLevel,
+                                         int32_t aValue) mutable {
+          if (strcmp(aName, "append") == 0) {
+            shouldAppend = true;
+          } else if (strcmp(aName, "timestamp") == 0) {
+            addTimestamp = true;
+          } else if (strcmp(aName, "sync") == 0) {
+            isSync = true;
+          } else if (strcmp(aName, "raw") == 0) {
+            isRaw = true;
+          } else if (strcmp(aName, "rotate") == 0) {
+            rotate = (aValue << 20) / kRotateFilesNumber;
+          } else if (strcmp(aName, "maxsize") == 0) {
+            maxSize = aValue << 20;
+          } else if (strcmp(aName, "prependheader") == 0) {
+            prependHeader = true;
+          } else if (strcmp(aName, "profilerstacks") == 0) {
+            captureStacks = true;
+          } else {
+            this->CreateOrGetModule(aName)->SetLevel(aLevel);
+          }
+        });
+
+    // Rotate implies timestamp to make the files readable
+    mAddTimestamp = addTimestamp || rotate > 0;
+    mIsSync = isSync;
+    mIsRaw = isRaw;
+    mRotate = rotate;
+    mCaptureProfilerStack = captureStacks;
+
+    if (rotate > 0 && shouldAppend) {
+      NS_WARNING("MOZ_LOG: when you rotate the log, you cannot use append!");
+    }
+
+    if (rotate > 0 && maxSize > 0) {
+      NS_WARNING(
+          "MOZ_LOG: when you rotate the log, you cannot use maxsize! (ignoring "
+          "maxsize)");
+      maxSize = 0;
+    }
+
+    if (maxSize > 0 && !shouldAppend) {
+      NS_WARNING(
+          "MOZ_LOG: when you limit the log to maxsize, you must use append! "
+          "(ignorning maxsize)");
+      maxSize = 0;
+    }
+
+    if (rotate > 0 && prependHeader) {
+      NS_WARNING(
+          "MOZ_LOG: when you rotate the log, you cannot use prependheader!");
+      prependHeader = false;
+    }
+
+    const char* logFile = PR_GetEnv("MOZ_LOG_FILE");
+    if (!logFile || !logFile[0]) {
+      logFile = PR_GetEnv("NSPR_LOG_FILE");
+    }
+
+    if (logFile && logFile[0]) {
+      char buf[2048];
+      logFile = detail::ExpandLogFileName(logFile, buf);
+      mOutFilePath.reset(strdup(logFile));
+
+      if (mRotate > 0) {
+        // Delete all the previously captured files, including non-rotated
+        // log files, so that users don't complain our logs eat space even
+        // after the rotate option has been added and don't happen to send
+        // us old large logs along with the rotated files.
+        remove(mOutFilePath.get());
+        for (uint32_t i = 0; i < kRotateFilesNumber; ++i) {
+          RemoveFile(i);
+        }
+      }
+
+      mOutFile = OpenFile(shouldAppend, mOutFileNum, maxSize);
+      mSetFromEnv = true;
+    }
+
+    if (prependHeader && XRE_IsParentProcess()) {
+      va_list va;
+      empty_va(&va);
+      Print("Logger", LogLevel::Info, nullptr, "\n***\n\n", "Opening log\n",
+            va);
+    }
+  }
+
+  void SetLogFile(const char* aFilename) {
+    // For now we don't allow you to change the file at runtime.
+    if (mSetFromEnv) {
+      NS_WARNING(
+          "LogModuleManager::SetLogFile - Log file was set from the "
+          "MOZ_LOG_FILE environment variable.");
+      return;
+    }
+
+    const char* filename = aFilename ? aFilename : "";
+    char buf[2048];
+    filename = detail::ExpandLogFileName(filename, buf);
+
+    // Can't use rotate or maxsize at runtime yet.
+    MOZ_ASSERT(mRotate == 0,
+               "We don't allow rotate for runtime logfile changes");
+    mOutFilePath.reset(strdup(filename));
+
+    // Exchange mOutFile and set it to be released once all the writes are done.
+    detail::LogFile* newFile = OpenFile(false, 0);
+    detail::LogFile* oldFile = mOutFile.exchange(newFile);
+
+    // Since we don't allow changing the logfile if MOZ_LOG_FILE is already set,
+    // and we don't allow log rotation when setting it at runtime,
+    // mToReleaseFile will be null, so we're not leaking.
+    DebugOnly<detail::LogFile*> prevFile = mToReleaseFile.exchange(oldFile);
+    MOZ_ASSERT(!prevFile, "Should be null because rotation is not allowed");
+
+    // If we just need to release a file, we must force print, in order to
+    // trigger the closing and release of mToReleaseFile.
+    if (oldFile) {
+      va_list va;
+      empty_va(&va);
+      Print("Logger", LogLevel::Info, "Flushing old log files\n", va);
+    }
+  }
+
+  uint32_t GetLogFile(char* aBuffer, size_t aLength) {
+    uint32_t len = strlen(mOutFilePath.get());
+    if (len + 1 > aLength) {
+      return 0;
+    }
+    snprintf(aBuffer, aLength, "%s", mOutFilePath.get());
+    return len;
+  }
+
+  void SetIsSync(bool aIsSync) { mIsSync = aIsSync; }
+
+  void SetCaptureStacks(bool aCaptureStacks) {
+    mCaptureProfilerStack = aCaptureStacks;
+  }
+
+  void SetAddTimestamp(bool aAddTimestamp) { mAddTimestamp = aAddTimestamp; }
+
+  detail::LogFile* OpenFile(bool aShouldAppend, uint32_t aFileNum,
+                            uint32_t aMaxSize = 0) {
+    FILE* file;
+
+    if (mRotate > 0) {
+      char buf[2048];
+      SprintfLiteral(buf, "%s.%d", mOutFilePath.get(), aFileNum);
+
+      // rotate doesn't support append (or maxsize).
+      file = fopen(buf, "w");
+    } else if (aShouldAppend && aMaxSize > 0) {
+      detail::LimitFileToLessThanSize(mOutFilePath.get(), aMaxSize >> 1);
+      file = fopen(mOutFilePath.get(), "a");
+    } else {
+      file = fopen(mOutFilePath.get(), aShouldAppend ? "a" : "w");
+    }
+
+    if (!file) {
+      return nullptr;
+    }
+
+    return new detail::LogFile(file, aFileNum);
+  }
+
+  void RemoveFile(uint32_t aFileNum) {
+    char buf[2048];
+    SprintfLiteral(buf, "%s.%d", mOutFilePath.get(), aFileNum);
+    remove(buf);
+  }
+
+  LogModule* CreateOrGetModule(const char* aName) {
+    OffTheBooksMutexAutoLock guard(mModulesLock);
+    return mModules
+        .LookupOrInsertWith(
+            aName,
+            [&] {
+#ifdef DEBUG
+              if (++mLoggingModuleRegistered > kInitialModuleCount) {
+                NS_WARNING(
+                    "kInitialModuleCount too low, consider increasing its "
+                    "value");
+              }
+#endif
+              return UniquePtr<LogModule>(
+                  new LogModule{aName, LogLevel::Disabled});
+            })
+        .get();
+  }
+
+  void Print(const char* aName, LogLevel aLevel, const char* aFmt,
+             va_list aArgs) MOZ_FORMAT_PRINTF(4, 0) {
+    Print(aName, aLevel, nullptr, "", aFmt, aArgs);
+  }
+
+  void Print(const char* aName, LogLevel aLevel, const TimeStamp* aStart,
+             const char* aPrepend, const char* aFmt, va_list aArgs)
+      MOZ_FORMAT_PRINTF(6, 0) {
+    AutoSuspendLateWriteChecks suspendLateWriteChecks;
+    long pid = static_cast<long>(base::GetCurrentProcId());
+    const size_t kBuffSize = 1024;
+    char buff[kBuffSize];
+
+    char* buffToWrite = buff;
+    SmprintfPointer allocatedBuff;
+
+    va_list argsCopy;
+    va_copy(argsCopy, aArgs);
+    int charsWritten = VsprintfLiteral(buff, aFmt, argsCopy);
+    va_end(argsCopy);
+
+    if (charsWritten < 0) {
+      // Print out at least something.  We must copy to the local buff,
+      // can't just assign aFmt to buffToWrite, since when
+      // buffToWrite != buff, we try to release it.
+      MOZ_ASSERT(false, "Probably incorrect format string in LOG?");
+      strncpy(buff, aFmt, kBuffSize - 1);
+      buff[kBuffSize - 1] = '\0';
+      charsWritten = strlen(buff);
+    } else if (static_cast<size_t>(charsWritten) >= kBuffSize - 1) {
+      // We may have maxed out, allocate a buffer instead.
+      allocatedBuff = mozilla::Vsmprintf(aFmt, aArgs);
+      buffToWrite = allocatedBuff.get();
+      charsWritten = strlen(buffToWrite);
+    }
+
+    if (profiler_thread_is_being_profiled_for_markers()) {
+      struct LogMarker {
+        static constexpr Span<const char> MarkerTypeName() {
+          return MakeStringSpan("Log");
+        }
+        static void StreamJSONMarkerData(
+            baseprofiler::SpliceableJSONWriter& aWriter,
+            const ProfilerString8View& aModule,
+            const ProfilerString8View& aText) {
+          aWriter.StringProperty("module", aModule);
+          aWriter.StringProperty("name", aText);
+        }
+        static MarkerSchema MarkerTypeDisplay() {
+          using MS = MarkerSchema;
+          MS schema{MS::Location::MarkerChart, MS::Location::MarkerTable};
+          schema.SetTableLabel("({marker.data.module}) {marker.data.name}");
+          schema.AddKeyLabelFormatSearchable("module", "Module",
+                                             MS::Format::String,
+                                             MS::Searchable::Searchable);
+          schema.AddKeyLabelFormatSearchable("name", "Name", MS::Format::String,
+                                             MS::Searchable::Searchable);
+          return schema;
+        }
+      };
+
+      profiler_add_marker(
+          "LogMessages", geckoprofiler::category::OTHER,
+          {aStart ? MarkerTiming::IntervalUntilNowFrom(*aStart)
+                  : MarkerTiming::InstantNow(),
+           MarkerStack::MaybeCapture(mCaptureProfilerStack)},
+          LogMarker{}, ProfilerString8View::WrapNullTerminatedString(aName),
+          ProfilerString8View::WrapNullTerminatedString(buffToWrite));
+    }
+
+    // Determine if a newline needs to be appended to the message.
+    const char* newline = "";
+    if (charsWritten == 0 || buffToWrite[charsWritten - 1] != '\n') {
+      newline = "\n";
+    }
+
+    FILE* out = stderr;
+
+    // In case we use rotate, this ensures the FILE is kept alive during
+    // its use.  Increased before we load mOutFile.
+    ++mPrintEntryCount;
+
+    detail::LogFile* outFile = mOutFile;
+    if (outFile) {
+      out = outFile->File();
+    }
+
+    // This differs from the NSPR format in that we do not output the
+    // opaque system specific thread pointer (ie pthread_t) cast
+    // to a long. The address of the current PR_Thread continues to be
+    // prefixed.
+    //
+    // Additionally we prefix the output with the abbreviated log level
+    // and the module name.
+    PRThread* currentThread = PR_GetCurrentThread();
+    const char* currentThreadName = (mMainThread == currentThread)
+                                        ? "Main Thread"
+                                        : PR_GetThreadName(currentThread);
+
+    char noNameThread[40];
+    if (!currentThreadName) {
+      SprintfLiteral(noNameThread, "Unnamed thread %p", currentThread);
+      currentThreadName = noNameThread;
+    }
+
+    if (!mAddTimestamp && !aStart) {
+      if (!mIsRaw) {
+        fprintf_stderr(out, "%s[%s %ld: %s]: %s/%s %s%s", aPrepend,
+                       nsDebugImpl::GetMultiprocessMode(), pid,
+                       currentThreadName, ToLogStr(aLevel), aName, buffToWrite,
+                       newline);
+      } else {
+        fprintf_stderr(out, "%s%s%s", aPrepend, buffToWrite, newline);
+      }
+    } else {
+      if (aStart) {
+        // XXX is there a reasonable way to convert one to the other?  this is
+        // bad
+        PRTime prnow = PR_Now();
+        TimeStamp tmnow = TimeStamp::Now();
+        TimeDuration duration = tmnow - *aStart;
+        PRTime prstart = prnow - duration.ToMicroseconds();
+
+        PRExplodedTime now;
+        PRExplodedTime start;
+        PR_ExplodeTime(prnow, PR_GMTParameters, &now);
+        PR_ExplodeTime(prstart, PR_GMTParameters, &start);
+        // Ignore that the start time might be in a different day
+        fprintf_stderr(
+            out,
+            "%s%04d-%02d-%02d %02d:%02d:%02d.%06d -> %02d:%02d:%02d.%06d UTC "
+            "(%.1gms)- [%s %ld: %s]: %s/%s %s%s",
+            aPrepend, now.tm_year, now.tm_month + 1, start.tm_mday,
+            start.tm_hour, start.tm_min, start.tm_sec, start.tm_usec,
+            now.tm_hour, now.tm_min, now.tm_sec, now.tm_usec,
+            duration.ToMilliseconds(), nsDebugImpl::GetMultiprocessMode(), pid,
+            currentThreadName, ToLogStr(aLevel), aName, buffToWrite, newline);
+      } else {
+        PRExplodedTime now;
+        PR_ExplodeTime(PR_Now(), PR_GMTParameters, &now);
+        fprintf_stderr(out,
+                       "%s%04d-%02d-%02d %02d:%02d:%02d.%06d UTC - [%s %ld: "
+                       "%s]: %s/%s %s%s",
+                       aPrepend, now.tm_year, now.tm_month + 1, now.tm_mday,
+                       now.tm_hour, now.tm_min, now.tm_sec, now.tm_usec,
+                       nsDebugImpl::GetMultiprocessMode(), pid,
+                       currentThreadName, ToLogStr(aLevel), aName, buffToWrite,
+                       newline);
+      }
+    }
+
+    if (mIsSync) {
+      fflush(out);
+    }
+
+    if (mRotate > 0 && outFile) {
+      int32_t fileSize = ftell(out);
+      if (fileSize > mRotate) {
+        uint32_t fileNum = outFile->Num();
+
+        uint32_t nextFileNum = fileNum + 1;
+        if (nextFileNum >= kRotateFilesNumber) {
+          nextFileNum = 0;
+        }
+
+        // And here is the trick.  The current out-file remembers its order
+        // number.  When no other thread shifted the global file number yet,
+        // we are the thread to open the next file.
+        if (mOutFileNum.compareExchange(fileNum, nextFileNum)) {
+          // We can work with mToReleaseFile because we are sure the
+          // mPrintEntryCount can't drop to zero now - the condition
+          // to actually delete what's stored in that member.
+          // And also, no other thread can enter this piece of code
+          // because mOutFile is still holding the current file with
+          // the non-shifted number.  The compareExchange() above is
+          // a no-op for other threads.
+          outFile->mNextToRelease = mToReleaseFile;
+          mToReleaseFile = outFile;
+
+          mOutFile = OpenFile(false, nextFileNum);
+        }
+      }
+    }
+
+    if (--mPrintEntryCount == 0 && mToReleaseFile) {
+      // We were the last Print() entered, if there is a file to release
+      // do it now.  exchange() is atomic and makes sure we release the file
+      // only once on one thread.
+      detail::LogFile* release = mToReleaseFile.exchange(nullptr);
+      delete release;
+    }
+  }
+
+ private:
+  OffTheBooksMutex mModulesLock;
+  nsClassHashtable<nsCharPtrHashKey, LogModule> mModules;
+
+#ifdef DEBUG
+  Atomic<uint32_t, ReleaseAcquire> mLoggingModuleRegistered;
+#endif
+  // Print() entry counter, actually reflects concurrent use of the current
+  // output file.  ReleaseAcquire ensures that manipulation with mOutFile
+  // and mToReleaseFile is synchronized by manipulation with this value.
+  Atomic<uint32_t, ReleaseAcquire> mPrintEntryCount;
+  // File to write to.  ReleaseAcquire because we need to sync mToReleaseFile
+  // with this.
+  Atomic<detail::LogFile*, ReleaseAcquire> mOutFile;
+  // File to be released when reference counter drops to zero.  This member
+  // is assigned mOutFile when the current file has reached the limit.
+  // It can be Relaxed, since it's synchronized with mPrintEntryCount
+  // manipulation and we do atomic exchange() on it.
+  Atomic<detail::LogFile*, Relaxed> mToReleaseFile;
+  // The next file number.  This is mostly only for synchronization sake.
+  // Can have relaxed ordering, since we only do compareExchange on it which
+  // is atomic regardless ordering.
+  Atomic<uint32_t, Relaxed> mOutFileNum;
+  // Just keeps the actual file path for further use.
+  UniqueFreePtr<char[]> mOutFilePath;
+
+  PRThread* mMainThread;
+  bool mSetFromEnv;
+  Atomic<bool, Relaxed> mAddTimestamp;
+  Atomic<bool, Relaxed> mCaptureProfilerStack;
+  Atomic<bool, Relaxed> mIsRaw;
+  Atomic<bool, Relaxed> mIsSync;
+  int32_t mRotate;
+  bool mInitialized;
+};
+
+StaticAutoPtr<LogModuleManager> sLogModuleManager;
+
+LogModule* LogModule::Get(const char* aName) {
+  // This is just a pass through to the LogModuleManager so
+  // that the LogModuleManager implementation can be kept internal.
+  MOZ_ASSERT(sLogModuleManager != nullptr);
+  return sLogModuleManager->CreateOrGetModule(aName);
+}
+
+void LogModule::SetLogFile(const char* aFilename) {
+  MOZ_ASSERT(sLogModuleManager);
+  sLogModuleManager->SetLogFile(aFilename);
+}
+
+uint32_t LogModule::GetLogFile(char* aBuffer, size_t aLength) {
+  MOZ_ASSERT(sLogModuleManager);
+  return sLogModuleManager->GetLogFile(aBuffer, aLength);
+}
+
+void LogModule::SetAddTimestamp(bool aAddTimestamp) {
+  sLogModuleManager->SetAddTimestamp(aAddTimestamp);
+}
+
+void LogModule::SetIsSync(bool aIsSync) {
+  sLogModuleManager->SetIsSync(aIsSync);
+}
+
+void LogModule::SetCaptureStacks(bool aCaptureStacks) {
+  sLogModuleManager->SetCaptureStacks(aCaptureStacks);
+}
+
+// This function is defined in gecko_logger/src/lib.rs
+// We mirror the level in rust code so we don't get forwarded all of the
+// rust logging and have to create an LogModule for each rust component.
+extern "C" void set_rust_log_level(const char* name, uint8_t level);
+
+void LogModule::SetLevel(LogLevel level) {
+  mLevel = level;
+
+  // If the log module contains `::` it is likely a rust module, so we
+  // pass the level into the rust code so it will know to forward the logging
+  // to Gecko.
+  if (strstr(mName, "::")) {
+    set_rust_log_level(mName, static_cast<uint8_t>(level));
+  }
+}
+
+void LogModule::Init(int argc, char* argv[]) {
+  // NB: This method is not threadsafe; it is expected to be called very early
+  //     in startup prior to any other threads being run.
+  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
+
+  if (sLogModuleManager) {
+    // Already initialized.
+    return;
+  }
+
+  // NB: We intentionally do not register for ClearOnShutdown as that happens
+  //     before all logging is complete. And, yes, that means we leak, but
+  //     we're doing that intentionally.
+
+  // Don't assign the pointer until after Init is called. This should help us
+  // detect if any of the functions called by Init somehow rely on logging.
+  auto mgr = new LogModuleManager();
+  mgr->Init(argc, argv);
+  sLogModuleManager = mgr;
+}
+
+void LogModule::Printv(LogLevel aLevel, const char* aFmt, va_list aArgs) const {
+  MOZ_ASSERT(sLogModuleManager != nullptr);
+
+  // Forward to LogModule manager w/ level and name
+  sLogModuleManager->Print(Name(), aLevel, aFmt, aArgs);
+}
+
+void LogModule::Printv(LogLevel aLevel, const TimeStamp* aStart,
+                       const char* aFmt, va_list aArgs) const {
+  MOZ_ASSERT(sLogModuleManager != nullptr);
+
+  // Forward to LogModule manager w/ level and name
+  sLogModuleManager->Print(Name(), aLevel, aStart, "", aFmt, aArgs);
+}
+
+}  // namespace mozilla
+
+extern "C" {
+
+// This function is called by external code (rust) to log to one of our
+// log modules.
+void ExternMozLog(const char* aModule, mozilla::LogLevel aLevel,
+                  const char* aMsg) {
+  MOZ_ASSERT(mozilla::sLogModuleManager != nullptr);
+
+  mozilla::LogModule* m =
+      mozilla::sLogModuleManager->CreateOrGetModule(aModule);
+  if (MOZ_LOG_TEST(m, aLevel)) {
+    mozilla::detail::log_print(m, aLevel, "%s", aMsg);
+  }
+}
+
+}  // extern "C"
diff --git a/xpcom/base/Logging.h b/xpcom/base/Logging.h
new file mode 100644
index 0000000000..6ed2752315
--- /dev/null
+++ b/xpcom/base/Logging.h
@@ -0,0 +1,322 @@
+/* -*- 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/. */
+
+#ifndef mozilla_logging_h
+#define mozilla_logging_h
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdarg.h>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Likely.h"
+
+// We normally have logging enabled everywhere, but measurements showed that
+// having logging enabled on Android is quite expensive (hundreds of kilobytes
+// for both the format strings for logging and the code to perform all the
+// logging calls).  Because retrieving logs from a mobile device is
+// comparatively more difficult for Android than it is for desktop and because
+// desktop machines tend to be less space/bandwidth-constrained than Android
+// devices, we've chosen to leave logging enabled on desktop, but disabled on
+// Android.  Given that logging can still be useful for development purposes,
+// however, we leave logging enabled on Android developer builds.
+#if !defined(ANDROID) || !defined(RELEASE_OR_BETA)
+#  define MOZ_LOGGING_ENABLED 1
+#else
+#  define MOZ_LOGGING_ENABLED 0
+#endif
+
+// The mandatory extension we add to log files.  Note that rotate will append
+// the file piece number still at the end.
+#define MOZ_LOG_FILE_EXTENSION ".moz_log"
+
+// Token for Process ID substitution.
+#define MOZ_LOG_PID_TOKEN "%PID"
+
+namespace mozilla {
+
+class TimeStamp;
+
+// While not a 100% mapping to PR_LOG's numeric values, mozilla::LogLevel does
+// maintain a direct mapping for the Disabled, Debug and Verbose levels.
+//
+// Mappings of LogLevel to PR_LOG's numeric values:
+//
+//   +---------+------------------+-----------------+
+//   | Numeric | NSPR Logging     | Mozilla Logging |
+//   +---------+------------------+-----------------+
+//   |       0 | PR_LOG_NONE      | Disabled        |
+//   |       1 | PR_LOG_ALWAYS    | Error           |
+//   |       2 | PR_LOG_ERROR     | Warning         |
+//   |       3 | PR_LOG_WARNING   | Info            |
+//   |       4 | PR_LOG_DEBUG     | Debug           |
+//   |       5 | PR_LOG_DEBUG + 1 | Verbose         |
+//   +---------+------------------+-----------------+
+//
+enum class LogLevel {
+  Disabled = 0,
+  Error,
+  Warning,
+  Info,
+  Debug,
+  Verbose,
+};
+
+/**
+ * Safely converts an integer into a valid LogLevel.
+ */
+LogLevel ToLogLevel(int32_t aLevel);
+
+class LogModule {
+ public:
+  ~LogModule() { ::free(mName); }
+
+  /**
+   * Retrieves the module with the given name. If it does not already exist
+   * it will be created.
+   *
+   * @param aName The name of the module.
+   * @return A log module for the given name. This may be shared.
+   */
+  static LogModule* Get(const char* aName);
+
+  /**
+   * Logging processes -MOZ_LOG and -MOZ_LOG_FILE command line arguments
+   * to override or set modules and the file as if passed through MOZ_LOG
+   * and MOZ_LOG_FILE env vars.  It's fine to pass (0, nullptr) if args
+   * are not accessible in the caller's context, it will just do nothing.
+   * Note that the args take effect (are processed) only when this function
+   * is called the first time.
+   */
+  static void Init(int argc, char* argv[]);
+
+  /**
+   * Sets the log file to the given filename.
+   */
+  static void SetLogFile(const char* aFilename);
+
+  /**
+   * @param aBuffer - pointer to a buffer
+   * @param aLength - the length of the buffer
+   *
+   * @return the actual length of the filepath.
+   */
+  static uint32_t GetLogFile(char* aBuffer, size_t aLength);
+
+  /**
+   * @param aAddTimestamp If we should log a time stamp with every message.
+   */
+  static void SetAddTimestamp(bool aAddTimestamp);
+
+  /**
+   * @param aIsSync If we should flush the file after every logged message.
+   */
+  static void SetIsSync(bool aIsSync);
+
+  /**
+   * @param aCaptureStacks If we should capture stacks for the Firefox
+   * Profiler markers that are recorded for for each log entry.
+   */
+  static void SetCaptureStacks(bool aCaptureStacks);
+
+  /**
+   * Indicates whether or not the given log level is enabled.
+   */
+  bool ShouldLog(LogLevel aLevel) const { return mLevel >= aLevel; }
+
+  /**
+   * Retrieves the log module's current level.
+   */
+  LogLevel Level() const { return mLevel; }
+
+  /**
+   * Sets the log module's level.
+   */
+  void SetLevel(LogLevel level);
+
+  /**
+   * Print a log message for this module.
+   */
+  void Printv(LogLevel aLevel, const char* aFmt, va_list aArgs) const
+      MOZ_FORMAT_PRINTF(3, 0);
+
+  void Printv(LogLevel aLevel, const TimeStamp* aStart, const char* aFmt,
+              va_list aArgs) const MOZ_FORMAT_PRINTF(4, 0);
+
+  /**
+   * Retrieves the module name.
+   */
+  const char* Name() const { return mName; }
+
+ private:
+  friend class LogModuleManager;
+
+  explicit LogModule(const char* aName, LogLevel aLevel)
+      : mName(strdup(aName)), mLevel(aLevel) {}
+
+  LogModule(LogModule&) = delete;
+  LogModule& operator=(const LogModule&) = delete;
+
+  char* mName;
+
+  Atomic<LogLevel, Relaxed> mLevel;
+};
+
+/**
+ * Helper class that lazy loads the given log module. This is safe to use for
+ * declaring static references to log modules and can be used as a replacement
+ * for accessing a LogModule directly.
+ *
+ * Example usage:
+ *   static LazyLogModule sLayoutLog("layout");
+ *
+ *   void Foo() {
+ *     MOZ_LOG(sLayoutLog, LogLevel::Verbose, ("Entering foo"));
+ *   }
+ */
+class LazyLogModule final {
+ public:
+  explicit constexpr LazyLogModule(const char* aLogName)
+      : mLogName(aLogName), mLog(nullptr) {}
+
+  MOZ_NEVER_INLINE_DEBUG operator LogModule*() {
+    // NB: The use of an atomic makes the reading and assignment of mLog
+    //     thread-safe. There is a small chance that mLog will be set more
+    //     than once, but that's okay as it will be set to the same LogModule
+    //     instance each time. Also note LogModule::Get is thread-safe.
+    LogModule* tmp = mLog;
+    if (MOZ_UNLIKELY(!tmp)) {
+      tmp = LogModule::Get(mLogName);
+      mLog = tmp;
+    }
+
+    return tmp;
+  }
+
+ private:
+  const char* const mLogName;
+
+  Atomic<LogModule*, ReleaseAcquire> mLog;
+};
+
+namespace detail {
+
+inline bool log_test(const LogModule* module, LogLevel level) {
+  MOZ_ASSERT(level != LogLevel::Disabled);
+  return module && module->ShouldLog(level);
+}
+
+void log_print(const LogModule* aModule, LogLevel aLevel, const char* aFmt, ...)
+    MOZ_FORMAT_PRINTF(3, 4);
+
+void log_print(const LogModule* aModule, LogLevel aLevel, TimeStamp* aStart,
+               const char* aFmt, ...) MOZ_FORMAT_PRINTF(4, 5);
+}  // namespace detail
+
+}  // namespace mozilla
+
+// Helper macro used convert MOZ_LOG's third parameter, |_args|, from a
+// parenthesized form to a varargs form. For example:
+//   ("%s", "a message") => "%s", "a message"
+#define MOZ_LOG_EXPAND_ARGS(...) __VA_ARGS__
+
+#if MOZ_LOGGING_ENABLED
+#  define MOZ_LOG_TEST(_module, _level) \
+    MOZ_UNLIKELY(mozilla::detail::log_test(_module, _level))
+#else
+// Define away MOZ_LOG_TEST here so the compiler will fold away entire
+// logging blocks via dead code elimination, e.g.:
+//
+//   if (MOZ_LOG_TEST(...)) {
+//     ...compute things to log and log them...
+//   }
+#  define MOZ_LOG_TEST(_module, _level) false
+#endif
+
+// The natural definition of the MOZ_LOG macro would expand to:
+//
+//   do {
+//     if (MOZ_LOG_TEST(_module, _level)) {
+//       mozilla::detail::log_print(_module, ...);
+//     }
+//   } while (0)
+//
+// However, since _module is a LazyLogModule, and we need to call
+// LazyLogModule::operator() to get a LogModule* for the MOZ_LOG_TEST
+// macro and for the logging call, we'll wind up doing *two* calls, one
+// for each, rather than a single call.  The compiler is not able to
+// fold the two calls into one, and the extra call can have a
+// significant effect on code size.  (Making LazyLogModule::operator() a
+// `const` function does not have any effect.)
+//
+// Therefore, we will have to make a single call ourselves.  But again,
+// the natural definition:
+//
+//   do {
+//     ::mozilla::LogModule* real_module = _module;
+//     if (MOZ_LOG_TEST(real_module, _level)) {
+//       mozilla::detail::log_print(real_module, ...);
+//     }
+//   } while (0)
+//
+// also has a problem: if logging is disabled, then we will call
+// LazyLogModule::operator() unnecessarily, and the compiler will not be
+// able to optimize away the call as dead code.  We would like to avoid
+// such a scenario, as the whole point of disabling logging is for the
+// logging statements to not generate any code.
+//
+// Therefore, we need different definitions of MOZ_LOG, depending on
+// whether logging is enabled or not.  (We need an actual definition of
+// MOZ_LOG even when logging is disabled to ensure the compiler sees that
+// variables only used during logging code are actually used, even if the
+// code will never be executed.)  Hence, the following code.
+//
+// MOZ_LOG_DURATION takes a start time, and will generate a time range
+// in the logs.  Also, if the Firefox Profiler is running,
+// MOZ_LOG_DURATION will generate a marker with a time duration
+// instead of a single point in time.
+#if MOZ_LOGGING_ENABLED
+#  define MOZ_LOG(_module, _level, _args)                      \
+    do {                                                       \
+      const ::mozilla::LogModule* moz_real_module = _module;   \
+      if (MOZ_LOG_TEST(moz_real_module, _level)) {             \
+        mozilla::detail::log_print(moz_real_module, _level,    \
+                                   MOZ_LOG_EXPAND_ARGS _args); \
+      }                                                        \
+    } while (0)
+#  define MOZ_LOG_DURATION(_module, _level, start, _args)          \
+    do {                                                           \
+      const ::mozilla::LogModule* moz_real_module = _module;       \
+      if (MOZ_LOG_TEST(moz_real_module, _level)) {                 \
+        mozilla::detail::log_print(moz_real_module, _level, start, \
+                                   MOZ_LOG_EXPAND_ARGS _args);     \
+      }                                                            \
+    } while (0)
+#else
+#  define MOZ_LOG(_module, _level, _args)                      \
+    do {                                                       \
+      if (MOZ_LOG_TEST(_module, _level)) {                     \
+        mozilla::detail::log_print(_module, _level,            \
+                                   MOZ_LOG_EXPAND_ARGS _args); \
+      }                                                        \
+    } while (0)
+#  define MOZ_LOG_DURATION(_module, _level, start, _args)      \
+    do {                                                       \
+      if (MOZ_LOG_TEST(_module, _level)) {                     \
+        mozilla::detail::log_print(_module, _level, start,     \
+                                   MOZ_LOG_EXPAND_ARGS _args); \
+      }                                                        \
+    } while (0)
+#endif
+
+// This #define is a Logging.h-only knob!  Don't encourage people to get fancy
+// with their log definitions by exporting it outside of Logging.h.
+#undef MOZ_LOGGING_ENABLED
+
+#endif  // mozilla_logging_h
diff --git a/xpcom/base/MacHelpers.h b/xpcom/base/MacHelpers.h
new file mode 100644
index 0000000000..baf4321034
--- /dev/null
+++ b/xpcom/base/MacHelpers.h
@@ -0,0 +1,18 @@
+/* -*- 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/. */
+
+#ifndef mozilla_MacHelpers_h
+#define mozilla_MacHelpers_h
+
+#include "nsString.h"
+
+namespace mozilla {
+
+nsresult GetSelectedCityInfo(nsAString& aCountryCode);
+
+}  // namespace mozilla
+
+#endif
diff --git a/xpcom/base/MacHelpers.mm b/xpcom/base/MacHelpers.mm
new file mode 100644
index 0000000000..22d8ef61a4
--- /dev/null
+++ b/xpcom/base/MacHelpers.mm
@@ -0,0 +1,32 @@
+/* -*- 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 "nsString.h"
+#include "MacHelpers.h"
+#include "MacStringHelpers.h"
+#include "nsObjCExceptions.h"
+
+#import <Foundation/Foundation.h>
+
+namespace mozilla {
+
+nsresult GetSelectedCityInfo(nsAString& aCountryCode) {
+  NS_OBJC_BEGIN_TRY_BLOCK_RETURN;
+
+  // Can be replaced with [[NSLocale currentLocale] countryCode] once we build
+  // with the 10.12 SDK.
+  id countryCode = [[NSLocale currentLocale] objectForKey:NSLocaleCountryCode];
+
+  if (![countryCode isKindOfClass:[NSString class]]) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return mozilla::CopyCocoaStringToXPCOMString((NSString*)countryCode, aCountryCode);
+
+  NS_OBJC_END_TRY_BLOCK_RETURN(NS_ERROR_FAILURE);
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/MacStringHelpers.h b/xpcom/base/MacStringHelpers.h
new file mode 100644
index 0000000000..c2f9ee82dc
--- /dev/null
+++ b/xpcom/base/MacStringHelpers.h
@@ -0,0 +1,20 @@
+/* -*- 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/. */
+
+#ifndef mozilla_MacStringHelpers_h
+#define mozilla_MacStringHelpers_h
+
+#include "nsString.h"
+
+#import <Foundation/Foundation.h>
+
+namespace mozilla {
+
+nsresult CopyCocoaStringToXPCOMString(NSString* aFrom, nsAString& aTo);
+
+}  // namespace mozilla
+
+#endif
diff --git a/xpcom/base/MacStringHelpers.mm b/xpcom/base/MacStringHelpers.mm
new file mode 100644
index 0000000000..9bfbdd912e
--- /dev/null
+++ b/xpcom/base/MacStringHelpers.mm
@@ -0,0 +1,34 @@
+/* -*- 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 "MacStringHelpers.h"
+#include "nsObjCExceptions.h"
+
+#include "mozilla/IntegerTypeTraits.h"
+#include <limits>
+
+namespace mozilla {
+
+nsresult CopyCocoaStringToXPCOMString(NSString* aFrom, nsAString& aTo) {
+  NS_OBJC_BEGIN_TRY_BLOCK_RETURN;
+
+  NSUInteger len = [aFrom length];
+  if (len > std::numeric_limits<nsAString::size_type>::max()) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  if (!aTo.SetLength(len, mozilla::fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  [aFrom getCharacters:reinterpret_cast<unichar*>(aTo.BeginWriting()) range:NSMakeRange(0, len)];
+
+  return NS_OK;
+
+  NS_OBJC_END_TRY_BLOCK_RETURN(NS_ERROR_FAILURE);
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/MemoryInfo.cpp b/xpcom/base/MemoryInfo.cpp
new file mode 100644
index 0000000000..6ce7f2b768
--- /dev/null
+++ b/xpcom/base/MemoryInfo.cpp
@@ -0,0 +1,105 @@
+/* -*- 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 "mozilla/MemoryInfo.h"
+
+#include "mozilla/DebugOnly.h"
+
+#include <algorithm>
+#include <windows.h>
+
+namespace mozilla {
+
+/* static */
+MemoryInfo MemoryInfo::Get(const void* aPtr, size_t aSize) {
+  MemoryInfo result;
+
+  result.mStart = uintptr_t(aPtr);
+  const char* ptr = reinterpret_cast<const char*>(aPtr);
+  const char* end = ptr + aSize;
+  DebugOnly<void*> base = nullptr;
+  while (ptr < end) {
+    MEMORY_BASIC_INFORMATION basicInfo;
+    if (!VirtualQuery(ptr, &basicInfo, sizeof(basicInfo))) {
+      break;
+    }
+
+    MOZ_ASSERT_IF(base, base == basicInfo.AllocationBase);
+    base = basicInfo.AllocationBase;
+
+    size_t regionSize =
+        std::min(size_t(basicInfo.RegionSize), size_t(end - ptr));
+
+    if (basicInfo.State == MEM_COMMIT) {
+      result.mCommitted += regionSize;
+    } else if (basicInfo.State == MEM_RESERVE) {
+      result.mReserved += regionSize;
+    } else if (basicInfo.State == MEM_FREE) {
+      result.mFree += regionSize;
+    } else {
+      MOZ_ASSERT_UNREACHABLE("Unexpected region state");
+    }
+    result.mSize += regionSize;
+    ptr += regionSize;
+
+    if (result.mType.isEmpty()) {
+      if (basicInfo.Type & MEM_IMAGE) {
+        result.mType += PageType::Image;
+      }
+      if (basicInfo.Type & MEM_MAPPED) {
+        result.mType += PageType::Mapped;
+      }
+      if (basicInfo.Type & MEM_PRIVATE) {
+        result.mType += PageType::Private;
+      }
+
+      // The first 8 bits of AllocationProtect are an enum. The remaining bits
+      // are flags.
+      switch (basicInfo.AllocationProtect & 0xff) {
+        case PAGE_EXECUTE_WRITECOPY:
+          result.mPerms += Perm::CopyOnWrite;
+          [[fallthrough]];
+        case PAGE_EXECUTE_READWRITE:
+          result.mPerms += Perm::Write;
+          [[fallthrough]];
+        case PAGE_EXECUTE_READ:
+          result.mPerms += Perm::Read;
+          [[fallthrough]];
+        case PAGE_EXECUTE:
+          result.mPerms += Perm::Execute;
+          break;
+
+        case PAGE_WRITECOPY:
+          result.mPerms += Perm::CopyOnWrite;
+          [[fallthrough]];
+        case PAGE_READWRITE:
+          result.mPerms += Perm::Write;
+          [[fallthrough]];
+        case PAGE_READONLY:
+          result.mPerms += Perm::Read;
+          break;
+
+        default:
+          break;
+      }
+
+      if (basicInfo.AllocationProtect & PAGE_GUARD) {
+        result.mPerms += Perm::Guard;
+      }
+      if (basicInfo.AllocationProtect & PAGE_NOCACHE) {
+        result.mPerms += Perm::NoCache;
+      }
+      if (basicInfo.AllocationProtect & PAGE_WRITECOMBINE) {
+        result.mPerms += Perm::WriteCombine;
+      }
+    }
+  }
+
+  result.mEnd = uintptr_t(ptr);
+  return result;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/MemoryInfo.h b/xpcom/base/MemoryInfo.h
new file mode 100644
index 0000000000..d122f6d377
--- /dev/null
+++ b/xpcom/base/MemoryInfo.h
@@ -0,0 +1,81 @@
+/* -*- 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/. */
+
+#ifndef mozilla_MemoryInfo_h
+#define mozilla_MemoryInfo_h
+
+#include <cstddef>
+#include <cstdint>
+#include "mozilla/Attributes.h"
+#include "mozilla/EnumSet.h"
+/**
+ * MemoryInfo is a helper class which describes the attributes and sizes of a
+ * particular region of VM memory on Windows. It roughtly corresponds to the
+ * values in a MEMORY_BASIC_INFORMATION struct, summed over an entire region or
+ * memory.
+ */
+
+namespace mozilla {
+
+class MemoryInfo final {
+ public:
+  enum class Perm : uint8_t {
+    Read,
+    Write,
+    Execute,
+    CopyOnWrite,
+    Guard,
+    NoCache,
+    WriteCombine,
+  };
+  enum class PageType : uint8_t {
+    Image,
+    Mapped,
+    Private,
+  };
+
+  using PermSet = EnumSet<Perm>;
+  using PageTypeSet = EnumSet<PageType>;
+
+  MemoryInfo() = default;
+  MOZ_IMPLICIT MemoryInfo(const MemoryInfo&) = default;
+
+  uintptr_t Start() const { return mStart; }
+  uintptr_t End() const { return mEnd; }
+
+  PageTypeSet Type() const { return mType; }
+  PermSet Perms() const { return mPerms; }
+
+  size_t Reserved() const { return mReserved; }
+  size_t Committed() const { return mCommitted; }
+  size_t Free() const { return mFree; }
+  size_t Size() const { return mSize; }
+
+  // Returns a MemoryInfo object containing the sums of all region sizes,
+  // divided into Reserved, Committed, and Free, depending on their State
+  // properties.
+  //
+  // The entire range of aSize bytes starting at aPtr must correspond to a
+  // single allocation. This restriction is enforced in debug builds.
+  static MemoryInfo Get(const void* aPtr, size_t aSize);
+
+ private:
+  uintptr_t mStart = 0;
+  uintptr_t mEnd = 0;
+
+  size_t mReserved = 0;
+  size_t mCommitted = 0;
+  size_t mFree = 0;
+  size_t mSize = 0;
+
+  PageTypeSet mType{};
+
+  PermSet mPerms{};
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_MemoryInfo_h
diff --git a/xpcom/base/MemoryMapping.cpp b/xpcom/base/MemoryMapping.cpp
new file mode 100644
index 0000000000..1ec1cf1f61
--- /dev/null
+++ b/xpcom/base/MemoryMapping.cpp
@@ -0,0 +1,208 @@
+/* -*- 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 "mozilla/MemoryMapping.h"
+
+#include "mozilla/BinarySearch.h"
+#include "mozilla/FileUtils.h"
+
+#include <fstream>
+#include <string>
+#include <sstream>
+
+namespace mozilla {
+
+namespace {
+struct VMFlagString {
+  const char* mName;
+  const char* mPrettyName;
+  VMFlag mFlag;
+};
+
+static const VMFlagString sVMFlagStrings[] = {
+    // clang-format off
+  {"ac", "Accountable",   VMFlag::Accountable},
+  {"ar", "ArchSpecific",  VMFlag::ArchSpecific},
+  {"dc", "NoFork",        VMFlag::NoFork},
+  {"dd", "NoCore",        VMFlag::NoCore},
+  {"de", "NoExpand",      VMFlag::NoExpand},
+  {"dw", "DisabledWrite", VMFlag::DisabledWrite},
+  {"ex", "Executable",    VMFlag::Executable},
+  {"gd", "GrowsDown",     VMFlag::GrowsDown},
+  {"hg", "HugePage",      VMFlag::HugePage},
+  {"ht", "HugeTLB",       VMFlag::HugeTLB},
+  {"io", "IO",            VMFlag::IO},
+  {"lo", "Locked",        VMFlag::Locked},
+  {"me", "MayExecute",    VMFlag::MayExecute},
+  {"mg", "Mergeable",     VMFlag::Mergeable},
+  {"mm", "MixedMap",      VMFlag::MixedMap},
+  {"mr", "MayRead",       VMFlag::MayRead},
+  {"ms", "MayShare",      VMFlag::MayShare},
+  {"mw", "MayWrite",      VMFlag::MayWrite},
+  {"nh", "NoHugePage",    VMFlag::NoHugePage},
+  {"nl", "NonLinear",     VMFlag::NonLinear},
+  {"nr", "NotReserved",   VMFlag::NotReserved},
+  {"pf", "PurePFN",       VMFlag::PurePFN},
+  {"rd", "Readable",      VMFlag::Readable},
+  {"rr", "Random",        VMFlag::Random},
+  {"sd", "SoftDirty",     VMFlag::SoftDirty},
+  {"sh", "Shared",        VMFlag::Shared},
+  {"sr", "Sequential",    VMFlag::Sequential},
+  {"wr", "Writable",      VMFlag::Writable},
+    // clang-format on
+};
+}  // anonymous namespace
+
+constexpr size_t kVMFlags = size_t(-1);
+
+// An array of known field names which may be present in an smaps file, and the
+// offsets of the corresponding fields in a MemoryMapping class.
+const MemoryMapping::Field MemoryMapping::sFields[] = {
+    // clang-format off
+  {"AnonHugePages",   offsetof(MemoryMapping, mAnonHugePages)},
+  {"Anonymous",       offsetof(MemoryMapping, mAnonymous)},
+  {"KernelPageSize",  offsetof(MemoryMapping, mKernelPageSize)},
+  {"LazyFree",        offsetof(MemoryMapping, mLazyFree)},
+  {"Locked",          offsetof(MemoryMapping, mLocked)},
+  {"MMUPageSize",     offsetof(MemoryMapping, mMMUPageSize)},
+  {"Private_Clean",   offsetof(MemoryMapping, mPrivate_Clean)},
+  {"Private_Dirty",   offsetof(MemoryMapping, mPrivate_Dirty)},
+  {"Private_Hugetlb", offsetof(MemoryMapping, mPrivate_Hugetlb)},
+  {"Pss",             offsetof(MemoryMapping, mPss)},
+  {"Referenced",      offsetof(MemoryMapping, mReferenced)},
+  {"Rss",             offsetof(MemoryMapping, mRss)},
+  {"Shared_Clean",    offsetof(MemoryMapping, mShared_Clean)},
+  {"Shared_Dirty",    offsetof(MemoryMapping, mShared_Dirty)},
+  {"Shared_Hugetlb",  offsetof(MemoryMapping, mShared_Hugetlb)},
+  {"ShmemPmdMapped",  offsetof(MemoryMapping, mShmemPmdMapped)},
+  {"Size",            offsetof(MemoryMapping, mSize)},
+  {"Swap",            offsetof(MemoryMapping, mSwap)},
+  {"SwapPss",         offsetof(MemoryMapping, mSwapPss)},
+  // VmFlags is a special case. It contains an array of flag strings, which
+  // describe attributes of the mapping, rather than a mapping size. We include
+  // it in this array to aid in parsing, but give it a separate sentinel value,
+  // and treat it specially.
+  {"VmFlags",         kVMFlags},
+    // clang-format on
+};
+
+template <typename T, int n>
+const T* FindEntry(const char* aName, const T (&aEntries)[n]) {
+  size_t index;
+  if (BinarySearchIf(
+          aEntries, 0, n,
+          [&](const T& aEntry) { return strcmp(aName, aEntry.mName); },
+          &index)) {
+    return &aEntries[index];
+  }
+  return nullptr;
+}
+
+using Perm = MemoryMapping::Perm;
+using PermSet = MemoryMapping::PermSet;
+
+nsresult GetMemoryMappings(nsTArray<MemoryMapping>& aMappings, pid_t aPid) {
+  std::ifstream stream;
+  if (aPid == 0) {
+    stream.open("/proc/self/smaps");
+  } else {
+    std::ostringstream path;
+    path << "/proc/" << aPid << "/smaps" << std::ends;
+    stream.open(path.str());
+  }
+  if (stream.fail()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  MemoryMapping* current = nullptr;
+  std::string buffer;
+  while (std::getline(stream, buffer)) {
+    size_t start, end, offset;
+    char flags[4] = "---";
+    char name[512];
+
+    name[0] = 0;
+
+    // clang-format off
+    // Match the start of an entry. A typical line looks something like:
+    //
+    // 1487118a7000-148711a5a000 r-xp 00000000 103:03 54004561                  /usr/lib/libc-2.27.so
+    // clang-format on
+    if (sscanf(buffer.c_str(), "%zx-%zx %4c %zx %*u:%*u %*u %511s\n", &start,
+               &end, flags, &offset, name) >= 4) {
+      PermSet perms;
+      if (flags[0] == 'r') {
+        perms += Perm::Read;
+      }
+      if (flags[1] == 'w') {
+        perms += Perm::Write;
+      }
+      if (flags[2] == 'x') {
+        perms += Perm::Execute;
+      }
+      if (flags[3] == 'p') {
+        perms += Perm::Private;
+      } else if (flags[3] == 's') {
+        perms += Perm::Shared;
+      }
+
+      current = aMappings.AppendElement(
+          MemoryMapping{start, end, perms, offset, name});
+      continue;
+    }
+    if (!current) {
+      continue;
+    }
+
+    nsAutoCStringN<128> line(buffer.c_str());
+    char* savePtr;
+    char* fieldName = strtok_r(line.BeginWriting(), ":", &savePtr);
+    if (!fieldName) {
+      continue;
+    }
+    auto* field = FindEntry(fieldName, MemoryMapping::sFields);
+    if (!field) {
+      continue;
+    }
+
+    if (field->mOffset == kVMFlags) {
+      while (char* flagName = strtok_r(nullptr, " \n", &savePtr)) {
+        if (auto* flag = FindEntry(flagName, sVMFlagStrings)) {
+          current->mFlags += flag->mFlag;
+        }
+      }
+      continue;
+    }
+
+    const char* rest = strtok_r(nullptr, "\n", &savePtr);
+    size_t value;
+    if (sscanf(rest, "%zd kB", &value) > 0) {
+      current->ValueForField(*field) = value * 1024;
+    }
+  }
+
+  return NS_OK;
+}
+
+void MemoryMapping::Dump(nsACString& aOut) const {
+  aOut.AppendPrintf("%zx-%zx Size: %zu Offset: %zx %s\n", mStart, mEnd,
+                    mEnd - mStart, mOffset, mName.get());
+
+  for (auto& field : MemoryMapping::sFields) {
+    if (field.mOffset < sizeof(*this)) {
+      aOut.AppendPrintf("  %s: %zd\n", field.mName, ValueForField(field));
+    }
+  }
+
+  aOut.AppendPrintf("  Flags: %x\n", mFlags.serialize());
+  for (auto& flag : sVMFlagStrings) {
+    if (mFlags.contains(flag.mFlag)) {
+      aOut.AppendPrintf("       : %s %s\n", flag.mName, flag.mPrettyName);
+    }
+  }
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/MemoryMapping.h b/xpcom/base/MemoryMapping.h
new file mode 100644
index 0000000000..51bbb0ab66
--- /dev/null
+++ b/xpcom/base/MemoryMapping.h
@@ -0,0 +1,183 @@
+/* -*- 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/. */
+
+#ifndef mozilla_MemoryMapping_h
+#define mozilla_MemoryMapping_h
+
+#include <cstdint>
+#include "mozilla/EnumSet.h"
+#include "nsString.h"
+#include "nsTArrayForwardDeclare.h"
+
+/**
+ * MemoryMapping is a helper class which describes an entry in the Linux
+ * /proc/<pid>/smaps file. See procfs(5) for details on the entry format.
+ *
+ * The GetMemoryMappings() function returns an array of such entries, sorted by
+ * start address, one for each entry in the current process's address space.
+ */
+
+namespace mozilla {
+
+enum class VMFlag : uint8_t {
+  Readable,       // rd  - readable
+  Writable,       // wr  - writable
+  Executable,     // ex  - executable
+  Shared,         // sh  - shared
+  MayRead,        // mr  - may read
+  MayWrite,       // mw  - may write
+  MayExecute,     // me  - may execute
+  MayShare,       // ms  - may share
+  GrowsDown,      // gd  - stack segment grows down
+  PurePFN,        // pf  - pure PFN range
+  DisabledWrite,  // dw  - disabled write to the mapped file
+  Locked,         // lo  - pages are locked in memory
+  IO,             // io  - memory mapped I/O area
+  Sequential,     // sr  - sequential read advise provided
+  Random,         // rr  - random read advise provided
+  NoFork,         // dc  - do not copy area on fork
+  NoExpand,       // de  - do not expand area on remapping
+  Accountable,    // ac  - area is accountable
+  NotReserved,    // nr  - swap space is not reserved for the area
+  HugeTLB,        // ht  - area uses huge tlb pages
+  NonLinear,      // nl  - non-linear mapping
+  ArchSpecific,   // ar  - architecture specific flag
+  NoCore,         // dd  - do not include area into core dump
+  SoftDirty,      // sd  - soft-dirty flag
+  MixedMap,       // mm  - mixed map area
+  HugePage,       // hg  - huge page advise flag
+  NoHugePage,     // nh  - no-huge page advise flag
+  Mergeable,      // mg  - mergeable advise flag
+};
+
+using VMFlagSet = EnumSet<VMFlag, uint32_t>;
+
+class MemoryMapping final {
+ public:
+  enum class Perm : uint8_t {
+    Read,
+    Write,
+    Execute,
+    Shared,
+    Private,
+  };
+
+  using PermSet = EnumSet<Perm>;
+
+  MemoryMapping(uintptr_t aStart, uintptr_t aEnd, PermSet aPerms,
+                size_t aOffset, const char* aName)
+      : mStart(aStart),
+        mEnd(aEnd),
+        mOffset(aOffset),
+        mName(aName),
+        mPerms(aPerms) {}
+
+  const nsCString& Name() const { return mName; }
+
+  uintptr_t Start() const { return mStart; }
+  uintptr_t End() const { return mEnd; }
+
+  bool Includes(const void* aPtr) const {
+    auto ptr = uintptr_t(aPtr);
+    return ptr >= mStart && ptr < mEnd;
+  }
+
+  PermSet Perms() const { return mPerms; }
+  VMFlagSet VMFlags() const { return mFlags; }
+
+  // For file mappings, the offset in the mapped file which corresponds to the
+  // start of the mapped region.
+  size_t Offset() const { return mOffset; }
+
+  size_t AnonHugePages() const { return mAnonHugePages; }
+  size_t Anonymous() const { return mAnonymous; }
+  size_t KernelPageSize() const { return mKernelPageSize; }
+  size_t LazyFree() const { return mLazyFree; }
+  size_t Locked() const { return mLocked; }
+  size_t MMUPageSize() const { return mMMUPageSize; }
+  size_t Private_Clean() const { return mPrivate_Clean; }
+  size_t Private_Dirty() const { return mPrivate_Dirty; }
+  size_t Private_Hugetlb() const { return mPrivate_Hugetlb; }
+  size_t Pss() const { return mPss; }
+  size_t Referenced() const { return mReferenced; }
+  size_t Rss() const { return mRss; }
+  size_t Shared_Clean() const { return mShared_Clean; }
+  size_t Shared_Dirty() const { return mShared_Dirty; }
+  size_t Shared_Hugetlb() const { return mShared_Hugetlb; }
+  size_t ShmemPmdMapped() const { return mShmemPmdMapped; }
+  size_t Size() const { return mSize; }
+  size_t Swap() const { return mSwap; }
+  size_t SwapPss() const { return mSwapPss; }
+
+  // Dumps a string representation of the entry, similar to its format in the
+  // smaps file, to the given string. Mainly useful for debugging.
+  void Dump(nsACString& aOut) const;
+
+  // These comparison operators are used for binary searching sorted arrays of
+  // MemoryMapping entries to find the one which contains a given pointer.
+  bool operator==(const void* aPtr) const { return Includes(aPtr); }
+  bool operator<(const void* aPtr) const { return mStart < uintptr_t(aPtr); }
+
+ private:
+  friend nsresult GetMemoryMappings(nsTArray<MemoryMapping>& aMappings,
+                                    pid_t aPid);
+
+  uintptr_t mStart = 0;
+  uintptr_t mEnd = 0;
+
+  size_t mOffset = 0;
+
+  nsCString mName;
+
+  // Members for size fields in the smaps file. Please keep these in sync with
+  // the sFields array.
+  size_t mAnonHugePages = 0;
+  size_t mAnonymous = 0;
+  size_t mKernelPageSize = 0;
+  size_t mLazyFree = 0;
+  size_t mLocked = 0;
+  size_t mMMUPageSize = 0;
+  size_t mPrivate_Clean = 0;
+  size_t mPrivate_Dirty = 0;
+  size_t mPrivate_Hugetlb = 0;
+  size_t mPss = 0;
+  size_t mReferenced = 0;
+  size_t mRss = 0;
+  size_t mShared_Clean = 0;
+  size_t mShared_Dirty = 0;
+  size_t mShared_Hugetlb = 0;
+  size_t mShmemPmdMapped = 0;
+  size_t mSize = 0;
+  size_t mSwap = 0;
+  size_t mSwapPss = 0;
+
+  PermSet mPerms{};
+  VMFlagSet mFlags{};
+
+  // Contains the name and offset of one of the above size_t fields, for use in
+  // parsing in dumping. The below helpers contain a list of the fields, and map
+  // Field entries to the appropriate member in a class instance.
+  struct Field {
+    const char* mName;
+    size_t mOffset;
+  };
+
+  static const Field sFields[20];
+
+  size_t& ValueForField(const Field& aField) {
+    char* fieldPtr = reinterpret_cast<char*>(this) + aField.mOffset;
+    return reinterpret_cast<size_t*>(fieldPtr)[0];
+  }
+  size_t ValueForField(const Field& aField) const {
+    return const_cast<MemoryMapping*>(this)->ValueForField(aField);
+  }
+};
+
+nsresult GetMemoryMappings(nsTArray<MemoryMapping>& aMappings, pid_t aPid = 0);
+
+}  // namespace mozilla
+
+#endif  // mozilla_MemoryMapping_h
diff --git a/xpcom/base/MemoryPressureLevelMac.h b/xpcom/base/MemoryPressureLevelMac.h
new file mode 100644
index 0000000000..38cb49a4fd
--- /dev/null
+++ b/xpcom/base/MemoryPressureLevelMac.h
@@ -0,0 +1,77 @@
+/* -*- 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/. */
+
+#ifndef mozilla_MemoryPressureLevelMac_h
+#define mozilla_MemoryPressureLevelMac_h
+
+namespace mozilla {
+
+#if defined(XP_DARWIN)
+// An internal representation of the Mac memory-pressure level constants.
+class MacMemoryPressureLevel {
+ public:
+  // Order enum values so that higher integer values represent higher
+  // memory pressure levels allowing comparison operators to be used.
+  enum class Value {
+    eUnset,
+    eUnexpected,
+    eNormal,
+    eWarning,
+    eCritical,
+  };
+
+  MacMemoryPressureLevel() : mValue(Value::eUnset) {}
+  MOZ_IMPLICIT MacMemoryPressureLevel(Value aValue) : mValue(aValue) {}
+
+  bool operator==(const Value& aRhsValue) const { return mValue == aRhsValue; }
+  bool operator==(const MacMemoryPressureLevel& aRhs) const {
+    return mValue == aRhs.mValue;
+  }
+
+  // Implement '<' and derive the other comparators from it.
+  bool operator<(const MacMemoryPressureLevel& aRhs) const {
+    return mValue < aRhs.mValue;
+  }
+  bool operator>(const MacMemoryPressureLevel& aRhs) const {
+    return aRhs < *this;
+  }
+  bool operator<=(const MacMemoryPressureLevel& aRhs) const {
+    return !(aRhs < *this);
+  }
+  bool operator>=(const MacMemoryPressureLevel& aRhs) const {
+    return !(*this < aRhs);
+  }
+
+  Value GetValue() { return mValue; }
+  bool IsNormal() { return mValue == Value::eNormal; }
+  bool IsUnsetOrNormal() { return IsNormal() || (mValue == Value::eUnset); }
+  bool IsWarningOrAbove() {
+    return (mValue == Value::eWarning) || (mValue == Value::eCritical);
+  }
+
+  const char* ToString() {
+    switch (mValue) {
+      case Value::eUnset:
+        return "Unset";
+      case Value::eUnexpected:
+        return "Unexpected";
+      case Value::eNormal:
+        return "Normal";
+      case Value::eWarning:
+        return "Warning";
+      case Value::eCritical:
+        return "Critical";
+    }
+  }
+
+ private:
+  Value mValue;
+};
+#endif
+
+}  // namespace mozilla
+
+#endif  // mozilla_MemoryPressureLevelMac_h
diff --git a/xpcom/base/MemoryReportingProcess.h b/xpcom/base/MemoryReportingProcess.h
new file mode 100644
index 0000000000..36410e702b
--- /dev/null
+++ b/xpcom/base/MemoryReportingProcess.h
@@ -0,0 +1,45 @@
+/* -*- 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/. */
+
+#ifndef xpcom_base_MemoryReportingProcess_h
+#define xpcom_base_MemoryReportingProcess_h
+
+#include <stdint.h>
+#include "nscore.h"
+
+namespace mozilla {
+namespace ipc {
+class FileDescriptor;
+}  // namespace ipc
+
+template <class T>
+class Maybe;
+
+// Top-level process actors should implement this to integrate with
+// nsMemoryReportManager.
+class MemoryReportingProcess {
+ public:
+  NS_IMETHOD_(MozExternalRefCountType) AddRef() = 0;
+  NS_IMETHOD_(MozExternalRefCountType) Release() = 0;
+
+  virtual ~MemoryReportingProcess() = default;
+
+  // Return true if the process is still alive, false otherwise.
+  virtual bool IsAlive() const = 0;
+
+  // Initiate a memory report request, returning true if a report was
+  // successfully initiated and false otherwise.
+  virtual bool SendRequestMemoryReport(
+      const uint32_t& aGeneration, const bool& aAnonymize,
+      const bool& aMinimizeMemoryUsage,
+      const Maybe<mozilla::ipc::FileDescriptor>& aDMDFile) = 0;
+
+  virtual int32_t Pid() const = 0;
+};
+
+}  // namespace mozilla
+
+#endif  // xpcom_base_MemoryReportingProcess_h
diff --git a/xpcom/base/MemoryTelemetry.cpp b/xpcom/base/MemoryTelemetry.cpp
new file mode 100644
index 0000000000..e9b6bff80e
--- /dev/null
+++ b/xpcom/base/MemoryTelemetry.cpp
@@ -0,0 +1,520 @@
+/* -*- 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 "MemoryTelemetry.h"
+#include "nsMemoryReporterManager.h"
+
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/Result.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/Services.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/SimpleEnumerator.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "nsContentUtils.h"
+#include "nsIBrowserDOMWindow.h"
+#include "nsIDOMChromeWindow.h"
+#include "nsIMemoryReporter.h"
+#include "nsIWindowMediator.h"
+#include "nsImportModule.h"
+#include "nsITelemetry.h"
+#include "nsNetCID.h"
+#include "nsObserverService.h"
+#include "nsReadableUtils.h"
+#include "nsThreadUtils.h"
+#include "nsXULAppAPI.h"
+#include "xpcpublic.h"
+
+#include <cstdlib>
+
+using namespace mozilla;
+
+using mozilla::dom::AutoJSAPI;
+using mozilla::dom::ContentParent;
+
+// Do not gather data more than once a minute (ms)
+static constexpr uint32_t kTelemetryInterval = 60 * 1000;
+
+static constexpr const char* kTopicCycleCollectorBegin =
+    "cycle-collector-begin";
+
+namespace {
+
+enum class PrevValue : uint32_t {
+#ifdef XP_WIN
+  LOW_MEMORY_EVENTS_VIRTUAL,
+  LOW_MEMORY_EVENTS_COMMIT_SPACE,
+  LOW_MEMORY_EVENTS_PHYSICAL,
+#endif
+#if defined(XP_LINUX) && !defined(ANDROID)
+  PAGE_FAULTS_HARD,
+#endif
+  SIZE_,
+};
+
+}  // anonymous namespace
+
+constexpr uint32_t kUninitialized = ~0;
+
+static uint32_t gPrevValues[uint32_t(PrevValue::SIZE_)];
+
+static uint32_t PrevValueIndex(Telemetry::HistogramID aId) {
+  switch (aId) {
+#ifdef XP_WIN
+    case Telemetry::LOW_MEMORY_EVENTS_VIRTUAL:
+      return uint32_t(PrevValue::LOW_MEMORY_EVENTS_VIRTUAL);
+    case Telemetry::LOW_MEMORY_EVENTS_COMMIT_SPACE:
+      return uint32_t(PrevValue::LOW_MEMORY_EVENTS_COMMIT_SPACE);
+    case Telemetry::LOW_MEMORY_EVENTS_PHYSICAL:
+      return uint32_t(PrevValue::LOW_MEMORY_EVENTS_PHYSICAL);
+#endif
+#if defined(XP_LINUX) && !defined(ANDROID)
+    case Telemetry::PAGE_FAULTS_HARD:
+      return uint32_t(PrevValue::PAGE_FAULTS_HARD);
+#endif
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unexpected histogram ID");
+      return 0;
+  }
+}
+
+NS_IMPL_ISUPPORTS(MemoryTelemetry, nsIObserver, nsISupportsWeakReference)
+
+MemoryTelemetry::MemoryTelemetry()
+    : mThreadPool(do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID)) {}
+
+void MemoryTelemetry::Init() {
+  for (auto& val : gPrevValues) {
+    val = kUninitialized;
+  }
+
+  if (XRE_IsContentProcess()) {
+    nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+    MOZ_RELEASE_ASSERT(obs);
+
+    obs->AddObserver(this, "content-child-shutdown", true);
+  }
+}
+
+/* static */ MemoryTelemetry& MemoryTelemetry::Get() {
+  static RefPtr<MemoryTelemetry> sInstance;
+
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!sInstance) {
+    sInstance = new MemoryTelemetry();
+    sInstance->Init();
+    ClearOnShutdown(&sInstance);
+  }
+  return *sInstance;
+}
+
+nsresult MemoryTelemetry::DelayedInit() {
+  if (Telemetry::CanRecordExtended()) {
+    nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+    MOZ_RELEASE_ASSERT(obs);
+
+    obs->AddObserver(this, kTopicCycleCollectorBegin, true);
+  }
+
+  GatherReports();
+
+  return NS_OK;
+}
+
+nsresult MemoryTelemetry::Shutdown() {
+  nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+  MOZ_RELEASE_ASSERT(obs);
+
+  obs->RemoveObserver(this, kTopicCycleCollectorBegin);
+
+  return NS_OK;
+}
+
+static inline void HandleMemoryReport(Telemetry::HistogramID aId,
+                                      int32_t aUnits, uint64_t aAmount,
+                                      const nsCString& aKey = VoidCString()) {
+  uint32_t val;
+  switch (aUnits) {
+    case nsIMemoryReporter::UNITS_BYTES:
+      val = uint32_t(aAmount / 1024);
+      break;
+
+    case nsIMemoryReporter::UNITS_PERCENTAGE:
+      // UNITS_PERCENTAGE amounts are 100x greater than their raw value.
+      val = uint32_t(aAmount / 100);
+      break;
+
+    case nsIMemoryReporter::UNITS_COUNT:
+      val = uint32_t(aAmount);
+      break;
+
+    case nsIMemoryReporter::UNITS_COUNT_CUMULATIVE: {
+      // If the reporter gives us a cumulative count, we'll report the
+      // difference in its value between now and our previous ping.
+
+      uint32_t idx = PrevValueIndex(aId);
+      uint32_t prev = gPrevValues[idx];
+      gPrevValues[idx] = aAmount;
+
+      if (prev == kUninitialized) {
+        // If this is the first time we're reading this reporter, store its
+        // current value but don't report it in the telemetry ping, so we
+        // ignore the effect startup had on the reporter.
+        return;
+      }
+      val = aAmount - prev;
+      break;
+    }
+
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unexpected aUnits value");
+      return;
+  }
+
+  // Note: The reference equality check here should allow the compiler to
+  // optimize this case out at compile time when we weren't given a key,
+  // while IsEmpty() or IsVoid() most likely will not.
+  if (&aKey == &VoidCString()) {
+    Telemetry::Accumulate(aId, val);
+  } else {
+    Telemetry::Accumulate(aId, aKey, val);
+  }
+}
+
+nsresult MemoryTelemetry::GatherReports(
+    const std::function<void()>& aCompletionCallback) {
+  auto cleanup = MakeScopeExit([&]() {
+    if (aCompletionCallback) {
+      aCompletionCallback();
+    }
+  });
+
+  RefPtr<nsMemoryReporterManager> mgr = nsMemoryReporterManager::GetOrCreate();
+  MOZ_DIAGNOSTIC_ASSERT(mgr);
+  NS_ENSURE_TRUE(mgr, NS_ERROR_FAILURE);
+
+#define RECORD(id, metric, units)                                       \
+  do {                                                                  \
+    int64_t amt;                                                        \
+    nsresult rv = mgr->Get##metric(&amt);                               \
+    if (NS_SUCCEEDED(rv)) {                                             \
+      HandleMemoryReport(Telemetry::id, nsIMemoryReporter::units, amt); \
+    } else if (rv != NS_ERROR_NOT_AVAILABLE) {                          \
+      NS_WARNING("Failed to retrieve memory telemetry for " #metric);   \
+    }                                                                   \
+  } while (0)
+
+  // GHOST_WINDOWS is opt-out as of Firefox 55
+  RECORD(GHOST_WINDOWS, GhostWindows, UNITS_COUNT);
+
+  // If we're running in the parent process, collect data from all processes for
+  // the MEMORY_TOTAL histogram.
+  if (XRE_IsParentProcess() && !mGatheringTotalMemory) {
+    GatherTotalMemory();
+  }
+
+  if (!Telemetry::CanRecordReleaseData()) {
+    return NS_OK;
+  }
+
+  // Get memory measurements from distinguished amount attributes.  We used
+  // to measure "explicit" too, but it could cause hangs, and the data was
+  // always really noisy anyway.  See bug 859657.
+  //
+  // test_TelemetrySession.js relies on some of these histograms being
+  // here.  If you remove any of the following histograms from here, you'll
+  // have to modify test_TelemetrySession.js:
+  //
+  //   * MEMORY_TOTAL,
+  //   * MEMORY_JS_GC_HEAP, and
+  //   * MEMORY_JS_COMPARTMENTS_SYSTEM.
+  //
+  // The distinguished amount attribute names don't match the telemetry id
+  // names in some cases due to a combination of (a) historical reasons, and
+  // (b) the fact that we can't change telemetry id names without breaking
+  // data continuity.
+
+  // Collect cheap or main-thread only metrics synchronously, on the main
+  // thread.
+  RECORD(MEMORY_JS_GC_HEAP, JSMainRuntimeGCHeap, UNITS_BYTES);
+  RECORD(MEMORY_JS_COMPARTMENTS_SYSTEM, JSMainRuntimeCompartmentsSystem,
+         UNITS_COUNT);
+  RECORD(MEMORY_JS_COMPARTMENTS_USER, JSMainRuntimeCompartmentsUser,
+         UNITS_COUNT);
+  RECORD(MEMORY_JS_REALMS_SYSTEM, JSMainRuntimeRealmsSystem, UNITS_COUNT);
+  RECORD(MEMORY_JS_REALMS_USER, JSMainRuntimeRealmsUser, UNITS_COUNT);
+  RECORD(MEMORY_IMAGES_CONTENT_USED_UNCOMPRESSED, ImagesContentUsedUncompressed,
+         UNITS_BYTES);
+  RECORD(MEMORY_STORAGE_SQLITE, StorageSQLite, UNITS_BYTES);
+#ifdef XP_WIN
+  RECORD(LOW_MEMORY_EVENTS_PHYSICAL, LowMemoryEventsPhysical,
+         UNITS_COUNT_CUMULATIVE);
+#endif
+#if defined(XP_LINUX) && !defined(ANDROID)
+  RECORD(PAGE_FAULTS_HARD, PageFaultsHard, UNITS_COUNT_CUMULATIVE);
+#endif
+
+  RefPtr<Runnable> completionRunnable;
+  if (aCompletionCallback) {
+    completionRunnable = NS_NewRunnableFunction(__func__, aCompletionCallback);
+  }
+
+  // Collect expensive metrics that can be calculated off-main-thread
+  // asynchronously, on a background thread.
+  RefPtr<Runnable> runnable = NS_NewRunnableFunction(
+      "MemoryTelemetry::GatherReports", [mgr, completionRunnable]() mutable {
+        Telemetry::AutoTimer<Telemetry::MEMORY_COLLECTION_TIME> autoTimer;
+        RECORD(MEMORY_VSIZE, Vsize, UNITS_BYTES);
+#if !defined(HAVE_64BIT_BUILD) || !defined(XP_WIN)
+        RECORD(MEMORY_VSIZE_MAX_CONTIGUOUS, VsizeMaxContiguous, UNITS_BYTES);
+#endif
+        RECORD(MEMORY_RESIDENT_FAST, ResidentFast, UNITS_BYTES);
+        RECORD(MEMORY_RESIDENT_PEAK, ResidentPeak, UNITS_BYTES);
+// Although we can measure unique memory on MacOS we choose not to, because
+// doing so is too slow for telemetry.
+#ifndef XP_MACOSX
+        RECORD(MEMORY_UNIQUE, ResidentUnique, UNITS_BYTES);
+#endif
+
+#ifdef HAVE_JEMALLOC_STATS
+        jemalloc_stats_t stats;
+        jemalloc_stats(&stats);
+        HandleMemoryReport(Telemetry::MEMORY_HEAP_ALLOCATED,
+                           nsIMemoryReporter::UNITS_BYTES,
+                           mgr->HeapAllocated(stats));
+        HandleMemoryReport(Telemetry::MEMORY_HEAP_OVERHEAD_FRACTION,
+                           nsIMemoryReporter::UNITS_PERCENTAGE,
+                           mgr->HeapOverheadFraction(stats));
+#endif
+
+        if (completionRunnable) {
+          NS_DispatchToMainThread(completionRunnable.forget(),
+                                  NS_DISPATCH_NORMAL);
+        }
+      });
+
+#undef RECORD
+
+  nsresult rv = mThreadPool->Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
+  if (!NS_WARN_IF(NS_FAILED(rv))) {
+    cleanup.release();
+  }
+
+  return NS_OK;
+}
+
+namespace {
+struct ChildProcessInfo {
+  GeckoProcessType mType;
+#if defined(XP_WIN)
+  HANDLE mHandle;
+#elif defined(XP_MACOSX)
+  task_t mHandle;
+#else
+  pid_t mHandle;
+#endif
+};
+}  // namespace
+
+/**
+ * Runs a task on the background thread pool to fetch the memory usage of all
+ * processes.
+ */
+void MemoryTelemetry::GatherTotalMemory() {
+  MOZ_ASSERT(!mGatheringTotalMemory);
+  mGatheringTotalMemory = true;
+
+  nsTArray<ChildProcessInfo> infos;
+  mozilla::ipc::GeckoChildProcessHost::GetAll(
+      [&](mozilla::ipc::GeckoChildProcessHost* aGeckoProcess) {
+        if (!aGeckoProcess->GetChildProcessHandle()) {
+          return;
+        }
+
+        ChildProcessInfo info{};
+        info.mType = aGeckoProcess->GetProcessType();
+
+        // NOTE: For now we ignore non-content processes here for compatibility
+        // with the existing probe. We may want to introduce a new probe in the
+        // future which also collects data for non-content processes.
+        if (info.mType != GeckoProcessType_Content) {
+          return;
+        }
+
+#if defined(XP_WIN)
+        if (!::DuplicateHandle(::GetCurrentProcess(),
+                               aGeckoProcess->GetChildProcessHandle(),
+                               ::GetCurrentProcess(), &info.mHandle, 0, false,
+                               DUPLICATE_SAME_ACCESS)) {
+          return;
+        }
+#elif defined(XP_MACOSX)
+        info.mHandle = aGeckoProcess->GetChildTask();
+        if (mach_port_mod_refs(mach_task_self(), info.mHandle,
+                               MACH_PORT_RIGHT_SEND, 1) != KERN_SUCCESS) {
+          return;
+        }
+#else
+        info.mHandle = aGeckoProcess->GetChildProcessId();
+#endif
+
+        infos.AppendElement(info);
+      });
+
+  mThreadPool->Dispatch(NS_NewRunnableFunction(
+      "MemoryTelemetry::GatherTotalMemory", [infos = std::move(infos)] {
+        RefPtr<nsMemoryReporterManager> mgr =
+            nsMemoryReporterManager::GetOrCreate();
+        MOZ_RELEASE_ASSERT(mgr);
+
+        int64_t totalMemory = mgr->ResidentFast();
+        nsTArray<int64_t> childSizes(infos.Length());
+
+        // Use our handle for the remote process to collect resident unique set
+        // size information for that process.
+        for (const auto& info : infos) {
+#ifdef XP_MACOSX
+          int64_t memory =
+              nsMemoryReporterManager::PhysicalFootprint(info.mHandle);
+#else
+	  int64_t memory =
+	      nsMemoryReporterManager::ResidentUnique(info.mHandle);
+#endif
+          if (memory > 0) {
+            childSizes.AppendElement(memory);
+            totalMemory += memory;
+          }
+
+#if defined(XP_WIN)
+          ::CloseHandle(info.mHandle);
+#elif defined(XP_MACOSX)
+          mach_port_deallocate(mach_task_self(), info.mHandle);
+#endif
+        }
+
+        NS_DispatchToMainThread(NS_NewRunnableFunction(
+            "MemoryTelemetry::FinishGatheringTotalMemory",
+            [totalMemory, childSizes = std::move(childSizes)] {
+              MemoryTelemetry::Get().FinishGatheringTotalMemory(totalMemory,
+                                                                childSizes);
+            }));
+      }));
+}
+
+nsresult MemoryTelemetry::FinishGatheringTotalMemory(
+    int64_t aTotalMemory, const nsTArray<int64_t>& aChildSizes) {
+  mGatheringTotalMemory = false;
+
+  // Total memory usage can be difficult to measure both accurately and fast
+  // enough for telemetry (iterating memory maps can jank whole processes on
+  // MacOS).  Therefore this shouldn't be relied on as an absolute measurement
+  // especially on MacOS where it double-counts shared memory.  For a more
+  // detailed explaination see:
+  // https://groups.google.com/a/mozilla.org/g/dev-platform/c/WGNOtjHdsdA
+  HandleMemoryReport(Telemetry::MEMORY_TOTAL, nsIMemoryReporter::UNITS_BYTES,
+                     aTotalMemory);
+
+  if (aChildSizes.Length() > 1) {
+    int32_t tabsCount;
+    MOZ_TRY_VAR(tabsCount, GetOpenTabsCount());
+
+    nsCString key;
+    if (tabsCount <= 10) {
+      key = "0 - 10 tabs";
+    } else if (tabsCount <= 500) {
+      key = "11 - 500 tabs";
+    } else {
+      key = "more tabs";
+    }
+
+    // Mean of the USS of all the content processes.
+    int64_t mean = 0;
+    for (auto size : aChildSizes) {
+      mean += size;
+    }
+    mean /= aChildSizes.Length();
+
+    // For some users, for unknown reasons (though most likely because they're
+    // in a sandbox without procfs mounted), we wind up with 0 here, which
+    // triggers a floating point exception if we try to calculate values using
+    // it.
+    if (!mean) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    // Absolute error of USS for each content process, normalized by the mean
+    // (*100 to get it in percentage). 20% means for a content process that it
+    // is using 20% more or 20% less than the mean.
+    for (auto size : aChildSizes) {
+      int64_t diff = llabs(size - mean) * 100 / mean;
+
+      HandleMemoryReport(Telemetry::MEMORY_DISTRIBUTION_AMONG_CONTENT,
+                         nsIMemoryReporter::UNITS_COUNT, diff, key);
+    }
+  }
+
+  // This notification is for testing only.
+  if (nsCOMPtr<nsIObserverService> obs = services::GetObserverService()) {
+    obs->NotifyObservers(nullptr, "gather-memory-telemetry-finished", nullptr);
+  }
+
+  return NS_OK;
+}
+
+/* static */ Result<uint32_t, nsresult> MemoryTelemetry::GetOpenTabsCount() {
+  nsresult rv;
+
+  nsCOMPtr<nsIWindowMediator> windowMediator(
+      do_GetService(NS_WINDOWMEDIATOR_CONTRACTID, &rv));
+  MOZ_TRY(rv);
+
+  nsCOMPtr<nsISimpleEnumerator> enumerator;
+  MOZ_TRY(windowMediator->GetEnumerator(u"navigator:browser",
+                                        getter_AddRefs(enumerator)));
+
+  uint32_t total = 0;
+  for (auto& window : SimpleEnumerator<nsIDOMChromeWindow>(enumerator)) {
+    nsCOMPtr<nsIBrowserDOMWindow> browserWin;
+    MOZ_TRY(window->GetBrowserDOMWindow(getter_AddRefs(browserWin)));
+
+    NS_ENSURE_TRUE(browserWin, Err(NS_ERROR_UNEXPECTED));
+
+    uint32_t tabCount;
+    MOZ_TRY(browserWin->GetTabCount(&tabCount));
+    total += tabCount;
+  }
+
+  return total;
+}
+
+nsresult MemoryTelemetry::Observe(nsISupports* aSubject, const char* aTopic,
+                                  const char16_t* aData) {
+  if (strcmp(aTopic, kTopicCycleCollectorBegin) == 0) {
+    auto now = TimeStamp::Now();
+    if (!mLastPoll.IsNull() &&
+        (now - mLastPoll).ToMilliseconds() < kTelemetryInterval) {
+      return NS_OK;
+    }
+
+    mLastPoll = now;
+
+    NS_DispatchToCurrentThreadQueue(
+        NewRunnableMethod<std::function<void()>>(
+            "MemoryTelemetry::GatherReports", this,
+            &MemoryTelemetry::GatherReports, nullptr),
+        EventQueuePriority::Idle);
+  } else if (strcmp(aTopic, "content-child-shutdown") == 0) {
+    if (nsCOMPtr<nsITelemetry> telemetry =
+            do_GetService("@mozilla.org/base/telemetry;1")) {
+      telemetry->FlushBatchedChildTelemetry();
+    }
+  }
+  return NS_OK;
+}
diff --git a/xpcom/base/MemoryTelemetry.h b/xpcom/base/MemoryTelemetry.h
new file mode 100644
index 0000000000..b7c7fe8ad6
--- /dev/null
+++ b/xpcom/base/MemoryTelemetry.h
@@ -0,0 +1,72 @@
+/* -*- 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/. */
+
+#ifndef mozilla_MemoryTelemetry_h
+#define mozilla_MemoryTelemetry_h
+
+#include "mozilla/TimeStamp.h"
+#include "mozilla/Result.h"
+#include "nsIObserver.h"
+#include "nsITimer.h"
+#include "nsTArray.h"
+#include "nsWeakReference.h"
+
+#include <functional>
+
+class nsIEventTarget;
+
+namespace mozilla {
+
+namespace ipc {
+enum class ResponseRejectReason;
+}
+
+/**
+ * Periodically gathers memory usage metrics after cycle collection, and
+ * populates telemetry histograms with their values.
+ */
+class MemoryTelemetry final : public nsIObserver,
+                              public nsSupportsWeakReference {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  static MemoryTelemetry& Get();
+
+  nsresult GatherReports(
+      const std::function<void()>& aCompletionCallback = nullptr);
+
+  /**
+   * Does expensive initialization, which should happen only after startup has
+   * completed, and the event loop is idle.
+   */
+  nsresult DelayedInit();
+
+  nsresult Shutdown();
+
+ private:
+  MemoryTelemetry();
+
+  ~MemoryTelemetry() = default;
+
+  void Init();
+
+  static Result<uint32_t, nsresult> GetOpenTabsCount();
+
+  void GatherTotalMemory();
+  nsresult FinishGatheringTotalMemory(int64_t aTotalMemory,
+                                      const nsTArray<int64_t>& aChildSizes);
+
+  nsCOMPtr<nsIEventTarget> mThreadPool;
+
+  bool mGatheringTotalMemory = false;
+
+  TimeStamp mLastPoll{};
+};
+
+}  // namespace mozilla
+
+#endif  // defined mozilla_MemoryTelemetry_h
diff --git a/xpcom/base/NSPRLogModulesParser.cpp b/xpcom/base/NSPRLogModulesParser.cpp
new file mode 100644
index 0000000000..44fb50dbc7
--- /dev/null
+++ b/xpcom/base/NSPRLogModulesParser.cpp
@@ -0,0 +1,66 @@
+/* -*- 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 "NSPRLogModulesParser.h"
+
+#include "mozilla/Tokenizer.h"
+
+const char kDelimiters[] = ", ";
+const char kAdditionalWordChars[] = "_-.*";
+
+namespace mozilla {
+
+void NSPRLogModulesParser(
+    const char* aLogModules,
+    const std::function<void(const char*, LogLevel, int32_t)>& aCallback) {
+  if (!aLogModules) {
+    return;
+  }
+
+  Tokenizer parser(aLogModules, kDelimiters, kAdditionalWordChars);
+  nsAutoCString moduleName;
+
+  Tokenizer::Token rustModSep =
+      parser.AddCustomToken("::", Tokenizer::CASE_SENSITIVE);
+
+  auto readModuleName = [&](nsAutoCString& moduleName) -> bool {
+    moduleName.Truncate();
+    nsDependentCSubstring sub;
+    parser.Record();
+    // If the name doesn't include at least one word, we've reached the end.
+    if (!parser.ReadWord(sub)) {
+      return false;
+    }
+    // We will exit this loop if when any of the condition fails
+    while (parser.Check(rustModSep) && parser.ReadWord(sub)) {
+    }
+    // Claim will include characters of the last sucessfully read item
+    parser.Claim(moduleName, Tokenizer::INCLUDE_LAST);
+    return true;
+  };
+
+  // Format: LOG_MODULES="Foo:2,Bar, Baz:5,rust_crate::mod::file:5"
+  while (readModuleName(moduleName)) {
+    // Next should be :<level>, default to Error if not provided.
+    LogLevel logLevel = LogLevel::Error;
+    int32_t levelValue = 0;
+    if (parser.CheckChar(':')) {
+      // NB: If a level isn't provided after the ':' we assume the default
+      //     Error level is desired. This differs from NSPR which will stop
+      //     processing the log module string in this case.
+      if (parser.ReadSignedInteger(&levelValue)) {
+        logLevel = ToLogLevel(levelValue);
+      }
+    }
+
+    aCallback(moduleName.get(), logLevel, levelValue);
+
+    // Skip ahead to the next token.
+    parser.SkipWhites();
+  }
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/NSPRLogModulesParser.h b/xpcom/base/NSPRLogModulesParser.h
new file mode 100644
index 0000000000..2aa6571e65
--- /dev/null
+++ b/xpcom/base/NSPRLogModulesParser.h
@@ -0,0 +1,24 @@
+/* -*- 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 "mozilla/Logging.h"
+
+#include <functional>
+
+namespace mozilla {
+
+/**
+ * Helper function that parses the legacy NSPR_LOG_MODULES env var format
+ * for specifying log levels and logging options.
+ *
+ * @param aLogModules The log modules configuration string.
+ * @param aCallback The callback to invoke for each log module config entry.
+ */
+void NSPRLogModulesParser(
+    const char* aLogModules,
+    const std::function<void(const char*, LogLevel, int32_t)>& aCallback);
+
+}  // namespace mozilla
diff --git a/xpcom/base/OwningNonNull.h b/xpcom/base/OwningNonNull.h
new file mode 100644
index 0000000000..24c22f8f60
--- /dev/null
+++ b/xpcom/base/OwningNonNull.h
@@ -0,0 +1,213 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* A class for non-null strong pointers to reference-counted objects. */
+
+#ifndef mozilla_OwningNonNull_h
+#define mozilla_OwningNonNull_h
+
+#include "nsCOMPtr.h"
+#include "nsCycleCollectionNoteChild.h"
+
+namespace mozilla {
+
+// OwningNonNull<T> is similar to a RefPtr<T>, which is not null after initial
+// initialization. It has a restricted interface compared to RefPtr, with some
+// additional operations defined. The main use is in DOM bindings. Use it
+// outside DOM bindings only if you can ensure it never escapes without being
+// properly initialized, and you don't need to move it. Otherwise, use a
+// RefPtr<T> instead.
+//
+// Compared to a plain RefPtr<T>, in particular
+// - it is copyable but not movable
+// - it can be constructed and assigned from T& and is convertible to T&
+// implicitly
+// - it cannot be cleared by the user once initialized, though it can be
+//   re-assigned a new (non-null) value
+// - it is not convertible to bool, but there is an explicit isInitialized
+//   member function
+//
+// Beware that there are two cases where an OwningNonNull<T> actually is nullptr
+// - it was default-constructed and not yet initialized
+// - it was cleared during CC unlinking.
+// All attempts to use it in an invalid state will trigger an assertion in debug
+// builds.
+//
+// The original intent of OwningNonNull<T> was to implement a class with the
+// same auto-conversion and annotation semantics as mozilla::dom::NonNull<T>
+// (i.e. never null once you have properly initialized it, auto-converts to T&),
+// but that holds a strong reference to the object involved. This was designed
+// for use in DOM bindings and in particular for storing what WebIDL represents
+// as InterfaceName (as opposed to `InterfaceName?`) in various containers
+// (dictionaries, sequences). DOM bindings never allow a default-constructed
+// uninitialized OwningNonNull to escape. RefPtr could have been used for this
+// use case, just like we could have used T* instead of NonNull<T>, but it
+// seemed desirable to explicitly annotate the non-null nature of the things
+// involved to eliminate pointless null-checks, which otherwise tend to
+// proliferate.
+template <class T>
+class MOZ_IS_SMARTPTR_TO_REFCOUNTED OwningNonNull {
+ public:
+  using element_type = T;
+
+  OwningNonNull() = default;
+
+  MOZ_IMPLICIT OwningNonNull(T& aValue) { init(&aValue); }
+
+  template <class U>
+  MOZ_IMPLICIT OwningNonNull(already_AddRefed<U>&& aValue) {
+    init(aValue);
+  }
+
+  template <class U>
+  MOZ_IMPLICIT OwningNonNull(RefPtr<U>&& aValue) {
+    init(std::move(aValue));
+  }
+
+  template <class U>
+  MOZ_IMPLICIT OwningNonNull(const OwningNonNull<U>& aValue) {
+    init(aValue);
+  }
+
+  // This is no worse than get() in terms of const handling.
+  operator T&() const { return ref(); }
+
+  operator T*() const { return get(); }
+
+  // Conversion to bool is always true, so delete to catch errors
+  explicit operator bool() const = delete;
+
+  T* operator->() const { return get(); }
+
+  T& operator*() const { return ref(); }
+
+  OwningNonNull<T>& operator=(T* aValue) {
+    init(aValue);
+    return *this;
+  }
+
+  OwningNonNull<T>& operator=(T& aValue) {
+    init(&aValue);
+    return *this;
+  }
+
+  template <class U>
+  OwningNonNull<T>& operator=(already_AddRefed<U>&& aValue) {
+    init(aValue);
+    return *this;
+  }
+
+  template <class U>
+  OwningNonNull<T>& operator=(RefPtr<U>&& aValue) {
+    init(std::move(aValue));
+    return *this;
+  }
+
+  template <class U>
+  OwningNonNull<T>& operator=(const OwningNonNull<U>& aValue) {
+    init(aValue);
+    return *this;
+  }
+
+  // Don't allow assigning nullptr, it makes no sense
+  void operator=(decltype(nullptr)) = delete;
+
+  T& ref() const {
+    MOZ_ASSERT(mInited);
+    MOZ_ASSERT(mPtr, "OwningNonNull<T> was set to null");
+    return *mPtr;
+  }
+
+  // Make us work with smart pointer helpers that expect a get().
+  T* get() const {
+    MOZ_ASSERT(mInited);
+    MOZ_ASSERT(mPtr, "OwningNonNull<T> was set to null");
+    return mPtr;
+  }
+
+  template <typename U>
+  void swap(U& aOther) {
+    mPtr.swap(aOther);
+#ifdef DEBUG
+    mInited = mPtr;
+#endif
+  }
+
+  // We have some consumers who want to check whether we're inited in non-debug
+  // builds as well.  Luckily, we have the invariant that we're inited precisely
+  // when mPtr is non-null.
+  bool isInitialized() const {
+    MOZ_ASSERT(!!mPtr == mInited, "mInited out of sync with mPtr?");
+    return mPtr;
+  }
+
+ private:
+  void unlinkForCC() {
+#ifdef DEBUG
+    mInited = false;
+#endif
+    mPtr = nullptr;
+  }
+
+  // Allow ImplCycleCollectionUnlink to call unlinkForCC().
+  template <typename U>
+  friend void ImplCycleCollectionUnlink(OwningNonNull<U>& aField);
+
+ protected:
+  template <typename U>
+  void init(U&& aValue) {
+    mPtr = std::move(aValue);
+    MOZ_ASSERT(mPtr);
+#ifdef DEBUG
+    mInited = true;
+#endif
+  }
+
+  RefPtr<T> mPtr;
+#ifdef DEBUG
+  bool mInited = false;
+#endif
+};
+
+template <typename T>
+inline void ImplCycleCollectionUnlink(OwningNonNull<T>& aField) {
+  aField.unlinkForCC();
+}
+
+template <typename T>
+inline void ImplCycleCollectionTraverse(
+    nsCycleCollectionTraversalCallback& aCallback, OwningNonNull<T>& aField,
+    const char* aName, uint32_t aFlags = 0) {
+  CycleCollectionNoteChild(aCallback, aField.get(), aName, aFlags);
+}
+
+}  // namespace mozilla
+
+// Declared in nsCOMPtr.h
+template <class T>
+template <class U>
+nsCOMPtr<T>::nsCOMPtr(const mozilla::OwningNonNull<U>& aOther)
+    : nsCOMPtr(aOther.get()) {}
+
+template <class T>
+template <class U>
+nsCOMPtr<T>& nsCOMPtr<T>::operator=(const mozilla::OwningNonNull<U>& aOther) {
+  return operator=(aOther.get());
+}
+
+// Declared in mozilla/RefPtr.h
+template <class T>
+template <class U>
+RefPtr<T>::RefPtr(const mozilla::OwningNonNull<U>& aOther)
+    : RefPtr(aOther.get()) {}
+
+template <class T>
+template <class U>
+RefPtr<T>& RefPtr<T>::operator=(const mozilla::OwningNonNull<U>& aOther) {
+  return operator=(aOther.get());
+}
+
+#endif  // mozilla_OwningNonNull_h
diff --git a/xpcom/base/RLBoxSandboxPool.cpp b/xpcom/base/RLBoxSandboxPool.cpp
new file mode 100644
index 0000000000..c3b86f1698
--- /dev/null
+++ b/xpcom/base/RLBoxSandboxPool.cpp
@@ -0,0 +1,111 @@
+/* -*- 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 "nsThreadUtils.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/RLBoxSandboxPool.h"
+#ifdef MOZ_USING_WASM_SANDBOXING
+#  include "wasm2c_rt_mem.h"
+#endif
+
+using namespace mozilla;
+
+NS_IMPL_ISUPPORTS(RLBoxSandboxPool, nsITimerCallback, nsINamed)
+
+void RLBoxSandboxPool::StartTimer() {
+  mMutex.AssertCurrentThreadOwns();
+  MOZ_ASSERT(!mTimer, "timer already initialized");
+  if (NS_IsMainThread() &&
+      PastShutdownPhase(ShutdownPhase::AppShutdownConfirmed)) {
+    // If we're shutting down, setting the time might fail, and we don't need it
+    // (since all the memory will be cleaned up soon anyway). Note that
+    // PastShutdownPhase() can only be called on the main thread, but that's
+    // fine, because other threads will have joined already by the point timers
+    // start failing to register.
+    mPool.Clear();
+    return;
+  }
+  DebugOnly<nsresult> rv = NS_NewTimerWithCallback(
+      getter_AddRefs(mTimer), this, mDelaySeconds * 1000,
+      nsITimer::TYPE_ONE_SHOT, GetMainThreadSerialEventTarget());
+  MOZ_ASSERT(NS_SUCCEEDED(rv), "failed to create timer");
+}
+
+void RLBoxSandboxPool::CancelTimer() {
+  mMutex.AssertCurrentThreadOwns();
+  if (mTimer) {
+    mTimer->Cancel();
+    mTimer = nullptr;
+  }
+}
+
+NS_IMETHODIMP RLBoxSandboxPool::Notify(nsITimer* aTimer) {
+  MutexAutoLock lock(mMutex);
+
+  mPool.Clear();
+  mTimer = nullptr;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP RLBoxSandboxPool::GetName(nsACString& aName) {
+  aName.AssignLiteral("RLBoxSandboxPool");
+  return NS_OK;
+}
+
+void RLBoxSandboxPool::Push(UniquePtr<RLBoxSandboxDataBase> sbxData) {
+  MutexAutoLock lock(mMutex);
+
+  mPool.AppendElement(std::move(sbxData));
+  if (!mTimer) {
+    StartTimer();
+  }
+}
+
+UniquePtr<RLBoxSandboxPoolData> RLBoxSandboxPool::PopOrCreate(
+    uint64_t aMinSize) {
+  MutexAutoLock lock(mMutex);
+
+  UniquePtr<RLBoxSandboxDataBase> sbxData;
+
+  if (!mPool.IsEmpty()) {
+    const int64_t lastIndex = ReleaseAssertedCast<int64_t>(mPool.Length()) - 1;
+    for (int64_t i = lastIndex; i >= 0; i--) {
+      if (mPool[i]->mSize >= aMinSize) {
+        sbxData = std::move(mPool[i]);
+        mPool.RemoveElementAt(i);
+
+        // If we reuse a sandbox from the pool, reset the timer to clear the
+        // pool
+        CancelTimer();
+        if (!mPool.IsEmpty()) {
+          StartTimer();
+        }
+        break;
+      }
+    }
+  }
+
+  if (!sbxData) {
+#ifdef MOZ_USING_WASM_SANDBOXING
+    // RLBox's wasm sandboxes have a limited platform dependent capacity. We
+    // track this capacity in this pool.
+    const w2c_mem_capacity w2c_capacity = get_valid_wasm2c_memory_capacity(
+        aMinSize, true /* 32-bit wasm memory*/);
+    const uint64_t chosenCapacity = w2c_capacity.max_size;
+#else
+    // Note the noop sandboxes have no capacity limit. In this case we simply
+    // specify a value of 4gb. This is not actually enforced by the noop
+    // sandbox.
+    const uint64_t chosenCapacity = static_cast<uint64_t>(1) << 32;
+#endif
+    sbxData = CreateSandboxData(chosenCapacity);
+    NS_ENSURE_TRUE(sbxData, nullptr);
+  }
+
+  return MakeUnique<RLBoxSandboxPoolData>(std::move(sbxData), this);
+}
diff --git a/xpcom/base/RLBoxSandboxPool.h b/xpcom/base/RLBoxSandboxPool.h
new file mode 100644
index 0000000000..47f3893548
--- /dev/null
+++ b/xpcom/base/RLBoxSandboxPool.h
@@ -0,0 +1,105 @@
+/* -*- Mode: C++; tab-width: 20; 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/. */
+
+#ifndef SECURITY_RLBOX_SANDBOX_POOL_H_
+#define SECURITY_RLBOX_SANDBOX_POOL_H_
+
+#include "nsCOMPtr.h"
+#include "nsITimer.h"
+#include "nsTArray.h"
+#include "nsINamed.h"
+
+#include "mozilla/Mutex.h"
+#include "mozilla/rlbox/rlbox_types.hpp"
+
+namespace mozilla {
+
+class RLBoxSandboxDataBase;
+class RLBoxSandboxPoolData;
+
+// The RLBoxSandboxPool class is used to manage a pool of sandboxes that are
+// reused -- to save sandbox creation time and memory -- and automatically
+// destroyed when no longer in used. The sandbox pool is threadsafe and can be
+// used to share unused sandboxes across a thread pool.
+//
+// Each sandbox pool manages a particular kind of sandbox (e.g., expat
+// sandboxes, woff2 sandboxes, etc.); this is largely because different
+// sandboxes might have different callbacks and attacker assumptions. Hence,
+// RLBoxSandboxPool is intended to be subclassed for the different kinds of
+// sandbox pools. Each sandbox pool class needs to implement the
+// CreateSandboxData() method, which returns a pointer to a RLBoxSandboxDataBase
+// object.  RLBoxSandboxDataBase itself should be subclassed to implement
+// sandbox-specific details.
+class RLBoxSandboxPool : public nsITimerCallback, public nsINamed {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSITIMERCALLBACK
+  NS_DECL_NSINAMED
+
+  RLBoxSandboxPool(size_t aDelaySeconds = 10)
+      : mPool(),
+        mDelaySeconds(aDelaySeconds),
+        mMutex("RLBoxSandboxPool::mMutex"){};
+
+  void Push(UniquePtr<RLBoxSandboxDataBase> sbx);
+  // PopOrCreate returns a sandbox from the pool if the pool is not empty and
+  // tries to mint a new one otherwise. If creating a new sandbox fails, the
+  // function returns a nullptr. The parameter aMinSize is the minimum size of
+  // the sandbox memory.
+  UniquePtr<RLBoxSandboxPoolData> PopOrCreate(uint64_t aMinSize = 0);
+
+ protected:
+  // CreateSandboxData takes a parameter which is the size of the sandbox memory
+  virtual UniquePtr<RLBoxSandboxDataBase> CreateSandboxData(uint64_t aSize) = 0;
+  virtual ~RLBoxSandboxPool() = default;
+
+ private:
+  void StartTimer() MOZ_REQUIRES(mMutex);
+  void CancelTimer() MOZ_REQUIRES(mMutex);
+
+  nsTArray<UniquePtr<RLBoxSandboxDataBase>> mPool MOZ_GUARDED_BY(mMutex);
+  const size_t mDelaySeconds MOZ_GUARDED_BY(mMutex);
+  nsCOMPtr<nsITimer> mTimer MOZ_GUARDED_BY(mMutex);
+  mozilla::Mutex mMutex;
+};
+
+// The RLBoxSandboxDataBase class serves as the subclass for all sandbox data
+// classes, which keep track of the RLBox sandbox and any relevant sandbox data
+// (e.g., callbacks).
+class RLBoxSandboxDataBase {
+ public:
+  const uint64_t mSize;
+  explicit RLBoxSandboxDataBase(uint64_t aSize) : mSize(aSize) {}
+  virtual ~RLBoxSandboxDataBase() = default;
+};
+
+// This class is used wrap sandbox data objects (RLBoxSandboxDataBase) when they
+// are popped from sandbox pools. The wrapper destructor pushes the sandbox back
+// into the pool.
+class RLBoxSandboxPoolData {
+ public:
+  RLBoxSandboxPoolData(UniquePtr<RLBoxSandboxDataBase> aSbxData,
+                       RefPtr<RLBoxSandboxPool> aPool) {
+    mSbxData = std::move(aSbxData);
+    mPool = aPool;
+    MOZ_COUNT_CTOR(RLBoxSandboxPoolData);
+  }
+
+  RLBoxSandboxDataBase* SandboxData() const { return mSbxData.get(); };
+
+  ~RLBoxSandboxPoolData() {
+    mPool->Push(std::move(mSbxData));
+    MOZ_COUNT_DTOR(RLBoxSandboxPoolData);
+  };
+
+ private:
+  UniquePtr<RLBoxSandboxDataBase> mSbxData;
+  RefPtr<RLBoxSandboxPool> mPool;
+};
+
+}  // namespace mozilla
+
+#endif
diff --git a/xpcom/base/RLBoxUtils.h b/xpcom/base/RLBoxUtils.h
new file mode 100644
index 0000000000..4a73affb63
--- /dev/null
+++ b/xpcom/base/RLBoxUtils.h
@@ -0,0 +1,70 @@
+/* -*- Mode: C++; tab-width: 20; 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/. */
+
+#ifndef SECURITY_RLBOX_UTILS_H_
+#define SECURITY_RLBOX_UTILS_H_
+
+#include "mozilla/rlbox/rlbox_types.hpp"
+
+namespace mozilla {
+
+/* The RLBoxTransferBufferToSandbox class is used to copy (or directly expose in
+ * the noop-sandbox case) buffers into the sandbox that are automatically freed
+ * when the RLBoxTransferBufferToSandbox is out of scope.  NOTE: The sandbox
+ * lifetime must outlive all of its RLBoxTransferBufferToSandbox.
+ */
+template <typename T, typename S>
+class MOZ_STACK_CLASS RLBoxTransferBufferToSandbox {
+ public:
+  RLBoxTransferBufferToSandbox() = delete;
+  RLBoxTransferBufferToSandbox(rlbox::rlbox_sandbox<S>* aSandbox, const T* aBuf,
+                               const size_t aLen)
+      : mSandbox(aSandbox), mCopied(false), mBuf(nullptr) {
+    if (aBuf) {
+      mBuf = rlbox::copy_memory_or_grant_access(*mSandbox, aBuf, aLen, false,
+                                                mCopied);
+    }
+  };
+  ~RLBoxTransferBufferToSandbox() {
+    if (mCopied) {
+      mSandbox->free_in_sandbox(mBuf);
+    }
+  };
+  rlbox::tainted<const T*, S> operator*() const { return mBuf; };
+
+ private:
+  rlbox::rlbox_sandbox<S>* mSandbox;
+  bool mCopied;
+  rlbox::tainted<const T*, S> mBuf;
+};
+
+/* The RLBoxAllocateInSandbox class is used to allocate data int sandbox that is
+ * automatically freed when the RLBoxAllocateInSandbox is out of scope.  NOTE:
+ * The sandbox lifetime must outlive all of its RLBoxAllocateInSandbox'ations.
+ */
+template <typename T, typename S>
+class MOZ_STACK_CLASS RLBoxAllocateInSandbox {
+ public:
+  RLBoxAllocateInSandbox() = delete;
+  explicit RLBoxAllocateInSandbox(rlbox::rlbox_sandbox<S>* aSandbox)
+      : mSandbox(aSandbox) {
+    mPtr = mSandbox->template malloc_in_sandbox<T>();
+  };
+  ~RLBoxAllocateInSandbox() {
+    if (mPtr) {
+      mSandbox->free_in_sandbox(mPtr);
+    }
+  };
+  rlbox::tainted<T*, S> get() const { return mPtr; };
+
+ private:
+  rlbox::rlbox_sandbox<S>* mSandbox;
+  rlbox::tainted<T*, S> mPtr;
+};
+
+}  // namespace mozilla
+
+#endif
diff --git a/xpcom/base/ShutdownPhase.h b/xpcom/base/ShutdownPhase.h
new file mode 100644
index 0000000000..ebe5ebd37e
--- /dev/null
+++ b/xpcom/base/ShutdownPhase.h
@@ -0,0 +1,32 @@
+/* -*- 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/. */
+
+#ifndef ShutdownPhase_h
+#define ShutdownPhase_h
+
+namespace mozilla {
+
+// Must be contiguous starting at 0
+enum class ShutdownPhase {
+  NotInShutdown = 0,
+  AppShutdownConfirmed,
+  AppShutdownNetTeardown,
+  AppShutdownTeardown,
+  AppShutdown,
+  AppShutdownQM,
+  AppShutdownTelemetry,
+  XPCOMWillShutdown,
+  XPCOMShutdown,
+  XPCOMShutdownThreads,
+  XPCOMShutdownFinal,
+  CCPostLastCycleCollection,
+  ShutdownPhase_Length,         // never pass this value
+  First = AppShutdownConfirmed  // for iteration
+};
+
+}  // namespace mozilla
+
+#endif  // ShutdownPhase_h
diff --git a/xpcom/base/SizeOfState.h b/xpcom/base/SizeOfState.h
new file mode 100644
index 0000000000..2df0b24e93
--- /dev/null
+++ b/xpcom/base/SizeOfState.h
@@ -0,0 +1,67 @@
+/* -*- 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/. */
+
+#ifndef SizeOfState_h
+#define SizeOfState_h
+
+#include "mozilla/fallible.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/Unused.h"
+#include "nsTHashtable.h"
+#include "nsHashKeys.h"
+
+// This file includes types that are useful during memory reporting, but which
+// cannot be put into mfbt/MemoryReporting.h because they depend on things that
+// are not in MFBT.
+
+namespace mozilla {
+
+// A table of seen pointers. Useful when measuring structures that contain
+// nodes that may be pointed to from multiple places, e.g. via RefPtr (in C++
+// code) or Arc (in Rust code).
+class SeenPtrs : public nsTHashtable<nsPtrHashKey<const void>> {
+ public:
+  // Returns true if we have seen this pointer before, false otherwise. Also
+  // remembers this pointer for later queries.
+  bool HaveSeenPtr(const void* aPtr) {
+    uint32_t oldCount = Count();
+
+    mozilla::Unused << PutEntry(aPtr, fallible);
+
+    // If the counts match, there are two possibilities.
+    //
+    // - Lookup succeeded: we've seen the pointer before, and didn't need to
+    //   add a new entry.
+    //
+    // - PutEntry() tried to add the entry and failed due to lack of memory. In
+    //   this case we can't tell if this pointer has been seen before (because
+    //   the table is in an unreliable state and may have dropped previous
+    //   insertions). When doing memory reporting it's better to err on the
+    //   side of under-reporting rather than over-reporting, so we assume we've
+    //   seen the pointer before.
+    //
+    return oldCount == Count();
+  }
+};
+
+// Memory reporting state. Some memory measuring functions
+// (SizeOfIncludingThis(), etc.) just need a MallocSizeOf parameter, but some
+// also need a record of pointers that have been seen and should not be
+// re-measured. This class encapsulates both of those things.
+class SizeOfState {
+ public:
+  explicit SizeOfState(MallocSizeOf aMallocSizeOf)
+      : mMallocSizeOf(aMallocSizeOf) {}
+
+  bool HaveSeenPtr(const void* aPtr) { return mSeenPtrs.HaveSeenPtr(aPtr); }
+
+  MallocSizeOf mMallocSizeOf;
+  SeenPtrs mSeenPtrs;
+};
+
+}  // namespace mozilla
+
+#endif  // SizeOfState_h
diff --git a/xpcom/base/StaticLocalPtr.h b/xpcom/base/StaticLocalPtr.h
new file mode 100644
index 0000000000..2e2fc035bd
--- /dev/null
+++ b/xpcom/base/StaticLocalPtr.h
@@ -0,0 +1,253 @@
+/* -*- 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 https://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_StaticLocalPtr_h
+#define mozilla_StaticLocalPtr_h
+
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/RefPtr.h"
+
+namespace mozilla {
+
+/**
+ * StaticLocalAutoPtr and StaticLocalRefPtr are like UniquePtr and RefPtr,
+ * except they are suitable for use as "magic static" local variables -- that
+ * is, they are able to take advantage of C++11's guarantee of thread safety
+ * during initialization by atomically constructing both the smart pointer
+ * itself as well as the object being pointed to.
+ *
+ * A static local instance of StaticLocal{Auto,Ref}Ptr does not cause the
+ * compiler to emit any atexit calls. In order to accomplish this,
+ * StaticLocal{Auto,Ref}Ptr must have a trivial destructor. As a consequence,
+ * it does not delete/release its raw pointer upon destruction.
+ *
+ * The clang plugin, run as part of our "static analysis" builds, makes it a
+ * compile-time error to use StaticLocal{Auto,Ref}Ptr as anything except a
+ * static local variable.
+ *
+ * StaticLocal{Auto,Ref}Ptr have a limited interface as compared to
+ * ns{Auto,Ref}Ptr; this is intentional, since their range of acceptable uses is
+ * smaller.
+ */
+
+template <typename T>
+class MOZ_STATIC_LOCAL_CLASS StaticLocalAutoPtr final {
+ public:
+  explicit StaticLocalAutoPtr(T* aRawPtr) : mRawPtr(aRawPtr) {}
+
+  StaticLocalAutoPtr(StaticLocalAutoPtr<T>&& aOther) : mRawPtr(aOther.mRawPtr) {
+    aOther.mRawPtr = nullptr;
+  }
+
+  StaticLocalAutoPtr<T>& operator=(T* aRhs) {
+    Assign(aRhs);
+    return *this;
+  }
+
+  T* get() const { return mRawPtr; }
+
+  operator T*() const { return get(); }
+
+  T* operator->() const {
+    MOZ_ASSERT(mRawPtr);
+    return get();
+  }
+
+  T& operator*() const { return *get(); }
+
+  T* forget() {
+    T* temp = mRawPtr;
+    mRawPtr = nullptr;
+    return temp;
+  }
+
+ private:
+  StaticLocalAutoPtr(const StaticLocalAutoPtr<T>& aOther) = delete;
+
+  // We do not allow assignment as the intention of this class is to only
+  // assign to mRawPtr during construction.
+  StaticLocalAutoPtr& operator=(const StaticLocalAutoPtr<T>& aOther) = delete;
+  StaticLocalAutoPtr& operator=(StaticLocalAutoPtr<T>&&) = delete;
+
+  void Assign(T* aNewPtr) {
+    MOZ_ASSERT(!aNewPtr || mRawPtr != aNewPtr);
+    T* oldPtr = mRawPtr;
+    mRawPtr = aNewPtr;
+    delete oldPtr;
+  }
+
+  T* mRawPtr;
+};
+
+template <typename T>
+class MOZ_STATIC_LOCAL_CLASS StaticLocalRefPtr final {
+ public:
+  explicit StaticLocalRefPtr(T* aRawPtr) : mRawPtr(nullptr) {
+    AssignWithAddref(aRawPtr);
+  }
+
+  explicit StaticLocalRefPtr(already_AddRefed<T>& aPtr) : mRawPtr(nullptr) {
+    AssignAssumingAddRef(aPtr.take());
+  }
+
+  explicit StaticLocalRefPtr(already_AddRefed<T>&& aPtr) : mRawPtr(nullptr) {
+    AssignAssumingAddRef(aPtr.take());
+  }
+
+  StaticLocalRefPtr(const StaticLocalRefPtr<T>& aPtr)
+      : StaticLocalRefPtr(aPtr.mRawPtr) {}
+
+  StaticLocalRefPtr(StaticLocalRefPtr<T>&& aPtr) : mRawPtr(aPtr.mRawPtr) {
+    aPtr.mRawPtr = nullptr;
+  }
+
+  StaticLocalRefPtr<T>& operator=(T* aRhs) {
+    AssignWithAddref(aRhs);
+    return *this;
+  }
+
+  already_AddRefed<T> forget() {
+    T* temp = mRawPtr;
+    mRawPtr = nullptr;
+    return already_AddRefed<T>(temp);
+  }
+
+  T* get() const { return mRawPtr; }
+
+  operator T*() const { return get(); }
+
+  T* operator->() const {
+    MOZ_ASSERT(mRawPtr);
+    return get();
+  }
+
+  T& operator*() const { return *get(); }
+
+ private:
+  // We do not allow assignment as the intention of this class is to only
+  // assign to mRawPtr during construction.
+  StaticLocalRefPtr<T>& operator=(const StaticLocalRefPtr<T>& aRhs) = delete;
+  StaticLocalRefPtr<T>& operator=(StaticLocalRefPtr<T>&& aRhs) = delete;
+
+  void AssignWithAddref(T* aNewPtr) {
+    if (aNewPtr) {
+      aNewPtr->AddRef();
+    }
+    AssignAssumingAddRef(aNewPtr);
+  }
+
+  void AssignAssumingAddRef(T* aNewPtr) {
+    T* oldPtr = mRawPtr;
+    mRawPtr = aNewPtr;
+    if (oldPtr) {
+      oldPtr->Release();
+    }
+  }
+
+  T* MOZ_OWNING_REF mRawPtr;
+};
+
+namespace StaticLocalPtr_internal {
+class Zero;
+}  // namespace StaticLocalPtr_internal
+
+#define REFLEXIVE_EQUALITY_OPERATORS(type1, type2, eq_fn, ...) \
+  template <__VA_ARGS__>                                       \
+  inline bool operator==(type1 lhs, type2 rhs) {               \
+    return eq_fn;                                              \
+  }                                                            \
+                                                               \
+  template <__VA_ARGS__>                                       \
+  inline bool operator==(type2 lhs, type1 rhs) {               \
+    return rhs == lhs;                                         \
+  }                                                            \
+                                                               \
+  template <__VA_ARGS__>                                       \
+  inline bool operator!=(type1 lhs, type2 rhs) {               \
+    return !(lhs == rhs);                                      \
+  }                                                            \
+                                                               \
+  template <__VA_ARGS__>                                       \
+  inline bool operator!=(type2 lhs, type1 rhs) {               \
+    return !(lhs == rhs);                                      \
+  }
+
+// StaticLocalAutoPtr (in)equality operators
+
+template <class T, class U>
+inline bool operator==(const StaticLocalAutoPtr<T>& aLhs,
+                       const StaticLocalAutoPtr<U>& aRhs) {
+  return aLhs.get() == aRhs.get();
+}
+
+template <class T, class U>
+inline bool operator!=(const StaticLocalAutoPtr<T>& aLhs,
+                       const StaticLocalAutoPtr<U>& aRhs) {
+  return !(aLhs == aRhs);
+}
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalAutoPtr<T>&, const U*,
+                             lhs.get() == rhs, class T, class U)
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalAutoPtr<T>&, U*, lhs.get() == rhs,
+                             class T, class U)
+
+// Let us compare StaticLocalAutoPtr to 0.
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalAutoPtr<T>&,
+                             StaticLocalPtr_internal::Zero*,
+                             lhs.get() == nullptr, class T)
+
+// StaticLocalRefPtr (in)equality operators
+
+template <class T, class U>
+inline bool operator==(const StaticLocalRefPtr<T>& aLhs,
+                       const StaticLocalRefPtr<U>& aRhs) {
+  return aLhs.get() == aRhs.get();
+}
+
+template <class T, class U>
+inline bool operator!=(const StaticLocalRefPtr<T>& aLhs,
+                       const StaticLocalRefPtr<U>& aRhs) {
+  return !(aLhs == aRhs);
+}
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalRefPtr<T>&, const U*,
+                             lhs.get() == rhs, class T, class U)
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalRefPtr<T>&, U*, lhs.get() == rhs,
+                             class T, class U)
+
+// Let us compare StaticLocalRefPtr to 0.
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalRefPtr<T>&,
+                             StaticLocalPtr_internal::Zero*,
+                             lhs.get() == nullptr, class T)
+
+#undef REFLEXIVE_EQUALITY_OPERATORS
+
+}  // namespace mozilla
+
+// Declared in mozilla/RefPtr.h
+template <class T>
+template <class U>
+RefPtr<T>::RefPtr(const mozilla::StaticLocalRefPtr<U>& aOther)
+    : RefPtr(aOther.get()) {}
+
+template <class T>
+template <class U>
+RefPtr<T>& RefPtr<T>::operator=(const mozilla::StaticLocalRefPtr<U>& aOther) {
+  return operator=(aOther.get());
+}
+
+template <class T>
+inline already_AddRefed<T> do_AddRef(
+    const mozilla::StaticLocalRefPtr<T>& aObj) {
+  RefPtr<T> ref(aObj);
+  return ref.forget();
+}
+
+#endif  // mozilla_StaticLocalPtr_h
diff --git a/xpcom/base/StaticMonitor.h b/xpcom/base/StaticMonitor.h
new file mode 100644
index 0000000000..b35d3871d2
--- /dev/null
+++ b/xpcom/base/StaticMonitor.h
@@ -0,0 +1,117 @@
+/* -*- 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/. */
+
+#ifndef mozilla_StaticMonitor_h
+#define mozilla_StaticMonitor_h
+
+#include "mozilla/Atomics.h"
+#include "mozilla/CondVar.h"
+#include "mozilla/ThreadSafety.h"
+
+namespace mozilla {
+
+class MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS MOZ_CAPABILITY("monitor")
+    StaticMonitor {
+ public:
+  // In debug builds, check that mMutex is initialized for us as we expect by
+  // the compiler.  In non-debug builds, don't declare a constructor so that
+  // the compiler can see that the constructor is trivial.
+#ifdef DEBUG
+  StaticMonitor() { MOZ_ASSERT(!mMutex); }
+#endif
+
+  void Lock() MOZ_CAPABILITY_ACQUIRE() { Mutex()->Lock(); }
+
+  void Unlock() MOZ_CAPABILITY_RELEASE() { Mutex()->Unlock(); }
+
+  void Wait() { CondVar()->Wait(); }
+  CVStatus Wait(TimeDuration aDuration) {
+    AssertCurrentThreadOwns();
+    return CondVar()->Wait(aDuration);
+  }
+
+  void Notify() { CondVar()->Notify(); }
+  void NotifyAll() { CondVar()->NotifyAll(); }
+
+  void AssertCurrentThreadOwns() MOZ_ASSERT_CAPABILITY(this) {
+#ifdef DEBUG
+    Mutex()->AssertCurrentThreadOwns();
+#endif
+  }
+
+ private:
+  OffTheBooksMutex* Mutex() {
+    if (mMutex) {
+      return mMutex;
+    }
+
+    OffTheBooksMutex* mutex = new OffTheBooksMutex("StaticMutex");
+    if (!mMutex.compareExchange(nullptr, mutex)) {
+      delete mutex;
+    }
+
+    return mMutex;
+  }
+
+  OffTheBooksCondVar* CondVar() {
+    if (mCondVar) {
+      return mCondVar;
+    }
+
+    OffTheBooksCondVar* condvar =
+        new OffTheBooksCondVar(*Mutex(), "StaticCondVar");
+    if (!mCondVar.compareExchange(nullptr, condvar)) {
+      delete condvar;
+    }
+
+    return mCondVar;
+  }
+
+  Atomic<OffTheBooksMutex*> mMutex;
+  Atomic<OffTheBooksCondVar*> mCondVar;
+
+  // Disallow copy constructor, but only in debug mode.  We only define
+  // a default constructor in debug mode (see above); if we declared
+  // this constructor always, the compiler wouldn't generate a trivial
+  // default constructor for us in non-debug mode.
+#ifdef DEBUG
+  StaticMonitor(const StaticMonitor& aOther);
+#endif
+
+  // Disallow these operators.
+  StaticMonitor& operator=(const StaticMonitor& aRhs);
+  static void* operator new(size_t) noexcept(true);
+  static void operator delete(void*);
+};
+
+class MOZ_STACK_CLASS MOZ_SCOPED_CAPABILITY StaticMonitorAutoLock {
+ public:
+  explicit StaticMonitorAutoLock(StaticMonitor& aMonitor)
+      MOZ_CAPABILITY_ACQUIRE(aMonitor)
+      : mMonitor(&aMonitor) {
+    mMonitor->Lock();
+  }
+
+  ~StaticMonitorAutoLock() MOZ_CAPABILITY_RELEASE() { mMonitor->Unlock(); }
+
+  void Wait() { mMonitor->Wait(); }
+  CVStatus Wait(TimeDuration aDuration) { return mMonitor->Wait(aDuration); }
+
+  void Notify() { mMonitor->Notify(); }
+  void NotifyAll() { mMonitor->NotifyAll(); }
+
+ private:
+  StaticMonitorAutoLock();
+  StaticMonitorAutoLock(const StaticMonitorAutoLock&);
+  StaticMonitorAutoLock& operator=(const StaticMonitorAutoLock&);
+  static void* operator new(size_t) noexcept(true);
+
+  StaticMonitor* mMonitor;
+};
+
+}  // namespace mozilla
+
+#endif
diff --git a/xpcom/base/StaticMutex.h b/xpcom/base/StaticMutex.h
new file mode 100644
index 0000000000..08c0288486
--- /dev/null
+++ b/xpcom/base/StaticMutex.h
@@ -0,0 +1,84 @@
+/* -*- 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/. */
+
+#ifndef mozilla_StaticMutex_h
+#define mozilla_StaticMutex_h
+
+#include "mozilla/Atomics.h"
+#include "mozilla/Mutex.h"
+
+namespace mozilla {
+
+/**
+ * StaticMutex is a Mutex that can (and in fact, must) be used as a
+ * global/static variable.
+ *
+ * The main reason to use StaticMutex as opposed to
+ * StaticAutoPtr<OffTheBooksMutex> is that we instantiate the StaticMutex in a
+ * thread-safe manner the first time it's used.
+ *
+ * The same caveats that apply to StaticAutoPtr apply to StaticMutex.  In
+ * particular, do not use StaticMutex as a stack variable or a class instance
+ * variable, because this class relies on the fact that global variablies are
+ * initialized to 0 in order to initialize mMutex.  It is only safe to use
+ * StaticMutex as a global or static variable.
+ */
+class MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS MOZ_CAPABILITY("mutex")
+    StaticMutex {
+ public:
+  // In debug builds, check that mMutex is initialized for us as we expect by
+  // the compiler.  In non-debug builds, don't declare a constructor so that
+  // the compiler can see that the constructor is trivial.
+#ifdef DEBUG
+  StaticMutex() { MOZ_ASSERT(!mMutex); }
+#endif
+
+  void Lock() MOZ_CAPABILITY_ACQUIRE() { Mutex()->Lock(); }
+
+  void Unlock() MOZ_CAPABILITY_RELEASE() { Mutex()->Unlock(); }
+
+  void AssertCurrentThreadOwns() MOZ_ASSERT_CAPABILITY(this) {
+#ifdef DEBUG
+    Mutex()->AssertCurrentThreadOwns();
+#endif
+  }
+
+ private:
+  OffTheBooksMutex* Mutex() {
+    if (mMutex) {
+      return mMutex;
+    }
+
+    OffTheBooksMutex* mutex = new OffTheBooksMutex("StaticMutex");
+    if (!mMutex.compareExchange(nullptr, mutex)) {
+      delete mutex;
+    }
+
+    return mMutex;
+  }
+
+  Atomic<OffTheBooksMutex*, SequentiallyConsistent> mMutex;
+
+  // Disallow copy constructor, but only in debug mode.  We only define
+  // a default constructor in debug mode (see above); if we declared
+  // this constructor always, the compiler wouldn't generate a trivial
+  // default constructor for us in non-debug mode.
+#ifdef DEBUG
+  StaticMutex(StaticMutex& aOther);
+#endif
+
+  // Disallow these operators.
+  StaticMutex& operator=(StaticMutex* aRhs);
+  static void* operator new(size_t) noexcept(true);
+  static void operator delete(void*);
+};
+
+typedef detail::BaseAutoLock<StaticMutex&> StaticMutexAutoLock;
+typedef detail::BaseAutoUnlock<StaticMutex&> StaticMutexAutoUnlock;
+
+}  // namespace mozilla
+
+#endif
diff --git a/xpcom/base/StaticPtr.h b/xpcom/base/StaticPtr.h
new file mode 100644
index 0000000000..38fcd82f97
--- /dev/null
+++ b/xpcom/base/StaticPtr.h
@@ -0,0 +1,235 @@
+/* -*- 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/. */
+
+#ifndef mozilla_StaticPtr_h
+#define mozilla_StaticPtr_h
+
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/RefPtr.h"
+
+namespace mozilla {
+
+/**
+ * StaticAutoPtr and StaticRefPtr are like UniquePtr and RefPtr, except they
+ * are suitable for use as global variables.
+ *
+ * In particular, a global instance of Static{Auto,Ref}Ptr doesn't cause the
+ * compiler to emit a static initializer.
+ *
+ * Since the compiler guarantees that all global variables are initialized to
+ * 0, the default constexpr constructors will result in no actual code being
+ * generated. Since we rely on this, the clang plugin, run as part of our
+ * "static analysis" builds, makes it a compile-time error to use
+ * Static{Auto,Ref}Ptr as anything except a global variable.
+ *
+ * Static{Auto,Ref}Ptr have a limited interface as compared to ns{Auto,Ref}Ptr;
+ * this is intentional, since their range of acceptable uses is smaller.
+ */
+
+template <class T>
+class MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS StaticAutoPtr {
+ public:
+  constexpr StaticAutoPtr() = default;
+  StaticAutoPtr(const StaticAutoPtr&) = delete;
+
+  StaticAutoPtr<T>& operator=(T* aRhs) {
+    Assign(aRhs);
+    return *this;
+  }
+
+  T* get() const { return mRawPtr; }
+
+  operator T*() const { return get(); }
+
+  T* operator->() const {
+    MOZ_ASSERT(mRawPtr);
+    return get();
+  }
+
+  T& operator*() const { return *get(); }
+
+  T* forget() {
+    T* temp = mRawPtr;
+    mRawPtr = nullptr;
+    return temp;
+  }
+
+ private:
+  void Assign(T* aNewPtr) {
+    MOZ_ASSERT(!aNewPtr || mRawPtr != aNewPtr);
+    T* oldPtr = mRawPtr;
+    mRawPtr = aNewPtr;
+    delete oldPtr;
+  }
+
+  T* mRawPtr = nullptr;
+};
+
+template <class T>
+class MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS StaticRefPtr {
+ public:
+  constexpr StaticRefPtr() = default;
+  StaticRefPtr(const StaticRefPtr&) = delete;
+
+  StaticRefPtr<T>& operator=(T* aRhs) {
+    AssignWithAddref(aRhs);
+    return *this;
+  }
+
+  StaticRefPtr<T>& operator=(const StaticRefPtr<T>& aRhs) {
+    return (this = aRhs.mRawPtr);
+  }
+
+  StaticRefPtr<T>& operator=(already_AddRefed<T>& aRhs) {
+    AssignAssumingAddRef(aRhs.take());
+    return *this;
+  }
+
+  template <typename U>
+  StaticRefPtr<T>& operator=(RefPtr<U>&& aRhs) {
+    AssignAssumingAddRef(aRhs.forget().take());
+    return *this;
+  }
+
+  StaticRefPtr<T>& operator=(already_AddRefed<T>&& aRhs) {
+    AssignAssumingAddRef(aRhs.take());
+    return *this;
+  }
+
+  already_AddRefed<T> forget() {
+    T* temp = mRawPtr;
+    mRawPtr = nullptr;
+    return already_AddRefed<T>(temp);
+  }
+
+  T* get() const { return mRawPtr; }
+
+  operator T*() const { return get(); }
+
+  T* operator->() const {
+    MOZ_ASSERT(mRawPtr);
+    return get();
+  }
+
+  T& operator*() const { return *get(); }
+
+ private:
+  void AssignWithAddref(T* aNewPtr) {
+    if (aNewPtr) {
+      RefPtrTraits<T>::AddRef(aNewPtr);
+    }
+    AssignAssumingAddRef(aNewPtr);
+  }
+
+  void AssignAssumingAddRef(T* aNewPtr) {
+    T* oldPtr = mRawPtr;
+    mRawPtr = aNewPtr;
+    if (oldPtr) {
+      RefPtrTraits<T>::Release(oldPtr);
+    }
+  }
+
+  T* MOZ_OWNING_REF mRawPtr = nullptr;
+};
+
+namespace StaticPtr_internal {
+class Zero;
+}  // namespace StaticPtr_internal
+
+#define REFLEXIVE_EQUALITY_OPERATORS(type1, type2, eq_fn, ...) \
+  template <__VA_ARGS__>                                       \
+  inline bool operator==(type1 lhs, type2 rhs) {               \
+    return eq_fn;                                              \
+  }                                                            \
+                                                               \
+  template <__VA_ARGS__>                                       \
+  inline bool operator==(type2 lhs, type1 rhs) {               \
+    return rhs == lhs;                                         \
+  }                                                            \
+                                                               \
+  template <__VA_ARGS__>                                       \
+  inline bool operator!=(type1 lhs, type2 rhs) {               \
+    return !(lhs == rhs);                                      \
+  }                                                            \
+                                                               \
+  template <__VA_ARGS__>                                       \
+  inline bool operator!=(type2 lhs, type1 rhs) {               \
+    return !(lhs == rhs);                                      \
+  }
+
+// StaticAutoPtr (in)equality operators
+
+template <class T, class U>
+inline bool operator==(const StaticAutoPtr<T>& aLhs,
+                       const StaticAutoPtr<U>& aRhs) {
+  return aLhs.get() == aRhs.get();
+}
+
+template <class T, class U>
+inline bool operator!=(const StaticAutoPtr<T>& aLhs,
+                       const StaticAutoPtr<U>& aRhs) {
+  return !(aLhs == aRhs);
+}
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticAutoPtr<T>&, const U*,
+                             lhs.get() == rhs, class T, class U)
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticAutoPtr<T>&, U*, lhs.get() == rhs,
+                             class T, class U)
+
+// Let us compare StaticAutoPtr to 0.
+REFLEXIVE_EQUALITY_OPERATORS(const StaticAutoPtr<T>&, StaticPtr_internal::Zero*,
+                             lhs.get() == nullptr, class T)
+
+// StaticRefPtr (in)equality operators
+
+template <class T, class U>
+inline bool operator==(const StaticRefPtr<T>& aLhs,
+                       const StaticRefPtr<U>& aRhs) {
+  return aLhs.get() == aRhs.get();
+}
+
+template <class T, class U>
+inline bool operator!=(const StaticRefPtr<T>& aLhs,
+                       const StaticRefPtr<U>& aRhs) {
+  return !(aLhs == aRhs);
+}
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticRefPtr<T>&, const U*, lhs.get() == rhs,
+                             class T, class U)
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticRefPtr<T>&, U*, lhs.get() == rhs,
+                             class T, class U)
+
+// Let us compare StaticRefPtr to 0.
+REFLEXIVE_EQUALITY_OPERATORS(const StaticRefPtr<T>&, StaticPtr_internal::Zero*,
+                             lhs.get() == nullptr, class T)
+
+#undef REFLEXIVE_EQUALITY_OPERATORS
+
+}  // namespace mozilla
+
+// Declared in mozilla/RefPtr.h
+template <class T>
+template <class U>
+RefPtr<T>::RefPtr(const mozilla::StaticRefPtr<U>& aOther)
+    : RefPtr(aOther.get()) {}
+
+template <class T>
+template <class U>
+RefPtr<T>& RefPtr<T>::operator=(const mozilla::StaticRefPtr<U>& aOther) {
+  return operator=(aOther.get());
+}
+
+template <class T>
+inline already_AddRefed<T> do_AddRef(const mozilla::StaticRefPtr<T>& aObj) {
+  RefPtr<T> ref(aObj);
+  return ref.forget();
+}
+
+#endif
diff --git a/xpcom/base/components.conf b/xpcom/base/components.conf
new file mode 100644
index 0000000000..40c78b033c
--- /dev/null
+++ b/xpcom/base/components.conf
@@ -0,0 +1,30 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+Classes = [
+    {
+        'cid': '{cb6cdb94-e417-4601-b4a5-f991bf41453d}',
+        'contract_ids': ['@mozilla.org/xpcom/debug;1'],
+        'legacy_constructor': 'nsDebugImpl::Create',
+        'headers': ['nsDebugImpl.h'],
+        'processes': ProcessSelector.ALLOW_IN_GPU_RDD_SOCKET_AND_UTILITY_PROCESS,
+    },
+    {
+        'cid': '{67b3ac0c-d806-4d48-939e-6a819e6c248f}',
+        'contract_ids': ['@mozilla.org/message-loop;1'],
+        'legacy_constructor': 'nsMessageLoopConstructor',
+        'headers': ['/xpcom/base/nsMessageLoop.h'],
+    },
+    {
+        'cid': '{68bf4793-5204-45cf-9ee2-69adffbc2e38}',
+        'contract_ids': ['@mozilla.org/xpcom/memory-watcher;1'],
+        'singleton': True,
+        'type': 'mozilla::nsAvailableMemoryWatcherBase',
+        'headers': ['/xpcom/base/AvailableMemoryWatcher.h'],
+        'constructor': 'mozilla::nsAvailableMemoryWatcherBase::GetSingleton',
+        'processes': ProcessSelector.MAIN_PROCESS_ONLY,
+    },
+]
diff --git a/xpcom/base/moz.build b/xpcom/base/moz.build
new file mode 100644
index 0000000000..f685758b6f
--- /dev/null
+++ b/xpcom/base/moz.build
@@ -0,0 +1,261 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+XPIDL_SOURCES += [
+    "nsIAvailableMemoryWatcherBase.idl",
+    "nsIConsoleListener.idl",
+    "nsIConsoleMessage.idl",
+    "nsIConsoleService.idl",
+    "nsICycleCollectorListener.idl",
+    "nsIDebug2.idl",
+    "nsIException.idl",
+    "nsIInterfaceRequestor.idl",
+    "nsIMemoryInfoDumper.idl",
+    "nsIMemoryReporter.idl",
+    "nsIMessageLoop.idl",
+    "nsISecurityConsoleMessage.idl",
+    "nsISupports.idl",
+    "nsIUUIDGenerator.idl",
+    "nsIVersionComparator.idl",
+    "nsIWeakReference.idl",
+    "nsrootidl.idl",
+]
+
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "cocoa":
+    XPIDL_SOURCES += [
+        "nsIMacPreferencesReader.idl",
+    ]
+    EXPORTS += [
+        "nsObjCExceptions.h",
+    ]
+    EXPORTS.mozilla += [
+        "MacHelpers.h",
+        "MacStringHelpers.h",
+        "nsMacPreferencesReader.h",
+    ]
+    UNIFIED_SOURCES += [
+        "MacHelpers.mm",
+        "MacStringHelpers.mm",
+        "nsMacPreferencesReader.mm",
+        "nsObjCExceptions.mm",
+    ]
+
+XPIDL_MODULE = "xpcom_base"
+
+XPCOM_MANIFESTS += [
+    "components.conf",
+]
+
+EXPORTS += [
+    "!ErrorList.h",
+    "!ErrorNamesInternal.h",
+    "CodeAddressService.h",
+    "nsAlgorithm.h",
+    "nsAutoRef.h",
+    "nsCom.h",
+    "nsCOMPtr.h",
+    "nscore.h",
+    "nsCRTGlue.h",
+    "nsCycleCollectionNoteChild.h",
+    "nsCycleCollectionNoteRootCallback.h",
+    "nsCycleCollectionParticipant.h",
+    "nsCycleCollectionTraversalCallback.h",
+    "nsCycleCollector.h",
+    "nsDebug.h",
+    "nsDebugImpl.h",
+    "nsDumpUtils.h",
+    "nsError.h",
+    "nsGZFileWriter.h",
+    "nsIClassInfoImpl.h",
+    "nsID.h",
+    "nsIDUtils.h",
+    "nsIInterfaceRequestorUtils.h",
+    "nsINIParser.h",
+    "nsInterfaceRequestorAgg.h",
+    "nsISizeOf.h",
+    "nsISupportsImpl.h",
+    "nsISupportsUtils.h",
+    "nsIWeakReferenceUtils.h",
+    "nsMaybeWeakPtr.h",
+    "nsMemory.h",
+    "nsMemoryReporterManager.h",
+    "nsQueryObject.h",
+    "nsSystemInfo.h",
+    "nsTraceRefcnt.h",
+    "nsVersionComparator.h",
+    "nsWeakReference.h",
+]
+
+if CONFIG["OS_ARCH"] == "WINNT":
+    EXPORTS += [
+        "nsWindowsHelpers.h",
+    ]
+    if CONFIG["CC_TYPE"] not in ("gcc", "clang"):
+        OS_LIBS += [
+            "wscapi",
+        ]
+
+EXPORTS.mozilla += [
+    "AppShutdown.h",
+    "AutoRestore.h",
+    "AvailableMemoryTracker.h",
+    "AvailableMemoryWatcher.h",
+    "ClearOnShutdown.h",
+    "CountingAllocatorBase.h",
+    "CycleCollectedJSContext.h",
+    "CycleCollectedJSRuntime.h",
+    "Debug.h",
+    "DebuggerOnGCRunnable.h",
+    "DeferredFinalize.h",
+    "EnumeratedArrayCycleCollection.h",
+    "ErrorNames.h",
+    "GkRustUtils.h",
+    "HoldDropJSObjects.h",
+    "IntentionalCrash.h",
+    "JSObjectHolder.h",
+    "JSONStringWriteFuncs.h",
+    "Logging.h",
+    "MemoryInfo.h",
+    "MemoryMapping.h",
+    "MemoryReportingProcess.h",
+    "MemoryTelemetry.h",
+    "nsMemoryInfoDumper.h",
+    "NSPRLogModulesParser.h",
+    "OwningNonNull.h",
+    "RLBoxSandboxPool.h",
+    "RLBoxUtils.h",
+    "ShutdownPhase.h",
+    "SizeOfState.h",
+    "StaticLocalPtr.h",
+    "StaticMonitor.h",
+    "StaticMutex.h",
+    "StaticPtr.h",
+]
+
+SOURCES += [
+    # nsDebugImpl isn't unified because we disable PGO so that NS_ABORT_OOM isn't
+    # optimized away oddly.
+    "nsDebugImpl.cpp",
+    # nsDumpUtils.cpp includes SpecialSystemDirectory.h which includes
+    # nsLocalFileMac.h which upsets other files in this dir that have a different
+    # idea about what `TextRange` means.
+    "nsDumpUtils.cpp",
+]
+SOURCES["nsDebugImpl.cpp"].no_pgo = True
+
+UNIFIED_SOURCES += [
+    "AppShutdown.cpp",
+    "AvailableMemoryTracker.cpp",
+    "AvailableMemoryWatcher.cpp",
+    "ClearOnShutdown.cpp",
+    "CycleCollectedJSContext.cpp",
+    "CycleCollectedJSRuntime.cpp",
+    "Debug.cpp",
+    "DebuggerOnGCRunnable.cpp",
+    "DeferredFinalize.cpp",
+    "ErrorNames.cpp",
+    "GkRustUtils.cpp",
+    "HoldDropJSObjects.cpp",
+    "JSObjectHolder.cpp",
+    "LogCommandLineHandler.cpp",
+    "Logging.cpp",
+    "LogModulePrefWatcher.cpp",
+    "MemoryTelemetry.cpp",
+    "nsClassInfoImpl.cpp",
+    "nsCOMPtr.cpp",
+    "nsConsoleMessage.cpp",
+    "nsConsoleService.cpp",
+    "nsCRTGlue.cpp",
+    "nsCycleCollectionParticipant.cpp",
+    "nsCycleCollector.cpp",
+    "nsCycleCollectorTraceJSHelpers.cpp",
+    "nsGZFileWriter.cpp",
+    "nsID.cpp",
+    "nsIInterfaceRequestorUtils.cpp",
+    "nsINIParser.cpp",
+    "nsInterfaceRequestorAgg.cpp",
+    "nsISupportsImpl.cpp",
+    "nsMemoryImpl.cpp",
+    "nsMemoryInfoDumper.cpp",
+    "nsMemoryReporterManager.cpp",
+    "nsMessageLoop.cpp",
+    "NSPRLogModulesParser.cpp",
+    "nsSecurityConsoleMessage.cpp",
+    "nsSystemInfo.cpp",
+    "nsTraceRefcnt.cpp",
+    "nsUUIDGenerator.cpp",
+    "nsVersionComparator.cpp",
+    "nsVersionComparatorImpl.cpp",
+    "nsWeakReference.cpp",
+    "RLBoxSandboxPool.cpp",
+]
+
+if CONFIG["OS_TARGET"] in ("Linux", "Android"):
+    UNIFIED_SOURCES += [
+        "MemoryMapping.cpp",
+    ]
+
+if CONFIG["OS_TARGET"] == "WINNT":
+    UNIFIED_SOURCES += [
+        "AvailableMemoryWatcherWin.cpp",
+        "MemoryInfo.cpp",
+    ]
+
+if CONFIG["OS_TARGET"] == "Darwin":
+    UNIFIED_SOURCES += [
+        "AvailableMemoryWatcherMac.cpp",
+    ]
+    EXPORTS.mozilla += [
+        "MemoryPressureLevelMac.h",
+    ]
+
+if CONFIG["OS_TARGET"] == "Linux":
+    UNIFIED_SOURCES += [
+        "AvailableMemoryWatcherLinux.cpp",
+    ]
+    EXPORTS.mozilla += [
+        "AvailableMemoryWatcherUtils.h",
+    ]
+
+if CONFIG["MOZ_PHC"]:
+    DEFINES["MOZ_PHC"] = True
+
+GeneratedFile("ErrorList.h", script="ErrorList.py", entry_point="error_list_h")
+GeneratedFile(
+    "ErrorNamesInternal.h", script="ErrorList.py", entry_point="error_names_internal_h"
+)
+GeneratedFile("error_list.rs", script="ErrorList.py", entry_point="error_list_rs")
+
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "cocoa":
+    SOURCES += [
+        "nsMacUtilsImpl.cpp",
+    ]
+elif CONFIG["MOZ_WIDGET_TOOLKIT"] == "windows":
+    SOURCES += [
+        "nsCrashOnException.cpp",
+    ]
+
+if CONFIG["COMPILE_ENVIRONMENT"]:
+    EXPORTS.mozilla += [
+        "!gk_rust_utils_ffi_generated.h",
+    ]
+
+    CbindgenHeader("gk_rust_utils_ffi_generated.h", inputs=["/xpcom/rust/gkrust_utils"])
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
+
+LOCAL_INCLUDES += [
+    "../build",
+    "/dom/base",
+    "/mfbt",
+    "/netwerk/base",
+    "/xpcom/ds",
+]
+
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
+    CXXFLAGS += CONFIG["MOZ_GTK3_CFLAGS"]
diff --git a/xpcom/base/nsAlgorithm.h b/xpcom/base/nsAlgorithm.h
new file mode 100644
index 0000000000..1c4bb0e9dc
--- /dev/null
+++ b/xpcom/base/nsAlgorithm.h
@@ -0,0 +1,54 @@
+/* -*- 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/. */
+
+#ifndef nsAlgorithm_h___
+#define nsAlgorithm_h___
+
+#include <cstdint>
+#include "mozilla/Assertions.h"
+
+template <class T>
+inline T NS_ROUNDUP(const T& aA, const T& aB) {
+  return ((aA + (aB - 1)) / aB) * aB;
+}
+
+// We use these instead of std::min/max because we can't include the algorithm
+// header in all of XPCOM because the stl wrappers will error out when included
+// in parts of XPCOM. These functions should never be used outside of XPCOM.
+template <class T>
+inline const T& XPCOM_MIN(const T& aA, const T& aB) {
+  return aB < aA ? aB : aA;
+}
+
+// Must return b when a == b in case a is -0
+template <class T>
+inline const T& XPCOM_MAX(const T& aA, const T& aB) {
+  return aA > aB ? aA : aB;
+}
+
+namespace mozilla {
+
+template <class T>
+inline const T& clamped(const T& aA, const T& aMin, const T& aMax) {
+  MOZ_ASSERT(aMax >= aMin,
+             "clamped(): aMax must be greater than or equal to aMin");
+  return XPCOM_MIN(XPCOM_MAX(aA, aMin), aMax);
+}
+
+}  // namespace mozilla
+
+template <class InputIterator, class T>
+inline uint32_t NS_COUNT(InputIterator& aFirst, const InputIterator& aLast,
+                         const T& aValue) {
+  uint32_t result = 0;
+  for (; aFirst != aLast; ++aFirst)
+    if (*aFirst == aValue) {
+      ++result;
+    }
+  return result;
+}
+
+#endif  // !defined(nsAlgorithm_h___)
diff --git a/xpcom/base/nsAutoRef.h b/xpcom/base/nsAutoRef.h
new file mode 100644
index 0000000000..9a1f3ddd93
--- /dev/null
+++ b/xpcom/base/nsAutoRef.h
@@ -0,0 +1,489 @@
+/* -*- 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/. */
+
+// NB: This code may be used from non-XPCOM code, in particular, the
+// Windows Default Browser Agent.
+
+#ifndef nsAutoRef_h_
+#define nsAutoRef_h_
+
+#include "mozilla/Attributes.h"
+
+template <class T>
+class nsSimpleRef;
+template <class T>
+class nsAutoRefBase;
+template <class T>
+class nsReturnRef;
+template <class T>
+class nsReturningRef;
+
+/**
+ * template <class T> class nsAutoRef
+ *
+ * A class that holds a handle to a resource that must be released.
+ * No reference is added on construction.
+ *
+ * No copy constructor nor copy assignment operators are available, so the
+ * resource will be held until released on destruction or explicitly
+ * |reset()| or transferred through provided methods.
+ *
+ * The publicly available methods are the public methods on this class and its
+ * public base classes |nsAutoRefBase<T>| and |nsSimpleRef<T>|.
+ *
+ * For function return values see |nsReturnRef<T>|.
+ *
+ * For each class |T|, |nsAutoRefTraits<T>| or |nsSimpleRef<T>| must be
+ * specialized to use |nsAutoRef<T>|.
+ *
+ * @param T  A class identifying the type of reference held by the
+ *           |nsAutoRef<T>| and the unique set methods for managing references
+ *           to the resource (defined by |nsAutoRefTraits<T>| or
+ *           |nsSimpleRef<T>|).
+ *
+ *           Often this is the class representing the resource.  Sometimes a
+ *           new possibly-incomplete class may need to be declared.
+ *
+ *
+ * Example:  An Automatically closing file descriptor
+ *
+ * // References that are simple integral types (as file-descriptors are)
+ * // usually need a new class to represent the resource and how to handle its
+ * // references.
+ * class nsRawFD;
+ *
+ * // Specializing nsAutoRefTraits<nsRawFD> describes how to manage file
+ * // descriptors, so that nsAutoRef<nsRawFD> provides automatic closing of
+ * // its file descriptor on destruction.
+ * template <>
+ * class nsAutoRefTraits<nsRawFD> {
+ * public:
+ *     // The file descriptor is held in an int.
+ *     typedef int RawRef;
+ *     // -1 means that there is no file associated with the handle.
+ *     static int Void() { return -1; }
+ *     // The file associated with a file descriptor is released with close().
+ *     static void Release(RawRef aFD) { close(aFD); }
+ * };
+ *
+ * // A function returning a file descriptor that must be closed.
+ * nsReturnRef<nsRawFD> get_file(const char *filename) {
+ *     // Constructing from a raw file descriptor assumes ownership.
+ *     nsAutoRef<nsRawFD> fd(open(filename, O_RDONLY));
+ *     fcntl(fd, F_SETFD, FD_CLOEXEC);
+ *     return fd.out();
+ * }
+ *
+ * void f() {
+ *     unsigned char buf[1024];
+ *
+ *     // Hold a file descriptor for /etc/hosts in fd1.
+ *     nsAutoRef<nsRawFD> fd1(get_file("/etc/hosts"));
+ *
+ *     nsAutoRef<nsRawFD> fd2;
+ *     fd2.steal(fd1); // fd2 takes the file descriptor from fd1
+ *     ssize_t count = read(fd1, buf, 1024); // error fd1 has no file
+ *     count = read(fd2, buf, 1024); // reads from /etc/hosts
+ *
+ *     // If the file descriptor is not stored then it is closed.
+ *     get_file("/etc/login.defs"); // login.defs is closed
+ *
+ *     // Now use fd1 to hold a file descriptor for /etc/passwd.
+ *     fd1 = get_file("/etc/passwd");
+ *
+ *     // The nsAutoRef<nsRawFD> can give up the file descriptor if explicitly
+ *     // instructed, but the caller must then ensure that the file is closed.
+ *     int rawfd = fd1.disown();
+ *
+ *     // Assume ownership of another file descriptor.
+ *     fd1.own(open("/proc/1/maps");
+ *
+ *     // On destruction, fd1 closes /proc/1/maps and fd2 closes /etc/hosts,
+ *     // but /etc/passwd is not closed.
+ * }
+ *
+ */
+
+template <class T>
+class nsAutoRef : public nsAutoRefBase<T> {
+ protected:
+  typedef nsAutoRef<T> ThisClass;
+  typedef nsAutoRefBase<T> BaseClass;
+  typedef nsSimpleRef<T> SimpleRef;
+  typedef typename BaseClass::RawRefOnly RawRefOnly;
+  typedef typename BaseClass::LocalSimpleRef LocalSimpleRef;
+
+ public:
+  nsAutoRef() = default;
+
+  // Explicit construction is required so as not to risk unintentionally
+  // releasing the resource associated with a raw ref.
+  explicit nsAutoRef(RawRefOnly aRefToRelease) : BaseClass(aRefToRelease) {}
+
+  // Construction from a nsReturnRef<T> function return value, which expects
+  // to give up ownership, transfers ownership.
+  // (nsReturnRef<T> is converted to const nsReturningRef<T>.)
+  explicit nsAutoRef(const nsReturningRef<T>& aReturning)
+      : BaseClass(aReturning) {}
+
+  // The only assignment operator provided is for transferring from an
+  // nsReturnRef smart reference, which expects to pass its ownership to
+  // another object.
+  //
+  // With raw references and other smart references, the type of the lhs and
+  // its taking and releasing nature is often not obvious from an assignment
+  // statement.  Assignment from a raw ptr especially is not normally
+  // expected to release the reference.
+  //
+  // Use |steal| for taking ownership from other smart refs.
+  //
+  // For raw references, use |own| to indicate intention to have the
+  // resource released.
+
+  ThisClass& operator=(const nsReturningRef<T>& aReturning) {
+    BaseClass::steal(aReturning.mReturnRef);
+    return *this;
+  }
+
+  // Conversion to a raw reference allow the nsAutoRef<T> to often be used
+  // like a raw reference.
+  operator typename SimpleRef::RawRef() const { return this->get(); }
+
+  explicit operator bool() const { return this->HaveResource(); }
+
+  // Transfer ownership from another smart reference.
+  void steal(ThisClass& aOtherRef) { BaseClass::steal(aOtherRef); }
+
+  // Assume ownership of a raw ref.
+  //
+  // |own| has similar function to |steal|, and is useful for receiving
+  // ownership from a return value of a function.  It is named differently
+  // because |own| requires more care to ensure that the function intends to
+  // give away ownership, and so that |steal| can be safely used, knowing
+  // that it won't steal ownership from any methods returning raw ptrs to
+  // data owned by a foreign object.
+  void own(RawRefOnly aRefToRelease) { BaseClass::own(aRefToRelease); }
+
+  // Exchange ownership with |aOther|
+  void swap(ThisClass& aOther) {
+    LocalSimpleRef temp;
+    temp.SimpleRef::operator=(*this);
+    SimpleRef::operator=(aOther);
+    aOther.SimpleRef::operator=(temp);
+  }
+
+  // Release the reference now.
+  void reset() {
+    this->SafeRelease();
+    LocalSimpleRef empty;
+    SimpleRef::operator=(empty);
+  }
+
+  // Pass out the reference for a function return values.
+  nsReturnRef<T> out() { return nsReturnRef<T>(this->disown()); }
+
+  // operator->() and disown() are provided by nsAutoRefBase<T>.
+  // The default nsSimpleRef<T> provides get().
+
+  // No copy constructor
+  explicit nsAutoRef(const ThisClass& aRefToSteal) = delete;
+};
+
+/**
+ * template <class T> class nsReturnRef
+ *
+ * A type for function return values that hold a reference to a resource that
+ * must be released.  See also |nsAutoRef<T>::out()|.
+ */
+
+template <class T>
+class nsReturnRef : public nsAutoRefBase<T> {
+ protected:
+  typedef nsAutoRefBase<T> BaseClass;
+  typedef typename BaseClass::RawRefOnly RawRefOnly;
+
+ public:
+  // For constructing a return value with no resource
+  nsReturnRef() = default;
+
+  // For returning a smart reference from a raw reference that must be
+  // released.  Explicit construction is required so as not to risk
+  // unintentionally releasing the resource associated with a raw ref.
+  MOZ_IMPLICIT nsReturnRef(RawRefOnly aRefToRelease)
+      : BaseClass(aRefToRelease) {}
+
+  // Move construction transfers ownership
+  nsReturnRef(nsReturnRef<T>&& aRefToSteal) = default;
+
+  MOZ_IMPLICIT nsReturnRef(const nsReturningRef<T>& aReturning)
+      : BaseClass(aReturning) {}
+
+  // Conversion to a temporary (const) object referring to this object so
+  // that the reference may be passed from a function return value
+  // (temporary) to another smart reference.  There is no need to use this
+  // explicitly.  Simply assign a nsReturnRef<T> function return value to a
+  // smart reference.
+  operator nsReturningRef<T>() { return nsReturningRef<T>(*this); }
+
+  // No conversion to RawRef operator is provided on nsReturnRef, to ensure
+  // that the return value is not carelessly assigned to a raw ptr (and the
+  // resource then released).  If passing to a function that takes a raw
+  // ptr, use get or disown as appropriate.
+};
+
+/**
+ * template <class T> class nsReturningRef
+ *
+ * A class to allow ownership to be transferred from nsReturnRef function
+ * return values.
+ *
+ * It should not be necessary for clients to reference this
+ * class directly.  Simply pass an nsReturnRef<T> to a parameter taking an
+ * |nsReturningRef<T>|.
+ *
+ * The conversion operator on nsReturnRef constructs a temporary wrapper of
+ * class nsReturningRef<T> around a non-const reference to the nsReturnRef.
+ * The wrapper can then be passed as an rvalue parameter.
+ */
+
+template <class T>
+class nsReturningRef {
+ private:
+  friend class nsReturnRef<T>;
+
+  explicit nsReturningRef(nsReturnRef<T>& aReturnRef)
+      : mReturnRef(aReturnRef) {}
+
+ public:
+  nsReturnRef<T>& mReturnRef;
+};
+
+/**
+ * template <class T> class nsAutoRefTraits
+ *
+ * A class describing traits of references managed by the default
+ * |nsSimpleRef<T>| implementation and thus |nsAutoRef<T>|.
+ * The default |nsSimpleRef<T> is suitable for resources with handles that
+ * have a void value.  (If there is no such void value for a handle,
+ * specialize |nsSimpleRef<T>|.)
+ *
+ * Specializations must be provided for each class |T| according to the
+ * following pattern:
+ *
+ * // The template parameter |T| should be a class such that the set of fields
+ * // in class nsAutoRefTraits<T> is unique for class |T|.  Usually the
+ * // resource object class is sufficient.  For handles that are simple
+ * // integral typedefs, a new unique possibly-incomplete class may need to be
+ * // declared.
+ *
+ * template <>
+ * class nsAutoRefTraits<T>
+ * {
+ *     // Specializations must provide a typedef for RawRef, describing the
+ *     // type of the handle to the resource.
+ *     typedef <handle-type> RawRef;
+ *
+ *     // Specializations should define Void(), a function returning a value
+ *     // suitable for a handle that does not have an associated resource.
+ *     //
+ *     // The return type must be a suitable as the parameter to a RawRef
+ *     // constructor and operator==.
+ *     //
+ *     // If this method is not accessible then some limited nsAutoRef
+ *     // functionality will still be available, but the default constructor,
+ *     // |reset|, and most transfer of ownership methods will not be available.
+ *     static <return-type> Void();
+ *
+ *     // Specializations must define Release() to properly finalize the
+ *     // handle to a non-void custom-deleted or reference-counted resource.
+ *     static void Release(RawRef aRawRef);
+ * };
+ *
+ * See nsPointerRefTraits for example specializations for simple pointer
+ * references.  See nsAutoRef for an example specialization for a non-pointer
+ * reference.
+ */
+
+template <class T>
+class nsAutoRefTraits;
+
+/**
+ * template <class T> class nsPointerRefTraits
+ *
+ * A convenience class useful as a base class for specializations of
+ * |nsAutoRefTraits<T>| where the handle to the resource is a pointer to |T|.
+ * By inheriting from this class, definitions of only Release(RawRef) and
+ * possibly AddRef(RawRef) need to be added.
+ *
+ * Examples of use:
+ *
+ * template <>
+ * class nsAutoRefTraits<PRFileDesc> : public nsPointerRefTraits<PRFileDesc>
+ * {
+ * public:
+ *     static void Release(PRFileDesc *ptr) { PR_Close(ptr); }
+ * };
+ *
+ * template <>
+ * class nsAutoRefTraits<FcPattern> : public nsPointerRefTraits<FcPattern>
+ * {
+ * public:
+ *     static void Release(FcPattern *ptr) { FcPatternDestroy(ptr); }
+ *     static void AddRef(FcPattern *ptr) { FcPatternReference(ptr); }
+ * };
+ */
+
+template <class T>
+class nsPointerRefTraits {
+ public:
+  // The handle is a pointer to T.
+  typedef T* RawRef;
+  // A nullptr does not have a resource.
+  static RawRef Void() { return nullptr; }
+};
+
+/**
+ * template <class T> class nsSimpleRef
+ *
+ * Constructs a non-smart reference, and provides methods to test whether
+ * there is an associated resource and (if so) get its raw handle.
+ *
+ * A default implementation is suitable for resources with handles that have a
+ * void value.  This is not intended for direct use but used by |nsAutoRef<T>|.
+ *
+ * Specialize this class if there is no particular void value for the resource
+ * handle.  A specialized implementation must also provide Release(RawRef),
+ */
+
+template <class T>
+class nsSimpleRef : protected nsAutoRefTraits<T> {
+ protected:
+  // The default implementation uses nsAutoRefTrait<T>.
+  // Specializations need not define this typedef.
+  typedef nsAutoRefTraits<T> Traits;
+  // The type of the handle to the resource.
+  // A specialization must provide a typedef for RawRef.
+  typedef typename Traits::RawRef RawRef;
+
+  // Construct with no resource.
+  //
+  // If this constructor is not accessible then some limited nsAutoRef
+  // functionality will still be available, but the default constructor,
+  // |reset|, and most transfer of ownership methods will not be available.
+  nsSimpleRef() : mRawRef(Traits::Void()) {}
+  // Construct with a handle to a resource.
+  // A specialization must provide this.
+  explicit nsSimpleRef(RawRef aRawRef) : mRawRef(aRawRef) {}
+
+  // Test whether there is an associated resource.  A specialization must
+  // provide this.  The function is permitted to always return true if the
+  // default constructor is not accessible, or if Release (and AddRef) can
+  // deal with void handles.
+  bool HaveResource() const { return mRawRef != Traits::Void(); }
+
+ public:
+  // A specialization must provide get() or loose some functionality.  This
+  // is inherited by derived classes and the specialization may choose
+  // whether it is public or protected.
+  RawRef get() const { return mRawRef; }
+
+ private:
+  RawRef mRawRef;
+};
+
+/**
+ * template <class T> class nsAutoRefBase
+ *
+ * Internal base class for |nsAutoRef<T>| and |nsReturnRef<T>|.
+ * Adds release on destruction to a |nsSimpleRef<T>|.
+ */
+
+template <class T>
+class nsAutoRefBase : public nsSimpleRef<T> {
+ protected:
+  typedef nsAutoRefBase<T> ThisClass;
+  typedef nsSimpleRef<T> SimpleRef;
+  typedef typename SimpleRef::RawRef RawRef;
+
+  nsAutoRefBase() = default;
+
+  // A type for parameters that should be passed a raw ref but should not
+  // accept implicit conversions (from another smart ref).  (The only
+  // conversion to this type is from a raw ref so only raw refs will be
+  // accepted.)
+  class RawRefOnly {
+   public:
+    MOZ_IMPLICIT RawRefOnly(RawRef aRawRef) : mRawRef(aRawRef) {}
+    operator RawRef() const { return mRawRef; }
+
+   private:
+    RawRef mRawRef;
+  };
+
+  // Construction from a raw ref assumes ownership
+  explicit nsAutoRefBase(RawRefOnly aRefToRelease) : SimpleRef(aRefToRelease) {}
+
+  // Constructors that steal ownership
+  nsAutoRefBase(ThisClass&& aRefToSteal) : SimpleRef(aRefToSteal.disown()) {}
+  explicit nsAutoRefBase(const nsReturningRef<T>& aReturning)
+      : SimpleRef(aReturning.mReturnRef.disown()) {}
+
+  ~nsAutoRefBase() { SafeRelease(); }
+
+  // An internal class providing access to protected nsSimpleRef<T>
+  // constructors for construction of temporary simple references (that are
+  // not ThisClass).
+  class LocalSimpleRef : public SimpleRef {
+   public:
+    LocalSimpleRef() = default;
+    explicit LocalSimpleRef(RawRef aRawRef) : SimpleRef(aRawRef) {}
+  };
+
+ public:
+  ThisClass& operator=(const ThisClass& aSmartRef) = delete;
+
+  RawRef operator->() const { return this->get(); }
+
+  // Transfer ownership to a raw reference.
+  //
+  // THE CALLER MUST ENSURE THAT THE REFERENCE IS EXPLICITLY RELEASED.
+  //
+  // Is this really what you want to use?  Using this removes any guarantee
+  // of release.  Use nsAutoRef<T>::out() for return values, or an
+  // nsAutoRef<T> modifiable lvalue for an out parameter.  Use disown() when
+  // the reference must be stored in a POD type object, such as may be
+  // preferred for a namespace-scope object with static storage duration,
+  // for example.
+  RawRef disown() {
+    RawRef temp = this->get();
+    LocalSimpleRef empty;
+    SimpleRef::operator=(empty);
+    return temp;
+  }
+
+ protected:
+  // steal and own are protected because they make no sense on nsReturnRef,
+  // but steal is implemented on this class for access to aOtherRef.disown()
+  // when aOtherRef is an nsReturnRef;
+
+  // Transfer ownership from another smart reference.
+  void steal(ThisClass& aOtherRef) { own(aOtherRef.disown()); }
+  // Assume ownership of a raw ref.
+  void own(RawRefOnly aRefToRelease) {
+    SafeRelease();
+    LocalSimpleRef ref(aRefToRelease);
+    SimpleRef::operator=(ref);
+  }
+
+  // Release a resource if there is one.
+  void SafeRelease() {
+    if (this->HaveResource()) {
+      this->Release(this->get());
+    }
+  }
+};
+
+#endif  // !defined(nsAutoRef_h_)
diff --git a/xpcom/base/nsCOMPtr.cpp b/xpcom/base/nsCOMPtr.cpp
new file mode 100644
index 0000000000..ffe0cb1acd
--- /dev/null
+++ b/xpcom/base/nsCOMPtr.cpp
@@ -0,0 +1,34 @@
+/* -*- 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 "nsCOMPtr.h"
+
+nsresult nsQueryInterfaceISupports::operator()(const nsIID& aIID,
+                                               void** aAnswer) const {
+  nsresult status;
+  if (mRawPtr) {
+    status = mRawPtr->QueryInterface(aIID, aAnswer);
+  } else {
+    status = NS_ERROR_NULL_POINTER;
+  }
+
+  return status;
+}
+
+nsresult nsQueryInterfaceISupportsWithError::operator()(const nsIID& aIID,
+                                                        void** aAnswer) const {
+  nsresult status;
+  if (mRawPtr) {
+    status = mRawPtr->QueryInterface(aIID, aAnswer);
+  } else {
+    status = NS_ERROR_NULL_POINTER;
+  }
+
+  if (mErrorPtr) {
+    *mErrorPtr = status;
+  }
+  return status;
+}
diff --git a/xpcom/base/nsCOMPtr.h b/xpcom/base/nsCOMPtr.h
new file mode 100644
index 0000000000..3ee56e9800
--- /dev/null
+++ b/xpcom/base/nsCOMPtr.h
@@ -0,0 +1,1170 @@
+/* -*- 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/. */
+
+#ifndef nsCOMPtr_h___
+#define nsCOMPtr_h___
+
+/*
+ * Having problems?
+ *
+ * See the documentation at:
+ *   https://firefox-source-docs.mozilla.org/xpcom/refptr.html
+ *
+ *
+ * nsCOMPtr
+ *   better than a raw pointer
+ * for owning objects
+ *                      -- scc
+ */
+
+#include <type_traits>
+
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/RefPtr.h"
+#include "nsCycleCollectionNoteChild.h"
+#include "nsDebug.h"  // for |NS_ASSERTION|
+#include "nsISupportsUtils.h"  // for |nsresult|, |NS_ADDREF|, |NS_GET_TEMPLATE_IID| et al
+
+/*
+ * WARNING: This file defines several macros for internal use only. These
+ * macros begin with the prefix |NSCAP_|. Do not use these macros in your own
+ * code. They are for internal use only for cross-platform compatibility, and
+ * are subject to change without notice.
+ */
+
+#ifdef _MSC_VER
+// Under VC++, we win by inlining StartAssignment.
+#  define NSCAP_FEATURE_INLINE_STARTASSIGNMENT
+
+// Also under VC++, at the highest warning level, we are overwhelmed with
+// warnings about (unused) inline functions being removed. This is to be
+// expected with templates, so we disable the warning.
+#  pragma warning(disable : 4514)
+#endif
+
+#ifdef DEBUG
+#  define NSCAP_FEATURE_TEST_DONTQUERY_CASES
+#endif
+
+#ifdef __GNUC__
+// Our use of nsCOMPtr_base::mRawPtr violates the C++ standard's aliasing
+// rules. Mark it with the may_alias attribute so that gcc 3.3 and higher
+// don't reorder instructions based on aliasing assumptions for
+// this variable.  Fortunately, gcc versions < 3.3 do not do any
+// optimizations that break nsCOMPtr.
+
+#  define NS_MAY_ALIAS_PTR(t) t* __attribute__((__may_alias__))
+#else
+#  define NS_MAY_ALIAS_PTR(t) t*
+#endif
+
+/*
+ * The following three macros (NSCAP_ADDREF, NSCAP_RELEASE, and
+ * NSCAP_LOG_ASSIGNMENT) allow external clients the ability to add logging or
+ * other interesting debug facilities. In fact, if you want |nsCOMPtr| to
+ * participate in the standard logging facility, you provide
+ * (e.g., in "nsISupportsImpl.h") suitable definitions
+ *
+ *   #define NSCAP_ADDREF(this, ptr)         NS_ADDREF(ptr)
+ *   #define NSCAP_RELEASE(this, ptr)        NS_RELEASE(ptr)
+ */
+
+#ifndef NSCAP_ADDREF
+#  define NSCAP_ADDREF(this, ptr) (ptr)->AddRef()
+#endif
+
+#ifndef NSCAP_RELEASE
+#  define NSCAP_RELEASE(this, ptr) (ptr)->Release()
+#endif
+
+// Clients can define |NSCAP_LOG_ASSIGNMENT| to perform logging.
+#ifdef NSCAP_LOG_ASSIGNMENT
+// Remember that |NSCAP_LOG_ASSIGNMENT| was defined by some client so that we
+// know to instantiate |~nsGetterAddRefs| in turn to note the external
+// assignment into the |nsCOMPtr|.
+#  define NSCAP_LOG_EXTERNAL_ASSIGNMENT
+#else
+// ...otherwise, just strip it out of the code
+#  define NSCAP_LOG_ASSIGNMENT(this, ptr)
+#endif
+
+#ifndef NSCAP_LOG_RELEASE
+#  define NSCAP_LOG_RELEASE(this, ptr)
+#endif
+
+namespace mozilla {
+template <class T>
+class OwningNonNull;
+}  // namespace mozilla
+
+template <class T>
+inline already_AddRefed<T> dont_AddRef(T* aRawPtr) {
+  return already_AddRefed<T>(aRawPtr);
+}
+
+template <class T>
+inline already_AddRefed<T>&& dont_AddRef(
+    already_AddRefed<T>&& aAlreadyAddRefedPtr) {
+  return std::move(aAlreadyAddRefedPtr);
+}
+
+/*
+ * An nsCOMPtr_helper transforms commonly called getters into typesafe forms
+ * that are more convenient to call, and more efficient to use with |nsCOMPtr|s.
+ * Good candidates for helpers are |QueryInterface()|, |CreateInstance()|, etc.
+ *
+ * Here are the rules for a helper:
+ *   - it implements |operator()| to produce an interface pointer
+ *   - (except for its name) |operator()| is a valid [XP]COM `getter'
+ *   - the interface pointer that it returns is already |AddRef()|ed (as from
+ *     any good getter)
+ *   - it matches the type requested with the supplied |nsIID| argument
+ *   - its constructor provides an optional |nsresult*| that |operator()| can
+ *     fill in with an error when it is executed
+ *
+ * See |class nsGetInterface| for an example.
+ */
+class MOZ_STACK_CLASS nsCOMPtr_helper {
+ public:
+  virtual nsresult NS_FASTCALL operator()(const nsIID&, void**) const = 0;
+};
+
+/*
+ * nsQueryInterface could have been implemented as an nsCOMPtr_helper to avoid
+ * adding specialized machinery in nsCOMPtr, but do_QueryInterface is called
+ * often enough that the codesize savings are big enough to warrant the
+ * specialcasing.
+ */
+class MOZ_STACK_CLASS nsQueryInterfaceISupports {
+ public:
+  explicit nsQueryInterfaceISupports(nsISupports* aRawPtr) : mRawPtr(aRawPtr) {}
+
+  nsresult NS_FASTCALL operator()(const nsIID& aIID, void**) const;
+
+ private:
+  nsISupports* MOZ_OWNING_REF mRawPtr;
+};
+
+template <typename T>
+class MOZ_STACK_CLASS nsQueryInterface final
+    : public nsQueryInterfaceISupports {
+ public:
+  explicit nsQueryInterface(T* aRawPtr)
+      : nsQueryInterfaceISupports(ToSupports(aRawPtr)) {}
+
+  nsresult NS_FASTCALL operator()(const nsIID& aIID, void** aAnswer) const {
+    return nsQueryInterfaceISupports::operator()(aIID, aAnswer);
+  }
+};
+
+class MOZ_STACK_CLASS nsQueryInterfaceISupportsWithError {
+ public:
+  nsQueryInterfaceISupportsWithError(nsISupports* aRawPtr, nsresult* aError)
+      : mRawPtr(aRawPtr), mErrorPtr(aError) {}
+
+  nsresult NS_FASTCALL operator()(const nsIID& aIID, void**) const;
+
+ private:
+  nsISupports* MOZ_OWNING_REF mRawPtr;
+  nsresult* mErrorPtr;
+};
+
+template <typename T>
+class MOZ_STACK_CLASS nsQueryInterfaceWithError final
+    : public nsQueryInterfaceISupportsWithError {
+ public:
+  explicit nsQueryInterfaceWithError(T* aRawPtr, nsresult* aError)
+      : nsQueryInterfaceISupportsWithError(ToSupports(aRawPtr), aError) {}
+
+  nsresult NS_FASTCALL operator()(const nsIID& aIID, void** aAnswer) const {
+    return nsQueryInterfaceISupportsWithError::operator()(aIID, aAnswer);
+  }
+};
+
+namespace mozilla {
+// PointedToType<> is needed so that do_QueryInterface() will work with a
+// variety of smart pointer types in addition to raw pointers. These types
+// include RefPtr<>, nsCOMPtr<>, and OwningNonNull<>.
+template <class T>
+using PointedToType = std::remove_pointer_t<decltype(&*std::declval<T>())>;
+}  // namespace mozilla
+
+template <class T>
+inline nsQueryInterface<mozilla::PointedToType<T>> do_QueryInterface(T aPtr) {
+  return nsQueryInterface<mozilla::PointedToType<T>>(aPtr);
+}
+
+template <class T>
+inline nsQueryInterfaceWithError<mozilla::PointedToType<T>> do_QueryInterface(
+    T aRawPtr, nsresult* aError) {
+  return nsQueryInterfaceWithError<mozilla::PointedToType<T>>(aRawPtr, aError);
+}
+
+template <class T>
+inline void do_QueryInterface(already_AddRefed<T>&) {
+  // This signature exists solely to _stop_ you from doing the bad thing.
+  // Saying |do_QueryInterface()| on a pointer that is not otherwise owned by
+  // someone else is an automatic leak. See bug 8221.
+}
+
+template <class T>
+inline void do_QueryInterface(already_AddRefed<T>&, nsresult*) {
+  // This signature exists solely to _stop_ you from doing the bad thing.
+  // Saying |do_QueryInterface()| on a pointer that is not otherwise owned by
+  // someone else is an automatic leak. See bug 8221.
+}
+
+////////////////////////////////////////////////////////////////////////////
+// Using servicemanager with COMPtrs
+class nsGetServiceByCID final {
+ public:
+  explicit nsGetServiceByCID(const nsCID& aCID) : mCID(aCID) {}
+
+  nsresult NS_FASTCALL operator()(const nsIID&, void**) const;
+
+ private:
+  const nsCID& mCID;
+};
+
+class nsGetServiceByCIDWithError final {
+ public:
+  nsGetServiceByCIDWithError(const nsCID& aCID, nsresult* aErrorPtr)
+      : mCID(aCID), mErrorPtr(aErrorPtr) {}
+
+  nsresult NS_FASTCALL operator()(const nsIID&, void**) const;
+
+ private:
+  const nsCID& mCID;
+  nsresult* mErrorPtr;
+};
+
+class nsGetServiceByContractID final {
+ public:
+  explicit nsGetServiceByContractID(const char* aContractID)
+      : mContractID(aContractID) {}
+
+  nsresult NS_FASTCALL operator()(const nsIID&, void**) const;
+
+ private:
+  const char* mContractID;
+};
+
+class nsGetServiceByContractIDWithError final {
+ public:
+  nsGetServiceByContractIDWithError(const char* aContractID,
+                                    nsresult* aErrorPtr)
+      : mContractID(aContractID), mErrorPtr(aErrorPtr) {}
+
+  nsresult NS_FASTCALL operator()(const nsIID&, void**) const;
+
+ private:
+  const char* mContractID;
+  nsresult* mErrorPtr;
+};
+
+class nsIWeakReference;
+
+// Weak references
+class MOZ_STACK_CLASS nsQueryReferent final {
+ public:
+  nsQueryReferent(nsIWeakReference* aWeakPtr, nsresult* aError)
+      : mWeakPtr(aWeakPtr), mErrorPtr(aError) {}
+
+  nsresult NS_FASTCALL operator()(const nsIID& aIID, void**) const;
+
+ private:
+  nsIWeakReference* MOZ_NON_OWNING_REF mWeakPtr;
+  nsresult* mErrorPtr;
+};
+
+// template<class T> class nsGetterAddRefs;
+
+// Helper for assert_validity method
+template <class T>
+char (&TestForIID(decltype(&NS_GET_TEMPLATE_IID(T))))[2];
+template <class T>
+char TestForIID(...);
+
+template <class T>
+class MOZ_IS_REFPTR nsCOMPtr final {
+ private:
+  void assign_with_AddRef(nsISupports*);
+  template <typename U>
+  void assign_from_qi(const nsQueryInterface<U>, const nsIID&);
+  template <typename U>
+  void assign_from_qi_with_error(const nsQueryInterfaceWithError<U>&,
+                                 const nsIID&);
+  void assign_from_gs_cid(const nsGetServiceByCID, const nsIID&);
+  void assign_from_gs_cid_with_error(const nsGetServiceByCIDWithError&,
+                                     const nsIID&);
+  void assign_from_gs_contractid(const nsGetServiceByContractID, const nsIID&);
+  void assign_from_gs_contractid_with_error(
+      const nsGetServiceByContractIDWithError&, const nsIID&);
+  void assign_from_query_referent(const nsQueryReferent&, const nsIID&);
+  void assign_from_helper(const nsCOMPtr_helper&, const nsIID&);
+  void** begin_assignment();
+
+  void assign_assuming_AddRef(T* aNewPtr) {
+    T* oldPtr = mRawPtr;
+    mRawPtr = aNewPtr;
+    NSCAP_LOG_ASSIGNMENT(this, aNewPtr);
+    NSCAP_LOG_RELEASE(this, oldPtr);
+    if (oldPtr) {
+      NSCAP_RELEASE(this, oldPtr);
+    }
+  }
+
+ private:
+  T* MOZ_OWNING_REF mRawPtr;
+
+  void assert_validity() {
+    static_assert(1 < sizeof(TestForIID<T>(nullptr)),
+                  "nsCOMPtr only works "
+                  "for types with IIDs.  Either use RefPtr; add an IID to "
+                  "your type with NS_DECLARE_STATIC_IID_ACCESSOR/"
+                  "NS_DEFINE_STATIC_IID_ACCESSOR; or make the nsCOMPtr point "
+                  "to a base class with an IID.");
+  }
+
+ public:
+  typedef T element_type;
+
+  ~nsCOMPtr() {
+    NSCAP_LOG_RELEASE(this, mRawPtr);
+    if (mRawPtr) {
+      NSCAP_RELEASE(this, mRawPtr);
+    }
+  }
+
+#ifdef NSCAP_FEATURE_TEST_DONTQUERY_CASES
+  void Assert_NoQueryNeeded() {
+    if (!mRawPtr) {
+      return;
+    }
+    if constexpr (std::is_same_v<T, nsISupports>) {
+      // FIXME: nsCOMPtr<nsISupports> never asserted this, and it currently
+      // fails...
+      return;
+    }
+    // This can't be defined in terms of do_QueryInterface because
+    // that bans casts from a class to itself.
+    void* out = nullptr;
+    mRawPtr->QueryInterface(NS_GET_TEMPLATE_IID(T), &out);
+    T* query_result = static_cast<T*>(out);
+    MOZ_ASSERT(query_result == mRawPtr, "QueryInterface needed");
+    NS_RELEASE(query_result);
+  }
+
+#  define NSCAP_ASSERT_NO_QUERY_NEEDED() Assert_NoQueryNeeded();
+#else
+#  define NSCAP_ASSERT_NO_QUERY_NEEDED()
+#endif
+
+  // Constructors
+
+  nsCOMPtr() : mRawPtr(nullptr) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, nullptr);
+  }
+
+  MOZ_IMPLICIT nsCOMPtr(decltype(nullptr)) : mRawPtr(nullptr) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, nullptr);
+  }
+
+  nsCOMPtr(const nsCOMPtr<T>& aSmartPtr) : mRawPtr(aSmartPtr.mRawPtr) {
+    assert_validity();
+    if (mRawPtr) {
+      NSCAP_ADDREF(this, mRawPtr);
+    }
+    NSCAP_LOG_ASSIGNMENT(this, aSmartPtr.mRawPtr);
+  }
+
+  template <class U>
+  MOZ_IMPLICIT nsCOMPtr(const nsCOMPtr<U>& aSmartPtr)
+      : mRawPtr(aSmartPtr.get()) {
+    // Make sure that U actually inherits from T
+    static_assert(std::is_base_of<T, U>::value, "U should be a subclass of T");
+    assert_validity();
+    if (mRawPtr) {
+      NSCAP_ADDREF(this, mRawPtr);
+    }
+    NSCAP_LOG_ASSIGNMENT(this, aSmartPtr.get());
+  }
+
+  nsCOMPtr(nsCOMPtr<T>&& aSmartPtr) : mRawPtr(aSmartPtr.mRawPtr) {
+    assert_validity();
+    aSmartPtr.mRawPtr = nullptr;
+    NSCAP_LOG_ASSIGNMENT(this, mRawPtr);
+  }
+
+  template <class U>
+  MOZ_IMPLICIT nsCOMPtr(nsCOMPtr<U>&& aSmartPtr)
+      : mRawPtr(aSmartPtr.forget().template downcast<T>().take()) {
+    // Make sure that U actually inherits from T
+    static_assert(std::is_base_of<T, U>::value, "U should be a subclass of T");
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, mRawPtr);
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+  }
+
+  MOZ_IMPLICIT nsCOMPtr(T* aRawPtr) : mRawPtr(aRawPtr) {
+    assert_validity();
+    if (mRawPtr) {
+      NSCAP_ADDREF(this, mRawPtr);
+    }
+    NSCAP_LOG_ASSIGNMENT(this, aRawPtr);
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+  }
+
+  MOZ_IMPLICIT nsCOMPtr(already_AddRefed<T>& aSmartPtr)
+      : mRawPtr(aSmartPtr.take()) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, mRawPtr);
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+  }
+
+  // Construct from |otherComPtr.forget()|.
+  MOZ_IMPLICIT nsCOMPtr(already_AddRefed<T>&& aSmartPtr)
+      : mRawPtr(aSmartPtr.take()) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, mRawPtr);
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+  }
+
+  // Construct from |std::move(otherRefPtr)|.
+  template <typename U>
+  MOZ_IMPLICIT nsCOMPtr(RefPtr<U>&& aSmartPtr)
+      : mRawPtr(static_cast<already_AddRefed<T>>(aSmartPtr.forget()).take()) {
+    assert_validity();
+    // Make sure that U actually inherits from T
+    static_assert(std::is_base_of<T, U>::value, "U is not a subclass of T");
+    NSCAP_LOG_ASSIGNMENT(this, mRawPtr);
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+  }
+
+  // Construct from |already_AddRefed|.
+  template <typename U>
+  MOZ_IMPLICIT nsCOMPtr(already_AddRefed<U>& aSmartPtr)
+      : mRawPtr(static_cast<T*>(aSmartPtr.take())) {
+    assert_validity();
+    // But make sure that U actually inherits from T.
+    static_assert(std::is_base_of<T, U>::value, "U is not a subclass of T");
+    NSCAP_LOG_ASSIGNMENT(this, static_cast<T*>(mRawPtr));
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+  }
+
+  // Construct from |otherComPtr.forget()|.
+  template <typename U>
+  MOZ_IMPLICIT nsCOMPtr(already_AddRefed<U>&& aSmartPtr)
+      : mRawPtr(static_cast<T*>(aSmartPtr.take())) {
+    assert_validity();
+    // But make sure that U actually inherits from T.
+    static_assert(std::is_base_of<T, U>::value, "U is not a subclass of T");
+    NSCAP_LOG_ASSIGNMENT(this, static_cast<T*>(mRawPtr));
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+  }
+
+  // Construct from |do_QueryInterface(expr)|.
+  template <typename U>
+  MOZ_IMPLICIT nsCOMPtr(const nsQueryInterface<U> aQI) : mRawPtr(nullptr) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, nullptr);
+    assign_from_qi(aQI, NS_GET_TEMPLATE_IID(T));
+  }
+
+  // Construct from |do_QueryInterface(expr, &rv)|.
+  template <typename U>
+  MOZ_IMPLICIT nsCOMPtr(const nsQueryInterfaceWithError<U>& aQI)
+      : mRawPtr(nullptr) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, nullptr);
+    assign_from_qi_with_error(aQI, NS_GET_TEMPLATE_IID(T));
+  }
+
+  // Construct from |do_GetService(cid_expr)|.
+  MOZ_IMPLICIT nsCOMPtr(const nsGetServiceByCID aGS) : mRawPtr(nullptr) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, nullptr);
+    assign_from_gs_cid(aGS, NS_GET_TEMPLATE_IID(T));
+  }
+
+  // Construct from |do_GetService(cid_expr, &rv)|.
+  MOZ_IMPLICIT nsCOMPtr(const nsGetServiceByCIDWithError& aGS)
+      : mRawPtr(nullptr) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, nullptr);
+    assign_from_gs_cid_with_error(aGS, NS_GET_TEMPLATE_IID(T));
+  }
+
+  // Construct from |do_GetService(contractid_expr)|.
+  MOZ_IMPLICIT nsCOMPtr(const nsGetServiceByContractID aGS) : mRawPtr(nullptr) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, nullptr);
+    assign_from_gs_contractid(aGS, NS_GET_TEMPLATE_IID(T));
+  }
+
+  // Construct from |do_GetService(contractid_expr, &rv)|.
+  MOZ_IMPLICIT nsCOMPtr(const nsGetServiceByContractIDWithError& aGS)
+      : mRawPtr(nullptr) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, nullptr);
+    assign_from_gs_contractid_with_error(aGS, NS_GET_TEMPLATE_IID(T));
+  }
+
+  // Construct from |do_QueryReferent(ptr)|
+  MOZ_IMPLICIT nsCOMPtr(const nsQueryReferent& aQueryReferent)
+      : mRawPtr(nullptr) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, nullptr);
+    assign_from_query_referent(aQueryReferent, NS_GET_TEMPLATE_IID(T));
+  }
+
+  // And finally, anything else we might need to construct from can exploit the
+  // nsCOMPtr_helper facility.
+  MOZ_IMPLICIT nsCOMPtr(const nsCOMPtr_helper& aHelper) : mRawPtr(nullptr) {
+    assert_validity();
+    NSCAP_LOG_ASSIGNMENT(this, nullptr);
+    assign_from_helper(aHelper, NS_GET_TEMPLATE_IID(T));
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+  }
+
+  // construct from |mozilla::NotNull|.
+  template <typename I,
+            typename = std::enable_if_t<!std::is_same_v<I, nsCOMPtr<T>> &&
+                                        std::is_convertible_v<I, nsCOMPtr<T>>>>
+  MOZ_IMPLICIT nsCOMPtr(const mozilla::NotNull<I>& aSmartPtr)
+      : mRawPtr(nsCOMPtr<T>(aSmartPtr.get()).forget().take()) {}
+
+  // construct from |mozilla::MovingNotNull|.
+  template <typename I,
+            typename = std::enable_if_t<!std::is_same_v<I, nsCOMPtr<T>> &&
+                                        std::is_convertible_v<I, nsCOMPtr<T>>>>
+  MOZ_IMPLICIT nsCOMPtr(mozilla::MovingNotNull<I>&& aSmartPtr)
+      : mRawPtr(
+            nsCOMPtr<T>(std::move(aSmartPtr).unwrapBasePtr()).forget().take()) {
+  }
+
+  // Defined in OwningNonNull.h
+  template <class U>
+  MOZ_IMPLICIT nsCOMPtr(const mozilla::OwningNonNull<U>& aOther);
+
+  // Assignment operators
+
+  nsCOMPtr<T>& operator=(const nsCOMPtr<T>& aRhs) {
+    assign_with_AddRef(ToSupports(aRhs.mRawPtr));
+    return *this;
+  }
+
+  template <class U>
+  nsCOMPtr<T>& operator=(const nsCOMPtr<U>& aRhs) {
+    // Make sure that U actually inherits from T
+    static_assert(std::is_base_of<T, U>::value, "U should be a subclass of T");
+    assign_with_AddRef(ToSupports(static_cast<T*>(aRhs.get())));
+    return *this;
+  }
+
+  nsCOMPtr<T>& operator=(nsCOMPtr<T>&& aRhs) {
+    assign_assuming_AddRef(aRhs.forget().take());
+    return *this;
+  }
+
+  template <class U>
+  nsCOMPtr<T>& operator=(nsCOMPtr<U>&& aRhs) {
+    // Make sure that U actually inherits from T
+    static_assert(std::is_base_of<T, U>::value, "U should be a subclass of T");
+    assign_assuming_AddRef(aRhs.forget().template downcast<T>().take());
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+    return *this;
+  }
+
+  nsCOMPtr<T>& operator=(T* aRhs) {
+    assign_with_AddRef(ToSupports(aRhs));
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+    return *this;
+  }
+
+  nsCOMPtr<T>& operator=(decltype(nullptr)) {
+    assign_assuming_AddRef(nullptr);
+    return *this;
+  }
+
+  // Assign from |already_AddRefed|.
+  template <typename U>
+  nsCOMPtr<T>& operator=(already_AddRefed<U>& aRhs) {
+    // Make sure that U actually inherits from T
+    static_assert(std::is_base_of<T, U>::value, "U is not a subclass of T");
+    assign_assuming_AddRef(static_cast<T*>(aRhs.take()));
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+    return *this;
+  }
+
+  // Assign from |otherComPtr.forget()|.
+  template <typename U>
+  nsCOMPtr<T>& operator=(already_AddRefed<U>&& aRhs) {
+    // Make sure that U actually inherits from T
+    static_assert(std::is_base_of<T, U>::value, "U is not a subclass of T");
+    assign_assuming_AddRef(static_cast<T*>(aRhs.take()));
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+    return *this;
+  }
+
+  // Assign from |std::move(otherRefPtr)|.
+  template <typename U>
+  nsCOMPtr<T>& operator=(RefPtr<U>&& aRhs) {
+    // Make sure that U actually inherits from T
+    static_assert(std::is_base_of<T, U>::value, "U is not a subclass of T");
+    assign_assuming_AddRef(static_cast<T*>(aRhs.forget().take()));
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+    return *this;
+  }
+
+  // Assign from |do_QueryInterface(expr)|.
+  template <typename U>
+  nsCOMPtr<T>& operator=(const nsQueryInterface<U> aRhs) {
+    assign_from_qi(aRhs, NS_GET_TEMPLATE_IID(T));
+    return *this;
+  }
+
+  // Assign from |do_QueryInterface(expr, &rv)|.
+  template <typename U>
+  nsCOMPtr<T>& operator=(const nsQueryInterfaceWithError<U>& aRhs) {
+    assign_from_qi_with_error(aRhs, NS_GET_TEMPLATE_IID(T));
+    return *this;
+  }
+
+  // Assign from |do_GetService(cid_expr)|.
+  nsCOMPtr<T>& operator=(const nsGetServiceByCID aRhs) {
+    assign_from_gs_cid(aRhs, NS_GET_TEMPLATE_IID(T));
+    return *this;
+  }
+
+  // Assign from |do_GetService(cid_expr, &rv)|.
+  nsCOMPtr<T>& operator=(const nsGetServiceByCIDWithError& aRhs) {
+    assign_from_gs_cid_with_error(aRhs, NS_GET_TEMPLATE_IID(T));
+    return *this;
+  }
+
+  // Assign from |do_GetService(contractid_expr)|.
+  nsCOMPtr<T>& operator=(const nsGetServiceByContractID aRhs) {
+    assign_from_gs_contractid(aRhs, NS_GET_TEMPLATE_IID(T));
+    return *this;
+  }
+
+  // Assign from |do_GetService(contractid_expr, &rv)|.
+  nsCOMPtr<T>& operator=(const nsGetServiceByContractIDWithError& aRhs) {
+    assign_from_gs_contractid_with_error(aRhs, NS_GET_TEMPLATE_IID(T));
+    return *this;
+  }
+
+  // Assign from |do_QueryReferent(ptr)|.
+  nsCOMPtr<T>& operator=(const nsQueryReferent& aRhs) {
+    assign_from_query_referent(aRhs, NS_GET_TEMPLATE_IID(T));
+    return *this;
+  }
+
+  // And finally, anything else we might need to assign from can exploit the
+  // nsCOMPtr_helper facility.
+  nsCOMPtr<T>& operator=(const nsCOMPtr_helper& aRhs) {
+    assign_from_helper(aRhs, NS_GET_TEMPLATE_IID(T));
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+    return *this;
+  }
+
+  // Assign from |mozilla::NotNull|.
+  template <typename I,
+            typename = std::enable_if_t<std::is_convertible_v<I, nsCOMPtr<T>>>>
+  nsCOMPtr<T>& operator=(const mozilla::NotNull<I>& aSmartPtr) {
+    assign_assuming_AddRef(nsCOMPtr<T>(aSmartPtr.get()).forget().take());
+    return *this;
+  }
+
+  // Assign from |mozilla::MovingNotNull|.
+  template <typename I,
+            typename = std::enable_if_t<std::is_convertible_v<I, nsCOMPtr<T>>>>
+  nsCOMPtr<T>& operator=(mozilla::MovingNotNull<I>&& aSmartPtr) {
+    assign_assuming_AddRef(
+        nsCOMPtr<T>(std::move(aSmartPtr).unwrapBasePtr()).forget().take());
+    return *this;
+  }
+
+  // Defined in OwningNonNull.h
+  template <class U>
+  nsCOMPtr<T>& operator=(const mozilla::OwningNonNull<U>& aOther);
+
+  // Exchange ownership with |aRhs|; can save a pair of refcount operations.
+  void swap(nsCOMPtr<T>& aRhs) {
+    T* temp = aRhs.mRawPtr;
+    NSCAP_LOG_ASSIGNMENT(&aRhs, mRawPtr);
+    NSCAP_LOG_ASSIGNMENT(this, temp);
+    NSCAP_LOG_RELEASE(this, mRawPtr);
+    NSCAP_LOG_RELEASE(&aRhs, temp);
+    aRhs.mRawPtr = mRawPtr;
+    mRawPtr = temp;
+    // |aRhs| maintains the same invariants, so we don't need to
+    // |NSCAP_ASSERT_NO_QUERY_NEEDED|
+  }
+
+  // Exchange ownership with |aRhs|; can save a pair of refcount operations.
+  void swap(T*& aRhs) {
+    T* temp = aRhs;
+    NSCAP_LOG_ASSIGNMENT(this, temp);
+    NSCAP_LOG_RELEASE(this, mRawPtr);
+    aRhs = reinterpret_cast<T*>(mRawPtr);
+    mRawPtr = temp;
+    NSCAP_ASSERT_NO_QUERY_NEEDED();
+  }
+
+  // Other pointer operators
+
+  // Return the value of mRawPtr and null out mRawPtr. Useful for
+  // already_AddRefed return values.
+  already_AddRefed<T> MOZ_MAY_CALL_AFTER_MUST_RETURN forget() {
+    T* temp = nullptr;
+    swap(temp);
+    return already_AddRefed<T>(temp);
+  }
+
+  // Set the target of aRhs to the value of mRawPtr and null out mRawPtr.
+  // Useful to avoid unnecessary AddRef/Release pairs with "out" parameters
+  // where aRhs bay be a T** or an I** where I is a base class of T.
+  template <typename I>
+  void forget(I** aRhs) {
+    NS_ASSERTION(aRhs, "Null pointer passed to forget!");
+    NSCAP_LOG_RELEASE(this, mRawPtr);
+    *aRhs = get();
+    mRawPtr = nullptr;
+  }
+
+  // Prefer the implicit conversion provided automatically by
+  // |operator T*() const|. Use |get()| to resolve ambiguity or to get a
+  // castable pointer.
+  T* get() const { return reinterpret_cast<T*>(mRawPtr); }
+
+  // Makes an nsCOMPtr act like its underlying raw pointer type whenever it is
+  // used in a context where a raw pointer is expected. It is this operator
+  // that makes an nsCOMPtr substitutable for a raw pointer.
+  //
+  // Prefer the implicit use of this operator to calling |get()|, except where
+  // necessary to resolve ambiguity.
+  operator T*() const& { return get(); }
+
+  // Don't allow implicit conversion of temporary nsCOMPtr to raw pointer,
+  // because the refcount might be one and the pointer will immediately become
+  // invalid.
+  operator T*() const&& = delete;
+
+  // Needed to avoid the deleted operator above
+  explicit operator bool() const { return !!mRawPtr; }
+
+  T* operator->() const MOZ_NO_ADDREF_RELEASE_ON_RETURN {
+    MOZ_ASSERT(mRawPtr != nullptr,
+               "You can't dereference a NULL nsCOMPtr with operator->().");
+    return get();
+  }
+
+  // These are not intended to be used by clients. See |address_of| below.
+  nsCOMPtr<T>* get_address() { return this; }
+  const nsCOMPtr<T>* get_address() const { return this; }
+
+ public:
+  T& operator*() const {
+    MOZ_ASSERT(mRawPtr != nullptr,
+               "You can't dereference a NULL nsCOMPtr with operator*().");
+    return *get();
+  }
+
+  T** StartAssignment() {
+#ifndef NSCAP_FEATURE_INLINE_STARTASSIGNMENT
+    return reinterpret_cast<T**>(begin_assignment());
+#else
+    assign_assuming_AddRef(nullptr);
+    return reinterpret_cast<T**>(&mRawPtr);
+#endif
+  }
+};
+
+template <typename T>
+inline void ImplCycleCollectionUnlink(nsCOMPtr<T>& aField) {
+  aField = nullptr;
+}
+
+template <typename T>
+inline void ImplCycleCollectionTraverse(
+    nsCycleCollectionTraversalCallback& aCallback, nsCOMPtr<T>& aField,
+    const char* aName, uint32_t aFlags = 0) {
+  CycleCollectionNoteChild(aCallback, aField.get(), aName, aFlags);
+}
+
+template <class T>
+void nsCOMPtr<T>::assign_with_AddRef(nsISupports* aRawPtr) {
+  if (aRawPtr) {
+    NSCAP_ADDREF(this, aRawPtr);
+  }
+  assign_assuming_AddRef(reinterpret_cast<T*>(aRawPtr));
+}
+
+template <class T>
+template <typename U>
+void nsCOMPtr<T>::assign_from_qi(const nsQueryInterface<U> aQI,
+                                 const nsIID& aIID) {
+  // Allow QIing to nsISupports from nsISupports as a special-case, since
+  // SameCOMIdentity uses it.
+  static_assert(
+      std::is_same_v<T, nsISupports> ||
+          !(std::is_same_v<T, U> || std::is_base_of<T, U>::value),
+      "don't use do_QueryInterface for compile-time-determinable casts");
+  void* newRawPtr;
+  if (NS_FAILED(aQI(aIID, &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  assign_assuming_AddRef(static_cast<T*>(newRawPtr));
+}
+
+template <class T>
+template <typename U>
+void nsCOMPtr<T>::assign_from_qi_with_error(
+    const nsQueryInterfaceWithError<U>& aQI, const nsIID& aIID) {
+  static_assert(
+      !(std::is_same_v<T, U> || std::is_base_of<T, U>::value),
+      "don't use do_QueryInterface for compile-time-determinable casts");
+  void* newRawPtr;
+  if (NS_FAILED(aQI(aIID, &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  assign_assuming_AddRef(static_cast<T*>(newRawPtr));
+}
+
+template <class T>
+void nsCOMPtr<T>::assign_from_gs_cid(const nsGetServiceByCID aGS,
+                                     const nsIID& aIID) {
+  void* newRawPtr;
+  if (NS_FAILED(aGS(aIID, &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  assign_assuming_AddRef(static_cast<T*>(newRawPtr));
+}
+
+template <class T>
+void nsCOMPtr<T>::assign_from_gs_cid_with_error(
+    const nsGetServiceByCIDWithError& aGS, const nsIID& aIID) {
+  void* newRawPtr;
+  if (NS_FAILED(aGS(aIID, &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  assign_assuming_AddRef(static_cast<T*>(newRawPtr));
+}
+
+template <class T>
+void nsCOMPtr<T>::assign_from_gs_contractid(const nsGetServiceByContractID aGS,
+                                            const nsIID& aIID) {
+  void* newRawPtr;
+  if (NS_FAILED(aGS(aIID, &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  assign_assuming_AddRef(static_cast<T*>(newRawPtr));
+}
+
+template <class T>
+void nsCOMPtr<T>::assign_from_gs_contractid_with_error(
+    const nsGetServiceByContractIDWithError& aGS, const nsIID& aIID) {
+  void* newRawPtr;
+  if (NS_FAILED(aGS(aIID, &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  assign_assuming_AddRef(static_cast<T*>(newRawPtr));
+}
+
+template <class T>
+void nsCOMPtr<T>::assign_from_query_referent(
+    const nsQueryReferent& aQueryReferent, const nsIID& aIID) {
+  void* newRawPtr;
+  if (NS_FAILED(aQueryReferent(aIID, &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  assign_assuming_AddRef(static_cast<T*>(newRawPtr));
+}
+
+template <class T>
+void nsCOMPtr<T>::assign_from_helper(const nsCOMPtr_helper& helper,
+                                     const nsIID& aIID) {
+  void* newRawPtr;
+  if (NS_FAILED(helper(aIID, &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  assign_assuming_AddRef(static_cast<T*>(newRawPtr));
+}
+
+template <class T>
+void** nsCOMPtr<T>::begin_assignment() {
+  assign_assuming_AddRef(nullptr);
+  union {
+    T** mT;
+    void** mVoid;
+  } result;
+  result.mT = &mRawPtr;
+  return result.mVoid;
+}
+
+template <class T>
+inline nsCOMPtr<T>* address_of(nsCOMPtr<T>& aPtr) {
+  return aPtr.get_address();
+}
+
+template <class T>
+inline const nsCOMPtr<T>* address_of(const nsCOMPtr<T>& aPtr) {
+  return aPtr.get_address();
+}
+
+/**
+ * This class is designed to be used for anonymous temporary objects in the
+ * argument list of calls that return COM interface pointers, e.g.,
+ *
+ *   nsCOMPtr<IFoo> fooP;
+ *   ...->QueryInterface(iid, getter_AddRefs(fooP))
+ *
+ * DO NOT USE THIS TYPE DIRECTLY IN YOUR CODE. Use |getter_AddRefs()| instead.
+ *
+ * When initialized with a |nsCOMPtr|, as in the example above, it returns
+ * a |void**|, a |T**|, or an |nsISupports**| as needed, that the outer call
+ * (|QueryInterface| in this case) can fill in.
+ *
+ * This type should be a nested class inside |nsCOMPtr<T>|.
+ */
+template <class T>
+class nsGetterAddRefs {
+ public:
+  explicit nsGetterAddRefs(nsCOMPtr<T>& aSmartPtr)
+      : mTargetSmartPtr(aSmartPtr) {}
+
+#if defined(NSCAP_FEATURE_TEST_DONTQUERY_CASES) || \
+    defined(NSCAP_LOG_EXTERNAL_ASSIGNMENT)
+  ~nsGetterAddRefs() {
+#  ifdef NSCAP_LOG_EXTERNAL_ASSIGNMENT
+    NSCAP_LOG_ASSIGNMENT(reinterpret_cast<void*>(address_of(mTargetSmartPtr)),
+                         mTargetSmartPtr.get());
+#  endif
+
+#  ifdef NSCAP_FEATURE_TEST_DONTQUERY_CASES
+    mTargetSmartPtr.Assert_NoQueryNeeded();
+#  endif
+  }
+#endif
+
+  operator void**() {
+    return reinterpret_cast<void**>(mTargetSmartPtr.StartAssignment());
+  }
+
+  operator T**() { return mTargetSmartPtr.StartAssignment(); }
+  T*& operator*() { return *(mTargetSmartPtr.StartAssignment()); }
+
+ private:
+  nsCOMPtr<T>& mTargetSmartPtr;
+};
+
+template <>
+class nsGetterAddRefs<nsISupports> {
+ public:
+  explicit nsGetterAddRefs(nsCOMPtr<nsISupports>& aSmartPtr)
+      : mTargetSmartPtr(aSmartPtr) {}
+
+#ifdef NSCAP_LOG_EXTERNAL_ASSIGNMENT
+  ~nsGetterAddRefs() {
+    NSCAP_LOG_ASSIGNMENT(reinterpret_cast<void*>(address_of(mTargetSmartPtr)),
+                         mTargetSmartPtr.get());
+  }
+#endif
+
+  operator void**() {
+    return reinterpret_cast<void**>(mTargetSmartPtr.StartAssignment());
+  }
+
+  operator nsISupports**() { return mTargetSmartPtr.StartAssignment(); }
+  nsISupports*& operator*() { return *(mTargetSmartPtr.StartAssignment()); }
+
+ private:
+  nsCOMPtr<nsISupports>& mTargetSmartPtr;
+};
+
+template <class T>
+inline nsGetterAddRefs<T> getter_AddRefs(nsCOMPtr<T>& aSmartPtr) {
+  return nsGetterAddRefs<T>(aSmartPtr);
+}
+
+template <class T, class DestinationType>
+inline nsresult CallQueryInterface(
+    T* aSource, nsGetterAddRefs<DestinationType> aDestination) {
+  return CallQueryInterface(aSource,
+                            static_cast<DestinationType**>(aDestination));
+}
+
+// Comparing two |nsCOMPtr|s
+
+template <class T, class U>
+inline bool operator==(const nsCOMPtr<T>& aLhs, const nsCOMPtr<U>& aRhs) {
+  return static_cast<const T*>(aLhs.get()) == static_cast<const U*>(aRhs.get());
+}
+
+template <class T, class U>
+inline bool operator!=(const nsCOMPtr<T>& aLhs, const nsCOMPtr<U>& aRhs) {
+  return static_cast<const T*>(aLhs.get()) != static_cast<const U*>(aRhs.get());
+}
+
+// Comparing an |nsCOMPtr| to a raw pointer
+
+template <class T, class U>
+inline bool operator==(const nsCOMPtr<T>& aLhs, const U* aRhs) {
+  return static_cast<const T*>(aLhs.get()) == aRhs;
+}
+
+template <class T, class U>
+inline bool operator==(const U* aLhs, const nsCOMPtr<T>& aRhs) {
+  return aLhs == static_cast<const T*>(aRhs.get());
+}
+
+template <class T, class U>
+inline bool operator!=(const nsCOMPtr<T>& aLhs, const U* aRhs) {
+  return static_cast<const T*>(aLhs.get()) != aRhs;
+}
+
+template <class T, class U>
+inline bool operator!=(const U* aLhs, const nsCOMPtr<T>& aRhs) {
+  return aLhs != static_cast<const T*>(aRhs.get());
+}
+
+template <class T, class U>
+inline bool operator==(const nsCOMPtr<T>& aLhs, U* aRhs) {
+  return static_cast<const T*>(aLhs.get()) == const_cast<const U*>(aRhs);
+}
+
+template <class T, class U>
+inline bool operator==(U* aLhs, const nsCOMPtr<T>& aRhs) {
+  return const_cast<const U*>(aLhs) == static_cast<const T*>(aRhs.get());
+}
+
+template <class T, class U>
+inline bool operator!=(const nsCOMPtr<T>& aLhs, U* aRhs) {
+  return static_cast<const T*>(aLhs.get()) != const_cast<const U*>(aRhs);
+}
+
+template <class T, class U>
+inline bool operator!=(U* aLhs, const nsCOMPtr<T>& aRhs) {
+  return const_cast<const U*>(aLhs) != static_cast<const T*>(aRhs.get());
+}
+
+// Comparing an |nsCOMPtr| to |nullptr|
+
+template <class T>
+inline bool operator==(const nsCOMPtr<T>& aLhs, decltype(nullptr)) {
+  return aLhs.get() == nullptr;
+}
+
+template <class T>
+inline bool operator==(decltype(nullptr), const nsCOMPtr<T>& aRhs) {
+  return nullptr == aRhs.get();
+}
+
+template <class T>
+inline bool operator!=(const nsCOMPtr<T>& aLhs, decltype(nullptr)) {
+  return aLhs.get() != nullptr;
+}
+
+template <class T>
+inline bool operator!=(decltype(nullptr), const nsCOMPtr<T>& aRhs) {
+  return nullptr != aRhs.get();
+}
+
+// Comparing any two [XP]COM objects for identity
+
+inline bool SameCOMIdentity(nsISupports* aLhs, nsISupports* aRhs) {
+  return nsCOMPtr<nsISupports>(do_QueryInterface(aLhs)) ==
+         nsCOMPtr<nsISupports>(do_QueryInterface(aRhs));
+}
+
+template <class SourceType, class DestinationType>
+inline nsresult CallQueryInterface(nsCOMPtr<SourceType>& aSourcePtr,
+                                   DestinationType** aDestPtr) {
+  return CallQueryInterface(aSourcePtr.get(), aDestPtr);
+}
+
+template <class T>
+RefPtr<T>::RefPtr(const nsQueryReferent& aQueryReferent) {
+  void* newRawPtr;
+  if (NS_FAILED(aQueryReferent(NS_GET_TEMPLATE_IID(T), &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  mRawPtr = static_cast<T*>(newRawPtr);
+}
+
+template <class T>
+RefPtr<T>::RefPtr(const nsCOMPtr_helper& aHelper) {
+  void* newRawPtr;
+  if (NS_FAILED(aHelper(NS_GET_TEMPLATE_IID(T), &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  mRawPtr = static_cast<T*>(newRawPtr);
+}
+
+template <class T>
+RefPtr<T>& RefPtr<T>::operator=(const nsQueryReferent& aQueryReferent) {
+  void* newRawPtr;
+  if (NS_FAILED(aQueryReferent(NS_GET_TEMPLATE_IID(T), &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  assign_assuming_AddRef(static_cast<T*>(newRawPtr));
+  return *this;
+}
+
+template <class T>
+RefPtr<T>& RefPtr<T>::operator=(const nsCOMPtr_helper& aHelper) {
+  void* newRawPtr;
+  if (NS_FAILED(aHelper(NS_GET_TEMPLATE_IID(T), &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  assign_assuming_AddRef(static_cast<T*>(newRawPtr));
+  return *this;
+}
+
+template <class T>
+inline already_AddRefed<T> do_AddRef(const nsCOMPtr<T>& aObj) {
+  nsCOMPtr<T> ref(aObj);
+  return ref.forget();
+}
+
+// MOZ_DBG support
+
+template <class T>
+std::ostream& operator<<(std::ostream& aOut, const nsCOMPtr<T>& aObj) {
+  return mozilla::DebugValue(aOut, aObj.get());
+}
+
+// ToRefPtr allows to move an nsCOMPtr<T> into a RefPtr<T>. Be mindful when
+// using this, because usually RefPtr<T> should only be used with concrete T and
+// nsCOMPtr<T> should only be used with XPCOM interface T.
+template <class T>
+RefPtr<T> ToRefPtr(nsCOMPtr<T>&& aObj) {
+  return aObj.forget();
+}
+
+// Integration with ResultExtensions.h
+template <typename R>
+auto ResultRefAsParam(nsCOMPtr<R>& aResult) {
+  return getter_AddRefs(aResult);
+}
+
+namespace mozilla::detail {
+template <typename T>
+struct outparam_as_pointer;
+
+template <typename T>
+struct outparam_as_pointer<nsGetterAddRefs<T>> {
+  using type = T**;
+};
+}  // namespace mozilla::detail
+
+#endif  // !defined(nsCOMPtr_h___)
diff --git a/xpcom/base/nsCRTGlue.cpp b/xpcom/base/nsCRTGlue.cpp
new file mode 100644
index 0000000000..925379f716
--- /dev/null
+++ b/xpcom/base/nsCRTGlue.cpp
@@ -0,0 +1,328 @@
+/* -*- 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 "nsCRTGlue.h"
+#include "nsXPCOM.h"
+#include "nsDebug.h"
+#include "prtime.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdarg.h>
+
+#include "mozilla/Sprintf.h"
+
+#ifdef XP_WIN
+#  include <io.h>
+#  include <windows.h>
+#  include "mozilla/LateWriteChecks.h"
+#  include "mozilla/UniquePtr.h"
+#endif
+
+#ifdef ANDROID
+#  include <android/log.h>
+#endif
+
+#ifdef FUZZING_SNAPSHOT
+#  include <mozilla/fuzzing/NyxWrapper.h>
+#endif
+
+using namespace mozilla;
+
+const char* NS_strspnp(const char* aDelims, const char* aStr) {
+  const char* d;
+  do {
+    for (d = aDelims; *d != '\0'; ++d) {
+      if (*aStr == *d) {
+        ++aStr;
+        break;
+      }
+    }
+  } while (*d);
+
+  return aStr;
+}
+
+char* NS_strtok(const char* aDelims, char** aStr) {
+  if (!*aStr) {
+    return nullptr;
+  }
+
+  char* ret = (char*)NS_strspnp(aDelims, *aStr);
+
+  if (!*ret) {
+    *aStr = ret;
+    return nullptr;
+  }
+
+  char* i = ret;
+  do {
+    for (const char* d = aDelims; *d != '\0'; ++d) {
+      if (*i == *d) {
+        *i = '\0';
+        *aStr = ++i;
+        return ret;
+      }
+    }
+    ++i;
+  } while (*i);
+
+  *aStr = nullptr;
+  return ret;
+}
+
+uint32_t NS_strlen(const char16_t* aString) {
+  MOZ_ASSERT(aString);
+  const char16_t* end;
+
+  for (end = aString; *end; ++end) {
+    // empty loop
+  }
+
+  return end - aString;
+}
+
+int NS_strcmp(const char16_t* aStrA, const char16_t* aStrB) {
+  while (*aStrB) {
+    int r = *aStrA - *aStrB;
+    if (r) {
+      return r;
+    }
+
+    ++aStrA;
+    ++aStrB;
+  }
+
+  return *aStrA != '\0';
+}
+
+int NS_strncmp(const char16_t* aStrA, const char16_t* aStrB, size_t aLen) {
+  while (aLen && *aStrB) {
+    int r = *aStrA - *aStrB;
+    if (r) {
+      return r;
+    }
+
+    ++aStrA;
+    ++aStrB;
+    --aLen;
+  }
+
+  return aLen ? *aStrA != '\0' : 0;
+}
+
+char16_t* NS_xstrdup(const char16_t* aString) {
+  uint32_t len = NS_strlen(aString);
+  return NS_xstrndup(aString, len);
+}
+
+template <typename CharT>
+CharT* NS_xstrndup(const CharT* aString, uint32_t aLen) {
+  auto newBuf = (CharT*)moz_xmalloc((aLen + 1) * sizeof(CharT));
+  memcpy(newBuf, aString, aLen * sizeof(CharT));
+  newBuf[aLen] = '\0';
+  return newBuf;
+}
+
+template char16_t* NS_xstrndup<char16_t>(const char16_t* aString,
+                                         uint32_t aLen);
+template char* NS_xstrndup<char>(const char* aString, uint32_t aLen);
+
+char* NS_xstrdup(const char* aString) {
+  uint32_t len = strlen(aString);
+  char* str = (char*)moz_xmalloc(len + 1);
+  memcpy(str, aString, len);
+  str[len] = '\0';
+  return str;
+}
+
+// clang-format off
+
+// This table maps uppercase characters to lower case characters;
+// characters that are neither upper nor lower case are unaffected.
+const unsigned char nsLowerUpperUtils::kUpper2Lower[256] = {
+    0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
+   16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
+   32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
+   48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
+   64,
+
+    // upper band mapped to lower [A-Z] => [a-z]
+       97, 98, 99,100,101,102,103,104,105,106,107,108,109,110,111,
+  112,113,114,115,116,117,118,119,120,121,122,
+
+                                               91, 92, 93, 94, 95,
+   96, 97, 98, 99,100,101,102,103,104,105,106,107,108,109,110,111,
+  112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,
+  128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,
+  144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,
+  160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,
+  176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,
+  192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,
+  208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,
+  224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,
+  240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255
+};
+
+const unsigned char nsLowerUpperUtils::kLower2Upper[256] = {
+    0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
+   16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
+   32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
+   48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
+   64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
+   80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95,
+   96,
+
+    // lower band mapped to upper [a-z] => [A-Z]
+       65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
+   80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90,
+
+                                              123,124,125,126,127,
+  128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,
+  144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,
+  160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,
+  176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,
+  192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,
+  208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,
+  224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,
+  240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255
+};
+
+// clang-format on
+
+bool NS_IsUpper(char aChar) {
+  return aChar != (char)nsLowerUpperUtils::kUpper2Lower[(unsigned char)aChar];
+}
+
+bool NS_IsLower(char aChar) {
+  return aChar != (char)nsLowerUpperUtils::kLower2Upper[(unsigned char)aChar];
+}
+
+#ifndef XPCOM_GLUE_AVOID_NSPR
+
+void NS_MakeRandomString(char* aBuf, int32_t aBufLen) {
+#  define TABLE_SIZE 36
+  static const char table[] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i',
+                               'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
+                               's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0',
+                               '1', '2', '3', '4', '5', '6', '7', '8', '9'};
+
+  // turn PR_Now() into milliseconds since epoch
+  // and salt rand with that.
+  static unsigned int seed = 0;
+  if (seed == 0) {
+    double fpTime = double(PR_Now());
+    seed =
+        (unsigned int)(fpTime * 1e-6 + 0.5);  // use 1e-6, granularity of
+                                              // PR_Now() on the mac is seconds
+    srand(seed);
+  }
+
+  int32_t i;
+  for (i = 0; i < aBufLen; ++i) {
+    *aBuf++ = table[rand() % TABLE_SIZE];
+  }
+  *aBuf = 0;
+}
+
+#endif
+
+#if defined(XP_WIN)
+void vprintf_stderr(const char* aFmt, va_list aArgs) {
+  if (IsDebuggerPresent()) {
+    int lengthNeeded = _vscprintf(aFmt, aArgs);
+    if (lengthNeeded) {
+      lengthNeeded++;
+      auto buf = MakeUnique<char[]>(lengthNeeded);
+      if (buf) {
+        va_list argsCpy;
+        va_copy(argsCpy, aArgs);
+        vsnprintf(buf.get(), lengthNeeded, aFmt, argsCpy);
+        buf[lengthNeeded - 1] = '\0';
+        va_end(argsCpy);
+        OutputDebugStringA(buf.get());
+      }
+    }
+  }
+
+  // stderr is unbuffered by default so we open a new FILE (which is buffered)
+  // so that calls to printf_stderr are not as likely to get mixed together.
+  int fd = _fileno(stderr);
+  if (fd == -2) {
+    return;
+  }
+
+  FILE* fp = _fdopen(_dup(fd), "a");
+  if (!fp) {
+    return;
+  }
+
+  vfprintf(fp, aFmt, aArgs);
+
+  AutoSuspendLateWriteChecks suspend;
+  fclose(fp);
+}
+
+#elif defined(ANDROID)
+void vprintf_stderr(const char* aFmt, va_list aArgs) {
+  __android_log_vprint(ANDROID_LOG_INFO, "Gecko", aFmt, aArgs);
+}
+#elif defined(FUZZING_SNAPSHOT)
+void vprintf_stderr(const char* aFmt, va_list aArgs) {
+  if (nyx_puts) {
+    auto msgbuf = mozilla::Vsmprintf(aFmt, aArgs);
+    nyx_puts(msgbuf.get());
+  } else {
+    vfprintf(stderr, aFmt, aArgs);
+  }
+}
+#else
+void vprintf_stderr(const char* aFmt, va_list aArgs) {
+  vfprintf(stderr, aFmt, aArgs);
+}
+#endif
+
+void printf_stderr(const char* aFmt, ...) {
+  va_list args;
+  va_start(args, aFmt);
+  vprintf_stderr(aFmt, args);
+  va_end(args);
+}
+
+void fprintf_stderr(FILE* aFile, const char* aFmt, ...) {
+  va_list args;
+  va_start(args, aFmt);
+  if (aFile == stderr) {
+    vprintf_stderr(aFmt, args);
+  } else {
+    vfprintf(aFile, aFmt, args);
+  }
+  va_end(args);
+}
+
+void print_stderr(std::stringstream& aStr) {
+#if defined(ANDROID)
+  // On Android logcat output is truncated to 1024 chars per line, and
+  // we usually use std::stringstream to build up giant multi-line gobs
+  // of output. So to avoid the truncation we find the newlines and
+  // print the lines individually.
+  std::string line;
+  while (std::getline(aStr, line)) {
+    printf_stderr("%s\n", line.c_str());
+  }
+#else
+  printf_stderr("%s", aStr.str().c_str());
+#endif
+}
+
+void fprint_stderr(FILE* aFile, std::stringstream& aStr) {
+  if (aFile == stderr) {
+    print_stderr(aStr);
+  } else {
+    fprintf_stderr(aFile, "%s", aStr.str().c_str());
+  }
+}
diff --git a/xpcom/base/nsCRTGlue.h b/xpcom/base/nsCRTGlue.h
new file mode 100644
index 0000000000..2bfe47b2a8
--- /dev/null
+++ b/xpcom/base/nsCRTGlue.h
@@ -0,0 +1,172 @@
+/* -*- 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/. */
+
+#ifndef nsCRTGlue_h__
+#define nsCRTGlue_h__
+
+#include "nscore.h"
+
+/**
+ * Scan a string for the first character that is *not* in a set of
+ * delimiters.  If the string is only delimiter characters, the end of the
+ * string is returned.
+ *
+ * @param aDelims The set of delimiters (null-terminated)
+ * @param aStr    The string to search (null-terminated)
+ */
+const char* NS_strspnp(const char* aDelims, const char* aStr);
+
+/**
+ * Tokenize a string. This function is similar to the strtok function in the
+ * C standard library, but it does not use static variables to maintain state
+ * and is therefore thread and reentrancy-safe.
+ *
+ * Any leading delimiters in str are skipped. Then the string is scanned
+ * until an additional delimiter or end-of-string is found. The final
+ * delimiter is set to '\0'.
+ *
+ * @param aDelims The set of delimiters.
+ * @param aStr    The string to search. This is an in-out parameter; it is
+ *                reset to the end of the found token + 1, or to the
+ *                end-of-string if there are no more tokens.
+ * @return        The token. If no token is found (the string is only
+ *                delimiter characters), nullptr is returned.
+ */
+char* NS_strtok(const char* aDelims, char** aStr);
+
+/**
+ * "strlen" for char16_t strings
+ */
+uint32_t NS_strlen(const char16_t* aString);
+
+/**
+ * "strcmp" for char16_t strings
+ */
+int NS_strcmp(const char16_t* aStrA, const char16_t* aStrB);
+
+/**
+ * "strncmp" for char16_t strings
+ */
+int NS_strncmp(const char16_t* aStrA, const char16_t* aStrB, size_t aLen);
+
+/**
+ * "strdup" for char16_t strings, uses the infallible moz_xmalloc allocator.
+ */
+char16_t* NS_xstrdup(const char16_t* aString);
+
+/**
+ * "strdup", but using the infallible moz_xmalloc allocator.
+ */
+char* NS_xstrdup(const char* aString);
+
+/**
+ * strndup for char16_t or char strings (normal strndup is not available on
+ * windows). This function will ensure that the new string is
+ * null-terminated. Uses the infallible moz_xmalloc allocator.
+ *
+ * CharT may be either char16_t or char.
+ */
+template <typename CharT>
+CharT* NS_xstrndup(const CharT* aString, uint32_t aLen);
+
+// The following case-conversion methods only deal in the ascii repertoire
+// A-Z and a-z
+
+// semi-private data declarations... don't use these directly.
+class nsLowerUpperUtils {
+ public:
+  static const unsigned char kLower2Upper[256];
+  static const unsigned char kUpper2Lower[256];
+};
+
+inline char NS_ToUpper(char aChar) {
+  return (char)nsLowerUpperUtils::kLower2Upper[(unsigned char)aChar];
+}
+
+inline char NS_ToLower(char aChar) {
+  return (char)nsLowerUpperUtils::kUpper2Lower[(unsigned char)aChar];
+}
+
+bool NS_IsUpper(char aChar);
+bool NS_IsLower(char aChar);
+
+constexpr bool NS_IsAscii(const char* aString) {
+  while (*aString) {
+    if (0x80 & *aString) {
+      return false;
+    }
+    aString++;
+  }
+  return true;
+}
+
+constexpr bool NS_IsAscii(const char* aString, uint32_t aLength) {
+  const char* end = aString + aLength;
+  while (aString < end) {
+    if (0x80 & *aString) {
+      return false;
+    }
+    aString++;
+  }
+  return true;
+}
+
+constexpr bool NS_IsAsciiWhitespace(char16_t aChar) {
+  return aChar == ' ' || aChar == '\r' || aChar == '\n' || aChar == '\t';
+}
+
+#ifndef XPCOM_GLUE_AVOID_NSPR
+void NS_MakeRandomString(char* aBuf, int32_t aBufLen);
+#endif
+
+#define FF '\f'
+#define TAB '\t'
+
+#define CRSTR "\015"
+#define LFSTR "\012"
+#define CRLF "\015\012" /* A CR LF equivalent string */
+
+#if defined(ANDROID)
+// On mobile devices, the file system may be very limited in what it
+// considers valid characters. To avoid errors, sanitize conservatively.
+#  define OS_FILE_ILLEGAL_CHARACTERS "/:*?\"<>|;,+=[]"
+#else
+// Otherwise, we use the most restrictive filesystem as our default set of
+// illegal filename characters. This is currently Windows.
+#  define OS_FILE_ILLEGAL_CHARACTERS "/:*?\"<>|"
+#endif
+
+// We also provide a list of all known file path separators for all filesystems.
+// This can be used in replacement of FILE_PATH_SEPARATOR when you need to
+// identify or replace all known path separators.
+#define KNOWN_PATH_SEPARATORS "\\/"
+
+#if defined(XP_MACOSX)
+#  define FILE_PATH_SEPARATOR "/"
+#elif defined(XP_WIN)
+#  define FILE_PATH_SEPARATOR "\\"
+#elif defined(XP_UNIX)
+#  define FILE_PATH_SEPARATOR "/"
+#else
+#  error need_to_define_your_file_path_separator_and_maybe_illegal_characters
+#endif
+
+// Not all these control characters are illegal in all OSs, but we don't really
+// want them appearing in filenames
+#define CONTROL_CHARACTERS           \
+  "\001\002\003\004\005\006\007"     \
+  "\010\011\012\013\014\015\016\017" \
+  "\020\021\022\023\024\025\026\027" \
+  "\030\031\032\033\034\035\036\037" \
+  "\177"                             \
+  "\200\201\202\203\204\205\206\207" \
+  "\210\211\212\213\214\215\216\217" \
+  "\220\221\222\223\224\225\226\227" \
+  "\230\231\232\233\234\235\236\237"
+
+#define FILE_ILLEGAL_CHARACTERS CONTROL_CHARACTERS OS_FILE_ILLEGAL_CHARACTERS
+
+#endif  // nsCRTGlue_h__
diff --git a/xpcom/base/nsClassInfoImpl.cpp b/xpcom/base/nsClassInfoImpl.cpp
new file mode 100644
index 0000000000..2189863a98
--- /dev/null
+++ b/xpcom/base/nsClassInfoImpl.cpp
@@ -0,0 +1,61 @@
+/* -*- 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 "nsIClassInfoImpl.h"
+#include "nsString.h"
+
+NS_IMETHODIMP_(MozExternalRefCountType)
+GenericClassInfo::AddRef() { return 2; }
+
+NS_IMETHODIMP_(MozExternalRefCountType)
+GenericClassInfo::Release() { return 1; }
+
+NS_IMPL_QUERY_INTERFACE(GenericClassInfo, nsIClassInfo)
+
+NS_IMETHODIMP
+GenericClassInfo::GetInterfaces(nsTArray<nsIID>& aArray) {
+  return mData->getinterfaces(aArray);
+}
+
+NS_IMETHODIMP
+GenericClassInfo::GetScriptableHelper(nsIXPCScriptable** aHelper) {
+  if (mData->getscriptablehelper) {
+    return mData->getscriptablehelper(aHelper);
+  }
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+GenericClassInfo::GetContractID(nsACString& aContractID) {
+  NS_ERROR("GetContractID not implemented");
+  aContractID.SetIsVoid(true);
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+GenericClassInfo::GetClassDescription(nsACString& aDescription) {
+  aDescription.SetIsVoid(true);
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+GenericClassInfo::GetClassID(nsCID** aClassID) {
+  NS_ERROR("GetClassID not implemented");
+  *aClassID = nullptr;
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+GenericClassInfo::GetFlags(uint32_t* aFlags) {
+  *aFlags = mData->flags;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+GenericClassInfo::GetClassIDNoAlloc(nsCID* aClassIDNoAlloc) {
+  *aClassIDNoAlloc = mData->cid;
+  return NS_OK;
+}
diff --git a/xpcom/base/nsCom.h b/xpcom/base/nsCom.h
new file mode 100644
index 0000000000..b6c3ed0296
--- /dev/null
+++ b/xpcom/base/nsCom.h
@@ -0,0 +1,10 @@
+/* -*- 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/. */
+
+#ifndef nsCom_h__
+#define nsCom_h__
+#include "nscore.h"
+#endif
diff --git a/xpcom/base/nsConsoleMessage.cpp b/xpcom/base/nsConsoleMessage.cpp
new file mode 100644
index 0000000000..db6ca8f216
--- /dev/null
+++ b/xpcom/base/nsConsoleMessage.cpp
@@ -0,0 +1,67 @@
+/* -*- 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/. */
+
+/*
+ * Base implementation for console messages.
+ */
+
+#include "nsConsoleMessage.h"
+#include "jsapi.h"
+
+NS_IMPL_ISUPPORTS(nsConsoleMessage, nsIConsoleMessage)
+
+nsConsoleMessage::nsConsoleMessage() : mMicroSecondTimeStamp(0), mMessage() {}
+
+nsConsoleMessage::nsConsoleMessage(const nsAString& aMessage) {
+  mMicroSecondTimeStamp = JS_Now();
+  mMessage.Assign(aMessage);
+  mIsForwardedFromContentProcess = false;
+}
+
+NS_IMETHODIMP
+nsConsoleMessage::GetMessageMoz(nsAString& aMessage) {
+  aMessage = mMessage;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsConsoleMessage::GetLogLevel(uint32_t* aLogLevel) {
+  *aLogLevel = nsConsoleMessage::info;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsConsoleMessage::GetTimeStamp(int64_t* aTimeStamp) {
+  *aTimeStamp = mMicroSecondTimeStamp / 1000;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsConsoleMessage::GetMicroSecondTimeStamp(int64_t* aTimeStamp) {
+  *aTimeStamp = mMicroSecondTimeStamp;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsConsoleMessage::ToString(nsACString& /*UTF8*/ aResult) {
+  CopyUTF16toUTF8(mMessage, aResult);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsConsoleMessage::GetIsForwardedFromContentProcess(
+    bool* aIsForwardedFromContentProcess) {
+  *aIsForwardedFromContentProcess = mIsForwardedFromContentProcess;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsConsoleMessage::SetIsForwardedFromContentProcess(
+    bool aIsForwardedFromContentProcess) {
+  mIsForwardedFromContentProcess = aIsForwardedFromContentProcess;
+  return NS_OK;
+}
diff --git a/xpcom/base/nsConsoleMessage.h b/xpcom/base/nsConsoleMessage.h
new file mode 100644
index 0000000000..42509707ba
--- /dev/null
+++ b/xpcom/base/nsConsoleMessage.h
@@ -0,0 +1,31 @@
+/* -*- 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/. */
+
+#ifndef __nsconsolemessage_h__
+#define __nsconsolemessage_h__
+
+#include "mozilla/Attributes.h"
+
+#include "nsIConsoleMessage.h"
+#include "nsString.h"
+
+class nsConsoleMessage final : public nsIConsoleMessage {
+ public:
+  nsConsoleMessage();
+  explicit nsConsoleMessage(const nsAString& aMessage);
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSICONSOLEMESSAGE
+
+ private:
+  ~nsConsoleMessage() = default;
+
+  int64_t mMicroSecondTimeStamp;
+  nsString mMessage;
+  bool mIsForwardedFromContentProcess;
+};
+
+#endif /* __nsconsolemessage_h__ */
diff --git a/xpcom/base/nsConsoleService.cpp b/xpcom/base/nsConsoleService.cpp
new file mode 100644
index 0000000000..1888e1f567
--- /dev/null
+++ b/xpcom/base/nsConsoleService.cpp
@@ -0,0 +1,569 @@
+/* -*- 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/. */
+
+/*
+ * Maintains a circular buffer of recent messages, and notifies
+ * listeners when new messages are logged.
+ */
+
+/* Threadsafe. */
+
+#include "nsCOMArray.h"
+#include "nsThreadUtils.h"
+
+#include "nsConsoleService.h"
+#include "nsConsoleMessage.h"
+#include "nsIClassInfoImpl.h"
+#include "nsIConsoleListener.h"
+#include "nsIObserverService.h"
+#include "nsPrintfCString.h"
+#include "nsProxyRelease.h"
+#include "nsIScriptError.h"
+#include "nsISupportsPrimitives.h"
+#include "nsGlobalWindowInner.h"
+#include "js/friend/ErrorMessages.h"
+#include "mozilla/dom/WindowGlobalParent.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/dom/BrowserParent.h"
+#include "mozilla/dom/ScriptSettings.h"
+
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/Services.h"
+
+#if defined(ANDROID)
+#  include <android/log.h>
+#  include "mozilla/dom/ContentChild.h"
+#  include "mozilla/StaticPrefs_consoleservice.h"
+#endif
+#ifdef XP_WIN
+#  include <windows.h>
+#endif
+
+using namespace mozilla;
+
+NS_IMPL_ADDREF(nsConsoleService)
+NS_IMPL_RELEASE(nsConsoleService)
+NS_IMPL_CLASSINFO(nsConsoleService, nullptr,
+                  nsIClassInfo::THREADSAFE | nsIClassInfo::SINGLETON,
+                  NS_CONSOLESERVICE_CID)
+NS_IMPL_QUERY_INTERFACE_CI(nsConsoleService, nsIConsoleService, nsIObserver)
+NS_IMPL_CI_INTERFACE_GETTER(nsConsoleService, nsIConsoleService, nsIObserver)
+
+static const bool gLoggingEnabled = true;
+static const bool gLoggingBuffered = true;
+#ifdef XP_WIN
+static bool gLoggingToDebugger = true;
+#endif  // XP_WIN
+
+nsConsoleService::MessageElement::~MessageElement() = default;
+
+nsConsoleService::nsConsoleService()
+    : mCurrentSize(0),
+      // XXX grab this from a pref!
+      // hm, but worry about circularity, bc we want to be able to report
+      // prefs errs...
+      mMaximumSize(250),
+      mDeliveringMessage(false),
+      mLock("nsConsoleService.mLock") {
+#ifdef XP_WIN
+  // This environment variable controls whether the console service
+  // should be prevented from putting output to the attached debugger.
+  // It only affects the Windows platform.
+  //
+  // To disable OutputDebugString, set:
+  //   MOZ_CONSOLESERVICE_DISABLE_DEBUGGER_OUTPUT=1
+  //
+  const char* disableDebugLoggingVar =
+      getenv("MOZ_CONSOLESERVICE_DISABLE_DEBUGGER_OUTPUT");
+  gLoggingToDebugger =
+      !disableDebugLoggingVar || (disableDebugLoggingVar[0] == '0');
+#endif  // XP_WIN
+}
+
+void nsConsoleService::ClearMessagesForWindowID(const uint64_t innerID) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  MutexAutoLock lock(mLock);
+
+  for (MessageElement* e = mMessages.getFirst(); e != nullptr;) {
+    // Only messages implementing nsIScriptError interface expose the
+    // inner window ID.
+    nsCOMPtr<nsIScriptError> scriptError = do_QueryInterface(e->Get());
+    if (!scriptError) {
+      e = e->getNext();
+      continue;
+    }
+    uint64_t innerWindowID;
+    nsresult rv = scriptError->GetInnerWindowID(&innerWindowID);
+    if (NS_FAILED(rv) || innerWindowID != innerID) {
+      e = e->getNext();
+      continue;
+    }
+
+    MessageElement* next = e->getNext();
+    e->remove();
+    delete e;
+    mCurrentSize--;
+    MOZ_ASSERT(mCurrentSize < mMaximumSize);
+
+    e = next;
+  }
+}
+
+void nsConsoleService::ClearMessages() {
+  // NB: A lock is not required here as it's only called from |Reset| which
+  //     locks for us and from the dtor.
+  while (!mMessages.isEmpty()) {
+    MessageElement* e = mMessages.popFirst();
+    delete e;
+  }
+  mCurrentSize = 0;
+}
+
+nsConsoleService::~nsConsoleService() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  ClearMessages();
+}
+
+class AddConsolePrefWatchers : public Runnable {
+ public:
+  explicit AddConsolePrefWatchers(nsConsoleService* aConsole)
+      : mozilla::Runnable("AddConsolePrefWatchers"), mConsole(aConsole) {}
+
+  NS_IMETHOD Run() override {
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    MOZ_ASSERT(obs);
+    obs->AddObserver(mConsole, NS_XPCOM_SHUTDOWN_OBSERVER_ID, false);
+    obs->AddObserver(mConsole, "inner-window-destroyed", false);
+
+    if (!gLoggingBuffered) {
+      mConsole->Reset();
+    }
+    return NS_OK;
+  }
+
+ private:
+  RefPtr<nsConsoleService> mConsole;
+};
+
+nsresult nsConsoleService::Init() {
+  NS_DispatchToMainThread(new AddConsolePrefWatchers(this));
+
+  return NS_OK;
+}
+
+nsresult nsConsoleService::MaybeForwardScriptError(nsIConsoleMessage* aMessage,
+                                                   bool* sent) {
+  *sent = false;
+
+  nsCOMPtr<nsIScriptError> scriptError = do_QueryInterface(aMessage);
+  if (!scriptError) {
+    // Not an nsIScriptError
+    return NS_OK;
+  }
+
+  uint64_t windowID;
+  nsresult rv;
+  rv = scriptError->GetInnerWindowID(&windowID);
+  NS_ENSURE_SUCCESS(rv, rv);
+  if (!windowID) {
+    // Does not set window id
+    return NS_OK;
+  }
+
+  RefPtr<mozilla::dom::WindowGlobalParent> windowGlobalParent =
+      mozilla::dom::WindowGlobalParent::GetByInnerWindowId(windowID);
+  if (!windowGlobalParent) {
+    // Could not find parent window by id
+    return NS_OK;
+  }
+
+  RefPtr<mozilla::dom::BrowserParent> browserParent =
+      windowGlobalParent->GetBrowserParent();
+  if (!browserParent) {
+    return NS_OK;
+  }
+
+  mozilla::dom::ContentParent* contentParent = browserParent->Manager();
+  if (!contentParent) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAutoString msg, sourceName, sourceLine;
+  nsCString category;
+  uint32_t lineNum, colNum, flags;
+  uint64_t innerWindowId;
+  bool fromPrivateWindow, fromChromeContext;
+
+  rv = scriptError->GetErrorMessage(msg);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = scriptError->GetSourceName(sourceName);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = scriptError->GetSourceLine(sourceLine);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = scriptError->GetCategory(getter_Copies(category));
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = scriptError->GetLineNumber(&lineNum);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = scriptError->GetColumnNumber(&colNum);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = scriptError->GetFlags(&flags);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = scriptError->GetIsFromPrivateWindow(&fromPrivateWindow);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = scriptError->GetIsFromChromeContext(&fromChromeContext);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = scriptError->GetInnerWindowID(&innerWindowId);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  *sent = contentParent->SendScriptError(
+      msg, sourceName, sourceLine, lineNum, colNum, flags, category,
+      fromPrivateWindow, innerWindowId, fromChromeContext);
+  return NS_OK;
+}
+
+namespace {
+
+class LogMessageRunnable : public Runnable {
+ public:
+  LogMessageRunnable(nsIConsoleMessage* aMessage, nsConsoleService* aService)
+      : mozilla::Runnable("LogMessageRunnable"),
+        mMessage(aMessage),
+        mService(aService) {}
+
+  NS_DECL_NSIRUNNABLE
+
+ private:
+  nsCOMPtr<nsIConsoleMessage> mMessage;
+  RefPtr<nsConsoleService> mService;
+};
+
+NS_IMETHODIMP
+LogMessageRunnable::Run() {
+  // Snapshot of listeners so that we don't reenter this hash during
+  // enumeration.
+  nsCOMArray<nsIConsoleListener> listeners;
+  mService->CollectCurrentListeners(listeners);
+
+  mService->SetIsDelivering();
+
+  for (int32_t i = 0; i < listeners.Count(); ++i) {
+    listeners[i]->Observe(mMessage);
+  }
+
+  mService->SetDoneDelivering();
+
+  return NS_OK;
+}
+
+}  // namespace
+
+// nsIConsoleService methods
+NS_IMETHODIMP
+nsConsoleService::LogMessage(nsIConsoleMessage* aMessage) {
+  return LogMessageWithMode(aMessage, nsIConsoleService::OutputToLog);
+}
+
+// This can be called off the main thread.
+nsresult nsConsoleService::LogMessageWithMode(
+    nsIConsoleMessage* aMessage, nsIConsoleService::OutputMode aOutputMode) {
+  if (!aMessage) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  if (!gLoggingEnabled) {
+    return NS_OK;
+  }
+
+  if (NS_IsMainThread() && mDeliveringMessage) {
+    nsCString msg;
+    aMessage->ToString(msg);
+    NS_WARNING(
+        nsPrintfCString(
+            "Reentrancy error: some client attempted to display a message to "
+            "the console while in a console listener. The following message "
+            "was discarded: \"%s\"",
+            msg.get())
+            .get());
+    return NS_ERROR_FAILURE;
+  }
+
+  if (XRE_IsParentProcess() && NS_IsMainThread()) {
+    // If mMessage is a scriptError with an innerWindowId set,
+    // forward it to the matching ContentParent
+    // This enables logging from parent to content process
+    bool sent;
+    nsresult rv = MaybeForwardScriptError(aMessage, &sent);
+    NS_ENSURE_SUCCESS(rv, rv);
+    if (sent) {
+      return NS_OK;
+    }
+  }
+
+  RefPtr<LogMessageRunnable> r;
+  nsCOMPtr<nsIConsoleMessage> retiredMessage;
+
+  /*
+   * Lock while updating buffer, and while taking snapshot of
+   * listeners array.
+   */
+  {
+    MutexAutoLock lock(mLock);
+
+#if defined(ANDROID)
+    if (StaticPrefs::consoleservice_logcat() && aOutputMode == OutputToLog) {
+      nsCString msg;
+      aMessage->ToString(msg);
+
+      /** Attempt to use the process name as the log tag. */
+      mozilla::dom::ContentChild* child =
+          mozilla::dom::ContentChild::GetSingleton();
+      nsCString appName;
+      if (child) {
+        child->GetProcessName(appName);
+      } else {
+        appName = "GeckoConsole";
+      }
+
+      uint32_t logLevel = 0;
+      aMessage->GetLogLevel(&logLevel);
+
+      android_LogPriority logPriority = ANDROID_LOG_INFO;
+      switch (logLevel) {
+        case nsIConsoleMessage::debug:
+          logPriority = ANDROID_LOG_DEBUG;
+          break;
+        case nsIConsoleMessage::info:
+          logPriority = ANDROID_LOG_INFO;
+          break;
+        case nsIConsoleMessage::warn:
+          logPriority = ANDROID_LOG_WARN;
+          break;
+        case nsIConsoleMessage::error:
+          logPriority = ANDROID_LOG_ERROR;
+          break;
+      }
+
+      __android_log_print(logPriority, appName.get(), "%s", msg.get());
+    }
+#endif
+#ifdef XP_WIN
+    if (gLoggingToDebugger && IsDebuggerPresent()) {
+      nsString msg;
+      aMessage->GetMessageMoz(msg);
+      msg.Append('\n');
+      OutputDebugStringW(msg.get());
+    }
+#endif
+
+    if (gLoggingBuffered) {
+      MessageElement* e = new MessageElement(aMessage);
+      mMessages.insertBack(e);
+      if (mCurrentSize != mMaximumSize) {
+        mCurrentSize++;
+      } else {
+        MessageElement* p = mMessages.popFirst();
+        MOZ_ASSERT(p);
+        p->swapMessage(retiredMessage);
+        delete p;
+      }
+    }
+
+    if (mListeners.Count() > 0) {
+      r = new LogMessageRunnable(aMessage, this);
+    }
+  }
+
+  if (retiredMessage) {
+    // Release |retiredMessage| on the main thread in case it is an instance of
+    // a mainthread-only class like nsScriptErrorWithStack and we're off the
+    // main thread.
+    NS_ReleaseOnMainThread("nsConsoleService::retiredMessage",
+                           retiredMessage.forget());
+  }
+
+  if (r) {
+    // avoid failing in XPCShell tests
+    nsCOMPtr<nsIThread> mainThread = do_GetMainThread();
+    if (mainThread) {
+      SchedulerGroup::Dispatch(TaskCategory::Other, r.forget());
+    }
+  }
+
+  return NS_OK;
+}
+
+// See nsIConsoleService.idl for more info about this method
+NS_IMETHODIMP
+nsConsoleService::CallFunctionAndLogException(
+    JS::Handle<JS::Value> targetGlobal, JS::HandleValue function, JSContext* cx,
+    JS::MutableHandleValue retval) {
+  if (!targetGlobal.isObject() || !function.isObject()) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  JS::Rooted<JS::Realm*> contextRealm(cx, JS::GetCurrentRealmOrNull(cx));
+  if (!contextRealm) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  JS::Rooted<JSObject*> global(
+      cx, js::CheckedUnwrapDynamic(&targetGlobal.toObject(), cx));
+  if (!global) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // Use AutoJSAPI in order to trigger AutoJSAPI::ReportException
+  // which will do most of the work required for this function.
+  //
+  // We only have to pick the right global for which we want to flag
+  // the exception against.
+  dom::AutoJSAPI jsapi;
+  if (!jsapi.Init(global)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  JSContext* ccx = jsapi.cx();
+
+  // AutoJSAPI picks `targetGlobal` as execution compartment
+  // whereas we expect to run `function` from the callsites compartment.
+  JSAutoRealm ar(ccx, JS::GetRealmGlobalOrNull(contextRealm));
+
+  JS::RootedValue funVal(ccx, function);
+  if (!JS_WrapValue(ccx, &funVal)) {
+    return NS_ERROR_FAILURE;
+  }
+  if (!JS_CallFunctionValue(ccx, nullptr, funVal, JS::HandleValueArray::empty(),
+                            retval)) {
+    return NS_ERROR_XPC_JAVASCRIPT_ERROR;
+  }
+
+  return NS_OK;
+}
+
+void nsConsoleService::CollectCurrentListeners(
+    nsCOMArray<nsIConsoleListener>& aListeners) {
+  MutexAutoLock lock(mLock);
+  // XXX When MakeBackInserter(nsCOMArray<T>&) is added, we can do:
+  // AppendToArray(aListeners, mListeners.Values());
+  for (const auto& listener : mListeners.Values()) {
+    aListeners.AppendObject(listener);
+  }
+}
+
+NS_IMETHODIMP
+nsConsoleService::LogStringMessage(const char16_t* aMessage) {
+  if (!gLoggingEnabled) {
+    return NS_OK;
+  }
+
+  RefPtr<nsConsoleMessage> msg(new nsConsoleMessage(
+      aMessage ? nsDependentString(aMessage) : EmptyString()));
+  return LogMessage(msg);
+}
+
+NS_IMETHODIMP
+nsConsoleService::GetMessageArray(
+    nsTArray<RefPtr<nsIConsoleMessage>>& aMessages) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  MutexAutoLock lock(mLock);
+
+  if (mMessages.isEmpty()) {
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(mCurrentSize <= mMaximumSize);
+  aMessages.SetCapacity(mCurrentSize);
+
+  for (MessageElement* e = mMessages.getFirst(); e != nullptr;
+       e = e->getNext()) {
+    aMessages.AppendElement(e->Get());
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsConsoleService::RegisterListener(nsIConsoleListener* aListener) {
+  if (!NS_IsMainThread()) {
+    NS_ERROR("nsConsoleService::RegisterListener is main thread only.");
+    return NS_ERROR_NOT_SAME_THREAD;
+  }
+
+  nsCOMPtr<nsISupports> canonical = do_QueryInterface(aListener);
+  MOZ_ASSERT(canonical);
+
+  MutexAutoLock lock(mLock);
+  return mListeners.WithEntryHandle(canonical, [&](auto&& entry) {
+    if (entry) {
+      // Reregistering a listener isn't good
+      return NS_ERROR_FAILURE;
+    }
+    entry.Insert(aListener);
+    return NS_OK;
+  });
+}
+
+NS_IMETHODIMP
+nsConsoleService::UnregisterListener(nsIConsoleListener* aListener) {
+  if (!NS_IsMainThread()) {
+    NS_ERROR("nsConsoleService::UnregisterListener is main thread only.");
+    return NS_ERROR_NOT_SAME_THREAD;
+  }
+
+  nsCOMPtr<nsISupports> canonical = do_QueryInterface(aListener);
+
+  MutexAutoLock lock(mLock);
+
+  return mListeners.Remove(canonical)
+             ? NS_OK
+             // Unregistering a listener that was never registered?
+             : NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsConsoleService::Reset() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  /*
+   * Make sure nobody trips into the buffer while it's being reset
+   */
+  MutexAutoLock lock(mLock);
+
+  ClearMessages();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsConsoleService::ResetWindow(uint64_t windowInnerId) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  ClearMessagesForWindowID(windowInnerId);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsConsoleService::Observe(nsISupports* aSubject, const char* aTopic,
+                          const char16_t* aData) {
+  if (!strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID)) {
+    // Dump all our messages, in case any are cycle collected.
+    Reset();
+    // We could remove ourselves from the observer service, but it is about to
+    // drop all observers anyways, so why bother.
+  } else if (!strcmp(aTopic, "inner-window-destroyed")) {
+    nsCOMPtr<nsISupportsPRUint64> supportsInt = do_QueryInterface(aSubject);
+    MOZ_ASSERT(supportsInt);
+
+    uint64_t windowId;
+    MOZ_ALWAYS_SUCCEEDS(supportsInt->GetData(&windowId));
+
+    ClearMessagesForWindowID(windowId);
+  } else {
+    MOZ_CRASH();
+  }
+  return NS_OK;
+}
diff --git a/xpcom/base/nsConsoleService.h b/xpcom/base/nsConsoleService.h
new file mode 100644
index 0000000000..fe86f4c0fe
--- /dev/null
+++ b/xpcom/base/nsConsoleService.h
@@ -0,0 +1,113 @@
+/* -*- 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/. */
+
+/*
+ * nsConsoleService class declaration.
+ */
+
+#ifndef __nsconsoleservice_h__
+#define __nsconsoleservice_h__
+
+#include <cstdint>
+#include <utility>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/LinkedList.h"
+#include "mozilla/Mutex.h"
+
+#include "MainThreadUtils.h"
+#include "nsCOMPtr.h"
+#include "nsInterfaceHashtable.h"
+#include "nsHashKeys.h"
+
+#include "nsIConsoleListener.h"
+#include "nsIConsoleMessage.h"
+#include "nsIConsoleService.h"
+#include "nsIObserver.h"
+#include "nsISupports.h"
+
+template <class T>
+class nsCOMArray;
+
+class nsConsoleService final : public nsIConsoleService, public nsIObserver {
+ public:
+  nsConsoleService();
+  nsresult Init();
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSICONSOLESERVICE
+  NS_DECL_NSIOBSERVER
+
+  void SetIsDelivering() {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(!mDeliveringMessage);
+    mDeliveringMessage = true;
+  }
+
+  void SetDoneDelivering() {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(mDeliveringMessage);
+    mDeliveringMessage = false;
+  }
+
+  typedef nsInterfaceHashtable<nsISupportsHashKey, nsIConsoleListener>
+      ListenerHash;
+  void CollectCurrentListeners(nsCOMArray<nsIConsoleListener>& aListeners);
+
+ private:
+  class MessageElement : public mozilla::LinkedListElement<MessageElement> {
+   public:
+    explicit MessageElement(nsIConsoleMessage* aMessage) : mMessage(aMessage) {}
+
+    nsIConsoleMessage* Get() { return mMessage.get(); }
+
+    // Swap directly into an nsCOMPtr to avoid spurious refcount
+    // traffic off the main thread in debug builds from
+    // NSCAP_ASSERT_NO_QUERY_NEEDED().
+    void swapMessage(nsCOMPtr<nsIConsoleMessage>& aRetVal) {
+      mMessage.swap(aRetVal);
+    }
+
+    ~MessageElement();
+
+   private:
+    nsCOMPtr<nsIConsoleMessage> mMessage;
+
+    MessageElement(const MessageElement&) = delete;
+    MessageElement& operator=(const MessageElement&) = delete;
+    MessageElement(MessageElement&&) = delete;
+    MessageElement& operator=(MessageElement&&) = delete;
+  };
+
+  ~nsConsoleService();
+
+  nsresult MaybeForwardScriptError(nsIConsoleMessage* aMessage, bool* sent);
+
+  void ClearMessagesForWindowID(const uint64_t innerID);
+  void ClearMessages() MOZ_REQUIRES(mLock);
+
+  mozilla::LinkedList<MessageElement> mMessages MOZ_GUARDED_BY(mLock);
+
+  // The current size of mMessages.
+  uint32_t mCurrentSize MOZ_GUARDED_BY(mLock);
+
+  // The maximum size of mMessages.
+  const uint32_t mMaximumSize;
+
+  // Are we currently delivering a console message on the main thread? If
+  // so, we suppress incoming messages on the main thread only, to avoid
+  // infinite repitition.
+  // Only touched on MainThread
+  bool mDeliveringMessage;
+
+  // Listeners to notify whenever a new message is logged.
+  ListenerHash mListeners MOZ_GUARDED_BY(mLock);
+
+  // To serialize interesting methods.
+  mozilla::Mutex mLock;
+};
+
+#endif /* __nsconsoleservice_h__ */
diff --git a/xpcom/base/nsCrashOnException.cpp b/xpcom/base/nsCrashOnException.cpp
new file mode 100644
index 0000000000..67436c15c4
--- /dev/null
+++ b/xpcom/base/nsCrashOnException.cpp
@@ -0,0 +1,34 @@
+/* -*- 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 "nsCrashOnException.h"
+#include "nsCOMPtr.h"
+#include "nsICrashReporter.h"
+#include "nsServiceManagerUtils.h"
+
+namespace mozilla {
+
+static int ReportException(EXCEPTION_POINTERS* aExceptionInfo) {
+  nsCOMPtr<nsICrashReporter> cr =
+      do_GetService("@mozilla.org/toolkit/crash-reporter;1");
+  if (cr) {
+    cr->WriteMinidumpForException(aExceptionInfo);
+  }
+
+  return EXCEPTION_EXECUTE_HANDLER;
+}
+
+XPCOM_API(LRESULT)
+CallWindowProcCrashProtected(WNDPROC aWndProc, HWND aHWnd, UINT aMsg,
+                             WPARAM aWParam, LPARAM aLParam) {
+  MOZ_SEH_TRY { return aWndProc(aHWnd, aMsg, aWParam, aLParam); }
+  MOZ_SEH_EXCEPT(ReportException(GetExceptionInformation())) {
+    ::TerminateProcess(::GetCurrentProcess(), 253);
+  }
+  return 0;  // not reached
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/nsCrashOnException.h b/xpcom/base/nsCrashOnException.h
new file mode 100644
index 0000000000..1291cd4961
--- /dev/null
+++ b/xpcom/base/nsCrashOnException.h
@@ -0,0 +1,23 @@
+/* -*- 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/. */
+
+#ifndef nsCrashOnException_h
+#define nsCrashOnException_h
+
+#include <nscore.h>
+#include <windows.h>
+
+namespace mozilla {
+
+// Call a given window procedure, and catch any Win32 exceptions raised from it,
+// and report them as crashes.
+XPCOM_API(LRESULT)
+CallWindowProcCrashProtected(WNDPROC aWndProc, HWND aHWnd, UINT aMsg,
+                             WPARAM aWParam, LPARAM aLParam);
+
+}  // namespace mozilla
+
+#endif
diff --git a/xpcom/base/nsCycleCollectionNoteChild.h b/xpcom/base/nsCycleCollectionNoteChild.h
new file mode 100644
index 0000000000..3e1d345aa3
--- /dev/null
+++ b/xpcom/base/nsCycleCollectionNoteChild.h
@@ -0,0 +1,85 @@
+/* -*- 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/. */
+
+// This header will be included by headers that define refpointer and array
+// classes in order to specialize CC helpers such as ImplCycleCollectionTraverse
+// for them.
+
+#ifndef nsCycleCollectionNoteChild_h__
+#define nsCycleCollectionNoteChild_h__
+
+#include "nsCycleCollectionTraversalCallback.h"
+#include "mozilla/Likely.h"
+
+enum { CycleCollectionEdgeNameArrayFlag = 1 };
+
+// Just a helper for appending "[i]". Didn't want to pull in string headers
+// here.
+void CycleCollectionNoteEdgeNameImpl(
+    nsCycleCollectionTraversalCallback& aCallback, const char* aName,
+    uint32_t aFlags = 0);
+
+// Should be inlined so that in the no-debug-info case this is just a simple
+// if().
+MOZ_ALWAYS_INLINE void CycleCollectionNoteEdgeName(
+    nsCycleCollectionTraversalCallback& aCallback, const char* aName,
+    uint32_t aFlags = 0) {
+  if (MOZ_UNLIKELY(aCallback.WantDebugInfo())) {
+    CycleCollectionNoteEdgeNameImpl(aCallback, aName, aFlags);
+  }
+}
+
+#define NS_CYCLE_COLLECTION_INNERCLASS cycleCollection
+
+#define NS_CYCLE_COLLECTION_INNERNAME _cycleCollectorGlobal
+
+#define NS_CYCLE_COLLECTION_PARTICIPANT(_class) \
+  _class::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant()
+
+template <typename T>
+nsISupports* ToSupports(
+    T* aPtr, typename T::NS_CYCLE_COLLECTION_INNERCLASS* aDummy = 0) {
+  return T::NS_CYCLE_COLLECTION_INNERCLASS::Upcast(aPtr);
+}
+
+// The default implementation of this class template is empty, because it
+// should never be used: see the partial specializations below.
+template <typename T, bool IsXPCOM = std::is_base_of<nsISupports, T>::value>
+struct CycleCollectionNoteChildImpl {};
+
+template <typename T>
+struct CycleCollectionNoteChildImpl<T, true> {
+  static void Run(nsCycleCollectionTraversalCallback& aCallback, T* aChild) {
+    aCallback.NoteXPCOMChild(ToSupports(aChild));
+  }
+};
+
+template <typename T>
+struct CycleCollectionNoteChildImpl<T, false> {
+  static void Run(nsCycleCollectionTraversalCallback& aCallback, T* aChild) {
+    aCallback.NoteNativeChild(aChild, NS_CYCLE_COLLECTION_PARTICIPANT(T));
+  }
+};
+
+// We declare CycleCollectionNoteChild in 3-argument and 4-argument variants,
+// rather than using default arguments, so that forward declarations work
+// regardless of header inclusion order.
+template <typename T>
+inline void CycleCollectionNoteChild(
+    nsCycleCollectionTraversalCallback& aCallback, T* aChild, const char* aName,
+    uint32_t aFlags) {
+  CycleCollectionNoteEdgeName(aCallback, aName, aFlags);
+  CycleCollectionNoteChildImpl<T>::Run(aCallback, aChild);
+}
+
+template <typename T>
+inline void CycleCollectionNoteChild(
+    nsCycleCollectionTraversalCallback& aCallback, T* aChild,
+    const char* aName) {
+  CycleCollectionNoteChild(aCallback, aChild, aName, 0);
+}
+
+#endif  // nsCycleCollectionNoteChild_h__
diff --git a/xpcom/base/nsCycleCollectionNoteRootCallback.h b/xpcom/base/nsCycleCollectionNoteRootCallback.h
new file mode 100644
index 0000000000..21dc89394a
--- /dev/null
+++ b/xpcom/base/nsCycleCollectionNoteRootCallback.h
@@ -0,0 +1,44 @@
+/* -*- 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/. */
+
+#ifndef nsCycleCollectionNoteRootCallback_h__
+#define nsCycleCollectionNoteRootCallback_h__
+
+#include "nscore.h"
+
+class nsCycleCollectionParticipant;
+class nsISupports;
+class JSObject;
+
+namespace JS {
+class GCCellPtr;
+}
+
+class nsCycleCollectionNoteRootCallback {
+ public:
+  // aRoot must be canonical (ie the result of QIing to
+  // nsCycleCollectionISupports).
+  NS_IMETHOD_(void)
+  NoteXPCOMRoot(nsISupports* aRoot,
+                nsCycleCollectionParticipant* aParticipant) = 0;
+
+  NS_IMETHOD_(void) NoteJSRoot(JSObject* aRoot) = 0;
+  NS_IMETHOD_(void)
+  NoteNativeRoot(void* aRoot, nsCycleCollectionParticipant* aParticipant) = 0;
+
+  NS_IMETHOD_(void)
+  NoteWeakMapping(JSObject* aMap, JS::GCCellPtr aKey, JSObject* aKeyDelegate,
+                  JS::GCCellPtr aVal) = 0;
+
+  bool WantAllTraces() const { return mWantAllTraces; }
+
+ protected:
+  nsCycleCollectionNoteRootCallback() : mWantAllTraces(false) {}
+
+  bool mWantAllTraces;
+};
+
+#endif  // nsCycleCollectionNoteRootCallback_h__
diff --git a/xpcom/base/nsCycleCollectionParticipant.cpp b/xpcom/base/nsCycleCollectionParticipant.cpp
new file mode 100644
index 0000000000..eaca656e23
--- /dev/null
+++ b/xpcom/base/nsCycleCollectionParticipant.cpp
@@ -0,0 +1,34 @@
+/* -*- 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 "nsCycleCollectionParticipant.h"
+#include "nsCOMPtr.h"
+
+NS_IMETHODIMP_(void)
+nsXPCOMCycleCollectionParticipant::Root(void* aPtr) {
+  nsISupports* s = static_cast<nsISupports*>(aPtr);
+  NS_ADDREF(s);
+}
+
+NS_IMETHODIMP_(void)
+nsXPCOMCycleCollectionParticipant::Unroot(void* aPtr) {
+  nsISupports* s = static_cast<nsISupports*>(aPtr);
+  NS_RELEASE(s);
+}
+
+// We define a default trace function because some participants don't need
+// to trace anything, so it is okay for them not to define one.
+NS_IMETHODIMP_(void)
+nsXPCOMCycleCollectionParticipant::Trace(void* aPtr, const TraceCallbacks& aCb,
+                                         void* aClosure) {}
+
+bool nsXPCOMCycleCollectionParticipant::CheckForRightISupports(
+    nsISupports* aSupports) {
+  nsISupports* foo;
+  aSupports->QueryInterface(NS_GET_IID(nsCycleCollectionISupports),
+                            reinterpret_cast<void**>(&foo));
+  return aSupports == foo;
+}
diff --git a/xpcom/base/nsCycleCollectionParticipant.h b/xpcom/base/nsCycleCollectionParticipant.h
new file mode 100644
index 0000000000..e4d293f42e
--- /dev/null
+++ b/xpcom/base/nsCycleCollectionParticipant.h
@@ -0,0 +1,1107 @@
+/* -*- 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/. */
+
+#ifndef nsCycleCollectionParticipant_h__
+#define nsCycleCollectionParticipant_h__
+
+#include <type_traits>
+#include "js/HeapAPI.h"
+#include "js/TypeDecls.h"
+#include "mozilla/MacroForEach.h"
+#include "nsCycleCollectionNoteChild.h"
+#include "nsDebug.h"
+#include "nsID.h"
+#include "nscore.h"
+
+/**
+ * Note: the following two IIDs only differ in one bit in the last byte.  This
+ * is a hack and is intentional in order to speed up the comparison inside
+ * NS_INTERFACE_TABLE_HEAD_CYCLE_COLLECTION_INHERITED.
+ */
+#define NS_XPCOMCYCLECOLLECTIONPARTICIPANT_IID       \
+  {                                                  \
+    0xc61eac14, 0x5f7a, 0x4481, {                    \
+      0x96, 0x5e, 0x7e, 0xaa, 0x6e, 0xff, 0xa8, 0x5e \
+    }                                                \
+  }
+
+/**
+ * Special IID to get at the base nsISupports for a class. Usually this is the
+ * canonical nsISupports pointer, but in the case of tearoffs for example it is
+ * the base nsISupports pointer of the tearoff. This allow the cycle collector
+ * to have separate nsCycleCollectionParticipant's for tearoffs or aggregated
+ * classes.
+ */
+#define NS_CYCLECOLLECTIONISUPPORTS_IID              \
+  {                                                  \
+    0xc61eac14, 0x5f7a, 0x4481, {                    \
+      0x96, 0x5e, 0x7e, 0xaa, 0x6e, 0xff, 0xa8, 0x5f \
+    }                                                \
+  }
+
+namespace mozilla {
+enum class CCReason : uint8_t {
+  NO_REASON,
+
+  // Purple buffer "overflow": enough objects are suspected to be cycle
+  // collectable to trigger an immediate CC.
+  MANY_SUSPECTED,
+
+  // The previous collection was kCCForced ago, and there are at least
+  // kCCForcedPurpleLimit objects suspected of being cycle collectable.
+  TIMED,
+
+  // Run a CC after a GC has completed.
+  GC_FINISHED,
+
+  // Run a slice of a collection.
+  SLICE,
+
+  // Manual reasons are explicitly triggered with a custom listener (as opposed
+  // to exceeding some internal threshold.) If a CC is already in progress,
+  // continue it. Otherwise, start a new one.
+  FIRST_MANUAL_REASON = 128,
+
+  // We want to GC, but must finish any ongoing cycle collection first.
+  GC_WAITING = FIRST_MANUAL_REASON,
+
+  // CC requested via an API. Used by tests.
+  API,
+
+  // Collecting in order to dump the heap.
+  DUMP_HEAP,
+
+  // Low memory situation detected.
+  MEM_PRESSURE,
+
+  // IPC message to a content process to trigger a CC. The original reason is
+  // not tracked.
+  IPC_MESSAGE,
+
+  // Cycle collection on a worker. The triggering reason is not tracked.
+  WORKER,
+
+  // Used for finding leaks.
+  SHUTDOWN
+};
+
+#define FOR_EACH_CCREASON(MACRO) \
+  MACRO(NO_REASON)               \
+  MACRO(MANY_SUSPECTED)          \
+  MACRO(TIMED)                   \
+  MACRO(GC_FINISHED)             \
+  MACRO(SLICE)                   \
+  MACRO(GC_WAITING)              \
+  MACRO(API)                     \
+  MACRO(DUMP_HEAP)               \
+  MACRO(MEM_PRESSURE)            \
+  MACRO(IPC_MESSAGE)             \
+  MACRO(WORKER)                  \
+  MACRO(SHUTDOWN)
+
+static inline bool IsManualCCReason(CCReason reason) {
+  return reason >= CCReason::FIRST_MANUAL_REASON;
+}
+
+static inline const char* CCReasonToString(CCReason aReason) {
+  switch (aReason) {
+#define SET_REASON_STR(name) \
+  case CCReason::name:       \
+    return #name;            \
+    break;
+    FOR_EACH_CCREASON(SET_REASON_STR)
+#undef SET_REASON_STR
+    default:
+      return "<unknown-reason>";
+  }
+}
+
+}  // namespace mozilla
+
+/**
+ * Just holds the IID so NS_GET_IID works.
+ */
+class nsCycleCollectionISupports {
+ public:
+  NS_DECLARE_STATIC_IID_ACCESSOR(NS_CYCLECOLLECTIONISUPPORTS_IID)
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(nsCycleCollectionISupports,
+                              NS_CYCLECOLLECTIONISUPPORTS_IID)
+
+class nsCycleCollectionTraversalCallback;
+class nsISupports;
+class nsWrapperCache;
+
+namespace JS {
+template <class T>
+class Heap;
+template <typename T>
+class TenuredHeap;
+} /* namespace JS */
+
+/*
+ * A struct defining pure virtual methods which are called when tracing cycle
+ * collection paticipants.  The appropriate method is called depending on the
+ * type of JS GC thing.
+ */
+struct TraceCallbacks {
+  virtual void Trace(JS::Heap<JS::Value>* aPtr, const char* aName,
+                     void* aClosure) const = 0;
+  virtual void Trace(JS::Heap<jsid>* aPtr, const char* aName,
+                     void* aClosure) const = 0;
+  virtual void Trace(JS::Heap<JSObject*>* aPtr, const char* aName,
+                     void* aClosure) const = 0;
+  virtual void Trace(nsWrapperCache* aPtr, const char* aName,
+                     void* aClosure) const = 0;
+  virtual void Trace(JS::TenuredHeap<JSObject*>* aPtr, const char* aName,
+                     void* aClosure) const = 0;
+  virtual void Trace(JS::Heap<JSString*>* aPtr, const char* aName,
+                     void* aClosure) const = 0;
+  virtual void Trace(JS::Heap<JSScript*>* aPtr, const char* aName,
+                     void* aClosure) const = 0;
+  virtual void Trace(JS::Heap<JSFunction*>* aPtr, const char* aName,
+                     void* aClosure) const = 0;
+};
+
+/*
+ * An implementation of TraceCallbacks that calls a single function for all JS
+ * GC thing types encountered. Implemented in
+ * nsCycleCollectorTraceJSHelpers.cpp.
+ */
+struct TraceCallbackFunc : public TraceCallbacks {
+  typedef void (*Func)(JS::GCCellPtr aPtr, const char* aName, void* aClosure);
+
+  explicit TraceCallbackFunc(Func aCb) : mCallback(aCb) {}
+
+  virtual void Trace(JS::Heap<JS::Value>* aPtr, const char* aName,
+                     void* aClosure) const override;
+  virtual void Trace(JS::Heap<jsid>* aPtr, const char* aName,
+                     void* aClosure) const override;
+  virtual void Trace(JS::Heap<JSObject*>* aPtr, const char* aName,
+                     void* aClosure) const override;
+  virtual void Trace(nsWrapperCache* aPtr, const char* aName,
+                     void* aClosure) const override;
+  virtual void Trace(JS::TenuredHeap<JSObject*>* aPtr, const char* aName,
+                     void* aClosure) const override;
+  virtual void Trace(JS::Heap<JSString*>* aPtr, const char* aName,
+                     void* aClosure) const override;
+  virtual void Trace(JS::Heap<JSScript*>* aPtr, const char* aName,
+                     void* aClosure) const override;
+  virtual void Trace(JS::Heap<JSFunction*>* aPtr, const char* aName,
+                     void* aClosure) const override;
+
+ private:
+  Func mCallback;
+};
+
+/**
+ * Participant implementation classes
+ */
+class NS_NO_VTABLE nsCycleCollectionParticipant {
+ public:
+  using Flags = uint8_t;
+  static constexpr Flags FlagMightSkip = 1u << 0;
+  static constexpr Flags FlagTraverseShouldTrace = 1u << 1;
+  // The object is a single zone js holder if FlagMaybeSingleZoneJSHolder is set
+  // and FlagMultiZoneJSHolder isn't set. This setup is needed so that
+  // inheriting classes can unset single zone behavior.
+  static constexpr Flags FlagMaybeSingleZoneJSHolder = 1u << 2;
+  static constexpr Flags FlagMultiZoneJSHolder = 1u << 3;
+  static constexpr Flags AllFlags = FlagMightSkip | FlagTraverseShouldTrace |
+                                    FlagMaybeSingleZoneJSHolder |
+                                    FlagMultiZoneJSHolder;
+
+  constexpr explicit nsCycleCollectionParticipant(Flags aFlags)
+      : mFlags(aFlags) {
+    MOZ_ASSERT((aFlags & ~AllFlags) == 0);
+  }
+
+  NS_IMETHOD TraverseNative(void* aPtr,
+                            nsCycleCollectionTraversalCallback& aCb) = 0;
+
+  nsresult TraverseNativeAndJS(void* aPtr,
+                               nsCycleCollectionTraversalCallback& aCb) {
+    nsresult rv = TraverseNative(aPtr, aCb);
+    if (TraverseShouldTrace()) {
+      // Note, we always call Trace, even if Traverse returned
+      // NS_SUCCESS_INTERRUPTED_TRAVERSE.
+      TraceCallbackFunc noteJsChild(&nsCycleCollectionParticipant::NoteJSChild);
+      Trace(aPtr, noteJsChild, &aCb);
+    }
+    return rv;
+  }
+
+  // Implemented in nsCycleCollectorTraceJSHelpers.cpp.
+  static void NoteJSChild(JS::GCCellPtr aGCThing, const char* aName,
+                          void* aClosure);
+
+  NS_IMETHOD_(void) Root(void* aPtr) = 0;
+  NS_IMETHOD_(void) Unlink(void* aPtr) = 0;
+  NS_IMETHOD_(void) Unroot(void* aPtr) = 0;
+  NS_IMETHOD_(const char*) ClassName() = 0;
+
+  NS_IMETHOD_(void)
+  Trace(void* aPtr, const TraceCallbacks& aCb, void* aClosure) {}
+
+  // CanSkip is called during nsCycleCollector_forgetSkippable.  If it returns
+  // true, aPtr is removed from the purple buffer and therefore might be left
+  // out from the cycle collector graph the next time that's constructed (unless
+  // it's reachable in some other way).
+  //
+  // CanSkip is allowed to expand the set of certainly-alive objects by removing
+  // other objects from the purple buffer, marking JS things black (in the GC
+  // sense), and so forth.  Furthermore, if aRemovingAllowed is true, this call
+  // is allowed to remove aPtr itself from the purple buffer.
+  //
+  // Things can return true from CanSkip if either they know they have no
+  // outgoing edges at all in the cycle collection graph (because then they
+  // can't be parts of a cycle) or they know for sure they're alive.
+  bool CanSkip(void* aPtr, bool aRemovingAllowed) {
+    return MightSkip() ? CanSkipReal(aPtr, aRemovingAllowed) : false;
+  }
+
+  // CanSkipInCC is called during construction of the initial set of roots for
+  // the cycle collector graph.  If it returns true, aPtr is left out of that
+  // set of roots.  Note that the set of roots includes whatever is in the
+  // purple buffer (after earlier CanSkip calls) plus various other sources of
+  // roots, so an object can end up having CanSkipInCC called on it even if it
+  // returned true from CanSkip.  One example of this would be an object that
+  // can potentially trace JS things.
+  //
+  // CanSkipInCC is allowed to remove other objects from the purple buffer but
+  // should not remove aPtr and should not mark JS things black.  It should also
+  // not modify any reference counts.
+  //
+  // Things can return true from CanSkipInCC if either they know they have no
+  // outgoing edges at all in the cycle collection graph or they know for sure
+  // they're alive _and_ none of their outgoing edges are to gray (in the GC
+  // sense) gcthings.  See also nsWrapperCache::HasNothingToTrace and
+  // nsWrapperCache::HasKnownLiveWrapperAndDoesNotNeedTracing. The restriction
+  // on not having outgoing edges to gray gcthings is because if we _do_ have
+  // them that means we have a "strong" edge to a JS thing and since we're alive
+  // we need to trace through it and mark keep them alive.  Outgoing edges to
+  // C++ things don't matter here, because the criteria for when a CC
+  // participant is considered alive are slightly different for JS and C++
+  // things: JS things are only considered alive when reachable via an edge from
+  // a live thing, while C++ things are also considered alive when their
+  // refcount exceeds the number of edges via which they are reachable.
+  bool CanSkipInCC(void* aPtr) {
+    return MightSkip() ? CanSkipInCCReal(aPtr) : false;
+  }
+
+  // CanSkipThis is called during construction of the cycle collector graph,
+  // when we traverse an edge to aPtr and consider adding it to the graph.  If
+  // it returns true, aPtr is not added to the graph.
+  //
+  // CanSkipThis is not allowed to change the liveness or reference count of any
+  // objects.
+  //
+  // Things can return true from CanSkipThis if either they know they have no
+  // outgoing edges at all in the cycle collection graph or they know for sure
+  // they're alive.
+  //
+  // Note that CanSkipThis doesn't have to worry about outgoing edges to gray GC
+  // things, because if this object could have those it already got added to the
+  // graph during root set construction.  An object should never have
+  // CanSkipThis called on it if it has outgoing strong references to JS things.
+  bool CanSkipThis(void* aPtr) {
+    return MightSkip() ? CanSkipThisReal(aPtr) : false;
+  }
+
+  NS_IMETHOD_(void) DeleteCycleCollectable(void* aPtr) = 0;
+
+  bool IsSingleZoneJSHolder() const {
+    return (mFlags & FlagMaybeSingleZoneJSHolder) &&
+           !(mFlags & FlagMultiZoneJSHolder);
+  }
+
+ protected:
+  NS_IMETHOD_(bool) CanSkipReal(void* aPtr, bool aRemovingAllowed) {
+    NS_ASSERTION(false, "Forgot to implement CanSkipReal?");
+    return false;
+  }
+  NS_IMETHOD_(bool) CanSkipInCCReal(void* aPtr) {
+    NS_ASSERTION(false, "Forgot to implement CanSkipInCCReal?");
+    return false;
+  }
+  NS_IMETHOD_(bool) CanSkipThisReal(void* aPtr) {
+    NS_ASSERTION(false, "Forgot to implement CanSkipThisReal?");
+    return false;
+  }
+
+ private:
+  bool MightSkip() const { return mFlags & FlagMightSkip; }
+  bool TraverseShouldTrace() const { return mFlags & FlagTraverseShouldTrace; }
+
+  const Flags mFlags;
+};
+
+class NS_NO_VTABLE nsScriptObjectTracer : public nsCycleCollectionParticipant {
+ public:
+  constexpr explicit nsScriptObjectTracer(Flags aFlags)
+      : nsCycleCollectionParticipant(aFlags | FlagTraverseShouldTrace) {}
+
+  NS_IMETHOD_(void)
+  Trace(void* aPtr, const TraceCallbacks& aCb, void* aClosure) override = 0;
+};
+
+class NS_NO_VTABLE nsXPCOMCycleCollectionParticipant
+    : public nsScriptObjectTracer {
+ public:
+  constexpr explicit nsXPCOMCycleCollectionParticipant(Flags aFlags)
+      : nsScriptObjectTracer(aFlags) {}
+
+  NS_DECLARE_STATIC_IID_ACCESSOR(NS_XPCOMCYCLECOLLECTIONPARTICIPANT_IID)
+
+  NS_IMETHOD_(void) Root(void* aPtr) override;
+  NS_IMETHOD_(void) Unroot(void* aPtr) override;
+
+  NS_IMETHOD_(void)
+  Trace(void* aPtr, const TraceCallbacks& aCb, void* aClosure) override;
+
+  static bool CheckForRightISupports(nsISupports* aSupports);
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(nsXPCOMCycleCollectionParticipant,
+                              NS_XPCOMCYCLECOLLECTIONPARTICIPANT_IID)
+
+///////////////////////////////////////////////////////////////////////////////
+// Helpers for implementing a QI to nsXPCOMCycleCollectionParticipant
+///////////////////////////////////////////////////////////////////////////////
+
+#define NS_CYCLE_COLLECTION_CLASSNAME(_class) \
+  _class::NS_CYCLE_COLLECTION_INNERCLASS
+
+// The IIDs for nsXPCOMCycleCollectionParticipant and nsCycleCollectionISupports
+// are special in that they only differ in their last byte.  This allows for the
+// optimization below where we first check the first three words of the IID and
+// if we find a match we check the last word to decide which case we have to
+// deal with.
+#define NS_INTERFACE_MAP_ENTRIES_CYCLE_COLLECTION(_class)                      \
+  if (TopThreeWordsEquals(                                                     \
+          aIID, NS_GET_IID(nsXPCOMCycleCollectionParticipant),                 \
+          NS_GET_IID(                                                          \
+              nsCycleCollectionISupports)) && /* The calls to LowWordEquals    \
+                                                 here are repeated inside the  \
+                                                 if branch. This is due to the \
+                                                 fact that we need to maintain \
+                                                 the if/else chain for these   \
+                                                 macros, so that the control   \
+                                                 flow never enters the if      \
+                                                 branch unless if we're        \
+                                                 certain one of the            \
+                                                 LowWordEquals() branches will \
+                                                 get executed. */              \
+      (LowWordEquals(aIID, NS_GET_IID(nsXPCOMCycleCollectionParticipant)) ||   \
+       LowWordEquals(aIID, NS_GET_IID(nsCycleCollectionISupports)))) {         \
+    if (LowWordEquals(aIID, NS_GET_IID(nsXPCOMCycleCollectionParticipant))) {  \
+      *aInstancePtr = NS_CYCLE_COLLECTION_PARTICIPANT(_class);                 \
+      return NS_OK;                                                            \
+    }                                                                          \
+    if (LowWordEquals(aIID, NS_GET_IID(nsCycleCollectionISupports))) {         \
+      *aInstancePtr = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this);     \
+      return NS_OK;                                                            \
+    }                                                                          \
+    /* Avoid warnings about foundInterface being left uninitialized. */        \
+    foundInterface = nullptr;                                                  \
+  } else
+
+#define NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(_class) \
+  NS_INTERFACE_MAP_BEGIN(_class)                        \
+    NS_INTERFACE_MAP_ENTRIES_CYCLE_COLLECTION(_class)
+
+#define NS_INTERFACE_TABLE_TO_MAP_SEGUE_CYCLE_COLLECTION(_class) \
+  if (rv == NS_OK) return rv;                                    \
+  nsISupports* foundInterface;                                   \
+  NS_INTERFACE_MAP_ENTRIES_CYCLE_COLLECTION(_class)
+
+// The IIDs for nsXPCOMCycleCollectionParticipant and nsCycleCollectionISupports
+// are special in that they only differ in their last byte.  This allows for the
+// optimization below where we first check the first three words of the IID and
+// if we find a match we check the last word to decide which case we have to
+// deal with.
+#define NS_INTERFACE_TABLE_HEAD_CYCLE_COLLECTION_INHERITED(_class)           \
+  NS_IMETHODIMP _class::QueryInterface(REFNSIID aIID, void** aInstancePtr) { \
+    MOZ_ASSERT(aInstancePtr, "null out param");                              \
+                                                                             \
+    if (TopThreeWordsEquals(aIID,                                            \
+                            NS_GET_IID(nsXPCOMCycleCollectionParticipant),   \
+                            NS_GET_IID(nsCycleCollectionISupports))) {       \
+      if (LowWordEquals(aIID,                                                \
+                        NS_GET_IID(nsXPCOMCycleCollectionParticipant))) {    \
+        *aInstancePtr = NS_CYCLE_COLLECTION_PARTICIPANT(_class);             \
+        return NS_OK;                                                        \
+      }                                                                      \
+      if (LowWordEquals(aIID, NS_GET_IID(nsCycleCollectionISupports))) {     \
+        *aInstancePtr = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this); \
+        return NS_OK;                                                        \
+      }                                                                      \
+    }                                                                        \
+    nsresult rv = NS_ERROR_FAILURE;
+
+#define NS_CYCLE_COLLECTION_UPCAST(obj, clazz) \
+  NS_CYCLE_COLLECTION_CLASSNAME(clazz)::Upcast(obj)
+
+#ifdef DEBUG
+#  define NS_CHECK_FOR_RIGHT_PARTICIPANT(_ptr) _ptr->CheckForRightParticipant()
+#else
+#  define NS_CHECK_FOR_RIGHT_PARTICIPANT(_ptr)
+#endif
+
+// The default implementation of this class template is empty, because it
+// should never be used: see the partial specializations below.
+template <typename T, bool IsXPCOM = std::is_base_of<nsISupports, T>::value>
+struct DowncastCCParticipantImpl {};
+
+// Specialization for XPCOM CC participants
+template <typename T>
+struct DowncastCCParticipantImpl<T, true> {
+  static T* Run(void* aPtr) {
+    nsISupports* s = static_cast<nsISupports*>(aPtr);
+    MOZ_ASSERT(NS_CYCLE_COLLECTION_CLASSNAME(T)::CheckForRightISupports(s),
+               "not the nsISupports pointer we expect");
+    T* rval = NS_CYCLE_COLLECTION_CLASSNAME(T)::Downcast(s);
+    NS_CHECK_FOR_RIGHT_PARTICIPANT(rval);
+    return rval;
+  }
+};
+
+// Specialization for native CC participants
+template <typename T>
+struct DowncastCCParticipantImpl<T, false> {
+  static T* Run(void* aPtr) { return static_cast<T*>(aPtr); }
+};
+
+template <typename T>
+T* DowncastCCParticipant(void* aPtr) {
+  return DowncastCCParticipantImpl<T>::Run(aPtr);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Helpers for implementing CanSkip methods
+///////////////////////////////////////////////////////////////////////////////
+
+// See documentation for nsCycleCollectionParticipant::CanSkip for documentation
+// about this method.
+#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_BEGIN(_class)                       \
+  NS_IMETHODIMP_(bool)                                                        \
+  NS_CYCLE_COLLECTION_CLASSNAME(_class)::CanSkipReal(void* p,                 \
+                                                     bool aRemovingAllowed) { \
+    _class* tmp = DowncastCCParticipant<_class>(p);
+
+#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_END \
+  (void)tmp;                                  \
+  return false;                               \
+  }
+
+// See documentation for nsCycleCollectionParticipant::CanSkipInCC for
+// documentation about this method.
+#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_BEGIN(_class)       \
+  NS_IMETHODIMP_(bool)                                              \
+  NS_CYCLE_COLLECTION_CLASSNAME(_class)::CanSkipInCCReal(void* p) { \
+    _class* tmp = DowncastCCParticipant<_class>(p);
+
+#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_END \
+  (void)tmp;                                        \
+  return false;                                     \
+  }
+
+// See documentation for nsCycleCollectionParticipant::CanSkipThis for
+// documentation about this method.
+#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_BEGIN(_class)        \
+  NS_IMETHODIMP_(bool)                                              \
+  NS_CYCLE_COLLECTION_CLASSNAME(_class)::CanSkipThisReal(void* p) { \
+    _class* tmp = DowncastCCParticipant<_class>(p);
+
+#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_END \
+  (void)tmp;                                       \
+  return false;                                    \
+  }
+
+///////////////////////////////////////////////////////////////////////////////
+// Helpers for implementing nsCycleCollectionParticipant::Unlink
+//
+// You need to use NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED if you want
+// the base class Unlink version to be called before your own implementation.
+// You can use NS_IMPL_CYCLE_COLLECTION_UNLINK_END_INHERITED if you want the
+// base class Unlink to get called after your own implementation.  You should
+// never use them together.
+///////////////////////////////////////////////////////////////////////////////
+
+#define NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)      \
+  NS_IMETHODIMP_(void)                                     \
+  NS_CYCLE_COLLECTION_CLASSNAME(_class)::Unlink(void* p) { \
+    _class* tmp = DowncastCCParticipant<_class>(p);
+
+#define NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(_class, _base_class) \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)                              \
+    nsISupports* s = static_cast<nsISupports*>(p);                           \
+    NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::Unlink(s);
+
+#define NS_IMPL_CYCLE_COLLECTION_UNLINK_HELPER(_field) \
+  ImplCycleCollectionUnlink(tmp->_field);
+
+#define NS_IMPL_CYCLE_COLLECTION_UNLINK(...) \
+  MOZ_FOR_EACH(NS_IMPL_CYCLE_COLLECTION_UNLINK_HELPER, (), (__VA_ARGS__))
+
+#define NS_IMPL_CYCLE_COLLECTION_UNLINK_END \
+  (void)tmp;                                \
+  }
+
+#define NS_IMPL_CYCLE_COLLECTION_UNLINK_END_INHERITED(_base_class) \
+  nsISupports* s = static_cast<nsISupports*>(p);                   \
+  NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::Unlink(s);           \
+  (void)tmp;                                                       \
+  }
+
+#define NS_IMPL_CYCLE_COLLECTION_UNLINK_0(_class) \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)   \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+///////////////////////////////////////////////////////////////////////////////
+// Helpers for implementing nsCycleCollectionParticipant::Traverse
+///////////////////////////////////////////////////////////////////////////////
+
+#define NS_IMPL_CYCLE_COLLECTION_DESCRIBE(_class, _refcnt) \
+  cb.DescribeRefCountedNode(_refcnt, #_class);
+
+#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(_class) \
+  NS_IMETHODIMP                                                  \
+  NS_CYCLE_COLLECTION_CLASSNAME(_class)::TraverseNative(         \
+      void* p, nsCycleCollectionTraversalCallback& cb) {         \
+    _class* tmp = DowncastCCParticipant<_class>(p);
+
+#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)    \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(_class) \
+    NS_IMPL_CYCLE_COLLECTION_DESCRIBE(_class, tmp->mRefCnt.get())
+
+// Base class' CC participant should return NS_SUCCESS_INTERRUPTED_TRAVERSE
+// from Traverse if it wants derived classes to not traverse anything from
+// their CC participant.
+
+#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(_class, _base_class) \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(_class)                     \
+    nsISupports* s = static_cast<nsISupports*>(p);                             \
+    if (NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::TraverseNative(s, cb) ==   \
+        NS_SUCCESS_INTERRUPTED_TRAVERSE) {                                     \
+      return NS_SUCCESS_INTERRUPTED_TRAVERSE;                                  \
+    }
+
+#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_HELPER(_field) \
+  ImplCycleCollectionTraverse(cb, tmp->_field, #_field, 0);
+
+#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE(...) \
+  MOZ_FOR_EACH(NS_IMPL_CYCLE_COLLECTION_TRAVERSE_HELPER, (), (__VA_ARGS__))
+
+#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_RAWPTR(_field) \
+  CycleCollectionNoteChild(cb, tmp->_field, #_field);
+
+#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END \
+  (void)tmp;                                  \
+  return NS_OK;                               \
+  }
+
+///////////////////////////////////////////////////////////////////////////////
+// Helpers for implementing nsScriptObjectTracer::Trace
+///////////////////////////////////////////////////////////////////////////////
+
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(_class)               \
+  void NS_CYCLE_COLLECTION_CLASSNAME(_class)::Trace(               \
+      void* p, const TraceCallbacks& aCallbacks, void* aClosure) { \
+    _class* tmp = DowncastCCParticipant<_class>(p);
+
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(_class, _base_class) \
+  NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(_class)                              \
+    nsISupports* s = static_cast<nsISupports*>(p);                          \
+    NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::Trace(s, aCallbacks, aClosure);
+
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(_field) \
+  aCallbacks.Trace(&tmp->_field, #_field, aClosure);
+
+// NB: The (void)tmp; hack in the TRACE_END macro exists to support
+// implementations that don't need to do anything in their Trace method.
+// Without this hack, some compilers warn about the unused tmp local.
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_END \
+  (void)tmp;                               \
+  }
+
+///////////////////////////////////////////////////////////////////////////////
+// Helpers for implementing a concrete nsCycleCollectionParticipant
+///////////////////////////////////////////////////////////////////////////////
+
+// If a class defines a participant, then QIing an instance of that class to
+// nsXPCOMCycleCollectionParticipant should produce that participant.
+#ifdef DEBUG
+#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_BASE \
+    virtual void CheckForRightParticipant()
+#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_DERIVED \
+    virtual void CheckForRightParticipant() override
+#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_BODY(_class)             \
+    {                                                             \
+      nsXPCOMCycleCollectionParticipant* p;                       \
+      CallQueryInterface(this, &p);                               \
+      MOZ_ASSERT(p == &NS_CYCLE_COLLECTION_INNERNAME,             \
+                 #_class " should QI to its own CC participant"); \
+    }
+#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class) \
+    NS_CHECK_FOR_RIGHT_PARTICIPANT_BASE               \
+    NS_CHECK_FOR_RIGHT_PARTICIPANT_BODY(_class)
+#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class) \
+    NS_CHECK_FOR_RIGHT_PARTICIPANT_DERIVED                      \
+    NS_CHECK_FOR_RIGHT_PARTICIPANT_BODY(_class)
+#else
+#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)
+#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)
+#endif
+
+#define NS_DECL_CYCLE_COLLECTION_CLASS_NAME_METHOD(_class) \
+  NS_IMETHOD_(const char*) ClassName() override { return #_class; };
+
+#define NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                     \
+ public:                                                                       \
+  NS_IMETHOD TraverseNative(void* p, nsCycleCollectionTraversalCallback& cb)   \
+      override;                                                                \
+  NS_DECL_CYCLE_COLLECTION_CLASS_NAME_METHOD(_class)                           \
+  NS_IMETHOD_(void) DeleteCycleCollectable(void* p) override {                 \
+    DowncastCCParticipant<_class>(p)->DeleteCycleCollectable();                \
+  }                                                                            \
+  static _class* Downcast(nsISupports* s) {                                    \
+    return static_cast<_class*>(static_cast<_base*>(s));                       \
+  }                                                                            \
+  static nsISupports* Upcast(_class* p) {                                      \
+    return NS_ISUPPORTS_CAST(_base*, p);                                       \
+  }                                                                            \
+  template <typename T>                                                        \
+  friend nsISupports* ToSupports(T* p, NS_CYCLE_COLLECTION_INNERCLASS* dummy); \
+  NS_IMETHOD_(void) Unlink(void* p) override;
+
+#define NS_PARTICIPANT_AS(type, participant) \
+  const_cast<type*>(reinterpret_cast<const type*>(participant))
+
+#define NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)           \
+  static constexpr nsXPCOMCycleCollectionParticipant* GetParticipant() { \
+    return &_class::NS_CYCLE_COLLECTION_INNERNAME;                       \
+  }
+
+/**
+ * We use this macro to force that classes that inherit from a ccable class and
+ * declare their own participant declare themselves as inherited cc classes.
+ * To avoid possibly unnecessary vtables we only do this checking in debug
+ * builds.
+ */
+#ifdef DEBUG
+#  define NOT_INHERITED_CANT_OVERRIDE \
+    virtual void BaseCycleCollectable() final {}
+#else
+#  define NOT_INHERITED_CANT_OVERRIDE
+#endif
+
+#define NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(_class, _base)         \
+  class NS_CYCLE_COLLECTION_INNERCLASS                                  \
+      : public nsXPCOMCycleCollectionParticipant {                      \
+   public:                                                              \
+    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0) \
+        : nsXPCOMCycleCollectionParticipant(aFlags) {}                  \
+                                                                        \
+   private:                                                             \
+    NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                  \
+    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)              \
+  };                                                                    \
+  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                           \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;  \
+  NOT_INHERITED_CANT_OVERRIDE
+
+#define NS_DECL_CYCLE_COLLECTION_CLASS(_class) \
+  NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(_class, _class)
+
+// Cycle collector helper for ambiguous classes that can sometimes be skipped.
+#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_CLASS_AMBIGUOUS(_class, _base)   \
+  class NS_CYCLE_COLLECTION_INNERCLASS                                      \
+      : public nsXPCOMCycleCollectionParticipant {                          \
+   public:                                                                  \
+    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(                      \
+        Flags aFlags = FlagMightSkip) /* We always want skippability. */    \
+        : nsXPCOMCycleCollectionParticipant(aFlags | FlagMightSkip) {}      \
+                                                                            \
+   private:                                                                 \
+    NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                      \
+    NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override; \
+    NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                    \
+    NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                    \
+    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                  \
+  };                                                                        \
+  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                               \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;      \
+  NOT_INHERITED_CANT_OVERRIDE
+
+#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_CLASS(_class) \
+  NS_DECL_CYCLE_COLLECTION_SKIPPABLE_CLASS_AMBIGUOUS(_class, _class)
+
+#define NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(_class, _base) \
+  class NS_CYCLE_COLLECTION_INNERCLASS                                        \
+      : public nsXPCOMCycleCollectionParticipant {                            \
+   public:                                                                    \
+    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)       \
+        : nsXPCOMCycleCollectionParticipant(aFlags) {}                        \
+                                                                              \
+   private:                                                                   \
+    NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                        \
+    NS_IMETHOD_(void)                                                         \
+    Trace(void* p, const TraceCallbacks& cb, void* closure) override;         \
+    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                    \
+  };                                                                          \
+  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                                 \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;        \
+  NOT_INHERITED_CANT_OVERRIDE
+
+#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS_AMBIGUOUS(   \
+    _class, _base)                                                          \
+  class NS_CYCLE_COLLECTION_INNERCLASS                                      \
+      : public nsXPCOMCycleCollectionParticipant {                          \
+   public:                                                                  \
+    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(                      \
+        Flags aFlags = FlagMightSkip) /* We always want skippability. */    \
+        : nsXPCOMCycleCollectionParticipant(aFlags | FlagMightSkip) {}      \
+                                                                            \
+   private:                                                                 \
+    NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                      \
+    NS_IMETHOD_(void)                                                       \
+    Trace(void* p, const TraceCallbacks& cb, void* closure) override;       \
+    NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override; \
+    NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                    \
+    NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                    \
+    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                  \
+  };                                                                        \
+  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                               \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;      \
+  NOT_INHERITED_CANT_OVERRIDE
+
+#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS(_class)     \
+  NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS_AMBIGUOUS(_class, \
+                                                                   _class)
+
+#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS_INHERITED(      \
+    _class, _base_class)                                                       \
+  class NS_CYCLE_COLLECTION_INNERCLASS                                         \
+      : public NS_CYCLE_COLLECTION_CLASSNAME(_base_class) {                    \
+   public:                                                                     \
+    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(                         \
+        Flags aFlags = FlagMightSkip | /* We always want skippability. */      \
+                       FlagMultiZoneJSHolder)                                  \
+        : NS_CYCLE_COLLECTION_CLASSNAME(_base_class)(aFlags | FlagMightSkip) { \
+    }                                                                          \
+                                                                               \
+   private:                                                                    \
+    NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_BODY(_class, _base_class)         \
+    NS_IMETHOD_(void)                                                          \
+    Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
+    NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override;    \
+    NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                       \
+    NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                       \
+    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
+  };                                                                           \
+  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)                        \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
+
+#define NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(_class) \
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(_class, _class)
+
+#define NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_BODY(_class, _base_class)   \
+ public:                                                                     \
+  NS_IMETHOD TraverseNative(void* p, nsCycleCollectionTraversalCallback& cb) \
+      override;                                                              \
+  NS_DECL_CYCLE_COLLECTION_CLASS_NAME_METHOD(_class)                         \
+  static _class* Downcast(nsISupports* s) {                                  \
+    return static_cast<_class*>(static_cast<_base_class*>(                   \
+        NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::Downcast(s)));           \
+  }                                                                          \
+  NS_IMETHOD_(void) Unlink(void* p) override;
+
+#define NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(_class, _base_class)   \
+  class NS_CYCLE_COLLECTION_INNERCLASS                                  \
+      : public NS_CYCLE_COLLECTION_CLASSNAME(_base_class) {             \
+   public:                                                              \
+    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0) \
+        : NS_CYCLE_COLLECTION_CLASSNAME(_base_class)(aFlags) {}         \
+                                                                        \
+   private:                                                             \
+    NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_BODY(_class, _base_class)  \
+    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)              \
+  };                                                                    \
+  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)                 \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
+
+#define NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(_class,         \
+                                                               _base_class)    \
+  class NS_CYCLE_COLLECTION_INNERCLASS                                         \
+      : public NS_CYCLE_COLLECTION_CLASSNAME(_base_class) {                    \
+   public:                                                                     \
+    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)        \
+        : NS_CYCLE_COLLECTION_CLASSNAME(_base_class)(aFlags |                  \
+                                                     FlagMultiZoneJSHolder) {} \
+                                                                               \
+   private:                                                                    \
+    NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_BODY(_class, _base_class)         \
+    NS_IMETHOD_(void)                                                          \
+    Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
+    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
+  };                                                                           \
+  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)                        \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
+
+// Cycle collector participant declarations.
+
+#define NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                   \
+ public:                                                                     \
+  NS_IMETHOD_(void) Root(void* p) override {                                 \
+    static_cast<_class*>(p)->AddRef();                                       \
+  }                                                                          \
+  NS_IMETHOD_(void) Unlink(void* n) override;                                \
+  NS_IMETHOD_(void) Unroot(void* p) override {                               \
+    static_cast<_class*>(p)->Release();                                      \
+  }                                                                          \
+  NS_IMETHOD TraverseNative(void* n, nsCycleCollectionTraversalCallback& cb) \
+      override;                                                              \
+  NS_DECL_CYCLE_COLLECTION_CLASS_NAME_METHOD(_class)                         \
+  NS_IMETHOD_(void) DeleteCycleCollectable(void* n) override {               \
+    DowncastCCParticipant<_class>(n)->DeleteCycleCollectable();              \
+  }                                                                          \
+  static _class* Downcast(void* s) {                                         \
+    return DowncastCCParticipant<_class>(s);                                 \
+  }                                                                          \
+  static void* Upcast(_class* p) { return static_cast<void*>(p); }
+
+#define NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS(_class)                          \
+  void DeleteCycleCollectable(void) { delete this; }                           \
+  class NS_CYCLE_COLLECTION_INNERCLASS : public nsCycleCollectionParticipant { \
+   public:                                                                     \
+    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)        \
+        : nsCycleCollectionParticipant(aFlags) {}                              \
+                                                                               \
+   private:                                                                    \
+    NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                         \
+    static constexpr nsCycleCollectionParticipant* GetParticipant() {          \
+      return &_class::NS_CYCLE_COLLECTION_INNERNAME;                           \
+    }                                                                          \
+  };                                                                           \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
+
+#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_NATIVE_CLASS(_class)                \
+  void DeleteCycleCollectable(void) { delete this; }                           \
+  class NS_CYCLE_COLLECTION_INNERCLASS : public nsCycleCollectionParticipant { \
+   public:                                                                     \
+    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(                         \
+        Flags aFlags = FlagMightSkip) /* We always want skippability. */       \
+        : nsCycleCollectionParticipant(aFlags | FlagMightSkip) {}              \
+                                                                               \
+   private:                                                                    \
+    NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                         \
+    NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override;    \
+    NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                       \
+    NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                       \
+    static nsCycleCollectionParticipant* GetParticipant() {                    \
+      return &_class::NS_CYCLE_COLLECTION_INNERNAME;                           \
+    }                                                                          \
+  };                                                                           \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
+
+#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_NATIVE_CLASS_WITH_CUSTOM_DELETE(    \
+    _class)                                                                    \
+  class NS_CYCLE_COLLECTION_INNERCLASS : public nsCycleCollectionParticipant { \
+   public:                                                                     \
+    constexpr NS_CYCLE_COLLECTION_INNERCLASS()                                 \
+        : nsCycleCollectionParticipant(true) {}                                \
+                                                                               \
+   private:                                                                    \
+    NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                         \
+    NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override;    \
+    NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                       \
+    NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                       \
+    static nsCycleCollectionParticipant* GetParticipant() {                    \
+      return &_class::NS_CYCLE_COLLECTION_INNERNAME;                           \
+    }                                                                          \
+  };                                                                           \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
+
+#define NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_NATIVE_CLASS(_class)     \
+  void DeleteCycleCollectable(void) { delete this; }                    \
+  class NS_CYCLE_COLLECTION_INNERCLASS : public nsScriptObjectTracer {  \
+   public:                                                              \
+    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0) \
+        : nsScriptObjectTracer(aFlags) {}                               \
+                                                                        \
+   private:                                                             \
+    NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                  \
+    NS_IMETHOD_(void)                                                   \
+    Trace(void* p, const TraceCallbacks& cb, void* closure) override;   \
+    static constexpr nsScriptObjectTracer* GetParticipant() {           \
+      return &_class::NS_CYCLE_COLLECTION_INNERNAME;                    \
+    }                                                                   \
+  };                                                                    \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
+
+#define NS_IMPL_CYCLE_COLLECTION_CLASS(_class) \
+  _class::NS_CYCLE_COLLECTION_INNERCLASS _class::NS_CYCLE_COLLECTION_INNERNAME;
+
+// By default JS holders are treated as if they may store pointers to multiple
+// zones, but one may optimize GC handling by using single zone holders.
+#define NS_IMPL_CYCLE_COLLECTION_SINGLE_ZONE_SCRIPT_HOLDER_CLASS(_class) \
+  _class::NS_CYCLE_COLLECTION_INNERCLASS                                 \
+      _class::NS_CYCLE_COLLECTION_INNERNAME(                             \
+          nsCycleCollectionParticipant::FlagMaybeSingleZoneJSHolder);
+
+// NB: This is not something you usually want to use.  It is here to allow
+// adding things to the CC graph to help debugging via CC logs, but it does not
+// traverse or unlink anything, so it is useless for anything else.
+#define NS_IMPL_CYCLE_COLLECTION_0(_class)        \
+  NS_IMPL_CYCLE_COLLECTION_CLASS(_class)          \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)   \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_END             \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class) \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+#define NS_IMPL_CYCLE_COLLECTION(_class, ...)      \
+  NS_IMPL_CYCLE_COLLECTION_CLASS(_class)           \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)    \
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)   \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_END              \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)  \
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__) \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+// If you are looking for NS_IMPL_CYCLE_COLLECTION_INHERITED_0(_class, _base)
+// you should instead not declare any cycle collected stuff in _class, so it
+// will just inherit the CC declarations from _base.
+
+#define NS_IMPL_CYCLE_COLLECTION_INHERITED(_class, _base, ...)     \
+  NS_IMPL_CYCLE_COLLECTION_CLASS(_class)                           \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(_class, _base)   \
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)                   \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_END                              \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(_class, _base) \
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__)                 \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+#define NS_CYCLE_COLLECTION_NOTE_EDGE_NAME CycleCollectionNoteEdgeName
+
+/**
+ * Convenience macros for defining nISupports methods in a cycle collected
+ * class.
+ */
+
+#define NS_IMPL_QUERY_INTERFACE_CYCLE_COLLECTION_INHERITED(aClass, aSuper, \
+                                                           ...)            \
+  NS_INTERFACE_TABLE_HEAD_CYCLE_COLLECTION_INHERITED(aClass)               \
+    NS_INTERFACE_TABLE_INHERITED(aClass, __VA_ARGS__)                      \
+  NS_INTERFACE_TABLE_TAIL_INHERITING(aSuper)
+
+#define NS_IMPL_ISUPPORTS_CYCLE_COLLECTION_INHERITED(aClass, aSuper, ...) \
+  NS_IMPL_QUERY_INTERFACE_CYCLE_COLLECTION_INHERITED(aClass, aSuper,      \
+                                                     __VA_ARGS__)         \
+  NS_IMPL_ADDREF_INHERITED(aClass, aSuper)                                \
+  NS_IMPL_RELEASE_INHERITED(aClass, aSuper)
+
+#define NS_IMPL_ISUPPORTS_CYCLE_COLLECTION_INHERITED_0(aClass, aSuper) \
+  NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(aClass)                      \
+  NS_INTERFACE_MAP_END_INHERITING(aSuper)                              \
+  NS_IMPL_ADDREF_INHERITED(aClass, aSuper)                             \
+  NS_IMPL_RELEASE_INHERITED(aClass, aSuper)
+
+/**
+ * Equivalency of the high three words where two IIDs have the same
+ * top three words but not the same low word.
+ */
+inline bool TopThreeWordsEquals(const nsID& aID, const nsID& aOther1,
+                                const nsID& aOther2) {
+  MOZ_ASSERT((((uint32_t*)&aOther1.m0)[0] == ((uint32_t*)&aOther2.m0)[0]) &&
+             (((uint32_t*)&aOther1.m0)[1] == ((uint32_t*)&aOther2.m0)[1]) &&
+             (((uint32_t*)&aOther1.m0)[2] == ((uint32_t*)&aOther2.m0)[2]) &&
+             (((uint32_t*)&aOther1.m0)[3] != ((uint32_t*)&aOther2.m0)[3]));
+
+  return ((((uint32_t*)&aID.m0)[0] == ((uint32_t*)&aOther1.m0)[0]) &&
+          (((uint32_t*)&aID.m0)[1] == ((uint32_t*)&aOther1.m0)[1]) &&
+          (((uint32_t*)&aID.m0)[2] == ((uint32_t*)&aOther1.m0)[2]));
+}
+
+/**
+ * Equivalency of the fourth word where the two IIDs have the same
+ * top three words but not the same low word.
+ */
+inline bool LowWordEquals(const nsID& aID, const nsID& aOther) {
+  return (((uint32_t*)&aID.m0)[3] == ((uint32_t*)&aOther.m0)[3]);
+}
+
+// Template magic to modify JS::Heap without including relevant headers, to
+// prevent excessive header dependency.
+template <typename T>
+inline void ImplCycleCollectionUnlink(JS::Heap<T>& aField) {
+  aField.setNull();
+}
+template <typename T>
+inline void ImplCycleCollectionUnlink(JS::Heap<T*>& aField) {
+  aField = nullptr;
+}
+
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBERS(...)                \
+  MOZ_ASSERT(!IsSingleZoneJSHolder());                                \
+  MOZ_FOR_EACH(NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK, (), \
+               (__VA_ARGS__))
+
+#define NS_IMPL_CYCLE_COLLECTION_WITH_JS_MEMBERS(class_, native_members_,   \
+                                                 js_members_)               \
+  NS_IMPL_CYCLE_COLLECTION_CLASS(class_)                                    \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(class_)                             \
+    using ::ImplCycleCollectionUnlink;                                      \
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(                                        \
+        MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(MOZ_FOR_EACH_EXPAND_HELPER js_members_) \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_END                                       \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(class_)                           \
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(                                      \
+        MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END                                     \
+  NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(class_)                              \
+    NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBERS(                              \
+        MOZ_FOR_EACH_EXPAND_HELPER js_members_)                             \
+  NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+#define NS_IMPL_CYCLE_COLLECTION_INHERITED_WITH_JS_MEMBERS(                 \
+    class_, _base, native_members_, js_members_)                            \
+  NS_IMPL_CYCLE_COLLECTION_CLASS(class_)                                    \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(class_, _base)            \
+    using ::ImplCycleCollectionUnlink;                                      \
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(                                        \
+        MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(MOZ_FOR_EACH_EXPAND_HELPER js_members_) \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_END                                       \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(class_, _base)          \
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(                                      \
+        MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END                                     \
+  NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(class_, _base)             \
+    NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBERS(                              \
+        MOZ_FOR_EACH_EXPAND_HELPER js_members_)                             \
+  NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+template <typename... Elements>
+inline void ImplCycleCollectionUnlink(std::tuple<Elements...>& aField) {
+  std::apply([](auto&&... aArgs) { (ImplCycleCollectionUnlink(aArgs), ...); },
+             aField);
+}
+template <typename... Elements>
+inline void ImplCycleCollectionTraverse(
+    nsCycleCollectionTraversalCallback& aCallback,
+    std::tuple<Elements...>& aField, const char* aName, uint32_t aFlags) {
+  aFlags |= CycleCollectionEdgeNameArrayFlag;
+  std::apply(
+      [&](auto&&... aArgs) {
+        (ImplCycleCollectionTraverse(aCallback, aArgs, aName, aFlags), ...);
+      },
+      aField);
+}
+
+#endif  // nsCycleCollectionParticipant_h__
diff --git a/xpcom/base/nsCycleCollectionTraversalCallback.h b/xpcom/base/nsCycleCollectionTraversalCallback.h
new file mode 100644
index 0000000000..9317a5e23a
--- /dev/null
+++ b/xpcom/base/nsCycleCollectionTraversalCallback.h
@@ -0,0 +1,70 @@
+/* -*- 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/. */
+
+#ifndef nsCycleCollectionTraversalCallback_h__
+#define nsCycleCollectionTraversalCallback_h__
+
+#include <cstdint>
+#include "nscore.h"
+
+class nsCycleCollectionParticipant;
+class nsISupports;
+class JSObject;
+
+namespace JS {
+class GCCellPtr;
+}
+
+class NS_NO_VTABLE nsCycleCollectionTraversalCallback {
+ public:
+  // You must call DescribeRefCountedNode() with an accurate
+  // refcount, otherwise cycle collection will fail, and probably crash.
+  // If the callback cares about objname, it should put
+  // WANT_DEBUG_INFO in mFlags.
+  NS_IMETHOD_(void)
+  DescribeRefCountedNode(nsrefcnt aRefcount, const char* aObjName) = 0;
+  // Note, aCompartmentAddress is 0 if it is unknown.
+  NS_IMETHOD_(void)
+  DescribeGCedNode(bool aIsMarked, const char* aObjName,
+                   uint64_t aCompartmentAddress = 0) = 0;
+
+  NS_IMETHOD_(void) NoteXPCOMChild(nsISupports* aChild) = 0;
+  NS_IMETHOD_(void) NoteJSChild(JS::GCCellPtr aThing) = 0;
+  NS_IMETHOD_(void)
+  NoteNativeChild(void* aChild, nsCycleCollectionParticipant* aHelper) = 0;
+
+  NS_IMETHOD_(void)
+  NoteWeakMapping(JSObject* aKey, nsISupports* aVal,
+                  nsCycleCollectionParticipant* aValParticipant) = 0;
+
+  // Give a name to the edge associated with the next call to
+  // NoteXPCOMChild, NoteJSObject, NoteJSScript, or NoteNativeChild.
+  // Callbacks who care about this should set WANT_DEBUG_INFO in the
+  // flags.
+  NS_IMETHOD_(void) NoteNextEdgeName(const char* aName) = 0;
+
+  enum {
+    // Values for flags:
+
+    // Caller should call NoteNextEdgeName and pass useful objName
+    // to DescribeRefCountedNode and DescribeGCedNode.
+    WANT_DEBUG_INFO = (1 << 0),
+
+    // Caller should not skip objects that we know will be
+    // uncollectable.
+    WANT_ALL_TRACES = (1 << 1)
+  };
+  uint32_t Flags() const { return mFlags; }
+  bool WantDebugInfo() const { return (mFlags & WANT_DEBUG_INFO) != 0; }
+  bool WantAllTraces() const { return (mFlags & WANT_ALL_TRACES) != 0; }
+
+ protected:
+  nsCycleCollectionTraversalCallback() : mFlags(0) {}
+
+  uint32_t mFlags;
+};
+
+#endif  // nsCycleCollectionTraversalCallback_h__
diff --git a/xpcom/base/nsCycleCollector.cpp b/xpcom/base/nsCycleCollector.cpp
new file mode 100644
index 0000000000..7bf0154448
--- /dev/null
+++ b/xpcom/base/nsCycleCollector.cpp
@@ -0,0 +1,4050 @@
+/* -*- 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/. */
+
+//
+// This file implements a garbage-cycle collector based on the paper
+//
+//   Concurrent Cycle Collection in Reference Counted Systems
+//   Bacon & Rajan (2001), ECOOP 2001 / Springer LNCS vol 2072
+//
+// We are not using the concurrent or acyclic cases of that paper; so
+// the green, red and orange colors are not used.
+//
+// The collector is based on tracking pointers of four colors:
+//
+// Black nodes are definitely live. If we ever determine a node is
+// black, it's ok to forget about, drop from our records.
+//
+// White nodes are definitely garbage cycles. Once we finish with our
+// scanning, we unlink all the white nodes and expect that by
+// unlinking them they will self-destruct (since a garbage cycle is
+// only keeping itself alive with internal links, by definition).
+//
+// Snow-white is an addition to the original algorithm. A snow-white node
+// has reference count zero and is just waiting for deletion.
+//
+// Grey nodes are being scanned. Nodes that turn grey will turn
+// either black if we determine that they're live, or white if we
+// determine that they're a garbage cycle. After the main collection
+// algorithm there should be no grey nodes.
+//
+// Purple nodes are *candidates* for being scanned. They are nodes we
+// haven't begun scanning yet because they're not old enough, or we're
+// still partway through the algorithm.
+//
+// XPCOM objects participating in garbage-cycle collection are obliged
+// to inform us when they ought to turn purple; that is, when their
+// refcount transitions from N+1 -> N, for nonzero N. Furthermore we
+// require that *after* an XPCOM object has informed us of turning
+// purple, they will tell us when they either transition back to being
+// black (incremented refcount) or are ultimately deleted.
+
+// Incremental cycle collection
+//
+// Beyond the simple state machine required to implement incremental
+// collection, the CC needs to be able to compensate for things the browser
+// is doing during the collection. There are two kinds of problems. For each
+// of these, there are two cases to deal with: purple-buffered C++ objects
+// and JS objects.
+
+// The first problem is that an object in the CC's graph can become garbage.
+// This is bad because the CC touches the objects in its graph at every
+// stage of its operation.
+//
+// All cycle collected C++ objects that die during a cycle collection
+// will end up actually getting deleted by the SnowWhiteKiller. Before
+// the SWK deletes an object, it checks if an ICC is running, and if so,
+// if the object is in the graph. If it is, the CC clears mPointer and
+// mParticipant so it does not point to the raw object any more. Because
+// objects could die any time the CC returns to the mutator, any time the CC
+// accesses a PtrInfo it must perform a null check on mParticipant to
+// ensure the object has not gone away.
+//
+// JS objects don't always run finalizers, so the CC can't remove them from
+// the graph when they die. Fortunately, JS objects can only die during a GC,
+// so if a GC is begun during an ICC, the browser synchronously finishes off
+// the ICC, which clears the entire CC graph. If the GC and CC are scheduled
+// properly, this should be rare.
+//
+// The second problem is that objects in the graph can be changed, say by
+// being addrefed or released, or by having a field updated, after the object
+// has been added to the graph. The problem is that ICC can miss a newly
+// created reference to an object, and end up unlinking an object that is
+// actually alive.
+//
+// The basic idea of the solution, from "An on-the-fly Reference Counting
+// Garbage Collector for Java" by Levanoni and Petrank, is to notice if an
+// object has had an additional reference to it created during the collection,
+// and if so, don't collect it during the current collection. This avoids having
+// to rerun the scan as in Bacon & Rajan 2001.
+//
+// For cycle collected C++ objects, we modify AddRef to place the object in
+// the purple buffer, in addition to Release. Then, in the CC, we treat any
+// objects in the purple buffer as being alive, after graph building has
+// completed. Because they are in the purple buffer, they will be suspected
+// in the next CC, so there's no danger of leaks. This is imprecise, because
+// we will treat as live an object that has been Released but not AddRefed
+// during graph building, but that's probably rare enough that the additional
+// bookkeeping overhead is not worthwhile.
+//
+// For JS objects, the cycle collector is only looking at gray objects. If a
+// gray object is touched during ICC, it will be made black by UnmarkGray.
+// Thus, if a JS object has become black during the ICC, we treat it as live.
+// Merged JS zones have to be handled specially: we scan all zone globals.
+// If any are black, we treat the zone as being black.
+
+// Safety
+//
+// An XPCOM object is either scan-safe or scan-unsafe, purple-safe or
+// purple-unsafe.
+//
+// An nsISupports object is scan-safe if:
+//
+//  - It can be QI'ed to |nsXPCOMCycleCollectionParticipant|, though
+//    this operation loses ISupports identity (like nsIClassInfo).
+//  - Additionally, the operation |traverse| on the resulting
+//    nsXPCOMCycleCollectionParticipant does not cause *any* refcount
+//    adjustment to occur (no AddRef / Release calls).
+//
+// A non-nsISupports ("native") object is scan-safe by explicitly
+// providing its nsCycleCollectionParticipant.
+//
+// An object is purple-safe if it satisfies the following properties:
+//
+//  - The object is scan-safe.
+//
+// When we receive a pointer |ptr| via
+// |nsCycleCollector::suspect(ptr)|, we assume it is purple-safe. We
+// can check the scan-safety, but have no way to ensure the
+// purple-safety; objects must obey, or else the entire system falls
+// apart. Don't involve an object in this scheme if you can't
+// guarantee its purple-safety. The easiest way to ensure that an
+// object is purple-safe is to use nsCycleCollectingAutoRefCnt.
+//
+// When we have a scannable set of purple nodes ready, we begin
+// our walks. During the walks, the nodes we |traverse| should only
+// feed us more scan-safe nodes, and should not adjust the refcounts
+// of those nodes.
+//
+// We do not |AddRef| or |Release| any objects during scanning. We
+// rely on the purple-safety of the roots that call |suspect| to
+// hold, such that we will clear the pointer from the purple buffer
+// entry to the object before it is destroyed. The pointers that are
+// merely scan-safe we hold only for the duration of scanning, and
+// there should be no objects released from the scan-safe set during
+// the scan.
+//
+// We *do* call |Root| and |Unroot| on every white object, on
+// either side of the calls to |Unlink|. This keeps the set of white
+// objects alive during the unlinking.
+//
+
+#if !defined(__MINGW32__)
+#  ifdef WIN32
+#    include <crtdbg.h>
+#    include <errno.h>
+#  endif
+#endif
+
+#include "base/process_util.h"
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/CycleCollectedJSRuntime.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/HashFunctions.h"
+#include "mozilla/HashTable.h"
+#include "mozilla/HoldDropJSObjects.h"
+/* This must occur *after* base/process_util.h to avoid typedefs conflicts. */
+#include <stdint.h>
+#include <stdio.h>
+
+#include <utility>
+
+#include "js/SliceBudget.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/AutoGlobalTimelineMarker.h"
+#include "mozilla/Likely.h"
+#include "mozilla/LinkedList.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/MruCache.h"
+#include "mozilla/PoisonIOInterposer.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/SegmentedVector.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/ThreadLocal.h"
+#include "mozilla/UniquePtr.h"
+#include "nsCycleCollectionNoteRootCallback.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsCycleCollector.h"
+#include "nsDeque.h"
+#include "nsDumpUtils.h"
+#include "nsExceptionHandler.h"
+#include "nsIConsoleService.h"
+#include "nsICycleCollectorListener.h"
+#include "nsIFile.h"
+#include "nsIMemoryReporter.h"
+#include "nsISerialEventTarget.h"
+#include "nsPrintfCString.h"
+#include "nsTArray.h"
+#include "nsThreadUtils.h"
+#include "nsXULAppAPI.h"
+#include "prenv.h"
+#include "xpcpublic.h"
+
+using namespace mozilla;
+
+struct NurseryPurpleBufferEntry {
+  void* mPtr;
+  nsCycleCollectionParticipant* mParticipant;
+  nsCycleCollectingAutoRefCnt* mRefCnt;
+};
+
+#define NURSERY_PURPLE_BUFFER_SIZE 2048
+bool gNurseryPurpleBufferEnabled = true;
+NurseryPurpleBufferEntry gNurseryPurpleBufferEntry[NURSERY_PURPLE_BUFFER_SIZE];
+uint32_t gNurseryPurpleBufferEntryCount = 0;
+
+void ClearNurseryPurpleBuffer();
+
+static void SuspectUsingNurseryPurpleBuffer(
+    void* aPtr, nsCycleCollectionParticipant* aCp,
+    nsCycleCollectingAutoRefCnt* aRefCnt) {
+  MOZ_ASSERT(NS_IsMainThread(), "Wrong thread!");
+  MOZ_ASSERT(gNurseryPurpleBufferEnabled);
+  if (gNurseryPurpleBufferEntryCount == NURSERY_PURPLE_BUFFER_SIZE) {
+    ClearNurseryPurpleBuffer();
+  }
+
+  gNurseryPurpleBufferEntry[gNurseryPurpleBufferEntryCount] = {aPtr, aCp,
+                                                               aRefCnt};
+  ++gNurseryPurpleBufferEntryCount;
+}
+
+// #define COLLECT_TIME_DEBUG
+
+// Enable assertions that are useful for diagnosing errors in graph
+// construction.
+// #define DEBUG_CC_GRAPH
+
+#define DEFAULT_SHUTDOWN_COLLECTIONS 5
+
+// One to do the freeing, then another to detect there is no more work to do.
+#define NORMAL_SHUTDOWN_COLLECTIONS 2
+
+// Cycle collector environment variables
+//
+// MOZ_CC_LOG_ALL: If defined, always log cycle collector heaps.
+//
+// MOZ_CC_LOG_SHUTDOWN: If defined, log cycle collector heaps at shutdown.
+//
+// MOZ_CC_LOG_SHUTDOWN_SKIP: If set to a non-negative integer value n, then
+// skip logging for the first n shutdown CCs. This implies MOZ_CC_LOG_SHUTDOWN.
+// The first log or two are much larger than the rest, so it can be useful to
+// reduce the total size of logs if you know already that the initial logs
+// aren't interesting.
+//
+// MOZ_CC_LOG_THREAD: If set to "main", only automatically log main thread
+// CCs. If set to "worker", only automatically log worker CCs. If set to "all",
+// log either. The default value is "all". This must be used with either
+// MOZ_CC_LOG_ALL or MOZ_CC_LOG_SHUTDOWN for it to do anything.
+//
+// MOZ_CC_LOG_PROCESS: If set to "main", only automatically log main process
+// CCs. If set to "content", only automatically log tab CCs. If set to "all",
+// log everything. The default value is "all". This must be used with either
+// MOZ_CC_LOG_ALL or MOZ_CC_LOG_SHUTDOWN for it to do anything.
+//
+// MOZ_CC_ALL_TRACES: If set to "all", any cycle collector
+// logging done will be WantAllTraces, which disables
+// various cycle collector optimizations to give a fuller picture of
+// the heap. If set to "shutdown", only shutdown logging will be WantAllTraces.
+// The default is none.
+//
+// MOZ_CC_RUN_DURING_SHUTDOWN: In non-DEBUG or builds, if this is set,
+// run cycle collections at shutdown.
+//
+// MOZ_CC_LOG_DIRECTORY: The directory in which logs are placed (such as
+// logs from MOZ_CC_LOG_ALL and MOZ_CC_LOG_SHUTDOWN, or other uses
+// of nsICycleCollectorListener)
+
+// Various parameters of this collector can be tuned using environment
+// variables.
+
+struct nsCycleCollectorParams {
+  bool mLogAll;
+  bool mLogShutdown;
+  bool mAllTracesAll;
+  bool mAllTracesShutdown;
+  bool mLogThisThread;
+  int32_t mLogShutdownSkip = 0;
+
+  nsCycleCollectorParams()
+      : mLogAll(PR_GetEnv("MOZ_CC_LOG_ALL") != nullptr),
+        mLogShutdown(PR_GetEnv("MOZ_CC_LOG_SHUTDOWN") != nullptr),
+        mAllTracesAll(false),
+        mAllTracesShutdown(false) {
+    if (const char* lssEnv = PR_GetEnv("MOZ_CC_LOG_SHUTDOWN_SKIP")) {
+      mLogShutdown = true;
+      nsDependentCString lssString(lssEnv);
+      nsresult rv;
+      int32_t lss = lssString.ToInteger(&rv);
+      if (NS_SUCCEEDED(rv) && lss >= 0) {
+        mLogShutdownSkip = lss;
+      }
+    }
+
+    const char* logThreadEnv = PR_GetEnv("MOZ_CC_LOG_THREAD");
+    bool threadLogging = true;
+    if (logThreadEnv && !!strcmp(logThreadEnv, "all")) {
+      if (NS_IsMainThread()) {
+        threadLogging = !strcmp(logThreadEnv, "main");
+      } else {
+        threadLogging = !strcmp(logThreadEnv, "worker");
+      }
+    }
+
+    const char* logProcessEnv = PR_GetEnv("MOZ_CC_LOG_PROCESS");
+    bool processLogging = true;
+    if (logProcessEnv && !!strcmp(logProcessEnv, "all")) {
+      switch (XRE_GetProcessType()) {
+        case GeckoProcessType_Default:
+          processLogging = !strcmp(logProcessEnv, "main");
+          break;
+        case GeckoProcessType_Content:
+          processLogging = !strcmp(logProcessEnv, "content");
+          break;
+        default:
+          processLogging = false;
+          break;
+      }
+    }
+    mLogThisThread = threadLogging && processLogging;
+
+    const char* allTracesEnv = PR_GetEnv("MOZ_CC_ALL_TRACES");
+    if (allTracesEnv) {
+      if (!strcmp(allTracesEnv, "all")) {
+        mAllTracesAll = true;
+      } else if (!strcmp(allTracesEnv, "shutdown")) {
+        mAllTracesShutdown = true;
+      }
+    }
+  }
+
+  // aShutdownCount is how many shutdown CCs we've started.
+  // For non-shutdown CCs, we'll pass in 0.
+  // For the first shutdown CC, we'll pass in 1.
+  bool LogThisCC(int32_t aShutdownCount) {
+    if (mLogAll) {
+      return mLogThisThread;
+    }
+    if (aShutdownCount == 0 || !mLogShutdown) {
+      return false;
+    }
+    if (aShutdownCount <= mLogShutdownSkip) {
+      return false;
+    }
+    return mLogThisThread;
+  }
+
+  bool AllTracesThisCC(bool aIsShutdown) {
+    return mAllTracesAll || (aIsShutdown && mAllTracesShutdown);
+  }
+};
+
+#ifdef COLLECT_TIME_DEBUG
+class TimeLog {
+ public:
+  TimeLog() : mLastCheckpoint(TimeStamp::Now()) {}
+
+  void Checkpoint(const char* aEvent) {
+    TimeStamp now = TimeStamp::Now();
+    double dur = (now - mLastCheckpoint).ToMilliseconds();
+    if (dur >= 0.5) {
+      printf("cc: %s took %.1fms\n", aEvent, dur);
+    }
+    mLastCheckpoint = now;
+  }
+
+ private:
+  TimeStamp mLastCheckpoint;
+};
+#else
+class TimeLog {
+ public:
+  TimeLog() = default;
+  void Checkpoint(const char* aEvent) {}
+};
+#endif
+
+////////////////////////////////////////////////////////////////////////
+// Base types
+////////////////////////////////////////////////////////////////////////
+
+class PtrInfo;
+
+class EdgePool {
+ public:
+  // EdgePool allocates arrays of void*, primarily to hold PtrInfo*.
+  // However, at the end of a block, the last two pointers are a null
+  // and then a void** pointing to the next block.  This allows
+  // EdgePool::Iterators to be a single word but still capable of crossing
+  // block boundaries.
+
+  EdgePool() {
+    mSentinelAndBlocks[0].block = nullptr;
+    mSentinelAndBlocks[1].block = nullptr;
+  }
+
+  ~EdgePool() {
+    MOZ_ASSERT(!mSentinelAndBlocks[0].block && !mSentinelAndBlocks[1].block,
+               "Didn't call Clear()?");
+  }
+
+  void Clear() {
+    EdgeBlock* b = EdgeBlocks();
+    while (b) {
+      EdgeBlock* next = b->Next();
+      delete b;
+      b = next;
+    }
+
+    mSentinelAndBlocks[0].block = nullptr;
+    mSentinelAndBlocks[1].block = nullptr;
+  }
+
+#ifdef DEBUG
+  bool IsEmpty() {
+    return !mSentinelAndBlocks[0].block && !mSentinelAndBlocks[1].block;
+  }
+#endif
+
+ private:
+  struct EdgeBlock;
+  union PtrInfoOrBlock {
+    // Use a union to avoid reinterpret_cast and the ensuing
+    // potential aliasing bugs.
+    PtrInfo* ptrInfo;
+    EdgeBlock* block;
+  };
+  struct EdgeBlock {
+    enum { EdgeBlockSize = 16 * 1024 };
+
+    PtrInfoOrBlock mPointers[EdgeBlockSize];
+    EdgeBlock() {
+      mPointers[EdgeBlockSize - 2].block = nullptr;  // sentinel
+      mPointers[EdgeBlockSize - 1].block = nullptr;  // next block pointer
+    }
+    EdgeBlock*& Next() { return mPointers[EdgeBlockSize - 1].block; }
+    PtrInfoOrBlock* Start() { return &mPointers[0]; }
+    PtrInfoOrBlock* End() { return &mPointers[EdgeBlockSize - 2]; }
+  };
+
+  // Store the null sentinel so that we can have valid iterators
+  // before adding any edges and without adding any blocks.
+  PtrInfoOrBlock mSentinelAndBlocks[2];
+
+  EdgeBlock*& EdgeBlocks() { return mSentinelAndBlocks[1].block; }
+  EdgeBlock* EdgeBlocks() const { return mSentinelAndBlocks[1].block; }
+
+ public:
+  class Iterator {
+   public:
+    Iterator() : mPointer(nullptr) {}
+    explicit Iterator(PtrInfoOrBlock* aPointer) : mPointer(aPointer) {}
+    Iterator(const Iterator& aOther) = default;
+
+    Iterator& operator++() {
+      if (!mPointer->ptrInfo) {
+        // Null pointer is a sentinel for link to the next block.
+        mPointer = (mPointer + 1)->block->mPointers;
+      }
+      ++mPointer;
+      return *this;
+    }
+
+    PtrInfo* operator*() const {
+      if (!mPointer->ptrInfo) {
+        // Null pointer is a sentinel for link to the next block.
+        return (mPointer + 1)->block->mPointers->ptrInfo;
+      }
+      return mPointer->ptrInfo;
+    }
+    bool operator==(const Iterator& aOther) const {
+      return mPointer == aOther.mPointer;
+    }
+    bool operator!=(const Iterator& aOther) const {
+      return mPointer != aOther.mPointer;
+    }
+
+#ifdef DEBUG_CC_GRAPH
+    bool Initialized() const { return mPointer != nullptr; }
+#endif
+
+   private:
+    PtrInfoOrBlock* mPointer;
+  };
+
+  class Builder;
+  friend class Builder;
+  class Builder {
+   public:
+    explicit Builder(EdgePool& aPool)
+        : mCurrent(&aPool.mSentinelAndBlocks[0]),
+          mBlockEnd(&aPool.mSentinelAndBlocks[0]),
+          mNextBlockPtr(&aPool.EdgeBlocks()) {}
+
+    Iterator Mark() { return Iterator(mCurrent); }
+
+    void Add(PtrInfo* aEdge) {
+      if (mCurrent == mBlockEnd) {
+        EdgeBlock* b = new EdgeBlock();
+        *mNextBlockPtr = b;
+        mCurrent = b->Start();
+        mBlockEnd = b->End();
+        mNextBlockPtr = &b->Next();
+      }
+      (mCurrent++)->ptrInfo = aEdge;
+    }
+
+   private:
+    // mBlockEnd points to space for null sentinel
+    PtrInfoOrBlock* mCurrent;
+    PtrInfoOrBlock* mBlockEnd;
+    EdgeBlock** mNextBlockPtr;
+  };
+
+  size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
+    size_t n = 0;
+    EdgeBlock* b = EdgeBlocks();
+    while (b) {
+      n += aMallocSizeOf(b);
+      b = b->Next();
+    }
+    return n;
+  }
+};
+
+#ifdef DEBUG_CC_GRAPH
+#  define CC_GRAPH_ASSERT(b) MOZ_ASSERT(b)
+#else
+#  define CC_GRAPH_ASSERT(b)
+#endif
+
+#define CC_TELEMETRY(_name, _value)                                            \
+  do {                                                                         \
+    if (NS_IsMainThread()) {                                                   \
+      Telemetry::Accumulate(Telemetry::CYCLE_COLLECTOR##_name, _value);        \
+    } else {                                                                   \
+      Telemetry::Accumulate(Telemetry::CYCLE_COLLECTOR_WORKER##_name, _value); \
+    }                                                                          \
+  } while (0)
+
+enum NodeColor { black, white, grey };
+
+// This structure should be kept as small as possible; we may expect
+// hundreds of thousands of them to be allocated and touched
+// repeatedly during each cycle collection.
+class PtrInfo final {
+ public:
+  // mParticipant knows a more concrete type.
+  void* mPointer;
+  nsCycleCollectionParticipant* mParticipant;
+  uint32_t mColor : 2;
+  uint32_t mInternalRefs : 30;
+  uint32_t mRefCount;
+
+ private:
+  EdgePool::Iterator mFirstChild;
+
+  static const uint32_t kInitialRefCount = UINT32_MAX - 1;
+
+ public:
+  PtrInfo(void* aPointer, nsCycleCollectionParticipant* aParticipant)
+      : mPointer(aPointer),
+        mParticipant(aParticipant),
+        mColor(grey),
+        mInternalRefs(0),
+        mRefCount(kInitialRefCount),
+        mFirstChild() {
+    MOZ_ASSERT(aParticipant);
+
+    // We initialize mRefCount to a large non-zero value so
+    // that it doesn't look like a JS object to the cycle collector
+    // in the case where the object dies before being traversed.
+    MOZ_ASSERT(!IsGrayJS() && !IsBlackJS());
+  }
+
+  // Allow NodePool::NodeBlock's constructor to compile.
+  PtrInfo()
+      : mPointer{nullptr},
+        mParticipant{nullptr},
+        mColor{0},
+        mInternalRefs{0},
+        mRefCount{0} {
+    MOZ_ASSERT_UNREACHABLE("should never be called");
+  }
+
+  bool IsGrayJS() const { return mRefCount == 0; }
+
+  bool IsBlackJS() const { return mRefCount == UINT32_MAX; }
+
+  bool WasTraversed() const { return mRefCount != kInitialRefCount; }
+
+  EdgePool::Iterator FirstChild() const {
+    CC_GRAPH_ASSERT(mFirstChild.Initialized());
+    return mFirstChild;
+  }
+
+  // this PtrInfo must be part of a NodePool
+  EdgePool::Iterator LastChild() const {
+    CC_GRAPH_ASSERT((this + 1)->mFirstChild.Initialized());
+    return (this + 1)->mFirstChild;
+  }
+
+  void SetFirstChild(EdgePool::Iterator aFirstChild) {
+    CC_GRAPH_ASSERT(aFirstChild.Initialized());
+    mFirstChild = aFirstChild;
+  }
+
+  // this PtrInfo must be part of a NodePool
+  void SetLastChild(EdgePool::Iterator aLastChild) {
+    CC_GRAPH_ASSERT(aLastChild.Initialized());
+    (this + 1)->mFirstChild = aLastChild;
+  }
+
+  void AnnotatedReleaseAssert(bool aCondition, const char* aMessage);
+};
+
+void PtrInfo::AnnotatedReleaseAssert(bool aCondition, const char* aMessage) {
+  if (aCondition) {
+    return;
+  }
+
+  const char* piName = "Unknown";
+  if (mParticipant) {
+    piName = mParticipant->ClassName();
+  }
+  nsPrintfCString msg("%s, for class %s", aMessage, piName);
+  NS_WARNING(msg.get());
+  CrashReporter::AnnotateCrashReport(CrashReporter::Annotation::CycleCollector,
+                                     msg);
+
+  MOZ_CRASH();
+}
+
+/**
+ * A structure designed to be used like a linked list of PtrInfo, except
+ * it allocates many PtrInfos at a time.
+ */
+class NodePool {
+ private:
+  // The -2 allows us to use |NodeBlockSize + 1| for |mEntries|, and fit
+  // |mNext|, all without causing slop.
+  enum { NodeBlockSize = 4 * 1024 - 2 };
+
+  struct NodeBlock {
+    // We create and destroy NodeBlock using moz_xmalloc/free rather than new
+    // and delete to avoid calling its constructor and destructor.
+    NodeBlock() : mNext{nullptr} {
+      MOZ_ASSERT_UNREACHABLE("should never be called");
+
+      // Ensure NodeBlock is the right size (see the comment on NodeBlockSize
+      // above).
+      static_assert(
+          sizeof(NodeBlock) == 81904 ||  // 32-bit; equals 19.996 x 4 KiB pages
+              sizeof(NodeBlock) ==
+                  131048,  // 64-bit; equals 31.994 x 4 KiB pages
+          "ill-sized NodeBlock");
+    }
+    ~NodeBlock() { MOZ_ASSERT_UNREACHABLE("should never be called"); }
+
+    NodeBlock* mNext;
+    PtrInfo mEntries[NodeBlockSize + 1];  // +1 to store last child of last node
+  };
+
+ public:
+  NodePool() : mBlocks(nullptr), mLast(nullptr) {}
+
+  ~NodePool() { MOZ_ASSERT(!mBlocks, "Didn't call Clear()?"); }
+
+  void Clear() {
+    NodeBlock* b = mBlocks;
+    while (b) {
+      NodeBlock* n = b->mNext;
+      free(b);
+      b = n;
+    }
+
+    mBlocks = nullptr;
+    mLast = nullptr;
+  }
+
+#ifdef DEBUG
+  bool IsEmpty() { return !mBlocks && !mLast; }
+#endif
+
+  class Builder;
+  friend class Builder;
+  class Builder {
+   public:
+    explicit Builder(NodePool& aPool)
+        : mNextBlock(&aPool.mBlocks), mNext(aPool.mLast), mBlockEnd(nullptr) {
+      MOZ_ASSERT(!aPool.mBlocks && !aPool.mLast, "pool not empty");
+    }
+    PtrInfo* Add(void* aPointer, nsCycleCollectionParticipant* aParticipant) {
+      if (mNext == mBlockEnd) {
+        NodeBlock* block = static_cast<NodeBlock*>(malloc(sizeof(NodeBlock)));
+        if (!block) {
+          return nullptr;
+        }
+
+        *mNextBlock = block;
+        mNext = block->mEntries;
+        mBlockEnd = block->mEntries + NodeBlockSize;
+        block->mNext = nullptr;
+        mNextBlock = &block->mNext;
+      }
+      return new (mozilla::KnownNotNull, mNext++)
+          PtrInfo(aPointer, aParticipant);
+    }
+
+   private:
+    NodeBlock** mNextBlock;
+    PtrInfo*& mNext;
+    PtrInfo* mBlockEnd;
+  };
+
+  class Enumerator;
+  friend class Enumerator;
+  class Enumerator {
+   public:
+    explicit Enumerator(NodePool& aPool)
+        : mFirstBlock(aPool.mBlocks),
+          mCurBlock(nullptr),
+          mNext(nullptr),
+          mBlockEnd(nullptr),
+          mLast(aPool.mLast) {}
+
+    bool IsDone() const { return mNext == mLast; }
+
+    bool AtBlockEnd() const { return mNext == mBlockEnd; }
+
+    PtrInfo* GetNext() {
+      MOZ_ASSERT(!IsDone(), "calling GetNext when done");
+      if (mNext == mBlockEnd) {
+        NodeBlock* nextBlock = mCurBlock ? mCurBlock->mNext : mFirstBlock;
+        mNext = nextBlock->mEntries;
+        mBlockEnd = mNext + NodeBlockSize;
+        mCurBlock = nextBlock;
+      }
+      return mNext++;
+    }
+
+   private:
+    // mFirstBlock is a reference to allow an Enumerator to be constructed
+    // for an empty graph.
+    NodeBlock*& mFirstBlock;
+    NodeBlock* mCurBlock;
+    // mNext is the next value we want to return, unless mNext == mBlockEnd
+    // NB: mLast is a reference to allow enumerating while building!
+    PtrInfo* mNext;
+    PtrInfo* mBlockEnd;
+    PtrInfo*& mLast;
+  };
+
+  size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
+    // We don't measure the things pointed to by mEntries[] because those
+    // pointers are non-owning.
+    size_t n = 0;
+    NodeBlock* b = mBlocks;
+    while (b) {
+      n += aMallocSizeOf(b);
+      b = b->mNext;
+    }
+    return n;
+  }
+
+ private:
+  NodeBlock* mBlocks;
+  PtrInfo* mLast;
+};
+
+struct PtrToNodeHashPolicy {
+  using Key = PtrInfo*;
+  using Lookup = void*;
+
+  static js::HashNumber hash(const Lookup& aLookup) {
+    return mozilla::HashGeneric(aLookup);
+  }
+
+  static bool match(const Key& aKey, const Lookup& aLookup) {
+    return aKey->mPointer == aLookup;
+  }
+};
+
+struct WeakMapping {
+  // map and key will be null if the corresponding objects are GC marked
+  PtrInfo* mMap;
+  PtrInfo* mKey;
+  PtrInfo* mKeyDelegate;
+  PtrInfo* mVal;
+};
+
+class CCGraphBuilder;
+
+struct CCGraph {
+  NodePool mNodes;
+  EdgePool mEdges;
+  nsTArray<WeakMapping> mWeakMaps;
+  uint32_t mRootCount;
+
+ private:
+  friend CCGraphBuilder;
+
+  mozilla::HashSet<PtrInfo*, PtrToNodeHashPolicy> mPtrInfoMap;
+
+  bool mOutOfMemory;
+
+  static const uint32_t kInitialMapLength = 16384;
+
+ public:
+  CCGraph()
+      : mRootCount(0), mPtrInfoMap(kInitialMapLength), mOutOfMemory(false) {}
+
+  ~CCGraph() = default;
+
+  void Init() { MOZ_ASSERT(IsEmpty(), "Failed to call CCGraph::Clear"); }
+
+  void Clear() {
+    mNodes.Clear();
+    mEdges.Clear();
+    mWeakMaps.Clear();
+    mRootCount = 0;
+    mPtrInfoMap.clearAndCompact();
+    mOutOfMemory = false;
+  }
+
+#ifdef DEBUG
+  bool IsEmpty() {
+    return mNodes.IsEmpty() && mEdges.IsEmpty() && mWeakMaps.IsEmpty() &&
+           mRootCount == 0 && mPtrInfoMap.empty();
+  }
+#endif
+
+  PtrInfo* FindNode(void* aPtr);
+  void RemoveObjectFromMap(void* aObject);
+
+  uint32_t MapCount() const { return mPtrInfoMap.count(); }
+
+  size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
+    size_t n = 0;
+
+    n += mNodes.SizeOfExcludingThis(aMallocSizeOf);
+    n += mEdges.SizeOfExcludingThis(aMallocSizeOf);
+
+    // We don't measure what the WeakMappings point to, because the
+    // pointers are non-owning.
+    n += mWeakMaps.ShallowSizeOfExcludingThis(aMallocSizeOf);
+
+    n += mPtrInfoMap.shallowSizeOfExcludingThis(aMallocSizeOf);
+
+    return n;
+  }
+};
+
+PtrInfo* CCGraph::FindNode(void* aPtr) {
+  auto p = mPtrInfoMap.lookup(aPtr);
+  return p ? *p : nullptr;
+}
+
+void CCGraph::RemoveObjectFromMap(void* aObj) {
+  auto p = mPtrInfoMap.lookup(aObj);
+  if (p) {
+    PtrInfo* pinfo = *p;
+    pinfo->mPointer = nullptr;
+    pinfo->mParticipant = nullptr;
+    mPtrInfoMap.remove(p);
+  }
+}
+
+static nsISupports* CanonicalizeXPCOMParticipant(nsISupports* aIn) {
+  nsISupports* out = nullptr;
+  aIn->QueryInterface(NS_GET_IID(nsCycleCollectionISupports),
+                      reinterpret_cast<void**>(&out));
+  return out;
+}
+
+struct nsPurpleBufferEntry {
+  nsPurpleBufferEntry(void* aObject, nsCycleCollectingAutoRefCnt* aRefCnt,
+                      nsCycleCollectionParticipant* aParticipant)
+      : mObject(aObject), mRefCnt(aRefCnt), mParticipant(aParticipant) {}
+
+  nsPurpleBufferEntry(nsPurpleBufferEntry&& aOther)
+      : mObject(nullptr), mRefCnt(nullptr), mParticipant(nullptr) {
+    Swap(aOther);
+  }
+
+  void Swap(nsPurpleBufferEntry& aOther) {
+    std::swap(mObject, aOther.mObject);
+    std::swap(mRefCnt, aOther.mRefCnt);
+    std::swap(mParticipant, aOther.mParticipant);
+  }
+
+  void Clear() {
+    mRefCnt->RemoveFromPurpleBuffer();
+    mRefCnt = nullptr;
+    mObject = nullptr;
+    mParticipant = nullptr;
+  }
+
+  ~nsPurpleBufferEntry() {
+    if (mRefCnt) {
+      mRefCnt->RemoveFromPurpleBuffer();
+    }
+  }
+
+  void* mObject;
+  nsCycleCollectingAutoRefCnt* mRefCnt;
+  nsCycleCollectionParticipant* mParticipant;  // nullptr for nsISupports
+};
+
+class nsCycleCollector;
+
+struct nsPurpleBuffer {
+ private:
+  uint32_t mCount;
+
+  // Try to match the size of a jemalloc bucket, to minimize slop bytes.
+  // - On 32-bit platforms sizeof(nsPurpleBufferEntry) is 12, so mEntries'
+  //   Segment is 16,372 bytes.
+  // - On 64-bit platforms sizeof(nsPurpleBufferEntry) is 24, so mEntries'
+  //   Segment is 32,760 bytes.
+  static const uint32_t kEntriesPerSegment = 1365;
+  static const size_t kSegmentSize =
+      sizeof(nsPurpleBufferEntry) * kEntriesPerSegment;
+  typedef SegmentedVector<nsPurpleBufferEntry, kSegmentSize,
+                          InfallibleAllocPolicy>
+      PurpleBufferVector;
+  PurpleBufferVector mEntries;
+
+ public:
+  nsPurpleBuffer() : mCount(0) {
+    static_assert(
+        sizeof(PurpleBufferVector::Segment) == 16372 ||      // 32-bit
+            sizeof(PurpleBufferVector::Segment) == 32760 ||  // 64-bit
+            sizeof(PurpleBufferVector::Segment) == 32744,    // 64-bit Windows
+        "ill-sized nsPurpleBuffer::mEntries");
+  }
+
+  ~nsPurpleBuffer() = default;
+
+  // This method compacts mEntries.
+  template <class PurpleVisitor>
+  void VisitEntries(PurpleVisitor& aVisitor) {
+    Maybe<AutoRestore<bool>> ar;
+    if (NS_IsMainThread()) {
+      ar.emplace(gNurseryPurpleBufferEnabled);
+      gNurseryPurpleBufferEnabled = false;
+      ClearNurseryPurpleBuffer();
+    }
+
+    if (mEntries.IsEmpty()) {
+      return;
+    }
+
+    uint32_t oldLength = mEntries.Length();
+    uint32_t keptLength = 0;
+    auto revIter = mEntries.IterFromLast();
+    auto iter = mEntries.Iter();
+    // After iteration this points to the first empty entry.
+    auto firstEmptyIter = mEntries.Iter();
+    auto iterFromLastEntry = mEntries.IterFromLast();
+    for (; !iter.Done(); iter.Next()) {
+      nsPurpleBufferEntry& e = iter.Get();
+      if (e.mObject) {
+        if (!aVisitor.Visit(*this, &e)) {
+          return;
+        }
+      }
+
+      // Visit call above may have cleared the entry, or the entry was empty
+      // already.
+      if (!e.mObject) {
+        // Try to find a non-empty entry from the end of the vector.
+        for (; !revIter.Done(); revIter.Prev()) {
+          nsPurpleBufferEntry& otherEntry = revIter.Get();
+          if (&e == &otherEntry) {
+            break;
+          }
+          if (otherEntry.mObject) {
+            if (!aVisitor.Visit(*this, &otherEntry)) {
+              return;
+            }
+            // Visit may have cleared otherEntry.
+            if (otherEntry.mObject) {
+              e.Swap(otherEntry);
+              revIter.Prev();  // We've swapped this now empty entry.
+              break;
+            }
+          }
+        }
+      }
+
+      // Entry is non-empty even after the Visit call, ensure it is kept
+      // in mEntries.
+      if (e.mObject) {
+        firstEmptyIter.Next();
+        ++keptLength;
+      }
+
+      if (&e == &revIter.Get()) {
+        break;
+      }
+    }
+
+    // There were some empty entries.
+    if (oldLength != keptLength) {
+      // While visiting entries, some new ones were possibly added. This can
+      // happen during CanSkip. Move all such new entries to be after other
+      // entries. Note, we don't call Visit on newly added entries!
+      if (&iterFromLastEntry.Get() != &mEntries.GetLast()) {
+        iterFromLastEntry.Next();  // Now pointing to the first added entry.
+        auto& iterForNewEntries = iterFromLastEntry;
+        while (!iterForNewEntries.Done()) {
+          MOZ_ASSERT(!firstEmptyIter.Done());
+          MOZ_ASSERT(!firstEmptyIter.Get().mObject);
+          firstEmptyIter.Get().Swap(iterForNewEntries.Get());
+          firstEmptyIter.Next();
+          iterForNewEntries.Next();
+        }
+      }
+
+      mEntries.PopLastN(oldLength - keptLength);
+    }
+  }
+
+  void FreeBlocks() {
+    mCount = 0;
+    mEntries.Clear();
+  }
+
+  void SelectPointers(CCGraphBuilder& aBuilder);
+
+  // RemoveSkippable removes entries from the purple buffer synchronously
+  // (1) if !aAsyncSnowWhiteFreeing and nsPurpleBufferEntry::mRefCnt is 0 or
+  // (2) if nsXPCOMCycleCollectionParticipant::CanSkip() for the obj or
+  // (3) if nsPurpleBufferEntry::mRefCnt->IsPurple() is false.
+  // (4) If aRemoveChildlessNodes is true, then any nodes in the purple buffer
+  //     that will have no children in the cycle collector graph will also be
+  //     removed. CanSkip() may be run on these children.
+  void RemoveSkippable(nsCycleCollector* aCollector, js::SliceBudget& aBudget,
+                       bool aRemoveChildlessNodes, bool aAsyncSnowWhiteFreeing,
+                       CC_ForgetSkippableCallback aCb);
+
+  MOZ_ALWAYS_INLINE void Put(void* aObject, nsCycleCollectionParticipant* aCp,
+                             nsCycleCollectingAutoRefCnt* aRefCnt) {
+    nsPurpleBufferEntry entry(aObject, aRefCnt, aCp);
+    Unused << mEntries.Append(std::move(entry));
+    MOZ_ASSERT(!entry.mRefCnt, "Move didn't work!");
+    ++mCount;
+  }
+
+  void Remove(nsPurpleBufferEntry* aEntry) {
+    MOZ_ASSERT(mCount != 0, "must have entries");
+    --mCount;
+    aEntry->Clear();
+  }
+
+  uint32_t Count() const { return mCount; }
+
+  size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
+    return mEntries.SizeOfExcludingThis(aMallocSizeOf);
+  }
+};
+
+static bool AddPurpleRoot(CCGraphBuilder& aBuilder, void* aRoot,
+                          nsCycleCollectionParticipant* aParti);
+
+struct SelectPointersVisitor {
+  explicit SelectPointersVisitor(CCGraphBuilder& aBuilder)
+      : mBuilder(aBuilder) {}
+
+  bool Visit(nsPurpleBuffer& aBuffer, nsPurpleBufferEntry* aEntry) {
+    MOZ_ASSERT(aEntry->mObject, "Null object in purple buffer");
+    MOZ_ASSERT(aEntry->mRefCnt->get() != 0,
+               "SelectPointersVisitor: snow-white object in the purple buffer");
+    if (!aEntry->mRefCnt->IsPurple() ||
+        AddPurpleRoot(mBuilder, aEntry->mObject, aEntry->mParticipant)) {
+      aBuffer.Remove(aEntry);
+    }
+    return true;
+  }
+
+ private:
+  CCGraphBuilder& mBuilder;
+};
+
+void nsPurpleBuffer::SelectPointers(CCGraphBuilder& aBuilder) {
+  SelectPointersVisitor visitor(aBuilder);
+  VisitEntries(visitor);
+
+  MOZ_ASSERT(mCount == 0, "AddPurpleRoot failed");
+  if (mCount == 0) {
+    FreeBlocks();
+  }
+}
+
+enum ccPhase {
+  IdlePhase,
+  GraphBuildingPhase,
+  ScanAndCollectWhitePhase,
+  CleanupPhase
+};
+
+enum ccIsManual { CCIsNotManual = false, CCIsManual = true };
+
+////////////////////////////////////////////////////////////////////////
+// Top level structure for the cycle collector.
+////////////////////////////////////////////////////////////////////////
+
+using js::SliceBudget;
+
+class JSPurpleBuffer;
+
+class nsCycleCollector : public nsIMemoryReporter {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIMEMORYREPORTER
+
+ private:
+  bool mActivelyCollecting;
+  bool mFreeingSnowWhite;
+  // mScanInProgress should be false when we're collecting white objects.
+  bool mScanInProgress;
+  CycleCollectorResults mResults;
+  TimeStamp mCollectionStart;
+
+  CycleCollectedJSRuntime* mCCJSRuntime;
+
+  ccPhase mIncrementalPhase;
+  int32_t mShutdownCount = 0;
+  CCGraph mGraph;
+  UniquePtr<CCGraphBuilder> mBuilder;
+  RefPtr<nsCycleCollectorLogger> mLogger;
+
+#ifdef DEBUG
+  nsISerialEventTarget* mEventTarget;
+#endif
+
+  nsCycleCollectorParams mParams;
+
+  uint32_t mWhiteNodeCount;
+
+  CC_BeforeUnlinkCallback mBeforeUnlinkCB;
+  CC_ForgetSkippableCallback mForgetSkippableCB;
+
+  nsPurpleBuffer mPurpleBuf;
+
+  uint32_t mUnmergedNeeded;
+  uint32_t mMergedInARow;
+
+  RefPtr<JSPurpleBuffer> mJSPurpleBuffer;
+
+ private:
+  virtual ~nsCycleCollector();
+
+ public:
+  nsCycleCollector();
+
+  void SetCCJSRuntime(CycleCollectedJSRuntime* aCCRuntime);
+  void ClearCCJSRuntime();
+
+  void SetBeforeUnlinkCallback(CC_BeforeUnlinkCallback aBeforeUnlinkCB) {
+    CheckThreadSafety();
+    mBeforeUnlinkCB = aBeforeUnlinkCB;
+  }
+
+  void SetForgetSkippableCallback(
+      CC_ForgetSkippableCallback aForgetSkippableCB) {
+    CheckThreadSafety();
+    mForgetSkippableCB = aForgetSkippableCB;
+  }
+
+  void Suspect(void* aPtr, nsCycleCollectionParticipant* aCp,
+               nsCycleCollectingAutoRefCnt* aRefCnt);
+  void SuspectNurseryEntries();
+  uint32_t SuspectedCount();
+  void ForgetSkippable(js::SliceBudget& aBudget, bool aRemoveChildlessNodes,
+                       bool aAsyncSnowWhiteFreeing);
+  bool FreeSnowWhite(bool aUntilNoSWInPurpleBuffer);
+  bool FreeSnowWhiteWithBudget(js::SliceBudget& aBudget);
+
+  // This method assumes its argument is already canonicalized.
+  void RemoveObjectFromGraph(void* aPtr);
+
+  void PrepareForGarbageCollection();
+  void FinishAnyCurrentCollection(CCReason aReason);
+
+  bool Collect(CCReason aReason, ccIsManual aIsManual, SliceBudget& aBudget,
+               nsICycleCollectorListener* aManualListener,
+               bool aPreferShorterSlices = false);
+  MOZ_CAN_RUN_SCRIPT
+  void Shutdown(bool aDoCollect);
+
+  bool IsIdle() const { return mIncrementalPhase == IdlePhase; }
+
+  void SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf,
+                           size_t* aObjectSize, size_t* aGraphSize,
+                           size_t* aPurpleBufferSize) const;
+
+  JSPurpleBuffer* GetJSPurpleBuffer();
+
+  CycleCollectedJSRuntime* Runtime() { return mCCJSRuntime; }
+
+ private:
+  void CheckThreadSafety();
+  MOZ_CAN_RUN_SCRIPT
+  void ShutdownCollect();
+
+  void FixGrayBits(bool aIsShutdown, TimeLog& aTimeLog);
+  bool IsIncrementalGCInProgress();
+  void FinishAnyIncrementalGCInProgress();
+  bool ShouldMergeZones(ccIsManual aIsManual);
+
+  void BeginCollection(CCReason aReason, ccIsManual aIsManual,
+                       nsICycleCollectorListener* aManualListener);
+  void MarkRoots(SliceBudget& aBudget);
+  void ScanRoots(bool aFullySynchGraphBuild);
+  void ScanIncrementalRoots();
+  void ScanWhiteNodes(bool aFullySynchGraphBuild);
+  void ScanBlackNodes();
+  void ScanWeakMaps();
+
+  // returns whether anything was collected
+  bool CollectWhite();
+
+  void CleanupAfterCollection();
+};
+
+NS_IMPL_ISUPPORTS(nsCycleCollector, nsIMemoryReporter)
+
+/**
+ * GraphWalker is templatized over a Visitor class that must provide
+ * the following two methods:
+ *
+ * bool ShouldVisitNode(PtrInfo const *pi);
+ * void VisitNode(PtrInfo *pi);
+ */
+template <class Visitor>
+class GraphWalker {
+ private:
+  Visitor mVisitor;
+
+  void DoWalk(nsDeque<PtrInfo>& aQueue);
+
+  void CheckedPush(nsDeque<PtrInfo>& aQueue, PtrInfo* aPi) {
+    if (!aPi) {
+      MOZ_CRASH();
+    }
+    if (!aQueue.Push(aPi, fallible)) {
+      mVisitor.Failed();
+    }
+  }
+
+ public:
+  void Walk(PtrInfo* aPi);
+  void WalkFromRoots(CCGraph& aGraph);
+  // copy-constructing the visitor should be cheap, and less
+  // indirection than using a reference
+  explicit GraphWalker(const Visitor aVisitor) : mVisitor(aVisitor) {}
+};
+
+////////////////////////////////////////////////////////////////////////
+// The static collector struct
+////////////////////////////////////////////////////////////////////////
+
+struct CollectorData {
+  RefPtr<nsCycleCollector> mCollector;
+  CycleCollectedJSContext* mContext;
+};
+
+static MOZ_THREAD_LOCAL(CollectorData*) sCollectorData;
+
+////////////////////////////////////////////////////////////////////////
+// Utility functions
+////////////////////////////////////////////////////////////////////////
+
+static inline void ToParticipant(nsISupports* aPtr,
+                                 nsXPCOMCycleCollectionParticipant** aCp) {
+  // We use QI to move from an nsISupports to an
+  // nsXPCOMCycleCollectionParticipant, which is a per-class singleton helper
+  // object that implements traversal and unlinking logic for the nsISupports
+  // in question.
+  *aCp = nullptr;
+  CallQueryInterface(aPtr, aCp);
+}
+
+static void ToParticipant(void* aParti, nsCycleCollectionParticipant** aCp) {
+  // If the participant is null, this is an nsISupports participant,
+  // so we must QI to get the real participant.
+
+  if (!*aCp) {
+    nsISupports* nsparti = static_cast<nsISupports*>(aParti);
+    MOZ_ASSERT(CanonicalizeXPCOMParticipant(nsparti) == nsparti);
+    nsXPCOMCycleCollectionParticipant* xcp;
+    ToParticipant(nsparti, &xcp);
+    *aCp = xcp;
+  }
+}
+
+template <class Visitor>
+MOZ_NEVER_INLINE void GraphWalker<Visitor>::Walk(PtrInfo* aPi) {
+  nsDeque<PtrInfo> queue;
+  CheckedPush(queue, aPi);
+  DoWalk(queue);
+}
+
+template <class Visitor>
+MOZ_NEVER_INLINE void GraphWalker<Visitor>::WalkFromRoots(CCGraph& aGraph) {
+  nsDeque<PtrInfo> queue;
+  NodePool::Enumerator etor(aGraph.mNodes);
+  for (uint32_t i = 0; i < aGraph.mRootCount; ++i) {
+    CheckedPush(queue, etor.GetNext());
+  }
+  DoWalk(queue);
+}
+
+template <class Visitor>
+MOZ_NEVER_INLINE void GraphWalker<Visitor>::DoWalk(nsDeque<PtrInfo>& aQueue) {
+  // Use a aQueue to match the breadth-first traversal used when we
+  // built the graph, for hopefully-better locality.
+  while (aQueue.GetSize() > 0) {
+    PtrInfo* pi = aQueue.PopFront();
+
+    if (pi->WasTraversed() && mVisitor.ShouldVisitNode(pi)) {
+      mVisitor.VisitNode(pi);
+      for (EdgePool::Iterator child = pi->FirstChild(),
+                              child_end = pi->LastChild();
+           child != child_end; ++child) {
+        CheckedPush(aQueue, *child);
+      }
+    }
+  }
+}
+
+struct CCGraphDescriber : public LinkedListElement<CCGraphDescriber> {
+  CCGraphDescriber() : mAddress("0x"), mCnt(0), mType(eUnknown) {}
+
+  enum Type {
+    eRefCountedObject,
+    eGCedObject,
+    eGCMarkedObject,
+    eEdge,
+    eRoot,
+    eGarbage,
+    eUnknown
+  };
+
+  nsCString mAddress;
+  nsCString mName;
+  nsCString mCompartmentOrToAddress;
+  uint32_t mCnt;
+  Type mType;
+};
+
+class LogStringMessageAsync : public DiscardableRunnable {
+ public:
+  explicit LogStringMessageAsync(const nsAString& aMsg)
+      : mozilla::DiscardableRunnable("LogStringMessageAsync"), mMsg(aMsg) {}
+
+  NS_IMETHOD Run() override {
+    nsCOMPtr<nsIConsoleService> cs =
+        do_GetService(NS_CONSOLESERVICE_CONTRACTID);
+    if (cs) {
+      cs->LogStringMessage(mMsg.get());
+    }
+    return NS_OK;
+  }
+
+ private:
+  nsString mMsg;
+};
+
+class nsCycleCollectorLogSinkToFile final : public nsICycleCollectorLogSink {
+ public:
+  NS_DECL_ISUPPORTS
+
+  nsCycleCollectorLogSinkToFile()
+      : mProcessIdentifier(base::GetCurrentProcId()),
+        mGCLog("gc-edges"),
+        mCCLog("cc-edges") {}
+
+  NS_IMETHOD GetFilenameIdentifier(nsAString& aIdentifier) override {
+    aIdentifier = mFilenameIdentifier;
+    return NS_OK;
+  }
+
+  NS_IMETHOD SetFilenameIdentifier(const nsAString& aIdentifier) override {
+    mFilenameIdentifier = aIdentifier;
+    return NS_OK;
+  }
+
+  NS_IMETHOD GetProcessIdentifier(int32_t* aIdentifier) override {
+    *aIdentifier = mProcessIdentifier;
+    return NS_OK;
+  }
+
+  NS_IMETHOD SetProcessIdentifier(int32_t aIdentifier) override {
+    mProcessIdentifier = aIdentifier;
+    return NS_OK;
+  }
+
+  NS_IMETHOD GetGcLog(nsIFile** aPath) override {
+    NS_IF_ADDREF(*aPath = mGCLog.mFile);
+    return NS_OK;
+  }
+
+  NS_IMETHOD GetCcLog(nsIFile** aPath) override {
+    NS_IF_ADDREF(*aPath = mCCLog.mFile);
+    return NS_OK;
+  }
+
+  NS_IMETHOD Open(FILE** aGCLog, FILE** aCCLog) override {
+    nsresult rv;
+
+    if (mGCLog.mStream || mCCLog.mStream) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    rv = OpenLog(&mGCLog);
+    NS_ENSURE_SUCCESS(rv, rv);
+    *aGCLog = mGCLog.mStream;
+
+    rv = OpenLog(&mCCLog);
+    NS_ENSURE_SUCCESS(rv, rv);
+    *aCCLog = mCCLog.mStream;
+
+    return NS_OK;
+  }
+
+  NS_IMETHOD CloseGCLog() override {
+    if (!mGCLog.mStream) {
+      return NS_ERROR_UNEXPECTED;
+    }
+    CloseLog(&mGCLog, u"Garbage"_ns);
+    return NS_OK;
+  }
+
+  NS_IMETHOD CloseCCLog() override {
+    if (!mCCLog.mStream) {
+      return NS_ERROR_UNEXPECTED;
+    }
+    CloseLog(&mCCLog, u"Cycle"_ns);
+    return NS_OK;
+  }
+
+ private:
+  ~nsCycleCollectorLogSinkToFile() {
+    if (mGCLog.mStream) {
+      MozillaUnRegisterDebugFILE(mGCLog.mStream);
+      fclose(mGCLog.mStream);
+    }
+    if (mCCLog.mStream) {
+      MozillaUnRegisterDebugFILE(mCCLog.mStream);
+      fclose(mCCLog.mStream);
+    }
+  }
+
+  struct FileInfo {
+    const char* const mPrefix;
+    nsCOMPtr<nsIFile> mFile;
+    FILE* mStream;
+
+    explicit FileInfo(const char* aPrefix)
+        : mPrefix(aPrefix), mStream(nullptr) {}
+  };
+
+  /**
+   * Create a new file named something like aPrefix.$PID.$IDENTIFIER.log in
+   * $MOZ_CC_LOG_DIRECTORY or in the system's temp directory.  No existing
+   * file will be overwritten; if aPrefix.$PID.$IDENTIFIER.log exists, we'll
+   * try a file named something like aPrefix.$PID.$IDENTIFIER-1.log, and so
+   * on.
+   */
+  already_AddRefed<nsIFile> CreateTempFile(const char* aPrefix) {
+    nsPrintfCString filename("%s.%d%s%s.log", aPrefix, mProcessIdentifier,
+                             mFilenameIdentifier.IsEmpty() ? "" : ".",
+                             NS_ConvertUTF16toUTF8(mFilenameIdentifier).get());
+
+    // Get the log directory either from $MOZ_CC_LOG_DIRECTORY or from
+    // the fallback directories in OpenTempFile.  We don't use an nsCOMPtr
+    // here because OpenTempFile uses an in/out param and getter_AddRefs
+    // wouldn't work.
+    nsIFile* logFile = nullptr;
+    if (char* env = PR_GetEnv("MOZ_CC_LOG_DIRECTORY")) {
+      NS_NewNativeLocalFile(nsCString(env), /* followLinks = */ true, &logFile);
+    }
+
+    // On Android or B2G, this function will open a file named
+    // aFilename under a memory-reporting-specific folder
+    // (/data/local/tmp/memory-reports). Otherwise, it will open a
+    // file named aFilename under "NS_OS_TEMP_DIR".
+    nsresult rv =
+        nsDumpUtils::OpenTempFile(filename, &logFile, "memory-reports"_ns);
+    if (NS_FAILED(rv)) {
+      NS_IF_RELEASE(logFile);
+      return nullptr;
+    }
+
+    return dont_AddRef(logFile);
+  }
+
+  nsresult OpenLog(FileInfo* aLog) {
+    // Initially create the log in a file starting with "incomplete-".
+    // We'll move the file and strip off the "incomplete-" once the dump
+    // completes.  (We do this because we don't want scripts which poll
+    // the filesystem looking for GC/CC dumps to grab a file before we're
+    // finished writing to it.)
+    nsAutoCString incomplete;
+    incomplete += "incomplete-";
+    incomplete += aLog->mPrefix;
+    MOZ_ASSERT(!aLog->mFile);
+    aLog->mFile = CreateTempFile(incomplete.get());
+    if (NS_WARN_IF(!aLog->mFile)) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    MOZ_ASSERT(!aLog->mStream);
+    nsresult rv = aLog->mFile->OpenANSIFileDesc("w", &aLog->mStream);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return NS_ERROR_UNEXPECTED;
+    }
+    MozillaRegisterDebugFILE(aLog->mStream);
+    return NS_OK;
+  }
+
+  nsresult CloseLog(FileInfo* aLog, const nsAString& aCollectorKind) {
+    MOZ_ASSERT(aLog->mStream);
+    MOZ_ASSERT(aLog->mFile);
+
+    MozillaUnRegisterDebugFILE(aLog->mStream);
+    fclose(aLog->mStream);
+    aLog->mStream = nullptr;
+
+    // Strip off "incomplete-".
+    nsCOMPtr<nsIFile> logFileFinalDestination = CreateTempFile(aLog->mPrefix);
+    if (NS_WARN_IF(!logFileFinalDestination)) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    nsAutoString logFileFinalDestinationName;
+    logFileFinalDestination->GetLeafName(logFileFinalDestinationName);
+    if (NS_WARN_IF(logFileFinalDestinationName.IsEmpty())) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    aLog->mFile->MoveTo(/* directory */ nullptr, logFileFinalDestinationName);
+
+    // Save the file path.
+    aLog->mFile = logFileFinalDestination;
+
+    // Log to the error console.
+    nsAutoString logPath;
+    logFileFinalDestination->GetPath(logPath);
+    nsAutoString msg =
+        aCollectorKind + u" Collector log dumped to "_ns + logPath;
+
+    // We don't want any JS to run between ScanRoots and CollectWhite calls,
+    // and since ScanRoots calls this method, better to log the message
+    // asynchronously.
+    RefPtr<LogStringMessageAsync> log = new LogStringMessageAsync(msg);
+    NS_DispatchToCurrentThread(log);
+    return NS_OK;
+  }
+
+  int32_t mProcessIdentifier;
+  nsString mFilenameIdentifier;
+  FileInfo mGCLog;
+  FileInfo mCCLog;
+};
+
+NS_IMPL_ISUPPORTS(nsCycleCollectorLogSinkToFile, nsICycleCollectorLogSink)
+
+class nsCycleCollectorLogger final : public nsICycleCollectorListener {
+  ~nsCycleCollectorLogger() { ClearDescribers(); }
+
+ public:
+  nsCycleCollectorLogger()
+      : mLogSink(nsCycleCollector_createLogSink()),
+        mWantAllTraces(false),
+        mDisableLog(false),
+        mWantAfterProcessing(false),
+        mCCLog(nullptr) {}
+
+  NS_DECL_ISUPPORTS
+
+  void SetAllTraces() { mWantAllTraces = true; }
+
+  bool IsAllTraces() { return mWantAllTraces; }
+
+  NS_IMETHOD AllTraces(nsICycleCollectorListener** aListener) override {
+    SetAllTraces();
+    NS_ADDREF(*aListener = this);
+    return NS_OK;
+  }
+
+  NS_IMETHOD GetWantAllTraces(bool* aAllTraces) override {
+    *aAllTraces = mWantAllTraces;
+    return NS_OK;
+  }
+
+  NS_IMETHOD GetDisableLog(bool* aDisableLog) override {
+    *aDisableLog = mDisableLog;
+    return NS_OK;
+  }
+
+  NS_IMETHOD SetDisableLog(bool aDisableLog) override {
+    mDisableLog = aDisableLog;
+    return NS_OK;
+  }
+
+  NS_IMETHOD GetWantAfterProcessing(bool* aWantAfterProcessing) override {
+    *aWantAfterProcessing = mWantAfterProcessing;
+    return NS_OK;
+  }
+
+  NS_IMETHOD SetWantAfterProcessing(bool aWantAfterProcessing) override {
+    mWantAfterProcessing = aWantAfterProcessing;
+    return NS_OK;
+  }
+
+  NS_IMETHOD GetLogSink(nsICycleCollectorLogSink** aLogSink) override {
+    NS_ADDREF(*aLogSink = mLogSink);
+    return NS_OK;
+  }
+
+  NS_IMETHOD SetLogSink(nsICycleCollectorLogSink* aLogSink) override {
+    if (!aLogSink) {
+      return NS_ERROR_INVALID_ARG;
+    }
+    mLogSink = aLogSink;
+    return NS_OK;
+  }
+
+  nsresult Begin() {
+    nsresult rv;
+
+    mCurrentAddress.AssignLiteral("0x");
+    ClearDescribers();
+    if (mDisableLog) {
+      return NS_OK;
+    }
+
+    FILE* gcLog;
+    rv = mLogSink->Open(&gcLog, &mCCLog);
+    NS_ENSURE_SUCCESS(rv, rv);
+    // Dump the JS heap.
+    CollectorData* data = sCollectorData.get();
+    if (data && data->mContext) {
+      data->mContext->Runtime()->DumpJSHeap(gcLog);
+    }
+    rv = mLogSink->CloseGCLog();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    fprintf(mCCLog, "# WantAllTraces=%s\n", mWantAllTraces ? "true" : "false");
+    return NS_OK;
+  }
+  void NoteRefCountedObject(uint64_t aAddress, uint32_t aRefCount,
+                            const char* aObjectDescription) {
+    if (!mDisableLog) {
+      fprintf(mCCLog, "%p [rc=%u] %s\n", (void*)aAddress, aRefCount,
+              aObjectDescription);
+    }
+    if (mWantAfterProcessing) {
+      CCGraphDescriber* d = new CCGraphDescriber();
+      mDescribers.insertBack(d);
+      mCurrentAddress.AssignLiteral("0x");
+      mCurrentAddress.AppendInt(aAddress, 16);
+      d->mType = CCGraphDescriber::eRefCountedObject;
+      d->mAddress = mCurrentAddress;
+      d->mCnt = aRefCount;
+      d->mName.Append(aObjectDescription);
+    }
+  }
+  void NoteGCedObject(uint64_t aAddress, bool aMarked,
+                      const char* aObjectDescription,
+                      uint64_t aCompartmentAddress) {
+    if (!mDisableLog) {
+      fprintf(mCCLog, "%p [gc%s] %s\n", (void*)aAddress,
+              aMarked ? ".marked" : "", aObjectDescription);
+    }
+    if (mWantAfterProcessing) {
+      CCGraphDescriber* d = new CCGraphDescriber();
+      mDescribers.insertBack(d);
+      mCurrentAddress.AssignLiteral("0x");
+      mCurrentAddress.AppendInt(aAddress, 16);
+      d->mType = aMarked ? CCGraphDescriber::eGCMarkedObject
+                         : CCGraphDescriber::eGCedObject;
+      d->mAddress = mCurrentAddress;
+      d->mName.Append(aObjectDescription);
+      if (aCompartmentAddress) {
+        d->mCompartmentOrToAddress.AssignLiteral("0x");
+        d->mCompartmentOrToAddress.AppendInt(aCompartmentAddress, 16);
+      } else {
+        d->mCompartmentOrToAddress.SetIsVoid(true);
+      }
+    }
+  }
+  void NoteEdge(uint64_t aToAddress, const char* aEdgeName) {
+    if (!mDisableLog) {
+      fprintf(mCCLog, "> %p %s\n", (void*)aToAddress, aEdgeName);
+    }
+    if (mWantAfterProcessing) {
+      CCGraphDescriber* d = new CCGraphDescriber();
+      mDescribers.insertBack(d);
+      d->mType = CCGraphDescriber::eEdge;
+      d->mAddress = mCurrentAddress;
+      d->mCompartmentOrToAddress.AssignLiteral("0x");
+      d->mCompartmentOrToAddress.AppendInt(aToAddress, 16);
+      d->mName.Append(aEdgeName);
+    }
+  }
+  void NoteWeakMapEntry(uint64_t aMap, uint64_t aKey, uint64_t aKeyDelegate,
+                        uint64_t aValue) {
+    if (!mDisableLog) {
+      fprintf(mCCLog, "WeakMapEntry map=%p key=%p keyDelegate=%p value=%p\n",
+              (void*)aMap, (void*)aKey, (void*)aKeyDelegate, (void*)aValue);
+    }
+    // We don't support after-processing for weak map entries.
+  }
+  void NoteIncrementalRoot(uint64_t aAddress) {
+    if (!mDisableLog) {
+      fprintf(mCCLog, "IncrementalRoot %p\n", (void*)aAddress);
+    }
+    // We don't support after-processing for incremental roots.
+  }
+  void BeginResults() {
+    if (!mDisableLog) {
+      fputs("==========\n", mCCLog);
+    }
+  }
+  void DescribeRoot(uint64_t aAddress, uint32_t aKnownEdges) {
+    if (!mDisableLog) {
+      fprintf(mCCLog, "%p [known=%u]\n", (void*)aAddress, aKnownEdges);
+    }
+    if (mWantAfterProcessing) {
+      CCGraphDescriber* d = new CCGraphDescriber();
+      mDescribers.insertBack(d);
+      d->mType = CCGraphDescriber::eRoot;
+      d->mAddress.AppendInt(aAddress, 16);
+      d->mCnt = aKnownEdges;
+    }
+  }
+  void DescribeGarbage(uint64_t aAddress) {
+    if (!mDisableLog) {
+      fprintf(mCCLog, "%p [garbage]\n", (void*)aAddress);
+    }
+    if (mWantAfterProcessing) {
+      CCGraphDescriber* d = new CCGraphDescriber();
+      mDescribers.insertBack(d);
+      d->mType = CCGraphDescriber::eGarbage;
+      d->mAddress.AppendInt(aAddress, 16);
+    }
+  }
+  void End() {
+    if (!mDisableLog) {
+      mCCLog = nullptr;
+      Unused << NS_WARN_IF(NS_FAILED(mLogSink->CloseCCLog()));
+    }
+  }
+  NS_IMETHOD ProcessNext(nsICycleCollectorHandler* aHandler,
+                         bool* aCanContinue) override {
+    if (NS_WARN_IF(!aHandler) || NS_WARN_IF(!mWantAfterProcessing)) {
+      return NS_ERROR_UNEXPECTED;
+    }
+    CCGraphDescriber* d = mDescribers.popFirst();
+    if (d) {
+      switch (d->mType) {
+        case CCGraphDescriber::eRefCountedObject:
+          aHandler->NoteRefCountedObject(d->mAddress, d->mCnt, d->mName);
+          break;
+        case CCGraphDescriber::eGCedObject:
+        case CCGraphDescriber::eGCMarkedObject:
+          aHandler->NoteGCedObject(
+              d->mAddress, d->mType == CCGraphDescriber::eGCMarkedObject,
+              d->mName, d->mCompartmentOrToAddress);
+          break;
+        case CCGraphDescriber::eEdge:
+          aHandler->NoteEdge(d->mAddress, d->mCompartmentOrToAddress, d->mName);
+          break;
+        case CCGraphDescriber::eRoot:
+          aHandler->DescribeRoot(d->mAddress, d->mCnt);
+          break;
+        case CCGraphDescriber::eGarbage:
+          aHandler->DescribeGarbage(d->mAddress);
+          break;
+        case CCGraphDescriber::eUnknown:
+          MOZ_ASSERT_UNREACHABLE("CCGraphDescriber::eUnknown");
+          break;
+      }
+      delete d;
+    }
+    if (!(*aCanContinue = !mDescribers.isEmpty())) {
+      mCurrentAddress.AssignLiteral("0x");
+    }
+    return NS_OK;
+  }
+  NS_IMETHOD AsLogger(nsCycleCollectorLogger** aRetVal) override {
+    RefPtr<nsCycleCollectorLogger> rval = this;
+    rval.forget(aRetVal);
+    return NS_OK;
+  }
+
+ private:
+  void ClearDescribers() {
+    CCGraphDescriber* d;
+    while ((d = mDescribers.popFirst())) {
+      delete d;
+    }
+  }
+
+  nsCOMPtr<nsICycleCollectorLogSink> mLogSink;
+  bool mWantAllTraces;
+  bool mDisableLog;
+  bool mWantAfterProcessing;
+  nsCString mCurrentAddress;
+  mozilla::LinkedList<CCGraphDescriber> mDescribers;
+  FILE* mCCLog;
+};
+
+NS_IMPL_ISUPPORTS(nsCycleCollectorLogger, nsICycleCollectorListener)
+
+already_AddRefed<nsICycleCollectorListener> nsCycleCollector_createLogger() {
+  nsCOMPtr<nsICycleCollectorListener> logger = new nsCycleCollectorLogger();
+  return logger.forget();
+}
+
+static bool GCThingIsGrayCCThing(JS::GCCellPtr thing) {
+  return JS::IsCCTraceKind(thing.kind()) && JS::GCThingIsMarkedGrayInCC(thing);
+}
+
+static bool ValueIsGrayCCThing(const JS::Value& value) {
+  return JS::IsCCTraceKind(value.traceKind()) &&
+         JS::GCThingIsMarkedGray(value.toGCCellPtr());
+}
+
+////////////////////////////////////////////////////////////////////////
+// Bacon & Rajan's |MarkRoots| routine.
+////////////////////////////////////////////////////////////////////////
+
+class CCGraphBuilder final : public nsCycleCollectionTraversalCallback,
+                             public nsCycleCollectionNoteRootCallback {
+ private:
+  CCGraph& mGraph;
+  CycleCollectorResults& mResults;
+  NodePool::Builder mNodeBuilder;
+  EdgePool::Builder mEdgeBuilder;
+  MOZ_INIT_OUTSIDE_CTOR PtrInfo* mCurrPi;
+  nsCycleCollectionParticipant* mJSParticipant;
+  nsCycleCollectionParticipant* mJSZoneParticipant;
+  nsCString mNextEdgeName;
+  RefPtr<nsCycleCollectorLogger> mLogger;
+  bool mMergeZones;
+  UniquePtr<NodePool::Enumerator> mCurrNode;
+  uint32_t mNoteChildCount;
+
+  struct PtrInfoCache : public MruCache<void*, PtrInfo*, PtrInfoCache, 491> {
+    static HashNumber Hash(const void* aKey) { return HashGeneric(aKey); }
+    static bool Match(const void* aKey, const PtrInfo* aVal) {
+      return aVal->mPointer == aKey;
+    }
+  };
+
+  PtrInfoCache mGraphCache;
+
+ public:
+  CCGraphBuilder(CCGraph& aGraph, CycleCollectorResults& aResults,
+                 CycleCollectedJSRuntime* aCCRuntime,
+                 nsCycleCollectorLogger* aLogger, bool aMergeZones);
+  virtual ~CCGraphBuilder();
+
+  bool WantAllTraces() const {
+    return nsCycleCollectionNoteRootCallback::WantAllTraces();
+  }
+
+  bool AddPurpleRoot(void* aRoot, nsCycleCollectionParticipant* aParti);
+
+  // This is called when all roots have been added to the graph, to prepare for
+  // BuildGraph().
+  void DoneAddingRoots();
+
+  // Do some work traversing nodes in the graph. Returns true if this graph
+  // building is finished.
+  bool BuildGraph(SliceBudget& aBudget);
+
+  void RemoveCachedEntry(void* aPtr) { mGraphCache.Remove(aPtr); }
+
+ private:
+  PtrInfo* AddNode(void* aPtr, nsCycleCollectionParticipant* aParticipant);
+  PtrInfo* AddWeakMapNode(JS::GCCellPtr aThing);
+  PtrInfo* AddWeakMapNode(JSObject* aObject);
+
+  void SetFirstChild() { mCurrPi->SetFirstChild(mEdgeBuilder.Mark()); }
+
+  void SetLastChild() { mCurrPi->SetLastChild(mEdgeBuilder.Mark()); }
+
+ public:
+  // nsCycleCollectionNoteRootCallback methods.
+  NS_IMETHOD_(void)
+  NoteXPCOMRoot(nsISupports* aRoot,
+                nsCycleCollectionParticipant* aParticipant) override;
+  NS_IMETHOD_(void) NoteJSRoot(JSObject* aRoot) override;
+  NS_IMETHOD_(void)
+  NoteNativeRoot(void* aRoot,
+                 nsCycleCollectionParticipant* aParticipant) override;
+  NS_IMETHOD_(void)
+  NoteWeakMapping(JSObject* aMap, JS::GCCellPtr aKey, JSObject* aKdelegate,
+                  JS::GCCellPtr aVal) override;
+  // This is used to create synthetic non-refcounted references to
+  // nsXPCWrappedJS from their wrapped JS objects. No map is needed, because
+  // the SubjectToFinalization list is like a known-black weak map, and
+  // no delegate is needed because the keys are all unwrapped objects.
+  NS_IMETHOD_(void)
+  NoteWeakMapping(JSObject* aKey, nsISupports* aVal,
+                  nsCycleCollectionParticipant* aValParticipant) override;
+
+  // nsCycleCollectionTraversalCallback methods.
+  NS_IMETHOD_(void)
+  DescribeRefCountedNode(nsrefcnt aRefCount, const char* aObjName) override;
+  NS_IMETHOD_(void)
+  DescribeGCedNode(bool aIsMarked, const char* aObjName,
+                   uint64_t aCompartmentAddress) override;
+
+  NS_IMETHOD_(void) NoteXPCOMChild(nsISupports* aChild) override;
+  NS_IMETHOD_(void) NoteJSChild(JS::GCCellPtr aThing) override;
+  NS_IMETHOD_(void)
+  NoteNativeChild(void* aChild,
+                  nsCycleCollectionParticipant* aParticipant) override;
+  NS_IMETHOD_(void) NoteNextEdgeName(const char* aName) override;
+
+ private:
+  NS_IMETHOD_(void)
+  NoteRoot(void* aRoot, nsCycleCollectionParticipant* aParticipant) {
+    MOZ_ASSERT(aRoot);
+    MOZ_ASSERT(aParticipant);
+
+    if (!aParticipant->CanSkipInCC(aRoot) || MOZ_UNLIKELY(WantAllTraces())) {
+      AddNode(aRoot, aParticipant);
+    }
+  }
+
+  NS_IMETHOD_(void)
+  NoteChild(void* aChild, nsCycleCollectionParticipant* aCp,
+            nsCString& aEdgeName) {
+    PtrInfo* childPi = AddNode(aChild, aCp);
+    if (!childPi) {
+      return;
+    }
+    mEdgeBuilder.Add(childPi);
+    if (mLogger) {
+      mLogger->NoteEdge((uint64_t)aChild, aEdgeName.get());
+    }
+    ++childPi->mInternalRefs;
+  }
+
+  JS::Zone* MergeZone(JS::GCCellPtr aGcthing) {
+    if (!mMergeZones) {
+      return nullptr;
+    }
+    JS::Zone* zone = JS::GetTenuredGCThingZone(aGcthing);
+    if (js::IsSystemZone(zone)) {
+      return nullptr;
+    }
+    return zone;
+  }
+};
+
+CCGraphBuilder::CCGraphBuilder(CCGraph& aGraph, CycleCollectorResults& aResults,
+                               CycleCollectedJSRuntime* aCCRuntime,
+                               nsCycleCollectorLogger* aLogger,
+                               bool aMergeZones)
+    : mGraph(aGraph),
+      mResults(aResults),
+      mNodeBuilder(aGraph.mNodes),
+      mEdgeBuilder(aGraph.mEdges),
+      mJSParticipant(nullptr),
+      mJSZoneParticipant(nullptr),
+      mLogger(aLogger),
+      mMergeZones(aMergeZones),
+      mNoteChildCount(0) {
+  // 4096 is an allocation bucket size.
+  static_assert(sizeof(CCGraphBuilder) <= 4096,
+                "Don't create too large CCGraphBuilder objects");
+
+  if (aCCRuntime) {
+    mJSParticipant = aCCRuntime->GCThingParticipant();
+    mJSZoneParticipant = aCCRuntime->ZoneParticipant();
+  }
+
+  if (mLogger) {
+    mFlags |= nsCycleCollectionTraversalCallback::WANT_DEBUG_INFO;
+    if (mLogger->IsAllTraces()) {
+      mFlags |= nsCycleCollectionTraversalCallback::WANT_ALL_TRACES;
+      mWantAllTraces = true;  // for nsCycleCollectionNoteRootCallback
+    }
+  }
+
+  mMergeZones = mMergeZones && MOZ_LIKELY(!WantAllTraces());
+
+  MOZ_ASSERT(nsCycleCollectionNoteRootCallback::WantAllTraces() ==
+             nsCycleCollectionTraversalCallback::WantAllTraces());
+}
+
+CCGraphBuilder::~CCGraphBuilder() = default;
+
+PtrInfo* CCGraphBuilder::AddNode(void* aPtr,
+                                 nsCycleCollectionParticipant* aParticipant) {
+  if (mGraph.mOutOfMemory) {
+    return nullptr;
+  }
+
+  PtrInfoCache::Entry cached = mGraphCache.Lookup(aPtr);
+  if (cached) {
+#ifdef DEBUG
+    if (cached.Data()->mParticipant != aParticipant) {
+      auto* parti1 = cached.Data()->mParticipant;
+      auto* parti2 = aParticipant;
+      NS_WARNING(
+          nsPrintfCString("cached participant: %s; AddNode participant: %s\n",
+                          parti1 ? parti1->ClassName() : "null",
+                          parti2 ? parti2->ClassName() : "null")
+              .get());
+    }
+#endif
+    MOZ_ASSERT(cached.Data()->mParticipant == aParticipant,
+               "nsCycleCollectionParticipant shouldn't change!");
+    return cached.Data();
+  }
+
+  PtrInfo* result;
+  auto p = mGraph.mPtrInfoMap.lookupForAdd(aPtr);
+  if (!p) {
+    // New entry
+    result = mNodeBuilder.Add(aPtr, aParticipant);
+    if (!result) {
+      return nullptr;
+    }
+
+    if (!mGraph.mPtrInfoMap.add(p, result)) {
+      // `result` leaks here, but we can't free it because it's
+      // pool-allocated within NodePool.
+      mGraph.mOutOfMemory = true;
+      MOZ_ASSERT(false, "OOM while building cycle collector graph");
+      return nullptr;
+    }
+
+  } else {
+    result = *p;
+    MOZ_ASSERT(result->mParticipant == aParticipant,
+               "nsCycleCollectionParticipant shouldn't change!");
+  }
+
+  cached.Set(result);
+
+  return result;
+}
+
+bool CCGraphBuilder::AddPurpleRoot(void* aRoot,
+                                   nsCycleCollectionParticipant* aParti) {
+  ToParticipant(aRoot, &aParti);
+
+  if (WantAllTraces() || !aParti->CanSkipInCC(aRoot)) {
+    PtrInfo* pinfo = AddNode(aRoot, aParti);
+    if (!pinfo) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+void CCGraphBuilder::DoneAddingRoots() {
+  // We've finished adding roots, and everything in the graph is a root.
+  mGraph.mRootCount = mGraph.MapCount();
+
+  mCurrNode = MakeUnique<NodePool::Enumerator>(mGraph.mNodes);
+}
+
+MOZ_NEVER_INLINE bool CCGraphBuilder::BuildGraph(SliceBudget& aBudget) {
+  MOZ_ASSERT(mCurrNode);
+
+  while (!aBudget.isOverBudget() && !mCurrNode->IsDone()) {
+    mNoteChildCount = 0;
+
+    PtrInfo* pi = mCurrNode->GetNext();
+    if (!pi) {
+      MOZ_CRASH();
+    }
+
+    mCurrPi = pi;
+
+    // We need to call SetFirstChild() even on deleted nodes, to set their
+    // firstChild() that may be read by a prior non-deleted neighbor.
+    SetFirstChild();
+
+    if (pi->mParticipant) {
+      nsresult rv = pi->mParticipant->TraverseNativeAndJS(pi->mPointer, *this);
+      MOZ_RELEASE_ASSERT(!NS_FAILED(rv),
+                         "Cycle collector Traverse method failed");
+    }
+
+    if (mCurrNode->AtBlockEnd()) {
+      SetLastChild();
+    }
+
+    aBudget.step(mNoteChildCount + 1);
+  }
+
+  if (!mCurrNode->IsDone()) {
+    return false;
+  }
+
+  if (mGraph.mRootCount > 0) {
+    SetLastChild();
+  }
+
+  mCurrNode = nullptr;
+
+  return true;
+}
+
+NS_IMETHODIMP_(void)
+CCGraphBuilder::NoteXPCOMRoot(nsISupports* aRoot,
+                              nsCycleCollectionParticipant* aParticipant) {
+  MOZ_ASSERT(aRoot == CanonicalizeXPCOMParticipant(aRoot));
+
+#ifdef DEBUG
+  nsXPCOMCycleCollectionParticipant* cp;
+  ToParticipant(aRoot, &cp);
+  MOZ_ASSERT(aParticipant == cp);
+#endif
+
+  NoteRoot(aRoot, aParticipant);
+}
+
+NS_IMETHODIMP_(void)
+CCGraphBuilder::NoteJSRoot(JSObject* aRoot) {
+  if (JS::Zone* zone = MergeZone(JS::GCCellPtr(aRoot))) {
+    NoteRoot(zone, mJSZoneParticipant);
+  } else {
+    NoteRoot(aRoot, mJSParticipant);
+  }
+}
+
+NS_IMETHODIMP_(void)
+CCGraphBuilder::NoteNativeRoot(void* aRoot,
+                               nsCycleCollectionParticipant* aParticipant) {
+  NoteRoot(aRoot, aParticipant);
+}
+
+NS_IMETHODIMP_(void)
+CCGraphBuilder::DescribeRefCountedNode(nsrefcnt aRefCount,
+                                       const char* aObjName) {
+  mCurrPi->AnnotatedReleaseAssert(aRefCount != 0,
+                                  "CCed refcounted object has zero refcount");
+  mCurrPi->AnnotatedReleaseAssert(
+      aRefCount != UINT32_MAX,
+      "CCed refcounted object has overflowing refcount");
+
+  mResults.mVisitedRefCounted++;
+
+  if (mLogger) {
+    mLogger->NoteRefCountedObject((uint64_t)mCurrPi->mPointer, aRefCount,
+                                  aObjName);
+  }
+
+  mCurrPi->mRefCount = aRefCount;
+}
+
+NS_IMETHODIMP_(void)
+CCGraphBuilder::DescribeGCedNode(bool aIsMarked, const char* aObjName,
+                                 uint64_t aCompartmentAddress) {
+  uint32_t refCount = aIsMarked ? UINT32_MAX : 0;
+  mResults.mVisitedGCed++;
+
+  if (mLogger) {
+    mLogger->NoteGCedObject((uint64_t)mCurrPi->mPointer, aIsMarked, aObjName,
+                            aCompartmentAddress);
+  }
+
+  mCurrPi->mRefCount = refCount;
+}
+
+NS_IMETHODIMP_(void)
+CCGraphBuilder::NoteXPCOMChild(nsISupports* aChild) {
+  nsCString edgeName;
+  if (WantDebugInfo()) {
+    edgeName.Assign(mNextEdgeName);
+    mNextEdgeName.Truncate();
+  }
+  if (!aChild || !(aChild = CanonicalizeXPCOMParticipant(aChild))) {
+    return;
+  }
+
+  ++mNoteChildCount;
+
+  nsXPCOMCycleCollectionParticipant* cp;
+  ToParticipant(aChild, &cp);
+  if (cp && (!cp->CanSkipThis(aChild) || WantAllTraces())) {
+    NoteChild(aChild, cp, edgeName);
+  }
+}
+
+NS_IMETHODIMP_(void)
+CCGraphBuilder::NoteNativeChild(void* aChild,
+                                nsCycleCollectionParticipant* aParticipant) {
+  nsCString edgeName;
+  if (WantDebugInfo()) {
+    edgeName.Assign(mNextEdgeName);
+    mNextEdgeName.Truncate();
+  }
+  if (!aChild) {
+    return;
+  }
+
+  ++mNoteChildCount;
+
+  MOZ_ASSERT(aParticipant, "Need a nsCycleCollectionParticipant!");
+  if (!aParticipant->CanSkipThis(aChild) || WantAllTraces()) {
+    NoteChild(aChild, aParticipant, edgeName);
+  }
+}
+
+NS_IMETHODIMP_(void)
+CCGraphBuilder::NoteJSChild(JS::GCCellPtr aChild) {
+  if (!aChild) {
+    return;
+  }
+
+  ++mNoteChildCount;
+
+  nsCString edgeName;
+  if (MOZ_UNLIKELY(WantDebugInfo())) {
+    edgeName.Assign(mNextEdgeName);
+    mNextEdgeName.Truncate();
+  }
+
+  if (GCThingIsGrayCCThing(aChild) || MOZ_UNLIKELY(WantAllTraces())) {
+    if (JS::Zone* zone = MergeZone(aChild)) {
+      NoteChild(zone, mJSZoneParticipant, edgeName);
+    } else {
+      NoteChild(aChild.asCell(), mJSParticipant, edgeName);
+    }
+  }
+}
+
+NS_IMETHODIMP_(void)
+CCGraphBuilder::NoteNextEdgeName(const char* aName) {
+  if (WantDebugInfo()) {
+    mNextEdgeName = aName;
+  }
+}
+
+PtrInfo* CCGraphBuilder::AddWeakMapNode(JS::GCCellPtr aNode) {
+  MOZ_ASSERT(aNode, "Weak map node should be non-null.");
+
+  if (!GCThingIsGrayCCThing(aNode) && !WantAllTraces()) {
+    return nullptr;
+  }
+
+  if (JS::Zone* zone = MergeZone(aNode)) {
+    return AddNode(zone, mJSZoneParticipant);
+  }
+  return AddNode(aNode.asCell(), mJSParticipant);
+}
+
+PtrInfo* CCGraphBuilder::AddWeakMapNode(JSObject* aObject) {
+  return AddWeakMapNode(JS::GCCellPtr(aObject));
+}
+
+NS_IMETHODIMP_(void)
+CCGraphBuilder::NoteWeakMapping(JSObject* aMap, JS::GCCellPtr aKey,
+                                JSObject* aKdelegate, JS::GCCellPtr aVal) {
+  // Don't try to optimize away the entry here, as we've already attempted to
+  // do that in TraceWeakMapping in nsXPConnect.
+  WeakMapping* mapping = mGraph.mWeakMaps.AppendElement();
+  mapping->mMap = aMap ? AddWeakMapNode(aMap) : nullptr;
+  mapping->mKey = aKey ? AddWeakMapNode(aKey) : nullptr;
+  mapping->mKeyDelegate =
+      aKdelegate ? AddWeakMapNode(aKdelegate) : mapping->mKey;
+  mapping->mVal = aVal ? AddWeakMapNode(aVal) : nullptr;
+
+  if (mLogger) {
+    mLogger->NoteWeakMapEntry((uint64_t)aMap, aKey ? aKey.unsafeAsInteger() : 0,
+                              (uint64_t)aKdelegate,
+                              aVal ? aVal.unsafeAsInteger() : 0);
+  }
+}
+
+NS_IMETHODIMP_(void)
+CCGraphBuilder::NoteWeakMapping(JSObject* aKey, nsISupports* aVal,
+                                nsCycleCollectionParticipant* aValParticipant) {
+  MOZ_ASSERT(aKey, "Don't call NoteWeakMapping with a null key");
+  MOZ_ASSERT(aVal, "Don't call NoteWeakMapping with a null value");
+  WeakMapping* mapping = mGraph.mWeakMaps.AppendElement();
+  mapping->mMap = nullptr;
+  mapping->mKey = AddWeakMapNode(aKey);
+  mapping->mKeyDelegate = mapping->mKey;
+  MOZ_ASSERT(js::UncheckedUnwrapWithoutExpose(aKey) == aKey);
+  mapping->mVal = AddNode(aVal, aValParticipant);
+
+  if (mLogger) {
+    mLogger->NoteWeakMapEntry(0, (uint64_t)aKey, 0, (uint64_t)aVal);
+  }
+}
+
+static bool AddPurpleRoot(CCGraphBuilder& aBuilder, void* aRoot,
+                          nsCycleCollectionParticipant* aParti) {
+  return aBuilder.AddPurpleRoot(aRoot, aParti);
+}
+
+// MayHaveChild() will be false after a Traverse if the object does
+// not have any children the CC will visit.
+class ChildFinder : public nsCycleCollectionTraversalCallback {
+ public:
+  ChildFinder() : mMayHaveChild(false) {}
+
+  // The logic of the Note*Child functions must mirror that of their
+  // respective functions in CCGraphBuilder.
+  NS_IMETHOD_(void) NoteXPCOMChild(nsISupports* aChild) override;
+  NS_IMETHOD_(void)
+  NoteNativeChild(void* aChild, nsCycleCollectionParticipant* aHelper) override;
+  NS_IMETHOD_(void) NoteJSChild(JS::GCCellPtr aThing) override;
+
+  NS_IMETHOD_(void)
+  NoteWeakMapping(JSObject* aKey, nsISupports* aVal,
+                  nsCycleCollectionParticipant* aValParticipant) override {}
+
+  NS_IMETHOD_(void)
+  DescribeRefCountedNode(nsrefcnt aRefcount, const char* aObjname) override {}
+  NS_IMETHOD_(void)
+  DescribeGCedNode(bool aIsMarked, const char* aObjname,
+                   uint64_t aCompartmentAddress) override {}
+  NS_IMETHOD_(void) NoteNextEdgeName(const char* aName) override {}
+  bool MayHaveChild() { return mMayHaveChild; }
+
+ private:
+  bool mMayHaveChild;
+};
+
+NS_IMETHODIMP_(void)
+ChildFinder::NoteXPCOMChild(nsISupports* aChild) {
+  if (!aChild || !(aChild = CanonicalizeXPCOMParticipant(aChild))) {
+    return;
+  }
+  nsXPCOMCycleCollectionParticipant* cp;
+  ToParticipant(aChild, &cp);
+  if (cp && !cp->CanSkip(aChild, true)) {
+    mMayHaveChild = true;
+  }
+}
+
+NS_IMETHODIMP_(void)
+ChildFinder::NoteNativeChild(void* aChild,
+                             nsCycleCollectionParticipant* aHelper) {
+  if (!aChild) {
+    return;
+  }
+  MOZ_ASSERT(aHelper, "Native child must have a participant");
+  if (!aHelper->CanSkip(aChild, true)) {
+    mMayHaveChild = true;
+  }
+}
+
+NS_IMETHODIMP_(void)
+ChildFinder::NoteJSChild(JS::GCCellPtr aChild) {
+  if (aChild && JS::GCThingIsMarkedGray(aChild)) {
+    mMayHaveChild = true;
+  }
+}
+
+static bool MayHaveChild(void* aObj, nsCycleCollectionParticipant* aCp) {
+  ChildFinder cf;
+  aCp->TraverseNativeAndJS(aObj, cf);
+  return cf.MayHaveChild();
+}
+
+// JSPurpleBuffer keeps references to GCThings which might affect the
+// next cycle collection. It is owned only by itself and during unlink its
+// self reference is broken down and the object ends up killing itself.
+// If GC happens before CC, references to GCthings and the self reference are
+// removed.
+class JSPurpleBuffer {
+  ~JSPurpleBuffer() {
+    MOZ_ASSERT(mValues.IsEmpty());
+    MOZ_ASSERT(mObjects.IsEmpty());
+  }
+
+ public:
+  explicit JSPurpleBuffer(RefPtr<JSPurpleBuffer>& aReferenceToThis)
+      : mReferenceToThis(aReferenceToThis),
+        mValues(kSegmentSize),
+        mObjects(kSegmentSize) {
+    mReferenceToThis = this;
+    mozilla::HoldJSObjects(this);
+  }
+
+  void Destroy() {
+    RefPtr<JSPurpleBuffer> referenceToThis;
+    mReferenceToThis.swap(referenceToThis);
+    mValues.Clear();
+    mObjects.Clear();
+    mozilla::DropJSObjects(this);
+  }
+
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(JSPurpleBuffer)
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_NATIVE_CLASS(JSPurpleBuffer)
+
+  RefPtr<JSPurpleBuffer>& mReferenceToThis;
+
+  // These are raw pointers instead of Heap<T> because we only need Heap<T> for
+  // pointers which may point into the nursery. The purple buffer never contains
+  // pointers to the nursery because nursery gcthings can never be gray and only
+  // gray things can be inserted into the purple buffer.
+  static const size_t kSegmentSize = 512;
+  SegmentedVector<JS::Value, kSegmentSize, InfallibleAllocPolicy> mValues;
+  SegmentedVector<JSObject*, kSegmentSize, InfallibleAllocPolicy> mObjects;
+};
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(JSPurpleBuffer)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(JSPurpleBuffer)
+  tmp->Destroy();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(JSPurpleBuffer)
+  CycleCollectionNoteChild(cb, tmp, "self");
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+#define NS_TRACE_SEGMENTED_ARRAY(_field, _type)                       \
+  {                                                                   \
+    for (auto iter = tmp->_field.Iter(); !iter.Done(); iter.Next()) { \
+      js::gc::CallTraceCallbackOnNonHeap<_type, TraceCallbacks>(      \
+          &iter.Get(), aCallbacks, #_field, aClosure);                \
+    }                                                                 \
+  }
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(JSPurpleBuffer)
+  NS_TRACE_SEGMENTED_ARRAY(mValues, JS::Value)
+  NS_TRACE_SEGMENTED_ARRAY(mObjects, JSObject*)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+class SnowWhiteKiller : public TraceCallbacks {
+  struct SnowWhiteObject {
+    void* mPointer;
+    nsCycleCollectionParticipant* mParticipant;
+    nsCycleCollectingAutoRefCnt* mRefCnt;
+  };
+
+  // Segments are 4 KiB on 32-bit and 8 KiB on 64-bit.
+  static const size_t kSegmentSize = sizeof(void*) * 1024;
+  typedef SegmentedVector<SnowWhiteObject, kSegmentSize, InfallibleAllocPolicy>
+      ObjectsVector;
+
+ public:
+  SnowWhiteKiller(nsCycleCollector* aCollector, js::SliceBudget* aBudget)
+      : mCollector(aCollector),
+        mObjects(kSegmentSize),
+        mBudget(aBudget),
+        mSawSnowWhiteObjects(false) {
+    MOZ_ASSERT(mCollector, "Calling SnowWhiteKiller after nsCC went away");
+  }
+
+  explicit SnowWhiteKiller(nsCycleCollector* aCollector)
+      : SnowWhiteKiller(aCollector, nullptr) {}
+
+  ~SnowWhiteKiller() {
+    for (auto iter = mObjects.Iter(); !iter.Done(); iter.Next()) {
+      SnowWhiteObject& o = iter.Get();
+      MaybeKillObject(o);
+    }
+  }
+
+ private:
+  void MaybeKillObject(SnowWhiteObject& aObject) {
+    if (!aObject.mRefCnt->get() && !aObject.mRefCnt->IsInPurpleBuffer()) {
+      mCollector->RemoveObjectFromGraph(aObject.mPointer);
+      aObject.mRefCnt->stabilizeForDeletion();
+      {
+        JS::AutoEnterCycleCollection autocc(mCollector->Runtime()->Runtime());
+        aObject.mParticipant->Trace(aObject.mPointer, *this, nullptr);
+      }
+      aObject.mParticipant->DeleteCycleCollectable(aObject.mPointer);
+    }
+  }
+
+ public:
+  bool Visit(nsPurpleBuffer& aBuffer, nsPurpleBufferEntry* aEntry) {
+    if (mBudget) {
+      if (mBudget->isOverBudget()) {
+        return false;
+      }
+      mBudget->step();
+    }
+
+    MOZ_ASSERT(aEntry->mObject, "Null object in purple buffer");
+    if (!aEntry->mRefCnt->get()) {
+      mSawSnowWhiteObjects = true;
+      void* o = aEntry->mObject;
+      nsCycleCollectionParticipant* cp = aEntry->mParticipant;
+      ToParticipant(o, &cp);
+      SnowWhiteObject swo = {o, cp, aEntry->mRefCnt};
+      if (!mBudget) {
+        mObjects.InfallibleAppend(swo);
+      }
+      aBuffer.Remove(aEntry);
+      if (mBudget) {
+        MaybeKillObject(swo);
+      }
+    }
+    return true;
+  }
+
+  bool HasSnowWhiteObjects() const { return !mObjects.IsEmpty(); }
+
+  bool SawSnowWhiteObjects() const { return mSawSnowWhiteObjects; }
+
+  virtual void Trace(JS::Heap<JS::Value>* aValue, const char* aName,
+                     void* aClosure) const override {
+    const JS::Value& val = aValue->unbarrieredGet();
+    if (val.isGCThing() && ValueIsGrayCCThing(val)) {
+      MOZ_ASSERT(!js::gc::IsInsideNursery(val.toGCThing()));
+      mCollector->GetJSPurpleBuffer()->mValues.InfallibleAppend(val);
+    }
+  }
+
+  virtual void Trace(JS::Heap<jsid>* aId, const char* aName,
+                     void* aClosure) const override {}
+
+  void AppendJSObjectToPurpleBuffer(JSObject* obj) const {
+    if (obj && JS::ObjectIsMarkedGray(obj)) {
+      MOZ_ASSERT(JS::ObjectIsTenured(obj));
+      mCollector->GetJSPurpleBuffer()->mObjects.InfallibleAppend(obj);
+    }
+  }
+
+  virtual void Trace(JS::Heap<JSObject*>* aObject, const char* aName,
+                     void* aClosure) const override {
+    AppendJSObjectToPurpleBuffer(aObject->unbarrieredGet());
+  }
+
+  virtual void Trace(nsWrapperCache* aWrapperCache, const char* aName,
+                     void* aClosure) const override {
+    AppendJSObjectToPurpleBuffer(aWrapperCache->GetWrapperPreserveColor());
+  }
+
+  virtual void Trace(JS::TenuredHeap<JSObject*>* aObject, const char* aName,
+                     void* aClosure) const override {
+    AppendJSObjectToPurpleBuffer(aObject->unbarrieredGetPtr());
+  }
+
+  virtual void Trace(JS::Heap<JSString*>* aString, const char* aName,
+                     void* aClosure) const override {}
+
+  virtual void Trace(JS::Heap<JSScript*>* aScript, const char* aName,
+                     void* aClosure) const override {}
+
+  virtual void Trace(JS::Heap<JSFunction*>* aFunction, const char* aName,
+                     void* aClosure) const override {}
+
+ private:
+  RefPtr<nsCycleCollector> mCollector;
+  ObjectsVector mObjects;
+  js::SliceBudget* mBudget;
+  bool mSawSnowWhiteObjects;
+};
+
+class RemoveSkippableVisitor : public SnowWhiteKiller {
+ public:
+  RemoveSkippableVisitor(nsCycleCollector* aCollector, js::SliceBudget& aBudget,
+                         bool aRemoveChildlessNodes,
+                         bool aAsyncSnowWhiteFreeing,
+                         CC_ForgetSkippableCallback aCb)
+      : SnowWhiteKiller(aCollector),
+        mBudget(aBudget),
+        mRemoveChildlessNodes(aRemoveChildlessNodes),
+        mAsyncSnowWhiteFreeing(aAsyncSnowWhiteFreeing),
+        mDispatchedDeferredDeletion(false),
+        mCallback(aCb) {}
+
+  ~RemoveSkippableVisitor() {
+    // Note, we must call the callback before SnowWhiteKiller calls
+    // DeleteCycleCollectable!
+    if (mCallback) {
+      mCallback();
+    }
+    if (HasSnowWhiteObjects()) {
+      // Effectively a continuation.
+      nsCycleCollector_dispatchDeferredDeletion(true);
+    }
+  }
+
+  bool Visit(nsPurpleBuffer& aBuffer, nsPurpleBufferEntry* aEntry) {
+    if (mBudget.isOverBudget()) {
+      return false;
+    }
+
+    // CanSkip calls can be a bit slow, so increase the likelihood that
+    // isOverBudget actually checks whether we're over the time budget.
+    mBudget.step(5);
+    MOZ_ASSERT(aEntry->mObject, "null mObject in purple buffer");
+    if (!aEntry->mRefCnt->get()) {
+      if (!mAsyncSnowWhiteFreeing) {
+        SnowWhiteKiller::Visit(aBuffer, aEntry);
+      } else if (!mDispatchedDeferredDeletion) {
+        mDispatchedDeferredDeletion = true;
+        nsCycleCollector_dispatchDeferredDeletion(false);
+      }
+      return true;
+    }
+    void* o = aEntry->mObject;
+    nsCycleCollectionParticipant* cp = aEntry->mParticipant;
+    ToParticipant(o, &cp);
+    if (aEntry->mRefCnt->IsPurple() && !cp->CanSkip(o, false) &&
+        (!mRemoveChildlessNodes || MayHaveChild(o, cp))) {
+      return true;
+    }
+    aBuffer.Remove(aEntry);
+    return true;
+  }
+
+ private:
+  js::SliceBudget& mBudget;
+  bool mRemoveChildlessNodes;
+  bool mAsyncSnowWhiteFreeing;
+  bool mDispatchedDeferredDeletion;
+  CC_ForgetSkippableCallback mCallback;
+};
+
+void nsPurpleBuffer::RemoveSkippable(nsCycleCollector* aCollector,
+                                     js::SliceBudget& aBudget,
+                                     bool aRemoveChildlessNodes,
+                                     bool aAsyncSnowWhiteFreeing,
+                                     CC_ForgetSkippableCallback aCb) {
+  RemoveSkippableVisitor visitor(aCollector, aBudget, aRemoveChildlessNodes,
+                                 aAsyncSnowWhiteFreeing, aCb);
+  VisitEntries(visitor);
+}
+
+bool nsCycleCollector::FreeSnowWhite(bool aUntilNoSWInPurpleBuffer) {
+  CheckThreadSafety();
+
+  if (mFreeingSnowWhite) {
+    return false;
+  }
+
+  AUTO_PROFILER_LABEL_CATEGORY_PAIR(GCCC_FreeSnowWhite);
+
+  AutoRestore<bool> ar(mFreeingSnowWhite);
+  mFreeingSnowWhite = true;
+
+  bool hadSnowWhiteObjects = false;
+  do {
+    SnowWhiteKiller visitor(this);
+    mPurpleBuf.VisitEntries(visitor);
+    hadSnowWhiteObjects = hadSnowWhiteObjects || visitor.HasSnowWhiteObjects();
+    if (!visitor.HasSnowWhiteObjects()) {
+      break;
+    }
+  } while (aUntilNoSWInPurpleBuffer);
+  return hadSnowWhiteObjects;
+}
+
+bool nsCycleCollector::FreeSnowWhiteWithBudget(js::SliceBudget& aBudget) {
+  CheckThreadSafety();
+
+  if (mFreeingSnowWhite) {
+    return false;
+  }
+
+  AUTO_PROFILER_LABEL_CATEGORY_PAIR(GCCC_FreeSnowWhite);
+  AutoRestore<bool> ar(mFreeingSnowWhite);
+  mFreeingSnowWhite = true;
+
+  SnowWhiteKiller visitor(this, &aBudget);
+  mPurpleBuf.VisitEntries(visitor);
+  return visitor.SawSnowWhiteObjects();
+  ;
+}
+
+void nsCycleCollector::ForgetSkippable(js::SliceBudget& aBudget,
+                                       bool aRemoveChildlessNodes,
+                                       bool aAsyncSnowWhiteFreeing) {
+  CheckThreadSafety();
+
+  if (mFreeingSnowWhite) {
+    return;
+  }
+
+  mozilla::Maybe<mozilla::AutoGlobalTimelineMarker> marker;
+  if (NS_IsMainThread()) {
+    marker.emplace("nsCycleCollector::ForgetSkippable",
+                   MarkerStackRequest::NO_STACK);
+  }
+
+  // If we remove things from the purple buffer during graph building, we may
+  // lose track of an object that was mutated during graph building.
+  MOZ_ASSERT(IsIdle());
+
+  if (mCCJSRuntime) {
+    mCCJSRuntime->PrepareForForgetSkippable();
+  }
+  MOZ_ASSERT(
+      !mScanInProgress,
+      "Don't forget skippable or free snow-white while scan is in progress.");
+  mPurpleBuf.RemoveSkippable(this, aBudget, aRemoveChildlessNodes,
+                             aAsyncSnowWhiteFreeing, mForgetSkippableCB);
+}
+
+MOZ_NEVER_INLINE void nsCycleCollector::MarkRoots(SliceBudget& aBudget) {
+  JS::AutoAssertNoGC nogc;
+  TimeLog timeLog;
+  AutoRestore<bool> ar(mScanInProgress);
+  MOZ_RELEASE_ASSERT(!mScanInProgress);
+  mScanInProgress = true;
+  MOZ_ASSERT(mIncrementalPhase == GraphBuildingPhase);
+
+  AUTO_PROFILER_LABEL_CATEGORY_PAIR(GCCC_BuildGraph);
+  JS::AutoEnterCycleCollection autocc(Runtime()->Runtime());
+  bool doneBuilding = mBuilder->BuildGraph(aBudget);
+
+  if (!doneBuilding) {
+    timeLog.Checkpoint("MarkRoots()");
+    return;
+  }
+
+  mBuilder = nullptr;
+  mIncrementalPhase = ScanAndCollectWhitePhase;
+  timeLog.Checkpoint("MarkRoots()");
+}
+
+////////////////////////////////////////////////////////////////////////
+// Bacon & Rajan's |ScanRoots| routine.
+////////////////////////////////////////////////////////////////////////
+
+struct ScanBlackVisitor {
+  ScanBlackVisitor(uint32_t& aWhiteNodeCount, bool& aFailed)
+      : mWhiteNodeCount(aWhiteNodeCount), mFailed(aFailed) {}
+
+  bool ShouldVisitNode(PtrInfo const* aPi) { return aPi->mColor != black; }
+
+  MOZ_NEVER_INLINE void VisitNode(PtrInfo* aPi) {
+    if (aPi->mColor == white) {
+      --mWhiteNodeCount;
+    }
+    aPi->mColor = black;
+  }
+
+  void Failed() { mFailed = true; }
+
+ private:
+  uint32_t& mWhiteNodeCount;
+  bool& mFailed;
+};
+
+static void FloodBlackNode(uint32_t& aWhiteNodeCount, bool& aFailed,
+                           PtrInfo* aPi) {
+  GraphWalker<ScanBlackVisitor>(ScanBlackVisitor(aWhiteNodeCount, aFailed))
+      .Walk(aPi);
+  MOZ_ASSERT(aPi->mColor == black || !aPi->WasTraversed(),
+             "FloodBlackNode should make aPi black");
+}
+
+// Iterate over the WeakMaps.  If we mark anything while iterating
+// over the WeakMaps, we must iterate over all of the WeakMaps again.
+void nsCycleCollector::ScanWeakMaps() {
+  bool anyChanged;
+  bool failed = false;
+  do {
+    anyChanged = false;
+    for (uint32_t i = 0; i < mGraph.mWeakMaps.Length(); i++) {
+      WeakMapping* wm = &mGraph.mWeakMaps[i];
+
+      // If any of these are null, the original object was marked black.
+      uint32_t mColor = wm->mMap ? wm->mMap->mColor : black;
+      uint32_t kColor = wm->mKey ? wm->mKey->mColor : black;
+      uint32_t kdColor = wm->mKeyDelegate ? wm->mKeyDelegate->mColor : black;
+      uint32_t vColor = wm->mVal ? wm->mVal->mColor : black;
+
+      MOZ_ASSERT(mColor != grey, "Uncolored weak map");
+      MOZ_ASSERT(kColor != grey, "Uncolored weak map key");
+      MOZ_ASSERT(kdColor != grey, "Uncolored weak map key delegate");
+      MOZ_ASSERT(vColor != grey, "Uncolored weak map value");
+
+      if (mColor == black && kColor != black && kdColor == black) {
+        FloodBlackNode(mWhiteNodeCount, failed, wm->mKey);
+        anyChanged = true;
+      }
+
+      if (mColor == black && kColor == black && vColor != black) {
+        FloodBlackNode(mWhiteNodeCount, failed, wm->mVal);
+        anyChanged = true;
+      }
+    }
+  } while (anyChanged);
+
+  if (failed) {
+    MOZ_ASSERT(false, "Ran out of memory in ScanWeakMaps");
+    CC_TELEMETRY(_OOM, true);
+  }
+}
+
+// Flood black from any objects in the purple buffer that are in the CC graph.
+class PurpleScanBlackVisitor {
+ public:
+  PurpleScanBlackVisitor(CCGraph& aGraph, nsCycleCollectorLogger* aLogger,
+                         uint32_t& aCount, bool& aFailed)
+      : mGraph(aGraph), mLogger(aLogger), mCount(aCount), mFailed(aFailed) {}
+
+  bool Visit(nsPurpleBuffer& aBuffer, nsPurpleBufferEntry* aEntry) {
+    MOZ_ASSERT(aEntry->mObject,
+               "Entries with null mObject shouldn't be in the purple buffer.");
+    MOZ_ASSERT(aEntry->mRefCnt->get() != 0,
+               "Snow-white objects shouldn't be in the purple buffer.");
+
+    void* obj = aEntry->mObject;
+
+    MOZ_ASSERT(
+        aEntry->mParticipant ||
+            CanonicalizeXPCOMParticipant(static_cast<nsISupports*>(obj)) == obj,
+        "Suspect nsISupports pointer must be canonical");
+
+    PtrInfo* pi = mGraph.FindNode(obj);
+    if (!pi) {
+      return true;
+    }
+    MOZ_ASSERT(pi->mParticipant,
+               "No dead objects should be in the purple buffer.");
+    if (MOZ_UNLIKELY(mLogger)) {
+      mLogger->NoteIncrementalRoot((uint64_t)pi->mPointer);
+    }
+    if (pi->mColor == black) {
+      return true;
+    }
+    FloodBlackNode(mCount, mFailed, pi);
+    return true;
+  }
+
+ private:
+  CCGraph& mGraph;
+  RefPtr<nsCycleCollectorLogger> mLogger;
+  uint32_t& mCount;
+  bool& mFailed;
+};
+
+// Objects that have been stored somewhere since the start of incremental graph
+// building must be treated as live for this cycle collection, because we may
+// not have accurate information about who holds references to them.
+void nsCycleCollector::ScanIncrementalRoots() {
+  TimeLog timeLog;
+
+  // Reference counted objects:
+  // We cleared the purple buffer at the start of the current ICC, so if a
+  // refcounted object is purple, it may have been AddRef'd during the current
+  // ICC. (It may also have only been released.) If that is the case, we cannot
+  // be sure that the set of things pointing to the object in the CC graph
+  // is accurate. Therefore, for safety, we treat any purple objects as being
+  // live during the current CC. We don't remove anything from the purple
+  // buffer here, so these objects will be suspected and freed in the next CC
+  // if they are garbage.
+  bool failed = false;
+  PurpleScanBlackVisitor purpleScanBlackVisitor(mGraph, mLogger,
+                                                mWhiteNodeCount, failed);
+  mPurpleBuf.VisitEntries(purpleScanBlackVisitor);
+  timeLog.Checkpoint("ScanIncrementalRoots::fix purple");
+
+  bool hasJSRuntime = !!mCCJSRuntime;
+  nsCycleCollectionParticipant* jsParticipant =
+      hasJSRuntime ? mCCJSRuntime->GCThingParticipant() : nullptr;
+  nsCycleCollectionParticipant* zoneParticipant =
+      hasJSRuntime ? mCCJSRuntime->ZoneParticipant() : nullptr;
+  bool hasLogger = !!mLogger;
+
+  NodePool::Enumerator etor(mGraph.mNodes);
+  while (!etor.IsDone()) {
+    PtrInfo* pi = etor.GetNext();
+
+    // As an optimization, if an object has already been determined to be live,
+    // don't consider it further.  We can't do this if there is a listener,
+    // because the listener wants to know the complete set of incremental roots.
+    if (pi->mColor == black && MOZ_LIKELY(!hasLogger)) {
+      continue;
+    }
+
+    // Garbage collected objects:
+    // If a GCed object was added to the graph with a refcount of zero, and is
+    // now marked black by the GC, it was probably gray before and was exposed
+    // to active JS, so it may have been stored somewhere, so it needs to be
+    // treated as live.
+    if (pi->IsGrayJS() && MOZ_LIKELY(hasJSRuntime)) {
+      // If the object is still marked gray by the GC, nothing could have gotten
+      // hold of it, so it isn't an incremental root.
+      if (pi->mParticipant == jsParticipant) {
+        JS::GCCellPtr ptr(pi->mPointer, JS::GCThingTraceKind(pi->mPointer));
+        if (GCThingIsGrayCCThing(ptr)) {
+          continue;
+        }
+      } else if (pi->mParticipant == zoneParticipant) {
+        JS::Zone* zone = static_cast<JS::Zone*>(pi->mPointer);
+        if (js::ZoneGlobalsAreAllGray(zone)) {
+          continue;
+        }
+      } else {
+        MOZ_ASSERT(false, "Non-JS thing with 0 refcount? Treating as live.");
+      }
+    } else if (!pi->mParticipant && pi->WasTraversed()) {
+      // Dead traversed refcounted objects:
+      // If the object was traversed, it must have been alive at the start of
+      // the CC, and thus had a positive refcount. It is dead now, so its
+      // refcount must have decreased at some point during the CC. Therefore,
+      // it would be in the purple buffer if it wasn't dead, so treat it as an
+      // incremental root.
+      //
+      // This should not cause leaks because as the object died it should have
+      // released anything it held onto, which will add them to the purple
+      // buffer, which will cause them to be considered in the next CC.
+    } else {
+      continue;
+    }
+
+    // At this point, pi must be an incremental root.
+
+    // If there's a listener, tell it about this root. We don't bother with the
+    // optimization of skipping the Walk() if pi is black: it will just return
+    // without doing anything and there's no need to make this case faster.
+    if (MOZ_UNLIKELY(hasLogger) && pi->mPointer) {
+      // Dead objects aren't logged. See bug 1031370.
+      mLogger->NoteIncrementalRoot((uint64_t)pi->mPointer);
+    }
+
+    FloodBlackNode(mWhiteNodeCount, failed, pi);
+  }
+
+  timeLog.Checkpoint("ScanIncrementalRoots::fix nodes");
+
+  if (failed) {
+    NS_ASSERTION(false, "Ran out of memory in ScanIncrementalRoots");
+    CC_TELEMETRY(_OOM, true);
+  }
+}
+
+// Mark nodes white and make sure their refcounts are ok.
+// No nodes are marked black during this pass to ensure that refcount
+// checking is run on all nodes not marked black by ScanIncrementalRoots.
+void nsCycleCollector::ScanWhiteNodes(bool aFullySynchGraphBuild) {
+  NodePool::Enumerator nodeEnum(mGraph.mNodes);
+  while (!nodeEnum.IsDone()) {
+    PtrInfo* pi = nodeEnum.GetNext();
+    if (pi->mColor == black) {
+      // Incremental roots can be in a nonsensical state, so don't
+      // check them. This will miss checking nodes that are merely
+      // reachable from incremental roots.
+      MOZ_ASSERT(!aFullySynchGraphBuild,
+                 "In a synch CC, no nodes should be marked black early on.");
+      continue;
+    }
+    MOZ_ASSERT(pi->mColor == grey);
+
+    if (!pi->WasTraversed()) {
+      // This node was deleted before it was traversed, so there's no reason
+      // to look at it.
+      MOZ_ASSERT(!pi->mParticipant,
+                 "Live nodes should all have been traversed");
+      continue;
+    }
+
+    if (pi->mInternalRefs == pi->mRefCount || pi->IsGrayJS()) {
+      pi->mColor = white;
+      ++mWhiteNodeCount;
+      continue;
+    }
+
+    pi->AnnotatedReleaseAssert(
+        pi->mInternalRefs <= pi->mRefCount,
+        "More references to an object than its refcount");
+
+    // This node will get marked black in the next pass.
+  }
+}
+
+// Any remaining grey nodes that haven't already been deleted must be alive,
+// so mark them and their children black. Any nodes that are black must have
+// already had their children marked black, so there's no need to look at them
+// again. This pass may turn some white nodes to black.
+void nsCycleCollector::ScanBlackNodes() {
+  bool failed = false;
+  NodePool::Enumerator nodeEnum(mGraph.mNodes);
+  while (!nodeEnum.IsDone()) {
+    PtrInfo* pi = nodeEnum.GetNext();
+    if (pi->mColor == grey && pi->WasTraversed()) {
+      FloodBlackNode(mWhiteNodeCount, failed, pi);
+    }
+  }
+
+  if (failed) {
+    NS_ASSERTION(false, "Ran out of memory in ScanBlackNodes");
+    CC_TELEMETRY(_OOM, true);
+  }
+}
+
+void nsCycleCollector::ScanRoots(bool aFullySynchGraphBuild) {
+  JS::AutoAssertNoGC nogc;
+  AutoRestore<bool> ar(mScanInProgress);
+  MOZ_RELEASE_ASSERT(!mScanInProgress);
+  mScanInProgress = true;
+  mWhiteNodeCount = 0;
+  MOZ_ASSERT(mIncrementalPhase == ScanAndCollectWhitePhase);
+
+  JS::AutoEnterCycleCollection autocc(Runtime()->Runtime());
+
+  if (!aFullySynchGraphBuild) {
+    ScanIncrementalRoots();
+  }
+
+  TimeLog timeLog;
+  ScanWhiteNodes(aFullySynchGraphBuild);
+  timeLog.Checkpoint("ScanRoots::ScanWhiteNodes");
+
+  ScanBlackNodes();
+  timeLog.Checkpoint("ScanRoots::ScanBlackNodes");
+
+  // Scanning weak maps must be done last.
+  ScanWeakMaps();
+  timeLog.Checkpoint("ScanRoots::ScanWeakMaps");
+
+  if (mLogger) {
+    mLogger->BeginResults();
+
+    NodePool::Enumerator etor(mGraph.mNodes);
+    while (!etor.IsDone()) {
+      PtrInfo* pi = etor.GetNext();
+      if (!pi->WasTraversed()) {
+        continue;
+      }
+      switch (pi->mColor) {
+        case black:
+          if (!pi->IsGrayJS() && !pi->IsBlackJS() &&
+              pi->mInternalRefs != pi->mRefCount) {
+            mLogger->DescribeRoot((uint64_t)pi->mPointer, pi->mInternalRefs);
+          }
+          break;
+        case white:
+          mLogger->DescribeGarbage((uint64_t)pi->mPointer);
+          break;
+        case grey:
+          MOZ_ASSERT(false, "All traversed objects should be black or white");
+          break;
+      }
+    }
+
+    mLogger->End();
+    mLogger = nullptr;
+    timeLog.Checkpoint("ScanRoots::listener");
+  }
+}
+
+////////////////////////////////////////////////////////////////////////
+// Bacon & Rajan's |CollectWhite| routine, somewhat modified.
+////////////////////////////////////////////////////////////////////////
+
+bool nsCycleCollector::CollectWhite() {
+  // Explanation of "somewhat modified": we have no way to collect the
+  // set of whites "all at once", we have to ask each of them to drop
+  // their outgoing links and assume this will cause the garbage cycle
+  // to *mostly* self-destruct (except for the reference we continue
+  // to hold).
+  //
+  // To do this "safely" we must make sure that the white nodes we're
+  // operating on are stable for the duration of our operation. So we
+  // make 3 sets of calls to language runtimes:
+  //
+  //   - Root(whites), which should pin the whites in memory.
+  //   - Unlink(whites), which drops outgoing links on each white.
+  //   - Unroot(whites), which returns the whites to normal GC.
+
+  // Segments are 4 KiB on 32-bit and 8 KiB on 64-bit.
+  static const size_t kSegmentSize = sizeof(void*) * 1024;
+  SegmentedVector<PtrInfo*, kSegmentSize, InfallibleAllocPolicy> whiteNodes(
+      kSegmentSize);
+  TimeLog timeLog;
+
+  MOZ_ASSERT(mIncrementalPhase == ScanAndCollectWhitePhase);
+
+  uint32_t numWhiteNodes = 0;
+  uint32_t numWhiteGCed = 0;
+  uint32_t numWhiteJSZones = 0;
+
+  {
+    JS::AutoAssertNoGC nogc;
+    bool hasJSRuntime = !!mCCJSRuntime;
+    nsCycleCollectionParticipant* zoneParticipant =
+        hasJSRuntime ? mCCJSRuntime->ZoneParticipant() : nullptr;
+
+    NodePool::Enumerator etor(mGraph.mNodes);
+    while (!etor.IsDone()) {
+      PtrInfo* pinfo = etor.GetNext();
+      if (pinfo->mColor == white && pinfo->mParticipant) {
+        if (pinfo->IsGrayJS()) {
+          MOZ_ASSERT(mCCJSRuntime);
+          ++numWhiteGCed;
+          JS::Zone* zone;
+          if (MOZ_UNLIKELY(pinfo->mParticipant == zoneParticipant)) {
+            ++numWhiteJSZones;
+            zone = static_cast<JS::Zone*>(pinfo->mPointer);
+          } else {
+            JS::GCCellPtr ptr(pinfo->mPointer,
+                              JS::GCThingTraceKind(pinfo->mPointer));
+            zone = JS::GetTenuredGCThingZone(ptr);
+          }
+          mCCJSRuntime->AddZoneWaitingForGC(zone);
+        } else {
+          whiteNodes.InfallibleAppend(pinfo);
+          pinfo->mParticipant->Root(pinfo->mPointer);
+          ++numWhiteNodes;
+        }
+      }
+    }
+  }
+
+  mResults.mFreedRefCounted += numWhiteNodes;
+  mResults.mFreedGCed += numWhiteGCed;
+  mResults.mFreedJSZones += numWhiteJSZones;
+
+  timeLog.Checkpoint("CollectWhite::Root");
+
+  if (mBeforeUnlinkCB) {
+    mBeforeUnlinkCB();
+    timeLog.Checkpoint("CollectWhite::BeforeUnlinkCB");
+  }
+
+  // Unlink() can trigger a GC, so do not touch any JS or anything
+  // else not in whiteNodes after here.
+
+  for (auto iter = whiteNodes.Iter(); !iter.Done(); iter.Next()) {
+    PtrInfo* pinfo = iter.Get();
+    MOZ_ASSERT(pinfo->mParticipant,
+               "Unlink shouldn't see objects removed from graph.");
+    pinfo->mParticipant->Unlink(pinfo->mPointer);
+#ifdef DEBUG
+    if (mCCJSRuntime) {
+      mCCJSRuntime->AssertNoObjectsToTrace(pinfo->mPointer);
+    }
+#endif
+  }
+  timeLog.Checkpoint("CollectWhite::Unlink");
+
+  JS::AutoAssertNoGC nogc;
+  for (auto iter = whiteNodes.Iter(); !iter.Done(); iter.Next()) {
+    PtrInfo* pinfo = iter.Get();
+    MOZ_ASSERT(pinfo->mParticipant,
+               "Unroot shouldn't see objects removed from graph.");
+    pinfo->mParticipant->Unroot(pinfo->mPointer);
+  }
+  timeLog.Checkpoint("CollectWhite::Unroot");
+
+  nsCycleCollector_dispatchDeferredDeletion(false, true);
+  timeLog.Checkpoint("CollectWhite::dispatchDeferredDeletion");
+
+  mIncrementalPhase = CleanupPhase;
+
+  return numWhiteNodes > 0 || numWhiteGCed > 0 || numWhiteJSZones > 0;
+}
+
+////////////////////////
+// Memory reporting
+////////////////////////
+
+MOZ_DEFINE_MALLOC_SIZE_OF(CycleCollectorMallocSizeOf)
+
+NS_IMETHODIMP
+nsCycleCollector::CollectReports(nsIHandleReportCallback* aHandleReport,
+                                 nsISupports* aData, bool aAnonymize) {
+  size_t objectSize, graphSize, purpleBufferSize;
+  SizeOfIncludingThis(CycleCollectorMallocSizeOf, &objectSize, &graphSize,
+                      &purpleBufferSize);
+
+  if (objectSize > 0) {
+    MOZ_COLLECT_REPORT("explicit/cycle-collector/collector-object", KIND_HEAP,
+                       UNITS_BYTES, objectSize,
+                       "Memory used for the cycle collector object itself.");
+  }
+
+  if (graphSize > 0) {
+    MOZ_COLLECT_REPORT(
+        "explicit/cycle-collector/graph", KIND_HEAP, UNITS_BYTES, graphSize,
+        "Memory used for the cycle collector's graph. This should be zero when "
+        "the collector is idle.");
+  }
+
+  if (purpleBufferSize > 0) {
+    MOZ_COLLECT_REPORT("explicit/cycle-collector/purple-buffer", KIND_HEAP,
+                       UNITS_BYTES, purpleBufferSize,
+                       "Memory used for the cycle collector's purple buffer.");
+  }
+
+  return NS_OK;
+};
+
+////////////////////////////////////////////////////////////////////////
+// Collector implementation
+////////////////////////////////////////////////////////////////////////
+
+nsCycleCollector::nsCycleCollector()
+    : mActivelyCollecting(false),
+      mFreeingSnowWhite(false),
+      mScanInProgress(false),
+      mCCJSRuntime(nullptr),
+      mIncrementalPhase(IdlePhase),
+#ifdef DEBUG
+      mEventTarget(GetCurrentSerialEventTarget()),
+#endif
+      mWhiteNodeCount(0),
+      mBeforeUnlinkCB(nullptr),
+      mForgetSkippableCB(nullptr),
+      mUnmergedNeeded(0),
+      mMergedInARow(0) {
+}
+
+nsCycleCollector::~nsCycleCollector() {
+  MOZ_ASSERT(!mJSPurpleBuffer, "Didn't call JSPurpleBuffer::Destroy?");
+
+  UnregisterWeakMemoryReporter(this);
+}
+
+void nsCycleCollector::SetCCJSRuntime(CycleCollectedJSRuntime* aCCRuntime) {
+  MOZ_RELEASE_ASSERT(
+      !mCCJSRuntime,
+      "Multiple registrations of CycleCollectedJSRuntime in cycle collector");
+  mCCJSRuntime = aCCRuntime;
+
+  if (!NS_IsMainThread()) {
+    return;
+  }
+
+  // We can't register as a reporter in nsCycleCollector() because that runs
+  // before the memory reporter manager is initialized.  So we do it here
+  // instead.
+  RegisterWeakMemoryReporter(this);
+}
+
+void nsCycleCollector::ClearCCJSRuntime() {
+  MOZ_RELEASE_ASSERT(mCCJSRuntime,
+                     "Clearing CycleCollectedJSRuntime in cycle collector "
+                     "before a runtime was registered");
+  mCCJSRuntime = nullptr;
+}
+
+#ifdef DEBUG
+static bool HasParticipant(void* aPtr, nsCycleCollectionParticipant* aParti) {
+  if (aParti) {
+    return true;
+  }
+
+  nsXPCOMCycleCollectionParticipant* xcp;
+  ToParticipant(static_cast<nsISupports*>(aPtr), &xcp);
+  return xcp != nullptr;
+}
+#endif
+
+MOZ_ALWAYS_INLINE void nsCycleCollector::Suspect(
+    void* aPtr, nsCycleCollectionParticipant* aParti,
+    nsCycleCollectingAutoRefCnt* aRefCnt) {
+  CheckThreadSafety();
+
+  // Don't call AddRef or Release of a CCed object in a Traverse() method.
+  MOZ_ASSERT(!mScanInProgress,
+             "Attempted to call Suspect() while a scan was in progress");
+
+  if (MOZ_UNLIKELY(mScanInProgress)) {
+    return;
+  }
+
+  MOZ_ASSERT(aPtr, "Don't suspect null pointers");
+
+  MOZ_ASSERT(HasParticipant(aPtr, aParti),
+             "Suspected nsISupports pointer must QI to "
+             "nsXPCOMCycleCollectionParticipant");
+
+  MOZ_ASSERT(aParti || CanonicalizeXPCOMParticipant(
+                           static_cast<nsISupports*>(aPtr)) == aPtr,
+             "Suspect nsISupports pointer must be canonical");
+
+  mPurpleBuf.Put(aPtr, aParti, aRefCnt);
+}
+
+void nsCycleCollector::SuspectNurseryEntries() {
+  MOZ_ASSERT(NS_IsMainThread(), "Wrong thread!");
+  while (gNurseryPurpleBufferEntryCount) {
+    NurseryPurpleBufferEntry& entry =
+        gNurseryPurpleBufferEntry[--gNurseryPurpleBufferEntryCount];
+    mPurpleBuf.Put(entry.mPtr, entry.mParticipant, entry.mRefCnt);
+  }
+}
+
+void nsCycleCollector::CheckThreadSafety() {
+#ifdef DEBUG
+  MOZ_ASSERT(mEventTarget->IsOnCurrentThread());
+#endif
+}
+
+// The cycle collector uses the mark bitmap to discover what JS objects are
+// reachable only from XPConnect roots that might participate in cycles. We ask
+// the JS runtime whether we need to force a GC before this CC. It should only
+// be true when UnmarkGray has run out of stack. We also force GCs on shutdown
+// to collect cycles involving both DOM and JS, and in WantAllTraces CCs to
+// prevent hijinks from ForgetSkippable and compartmental GCs.
+void nsCycleCollector::FixGrayBits(bool aIsShutdown, TimeLog& aTimeLog) {
+  CheckThreadSafety();
+
+  if (!mCCJSRuntime) {
+    return;
+  }
+
+  // If we're not forcing a GC anyways due to shutdown or an all traces CC,
+  // check to see if we still need to do one to fix the gray bits.
+  if (!(aIsShutdown || (mLogger && mLogger->IsAllTraces()))) {
+    mCCJSRuntime->FixWeakMappingGrayBits();
+    aTimeLog.Checkpoint("FixWeakMappingGrayBits");
+
+    bool needGC = !mCCJSRuntime->AreGCGrayBitsValid();
+    // Only do a telemetry ping for non-shutdown CCs.
+    CC_TELEMETRY(_NEED_GC, needGC);
+    if (!needGC) {
+      return;
+    }
+  }
+
+  mResults.mForcedGC = true;
+
+  uint32_t count = 0;
+  do {
+    if (aIsShutdown) {
+      mCCJSRuntime->GarbageCollect(JS::GCOptions::Shutdown,
+                                   JS::GCReason::SHUTDOWN_CC);
+    } else {
+      mCCJSRuntime->GarbageCollect(JS::GCOptions::Normal,
+                                   JS::GCReason::CC_FORCED);
+    }
+
+    mCCJSRuntime->FixWeakMappingGrayBits();
+
+    // It's possible that FixWeakMappingGrayBits will hit OOM when unmarking
+    // gray and we will have to go round again. The second time there should not
+    // be any weak mappings to fix up so the loop body should run at most twice.
+    MOZ_RELEASE_ASSERT(count < 2);
+    count++;
+  } while (!mCCJSRuntime->AreGCGrayBitsValid());
+
+  aTimeLog.Checkpoint("FixGrayBits");
+}
+
+bool nsCycleCollector::IsIncrementalGCInProgress() {
+  return mCCJSRuntime && JS::IsIncrementalGCInProgress(mCCJSRuntime->Runtime());
+}
+
+void nsCycleCollector::FinishAnyIncrementalGCInProgress() {
+  if (IsIncrementalGCInProgress()) {
+    NS_WARNING("Finishing incremental GC in progress during CC");
+    JSContext* cx = CycleCollectedJSContext::Get()->Context();
+    JS::PrepareForIncrementalGC(cx);
+    JS::FinishIncrementalGC(cx, JS::GCReason::CC_FORCED);
+  }
+}
+
+void nsCycleCollector::CleanupAfterCollection() {
+  TimeLog timeLog;
+  MOZ_ASSERT(mIncrementalPhase == CleanupPhase);
+  MOZ_RELEASE_ASSERT(!mScanInProgress);
+  mGraph.Clear();
+  timeLog.Checkpoint("CleanupAfterCollection::mGraph.Clear()");
+
+  uint32_t interval =
+      (uint32_t)((TimeStamp::Now() - mCollectionStart).ToMilliseconds());
+#ifdef COLLECT_TIME_DEBUG
+  printf("cc: total cycle collector time was %ums in %u slices\n", interval,
+         mResults.mNumSlices);
+  printf(
+      "cc: visited %u ref counted and %u GCed objects, freed %d ref counted "
+      "and %d GCed objects",
+      mResults.mVisitedRefCounted, mResults.mVisitedGCed,
+      mResults.mFreedRefCounted, mResults.mFreedGCed);
+  uint32_t numVisited = mResults.mVisitedRefCounted + mResults.mVisitedGCed;
+  if (numVisited > 1000) {
+    uint32_t numFreed = mResults.mFreedRefCounted + mResults.mFreedGCed;
+    printf(" (%d%%)", 100 * numFreed / numVisited);
+  }
+  printf(".\ncc: \n");
+#endif
+
+  CC_TELEMETRY(, interval);
+  CC_TELEMETRY(_VISITED_REF_COUNTED, mResults.mVisitedRefCounted);
+  CC_TELEMETRY(_VISITED_GCED, mResults.mVisitedGCed);
+  CC_TELEMETRY(_COLLECTED, mWhiteNodeCount);
+  timeLog.Checkpoint("CleanupAfterCollection::telemetry");
+
+  if (mCCJSRuntime) {
+    mCCJSRuntime->FinalizeDeferredThings(
+        mResults.mAnyManual ? CycleCollectedJSRuntime::FinalizeNow
+                            : CycleCollectedJSRuntime::FinalizeIncrementally);
+    mCCJSRuntime->EndCycleCollectionCallback(mResults);
+    timeLog.Checkpoint("CleanupAfterCollection::EndCycleCollectionCallback()");
+  }
+  mIncrementalPhase = IdlePhase;
+}
+
+void nsCycleCollector::ShutdownCollect() {
+  FinishAnyIncrementalGCInProgress();
+  CycleCollectedJSContext* ccJSContext = CycleCollectedJSContext::Get();
+  JS::ShutdownAsyncTasks(ccJSContext->Context());
+
+  SliceBudget unlimitedBudget = SliceBudget::unlimited();
+  uint32_t i;
+  bool collectedAny = true;
+  for (i = 0; i < DEFAULT_SHUTDOWN_COLLECTIONS && collectedAny; ++i) {
+    collectedAny = Collect(CCReason::SHUTDOWN, ccIsManual::CCIsManual,
+                           unlimitedBudget, nullptr);
+    // Run any remaining tasks that may have been enqueued via RunInStableState
+    // or DispatchToMicroTask. These can hold alive CCed objects, and we want to
+    // clear them out before we run the CC again or finish shutting down.
+    ccJSContext->PerformMicroTaskCheckPoint(true);
+    ccJSContext->ProcessStableStateQueue();
+  }
+  NS_WARNING_ASSERTION(i < NORMAL_SHUTDOWN_COLLECTIONS, "Extra shutdown CC");
+}
+
+static void PrintPhase(const char* aPhase) {
+#ifdef DEBUG_PHASES
+  printf("cc: begin %s on %s\n", aPhase,
+         NS_IsMainThread() ? "mainthread" : "worker");
+#endif
+}
+
+bool nsCycleCollector::Collect(CCReason aReason, ccIsManual aIsManual,
+                               SliceBudget& aBudget,
+                               nsICycleCollectorListener* aManualListener,
+                               bool aPreferShorterSlices) {
+  AUTO_PROFILER_LABEL_RELEVANT_FOR_JS("Incremental CC", GCCC);
+
+  CheckThreadSafety();
+
+  // This can legitimately happen in a few cases. See bug 383651.
+  if (mActivelyCollecting || mFreeingSnowWhite) {
+    return false;
+  }
+  mActivelyCollecting = true;
+
+  MOZ_ASSERT(!IsIncrementalGCInProgress());
+
+  mozilla::Maybe<mozilla::AutoGlobalTimelineMarker> marker;
+  if (NS_IsMainThread()) {
+    marker.emplace("nsCycleCollector::Collect", MarkerStackRequest::NO_STACK);
+  }
+
+  bool startedIdle = IsIdle();
+  bool collectedAny = false;
+
+  // If the CC started idle, it will call BeginCollection, which
+  // will do FreeSnowWhite, so it doesn't need to be done here.
+  if (!startedIdle) {
+    TimeLog timeLog;
+    FreeSnowWhite(true);
+    timeLog.Checkpoint("Collect::FreeSnowWhite");
+  }
+
+  if (aIsManual == ccIsManual::CCIsManual) {
+    mResults.mAnyManual = true;
+  }
+
+  ++mResults.mNumSlices;
+
+  bool continueSlice = aBudget.isUnlimited() || !aPreferShorterSlices;
+  do {
+    switch (mIncrementalPhase) {
+      case IdlePhase:
+        PrintPhase("BeginCollection");
+        BeginCollection(aReason, aIsManual, aManualListener);
+        break;
+      case GraphBuildingPhase:
+        PrintPhase("MarkRoots");
+        MarkRoots(aBudget);
+
+        // Only continue this slice if we're running synchronously or the
+        // next phase will probably be short, to reduce the max pause for this
+        // collection.
+        // (There's no need to check if we've finished graph building, because
+        // if we haven't, we've already exceeded our budget, and will finish
+        // this slice anyways.)
+        continueSlice = aBudget.isUnlimited() ||
+                        (mResults.mNumSlices < 3 && !aPreferShorterSlices);
+        break;
+      case ScanAndCollectWhitePhase:
+        // We do ScanRoots and CollectWhite in a single slice to ensure
+        // that we won't unlink a live object if a weak reference is
+        // promoted to a strong reference after ScanRoots has finished.
+        // See bug 926533.
+        {
+          AUTO_PROFILER_LABEL_CATEGORY_PAIR(GCCC_ScanRoots);
+          PrintPhase("ScanRoots");
+          ScanRoots(startedIdle);
+        }
+        {
+          AUTO_PROFILER_LABEL_CATEGORY_PAIR(GCCC_CollectWhite);
+          PrintPhase("CollectWhite");
+          collectedAny = CollectWhite();
+        }
+        break;
+      case CleanupPhase:
+        PrintPhase("CleanupAfterCollection");
+        CleanupAfterCollection();
+        continueSlice = false;
+        break;
+    }
+    if (continueSlice) {
+      aBudget.stepAndForceCheck();
+      continueSlice = !aBudget.isOverBudget();
+    }
+  } while (continueSlice);
+
+  // Clear mActivelyCollecting here to ensure that a recursive call to
+  // Collect() does something.
+  mActivelyCollecting = false;
+
+  if (aIsManual && !startedIdle) {
+    // We were in the middle of an incremental CC (using its own listener).
+    // Somebody has forced a CC, so after having finished out the current CC,
+    // run the CC again using the new listener.
+    MOZ_ASSERT(IsIdle());
+    if (Collect(aReason, ccIsManual::CCIsManual, aBudget, aManualListener)) {
+      collectedAny = true;
+    }
+  }
+
+  MOZ_ASSERT_IF(aIsManual == CCIsManual, IsIdle());
+
+  return collectedAny;
+}
+
+// Any JS objects we have in the graph could die when we GC, but we
+// don't want to abandon the current CC, because the graph contains
+// information about purple roots. So we synchronously finish off
+// the current CC.
+void nsCycleCollector::PrepareForGarbageCollection() {
+  if (IsIdle()) {
+    MOZ_ASSERT(mGraph.IsEmpty(), "Non-empty graph when idle");
+    MOZ_ASSERT(!mBuilder, "Non-null builder when idle");
+    if (mJSPurpleBuffer) {
+      mJSPurpleBuffer->Destroy();
+    }
+    return;
+  }
+
+  FinishAnyCurrentCollection(CCReason::GC_WAITING);
+}
+
+void nsCycleCollector::FinishAnyCurrentCollection(CCReason aReason) {
+  if (IsIdle()) {
+    return;
+  }
+
+  SliceBudget unlimitedBudget = SliceBudget::unlimited();
+  PrintPhase("FinishAnyCurrentCollection");
+  // Use CCIsNotManual because we only want to finish the CC in progress.
+  Collect(aReason, ccIsManual::CCIsNotManual, unlimitedBudget, nullptr);
+
+  // It is only okay for Collect() to have failed to finish the
+  // current CC if we're reentering the CC at some point past
+  // graph building. We need to be past the point where the CC will
+  // look at JS objects so that it is safe to GC.
+  MOZ_ASSERT(IsIdle() || (mActivelyCollecting &&
+                          mIncrementalPhase != GraphBuildingPhase),
+             "Reentered CC during graph building");
+}
+
+// Don't merge too many times in a row, and do at least a minimum
+// number of unmerged CCs in a row.
+static const uint32_t kMinConsecutiveUnmerged = 3;
+static const uint32_t kMaxConsecutiveMerged = 3;
+
+bool nsCycleCollector::ShouldMergeZones(ccIsManual aIsManual) {
+  if (!mCCJSRuntime) {
+    return false;
+  }
+
+  MOZ_ASSERT(mUnmergedNeeded <= kMinConsecutiveUnmerged);
+  MOZ_ASSERT(mMergedInARow <= kMaxConsecutiveMerged);
+
+  if (mMergedInARow == kMaxConsecutiveMerged) {
+    MOZ_ASSERT(mUnmergedNeeded == 0);
+    mUnmergedNeeded = kMinConsecutiveUnmerged;
+  }
+
+  if (mUnmergedNeeded > 0) {
+    mUnmergedNeeded--;
+    mMergedInARow = 0;
+    return false;
+  }
+
+  if (aIsManual == CCIsNotManual && mCCJSRuntime->UsefulToMergeZones()) {
+    mMergedInARow++;
+    return true;
+  } else {
+    mMergedInARow = 0;
+    return false;
+  }
+}
+
+void nsCycleCollector::BeginCollection(
+    CCReason aReason, ccIsManual aIsManual,
+    nsICycleCollectorListener* aManualListener) {
+  TimeLog timeLog;
+  MOZ_ASSERT(IsIdle());
+  MOZ_RELEASE_ASSERT(!mScanInProgress);
+
+  mCollectionStart = TimeStamp::Now();
+
+  if (mCCJSRuntime) {
+    mCCJSRuntime->BeginCycleCollectionCallback(aReason);
+    timeLog.Checkpoint("BeginCycleCollectionCallback()");
+  }
+
+  bool isShutdown = (aReason == CCReason::SHUTDOWN);
+  if (isShutdown) {
+    mShutdownCount += 1;
+  }
+
+  // Set up the listener for this CC.
+  MOZ_ASSERT_IF(isShutdown, !aManualListener);
+  MOZ_ASSERT(!mLogger, "Forgot to clear a previous listener?");
+
+  if (aManualListener) {
+    aManualListener->AsLogger(getter_AddRefs(mLogger));
+  }
+
+  aManualListener = nullptr;
+  if (!mLogger && mParams.LogThisCC(mShutdownCount)) {
+    mLogger = new nsCycleCollectorLogger();
+    if (mParams.AllTracesThisCC(isShutdown)) {
+      mLogger->SetAllTraces();
+    }
+  }
+
+  // BeginCycleCollectionCallback() might have started an IGC, and we need
+  // to finish it before we run FixGrayBits.
+  FinishAnyIncrementalGCInProgress();
+  timeLog.Checkpoint("Pre-FixGrayBits finish IGC");
+
+  FixGrayBits(isShutdown, timeLog);
+  if (mCCJSRuntime) {
+    mCCJSRuntime->CheckGrayBits();
+  }
+
+  FreeSnowWhite(true);
+  timeLog.Checkpoint("BeginCollection FreeSnowWhite");
+
+  if (mLogger && NS_FAILED(mLogger->Begin())) {
+    mLogger = nullptr;
+  }
+
+  // FreeSnowWhite could potentially have started an IGC, which we need
+  // to finish before we look at any JS roots.
+  FinishAnyIncrementalGCInProgress();
+  timeLog.Checkpoint("Post-FreeSnowWhite finish IGC");
+
+  // Set up the data structures for building the graph.
+  JS::AutoAssertNoGC nogc;
+  JS::AutoEnterCycleCollection autocc(mCCJSRuntime->Runtime());
+  mGraph.Init();
+  mResults.Init();
+  mResults.mSuspectedAtCCStart = SuspectedCount();
+  mResults.mAnyManual = aIsManual;
+  bool mergeZones = ShouldMergeZones(aIsManual);
+  mResults.mMergedZones = mergeZones;
+
+  MOZ_ASSERT(!mBuilder, "Forgot to clear mBuilder");
+  mBuilder = MakeUnique<CCGraphBuilder>(mGraph, mResults, mCCJSRuntime, mLogger,
+                                        mergeZones);
+  timeLog.Checkpoint("BeginCollection prepare graph builder");
+
+  if (mCCJSRuntime) {
+    mCCJSRuntime->TraverseRoots(*mBuilder);
+    timeLog.Checkpoint("mJSContext->TraverseRoots()");
+  }
+
+  AutoRestore<bool> ar(mScanInProgress);
+  MOZ_RELEASE_ASSERT(!mScanInProgress);
+  mScanInProgress = true;
+  mPurpleBuf.SelectPointers(*mBuilder);
+  timeLog.Checkpoint("SelectPointers()");
+
+  mBuilder->DoneAddingRoots();
+  mIncrementalPhase = GraphBuildingPhase;
+}
+
+uint32_t nsCycleCollector::SuspectedCount() {
+  CheckThreadSafety();
+  if (NS_IsMainThread()) {
+    return gNurseryPurpleBufferEntryCount + mPurpleBuf.Count();
+  }
+
+  return mPurpleBuf.Count();
+}
+
+void nsCycleCollector::Shutdown(bool aDoCollect) {
+  CheckThreadSafety();
+
+  if (NS_IsMainThread()) {
+    gNurseryPurpleBufferEnabled = false;
+  }
+
+  // Always delete snow white objects.
+  FreeSnowWhite(true);
+
+  if (aDoCollect) {
+    ShutdownCollect();
+  }
+
+  if (mJSPurpleBuffer) {
+    mJSPurpleBuffer->Destroy();
+  }
+}
+
+void nsCycleCollector::RemoveObjectFromGraph(void* aObj) {
+  if (IsIdle()) {
+    return;
+  }
+
+  mGraph.RemoveObjectFromMap(aObj);
+  if (mBuilder) {
+    mBuilder->RemoveCachedEntry(aObj);
+  }
+}
+
+void nsCycleCollector::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf,
+                                           size_t* aObjectSize,
+                                           size_t* aGraphSize,
+                                           size_t* aPurpleBufferSize) const {
+  *aObjectSize = aMallocSizeOf(this);
+
+  *aGraphSize = mGraph.SizeOfExcludingThis(aMallocSizeOf);
+
+  *aPurpleBufferSize = mPurpleBuf.SizeOfExcludingThis(aMallocSizeOf);
+
+  // These fields are deliberately not measured:
+  // - mCCJSRuntime: because it's non-owning and measured by JS reporters.
+  // - mParams: because it only contains scalars.
+}
+
+JSPurpleBuffer* nsCycleCollector::GetJSPurpleBuffer() {
+  if (!mJSPurpleBuffer) {
+    // The Release call here confuses the GC analysis.
+    JS::AutoSuppressGCAnalysis nogc;
+    // JSPurpleBuffer keeps itself alive, but we need to create it in such way
+    // that it ends up in the normal purple buffer. That happens when
+    // nsRefPtr goes out of the scope and calls Release.
+    RefPtr<JSPurpleBuffer> pb = new JSPurpleBuffer(mJSPurpleBuffer);
+  }
+  return mJSPurpleBuffer;
+}
+
+////////////////////////////////////////////////////////////////////////
+// Module public API (exported in nsCycleCollector.h)
+// Just functions that redirect into the singleton, once it's built.
+////////////////////////////////////////////////////////////////////////
+
+void nsCycleCollector_registerJSContext(CycleCollectedJSContext* aCx) {
+  CollectorData* data = sCollectorData.get();
+
+  // We should have started the cycle collector by now.
+  MOZ_ASSERT(data);
+  MOZ_ASSERT(data->mCollector);
+  // But we shouldn't already have a context.
+  MOZ_ASSERT(!data->mContext);
+
+  data->mContext = aCx;
+  data->mCollector->SetCCJSRuntime(aCx->Runtime());
+}
+
+void nsCycleCollector_forgetJSContext() {
+  CollectorData* data = sCollectorData.get();
+
+  // We should have started the cycle collector by now.
+  MOZ_ASSERT(data);
+  // And we shouldn't have already forgotten our context.
+  MOZ_ASSERT(data->mContext);
+
+  // But it may have shutdown already.
+  if (data->mCollector) {
+    data->mCollector->ClearCCJSRuntime();
+    data->mContext = nullptr;
+  } else {
+    data->mContext = nullptr;
+    delete data;
+    sCollectorData.set(nullptr);
+  }
+}
+
+/* static */
+CycleCollectedJSContext* CycleCollectedJSContext::Get() {
+  CollectorData* data = sCollectorData.get();
+  if (data) {
+    return data->mContext;
+  }
+  return nullptr;
+}
+
+MOZ_NEVER_INLINE static void SuspectAfterShutdown(
+    void* aPtr, nsCycleCollectionParticipant* aCp,
+    nsCycleCollectingAutoRefCnt* aRefCnt, bool* aShouldDelete) {
+  if (aRefCnt->get() == 0) {
+    if (!aShouldDelete) {
+      // The CC is shut down, so we can't be in the middle of an ICC.
+      ToParticipant(aPtr, &aCp);
+      aRefCnt->stabilizeForDeletion();
+      aCp->DeleteCycleCollectable(aPtr);
+    } else {
+      *aShouldDelete = true;
+    }
+  } else {
+    // Make sure we'll get called again.
+    aRefCnt->RemoveFromPurpleBuffer();
+  }
+}
+
+void NS_CycleCollectorSuspect3(void* aPtr, nsCycleCollectionParticipant* aCp,
+                               nsCycleCollectingAutoRefCnt* aRefCnt,
+                               bool* aShouldDelete) {
+  CollectorData* data = sCollectorData.get();
+
+  // This assertion will happen if you AddRef or Release a cycle collected
+  // object on a thread that does not have an active cycle collector.
+  // This can happen in a few situations:
+  // 1. We never cycle collect on this thread. (The cycle collector is only
+  // run on the main thread and DOM worker threads.)
+  // 2. The cycle collector hasn't been initialized on this thread yet.
+  // 3. The cycle collector has already been shut down on this thread.
+  MOZ_DIAGNOSTIC_ASSERT(
+      data,
+      "Cycle collected object used on a thread without a cycle collector.");
+
+  if (MOZ_LIKELY(data->mCollector)) {
+    data->mCollector->Suspect(aPtr, aCp, aRefCnt);
+    return;
+  }
+  SuspectAfterShutdown(aPtr, aCp, aRefCnt, aShouldDelete);
+}
+
+void ClearNurseryPurpleBuffer() {
+  MOZ_ASSERT(NS_IsMainThread(), "Wrong thread!");
+  CollectorData* data = sCollectorData.get();
+  MOZ_ASSERT(data);
+  MOZ_ASSERT(data->mCollector);
+  data->mCollector->SuspectNurseryEntries();
+}
+
+void NS_CycleCollectorSuspectUsingNursery(void* aPtr,
+                                          nsCycleCollectionParticipant* aCp,
+                                          nsCycleCollectingAutoRefCnt* aRefCnt,
+                                          bool* aShouldDelete) {
+  MOZ_ASSERT(NS_IsMainThread(), "Wrong thread!");
+  if (!gNurseryPurpleBufferEnabled) {
+    NS_CycleCollectorSuspect3(aPtr, aCp, aRefCnt, aShouldDelete);
+    return;
+  }
+
+  SuspectUsingNurseryPurpleBuffer(aPtr, aCp, aRefCnt);
+}
+
+uint32_t nsCycleCollector_suspectedCount() {
+  CollectorData* data = sCollectorData.get();
+
+  // We should have started the cycle collector by now.
+  MOZ_ASSERT(data);
+
+  if (!data->mCollector) {
+    return 0;
+  }
+
+  return data->mCollector->SuspectedCount();
+}
+
+bool nsCycleCollector_init() {
+#ifdef DEBUG
+  static bool sInitialized;
+
+  MOZ_ASSERT(NS_IsMainThread(), "Wrong thread!");
+  MOZ_ASSERT(!sInitialized, "Called twice!?");
+  sInitialized = true;
+#endif
+
+  return sCollectorData.init();
+}
+
+void nsCycleCollector_startup() {
+  if (sCollectorData.get()) {
+    MOZ_CRASH();
+  }
+
+  CollectorData* data = new CollectorData;
+  data->mCollector = new nsCycleCollector();
+  data->mContext = nullptr;
+
+  sCollectorData.set(data);
+}
+
+void nsCycleCollector_setBeforeUnlinkCallback(CC_BeforeUnlinkCallback aCB) {
+  CollectorData* data = sCollectorData.get();
+
+  // We should have started the cycle collector by now.
+  MOZ_ASSERT(data);
+  MOZ_ASSERT(data->mCollector);
+
+  data->mCollector->SetBeforeUnlinkCallback(aCB);
+}
+
+void nsCycleCollector_setForgetSkippableCallback(
+    CC_ForgetSkippableCallback aCB) {
+  CollectorData* data = sCollectorData.get();
+
+  // We should have started the cycle collector by now.
+  MOZ_ASSERT(data);
+  MOZ_ASSERT(data->mCollector);
+
+  data->mCollector->SetForgetSkippableCallback(aCB);
+}
+
+void nsCycleCollector_forgetSkippable(js::SliceBudget& aBudget,
+                                      bool aRemoveChildlessNodes,
+                                      bool aAsyncSnowWhiteFreeing) {
+  CollectorData* data = sCollectorData.get();
+
+  // We should have started the cycle collector by now.
+  MOZ_ASSERT(data);
+  MOZ_ASSERT(data->mCollector);
+
+  TimeLog timeLog;
+  data->mCollector->ForgetSkippable(aBudget, aRemoveChildlessNodes,
+                                    aAsyncSnowWhiteFreeing);
+  timeLog.Checkpoint("ForgetSkippable()");
+}
+
+void nsCycleCollector_dispatchDeferredDeletion(bool aContinuation,
+                                               bool aPurge) {
+  CycleCollectedJSRuntime* rt = CycleCollectedJSRuntime::Get();
+  if (rt) {
+    rt->DispatchDeferredDeletion(aContinuation, aPurge);
+  }
+}
+
+bool nsCycleCollector_doDeferredDeletion() {
+  CollectorData* data = sCollectorData.get();
+
+  // We should have started the cycle collector by now.
+  MOZ_ASSERT(data);
+  MOZ_ASSERT(data->mCollector);
+  MOZ_ASSERT(data->mContext);
+
+  return data->mCollector->FreeSnowWhite(false);
+}
+
+bool nsCycleCollector_doDeferredDeletionWithBudget(js::SliceBudget& aBudget) {
+  CollectorData* data = sCollectorData.get();
+
+  // We should have started the cycle collector by now.
+  MOZ_ASSERT(data);
+  MOZ_ASSERT(data->mCollector);
+  MOZ_ASSERT(data->mContext);
+
+  return data->mCollector->FreeSnowWhiteWithBudget(aBudget);
+}
+
+already_AddRefed<nsICycleCollectorLogSink> nsCycleCollector_createLogSink() {
+  nsCOMPtr<nsICycleCollectorLogSink> sink = new nsCycleCollectorLogSinkToFile();
+  return sink.forget();
+}
+
+bool nsCycleCollector_collect(CCReason aReason,
+                              nsICycleCollectorListener* aManualListener) {
+  CollectorData* data = sCollectorData.get();
+
+  // We should have started the cycle collector by now.
+  MOZ_ASSERT(data);
+  MOZ_ASSERT(data->mCollector);
+
+  AUTO_PROFILER_LABEL("nsCycleCollector_collect", GCCC);
+
+  SliceBudget unlimitedBudget = SliceBudget::unlimited();
+  return data->mCollector->Collect(aReason, ccIsManual::CCIsManual,
+                                   unlimitedBudget, aManualListener);
+}
+
+void nsCycleCollector_collectSlice(SliceBudget& budget, CCReason aReason,
+                                   bool aPreferShorterSlices) {
+  CollectorData* data = sCollectorData.get();
+
+  // We should have started the cycle collector by now.
+  MOZ_ASSERT(data);
+  MOZ_ASSERT(data->mCollector);
+
+  AUTO_PROFILER_LABEL("nsCycleCollector_collectSlice", GCCC);
+
+  data->mCollector->Collect(aReason, ccIsManual::CCIsNotManual, budget, nullptr,
+                            aPreferShorterSlices);
+}
+
+void nsCycleCollector_prepareForGarbageCollection() {
+  CollectorData* data = sCollectorData.get();
+
+  MOZ_ASSERT(data);
+
+  if (!data->mCollector) {
+    return;
+  }
+
+  data->mCollector->PrepareForGarbageCollection();
+}
+
+void nsCycleCollector_finishAnyCurrentCollection() {
+  CollectorData* data = sCollectorData.get();
+
+  MOZ_ASSERT(data);
+
+  if (!data->mCollector) {
+    return;
+  }
+
+  data->mCollector->FinishAnyCurrentCollection(CCReason::API);
+}
+
+void nsCycleCollector_shutdown(bool aDoCollect) {
+  CollectorData* data = sCollectorData.get();
+
+  if (data) {
+    MOZ_ASSERT(data->mCollector);
+    AUTO_PROFILER_LABEL("nsCycleCollector_shutdown", OTHER);
+
+    {
+      RefPtr<nsCycleCollector> collector = data->mCollector;
+      collector->Shutdown(aDoCollect);
+      data->mCollector = nullptr;
+    }
+
+    if (!data->mContext) {
+      delete data;
+      sCollectorData.set(nullptr);
+    }
+  }
+}
diff --git a/xpcom/base/nsCycleCollector.h b/xpcom/base/nsCycleCollector.h
new file mode 100644
index 0000000000..1c583e04cf
--- /dev/null
+++ b/xpcom/base/nsCycleCollector.h
@@ -0,0 +1,74 @@
+/* -*- 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/. */
+
+#ifndef nsCycleCollector_h__
+#define nsCycleCollector_h__
+
+class nsICycleCollectorListener;
+class nsICycleCollectorLogSink;
+class nsISupports;
+template <class T>
+struct already_AddRefed;
+
+#include <cstdint>
+#include "mozilla/Attributes.h"
+
+namespace js {
+class SliceBudget;
+}
+
+namespace mozilla {
+class CycleCollectedJSContext;
+}  // namespace mozilla
+
+bool nsCycleCollector_init();
+
+void nsCycleCollector_startup();
+
+typedef void (*CC_BeforeUnlinkCallback)(void);
+void nsCycleCollector_setBeforeUnlinkCallback(CC_BeforeUnlinkCallback aCB);
+
+typedef void (*CC_ForgetSkippableCallback)(void);
+void nsCycleCollector_setForgetSkippableCallback(
+    CC_ForgetSkippableCallback aCB);
+
+void nsCycleCollector_forgetSkippable(js::SliceBudget& aBudget,
+                                      bool aRemoveChildlessNodes = false,
+                                      bool aAsyncSnowWhiteFreeing = false);
+
+void nsCycleCollector_prepareForGarbageCollection();
+
+// If an incremental cycle collection is in progress, finish it.
+void nsCycleCollector_finishAnyCurrentCollection();
+
+void nsCycleCollector_dispatchDeferredDeletion(bool aContinuation = false,
+                                               bool aPurge = false);
+bool nsCycleCollector_doDeferredDeletion();
+bool nsCycleCollector_doDeferredDeletionWithBudget(js::SliceBudget& aBudget);
+
+already_AddRefed<nsICycleCollectorLogSink> nsCycleCollector_createLogSink();
+already_AddRefed<nsICycleCollectorListener> nsCycleCollector_createLogger();
+
+// Run a cycle collection and return whether anything was collected.
+bool nsCycleCollector_collect(mozilla::CCReason aReason,
+                              nsICycleCollectorListener* aManualListener);
+
+void nsCycleCollector_collectSlice(js::SliceBudget& budget,
+                                   mozilla::CCReason aReason,
+                                   bool aPreferShorterSlices = false);
+
+uint32_t nsCycleCollector_suspectedCount();
+
+// If aDoCollect is true, then run the GC and CC a few times before
+// shutting down the CC completely.
+MOZ_CAN_RUN_SCRIPT
+void nsCycleCollector_shutdown(bool aDoCollect = true);
+
+// Helpers for interacting with JS
+void nsCycleCollector_registerJSContext(mozilla::CycleCollectedJSContext* aCx);
+void nsCycleCollector_forgetJSContext();
+
+#endif  // nsCycleCollector_h__
diff --git a/xpcom/base/nsCycleCollectorTraceJSHelpers.cpp b/xpcom/base/nsCycleCollectorTraceJSHelpers.cpp
new file mode 100644
index 0000000000..02bc92ddab
--- /dev/null
+++ b/xpcom/base/nsCycleCollectorTraceJSHelpers.cpp
@@ -0,0 +1,89 @@
+/* -*- 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 "nsCycleCollectionParticipant.h"
+#include "nsString.h"
+#include "nsWrapperCacheInlines.h"
+#include "jsapi.h"
+#include "jsfriendapi.h"
+
+void CycleCollectionNoteEdgeNameImpl(
+    nsCycleCollectionTraversalCallback& aCallback, const char* aName,
+    uint32_t aFlags) {
+  nsAutoCString arrayEdgeName(aName);
+  if (aFlags & CycleCollectionEdgeNameArrayFlag) {
+    arrayEdgeName.AppendLiteral("[i]");
+  }
+  aCallback.NoteNextEdgeName(arrayEdgeName.get());
+}
+
+void nsCycleCollectionParticipant::NoteJSChild(JS::GCCellPtr aGCThing,
+                                               const char* aName,
+                                               void* aClosure) {
+  nsCycleCollectionTraversalCallback* cb =
+      static_cast<nsCycleCollectionTraversalCallback*>(aClosure);
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(*cb, aName);
+  if (JS::IsCCTraceKind(aGCThing.kind())) {
+    cb->NoteJSChild(aGCThing);
+  }
+}
+
+void TraceCallbackFunc::Trace(JS::Heap<JS::Value>* aPtr, const char* aName,
+                              void* aClosure) const {
+  if (aPtr->unbarrieredGet().isGCThing()) {
+    mCallback(aPtr->unbarrieredGet().toGCCellPtr(), aName, aClosure);
+  }
+}
+
+void TraceCallbackFunc::Trace(JS::Heap<jsid>* aPtr, const char* aName,
+                              void* aClosure) const {
+  if (aPtr->unbarrieredGet().isGCThing()) {
+    mCallback(aPtr->unbarrieredGet().toGCCellPtr(), aName, aClosure);
+  }
+}
+
+void TraceCallbackFunc::Trace(JS::Heap<JSObject*>* aPtr, const char* aName,
+                              void* aClosure) const {
+  if (*aPtr) {
+    mCallback(JS::GCCellPtr(aPtr->unbarrieredGet()), aName, aClosure);
+  }
+}
+
+void TraceCallbackFunc::Trace(nsWrapperCache* aPtr, const char* aName,
+                              void* aClosure) const {
+  JSObject* obj = aPtr->GetWrapperPreserveColor();
+  if (obj) {
+    mCallback(JS::GCCellPtr(obj), aName, aClosure);
+  }
+}
+
+void TraceCallbackFunc::Trace(JS::TenuredHeap<JSObject*>* aPtr,
+                              const char* aName, void* aClosure) const {
+  if (*aPtr) {
+    mCallback(JS::GCCellPtr(aPtr->unbarrieredGetPtr()), aName, aClosure);
+  }
+}
+
+void TraceCallbackFunc::Trace(JS::Heap<JSFunction*>* aPtr, const char* aName,
+                              void* aClosure) const {
+  if (*aPtr) {
+    mCallback(JS::GCCellPtr(aPtr->unbarrieredGet()), aName, aClosure);
+  }
+}
+
+void TraceCallbackFunc::Trace(JS::Heap<JSString*>* aPtr, const char* aName,
+                              void* aClosure) const {
+  if (*aPtr) {
+    mCallback(JS::GCCellPtr(aPtr->unbarrieredGet()), aName, aClosure);
+  }
+}
+
+void TraceCallbackFunc::Trace(JS::Heap<JSScript*>* aPtr, const char* aName,
+                              void* aClosure) const {
+  if (*aPtr) {
+    mCallback(JS::GCCellPtr(aPtr->unbarrieredGet()), aName, aClosure);
+  }
+}
diff --git a/xpcom/base/nsDebug.h b/xpcom/base/nsDebug.h
new file mode 100644
index 0000000000..349c297ea8
--- /dev/null
+++ b/xpcom/base/nsDebug.h
@@ -0,0 +1,384 @@
+/* -*- 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/. */
+
+#ifndef nsDebug_h___
+#define nsDebug_h___
+
+#include "nscore.h"
+#include "nsError.h"
+
+#include "nsXPCOM.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/DbgMacro.h"
+#include "mozilla/Likely.h"
+#include <stdarg.h>
+
+#ifdef DEBUG
+#  include "mozilla/ErrorNames.h"
+#  include "mozilla/IntegerPrintfMacros.h"
+#  include "mozilla/Printf.h"
+#endif
+
+/**
+ * Warn if the given condition is true. The condition is evaluated in both
+ * release and debug builds, and the result is an expression which can be
+ * used in subsequent expressions, such as:
+ *
+ * if (NS_WARN_IF(NS_FAILED(rv)) {
+ *   return rv;
+ * }
+ *
+ * This explicit warning and return is preferred to the NS_ENSURE_* macros
+ * which hide the warning and the return control flow.
+ *
+ * This macro can also be used outside of conditions just to issue a warning,
+ * like so:
+ *
+ *   Unused << NS_WARN_IF(NS_FAILED(FnWithSideEffects());
+ *
+ * (The |Unused <<| is necessary because of the [[nodiscard]] annotation.)
+ *
+ * However, note that the argument to this macro is evaluated in all builds. If
+ * you just want a warning assertion, it is better to use NS_WARNING_ASSERTION
+ * (which evaluates the condition only in debug builds) like so:
+ *
+ *   NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "operation failed");
+ *
+ * @note This is C++-only
+ */
+#ifdef __cplusplus
+#  ifdef DEBUG
+[[nodiscard]] inline bool NS_warn_if_impl(bool aCondition, const char* aExpr,
+                                          const char* aFile, int32_t aLine) {
+  if (MOZ_UNLIKELY(aCondition)) {
+    NS_DebugBreak(NS_DEBUG_WARNING, nullptr, aExpr, aFile, aLine);
+  }
+  return aCondition;
+}
+#    define NS_WARN_IF(condition) \
+      NS_warn_if_impl(condition, #condition, __FILE__, __LINE__)
+#  else
+#    define NS_WARN_IF(condition) (bool)(condition)
+#  endif
+#endif
+
+/**
+ * Test an assertion for truth. If the expression is not true then
+ * emit a warning.
+ *
+ * Program execution continues past the usage of this macro.
+ *
+ * Note also that the non-debug version of this macro does <b>not</b>
+ * evaluate the message argument.
+ */
+#ifdef DEBUG
+#  define NS_WARNING_ASSERTION(_expr, _msg)                                \
+    do {                                                                   \
+      if (!(_expr)) {                                                      \
+        NS_DebugBreak(NS_DEBUG_WARNING, _msg, #_expr, __FILE__, __LINE__); \
+      }                                                                    \
+    } while (false)
+#else
+#  define NS_WARNING_ASSERTION(_expr, _msg) \
+    do { /* nothing */                      \
+    } while (false)
+#endif
+
+/**
+ * Test an assertion for truth. If the expression is not true then
+ * trigger a program failure.
+ *
+ * Note that the non-debug version of this macro does <b>not</b>
+ * evaluate the message argument.
+ */
+#ifdef DEBUG
+inline void MOZ_PretendNoReturn() MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS {}
+#  define NS_ASSERTION(expr, str)                                          \
+    do {                                                                   \
+      if (!(expr)) {                                                       \
+        NS_DebugBreak(NS_DEBUG_ASSERTION, str, #expr, __FILE__, __LINE__); \
+        MOZ_PretendNoReturn();                                             \
+      }                                                                    \
+    } while (0)
+#else
+#  define NS_ASSERTION(expr, str) \
+    do { /* nothing */            \
+    } while (0)
+#endif
+
+/**
+ * Log an error message.
+ */
+#ifdef DEBUG
+#  define NS_ERROR(str)                                                    \
+    do {                                                                   \
+      NS_DebugBreak(NS_DEBUG_ASSERTION, str, "Error", __FILE__, __LINE__); \
+      MOZ_PretendNoReturn();                                               \
+    } while (0)
+#else
+#  define NS_ERROR(str) \
+    do { /* nothing */  \
+    } while (0)
+#endif
+
+/**
+ * Log a warning message.
+ */
+#ifdef DEBUG
+#  define NS_WARNING(str) \
+    NS_DebugBreak(NS_DEBUG_WARNING, str, nullptr, __FILE__, __LINE__)
+#else
+#  define NS_WARNING(str) \
+    do { /* nothing */    \
+    } while (0)
+#endif
+
+/**
+ * Trigger a debugger breakpoint, only in debug builds.
+ */
+#ifdef DEBUG
+#  define NS_BREAK()                                                       \
+    do {                                                                   \
+      NS_DebugBreak(NS_DEBUG_BREAK, nullptr, nullptr, __FILE__, __LINE__); \
+      MOZ_PretendNoReturn();                                               \
+    } while (0)
+#else
+#  define NS_BREAK()   \
+    do { /* nothing */ \
+    } while (0)
+#endif
+
+/******************************************************************************
+** Macros for static assertions.  These are used by the sixgill tool.
+** When the tool is not running these macros are no-ops.
+******************************************************************************/
+
+/* Avoid name collision if included with other headers defining annotations. */
+#ifndef HAVE_STATIC_ANNOTATIONS
+#  define HAVE_STATIC_ANNOTATIONS
+
+#  ifdef XGILL_PLUGIN
+
+#    define STATIC_PRECONDITION(COND) __attribute__((precondition(#COND)))
+#    define STATIC_PRECONDITION_ASSUME(COND) \
+      __attribute__((precondition_assume(#COND)))
+#    define STATIC_POSTCONDITION(COND) __attribute__((postcondition(#COND)))
+#    define STATIC_POSTCONDITION_ASSUME(COND) \
+      __attribute__((postcondition_assume(#COND)))
+#    define STATIC_INVARIANT(COND) __attribute__((invariant(#COND)))
+#    define STATIC_INVARIANT_ASSUME(COND) \
+      __attribute__((invariant_assume(#COND)))
+
+/* Used to make identifiers for assert/assume annotations in a function. */
+#    define STATIC_PASTE2(X, Y) X##Y
+#    define STATIC_PASTE1(X, Y) STATIC_PASTE2(X, Y)
+
+#    define STATIC_ASSUME(COND)                                          \
+      do {                                                               \
+        __attribute__((assume_static(#COND), unused)) int STATIC_PASTE1( \
+            assume_static_, __COUNTER__);                                \
+      } while (false)
+
+#    define STATIC_ASSERT_RUNTIME(COND)                                   \
+      do {                                                                \
+        __attribute__((assert_static_runtime(#COND),                      \
+                       unused)) int STATIC_PASTE1(assert_static_runtime_, \
+                                                  __COUNTER__);           \
+      } while (false)
+
+#  else /* XGILL_PLUGIN */
+
+#    define STATIC_PRECONDITION(COND)         /* nothing */
+#    define STATIC_PRECONDITION_ASSUME(COND)  /* nothing */
+#    define STATIC_POSTCONDITION(COND)        /* nothing */
+#    define STATIC_POSTCONDITION_ASSUME(COND) /* nothing */
+#    define STATIC_INVARIANT(COND)            /* nothing */
+#    define STATIC_INVARIANT_ASSUME(COND)     /* nothing */
+
+#    define STATIC_ASSUME(COND) \
+      do { /* nothing */        \
+      } while (false)
+#    define STATIC_ASSERT_RUNTIME(COND) \
+      do { /* nothing */                \
+      } while (false)
+
+#  endif /* XGILL_PLUGIN */
+
+#  define STATIC_SKIP_INFERENCE STATIC_INVARIANT(skip_inference())
+
+#endif /* HAVE_STATIC_ANNOTATIONS */
+
+/******************************************************************************
+** Macros for terminating execution when an unrecoverable condition is
+** reached.  These need to be compiled regardless of the DEBUG flag.
+******************************************************************************/
+
+/* Macros for checking the trueness of an expression passed in within an
+ * interface implementation.  These need to be compiled regardless of the
+ * DEBUG flag. New code should use NS_WARN_IF(condition) instead!
+ * @status deprecated
+ */
+
+#define NS_ENSURE_TRUE(x, ret)                     \
+  do {                                             \
+    if (MOZ_UNLIKELY(!(x))) {                      \
+      NS_WARNING("NS_ENSURE_TRUE(" #x ") failed"); \
+      return ret;                                  \
+    }                                              \
+  } while (false)
+
+#define NS_ENSURE_FALSE(x, ret) NS_ENSURE_TRUE(!(x), ret)
+
+#define NS_ENSURE_TRUE_VOID(x)                     \
+  do {                                             \
+    if (MOZ_UNLIKELY(!(x))) {                      \
+      NS_WARNING("NS_ENSURE_TRUE(" #x ") failed"); \
+      return;                                      \
+    }                                              \
+  } while (false)
+
+#define NS_ENSURE_FALSE_VOID(x) NS_ENSURE_TRUE_VOID(!(x))
+
+/******************************************************************************
+** Macros for checking results
+******************************************************************************/
+
+#if defined(DEBUG) && !defined(XPCOM_GLUE_AVOID_NSPR)
+
+#  define NS_ENSURE_SUCCESS_BODY(res, ret)                         \
+    const char* name = mozilla::GetStaticErrorName(__rv);          \
+    mozilla::SmprintfPointer msg = mozilla::Smprintf(              \
+        "NS_ENSURE_SUCCESS(%s, %s) failed with "                   \
+        "result 0x%" PRIX32 "%s%s%s",                              \
+        #res, #ret, static_cast<uint32_t>(__rv), name ? " (" : "", \
+        name ? name : "", name ? ")" : "");                        \
+    NS_WARNING(msg.get());
+
+#  define NS_ENSURE_SUCCESS_BODY_VOID(res)                                     \
+    const char* name = mozilla::GetStaticErrorName(__rv);                      \
+    mozilla::SmprintfPointer msg = mozilla::Smprintf(                          \
+        "NS_ENSURE_SUCCESS_VOID(%s) failed with "                              \
+        "result 0x%" PRIX32 "%s%s%s",                                          \
+        #res, static_cast<uint32_t>(__rv), name ? " (" : "", name ? name : "", \
+        name ? ")" : "");                                                      \
+    NS_WARNING(msg.get());
+
+#else
+
+#  define NS_ENSURE_SUCCESS_BODY(res, ret) \
+    NS_WARNING("NS_ENSURE_SUCCESS(" #res ", " #ret ") failed");
+
+#  define NS_ENSURE_SUCCESS_BODY_VOID(res) \
+    NS_WARNING("NS_ENSURE_SUCCESS_VOID(" #res ") failed");
+
+#endif
+
+#define NS_ENSURE_SUCCESS(res, ret)                                \
+  do {                                                             \
+    nsresult __rv = res; /* Don't evaluate |res| more than once */ \
+    if (NS_FAILED(__rv)) {                                         \
+      NS_ENSURE_SUCCESS_BODY(res, ret)                             \
+      return ret;                                                  \
+    }                                                              \
+  } while (false)
+
+#define NS_ENSURE_SUCCESS_VOID(res)    \
+  do {                                 \
+    nsresult __rv = res;               \
+    if (NS_FAILED(__rv)) {             \
+      NS_ENSURE_SUCCESS_BODY_VOID(res) \
+      return;                          \
+    }                                  \
+  } while (false)
+
+/******************************************************************************
+** Macros for checking state and arguments upon entering interface boundaries
+******************************************************************************/
+
+#define NS_ENSURE_ARG(arg) NS_ENSURE_TRUE(arg, NS_ERROR_INVALID_ARG)
+
+#define NS_ENSURE_ARG_POINTER(arg) NS_ENSURE_TRUE(arg, NS_ERROR_INVALID_POINTER)
+
+#define NS_ENSURE_ARG_MIN(arg, min) \
+  NS_ENSURE_TRUE((arg) >= min, NS_ERROR_INVALID_ARG)
+
+#define NS_ENSURE_ARG_MAX(arg, max) \
+  NS_ENSURE_TRUE((arg) <= max, NS_ERROR_INVALID_ARG)
+
+#define NS_ENSURE_ARG_RANGE(arg, min, max) \
+  NS_ENSURE_TRUE(((arg) >= min) && ((arg) <= max), NS_ERROR_INVALID_ARG)
+
+#define NS_ENSURE_STATE(state) NS_ENSURE_TRUE(state, NS_ERROR_UNEXPECTED)
+
+/*****************************************************************************/
+
+#if (defined(DEBUG) || (defined(NIGHTLY_BUILD) && !defined(MOZ_PROFILING))) && \
+    !defined(XPCOM_GLUE_AVOID_NSPR)
+#  define MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED 1
+#endif
+
+#ifdef MOZILLA_INTERNAL_API
+void NS_ABORT_OOM(size_t aSize);
+#else
+inline void NS_ABORT_OOM(size_t) { MOZ_CRASH(); }
+#endif
+
+/* When compiling the XPCOM Glue on Windows, we pretend that it's going to
+ * be linked with a static CRT (-MT) even when it's not. This means that we
+ * cannot link to data exports from the CRT, only function exports. So,
+ * instead of referencing "stderr" directly, use fdopen.
+ */
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * printf_stderr(...) is much like fprintf(stderr, ...), except that:
+ *  - on Android and Firefox OS, *instead* of printing to stderr, it
+ *    prints to logcat.  (Newlines in the string lead to multiple lines
+ *    of logcat, but each function call implicitly completes a line even
+ *    if the string does not end with a newline.)
+ *  - on Windows, if a debugger is present, it calls OutputDebugString
+ *    in *addition* to writing to stderr
+ */
+void printf_stderr(const char* aFmt, ...) MOZ_FORMAT_PRINTF(1, 2);
+
+/**
+ * Same as printf_stderr, but taking va_list instead of varargs
+ */
+void vprintf_stderr(const char* aFmt, va_list aArgs) MOZ_FORMAT_PRINTF(1, 0);
+
+/**
+ * fprintf_stderr is like fprintf, except that if its file argument
+ * is stderr, it invokes printf_stderr instead.
+ *
+ * This is useful for general debugging code that logs information to a
+ * file, but that you would like to be useful on Android and Firefox OS.
+ * If you use fprintf_stderr instead of fprintf in such debugging code,
+ * then callers can pass stderr to get logging that works on Android and
+ * Firefox OS (and also the other side-effects of using printf_stderr).
+ *
+ * Code that is structured this way needs to be careful not to split a
+ * line of output across multiple calls to fprintf_stderr, since doing
+ * so will cause it to appear in multiple lines in logcat output.
+ * (Producing multiple lines at once is fine.)
+ */
+void fprintf_stderr(FILE* aFile, const char* aFmt, ...) MOZ_FORMAT_PRINTF(2, 3);
+
+/*
+ * print_stderr and fprint_stderr are like printf_stderr and fprintf_stderr,
+ * except they deal with Android logcat line length limitations. They do this
+ * by printing individual lines out of the provided stringstream using separate
+ * calls to logcat.
+ */
+void print_stderr(std::stringstream& aStr);
+void fprint_stderr(FILE* aFile, std::stringstream& aStr);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* nsDebug_h___ */
diff --git a/xpcom/base/nsDebugImpl.cpp b/xpcom/base/nsDebugImpl.cpp
new file mode 100644
index 0000000000..4023efd0ec
--- /dev/null
+++ b/xpcom/base/nsDebugImpl.cpp
@@ -0,0 +1,675 @@
+/* -*- 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/. */
+
+// Chromium headers must come before Mozilla headers.
+#include "base/process_util.h"
+
+#include "mozilla/Atomics.h"
+#include "mozilla/IntentionalCrash.h"
+#include "mozilla/Printf.h"
+#include "mozilla/ProfilerMarkers.h"
+
+#include "MainThreadUtils.h"
+#include "nsDebugImpl.h"
+#include "nsDebug.h"
+#include "nsExceptionHandler.h"
+#include "nsString.h"
+#include "nsXULAppAPI.h"
+#include "prerror.h"
+#include "prerr.h"
+#include "prenv.h"
+
+#ifdef ANDROID
+#  include <android/log.h>
+#endif
+
+#ifdef _WIN32
+/* for getenv() */
+#  include <stdlib.h>
+#endif
+
+#include "mozilla/StackWalk.h"
+
+#if defined(XP_UNIX)
+#  include <signal.h>
+#endif
+
+#if defined(XP_WIN)
+#  include <tchar.h>
+#  include "nsString.h"
+#endif
+
+#if defined(XP_MACOSX) || defined(__DragonFly__) || defined(__FreeBSD__) || \
+    defined(__NetBSD__) || defined(__OpenBSD__)
+#  include <stdbool.h>
+#  include <unistd.h>
+#  include <sys/param.h>
+#  include <sys/sysctl.h>
+#endif
+
+#if defined(__OpenBSD__)
+#  include <sys/proc.h>
+#endif
+
+#if defined(__DragonFly__) || defined(__FreeBSD__)
+#  include <sys/user.h>
+#endif
+
+#if defined(__NetBSD__)
+#  undef KERN_PROC
+#  define KERN_PROC KERN_PROC2
+#  define KINFO_PROC struct kinfo_proc2
+#else
+#  define KINFO_PROC struct kinfo_proc
+#endif
+
+#if defined(XP_MACOSX)
+#  define KP_FLAGS kp_proc.p_flag
+#elif defined(__DragonFly__)
+#  define KP_FLAGS kp_flags
+#elif defined(__FreeBSD__)
+#  define KP_FLAGS ki_flag
+#elif defined(__OpenBSD__) && !defined(_P_TRACED)
+#  define KP_FLAGS p_psflags
+#  define P_TRACED PS_TRACED
+#else
+#  define KP_FLAGS p_flag
+#endif
+
+static void Abort(const char* aMsg);
+
+static void RealBreak();
+
+static void Break(const char* aMsg);
+
+#if defined(_WIN32)
+#  include <windows.h>
+#  include <signal.h>
+#  include <malloc.h>  // for _alloca
+#endif
+
+using namespace mozilla;
+
+static const char* sMultiprocessDescription = nullptr;
+
+static Atomic<int32_t> gAssertionCount;
+
+NS_IMPL_QUERY_INTERFACE(nsDebugImpl, nsIDebug2)
+
+NS_IMETHODIMP_(MozExternalRefCountType)
+nsDebugImpl::AddRef() { return 2; }
+
+NS_IMETHODIMP_(MozExternalRefCountType)
+nsDebugImpl::Release() { return 1; }
+
+NS_IMETHODIMP
+nsDebugImpl::Assertion(const char* aStr, const char* aExpr, const char* aFile,
+                       int32_t aLine) {
+  NS_DebugBreak(NS_DEBUG_ASSERTION, aStr, aExpr, aFile, aLine);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDebugImpl::Warning(const char* aStr, const char* aFile, int32_t aLine) {
+  NS_DebugBreak(NS_DEBUG_WARNING, aStr, nullptr, aFile, aLine);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDebugImpl::Break(const char* aFile, int32_t aLine) {
+  NS_DebugBreak(NS_DEBUG_BREAK, nullptr, nullptr, aFile, aLine);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDebugImpl::Abort(const char* aFile, int32_t aLine) {
+  NS_DebugBreak(NS_DEBUG_ABORT, nullptr, nullptr, aFile, aLine);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDebugImpl::CrashWithOOM() {
+  NS_ABORT_OOM(-1);
+  return NS_OK;
+}
+
+// From toolkit/library/rust/lib.rs
+extern "C" void intentional_panic(const char* message);
+
+NS_IMETHODIMP
+nsDebugImpl::RustPanic(const char* aMessage) {
+  intentional_panic(aMessage);
+  return NS_OK;
+}
+
+// From toolkit/library/rust/lib.rs
+extern "C" void debug_log(const char* target, const char* message);
+
+NS_IMETHODIMP
+nsDebugImpl::RustLog(const char* aTarget, const char* aMessage) {
+  debug_log(aTarget, aMessage);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDebugImpl::GetIsDebugBuild(bool* aResult) {
+#ifdef DEBUG
+  *aResult = true;
+#else
+  *aResult = false;
+#endif
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDebugImpl::GetAssertionCount(int32_t* aResult) {
+  *aResult = gAssertionCount;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDebugImpl::GetIsDebuggerAttached(bool* aResult) {
+  *aResult = false;
+
+#if defined(__OpenBSD__) && defined(MOZ_SANDBOX)
+  // no access to KERN_PROC_PID sysctl when pledge'd
+  return NS_OK;
+#endif
+#if defined(XP_WIN)
+  *aResult = ::IsDebuggerPresent();
+#elif defined(XP_MACOSX) || defined(__DragonFly__) || defined(__FreeBSD__) || \
+    defined(__NetBSD__) || defined(__OpenBSD__)
+  // Specify the info we're looking for
+  int mib[] = {
+    CTL_KERN,
+    KERN_PROC,
+    KERN_PROC_PID,
+    getpid(),
+#  if defined(__NetBSD__) || defined(__OpenBSD__)
+    sizeof(KINFO_PROC),
+    1,
+#  endif
+  };
+  u_int mibSize = sizeof(mib) / sizeof(int);
+
+  KINFO_PROC info;
+  size_t infoSize = sizeof(info);
+  memset(&info, 0, infoSize);
+
+  if (sysctl(mib, mibSize, &info, &infoSize, nullptr, 0)) {
+    // if the call fails, default to false
+    *aResult = false;
+    return NS_OK;
+  }
+
+  if (info.KP_FLAGS & P_TRACED) {
+    *aResult = true;
+  }
+#endif
+
+  return NS_OK;
+}
+
+/* static */
+void nsDebugImpl::SetMultiprocessMode(const char* aDesc) {
+  sMultiprocessDescription = aDesc;
+}
+
+/* static */ const char* nsDebugImpl::GetMultiprocessMode() {
+  return sMultiprocessDescription;
+}
+
+/**
+ * Implementation of the nsDebug methods. Note that this code is
+ * always compiled in, in case some other module that uses it is
+ * compiled with debugging even if this library is not.
+ */
+enum nsAssertBehavior {
+  NS_ASSERT_UNINITIALIZED,
+  NS_ASSERT_WARN,
+  NS_ASSERT_SUSPEND,
+  NS_ASSERT_STACK,
+  NS_ASSERT_TRAP,
+  NS_ASSERT_ABORT,
+  NS_ASSERT_STACK_AND_ABORT
+};
+
+static nsAssertBehavior GetAssertBehavior() {
+  static nsAssertBehavior gAssertBehavior = NS_ASSERT_UNINITIALIZED;
+  if (gAssertBehavior != NS_ASSERT_UNINITIALIZED) {
+    return gAssertBehavior;
+  }
+
+  gAssertBehavior = NS_ASSERT_WARN;
+
+  const char* assertString = PR_GetEnv("XPCOM_DEBUG_BREAK");
+  if (!assertString || !*assertString) {
+    return gAssertBehavior;
+  }
+  if (!strcmp(assertString, "warn")) {
+    return gAssertBehavior = NS_ASSERT_WARN;
+  }
+  if (!strcmp(assertString, "suspend")) {
+    return gAssertBehavior = NS_ASSERT_SUSPEND;
+  }
+  if (!strcmp(assertString, "stack")) {
+    return gAssertBehavior = NS_ASSERT_STACK;
+  }
+  if (!strcmp(assertString, "abort")) {
+    return gAssertBehavior = NS_ASSERT_ABORT;
+  }
+  if (!strcmp(assertString, "trap") || !strcmp(assertString, "break")) {
+    return gAssertBehavior = NS_ASSERT_TRAP;
+  }
+  if (!strcmp(assertString, "stack-and-abort")) {
+    return gAssertBehavior = NS_ASSERT_STACK_AND_ABORT;
+  }
+
+  fprintf(stderr, "Unrecognized value of XPCOM_DEBUG_BREAK\n");
+  return gAssertBehavior;
+}
+
+struct FixedBuffer final : public mozilla::PrintfTarget {
+  FixedBuffer() : curlen(0) { buffer[0] = '\0'; }
+
+  char buffer[764];
+  uint32_t curlen;
+
+  bool append(const char* sp, size_t len) override;
+};
+
+bool FixedBuffer::append(const char* aBuf, size_t aLen) {
+  if (!aLen) {
+    return true;
+  }
+
+  if (curlen + aLen >= sizeof(buffer)) {
+    aLen = sizeof(buffer) - curlen - 1;
+  }
+
+  if (aLen) {
+    memcpy(buffer + curlen, aBuf, aLen);
+    curlen += aLen;
+    buffer[curlen] = '\0';
+  }
+
+  return true;
+}
+
+namespace geckoprofiler::markers {
+
+struct DebugBreakMarker {
+  static constexpr Span<const char> MarkerTypeName() {
+    return MakeStringSpan("DebugBreak");
+  }
+  static void StreamJSONMarkerData(baseprofiler::SpliceableJSONWriter& aWriter,
+                                   uint32_t aSeverity,
+                                   const ProfilerString8View& aStr,
+                                   const ProfilerString8View& aExpr,
+                                   const ProfilerString8View& aFile,
+                                   int32_t aLine) {
+    nsAutoCString sevString("WARNING");
+    switch (aSeverity) {
+      case NS_DEBUG_ASSERTION:
+        sevString = "ASSERTION";
+        break;
+
+      case NS_DEBUG_BREAK:
+        sevString = "BREAK";
+        break;
+
+      case NS_DEBUG_ABORT:
+        sevString = "ABORT";
+        break;
+    }
+    aWriter.StringProperty("Severity", sevString);
+    // The 'name' property is searchable on the front-end.
+    if (aStr.Length() != 0) {
+      aWriter.StringProperty("Message", aStr);
+      aWriter.StringProperty("name", aStr);
+    } else if (aExpr.Length() != 0) {
+      aWriter.StringProperty("name", aExpr);
+    }
+    if (aExpr.Length() != 0) {
+      aWriter.StringProperty("Expression", aExpr);
+    }
+    if (aFile.Length() != 0) {
+      aWriter.StringProperty("File", aFile);
+    }
+    if (aLine != 0) {
+      aWriter.IntProperty("Line", aLine);
+    }
+  }
+  static MarkerSchema MarkerTypeDisplay() {
+    using MS = MarkerSchema;
+    MS schema{MS::Location::TimelineOverview, MS::Location::MarkerChart,
+              MS::Location::MarkerTable};
+    schema.SetAllLabels("{marker.data.Severity}: {marker.data.name}");
+    schema.AddKeyFormat("Message", MS::Format::String);
+    schema.AddKeyFormat("Severity", MS::Format::String);
+    schema.AddKeyFormat("Expression", MS::Format::String);
+    schema.AddKeyFormat("File", MS::Format::String);
+    schema.AddKeyFormat("Line", MS::Format::Integer);
+    return schema;
+  }
+};
+
+}  // namespace geckoprofiler::markers
+
+EXPORT_XPCOM_API(void)
+NS_DebugBreak(uint32_t aSeverity, const char* aStr, const char* aExpr,
+              const char* aFile, int32_t aLine) {
+  FixedBuffer nonPIDBuf;
+  FixedBuffer buf;
+  const char* sevString = "WARNING";
+
+  switch (aSeverity) {
+    case NS_DEBUG_ASSERTION:
+      sevString = "###!!! ASSERTION";
+      break;
+
+    case NS_DEBUG_BREAK:
+      sevString = "###!!! BREAK";
+      break;
+
+    case NS_DEBUG_ABORT:
+      sevString = "###!!! ABORT";
+      break;
+
+    default:
+      aSeverity = NS_DEBUG_WARNING;
+  }
+
+  nonPIDBuf.print("%s: ", sevString);
+  if (aStr) {
+    nonPIDBuf.print("%s: ", aStr);
+  }
+  if (aExpr) {
+    nonPIDBuf.print("'%s', ", aExpr);
+  }
+  if (aFile || aLine != -1) {
+    nonPIDBuf.print("file %s:%d", aFile ? aFile : "<unknown>",
+                    aLine != -1 ? aLine : 0);
+  }
+
+  // Print "[PID]" or "[Desc PID]" at the beginning of the message.
+  buf.print("[");
+  if (sMultiprocessDescription) {
+    buf.print("%s ", sMultiprocessDescription);
+  }
+
+  bool isMainthread = (NS_IsMainThreadTLSInitialized() && NS_IsMainThread());
+  PRThread* currentThread = PR_GetCurrentThread();
+  const char* currentThreadName =
+      isMainthread ? "Main Thread" : PR_GetThreadName(currentThread);
+  if (currentThreadName) {
+    buf.print("%" PRIPID ", %s] %s", base::GetCurrentProcId(),
+              currentThreadName, nonPIDBuf.buffer);
+  } else {
+    buf.print("%" PRIPID ", Unnamed thread %p] %s", base::GetCurrentProcId(),
+              currentThread, nonPIDBuf.buffer);
+  }
+
+  // errors on platforms without a debugdlg ring a bell on stderr
+#if !defined(XP_WIN)
+  if (aSeverity != NS_DEBUG_WARNING) {
+    fprintf(stderr, "\07");
+  }
+#endif
+
+#ifdef ANDROID
+  __android_log_print(ANDROID_LOG_INFO, "Gecko", "%s", buf.buffer);
+#endif
+
+  PROFILER_MARKER("NS_DebugBreak", OTHER, MarkerStack::Capture(),
+                  DebugBreakMarker, aSeverity,
+                  ProfilerString8View::WrapNullTerminatedString(aStr),
+                  ProfilerString8View::WrapNullTerminatedString(aExpr),
+                  ProfilerString8View::WrapNullTerminatedString(aFile), aLine);
+
+  // Write the message to stderr unless it's a warning and MOZ_IGNORE_WARNINGS
+  // is set.
+  if (!(PR_GetEnv("MOZ_IGNORE_WARNINGS") && aSeverity == NS_DEBUG_WARNING)) {
+    fprintf(stderr, "%s\n", buf.buffer);
+    fflush(stderr);
+  }
+
+  switch (aSeverity) {
+    case NS_DEBUG_WARNING:
+      return;
+
+    case NS_DEBUG_BREAK:
+      Break(buf.buffer);
+      return;
+
+    case NS_DEBUG_ABORT: {
+      // Updating crash annotations in the child causes us to do IPC. This can
+      // really cause trouble if we're asserting from within IPC code. So we
+      // have to do without the annotations in that case.
+      if (XRE_IsParentProcess()) {
+        // Don't include the PID in the crash report annotation to
+        // allow faceting on crash-stats.mozilla.org.
+        nsCString note("xpcom_runtime_abort(");
+        note += nonPIDBuf.buffer;
+        note += ")";
+        CrashReporter::AppendAppNotesToCrashReport(note);
+        CrashReporter::AnnotateCrashReport(
+            CrashReporter::Annotation::AbortMessage,
+            nsDependentCString(nonPIDBuf.buffer));
+      }
+
+#if defined(DEBUG) && defined(_WIN32)
+      RealBreak();
+#endif
+#if defined(DEBUG)
+      MozWalkTheStack(stderr);
+#endif
+      Abort(buf.buffer);
+      return;
+    }
+  }
+
+  // Now we deal with assertions
+  gAssertionCount++;
+
+  switch (GetAssertBehavior()) {
+    case NS_ASSERT_WARN:
+      return;
+
+    case NS_ASSERT_SUSPEND:
+#ifdef XP_UNIX
+      fprintf(stderr, "Suspending process; attach with the debugger.\n");
+      kill(0, SIGSTOP);
+#else
+      Break(buf.buffer);
+#endif
+      return;
+
+    case NS_ASSERT_STACK:
+      MozWalkTheStack(stderr);
+      return;
+
+    case NS_ASSERT_STACK_AND_ABORT:
+      MozWalkTheStack(stderr);
+      // Fall through to abort
+      [[fallthrough]];
+
+    case NS_ASSERT_ABORT:
+      Abort(buf.buffer);
+      return;
+
+    case NS_ASSERT_TRAP:
+    case NS_ASSERT_UNINITIALIZED:  // Default to "trap" behavior
+      Break(buf.buffer);
+      return;
+  }
+}
+
+static void Abort(const char* aMsg) {
+  NoteIntentionalCrash(XRE_GetProcessTypeString());
+  MOZ_CRASH_UNSAFE(aMsg);
+}
+
+static void RealBreak() {
+#if defined(_WIN32)
+  ::DebugBreak();
+#elif defined(XP_MACOSX)
+  raise(SIGTRAP);
+#elif defined(__GNUC__) && \
+    (defined(__i386__) || defined(__i386) || defined(__x86_64__))
+  asm("int $3");
+#elif defined(__arm__)
+  asm(
+#  ifdef __ARM_ARCH_4T__
+      /* ARMv4T doesn't support the BKPT instruction, so if the compiler target
+       * is ARMv4T, we want to ensure the assembler will understand that ARMv5T
+       * instruction, while keeping the resulting object tagged as ARMv4T.
+       */
+      ".arch armv5t\n"
+      ".object_arch armv4t\n"
+#  endif
+      "BKPT #0");
+#elif defined(__aarch64__)
+  asm("brk #0");
+#elif defined(SOLARIS)
+#  if defined(__i386__) || defined(__i386) || defined(__x86_64__)
+  asm("int $3");
+#  else
+  raise(SIGTRAP);
+#  endif
+#else
+#  warning do not know how to break on this platform
+#endif
+}
+
+// Abort() calls this function, don't call it!
+static void Break(const char* aMsg) {
+#if defined(_WIN32)
+  static int ignoreDebugger;
+  if (!ignoreDebugger) {
+    const char* shouldIgnoreDebugger = getenv("XPCOM_DEBUG_DLG");
+    ignoreDebugger =
+        1 + (shouldIgnoreDebugger && !strcmp(shouldIgnoreDebugger, "1"));
+  }
+  if ((ignoreDebugger == 2) || !::IsDebuggerPresent()) {
+    DWORD code = IDRETRY;
+
+    /* Create the debug dialog out of process to avoid the crashes caused by
+     * Windows events leaking into our event loop from an in process dialog.
+     * We do this by launching windbgdlg.exe (built in xpcom/windbgdlg).
+     * See http://bugzilla.mozilla.org/show_bug.cgi?id=54792
+     */
+    PROCESS_INFORMATION pi;
+    STARTUPINFOW si;
+    wchar_t executable[MAX_PATH];
+    wchar_t* pName;
+
+    memset(&pi, 0, sizeof(pi));
+
+    memset(&si, 0, sizeof(si));
+    si.cb = sizeof(si);
+    si.wShowWindow = SW_SHOW;
+
+    // 2nd arg of CreateProcess is in/out
+    wchar_t* msgCopy = (wchar_t*)_alloca((strlen(aMsg) + 1) * sizeof(wchar_t));
+    wcscpy(msgCopy, NS_ConvertUTF8toUTF16(aMsg).get());
+
+    if (GetModuleFileNameW(GetModuleHandleW(L"xpcom.dll"), executable,
+                           MAX_PATH) &&
+        (pName = wcsrchr(executable, '\\')) != nullptr &&
+        wcscpy(pName + 1, L"windbgdlg.exe") &&
+        CreateProcessW(executable, msgCopy, nullptr, nullptr, false,
+                       DETACHED_PROCESS | NORMAL_PRIORITY_CLASS, nullptr,
+                       nullptr, &si, &pi)) {
+      WaitForSingleObject(pi.hProcess, INFINITE);
+      GetExitCodeProcess(pi.hProcess, &code);
+      CloseHandle(pi.hProcess);
+      CloseHandle(pi.hThread);
+    }
+
+    switch (code) {
+      case IDABORT:
+        // This should exit us
+        raise(SIGABRT);
+        // If we are ignored exit this way..
+        _exit(3);
+
+      case IDIGNORE:
+        return;
+    }
+  }
+
+  RealBreak();
+#elif defined(XP_MACOSX)
+  /* Note that we put this Mac OS X test above the GNUC/x86 test because the
+   * GNUC/x86 test is also true on Intel Mac OS X and we want the PPC/x86
+   * impls to be the same.
+   */
+  RealBreak();
+#elif defined(__GNUC__) && \
+    (defined(__i386__) || defined(__i386) || defined(__x86_64__))
+  RealBreak();
+#elif defined(__arm__) || defined(__aarch64__)
+  RealBreak();
+#elif defined(SOLARIS)
+  RealBreak();
+#else
+#  warning do not know how to break on this platform
+#endif
+}
+
+nsresult nsDebugImpl::Create(const nsIID& aIID, void** aInstancePtr) {
+  static const nsDebugImpl* sImpl;
+
+  if (!sImpl) {
+    sImpl = new nsDebugImpl();
+  }
+
+  return const_cast<nsDebugImpl*>(sImpl)->QueryInterface(aIID, aInstancePtr);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+nsresult NS_ErrorAccordingToNSPR() {
+  PRErrorCode err = PR_GetError();
+  switch (err) {
+    case PR_OUT_OF_MEMORY_ERROR:
+      return NS_ERROR_OUT_OF_MEMORY;
+    case PR_WOULD_BLOCK_ERROR:
+      return NS_BASE_STREAM_WOULD_BLOCK;
+    case PR_FILE_NOT_FOUND_ERROR:
+      return NS_ERROR_FILE_NOT_FOUND;
+    case PR_READ_ONLY_FILESYSTEM_ERROR:
+      return NS_ERROR_FILE_READ_ONLY;
+    case PR_NOT_DIRECTORY_ERROR:
+      return NS_ERROR_FILE_NOT_DIRECTORY;
+    case PR_IS_DIRECTORY_ERROR:
+      return NS_ERROR_FILE_IS_DIRECTORY;
+    case PR_LOOP_ERROR:
+      return NS_ERROR_FILE_UNRESOLVABLE_SYMLINK;
+    case PR_FILE_EXISTS_ERROR:
+      return NS_ERROR_FILE_ALREADY_EXISTS;
+    case PR_FILE_IS_LOCKED_ERROR:
+      return NS_ERROR_FILE_IS_LOCKED;
+    case PR_FILE_TOO_BIG_ERROR:
+      return NS_ERROR_FILE_TOO_BIG;
+    case PR_NO_DEVICE_SPACE_ERROR:
+      return NS_ERROR_FILE_NO_DEVICE_SPACE;
+    case PR_NAME_TOO_LONG_ERROR:
+      return NS_ERROR_FILE_NAME_TOO_LONG;
+    case PR_DIRECTORY_NOT_EMPTY_ERROR:
+      return NS_ERROR_FILE_DIR_NOT_EMPTY;
+    case PR_NO_ACCESS_RIGHTS_ERROR:
+      return NS_ERROR_FILE_ACCESS_DENIED;
+    default:
+      return NS_ERROR_FAILURE;
+  }
+}
+
+void NS_ABORT_OOM(size_t aSize) {
+  CrashReporter::AnnotateOOMAllocationSize(aSize);
+  MOZ_CRASH("OOM");
+}
diff --git a/xpcom/base/nsDebugImpl.h b/xpcom/base/nsDebugImpl.h
new file mode 100644
index 0000000000..a3adcad3d7
--- /dev/null
+++ b/xpcom/base/nsDebugImpl.h
@@ -0,0 +1,42 @@
+/* -*- 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/. */
+
+#ifndef nsDebugImpl_h
+#define nsDebugImpl_h
+
+#include "nsIDebug2.h"
+
+class nsDebugImpl : public nsIDebug2 {
+ public:
+  nsDebugImpl() = default;
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIDEBUG2
+
+  static nsresult Create(const nsIID& aIID, void** aInstancePtr);
+
+  /*
+   * If we are in multiprocess mode, return the process name.
+   */
+  static const char* GetMultiprocessMode();
+
+  /*
+   * Inform nsDebugImpl that we're in multiprocess mode.
+   *
+   * If aDesc is not nullptr, the string it points to must be
+   * statically-allocated (i.e., it must be a string literal).
+   */
+  static void SetMultiprocessMode(const char* aDesc);
+};
+
+#define NS_DEBUG_CONTRACTID "@mozilla.org/xpcom/debug;1"
+#define NS_DEBUG_CID                                 \
+  { /* cb6cdb94-e417-4601-b4a5-f991bf41453d */       \
+    0xcb6cdb94, 0xe417, 0x4601, {                    \
+      0xb4, 0xa5, 0xf9, 0x91, 0xbf, 0x41, 0x45, 0x3d \
+    }                                                \
+  }
+
+#endif  // nsDebugImpl_h
diff --git a/xpcom/base/nsDumpUtils.cpp b/xpcom/base/nsDumpUtils.cpp
new file mode 100644
index 0000000000..c7bbbf4eb3
--- /dev/null
+++ b/xpcom/base/nsDumpUtils.cpp
@@ -0,0 +1,488 @@
+/* -*- 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 "nsDumpUtils.h"
+#include "nsDirectoryServiceDefs.h"
+#include "nsDirectoryServiceUtils.h"
+#include <errno.h>
+#include "prenv.h"
+#include "mozilla/Services.h"
+#include "nsIObserverService.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/Unused.h"
+#include "SpecialSystemDirectory.h"
+
+#ifdef XP_UNIX  // {
+#  include "mozilla/Preferences.h"
+#  include <fcntl.h>
+#  include <unistd.h>
+#  include <sys/stat.h>
+
+using namespace mozilla;
+
+/*
+ * The following code supports triggering a registered callback upon
+ * receiving a specific signal.
+ *
+ * Take about:memory for example, we register
+ * 1. doGCCCDump for doMemoryReport
+ * 2. doMemoryReport for sDumpAboutMemorySignum(SIGRTMIN)
+ *                       and sDumpAboutMemoryAfterMMUSignum(SIGRTMIN+1).
+ *
+ * When we receive one of these signals, we write the signal number to a pipe.
+ * The IO thread then notices that the pipe has been written to, and kicks off
+ * the appropriate task on the main thread.
+ *
+ * This scheme is similar to using signalfd(), except it's portable and it
+ * doesn't require the use of sigprocmask, which is problematic because it
+ * masks signals received by child processes.
+ *
+ * In theory, we could use Chromium's MessageLoopForIO::CatchSignal() for this.
+ * But that uses libevent, which does not handle the realtime signals (bug
+ * 794074).
+ */
+
+// This is the write-end of a pipe that we use to notice when a
+// specific signal occurs.
+static Atomic<int> sDumpPipeWriteFd(-1);
+
+const char FifoWatcher::kPrefName[] = "memory_info_dumper.watch_fifo.enabled";
+
+static void DumpSignalHandler(int aSignum) {
+  // This is a signal handler, so everything in here needs to be
+  // async-signal-safe.  Be careful!
+
+  if (sDumpPipeWriteFd != -1) {
+    uint8_t signum = static_cast<int>(aSignum);
+    Unused << write(sDumpPipeWriteFd, &signum, sizeof(signum));
+  }
+}
+
+NS_IMPL_ISUPPORTS(FdWatcher, nsIObserver);
+
+void FdWatcher::Init() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+  os->AddObserver(this, "xpcom-shutdown", /* ownsWeak = */ false);
+
+  XRE_GetIOMessageLoop()->PostTask(NewRunnableMethod(
+      "FdWatcher::StartWatching", this, &FdWatcher::StartWatching));
+}
+
+// Implementations may call this function multiple times if they ensure that
+// it's safe to call OpenFd() multiple times and they call StopWatching()
+// first.
+void FdWatcher::StartWatching() {
+  MOZ_ASSERT(XRE_GetIOMessageLoop() == MessageLoopForIO::current());
+  MOZ_ASSERT(mFd == -1);
+
+  mFd = OpenFd();
+  if (mFd == -1) {
+    LOG("FdWatcher: OpenFd failed.");
+    return;
+  }
+
+  MessageLoopForIO::current()->WatchFileDescriptor(mFd, /* persistent = */ true,
+                                                   MessageLoopForIO::WATCH_READ,
+                                                   &mReadWatcher, this);
+}
+
+// Since implementations can call StartWatching() multiple times, they can of
+// course call StopWatching() multiple times.
+void FdWatcher::StopWatching() {
+  MOZ_ASSERT(XRE_GetIOMessageLoop() == MessageLoopForIO::current());
+
+  mReadWatcher.StopWatchingFileDescriptor();
+  if (mFd != -1) {
+    close(mFd);
+    mFd = -1;
+  }
+}
+
+StaticRefPtr<SignalPipeWatcher> SignalPipeWatcher::sSingleton;
+
+/* static */
+SignalPipeWatcher* SignalPipeWatcher::GetSingleton() {
+  if (!sSingleton) {
+    sSingleton = new SignalPipeWatcher();
+    sSingleton->Init();
+    ClearOnShutdown(&sSingleton);
+  }
+  return sSingleton;
+}
+
+void SignalPipeWatcher::RegisterCallback(uint8_t aSignal,
+                                         PipeCallback aCallback) {
+  MutexAutoLock lock(mSignalInfoLock);
+
+  for (SignalInfoArray::index_type i = 0; i < mSignalInfo.Length(); ++i) {
+    if (mSignalInfo[i].mSignal == aSignal) {
+      LOG("Register Signal(%d) callback failed! (DUPLICATE)", aSignal);
+      return;
+    }
+  }
+  SignalInfo signalInfo = {aSignal, aCallback};
+  mSignalInfo.AppendElement(signalInfo);
+  RegisterSignalHandler(signalInfo.mSignal);
+}
+
+void SignalPipeWatcher::RegisterSignalHandler(uint8_t aSignal) {
+  struct sigaction action;
+  memset(&action, 0, sizeof(action));
+  sigemptyset(&action.sa_mask);
+  action.sa_handler = DumpSignalHandler;
+
+  if (aSignal) {
+    if (sigaction(aSignal, &action, nullptr)) {
+      LOG("SignalPipeWatcher failed to register sig %d.", aSignal);
+    }
+  } else {
+    MutexAutoLock lock(mSignalInfoLock);
+    for (SignalInfoArray::index_type i = 0; i < mSignalInfo.Length(); i++) {
+      if (sigaction(mSignalInfo[i].mSignal, &action, nullptr)) {
+        LOG("SignalPipeWatcher failed to register signal(%d) "
+            "dump signal handler.",
+            mSignalInfo[i].mSignal);
+      }
+    }
+  }
+}
+
+SignalPipeWatcher::~SignalPipeWatcher() {
+  if (sDumpPipeWriteFd != -1) {
+    StopWatching();
+  }
+}
+
+int SignalPipeWatcher::OpenFd() {
+  MOZ_ASSERT(XRE_GetIOMessageLoop() == MessageLoopForIO::current());
+
+  // Create a pipe.  When we receive a signal in our signal handler, we'll
+  // write the signum to the write-end of this pipe.
+  int pipeFds[2];
+  if (pipe(pipeFds)) {
+    LOG("SignalPipeWatcher failed to create pipe.");
+    return -1;
+  }
+
+  // Close this pipe on calls to exec().
+  fcntl(pipeFds[0], F_SETFD, FD_CLOEXEC);
+  fcntl(pipeFds[1], F_SETFD, FD_CLOEXEC);
+
+  int readFd = pipeFds[0];
+  sDumpPipeWriteFd = pipeFds[1];
+
+  RegisterSignalHandler();
+  return readFd;
+}
+
+void SignalPipeWatcher::StopWatching() {
+  MOZ_ASSERT(XRE_GetIOMessageLoop() == MessageLoopForIO::current());
+
+  // Close sDumpPipeWriteFd /after/ setting the fd to -1.
+  // Otherwise we have the (admittedly far-fetched) race where we
+  //
+  //  1) close sDumpPipeWriteFd
+  //  2) open a new fd with the same number as sDumpPipeWriteFd
+  //     had.
+  //  3) receive a signal, then write to the fd.
+  int pipeWriteFd = sDumpPipeWriteFd.exchange(-1);
+  close(pipeWriteFd);
+
+  FdWatcher::StopWatching();
+}
+
+void SignalPipeWatcher::OnFileCanReadWithoutBlocking(int aFd) {
+  MOZ_ASSERT(XRE_GetIOMessageLoop() == MessageLoopForIO::current());
+
+  uint8_t signum;
+  ssize_t numReceived = read(aFd, &signum, sizeof(signum));
+  if (numReceived != sizeof(signum)) {
+    LOG("Error reading from buffer in "
+        "SignalPipeWatcher::OnFileCanReadWithoutBlocking.");
+    return;
+  }
+
+  {
+    MutexAutoLock lock(mSignalInfoLock);
+    for (SignalInfoArray::index_type i = 0; i < mSignalInfo.Length(); i++) {
+      if (signum == mSignalInfo[i].mSignal) {
+        mSignalInfo[i].mCallback(signum);
+        return;
+      }
+    }
+  }
+  LOG("SignalPipeWatcher got unexpected signum.");
+}
+
+StaticRefPtr<FifoWatcher> FifoWatcher::sSingleton;
+
+/* static */
+FifoWatcher* FifoWatcher::GetSingleton() {
+  if (!sSingleton) {
+    nsAutoCString dirPath;
+    Preferences::GetCString("memory_info_dumper.watch_fifo.directory", dirPath);
+    sSingleton = new FifoWatcher(dirPath);
+    sSingleton->Init();
+    ClearOnShutdown(&sSingleton);
+  }
+  return sSingleton;
+}
+
+/* static */
+bool FifoWatcher::MaybeCreate() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!XRE_IsParentProcess()) {
+    // We want this to be main-process only, since two processes can't listen
+    // to the same fifo.
+    return false;
+  }
+
+  if (!Preferences::GetBool(kPrefName, false)) {
+    LOG("Fifo watcher disabled via pref.");
+    return false;
+  }
+
+  // The FifoWatcher is held alive by the observer service.
+  if (!sSingleton) {
+    GetSingleton();
+  }
+  return true;
+}
+
+void FifoWatcher::RegisterCallback(const nsCString& aCommand,
+                                   FifoCallback aCallback) {
+  MutexAutoLock lock(mFifoInfoLock);
+
+  for (FifoInfoArray::index_type i = 0; i < mFifoInfo.Length(); ++i) {
+    if (mFifoInfo[i].mCommand.Equals(aCommand)) {
+      LOG("Register command(%s) callback failed! (DUPLICATE)", aCommand.get());
+      return;
+    }
+  }
+  FifoInfo aFifoInfo = {aCommand, aCallback};
+  mFifoInfo.AppendElement(aFifoInfo);
+}
+
+FifoWatcher::~FifoWatcher() = default;
+
+int FifoWatcher::OpenFd() {
+  // If the memory_info_dumper.directory pref is specified, put the fifo
+  // there.  Otherwise, put it into the system's tmp directory.
+
+  nsCOMPtr<nsIFile> file;
+
+  nsresult rv;
+  if (mDirPath.Length() > 0) {
+    rv = XRE_GetFileFromPath(mDirPath.get(), getter_AddRefs(file));
+    if (NS_FAILED(rv)) {
+      LOG("FifoWatcher failed to open file \"%s\"", mDirPath.get());
+      return -1;
+    }
+  } else {
+    rv = NS_GetSpecialDirectory(NS_OS_TEMP_DIR, getter_AddRefs(file));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return -1;
+    }
+  }
+
+  rv = file->AppendNative("debug_info_trigger"_ns);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return -1;
+  }
+
+  nsAutoCString path;
+  rv = file->GetNativePath(path);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return -1;
+  }
+
+  // unlink might fail because the file doesn't exist, or for other reasons.
+  // But we don't care it fails; any problems will be detected later, when we
+  // try to mkfifo or open the file.
+  if (unlink(path.get())) {
+    LOG("FifoWatcher::OpenFifo unlink failed; errno=%d.  "
+        "Continuing despite error.",
+        errno);
+  }
+
+  if (mkfifo(path.get(), 0766)) {
+    LOG("FifoWatcher::OpenFifo mkfifo failed; errno=%d", errno);
+    return -1;
+  }
+
+#  ifdef ANDROID
+  // Android runs with a umask, so we need to chmod our fifo to make it
+  // world-writable.
+  chmod(path.get(), 0666);
+#  endif
+
+  int fd;
+  do {
+    // The fifo will block until someone else has written to it.  In
+    // particular, open() will block until someone else has opened it for
+    // writing!  We want open() to succeed and read() to block, so we open
+    // with NONBLOCK and then fcntl that away.
+    fd = open(path.get(), O_RDONLY | O_NONBLOCK);
+  } while (fd == -1 && errno == EINTR);
+
+  if (fd == -1) {
+    LOG("FifoWatcher::OpenFifo open failed; errno=%d", errno);
+    return -1;
+  }
+
+  // Make fd blocking now that we've opened it.
+  if (fcntl(fd, F_SETFL, 0)) {
+    close(fd);
+    return -1;
+  }
+
+  return fd;
+}
+
+void FifoWatcher::OnFileCanReadWithoutBlocking(int aFd) {
+  MOZ_ASSERT(XRE_GetIOMessageLoop() == MessageLoopForIO::current());
+
+  char buf[1024];
+  int nread;
+  do {
+    // sizeof(buf) - 1 to leave space for the null-terminator.
+    nread = read(aFd, buf, sizeof(buf));
+  } while (nread == -1 && errno == EINTR);
+
+  if (nread == -1) {
+    // We want to avoid getting into a situation where
+    // OnFileCanReadWithoutBlocking is called in an infinite loop, so when
+    // something goes wrong, stop watching the fifo altogether.
+    LOG("FifoWatcher hit an error (%d) and is quitting.", errno);
+    StopWatching();
+    return;
+  }
+
+  if (nread == 0) {
+    // If we get EOF, that means that the other side closed the fifo.  We need
+    // to close and re-open the fifo; if we don't,
+    // OnFileCanWriteWithoutBlocking will be called in an infinite loop.
+
+    LOG("FifoWatcher closing and re-opening fifo.");
+    StopWatching();
+    StartWatching();
+    return;
+  }
+
+  nsAutoCString inputStr;
+  inputStr.Append(buf, nread);
+
+  // Trimming whitespace is important because if you do
+  //   |echo "foo" >> debug_info_trigger|,
+  // it'll actually write "foo\n" to the fifo.
+  inputStr.Trim("\b\t\r\n");
+
+  {
+    MutexAutoLock lock(mFifoInfoLock);
+
+    for (FifoInfoArray::index_type i = 0; i < mFifoInfo.Length(); i++) {
+      const nsCString commandStr = mFifoInfo[i].mCommand;
+      if (inputStr == commandStr.get()) {
+        mFifoInfo[i].mCallback(inputStr);
+        return;
+      }
+    }
+  }
+  LOG("Got unexpected value from fifo; ignoring it.");
+}
+
+#endif  // XP_UNIX }
+
+// In Android case, this function will open a file named aFilename under
+// /data/local/tmp/"aFoldername".
+// Otherwise, it will open a file named aFilename under "NS_OS_TEMP_DIR".
+/* static */
+nsresult nsDumpUtils::OpenTempFile(const nsACString& aFilename, nsIFile** aFile,
+                                   const nsACString& aFoldername, Mode aMode) {
+#ifdef ANDROID
+  // For Android, first try the downloads directory which is world-readable
+  // rather than the temp directory which is not.
+  if (!*aFile) {
+    char* env = PR_GetEnv("DOWNLOADS_DIRECTORY");
+    if (env) {
+      NS_NewNativeLocalFile(nsCString(env), /* followLinks = */ true, aFile);
+    }
+  }
+#endif
+  nsresult rv;
+  if (!*aFile) {
+    if (NS_IsMainThread()) {
+      // This allows tests to override, but isn't safe off-mainthread.
+      rv = NS_GetSpecialDirectory(NS_OS_TEMP_DIR, aFile);
+    } else {
+      rv = GetSpecialSystemDirectory(OS_TemporaryDirectory, aFile);
+    }
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+#ifdef ANDROID
+  // /data/local/tmp is a true tmp directory; anyone can create a file there,
+  // but only the user which created the file can remove it.  We want non-root
+  // users to be able to remove these files, so we write them into a
+  // subdirectory of the temp directory and chmod 777 that directory.
+  if (!aFoldername.IsEmpty()) {
+    rv = (*aFile)->AppendNative(aFoldername);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    // It's OK if this fails; that probably just means that the directory
+    // already exists.
+    Unused << (*aFile)->Create(nsIFile::DIRECTORY_TYPE, 0777);
+
+    nsAutoCString dirPath;
+    rv = (*aFile)->GetNativePath(dirPath);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    while (chmod(dirPath.get(), 0777) == -1 && errno == EINTR) {
+    }
+  }
+#endif
+
+  nsCOMPtr<nsIFile> file(*aFile);
+
+  rv = file->AppendNative(aFilename);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (aMode == CREATE_UNIQUE) {
+    rv = file->CreateUnique(nsIFile::NORMAL_FILE_TYPE, 0666);
+  } else {
+    rv = file->Create(nsIFile::NORMAL_FILE_TYPE, 0666);
+  }
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+#ifdef ANDROID
+  // Make this file world-read/writable; the permissions passed to the
+  // CreateUnique call above are not sufficient on Android, which runs with a
+  // umask.
+  nsAutoCString path;
+  rv = file->GetNativePath(path);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  while (chmod(path.get(), 0666) == -1 && errno == EINTR) {
+  }
+#endif
+
+  return NS_OK;
+}
diff --git a/xpcom/base/nsDumpUtils.h b/xpcom/base/nsDumpUtils.h
new file mode 100644
index 0000000000..7aa9c6b735
--- /dev/null
+++ b/xpcom/base/nsDumpUtils.h
@@ -0,0 +1,184 @@
+/* -*- 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/. */
+
+#ifndef mozilla_nsDumpUtils_h
+#define mozilla_nsDumpUtils_h
+
+#include "nsIObserver.h"
+#include "base/message_loop.h"
+#include "nsXULAppAPI.h"
+#include "nsThreadUtils.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/StaticPtr.h"
+#include "nsTArray.h"
+
+#ifdef LOG
+#  undef LOG
+#endif
+
+#ifdef ANDROID
+#  include "android/log.h"
+#  define LOG(...) \
+    __android_log_print(ANDROID_LOG_INFO, "Gecko:DumpUtils", ##__VA_ARGS__)
+#else
+#  define LOG(...)
+#endif
+
+#ifdef XP_UNIX  // {
+
+/**
+ * Abstract base class for something which watches an fd and takes action when
+ * we can read from it without blocking.
+ */
+class FdWatcher : public MessageLoopForIO::Watcher, public nsIObserver {
+ protected:
+  MessageLoopForIO::FileDescriptorWatcher mReadWatcher;
+  int mFd;
+
+  virtual ~FdWatcher() {
+    // StopWatching should have run.
+    MOZ_ASSERT(mFd == -1);
+  }
+
+ public:
+  FdWatcher() : mFd(-1) { MOZ_ASSERT(NS_IsMainThread()); }
+
+  /**
+   * Open the fd to watch.  If we encounter an error, return -1.
+   */
+  virtual int OpenFd() = 0;
+
+  /**
+   * Called when you can read() from the fd without blocking.  Note that this
+   * function is also called when you're at eof (read() returns 0 in this case).
+   */
+  virtual void OnFileCanReadWithoutBlocking(int aFd) override = 0;
+  virtual void OnFileCanWriteWithoutBlocking(int aFd) override{};
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  /**
+   * Initialize this object.  This should be called right after the object is
+   * constructed.  (This would go in the constructor, except we interact with
+   * XPCOM, which we can't do from a constructor because our refcount is 0 at
+   * that point.)
+   */
+  void Init();
+
+  // Implementations may call this function multiple times if they ensure that
+
+  virtual void StartWatching();
+
+  // Since implementations can call StartWatching() multiple times, they can of
+  // course call StopWatching() multiple times.
+  virtual void StopWatching();
+
+  NS_IMETHOD Observe(nsISupports* aSubject, const char* aTopic,
+                     const char16_t* aData) override {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(!strcmp(aTopic, "xpcom-shutdown"));
+
+    XRE_GetIOMessageLoop()->PostTask(mozilla::NewRunnableMethod(
+        "FdWatcher::StopWatching", this, &FdWatcher::StopWatching));
+
+    return NS_OK;
+  }
+};
+
+typedef void (*FifoCallback)(const nsCString& aInputStr);
+struct FifoInfo {
+  nsCString mCommand;
+  FifoCallback mCallback;
+};
+typedef nsTArray<FifoInfo> FifoInfoArray;
+
+class FifoWatcher : public FdWatcher {
+ public:
+  /**
+   * The name of the preference used to enable/disable the FifoWatcher.
+   */
+  // The length of this array must match the size of the string constant in
+  // the definition in nsDumpUtils.cpp. A mismatch will result in a compile-time
+  // error.
+  static const char kPrefName[38];
+
+  static FifoWatcher* GetSingleton();
+
+  static bool MaybeCreate();
+
+  void RegisterCallback(const nsCString& aCommand, FifoCallback aCallback);
+
+  virtual ~FifoWatcher();
+
+  virtual int OpenFd() override;
+
+  virtual void OnFileCanReadWithoutBlocking(int aFd) override;
+
+ private:
+  nsAutoCString mDirPath;
+
+  static mozilla::StaticRefPtr<FifoWatcher> sSingleton;
+
+  explicit FifoWatcher(nsCString aPath)
+      : mDirPath(aPath), mFifoInfoLock("FifoWatcher.mFifoInfoLock") {}
+
+  mozilla::Mutex mFifoInfoLock;  // protects mFifoInfo
+  FifoInfoArray mFifoInfo MOZ_GUARDED_BY(mFifoInfoLock);
+};
+
+typedef void (*PipeCallback)(const uint8_t aRecvSig);
+struct SignalInfo {
+  uint8_t mSignal;
+  PipeCallback mCallback;
+};
+typedef nsTArray<SignalInfo> SignalInfoArray;
+
+class SignalPipeWatcher : public FdWatcher {
+ public:
+  static SignalPipeWatcher* GetSingleton();
+
+  void RegisterCallback(uint8_t aSignal, PipeCallback aCallback);
+
+  void RegisterSignalHandler(uint8_t aSignal = 0);
+
+  virtual ~SignalPipeWatcher();
+
+  virtual int OpenFd() override;
+
+  virtual void StopWatching() override;
+
+  virtual void OnFileCanReadWithoutBlocking(int aFd) override;
+
+ private:
+  static mozilla::StaticRefPtr<SignalPipeWatcher> sSingleton;
+
+  SignalPipeWatcher() : mSignalInfoLock("SignalPipeWatcher.mSignalInfoLock") {
+    MOZ_ASSERT(NS_IsMainThread());
+  }
+
+  mozilla::Mutex mSignalInfoLock;  // protects mSignalInfo
+  SignalInfoArray mSignalInfo MOZ_GUARDED_BY(mSignalInfoLock);
+};
+
+#endif  // XP_UNIX }
+
+class nsDumpUtils {
+ public:
+  enum Mode { CREATE, CREATE_UNIQUE };
+
+  /**
+   * This function creates a new unique file based on |aFilename| in a
+   * world-readable temp directory. This is the system temp directory
+   * or, in the case of Android, the downloads directory. If |aFile| is
+   * non-null, it is assumed to point to a folder, and that folder is used
+   * instead.
+   */
+  static nsresult OpenTempFile(const nsACString& aFilename, nsIFile** aFile,
+                               const nsACString& aFoldername = ""_ns,
+                               Mode aMode = CREATE_UNIQUE);
+};
+
+#endif
diff --git a/xpcom/base/nsError.h b/xpcom/base/nsError.h
new file mode 100644
index 0000000000..040cd4612c
--- /dev/null
+++ b/xpcom/base/nsError.h
@@ -0,0 +1,90 @@
+/* -*- 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/. */
+
+#ifndef nsError_h__
+#define nsError_h__
+
+#ifndef __cplusplus
+#  error nsError.h no longer supports C sources
+#endif
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Likely.h"
+
+#include <stdint.h>
+
+#define NS_ERROR_SEVERITY_SUCCESS 0
+#define NS_ERROR_SEVERITY_ERROR 1
+
+#include "ErrorList.h"  // IWYU pragma: export
+
+/**
+ * @name Standard Error Handling Macros
+ * @return 0 or 1 (false/true with bool type for C++)
+ */
+
+inline uint32_t NS_FAILED_impl(nsresult aErr) {
+  return static_cast<uint32_t>(aErr) & 0x80000000;
+}
+#define NS_FAILED(_nsresult) ((bool)MOZ_UNLIKELY(NS_FAILED_impl(_nsresult)))
+#define NS_SUCCEEDED(_nsresult) ((bool)MOZ_LIKELY(!NS_FAILED_impl(_nsresult)))
+
+/* Check that our enum type is actually uint32_t as expected */
+static_assert(((nsresult)0) < ((nsresult)-1),
+              "nsresult must be an unsigned type");
+static_assert(sizeof(nsresult) == sizeof(uint32_t), "nsresult must be 32 bits");
+
+#define MOZ_ALWAYS_SUCCEEDS(expr) MOZ_ALWAYS_TRUE(NS_SUCCEEDED(expr))
+
+/**
+ * @name Standard Error Generating Macros
+ */
+
+#define NS_ERROR_GENERATE(sev, module, code)                            \
+  (nsresult)(((uint32_t)(sev) << 31) |                                  \
+             ((uint32_t)(module + NS_ERROR_MODULE_BASE_OFFSET) << 16) | \
+             ((uint32_t)(code)))
+
+#define NS_ERROR_GENERATE_SUCCESS(module, code) \
+  NS_ERROR_GENERATE(NS_ERROR_SEVERITY_SUCCESS, module, code)
+
+#define NS_ERROR_GENERATE_FAILURE(module, code) \
+  NS_ERROR_GENERATE(NS_ERROR_SEVERITY_ERROR, module, code)
+
+/*
+ * This will return the nsresult corresponding to the most recent NSPR failure
+ * returned by PR_GetError.
+ *
+ ***********************************************************************
+ *      Do not depend on this function. It will be going away!
+ ***********************************************************************
+ */
+extern nsresult NS_ErrorAccordingToNSPR();
+
+/**
+ * @name Standard Macros for retrieving error bits
+ */
+
+inline constexpr uint16_t NS_ERROR_GET_CODE(nsresult aErr) {
+  return uint32_t(aErr) & 0xffff;
+}
+inline constexpr uint16_t NS_ERROR_GET_MODULE(nsresult aErr) {
+  return ((uint32_t(aErr) >> 16) - NS_ERROR_MODULE_BASE_OFFSET) & 0x1fff;
+}
+inline bool NS_ERROR_GET_SEVERITY(nsresult aErr) {
+  return uint32_t(aErr) >> 31;
+}
+
+#ifdef _MSC_VER
+#  pragma warning(disable : 4251) /* 'nsCOMPtr<class nsIInputStream>' needs to \
+                                     have dll-interface to be used by clients  \
+                                     of class 'nsInputStream' */
+#  pragma warning(                                                          \
+      disable : 4275) /* non dll-interface class 'nsISupports' used as base \
+                         for dll-interface class 'nsIRDFNode' */
+#endif
+
+#endif
diff --git a/xpcom/base/nsGZFileWriter.cpp b/xpcom/base/nsGZFileWriter.cpp
new file mode 100644
index 0000000000..2d8e14e944
--- /dev/null
+++ b/xpcom/base/nsGZFileWriter.cpp
@@ -0,0 +1,97 @@
+/* -*- 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 "nsGZFileWriter.h"
+#include "nsIFile.h"
+#include "nsString.h"
+#include "zlib.h"
+
+#ifdef XP_WIN
+#  include <io.h>
+#  define _dup dup
+#else
+#  include <unistd.h>
+#endif
+
+nsGZFileWriter::nsGZFileWriter(Operation aMode)
+    : mMode(aMode), mInitialized(false), mFinished(false), mGZFile(nullptr) {}
+
+nsGZFileWriter::~nsGZFileWriter() {
+  if (mInitialized && !mFinished) {
+    Finish();
+  }
+}
+
+nsresult nsGZFileWriter::Init(nsIFile* aFile) {
+  if (NS_WARN_IF(mInitialized) || NS_WARN_IF(mFinished)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Get a FILE out of our nsIFile.  Convert that into a file descriptor which
+  // gzip can own.  Then close our FILE, leaving only gzip's fd open.
+
+  FILE* file;
+  nsresult rv = aFile->OpenANSIFileDesc(mMode == Create ? "wb" : "ab", &file);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  return InitANSIFileDesc(file);
+}
+
+nsresult nsGZFileWriter::InitANSIFileDesc(FILE* aFile) {
+  if (NS_WARN_IF(mInitialized) || NS_WARN_IF(mFinished)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  mGZFile = gzdopen(dup(fileno(aFile)), mMode == Create ? "wb" : "ab");
+  fclose(aFile);
+
+  // gzdopen returns nullptr on error.
+  if (NS_WARN_IF(!mGZFile)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  mInitialized = true;
+
+  return NS_OK;
+}
+
+nsresult nsGZFileWriter::Write(const nsACString& aStr) {
+  if (NS_WARN_IF(!mInitialized) || NS_WARN_IF(mFinished)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // gzwrite uses a return value of 0 to indicate failure.  Otherwise, it
+  // returns the number of uncompressed bytes written.  To ensure we can
+  // distinguish between success and failure, don't call gzwrite when we have 0
+  // bytes to write.
+  if (aStr.IsEmpty()) {
+    return NS_OK;
+  }
+
+  // gzwrite never does a short write -- that is, the return value should
+  // always be either 0 or aStr.Length(), and we shouldn't have to call it
+  // multiple times in order to get it to read the whole buffer.
+  int rv = gzwrite(mGZFile, aStr.BeginReading(), aStr.Length());
+  if (NS_WARN_IF(rv != static_cast<int>(aStr.Length()))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+nsresult nsGZFileWriter::Finish() {
+  if (NS_WARN_IF(!mInitialized) || NS_WARN_IF(mFinished)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  mFinished = true;
+  gzclose(mGZFile);
+
+  // Ignore errors from gzclose; it's not like there's anything we can do about
+  // it, at this point!
+  return NS_OK;
+}
diff --git a/xpcom/base/nsGZFileWriter.h b/xpcom/base/nsGZFileWriter.h
new file mode 100644
index 0000000000..dc33b4a2de
--- /dev/null
+++ b/xpcom/base/nsGZFileWriter.h
@@ -0,0 +1,79 @@
+/* -*- 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/. */
+
+#ifndef nsGZFileWriter_h
+#define nsGZFileWriter_h
+
+#include "nsISupportsImpl.h"
+#include "zlib.h"
+#include "nsDependentString.h"
+#include <stdio.h>
+
+/**
+ * A simple class for writing to a .gz file.
+ *
+ * Note that the file that this interface produces has a different format than
+ * what you'd get if you compressed your data as a gzip stream and dumped the
+ * result to a file.
+ *
+ * The standard gunzip tool cannot decompress a raw gzip stream, but can handle
+ * the files produced by this interface.
+ */
+class nsGZFileWriter final {
+  virtual ~nsGZFileWriter();
+
+ public:
+  enum Operation { Append, Create };
+
+  explicit nsGZFileWriter(Operation aMode = Create);
+
+  NS_INLINE_DECL_REFCOUNTING(nsGZFileWriter)
+
+  /**
+   * Initialize this object.  We'll write our gzip'ed data to the given file,
+   * overwriting its contents if the file exists.
+   *
+   * Init() will return an error if called twice.  It's an error to call any
+   * other method on this interface without first calling Init().
+   */
+  [[nodiscard]] nsresult Init(nsIFile* aFile);
+
+  /**
+   * Alternate version of Init() for use when the file is already opened;
+   * e.g., with a FileDescriptor passed over IPC.
+   */
+  [[nodiscard]] nsresult InitANSIFileDesc(FILE* aFile);
+
+  /**
+   * Write the given string to the file.
+   */
+  [[nodiscard]] nsresult Write(const nsACString& aStr);
+
+  /**
+   * Write |length| bytes of |str| to the file.
+   */
+  [[nodiscard]] nsresult Write(const char* aStr, uint32_t aLen) {
+    return Write(nsDependentCSubstring(aStr, aLen));
+  }
+
+  /**
+   * Close this nsGZFileWriter. This method will be run when the underlying
+   * object is destroyed, so it's not strictly necessary to explicitly call it
+   * from your code.
+   *
+   * It's an error to call this method twice, and it's an error to call Write()
+   * after Finish() has been called.
+   */
+  nsresult Finish();
+
+ private:
+  Operation mMode;
+  bool mInitialized;
+  bool mFinished;
+  gzFile mGZFile;
+};
+
+#endif
diff --git a/xpcom/base/nsIAvailableMemoryWatcherBase.idl b/xpcom/base/nsIAvailableMemoryWatcherBase.idl
new file mode 100644
index 0000000000..07d48e8571
--- /dev/null
+++ b/xpcom/base/nsIAvailableMemoryWatcherBase.idl
@@ -0,0 +1,36 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* 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 "nsISupports.idl"
+
+/**
+ * nsITabUnloader: interface to represent TabUnloader
+ *
+ * nsIAvailableMemoryWatcherBase: interface to watch the system's memory
+ * status and invoke a registered TabUnloader when it detected a low-memory
+ * and high-memory situation.  The logic to detect such a memory situation
+ * is defined per platform.
+ */
+
+[scriptable, uuid(2e530956-6054-464f-9f4c-0ae6f8de5523)]
+interface nsITabUnloader : nsISupports
+{
+  /*
+   * Unload the least-recently-used tab.
+   * JS implementation of this interface TabUnloader.unloadTabAsync takes
+   * one parameter that defines a threshold to exclude fresh tabs from the
+   * unloading candidate tabs.  Currently the memory watcher is the only one
+   * caller of this interface and it always expects the default threshold,
+   * so this interface takes no parameter.
+   */
+  void unloadTabAsync();
+};
+
+[scriptable, uuid(b0b5701e-239d-49db-9009-37e89f86441c)]
+interface nsIAvailableMemoryWatcherBase : nsISupports
+{
+  void registerTabUnloader(in nsITabUnloader aTabUnloader);
+  void onUnloadAttemptCompleted(in nsresult aResult);
+};
diff --git a/xpcom/base/nsIClassInfoImpl.h b/xpcom/base/nsIClassInfoImpl.h
new file mode 100644
index 0000000000..045e75e5af
--- /dev/null
+++ b/xpcom/base/nsIClassInfoImpl.h
@@ -0,0 +1,193 @@
+/* -*- 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/. */
+
+#ifndef nsIClassInfoImpl_h__
+#define nsIClassInfoImpl_h__
+
+#include "mozilla/Alignment.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/MacroArgs.h"
+#include "mozilla/MacroForEach.h"
+#include "nsIClassInfo.h"
+#include "nsISupportsImpl.h"
+
+#include <new>
+
+/**
+ * This header file provides macros which help you make your class implement
+ * nsIClassInfo.  Implementing nsIClassInfo is particularly helpful if you have
+ * a C++ class which implements multiple interfaces and which you access from
+ * JavaScript.  If that class implements nsIClassInfo, the JavaScript code
+ * won't have to call QueryInterface on instances of the class; all methods
+ * from all interfaces returned by GetInterfaces() will be available
+ * automagically.
+ *
+ * Here's all you need to do.  Given a class
+ *
+ *   class nsFooBar : public nsIFoo, public nsIBar { };
+ *
+ * you should already have the following nsISupports implementation in its cpp
+ * file:
+ *
+ *   NS_IMPL_ISUPPORTS(nsFooBar, nsIFoo, nsIBar).
+ *
+ * Change this to
+ *
+ *   NS_IMPL_CLASSINFO(nsFooBar, nullptr, 0, NS_FOOBAR_CID)
+ *   NS_IMPL_ISUPPORTS_CI(nsFooBar, nsIFoo, nsIBar)
+ *
+ * If nsFooBar is threadsafe, change the 0 above to nsIClassInfo::THREADSAFE.
+ * If it's a singleton, use nsIClassInfo::SINGLETON.  The full list of flags is
+ * in nsIClassInfo.idl.
+ *
+ * The nullptr parameter is there so you can pass a function for converting
+ * from an XPCOM object to a scriptable helper.  Unless you're doing
+ * specialized JS work, you can probably leave this as nullptr.
+ *
+ * This file also defines the NS_IMPL_QUERY_INTERFACE_CI macro, which you can
+ * use to replace NS_IMPL_QUERY_INTERFACE, if you use that instead of
+ * NS_IMPL_ISUPPORTS.
+ *
+ * That's it!  The rest is gory details.
+ *
+ *
+ * Notice that nsFooBar didn't need to inherit from nsIClassInfo in order to
+ * "implement" it.  However, after adding these macros to nsFooBar, you you can
+ * QueryInterface an instance of nsFooBar to nsIClassInfo.  How can this be?
+ *
+ * The answer lies in the NS_IMPL_ISUPPORTS_CI macro.  It modifies nsFooBar's
+ * QueryInterface implementation such that, if we ask to QI to nsIClassInfo, it
+ * returns a singleton object associated with the class.  (That singleton is
+ * defined by NS_IMPL_CLASSINFO.)  So all nsFooBar instances will return the
+ * same object when QI'ed to nsIClassInfo.  (You can see this in
+ * NS_IMPL_QUERY_CLASSINFO below.)
+ *
+ * This hack breaks XPCOM's rules, since if you take an instance of nsFooBar,
+ * QI it to nsIClassInfo, and then try to QI to nsIFoo, that will fail.  On the
+ * upside, implementing nsIClassInfo doesn't add a vtable pointer to instances
+ * of your class.
+ *
+ * In principal, you can also implement nsIClassInfo by inheriting from the
+ * interface.  But some code expects that when it QI's an object to
+ * nsIClassInfo, it gets back a singleton which isn't attached to any
+ * particular object.  If a class were to implement nsIClassInfo through
+ * inheritance, that code might QI to nsIClassInfo and keep the resulting
+ * object alive, thinking it was only keeping alive the classinfo singleton,
+ * but in fact keeping a whole instance of the class alive.  See, e.g., bug
+ * 658632.
+ *
+ * Unless you specifically need to have a different nsIClassInfo instance for
+ * each instance of your class, you should probably just implement nsIClassInfo
+ * as a singleton.
+ */
+
+class GenericClassInfo : public nsIClassInfo {
+ public:
+  struct ClassInfoData {
+    // This function pointer uses NS_CALLBACK_ because it's always set to an
+    // NS_IMETHOD function, which uses __stdcall on Win32.
+    typedef NS_CALLBACK_(nsresult, GetInterfacesProc)(nsTArray<nsIID>& aArray);
+    GetInterfacesProc getinterfaces;
+
+    // This function pointer doesn't use NS_CALLBACK_ because it's always set to
+    // a vanilla function.
+    typedef nsresult (*GetScriptableHelperProc)(nsIXPCScriptable** aHelper);
+    GetScriptableHelperProc getscriptablehelper;
+
+    uint32_t flags;
+    nsCID cid;
+  };
+
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_NSICLASSINFO
+
+  explicit GenericClassInfo(const ClassInfoData* aData) : mData(aData) {}
+
+ private:
+  const ClassInfoData* mData;
+};
+
+#define NS_CLASSINFO_NAME(_class) g##_class##_classInfoGlobal
+#define NS_CI_INTERFACE_GETTER_NAME(_class) _class##_GetInterfacesHelper
+#define NS_DECL_CI_INTERFACE_GETTER(_class)                                  \
+  extern NS_IMETHODIMP NS_CI_INTERFACE_GETTER_NAME(_class)(nsTArray<nsIID> & \
+                                                           array);
+
+#define NS_IMPL_CLASSINFO(_class, _getscriptablehelper, _flags, _cid)       \
+  NS_DECL_CI_INTERFACE_GETTER(_class)                                       \
+  static const GenericClassInfo::ClassInfoData k##_class##ClassInfoData = { \
+      NS_CI_INTERFACE_GETTER_NAME(_class),                                  \
+      _getscriptablehelper,                                                 \
+      _flags | nsIClassInfo::SINGLETON_CLASSINFO,                           \
+      _cid,                                                                 \
+  };                                                                        \
+  mozilla::AlignedStorage2<GenericClassInfo> k##_class##ClassInfoDataPlace; \
+  nsIClassInfo* NS_CLASSINFO_NAME(_class) = nullptr;
+
+#define NS_IMPL_QUERY_CLASSINFO(_class)                                      \
+  if (aIID.Equals(NS_GET_IID(nsIClassInfo))) {                               \
+    if (!NS_CLASSINFO_NAME(_class))                                          \
+      NS_CLASSINFO_NAME(_class) = new (k##_class##ClassInfoDataPlace.addr()) \
+          GenericClassInfo(&k##_class##ClassInfoData);                       \
+    foundInterface = NS_CLASSINFO_NAME(_class);                              \
+  } else
+
+#define NS_CLASSINFO_HELPER_BEGIN(_class, _c)                    \
+  NS_IMETHODIMP                                                  \
+  NS_CI_INTERFACE_GETTER_NAME(_class)(nsTArray<nsIID> & array) { \
+    array.Clear();                                               \
+    array.SetCapacity(_c);
+
+#define NS_CLASSINFO_HELPER_ENTRY(_interface) \
+  array.AppendElement(NS_GET_IID(_interface));
+
+#define NS_CLASSINFO_HELPER_END \
+  return NS_OK;                 \
+  }
+
+#define NS_IMPL_CI_INTERFACE_GETTER(aClass, ...)                       \
+  static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0,                        \
+                "Need more arguments to NS_IMPL_CI_INTERFACE_GETTER"); \
+  NS_CLASSINFO_HELPER_BEGIN(aClass, MOZ_ARG_COUNT(__VA_ARGS__))        \
+  MOZ_FOR_EACH(NS_CLASSINFO_HELPER_ENTRY, (), (__VA_ARGS__))           \
+  NS_CLASSINFO_HELPER_END
+
+#define NS_IMPL_CI_INTERFACE_GETTER0(aClass) \
+  NS_CLASSINFO_HELPER_BEGIN(aClass, 0)       \
+  NS_CLASSINFO_HELPER_END
+
+// Note that this macro is an internal implementation of this header and
+// should not be used outside it. It does not end the interface map as this
+// is done in NS_IMPL_QUERY_INTERFACE_CI or the _INHERITED variant.
+#define NS_IMPL_QUERY_INTERFACE_CI_GUTS(aClass, ...)                      \
+  static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0,                           \
+                "Need more arguments to NS_IMPL_QUERY_INTERFACE_CI");     \
+  NS_INTERFACE_MAP_BEGIN(aClass)                                          \
+    MOZ_FOR_EACH(NS_INTERFACE_MAP_ENTRY, (), (__VA_ARGS__))               \
+    NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, MOZ_ARG_1(__VA_ARGS__)) \
+    NS_IMPL_QUERY_CLASSINFO(aClass)
+
+#define NS_IMPL_QUERY_INTERFACE_CI(aClass, ...)        \
+  NS_IMPL_QUERY_INTERFACE_CI_GUTS(aClass, __VA_ARGS__) \
+  NS_INTERFACE_MAP_END
+
+#define NS_IMPL_QUERY_INTERFACE_CI_INHERITED(aClass, aSuper, ...) \
+  NS_IMPL_QUERY_INTERFACE_CI_GUTS(aClass, __VA_ARGS__)            \
+  NS_INTERFACE_MAP_END_INHERITING                                 \
+  (aSuper)
+
+#define NS_IMPL_QUERY_INTERFACE_CI_INHERITED0(aClass, aSuper) \
+  NS_INTERFACE_MAP_BEGIN(aClass)                              \
+    NS_IMPL_QUERY_CLASSINFO(aClass)                           \
+  NS_INTERFACE_MAP_END_INHERITING(aSuper)
+
+#define NS_IMPL_ISUPPORTS_CI(aClass, ...)         \
+  NS_IMPL_ADDREF(aClass)                          \
+  NS_IMPL_RELEASE(aClass)                         \
+  NS_IMPL_QUERY_INTERFACE_CI(aClass, __VA_ARGS__) \
+  NS_IMPL_CI_INTERFACE_GETTER(aClass, __VA_ARGS__)
+
+#endif  // nsIClassInfoImpl_h__
diff --git a/xpcom/base/nsIConsoleListener.idl b/xpcom/base/nsIConsoleListener.idl
new file mode 100644
index 0000000000..45e6fcb1fc
--- /dev/null
+++ b/xpcom/base/nsIConsoleListener.idl
@@ -0,0 +1,18 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* 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/. */
+
+/*
+ * Used by the console service to notify listeners of new console messages.
+ */
+
+#include "nsISupports.idl"
+
+interface nsIConsoleMessage;
+
+[scriptable, function, uuid(35c400a4-5792-438c-b915-65e30d58d557)]
+interface nsIConsoleListener : nsISupports
+{
+    void observe(in nsIConsoleMessage aMessage);
+};
diff --git a/xpcom/base/nsIConsoleMessage.idl b/xpcom/base/nsIConsoleMessage.idl
new file mode 100644
index 0000000000..ec9b901aaa
--- /dev/null
+++ b/xpcom/base/nsIConsoleMessage.idl
@@ -0,0 +1,52 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "nsISupports.idl"
+
+/**
+ * This is intended as a base interface; implementations may want to
+ * provide an object that can be qi'ed to provide more specific
+ * message information.
+ */
+[scriptable, uuid(3aba9617-10e2-4839-83ae-2e6fc4df428b)]
+interface nsIConsoleMessage : nsISupports
+{
+    /** Log level constants. */
+    const uint32_t debug = 0;
+    const uint32_t info = 1;
+    const uint32_t warn = 2;
+    const uint32_t error = 3;
+
+    /**
+     * The log level of this message.
+     */
+    readonly attribute uint32_t logLevel;
+
+    /**
+     * The time (in milliseconds from the Epoch) that the message instance
+     * was initialised.
+     * The timestamp is initialized as JS_now/1000 so that it can be
+     * compared to Date.now in Javascript.
+     */
+    readonly attribute long long timeStamp;
+
+    /**
+     * The time (in microseconds from the Epoch) that the message instance
+     * was initialised.
+     * The timestamp is initialized as JS_now.
+     */
+    readonly attribute long long microSecondTimeStamp;
+
+    [binaryname(MessageMoz)] readonly attribute AString message;
+
+    attribute boolean isForwardedFromContentProcess;
+
+    AUTF8String toString();
+};
+
+%{ C++
+#define NS_CONSOLEMESSAGE_CID \
+{ 0x024efc9e, 0x54dc, 0x4844, { 0x80, 0x4b, 0x41, 0xd3, 0xf3, 0x69, 0x90, 0x73 }}
+%}
diff --git a/xpcom/base/nsIConsoleService.idl b/xpcom/base/nsIConsoleService.idl
new file mode 100644
index 0000000000..1122875aa5
--- /dev/null
+++ b/xpcom/base/nsIConsoleService.idl
@@ -0,0 +1,78 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* 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 "nsISupports.idl"
+
+interface nsIConsoleListener;
+interface nsIConsoleMessage;
+
+[scriptable, builtinclass, uuid(0eb81d20-c37e-42d4-82a8-ca9ae96bdf52)]
+interface nsIConsoleService : nsISupports
+{
+    void logMessage(in nsIConsoleMessage message);
+
+    // This helper function executes `function` and redirects any exception
+    // that may be thrown while running it to the DevTools Console currently
+    // debugging `targetGlobal`.
+    //
+    // This helps flag the nsIScriptError with a particular innerWindowID
+    // which is especially useful for WebExtension content scripts
+    // where script are running in a Sandbox whose prototype is the content window.
+    // We expect content script exception to be flaged with the content window
+    // innerWindowID in order to appear in the tab's DevTools.
+    [implicit_jscontext]
+    jsval callFunctionAndLogException(in jsval targetGlobal, in jsval function);
+
+    // This is a variant of LogMessage which allows the caller to determine
+    // if the message should be output to an OS-specific log. This is used on
+    // B2G to control whether the message is logged to the android log or not.
+    cenum OutputMode : 8 {
+        SuppressLog = 0,
+        OutputToLog
+    };
+    void logMessageWithMode(in nsIConsoleMessage message,
+                            in nsIConsoleService_OutputMode mode);
+
+    /**
+     * Convenience method for logging simple messages.
+     */
+    void logStringMessage(in wstring message);
+
+    /**
+     * Get an array of all the messages logged so far.
+     */
+    Array<nsIConsoleMessage> getMessageArray();
+
+    /**
+     * To guard against stack overflows from listeners that could log
+     * messages (it's easy to do this inadvertently from listeners
+     * implemented in JavaScript), we don't call any listeners when
+     * another error is already being logged.
+     */
+    void registerListener(in nsIConsoleListener listener);
+
+    /**
+     * Each registered listener should also be unregistered.
+     */
+    void unregisterListener(in nsIConsoleListener listener);
+
+    /**
+     * Clear the message buffer (e.g. for privacy reasons).
+     */
+    void reset();
+
+    /**
+     * Clear the message buffer for a given window.
+     */
+    void resetWindow(in uint64_t windowInnerId);
+};
+
+
+%{ C++
+#define NS_CONSOLESERVICE_CID \
+{ 0x7e3ff85c, 0x1dd2, 0x11b2, { 0x8d, 0x4b, 0xeb, 0x45, 0x2c, 0xb0, 0xff, 0x40 }}
+
+#define NS_CONSOLESERVICE_CONTRACTID "@mozilla.org/consoleservice;1"
+%}
diff --git a/xpcom/base/nsICycleCollectorListener.idl b/xpcom/base/nsICycleCollectorListener.idl
new file mode 100644
index 0000000000..5e0b059a13
--- /dev/null
+++ b/xpcom/base/nsICycleCollectorListener.idl
@@ -0,0 +1,166 @@
+/* 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 "nsISupports.idl"
+
+%{C++
+#include <stdio.h>
+
+class nsCycleCollectorLogger;
+%}
+
+[ptr] native FILE(FILE);
+[ptr] native nsCycleCollectorLoggerPtr(nsCycleCollectorLogger);
+interface nsIFile;
+
+/**
+ * A set of interfaces for recording the cycle collector's work. An instance
+ * of nsICycleCollectorListener can be configured to enable various
+ * options, then passed to the cycle collector when it runs.
+ * Note that additional logging options are available by setting environment
+ * variables, as described at the top of nsCycleCollector.cpp.
+ */
+
+/**
+ * nsICycleCollectorHandler is the interface JS code should implement to
+ * receive the results logged by an nsICycleCollectorListener
+ * instance. Pass an instance of this to the logger's 'processNext' method
+ * after the collection has run. This will describe the objects the cycle
+ * collector visited, the edges it found, and the conclusions it reached
+ * about the liveness of objects.
+ *
+ * In more detail:
+ * - For each node in the graph:
+ *   - a call is made to either |noteRefCountedObject| or |noteGCedObject|, to
+ *     describe the node itself; and
+ *   - for each edge starting at that node, a call is made to |noteEdge|.
+ *
+ * - Then, a series of calls are made to:
+ *   - |describeRoot|, for reference-counted nodes that the CC has identified as
+ *     being alive because there are unknown references to those nodes.
+ *   - |describeGarbage|, for nodes the cycle collector has identified as garbage.
+ *
+ *   Any node not mentioned in a call to |describeRoot| or |describeGarbage| is
+ *   neither a root nor garbage. The cycle collector was able to find all of the
+ *   edges implied by the node's reference count.
+ */
+[scriptable, uuid(7f093367-1492-4b89-87af-c01dbc831246)]
+interface nsICycleCollectorHandler : nsISupports
+{
+    void noteRefCountedObject(in ACString aAddress,
+                              in unsigned long aRefCount,
+                              in ACString aObjectDescription);
+    void noteGCedObject(in ACString aAddress,
+                        in boolean aMarked,
+                        in ACString aObjectDescription,
+                        in ACString aCompartmentAddress);
+    void noteEdge(in ACString aFromAddress,
+                  in ACString aToAddress,
+                  in ACString aEdgeName);
+    void describeRoot(in ACString aAddress,
+                      in unsigned long aKnownEdges);
+    void describeGarbage(in ACString aAddress);
+};
+
+
+/**
+ * This interface allows replacing the log-writing backend for an
+ * nsICycleCollectorListener.  As this interface is also called while
+ * the cycle collector is running, it cannot be implemented in JS.
+ */
+[scriptable, builtinclass, uuid(3ad9875f-d0e4-4ac2-87e3-f127f6c02ce1)]
+interface nsICycleCollectorLogSink : nsISupports
+{
+  [noscript] void open(out FILE aGCLog, out FILE aCCLog);
+  void closeGCLog();
+  void closeCCLog();
+
+  // This string will appear somewhere in the log's filename.
+  attribute AString filenameIdentifier;
+
+  // This is the process ID; it can be changed if logging is on behalf
+  // of another process.
+  attribute int32_t processIdentifier;
+
+  // The GC log file, if logging to files.
+  readonly attribute nsIFile gcLog;
+
+  // The CC log file, if logging to files.
+  readonly attribute nsIFile ccLog;
+};
+
+
+/**
+ * This interface is used to configure some reporting options for the cycle
+ * collector. This interface cannot be implemented by JavaScript code, as it
+ * is called while the cycle collector is running.
+ *
+ * To analyze cycle collection data in JS:
+ *
+ * - Create an instance of nsICycleCollectorListener, which implements this
+ *   interface. In C++, this can be done by calling
+ *   nsCycleCollector_createLogger(). In JS, this can be done by calling
+ *   Components.utils.createCCLogger().
+ *
+ * - Set its |disableLog| property to true. This prevents the logger from
+ *   printing messages about each method call to a temporary log file.
+ *
+ * - Set its |wantAfterProcessing| property to true. This tells the logger
+ *   to record calls to its methods in memory. The |processNext| method
+ *   returns events from this record.
+ *
+ * - Perform a collection using the logger. For example, call
+ *   |nsIDOMWindowUtils|'s |garbageCollect| method, passing the logger as
+ *   the |aListener| argument.
+ *
+ * - When the collection is complete, loop calling the logger's
+ *   |processNext| method, passing a JavaScript object that implements
+ *   nsICycleCollectorHandler. This JS code is free to allocate and operate
+ *   on objects however it pleases: the cycle collector has finished its
+ *   work, and the JS code is simply consuming recorded data.
+ */
+[scriptable, builtinclass, uuid(703b53b6-24f6-40c6-9ea9-aeb2dc53d170)]
+interface nsICycleCollectorListener : nsISupports
+{
+    // Return a listener that directs the cycle collector to traverse
+    // objects that it knows won't be collectable.
+    //
+    // Note that even this listener will not visit every node in the heap;
+    // the cycle collector can't see the entire heap. But while this
+    // listener is in use, the collector disables some optimizations it
+    // normally uses to avoid certain classes of objects that are certainly
+    // alive. So, if your purpose is to get a view of the portion of the
+    // heap that is of interest to the cycle collector, and not simply find
+    // garbage, then you should use the listener this returns.
+    //
+    // Note that this does not necessarily return a new listener; rather, it may
+    // simply set a flag on this listener (a side effect!) and return it.
+    nsICycleCollectorListener allTraces();
+
+    // True if this listener will behave like one returned by allTraces().
+    readonly attribute boolean wantAllTraces;
+
+    // If true, do not log each method call to a temporary file.
+    // Initially false.
+    attribute boolean disableLog;
+
+    // If |disableLog| is false, this object will be sent the log text.
+    attribute nsICycleCollectorLogSink logSink;
+
+    // If true, record all method calls in memory, to be retrieved later
+    // using |processNext|. Initially false.
+    attribute boolean wantAfterProcessing;
+
+    // Report the next recorded event to |aHandler|, and remove it from the
+    // record. Return false if there isn't anything more to process.
+    //
+    // Note that we only record events to report here if our
+    // |wantAfterProcessing| property is true.
+    boolean processNext(in nsICycleCollectorHandler aHandler);
+
+    // Return the current object as an nsCycleCollectorLogger*, which is the
+    // only class that should be implementing this interface. We need the
+    // concrete implementation type to help the GC rooting analysis.
+    [noscript] nsCycleCollectorLoggerPtr asLogger();
+};
diff --git a/xpcom/base/nsID.cpp b/xpcom/base/nsID.cpp
new file mode 100644
index 0000000000..701bf647d1
--- /dev/null
+++ b/xpcom/base/nsID.cpp
@@ -0,0 +1,239 @@
+/* -*- 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 "nsID.h"
+
+#include <limits.h>
+
+#include "MainThreadUtils.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/RandomNum.h"
+#include "mozilla/Sprintf.h"
+#include "nss.h"
+#include "ScopedNSSTypes.h"
+
+[[nodiscard]] static bool GenerateRandomBytesFromNSS(void* aBuffer,
+                                                     size_t aLength) {
+  MOZ_ASSERT(aBuffer);
+
+  // Bounds check that we can safely truncate size_t `aLength` to an int.
+  if (aLength == 0 || aLength > INT_MAX) {
+    MOZ_ASSERT_UNREACHABLE("Bad aLength");
+    return false;
+  }
+  int len = static_cast<int>(aLength);
+
+  // Only try to use NSS on the main thread.
+  if (!NS_IsMainThread() || !NSS_IsInitialized()) {
+    return false;
+  }
+
+  mozilla::UniquePK11SlotInfo slot(PK11_GetInternalSlot());
+  if (!slot) {
+    MOZ_ASSERT_UNREACHABLE("Null slot");
+    return false;
+  }
+
+  SECStatus srv = PK11_GenerateRandomOnSlot(
+      slot.get(), static_cast<unsigned char*>(aBuffer), len);
+  MOZ_ASSERT(srv == SECSuccess);
+  return (srv == SECSuccess);
+}
+
+nsresult nsID::GenerateUUIDInPlace(nsID& aId) {
+  // Firefox needs to generate some UUIDs before NSS has been initialized. We
+  // prefer NSS's RNG, but if NSS is not available yet or returns an error, fall
+  // back to MFBT's GenerateRandomBytes().
+  if (!GenerateRandomBytesFromNSS(&aId, sizeof(nsID)) &&
+      !mozilla::GenerateRandomBytesFromOS(&aId, sizeof(nsID))) {
+    MOZ_ASSERT_UNREACHABLE("GenerateRandomBytesFromOS() failed");
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  // Put in the version
+  aId.m2 &= 0x0fff;
+  aId.m2 |= 0x4000;
+
+  // Put in the variant
+  aId.m3[0] &= 0x3f;
+  aId.m3[0] |= 0x80;
+
+  return NS_OK;
+}
+
+nsID nsID::GenerateUUID() {
+  nsID uuid;
+  nsresult rv = GenerateUUIDInPlace(uuid);
+  MOZ_RELEASE_ASSERT(NS_SUCCEEDED(rv));
+  return uuid;
+}
+
+void nsID::Clear() {
+  m0 = 0;
+  m1 = 0;
+  m2 = 0;
+  memset(m3, 0, sizeof(m3));
+}
+
+/**
+ * Multiplies the_int_var with 16 (0x10) and adds the value of the
+ * hexadecimal digit the_char. If it fails it returns false from
+ * the function it's used in.
+ */
+
+#define ADD_HEX_CHAR_TO_INT_OR_RETURN_FALSE(the_char, the_int_var) \
+  the_int_var = (the_int_var << 4) + the_char;                     \
+  if (the_char >= '0' && the_char <= '9')                          \
+    the_int_var -= '0';                                            \
+  else if (the_char >= 'a' && the_char <= 'f')                     \
+    the_int_var -= 'a' - 10;                                       \
+  else if (the_char >= 'A' && the_char <= 'F')                     \
+    the_int_var -= 'A' - 10;                                       \
+  else                                                             \
+    return false
+
+/**
+ * Parses number_of_chars characters from the char_pointer pointer and
+ * puts the number in the dest_variable. The pointer is moved to point
+ * at the first character after the parsed ones. If it fails it returns
+ * false from the function the macro is used in.
+ */
+
+#define PARSE_CHARS_TO_NUM(char_pointer, dest_variable, number_of_chars) \
+  do {                                                                   \
+    int32_t _i = number_of_chars;                                        \
+    dest_variable = 0;                                                   \
+    while (_i) {                                                         \
+      ADD_HEX_CHAR_TO_INT_OR_RETURN_FALSE(*char_pointer, dest_variable); \
+      char_pointer++;                                                    \
+      _i--;                                                              \
+    }                                                                    \
+  } while (0)
+
+/**
+ * Parses a hyphen from the char_pointer string. If there is no hyphen there
+ * the function returns false from the function it's used in. The
+ * char_pointer is advanced one step.
+ */
+
+#define PARSE_HYPHEN(char_pointer) \
+  if (*(char_pointer++) != '-') return false
+
+/*
+ * Turns a {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} string into
+ * an nsID. It can also handle the old format without the { and }.
+ */
+
+bool nsID::Parse(const char* aIDStr) {
+  /* Optimized for speed */
+  if (!aIDStr) {
+    return false;
+  }
+
+  bool expectFormat1 = (aIDStr[0] == '{');
+  if (expectFormat1) {
+    ++aIDStr;
+  }
+
+  PARSE_CHARS_TO_NUM(aIDStr, m0, 8);
+  PARSE_HYPHEN(aIDStr);
+  PARSE_CHARS_TO_NUM(aIDStr, m1, 4);
+  PARSE_HYPHEN(aIDStr);
+  PARSE_CHARS_TO_NUM(aIDStr, m2, 4);
+  PARSE_HYPHEN(aIDStr);
+  int i;
+  for (i = 0; i < 2; ++i) {
+    PARSE_CHARS_TO_NUM(aIDStr, m3[i], 2);
+  }
+  PARSE_HYPHEN(aIDStr);
+  while (i < 8) {
+    PARSE_CHARS_TO_NUM(aIDStr, m3[i], 2);
+    i++;
+  }
+
+  return expectFormat1 ? *aIDStr == '}' : true;
+}
+
+#ifndef XPCOM_GLUE_AVOID_NSPR
+
+/*
+ * Returns a managed string in {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}
+ * format.
+ */
+nsIDToCString nsID::ToString() const { return nsIDToCString(*this); }
+
+static const char sHexChars[256 * 2 + 1] =
+    "000102030405060708090a0b0c0d0e0f"
+    "101112131415161718191a1b1c1d1e1f"
+    "202122232425262728292a2b2c2d2e2f"
+    "303132333435363738393a3b3c3d3e3f"
+    "404142434445464748494a4b4c4d4e4f"
+    "505152535455565758595a5b5c5d5e5f"
+    "606162636465666768696a6b6c6d6e6f"
+    "707172737475767778797a7b7c7d7e7f"
+    "808182838485868788898a8b8c8d8e8f"
+    "909192939495969798999a9b9c9d9e9f"
+    "a0a1a2a3a4a5a6a7a8a9aaabacadaeaf"
+    "b0b1b2b3b4b5b6b7b8b9babbbcbdbebf"
+    "c0c1c2c3c4c5c6c7c8c9cacbcccdcecf"
+    "d0d1d2d3d4d5d6d7d8d9dadbdcdddedf"
+    "e0e1e2e3e4e5e6e7e8e9eaebecedeeef"
+    "f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff";
+
+// Writes a zero-padded 8-bit integer as lowercase hex into aDest[0..2]
+static void ToHex8Bit(uint8_t aValue, char* aDest) {
+  aDest[0] = sHexChars[2 * aValue];
+  aDest[1] = sHexChars[2 * aValue + 1];
+}
+
+// Writes a zero-padded 16-bit integer as lowercase hex into aDest[0..4]
+static void ToHex16Bit(uint16_t aValue, char* aDest) {
+  const uint8_t hi = (aValue >> 8);
+  const uint8_t lo = aValue;
+  ToHex8Bit(hi, &aDest[0]);
+  ToHex8Bit(lo, &aDest[2]);
+}
+
+// Writes a zero-padded 32-bit integer as lowercase hex into aDest[0..8]
+static void ToHex32Bit(uint32_t aValue, char* aDest) {
+  const uint16_t hi = (aValue >> 16);
+  const uint16_t lo = aValue;
+  ToHex16Bit(hi, &aDest[0]);
+  ToHex16Bit(lo, &aDest[4]);
+}
+
+void nsID::ToProvidedString(char (&aDest)[NSID_LENGTH]) const {
+  // Stringify manually, for best performance.
+  //
+  // "{%08x-%04x-%04x-%02x%02x-%02x%02x%02x%02x%02x%02x}"
+  // "{ecc35fd2-9029-4287-a826-b0a241d48d31}"
+  aDest[0] = '{';
+  ToHex32Bit(m0, &aDest[1]);
+  aDest[9] = '-';
+  ToHex16Bit(m1, &aDest[10]);
+  aDest[14] = '-';
+  ToHex16Bit(m2, &aDest[15]);
+  aDest[19] = '-';
+  ToHex8Bit(m3[0], &aDest[20]);
+  ToHex8Bit(m3[1], &aDest[22]);
+  aDest[24] = '-';
+  ToHex8Bit(m3[2], &aDest[25]);
+  ToHex8Bit(m3[3], &aDest[27]);
+  ToHex8Bit(m3[4], &aDest[29]);
+  ToHex8Bit(m3[5], &aDest[31]);
+  ToHex8Bit(m3[6], &aDest[33]);
+  ToHex8Bit(m3[7], &aDest[35]);
+  aDest[37] = '}';
+  aDest[38] = '\0';
+}
+
+#endif  // XPCOM_GLUE_AVOID_NSPR
+
+nsID* nsID::Clone() const {
+  auto id = static_cast<nsID*>(moz_xmalloc(sizeof(nsID)));
+  *id = *this;
+  return id;
+}
diff --git a/xpcom/base/nsID.h b/xpcom/base/nsID.h
new file mode 100644
index 0000000000..c7feddd1cc
--- /dev/null
+++ b/xpcom/base/nsID.h
@@ -0,0 +1,173 @@
+/* -*- 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/. */
+
+#ifndef nsID_h__
+#define nsID_h__
+
+#include <string.h>
+
+#include "nscore.h"
+
+#define NSID_LENGTH 39
+
+#ifndef XPCOM_GLUE_AVOID_NSPR
+class nsIDToCString;
+#endif
+
+/**
+ * A "unique identifier". This is modeled after OSF DCE UUIDs.
+ */
+
+struct nsID {
+  uint32_t m0;
+  uint16_t m1;
+  uint16_t m2;
+  uint8_t m3[8];
+
+  /**
+   * Create a new random UUID.
+   * GenerateUUIDInPlace() is fallible, whereas GenerateUUID() will abort in
+   * the unlikely case that the OS RNG returns an error.
+   */
+  [[nodiscard]] static nsresult GenerateUUIDInPlace(nsID& aId);
+  static nsID GenerateUUID();
+
+  /**
+   * Ensures everything is zeroed out.
+   */
+  void Clear();
+
+  /**
+   * Equivalency method. Compares this nsID with another.
+   * @return true if they are the same, false if not.
+   */
+
+  inline bool Equals(const nsID& aOther) const {
+    // At the time of this writing, modern compilers (namely Clang) inline this
+    // memcmp call into a single SIMD operation on x86/x86-64 architectures (as
+    // long as we compare to zero rather than returning the full integer return
+    // value), which is measurably more efficient to any manual comparisons we
+    // can do directly.
+#if defined(__x86_64__) || defined(__i386__)
+    return !memcmp(this, &aOther, sizeof *this);
+#else
+    // However, on ARM architectures, compilers still tend to generate a direct
+    // memcmp call, which we'd like to avoid.
+    return (((uint32_t*)&m0)[0] == ((uint32_t*)&aOther.m0)[0]) &&
+           (((uint32_t*)&m0)[1] == ((uint32_t*)&aOther.m0)[1]) &&
+           (((uint32_t*)&m0)[2] == ((uint32_t*)&aOther.m0)[2]) &&
+           (((uint32_t*)&m0)[3] == ((uint32_t*)&aOther.m0)[3]);
+#endif
+  }
+
+  inline bool operator==(const nsID& aOther) const { return Equals(aOther); }
+
+  /**
+   * nsID Parsing method. Turns a {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}
+   * string into an nsID
+   */
+  bool Parse(const char* aIDStr);
+
+#ifndef XPCOM_GLUE_AVOID_NSPR
+  /**
+   * nsID string encoder. Returns a managed string in
+   * {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} format.
+   */
+  nsIDToCString ToString() const;
+
+  /**
+   * nsID string encoder. Builds a string in
+   * {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} format, into a char[NSID_LENGTH]
+   * buffer provided by the caller (for instance, on the stack).
+   */
+  void ToProvidedString(char (&aDest)[NSID_LENGTH]) const;
+
+#endif  // XPCOM_GLUE_AVOID_NSPR
+
+  // Infallibly duplicate an nsID. Must be freed with free().
+  nsID* Clone() const;
+};
+
+#ifndef XPCOM_GLUE_AVOID_NSPR
+/**
+ * A stack helper class to convert a nsID to a string.  Useful
+ * for printing nsIDs.  For example:
+ *   nsID aID = ...;
+ *   printf("%s", nsIDToCString(aID).get());
+ */
+class nsIDToCString {
+ public:
+  explicit nsIDToCString(const nsID& aID) {
+    aID.ToProvidedString(mStringBytes);
+  }
+
+  const char* get() const { return mStringBytes; }
+
+ protected:
+  char mStringBytes[NSID_LENGTH];
+};
+#endif
+
+/*
+ * Class IDs
+ */
+
+typedef nsID nsCID;
+
+// Define an CID
+#define NS_DEFINE_CID(_name, _cidspec) const nsCID _name = _cidspec
+
+#define NS_DEFINE_NAMED_CID(_name) static const nsCID k##_name = _name
+
+#define REFNSCID const nsCID&
+
+/**
+ * An "interface id" which can be used to uniquely identify a given
+ * interface.
+ */
+
+typedef nsID nsIID;
+
+/**
+ * A macro shorthand for <tt>const nsIID&<tt>
+ */
+
+#define REFNSIID const nsIID&
+
+/**
+ * A macro to build the static const IID accessor method. The Dummy
+ * template parameter only exists so that the kIID symbol will be linked
+ * properly (weak symbol on linux, gnu_linkonce on mac, multiple-definitions
+ * merged on windows). Dummy should always be instantiated as "void".
+ */
+
+#define NS_DECLARE_STATIC_IID_ACCESSOR(the_iid) \
+  template <typename T, typename U>             \
+  struct COMTypeInfo;
+
+#define NS_DEFINE_STATIC_IID_ACCESSOR(the_interface, the_iid)                \
+  template <typename T>                                                      \
+  struct the_interface::COMTypeInfo<the_interface, T> {                      \
+    static const nsIID kIID NS_HIDDEN;                                       \
+  };                                                                         \
+  template <typename T>                                                      \
+  const nsIID the_interface::COMTypeInfo<the_interface, T>::kIID NS_HIDDEN = \
+      the_iid;
+
+/**
+ * A macro to build the static const CID accessor method
+ */
+
+#define NS_DEFINE_STATIC_CID_ACCESSOR(the_cid) \
+  static const nsID& GetCID() {                \
+    static const nsID cid = the_cid;           \
+    return cid;                                \
+  }
+
+#define NS_GET_IID(T) (T::COMTypeInfo<T, void>::kIID)
+#define NS_GET_TEMPLATE_IID(T) (T::template COMTypeInfo<T, void>::kIID)
+
+#endif
diff --git a/xpcom/base/nsIDUtils.h b/xpcom/base/nsIDUtils.h
new file mode 100644
index 0000000000..ffb9d02f19
--- /dev/null
+++ b/xpcom/base/nsIDUtils.h
@@ -0,0 +1,32 @@
+/* -*- 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/. */
+
+#ifndef XPCOM_BASE_NSIDUTILS_H_
+#define XPCOM_BASE_NSIDUTILS_H_
+
+#include "nsID.h"
+#include "nsString.h"
+#include "nsTString.h"
+
+/**
+ * Trims the brackets around the nsID string, since it wraps its ID with
+ * brackets: {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}.
+ */
+template <typename T>
+class NSID_TrimBrackets : public nsTAutoString<T> {
+ public:
+  explicit NSID_TrimBrackets(const nsID& aID) {
+    nsIDToCString toCString(aID);
+    // The string from nsIDToCString::get() includes a null terminator.
+    // Thus this trims 3 characters: `{`, `}`, and the null terminator.
+    this->AssignASCII(toCString.get() + 1, NSID_LENGTH - 3);
+  }
+};
+
+using NSID_TrimBracketsUTF16 = NSID_TrimBrackets<char16_t>;
+using NSID_TrimBracketsASCII = NSID_TrimBrackets<char>;
+
+#endif  // XPCOM_BASE_NSIDUTILS_H_
diff --git a/xpcom/base/nsIDebug2.idl b/xpcom/base/nsIDebug2.idl
new file mode 100644
index 0000000000..4672fea7ea
--- /dev/null
+++ b/xpcom/base/nsIDebug2.idl
@@ -0,0 +1,100 @@
+/* vim: set shiftwidth=4 tabstop=8 autoindent cindent expandtab: */
+/* 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/. */
+
+/* interface to expose information about calls to NS_DebugBreak */
+
+#include "nsISupports.idl"
+
+/**
+ *   @note C/C++ consumers who are planning to use the nsIDebug2 interface with
+ *   the "@mozilla.org/xpcom;1" contract should use NS_DebugBreak from xpcom
+ *   glue instead.
+ *
+ */
+
+[builtinclass, scriptable, uuid(9641dc15-10fb-42e3-a285-18be90a5c10b)]
+interface nsIDebug2 : nsISupports
+{
+    /**
+     * Whether XPCOM was compiled with DEBUG defined.  This often
+     * correlates to whether other code (e.g., Firefox, XULRunner) was
+     * compiled with DEBUG defined.
+     */
+    readonly attribute boolean isDebugBuild;
+
+    /**
+     * The number of assertions since process start.
+     */
+    readonly attribute long assertionCount;
+
+    /**
+     * Whether a debugger is currently attached.
+     * Supports Windows + Mac
+     */
+    readonly attribute bool isDebuggerAttached;
+
+    /**
+     * Show an assertion and trigger nsIDebug2.break().
+     *
+     * @param aStr assertion message
+     * @param aExpr expression that failed
+     * @param aFile file containing assertion
+     * @param aLine line number of assertion
+     */
+    void assertion(in string aStr,
+                   in string aExpr,
+                   in string aFile,
+                   in long aLine);
+
+    /**
+     * Show a warning.
+     *
+     * @param aStr warning message
+     * @param aFile file containing assertion
+     * @param aLine line number of assertion
+     */
+    void warning(in string aStr,
+                 in string aFile,
+                 in long aLine);
+
+    /**
+     * Request to break into a debugger.
+     *
+     * @param aFile file containing break request
+     * @param aLine line number of break request
+     */
+    void break(in string aFile,
+               in long aLine);
+
+    /**
+     * Request the process to trigger a fatal abort.
+     *
+     * @param aFile file containing abort request
+     * @param aLine line number of abort request
+     */
+    void abort(in string aFile,
+               in long aLine);
+
+    /**
+     * Request the process to trigger a fatal panic!() from Rust code.
+     *
+     * @param aMessage the string to pass to panic!().
+     */
+    void rustPanic(in string aMessage);
+
+    /**
+     * Request the process to log a message for a target and level from Rust code.
+     *
+     * @param aTarget the string representing the log target.
+     * @param aMessage the string representing the log message.
+     */
+    void rustLog(in string aTarget,
+                 in string aMessage);
+
+    /**
+     * Cause an Out of Memory Crash.
+     */
+    void crashWithOOM();
+};
diff --git a/xpcom/base/nsIException.idl b/xpcom/base/nsIException.idl
new file mode 100644
index 0000000000..7f529e1c08
--- /dev/null
+++ b/xpcom/base/nsIException.idl
@@ -0,0 +1,80 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* 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/. */
+
+/*
+ * Interfaces for representing cross-language exceptions and stack traces.
+ */
+#include "nsISupports.idl"
+
+[ptr] native JSContext(JSContext);
+native StackFrameRef(already_AddRefed<nsIStackFrame>);
+
+[scriptable, builtinclass, uuid(28bfb2a2-5ea6-4738-918b-049dc4d51f0b)]
+interface nsIStackFrame : nsISupports
+{
+    [implicit_jscontext, binaryname(FilenameXPCOM)]
+    readonly attribute AString                 filename;
+    [implicit_jscontext, binaryname(NameXPCOM)]
+    readonly attribute AString                 name;
+    // Unique identifier of the script source for the frame, or zero.
+    [implicit_jscontext, binaryname(SourceIdXPCOM)]
+    readonly attribute int32_t                 sourceId;
+    // Valid line numbers begin at '1'. '0' indicates unknown.
+    [implicit_jscontext, binaryname(LineNumberXPCOM)]
+    readonly attribute int32_t                 lineNumber;
+    [implicit_jscontext, binaryname(ColumnNumberXPCOM)]
+    readonly attribute int32_t                 columnNumber;
+    readonly attribute AUTF8String             sourceLine;
+    [implicit_jscontext, binaryname(AsyncCauseXPCOM)]
+    readonly attribute AString                 asyncCause;
+    [implicit_jscontext, binaryname(AsyncCallerXPCOM)]
+    readonly attribute nsIStackFrame           asyncCaller;
+    [implicit_jscontext, binaryname(CallerXPCOM)]
+    readonly attribute nsIStackFrame           caller;
+
+    // Returns a formatted stack string that looks like the sort of
+    // string that would be returned by .stack on JS Error objects.
+    // Only works on JS-language stack frames.
+    [implicit_jscontext, binaryname(FormattedStackXPCOM)]
+    readonly attribute AString                 formattedStack;
+
+    // Returns the underlying SavedFrame object for native JavaScript stacks,
+    // or null if this is not a native JavaScript stack frame.
+    readonly attribute jsval                   nativeSavedFrame;
+
+    [implicit_jscontext, binaryname(ToStringXPCOM)]
+    AUTF8String toString();
+
+    // Infallible things to be called from C++.
+    [notxpcom, nostdcall]
+    void getFilename(in JSContext aCx, out AString aFilename);
+    [notxpcom, nostdcall]
+    void getName(in JSContext aCx, out AString aName);
+    [notxpcom, nostdcall]
+    int32_t getSourceId(in JSContext aCx);
+    [notxpcom, nostdcall]
+    int32_t getLineNumber(in JSContext aCx);
+    [notxpcom, nostdcall]
+    int32_t getColumnNumber(in JSContext aCx);
+    [notxpcom, nostdcall]
+    void getAsyncCause(in JSContext aCx, out AString aAsyncCause);
+    [notxpcom, nostdcall]
+    StackFrameRef getAsyncCaller(in JSContext aCx);
+    [notxpcom, nostdcall]
+    StackFrameRef getCaller(in JSContext aCx);
+    [notxpcom, nostdcall]
+    void getFormattedStack(in JSContext aCx, out AString aFormattedStack);
+    [notxpcom, nostdcall, binaryname(ToString)]
+    void toStringInfallible(in JSContext aCx, out AUTF8String aString);
+};
+
+// This interface only exists because of all the JS consumers doing
+// "instanceof Ci.nsIException".  We should switch them to something else and
+// get rid of it; bug 1435856 tracks that.  C++ code should NOT use this; use
+// mozilla::dom::Exception instead.
+[scriptable, builtinclass, uuid(4371b5bf-6845-487f-8d9d-3f1e4a9badd2)]
+interface nsIException : nsISupports
+{
+};
diff --git a/xpcom/base/nsIInterfaceRequestor.idl b/xpcom/base/nsIInterfaceRequestor.idl
new file mode 100644
index 0000000000..e0c4c0d7bb
--- /dev/null
+++ b/xpcom/base/nsIInterfaceRequestor.idl
@@ -0,0 +1,35 @@
+/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 "nsISupports.idl"
+
+/**
+ * The nsIInterfaceRequestor interface defines a generic interface for
+ * requesting interfaces that a given object might provide access to.
+ * This is very similar to QueryInterface found in nsISupports.
+ * The main difference is that interfaces returned from GetInterface()
+ * are not required to provide a way back to the object implementing this
+ * interface.  The semantics of QI() dictate that given an interface A that
+ * you QI() on to get to interface B, you must be able to QI on B to get back
+ * to A.  This interface however allows you to obtain an interface C from A
+ * that may or most likely will not have the ability to get back to A.
+ */
+
+[scriptable, uuid(033A1470-8B2A-11d3-AF88-00A024FFC08C)]
+interface nsIInterfaceRequestor : nsISupports
+{
+   /**
+    * Retrieves the specified interface pointer.
+    *
+    * @param uuid The IID of the interface being requested.
+    * @param result [out] The interface pointer to be filled in if
+    *               the interface is accessible.
+    * @throws NS_NOINTERFACE - interface not accessible.
+    * @throws NS_ERROR* - method failure.
+    */
+    void getInterface(in nsIIDRef uuid,
+                      [iid_is(uuid),retval] out nsQIResult result);
+};
diff --git a/xpcom/base/nsIInterfaceRequestorUtils.cpp b/xpcom/base/nsIInterfaceRequestorUtils.cpp
new file mode 100644
index 0000000000..44dd51921d
--- /dev/null
+++ b/xpcom/base/nsIInterfaceRequestorUtils.cpp
@@ -0,0 +1,32 @@
+/* -*- 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 "nsIInterfaceRequestor.h"
+#include "nsIInterfaceRequestorUtils.h"
+
+nsresult nsGetInterface::operator()(const nsIID& aIID,
+                                    void** aInstancePtr) const {
+  nsresult status;
+
+  if (mSource) {
+    nsCOMPtr<nsIInterfaceRequestor> factoryPtr = do_QueryInterface(mSource);
+    if (factoryPtr) {
+      status = factoryPtr->GetInterface(aIID, aInstancePtr);
+    } else {
+      status = NS_ERROR_NO_INTERFACE;
+    }
+  } else {
+    status = NS_ERROR_NULL_POINTER;
+  }
+
+  if (NS_FAILED(status)) {
+    *aInstancePtr = 0;
+  }
+  if (mErrorPtr) {
+    *mErrorPtr = status;
+  }
+  return status;
+}
diff --git a/xpcom/base/nsIInterfaceRequestorUtils.h b/xpcom/base/nsIInterfaceRequestorUtils.h
new file mode 100644
index 0000000000..c3116ea9f2
--- /dev/null
+++ b/xpcom/base/nsIInterfaceRequestorUtils.h
@@ -0,0 +1,40 @@
+/* -*- 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/. */
+
+#ifndef __nsInterfaceRequestorUtils_h
+#define __nsInterfaceRequestorUtils_h
+
+#include "nsCOMPtr.h"
+
+// a type-safe shortcut for calling the |GetInterface()| member function
+// T must inherit from nsIInterfaceRequestor, but the cast may be ambiguous.
+template <class T, class DestinationType>
+inline nsresult CallGetInterface(T* aSource, DestinationType** aDestination) {
+  MOZ_ASSERT(aSource, "null parameter");
+  MOZ_ASSERT(aDestination, "null parameter");
+
+  return aSource->GetInterface(NS_GET_TEMPLATE_IID(DestinationType),
+                               reinterpret_cast<void**>(aDestination));
+}
+
+class MOZ_STACK_CLASS nsGetInterface final : public nsCOMPtr_helper {
+ public:
+  nsGetInterface(nsISupports* aSource, nsresult* aError)
+      : mSource(aSource), mErrorPtr(aError) {}
+
+  virtual nsresult NS_FASTCALL operator()(const nsIID&, void**) const override;
+
+ private:
+  nsISupports* MOZ_NON_OWNING_REF mSource;
+  nsresult* mErrorPtr;
+};
+
+inline const nsGetInterface do_GetInterface(nsISupports* aSource,
+                                            nsresult* aError = 0) {
+  return nsGetInterface(aSource, aError);
+}
+
+#endif  // __nsInterfaceRequestorUtils_h
diff --git a/xpcom/base/nsIMacPreferencesReader.idl b/xpcom/base/nsIMacPreferencesReader.idl
new file mode 100644
index 0000000000..470fd92ec9
--- /dev/null
+++ b/xpcom/base/nsIMacPreferencesReader.idl
@@ -0,0 +1,34 @@
+/* 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 "nsISupportsPrimitives.idl"
+
+%{C++
+#define ENTERPRISE_POLICIES_ENABLED_KEY "EnterprisePoliciesEnabled"
+%}
+
+/**
+ * This interface is designed to provide scriptable access to the macOS
+ * preferences system.
+ *
+ * This interface is highly macOS specific.
+ */
+[builtinclass, scriptable, uuid(b0f20595-88ce-4738-a1a4-24de78eb8051)]
+interface nsIMacPreferencesReader : nsISupports
+{
+  /**
+   * This method checks whether macOS policies are enabled.
+   *
+   * @return true if macOS policies are enabled, false otherwise.
+   */
+  bool policiesEnabled();
+
+  /**
+   * This method reads and returns the macOS preferences.
+   *
+   * @return A JSON object containing all macOS preferences.
+   */
+  [implicit_jscontext]
+  jsval readPreferences();
+};
diff --git a/xpcom/base/nsIMemoryInfoDumper.idl b/xpcom/base/nsIMemoryInfoDumper.idl
new file mode 100644
index 0000000000..79b03a709d
--- /dev/null
+++ b/xpcom/base/nsIMemoryInfoDumper.idl
@@ -0,0 +1,167 @@
+/* -*- Mode: C++; tab-width: 50; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "nsISupports.idl"
+
+interface nsIFile;
+interface nsICycleCollectorLogSink;
+
+[scriptable, function, uuid(2dea18fc-fbfa-4bf7-ad45-0efaf5495f5e)]
+interface nsIFinishDumpingCallback : nsISupports
+{
+  void callback(in nsISupports data);
+};
+
+/**
+ * Callback interface for |dumpGCAndCCLogsToFile|, below.  Note that
+ * these method calls can occur before |dumpGCAndCCLogsToFile|
+ * returns.
+ */
+[scriptable, uuid(dc1b2b24-65bd-441b-b6bd-cb5825a7ed14)]
+interface nsIDumpGCAndCCLogsCallback : nsISupports
+{
+  /**
+   * Called whenever a process has successfully finished dumping its GC/CC logs.
+   * Incomplete dumps (e.g., if the child crashes or is killed due to memory
+   * exhaustion) are not reported.
+   *
+   * @param aGCLog The file that the GC log was written to.
+   *
+   * @param aCCLog The file that the CC log was written to.
+   *
+   * @param aIsParent indicates whether this log file pair is from the
+   * parent process.
+   */
+  void onDump(in nsIFile aGCLog,
+              in nsIFile aCCLog,
+              in bool aIsParent);
+
+  /**
+   * Called when GC/CC logging has finished, after all calls to |onDump|.
+   */
+  void onFinish();
+};
+
+[scriptable, builtinclass, uuid(48541b74-47ee-4a62-9557-7f4b809bda5c)]
+interface nsIMemoryInfoDumper : nsISupports
+{
+  /**
+   * This dumps gzipped memory reports for this process and its child
+   * processes.  If a file of the given name exists, it will be overwritten.
+   *
+   * @param aFilename The output file.
+   *
+   * @param aFinishDumping The callback called on completion.
+   *
+   * @param aFinishDumpingData The environment for the callback.
+   *
+   * @param aAnonymize Should the reports be anonymized?
+   *
+   * @param aMinimizeMemoryUsage indicates whether we should run a series of
+   *   GC/CC's in an attempt to reduce our memory usage before collecting our
+   *   memory report.
+   *
+   * Sample output, annotated with comments for explanatory purposes.
+   *
+   * {
+   *   // The version number of the format, which will be incremented each time
+   *   // backwards-incompatible changes are made. A mandatory integer.
+   *   "version": 1
+   *
+   *   // Equal to nsIMemoryReporterManager::hasMozMallocUsableSize. A
+   *   // mandatory boolean.
+   *   "hasMozMallocUsableSize": true,
+   *
+   *   // The memory reports. A mandatory array.
+   *   "reports": [
+   *     // The properties correspond to the arguments of
+   *     // nsIHandleReportCallback::callback. Every one is mandatory.
+   *     {"process":"Main Process (pid 12345)", "path":"explicit/foo/bar",
+   *      "kind":1, "units":0, "amount":2000000, "description":"Foo bar."},
+   *     {"process":"Main Process (pid 12345)", "path":"heap-allocated",
+   *      "kind":1, "units":0, "amount":3000000, "description":"Heap allocated."},
+   *     {"process":"Main Process (pid 12345)", "path":"vsize",
+   *      "kind":1, "units":0, "amount":10000000, "description":"Vsize."}
+   *   ]
+   * }
+   */
+  void dumpMemoryReportsToNamedFile(in AString aFilename,
+                                    in nsIFinishDumpingCallback aFinishDumping,
+                                    in nsISupports aFinishDumpingData,
+                                    in boolean aAnonymize,
+                                    in boolean aMinimizeMemoryUsage);
+
+  /**
+   * Similar to dumpMemoryReportsToNamedFile, this method dumps gzipped memory
+   * reports for this process and its child processes to files in the tmp
+   * directory called memory-reports-<identifier>-<pid>.json.gz (or something
+   * similar, such as memory-reports-<identifier>-<pid>-1.json.gz; no existing
+   * file will be overwritten).
+   *
+   * If DMD is enabled, this method also dumps gzipped DMD output for this
+   * process and its child processes to files in the tmp directory called
+   * dmd-<identifier>-<pid>.txt.gz (or something similar; again, no existing
+   * file will be overwritten).
+   *
+   * @param aIdentifier this identifier will appear in the filename of our
+   *   about:memory dump and those of our children.
+   *
+   *   If the identifier is empty, the implementation may set it arbitrarily
+   *   and use that new value for its own dump and the dumps of its child
+   *   processes.  For example, the implementation may set |aIdentifier| to the
+   *   number of seconds since the epoch.
+   *
+   * @param aAnonymize Should the reports be anonymized?
+   *
+   * @param aMinimizeMemoryUsage indicates whether we should run a series of
+   *   GC/CC's in an attempt to reduce our memory usage before collecting our
+   *   memory report.
+   */
+  void dumpMemoryInfoToTempDir(
+    in AString aIdentifier,
+    in boolean aAnonymize,
+    in boolean aMinimizeMemoryUsage);
+
+  /**
+   * Dump GC and CC logs to files in the OS's temp directory (or in
+   * $MOZ_CC_LOG_DIRECTORY, if that environment variable is specified).
+   *
+   * @param aIdentifier If aIdentifier is non-empty, this string will appear in
+   *   the filenames of the logs we create (both for this process and, if
+   *   aDumpChildProcesses is true, for our child processes).
+   *
+   *   If aIdentifier is empty, the implementation may set it to an
+   *   arbitrary value; for example, it may set aIdentifier to the number
+   *   of seconds since the epoch.
+   *
+   * @param aDumpAllTraces indicates whether we should run an all-traces CC
+   *   log.  An all-traces log visits all objects currently eligible for cycle
+   *   collection, while a non-all-traces log avoids visiting some objects
+   *   which we know are reachable.
+   *
+   *   All-traces logs are much bigger than the alternative, but they may be
+   *   helpful when trying to understand why a particular object is alive.  For
+   *   example, a non-traces-log will skip references held by an active
+   *   document; if your object is being held alive by such a document, you
+   *   probably want to see those references.
+   *
+   * @param aDumpChildProcesses indicates whether we should call
+   *   DumpGCAndCCLogsToFile in our child processes.  If so, the child processes
+   *   will dump their children, and so on.
+   *
+   */
+  void dumpGCAndCCLogsToFile(in AString aIdentifier,
+                             in bool aDumpAllTraces,
+                             in bool aDumpChildProcesses,
+                             in nsIDumpGCAndCCLogsCallback aCallback);
+
+  /**
+   * Like |dumpGCAndCCLogsToFile|, but sends the logs to the given log
+   * sink object instead of accessing the filesystem directly, and
+   * dumps the current process only.
+   */
+  void dumpGCAndCCLogsToSink(in bool aDumpAllTraces,
+                             in nsICycleCollectorLogSink aSink);
+};
diff --git a/xpcom/base/nsIMemoryReporter.idl b/xpcom/base/nsIMemoryReporter.idl
new file mode 100644
index 0000000000..05b5701519
--- /dev/null
+++ b/xpcom/base/nsIMemoryReporter.idl
@@ -0,0 +1,615 @@
+/* -*- 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 "nsISupports.idl"
+%{C++
+#include <stdio.h>
+%}
+
+interface mozIDOMWindowProxy;
+interface nsIRunnable;
+interface nsISimpleEnumerator;
+[ptr] native FILE(FILE);
+
+/*
+ * Memory reporters measure Firefox's memory usage.  They are primarily used to
+ * generate the about:memory page.  You should read
+ * https://developer.mozilla.org/en-US/docs/Mozilla/Performance/Memory_reporting
+ * before writing a memory reporter.
+ */
+
+[scriptable, function, uuid(62ef0e1c-dbd6-11e3-aa75-3c970e9f4238)]
+interface nsIHandleReportCallback : nsISupports
+{
+  /*
+   * The arguments to the callback are as follows.
+   *
+   *
+   * |process|  The name of the process containing this reporter.  Each
+   * reporter initially has "" in this field, indicating that it applies to the
+   * current process.  (This is true even for reporters in a child process.)
+   * When a reporter from a child process is copied into the main process, the
+   * copy has its 'process' field set appropriately.
+   *
+   *
+   * |path|  The path that this memory usage should be reported under.  Paths
+   * are '/'-delimited, eg. "a/b/c".
+   *
+   * Each reporter can be viewed as representing a leaf node in a tree.
+   * Internal nodes of the tree don't have reporters.  So, for example, the
+   * reporters "explicit/a/b", "explicit/a/c", "explicit/d/e", and
+   * "explicit/d/f" define this tree:
+   *
+   *   explicit
+   *   |--a
+   *   |  |--b [*]
+   *   |  \--c [*]
+   *   \--d
+   *      |--e [*]
+   *      \--f [*]
+   *
+   * Nodes marked with a [*] have a reporter.  Notice that the internal
+   * nodes are implicitly defined by the paths.
+   *
+   * Nodes within a tree should not overlap measurements, otherwise the
+   * parent node measurements will be double-counted.  So in the example
+   * above, |b| should not count any allocations counted by |c|, and vice
+   * versa.
+   *
+   * All nodes within each tree must have the same units.
+   *
+   * If you want to include a '/' not as a path separator, e.g. because the
+   * path contains a URL, you need to convert each '/' in the URL to a '\'.
+   * Consumers of the path will undo this change.  Any other '\' character
+   * in a path will also be changed.  This is clumsy but hasn't caused any
+   * problems so far.
+   *
+   * The paths of all reporters form a set of trees.  Trees can be
+   * "degenerate", i.e. contain a single entry with no '/'.
+   *
+   *
+   * |kind|  There are three kinds of memory reporters.
+   *
+   *  - HEAP: reporters measuring memory allocated by the heap allocator,
+   *    e.g. by calling malloc, calloc, realloc, memalign, operator new, or
+   *    operator new[].  Reporters in this category must have units
+   *    UNITS_BYTES.
+   *
+   *  - NONHEAP: reporters measuring memory which the program explicitly
+   *    allocated, but does not live on the heap.  Such memory is commonly
+   *    allocated by calling one of the OS's memory-mapping functions (e.g.
+   *    mmap, VirtualAlloc, or vm_allocate).  Reporters in this category
+   *    must have units UNITS_BYTES.
+   *
+   *  - OTHER: reporters which don't fit into either of these categories.
+   *    They can have any units.
+   *
+   * The kind only matters for reporters in the "explicit" tree;
+   * aboutMemory.js uses it to calculate "heap-unclassified".
+   *
+   *
+   * |units|  The units on the reporter's amount.  One of the following.
+   *
+   *  - BYTES: The amount contains a number of bytes.
+   *
+   *  - COUNT: The amount is an instantaneous count of things currently in
+   *    existence.  For instance, the number of tabs currently open would have
+   *    units COUNT.
+   *
+   *  - COUNT_CUMULATIVE: The amount contains the number of times some event
+   *    has occurred since the application started up.  For instance, the
+   *    number of times the user has opened a new tab would have units
+   *    COUNT_CUMULATIVE.
+   *
+   *    The amount returned by a reporter with units COUNT_CUMULATIVE must
+   *    never decrease over the lifetime of the application.
+   *
+   *  - PERCENTAGE: The amount contains a fraction that should be expressed as
+   *    a percentage.  NOTE!  The |amount| field should be given a value 100x
+   *    the actual percentage;  this number will be divided by 100 when shown.
+   *    This allows a fractional percentage to be shown even though |amount| is
+   *    an integer.  E.g. if the actual percentage is 12.34%, |amount| should
+   *    be 1234.
+   *
+   *    Values greater than 100% are allowed.
+   *
+   *
+   * |amount|  The numeric value reported by this memory reporter.  Accesses
+   * can fail if something goes wrong when getting the amount.
+   *
+   *
+   * |description|  A human-readable description of this memory usage report.
+   */
+  void callback(in ACString process, in AUTF8String path, in int32_t kind,
+                in int32_t units, in int64_t amount,
+                in AUTF8String description, in nsISupports data);
+};
+
+/*
+ * An nsIMemoryReporter reports one or more memory measurements via a
+ * callback function which is called once for each measurement.
+ *
+ * An nsIMemoryReporter that reports a single measurement is sometimes called a
+ * "uni-reporter".  One that reports multiple measurements is sometimes called
+ * a "multi-reporter".
+ *
+ * aboutMemory.js is the most important consumer of memory reports.  It
+ * places the following constraints on reports.
+ *
+ * - All reports within a single sub-tree must have the same units.
+ *
+ * - There may be an "explicit" tree.  If present, it represents
+ *   non-overlapping regions of memory that have been explicitly allocated with
+ *   an OS-level allocation (e.g. mmap/VirtualAlloc/vm_allocate) or a
+ *   heap-level allocation (e.g. malloc/calloc/operator new).  Reporters in
+ *   this tree must have kind HEAP or NONHEAP, units BYTES.
+ *
+ * It is preferred, but not required, that report descriptions use complete
+ * sentences (i.e. start with a capital letter and end with a period, or
+ * similar).
+ */
+[scriptable, uuid(92a36db1-46bd-4fe6-988e-47db47236d8b)]
+interface nsIMemoryReporter : nsISupports
+{
+  /*
+   * Run the reporter.
+   *
+   * If |anonymize| is true, the memory reporter should anonymize any
+   * privacy-sensitive details in memory report paths, by replacing them with a
+   * string such as "<anonymized>". Anonymized memory reports may be sent
+   * automatically via crash reports or telemetry.
+   *
+   * The following things are considered privacy-sensitive.
+   *
+   * - Content domains and URLs, and information derived from them.
+   * - Content data, such as strings.
+   * - Details about content code, such as filenames, function names or stack
+   *   traces.
+   * - Details about or data from the user's system, such as filenames.
+   * - Running apps.
+   *
+   * In short, anything that could identify parts of the user's browsing
+   * history is considered privacy-sensitive.
+   *
+   * The following thing are not considered privacy-sensitive.
+   *
+   * - Chrome domains and URLs.
+   * - Information about installed extensions.
+   */
+  void collectReports(in nsIHandleReportCallback callback,
+                      in nsISupports data,
+                      in boolean anonymize);
+
+  /*
+   * Kinds. See the |kind| comment in nsIHandleReportCallback.
+   */
+  const int32_t KIND_NONHEAP = 0;
+  const int32_t KIND_HEAP    = 1;
+  const int32_t KIND_OTHER   = 2;
+
+  /*
+   * Units. See the |units| comment in nsIHandleReportCallback.
+   */
+  const int32_t UNITS_BYTES = 0;
+  const int32_t UNITS_COUNT = 1;
+  const int32_t UNITS_COUNT_CUMULATIVE = 2;
+  const int32_t UNITS_PERCENTAGE = 3;
+};
+
+[scriptable, function, uuid(548b3909-c04d-4ca6-8466-b8bee3837457)]
+interface nsIFinishReportingCallback : nsISupports
+{
+  void callback(in nsISupports data);
+};
+
+[scriptable, function, uuid(1a80cd0f-0d9e-4397-be69-68ad28fe5175)]
+interface nsIHeapAllocatedCallback : nsISupports
+{
+  void callback(in int64_t bytesAllocated);
+};
+
+[scriptable, builtinclass, uuid(2998574d-8993-407a-b1a5-8ad7417653e1)]
+interface nsIMemoryReporterManager : nsISupports
+{
+  /*
+   * Initialize.
+   */
+  [must_use] void init();
+
+  /*
+   * Register the given nsIMemoryReporter.  The Manager service will hold a
+   * strong reference to the given reporter, and will be responsible for freeing
+   * the reporter at shutdown.  You may manually unregister the reporter with
+   * unregisterStrongReporter() at any point.
+   */
+  void registerStrongReporter(in nsIMemoryReporter reporter);
+  void registerStrongAsyncReporter(in nsIMemoryReporter reporter);
+
+  /*
+   * Like registerReporter, but the Manager service will hold a weak reference
+   * via a raw pointer to the given reporter.  The reporter should be
+   * unregistered before shutdown.
+   * You cannot register JavaScript components with this function!  Always
+   * register your JavaScript components with registerStrongReporter().
+   */
+  void registerWeakReporter(in nsIMemoryReporter reporter);
+  void registerWeakAsyncReporter(in nsIMemoryReporter reporter);
+
+  /*
+   * Unregister the given memory reporter, which must have been registered with
+   * registerStrongReporter().  You normally don't need to unregister your
+   * strong reporters, as nsIMemoryReporterManager will take care of that at
+   * shutdown.
+   */
+  void unregisterStrongReporter(in nsIMemoryReporter reporter);
+
+  /*
+   * Unregister the given memory reporter, which must have been registered with
+   * registerWeakReporter().
+   */
+  void unregisterWeakReporter(in nsIMemoryReporter reporter);
+
+  /*
+   * These functions should only be used for testing purposes.
+   */
+  void blockRegistrationAndHideExistingReporters();
+  void unblockRegistrationAndRestoreOriginalReporters();
+  void registerStrongReporterEvenIfBlocked(in nsIMemoryReporter aReporter);
+
+  /*
+   * Get memory reports for the current process and all child processes.
+   * |handleReport| is called for each report, and |finishReporting| is called
+   * once all reports have been handled.
+   *
+   * |finishReporting| is called even if, for example, some child processes
+   * fail to report back.  However, calls to this method will silently and
+   * immediately abort -- and |finishReporting| will not be called -- if a
+   * previous getReports() call is still in flight, i.e. if it has not yet
+   * finished invoking |finishReporting|.  The silent abort is because the
+   * in-flight request will finish soon, and the caller would very likely just
+   * catch and ignore any error anyway.
+   *
+   * If |anonymize| is true, it indicates that the memory reporters should
+   * anonymize any privacy-sensitive data (see above).
+   */
+  void getReports(in nsIHandleReportCallback handleReport,
+                  in nsISupports handleReportData,
+                  in nsIFinishReportingCallback finishReporting,
+                  in nsISupports finishReportingData,
+                  in boolean anonymize);
+
+  /*
+   * As above, but: If |minimizeMemoryUsage| is true, then each process will
+   * minimize its memory usage (see the |minimizeMemoryUsage| method) before
+   * gathering its report.  If DMD is enabled and |DMDDumpIdent| is non-empty
+   * then write a DMD report to a file in the usual temporary directory (see
+   * |dumpMemoryInfoToTempDir| in |nsIMemoryInfoDumper|.)
+   */
+  [noscript] void
+    getReportsExtended(in nsIHandleReportCallback handleReport,
+                       in nsISupports handleReportData,
+                       in nsIFinishReportingCallback finishReporting,
+                       in nsISupports finishReportingData,
+                       in boolean anonymize,
+                       in boolean minimizeMemoryUsage,
+                       in AString DMDDumpIdent);
+
+  /*
+   * As above, but if DMD is enabled and |DMDFile| is non-null then
+   * write a DMD report to that file and close it.
+   */
+  [noscript] void
+    getReportsForThisProcessExtended(in nsIHandleReportCallback handleReport,
+                                     in nsISupports handleReportData,
+                                     in boolean anonymize,
+                                     in FILE DMDFile,
+                                     in nsIFinishReportingCallback finishReporting,
+                                     in nsISupports finishReportingData);
+
+  /*
+   * Called by an asynchronous memory reporter upon completion.
+   */
+  [noscript] void endReport();
+
+  /*
+   * The memory reporter manager, for the most part, treats reporters
+   * registered with it as a black box.  However, there are some
+   * "distinguished" amounts (as could be reported by a memory reporter) that
+   * the manager provides as attributes, because they are sufficiently
+   * interesting that we want external code (e.g. telemetry) to be able to rely
+   * on them.
+   *
+   * Note that these are not reporters and so getReports() does not look at
+   * them.  However, distinguished amounts can be embedded in a reporter.
+   *
+   * Access to these attributes can fail.  In particular, some of them are not
+   * available on all platforms.
+   *
+   * If you add a new distinguished amount, please update
+   * toolkit/components/aboutmemory/tests/test_memoryReporters.xul.
+   *
+   * |vsize| (UNITS_BYTES)  The virtual size, i.e. the amount of address space
+   * taken up.
+   *
+   * |vsizeMaxContiguous| (UNITS_BYTES)  The size of the largest contiguous
+   * block of virtual memory.
+   *
+   * |resident| (UNITS_BYTES)  The resident size (a.k.a. RSS or physical memory
+   * used).
+   *
+   * |residentFast| (UNITS_BYTES)  This is like |resident|, but on Mac OS
+   * |resident| can purge pages, which is slow.  It also affects the result of
+   * |residentFast|, and so |resident| and |residentFast| should not be used
+   * together.
+   *
+   * |residentPeak| (UNITS_BYTES)  The peak resident size.
+   *
+   * |residentUnique| (UNITS_BYTES)  The unique set size (a.k.a. USS).
+   *
+   * |heapAllocated| (UNITS_BYTES)  Memory mapped by the heap allocator.
+   *
+   * |heapOverheadFraction| (UNITS_PERCENTAGE)  In the heap allocator, this is
+   * the fraction of committed heap bytes that are overhead. Like all
+   * UNITS_PERCENTAGE measurements, its amount is multiplied by 100x so it can
+   * be represented by an int64_t.
+   *
+   * |JSMainRuntimeGCHeap| (UNITS_BYTES)  Size of the main JS runtime's GC
+   * heap.
+   *
+   * |JSMainRuntimeTemporaryPeak| (UNITS_BYTES)  Peak size of the transient
+   * storage in the main JSRuntime.
+   *
+   * |JSMainRuntimeCompartments{System,User}| (UNITS_COUNT)  The number of
+   * {system,user} compartments in the main JS runtime.
+   *
+   * |JSMainRuntimeRealms{System,User}| (UNITS_COUNT)  The number of
+   * {system,user} realms in the main JS runtime.
+   *
+   * |imagesContentUsedUncompressed| (UNITS_BYTES)  Memory used for decoded
+   * raster images in content.
+   *
+   * |storageSQLite| (UNITS_BYTES)  Memory used by SQLite.
+   *
+   * |lowMemoryEventsPhysical| (UNITS_COUNT_CUMULATIVE)
+   * The number of low-physical-memory events that have occurred since the
+   * process started.
+   *
+   * |ghostWindows| (UNITS_COUNT)  A cached value of the number of ghost
+   * windows. This should have been updated within the past 60s.
+   *
+   * |pageFaultsHard| (UNITS_COUNT_CUMULATIVE)  The number of hard (a.k.a.
+   * major) page faults that have occurred since the process started.
+   */
+  [must_use] readonly attribute int64_t vsize;
+  [must_use] readonly attribute int64_t vsizeMaxContiguous;
+  [must_use] readonly attribute int64_t resident;
+  [must_use] readonly attribute int64_t residentFast;
+  [must_use] readonly attribute int64_t residentPeak;
+  [must_use] readonly attribute int64_t residentUnique;
+
+  [must_use] readonly attribute int64_t heapAllocated;
+  [must_use] readonly attribute int64_t heapOverheadFraction;
+
+  [must_use] readonly attribute int64_t JSMainRuntimeGCHeap;
+  [must_use] readonly attribute int64_t JSMainRuntimeTemporaryPeak;
+  [must_use] readonly attribute int64_t JSMainRuntimeCompartmentsSystem;
+  [must_use] readonly attribute int64_t JSMainRuntimeCompartmentsUser;
+  [must_use] readonly attribute int64_t JSMainRuntimeRealmsSystem;
+  [must_use] readonly attribute int64_t JSMainRuntimeRealmsUser;
+
+  [must_use] readonly attribute int64_t imagesContentUsedUncompressed;
+
+  [must_use] readonly attribute int64_t storageSQLite;
+
+  [must_use] readonly attribute int64_t lowMemoryEventsPhysical;
+
+  [must_use] readonly attribute int64_t ghostWindows;
+
+  [must_use] readonly attribute int64_t pageFaultsHard;
+
+  /*
+   * This attribute indicates if moz_malloc_usable_size() works.
+   */
+  [infallible] readonly attribute boolean hasMozMallocUsableSize;
+
+  /*
+   * These attributes indicate DMD's status. "Enabled" means enabled at
+   * build-time.
+   */
+  [infallible] readonly attribute boolean isDMDEnabled;
+  [infallible] readonly attribute boolean isDMDRunning;
+
+  /*
+   * Run a series of GC/CC's in an attempt to minimize the application's memory
+   * usage.  When we're finished doing this for the current process, we invoke
+   * the given runnable if it's not null.  We do not wait for any child processes
+   * that might be doing their own minimization via child-mmu-request to finish.
+   */
+  [must_use] void minimizeMemoryUsage(in nsIRunnable callback);
+
+  /*
+   * Measure the memory that is known to be owned by this tab, split up into
+   * several broad categories.  Note that this will be an underestimate of the
+   * true number, due to imperfect memory reporter coverage (corresponding to
+   * about:memory's "heap-unclassified"), and due to some memory shared between
+   * tabs not being counted.
+   *
+   * The time taken for the measurement (split into JS and non-JS parts) is
+   * also returned.
+   */
+  [must_use]
+  void sizeOfTab(in mozIDOMWindowProxy window,
+                 out int64_t jsObjectsSize, out int64_t jsStringsSize,
+                 out int64_t jsOtherSize, out int64_t domSize,
+                 out int64_t styleSize, out int64_t otherSize,
+                 out int64_t totalSize,
+                 out double jsMilliseconds, out double nonJSMilliseconds);
+};
+
+%{C++
+
+#include "js/TypeDecls.h"
+#include "nsString.h"
+#include "nsTArray.h"
+
+class nsPIDOMWindowOuter;
+
+namespace mozilla {
+
+// All the following registration/unregistration functions don't use
+// [[nodiscard]] because ignoring failures is common and reasonable.
+
+// Register a memory reporter.  The manager service will hold a strong
+// reference to this reporter.
+XPCOM_API(nsresult) RegisterStrongMemoryReporter(nsIMemoryReporter* aReporter);
+XPCOM_API(nsresult) RegisterStrongAsyncMemoryReporter(nsIMemoryReporter* aReporter);
+
+// Register a memory reporter.  The manager service will hold a weak reference
+// to this reporter.
+XPCOM_API(nsresult) RegisterWeakMemoryReporter(nsIMemoryReporter* aReporter);
+XPCOM_API(nsresult) RegisterWeakAsyncMemoryReporter(nsIMemoryReporter* aReporter);
+
+// Unregister a strong memory reporter.
+XPCOM_API(nsresult) UnregisterStrongMemoryReporter(nsIMemoryReporter* aReporter);
+
+// Unregister a weak memory reporter.
+XPCOM_API(nsresult) UnregisterWeakMemoryReporter(nsIMemoryReporter* aReporter);
+
+// The memory reporter manager provides access to several distinguished
+// amounts via attributes.  Some of these amounts are provided by Gecko
+// components that cannot be accessed directly from XPCOM code.  So we provide
+// the following functions for those components to be registered with the
+// manager.
+
+typedef int64_t (*InfallibleAmountFn)();
+
+#define DECL_REGISTER_DISTINGUISHED_AMOUNT(kind, name) \
+    nsresult Register##name##DistinguishedAmount(kind##AmountFn aAmountFn);
+#define DECL_UNREGISTER_DISTINGUISHED_AMOUNT(name) \
+    nsresult Unregister##name##DistinguishedAmount();
+
+DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeGCHeap)
+DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeTemporaryPeak)
+DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeCompartmentsSystem)
+DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeCompartmentsUser)
+DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeRealmsSystem)
+DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeRealmsUser)
+
+DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, ImagesContentUsedUncompressed)
+DECL_UNREGISTER_DISTINGUISHED_AMOUNT(ImagesContentUsedUncompressed)
+
+DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, StorageSQLite)
+DECL_UNREGISTER_DISTINGUISHED_AMOUNT(StorageSQLite)
+
+DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, LowMemoryEventsPhysical)
+
+DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, GhostWindows)
+
+#undef DECL_REGISTER_DISTINGUISHED_AMOUNT
+#undef DECL_UNREGISTER_DISTINGUISHED_AMOUNT
+
+// Likewise for per-tab measurement.
+
+typedef nsresult (*JSSizeOfTabFn)(JSObject* aObj,
+                                  size_t* aJsObjectsSize,
+                                  size_t* aJsStringSize,
+                                  size_t* aJsPrivateSize,
+                                  size_t* aJsOtherSize);
+typedef nsresult (*NonJSSizeOfTabFn)(nsPIDOMWindowOuter* aWindow,
+                                     size_t* aDomSize,
+                                     size_t* aStyleSize,
+                                     size_t* aOtherSize);
+
+nsresult RegisterJSSizeOfTab(JSSizeOfTabFn aSizeOfTabFn);
+nsresult RegisterNonJSSizeOfTab(NonJSSizeOfTabFn aSizeOfTabFn);
+
+}
+
+#if defined(MOZ_DMD)
+#if !defined(MOZ_MEMORY)
+#error "MOZ_DMD requires MOZ_MEMORY"
+#endif
+
+#include "DMD.h"
+
+#define MOZ_REPORT(ptr)          mozilla::dmd::Report(ptr)
+#define MOZ_REPORT_ON_ALLOC(ptr) mozilla::dmd::ReportOnAlloc(ptr)
+
+#else
+
+#define MOZ_REPORT(ptr)
+#define MOZ_REPORT_ON_ALLOC(ptr)
+
+#endif  // defined(MOZ_DMD)
+
+// Functions generated via this macro should be used by all traversal-based
+// memory reporters.  Such functions return |moz_malloc_size_of(ptr)|;  this
+// will always be zero on some obscure platforms.
+//
+// You might be wondering why we have a macro that creates multiple functions
+// that differ only in their name, instead of a single MallocSizeOf function.
+// It's mostly to help with DMD integration, though it sometimes also helps
+// with debugging and temporary ad hoc profiling.  The function name chosen
+// doesn't matter greatly, but it's best to make it similar to the path used by
+// the relevant memory reporter(s).
+#define MOZ_DEFINE_MALLOC_SIZE_OF(fn)                                         \
+  static size_t fn(const void* aPtr)                                          \
+  {                                                                           \
+      MOZ_REPORT(aPtr);                                                       \
+      return moz_malloc_size_of(aPtr);                                        \
+  }
+
+// This is an alternative to MOZ_DEFINE_MALLOC_SIZE_OF that defines a
+// MallocSizeOf function that can handle interior pointers.
+#ifdef MOZ_MEMORY
+
+#include "mozmemory.h"
+
+#define MOZ_DEFINE_MALLOC_ENCLOSING_SIZE_OF(fn)                               \
+  static size_t fn(const void* aPtr)                                          \
+  {                                                                           \
+      jemalloc_ptr_info_t info;                                               \
+      jemalloc_ptr_info(aPtr, &info);                                         \
+      MOZ_REPORT(info.addr);                                                  \
+      return jemalloc_ptr_is_live(&info) ? info.size : 0;                     \
+  }
+
+#else
+
+#define MOZ_DEFINE_MALLOC_ENCLOSING_SIZE_OF(fn)                               \
+  static size_t fn(const void* aPtr)                                          \
+  {                                                                           \
+      return 0;                                                               \
+  }
+
+#endif
+
+// Functions generated by the next two macros should be used by wrapping
+// allocators that report heap blocks as soon as they are allocated and
+// unreport them as soon as they are freed.  Such allocators are used in cases
+// where we have third-party code that we cannot modify.  The two functions
+// must always be used in tandem.
+#define MOZ_DEFINE_MALLOC_SIZE_OF_ON_ALLOC(fn)                                \
+  static size_t fn(const void* aPtr)                                          \
+  {                                                                           \
+      MOZ_REPORT_ON_ALLOC(aPtr);                                              \
+      return moz_malloc_size_of(aPtr);                                        \
+  }
+#define MOZ_DEFINE_MALLOC_SIZE_OF_ON_FREE(fn)                                 \
+  static size_t fn(const void* aPtr)                                          \
+  {                                                                           \
+      return moz_malloc_size_of(aPtr);                                        \
+  }
+
+// This macro assumes the presence of appropriate |aHandleReport| and |aData|
+// variables. The (void) is there because we should always ignore the return
+// value of the callback, because callback failures aren't fatal.
+#define MOZ_COLLECT_REPORT(path, kind, units, amount, description)            \
+  (void)aHandleReport->Callback(""_ns, nsLiteralCString(path),     \
+                                kind, units, amount,                          \
+                                nsLiteralCString(description), aData)
+
+%}
diff --git a/xpcom/base/nsIMessageLoop.idl b/xpcom/base/nsIMessageLoop.idl
new file mode 100644
index 0000000000..070883ed89
--- /dev/null
+++ b/xpcom/base/nsIMessageLoop.idl
@@ -0,0 +1,36 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "nsISupports.idl"
+
+interface nsIRunnable;
+
+/**
+ * This service allows access to the current thread's Chromium MessageLoop
+ * instance, with some extra sugar added.  If you're calling from C++, it may
+ * or may not make sense for you to use this interface.  If you're calling from
+ * JS, you don't have a choice!
+ *
+ * Right now, you can only call PostIdleTask(), and the wrath of khuey is
+ * stopping you from adding other methods.
+ *
+ * nsIMessageLoop's contractid is "@mozilla.org/message-loop;1".
+ */
+[builtinclass, scriptable, uuid(3E8C58E8-E52C-43E0-8E66-669CA788FF5F)]
+interface nsIMessageLoop : nsISupports
+{
+  /**
+   * Posts a task to be run when this thread's message loop is idle, or after
+   * ensureRunsAfterMS milliseconds have elapsed.  (That is, the task is
+   * guaranteed to run /eventually/.)
+   *
+   * Note that if the event loop is busy, we will hold a reference to the task
+   * until ensureRunsAfterMS milliseconds have elapsed.  Be careful when
+   * specifying long timeouts and tasks which hold references to windows or
+   * other large objects, because you can leak memory in a difficult-to-detect
+   * way!
+   */
+  void postIdleTask(in nsIRunnable task, in uint32_t ensureRunsAfterMS);
+};
diff --git a/xpcom/base/nsINIParser.cpp b/xpcom/base/nsINIParser.cpp
new file mode 100644
index 0000000000..c1eec56f10
--- /dev/null
+++ b/xpcom/base/nsINIParser.cpp
@@ -0,0 +1,324 @@
+/* -*- 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/. */
+
+// Moz headers (alphabetical)
+#include "nsCRTGlue.h"
+#include "nsError.h"
+#include "nsIFile.h"
+#include "nsINIParser.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/URLPreloader.h"
+
+using namespace mozilla;
+
+nsresult nsINIParser::Init(nsIFile* aFile) {
+  nsCString result;
+  MOZ_TRY_VAR(result, URLPreloader::ReadFile(aFile));
+
+  return InitFromString(result);
+}
+
+static const char kNL[] = "\r\n";
+static const char kEquals[] = "=";
+static const char kWhitespace[] = " \t";
+static const char kRBracket[] = "]";
+
+nsresult nsINIParser::InitFromString(const nsCString& aStr) {
+  nsCString fileContents;
+  char* buffer;
+
+  if (StringHead(aStr, 3) == "\xEF\xBB\xBF") {
+    // Someone set us up the Utf-8 BOM
+    // This case is easy, since we assume that BOM-less
+    // files are Utf-8 anyway.  Just skip the BOM and process as usual.
+    fileContents.Append(aStr);
+    buffer = fileContents.BeginWriting() + 3;
+  } else {
+    if (StringHead(aStr, 2) == "\xFF\xFE") {
+      // Someone set us up the Utf-16LE BOM
+      nsDependentSubstring str(reinterpret_cast<const char16_t*>(aStr.get()),
+                               aStr.Length() / 2);
+
+      AppendUTF16toUTF8(Substring(str, 1), fileContents);
+    } else {
+      fileContents.Append(aStr);
+    }
+
+    buffer = fileContents.BeginWriting();
+  }
+
+  char* currSection = nullptr;
+
+  // outer loop tokenizes into lines
+  while (char* token = NS_strtok(kNL, &buffer)) {
+    if (token[0] == '#' || token[0] == ';') {  // it's a comment
+      continue;
+    }
+
+    token = (char*)NS_strspnp(kWhitespace, token);
+    if (!*token) {  // empty line
+      continue;
+    }
+
+    if (token[0] == '[') {  // section header!
+      ++token;
+      currSection = token;
+
+      char* rb = NS_strtok(kRBracket, &token);
+      if (!rb || NS_strtok(kWhitespace, &token)) {
+        // there's either an unclosed [Section or a [Section]Moretext!
+        // we could frankly decide that this INI file is malformed right
+        // here and stop, but we won't... keep going, looking for
+        // a well-formed [section] to continue working with
+        currSection = nullptr;
+      }
+
+      continue;
+    }
+
+    if (!currSection) {
+      // If we haven't found a section header (or we found a malformed
+      // section header), don't bother parsing this line.
+      continue;
+    }
+
+    char* key = token;
+    char* e = NS_strtok(kEquals, &token);
+    if (!e || !token) {
+      continue;
+    }
+
+    SetString(currSection, key, token);
+  }
+
+  return NS_OK;
+}
+
+bool nsINIParser::IsValidSection(const char* aSection) {
+  if (aSection[0] == '\0') {
+    return false;
+  }
+
+  const char* found = strpbrk(aSection, "\r\n[]");
+  return found == nullptr;
+}
+
+bool nsINIParser::IsValidKey(const char* aKey) {
+  if (aKey[0] == '\0') {
+    return false;
+  }
+
+  const char* found = strpbrk(aKey, "\r\n=");
+  return found == nullptr;
+}
+
+bool nsINIParser::IsValidValue(const char* aValue) {
+  const char* found = strpbrk(aValue, "\r\n");
+  return found == nullptr;
+}
+
+nsresult nsINIParser::GetString(const char* aSection, const char* aKey,
+                                nsACString& aResult) {
+  if (!IsValidSection(aSection) || !IsValidKey(aKey)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  INIValue* val;
+  mSections.Get(aSection, &val);
+
+  while (val) {
+    if (strcmp(val->key, aKey) == 0) {
+      aResult.Assign(val->value);
+      return NS_OK;
+    }
+
+    val = val->next.get();
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+nsresult nsINIParser::GetString(const char* aSection, const char* aKey,
+                                char* aResult, uint32_t aResultLen) {
+  if (!IsValidSection(aSection) || !IsValidKey(aKey)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  INIValue* val;
+  mSections.Get(aSection, &val);
+
+  while (val) {
+    if (strcmp(val->key, aKey) == 0) {
+      strncpy(aResult, val->value, aResultLen);
+      aResult[aResultLen - 1] = '\0';
+      if (strlen(val->value) >= aResultLen) {
+        return NS_ERROR_LOSS_OF_SIGNIFICANT_DATA;
+      }
+
+      return NS_OK;
+    }
+
+    val = val->next.get();
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+nsresult nsINIParser::GetSections(INISectionCallback aCB, void* aClosure) {
+  for (const auto& key : mSections.Keys()) {
+    if (!aCB(key, aClosure)) {
+      break;
+    }
+  }
+  return NS_OK;
+}
+
+nsresult nsINIParser::GetStrings(const char* aSection, INIStringCallback aCB,
+                                 void* aClosure) {
+  if (!IsValidSection(aSection)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  INIValue* val;
+
+  for (mSections.Get(aSection, &val); val; val = val->next.get()) {
+    if (!aCB(val->key, val->value, aClosure)) {
+      return NS_OK;
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult nsINIParser::SetString(const char* aSection, const char* aKey,
+                                const char* aValue) {
+  if (!IsValidSection(aSection) || !IsValidKey(aKey) || !IsValidValue(aValue)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  mSections.WithEntryHandle(aSection, [&](auto&& entry) {
+    if (!entry) {
+      entry.Insert(MakeUnique<INIValue>(aKey, aValue));
+      return;
+    }
+
+    INIValue* v = entry->get();
+
+    // Check whether this key has already been specified; overwrite
+    // if so, or append if not.
+    while (v) {
+      if (!strcmp(aKey, v->key)) {
+        v->SetValue(aValue);
+        break;
+      }
+      if (!v->next) {
+        v->next = MakeUnique<INIValue>(aKey, aValue);
+        break;
+      }
+      v = v->next.get();
+    }
+    NS_ASSERTION(v, "v should never be null coming out of this loop");
+  });
+
+  return NS_OK;
+}
+
+nsresult nsINIParser::DeleteString(const char* aSection, const char* aKey) {
+  if (!IsValidSection(aSection) || !IsValidKey(aKey)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  INIValue* val;
+  if (!mSections.Get(aSection, &val)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Special case the first result
+  if (strcmp(val->key, aKey) == 0) {
+    if (!val->next) {
+      mSections.Remove(aSection);
+    } else {
+      mSections.InsertOrUpdate(aSection, std::move(val->next));
+      delete val;
+    }
+    return NS_OK;
+  }
+
+  while (val->next) {
+    if (strcmp(val->next->key, aKey) == 0) {
+      val->next = std::move(val->next->next);
+
+      return NS_OK;
+    }
+
+    val = val->next.get();
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+nsresult nsINIParser::DeleteSection(const char* aSection) {
+  if (!IsValidSection(aSection)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  if (!mSections.Remove(aSection)) {
+    return NS_ERROR_FAILURE;
+  }
+  return NS_OK;
+}
+
+nsresult nsINIParser::RenameSection(const char* aSection,
+                                    const char* aNewName) {
+  if (!IsValidSection(aSection) || !IsValidSection(aNewName)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  if (mSections.Contains(aNewName)) {
+    return NS_ERROR_ILLEGAL_VALUE;
+  }
+
+  mozilla::UniquePtr<INIValue> val;
+  if (mSections.Remove(aSection, &val)) {
+    mSections.InsertOrUpdate(aNewName, std::move(val));
+  } else {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+nsresult nsINIParser::WriteToFile(nsIFile* aFile) {
+  nsCString buffer;
+
+  WriteToString(buffer);
+
+  FILE* writeFile;
+  nsresult rv = aFile->OpenANSIFileDesc("w", &writeFile);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  unsigned int length = buffer.Length();
+
+  if (fwrite(buffer.get(), sizeof(char), length, writeFile) != length) {
+    fclose(writeFile);
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  fclose(writeFile);
+  return NS_OK;
+}
+
+void nsINIParser::WriteToString(nsACString& aOutput) {
+  for (const auto& entry : mSections) {
+    aOutput.AppendPrintf("[%s]\n", entry.GetKey());
+    INIValue* val = entry.GetWeak();
+    while (val) {
+      aOutput.AppendPrintf("%s=%s\n", val->key, val->value);
+      val = val->next.get();
+    }
+    aOutput.AppendLiteral("\n");
+  }
+}
diff --git a/xpcom/base/nsINIParser.h b/xpcom/base/nsINIParser.h
new file mode 100644
index 0000000000..3b26a0d511
--- /dev/null
+++ b/xpcom/base/nsINIParser.h
@@ -0,0 +1,168 @@
+/* -*- 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/. */
+
+// This file was shamelessly copied from mozilla/xpinstall/wizard/unix/src2
+
+#ifndef nsINIParser_h__
+#define nsINIParser_h__
+
+#ifdef MOZILLA_INTERNAL_API
+#  define nsINIParser nsINIParser_internal
+#endif
+
+#include "nscore.h"
+#include "nsClassHashtable.h"
+#include "mozilla/UniquePtr.h"
+
+#include <stdio.h>
+
+class nsIFile;
+
+class nsINIParser {
+ public:
+  nsINIParser() {}
+  ~nsINIParser() = default;
+
+  /**
+   * Initialize the INIParser with a nsIFile. If this method fails, no
+   * other methods should be called. This method reads and parses the file,
+   * the class does not hold a file handle open. An instance must only be
+   * initialized once.
+   */
+  nsresult Init(nsIFile* aFile);
+
+  nsresult InitFromString(const nsCString& aStr);
+
+  /**
+   * Callback for GetSections
+   * @return false to stop enumeration, or true to continue.
+   */
+  typedef bool (*INISectionCallback)(const char* aSection, void* aClosure);
+
+  /**
+   * Enumerate the sections within the INI file.
+   */
+  nsresult GetSections(INISectionCallback aCB, void* aClosure);
+
+  /**
+   * Callback for GetStrings
+   * @return false to stop enumeration, or true to continue
+   */
+  typedef bool (*INIStringCallback)(const char* aString, const char* aValue,
+                                    void* aClosure);
+
+  /**
+   * Enumerate the strings within a section. If the section does
+   * not exist, this function will silently return.
+   */
+  nsresult GetStrings(const char* aSection, INIStringCallback aCB,
+                      void* aClosure);
+
+  /**
+   * Get the value of the specified key in the specified section
+   * of the INI file represented by this instance.
+   *
+   * @param aSection      section name
+   * @param aKey          key name
+   * @param aResult       the value found
+   * @throws NS_ERROR_FAILURE if the specified section/key could not be
+   *                          found.
+   */
+  nsresult GetString(const char* aSection, const char* aKey,
+                     nsACString& aResult);
+
+  /**
+   * Alternate signature of GetString that uses a pre-allocated buffer
+   * instead of a nsACString (for use in the standalone glue before
+   * the glue is initialized).
+   *
+   * @throws NS_ERROR_LOSS_OF_SIGNIFICANT_DATA if the aResult buffer is not
+   *         large enough for the data. aResult will be filled with as
+   *         much data as possible.
+   *
+   * @see GetString [1]
+   */
+  nsresult GetString(const char* aSection, const char* aKey, char* aResult,
+                     uint32_t aResultLen);
+
+  /**
+   * Sets the value of the specified key in the specified section. The section
+   * is created if it does not already exist.
+   *
+   * @oaram aSection      section name
+   * @param aKey          key name
+   * @param aValue        the value to set
+   */
+  nsresult SetString(const char* aSection, const char* aKey,
+                     const char* aValue);
+
+  /**
+   * Deletes the value of the specified key in the specified section.
+   *
+   * @param aSection      section name
+   * @param aKey          key name
+   *
+   * @throws NS_ERROR_FAILURE if the string was not set.
+   */
+  nsresult DeleteString(const char* aSection, const char* aKey);
+
+  /**
+   * Deletes the specified section.
+   *
+   * @param aSection      section name
+   *
+   * @throws NS_ERROR_FAILURE if the section did not exist.
+   */
+  nsresult DeleteSection(const char* aSection);
+
+  /**
+   * Renames the specified section.
+   *
+   * @param aSection      section name
+   * @param aNewName      new section name
+   *
+   * @throws NS_ERROR_FAILURE if the section did not exist.
+   * @throws NS_ERROR_ILLEGAL_VALUE if the new section name already exists.
+   */
+  nsresult RenameSection(const char* aSection, const char* aNewName);
+
+  /**
+   * Writes the ini data to disk.
+   * @param aFile         the file to write to
+   * @throws NS_ERROR_FAILURE on failure.
+   */
+  nsresult WriteToFile(nsIFile* aFile);
+
+  void WriteToString(nsACString& aOutput);
+
+ private:
+  struct INIValue {
+    INIValue(const char* aKey, const char* aValue)
+        : key(strdup(aKey)), value(strdup(aValue)) {}
+
+    ~INIValue() {
+      delete key;
+      delete value;
+    }
+
+    void SetValue(const char* aValue) {
+      delete value;
+      value = strdup(aValue);
+    }
+
+    const char* key;
+    const char* value;
+    mozilla::UniquePtr<INIValue> next;
+  };
+
+  nsClassHashtable<nsCharPtrHashKey, INIValue> mSections;
+
+  bool IsValidSection(const char* aSection);
+  bool IsValidKey(const char* aKey);
+  bool IsValidValue(const char* aValue);
+};
+
+#endif /* nsINIParser_h__ */
diff --git a/xpcom/base/nsISecurityConsoleMessage.idl b/xpcom/base/nsISecurityConsoleMessage.idl
new file mode 100644
index 0000000000..917968d83b
--- /dev/null
+++ b/xpcom/base/nsISecurityConsoleMessage.idl
@@ -0,0 +1,20 @@
+/* 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 "nsISupports.idl"
+
+/*
+ * Holds localization message tag and message category
+ * for security related console messages.
+ */
+[uuid(FE9FC9B6-DDE2-11E2-A8F1-0A326188709B)]
+interface nsISecurityConsoleMessage : nsISupports
+{
+  attribute AString tag;
+  attribute AString category;
+};
+
+%{ C++
+#define NS_SECURITY_CONSOLE_MESSAGE_CONTRACTID "@mozilla.org/securityconsole/message;1"
+%}
diff --git a/xpcom/base/nsISizeOf.h b/xpcom/base/nsISizeOf.h
new file mode 100644
index 0000000000..7d0ef4d74f
--- /dev/null
+++ b/xpcom/base/nsISizeOf.h
@@ -0,0 +1,39 @@
+/* -*- 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/. */
+
+#ifndef nsISizeOf_h___
+#define nsISizeOf_h___
+
+#include "mozilla/MemoryReporting.h"
+#include "nsISupports.h"
+
+#define NS_ISIZEOF_IID                               \
+  {                                                  \
+    0x61d05579, 0xd7ec, 0x485c, {                    \
+      0xa4, 0x0c, 0x31, 0xc7, 0x9a, 0x5c, 0xf9, 0xf3 \
+    }                                                \
+  }
+
+class nsISizeOf : public nsISupports {
+ public:
+  NS_DECLARE_STATIC_IID_ACCESSOR(NS_ISIZEOF_IID)
+
+  /**
+   * Measures the size of the things pointed to by the object.
+   */
+  virtual size_t SizeOfExcludingThis(
+      mozilla::MallocSizeOf aMallocSizeOf) const = 0;
+
+  /**
+   * Like SizeOfExcludingThis, but also includes the size of the object itself.
+   */
+  virtual size_t SizeOfIncludingThis(
+      mozilla::MallocSizeOf aMallocSizeOf) const = 0;
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(nsISizeOf, NS_ISIZEOF_IID)
+
+#endif /* nsISizeOf_h___ */
diff --git a/xpcom/base/nsISupports.idl b/xpcom/base/nsISupports.idl
new file mode 100644
index 0000000000..45c6c5d589
--- /dev/null
+++ b/xpcom/base/nsISupports.idl
@@ -0,0 +1,60 @@
+/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* 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/. */
+
+/**
+ * The mother of all xpcom interfaces.
+ */
+
+#include "nsrootidl.idl"
+
+/**
+ * Basic component object model interface. Objects which implement
+ * this interface support runtime interface discovery (QueryInterface)
+ * and a reference counted memory model (AddRef/Release). This is
+ * modelled after the win32 IUnknown API.
+ *
+ * Historically, nsISupports needed to be binary compatible with COM's
+ * IUnknown, so the IID of nsISupports is the same as it. That is no
+ * longer a goal, and hopefully nobody depends on it. We may break
+ * this compatibility at any time.
+ */
+[scriptable, uuid(00000000-0000-0000-c000-000000000046)]
+interface nsISupports {
+
+  /**
+   * A run time mechanism for interface discovery.
+   * @param aIID [in] A requested interface IID
+   * @param aInstancePtr [out] A pointer to an interface pointer to
+   * receive the result.
+   * @return <b>NS_OK</b> if the interface is supported by the associated
+   * instance, <b>NS_NOINTERFACE</b> if it is not.
+   *
+   * aInstancePtr must not be null.
+   */
+  void QueryInterface(in nsIIDRef aIID,
+                      [iid_is(aIID), retval] out nsQIResult aInstancePtr);
+
+  /**
+   * Increases the reference count for this interface.
+   * The associated instance will not be deleted unless
+   * the reference count is returned to zero.
+   *
+   * @return The resulting reference count.
+   */
+  [noscript, notxpcom] MozExternalRefCountType AddRef();
+
+  /**
+   * Decreases the reference count for this interface.
+   * Generally, if the reference count returns to zero,
+   * the associated instance is deleted.
+   *
+   * @return The resulting reference count.
+   */
+  [noscript, notxpcom] MozExternalRefCountType Release();
+};
+
+%{C++
+#include "nsISupportsUtils.h"
+%}
diff --git a/xpcom/base/nsISupportsImpl.cpp b/xpcom/base/nsISupportsImpl.cpp
new file mode 100644
index 0000000000..c282ec14db
--- /dev/null
+++ b/xpcom/base/nsISupportsImpl.cpp
@@ -0,0 +1,144 @@
+/* -*- 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 "nsISupportsImpl.h"
+
+#include "mozilla/Assertions.h"
+#ifndef XPCOM_GLUE_AVOID_NSPR
+#  include "nsPrintfCString.h"
+#  include "nsThreadUtils.h"
+#endif
+
+using namespace mozilla;
+
+nsresult NS_FASTCALL NS_TableDrivenQI(void* aThis, REFNSIID aIID,
+                                      void** aInstancePtr,
+                                      const QITableEntry* aEntries) {
+  do {
+    if (aIID.Equals(*aEntries->iid)) {
+      nsISupports* r = reinterpret_cast<nsISupports*>(
+          reinterpret_cast<char*>(aThis) + aEntries->offset);
+      NS_ADDREF(r);
+      *aInstancePtr = r;
+      return NS_OK;
+    }
+
+    ++aEntries;
+  } while (aEntries->iid);
+
+  *aInstancePtr = nullptr;
+  return NS_ERROR_NO_INTERFACE;
+}
+
+#ifndef XPCOM_GLUE_AVOID_NSPR
+#  ifdef MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED
+nsAutoOwningThread::nsAutoOwningThread() : mThread(PR_GetCurrentThread()) {}
+
+void nsAutoOwningThread::AssertCurrentThreadOwnsMe(const char* msg) const {
+  if (MOZ_UNLIKELY(!IsCurrentThread())) {
+    // `msg` is a string literal by construction.
+    MOZ_CRASH_UNSAFE(msg);
+  }
+}
+
+bool nsAutoOwningThread::IsCurrentThread() const {
+  return mThread == PR_GetCurrentThread();
+}
+
+nsAutoOwningEventTarget::nsAutoOwningEventTarget()
+    : mTarget(GetCurrentSerialEventTarget()) {
+  mTarget->AddRef();
+}
+
+nsAutoOwningEventTarget::~nsAutoOwningEventTarget() {
+  nsCOMPtr<nsISerialEventTarget> target = dont_AddRef(mTarget);
+}
+
+void nsAutoOwningEventTarget ::AssertCurrentThreadOwnsMe(
+    const char* msg) const {
+  if (MOZ_UNLIKELY(!IsCurrentThread())) {
+    // `msg` is a string literal by construction.
+    MOZ_CRASH_UNSAFE(msg);
+  }
+}
+
+bool nsAutoOwningEventTarget::IsCurrentThread() const {
+  return mTarget->IsOnCurrentThread();
+}
+
+#  endif
+
+namespace mozilla::detail {
+class ProxyDeleteVoidRunnable final : public CancelableRunnable {
+ public:
+  ProxyDeleteVoidRunnable(const char* aName, void* aPtr,
+                          DeleteVoidFunction* aDeleteFunc)
+      : CancelableRunnable(aName), mPtr(aPtr), mDeleteFunc(aDeleteFunc) {}
+
+  NS_IMETHOD Run() override {
+    if (mPtr) {
+      mDeleteFunc(mPtr);
+      mPtr = nullptr;
+    }
+    return NS_OK;
+  }
+
+  // Mimics the behaviour in `ProxyRelease`, freeing the resource when
+  // cancelled.
+  nsresult Cancel() override { return Run(); }
+
+#  ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+  NS_IMETHOD GetName(nsACString& aName) override {
+    if (mName) {
+      aName.Append(mName);
+    } else {
+      aName.AssignLiteral("ProxyDeleteVoidRunnable");
+    }
+    return NS_OK;
+  }
+#  endif
+
+ private:
+  ~ProxyDeleteVoidRunnable() {
+    if (mPtr) {
+#  ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+      NS_WARNING(
+          nsPrintfCString(
+              "ProxyDeleteVoidRunnable for '%s' never run, leaking!", mName)
+              .get());
+#  else
+      NS_WARNING("ProxyDeleteVoidRunnable never run, leaking!");
+#  endif
+    }
+  }
+
+  void* mPtr;
+  DeleteVoidFunction* mDeleteFunc;
+};
+
+void ProxyDeleteVoid(const char* aName, nsISerialEventTarget* aTarget,
+                     void* aPtr, DeleteVoidFunction* aDeleteFunc) {
+  MOZ_ASSERT(aName);
+  MOZ_ASSERT(aPtr);
+  MOZ_ASSERT(aDeleteFunc);
+  if (!aTarget) {
+    NS_WARNING(nsPrintfCString("no target for '%s', leaking!", aName).get());
+    return;
+  }
+
+  if (aTarget->IsOnCurrentThread()) {
+    aDeleteFunc(aPtr);
+    return;
+  }
+  nsresult rv = aTarget->Dispatch(
+      MakeAndAddRef<ProxyDeleteVoidRunnable>(aName, aPtr, aDeleteFunc),
+      NS_DISPATCH_NORMAL);
+  if (NS_FAILED(rv)) {
+    NS_WARNING(nsPrintfCString("failed to post '%s', leaking!", aName).get());
+  }
+}
+}  // namespace mozilla::detail
+#endif
diff --git a/xpcom/base/nsISupportsImpl.h b/xpcom/base/nsISupportsImpl.h
new file mode 100644
index 0000000000..6a232daae9
--- /dev/null
+++ b/xpcom/base/nsISupportsImpl.h
@@ -0,0 +1,1539 @@
+/* -*- 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/. */
+// IWYU pragma: private, include "nsISupports.h"
+
+#ifndef nsISupportsImpl_h__
+#define nsISupportsImpl_h__
+
+#include "nscore.h"
+#include "nsISupports.h"
+#include "nsISupportsUtils.h"
+
+#if !defined(XPCOM_GLUE_AVOID_NSPR)
+#  include "prthread.h" /* needed for cargo-culting headers */
+#endif
+
+#include "nsDebug.h"
+#include "nsXPCOM.h"
+#include <atomic>
+#include <type_traits>
+#include "mozilla/Attributes.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Compiler.h"
+#include "mozilla/Likely.h"
+#include "mozilla/MacroArgs.h"
+#include "mozilla/MacroForEach.h"
+
+#define MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(X)            \
+  static_assert(!std::is_destructible_v<X>,              \
+                "Reference-counted class " #X            \
+                " should not have a public destructor. " \
+                "Make this class's destructor non-public");
+
+inline nsISupports* ToSupports(decltype(nullptr)) { return nullptr; }
+
+inline nsISupports* ToSupports(nsISupports* aSupports) { return aSupports; }
+
+////////////////////////////////////////////////////////////////////////////////
+// Macros to help detect thread-safety:
+
+#ifdef MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED
+
+#  include "prthread.h" /* needed for thread-safety checks */
+
+class nsAutoOwningThread {
+ public:
+  nsAutoOwningThread();
+
+  // We move the actual assertion checks out-of-line to minimize code bloat,
+  // but that means we have to pass a non-literal string to MOZ_CRASH_UNSAFE.
+  // To make that more safe, the public interface requires a literal string
+  // and passes that to the private interface; we can then be assured that we
+  // effectively are passing a literal string to MOZ_CRASH_UNSAFE.
+  template <int N>
+  void AssertOwnership(const char (&aMsg)[N]) const {
+    AssertCurrentThreadOwnsMe(aMsg);
+  }
+
+  bool IsCurrentThread() const;
+
+ private:
+  void AssertCurrentThreadOwnsMe(const char* aMsg) const;
+
+  void* mThread;
+};
+
+class nsISerialEventTarget;
+class nsAutoOwningEventTarget {
+ public:
+  nsAutoOwningEventTarget();
+  ~nsAutoOwningEventTarget();
+
+  // We move the actual assertion checks out-of-line to minimize code bloat,
+  // but that means we have to pass a non-literal string to MOZ_CRASH_UNSAFE.
+  // To make that more safe, the public interface requires a literal string
+  // and passes that to the private interface; we can then be assured that we
+  // effectively are passing a literal string to MOZ_CRASH_UNSAFE.
+  template <int N>
+  void AssertOwnership(const char (&aMsg)[N]) const {
+    AssertCurrentThreadOwnsMe(aMsg);
+  }
+
+  bool IsCurrentThread() const;
+
+ private:
+  void AssertCurrentThreadOwnsMe(const char* aMsg) const;
+
+  nsISerialEventTarget* mTarget;
+};
+
+#  define NS_DECL_OWNINGTHREAD nsAutoOwningThread _mOwningThread;
+#  define NS_DECL_OWNINGEVENTTARGET nsAutoOwningEventTarget _mOwningThread;
+#  define NS_ASSERT_OWNINGTHREAD(_class) \
+    _mOwningThread.AssertOwnership(#_class " not thread-safe")
+#else  // !MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED
+
+#  define NS_DECL_OWNINGTHREAD      /* nothing */
+#  define NS_DECL_OWNINGEVENTTARGET /* nothing */
+#  define NS_ASSERT_OWNINGTHREAD(_class) ((void)0)
+
+#endif  // MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED
+
+// Macros for reference-count and constructor logging
+
+#if defined(NS_BUILD_REFCNT_LOGGING)
+
+#  define NS_LOG_ADDREF(_p, _rc, _type, _size) \
+    NS_LogAddRef((_p), (_rc), (_type), (uint32_t)(_size))
+
+#  define NS_LOG_RELEASE(_p, _rc, _type) NS_LogRelease((_p), (_rc), (_type))
+
+#  define MOZ_ASSERT_CLASSNAME(_type)     \
+    static_assert(std::is_class_v<_type>, \
+                  "Token '" #_type "' is not a class type.")
+
+#  define MOZ_ASSERT_NOT_ISUPPORTS(_type)                                     \
+    static_assert(!std::is_base_of<nsISupports, _type>::value,                \
+                  "nsISupports classes don't need to call MOZ_COUNT_CTOR or " \
+                  "MOZ_COUNT_DTOR");
+
+// Note that the following constructor/destructor logging macros are redundant
+// for refcounted objects that log via the NS_LOG_ADDREF/NS_LOG_RELEASE macros.
+// Refcount logging is preferred.
+#  define MOZ_COUNT_CTOR(_type)                       \
+    do {                                              \
+      MOZ_ASSERT_CLASSNAME(_type);                    \
+      MOZ_ASSERT_NOT_ISUPPORTS(_type);                \
+      NS_LogCtor((void*)this, #_type, sizeof(*this)); \
+    } while (0)
+
+#  define MOZ_COUNT_CTOR_INHERITED(_type, _base)                      \
+    do {                                                              \
+      MOZ_ASSERT_CLASSNAME(_type);                                    \
+      MOZ_ASSERT_CLASSNAME(_base);                                    \
+      MOZ_ASSERT_NOT_ISUPPORTS(_type);                                \
+      NS_LogCtor((void*)this, #_type, sizeof(*this) - sizeof(_base)); \
+    } while (0)
+
+#  define MOZ_LOG_CTOR(_ptr, _name, _size)   \
+    do {                                     \
+      NS_LogCtor((void*)_ptr, _name, _size); \
+    } while (0)
+
+#  define MOZ_COUNT_DTOR(_type)                       \
+    do {                                              \
+      MOZ_ASSERT_CLASSNAME(_type);                    \
+      MOZ_ASSERT_NOT_ISUPPORTS(_type);                \
+      NS_LogDtor((void*)this, #_type, sizeof(*this)); \
+    } while (0)
+
+#  define MOZ_COUNT_DTOR_INHERITED(_type, _base)                      \
+    do {                                                              \
+      MOZ_ASSERT_CLASSNAME(_type);                                    \
+      MOZ_ASSERT_CLASSNAME(_base);                                    \
+      MOZ_ASSERT_NOT_ISUPPORTS(_type);                                \
+      NS_LogDtor((void*)this, #_type, sizeof(*this) - sizeof(_base)); \
+    } while (0)
+
+#  define MOZ_LOG_DTOR(_ptr, _name, _size)   \
+    do {                                     \
+      NS_LogDtor((void*)_ptr, _name, _size); \
+    } while (0)
+
+#  define MOZ_COUNTED_DEFAULT_CTOR(_type) \
+    _type() { MOZ_COUNT_CTOR(_type); }
+
+#  define MOZ_COUNTED_DTOR_META(_type, _prefix, _postfix) \
+    _prefix ~_type() _postfix { MOZ_COUNT_DTOR(_type); }
+#  define MOZ_COUNTED_DTOR_NESTED(_type, _nestedName) \
+    ~_type() { MOZ_COUNT_DTOR(_nestedName); }
+
+/* nsCOMPtr.h allows these macros to be defined by clients
+ * These logging functions require dynamic_cast<void*>, so they don't
+ * do anything useful if we don't have dynamic_cast<void*>.
+ * Note: The explicit comparison to nullptr is needed to avoid warnings
+ *       when _p is a nullptr itself. */
+#  define NSCAP_LOG_ASSIGNMENT(_c, _p) \
+    if (_p != nullptr) NS_LogCOMPtrAddRef((_c), ToSupports(_p))
+
+#  define NSCAP_LOG_RELEASE(_c, _p) \
+    if (_p) NS_LogCOMPtrRelease((_c), ToSupports(_p))
+
+#else /* !NS_BUILD_REFCNT_LOGGING */
+
+#  define NS_LOG_ADDREF(_p, _rc, _type, _size)
+#  define NS_LOG_RELEASE(_p, _rc, _type)
+#  define MOZ_COUNT_CTOR(_type)
+#  define MOZ_COUNT_CTOR_INHERITED(_type, _base)
+#  define MOZ_LOG_CTOR(_ptr, _name, _size)
+#  define MOZ_COUNT_DTOR(_type)
+#  define MOZ_COUNT_DTOR_INHERITED(_type, _base)
+#  define MOZ_LOG_DTOR(_ptr, _name, _size)
+#  define MOZ_COUNTED_DEFAULT_CTOR(_type) _type() = default;
+#  define MOZ_COUNTED_DTOR_META(_type, _prefix, _postfix) \
+    _prefix ~_type() _postfix = default;
+#  define MOZ_COUNTED_DTOR_NESTED(_type, _nestedName) ~_type() = default;
+
+#endif /* NS_BUILD_REFCNT_LOGGING */
+
+#define MOZ_COUNTED_DTOR(_type) MOZ_COUNTED_DTOR_META(_type, , )
+#define MOZ_COUNTED_DTOR_OVERRIDE(_type) \
+  MOZ_COUNTED_DTOR_META(_type, , override)
+#define MOZ_COUNTED_DTOR_FINAL(_type) MOZ_COUNTED_DTOR_META(_type, , final)
+#define MOZ_COUNTED_DTOR_VIRTUAL(_type) MOZ_COUNTED_DTOR_META(_type, virtual, )
+
+// Support for ISupports classes which interact with cycle collector.
+
+#define NS_NUMBER_OF_FLAGS_IN_REFCNT 2
+#define NS_IN_PURPLE_BUFFER (1 << 0)
+#define NS_IS_PURPLE (1 << 1)
+#define NS_REFCOUNT_CHANGE (1 << NS_NUMBER_OF_FLAGS_IN_REFCNT)
+#define NS_REFCOUNT_VALUE(_val) (_val >> NS_NUMBER_OF_FLAGS_IN_REFCNT)
+
+class nsCycleCollectingAutoRefCnt {
+ public:
+  typedef void (*Suspect)(void* aPtr, nsCycleCollectionParticipant* aCp,
+                          nsCycleCollectingAutoRefCnt* aRefCnt,
+                          bool* aShouldDelete);
+
+  nsCycleCollectingAutoRefCnt() : mRefCntAndFlags(0) {}
+
+  explicit nsCycleCollectingAutoRefCnt(uintptr_t aValue)
+      : mRefCntAndFlags(aValue << NS_NUMBER_OF_FLAGS_IN_REFCNT) {}
+
+  nsCycleCollectingAutoRefCnt(const nsCycleCollectingAutoRefCnt&) = delete;
+  void operator=(const nsCycleCollectingAutoRefCnt&) = delete;
+
+  template <Suspect suspect = NS_CycleCollectorSuspect3>
+  MOZ_ALWAYS_INLINE uintptr_t incr(nsISupports* aOwner) {
+    return incr<suspect>(aOwner, nullptr);
+  }
+
+  template <Suspect suspect = NS_CycleCollectorSuspect3>
+  MOZ_ALWAYS_INLINE uintptr_t incr(void* aOwner,
+                                   nsCycleCollectionParticipant* aCp) {
+    mRefCntAndFlags += NS_REFCOUNT_CHANGE;
+    mRefCntAndFlags &= ~NS_IS_PURPLE;
+    // For incremental cycle collection, use the purple buffer to track objects
+    // that have been AddRef'd.
+    if (!IsInPurpleBuffer()) {
+      mRefCntAndFlags |= NS_IN_PURPLE_BUFFER;
+      // Refcount isn't zero, so Suspect won't delete anything.
+      MOZ_ASSERT(get() > 0);
+      suspect(aOwner, aCp, this, nullptr);
+    }
+    return NS_REFCOUNT_VALUE(mRefCntAndFlags);
+  }
+
+  MOZ_ALWAYS_INLINE void stabilizeForDeletion() {
+    // Set refcnt to 1 and mark us to be in the purple buffer.
+    // This way decr won't call suspect again.
+    mRefCntAndFlags = NS_REFCOUNT_CHANGE | NS_IN_PURPLE_BUFFER;
+  }
+
+  template <Suspect suspect = NS_CycleCollectorSuspect3>
+  MOZ_ALWAYS_INLINE uintptr_t decr(nsISupports* aOwner,
+                                   bool* aShouldDelete = nullptr) {
+    return decr<suspect>(aOwner, nullptr, aShouldDelete);
+  }
+
+  template <Suspect suspect = NS_CycleCollectorSuspect3>
+  MOZ_ALWAYS_INLINE uintptr_t decr(void* aOwner,
+                                   nsCycleCollectionParticipant* aCp,
+                                   bool* aShouldDelete = nullptr) {
+    MOZ_ASSERT(get() > 0);
+    if (!IsInPurpleBuffer()) {
+      mRefCntAndFlags -= NS_REFCOUNT_CHANGE;
+      mRefCntAndFlags |= (NS_IN_PURPLE_BUFFER | NS_IS_PURPLE);
+      uintptr_t retval = NS_REFCOUNT_VALUE(mRefCntAndFlags);
+      // Suspect may delete 'aOwner' and 'this'!
+      suspect(aOwner, aCp, this, aShouldDelete);
+      return retval;
+    }
+    mRefCntAndFlags -= NS_REFCOUNT_CHANGE;
+    mRefCntAndFlags |= (NS_IN_PURPLE_BUFFER | NS_IS_PURPLE);
+    return NS_REFCOUNT_VALUE(mRefCntAndFlags);
+  }
+
+  MOZ_ALWAYS_INLINE void RemovePurple() {
+    MOZ_ASSERT(IsPurple(), "must be purple");
+    mRefCntAndFlags &= ~NS_IS_PURPLE;
+  }
+
+  MOZ_ALWAYS_INLINE void RemoveFromPurpleBuffer() {
+    MOZ_ASSERT(IsInPurpleBuffer());
+    mRefCntAndFlags &= ~(NS_IS_PURPLE | NS_IN_PURPLE_BUFFER);
+  }
+
+  MOZ_ALWAYS_INLINE bool IsPurple() const {
+    return !!(mRefCntAndFlags & NS_IS_PURPLE);
+  }
+
+  MOZ_ALWAYS_INLINE bool IsInPurpleBuffer() const {
+    return !!(mRefCntAndFlags & NS_IN_PURPLE_BUFFER);
+  }
+
+  MOZ_ALWAYS_INLINE nsrefcnt get() const {
+    return NS_REFCOUNT_VALUE(mRefCntAndFlags);
+  }
+
+  MOZ_ALWAYS_INLINE operator nsrefcnt() const { return get(); }
+
+ private:
+  uintptr_t mRefCntAndFlags;
+};
+
+class nsAutoRefCnt {
+ public:
+  nsAutoRefCnt() : mValue(0) {}
+  explicit nsAutoRefCnt(nsrefcnt aValue) : mValue(aValue) {}
+
+  nsAutoRefCnt(const nsAutoRefCnt&) = delete;
+  void operator=(const nsAutoRefCnt&) = delete;
+
+  // only support prefix increment/decrement
+  nsrefcnt operator++() { return ++mValue; }
+  nsrefcnt operator--() { return --mValue; }
+
+  nsrefcnt operator=(nsrefcnt aValue) { return (mValue = aValue); }
+  operator nsrefcnt() const { return mValue; }
+  nsrefcnt get() const { return mValue; }
+
+  static const bool isThreadSafe = false;
+
+ private:
+  nsrefcnt operator++(int) = delete;
+  nsrefcnt operator--(int) = delete;
+  nsrefcnt mValue;
+};
+
+namespace mozilla {
+class ThreadSafeAutoRefCnt {
+ public:
+  ThreadSafeAutoRefCnt() : mValue(0) {}
+  explicit ThreadSafeAutoRefCnt(nsrefcnt aValue) : mValue(aValue) {}
+
+  ThreadSafeAutoRefCnt(const ThreadSafeAutoRefCnt&) = delete;
+  void operator=(const ThreadSafeAutoRefCnt&) = delete;
+
+  // only support prefix increment/decrement
+  MOZ_ALWAYS_INLINE nsrefcnt operator++() {
+    // Memory synchronization is not required when incrementing a
+    // reference count.  The first increment of a reference count on a
+    // thread is not important, since the first use of the object on a
+    // thread can happen before it.  What is important is the transfer
+    // of the pointer to that thread, which may happen prior to the
+    // first increment on that thread.  The necessary memory
+    // synchronization is done by the mechanism that transfers the
+    // pointer between threads.
+    return mValue.fetch_add(1, std::memory_order_relaxed) + 1;
+  }
+  MOZ_ALWAYS_INLINE nsrefcnt operator--() {
+    // Since this may be the last release on this thread, we need
+    // release semantics so that prior writes on this thread are visible
+    // to the thread that destroys the object when it reads mValue with
+    // acquire semantics.
+    nsrefcnt result = mValue.fetch_sub(1, std::memory_order_release) - 1;
+    if (result == 0) {
+      // We're going to destroy the object on this thread, so we need
+      // acquire semantics to synchronize with the memory released by
+      // the last release on other threads, that is, to ensure that
+      // writes prior to that release are now visible on this thread.
+#ifdef MOZ_TSAN
+      // TSan doesn't understand std::atomic_thread_fence, so in order
+      // to avoid a false positive for every time a refcounted object
+      // is deleted, we replace the fence with an atomic operation.
+      mValue.load(std::memory_order_acquire);
+#else
+      std::atomic_thread_fence(std::memory_order_acquire);
+#endif
+    }
+    return result;
+  }
+
+  MOZ_ALWAYS_INLINE nsrefcnt operator=(nsrefcnt aValue) {
+    // Use release semantics since we're not sure what the caller is
+    // doing.
+    mValue.store(aValue, std::memory_order_release);
+    return aValue;
+  }
+  MOZ_ALWAYS_INLINE operator nsrefcnt() const { return get(); }
+  MOZ_ALWAYS_INLINE nsrefcnt get() const {
+    // Use acquire semantics since we're not sure what the caller is
+    // doing.
+    return mValue.load(std::memory_order_acquire);
+  }
+
+  static const bool isThreadSafe = true;
+
+ private:
+  nsrefcnt operator++(int) = delete;
+  nsrefcnt operator--(int) = delete;
+  std::atomic<nsrefcnt> mValue;
+};
+
+}  // namespace mozilla
+
+///////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Declare the reference count variable and the implementations of the
+ * AddRef and QueryInterface methods.
+ */
+
+#define NS_DECL_ISUPPORTS                                                 \
+ public:                                                                  \
+  NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) override; \
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void) override;             \
+  NS_IMETHOD_(MozExternalRefCountType) Release(void) override;            \
+  using HasThreadSafeRefCnt = std::false_type;                            \
+                                                                          \
+ protected:                                                               \
+  nsAutoRefCnt mRefCnt;                                                   \
+  NS_DECL_OWNINGTHREAD                                                    \
+ public:
+
+#define NS_DECL_ISUPPORTS_ONEVENTTARGET                                   \
+ public:                                                                  \
+  NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) override; \
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void) override;             \
+  NS_IMETHOD_(MozExternalRefCountType) Release(void) override;            \
+  using HasThreadSafeRefCnt = std::false_type;                            \
+                                                                          \
+ protected:                                                               \
+  nsAutoRefCnt mRefCnt;                                                   \
+  NS_DECL_OWNINGEVENTTARGET                                               \
+ public:
+
+#define NS_DECL_THREADSAFE_ISUPPORTS                                      \
+ public:                                                                  \
+  NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) override; \
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void) override;             \
+  NS_IMETHOD_(MozExternalRefCountType) Release(void) override;            \
+  using HasThreadSafeRefCnt = std::true_type;                             \
+                                                                          \
+ protected:                                                               \
+  ::mozilla::ThreadSafeAutoRefCnt mRefCnt;                                \
+  NS_DECL_OWNINGTHREAD                                                    \
+ public:
+
+#define NS_DECL_CYCLE_COLLECTING_ISUPPORTS          \
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS_META(override) \
+  NS_IMETHOD_(void) DeleteCycleCollectable(void);   \
+                                                    \
+ public:
+
+#define NS_DECL_CYCLE_COLLECTING_ISUPPORTS_FINAL  \
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS_META(final)  \
+  NS_IMETHOD_(void) DeleteCycleCollectable(void); \
+                                                  \
+ public:
+
+#define NS_DECL_CYCLE_COLLECTING_ISUPPORTS_FINAL_DELETECYCLECOLLECTABLE \
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS_META(override)                     \
+  NS_IMETHOD_(void) DeleteCycleCollectable(void) final;                 \
+                                                                        \
+ public:
+
+#define NS_DECL_CYCLE_COLLECTING_ISUPPORTS_META(...)                         \
+ public:                                                                     \
+  NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) __VA_ARGS__; \
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void) __VA_ARGS__;             \
+  NS_IMETHOD_(MozExternalRefCountType) Release(void) __VA_ARGS__;            \
+  using HasThreadSafeRefCnt = std::false_type;                               \
+                                                                             \
+ protected:                                                                  \
+  nsCycleCollectingAutoRefCnt mRefCnt;                                       \
+  NS_DECL_OWNINGTHREAD                                                       \
+ public:
+
+///////////////////////////////////////////////////////////////////////////////
+
+/*
+ * Implementation of AddRef and Release for non-nsISupports (ie "native")
+ * cycle-collected classes that use the purple buffer to avoid leaks.
+ */
+
+#define NS_IMPL_CC_NATIVE_ADDREF_BODY(_class)                                 \
+  MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(_class)                                  \
+  MOZ_ASSERT(int32_t(mRefCnt) >= 0, "illegal refcnt");                        \
+  NS_ASSERT_OWNINGTHREAD(_class);                                             \
+  nsrefcnt count =                                                            \
+      mRefCnt.incr(static_cast<void*>(this),                                  \
+                   _class::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant()); \
+  NS_LOG_ADDREF(this, count, #_class, sizeof(*this));                         \
+  return count;
+
+#define NS_IMPL_CC_MAIN_THREAD_ONLY_NATIVE_ADDREF_BODY(_class)         \
+  MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(_class)                           \
+  MOZ_ASSERT(int32_t(mRefCnt) >= 0, "illegal refcnt");                 \
+  NS_ASSERT_OWNINGTHREAD(_class);                                      \
+  nsrefcnt count = mRefCnt.incr<NS_CycleCollectorSuspectUsingNursery>( \
+      static_cast<void*>(this),                                        \
+      _class::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant());       \
+  NS_LOG_ADDREF(this, count, #_class, sizeof(*this));                  \
+  return count;
+
+#define NS_IMPL_CC_NATIVE_RELEASE_BODY(_class)                                \
+  MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                            \
+  NS_ASSERT_OWNINGTHREAD(_class);                                             \
+  nsrefcnt count =                                                            \
+      mRefCnt.decr(static_cast<void*>(this),                                  \
+                   _class::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant()); \
+  NS_LOG_RELEASE(this, count, #_class);                                       \
+  return count;
+
+#define NS_IMPL_CC_MAIN_THREAD_ONLY_NATIVE_RELEASE_BODY(_class)        \
+  MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                     \
+  NS_ASSERT_OWNINGTHREAD(_class);                                      \
+  nsrefcnt count = mRefCnt.decr<NS_CycleCollectorSuspectUsingNursery>( \
+      static_cast<void*>(this),                                        \
+      _class::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant());       \
+  NS_LOG_RELEASE(this, count, #_class);                                \
+  return count;
+
+#define NS_IMPL_CYCLE_COLLECTING_NATIVE_ADDREF(_class)       \
+  NS_METHOD_(MozExternalRefCountType) _class::AddRef(void) { \
+    NS_IMPL_CC_NATIVE_ADDREF_BODY(_class)                    \
+  }
+
+#define NS_IMPL_CYCLE_COLLECTING_NATIVE_RELEASE_WITH_LAST_RELEASE(_class,      \
+                                                                  _last)       \
+  NS_METHOD_(MozExternalRefCountType) _class::Release(void) {                  \
+    MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                           \
+    NS_ASSERT_OWNINGTHREAD(_class);                                            \
+    bool shouldDelete = false;                                                 \
+    nsrefcnt count =                                                           \
+        mRefCnt.decr(static_cast<void*>(this),                                 \
+                     _class::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant(), \
+                     &shouldDelete);                                           \
+    NS_LOG_RELEASE(this, count, #_class);                                      \
+    if (count == 0) {                                                          \
+      mRefCnt.incr(static_cast<void*>(this),                                   \
+                   _class::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant());  \
+      _last;                                                                   \
+      mRefCnt.decr(static_cast<void*>(this),                                   \
+                   _class::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant());  \
+      if (shouldDelete) {                                                      \
+        mRefCnt.stabilizeForDeletion();                                        \
+        DeleteCycleCollectable();                                              \
+      }                                                                        \
+    }                                                                          \
+    return count;                                                              \
+  }
+
+#define NS_IMPL_CYCLE_COLLECTING_NATIVE_RELEASE(_class)       \
+  NS_METHOD_(MozExternalRefCountType) _class::Release(void) { \
+    NS_IMPL_CC_NATIVE_RELEASE_BODY(_class)                    \
+  }
+
+#define NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(_class) \
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING_META(_class, NS_METHOD_)
+
+#define NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING_VIRTUAL(_class) \
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING_META(_class, NS_IMETHOD_)
+
+#define NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING_INHERITED(_class)  \
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING_META(_class, NS_METHOD_, \
+                                                          override)
+
+#define NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING_META(_class, _decl, \
+                                                                ...)           \
+ public:                                                                       \
+  _decl(MozExternalRefCountType) AddRef(void) __VA_ARGS__{                     \
+      NS_IMPL_CC_NATIVE_ADDREF_BODY(_class)} _decl(MozExternalRefCountType)    \
+      Release(void) __VA_ARGS__ {                                              \
+    NS_IMPL_CC_NATIVE_RELEASE_BODY(_class)                                     \
+  }                                                                            \
+  using HasThreadSafeRefCnt = std::false_type;                                 \
+                                                                               \
+ protected:                                                                    \
+  nsCycleCollectingAutoRefCnt mRefCnt;                                         \
+  NS_DECL_OWNINGTHREAD                                                         \
+ public:
+
+#define NS_INLINE_DECL_MAIN_THREAD_ONLY_CYCLE_COLLECTING_NATIVE_REFCOUNTING( \
+    _class)                                                                  \
+ public:                                                                     \
+  NS_METHOD_(MozExternalRefCountType)                                        \
+  AddRef(void){NS_IMPL_CC_MAIN_THREAD_ONLY_NATIVE_ADDREF_BODY(               \
+      _class)} NS_METHOD_(MozExternalRefCountType) Release(void) {           \
+    NS_IMPL_CC_MAIN_THREAD_ONLY_NATIVE_RELEASE_BODY(_class)                  \
+  }                                                                          \
+  using HasThreadSafeRefCnt = std::false_type;                               \
+                                                                             \
+ protected:                                                                  \
+  nsCycleCollectingAutoRefCnt mRefCnt;                                       \
+  NS_DECL_OWNINGTHREAD                                                       \
+ public:
+
+///////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Use this macro to declare and implement the AddRef & Release methods for a
+ * given non-XPCOM <i>_class</i>.
+ *
+ * @param _class The name of the class implementing the method
+ * @param _destroy A statement that is executed when the object's
+ *   refcount drops to zero.
+ * @param _decl Name of the macro to be used for the return type of the
+ *   AddRef & Release methods (typically NS_IMETHOD_ or NS_METHOD_).
+ * @param optional override Mark the AddRef & Release methods as overrides.
+ */
+#define NS_INLINE_DECL_REFCOUNTING_META(_class, _decl, _destroy, _owning, ...) \
+ public:                                                                       \
+  _decl(MozExternalRefCountType) AddRef(void) __VA_ARGS__ {                    \
+    MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(_class)                                 \
+    MOZ_ASSERT(int32_t(mRefCnt) >= 0, "illegal refcnt");                       \
+    NS_ASSERT_OWNINGTHREAD(_class);                                            \
+    ++mRefCnt;                                                                 \
+    NS_LOG_ADDREF(this, mRefCnt, #_class, sizeof(*this));                      \
+    return mRefCnt;                                                            \
+  }                                                                            \
+  _decl(MozExternalRefCountType) Release(void) __VA_ARGS__ {                   \
+    MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                           \
+    NS_ASSERT_OWNINGTHREAD(_class);                                            \
+    --mRefCnt;                                                                 \
+    NS_LOG_RELEASE(this, mRefCnt, #_class);                                    \
+    if (mRefCnt == 0) {                                                        \
+      mRefCnt = 1; /* stabilize */                                             \
+      _destroy;                                                                \
+      return 0;                                                                \
+    }                                                                          \
+    return mRefCnt;                                                            \
+  }                                                                            \
+  using HasThreadSafeRefCnt = std::false_type;                                 \
+                                                                               \
+ protected:                                                                    \
+  nsAutoRefCnt mRefCnt;                                                        \
+  _owning public:
+
+/**
+ * Use this macro to declare and implement the AddRef & Release methods for a
+ * given non-XPCOM <i>_class</i>.
+ *
+ * @param _class The name of the class implementing the method
+ * @param _destroy A statement that is executed when the object's
+ *   refcount drops to zero.
+ * @param optional override Mark the AddRef & Release methods as overrides.
+ */
+#define NS_INLINE_DECL_REFCOUNTING_WITH_DESTROY(_class, _destroy, ...) \
+  NS_INLINE_DECL_REFCOUNTING_META(_class, NS_METHOD_, _destroy,        \
+                                  NS_DECL_OWNINGTHREAD, __VA_ARGS__)
+
+/**
+ * Like NS_INLINE_DECL_REFCOUNTING_WITH_DESTROY with AddRef & Release declared
+ * virtual.
+ */
+#define NS_INLINE_DECL_VIRTUAL_REFCOUNTING_WITH_DESTROY(_class, _destroy, ...) \
+  NS_INLINE_DECL_REFCOUNTING_META(_class, NS_IMETHOD_, _destroy,               \
+                                  NS_DECL_OWNINGTHREAD, __VA_ARGS__)
+
+/**
+ * Use this macro to declare and implement the AddRef & Release methods for a
+ * given non-XPCOM <i>_class</i>.
+ *
+ * @param _class The name of the class implementing the method
+ * @param optional override Mark the AddRef & Release methods as overrides.
+ */
+#define NS_INLINE_DECL_REFCOUNTING(_class, ...) \
+  NS_INLINE_DECL_REFCOUNTING_WITH_DESTROY(_class, delete (this), __VA_ARGS__)
+
+/**
+ * Like NS_INLINE_DECL_REFCOUNTING, however the thread safety check will work
+ * with any nsISerialEventTarget. This is a workaround until bug 1648031 is
+ * properly resolved. Once this is done, it will be possible to use
+ * NS_INLINE_DECL_REFCOUNTING under all circumstances.
+ */
+#define NS_INLINE_DECL_REFCOUNTING_ONEVENTTARGET(_class, ...)        \
+  NS_INLINE_DECL_REFCOUNTING_META(_class, NS_METHOD_, delete (this), \
+                                  NS_DECL_OWNINGEVENTTARGET, __VA_ARGS__)
+
+#define NS_INLINE_DECL_THREADSAFE_REFCOUNTING_META(_class, _decl, _destroy, \
+                                                   ...)                     \
+ public:                                                                    \
+  _decl(MozExternalRefCountType) AddRef(void) __VA_ARGS__ {                 \
+    MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(_class)                              \
+    MOZ_ASSERT(int32_t(mRefCnt) >= 0, "illegal refcnt");                    \
+    nsrefcnt count = ++mRefCnt;                                             \
+    NS_LOG_ADDREF(this, count, #_class, sizeof(*this));                     \
+    return (nsrefcnt)count;                                                 \
+  }                                                                         \
+  _decl(MozExternalRefCountType) Release(void) __VA_ARGS__ {                \
+    MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                        \
+    nsrefcnt count = --mRefCnt;                                             \
+    NS_LOG_RELEASE(this, count, #_class);                                   \
+    if (count == 0) {                                                       \
+      _destroy;                                                             \
+      return 0;                                                             \
+    }                                                                       \
+    return count;                                                           \
+  }                                                                         \
+  using HasThreadSafeRefCnt = std::true_type;                               \
+                                                                            \
+ protected:                                                                 \
+  ::mozilla::ThreadSafeAutoRefCnt mRefCnt;                                  \
+                                                                            \
+ public:
+
+/**
+ * Use this macro to declare and implement the AddRef & Release methods for a
+ * given non-XPCOM <i>_class</i> in a threadsafe manner.
+ *
+ * DOES NOT DO REFCOUNT STABILIZATION!
+ *
+ * @param _class The name of the class implementing the method
+ * @param _destroy A statement that is executed when the object's
+ *   refcount drops to zero.
+ * @param optional override Mark the AddRef & Release methods as overrides.
+ */
+#define NS_INLINE_DECL_THREADSAFE_REFCOUNTING_WITH_DESTROY(_class, _destroy, \
+                                                           ...)              \
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING_META(_class, NS_METHOD_, _destroy,   \
+                                             __VA_ARGS__)
+
+/**
+ * Like NS_INLINE_DECL_THREADSAFE_REFCOUNTING_WITH_DESTROY with AddRef & Release
+ * declared virtual.
+ */
+#define NS_INLINE_DECL_THREADSAFE_VIRTUAL_REFCOUNTING_WITH_DESTROY(         \
+    _class, _destroy, ...)                                                  \
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING_META(_class, NS_IMETHOD_, _destroy, \
+                                             __VA_ARGS__)
+
+/**
+ * Use this macro to declare and implement the AddRef & Release methods for a
+ * given non-XPCOM <i>_class</i> in a threadsafe manner.
+ *
+ * DOES NOT DO REFCOUNT STABILIZATION!
+ *
+ * @param _class The name of the class implementing the method
+ * @param optional override Mark the AddRef & Release methods as overrides.
+ */
+#define NS_INLINE_DECL_THREADSAFE_REFCOUNTING(_class, ...)                  \
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING_WITH_DESTROY(_class, delete (this), \
+                                                     __VA_ARGS__)
+
+/**
+ * Like NS_INLINE_DECL_THREADSAFE_REFCOUNTING with AddRef & Release declared
+ * virtual.
+ */
+#define NS_INLINE_DECL_THREADSAFE_VIRTUAL_REFCOUNTING(_class, ...) \
+  NS_INLINE_DECL_THREADSAFE_VIRTUAL_REFCOUNTING_WITH_DESTROY(      \
+      _class, delete (this), __VA_ARGS__)
+
+#if !defined(XPCOM_GLUE_AVOID_NSPR)
+class nsISerialEventTarget;
+namespace mozilla {
+// Forward-declare `GetMainThreadSerialEventTarget`, as `nsISupportsImpl.h`
+// cannot include `nsThreadUtils.h`.
+nsISerialEventTarget* GetMainThreadSerialEventTarget();
+
+namespace detail {
+using DeleteVoidFunction = void(void*);
+void ProxyDeleteVoid(const char* aRunnableName,
+                     nsISerialEventTarget* aEventTarget, void* aSelf,
+                     DeleteVoidFunction* aDeleteFunc);
+}  // namespace detail
+}  // namespace mozilla
+
+/**
+ * Helper for _WITH_DELETE_ON_EVENT_TARGET threadsafe refcounting macros which
+ * provides an implementation of `_destroy`
+ */
+#  define NS_PROXY_DELETE_TO_EVENT_TARGET(_class, _target) \
+    ::mozilla::detail::ProxyDeleteVoid(                    \
+        "ProxyDelete " #_class, _target, this,             \
+        [](void* self) { delete static_cast<_class*>(self); })
+
+/**
+ * Use this macro to declare and implement the AddRef & Release methods for a
+ * given non-XPCOM <i>_class</i> in a threadsafe manner, ensuring the
+ * destructor runs on a specific nsISerialEventTarget.
+ *
+ * DOES NOT DO REFCOUNT STABILIZATION!
+ *
+ * @param _class The name of the class implementing the method
+ * @param _target nsISerialEventTarget to run the class's destructor on
+ * @param optional override Mark the AddRef & Release methods as overrides
+ */
+#  define NS_INLINE_DECL_THREADSAFE_REFCOUNTING_WITH_DELETE_ON_EVENT_TARGET( \
+      _class, _target, ...)                                                  \
+    NS_INLINE_DECL_THREADSAFE_REFCOUNTING_WITH_DESTROY(                      \
+        _class, NS_PROXY_DELETE_TO_EVENT_TARGET(_class, _target), __VA_ARGS__)
+
+/**
+ * Use this macro to declare and implement the AddRef & Release methods for a
+ * given non-XPCOM <i>_class</i> in a threadsafe manner, ensuring the
+ * destructor runs on the main thread.
+ *
+ * DOES NOT DO REFCOUNT STABILIZATION!
+ *
+ * @param _class The name of the class implementing the method
+ * @param optional override Mark the AddRef & Release methods as overrides
+ */
+#  define NS_INLINE_DECL_THREADSAFE_REFCOUNTING_WITH_DELETE_ON_MAIN_THREAD( \
+      _class, ...)                                                          \
+    NS_INLINE_DECL_THREADSAFE_REFCOUNTING_WITH_DELETE_ON_EVENT_TARGET(      \
+        _class, ::mozilla::GetMainThreadSerialEventTarget(), __VA_ARGS__)
+#endif
+
+/**
+ * Use this macro in interface classes that you want to be able to reference
+ * using RefPtr, but don't want to provide a refcounting implemenation. The
+ * refcounting implementation can be provided by concrete subclasses that
+ * implement the interface.
+ */
+#define NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING           \
+ public:                                                  \
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void) = 0;  \
+  NS_IMETHOD_(MozExternalRefCountType) Release(void) = 0; \
+                                                          \
+ public:
+
+/**
+ * Use this macro to implement the AddRef method for a given <i>_class</i>
+ * @param _class The name of the class implementing the method
+ * @param _name The class name to be passed to XPCOM leak checking
+ */
+#define NS_IMPL_NAMED_ADDREF(_class, _name)                      \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::AddRef(void) { \
+    MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(_class)                   \
+    MOZ_ASSERT(int32_t(mRefCnt) >= 0, "illegal refcnt");         \
+    MOZ_ASSERT(_name != nullptr, "Must specify a name");         \
+    if (!mRefCnt.isThreadSafe) NS_ASSERT_OWNINGTHREAD(_class);   \
+    nsrefcnt count = ++mRefCnt;                                  \
+    NS_LOG_ADDREF(this, count, _name, sizeof(*this));            \
+    return count;                                                \
+  }
+
+/**
+ * Use this macro to implement the AddRef method for a given <i>_class</i>
+ * @param _class The name of the class implementing the method
+ */
+#define NS_IMPL_ADDREF(_class) NS_IMPL_NAMED_ADDREF(_class, #_class)
+
+/**
+ * Use this macro to implement the AddRef method for a given <i>_class</i>
+ * implemented as a wholly owned aggregated object intended to implement
+ * interface(s) for its owner
+ * @param _class The name of the class implementing the method
+ * @param _aggregator the owning/containing object
+ */
+#define NS_IMPL_ADDREF_USING_AGGREGATOR(_class, _aggregator)     \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::AddRef(void) { \
+    MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(_class)                   \
+    MOZ_ASSERT(_aggregator, "null aggregator");                  \
+    return (_aggregator)->AddRef();                              \
+  }
+
+// We decrement the refcnt before logging the actual release, but when logging
+// named things, accessing the name may not be valid after the refcnt
+// decrement, because the object may have been destroyed on a different thread.
+// Use this macro to ensure that we have a local copy of the name prior to
+// the refcnt decrement.  (We use a macro to make absolutely sure the name
+// isn't loaded in builds where it wouldn't be used.)
+#ifdef NS_BUILD_REFCNT_LOGGING
+#  define NS_LOAD_NAME_BEFORE_RELEASE(localname, _name) \
+    const char* const localname = _name
+#else
+#  define NS_LOAD_NAME_BEFORE_RELEASE(localname, _name)
+#endif
+
+/**
+ * Use this macro to implement the Release method for a given
+ * <i>_class</i>.
+ * @param _class The name of the class implementing the method
+ * @param _name The class name to be passed to XPCOM leak checking
+ * @param _destroy A statement that is executed when the object's
+ *   refcount drops to zero.
+ *
+ * For example,
+ *
+ *   NS_IMPL_RELEASE_WITH_DESTROY(Foo, "Foo", Destroy(this))
+ *
+ * will cause
+ *
+ *   Destroy(this);
+ *
+ * to be invoked when the object's refcount drops to zero. This
+ * allows for arbitrary teardown activity to occur (e.g., deallocation
+ * of object allocated with placement new).
+ */
+#define NS_IMPL_NAMED_RELEASE_WITH_DESTROY(_class, _name, _destroy) \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::Release(void) {   \
+    MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                \
+    MOZ_ASSERT(_name != nullptr, "Must specify a name");            \
+    if (!mRefCnt.isThreadSafe) NS_ASSERT_OWNINGTHREAD(_class);      \
+    NS_LOAD_NAME_BEFORE_RELEASE(nametmp, _name);                    \
+    nsrefcnt count = --mRefCnt;                                     \
+    NS_LOG_RELEASE(this, count, nametmp);                           \
+    if (count == 0) {                                               \
+      mRefCnt = 1; /* stabilize */                                  \
+      _destroy;                                                     \
+      return 0;                                                     \
+    }                                                               \
+    return count;                                                   \
+  }
+
+#define NS_IMPL_RELEASE_WITH_DESTROY(_class, _destroy) \
+  NS_IMPL_NAMED_RELEASE_WITH_DESTROY(_class, #_class, _destroy)
+
+/**
+ * Use this macro to implement the Release method for a given <i>_class</i>
+ * @param _class The name of the class implementing the method
+ *
+ * A note on the 'stabilization' of the refcnt to one. At that point,
+ * the object's refcount will have gone to zero. The object's
+ * destructor may trigger code that attempts to QueryInterface() and
+ * Release() 'this' again. Doing so will temporarily increment and
+ * decrement the refcount. (Only a logic error would make one try to
+ * keep a permanent hold on 'this'.)  To prevent re-entering the
+ * destructor, we make sure that no balanced refcounting can return
+ * the refcount to |0|.
+ */
+#define NS_IMPL_RELEASE(_class) \
+  NS_IMPL_RELEASE_WITH_DESTROY(_class, delete (this))
+
+#define NS_IMPL_NAMED_RELEASE(_class, _name) \
+  NS_IMPL_NAMED_RELEASE_WITH_DESTROY(_class, _name, delete (this))
+
+/**
+ * Use this macro to implement the Release method for a given <i>_class</i>
+ * implemented as a wholly owned aggregated object intended to implement
+ * interface(s) for its owner
+ * @param _class The name of the class implementing the method
+ * @param _aggregator the owning/containing object
+ */
+#define NS_IMPL_RELEASE_USING_AGGREGATOR(_class, _aggregator)     \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::Release(void) { \
+    MOZ_ASSERT(_aggregator, "null aggregator");                   \
+    return (_aggregator)->Release();                              \
+  }
+
+#define NS_IMPL_CYCLE_COLLECTING_ADDREF(_class)                              \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::AddRef(void) {             \
+    MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(_class)                               \
+    MOZ_ASSERT(int32_t(mRefCnt) >= 0, "illegal refcnt");                     \
+    NS_ASSERT_OWNINGTHREAD(_class);                                          \
+    nsISupports* base = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this); \
+    nsrefcnt count = mRefCnt.incr(base);                                     \
+    NS_LOG_ADDREF(this, count, #_class, sizeof(*this));                      \
+    return count;                                                            \
+  }
+
+#define NS_IMPL_MAIN_THREAD_ONLY_CYCLE_COLLECTING_ADDREF(_class)               \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::AddRef(void) {               \
+    MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(_class)                                 \
+    MOZ_ASSERT(int32_t(mRefCnt) >= 0, "illegal refcnt");                       \
+    NS_ASSERT_OWNINGTHREAD(_class);                                            \
+    nsISupports* base = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this);   \
+    nsrefcnt count = mRefCnt.incr<NS_CycleCollectorSuspectUsingNursery>(base); \
+    NS_LOG_ADDREF(this, count, #_class, sizeof(*this));                        \
+    return count;                                                              \
+  }
+
+#define NS_IMPL_CYCLE_COLLECTING_RELEASE_WITH_DESTROY(_class, _destroy)      \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::Release(void) {            \
+    MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                         \
+    NS_ASSERT_OWNINGTHREAD(_class);                                          \
+    nsISupports* base = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this); \
+    nsrefcnt count = mRefCnt.decr(base);                                     \
+    NS_LOG_RELEASE(this, count, #_class);                                    \
+    return count;                                                            \
+  }                                                                          \
+  NS_IMETHODIMP_(void) _class::DeleteCycleCollectable(void) { _destroy; }
+
+#define NS_IMPL_CYCLE_COLLECTING_RELEASE(_class) \
+  NS_IMPL_CYCLE_COLLECTING_RELEASE_WITH_DESTROY(_class, delete (this))
+
+// _LAST_RELEASE can be useful when certain resources should be released
+// as soon as we know the object will be deleted.
+#define NS_IMPL_CYCLE_COLLECTING_RELEASE_WITH_LAST_RELEASE(_class, _last)    \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::Release(void) {            \
+    MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                         \
+    NS_ASSERT_OWNINGTHREAD(_class);                                          \
+    bool shouldDelete = false;                                               \
+    nsISupports* base = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this); \
+    nsrefcnt count = mRefCnt.decr(base, &shouldDelete);                      \
+    NS_LOG_RELEASE(this, count, #_class);                                    \
+    if (count == 0) {                                                        \
+      mRefCnt.incr(base);                                                    \
+      _last;                                                                 \
+      mRefCnt.decr(base);                                                    \
+      if (shouldDelete) {                                                    \
+        mRefCnt.stabilizeForDeletion();                                      \
+        DeleteCycleCollectable();                                            \
+      }                                                                      \
+    }                                                                        \
+    return count;                                                            \
+  }                                                                          \
+  NS_IMETHODIMP_(void) _class::DeleteCycleCollectable(void) { delete this; }
+
+// This macro is same as NS_IMPL_CYCLE_COLLECTING_RELEASE_WITH_LAST_RELEASE
+// except it doesn't have DeleteCycleCollectable.
+#define NS_IMPL_CYCLE_COLLECTING_RELEASE_WITH_LAST_RELEASE_AND_DESTROY(      \
+    _class, _last, _destroy)                                                 \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::Release(void) {            \
+    MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                         \
+    NS_ASSERT_OWNINGTHREAD(_class);                                          \
+    bool shouldDelete = false;                                               \
+    nsISupports* base = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this); \
+    nsrefcnt count = mRefCnt.decr(base, &shouldDelete);                      \
+    NS_LOG_RELEASE(this, count, #_class);                                    \
+    if (count == 0) {                                                        \
+      mRefCnt.incr(base);                                                    \
+      _last;                                                                 \
+      mRefCnt.decr(base);                                                    \
+      if (shouldDelete) {                                                    \
+        mRefCnt.stabilizeForDeletion();                                      \
+        DeleteCycleCollectable();                                            \
+      }                                                                      \
+    }                                                                        \
+    return count;                                                            \
+  }                                                                          \
+  NS_IMETHODIMP_(void) _class::DeleteCycleCollectable(void) { _destroy; }
+
+#define NS_IMPL_MAIN_THREAD_ONLY_CYCLE_COLLECTING_RELEASE(_class)              \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::Release(void) {              \
+    MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                           \
+    NS_ASSERT_OWNINGTHREAD(_class);                                            \
+    nsISupports* base = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this);   \
+    nsrefcnt count = mRefCnt.decr<NS_CycleCollectorSuspectUsingNursery>(base); \
+    NS_LOG_RELEASE(this, count, #_class);                                      \
+    return count;                                                              \
+  }                                                                            \
+  NS_IMETHODIMP_(void) _class::DeleteCycleCollectable(void) { delete this; }
+
+// _LAST_RELEASE can be useful when certain resources should be released
+// as soon as we know the object will be deleted.
+#define NS_IMPL_MAIN_THREAD_ONLY_CYCLE_COLLECTING_RELEASE_WITH_LAST_RELEASE( \
+    _class, _last)                                                           \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::Release(void) {            \
+    MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                         \
+    NS_ASSERT_OWNINGTHREAD(_class);                                          \
+    bool shouldDelete = false;                                               \
+    nsISupports* base = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this); \
+    nsrefcnt count = mRefCnt.decr<NS_CycleCollectorSuspectUsingNursery>(     \
+        base, &shouldDelete);                                                \
+    NS_LOG_RELEASE(this, count, #_class);                                    \
+    if (count == 0) {                                                        \
+      mRefCnt.incr<NS_CycleCollectorSuspectUsingNursery>(base);              \
+      _last;                                                                 \
+      mRefCnt.decr<NS_CycleCollectorSuspectUsingNursery>(base);              \
+      if (shouldDelete) {                                                    \
+        mRefCnt.stabilizeForDeletion();                                      \
+        DeleteCycleCollectable();                                            \
+      }                                                                      \
+    }                                                                        \
+    return count;                                                            \
+  }                                                                          \
+  NS_IMETHODIMP_(void) _class::DeleteCycleCollectable(void) { delete this; }
+
+// _WITH_INTERRUPTABLE_LAST_RELEASE can be useful when certain resources
+// should be released as soon as we know the object will be deleted and the
+// instance may be cached for reuse.
+// _last is performed for cleaning up its resources.  Then, _maybeInterrupt is
+// tested and when it returns true, this stops deleting the instance.
+// (Note that it's not allowed to grab the instance with nsCOMPtr or RefPtr
+// during _last is performed.)
+// Therefore, when _maybeInterrupt returns true, the instance has to be grabbed
+// by nsCOMPtr or RefPtr.
+#define NS_IMPL_MAIN_THREAD_ONLY_CYCLE_COLLECTING_RELEASE_WITH_INTERRUPTABLE_LAST_RELEASE( \
+    _class, _last, _maybeInterrupt)                                                        \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::Release(void) {                          \
+    MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                                       \
+    NS_ASSERT_OWNINGTHREAD(_class);                                                        \
+    bool shouldDelete = false;                                                             \
+    nsISupports* base = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this);               \
+    nsrefcnt count = mRefCnt.decr<NS_CycleCollectorSuspectUsingNursery>(                   \
+        base, &shouldDelete);                                                              \
+    NS_LOG_RELEASE(this, count, #_class);                                                  \
+    if (count == 0) {                                                                      \
+      mRefCnt.incr<NS_CycleCollectorSuspectUsingNursery>(base);                            \
+      _last;                                                                               \
+      mRefCnt.decr<NS_CycleCollectorSuspectUsingNursery>(base);                            \
+      if (_maybeInterrupt) {                                                               \
+        MOZ_ASSERT(mRefCnt.get() > 0);                                                     \
+        return mRefCnt.get();                                                              \
+      }                                                                                    \
+      if (shouldDelete) {                                                                  \
+        mRefCnt.stabilizeForDeletion();                                                    \
+        DeleteCycleCollectable();                                                          \
+      }                                                                                    \
+    }                                                                                      \
+    return count;                                                                          \
+  }                                                                                        \
+  NS_IMETHODIMP_(void) _class::DeleteCycleCollectable(void) { delete this; }
+
+// _LAST_RELEASE can be useful when certain resources should be released
+// as soon as we know the object will be deleted.
+#define NS_IMPL_MAIN_THREAD_ONLY_CYCLE_COLLECTING_RELEASE_WITH_LAST_RELEASE_AND_DESTROY( \
+    _class, _last, _destroy)                                                             \
+  NS_IMETHODIMP_(MozExternalRefCountType) _class::Release(void) {                        \
+    MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");                                     \
+    NS_ASSERT_OWNINGTHREAD(_class);                                                      \
+    bool shouldDelete = false;                                                           \
+    nsISupports* base = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this);             \
+    nsrefcnt count = mRefCnt.decr<NS_CycleCollectorSuspectUsingNursery>(                 \
+        base, &shouldDelete);                                                            \
+    NS_LOG_RELEASE(this, count, #_class);                                                \
+    if (count == 0) {                                                                    \
+      mRefCnt.incr<NS_CycleCollectorSuspectUsingNursery>(base);                          \
+      _last;                                                                             \
+      mRefCnt.decr<NS_CycleCollectorSuspectUsingNursery>(base);                          \
+      if (shouldDelete) {                                                                \
+        mRefCnt.stabilizeForDeletion();                                                  \
+        DeleteCycleCollectable();                                                        \
+      }                                                                                  \
+    }                                                                                    \
+    return count;                                                                        \
+  }                                                                                      \
+  NS_IMETHODIMP_(void) _class::DeleteCycleCollectable(void) { _destroy; }
+
+///////////////////////////////////////////////////////////////////////////////
+
+/**
+ * There are two ways of implementing QueryInterface, and we use both:
+ *
+ * Table-driven QueryInterface uses a static table of IID->offset mappings
+ * and a shared helper function. Using it tends to reduce codesize and improve
+ * runtime performance (due to processor cache hits).
+ *
+ * Macro-driven QueryInterface generates a QueryInterface function directly
+ * using common macros. This is necessary if special QueryInterface features
+ * are being used (such as tearoffs and conditional interfaces).
+ *
+ * These methods can be combined into a table-driven function call followed
+ * by custom code for tearoffs and conditionals.
+ */
+
+struct QITableEntry {
+  const nsIID* iid;  // null indicates end of the QITableEntry array
+  int32_t offset;
+};
+
+nsresult NS_FASTCALL NS_TableDrivenQI(void* aThis, REFNSIID aIID,
+                                      void** aInstancePtr,
+                                      const QITableEntry* aEntries);
+
+/**
+ * Implement table-driven queryinterface
+ */
+
+#define NS_INTERFACE_TABLE_HEAD(_class)                                      \
+  NS_IMETHODIMP _class::QueryInterface(REFNSIID aIID, void** aInstancePtr) { \
+    NS_ASSERTION(aInstancePtr,                                               \
+                 "QueryInterface requires a non-NULL destination!");         \
+    nsresult rv = NS_ERROR_FAILURE;
+
+#define NS_INTERFACE_TABLE_BEGIN static const QITableEntry table[] = {
+#define NS_INTERFACE_TABLE_ENTRY(_class, _interface)                        \
+  {&NS_GET_IID(_interface),                                                 \
+   int32_t(                                                                 \
+       reinterpret_cast<char*>(static_cast<_interface*>((_class*)0x1000)) - \
+       reinterpret_cast<char*>((_class*)0x1000))},
+
+#define NS_INTERFACE_TABLE_ENTRY_AMBIGUOUS(_class, _interface, _implClass) \
+  {&NS_GET_IID(_interface),                                                \
+   int32_t(reinterpret_cast<char*>(static_cast<_interface*>(               \
+               static_cast<_implClass*>((_class*)0x1000))) -               \
+           reinterpret_cast<char*>((_class*)0x1000))},
+
+/*
+ * XXX: we want to use mozilla::ArrayLength (or equivalent,
+ * MOZ_ARRAY_LENGTH) in this condition, but some versions of GCC don't
+ * see that the static_assert condition is actually constant in those
+ * cases, even with constexpr support (?).
+ */
+#define NS_INTERFACE_TABLE_END_WITH_PTR(_ptr)           \
+  { nullptr, 0 }                                        \
+  }                                                     \
+  ;                                                     \
+  static_assert((sizeof(table) / sizeof(table[0])) > 1, \
+                "need at least 1 interface");           \
+  rv = NS_TableDrivenQI(static_cast<void*>(_ptr), aIID, aInstancePtr, table);
+
+#define NS_INTERFACE_TABLE_END    \
+  NS_INTERFACE_TABLE_END_WITH_PTR \
+  (this)
+
+#define NS_INTERFACE_TABLE_TAIL \
+  return rv;                    \
+  }
+
+#define NS_INTERFACE_TABLE_TAIL_INHERITING(_baseclass)   \
+  if (NS_SUCCEEDED(rv)) return rv;                       \
+  return _baseclass::QueryInterface(aIID, aInstancePtr); \
+  }
+
+#define NS_INTERFACE_TABLE_TAIL_USING_AGGREGATOR(_aggregator) \
+  if (NS_SUCCEEDED(rv)) return rv;                            \
+  NS_ASSERTION(_aggregator, "null aggregator");               \
+  return _aggregator->QueryInterface(aIID, aInstancePtr)      \
+  }
+
+/**
+ * This implements query interface with two assumptions: First, the
+ * class in question implements nsISupports and its own interface and
+ * nothing else. Second, the implementation of the class's primary
+ * inheritance chain leads to its own interface.
+ *
+ * @param _class The name of the class implementing the method
+ * @param _classiiddef The name of the #define symbol that defines the IID
+ * for the class (e.g. NS_ISUPPORTS_IID)
+ */
+
+#define NS_IMPL_QUERY_HEAD(_class)                                           \
+  NS_IMETHODIMP _class::QueryInterface(REFNSIID aIID, void** aInstancePtr) { \
+    NS_ASSERTION(aInstancePtr,                                               \
+                 "QueryInterface requires a non-NULL destination!");         \
+    nsISupports* foundInterface;
+
+#define NS_IMPL_QUERY_BODY(_interface)               \
+  if (aIID.Equals(NS_GET_IID(_interface)))           \
+    foundInterface = static_cast<_interface*>(this); \
+  else
+
+#define NS_IMPL_QUERY_BODY_CONDITIONAL(_interface, condition) \
+  if ((condition) && aIID.Equals(NS_GET_IID(_interface)))     \
+    foundInterface = static_cast<_interface*>(this);          \
+  else
+
+#define NS_IMPL_QUERY_BODY_AMBIGUOUS(_interface, _implClass)                   \
+  if (aIID.Equals(NS_GET_IID(_interface)))                                     \
+    foundInterface = static_cast<_interface*>(static_cast<_implClass*>(this)); \
+  else
+
+// Use this for querying to concrete class types which cannot be unambiguously
+// cast to nsISupports. See also nsQueryObject.h.
+#define NS_IMPL_QUERY_BODY_CONCRETE(_class)                       \
+  if (aIID.Equals(NS_GET_IID(_class))) {                          \
+    *aInstancePtr = do_AddRef(static_cast<_class*>(this)).take(); \
+    return NS_OK;                                                 \
+  } else
+
+#define NS_IMPL_QUERY_BODY_AGGREGATED(_interface, _aggregate) \
+  if (aIID.Equals(NS_GET_IID(_interface)))                    \
+    foundInterface = static_cast<_interface*>(_aggregate);    \
+  else
+
+#define NS_IMPL_QUERY_TAIL_GUTS                                      \
+  foundInterface = 0;                                                \
+  nsresult status;                                                   \
+  if (!foundInterface) {                                             \
+    /* nsISupports should be handled by this point. If not, fail. */ \
+    MOZ_ASSERT(!aIID.Equals(NS_GET_IID(nsISupports)));               \
+    status = NS_NOINTERFACE;                                         \
+  } else {                                                           \
+    NS_ADDREF(foundInterface);                                       \
+    status = NS_OK;                                                  \
+  }                                                                  \
+  *aInstancePtr = foundInterface;                                    \
+  return status;                                                     \
+  }
+
+#define NS_IMPL_QUERY_TAIL_INHERITING(_baseclass)                       \
+  foundInterface = 0;                                                   \
+  nsresult status;                                                      \
+  if (!foundInterface)                                                  \
+    status = _baseclass::QueryInterface(aIID, (void**)&foundInterface); \
+  else {                                                                \
+    NS_ADDREF(foundInterface);                                          \
+    status = NS_OK;                                                     \
+  }                                                                     \
+  *aInstancePtr = foundInterface;                                       \
+  return status;                                                        \
+  }
+
+#define NS_IMPL_QUERY_TAIL_USING_AGGREGATOR(_aggregator)                 \
+  foundInterface = 0;                                                    \
+  nsresult status;                                                       \
+  if (!foundInterface) {                                                 \
+    NS_ASSERTION(_aggregator, "null aggregator");                        \
+    status = _aggregator->QueryInterface(aIID, (void**)&foundInterface); \
+  } else {                                                               \
+    NS_ADDREF(foundInterface);                                           \
+    status = NS_OK;                                                      \
+  }                                                                      \
+  *aInstancePtr = foundInterface;                                        \
+  return status;                                                         \
+  }
+
+#define NS_IMPL_QUERY_TAIL(_supports_interface)                  \
+  NS_IMPL_QUERY_BODY_AMBIGUOUS(nsISupports, _supports_interface) \
+  NS_IMPL_QUERY_TAIL_GUTS
+
+/*
+  This is the new scheme.  Using this notation now will allow us to switch to
+  a table driven mechanism when it's ready.  Note the difference between this
+  and the (currently) underlying NS_IMPL_QUERY_INTERFACE mechanism.  You must
+  explicitly mention |nsISupports| when using the interface maps.
+*/
+#define NS_INTERFACE_MAP_BEGIN(_implClass) NS_IMPL_QUERY_HEAD(_implClass)
+#define NS_INTERFACE_MAP_ENTRY(_interface) NS_IMPL_QUERY_BODY(_interface)
+#define NS_INTERFACE_MAP_ENTRY_CONDITIONAL(_interface, condition) \
+  NS_IMPL_QUERY_BODY_CONDITIONAL(_interface, condition)
+#define NS_INTERFACE_MAP_ENTRY_AGGREGATED(_interface, _aggregate) \
+  NS_IMPL_QUERY_BODY_AGGREGATED(_interface, _aggregate)
+
+#define NS_INTERFACE_MAP_END NS_IMPL_QUERY_TAIL_GUTS
+#define NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(_interface, _implClass) \
+  NS_IMPL_QUERY_BODY_AMBIGUOUS(_interface, _implClass)
+#define NS_INTERFACE_MAP_ENTRY_CONCRETE(_class) \
+  NS_IMPL_QUERY_BODY_CONCRETE(_class)
+#define NS_INTERFACE_MAP_END_INHERITING(_baseClass) \
+  NS_IMPL_QUERY_TAIL_INHERITING(_baseClass)
+#define NS_INTERFACE_MAP_END_AGGREGATED(_aggregator) \
+  NS_IMPL_QUERY_TAIL_USING_AGGREGATOR(_aggregator)
+
+#define NS_INTERFACE_TABLE0(_class)               \
+  NS_INTERFACE_TABLE_BEGIN                        \
+    NS_INTERFACE_TABLE_ENTRY(_class, nsISupports) \
+  NS_INTERFACE_TABLE_END
+
+#define NS_INTERFACE_TABLE(aClass, ...)                               \
+  static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0,                       \
+                "Need more arguments to NS_INTERFACE_TABLE");         \
+  NS_INTERFACE_TABLE_BEGIN                                            \
+    MOZ_FOR_EACH(NS_INTERFACE_TABLE_ENTRY, (aClass, ), (__VA_ARGS__)) \
+    NS_INTERFACE_TABLE_ENTRY_AMBIGUOUS(aClass, nsISupports,           \
+                                       MOZ_ARG_1(__VA_ARGS__))        \
+  NS_INTERFACE_TABLE_END
+
+#define NS_IMPL_QUERY_INTERFACE0(_class) \
+  NS_INTERFACE_TABLE_HEAD(_class)        \
+    NS_INTERFACE_TABLE0(_class)          \
+  NS_INTERFACE_TABLE_TAIL
+
+#define NS_IMPL_QUERY_INTERFACE(aClass, ...) \
+  NS_INTERFACE_TABLE_HEAD(aClass)            \
+    NS_INTERFACE_TABLE(aClass, __VA_ARGS__)  \
+  NS_INTERFACE_TABLE_TAIL
+
+/**
+ * Declare that you're going to inherit from something that already
+ * implements nsISupports, but also implements an additional interface, thus
+ * causing an ambiguity. In this case you don't need another mRefCnt, you
+ * just need to forward the definitions to the appropriate superclass. E.g.
+ *
+ * class Bar : public Foo, public nsIBar {  // both provide nsISupports
+ * public:
+ *   NS_DECL_ISUPPORTS_INHERITED
+ *   ...other nsIBar and Bar methods...
+ * };
+ */
+#define NS_DECL_ISUPPORTS_INHERITED                                       \
+ public:                                                                  \
+  NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) override; \
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void) override;             \
+  NS_IMETHOD_(MozExternalRefCountType) Release(void) override;
+
+/**
+ * These macros can be used in conjunction with NS_DECL_ISUPPORTS_INHERITED
+ * to implement the nsISupports methods, forwarding the invocations to a
+ * superclass that already implements nsISupports. Don't do anything for
+ * subclasses of Runnable because it deals with subclass logging in its own
+ * way, using the mName field.
+ *
+ * Note that I didn't make these inlined because they're virtual methods.
+ */
+
+namespace mozilla {
+class Runnable;
+namespace detail {
+class SupportsThreadSafeWeakPtrBase;
+
+// Don't NS_LOG_{ADDREF,RELEASE} when inheriting from `Runnable*` or types with
+// thread safe weak references, as it will generate incorrect refcnt logs due to
+// the thread-safe `Upgrade()` call's refcount modifications not calling through
+// the derived class' `AddRef()` and `Release()` methods.
+template <typename T>
+constexpr bool ShouldLogInheritedRefcnt =
+    !std::is_convertible_v<T*, Runnable*> &&
+    !std::is_base_of_v<SupportsThreadSafeWeakPtrBase, T>;
+}
+}  // namespace mozilla
+
+#define NS_IMPL_ADDREF_INHERITED_GUTS(Class, Super)                   \
+  MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(Class)                           \
+  nsrefcnt r = Super::AddRef();                                       \
+  if constexpr (::mozilla::detail::ShouldLogInheritedRefcnt<Class>) { \
+    NS_LOG_ADDREF(this, r, #Class, sizeof(*this));                    \
+  }                                                                   \
+  return r /* Purposefully no trailing semicolon */
+
+#define NS_IMPL_ADDREF_INHERITED(Class, Super)                  \
+  NS_IMETHODIMP_(MozExternalRefCountType) Class::AddRef(void) { \
+    NS_IMPL_ADDREF_INHERITED_GUTS(Class, Super);                \
+  }
+
+#define NS_IMPL_RELEASE_INHERITED_GUTS(Class, Super)                  \
+  nsrefcnt r = Super::Release();                                      \
+  if constexpr (::mozilla::detail::ShouldLogInheritedRefcnt<Class>) { \
+    NS_LOG_RELEASE(this, r, #Class);                                  \
+  }                                                                   \
+  return r /* Purposefully no trailing semicolon */
+
+#define NS_IMPL_RELEASE_INHERITED(Class, Super)                  \
+  NS_IMETHODIMP_(MozExternalRefCountType) Class::Release(void) { \
+    NS_IMPL_RELEASE_INHERITED_GUTS(Class, Super);                \
+  }
+
+/**
+ * As above but not logging the addref/release; needed if the base
+ * class might be aggregated.
+ */
+#define NS_IMPL_NONLOGGING_ADDREF_INHERITED(Class, Super)       \
+  NS_IMETHODIMP_(MozExternalRefCountType) Class::AddRef(void) { \
+    MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(Class)                   \
+    return Super::AddRef();                                     \
+  }
+
+#define NS_IMPL_NONLOGGING_RELEASE_INHERITED(Class, Super)       \
+  NS_IMETHODIMP_(MozExternalRefCountType) Class::Release(void) { \
+    return Super::Release();                                     \
+  }
+
+#define NS_INTERFACE_TABLE_INHERITED0(Class) /* Nothing to do here */
+
+#define NS_INTERFACE_TABLE_INHERITED(aClass, ...)                       \
+  static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0,                         \
+                "Need more arguments to NS_INTERFACE_TABLE_INHERITED"); \
+  NS_INTERFACE_TABLE_BEGIN                                              \
+    MOZ_FOR_EACH(NS_INTERFACE_TABLE_ENTRY, (aClass, ), (__VA_ARGS__))   \
+  NS_INTERFACE_TABLE_END
+
+#define NS_IMPL_QUERY_INTERFACE_INHERITED(aClass, aSuper, ...) \
+  NS_INTERFACE_TABLE_HEAD(aClass)                              \
+    NS_INTERFACE_TABLE_INHERITED(aClass, __VA_ARGS__)          \
+  NS_INTERFACE_TABLE_TAIL_INHERITING(aSuper)
+
+/**
+ * Convenience macros for implementing all nsISupports methods for
+ * a simple class.
+ * @param _class The name of the class implementing the method
+ * @param _classiiddef The name of the #define symbol that defines the IID
+ * for the class (e.g. NS_ISUPPORTS_IID)
+ */
+
+#define NS_IMPL_ISUPPORTS0(_class) \
+  NS_IMPL_ADDREF(_class)           \
+  NS_IMPL_RELEASE(_class)          \
+  NS_IMPL_QUERY_INTERFACE0(_class)
+
+#define NS_IMPL_ISUPPORTS(aClass, ...) \
+  NS_IMPL_ADDREF(aClass)               \
+  NS_IMPL_RELEASE(aClass)              \
+  NS_IMPL_QUERY_INTERFACE(aClass, __VA_ARGS__)
+
+// When possible, prefer NS_INLINE_DECL_REFCOUNTING_INHERITED to
+// NS_IMPL_ISUPPORTS_INHERITED0.
+#define NS_IMPL_ISUPPORTS_INHERITED0(aClass, aSuper) \
+  NS_INTERFACE_TABLE_HEAD(aClass)                    \
+  NS_INTERFACE_TABLE_TAIL_INHERITING(aSuper)         \
+  NS_IMPL_ADDREF_INHERITED(aClass, aSuper)           \
+  NS_IMPL_RELEASE_INHERITED(aClass, aSuper)
+
+#define NS_IMPL_ISUPPORTS_INHERITED(aClass, aSuper, ...)         \
+  NS_IMPL_QUERY_INTERFACE_INHERITED(aClass, aSuper, __VA_ARGS__) \
+  NS_IMPL_ADDREF_INHERITED(aClass, aSuper)                       \
+  NS_IMPL_RELEASE_INHERITED(aClass, aSuper)
+
+/**
+ * A macro to declare and implement inherited addref/release for a class which
+ * doesn't have or need to override QueryInterface from its base class.
+ *
+ * Note: This macro always overrides the `AddRef` and `Release` methods,
+ * including when refcount logging is disabled, meaning that it will implement
+ * the `AddRef` or `Release` method from another virtual base class.
+ */
+#define NS_INLINE_DECL_REFCOUNTING_INHERITED(Class, Super)  \
+  NS_IMETHOD_(MozExternalRefCountType) AddRef() override {  \
+    NS_IMPL_ADDREF_INHERITED_GUTS(Class, Super);            \
+  }                                                         \
+  NS_IMETHOD_(MozExternalRefCountType) Release() override { \
+    NS_IMPL_RELEASE_INHERITED_GUTS(Class, Super);           \
+  }
+
+/*
+ * Macro to glue together a QI that starts with an interface table
+ * and segues into an interface map (e.g. it uses singleton classinfo
+ * or tearoffs).
+ */
+#define NS_INTERFACE_TABLE_TO_MAP_SEGUE \
+  if (rv == NS_OK) return rv;           \
+  nsISupports* foundInterface;
+
+///////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Macro to generate nsIClassInfo methods for classes which do not have
+ * corresponding nsIFactory implementations.
+ */
+#define NS_IMPL_THREADSAFE_CI(_class)                          \
+  NS_IMETHODIMP                                                \
+  _class::GetInterfaces(nsTArray<nsIID>& _array) {             \
+    return NS_CI_INTERFACE_GETTER_NAME(_class)(_array);        \
+  }                                                            \
+                                                               \
+  NS_IMETHODIMP                                                \
+  _class::GetScriptableHelper(nsIXPCScriptable** _retval) {    \
+    *_retval = nullptr;                                        \
+    return NS_OK;                                              \
+  }                                                            \
+                                                               \
+  NS_IMETHODIMP                                                \
+  _class::GetContractID(nsACString& _contractID) {             \
+    _contractID.SetIsVoid(true);                               \
+    return NS_OK;                                              \
+  }                                                            \
+                                                               \
+  NS_IMETHODIMP                                                \
+  _class::GetClassDescription(nsACString& _classDescription) { \
+    _classDescription.SetIsVoid(true);                         \
+    return NS_OK;                                              \
+  }                                                            \
+                                                               \
+  NS_IMETHODIMP                                                \
+  _class::GetClassID(nsCID** _classID) {                       \
+    *_classID = nullptr;                                       \
+    return NS_OK;                                              \
+  }                                                            \
+                                                               \
+  NS_IMETHODIMP                                                \
+  _class::GetFlags(uint32_t* _flags) {                         \
+    *_flags = nsIClassInfo::THREADSAFE;                        \
+    return NS_OK;                                              \
+  }                                                            \
+                                                               \
+  NS_IMETHODIMP                                                \
+  _class::GetClassIDNoAlloc(nsCID* _classIDNoAlloc) {          \
+    return NS_ERROR_NOT_AVAILABLE;                             \
+  }
+
+#endif
diff --git a/xpcom/base/nsISupportsUtils.h b/xpcom/base/nsISupportsUtils.h
new file mode 100644
index 0000000000..a885c5cb14
--- /dev/null
+++ b/xpcom/base/nsISupportsUtils.h
@@ -0,0 +1,142 @@
+/* -*- 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/. */
+
+#ifndef nsISupportsUtils_h__
+#define nsISupportsUtils_h__
+
+#include <type_traits>
+
+#include "nscore.h"
+#include "nsIOutputStream.h"
+#include "nsISupports.h"
+#include "nsError.h"
+#include "nsDebug.h"
+#include "nsISupportsImpl.h"
+#include "mozilla/RefPtr.h"
+
+/**
+ * Macro for adding a reference to an interface.
+ * @param _ptr The interface pointer.
+ */
+#define NS_ADDREF(_ptr) (_ptr)->AddRef()
+
+/**
+ * Macro for adding a reference to this. This macro should be used
+ * because NS_ADDREF (when tracing) may require an ambiguous cast
+ * from the pointers primary type to nsISupports. This macro sidesteps
+ * that entire problem.
+ */
+#define NS_ADDREF_THIS() AddRef()
+
+// Making this a |inline| |template| allows |aExpr| to be evaluated only once,
+// yet still denies you the ability to |AddRef()| an |nsCOMPtr|.
+template <class T>
+inline void ns_if_addref(T aExpr) {
+  if (aExpr) {
+    aExpr->AddRef();
+  }
+}
+
+/**
+ * Macro for adding a reference to an interface that checks for nullptr.
+ * @param _expr The interface pointer.
+ */
+#define NS_IF_ADDREF(_expr) ns_if_addref(_expr)
+
+/*
+ * Given these declarations, it explicitly OK and efficient to end a `getter'
+ * with:
+ *
+ *    NS_IF_ADDREF(*result = mThing);
+ *
+ * even if |mThing| is an |nsCOMPtr|.  If |mThing| is an |nsCOMPtr|, however, it
+ * is still _illegal_ to say |NS_IF_ADDREF(mThing)|.
+ */
+
+/**
+ * Macro for releasing a reference to an interface.
+ * @param _ptr The interface pointer.
+ */
+#define NS_RELEASE(_ptr) \
+  do {                   \
+    (_ptr)->Release();   \
+    (_ptr) = 0;          \
+  } while (0)
+
+/**
+ * Macro for releasing a reference to this interface.
+ */
+#define NS_RELEASE_THIS() Release()
+
+/**
+ * Macro for releasing a reference to an interface, except that this
+ * macro preserves the return value from the underlying Release call.
+ * The interface pointer argument will only be NULLed if the reference count
+ * goes to zero.
+ *
+ * @param _ptr The interface pointer.
+ * @param _rc  The reference count.
+ */
+#define NS_RELEASE2(_ptr, _rc)  \
+  do {                          \
+    _rc = (_ptr)->Release();    \
+    if (0 == (_rc)) (_ptr) = 0; \
+  } while (0)
+
+/**
+ * Macro for releasing a reference to an interface that checks for nullptr;
+ * @param _ptr The interface pointer.
+ */
+#define NS_IF_RELEASE(_ptr) \
+  do {                      \
+    if (_ptr) {             \
+      (_ptr)->Release();    \
+      (_ptr) = 0;           \
+    }                       \
+  } while (0)
+
+/*
+ * Often you have to cast an implementation pointer, e.g., |this|, to an
+ * |nsISupports*|, but because you have multiple inheritance, a simple cast
+ * is ambiguous.  One could simply say, e.g., (given a base |nsIBase|),
+ * |static_cast<nsIBase*>(this)|; but that disguises the fact that what
+ * you are really doing is disambiguating the |nsISupports|.  You could make
+ * that more obvious with a double cast, e.g., |static_cast<nsISupports*>
+                                                           (*
+ static_cast<nsIBase*>(this))|, but that is bulky and harder to read...
+ *
+ * The following macro is clean, short, and obvious.  In the example above,
+ * you would use it like this: |NS_ISUPPORTS_CAST(nsIBase*, this)|.
+ */
+
+#define NS_ISUPPORTS_CAST(__unambiguousBase, __expr) \
+  static_cast<nsISupports*>(static_cast<__unambiguousBase>(__expr))
+
+// a type-safe shortcut for calling the |QueryInterface()| member function
+template <class T, class DestinationType>
+inline nsresult CallQueryInterface(T* aSource, DestinationType** aDestination) {
+  // We permit nsISupports-to-nsISupports here so that one can still obtain
+  // the canonical nsISupports pointer with CallQueryInterface.
+  static_assert(
+      !(std::is_same_v<DestinationType, T> ||
+        std::is_base_of<DestinationType, T>::value) ||
+          std::is_same_v<DestinationType, nsISupports>,
+      "don't use CallQueryInterface for compile-time-determinable casts");
+
+  MOZ_ASSERT(aSource, "null parameter");
+  MOZ_ASSERT(aDestination, "null parameter");
+
+  return aSource->QueryInterface(NS_GET_TEMPLATE_IID(DestinationType),
+                                 reinterpret_cast<void**>(aDestination));
+}
+
+template <class SourceType, class DestinationType>
+inline nsresult CallQueryInterface(RefPtr<SourceType>& aSourcePtr,
+                                   DestinationType** aDestPtr) {
+  return CallQueryInterface(aSourcePtr.get(), aDestPtr);
+}
+
+#endif /* __nsISupportsUtils_h */
diff --git a/xpcom/base/nsIUUIDGenerator.idl b/xpcom/base/nsIUUIDGenerator.idl
new file mode 100644
index 0000000000..22087adfa8
--- /dev/null
+++ b/xpcom/base/nsIUUIDGenerator.idl
@@ -0,0 +1,39 @@
+/* -*- Mode: C++; tab-width: 50; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "nsISupports.idl"
+
+[ptr] native nsNonConstIDPtr(nsID);
+
+/**
+ * nsIUUIDGenerator is implemented by a service that can generate
+ * universally unique identifiers, ideally using any platform-native
+ * method for generating UUIDs.
+ */
+[builtinclass, scriptable, uuid(138ad1b2-c694-41cc-b201-333ce936d8b8)]
+interface nsIUUIDGenerator : nsISupports
+{
+  /**
+   * Obtains a new UUID using appropriate platform-specific methods to
+   * obtain a nsID that can be considered to be globally unique.
+   *
+   * @returns an nsID filled in with a new UUID.
+   *
+   * @throws NS_ERROR_FAILURE if a UUID cannot be generated (e.g. if
+   * an underlying source of randomness is not available)
+   */
+  nsIDPtr generateUUID();
+
+  /**
+   * Obtain a new UUID like the generateUUID method, but place it in
+   * the provided nsID pointer instead of allocating a new nsID.
+   *
+   * @param id an existing nsID pointer where the UUID will be stored.
+   *
+   * @throws NS_ERROR_FAILURE if a UUID cannot be generated (e.g. if
+   * an underlying source of randomness is not available)
+   */
+  [noscript] void generateUUIDInPlace(in nsNonConstIDPtr id);
+};
diff --git a/xpcom/base/nsIVersionComparator.idl b/xpcom/base/nsIVersionComparator.idl
new file mode 100644
index 0000000000..462a07dff3
--- /dev/null
+++ b/xpcom/base/nsIVersionComparator.idl
@@ -0,0 +1,48 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "nsISupports.idl"
+
+/**
+ * Version strings are dot-separated sequences of version-parts.
+ *
+ * A version-part consists of up to four parts, all of which are optional:
+ *
+ * <number-a><string-b><number-c><string-d (everything else)>
+ *
+ * A version-part may also consist of a single asterisk "*" which indicates
+ * "infinity".
+ *
+ * Numbers are base-10, and are zero if left out.
+ * Strings are compared bytewise.
+ *
+ * For additional backwards compatibility, if "string-b" is "+" then
+ * "number-a" is incremented by 1 and "string-b" becomes "pre".
+ *
+ * 1.0pre1
+ * < 1.0pre2
+ *   < 1.0 == 1.0.0 == 1.0.0.0
+ *     < 1.1pre == 1.1pre0 == 1.0+
+ *       < 1.1pre1a
+ *         < 1.1pre1
+ *           < 1.1pre10a
+ *             < 1.1pre10
+ *
+ * Although not required by this interface, it is recommended that
+ * numbers remain within the limits of a signed char, i.e. -127 to 128.
+ */
+[builtinclass, scriptable, uuid(e6cd620a-edbb-41d2-9e42-9a2ffc8107f3)]
+interface nsIVersionComparator : nsISupports
+{
+  /**
+   * Compare two version strings
+   * @param   A   The first version
+   * @param   B   The second version
+   * @returns < 0 if A < B
+   *          = 0 if A == B
+   *          > 0 if A > B
+   */
+  long compare(in ACString A, in ACString B);
+};
diff --git a/xpcom/base/nsIWeakReference.idl b/xpcom/base/nsIWeakReference.idl
new file mode 100644
index 0000000000..723fa84344
--- /dev/null
+++ b/xpcom/base/nsIWeakReference.idl
@@ -0,0 +1,114 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 "nsISupports.idl"
+
+%{C++
+#include "mozilla/Attributes.h"
+#include "mozilla/MemoryReporting.h"
+
+// For MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED.
+#include "nsDebug.h"
+
+#ifdef MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED
+
+#define MOZ_WEAKREF_DECL_OWNINGTHREAD nsAutoOwningThread _mWeakRefOwningThread;
+#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD \
+  _mWeakRefOwningThread.AssertOwnership("nsWeakReference not thread-safe")
+#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD_DELEGATED(that) \
+  (that)->_mWeakRefOwningThread.AssertOwnership("nsWeakReference not thread-safe")
+
+#else
+
+#define MOZ_WEAKREF_DECL_OWNINGTHREAD
+#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD do { } while (false)
+#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD_DELEGATED(that) do { } while (false)
+
+#endif
+
+%}
+
+native MallocSizeOf(mozilla::MallocSizeOf);
+
+/**
+ * An instance of |nsIWeakReference| is a proxy object that cooperates with
+ * its referent to give clients a non-owning, non-dangling reference.  Clients
+ * own the proxy, and should generally manage it with an |nsCOMPtr| (see the
+ * type |nsWeakPtr| for a |typedef| name that stands out) as they would any
+ * other XPCOM object.  The |QueryReferent| member function provides a
+ * (hopefully short-lived) owning reference on demand, through which clients
+ * can get useful access to the referent, while it still exists.
+ *
+ * @version 1.0
+ * @see nsISupportsWeakReference
+ * @see nsWeakReference
+ * @see nsWeakPtr
+ */
+[scriptable, builtinclass, uuid(9188bc85-f92e-11d2-81ef-0060083a0bcf)]
+interface nsIWeakReference : nsISupports
+  {
+    /**
+     * |QueryReferent| queries the referent, if it exists, and like |QueryInterface|, produces
+     * an owning reference to the desired interface.  It is designed to look and act exactly
+     * like (a proxied) |QueryInterface|.  Don't hold on to the produced interface permanently;
+     * that would defeat the purpose of using a non-owning |nsIWeakReference| in the first place.
+     */
+    [binaryname(QueryReferentFromScript)]
+    void QueryReferent( in nsIIDRef uuid, [iid_is(uuid), retval] out nsQIResult result );
+
+    [notxpcom, nostdcall] size_t sizeOfOnlyThis(in MallocSizeOf aMallocSizeOf);
+%{C++
+  /**
+   * Returns true if the referring object is alive.  Otherwise, false.
+   */
+  bool IsAlive() const
+  {
+    return !!mObject;
+  }
+
+  nsresult QueryReferent(const nsIID& aIID, void** aInstancePtr);
+
+protected:
+  friend class nsSupportsWeakReference;
+
+  nsIWeakReference(nsISupports* aObject)
+    : mObject(aObject)
+  {
+  }
+
+  nsIWeakReference() = delete;
+
+  MOZ_WEAKREF_DECL_OWNINGTHREAD
+
+  // The object we're holding a weak reference to.
+  nsISupports* MOZ_NON_OWNING_REF mObject;
+%}
+  };
+
+
+/**
+ * |nsISupportsWeakReference| is a factory interface which produces appropriate
+ * instances of |nsIWeakReference|.  Weak references in this scheme can only be
+ * produced for objects that implement this interface.
+ *
+ * @version 1.0
+ * @see nsIWeakReference
+ * @see nsSupportsWeakReference
+ */
+[scriptable, uuid(9188bc86-f92e-11d2-81ef-0060083a0bcf)]
+interface nsISupportsWeakReference : nsISupports
+  {
+    /**
+     * |GetWeakReference| produces an appropriate instance of |nsIWeakReference|.
+     * As with all good XPCOM `getters', you own the resulting interface and should
+     * manage it with an |nsCOMPtr|.
+     *
+     * @see nsIWeakReference
+     * @see nsWeakPtr
+     * @see nsCOMPtr
+     */
+    nsIWeakReference GetWeakReference();
+  };
diff --git a/xpcom/base/nsIWeakReferenceUtils.h b/xpcom/base/nsIWeakReferenceUtils.h
new file mode 100644
index 0000000000..b76303096e
--- /dev/null
+++ b/xpcom/base/nsIWeakReferenceUtils.h
@@ -0,0 +1,84 @@
+/* -*- 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/. */
+
+#ifndef nsIWeakReferenceUtils_h__
+#define nsIWeakReferenceUtils_h__
+
+#include "nsCOMPtr.h"
+#include "nsIWeakReference.h"
+
+typedef nsCOMPtr<nsIWeakReference> nsWeakPtr;
+
+/**
+ *
+ */
+
+// a type-safe shortcut for calling the |QueryReferent()| member function
+// T must inherit from nsIWeakReference, but the cast may be ambiguous.
+template <class T, class DestinationType>
+inline nsresult CallQueryReferent(T* aSource, DestinationType** aDestination) {
+  MOZ_ASSERT(aSource, "null parameter");
+  MOZ_ASSERT(aDestination, "null parameter");
+
+  return aSource->QueryReferent(NS_GET_TEMPLATE_IID(DestinationType),
+                                reinterpret_cast<void**>(aDestination));
+}
+
+inline const nsQueryReferent do_QueryReferent(nsIWeakReference* aRawPtr,
+                                              nsresult* aError = 0) {
+  return nsQueryReferent(aRawPtr, aError);
+}
+
+/**
+ * Deprecated, use |do_GetWeakReference| instead.
+ */
+extern nsIWeakReference* NS_GetWeakReference(nsISupports*,
+                                             nsresult* aResult = 0);
+extern nsIWeakReference* NS_GetWeakReference(nsISupportsWeakReference*,
+                                             nsresult* aResult = 0);
+
+/**
+ * |do_GetWeakReference| is a convenience function that bundles up all the work
+ * needed to get a weak reference to an arbitrary object, i.e., the
+ * |QueryInterface|, test, and call through to |GetWeakReference|, and put it
+ * into your |nsCOMPtr|. It is specifically designed to cooperate with
+ * |nsCOMPtr| (or |nsWeakPtr|) like so: |nsWeakPtr myWeakPtr =
+ * do_GetWeakReference(aPtr);|.
+ */
+inline already_AddRefed<nsIWeakReference> do_GetWeakReference(
+    nsISupports* aRawPtr, nsresult* aError = 0) {
+  return dont_AddRef(NS_GetWeakReference(aRawPtr, aError));
+}
+
+inline already_AddRefed<nsIWeakReference> do_GetWeakReference(
+    nsISupportsWeakReference* aRawPtr, nsresult* aError = 0) {
+  return dont_AddRef(NS_GetWeakReference(aRawPtr, aError));
+}
+
+inline void do_GetWeakReference(nsIWeakReference* aRawPtr,
+                                nsresult* aError = 0) {
+  // This signature exists solely to _stop_ you from doing a bad thing.
+  //  Saying |do_GetWeakReference()| on a weak reference itself,
+  //  is very likely to be a programmer error.
+}
+
+template <class T>
+inline void do_GetWeakReference(already_AddRefed<T>&) {
+  // This signature exists solely to _stop_ you from doing the bad thing.
+  //  Saying |do_GetWeakReference()| on a pointer that is not otherwise owned by
+  //  someone else is an automatic leak.  See
+  //  <http://bugzilla.mozilla.org/show_bug.cgi?id=8221>.
+}
+
+template <class T>
+inline void do_GetWeakReference(already_AddRefed<T>&, nsresult*) {
+  // This signature exists solely to _stop_ you from doing the bad thing.
+  //  Saying |do_GetWeakReference()| on a pointer that is not otherwise owned by
+  //  someone else is an automatic leak.  See
+  //  <http://bugzilla.mozilla.org/show_bug.cgi?id=8221>.
+}
+
+#endif
diff --git a/xpcom/base/nsInterfaceRequestorAgg.cpp b/xpcom/base/nsInterfaceRequestorAgg.cpp
new file mode 100644
index 0000000000..490341aac2
--- /dev/null
+++ b/xpcom/base/nsInterfaceRequestorAgg.cpp
@@ -0,0 +1,74 @@
+/* -*- 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 "nsInterfaceRequestorAgg.h"
+#include "nsIInterfaceRequestor.h"
+#include "nsCOMPtr.h"
+#include "mozilla/Attributes.h"
+#include "nsThreadUtils.h"
+#include "nsProxyRelease.h"
+
+class nsInterfaceRequestorAgg final : public nsIInterfaceRequestor {
+ public:
+  // XXX This needs to support threadsafe refcounting until we fix bug 243591.
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINTERFACEREQUESTOR
+
+  nsInterfaceRequestorAgg(nsIInterfaceRequestor* aFirst,
+                          nsIInterfaceRequestor* aSecond,
+                          nsIEventTarget* aConsumerTarget = nullptr)
+      : mFirst(aFirst), mSecond(aSecond), mConsumerTarget(aConsumerTarget) {
+    if (!mConsumerTarget) {
+      mConsumerTarget = mozilla::GetCurrentSerialEventTarget();
+    }
+  }
+
+ private:
+  ~nsInterfaceRequestorAgg();
+
+  nsCOMPtr<nsIInterfaceRequestor> mFirst, mSecond;
+  nsCOMPtr<nsIEventTarget> mConsumerTarget;
+};
+
+NS_IMPL_ISUPPORTS(nsInterfaceRequestorAgg, nsIInterfaceRequestor)
+
+NS_IMETHODIMP
+nsInterfaceRequestorAgg::GetInterface(const nsIID& aIID, void** aResult) {
+  nsresult rv = NS_ERROR_NO_INTERFACE;
+  if (mFirst) {
+    rv = mFirst->GetInterface(aIID, aResult);
+  }
+  if (mSecond && NS_FAILED(rv)) {
+    rv = mSecond->GetInterface(aIID, aResult);
+  }
+  return rv;
+}
+
+nsInterfaceRequestorAgg::~nsInterfaceRequestorAgg() {
+  NS_ProxyRelease("nsInterfaceRequestorAgg::mFirst", mConsumerTarget,
+                  mFirst.forget());
+  NS_ProxyRelease("nsInterfaceRequestorAgg::mSecond", mConsumerTarget,
+                  mSecond.forget());
+}
+
+nsresult NS_NewInterfaceRequestorAggregation(nsIInterfaceRequestor* aFirst,
+                                             nsIInterfaceRequestor* aSecond,
+                                             nsIInterfaceRequestor** aResult) {
+  *aResult = new nsInterfaceRequestorAgg(aFirst, aSecond);
+
+  NS_ADDREF(*aResult);
+  return NS_OK;
+}
+
+nsresult NS_NewInterfaceRequestorAggregation(nsIInterfaceRequestor* aFirst,
+                                             nsIInterfaceRequestor* aSecond,
+                                             nsIEventTarget* aTarget,
+                                             nsIInterfaceRequestor** aResult) {
+  *aResult = new nsInterfaceRequestorAgg(aFirst, aSecond, aTarget);
+
+  NS_ADDREF(*aResult);
+  return NS_OK;
+}
diff --git a/xpcom/base/nsInterfaceRequestorAgg.h b/xpcom/base/nsInterfaceRequestorAgg.h
new file mode 100644
index 0000000000..06c6b3d3a3
--- /dev/null
+++ b/xpcom/base/nsInterfaceRequestorAgg.h
@@ -0,0 +1,35 @@
+/* -*- 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/. */
+
+#ifndef nsInterfaceRequestorAgg_h__
+#define nsInterfaceRequestorAgg_h__
+
+#include "nsError.h"
+
+class nsIEventTarget;
+class nsIInterfaceRequestor;
+
+/**
+ * This function returns an instance of nsIInterfaceRequestor that aggregates
+ * two nsIInterfaceRequestor instances.  Its GetInterface method queries
+ * aFirst for the requested interface and will query aSecond only if aFirst
+ * failed to supply the requested interface.  Both aFirst and aSecond may
+ * be null, and will be released on the main thread when the aggregator is
+ * destroyed.
+ */
+extern nsresult NS_NewInterfaceRequestorAggregation(
+    nsIInterfaceRequestor* aFirst, nsIInterfaceRequestor* aSecond,
+    nsIInterfaceRequestor** aResult);
+
+/**
+ * Like the previous method, but aFirst and aSecond will be released on the
+ * provided target thread.
+ */
+extern nsresult NS_NewInterfaceRequestorAggregation(
+    nsIInterfaceRequestor* aFirst, nsIInterfaceRequestor* aSecond,
+    nsIEventTarget* aTarget, nsIInterfaceRequestor** aResult);
+
+#endif  // !defined( nsInterfaceRequestorAgg_h__ )
diff --git a/xpcom/base/nsMacPreferencesReader.h b/xpcom/base/nsMacPreferencesReader.h
new file mode 100644
index 0000000000..40d5af553a
--- /dev/null
+++ b/xpcom/base/nsMacPreferencesReader.h
@@ -0,0 +1,34 @@
+/* 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/. */
+
+#ifndef MacPreferencesReader_h__
+#define MacPreferencesReader_h__
+
+//-----------------------------------------------------------------------------
+
+#include "nsIMacPreferencesReader.h"
+
+#define NS_MACPREFERENCESREADER_CID                  \
+  {                                                  \
+    0xb0f20595, 0x88ce, 0x4738, {                    \
+      0xa1, 0xa4, 0x24, 0xde, 0x78, 0xeb, 0x80, 0x51 \
+    }                                                \
+  }
+#define NS_MACPREFERENCESREADER_CONTRACTID \
+  "@mozilla.org/mac-preferences-reader;1"
+
+//-----------------------------------------------------------------------------
+
+class nsMacPreferencesReader : public nsIMacPreferencesReader {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIMACPREFERENCESREADER
+
+  nsMacPreferencesReader(){};
+
+ protected:
+  virtual ~nsMacPreferencesReader() = default;
+};
+
+#endif  // MacPreferencesReader_h__
diff --git a/xpcom/base/nsMacPreferencesReader.mm b/xpcom/base/nsMacPreferencesReader.mm
new file mode 100644
index 0000000000..ad9a59a9f4
--- /dev/null
+++ b/xpcom/base/nsMacPreferencesReader.mm
@@ -0,0 +1,79 @@
+/* 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 "MacStringHelpers.h"
+#include "nsMacPreferencesReader.h"
+#include "nsString.h"
+
+#include "js/JSON.h"
+#include "js/RootingAPI.h"
+#include "js/Value.h"
+#include "mozilla/JSONStringWriteFuncs.h"
+
+NS_IMPL_ISUPPORTS(nsMacPreferencesReader, nsIMacPreferencesReader)
+
+using namespace mozilla;
+
+static void EvaluateDict(JSONWriter* aWriter, NSDictionary<NSString*, id>* aDict);
+
+static void EvaluateArray(JSONWriter* aWriter, NSArray* aArray) {
+  for (id elem in aArray) {
+    if ([elem isKindOfClass:[NSString class]]) {
+      aWriter->StringElement(MakeStringSpan([elem UTF8String]));
+    } else if ([elem isKindOfClass:[NSNumber class]]) {
+      aWriter->IntElement([elem longLongValue]);
+    } else if ([elem isKindOfClass:[NSArray class]]) {
+      aWriter->StartArrayElement();
+      EvaluateArray(aWriter, elem);
+      aWriter->EndArray();
+    } else if ([elem isKindOfClass:[NSDictionary class]]) {
+      aWriter->StartObjectElement();
+      EvaluateDict(aWriter, elem);
+      aWriter->EndObject();
+    }
+  }
+}
+
+static void EvaluateDict(JSONWriter* aWriter, NSDictionary<NSString*, id>* aDict) {
+  for (NSString* key in aDict) {
+    id value = aDict[key];
+    if ([value isKindOfClass:[NSString class]]) {
+      aWriter->StringProperty(MakeStringSpan([key UTF8String]), MakeStringSpan([value UTF8String]));
+    } else if ([value isKindOfClass:[NSNumber class]]) {
+      aWriter->IntProperty(MakeStringSpan([key UTF8String]), [value longLongValue]);
+    } else if ([value isKindOfClass:[NSArray class]]) {
+      aWriter->StartArrayProperty(MakeStringSpan([key UTF8String]));
+      EvaluateArray(aWriter, value);
+      aWriter->EndArray();
+    } else if ([value isKindOfClass:[NSDictionary class]]) {
+      aWriter->StartObjectProperty(MakeStringSpan([key UTF8String]));
+      EvaluateDict(aWriter, value);
+      aWriter->EndObject();
+    }
+  }
+}
+
+NS_IMETHODIMP
+nsMacPreferencesReader::PoliciesEnabled(bool* aPoliciesEnabled) {
+  NSString* policiesEnabledStr = [NSString stringWithUTF8String:ENTERPRISE_POLICIES_ENABLED_KEY];
+  *aPoliciesEnabled = [[NSUserDefaults standardUserDefaults] boolForKey:policiesEnabledStr] == YES;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMacPreferencesReader::ReadPreferences(JSContext* aCx, JS::MutableHandle<JS::Value> aResult) {
+  JSONStringWriteFunc<nsAutoCString> jsonStr;
+  JSONWriter w(jsonStr);
+  w.Start();
+  EvaluateDict(&w, [[NSUserDefaults standardUserDefaults] dictionaryRepresentation]);
+  w.End();
+
+  NS_ConvertUTF8toUTF16 jsonStr16(jsonStr.StringCRef());
+
+  JS::RootedValue val(aCx);
+  MOZ_ALWAYS_TRUE(JS_ParseJSON(aCx, jsonStr16.get(), jsonStr16.Length(), &val));
+
+  aResult.set(val);
+  return NS_OK;
+}
diff --git a/xpcom/base/nsMacUtilsImpl.cpp b/xpcom/base/nsMacUtilsImpl.cpp
new file mode 100644
index 0000000000..86227b7aca
--- /dev/null
+++ b/xpcom/base/nsMacUtilsImpl.cpp
@@ -0,0 +1,544 @@
+/* -*- 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 "nsMacUtilsImpl.h"
+
+#include "base/command_line.h"
+#include "base/process_util.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/Omnijar.h"
+#include "nsDirectoryServiceDefs.h"
+#include "nsCOMPtr.h"
+#include "nsComponentManagerUtils.h"
+#include "nsIFile.h"
+#include "nsServiceManagerUtils.h"
+#include "nsThreadUtils.h"
+#include "nsXULAppAPI.h"
+#include "prenv.h"
+
+#if defined(MOZ_SANDBOX)
+#  include "mozilla/SandboxSettings.h"
+#endif
+
+#include <CoreFoundation/CoreFoundation.h>
+#include <CoreServices/CoreServices.h>
+#if defined(__aarch64__)
+#  include <dlfcn.h>
+#endif
+#include <sys/sysctl.h>
+
+using mozilla::StaticMutexAutoLock;
+using mozilla::Unused;
+
+#if defined(MOZ_SANDBOX) || defined(__aarch64__)
+// For thread safe setting/checking of sCachedAppPath
+static StaticMutex sCachedAppPathMutex;
+
+// Cache the appDir returned from GetAppPath to avoid doing I/O
+static StaticAutoPtr<nsCString> sCachedAppPath
+    MOZ_GUARDED_BY(sCachedAppPathMutex);
+#endif
+
+// The cached machine architectures of the .app bundle which can
+// be multiple architectures for universal binaries.
+static std::atomic<uint32_t> sBundleArchMaskAtomic = 0;
+
+#if defined(__aarch64__)
+// Limit XUL translation to one attempt
+static std::atomic<bool> sIsXULTranslated = false;
+#endif
+
+// Info.plist key associated with the developer repo path
+#define MAC_DEV_REPO_KEY "MozillaDeveloperRepoPath"
+// Info.plist key associated with the developer repo object directory
+#define MAC_DEV_OBJ_KEY "MozillaDeveloperObjPath"
+
+// Workaround this constant not being available in the macOS SDK
+#define kCFBundleExecutableArchitectureARM64 0x0100000c
+
+enum TCSMStatus { TCSM_Unknown = 0, TCSM_Available, TCSM_Unavailable };
+
+// Initialize with Unknown until we've checked if TCSM is available to set
+static Atomic<TCSMStatus> sTCSMStatus(TCSM_Unknown);
+
+#if defined(MOZ_SANDBOX) || defined(__aarch64__)
+
+// Utility method to call ClearOnShutdown() on the main thread
+static nsresult ClearCachedAppPathOnShutdown() {
+  MOZ_ASSERT(NS_IsMainThread());
+  ClearOnShutdown(&sCachedAppPath);
+  return NS_OK;
+}
+
+// Get the path to the .app directory (aka bundle) for the parent process.
+// When executing in the child process, this is the outer .app (such as
+// Firefox.app) and not the inner .app containing the child process
+// executable. We don't rely on the actual .app extension to allow for the
+// bundle being renamed.
+bool nsMacUtilsImpl::GetAppPath(nsCString& aAppPath) {
+  StaticMutexAutoLock lock(sCachedAppPathMutex);
+  if (sCachedAppPath) {
+    aAppPath.Assign(*sCachedAppPath);
+    return true;
+  }
+
+  nsAutoCString appPath;
+  nsAutoCString appBinaryPath(
+      (CommandLine::ForCurrentProcess()->argv()[0]).c_str());
+
+  // The binary path resides within the .app dir in Contents/MacOS,
+  // e.g., Firefox.app/Contents/MacOS/firefox. Search backwards in
+  // the binary path for the end of .app path.
+  auto pattern = "/Contents/MacOS/"_ns;
+  nsAutoCString::const_iterator start, end;
+  appBinaryPath.BeginReading(start);
+  appBinaryPath.EndReading(end);
+  if (RFindInReadable(pattern, start, end)) {
+    end = start;
+    appBinaryPath.BeginReading(start);
+
+    // If we're executing in a child process, get the parent .app path
+    // by searching backwards once more. The child executable resides
+    // in Firefox.app/Contents/MacOS/plugin-container/Contents/MacOS.
+    if (!XRE_IsParentProcess()) {
+      if (RFindInReadable(pattern, start, end)) {
+        end = start;
+        appBinaryPath.BeginReading(start);
+      } else {
+        return false;
+      }
+    }
+
+    appPath.Assign(Substring(start, end));
+  } else {
+    return false;
+  }
+
+  nsCOMPtr<nsIFile> app;
+  nsresult rv = NS_NewLocalFile(NS_ConvertUTF8toUTF16(appPath), true,
+                                getter_AddRefs(app));
+  if (NS_FAILED(rv)) {
+    return false;
+  }
+
+  rv = app->Normalize();
+  if (NS_FAILED(rv)) {
+    return false;
+  }
+  app->GetNativePath(aAppPath);
+
+  if (!sCachedAppPath) {
+    sCachedAppPath = new nsCString(aAppPath);
+
+    if (NS_IsMainThread()) {
+      ClearCachedAppPathOnShutdown();
+    } else {
+      NS_DispatchToMainThread(
+          NS_NewRunnableFunction("ClearCachedAppPathOnShutdown",
+                                 [] { ClearCachedAppPathOnShutdown(); }));
+    }
+  }
+
+  return true;
+}
+
+#endif /* MOZ_SANDBOX || __aarch64__ */
+
+#if defined(MOZ_SANDBOX) && defined(DEBUG)
+// If XPCOM_MEM_BLOAT_LOG or XPCOM_MEM_LEAK_LOG is set to a log file
+// path, return the path to the parent directory (where sibling log
+// files will be saved.)
+nsresult nsMacUtilsImpl::GetBloatLogDir(nsCString& aDirectoryPath) {
+  nsAutoCString bloatLog(PR_GetEnv("XPCOM_MEM_BLOAT_LOG"));
+  if (bloatLog.IsEmpty()) {
+    bloatLog = PR_GetEnv("XPCOM_MEM_LEAK_LOG");
+  }
+  if (!bloatLog.IsEmpty() && bloatLog != "1" && bloatLog != "2") {
+    return GetDirectoryPath(bloatLog.get(), aDirectoryPath);
+  }
+  return NS_OK;
+}
+
+// Given a path to a file, return the directory which contains it.
+nsresult nsMacUtilsImpl::GetDirectoryPath(const char* aPath,
+                                          nsCString& aDirectoryPath) {
+  nsresult rv = NS_OK;
+  nsCOMPtr<nsIFile> file = do_CreateInstance(NS_LOCAL_FILE_CONTRACTID, &rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = file->InitWithNativePath(nsDependentCString(aPath));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIFile> directoryFile;
+  rv = file->GetParent(getter_AddRefs(directoryFile));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = directoryFile->Normalize();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (NS_FAILED(directoryFile->GetNativePath(aDirectoryPath))) {
+    MOZ_CRASH("Failed to get path for an nsIFile");
+  }
+  return NS_OK;
+}
+#endif /* MOZ_SANDBOX  && DEBUG */
+
+/* static */
+bool nsMacUtilsImpl::IsTCSMAvailable() {
+  if (sTCSMStatus == TCSM_Unknown) {
+    uint32_t oldVal = 0;
+    size_t oldValSize = sizeof(oldVal);
+    int rv = sysctlbyname("kern.tcsm_available", &oldVal, &oldValSize, NULL, 0);
+    TCSMStatus newStatus;
+    if (rv < 0 || oldVal == 0) {
+      newStatus = TCSM_Unavailable;
+    } else {
+      newStatus = TCSM_Available;
+    }
+    // The value of sysctl kern.tcsm_available is the same for all
+    // threads within the same process. If another thread raced with us
+    // and initialized sTCSMStatus first (changing it from
+    // TCSM_Unknown), we can continue without needing to update it
+    // again. Hence, we ignore compareExchange's return value.
+    Unused << sTCSMStatus.compareExchange(TCSM_Unknown, newStatus);
+  }
+  return (sTCSMStatus == TCSM_Available);
+}
+
+static nsresult EnableTCSM() {
+  uint32_t newVal = 1;
+  int rv = sysctlbyname("kern.tcsm_enable", NULL, 0, &newVal, sizeof(newVal));
+  if (rv < 0) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return NS_OK;
+}
+
+#if defined(DEBUG)
+static bool IsTCSMEnabled() {
+  uint32_t oldVal = 0;
+  size_t oldValSize = sizeof(oldVal);
+  int rv = sysctlbyname("kern.tcsm_enable", &oldVal, &oldValSize, NULL, 0);
+  return (rv == 0) && (oldVal != 0);
+}
+#endif
+
+/*
+ * Intentionally return void so that failures will be ignored in non-debug
+ * builds. This method uses new sysctls which may not be as thoroughly tested
+ * and we don't want to cause crashes handling the failure due to an OS bug.
+ */
+/* static */
+void nsMacUtilsImpl::EnableTCSMIfAvailable() {
+  if (IsTCSMAvailable()) {
+    if (NS_FAILED(EnableTCSM())) {
+      NS_WARNING("Failed to enable TCSM");
+    }
+    MOZ_ASSERT(IsTCSMEnabled());
+  }
+}
+
+// Returns 0 on error.
+/* static */
+uint32_t nsMacUtilsImpl::GetPhysicalCPUCount() {
+  uint32_t oldVal = 0;
+  size_t oldValSize = sizeof(oldVal);
+  int rv = sysctlbyname("hw.physicalcpu_max", &oldVal, &oldValSize, NULL, 0);
+  if (rv == -1) {
+    return 0;
+  }
+  return oldVal;
+}
+
+/*
+ * Helper function to read a string value for a given key from the .app's
+ * Info.plist.
+ */
+static nsresult GetStringValueFromBundlePlist(const nsAString& aKey,
+                                              nsAutoCString& aValue) {
+  CFBundleRef mainBundle = CFBundleGetMainBundle();
+  if (mainBundle == nullptr) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Read this app's bundle Info.plist as a dictionary
+  CFDictionaryRef bundleInfoDict = CFBundleGetInfoDictionary(mainBundle);
+  if (bundleInfoDict == nullptr) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAutoCString keyAutoCString = NS_ConvertUTF16toUTF8(aKey);
+  CFStringRef key = CFStringCreateWithCString(
+      kCFAllocatorDefault, keyAutoCString.get(), kCFStringEncodingUTF8);
+  if (key == nullptr) {
+    return NS_ERROR_FAILURE;
+  }
+
+  CFStringRef value = (CFStringRef)CFDictionaryGetValue(bundleInfoDict, key);
+  CFRelease(key);
+  if (value == nullptr) {
+    return NS_ERROR_FAILURE;
+  }
+
+  CFIndex valueLength = CFStringGetLength(value);
+  if (valueLength == 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  const char* valueCString =
+      CFStringGetCStringPtr(value, kCFStringEncodingUTF8);
+  if (valueCString) {
+    aValue.Assign(valueCString);
+    return NS_OK;
+  }
+
+  CFIndex maxLength =
+      CFStringGetMaximumSizeForEncoding(valueLength, kCFStringEncodingUTF8) + 1;
+  char* valueBuffer = static_cast<char*>(moz_xmalloc(maxLength));
+
+  if (!CFStringGetCString(value, valueBuffer, maxLength,
+                          kCFStringEncodingUTF8)) {
+    free(valueBuffer);
+    return NS_ERROR_FAILURE;
+  }
+
+  aValue.Assign(valueBuffer);
+  free(valueBuffer);
+  return NS_OK;
+}
+
+/*
+ * Helper function for reading a path string from the .app's Info.plist
+ * and returning a directory object for that path with symlinks resolved.
+ */
+static nsresult GetDirFromBundlePlist(const nsAString& aKey, nsIFile** aDir) {
+  nsresult rv;
+
+  nsAutoCString dirPath;
+  rv = GetStringValueFromBundlePlist(aKey, dirPath);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIFile> dir;
+  rv = NS_NewLocalFile(NS_ConvertUTF8toUTF16(dirPath), false,
+                       getter_AddRefs(dir));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = dir->Normalize();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  bool isDirectory = false;
+  rv = dir->IsDirectory(&isDirectory);
+  NS_ENSURE_SUCCESS(rv, rv);
+  if (!isDirectory) {
+    return NS_ERROR_FILE_NOT_DIRECTORY;
+  }
+
+  dir.swap(*aDir);
+  return NS_OK;
+}
+
+nsresult nsMacUtilsImpl::GetRepoDir(nsIFile** aRepoDir) {
+#if defined(MOZ_SANDBOX)
+  MOZ_ASSERT(!mozilla::IsPackagedBuild());
+#endif
+  return GetDirFromBundlePlist(NS_LITERAL_STRING_FROM_CSTRING(MAC_DEV_REPO_KEY),
+                               aRepoDir);
+}
+
+nsresult nsMacUtilsImpl::GetObjDir(nsIFile** aObjDir) {
+#if defined(MOZ_SANDBOX)
+  MOZ_ASSERT(!mozilla::IsPackagedBuild());
+#endif
+  return GetDirFromBundlePlist(NS_LITERAL_STRING_FROM_CSTRING(MAC_DEV_OBJ_KEY),
+                               aObjDir);
+}
+
+/* static */
+nsresult nsMacUtilsImpl::GetArchitecturesForBundle(uint32_t* aArchMask) {
+  MOZ_ASSERT(aArchMask);
+
+  *aArchMask = sBundleArchMaskAtomic;
+  if (*aArchMask != 0) {
+    return NS_OK;
+  }
+
+  CFBundleRef mainBundle = ::CFBundleGetMainBundle();
+  if (!mainBundle) {
+    return NS_ERROR_FAILURE;
+  }
+
+  CFArrayRef archList = ::CFBundleCopyExecutableArchitectures(mainBundle);
+  if (!archList) {
+    return NS_ERROR_FAILURE;
+  }
+
+  CFIndex archCount = ::CFArrayGetCount(archList);
+  for (CFIndex i = 0; i < archCount; i++) {
+    CFNumberRef arch =
+        static_cast<CFNumberRef>(::CFArrayGetValueAtIndex(archList, i));
+
+    int archInt = 0;
+    if (!::CFNumberGetValue(arch, kCFNumberIntType, &archInt)) {
+      ::CFRelease(archList);
+      return NS_ERROR_FAILURE;
+    }
+
+    if (archInt == kCFBundleExecutableArchitecturePPC) {
+      *aArchMask |= base::PROCESS_ARCH_PPC;
+    } else if (archInt == kCFBundleExecutableArchitectureI386) {
+      *aArchMask |= base::PROCESS_ARCH_I386;
+    } else if (archInt == kCFBundleExecutableArchitecturePPC64) {
+      *aArchMask |= base::PROCESS_ARCH_PPC_64;
+    } else if (archInt == kCFBundleExecutableArchitectureX86_64) {
+      *aArchMask |= base::PROCESS_ARCH_X86_64;
+    } else if (archInt == kCFBundleExecutableArchitectureARM64) {
+      *aArchMask |= base::PROCESS_ARCH_ARM_64;
+    }
+  }
+
+  ::CFRelease(archList);
+
+  sBundleArchMaskAtomic = *aArchMask;
+
+  return NS_OK;
+}
+
+/* static */
+nsresult nsMacUtilsImpl::GetArchitecturesForBinary(const char* aPath,
+                                                   uint32_t* aArchMask) {
+  MOZ_ASSERT(aArchMask);
+
+  *aArchMask = 0;
+
+  CFURLRef url = ::CFURLCreateFromFileSystemRepresentation(
+      kCFAllocatorDefault, (const UInt8*)aPath, strlen(aPath), false);
+  if (!url) {
+    return NS_ERROR_FAILURE;
+  }
+
+  CFArrayRef archs = ::CFBundleCopyExecutableArchitecturesForURL(url);
+  if (!archs) {
+    CFRelease(url);
+    return NS_ERROR_FAILURE;
+  }
+
+  CFIndex archCount = ::CFArrayGetCount(archs);
+  for (CFIndex i = 0; i < archCount; i++) {
+    CFNumberRef currentArch =
+        static_cast<CFNumberRef>(::CFArrayGetValueAtIndex(archs, i));
+    int currentArchInt = 0;
+    if (!::CFNumberGetValue(currentArch, kCFNumberIntType, &currentArchInt)) {
+      continue;
+    }
+    switch (currentArchInt) {
+      case kCFBundleExecutableArchitectureX86_64:
+        *aArchMask |= base::PROCESS_ARCH_X86_64;
+        break;
+      case kCFBundleExecutableArchitectureARM64:
+        *aArchMask |= base::PROCESS_ARCH_ARM_64;
+        break;
+      default:
+        break;
+    }
+  }
+
+  CFRelease(url);
+  CFRelease(archs);
+
+  // We expect x86 or ARM64 or both.
+  if (*aArchMask == 0) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  return NS_OK;
+}
+
+#if defined(__aarch64__)
+// Pre-translate XUL so that x64 child processes launched after this
+// translation will not incur the translation overhead delaying startup.
+// Returns 1 if translation is in progress, -1 on an error encountered before
+// translation, and otherwise returns the result of rosetta_translate_binaries.
+/* static */
+int nsMacUtilsImpl::PreTranslateXUL() {
+  bool expected = false;
+  if (!sIsXULTranslated.compare_exchange_strong(expected, true)) {
+    // Translation is already done or in progress.
+    return 1;
+  }
+
+  // Get the path to XUL by first getting the
+  // outer .app path and appending the path to XUL.
+  nsCString xulPath;
+  if (!GetAppPath(xulPath)) {
+    return -1;
+  }
+  xulPath.Append("/Contents/MacOS/XUL");
+
+  return PreTranslateBinary(xulPath);
+}
+
+// Use Chromium's method to pre-translate the provided binary using the
+// undocumented function "rosetta_translate_binaries" from libRosetta.dylib.
+// Re-translating the same binary does not cause translation to occur again.
+// Returns -1 on an error encountered before translation, otherwise returns
+// the rosetta_translate_binaries result. This method is partly copied from
+// Chromium code.
+/* static */
+int nsMacUtilsImpl::PreTranslateBinary(nsCString aBinaryPath) {
+  // Do not attempt to use this in child processes. Child
+  // processes executing should already be translated and
+  // sandboxing may interfere with translation.
+  MOZ_ASSERT(XRE_IsParentProcess());
+  if (!XRE_IsParentProcess()) {
+    return -1;
+  }
+
+  // Translation can take several seconds and therefore
+  // should not be done on the main thread.
+  MOZ_ASSERT(!NS_IsMainThread());
+  if (NS_IsMainThread()) {
+    return -1;
+  }
+
+  // @available() is not available for macOS 11 at this time so use
+  // -Wunguarded-availability-new to avoid compiler warnings caused
+  // by an earlier minimum SDK. ARM64 builds require the 11.0 SDK and
+  // can not be run on earlier OS versions so this is not a concern.
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Wunguarded-availability-new"
+  // If Rosetta is not installed, do not proceed.
+  if (!CFBundleIsArchitectureLoadable(CPU_TYPE_X86_64)) {
+    return -1;
+  }
+#  pragma clang diagnostic pop
+
+  if (aBinaryPath.IsEmpty()) {
+    return -1;
+  }
+
+  // int rosetta_translate_binaries(const char*[] paths, int npaths)
+  using rosetta_translate_binaries_t = int (*)(const char*[], int);
+
+  static auto rosetta_translate_binaries = []() {
+    void* libRosetta =
+        dlopen("/usr/lib/libRosetta.dylib", RTLD_LAZY | RTLD_LOCAL);
+    if (!libRosetta) {
+      return static_cast<rosetta_translate_binaries_t>(nullptr);
+    }
+
+    return reinterpret_cast<rosetta_translate_binaries_t>(
+        dlsym(libRosetta, "rosetta_translate_binaries"));
+  }();
+
+  if (!rosetta_translate_binaries) {
+    return -1;
+  }
+
+  const char* pathPtr = aBinaryPath.get();
+  return rosetta_translate_binaries(&pathPtr, 1);
+}
+
+#endif
diff --git a/xpcom/base/nsMacUtilsImpl.h b/xpcom/base/nsMacUtilsImpl.h
new file mode 100644
index 0000000000..9a20b539d1
--- /dev/null
+++ b/xpcom/base/nsMacUtilsImpl.h
@@ -0,0 +1,55 @@
+/* -*- 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/. */
+
+#ifndef nsMacUtilsImpl_h___
+#define nsMacUtilsImpl_h___
+
+#include "nsString.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/StaticMutex.h"
+#include "mozilla/StaticPtr.h"
+
+using mozilla::Atomic;
+using mozilla::StaticAutoPtr;
+using mozilla::StaticMutex;
+
+class nsIFile;
+
+namespace nsMacUtilsImpl {
+
+// Return the repo directory and the repo object directory respectively.
+// These should only be used on Mac developer builds to determine the path
+// to the repo or object directory.
+nsresult GetRepoDir(nsIFile** aRepoDir);
+nsresult GetObjDir(nsIFile** aObjDir);
+
+#if defined(MOZ_SANDBOX) || defined(__aarch64__)
+bool GetAppPath(nsCString& aAppPath);
+#endif /* MOZ_SANDBOX || __aarch64__ */
+
+#if defined(MOZ_SANDBOX) && defined(DEBUG)
+nsresult GetBloatLogDir(nsCString& aDirectoryPath);
+nsresult GetDirectoryPath(const char* aPath, nsCString& aDirectoryPath);
+#endif /* MOZ_SANDBOX && DEBUG */
+
+void EnableTCSMIfAvailable();
+bool IsTCSMAvailable();
+uint32_t GetPhysicalCPUCount();
+nsresult GetArchitecturesForBundle(uint32_t* aArchMask);
+nsresult GetArchitecturesForBinary(const char* aPath, uint32_t* aArchMask);
+
+#if defined(__aarch64__)
+// Pre-translate binaries to avoid translation delays when launching
+// x64 child process instances for the first time. i.e. on first launch
+// after installation or after an update. Translations are cached so
+// repeated launches of the binaries do not encounter delays.
+int PreTranslateXUL();
+int PreTranslateBinary(nsCString aBinaryPath);
+#endif
+}  // namespace nsMacUtilsImpl
+
+#endif /* nsMacUtilsImpl_h___ */
diff --git a/xpcom/base/nsMaybeWeakPtr.h b/xpcom/base/nsMaybeWeakPtr.h
new file mode 100644
index 0000000000..165a8c23c1
--- /dev/null
+++ b/xpcom/base/nsMaybeWeakPtr.h
@@ -0,0 +1,170 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#ifndef nsMaybeWeakPtr_h_
+#define nsMaybeWeakPtr_h_
+
+#include "mozilla/Attributes.h"
+#include "nsCOMPtr.h"
+#include "nsIWeakReferenceUtils.h"
+#include "nsTArray.h"
+#include "nsCycleCollectionNoteChild.h"
+
+// nsMaybeWeakPtr is a helper object to hold a strong-or-weak reference
+// to the template class.  It's pretty minimal, but sufficient.
+
+template <class T>
+class nsMaybeWeakPtr {
+ public:
+  nsMaybeWeakPtr() = default;
+  MOZ_IMPLICIT nsMaybeWeakPtr(T* aRef) : mPtr(aRef), mWeak(false) {}
+  MOZ_IMPLICIT nsMaybeWeakPtr(const nsCOMPtr<nsIWeakReference>& aRef)
+      : mPtr(aRef), mWeak(true) {}
+
+  nsMaybeWeakPtr<T>& operator=(T* aRef) {
+    mPtr = aRef;
+    mWeak = false;
+    return *this;
+  }
+
+  nsMaybeWeakPtr<T>& operator=(const nsCOMPtr<nsIWeakReference>& aRef) {
+    mPtr = aRef;
+    mWeak = true;
+    return *this;
+  }
+
+  bool operator==(const nsMaybeWeakPtr<T>& other) const {
+    return mPtr == other.mPtr;
+  }
+
+  nsISupports* GetRawValue() const { return mPtr.get(); }
+  bool IsWeak() const { return mWeak; }
+
+  const nsCOMPtr<T> GetValue() const;
+
+ private:
+  nsCOMPtr<nsISupports> mPtr;
+  bool mWeak;
+};
+
+// nsMaybeWeakPtrArray is an array of MaybeWeakPtr objects, that knows how to
+// grab a weak reference to a given object if requested.  It only allows a
+// given object to appear in the array once.
+
+template <class T>
+class nsMaybeWeakPtrArray : public CopyableTArray<nsMaybeWeakPtr<T>> {
+  typedef nsTArray<nsMaybeWeakPtr<T>> MaybeWeakArray;
+
+  nsresult SetMaybeWeakPtr(nsMaybeWeakPtr<T>& aRef, T* aElement,
+                           bool aOwnsWeak) {
+    nsresult rv = NS_OK;
+
+    if (aOwnsWeak) {
+      aRef = do_GetWeakReference(aElement, &rv);
+    } else {
+      aRef = aElement;
+    }
+
+    return rv;
+  }
+
+ public:
+  nsresult AppendWeakElement(T* aElement, bool aOwnsWeak) {
+    nsMaybeWeakPtr<T> ref;
+    MOZ_TRY(SetMaybeWeakPtr(ref, aElement, aOwnsWeak));
+
+    MaybeWeakArray::AppendElement(ref);
+    return NS_OK;
+  }
+
+  nsresult AppendWeakElementUnlessExists(T* aElement, bool aOwnsWeak) {
+    nsMaybeWeakPtr<T> ref;
+    MOZ_TRY(SetMaybeWeakPtr(ref, aElement, aOwnsWeak));
+
+    if (MaybeWeakArray::Contains(ref)) {
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    MaybeWeakArray::AppendElement(ref);
+    return NS_OK;
+  }
+
+  nsresult RemoveWeakElement(T* aElement) {
+    if (MaybeWeakArray::RemoveElement(aElement)) {
+      return NS_OK;
+    }
+
+    // Don't use do_GetWeakReference; it should only be called if we know
+    // the object supports weak references.
+    nsCOMPtr<nsISupportsWeakReference> supWeakRef = do_QueryInterface(aElement);
+    if (!supWeakRef) {
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    nsCOMPtr<nsIWeakReference> weakRef;
+    nsresult rv = supWeakRef->GetWeakReference(getter_AddRefs(weakRef));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (MaybeWeakArray::RemoveElement(weakRef)) {
+      return NS_OK;
+    }
+
+    return NS_ERROR_INVALID_ARG;
+  }
+};
+
+template <class T>
+const nsCOMPtr<T> nsMaybeWeakPtr<T>::GetValue() const {
+  if (!mPtr) {
+    return nullptr;
+  }
+
+  nsCOMPtr<T> ref;
+  nsresult rv;
+
+  if (mWeak) {
+    nsCOMPtr<nsIWeakReference> weakRef = do_QueryInterface(mPtr);
+    if (weakRef) {
+      ref = do_QueryReferent(weakRef, &rv);
+      if (NS_SUCCEEDED(rv)) {
+        return ref;
+      }
+    }
+  } else {
+    ref = do_QueryInterface(mPtr, &rv);
+    if (NS_SUCCEEDED(rv)) {
+      return ref;
+    }
+  }
+
+  return nullptr;
+}
+
+template <typename T>
+inline void ImplCycleCollectionUnlink(nsMaybeWeakPtrArray<T>& aField) {
+  aField.Clear();
+}
+
+template <typename E>
+inline void ImplCycleCollectionTraverse(
+    nsCycleCollectionTraversalCallback& aCallback,
+    nsMaybeWeakPtrArray<E>& aField, const char* aName, uint32_t aFlags = 0) {
+  aFlags |= CycleCollectionEdgeNameArrayFlag;
+  size_t length = aField.Length();
+  for (size_t i = 0; i < length; ++i) {
+    CycleCollectionNoteChild(aCallback, aField[i].GetRawValue(), aName, aFlags);
+  }
+}
+
+// Call a method on each element in the array, but only if the element is
+// non-null.
+
+#define ENUMERATE_WEAKARRAY(array, type, method)                          \
+  for (uint32_t array_idx = 0; array_idx < array.Length(); ++array_idx) { \
+    const nsCOMPtr<type>& e = array.ElementAt(array_idx).GetValue();      \
+    if (e) e->method;                                                     \
+  }
+
+#endif
diff --git a/xpcom/base/nsMemory.h b/xpcom/base/nsMemory.h
new file mode 100644
index 0000000000..7fda7ae837
--- /dev/null
+++ b/xpcom/base/nsMemory.h
@@ -0,0 +1,62 @@
+/* -*- 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/. */
+
+#ifndef nsMemory_h__
+#define nsMemory_h__
+
+#include "nsError.h"
+
+/**
+ *
+ * A client that wishes to be notified of low memory situations (for
+ * example, because the client maintains a large memory cache that
+ * could be released when memory is tight) should register with the
+ * observer service (see nsIObserverService) using the topic
+ * "memory-pressure".  There are specific types of notifications
+ * that can occur.  These types will be passed as the |aData|
+ * parameter of the of the "memory-pressure" notification:
+ *
+ * "low-memory"
+ * This will be passed as the extra data when the pressure
+ * observer is being asked to flush for low-memory conditions.
+ *
+ * "low-memory-ongoing"
+ * This will be passed when we continue to be in a low-memory
+ * condition and we want to flush caches and do other cheap
+ * forms of memory minimization, but heavy handed approaches like
+ * a GC are unlikely to succeed.
+ *
+ * "heap-minimize"
+ * This will be passed as the extra data when the pressure
+ * observer is being asked to flush because of a heap minimize
+ * call.
+ */
+
+// This is implemented in nsMemoryImpl.cpp.
+
+namespace nsMemory {
+
+/**
+ * Attempts to shrink the heap.
+ * @param immediate - if true, heap minimization will occur
+ *   immediately if the call was made on the main thread. If
+ *   false, the flush will be scheduled to happen when the app is
+ *   idle.
+ * @throws NS_ERROR_FAILURE if 'immediate' is set and the call
+ *   was not on the application's main thread.
+ */
+nsresult HeapMinimize(bool aImmediate);
+
+/**
+ * This predicate can be used to determine if the platform is a "low-memory"
+ * platform. Callers may use this to dynamically tune their behaviour
+ * to favour reduced memory usage at the expense of performance. The value
+ * returned by this function will not change over the lifetime of the process.
+ */
+bool IsLowMemoryPlatform();
+}  // namespace nsMemory
+
+#endif  // nsMemory_h__
diff --git a/xpcom/base/nsMemoryImpl.cpp b/xpcom/base/nsMemoryImpl.cpp
new file mode 100644
index 0000000000..4996d27c7a
--- /dev/null
+++ b/xpcom/base/nsMemoryImpl.cpp
@@ -0,0 +1,131 @@
+/* -*- 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 "nsMemory.h"
+#include "nsThreadUtils.h"
+
+#include "nsIObserver.h"
+#include "nsIObserverService.h"
+#include "nsIRunnable.h"
+#include "nsISimpleEnumerator.h"
+
+#include "nsCOMPtr.h"
+#include "mozilla/Services.h"
+#include "mozilla/Atomics.h"
+
+#ifdef ANDROID
+#  include <stdio.h>
+
+// Minimum memory threshold for a device to be considered
+// a low memory platform. This value has be in sync with
+// Java's equivalent threshold, defined in HardwareUtils.java
+#  define LOW_MEMORY_THRESHOLD_KB (384 * 1024)
+#endif
+
+static mozilla::Atomic<bool> sIsFlushing;
+static PRIntervalTime sLastFlushTime = 0;
+
+// static
+bool nsMemory::IsLowMemoryPlatform() {
+#ifdef ANDROID
+  static int sLowMemory =
+      -1;  // initialize to unknown, lazily evaluate to 0 or 1
+  if (sLowMemory == -1) {
+    sLowMemory = 0;  // assume "not low memory" in case file operations fail
+
+    // check if MemTotal from /proc/meminfo is less than LOW_MEMORY_THRESHOLD_KB
+    FILE* fd = fopen("/proc/meminfo", "r");
+    if (!fd) {
+      return false;
+    }
+    uint64_t mem = 0;
+    int rv = fscanf(fd, "MemTotal: %" PRIu64 " kB", &mem);
+    if (fclose(fd)) {
+      return false;
+    }
+    if (rv != 1) {
+      return false;
+    }
+    sLowMemory = (mem < LOW_MEMORY_THRESHOLD_KB) ? 1 : 0;
+  }
+  return (sLowMemory == 1);
+#else
+  return false;
+#endif
+}
+
+static void RunFlushers(const char16_t* aReason) {
+  nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
+  if (os) {
+    // Instead of:
+    //  os->NotifyObservers(this, "memory-pressure", aReason);
+    // we are going to do this manually to see who/what is
+    // deallocating.
+
+    nsCOMPtr<nsISimpleEnumerator> e;
+    os->EnumerateObservers("memory-pressure", getter_AddRefs(e));
+
+    if (e) {
+      nsCOMPtr<nsIObserver> observer;
+      bool loop = true;
+
+      while (NS_SUCCEEDED(e->HasMoreElements(&loop)) && loop) {
+        nsCOMPtr<nsISupports> supports;
+        e->GetNext(getter_AddRefs(supports));
+
+        if (!supports) {
+          continue;
+        }
+
+        observer = do_QueryInterface(supports);
+        observer->Observe(observer, "memory-pressure", aReason);
+      }
+    }
+  }
+
+  sIsFlushing = false;
+}
+
+static nsresult FlushMemory(const char16_t* aReason, bool aImmediate) {
+  if (aImmediate) {
+    // They've asked us to run the flusher *immediately*. We've
+    // got to be on the UI main thread for us to be able to do
+    // that...are we?
+    if (!NS_IsMainThread()) {
+      NS_ERROR("can't synchronously flush memory: not on UI thread");
+      return NS_ERROR_FAILURE;
+    }
+  }
+
+  bool lastVal = sIsFlushing.exchange(true);
+  if (lastVal) {
+    return NS_OK;
+  }
+
+  PRIntervalTime now = PR_IntervalNow();
+
+  // Run the flushers immediately if we can; otherwise, proxy to the
+  // UI thread and run 'em asynchronously.
+  nsresult rv = NS_OK;
+  if (aImmediate) {
+    RunFlushers(aReason);
+  } else {
+    // Don't broadcast more than once every 1000ms to avoid being noisy
+    if (PR_IntervalToMicroseconds(now - sLastFlushTime) > 1000) {
+      nsCOMPtr<nsIRunnable> runnable(NS_NewRunnableFunction(
+          "FlushMemory",
+          [reason = aReason]() -> void { RunFlushers(reason); }));
+      NS_DispatchToMainThread(runnable.forget());
+    }
+  }
+
+  sLastFlushTime = now;
+  return rv;
+}
+
+nsresult nsMemory::HeapMinimize(bool aImmediate) {
+  return FlushMemory(u"heap-minimize", aImmediate);
+}
diff --git a/xpcom/base/nsMemoryInfoDumper.cpp b/xpcom/base/nsMemoryInfoDumper.cpp
new file mode 100644
index 0000000000..28af408178
--- /dev/null
+++ b/xpcom/base/nsMemoryInfoDumper.cpp
@@ -0,0 +1,742 @@
+/* -*- 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 "mozilla/JSONWriter.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/nsMemoryInfoDumper.h"
+#include "mozilla/DebugOnly.h"
+#include "nsDumpUtils.h"
+
+#include "mozilla/Unused.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/dom/ContentChild.h"
+#include "nsIConsoleService.h"
+#include "nsCycleCollector.h"
+#include "nsICycleCollectorListener.h"
+#include "nsIMemoryReporter.h"
+#include "nsDirectoryServiceDefs.h"
+#include "nsGZFileWriter.h"
+#include "nsJSEnvironment.h"
+#include "nsPrintfCString.h"
+#include "nsServiceManagerUtils.h"
+#include "nsIFile.h"
+
+#ifdef XP_WIN
+#  include <process.h>
+#  ifndef getpid
+#    define getpid _getpid
+#  endif
+#else
+#  include <unistd.h>
+#endif
+
+#ifdef XP_UNIX
+#  define MOZ_SUPPORTS_FIFO 1
+#endif
+
+// Some Android devices seem to send RT signals to Firefox so we want to avoid
+// consuming those as they're not user triggered.
+#if !defined(ANDROID) && (defined(XP_LINUX) || defined(__FreeBSD__))
+#  define MOZ_SUPPORTS_RT_SIGNALS 1
+#endif
+
+#if defined(MOZ_SUPPORTS_RT_SIGNALS)
+#  include <fcntl.h>
+#  include <sys/types.h>
+#  include <sys/stat.h>
+#endif
+
+#if defined(MOZ_SUPPORTS_FIFO)
+#  include "mozilla/Preferences.h"
+#endif
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+namespace {
+
+class DumpMemoryInfoToTempDirRunnable : public Runnable {
+ public:
+  DumpMemoryInfoToTempDirRunnable(const nsAString& aIdentifier, bool aAnonymize,
+                                  bool aMinimizeMemoryUsage)
+      : mozilla::Runnable("DumpMemoryInfoToTempDirRunnable"),
+        mIdentifier(aIdentifier),
+        mAnonymize(aAnonymize),
+        mMinimizeMemoryUsage(aMinimizeMemoryUsage) {}
+
+  NS_IMETHOD Run() override {
+    nsCOMPtr<nsIMemoryInfoDumper> dumper =
+        do_GetService("@mozilla.org/memory-info-dumper;1");
+    dumper->DumpMemoryInfoToTempDir(mIdentifier, mAnonymize,
+                                    mMinimizeMemoryUsage);
+    return NS_OK;
+  }
+
+ private:
+  const nsString mIdentifier;
+  const bool mAnonymize;
+  const bool mMinimizeMemoryUsage;
+};
+
+class GCAndCCLogDumpRunnable final : public Runnable,
+                                     public nsIDumpGCAndCCLogsCallback {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+
+  GCAndCCLogDumpRunnable(const nsAString& aIdentifier, bool aDumpAllTraces,
+                         bool aDumpChildProcesses)
+      : mozilla::Runnable("GCAndCCLogDumpRunnable"),
+        mIdentifier(aIdentifier),
+        mDumpAllTraces(aDumpAllTraces),
+        mDumpChildProcesses(aDumpChildProcesses) {}
+
+  NS_IMETHOD Run() override {
+    nsCOMPtr<nsIMemoryInfoDumper> dumper =
+        do_GetService("@mozilla.org/memory-info-dumper;1");
+
+    dumper->DumpGCAndCCLogsToFile(mIdentifier, mDumpAllTraces,
+                                  mDumpChildProcesses, this);
+    return NS_OK;
+  }
+
+  NS_IMETHOD OnDump(nsIFile* aGCLog, nsIFile* aCCLog, bool aIsParent) override {
+    return NS_OK;
+  }
+
+  NS_IMETHOD OnFinish() override { return NS_OK; }
+
+ private:
+  ~GCAndCCLogDumpRunnable() = default;
+
+  const nsString mIdentifier;
+  const bool mDumpAllTraces;
+  const bool mDumpChildProcesses;
+};
+
+NS_IMPL_ISUPPORTS_INHERITED(GCAndCCLogDumpRunnable, Runnable,
+                            nsIDumpGCAndCCLogsCallback)
+
+}  // namespace
+
+#if defined(MOZ_SUPPORTS_RT_SIGNALS)  // {
+namespace {
+
+/*
+ * The following code supports dumping about:memory upon receiving a signal.
+ *
+ * We listen for the following signals:
+ *
+ *  - SIGRTMIN:     Dump our memory reporters (and those of our child
+ *                  processes),
+ *  - SIGRTMIN + 1: Dump our memory reporters (and those of our child
+ *                  processes) after minimizing memory usage, and
+ *  - SIGRTMIN + 2: Dump the GC and CC logs in this and our child processes.
+ *
+ * When we receive one of these signals, we write the signal number to a pipe.
+ * The IO thread then notices that the pipe has been written to, and kicks off
+ * the appropriate task on the main thread.
+ *
+ * This scheme is similar to using signalfd(), except it's portable and it
+ * doesn't require the use of sigprocmask, which is problematic because it
+ * masks signals received by child processes.
+ *
+ * In theory, we could use Chromium's MessageLoopForIO::CatchSignal() for this.
+ * But that uses libevent, which does not handle the realtime signals (bug
+ * 794074).
+ */
+
+// It turns out that at least on some systems, SIGRTMIN is not a compile-time
+// constant, so these have to be set at runtime.
+static uint8_t sDumpAboutMemorySignum;          // SIGRTMIN
+static uint8_t sDumpAboutMemoryAfterMMUSignum;  // SIGRTMIN + 1
+static uint8_t sGCAndCCDumpSignum;              // SIGRTMIN + 2
+
+void doMemoryReport(const uint8_t aRecvSig) {
+  // Dump our memory reports (but run this on the main thread!).
+  bool minimize = aRecvSig == sDumpAboutMemoryAfterMMUSignum;
+  LOG("SignalWatcher(sig %d) dispatching memory report runnable.", aRecvSig);
+  RefPtr<DumpMemoryInfoToTempDirRunnable> runnable =
+      new DumpMemoryInfoToTempDirRunnable(/* identifier = */ u""_ns,
+                                          /* anonymize = */ false, minimize);
+  NS_DispatchToMainThread(runnable);
+}
+
+void doGCCCDump(const uint8_t aRecvSig) {
+  LOG("SignalWatcher(sig %d) dispatching GC/CC log runnable.", aRecvSig);
+  // Dump GC and CC logs (from the main thread).
+  RefPtr<GCAndCCLogDumpRunnable> runnable =
+      new GCAndCCLogDumpRunnable(/* identifier = */ u""_ns,
+                                 /* allTraces = */ true,
+                                 /* dumpChildProcesses = */ true);
+  NS_DispatchToMainThread(runnable);
+}
+
+}  // namespace
+#endif  // MOZ_SUPPORTS_RT_SIGNALS }
+
+#if defined(MOZ_SUPPORTS_FIFO)  // {
+namespace {
+
+void doMemoryReport(const nsCString& aInputStr) {
+  bool minimize = aInputStr.EqualsLiteral("minimize memory report");
+  LOG("FifoWatcher(command:%s) dispatching memory report runnable.",
+      aInputStr.get());
+  RefPtr<DumpMemoryInfoToTempDirRunnable> runnable =
+      new DumpMemoryInfoToTempDirRunnable(/* identifier = */ u""_ns,
+                                          /* anonymize = */ false, minimize);
+  NS_DispatchToMainThread(runnable);
+}
+
+void doGCCCDump(const nsCString& aInputStr) {
+  bool doAllTracesGCCCDump = aInputStr.EqualsLiteral("gc log");
+  LOG("FifoWatcher(command:%s) dispatching GC/CC log runnable.",
+      aInputStr.get());
+  RefPtr<GCAndCCLogDumpRunnable> runnable = new GCAndCCLogDumpRunnable(
+      /* identifier = */ u""_ns, doAllTracesGCCCDump,
+      /* dumpChildProcesses = */ true);
+  NS_DispatchToMainThread(runnable);
+}
+
+bool SetupFifo() {
+#  ifdef DEBUG
+  static bool fifoCallbacksRegistered = false;
+#  endif
+
+  if (!FifoWatcher::MaybeCreate()) {
+    return false;
+  }
+
+  MOZ_ASSERT(!fifoCallbacksRegistered,
+             "FifoWatcher callbacks should be registered only once");
+
+  FifoWatcher* fw = FifoWatcher::GetSingleton();
+  // Dump our memory reports (but run this on the main thread!).
+  fw->RegisterCallback("memory report"_ns, doMemoryReport);
+  fw->RegisterCallback("minimize memory report"_ns, doMemoryReport);
+  // Dump GC and CC logs (from the main thread).
+  fw->RegisterCallback("gc log"_ns, doGCCCDump);
+  fw->RegisterCallback("abbreviated gc log"_ns, doGCCCDump);
+
+#  ifdef DEBUG
+  fifoCallbacksRegistered = true;
+#  endif
+  return true;
+}
+
+void OnFifoEnabledChange(const char* /*unused*/, void* /*unused*/) {
+  LOG("%s changed", FifoWatcher::kPrefName);
+  if (SetupFifo()) {
+    Preferences::UnregisterCallback(OnFifoEnabledChange,
+                                    FifoWatcher::kPrefName);
+  }
+}
+
+}  // namespace
+#endif  // MOZ_SUPPORTS_FIFO }
+
+NS_IMPL_ISUPPORTS(nsMemoryInfoDumper, nsIMemoryInfoDumper)
+
+nsMemoryInfoDumper::nsMemoryInfoDumper() = default;
+
+nsMemoryInfoDumper::~nsMemoryInfoDumper() = default;
+
+/* static */
+void nsMemoryInfoDumper::Initialize() {
+#if defined(MOZ_SUPPORTS_RT_SIGNALS)
+  SignalPipeWatcher* sw = SignalPipeWatcher::GetSingleton();
+
+  // Dump memory reporters (and those of our child processes)
+  sDumpAboutMemorySignum = SIGRTMIN;
+  sw->RegisterCallback(sDumpAboutMemorySignum, doMemoryReport);
+  // Dump our memory reporters after minimizing memory usage
+  sDumpAboutMemoryAfterMMUSignum = SIGRTMIN + 1;
+  sw->RegisterCallback(sDumpAboutMemoryAfterMMUSignum, doMemoryReport);
+  // Dump the GC and CC logs in this and our child processes.
+  sGCAndCCDumpSignum = SIGRTMIN + 2;
+  sw->RegisterCallback(sGCAndCCDumpSignum, doGCCCDump);
+#endif
+
+#if defined(MOZ_SUPPORTS_FIFO)
+  if (!SetupFifo()) {
+    // NB: This gets loaded early enough that it's possible there is a user pref
+    //     set to enable the fifo watcher that has not been loaded yet. Register
+    //     to attempt to initialize if the fifo watcher becomes enabled by
+    //     a user pref.
+    Preferences::RegisterCallback(OnFifoEnabledChange, FifoWatcher::kPrefName);
+  }
+#endif
+}
+
+static void EnsureNonEmptyIdentifier(nsAString& aIdentifier) {
+  if (!aIdentifier.IsEmpty()) {
+    return;
+  }
+
+  // If the identifier is empty, set it to the number of whole seconds since the
+  // epoch.  This identifier will appear in the files that this process
+  // generates and also the files generated by this process's children, allowing
+  // us to identify which files are from the same memory report request.
+  aIdentifier.AppendInt(static_cast<int64_t>(PR_Now()) / 1000000);
+}
+
+// Use XPCOM refcounting to fire |onFinish| when all reference-holders
+// (remote dump actors or the |DumpGCAndCCLogsToFile| activation itself)
+// have gone away.
+class nsDumpGCAndCCLogsCallbackHolder final
+    : public nsIDumpGCAndCCLogsCallback {
+ public:
+  NS_DECL_ISUPPORTS
+
+  explicit nsDumpGCAndCCLogsCallbackHolder(
+      nsIDumpGCAndCCLogsCallback* aCallback)
+      : mCallback(aCallback) {}
+
+  NS_IMETHOD OnFinish() override { return NS_ERROR_UNEXPECTED; }
+
+  NS_IMETHOD OnDump(nsIFile* aGCLog, nsIFile* aCCLog, bool aIsParent) override {
+    return mCallback->OnDump(aGCLog, aCCLog, aIsParent);
+  }
+
+ private:
+  ~nsDumpGCAndCCLogsCallbackHolder() { Unused << mCallback->OnFinish(); }
+
+  nsCOMPtr<nsIDumpGCAndCCLogsCallback> mCallback;
+};
+
+NS_IMPL_ISUPPORTS(nsDumpGCAndCCLogsCallbackHolder, nsIDumpGCAndCCLogsCallback)
+
+NS_IMETHODIMP
+nsMemoryInfoDumper::DumpGCAndCCLogsToFile(
+    const nsAString& aIdentifier, bool aDumpAllTraces, bool aDumpChildProcesses,
+    nsIDumpGCAndCCLogsCallback* aCallback) {
+  nsString identifier(aIdentifier);
+  EnsureNonEmptyIdentifier(identifier);
+  nsCOMPtr<nsIDumpGCAndCCLogsCallback> callbackHolder =
+      new nsDumpGCAndCCLogsCallbackHolder(aCallback);
+
+  if (aDumpChildProcesses) {
+    nsTArray<ContentParent*> children;
+    ContentParent::GetAll(children);
+    for (uint32_t i = 0; i < children.Length(); i++) {
+      ContentParent* cp = children[i];
+      nsCOMPtr<nsICycleCollectorLogSink> logSink =
+          nsCycleCollector_createLogSink();
+
+      logSink->SetFilenameIdentifier(identifier);
+      logSink->SetProcessIdentifier(cp->Pid());
+
+      Unused << cp->CycleCollectWithLogs(aDumpAllTraces, logSink,
+                                         callbackHolder);
+    }
+  }
+
+  nsCOMPtr<nsICycleCollectorListener> logger = nsCycleCollector_createLogger();
+
+  if (aDumpAllTraces) {
+    nsCOMPtr<nsICycleCollectorListener> allTracesLogger;
+    logger->AllTraces(getter_AddRefs(allTracesLogger));
+    logger = allTracesLogger;
+  }
+
+  nsCOMPtr<nsICycleCollectorLogSink> logSink;
+  logger->GetLogSink(getter_AddRefs(logSink));
+
+  logSink->SetFilenameIdentifier(identifier);
+
+  nsJSContext::CycleCollectNow(CCReason::DUMP_HEAP, logger);
+
+  nsCOMPtr<nsIFile> gcLog, ccLog;
+  logSink->GetGcLog(getter_AddRefs(gcLog));
+  logSink->GetCcLog(getter_AddRefs(ccLog));
+  callbackHolder->OnDump(gcLog, ccLog, /* parent = */ true);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMemoryInfoDumper::DumpGCAndCCLogsToSink(bool aDumpAllTraces,
+                                          nsICycleCollectorLogSink* aSink) {
+  nsCOMPtr<nsICycleCollectorListener> logger = nsCycleCollector_createLogger();
+
+  if (aDumpAllTraces) {
+    nsCOMPtr<nsICycleCollectorListener> allTracesLogger;
+    logger->AllTraces(getter_AddRefs(allTracesLogger));
+    logger = allTracesLogger;
+  }
+
+  logger->SetLogSink(aSink);
+
+  nsJSContext::CycleCollectNow(CCReason::DUMP_HEAP, logger);
+
+  return NS_OK;
+}
+
+static void MakeFilename(const char* aPrefix, const nsAString& aIdentifier,
+                         int aPid, const char* aSuffix, nsACString& aResult) {
+  aResult =
+      nsPrintfCString("%s-%s-%d.%s", aPrefix,
+                      NS_ConvertUTF16toUTF8(aIdentifier).get(), aPid, aSuffix);
+}
+
+// This class wraps GZFileWriter so it can be used with JSONWriter, overcoming
+// the following two problems:
+// - It provides a JSONWriterFunc::Write() that calls nsGZFileWriter::Write().
+// - It can be stored as a UniquePtr, whereas nsGZFileWriter is refcounted.
+class GZWriterWrapper final : public JSONWriteFunc {
+ public:
+  explicit GZWriterWrapper(nsGZFileWriter* aGZWriter) : mGZWriter(aGZWriter) {}
+
+  void Write(const Span<const char>& aStr) final {
+    // Ignore any failure because JSONWriteFunc doesn't have a mechanism for
+    // handling errors.
+    Unused << mGZWriter->Write(aStr.data(), aStr.size());
+  }
+
+  nsresult Finish() { return mGZWriter->Finish(); }
+
+ private:
+  RefPtr<nsGZFileWriter> mGZWriter;
+};
+
+// We need two callbacks: one that handles reports, and one that is called at
+// the end of reporting. Both the callbacks need access to the same JSONWriter,
+// so we implement both of them in this one class.
+class HandleReportAndFinishReportingCallbacks final
+    : public nsIHandleReportCallback,
+      public nsIFinishReportingCallback {
+ public:
+  NS_DECL_ISUPPORTS
+
+  HandleReportAndFinishReportingCallbacks(
+      UniquePtr<JSONWriter> aWriter, nsIFinishDumpingCallback* aFinishDumping,
+      nsISupports* aFinishDumpingData)
+      : mWriter(std::move(aWriter)),
+        mFinishDumping(aFinishDumping),
+        mFinishDumpingData(aFinishDumpingData) {}
+
+  // This is the callback for nsIHandleReportCallback.
+  NS_IMETHOD Callback(const nsACString& aProcess, const nsACString& aPath,
+                      int32_t aKind, int32_t aUnits, int64_t aAmount,
+                      const nsACString& aDescription,
+                      nsISupports* aData) override {
+    nsAutoCString process;
+    if (aProcess.IsEmpty()) {
+      // If the process is empty, the report originated with the process doing
+      // the dumping.  In that case, generate the process identifier, which is
+      // of the form "$PROCESS_NAME (pid $PID)", or just "(pid $PID)" if we
+      // don't have a process name.  If we're the main process, we let
+      // $PROCESS_NAME be "Main Process".
+      //
+      // `appendAboutMemoryMain()` in aboutMemory.js does much the same thing
+      // for live memory reports.
+      if (XRE_IsParentProcess()) {
+        // We're the main process.
+        process.AssignLiteral("Main Process");
+      } else if (ContentChild* cc = ContentChild::GetSingleton()) {
+        // Try to get the process name from ContentChild.
+        cc->GetProcessName(process);
+      }
+      ContentChild::AppendProcessId(process);
+
+    } else {
+      // Otherwise, the report originated with another process and already has a
+      // process name.  Just use that.
+      process = aProcess;
+    }
+
+    mWriter->StartObjectElement();
+    {
+      mWriter->StringProperty("process", process);
+      mWriter->StringProperty("path", PromiseFlatCString(aPath));
+      mWriter->IntProperty("kind", aKind);
+      mWriter->IntProperty("units", aUnits);
+      mWriter->IntProperty("amount", aAmount);
+      mWriter->StringProperty("description", PromiseFlatCString(aDescription));
+    }
+    mWriter->EndObject();
+
+    return NS_OK;
+  }
+
+  // This is the callback for nsIFinishReportingCallback.
+  NS_IMETHOD Callback(nsISupports* aData) override {
+    mWriter->EndArray();  // end of "reports" array
+    mWriter->End();
+
+    // The call to Finish() deallocates the memory allocated by the first Write
+    // call. Because that memory was live while the memory reporters ran and
+    // was measured by them -- by "heap-allocated" if nothing else -- we want
+    // DMD to see it as well. So we deliberately don't call Finish() until
+    // after DMD finishes.
+    nsresult rv = static_cast<GZWriterWrapper&>(mWriter->WriteFunc()).Finish();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (!mFinishDumping) {
+      return NS_OK;
+    }
+
+    return mFinishDumping->Callback(mFinishDumpingData);
+  }
+
+ private:
+  ~HandleReportAndFinishReportingCallbacks() = default;
+
+  UniquePtr<JSONWriter> mWriter;
+  nsCOMPtr<nsIFinishDumpingCallback> mFinishDumping;
+  nsCOMPtr<nsISupports> mFinishDumpingData;
+};
+
+NS_IMPL_ISUPPORTS(HandleReportAndFinishReportingCallbacks,
+                  nsIHandleReportCallback, nsIFinishReportingCallback)
+
+class TempDirFinishCallback final : public nsIFinishDumpingCallback {
+ public:
+  NS_DECL_ISUPPORTS
+
+  TempDirFinishCallback(nsIFile* aReportsTmpFile,
+                        const nsCString& aReportsFinalFilename)
+      : mReportsTmpFile(aReportsTmpFile),
+        mReportsFilename(aReportsFinalFilename) {}
+
+  NS_IMETHOD Callback(nsISupports* aData) override {
+    // Rename the memory reports file, now that we're done writing all the
+    // files. Its final name is "memory-report<-identifier>-<pid>.json.gz".
+
+    nsCOMPtr<nsIFile> reportsFinalFile;
+    nsresult rv = NS_GetSpecialDirectory(NS_OS_TEMP_DIR,
+                                         getter_AddRefs(reportsFinalFile));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+#ifdef ANDROID
+    rv = reportsFinalFile->AppendNative("memory-reports"_ns);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+#endif
+
+    rv = reportsFinalFile->AppendNative(mReportsFilename);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    rv = reportsFinalFile->CreateUnique(nsIFile::NORMAL_FILE_TYPE, 0600);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    nsAutoString reportsFinalFilename;
+    rv = reportsFinalFile->GetLeafName(reportsFinalFilename);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    rv = mReportsTmpFile->MoveTo(/* directory */ nullptr, reportsFinalFilename);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    // Write a message to the console.
+
+    nsCOMPtr<nsIConsoleService> cs =
+        do_GetService(NS_CONSOLESERVICE_CONTRACTID, &rv);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    nsString path;
+    mReportsTmpFile->GetPath(path);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    nsString msg = u"nsIMemoryInfoDumper dumped reports to "_ns;
+    msg.Append(path);
+    return cs->LogStringMessage(msg.get());
+  }
+
+ private:
+  ~TempDirFinishCallback() = default;
+
+  nsCOMPtr<nsIFile> mReportsTmpFile;
+  nsCString mReportsFilename;
+};
+
+NS_IMPL_ISUPPORTS(TempDirFinishCallback, nsIFinishDumpingCallback)
+
+static nsresult DumpMemoryInfoToFile(nsIFile* aReportsFile,
+                                     nsIFinishDumpingCallback* aFinishDumping,
+                                     nsISupports* aFinishDumpingData,
+                                     bool aAnonymize, bool aMinimizeMemoryUsage,
+                                     nsAString& aDMDIdentifier) {
+  RefPtr<nsGZFileWriter> gzWriter = new nsGZFileWriter();
+  nsresult rv = gzWriter->Init(aReportsFile);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  auto jsonWriter =
+      MakeUnique<JSONWriter>(MakeUnique<GZWriterWrapper>(gzWriter));
+
+  nsCOMPtr<nsIMemoryReporterManager> mgr =
+      do_GetService("@mozilla.org/memory-reporter-manager;1");
+
+  // This is the first write to the file, and it causes |aWriter| to allocate
+  // over 200 KiB of memory.
+  jsonWriter->Start();
+  {
+    // Increment this number if the format changes.
+    jsonWriter->IntProperty("version", 1);
+    jsonWriter->BoolProperty("hasMozMallocUsableSize",
+                             mgr->GetHasMozMallocUsableSize());
+    jsonWriter->StartArrayProperty("reports");
+  }
+
+  RefPtr<HandleReportAndFinishReportingCallbacks>
+      handleReportAndFinishReporting =
+          new HandleReportAndFinishReportingCallbacks(
+              std::move(jsonWriter), aFinishDumping, aFinishDumpingData);
+  rv = mgr->GetReportsExtended(
+      handleReportAndFinishReporting, nullptr, handleReportAndFinishReporting,
+      nullptr, aAnonymize, aMinimizeMemoryUsage, aDMDIdentifier);
+  return rv;
+}
+
+NS_IMETHODIMP
+nsMemoryInfoDumper::DumpMemoryReportsToNamedFile(
+    const nsAString& aFilename, nsIFinishDumpingCallback* aFinishDumping,
+    nsISupports* aFinishDumpingData, bool aAnonymize,
+    bool aMinimizeMemoryUsage) {
+  MOZ_ASSERT(!aFilename.IsEmpty());
+
+  // Create the file.
+
+  nsCOMPtr<nsIFile> reportsFile;
+  nsresult rv = NS_NewLocalFile(aFilename, false, getter_AddRefs(reportsFile));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  reportsFile->InitWithPath(aFilename);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  bool exists;
+  rv = reportsFile->Exists(&exists);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (!exists) {
+    rv = reportsFile->Create(nsIFile::NORMAL_FILE_TYPE, 0644);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  nsString dmdIdent;
+  return DumpMemoryInfoToFile(reportsFile, aFinishDumping, aFinishDumpingData,
+                              aAnonymize, aMinimizeMemoryUsage, dmdIdent);
+}
+
+NS_IMETHODIMP
+nsMemoryInfoDumper::DumpMemoryInfoToTempDir(const nsAString& aIdentifier,
+                                            bool aAnonymize,
+                                            bool aMinimizeMemoryUsage) {
+  nsString identifier(aIdentifier);
+  EnsureNonEmptyIdentifier(identifier);
+
+  // Open a new file named something like
+  //
+  //   incomplete-memory-report-<identifier>-<pid>.json.gz
+  //
+  // in NS_OS_TEMP_DIR for writing.  When we're finished writing the report,
+  // we'll rename this file and get rid of the "incomplete-" prefix.
+  //
+  // We do this because we don't want scripts which poll the filesystem
+  // looking for memory report dumps to grab a file before we're finished
+  // writing to it.
+
+  // The "unified" indicates that we merge the memory reports from all
+  // processes and write out one file, rather than a separate file for
+  // each process as was the case before bug 946407.  This is so that
+  // the get_about_memory.py script in the B2G repository can
+  // determine when it's done waiting for files to appear.
+  nsCString reportsFinalFilename;
+  MakeFilename("unified-memory-report", identifier, getpid(), "json.gz",
+               reportsFinalFilename);
+
+  nsCOMPtr<nsIFile> reportsTmpFile;
+  nsresult rv;
+  // In Android case, this function will open a file named aFilename under
+  // specific folder (/data/local/tmp/memory-reports). Otherwise, it will
+  // open a file named aFilename under "NS_OS_TEMP_DIR".
+  rv = nsDumpUtils::OpenTempFile("incomplete-"_ns + reportsFinalFilename,
+                                 getter_AddRefs(reportsTmpFile),
+                                 "memory-reports"_ns);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  RefPtr<TempDirFinishCallback> finishDumping =
+      new TempDirFinishCallback(reportsTmpFile, reportsFinalFilename);
+
+  return DumpMemoryInfoToFile(reportsTmpFile, finishDumping, nullptr,
+                              aAnonymize, aMinimizeMemoryUsage, identifier);
+}
+
+#ifdef MOZ_DMD
+dmd::DMDFuncs::Singleton dmd::DMDFuncs::sSingleton;
+
+nsresult nsMemoryInfoDumper::OpenDMDFile(const nsAString& aIdentifier, int aPid,
+                                         FILE** aOutFile) {
+  if (!dmd::IsRunning()) {
+    *aOutFile = nullptr;
+    return NS_OK;
+  }
+
+  // Create a filename like dmd-<identifier>-<pid>.json.gz, which will be used
+  // if DMD is enabled.
+  nsCString dmdFilename;
+  MakeFilename("dmd", aIdentifier, aPid, "json.gz", dmdFilename);
+
+  // Open a new DMD file named |dmdFilename| in NS_OS_TEMP_DIR for writing,
+  // and dump DMD output to it.  This must occur after the memory reporters
+  // have been run (above), but before the memory-reports file has been
+  // renamed (so scripts can detect the DMD file, if present).
+
+  nsresult rv;
+  nsCOMPtr<nsIFile> dmdFile;
+  rv = nsDumpUtils::OpenTempFile(dmdFilename, getter_AddRefs(dmdFile),
+                                 "memory-reports"_ns);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  rv = dmdFile->OpenANSIFileDesc("wb", aOutFile);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "OpenANSIFileDesc failed");
+
+  // Print the path, because on some platforms (e.g. Mac) it's not obvious.
+  dmd::StatusMsg("opened %s for writing\n", dmdFile->HumanReadablePath().get());
+
+  return rv;
+}
+
+nsresult nsMemoryInfoDumper::DumpDMDToFile(FILE* aFile) {
+  RefPtr<nsGZFileWriter> gzWriter = new nsGZFileWriter();
+  nsresult rv = gzWriter->InitANSIFileDesc(aFile);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Dump DMD's memory reports analysis to the file.
+  dmd::Analyze(MakeUnique<GZWriterWrapper>(gzWriter));
+
+  rv = gzWriter->Finish();
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "Finish failed");
+  return rv;
+}
+#endif  // MOZ_DMD
diff --git a/xpcom/base/nsMemoryInfoDumper.h b/xpcom/base/nsMemoryInfoDumper.h
new file mode 100644
index 0000000000..68f6d46de7
--- /dev/null
+++ b/xpcom/base/nsMemoryInfoDumper.h
@@ -0,0 +1,48 @@
+/* -*- 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/. */
+
+#ifndef mozilla_nsMemoryInfoDumper_h
+#define mozilla_nsMemoryInfoDumper_h
+
+#include "nsIMemoryInfoDumper.h"
+#include <stdio.h>
+
+/**
+ * This class facilitates dumping information about our memory usage to disk.
+ *
+ * Its cpp file also has Linux-only code which watches various OS signals and
+ * dumps memory info upon receiving a signal.  You can activate these listeners
+ * by calling Initialize().
+ */
+class nsMemoryInfoDumper : public nsIMemoryInfoDumper {
+  virtual ~nsMemoryInfoDumper();
+
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIMEMORYINFODUMPER
+
+  nsMemoryInfoDumper();
+
+  static void Initialize();
+
+#ifdef MOZ_DMD
+  // Open an appropriately named file for a DMD report.  If DMD is
+  // disabled, return a null FILE* instead.
+  static nsresult OpenDMDFile(const nsAString& aIdentifier, int aPid,
+                              FILE** aOutFile);
+  // Write a DMD report to the given file and close it.
+  static nsresult DumpDMDToFile(FILE* aFile);
+#endif
+};
+
+#define NS_MEMORY_INFO_DUMPER_CID                    \
+  {                                                  \
+    0x00bd71fb, 0x7f09, 0x4ec3, {                    \
+      0x96, 0xaf, 0xa0, 0xb5, 0x22, 0xb7, 0x79, 0x69 \
+    }                                                \
+  }
+
+#endif
diff --git a/xpcom/base/nsMemoryReporterManager.cpp b/xpcom/base/nsMemoryReporterManager.cpp
new file mode 100644
index 0000000000..b3763d8f01
--- /dev/null
+++ b/xpcom/base/nsMemoryReporterManager.cpp
@@ -0,0 +1,2916 @@
+/* -*- 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 "nsMemoryReporterManager.h"
+
+#include "nsAtomTable.h"
+#include "nsCOMPtr.h"
+#include "nsCOMArray.h"
+#include "nsPrintfCString.h"
+#include "nsProxyRelease.h"
+#include "nsServiceManagerUtils.h"
+#include "nsITimer.h"
+#include "nsThreadUtils.h"
+#include "nsPIDOMWindow.h"
+#include "nsIObserverService.h"
+#include "nsIOService.h"
+#include "nsIGlobalObject.h"
+#include "nsIXPConnect.h"
+#ifdef MOZ_GECKO_PROFILER
+#  include "GeckoProfilerReporter.h"
+#endif
+#if defined(XP_UNIX) || defined(MOZ_DMD)
+#  include "nsMemoryInfoDumper.h"
+#endif
+#include "nsNetCID.h"
+#include "nsThread.h"
+#include "VRProcessManager.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/MemoryReportingProcess.h"
+#include "mozilla/PodOperations.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/RDDProcessManager.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/Services.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/UniquePtrExtensions.h"
+#include "mozilla/dom/MemoryReportTypes.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/gfx/GPUProcessManager.h"
+#include "mozilla/ipc/UtilityProcessManager.h"
+#include "mozilla/ipc/FileDescriptorUtils.h"
+#ifdef MOZ_PHC
+#  include "replace_malloc_bridge.h"
+#endif
+
+#ifdef MOZ_WIDGET_ANDROID
+#  include "mozilla/java/GeckoAppShellWrappers.h"
+#  include "mozilla/jni/Utils.h"
+#endif
+
+#ifdef XP_WIN
+#  include "mozilla/MemoryInfo.h"
+
+#  include <process.h>
+#  ifndef getpid
+#    define getpid _getpid
+#  endif
+#else
+#  include <unistd.h>
+#endif
+
+using namespace mozilla;
+using namespace mozilla::ipc;
+using namespace dom;
+
+#if defined(XP_LINUX)
+
+#  include "mozilla/MemoryMapping.h"
+
+#  include <malloc.h>
+#  include <string.h>
+#  include <stdlib.h>
+
+[[nodiscard]] static nsresult GetProcSelfStatmField(int aField, int64_t* aN) {
+  // There are more than two fields, but we're only interested in the first
+  // two.
+  static const int MAX_FIELD = 2;
+  size_t fields[MAX_FIELD];
+  MOZ_ASSERT(aField < MAX_FIELD, "bad field number");
+  FILE* f = fopen("/proc/self/statm", "r");
+  if (f) {
+    int nread = fscanf(f, "%zu %zu", &fields[0], &fields[1]);
+    fclose(f);
+    if (nread == MAX_FIELD) {
+      *aN = fields[aField] * getpagesize();
+      return NS_OK;
+    }
+  }
+  return NS_ERROR_FAILURE;
+}
+
+[[nodiscard]] static nsresult GetProcSelfSmapsPrivate(int64_t* aN, pid_t aPid) {
+  // You might be tempted to calculate USS by subtracting the "shared" value
+  // from the "resident" value in /proc/<pid>/statm. But at least on Linux,
+  // statm's "shared" value actually counts pages backed by files, which has
+  // little to do with whether the pages are actually shared. /proc/self/smaps
+  // on the other hand appears to give us the correct information.
+
+  nsTArray<MemoryMapping> mappings(1024);
+  MOZ_TRY(GetMemoryMappings(mappings, aPid));
+
+  int64_t amount = 0;
+  for (auto& mapping : mappings) {
+    amount += mapping.Private_Clean();
+    amount += mapping.Private_Dirty();
+  }
+  *aN = amount;
+  return NS_OK;
+}
+
+#  define HAVE_VSIZE_AND_RESIDENT_REPORTERS 1
+[[nodiscard]] static nsresult VsizeDistinguishedAmount(int64_t* aN) {
+  return GetProcSelfStatmField(0, aN);
+}
+
+[[nodiscard]] static nsresult ResidentDistinguishedAmount(int64_t* aN) {
+  return GetProcSelfStatmField(1, aN);
+}
+
+[[nodiscard]] static nsresult ResidentFastDistinguishedAmount(int64_t* aN) {
+  return ResidentDistinguishedAmount(aN);
+}
+
+#  define HAVE_RESIDENT_UNIQUE_REPORTER 1
+[[nodiscard]] static nsresult ResidentUniqueDistinguishedAmount(
+    int64_t* aN, pid_t aPid = 0) {
+  return GetProcSelfSmapsPrivate(aN, aPid);
+}
+
+#  ifdef HAVE_MALLINFO
+#    define HAVE_SYSTEM_HEAP_REPORTER 1
+[[nodiscard]] static nsresult SystemHeapSize(int64_t* aSizeOut) {
+  struct mallinfo info = mallinfo();
+
+  // The documentation in the glibc man page makes it sound like |uordblks|
+  // would suffice, but that only gets the small allocations that are put in
+  // the brk heap. We need |hblkhd| as well to get the larger allocations
+  // that are mmapped.
+  //
+  // The fields in |struct mallinfo| are all |int|, <sigh>, so it is
+  // unreliable if memory usage gets high. However, the system heap size on
+  // Linux should usually be zero (so long as jemalloc is enabled) so that
+  // shouldn't be a problem. Nonetheless, cast the |int|s to |size_t| before
+  // adding them to provide a small amount of extra overflow protection.
+  *aSizeOut = size_t(info.hblkhd) + size_t(info.uordblks);
+  return NS_OK;
+}
+#  endif
+
+#elif defined(__DragonFly__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
+    defined(__OpenBSD__) || defined(__FreeBSD_kernel__)
+
+#  include <sys/param.h>
+#  include <sys/sysctl.h>
+#  if defined(__DragonFly__) || defined(__FreeBSD__) || \
+      defined(__FreeBSD_kernel__)
+#    include <sys/user.h>
+#  endif
+
+#  include <unistd.h>
+
+#  if defined(__NetBSD__)
+#    undef KERN_PROC
+#    define KERN_PROC KERN_PROC2
+#    define KINFO_PROC struct kinfo_proc2
+#  else
+#    define KINFO_PROC struct kinfo_proc
+#  endif
+
+#  if defined(__DragonFly__)
+#    define KP_SIZE(kp) (kp.kp_vm_map_size)
+#    define KP_RSS(kp) (kp.kp_vm_rssize * getpagesize())
+#  elif defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
+#    define KP_SIZE(kp) (kp.ki_size)
+#    define KP_RSS(kp) (kp.ki_rssize * getpagesize())
+#  elif defined(__NetBSD__)
+#    define KP_SIZE(kp) (kp.p_vm_msize * getpagesize())
+#    define KP_RSS(kp) (kp.p_vm_rssize * getpagesize())
+#  elif defined(__OpenBSD__)
+#    define KP_SIZE(kp) \
+      ((kp.p_vm_dsize + kp.p_vm_ssize + kp.p_vm_tsize) * getpagesize())
+#    define KP_RSS(kp) (kp.p_vm_rssize * getpagesize())
+#  endif
+
+[[nodiscard]] static nsresult GetKinfoProcSelf(KINFO_PROC* aProc) {
+#  if defined(__OpenBSD__) && defined(MOZ_SANDBOX)
+  static LazyLogModule sPledgeLog("SandboxPledge");
+  MOZ_LOG(sPledgeLog, LogLevel::Debug,
+          ("%s called when pledged, returning NS_ERROR_FAILURE\n", __func__));
+  return NS_ERROR_FAILURE;
+#  endif
+  int mib[] = {
+    CTL_KERN,
+    KERN_PROC,
+    KERN_PROC_PID,
+    getpid(),
+#  if defined(__NetBSD__) || defined(__OpenBSD__)
+    sizeof(KINFO_PROC),
+    1,
+#  endif
+  };
+  u_int miblen = sizeof(mib) / sizeof(mib[0]);
+  size_t size = sizeof(KINFO_PROC);
+  if (sysctl(mib, miblen, aProc, &size, nullptr, 0)) {
+    return NS_ERROR_FAILURE;
+  }
+  return NS_OK;
+}
+
+#  define HAVE_VSIZE_AND_RESIDENT_REPORTERS 1
+[[nodiscard]] static nsresult VsizeDistinguishedAmount(int64_t* aN) {
+  KINFO_PROC proc;
+  nsresult rv = GetKinfoProcSelf(&proc);
+  if (NS_SUCCEEDED(rv)) {
+    *aN = KP_SIZE(proc);
+  }
+  return rv;
+}
+
+[[nodiscard]] static nsresult ResidentDistinguishedAmount(int64_t* aN) {
+  KINFO_PROC proc;
+  nsresult rv = GetKinfoProcSelf(&proc);
+  if (NS_SUCCEEDED(rv)) {
+    *aN = KP_RSS(proc);
+  }
+  return rv;
+}
+
+[[nodiscard]] static nsresult ResidentFastDistinguishedAmount(int64_t* aN) {
+  return ResidentDistinguishedAmount(aN);
+}
+
+#  ifdef __FreeBSD__
+#    include <libutil.h>
+#    include <algorithm>
+
+[[nodiscard]] static nsresult GetKinfoVmentrySelf(int64_t* aPrss,
+                                                  uint64_t* aMaxreg) {
+  int cnt;
+  struct kinfo_vmentry* vmmap;
+  struct kinfo_vmentry* kve;
+  if (!(vmmap = kinfo_getvmmap(getpid(), &cnt))) {
+    return NS_ERROR_FAILURE;
+  }
+  if (aPrss) {
+    *aPrss = 0;
+  }
+  if (aMaxreg) {
+    *aMaxreg = 0;
+  }
+
+  for (int i = 0; i < cnt; i++) {
+    kve = &vmmap[i];
+    if (aPrss) {
+      *aPrss += kve->kve_private_resident;
+    }
+    if (aMaxreg) {
+      *aMaxreg = std::max(*aMaxreg, kve->kve_end - kve->kve_start);
+    }
+  }
+
+  free(vmmap);
+  return NS_OK;
+}
+
+#    define HAVE_PRIVATE_REPORTER 1
+[[nodiscard]] static nsresult PrivateDistinguishedAmount(int64_t* aN) {
+  int64_t priv;
+  nsresult rv = GetKinfoVmentrySelf(&priv, nullptr);
+  NS_ENSURE_SUCCESS(rv, rv);
+  *aN = priv * getpagesize();
+  return NS_OK;
+}
+
+#    define HAVE_VSIZE_MAX_CONTIGUOUS_REPORTER 1
+[[nodiscard]] static nsresult VsizeMaxContiguousDistinguishedAmount(
+    int64_t* aN) {
+  uint64_t biggestRegion;
+  nsresult rv = GetKinfoVmentrySelf(nullptr, &biggestRegion);
+  if (NS_SUCCEEDED(rv)) {
+    *aN = biggestRegion;
+  }
+  return NS_OK;
+}
+#  endif  // FreeBSD
+
+#elif defined(SOLARIS)
+
+#  include <procfs.h>
+#  include <fcntl.h>
+#  include <unistd.h>
+
+static void XMappingIter(int64_t& aVsize, int64_t& aResident,
+                         int64_t& aShared) {
+  aVsize = -1;
+  aResident = -1;
+  aShared = -1;
+  int mapfd = open("/proc/self/xmap", O_RDONLY);
+  struct stat st;
+  prxmap_t* prmapp = nullptr;
+  if (mapfd >= 0) {
+    if (!fstat(mapfd, &st)) {
+      int nmap = st.st_size / sizeof(prxmap_t);
+      while (1) {
+        // stat(2) on /proc/<pid>/xmap returns an incorrect value,
+        // prior to the release of Solaris 11.
+        // Here is a workaround for it.
+        nmap *= 2;
+        prmapp = (prxmap_t*)malloc((nmap + 1) * sizeof(prxmap_t));
+        if (!prmapp) {
+          // out of memory
+          break;
+        }
+        int n = pread(mapfd, prmapp, (nmap + 1) * sizeof(prxmap_t), 0);
+        if (n < 0) {
+          break;
+        }
+        if (nmap >= n / sizeof(prxmap_t)) {
+          aVsize = 0;
+          aResident = 0;
+          aShared = 0;
+          for (int i = 0; i < n / sizeof(prxmap_t); i++) {
+            aVsize += prmapp[i].pr_size;
+            aResident += prmapp[i].pr_rss * prmapp[i].pr_pagesize;
+            if (prmapp[i].pr_mflags & MA_SHARED) {
+              aShared += prmapp[i].pr_rss * prmapp[i].pr_pagesize;
+            }
+          }
+          break;
+        }
+        free(prmapp);
+      }
+      free(prmapp);
+    }
+    close(mapfd);
+  }
+}
+
+#  define HAVE_VSIZE_AND_RESIDENT_REPORTERS 1
+[[nodiscard]] static nsresult VsizeDistinguishedAmount(int64_t* aN) {
+  int64_t vsize, resident, shared;
+  XMappingIter(vsize, resident, shared);
+  if (vsize == -1) {
+    return NS_ERROR_FAILURE;
+  }
+  *aN = vsize;
+  return NS_OK;
+}
+
+[[nodiscard]] static nsresult ResidentDistinguishedAmount(int64_t* aN) {
+  int64_t vsize, resident, shared;
+  XMappingIter(vsize, resident, shared);
+  if (resident == -1) {
+    return NS_ERROR_FAILURE;
+  }
+  *aN = resident;
+  return NS_OK;
+}
+
+[[nodiscard]] static nsresult ResidentFastDistinguishedAmount(int64_t* aN) {
+  return ResidentDistinguishedAmount(aN);
+}
+
+#  define HAVE_RESIDENT_UNIQUE_REPORTER 1
+[[nodiscard]] static nsresult ResidentUniqueDistinguishedAmount(int64_t* aN) {
+  int64_t vsize, resident, shared;
+  XMappingIter(vsize, resident, shared);
+  if (resident == -1) {
+    return NS_ERROR_FAILURE;
+  }
+  *aN = resident - shared;
+  return NS_OK;
+}
+
+#elif defined(XP_MACOSX)
+
+#  include <mach/mach_init.h>
+#  include <mach/mach_vm.h>
+#  include <mach/shared_region.h>
+#  include <mach/task.h>
+#  include <sys/sysctl.h>
+
+[[nodiscard]] static bool GetTaskBasicInfo(struct task_basic_info* aTi) {
+  mach_msg_type_number_t count = TASK_BASIC_INFO_COUNT;
+  kern_return_t kr =
+      task_info(mach_task_self(), TASK_BASIC_INFO, (task_info_t)aTi, &count);
+  return kr == KERN_SUCCESS;
+}
+
+// The VSIZE figure on Mac includes huge amounts of shared memory and is always
+// absurdly high, eg. 2GB+ even at start-up.  But both 'top' and 'ps' report
+// it, so we might as well too.
+#  define HAVE_VSIZE_AND_RESIDENT_REPORTERS 1
+[[nodiscard]] static nsresult VsizeDistinguishedAmount(int64_t* aN) {
+  task_basic_info ti;
+  if (!GetTaskBasicInfo(&ti)) {
+    return NS_ERROR_FAILURE;
+  }
+  *aN = ti.virtual_size;
+  return NS_OK;
+}
+
+// If we're using jemalloc on Mac, we need to instruct jemalloc to purge the
+// pages it has madvise(MADV_FREE)'d before we read our RSS in order to get
+// an accurate result.  The OS will take away MADV_FREE'd pages when there's
+// memory pressure, so ideally, they shouldn't count against our RSS.
+//
+// Purging these pages can take a long time for some users (see bug 789975),
+// so we provide the option to get the RSS without purging first.
+[[nodiscard]] static nsresult ResidentDistinguishedAmountHelper(int64_t* aN,
+                                                                bool aDoPurge) {
+#  ifdef HAVE_JEMALLOC_STATS
+  if (aDoPurge) {
+    Telemetry::AutoTimer<Telemetry::MEMORY_FREE_PURGED_PAGES_MS> timer;
+    jemalloc_purge_freed_pages();
+  }
+#  endif
+
+  task_basic_info ti;
+  if (!GetTaskBasicInfo(&ti)) {
+    return NS_ERROR_FAILURE;
+  }
+  *aN = ti.resident_size;
+  return NS_OK;
+}
+
+[[nodiscard]] static nsresult ResidentFastDistinguishedAmount(int64_t* aN) {
+  return ResidentDistinguishedAmountHelper(aN, /* doPurge = */ false);
+}
+
+[[nodiscard]] static nsresult ResidentDistinguishedAmount(int64_t* aN) {
+  return ResidentDistinguishedAmountHelper(aN, /* doPurge = */ true);
+}
+
+#  define HAVE_RESIDENT_UNIQUE_REPORTER 1
+
+static bool InSharedRegion(mach_vm_address_t aAddr, cpu_type_t aType) {
+  mach_vm_address_t base;
+  mach_vm_address_t size;
+
+  switch (aType) {
+    case CPU_TYPE_ARM:
+      base = SHARED_REGION_BASE_ARM;
+      size = SHARED_REGION_SIZE_ARM;
+      break;
+    case CPU_TYPE_ARM64:
+      base = SHARED_REGION_BASE_ARM64;
+      size = SHARED_REGION_SIZE_ARM64;
+      break;
+    case CPU_TYPE_I386:
+      base = SHARED_REGION_BASE_I386;
+      size = SHARED_REGION_SIZE_I386;
+      break;
+    case CPU_TYPE_X86_64:
+      base = SHARED_REGION_BASE_X86_64;
+      size = SHARED_REGION_SIZE_X86_64;
+      break;
+    default:
+      return false;
+  }
+
+  return base <= aAddr && aAddr < (base + size);
+}
+
+[[nodiscard]] static nsresult ResidentUniqueDistinguishedAmount(
+    int64_t* aN, mach_port_t aPort = 0) {
+  if (!aN) {
+    return NS_ERROR_FAILURE;
+  }
+
+  cpu_type_t cpu_type;
+  size_t len = sizeof(cpu_type);
+  if (sysctlbyname("sysctl.proc_cputype", &cpu_type, &len, NULL, 0) != 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Roughly based on libtop_update_vm_regions in
+  // http://www.opensource.apple.com/source/top/top-100.1.2/libtop.c
+  size_t privatePages = 0;
+  mach_vm_size_t topSize = 0;
+  for (mach_vm_address_t addr = MACH_VM_MIN_ADDRESS;; addr += topSize) {
+    vm_region_top_info_data_t topInfo;
+    mach_msg_type_number_t topInfoCount = VM_REGION_TOP_INFO_COUNT;
+    mach_port_t topObjectName;
+
+    kern_return_t kr = mach_vm_region(
+        aPort ? aPort : mach_task_self(), &addr, &topSize, VM_REGION_TOP_INFO,
+        reinterpret_cast<vm_region_info_t>(&topInfo), &topInfoCount,
+        &topObjectName);
+    if (kr == KERN_INVALID_ADDRESS) {
+      // Done iterating VM regions.
+      break;
+    } else if (kr != KERN_SUCCESS) {
+      return NS_ERROR_FAILURE;
+    }
+
+    if (InSharedRegion(addr, cpu_type) && topInfo.share_mode != SM_PRIVATE) {
+      continue;
+    }
+
+    switch (topInfo.share_mode) {
+      case SM_LARGE_PAGE:
+        // NB: Large pages are not shareable and always resident.
+      case SM_PRIVATE:
+        privatePages += topInfo.private_pages_resident;
+        privatePages += topInfo.shared_pages_resident;
+        break;
+      case SM_COW:
+        privatePages += topInfo.private_pages_resident;
+        if (topInfo.ref_count == 1) {
+          // Treat copy-on-write pages as private if they only have one
+          // reference.
+          privatePages += topInfo.shared_pages_resident;
+        }
+        break;
+      case SM_SHARED: {
+        // Using mprotect() or similar to protect a page in the middle of a
+        // mapping can create aliased mappings. They look like shared mappings
+        // to the VM_REGION_TOP_INFO interface, so re-check with
+        // VM_REGION_EXTENDED_INFO.
+
+        mach_vm_size_t exSize = 0;
+        vm_region_extended_info_data_t exInfo;
+        mach_msg_type_number_t exInfoCount = VM_REGION_EXTENDED_INFO_COUNT;
+        mach_port_t exObjectName;
+        kr = mach_vm_region(aPort ? aPort : mach_task_self(), &addr, &exSize,
+                            VM_REGION_EXTENDED_INFO,
+                            reinterpret_cast<vm_region_info_t>(&exInfo),
+                            &exInfoCount, &exObjectName);
+        if (kr == KERN_INVALID_ADDRESS) {
+          // Done iterating VM regions.
+          break;
+        } else if (kr != KERN_SUCCESS) {
+          return NS_ERROR_FAILURE;
+        }
+
+        if (exInfo.share_mode == SM_PRIVATE_ALIASED) {
+          privatePages += exInfo.pages_resident;
+        }
+        break;
+      }
+      default:
+        break;
+    }
+  }
+
+  vm_size_t pageSize;
+  if (host_page_size(aPort ? aPort : mach_task_self(), &pageSize) !=
+      KERN_SUCCESS) {
+    pageSize = PAGE_SIZE;
+  }
+
+  *aN = privatePages * pageSize;
+  return NS_OK;
+}
+
+[[nodiscard]] static nsresult PhysicalFootprintAmount(int64_t* aN,
+                                                      mach_port_t aPort = 0) {
+  MOZ_ASSERT(aN);
+
+  // The phys_footprint value (introduced in 10.11) of the TASK_VM_INFO data
+  // matches the value in the 'Memory' column of the Activity Monitor.
+  task_vm_info_data_t task_vm_info;
+  mach_msg_type_number_t count = TASK_VM_INFO_COUNT;
+  kern_return_t kr = task_info(aPort ? aPort : mach_task_self(), TASK_VM_INFO,
+                               (task_info_t)&task_vm_info, &count);
+  if (kr != KERN_SUCCESS) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *aN = task_vm_info.phys_footprint;
+  return NS_OK;
+}
+
+#elif defined(XP_WIN)
+
+#  include <windows.h>
+#  include <psapi.h>
+#  include <algorithm>
+
+#  define HAVE_VSIZE_AND_RESIDENT_REPORTERS 1
+[[nodiscard]] static nsresult VsizeDistinguishedAmount(int64_t* aN) {
+  MEMORYSTATUSEX s;
+  s.dwLength = sizeof(s);
+
+  if (!GlobalMemoryStatusEx(&s)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *aN = s.ullTotalVirtual - s.ullAvailVirtual;
+  return NS_OK;
+}
+
+[[nodiscard]] static nsresult ResidentDistinguishedAmount(int64_t* aN) {
+  PROCESS_MEMORY_COUNTERS pmc;
+  pmc.cb = sizeof(PROCESS_MEMORY_COUNTERS);
+
+  if (!GetProcessMemoryInfo(GetCurrentProcess(), &pmc, sizeof(pmc))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *aN = pmc.WorkingSetSize;
+  return NS_OK;
+}
+
+[[nodiscard]] static nsresult ResidentFastDistinguishedAmount(int64_t* aN) {
+  return ResidentDistinguishedAmount(aN);
+}
+
+#  define HAVE_RESIDENT_UNIQUE_REPORTER 1
+
+[[nodiscard]] static nsresult ResidentUniqueDistinguishedAmount(
+    int64_t* aN, HANDLE aProcess = nullptr) {
+  // Determine how many entries we need.
+  PSAPI_WORKING_SET_INFORMATION tmp;
+  DWORD tmpSize = sizeof(tmp);
+  memset(&tmp, 0, tmpSize);
+
+  HANDLE proc = aProcess ? aProcess : GetCurrentProcess();
+  QueryWorkingSet(proc, &tmp, tmpSize);
+
+  // Fudge the size in case new entries are added between calls.
+  size_t entries = tmp.NumberOfEntries * 2;
+
+  if (!entries) {
+    return NS_ERROR_FAILURE;
+  }
+
+  DWORD infoArraySize = tmpSize + (entries * sizeof(PSAPI_WORKING_SET_BLOCK));
+  UniqueFreePtr<PSAPI_WORKING_SET_INFORMATION> infoArray(
+      static_cast<PSAPI_WORKING_SET_INFORMATION*>(malloc(infoArraySize)));
+
+  if (!infoArray) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (!QueryWorkingSet(proc, infoArray.get(), infoArraySize)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  entries = static_cast<size_t>(infoArray->NumberOfEntries);
+  size_t privatePages = 0;
+  for (size_t i = 0; i < entries; i++) {
+    // Count shared pages that only one process is using as private.
+    if (!infoArray->WorkingSetInfo[i].Shared ||
+        infoArray->WorkingSetInfo[i].ShareCount <= 1) {
+      privatePages++;
+    }
+  }
+
+  SYSTEM_INFO si;
+  GetSystemInfo(&si);
+
+  *aN = privatePages * si.dwPageSize;
+  return NS_OK;
+}
+
+#  define HAVE_VSIZE_MAX_CONTIGUOUS_REPORTER 1
+[[nodiscard]] static nsresult VsizeMaxContiguousDistinguishedAmount(
+    int64_t* aN) {
+  SIZE_T biggestRegion = 0;
+  MEMORY_BASIC_INFORMATION vmemInfo = {0};
+  for (size_t currentAddress = 0;;) {
+    if (!VirtualQuery((LPCVOID)currentAddress, &vmemInfo, sizeof(vmemInfo))) {
+      // Something went wrong, just return whatever we've got already.
+      break;
+    }
+
+    if (vmemInfo.State == MEM_FREE) {
+      biggestRegion = std::max(biggestRegion, vmemInfo.RegionSize);
+    }
+
+    SIZE_T lastAddress = currentAddress;
+    currentAddress += vmemInfo.RegionSize;
+
+    // If we overflow, we've examined all of the address space.
+    if (currentAddress < lastAddress) {
+      break;
+    }
+  }
+
+  *aN = biggestRegion;
+  return NS_OK;
+}
+
+#  define HAVE_PRIVATE_REPORTER 1
+[[nodiscard]] static nsresult PrivateDistinguishedAmount(int64_t* aN) {
+  PROCESS_MEMORY_COUNTERS_EX pmcex;
+  pmcex.cb = sizeof(PROCESS_MEMORY_COUNTERS_EX);
+
+  if (!GetProcessMemoryInfo(GetCurrentProcess(),
+                            (PPROCESS_MEMORY_COUNTERS)&pmcex, sizeof(pmcex))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *aN = pmcex.PrivateUsage;
+  return NS_OK;
+}
+
+#  define HAVE_SYSTEM_HEAP_REPORTER 1
+// Windows can have multiple separate heaps, but we should not touch non-default
+// heaps because they may be destroyed at anytime while we hold a handle.  So we
+// count only the default heap.
+[[nodiscard]] static nsresult SystemHeapSize(int64_t* aSizeOut) {
+  HANDLE heap = GetProcessHeap();
+
+  NS_ENSURE_TRUE(HeapLock(heap), NS_ERROR_FAILURE);
+
+  int64_t heapSize = 0;
+  PROCESS_HEAP_ENTRY entry;
+  entry.lpData = nullptr;
+  while (HeapWalk(heap, &entry)) {
+    // We don't count entry.cbOverhead, because we just want to measure the
+    // space available to the program.
+    if (entry.wFlags & PROCESS_HEAP_ENTRY_BUSY) {
+      heapSize += entry.cbData;
+    }
+  }
+
+  // Check this result only after unlocking the heap, so that we don't leave
+  // the heap locked if there was an error.
+  DWORD lastError = GetLastError();
+
+  // I have no idea how things would proceed if unlocking this heap failed...
+  NS_ENSURE_TRUE(HeapUnlock(heap), NS_ERROR_FAILURE);
+
+  NS_ENSURE_TRUE(lastError == ERROR_NO_MORE_ITEMS, NS_ERROR_FAILURE);
+
+  *aSizeOut = heapSize;
+  return NS_OK;
+}
+
+struct SegmentKind {
+  DWORD mState;
+  DWORD mType;
+  DWORD mProtect;
+  int mIsStack;
+};
+
+struct SegmentEntry : public PLDHashEntryHdr {
+  static PLDHashNumber HashKey(const void* aKey) {
+    auto kind = static_cast<const SegmentKind*>(aKey);
+    return mozilla::HashGeneric(kind->mState, kind->mType, kind->mProtect,
+                                kind->mIsStack);
+  }
+
+  static bool MatchEntry(const PLDHashEntryHdr* aEntry, const void* aKey) {
+    auto kind = static_cast<const SegmentKind*>(aKey);
+    auto entry = static_cast<const SegmentEntry*>(aEntry);
+    return kind->mState == entry->mKind.mState &&
+           kind->mType == entry->mKind.mType &&
+           kind->mProtect == entry->mKind.mProtect &&
+           kind->mIsStack == entry->mKind.mIsStack;
+  }
+
+  static void InitEntry(PLDHashEntryHdr* aEntry, const void* aKey) {
+    auto kind = static_cast<const SegmentKind*>(aKey);
+    auto entry = static_cast<SegmentEntry*>(aEntry);
+    entry->mKind = *kind;
+    entry->mCount = 0;
+    entry->mSize = 0;
+  }
+
+  static const PLDHashTableOps Ops;
+
+  SegmentKind mKind;  // The segment kind.
+  uint32_t mCount;    // The number of segments of this kind.
+  size_t mSize;       // The combined size of segments of this kind.
+};
+
+/* static */ const PLDHashTableOps SegmentEntry::Ops = {
+    SegmentEntry::HashKey, SegmentEntry::MatchEntry,
+    PLDHashTable::MoveEntryStub, PLDHashTable::ClearEntryStub,
+    SegmentEntry::InitEntry};
+
+class WindowsAddressSpaceReporter final : public nsIMemoryReporter {
+  ~WindowsAddressSpaceReporter() {}
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    // First iterate over all the segments and record how many of each kind
+    // there were and their aggregate sizes. We use a hash table for this
+    // because there are a couple of dozen different kinds possible.
+
+    PLDHashTable table(&SegmentEntry::Ops, sizeof(SegmentEntry));
+    MEMORY_BASIC_INFORMATION info = {0};
+    bool isPrevSegStackGuard = false;
+    for (size_t currentAddress = 0;;) {
+      if (!VirtualQuery((LPCVOID)currentAddress, &info, sizeof(info))) {
+        // Something went wrong, just return whatever we've got already.
+        break;
+      }
+
+      size_t size = info.RegionSize;
+
+      // Note that |type| and |protect| are ignored in some cases.
+      DWORD state = info.State;
+      DWORD type =
+          (state == MEM_RESERVE || state == MEM_COMMIT) ? info.Type : 0;
+      DWORD protect = (state == MEM_COMMIT) ? info.Protect : 0;
+      bool isStack = isPrevSegStackGuard && state == MEM_COMMIT &&
+                     type == MEM_PRIVATE && protect == PAGE_READWRITE;
+
+      SegmentKind kind = {state, type, protect, isStack ? 1 : 0};
+      auto entry =
+          static_cast<SegmentEntry*>(table.Add(&kind, mozilla::fallible));
+      if (entry) {
+        entry->mCount += 1;
+        entry->mSize += size;
+      }
+
+      isPrevSegStackGuard = info.State == MEM_COMMIT &&
+                            info.Type == MEM_PRIVATE &&
+                            info.Protect == (PAGE_READWRITE | PAGE_GUARD);
+
+      size_t lastAddress = currentAddress;
+      currentAddress += size;
+
+      // If we overflow, we've examined all of the address space.
+      if (currentAddress < lastAddress) {
+        break;
+      }
+    }
+
+    // Then iterate over the hash table and report the details for each segment
+    // kind.
+
+    for (auto iter = table.Iter(); !iter.Done(); iter.Next()) {
+      // For each range of pages, we consider one or more of its State, Type
+      // and Protect values. These are documented at
+      // https://msdn.microsoft.com/en-us/library/windows/desktop/aa366775%28v=vs.85%29.aspx
+      // (for State and Type) and
+      // https://msdn.microsoft.com/en-us/library/windows/desktop/aa366786%28v=vs.85%29.aspx
+      // (for Protect).
+      //
+      // Not all State values have accompanying Type and Protection values.
+      bool doType = false;
+      bool doProtect = false;
+
+      auto entry = static_cast<const SegmentEntry*>(iter.Get());
+
+      nsCString path("address-space");
+
+      switch (entry->mKind.mState) {
+        case MEM_FREE:
+          path.AppendLiteral("/free");
+          break;
+
+        case MEM_RESERVE:
+          path.AppendLiteral("/reserved");
+          doType = true;
+          break;
+
+        case MEM_COMMIT:
+          path.AppendLiteral("/commit");
+          doType = true;
+          doProtect = true;
+          break;
+
+        default:
+          // Should be impossible, but handle it just in case.
+          path.AppendLiteral("/???");
+          break;
+      }
+
+      if (doType) {
+        switch (entry->mKind.mType) {
+          case MEM_IMAGE:
+            path.AppendLiteral("/image");
+            break;
+
+          case MEM_MAPPED:
+            path.AppendLiteral("/mapped");
+            break;
+
+          case MEM_PRIVATE:
+            path.AppendLiteral("/private");
+            break;
+
+          default:
+            // Should be impossible, but handle it just in case.
+            path.AppendLiteral("/???");
+            break;
+        }
+      }
+
+      if (doProtect) {
+        DWORD protect = entry->mKind.mProtect;
+        // Basic attributes. Exactly one of these should be set.
+        if (protect & PAGE_EXECUTE) {
+          path.AppendLiteral("/execute");
+        }
+        if (protect & PAGE_EXECUTE_READ) {
+          path.AppendLiteral("/execute-read");
+        }
+        if (protect & PAGE_EXECUTE_READWRITE) {
+          path.AppendLiteral("/execute-readwrite");
+        }
+        if (protect & PAGE_EXECUTE_WRITECOPY) {
+          path.AppendLiteral("/execute-writecopy");
+        }
+        if (protect & PAGE_NOACCESS) {
+          path.AppendLiteral("/noaccess");
+        }
+        if (protect & PAGE_READONLY) {
+          path.AppendLiteral("/readonly");
+        }
+        if (protect & PAGE_READWRITE) {
+          path.AppendLiteral("/readwrite");
+        }
+        if (protect & PAGE_WRITECOPY) {
+          path.AppendLiteral("/writecopy");
+        }
+
+        // Modifiers. At most one of these should be set.
+        if (protect & PAGE_GUARD) {
+          path.AppendLiteral("+guard");
+        }
+        if (protect & PAGE_NOCACHE) {
+          path.AppendLiteral("+nocache");
+        }
+        if (protect & PAGE_WRITECOMBINE) {
+          path.AppendLiteral("+writecombine");
+        }
+
+        // Annotate likely stack segments, too.
+        if (entry->mKind.mIsStack) {
+          path.AppendLiteral("+stack");
+        }
+      }
+
+      // Append the segment count.
+      path.AppendPrintf("(segments=%u)", entry->mCount);
+
+      aHandleReport->Callback(""_ns, path, KIND_OTHER, UNITS_BYTES,
+                              entry->mSize, "From MEMORY_BASIC_INFORMATION."_ns,
+                              aData);
+    }
+
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(WindowsAddressSpaceReporter, nsIMemoryReporter)
+
+#endif  // XP_<PLATFORM>
+
+#ifdef HAVE_VSIZE_MAX_CONTIGUOUS_REPORTER
+class VsizeMaxContiguousReporter final : public nsIMemoryReporter {
+  ~VsizeMaxContiguousReporter() {}
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    int64_t amount;
+    if (NS_SUCCEEDED(VsizeMaxContiguousDistinguishedAmount(&amount))) {
+      MOZ_COLLECT_REPORT(
+          "vsize-max-contiguous", KIND_OTHER, UNITS_BYTES, amount,
+          "Size of the maximum contiguous block of available virtual memory.");
+    }
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(VsizeMaxContiguousReporter, nsIMemoryReporter)
+#endif
+
+#ifdef HAVE_PRIVATE_REPORTER
+class PrivateReporter final : public nsIMemoryReporter {
+  ~PrivateReporter() {}
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    int64_t amount;
+    if (NS_SUCCEEDED(PrivateDistinguishedAmount(&amount))) {
+      // clang-format off
+      MOZ_COLLECT_REPORT(
+        "private", KIND_OTHER, UNITS_BYTES, amount,
+"Memory that cannot be shared with other processes, including memory that is "
+"committed and marked MEM_PRIVATE, data that is not mapped, and executable "
+"pages that have been written to.");
+      // clang-format on
+    }
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(PrivateReporter, nsIMemoryReporter)
+#endif
+
+#ifdef HAVE_VSIZE_AND_RESIDENT_REPORTERS
+class VsizeReporter final : public nsIMemoryReporter {
+  ~VsizeReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    int64_t amount;
+    if (NS_SUCCEEDED(VsizeDistinguishedAmount(&amount))) {
+      // clang-format off
+      MOZ_COLLECT_REPORT(
+        "vsize", KIND_OTHER, UNITS_BYTES, amount,
+"Memory mapped by the process, including code and data segments, the heap, "
+"thread stacks, memory explicitly mapped by the process via mmap and similar "
+"operations, and memory shared with other processes. This is the vsize figure "
+"as reported by 'top' and 'ps'.  This figure is of limited use on Mac, where "
+"processes share huge amounts of memory with one another.  But even on other "
+"operating systems, 'resident' is a much better measure of the memory "
+"resources used by the process.");
+      // clang-format on
+    }
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(VsizeReporter, nsIMemoryReporter)
+
+class ResidentReporter final : public nsIMemoryReporter {
+  ~ResidentReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    int64_t amount;
+    if (NS_SUCCEEDED(ResidentDistinguishedAmount(&amount))) {
+      // clang-format off
+      MOZ_COLLECT_REPORT(
+        "resident", KIND_OTHER, UNITS_BYTES, amount,
+"Memory mapped by the process that is present in physical memory, also known "
+"as the resident set size (RSS).  This is the best single figure to use when "
+"considering the memory resources used by the process, but it depends both on "
+"other processes being run and details of the OS kernel and so is best used "
+"for comparing the memory usage of a single process at different points in "
+"time.");
+      // clang-format on
+    }
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(ResidentReporter, nsIMemoryReporter)
+
+#endif  // HAVE_VSIZE_AND_RESIDENT_REPORTERS
+
+#ifdef HAVE_RESIDENT_UNIQUE_REPORTER
+class ResidentUniqueReporter final : public nsIMemoryReporter {
+  ~ResidentUniqueReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    int64_t amount = 0;
+    // clang-format off
+    if (NS_SUCCEEDED(ResidentUniqueDistinguishedAmount(&amount))) {
+      MOZ_COLLECT_REPORT(
+        "resident-unique", KIND_OTHER, UNITS_BYTES, amount,
+"Memory mapped by the process that is present in physical memory and not "
+"shared with any other processes.  This is also known as the process's unique "
+"set size (USS).  This is the amount of RAM we'd expect to be freed if we "
+"closed this process.");
+    }
+#ifdef XP_MACOSX
+    if (NS_SUCCEEDED(PhysicalFootprintAmount(&amount))) {
+      MOZ_COLLECT_REPORT(
+        "resident-phys-footprint", KIND_OTHER, UNITS_BYTES, amount,
+"Memory footprint reported by MacOS's task_info API's phys_footprint field. "
+"This matches the memory column in Activity Monitor.");
+    }
+#endif
+    // clang-format on
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(ResidentUniqueReporter, nsIMemoryReporter)
+
+#endif  // HAVE_RESIDENT_UNIQUE_REPORTER
+
+#ifdef HAVE_SYSTEM_HEAP_REPORTER
+
+class SystemHeapReporter final : public nsIMemoryReporter {
+  ~SystemHeapReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    int64_t amount;
+    if (NS_SUCCEEDED(SystemHeapSize(&amount))) {
+      // clang-format off
+      MOZ_COLLECT_REPORT(
+        "system-heap-allocated", KIND_OTHER, UNITS_BYTES, amount,
+"Memory used by the system allocator that is currently allocated to the "
+"application. This is distinct from the jemalloc heap that Firefox uses for "
+"most or all of its heap allocations. Ideally this number is zero, but "
+"on some platforms we cannot force every heap allocation through jemalloc.");
+      // clang-format on
+    }
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(SystemHeapReporter, nsIMemoryReporter)
+#endif  // HAVE_SYSTEM_HEAP_REPORTER
+
+#ifdef XP_UNIX
+
+#  include <sys/resource.h>
+
+#  define HAVE_RESIDENT_PEAK_REPORTER 1
+
+[[nodiscard]] static nsresult ResidentPeakDistinguishedAmount(int64_t* aN) {
+  struct rusage usage;
+  if (0 == getrusage(RUSAGE_SELF, &usage)) {
+    // The units for ru_maxrrs:
+    // - Mac: bytes
+    // - Solaris: pages? But some sources it actually always returns 0, so
+    //   check for that
+    // - Linux, {Net/Open/Free}BSD, DragonFly: KiB
+#  ifdef XP_MACOSX
+    *aN = usage.ru_maxrss;
+#  elif defined(SOLARIS)
+    *aN = usage.ru_maxrss * getpagesize();
+#  else
+    *aN = usage.ru_maxrss * 1024;
+#  endif
+    if (*aN > 0) {
+      return NS_OK;
+    }
+  }
+  return NS_ERROR_FAILURE;
+}
+
+class ResidentPeakReporter final : public nsIMemoryReporter {
+  ~ResidentPeakReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    int64_t amount = 0;
+    if (NS_SUCCEEDED(ResidentPeakDistinguishedAmount(&amount))) {
+      MOZ_COLLECT_REPORT(
+          "resident-peak", KIND_OTHER, UNITS_BYTES, amount,
+          "The peak 'resident' value for the lifetime of the process.");
+    }
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(ResidentPeakReporter, nsIMemoryReporter)
+
+#  define HAVE_PAGE_FAULT_REPORTERS 1
+
+class PageFaultsSoftReporter final : public nsIMemoryReporter {
+  ~PageFaultsSoftReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    struct rusage usage;
+    int err = getrusage(RUSAGE_SELF, &usage);
+    if (err == 0) {
+      int64_t amount = usage.ru_minflt;
+      // clang-format off
+      MOZ_COLLECT_REPORT(
+        "page-faults-soft", KIND_OTHER, UNITS_COUNT_CUMULATIVE, amount,
+"The number of soft page faults (also known as 'minor page faults') that "
+"have occurred since the process started.  A soft page fault occurs when the "
+"process tries to access a page which is present in physical memory but is "
+"not mapped into the process's address space.  For instance, a process might "
+"observe soft page faults when it loads a shared library which is already "
+"present in physical memory. A process may experience many thousands of soft "
+"page faults even when the machine has plenty of available physical memory, "
+"and because the OS services a soft page fault without accessing the disk, "
+"they impact performance much less than hard page faults.");
+      // clang-format on
+    }
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(PageFaultsSoftReporter, nsIMemoryReporter)
+
+[[nodiscard]] static nsresult PageFaultsHardDistinguishedAmount(
+    int64_t* aAmount) {
+  struct rusage usage;
+  int err = getrusage(RUSAGE_SELF, &usage);
+  if (err != 0) {
+    return NS_ERROR_FAILURE;
+  }
+  *aAmount = usage.ru_majflt;
+  return NS_OK;
+}
+
+class PageFaultsHardReporter final : public nsIMemoryReporter {
+  ~PageFaultsHardReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    int64_t amount = 0;
+    if (NS_SUCCEEDED(PageFaultsHardDistinguishedAmount(&amount))) {
+      // clang-format off
+      MOZ_COLLECT_REPORT(
+        "page-faults-hard", KIND_OTHER, UNITS_COUNT_CUMULATIVE, amount,
+"The number of hard page faults (also known as 'major page faults') that have "
+"occurred since the process started.  A hard page fault occurs when a process "
+"tries to access a page which is not present in physical memory. The "
+"operating system must access the disk in order to fulfill a hard page fault. "
+"When memory is plentiful, you should see very few hard page faults. But if "
+"the process tries to use more memory than your machine has available, you "
+"may see many thousands of hard page faults. Because accessing the disk is up "
+"to a million times slower than accessing RAM, the program may run very "
+"slowly when it is experiencing more than 100 or so hard page faults a "
+"second.");
+      // clang-format on
+    }
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(PageFaultsHardReporter, nsIMemoryReporter)
+
+#endif  // XP_UNIX
+
+/**
+ ** memory reporter implementation for jemalloc and OSX malloc,
+ ** to obtain info on total memory in use (that we know about,
+ ** at least -- on OSX, there are sometimes other zones in use).
+ **/
+
+#ifdef HAVE_JEMALLOC_STATS
+
+static size_t HeapOverhead(const jemalloc_stats_t& aStats) {
+  return aStats.waste + aStats.bookkeeping + aStats.page_cache +
+         aStats.bin_unused;
+}
+
+// This has UNITS_PERCENTAGE, so it is multiplied by 100x *again* on top of the
+// 100x for the percentage.
+
+// static
+int64_t nsMemoryReporterManager::HeapOverheadFraction(
+    const jemalloc_stats_t& aStats) {
+  size_t heapOverhead = HeapOverhead(aStats);
+  size_t heapCommitted = aStats.allocated + heapOverhead;
+  return int64_t(10000 * (heapOverhead / (double)heapCommitted));
+}
+
+class JemallocHeapReporter final : public nsIMemoryReporter {
+  ~JemallocHeapReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    jemalloc_stats_t stats;
+    const size_t num_bins = jemalloc_stats_num_bins();
+    nsTArray<jemalloc_bin_stats_t> bin_stats(num_bins);
+    bin_stats.SetLength(num_bins);
+    jemalloc_stats(&stats, bin_stats.Elements());
+
+    // clang-format off
+    MOZ_COLLECT_REPORT(
+      "heap-committed/allocated", KIND_OTHER, UNITS_BYTES, stats.allocated,
+"Memory mapped by the heap allocator that is currently allocated to the "
+"application.  This may exceed the amount of memory requested by the "
+"application because the allocator regularly rounds up request sizes. (The "
+"exact amount requested is not recorded.)");
+
+    MOZ_COLLECT_REPORT(
+      "heap-allocated", KIND_OTHER, UNITS_BYTES, stats.allocated,
+"The same as 'heap-committed/allocated'.");
+
+    // We mark this and the other heap-overhead reporters as KIND_NONHEAP
+    // because KIND_HEAP memory means "counted in heap-allocated", which
+    // this is not.
+    for (auto& bin : bin_stats) {
+      MOZ_ASSERT(bin.size);
+      nsPrintfCString path("explicit/heap-overhead/bin-unused/bin-%zu",
+          bin.size);
+      aHandleReport->Callback(EmptyCString(), path, KIND_NONHEAP, UNITS_BYTES,
+        bin.bytes_unused,
+        nsLiteralCString(
+          "Unused bytes in all runs of all bins for this size class"),
+        aData);
+    }
+
+    if (stats.waste > 0) {
+      MOZ_COLLECT_REPORT(
+        "explicit/heap-overhead/waste", KIND_NONHEAP, UNITS_BYTES,
+        stats.waste,
+"Committed bytes which do not correspond to an active allocation and which the "
+"allocator is not intentionally keeping alive (i.e., not "
+"'explicit/heap-overhead/{bookkeeping,page-cache,bin-unused}').");
+    }
+
+    MOZ_COLLECT_REPORT(
+      "explicit/heap-overhead/bookkeeping", KIND_NONHEAP, UNITS_BYTES,
+      stats.bookkeeping,
+"Committed bytes which the heap allocator uses for internal data structures.");
+
+    MOZ_COLLECT_REPORT(
+      "explicit/heap-overhead/page-cache", KIND_NONHEAP, UNITS_BYTES,
+      stats.page_cache,
+"Memory which the allocator could return to the operating system, but hasn't. "
+"The allocator keeps this memory around as an optimization, so it doesn't "
+"have to ask the OS the next time it needs to fulfill a request. This value "
+"is typically not larger than a few megabytes.");
+
+    MOZ_COLLECT_REPORT(
+      "heap-committed/overhead", KIND_OTHER, UNITS_BYTES,
+      HeapOverhead(stats),
+"The sum of 'explicit/heap-overhead/*'.");
+
+    MOZ_COLLECT_REPORT(
+      "heap-mapped", KIND_OTHER, UNITS_BYTES, stats.mapped,
+"Amount of memory currently mapped. Includes memory that is uncommitted, i.e. "
+"neither in physical memory nor paged to disk.");
+
+    MOZ_COLLECT_REPORT(
+      "heap-chunksize", KIND_OTHER, UNITS_BYTES, stats.chunksize,
+      "Size of chunks.");
+
+#ifdef MOZ_PHC
+    mozilla::phc::MemoryUsage usage;
+    ReplaceMalloc::PHCMemoryUsage(usage);
+
+    MOZ_COLLECT_REPORT(
+      "explicit/heap-overhead/phc/metadata", KIND_NONHEAP, UNITS_BYTES,
+      usage.mMetadataBytes,
+"Memory used by PHC to store stacks and other metadata for each allocation");
+    MOZ_COLLECT_REPORT(
+      "explicit/heap-overhead/phc/fragmentation", KIND_NONHEAP, UNITS_BYTES,
+      usage.mFragmentationBytes,
+"The amount of memory lost due to rounding up allocations to the next page "
+"size. "
+"This is also known as 'internal fragmentation'. "
+"Note that all allocators have some internal fragmentation, there may still "
+"be some internal fragmentation without PHC.");
+#endif
+
+    // clang-format on
+
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(JemallocHeapReporter, nsIMemoryReporter)
+
+#endif  // HAVE_JEMALLOC_STATS
+
+// Why is this here?  At first glance, you'd think it could be defined and
+// registered with nsMemoryReporterManager entirely within nsAtomTable.cpp.
+// However, the obvious time to register it is when the table is initialized,
+// and that happens before XPCOM components are initialized, which means the
+// RegisterStrongMemoryReporter call fails.  So instead we do it here.
+class AtomTablesReporter final : public nsIMemoryReporter {
+  MOZ_DEFINE_MALLOC_SIZE_OF(MallocSizeOf)
+
+  ~AtomTablesReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    AtomsSizes sizes;
+    NS_AddSizeOfAtoms(MallocSizeOf, sizes);
+
+    MOZ_COLLECT_REPORT("explicit/atoms/table", KIND_HEAP, UNITS_BYTES,
+                       sizes.mTable, "Memory used by the atom table.");
+
+    MOZ_COLLECT_REPORT(
+        "explicit/atoms/dynamic-objects-and-chars", KIND_HEAP, UNITS_BYTES,
+        sizes.mDynamicAtoms,
+        "Memory used by dynamic atom objects and chars (which are stored "
+        "at the end of each atom object).");
+
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(AtomTablesReporter, nsIMemoryReporter)
+
+class ThreadsReporter final : public nsIMemoryReporter {
+  MOZ_DEFINE_MALLOC_SIZE_OF(MallocSizeOf)
+  ~ThreadsReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+#ifdef XP_LINUX
+    nsTArray<MemoryMapping> mappings(1024);
+    MOZ_TRY(GetMemoryMappings(mappings));
+#endif
+
+    // Enumerating over active threads requires holding a lock, so we collect
+    // info on all threads, and then call our reporter callbacks after releasing
+    // the lock.
+    struct ThreadData {
+      nsCString mName;
+      uint32_t mThreadId;
+      size_t mPrivateSize;
+    };
+    AutoTArray<ThreadData, 32> threads;
+
+    size_t eventQueueSizes = 0;
+    size_t wrapperSizes = 0;
+    size_t threadCount = 0;
+
+    for (auto* thread : nsThread::Enumerate()) {
+      threadCount++;
+      eventQueueSizes += thread->SizeOfEventQueues(MallocSizeOf);
+      wrapperSizes += thread->ShallowSizeOfIncludingThis(MallocSizeOf);
+
+      if (!thread->StackBase()) {
+        continue;
+      }
+
+#if defined(XP_LINUX)
+      int idx = mappings.BinaryIndexOf(thread->StackBase());
+      if (idx < 0) {
+        continue;
+      }
+      // Referenced() is the combined size of all pages in the region which have
+      // ever been touched, and are therefore consuming memory. For stack
+      // regions, these pages are guaranteed to be un-shared unless we fork
+      // after creating threads (which we don't).
+      size_t privateSize = mappings[idx].Referenced();
+
+      // On Linux, we have to be very careful matching memory regions to thread
+      // stacks.
+      //
+      // To begin with, the kernel only reports VM stats for regions of all
+      // adjacent pages with the same flags, protection, and backing file.
+      // There's no way to get finer-grained usage information for a subset of
+      // those pages.
+      //
+      // Stack segments always have a guard page at the bottom of the stack
+      // (assuming we only support stacks that grow down), so there's no danger
+      // of them being merged with other stack regions. At the top, there's no
+      // protection page, and no way to allocate one without using pthreads
+      // directly and allocating our own stacks. So we get around the problem by
+      // adding an extra VM flag (NOHUGEPAGES) to our stack region, which we
+      // don't expect to be set on any heap regions. But this is not fool-proof.
+      //
+      // A second kink is that different C libraries (and different versions
+      // thereof) report stack base locations and sizes differently with regard
+      // to the guard page. For the libraries that include the guard page in the
+      // stack size base pointer, we need to adjust those values to compensate.
+      // But it's possible that our logic will get out of sync with library
+      // changes, or someone will compile with an unexpected library.
+      //
+      //
+      // The upshot of all of this is that there may be configurations that our
+      // special cases don't cover. And if there are, we want to know about it.
+      // So assert that total size of the memory region we're reporting actually
+      // matches the allocated size of the thread stack.
+#  ifndef ANDROID
+      MOZ_ASSERT(mappings[idx].Size() == thread->StackSize(),
+                 "Mapping region size doesn't match stack allocation size");
+#  endif
+#elif defined(XP_WIN)
+      auto memInfo = MemoryInfo::Get(thread->StackBase(), thread->StackSize());
+      size_t privateSize = memInfo.Committed();
+#else
+      size_t privateSize = thread->StackSize();
+      MOZ_ASSERT_UNREACHABLE(
+          "Shouldn't have stack base pointer on this "
+          "platform");
+#endif
+
+      nsCString threadName;
+      thread->GetThreadName(threadName);
+      threads.AppendElement(ThreadData{
+          std::move(threadName),
+          thread->ThreadId(),
+          // On Linux, it's possible (but unlikely) that our stack region will
+          // have been merged with adjacent heap regions, in which case we'll
+          // get combined size information for both. So we take the minimum of
+          // the reported private size and the requested stack size to avoid the
+          // possible of majorly over-reporting in that case.
+          std::min(privateSize, thread->StackSize()),
+      });
+    }
+
+    for (auto& thread : threads) {
+      nsPrintfCString path("explicit/threads/stacks/%s (tid=%u)",
+                           thread.mName.get(), thread.mThreadId);
+
+      aHandleReport->Callback(
+          ""_ns, path, KIND_NONHEAP, UNITS_BYTES, thread.mPrivateSize,
+          nsLiteralCString("The sizes of thread stacks which have been "
+                           "committed to memory."),
+          aData);
+    }
+
+    MOZ_COLLECT_REPORT("explicit/threads/overhead/event-queues", KIND_HEAP,
+                       UNITS_BYTES, eventQueueSizes,
+                       "The sizes of nsThread event queues and observers.");
+
+    MOZ_COLLECT_REPORT("explicit/threads/overhead/wrappers", KIND_HEAP,
+                       UNITS_BYTES, wrapperSizes,
+                       "The sizes of nsThread/PRThread wrappers.");
+
+#if defined(XP_WIN)
+    // Each thread on Windows has a fixed kernel overhead. For 32 bit Windows,
+    // that's 12K. For 64 bit, it's 24K.
+    //
+    // See
+    // https://blogs.technet.microsoft.com/markrussinovich/2009/07/05/pushing-the-limits-of-windows-processes-and-threads/
+    constexpr size_t kKernelSize = (sizeof(void*) == 8 ? 24 : 12) * 1024;
+#elif defined(XP_LINUX)
+    // On Linux, kernel stacks are usually 8K. However, on x86, they are
+    // allocated virtually, and start out at 4K. They may grow to 8K, but we
+    // have no way of knowing which ones do, so all we can do is guess.
+#  if defined(__x86_64__) || defined(__i386__)
+    constexpr size_t kKernelSize = 4 * 1024;
+#  else
+    constexpr size_t kKernelSize = 8 * 1024;
+#  endif
+#elif defined(XP_MACOSX)
+    // On Darwin, kernel stacks are 16K:
+    //
+    // https://books.google.com/books?id=K8vUkpOXhN4C&lpg=PA513&dq=mach%20kernel%20thread%20stack%20size&pg=PA513#v=onepage&q=mach%20kernel%20thread%20stack%20size&f=false
+    constexpr size_t kKernelSize = 16 * 1024;
+#else
+    // Elsewhere, just assume that kernel stacks require at least 8K.
+    constexpr size_t kKernelSize = 8 * 1024;
+#endif
+
+    MOZ_COLLECT_REPORT("explicit/threads/overhead/kernel", KIND_NONHEAP,
+                       UNITS_BYTES, threadCount * kKernelSize,
+                       "The total kernel overhead for all active threads.");
+
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(ThreadsReporter, nsIMemoryReporter)
+
+#ifdef DEBUG
+
+// Ideally, this would be implemented in BlockingResourceBase.cpp.
+// However, this ends up breaking the linking step of various unit tests due
+// to adding a new dependency to libdmd for a commonly used feature (mutexes)
+// in  DMD  builds. So instead we do it here.
+class DeadlockDetectorReporter final : public nsIMemoryReporter {
+  MOZ_DEFINE_MALLOC_SIZE_OF(MallocSizeOf)
+
+  ~DeadlockDetectorReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    MOZ_COLLECT_REPORT(
+        "explicit/deadlock-detector", KIND_HEAP, UNITS_BYTES,
+        BlockingResourceBase::SizeOfDeadlockDetector(MallocSizeOf),
+        "Memory used by the deadlock detector.");
+
+    return NS_OK;
+  }
+};
+NS_IMPL_ISUPPORTS(DeadlockDetectorReporter, nsIMemoryReporter)
+
+#endif
+
+#ifdef MOZ_DMD
+
+namespace mozilla {
+namespace dmd {
+
+class DMDReporter final : public nsIMemoryReporter {
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    dmd::Sizes sizes;
+    dmd::SizeOf(&sizes);
+
+    MOZ_COLLECT_REPORT(
+        "explicit/dmd/stack-traces/used", KIND_HEAP, UNITS_BYTES,
+        sizes.mStackTracesUsed,
+        "Memory used by stack traces which correspond to at least "
+        "one heap block DMD is tracking.");
+
+    MOZ_COLLECT_REPORT(
+        "explicit/dmd/stack-traces/unused", KIND_HEAP, UNITS_BYTES,
+        sizes.mStackTracesUnused,
+        "Memory used by stack traces which don't correspond to any heap "
+        "blocks DMD is currently tracking.");
+
+    MOZ_COLLECT_REPORT("explicit/dmd/stack-traces/table", KIND_HEAP,
+                       UNITS_BYTES, sizes.mStackTraceTable,
+                       "Memory used by DMD's stack trace table.");
+
+    MOZ_COLLECT_REPORT("explicit/dmd/live-block-table", KIND_HEAP, UNITS_BYTES,
+                       sizes.mLiveBlockTable,
+                       "Memory used by DMD's live block table.");
+
+    MOZ_COLLECT_REPORT("explicit/dmd/dead-block-list", KIND_HEAP, UNITS_BYTES,
+                       sizes.mDeadBlockTable,
+                       "Memory used by DMD's dead block list.");
+
+    return NS_OK;
+  }
+
+ private:
+  ~DMDReporter() = default;
+};
+NS_IMPL_ISUPPORTS(DMDReporter, nsIMemoryReporter)
+
+}  // namespace dmd
+}  // namespace mozilla
+
+#endif  // MOZ_DMD
+
+#ifdef MOZ_WIDGET_ANDROID
+class AndroidMemoryReporter final : public nsIMemoryReporter {
+ public:
+  NS_DECL_ISUPPORTS
+
+  AndroidMemoryReporter() = default;
+
+  NS_IMETHOD
+  CollectReports(nsIHandleReportCallback* aHandleReport, nsISupports* aData,
+                 bool aAnonymize) override {
+    if (!jni::IsAvailable() || jni::GetAPIVersion() < 23) {
+      return NS_OK;
+    }
+
+    int32_t heap = java::GeckoAppShell::GetMemoryUsage("summary.java-heap"_ns);
+    if (heap > 0) {
+      MOZ_COLLECT_REPORT("java-heap", KIND_OTHER, UNITS_BYTES, heap * 1024,
+                         "The private Java Heap usage");
+    }
+    return NS_OK;
+  }
+
+ private:
+  ~AndroidMemoryReporter() = default;
+};
+
+NS_IMPL_ISUPPORTS(AndroidMemoryReporter, nsIMemoryReporter)
+#endif
+
+/**
+ ** nsMemoryReporterManager implementation
+ **/
+
+NS_IMPL_ISUPPORTS(nsMemoryReporterManager, nsIMemoryReporterManager,
+                  nsIMemoryReporter)
+
+NS_IMETHODIMP
+nsMemoryReporterManager::Init() {
+  if (!NS_IsMainThread()) {
+    MOZ_CRASH();
+  }
+
+  // Under normal circumstances this function is only called once. However,
+  // we've (infrequently) seen memory report dumps in crash reports that
+  // suggest that this function is sometimes called multiple times. That in
+  // turn means that multiple reporters of each kind are registered, which
+  // leads to duplicated reports of individual measurements such as "resident",
+  // "vsize", etc.
+  //
+  // It's unclear how these multiple calls can occur. The only plausible theory
+  // so far is badly-written extensions, because this function is callable from
+  // JS code via nsIMemoryReporter.idl.
+  //
+  // Whatever the cause, it's a bad thing. So we protect against it with the
+  // following check.
+  static bool isInited = false;
+  if (isInited) {
+    NS_WARNING("nsMemoryReporterManager::Init() has already been called!");
+    return NS_OK;
+  }
+  isInited = true;
+
+#ifdef HAVE_JEMALLOC_STATS
+  RegisterStrongReporter(new JemallocHeapReporter());
+#endif
+
+#ifdef HAVE_VSIZE_AND_RESIDENT_REPORTERS
+  RegisterStrongReporter(new VsizeReporter());
+  RegisterStrongReporter(new ResidentReporter());
+#endif
+
+#ifdef HAVE_VSIZE_MAX_CONTIGUOUS_REPORTER
+  RegisterStrongReporter(new VsizeMaxContiguousReporter());
+#endif
+
+#ifdef HAVE_RESIDENT_PEAK_REPORTER
+  RegisterStrongReporter(new ResidentPeakReporter());
+#endif
+
+#ifdef HAVE_RESIDENT_UNIQUE_REPORTER
+  RegisterStrongReporter(new ResidentUniqueReporter());
+#endif
+
+#ifdef HAVE_PAGE_FAULT_REPORTERS
+  RegisterStrongReporter(new PageFaultsSoftReporter());
+  RegisterStrongReporter(new PageFaultsHardReporter());
+#endif
+
+#ifdef HAVE_PRIVATE_REPORTER
+  RegisterStrongReporter(new PrivateReporter());
+#endif
+
+#ifdef HAVE_SYSTEM_HEAP_REPORTER
+  RegisterStrongReporter(new SystemHeapReporter());
+#endif
+
+  RegisterStrongReporter(new AtomTablesReporter());
+
+  RegisterStrongReporter(new ThreadsReporter());
+
+#ifdef DEBUG
+  RegisterStrongReporter(new DeadlockDetectorReporter());
+#endif
+
+#ifdef MOZ_GECKO_PROFILER
+  // We have to register this here rather than in profiler_init() because
+  // profiler_init() runs prior to nsMemoryReporterManager's creation.
+  RegisterStrongReporter(new GeckoProfilerReporter());
+#endif
+
+#ifdef MOZ_DMD
+  RegisterStrongReporter(new mozilla::dmd::DMDReporter());
+#endif
+
+#ifdef XP_WIN
+  RegisterStrongReporter(new WindowsAddressSpaceReporter());
+#endif
+
+#ifdef MOZ_WIDGET_ANDROID
+  RegisterStrongReporter(new AndroidMemoryReporter());
+#endif
+
+#ifdef XP_UNIX
+  nsMemoryInfoDumper::Initialize();
+#endif
+
+  // Report our own memory usage as well.
+  RegisterWeakReporter(this);
+
+  return NS_OK;
+}
+
+nsMemoryReporterManager::nsMemoryReporterManager()
+    : mMutex("nsMemoryReporterManager::mMutex"),
+      mIsRegistrationBlocked(false),
+      mStrongReporters(new StrongReportersTable()),
+      mWeakReporters(new WeakReportersTable()),
+      mSavedStrongReporters(nullptr),
+      mSavedWeakReporters(nullptr),
+      mNextGeneration(1),
+      mPendingProcessesState(nullptr),
+      mPendingReportersState(nullptr)
+#ifdef HAVE_JEMALLOC_STATS
+      ,
+      mThreadPool(do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID))
+#endif
+{
+}
+
+nsMemoryReporterManager::~nsMemoryReporterManager() {
+  delete mStrongReporters;
+  delete mWeakReporters;
+  NS_ASSERTION(!mSavedStrongReporters, "failed to restore strong reporters");
+  NS_ASSERTION(!mSavedWeakReporters, "failed to restore weak reporters");
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::CollectReports(nsIHandleReportCallback* aHandleReport,
+                                        nsISupports* aData, bool aAnonymize) {
+  size_t n = MallocSizeOf(this);
+  {
+    mozilla::MutexAutoLock autoLock(mMutex);
+    n += mStrongReporters->ShallowSizeOfIncludingThis(MallocSizeOf);
+    n += mWeakReporters->ShallowSizeOfIncludingThis(MallocSizeOf);
+  }
+
+  MOZ_COLLECT_REPORT("explicit/memory-reporter-manager", KIND_HEAP, UNITS_BYTES,
+                     n, "Memory used by the memory reporter infrastructure.");
+
+  return NS_OK;
+}
+
+#ifdef DEBUG_CHILD_PROCESS_MEMORY_REPORTING
+#  define MEMORY_REPORTING_LOG(format, ...) \
+    printf_stderr("++++ MEMORY REPORTING: " format, ##__VA_ARGS__);
+#else
+#  define MEMORY_REPORTING_LOG(...)
+#endif
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetReports(
+    nsIHandleReportCallback* aHandleReport, nsISupports* aHandleReportData,
+    nsIFinishReportingCallback* aFinishReporting,
+    nsISupports* aFinishReportingData, bool aAnonymize) {
+  return GetReportsExtended(aHandleReport, aHandleReportData, aFinishReporting,
+                            aFinishReportingData, aAnonymize,
+                            /* minimize = */ false,
+                            /* DMDident = */ u""_ns);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetReportsExtended(
+    nsIHandleReportCallback* aHandleReport, nsISupports* aHandleReportData,
+    nsIFinishReportingCallback* aFinishReporting,
+    nsISupports* aFinishReportingData, bool aAnonymize, bool aMinimize,
+    const nsAString& aDMDDumpIdent) {
+  nsresult rv;
+
+  // Memory reporters are not necessarily threadsafe, so this function must
+  // be called from the main thread.
+  if (!NS_IsMainThread()) {
+    MOZ_CRASH();
+  }
+
+  uint32_t generation = mNextGeneration++;
+
+  if (mPendingProcessesState) {
+    // A request is in flight.  Don't start another one.  And don't report
+    // an error;  just ignore it, and let the in-flight request finish.
+    MEMORY_REPORTING_LOG("GetReports (gen=%u, s->gen=%u): abort\n", generation,
+                         mPendingProcessesState->mGeneration);
+    return NS_OK;
+  }
+
+  MEMORY_REPORTING_LOG("GetReports (gen=%u)\n", generation);
+
+  uint32_t concurrency = Preferences::GetUint("memory.report_concurrency", 1);
+  MOZ_ASSERT(concurrency >= 1);
+  if (concurrency < 1) {
+    concurrency = 1;
+  }
+  mPendingProcessesState = new PendingProcessesState(
+      generation, aAnonymize, aMinimize, concurrency, aHandleReport,
+      aHandleReportData, aFinishReporting, aFinishReportingData, aDMDDumpIdent);
+
+  if (aMinimize) {
+    nsCOMPtr<nsIRunnable> callback =
+        NewRunnableMethod("nsMemoryReporterManager::StartGettingReports", this,
+                          &nsMemoryReporterManager::StartGettingReports);
+    rv = MinimizeMemoryUsage(callback);
+  } else {
+    rv = StartGettingReports();
+  }
+  return rv;
+}
+
+// MainThread only
+nsresult nsMemoryReporterManager::StartGettingReports() {
+  PendingProcessesState* s = mPendingProcessesState;
+  nsresult rv;
+
+  // Get reports for this process.
+  FILE* parentDMDFile = nullptr;
+#ifdef MOZ_DMD
+  if (!s->mDMDDumpIdent.IsEmpty()) {
+    rv = nsMemoryInfoDumper::OpenDMDFile(s->mDMDDumpIdent, getpid(),
+                                         &parentDMDFile);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      // Proceed with the memory report as if DMD were disabled.
+      parentDMDFile = nullptr;
+    }
+  }
+#endif
+
+  // This is async.
+  GetReportsForThisProcessExtended(
+      s->mHandleReport, s->mHandleReportData, s->mAnonymize, parentDMDFile,
+      s->mFinishReporting, s->mFinishReportingData);
+
+  nsTArray<dom::ContentParent*> childWeakRefs;
+  dom::ContentParent::GetAll(childWeakRefs);
+  if (!childWeakRefs.IsEmpty()) {
+    // Request memory reports from child processes.  This happens
+    // after the parent report so that the parent's main thread will
+    // be free to process the child reports, instead of causing them
+    // to be buffered and consume (possibly scarce) memory.
+
+    for (size_t i = 0; i < childWeakRefs.Length(); ++i) {
+      s->mChildrenPending.AppendElement(childWeakRefs[i]);
+    }
+  }
+
+  if (gfx::GPUProcessManager* gpu = gfx::GPUProcessManager::Get()) {
+    if (RefPtr<MemoryReportingProcess> proc = gpu->GetProcessMemoryReporter()) {
+      s->mChildrenPending.AppendElement(proc.forget());
+    }
+  }
+
+  if (RDDProcessManager* rdd = RDDProcessManager::Get()) {
+    if (RefPtr<MemoryReportingProcess> proc = rdd->GetProcessMemoryReporter()) {
+      s->mChildrenPending.AppendElement(proc.forget());
+    }
+  }
+
+  if (gfx::VRProcessManager* vr = gfx::VRProcessManager::Get()) {
+    if (RefPtr<MemoryReportingProcess> proc = vr->GetProcessMemoryReporter()) {
+      s->mChildrenPending.AppendElement(proc.forget());
+    }
+  }
+
+  if (!IsRegistrationBlocked() && net::gIOService) {
+    if (RefPtr<MemoryReportingProcess> proc =
+            net::gIOService->GetSocketProcessMemoryReporter()) {
+      s->mChildrenPending.AppendElement(proc.forget());
+    }
+  }
+
+  if (!IsRegistrationBlocked()) {
+    if (RefPtr<UtilityProcessManager> utility =
+            UtilityProcessManager::GetIfExists()) {
+      for (RefPtr<UtilityProcessParent>& parent :
+           utility->GetAllProcessesProcessParent()) {
+        if (RefPtr<MemoryReportingProcess> proc =
+                utility->GetProcessMemoryReporter(parent)) {
+          s->mChildrenPending.AppendElement(proc.forget());
+        }
+      }
+    }
+  }
+
+  if (!s->mChildrenPending.IsEmpty()) {
+    nsCOMPtr<nsITimer> timer;
+    rv = NS_NewTimerWithFuncCallback(
+        getter_AddRefs(timer), TimeoutCallback, this, kTimeoutLengthMS,
+        nsITimer::TYPE_ONE_SHOT,
+        "nsMemoryReporterManager::StartGettingReports");
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      FinishReporting();
+      return rv;
+    }
+
+    MOZ_ASSERT(!s->mTimer);
+    s->mTimer.swap(timer);
+  }
+
+  return NS_OK;
+}
+
+void nsMemoryReporterManager::DispatchReporter(
+    nsIMemoryReporter* aReporter, bool aIsAsync,
+    nsIHandleReportCallback* aHandleReport, nsISupports* aHandleReportData,
+    bool aAnonymize) {
+  MOZ_ASSERT(mPendingReportersState);
+
+  // Grab refs to everything used in the lambda function.
+  RefPtr<nsMemoryReporterManager> self = this;
+  nsCOMPtr<nsIMemoryReporter> reporter = aReporter;
+  nsCOMPtr<nsIHandleReportCallback> handleReport = aHandleReport;
+  nsCOMPtr<nsISupports> handleReportData = aHandleReportData;
+
+  nsCOMPtr<nsIRunnable> event = NS_NewRunnableFunction(
+      "nsMemoryReporterManager::DispatchReporter",
+      [self, reporter, aIsAsync, handleReport, handleReportData, aAnonymize]() {
+        reporter->CollectReports(handleReport, handleReportData, aAnonymize);
+        if (!aIsAsync) {
+          self->EndReport();
+        }
+      });
+
+  NS_DispatchToMainThread(event);
+  mPendingReportersState->mReportsPending++;
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetReportsForThisProcessExtended(
+    nsIHandleReportCallback* aHandleReport, nsISupports* aHandleReportData,
+    bool aAnonymize, FILE* aDMDFile,
+    nsIFinishReportingCallback* aFinishReporting,
+    nsISupports* aFinishReportingData) {
+  // Memory reporters are not necessarily threadsafe, so this function must
+  // be called from the main thread.
+  if (!NS_IsMainThread()) {
+    MOZ_CRASH();
+  }
+
+  if (NS_WARN_IF(mPendingReportersState)) {
+    // Report is already in progress.
+    return NS_ERROR_IN_PROGRESS;
+  }
+
+#ifdef MOZ_DMD
+  if (aDMDFile) {
+    // Clear DMD's reportedness state before running the memory
+    // reporters, to avoid spurious twice-reported warnings.
+    dmd::ClearReports();
+  }
+#else
+  MOZ_ASSERT(!aDMDFile);
+#endif
+
+  mPendingReportersState = new PendingReportersState(
+      aFinishReporting, aFinishReportingData, aDMDFile);
+
+  {
+    mozilla::MutexAutoLock autoLock(mMutex);
+
+    for (const auto& entry : *mStrongReporters) {
+      DispatchReporter(entry.GetKey(), entry.GetData(), aHandleReport,
+                       aHandleReportData, aAnonymize);
+    }
+
+    for (const auto& entry : *mWeakReporters) {
+      nsCOMPtr<nsIMemoryReporter> reporter = entry.GetKey();
+      DispatchReporter(reporter, entry.GetData(), aHandleReport,
+                       aHandleReportData, aAnonymize);
+    }
+  }
+
+  return NS_OK;
+}
+
+// MainThread only
+NS_IMETHODIMP
+nsMemoryReporterManager::EndReport() {
+  if (--mPendingReportersState->mReportsPending == 0) {
+#ifdef MOZ_DMD
+    if (mPendingReportersState->mDMDFile) {
+      nsMemoryInfoDumper::DumpDMDToFile(mPendingReportersState->mDMDFile);
+    }
+#endif
+    if (mPendingProcessesState) {
+      // This is the parent process.
+      EndProcessReport(mPendingProcessesState->mGeneration, true);
+    } else {
+      mPendingReportersState->mFinishReporting->Callback(
+          mPendingReportersState->mFinishReportingData);
+    }
+
+    delete mPendingReportersState;
+    mPendingReportersState = nullptr;
+  }
+
+  return NS_OK;
+}
+
+nsMemoryReporterManager::PendingProcessesState*
+nsMemoryReporterManager::GetStateForGeneration(uint32_t aGeneration) {
+  // Memory reporting only happens on the main thread.
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  PendingProcessesState* s = mPendingProcessesState;
+
+  if (!s) {
+    // If we reach here, then:
+    //
+    // - A child process reported back too late, and no subsequent request
+    //   is in flight.
+    //
+    // So there's nothing to be done.  Just ignore it.
+    MEMORY_REPORTING_LOG("HandleChildReports: no request in flight (aGen=%u)\n",
+                         aGeneration);
+    return nullptr;
+  }
+
+  if (aGeneration != s->mGeneration) {
+    // If we reach here, a child process must have reported back, too late,
+    // while a subsequent (higher-numbered) request is in flight.  Again,
+    // ignore it.
+    MOZ_ASSERT(aGeneration < s->mGeneration);
+    MEMORY_REPORTING_LOG(
+        "HandleChildReports: gen mismatch (aGen=%u, s->gen=%u)\n", aGeneration,
+        s->mGeneration);
+    return nullptr;
+  }
+
+  return s;
+}
+
+// This function has no return value.  If something goes wrong, there's no
+// clear place to report the problem to, but that's ok -- we will end up
+// hitting the timeout and executing TimeoutCallback().
+void nsMemoryReporterManager::HandleChildReport(
+    uint32_t aGeneration, const dom::MemoryReport& aChildReport) {
+  PendingProcessesState* s = GetStateForGeneration(aGeneration);
+  if (!s) {
+    return;
+  }
+
+  // Child reports should have a non-empty process.
+  MOZ_ASSERT(!aChildReport.process().IsEmpty());
+
+  // If the call fails, ignore and continue.
+  s->mHandleReport->Callback(aChildReport.process(), aChildReport.path(),
+                             aChildReport.kind(), aChildReport.units(),
+                             aChildReport.amount(), aChildReport.desc(),
+                             s->mHandleReportData);
+}
+
+/* static */
+bool nsMemoryReporterManager::StartChildReport(
+    mozilla::MemoryReportingProcess* aChild,
+    const PendingProcessesState* aState) {
+  if (!aChild->IsAlive()) {
+    MEMORY_REPORTING_LOG(
+        "StartChildReports (gen=%u): child exited before"
+        " its report was started\n",
+        aState->mGeneration);
+    return false;
+  }
+
+  Maybe<mozilla::ipc::FileDescriptor> dmdFileDesc;
+#ifdef MOZ_DMD
+  if (!aState->mDMDDumpIdent.IsEmpty()) {
+    FILE* dmdFile = nullptr;
+    nsresult rv = nsMemoryInfoDumper::OpenDMDFile(aState->mDMDDumpIdent,
+                                                  aChild->Pid(), &dmdFile);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      // Proceed with the memory report as if DMD were disabled.
+      dmdFile = nullptr;
+    }
+    if (dmdFile) {
+      dmdFileDesc = Some(mozilla::ipc::FILEToFileDescriptor(dmdFile));
+      fclose(dmdFile);
+    }
+  }
+#endif
+  return aChild->SendRequestMemoryReport(
+      aState->mGeneration, aState->mAnonymize, aState->mMinimize, dmdFileDesc);
+}
+
+void nsMemoryReporterManager::EndProcessReport(uint32_t aGeneration,
+                                               bool aSuccess) {
+  PendingProcessesState* s = GetStateForGeneration(aGeneration);
+  if (!s) {
+    return;
+  }
+
+  MOZ_ASSERT(s->mNumProcessesRunning > 0);
+  s->mNumProcessesRunning--;
+  s->mNumProcessesCompleted++;
+  MEMORY_REPORTING_LOG(
+      "HandleChildReports (aGen=%u): process %u %s"
+      " (%u running, %u pending)\n",
+      aGeneration, s->mNumProcessesCompleted,
+      aSuccess ? "completed" : "exited during report", s->mNumProcessesRunning,
+      static_cast<unsigned>(s->mChildrenPending.Length()));
+
+  // Start pending children up to the concurrency limit.
+  while (s->mNumProcessesRunning < s->mConcurrencyLimit &&
+         !s->mChildrenPending.IsEmpty()) {
+    // Pop last element from s->mChildrenPending
+    const RefPtr<MemoryReportingProcess> nextChild =
+        s->mChildrenPending.PopLastElement();
+    // Start report (if the child is still alive).
+    if (StartChildReport(nextChild, s)) {
+      ++s->mNumProcessesRunning;
+      MEMORY_REPORTING_LOG(
+          "HandleChildReports (aGen=%u): started child report"
+          " (%u running, %u pending)\n",
+          aGeneration, s->mNumProcessesRunning,
+          static_cast<unsigned>(s->mChildrenPending.Length()));
+    }
+  }
+
+  // If all the child processes (if any) have reported, we can cancel
+  // the timer (if started) and finish up.  Otherwise, just return.
+  if (s->mNumProcessesRunning == 0) {
+    MOZ_ASSERT(s->mChildrenPending.IsEmpty());
+    if (s->mTimer) {
+      s->mTimer->Cancel();
+    }
+    FinishReporting();
+  }
+}
+
+/* static */
+void nsMemoryReporterManager::TimeoutCallback(nsITimer* aTimer, void* aData) {
+  nsMemoryReporterManager* mgr = static_cast<nsMemoryReporterManager*>(aData);
+  PendingProcessesState* s = mgr->mPendingProcessesState;
+
+  // Release assert because: if the pointer is null we're about to
+  // crash regardless of DEBUG, and this way the compiler doesn't
+  // complain about unused variables.
+  MOZ_RELEASE_ASSERT(s, "mgr->mPendingProcessesState");
+  MEMORY_REPORTING_LOG("TimeoutCallback (s->gen=%u; %u running, %u pending)\n",
+                       s->mGeneration, s->mNumProcessesRunning,
+                       static_cast<unsigned>(s->mChildrenPending.Length()));
+
+  // We don't bother sending any kind of cancellation message to the child
+  // processes that haven't reported back.
+  mgr->FinishReporting();
+}
+
+nsresult nsMemoryReporterManager::FinishReporting() {
+  // Memory reporting only happens on the main thread.
+  if (!NS_IsMainThread()) {
+    MOZ_CRASH();
+  }
+
+  MOZ_ASSERT(mPendingProcessesState);
+  MEMORY_REPORTING_LOG("FinishReporting (s->gen=%u; %u processes reported)\n",
+                       mPendingProcessesState->mGeneration,
+                       mPendingProcessesState->mNumProcessesCompleted);
+
+  // Call this before deleting |mPendingProcessesState|.  That way, if
+  // |mFinishReportData| calls GetReports(), it will silently abort, as
+  // required.
+  nsresult rv = mPendingProcessesState->mFinishReporting->Callback(
+      mPendingProcessesState->mFinishReportingData);
+
+  delete mPendingProcessesState;
+  mPendingProcessesState = nullptr;
+  return rv;
+}
+
+nsMemoryReporterManager::PendingProcessesState::PendingProcessesState(
+    uint32_t aGeneration, bool aAnonymize, bool aMinimize,
+    uint32_t aConcurrencyLimit, nsIHandleReportCallback* aHandleReport,
+    nsISupports* aHandleReportData,
+    nsIFinishReportingCallback* aFinishReporting,
+    nsISupports* aFinishReportingData, const nsAString& aDMDDumpIdent)
+    : mGeneration(aGeneration),
+      mAnonymize(aAnonymize),
+      mMinimize(aMinimize),
+      mChildrenPending(),
+      mNumProcessesRunning(1),  // reporting starts with the parent
+      mNumProcessesCompleted(0),
+      mConcurrencyLimit(aConcurrencyLimit),
+      mHandleReport(aHandleReport),
+      mHandleReportData(aHandleReportData),
+      mFinishReporting(aFinishReporting),
+      mFinishReportingData(aFinishReportingData),
+      mDMDDumpIdent(aDMDDumpIdent) {}
+
+static void CrashIfRefcountIsZero(nsISupports* aObj) {
+  // This will probably crash if the object's refcount is 0.
+  uint32_t refcnt = NS_ADDREF(aObj);
+  if (refcnt <= 1) {
+    MOZ_CRASH("CrashIfRefcountIsZero: refcount is zero");
+  }
+  NS_RELEASE(aObj);
+}
+
+nsresult nsMemoryReporterManager::RegisterReporterHelper(
+    nsIMemoryReporter* aReporter, bool aForce, bool aStrong, bool aIsAsync) {
+  // This method is thread-safe.
+  mozilla::MutexAutoLock autoLock(mMutex);
+
+  if (mIsRegistrationBlocked && !aForce) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (mStrongReporters->Contains(aReporter) ||
+      mWeakReporters->Contains(aReporter)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // If |aStrong| is true, |aReporter| may have a refcnt of 0, so we take
+  // a kung fu death grip before calling PutEntry.  Otherwise, if PutEntry
+  // addref'ed and released |aReporter| before finally addref'ing it for
+  // good, it would free aReporter!  The kung fu death grip could itself be
+  // problematic if PutEntry didn't addref |aReporter| (because then when the
+  // death grip goes out of scope, we would delete the reporter).  In debug
+  // mode, we check that this doesn't happen.
+  //
+  // If |aStrong| is false, we require that |aReporter| have a non-zero
+  // refcnt.
+  //
+  if (aStrong) {
+    nsCOMPtr<nsIMemoryReporter> kungFuDeathGrip = aReporter;
+    mStrongReporters->InsertOrUpdate(aReporter, aIsAsync);
+    CrashIfRefcountIsZero(aReporter);
+  } else {
+    CrashIfRefcountIsZero(aReporter);
+    nsCOMPtr<nsIXPConnectWrappedJS> jsComponent = do_QueryInterface(aReporter);
+    if (jsComponent) {
+      // We cannot allow non-native reporters (WrappedJS), since we'll be
+      // holding onto a raw pointer, which would point to the wrapper,
+      // and that wrapper is likely to go away as soon as this register
+      // call finishes.  This would then lead to subsequent crashes in
+      // CollectReports().
+      return NS_ERROR_XPC_BAD_CONVERT_JS;
+    }
+    mWeakReporters->InsertOrUpdate(aReporter, aIsAsync);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::RegisterStrongReporter(nsIMemoryReporter* aReporter) {
+  return RegisterReporterHelper(aReporter, /* force = */ false,
+                                /* strong = */ true,
+                                /* async = */ false);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::RegisterStrongAsyncReporter(
+    nsIMemoryReporter* aReporter) {
+  return RegisterReporterHelper(aReporter, /* force = */ false,
+                                /* strong = */ true,
+                                /* async = */ true);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::RegisterWeakReporter(nsIMemoryReporter* aReporter) {
+  return RegisterReporterHelper(aReporter, /* force = */ false,
+                                /* strong = */ false,
+                                /* async = */ false);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::RegisterWeakAsyncReporter(
+    nsIMemoryReporter* aReporter) {
+  return RegisterReporterHelper(aReporter, /* force = */ false,
+                                /* strong = */ false,
+                                /* async = */ true);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::RegisterStrongReporterEvenIfBlocked(
+    nsIMemoryReporter* aReporter) {
+  return RegisterReporterHelper(aReporter, /* force = */ true,
+                                /* strong = */ true,
+                                /* async = */ false);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::UnregisterStrongReporter(
+    nsIMemoryReporter* aReporter) {
+  // This method is thread-safe.
+  mozilla::MutexAutoLock autoLock(mMutex);
+
+  MOZ_ASSERT(!mWeakReporters->Contains(aReporter));
+
+  if (mStrongReporters->Contains(aReporter)) {
+    mStrongReporters->Remove(aReporter);
+    return NS_OK;
+  }
+
+  // We don't register new reporters when the block is in place, but we do
+  // unregister existing reporters. This is so we don't keep holding strong
+  // references that these reporters aren't expecting (which can keep them
+  // alive longer than intended).
+  if (mSavedStrongReporters && mSavedStrongReporters->Contains(aReporter)) {
+    mSavedStrongReporters->Remove(aReporter);
+    return NS_OK;
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::UnregisterWeakReporter(nsIMemoryReporter* aReporter) {
+  // This method is thread-safe.
+  mozilla::MutexAutoLock autoLock(mMutex);
+
+  MOZ_ASSERT(!mStrongReporters->Contains(aReporter));
+
+  if (mWeakReporters->Contains(aReporter)) {
+    mWeakReporters->Remove(aReporter);
+    return NS_OK;
+  }
+
+  // We don't register new reporters when the block is in place, but we do
+  // unregister existing reporters. This is so we don't keep holding weak
+  // references that the old reporters aren't expecting (which can end up as
+  // dangling pointers that lead to use-after-frees).
+  if (mSavedWeakReporters && mSavedWeakReporters->Contains(aReporter)) {
+    mSavedWeakReporters->Remove(aReporter);
+    return NS_OK;
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::BlockRegistrationAndHideExistingReporters() {
+  // This method is thread-safe.
+  mozilla::MutexAutoLock autoLock(mMutex);
+  if (mIsRegistrationBlocked) {
+    return NS_ERROR_FAILURE;
+  }
+  mIsRegistrationBlocked = true;
+
+  // Hide the existing reporters, saving them for later restoration.
+  MOZ_ASSERT(!mSavedStrongReporters);
+  MOZ_ASSERT(!mSavedWeakReporters);
+  mSavedStrongReporters = mStrongReporters;
+  mSavedWeakReporters = mWeakReporters;
+  mStrongReporters = new StrongReportersTable();
+  mWeakReporters = new WeakReportersTable();
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::UnblockRegistrationAndRestoreOriginalReporters() {
+  // This method is thread-safe.
+  mozilla::MutexAutoLock autoLock(mMutex);
+  if (!mIsRegistrationBlocked) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Banish the current reporters, and restore the hidden ones.
+  delete mStrongReporters;
+  delete mWeakReporters;
+  mStrongReporters = mSavedStrongReporters;
+  mWeakReporters = mSavedWeakReporters;
+  mSavedStrongReporters = nullptr;
+  mSavedWeakReporters = nullptr;
+
+  mIsRegistrationBlocked = false;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetVsize(int64_t* aVsize) {
+#ifdef HAVE_VSIZE_AND_RESIDENT_REPORTERS
+  return VsizeDistinguishedAmount(aVsize);
+#else
+  *aVsize = 0;
+  return NS_ERROR_NOT_AVAILABLE;
+#endif
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetVsizeMaxContiguous(int64_t* aAmount) {
+#ifdef HAVE_VSIZE_MAX_CONTIGUOUS_REPORTER
+  return VsizeMaxContiguousDistinguishedAmount(aAmount);
+#else
+  *aAmount = 0;
+  return NS_ERROR_NOT_AVAILABLE;
+#endif
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetResident(int64_t* aAmount) {
+#ifdef HAVE_VSIZE_AND_RESIDENT_REPORTERS
+  return ResidentDistinguishedAmount(aAmount);
+#else
+  *aAmount = 0;
+  return NS_ERROR_NOT_AVAILABLE;
+#endif
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetResidentFast(int64_t* aAmount) {
+#ifdef HAVE_VSIZE_AND_RESIDENT_REPORTERS
+  return ResidentFastDistinguishedAmount(aAmount);
+#else
+  *aAmount = 0;
+  return NS_ERROR_NOT_AVAILABLE;
+#endif
+}
+
+/*static*/
+int64_t nsMemoryReporterManager::ResidentFast() {
+#ifdef HAVE_VSIZE_AND_RESIDENT_REPORTERS
+  int64_t amount;
+  nsresult rv = ResidentFastDistinguishedAmount(&amount);
+  NS_ENSURE_SUCCESS(rv, 0);
+  return amount;
+#else
+  return 0;
+#endif
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetResidentPeak(int64_t* aAmount) {
+#ifdef HAVE_RESIDENT_PEAK_REPORTER
+  return ResidentPeakDistinguishedAmount(aAmount);
+#else
+  *aAmount = 0;
+  return NS_ERROR_NOT_AVAILABLE;
+#endif
+}
+
+/*static*/
+int64_t nsMemoryReporterManager::ResidentPeak() {
+#ifdef HAVE_RESIDENT_PEAK_REPORTER
+  int64_t amount = 0;
+  nsresult rv = ResidentPeakDistinguishedAmount(&amount);
+  NS_ENSURE_SUCCESS(rv, 0);
+  return amount;
+#else
+  return 0;
+#endif
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetResidentUnique(int64_t* aAmount) {
+#ifdef HAVE_RESIDENT_UNIQUE_REPORTER
+  return ResidentUniqueDistinguishedAmount(aAmount);
+#else
+  *aAmount = 0;
+  return NS_ERROR_NOT_AVAILABLE;
+#endif
+}
+
+#ifdef XP_MACOSX
+/*static*/
+int64_t nsMemoryReporterManager::PhysicalFootprint(mach_port_t aPort) {
+  int64_t amount = 0;
+  nsresult rv = PhysicalFootprintAmount(&amount, aPort);
+  NS_ENSURE_SUCCESS(rv, 0);
+  return amount;
+}
+#endif
+
+typedef
+#ifdef XP_WIN
+    HANDLE
+#elif XP_MACOSX
+    mach_port_t
+#elif XP_LINUX
+    pid_t
+#else
+    int /*dummy type */
+#endif
+        ResidentUniqueArg;
+
+#if defined(XP_WIN) || defined(XP_MACOSX) || defined(XP_LINUX)
+
+/*static*/
+int64_t nsMemoryReporterManager::ResidentUnique(ResidentUniqueArg aProcess) {
+  int64_t amount = 0;
+  nsresult rv = ResidentUniqueDistinguishedAmount(&amount, aProcess);
+  NS_ENSURE_SUCCESS(rv, 0);
+  return amount;
+}
+
+#else
+
+/*static*/
+int64_t nsMemoryReporterManager::ResidentUnique(ResidentUniqueArg) {
+#  ifdef HAVE_RESIDENT_UNIQUE_REPORTER
+  int64_t amount = 0;
+  nsresult rv = ResidentUniqueDistinguishedAmount(&amount);
+  NS_ENSURE_SUCCESS(rv, 0);
+  return amount;
+#  else
+  return 0;
+#  endif
+}
+
+#endif  // XP_{WIN, MACOSX, LINUX, *}
+
+#ifdef HAVE_JEMALLOC_STATS
+// static
+size_t nsMemoryReporterManager::HeapAllocated(const jemalloc_stats_t& aStats) {
+  return aStats.allocated;
+}
+#endif
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetHeapAllocated(int64_t* aAmount) {
+#ifdef HAVE_JEMALLOC_STATS
+  jemalloc_stats_t stats;
+  jemalloc_stats(&stats);
+  *aAmount = HeapAllocated(stats);
+  return NS_OK;
+#else
+  *aAmount = 0;
+  return NS_ERROR_NOT_AVAILABLE;
+#endif
+}
+
+// This has UNITS_PERCENTAGE, so it is multiplied by 100x.
+NS_IMETHODIMP
+nsMemoryReporterManager::GetHeapOverheadFraction(int64_t* aAmount) {
+#ifdef HAVE_JEMALLOC_STATS
+  jemalloc_stats_t stats;
+  jemalloc_stats(&stats);
+  *aAmount = HeapOverheadFraction(stats);
+  return NS_OK;
+#else
+  *aAmount = 0;
+  return NS_ERROR_NOT_AVAILABLE;
+#endif
+}
+
+[[nodiscard]] static nsresult GetInfallibleAmount(InfallibleAmountFn aAmountFn,
+                                                  int64_t* aAmount) {
+  if (aAmountFn) {
+    *aAmount = aAmountFn();
+    return NS_OK;
+  }
+  *aAmount = 0;
+  return NS_ERROR_NOT_AVAILABLE;
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetJSMainRuntimeGCHeap(int64_t* aAmount) {
+  return GetInfallibleAmount(mAmountFns.mJSMainRuntimeGCHeap, aAmount);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetJSMainRuntimeTemporaryPeak(int64_t* aAmount) {
+  return GetInfallibleAmount(mAmountFns.mJSMainRuntimeTemporaryPeak, aAmount);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetJSMainRuntimeCompartmentsSystem(int64_t* aAmount) {
+  return GetInfallibleAmount(mAmountFns.mJSMainRuntimeCompartmentsSystem,
+                             aAmount);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetJSMainRuntimeCompartmentsUser(int64_t* aAmount) {
+  return GetInfallibleAmount(mAmountFns.mJSMainRuntimeCompartmentsUser,
+                             aAmount);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetJSMainRuntimeRealmsSystem(int64_t* aAmount) {
+  return GetInfallibleAmount(mAmountFns.mJSMainRuntimeRealmsSystem, aAmount);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetJSMainRuntimeRealmsUser(int64_t* aAmount) {
+  return GetInfallibleAmount(mAmountFns.mJSMainRuntimeRealmsUser, aAmount);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetImagesContentUsedUncompressed(int64_t* aAmount) {
+  return GetInfallibleAmount(mAmountFns.mImagesContentUsedUncompressed,
+                             aAmount);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetStorageSQLite(int64_t* aAmount) {
+  return GetInfallibleAmount(mAmountFns.mStorageSQLite, aAmount);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetLowMemoryEventsPhysical(int64_t* aAmount) {
+  return GetInfallibleAmount(mAmountFns.mLowMemoryEventsPhysical, aAmount);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetGhostWindows(int64_t* aAmount) {
+  return GetInfallibleAmount(mAmountFns.mGhostWindows, aAmount);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetPageFaultsHard(int64_t* aAmount) {
+#ifdef HAVE_PAGE_FAULT_REPORTERS
+  return PageFaultsHardDistinguishedAmount(aAmount);
+#else
+  *aAmount = 0;
+  return NS_ERROR_NOT_AVAILABLE;
+#endif
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetHasMozMallocUsableSize(bool* aHas) {
+  void* p = malloc(16);
+  if (!p) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  size_t usable = moz_malloc_usable_size(p);
+  free(p);
+  *aHas = !!(usable > 0);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetIsDMDEnabled(bool* aIsEnabled) {
+#ifdef MOZ_DMD
+  *aIsEnabled = true;
+#else
+  *aIsEnabled = false;
+#endif
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::GetIsDMDRunning(bool* aIsRunning) {
+#ifdef MOZ_DMD
+  *aIsRunning = dmd::IsRunning();
+#else
+  *aIsRunning = false;
+#endif
+  return NS_OK;
+}
+
+namespace {
+
+/**
+ * This runnable lets us implement
+ * nsIMemoryReporterManager::MinimizeMemoryUsage().  We fire a heap-minimize
+ * notification, spin the event loop, and repeat this process a few times.
+ *
+ * When this sequence finishes, we invoke the callback function passed to the
+ * runnable's constructor.
+ */
+class MinimizeMemoryUsageRunnable : public Runnable {
+ public:
+  explicit MinimizeMemoryUsageRunnable(nsIRunnable* aCallback)
+      : mozilla::Runnable("MinimizeMemoryUsageRunnable"),
+        mCallback(aCallback),
+        mRemainingIters(sNumIters) {}
+
+  NS_IMETHOD Run() override {
+    nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+    if (!os) {
+      return NS_ERROR_FAILURE;
+    }
+
+    if (mRemainingIters == 0) {
+      os->NotifyObservers(nullptr, "after-minimize-memory-usage",
+                          u"MinimizeMemoryUsageRunnable");
+      if (mCallback) {
+        mCallback->Run();
+      }
+      return NS_OK;
+    }
+
+    os->NotifyObservers(nullptr, "memory-pressure", u"heap-minimize");
+    mRemainingIters--;
+    NS_DispatchToMainThread(this);
+
+    return NS_OK;
+  }
+
+ private:
+  // Send sNumIters heap-minimize notifications, spinning the event
+  // loop after each notification (see bug 610166 comment 12 for an
+  // explanation), because one notification doesn't cut it.
+  static const uint32_t sNumIters = 3;
+
+  nsCOMPtr<nsIRunnable> mCallback;
+  uint32_t mRemainingIters;
+};
+
+}  // namespace
+
+NS_IMETHODIMP
+nsMemoryReporterManager::MinimizeMemoryUsage(nsIRunnable* aCallback) {
+  RefPtr<MinimizeMemoryUsageRunnable> runnable =
+      new MinimizeMemoryUsageRunnable(aCallback);
+
+  return NS_DispatchToMainThread(runnable);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::SizeOfTab(mozIDOMWindowProxy* aTopWindow,
+                                   int64_t* aJSObjectsSize,
+                                   int64_t* aJSStringsSize,
+                                   int64_t* aJSOtherSize, int64_t* aDomSize,
+                                   int64_t* aStyleSize, int64_t* aOtherSize,
+                                   int64_t* aTotalSize, double* aJSMilliseconds,
+                                   double* aNonJSMilliseconds) {
+  nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(aTopWindow);
+  auto* piWindow = nsPIDOMWindowOuter::From(aTopWindow);
+  if (NS_WARN_IF(!global) || NS_WARN_IF(!piWindow)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  TimeStamp t1 = TimeStamp::Now();
+
+  // Measure JS memory consumption (and possibly some non-JS consumption, via
+  // |jsPrivateSize|).
+  size_t jsObjectsSize, jsStringsSize, jsPrivateSize, jsOtherSize;
+  nsresult rv = mSizeOfTabFns.mJS(global->GetGlobalJSObject(), &jsObjectsSize,
+                                  &jsStringsSize, &jsPrivateSize, &jsOtherSize);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  TimeStamp t2 = TimeStamp::Now();
+
+  // Measure non-JS memory consumption.
+  size_t domSize, styleSize, otherSize;
+  rv = mSizeOfTabFns.mNonJS(piWindow, &domSize, &styleSize, &otherSize);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  TimeStamp t3 = TimeStamp::Now();
+
+  *aTotalSize = 0;
+#define DO(aN, n)       \
+  {                     \
+    *aN = (n);          \
+    *aTotalSize += (n); \
+  }
+  DO(aJSObjectsSize, jsObjectsSize);
+  DO(aJSStringsSize, jsStringsSize);
+  DO(aJSOtherSize, jsOtherSize);
+  DO(aDomSize, jsPrivateSize + domSize);
+  DO(aStyleSize, styleSize);
+  DO(aOtherSize, otherSize);
+#undef DO
+
+  *aJSMilliseconds = (t2 - t1).ToMilliseconds();
+  *aNonJSMilliseconds = (t3 - t2).ToMilliseconds();
+
+  return NS_OK;
+}
+
+namespace mozilla {
+
+#define GET_MEMORY_REPORTER_MANAGER(mgr)      \
+  RefPtr<nsMemoryReporterManager> mgr =       \
+      nsMemoryReporterManager::GetOrCreate(); \
+  if (!mgr) {                                 \
+    return NS_ERROR_FAILURE;                  \
+  }
+
+nsresult RegisterStrongMemoryReporter(nsIMemoryReporter* aReporter) {
+  // Hold a strong reference to the argument to make sure it gets released if
+  // we return early below.
+  nsCOMPtr<nsIMemoryReporter> reporter = aReporter;
+  GET_MEMORY_REPORTER_MANAGER(mgr)
+  return mgr->RegisterStrongReporter(reporter);
+}
+
+nsresult RegisterStrongAsyncMemoryReporter(nsIMemoryReporter* aReporter) {
+  // Hold a strong reference to the argument to make sure it gets released if
+  // we return early below.
+  nsCOMPtr<nsIMemoryReporter> reporter = aReporter;
+  GET_MEMORY_REPORTER_MANAGER(mgr)
+  return mgr->RegisterStrongAsyncReporter(reporter);
+}
+
+nsresult RegisterWeakMemoryReporter(nsIMemoryReporter* aReporter) {
+  GET_MEMORY_REPORTER_MANAGER(mgr)
+  return mgr->RegisterWeakReporter(aReporter);
+}
+
+nsresult RegisterWeakAsyncMemoryReporter(nsIMemoryReporter* aReporter) {
+  GET_MEMORY_REPORTER_MANAGER(mgr)
+  return mgr->RegisterWeakAsyncReporter(aReporter);
+}
+
+nsresult UnregisterStrongMemoryReporter(nsIMemoryReporter* aReporter) {
+  GET_MEMORY_REPORTER_MANAGER(mgr)
+  return mgr->UnregisterStrongReporter(aReporter);
+}
+
+nsresult UnregisterWeakMemoryReporter(nsIMemoryReporter* aReporter) {
+  GET_MEMORY_REPORTER_MANAGER(mgr)
+  return mgr->UnregisterWeakReporter(aReporter);
+}
+
+// Macro for generating functions that register distinguished amount functions
+// with the memory reporter manager.
+#define DEFINE_REGISTER_DISTINGUISHED_AMOUNT(kind, name)                   \
+  nsresult Register##name##DistinguishedAmount(kind##AmountFn aAmountFn) { \
+    GET_MEMORY_REPORTER_MANAGER(mgr)                                       \
+    mgr->mAmountFns.m##name = aAmountFn;                                   \
+    return NS_OK;                                                          \
+  }
+
+// Macro for generating functions that unregister distinguished amount
+// functions with the memory reporter manager.
+#define DEFINE_UNREGISTER_DISTINGUISHED_AMOUNT(name) \
+  nsresult Unregister##name##DistinguishedAmount() { \
+    GET_MEMORY_REPORTER_MANAGER(mgr)                 \
+    mgr->mAmountFns.m##name = nullptr;               \
+    return NS_OK;                                    \
+  }
+
+DEFINE_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeGCHeap)
+DEFINE_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeTemporaryPeak)
+DEFINE_REGISTER_DISTINGUISHED_AMOUNT(Infallible,
+                                     JSMainRuntimeCompartmentsSystem)
+DEFINE_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeCompartmentsUser)
+DEFINE_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeRealmsSystem)
+DEFINE_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeRealmsUser)
+
+DEFINE_REGISTER_DISTINGUISHED_AMOUNT(Infallible, ImagesContentUsedUncompressed)
+DEFINE_UNREGISTER_DISTINGUISHED_AMOUNT(ImagesContentUsedUncompressed)
+
+DEFINE_REGISTER_DISTINGUISHED_AMOUNT(Infallible, StorageSQLite)
+DEFINE_UNREGISTER_DISTINGUISHED_AMOUNT(StorageSQLite)
+
+DEFINE_REGISTER_DISTINGUISHED_AMOUNT(Infallible, LowMemoryEventsPhysical)
+
+DEFINE_REGISTER_DISTINGUISHED_AMOUNT(Infallible, GhostWindows)
+
+#undef DEFINE_REGISTER_DISTINGUISHED_AMOUNT
+#undef DEFINE_UNREGISTER_DISTINGUISHED_AMOUNT
+
+#define DEFINE_REGISTER_SIZE_OF_TAB(name)                              \
+  nsresult Register##name##SizeOfTab(name##SizeOfTabFn aSizeOfTabFn) { \
+    GET_MEMORY_REPORTER_MANAGER(mgr)                                   \
+    mgr->mSizeOfTabFns.m##name = aSizeOfTabFn;                         \
+    return NS_OK;                                                      \
+  }
+
+DEFINE_REGISTER_SIZE_OF_TAB(JS);
+DEFINE_REGISTER_SIZE_OF_TAB(NonJS);
+
+#undef DEFINE_REGISTER_SIZE_OF_TAB
+
+#undef GET_MEMORY_REPORTER_MANAGER
+
+}  // namespace mozilla
diff --git a/xpcom/base/nsMemoryReporterManager.h b/xpcom/base/nsMemoryReporterManager.h
new file mode 100644
index 0000000000..7064524521
--- /dev/null
+++ b/xpcom/base/nsMemoryReporterManager.h
@@ -0,0 +1,321 @@
+/* -*- 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/. */
+
+#ifndef nsMemoryReporterManager_h__
+#define nsMemoryReporterManager_h__
+
+#include "mozilla/Mutex.h"
+#include "nsTHashMap.h"
+#include "nsHashKeys.h"
+#include "nsIMemoryReporter.h"
+#include "nsISupports.h"
+#include "nsServiceManagerUtils.h"
+
+#ifdef XP_WIN
+#  include <windows.h>
+#endif  // XP_WIN
+
+#if defined(MOZ_MEMORY)
+#  define HAVE_JEMALLOC_STATS 1
+#  include "mozmemory.h"
+#endif  // MOZ_MEMORY
+
+namespace mozilla {
+class MemoryReportingProcess;
+namespace dom {
+class MemoryReport;
+}  // namespace dom
+}  // namespace mozilla
+
+class mozIDOMWindowProxy;
+class nsIEventTarget;
+class nsIRunnable;
+class nsITimer;
+
+class nsMemoryReporterManager final : public nsIMemoryReporterManager,
+                                      public nsIMemoryReporter {
+  virtual ~nsMemoryReporterManager();
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIMEMORYREPORTERMANAGER
+  NS_DECL_NSIMEMORYREPORTER
+
+  MOZ_DEFINE_MALLOC_SIZE_OF(MallocSizeOf)
+
+  nsMemoryReporterManager();
+
+  // Gets the memory reporter manager service.
+  static already_AddRefed<nsMemoryReporterManager> GetOrCreate() {
+    nsCOMPtr<nsIMemoryReporterManager> imgr =
+        do_GetService("@mozilla.org/memory-reporter-manager;1");
+    return imgr.forget().downcast<nsMemoryReporterManager>();
+  }
+
+  typedef nsTHashMap<nsRefPtrHashKey<nsIMemoryReporter>, bool>
+      StrongReportersTable;
+  typedef nsTHashMap<nsPtrHashKey<nsIMemoryReporter>, bool> WeakReportersTable;
+
+  // Inter-process memory reporting proceeds as follows.
+  //
+  // - GetReports() (declared within NS_DECL_NSIMEMORYREPORTERMANAGER)
+  //   synchronously gets memory reports for the current process, sets up some
+  //   state (mPendingProcessesState) for when child processes report back --
+  //   including a timer -- and starts telling child processes to get memory
+  //   reports.  Control then returns to the main event loop.
+  //
+  //   The number of concurrent child process reports is limited by the pref
+  //   "memory.report_concurrency" in order to prevent the memory overhead of
+  //   memory reporting from causing problems, especially on B2G when swapping
+  //   to compressed RAM; see bug 1154053.
+  //
+  // - HandleChildReport() is called (asynchronously) once per child process
+  //   reporter callback.
+  //
+  // - EndProcessReport() is called (asynchronously) once per process that
+  //   finishes reporting back, including the parent.  If all processes do so
+  //   before time-out, the timer is cancelled.  If there are child processes
+  //   whose requests have not yet been sent, they will be started until the
+  //   concurrency limit is (again) reached.
+  //
+  // - TimeoutCallback() is called (asynchronously) if all the child processes
+  //   don't respond within the time threshold.
+  //
+  // - FinishReporting() finishes things off.  It is *always* called -- either
+  //   from EndChildReport() (if all child processes have reported back) or
+  //   from TimeoutCallback() (if time-out occurs).
+  //
+  // All operations occur on the main thread.
+  //
+  // The above sequence of steps is a "request".  A partially-completed request
+  // is described as "in flight".
+  //
+  // Each request has a "generation", a unique number that identifies it.  This
+  // is used to ensure that each reports from a child process corresponds to
+  // the appropriate request from the parent process.  (It's easier to
+  // implement a generation system than to implement a child report request
+  // cancellation mechanism.)
+  //
+  // Failures are mostly ignored, because it's (a) typically the most sensible
+  // thing to do, and (b) often hard to do anything else.  The following are
+  // the failure cases of note.
+  //
+  // - If a request is made while the previous request is in flight, the new
+  //   request is ignored, as per getReports()'s specification.  No error is
+  //   reported, because the previous request will complete soon enough.
+  //
+  // - If one or more child processes fail to respond within the time limit,
+  //   things will proceed as if they don't exist.  No error is reported,
+  //   because partial information is better than nothing.
+  //
+  // - If a child process reports after the time-out occurs, it is ignored.
+  //   (Generation checking will ensure it is ignored even if a subsequent
+  //   request is in flight;  this is the main use of generations.)  No error
+  //   is reported, because there's nothing sensible to be done about it at
+  //   this late stage.
+  //
+  // - If the time-out occurs after a child process has sent some reports but
+  //   before it has signaled completion (see bug 1151597), then what it
+  //   successfully sent will be included, with no explicit indication that it
+  //   is incomplete.
+  //
+  // Now, what what happens if a child process is created/destroyed in the
+  // middle of a request?  Well, PendingProcessesState is initialized with an
+  // array of child process actors as of when the report started.  So...
+  //
+  // - If a process is created after reporting starts, it won't be sent a
+  //   request for reports.  So the reported data will reflect how things were
+  //   when the request began.
+  //
+  // - If a process is destroyed before it starts reporting back, the reported
+  //   data will reflect how things are when the request ends.
+  //
+  // - If a process is destroyed after it starts reporting back but before it
+  //   finishes, the reported data will contain a partial report for it.
+  //
+  // - If a process is destroyed after reporting back, but before all other
+  //   child processes have reported back, it will be included in the reported
+  //   data.  So the reported data will reflect how things were when the
+  //   request began.
+  //
+  // The inconsistencies between these cases are unfortunate but difficult to
+  // avoid.  It's enough of an edge case to not be worth doing more.
+  //
+  void HandleChildReport(uint32_t aGeneration,
+                         const mozilla::dom::MemoryReport& aChildReport);
+  void EndProcessReport(uint32_t aGeneration, bool aSuccess);
+
+  // Functions that (a) implement distinguished amounts, and (b) are outside of
+  // this module.
+  struct AmountFns {
+    mozilla::InfallibleAmountFn mJSMainRuntimeGCHeap = nullptr;
+    mozilla::InfallibleAmountFn mJSMainRuntimeTemporaryPeak = nullptr;
+    mozilla::InfallibleAmountFn mJSMainRuntimeCompartmentsSystem = nullptr;
+    mozilla::InfallibleAmountFn mJSMainRuntimeCompartmentsUser = nullptr;
+    mozilla::InfallibleAmountFn mJSMainRuntimeRealmsSystem = nullptr;
+    mozilla::InfallibleAmountFn mJSMainRuntimeRealmsUser = nullptr;
+
+    mozilla::InfallibleAmountFn mImagesContentUsedUncompressed = nullptr;
+
+    mozilla::InfallibleAmountFn mStorageSQLite = nullptr;
+
+    mozilla::InfallibleAmountFn mLowMemoryEventsPhysical = nullptr;
+
+    mozilla::InfallibleAmountFn mGhostWindows = nullptr;
+  };
+  AmountFns mAmountFns;
+
+  // Convenience function to get RSS easily from other code.  This is useful
+  // when debugging transient memory spikes with printf instrumentation.
+  static int64_t ResidentFast();
+
+  // Convenience function to get peak RSS easily from other code.
+  static int64_t ResidentPeak();
+
+  // Convenience function to get USS easily from other code.  This is useful
+  // when debugging unshared memory pages for forked processes.
+  //
+  // Returns 0 if, for some reason, the resident unique memory cannot be
+  // determined - typically if there is a race between us and someone else
+  // closing the process and we lost that race.
+#ifdef XP_WIN
+  static int64_t ResidentUnique(HANDLE aProcess = nullptr);
+#elif XP_MACOSX
+  // On MacOS this can sometimes be significantly slow. It should not be used
+  // except in debugging or at the request of a user (eg about:memory).
+  static int64_t ResidentUnique(mach_port_t aPort = 0);
+#else
+  static int64_t ResidentUnique(pid_t aPid = 0);
+#endif  // XP_{WIN, MACOSX, LINUX, *}
+
+#ifdef XP_MACOSX
+  // Retrive the "phys_footprint" memory statistic on MacOS.
+  static int64_t PhysicalFootprint(mach_port_t aPort = 0);
+#endif
+
+  // Functions that measure per-tab memory consumption.
+  struct SizeOfTabFns {
+    mozilla::JSSizeOfTabFn mJS = nullptr;
+    mozilla::NonJSSizeOfTabFn mNonJS = nullptr;
+  };
+  SizeOfTabFns mSizeOfTabFns;
+
+#ifdef HAVE_JEMALLOC_STATS
+  // These C++ only versions of HeapAllocated and HeapOverheadFraction avoid
+  // extra calls to jemalloc_stats;
+  static size_t HeapAllocated(const jemalloc_stats_t& stats);
+  static int64_t HeapOverheadFraction(const jemalloc_stats_t& stats);
+#endif
+
+ private:
+  bool IsRegistrationBlocked() MOZ_EXCLUDES(mMutex) {
+    mozilla::MutexAutoLock lock(mMutex);
+    return mIsRegistrationBlocked;
+  }
+
+  [[nodiscard]] nsresult RegisterReporterHelper(nsIMemoryReporter* aReporter,
+                                                bool aForce, bool aStrongRef,
+                                                bool aIsAsync);
+
+  [[nodiscard]] nsresult StartGettingReports();
+  // No [[nodiscard]] here because ignoring the result is common and reasonable.
+  nsresult FinishReporting();
+
+  void DispatchReporter(nsIMemoryReporter* aReporter, bool aIsAsync,
+                        nsIHandleReportCallback* aHandleReport,
+                        nsISupports* aHandleReportData, bool aAnonymize);
+
+  static void TimeoutCallback(nsITimer* aTimer, void* aData);
+  // Note: this timeout needs to be long enough to allow for the
+  // possibility of DMD reports and/or running on a low-end phone.
+  static const uint32_t kTimeoutLengthMS = 180000;
+
+  mozilla::Mutex mMutex;
+  bool mIsRegistrationBlocked MOZ_GUARDED_BY(mMutex);
+
+  StrongReportersTable* mStrongReporters MOZ_GUARDED_BY(mMutex);
+  WeakReportersTable* mWeakReporters MOZ_GUARDED_BY(mMutex);
+
+  // These two are only used for testing purposes.
+  StrongReportersTable* mSavedStrongReporters MOZ_GUARDED_BY(mMutex);
+  WeakReportersTable* mSavedWeakReporters MOZ_GUARDED_BY(mMutex);
+
+  uint32_t mNextGeneration;  // MainThread only
+
+  // Used to keep track of state of which processes are currently running and
+  // waiting to run memory reports. Holds references to parameters needed when
+  // requesting a memory report and finishing reporting.
+  struct PendingProcessesState {
+    uint32_t mGeneration;
+    bool mAnonymize;
+    bool mMinimize;
+    nsCOMPtr<nsITimer> mTimer;
+    nsTArray<RefPtr<mozilla::MemoryReportingProcess>> mChildrenPending;
+    uint32_t mNumProcessesRunning;
+    uint32_t mNumProcessesCompleted;
+    uint32_t mConcurrencyLimit;
+    nsCOMPtr<nsIHandleReportCallback> mHandleReport;
+    nsCOMPtr<nsISupports> mHandleReportData;
+    nsCOMPtr<nsIFinishReportingCallback> mFinishReporting;
+    nsCOMPtr<nsISupports> mFinishReportingData;
+    nsString mDMDDumpIdent;
+
+    PendingProcessesState(uint32_t aGeneration, bool aAnonymize, bool aMinimize,
+                          uint32_t aConcurrencyLimit,
+                          nsIHandleReportCallback* aHandleReport,
+                          nsISupports* aHandleReportData,
+                          nsIFinishReportingCallback* aFinishReporting,
+                          nsISupports* aFinishReportingData,
+                          const nsAString& aDMDDumpIdent);
+  };
+
+  // Used to keep track of the state of the asynchronously run memory
+  // reporters. The callback and file handle used when all memory reporters
+  // have finished are also stored here.
+  struct PendingReportersState {
+    // Number of memory reporters currently running.
+    uint32_t mReportsPending;
+
+    // Callback for when all memory reporters have completed.
+    nsCOMPtr<nsIFinishReportingCallback> mFinishReporting;
+    nsCOMPtr<nsISupports> mFinishReportingData;
+
+    // File handle to write a DMD report to if requested.
+    FILE* mDMDFile;
+
+    PendingReportersState(nsIFinishReportingCallback* aFinishReporting,
+                          nsISupports* aFinishReportingData, FILE* aDMDFile)
+        : mReportsPending(0),
+          mFinishReporting(aFinishReporting),
+          mFinishReportingData(aFinishReportingData),
+          mDMDFile(aDMDFile) {}
+  };
+
+  // When this is non-null, a request is in flight.  Note: We use manual
+  // new/delete for this because its lifetime doesn't match block scope or
+  // anything like that.
+  PendingProcessesState* mPendingProcessesState;  // MainThread only
+
+  // This is reinitialized each time a call to GetReports is initiated.
+  PendingReportersState* mPendingReportersState;  // MainThread only
+
+  // Used in GetHeapAllocatedAsync() to run jemalloc_stats async.
+  nsCOMPtr<nsIEventTarget> mThreadPool MOZ_GUARDED_BY(mMutex);
+
+  PendingProcessesState* GetStateForGeneration(uint32_t aGeneration);
+  [[nodiscard]] static bool StartChildReport(
+      mozilla::MemoryReportingProcess* aChild,
+      const PendingProcessesState* aState);
+};
+
+#define NS_MEMORY_REPORTER_MANAGER_CID              \
+  {                                                 \
+    0xfb97e4f5, 0x32dd, 0x497a, {                   \
+      0xba, 0xa2, 0x7d, 0x1e, 0x55, 0x7, 0x99, 0x10 \
+    }                                               \
+  }
+
+#endif  // nsMemoryReporterManager_h__
diff --git a/xpcom/base/nsMessageLoop.cpp b/xpcom/base/nsMessageLoop.cpp
new file mode 100644
index 0000000000..08f73cae37
--- /dev/null
+++ b/xpcom/base/nsMessageLoop.cpp
@@ -0,0 +1,151 @@
+/* -*- 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 "nsMessageLoop.h"
+#include "mozilla/WeakPtr.h"
+#include "base/message_loop.h"
+#include "base/task.h"
+#include "nsINamed.h"
+#include "nsIRunnable.h"
+#include "nsITimer.h"
+#include "nsCOMPtr.h"
+#include "nsComponentManagerUtils.h"
+#include "nsThreadUtils.h"
+
+using namespace mozilla;
+
+namespace {
+
+/**
+ * This Task runs its nsIRunnable when Run() is called, or after
+ * aEnsureRunsAfterMS milliseconds have elapsed since the object was
+ * constructed.
+ *
+ * Note that the MessageLoop owns this object and will delete it after it calls
+ * Run().  Tread lightly.
+ */
+class MessageLoopIdleTask : public Runnable, public SupportsWeakPtr {
+ public:
+  MessageLoopIdleTask(nsIRunnable* aTask, uint32_t aEnsureRunsAfterMS);
+  NS_IMETHOD Run() override;
+
+ private:
+  nsresult Init(uint32_t aEnsureRunsAfterMS);
+
+  nsCOMPtr<nsIRunnable> mTask;
+  nsCOMPtr<nsITimer> mTimer;
+
+  virtual ~MessageLoopIdleTask() = default;
+};
+
+/**
+ * This timer callback calls MessageLoopIdleTask::Run() when its timer fires.
+ * (The timer can't call back into MessageLoopIdleTask directly since that's
+ * not a refcounted object; it's owned by the MessageLoop.)
+ *
+ * We keep a weak reference to the MessageLoopIdleTask, although a raw pointer
+ * should in theory suffice: When the MessageLoopIdleTask runs (right before
+ * the MessageLoop deletes it), it cancels its timer.  But the weak pointer
+ * saves us from worrying about an edge case somehow messing us up here.
+ */
+class MessageLoopTimerCallback : public nsITimerCallback, public nsINamed {
+ public:
+  explicit MessageLoopTimerCallback(MessageLoopIdleTask* aTask);
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSITIMERCALLBACK
+
+  NS_IMETHOD GetName(nsACString& aName) override {
+    aName.AssignLiteral("MessageLoopTimerCallback");
+    return NS_OK;
+  }
+
+ private:
+  WeakPtr<MessageLoopIdleTask> mTask;
+
+  virtual ~MessageLoopTimerCallback() = default;
+};
+
+MessageLoopIdleTask::MessageLoopIdleTask(nsIRunnable* aTask,
+                                         uint32_t aEnsureRunsAfterMS)
+    : mozilla::Runnable("MessageLoopIdleTask"), mTask(aTask) {
+  // Init() really shouldn't fail, but if it does, we schedule our runnable
+  // immediately, because it's more important to guarantee that we run the task
+  // eventually than it is to run the task when we're idle.
+  nsresult rv = Init(aEnsureRunsAfterMS);
+  if (NS_FAILED(rv)) {
+    NS_WARNING(
+        "Running idle task early because we couldn't initialize our timer.");
+    NS_DispatchToCurrentThread(mTask);
+
+    mTask = nullptr;
+    mTimer = nullptr;
+  }
+}
+
+nsresult MessageLoopIdleTask::Init(uint32_t aEnsureRunsAfterMS) {
+  RefPtr<MessageLoopTimerCallback> callback =
+      new MessageLoopTimerCallback(this);
+  return NS_NewTimerWithCallback(getter_AddRefs(mTimer), callback,
+                                 aEnsureRunsAfterMS, nsITimer::TYPE_ONE_SHOT);
+}
+
+NS_IMETHODIMP
+MessageLoopIdleTask::Run() {
+  // Null out our pointers because if Run() was called by the timer, this
+  // object will be kept alive by the MessageLoop until the MessageLoop calls
+  // Run().
+
+  if (mTimer) {
+    mTimer->Cancel();
+    mTimer = nullptr;
+  }
+
+  if (mTask) {
+    mTask->Run();
+    mTask = nullptr;
+  }
+
+  return NS_OK;
+}
+
+MessageLoopTimerCallback::MessageLoopTimerCallback(MessageLoopIdleTask* aTask)
+    : mTask(aTask) {}
+
+NS_IMETHODIMP
+MessageLoopTimerCallback::Notify(nsITimer* aTimer) {
+  // We don't expect to hit the case when the timer fires but mTask has been
+  // deleted, because mTask should cancel the timer before the mTask is
+  // deleted.  But you never know...
+  NS_WARNING_ASSERTION(mTask, "This timer shouldn't have fired.");
+
+  if (mTask) {
+    mTask->Run();
+  }
+  return NS_OK;
+}
+
+NS_IMPL_ISUPPORTS(MessageLoopTimerCallback, nsITimerCallback, nsINamed)
+
+}  // namespace
+
+NS_IMPL_ISUPPORTS(nsMessageLoop, nsIMessageLoop)
+
+NS_IMETHODIMP
+nsMessageLoop::PostIdleTask(nsIRunnable* aTask, uint32_t aEnsureRunsAfterMS) {
+  // The message loop owns MessageLoopIdleTask and deletes it after calling
+  // Run().  Be careful...
+  RefPtr<MessageLoopIdleTask> idle =
+      new MessageLoopIdleTask(aTask, aEnsureRunsAfterMS);
+  MessageLoop::current()->PostIdleTask(idle.forget());
+
+  return NS_OK;
+}
+
+nsresult nsMessageLoopConstructor(const nsIID& aIID, void** aInstancePtr) {
+  nsISupports* messageLoop = new nsMessageLoop();
+  return messageLoop->QueryInterface(aIID, aInstancePtr);
+}
diff --git a/xpcom/base/nsMessageLoop.h b/xpcom/base/nsMessageLoop.h
new file mode 100644
index 0000000000..d6475cf797
--- /dev/null
+++ b/xpcom/base/nsMessageLoop.h
@@ -0,0 +1,29 @@
+/* -*- 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 "nsIMessageLoop.h"
+
+/*
+ * nsMessageLoop implements nsIMessageLoop, which wraps Chromium's MessageLoop
+ * class and adds a bit of sugar.
+ */
+class nsMessageLoop : public nsIMessageLoop {
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIMESSAGELOOP
+
+ private:
+  virtual ~nsMessageLoop() = default;
+};
+
+#define NS_MESSAGE_LOOP_CID                          \
+  {                                                  \
+    0x67b3ac0c, 0xd806, 0x4d48, {                    \
+      0x93, 0x9e, 0x6a, 0x81, 0x9e, 0x6c, 0x24, 0x8f \
+    }                                                \
+  }
+
+extern nsresult nsMessageLoopConstructor(const nsIID& aIID,
+                                         void** aInstancePtr);
diff --git a/xpcom/base/nsObjCExceptions.h b/xpcom/base/nsObjCExceptions.h
new file mode 100644
index 0000000000..e8c2059d8e
--- /dev/null
+++ b/xpcom/base/nsObjCExceptions.h
@@ -0,0 +1,56 @@
+/* -*- 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/. */
+
+#ifndef nsObjCExceptions_h_
+#define nsObjCExceptions_h_
+
+// Undo the damage that exception_defines.h does.
+#undef try
+#undef catch
+
+@class NSException;
+
+// See Mozilla bug 163260.
+// This file can only be included in an Objective-C context.
+
+void nsObjCExceptionLog(NSException* aException);
+
+namespace mozilla {
+
+// Check if this is an exception that's outside of our control.
+// Called when an exception bubbles up to the native event loop.
+bool ShouldIgnoreObjCException(NSException* aException);
+
+}  // namespace mozilla
+
+// For wrapping blocks of Obj-C calls which are not expected to throw exception.
+// Causes a MOZ_CRASH if an Obj-C exception is encountered.
+#define NS_OBJC_BEGIN_TRY_ABORT_BLOCK @try {
+#define NS_OBJC_END_TRY_ABORT_BLOCK                            \
+  }                                                            \
+  @catch (NSException * _exn) {                                \
+    nsObjCExceptionLog(_exn);                                  \
+    MOZ_CRASH("Encountered unexpected Objective C exception"); \
+  }
+
+// For wrapping blocks of Obj-C calls. Logs the exception and moves on.
+#define NS_OBJC_BEGIN_TRY_IGNORE_BLOCK @try {
+#define NS_OBJC_END_TRY_IGNORE_BLOCK \
+  }                                  \
+  @catch (NSException * _exn) {      \
+    nsObjCExceptionLog(_exn);        \
+  }
+
+// Same as above IGNORE_BLOCK but returns a value after the try/catch block.
+#define NS_OBJC_BEGIN_TRY_BLOCK_RETURN @try {
+#define NS_OBJC_END_TRY_BLOCK_RETURN(_rv) \
+  }                                       \
+  @catch (NSException * _exn) {           \
+    nsObjCExceptionLog(_exn);             \
+  }                                       \
+  return _rv;
+
+#endif  // nsObjCExceptions_h_
diff --git a/xpcom/base/nsObjCExceptions.mm b/xpcom/base/nsObjCExceptions.mm
new file mode 100644
index 0000000000..9921c746a1
--- /dev/null
+++ b/xpcom/base/nsObjCExceptions.mm
@@ -0,0 +1,48 @@
+/* -*- 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 "nsObjCExceptions.h"
+
+#import <Foundation/Foundation.h>
+
+#include <unistd.h>
+#include <signal.h>
+
+#include "nsICrashReporter.h"
+#include "nsCOMPtr.h"
+#include "nsServiceManagerUtils.h"
+
+#include "nsError.h"
+
+void nsObjCExceptionLog(NSException* aException) {
+  NSLog(@"Mozilla has caught an Obj-C exception [%@: %@]", [aException name], [aException reason]);
+
+  // Attach exception info to the crash report.
+  nsCOMPtr<nsICrashReporter> crashReporter = do_GetService("@mozilla.org/toolkit/crash-reporter;1");
+  if (crashReporter) {
+    crashReporter->AppendObjCExceptionInfoToAppNotes(static_cast<void*>(aException));
+  }
+
+#ifdef DEBUG
+  NSLog(@"Stack trace:\n%@", [aException callStackSymbols]);
+#endif
+}
+
+namespace mozilla {
+
+bool ShouldIgnoreObjCException(NSException* aException) {
+  // Ignore known exceptions that we've seen in crash reports, which shouldn't cause a MOZ_CRASH in
+  // Nightly.
+  if (aException.name == NSInternalInconsistencyException) {
+    if ([aException.reason containsString:@"Missing Touches."]) {
+      // Seen in bug 1694000.
+      return true;
+    }
+  }
+  return false;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/nsQueryObject.h b/xpcom/base/nsQueryObject.h
new file mode 100644
index 0000000000..7cfbe954ce
--- /dev/null
+++ b/xpcom/base/nsQueryObject.h
@@ -0,0 +1,93 @@
+/* -*- 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/. */
+
+#ifndef nsQueryObject_h
+#define nsQueryObject_h
+
+#include "mozilla/Attributes.h"
+
+#include "nsCOMPtr.h"
+#include "mozilla/RefPtr.h"
+
+/*****************************************************************************/
+
+template <class T>
+class MOZ_STACK_CLASS nsQueryObject final : public nsCOMPtr_helper {
+ public:
+  explicit nsQueryObject(T* aRawPtr) : mRawPtr(aRawPtr) {}
+
+  virtual nsresult NS_FASTCALL operator()(const nsIID& aIID,
+                                          void** aResult) const override {
+    nsresult status = mRawPtr ? mRawPtr->QueryInterface(aIID, aResult)
+                              : NS_ERROR_NULL_POINTER;
+    return status;
+  }
+
+ private:
+  T* MOZ_NON_OWNING_REF mRawPtr;
+};
+
+template <class T>
+class MOZ_STACK_CLASS nsQueryObjectWithError final : public nsCOMPtr_helper {
+ public:
+  nsQueryObjectWithError(T* aRawPtr, nsresult* aErrorPtr)
+      : mRawPtr(aRawPtr), mErrorPtr(aErrorPtr) {}
+
+  virtual nsresult NS_FASTCALL operator()(const nsIID& aIID,
+                                          void** aResult) const override {
+    nsresult status = mRawPtr ? mRawPtr->QueryInterface(aIID, aResult)
+                              : NS_ERROR_NULL_POINTER;
+    if (mErrorPtr) {
+      *mErrorPtr = status;
+    }
+    return status;
+  }
+
+ private:
+  T* MOZ_NON_OWNING_REF mRawPtr;
+  nsresult* mErrorPtr;
+};
+
+/*****************************************************************************/
+
+/*****************************************************************************/
+
+template <class T>
+inline nsQueryObject<T> do_QueryObject(T* aRawPtr) {
+  return nsQueryObject<T>(aRawPtr);
+}
+
+template <class T>
+inline nsQueryObject<T> do_QueryObject(const nsCOMPtr<T>& aRawPtr) {
+  return nsQueryObject<T>(aRawPtr);
+}
+
+template <class T>
+inline nsQueryObject<T> do_QueryObject(const RefPtr<T>& aRawPtr) {
+  return nsQueryObject<T>(aRawPtr);
+}
+
+template <class T>
+inline nsQueryObjectWithError<T> do_QueryObject(T* aRawPtr,
+                                                nsresult* aErrorPtr) {
+  return nsQueryObjectWithError<T>(aRawPtr, aErrorPtr);
+}
+
+template <class T>
+inline nsQueryObjectWithError<T> do_QueryObject(const nsCOMPtr<T>& aRawPtr,
+                                                nsresult* aErrorPtr) {
+  return nsQueryObjectWithError<T>(aRawPtr, aErrorPtr);
+}
+
+template <class T>
+inline nsQueryObjectWithError<T> do_QueryObject(const RefPtr<T>& aRawPtr,
+                                                nsresult* aErrorPtr) {
+  return nsQueryObjectWithError<T>(aRawPtr, aErrorPtr);
+}
+
+/*****************************************************************************/
+
+#endif  // !defined(nsQueryObject_h)
diff --git a/xpcom/base/nsSecurityConsoleMessage.cpp b/xpcom/base/nsSecurityConsoleMessage.cpp
new file mode 100644
index 0000000000..84074b57bc
--- /dev/null
+++ b/xpcom/base/nsSecurityConsoleMessage.cpp
@@ -0,0 +1,37 @@
+/* -*- 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 "nsSecurityConsoleMessage.h"
+
+NS_IMPL_ISUPPORTS(nsSecurityConsoleMessage, nsISecurityConsoleMessage)
+
+nsSecurityConsoleMessage::nsSecurityConsoleMessage() = default;
+
+nsSecurityConsoleMessage::~nsSecurityConsoleMessage() = default;
+
+NS_IMETHODIMP
+nsSecurityConsoleMessage::GetTag(nsAString& aTag) {
+  aTag = mTag;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSecurityConsoleMessage::SetTag(const nsAString& aTag) {
+  mTag = aTag;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSecurityConsoleMessage::GetCategory(nsAString& aCategory) {
+  aCategory = mCategory;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSecurityConsoleMessage::SetCategory(const nsAString& aCategory) {
+  mCategory = aCategory;
+  return NS_OK;
+}
diff --git a/xpcom/base/nsSecurityConsoleMessage.h b/xpcom/base/nsSecurityConsoleMessage.h
new file mode 100644
index 0000000000..9a74d3e38b
--- /dev/null
+++ b/xpcom/base/nsSecurityConsoleMessage.h
@@ -0,0 +1,33 @@
+/* -*- 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/. */
+
+#ifndef nsSecurityConsoleMessage_h__
+#define nsSecurityConsoleMessage_h__
+#include "nsISecurityConsoleMessage.h"
+#include "nsString.h"
+
+class nsSecurityConsoleMessage final : public nsISecurityConsoleMessage {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSISECURITYCONSOLEMESSAGE
+
+  nsSecurityConsoleMessage();
+
+ private:
+  ~nsSecurityConsoleMessage();
+
+ protected:
+  nsString mTag;
+  nsString mCategory;
+};
+
+#define NS_SECURITY_CONSOLE_MESSAGE_CID              \
+  {                                                  \
+    0x43ebf210, 0x8a7b, 0x4ddb, {                    \
+      0xa8, 0x3d, 0xb8, 0x7c, 0x51, 0xa0, 0x58, 0xdb \
+    }                                                \
+  }
+#endif  // nsSecurityConsoleMessage_h__
diff --git a/xpcom/base/nsSystemInfo.cpp b/xpcom/base/nsSystemInfo.cpp
new file mode 100644
index 0000000000..9a389f6938
--- /dev/null
+++ b/xpcom/base/nsSystemInfo.cpp
@@ -0,0 +1,1669 @@
+/* -*- 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 "mozilla/ArrayUtils.h"
+
+#include "nsAppRunner.h"
+#include "nsSystemInfo.h"
+#include "prsystem.h"
+#include "prio.h"
+#include "mozilla/SSE.h"
+#include "mozilla/arm.h"
+#include "mozilla/LazyIdleThread.h"
+#include "mozilla/LookAndFeel.h"
+#include "mozilla/Sprintf.h"
+#include "jsapi.h"
+#include "js/PropertyAndElement.h"  // JS_SetProperty
+#include "mozilla/dom/Promise.h"
+
+#ifdef XP_WIN
+#  include <comutil.h>
+#  include <time.h>
+#  ifndef __MINGW32__
+#    include <iwscapi.h>
+#  endif  // __MINGW32__
+#  include <windows.h>
+#  include <winioctl.h>
+#  ifndef __MINGW32__
+#    include <wrl.h>
+#    include <wscapi.h>
+#  endif  // __MINGW32__
+#  include "base/scoped_handle_win.h"
+#  include "mozilla/DynamicallyLinkedFunctionPtr.h"
+#  include "mozilla/WindowsVersion.h"
+#  include "nsAppDirectoryServiceDefs.h"
+#  include "nsDirectoryServiceDefs.h"
+#  include "nsDirectoryServiceUtils.h"
+#  include "nsWindowsHelpers.h"
+#  include "WinUtils.h"
+#  include "mozilla/NotNull.h"
+
+#endif
+
+#ifdef XP_MACOSX
+#  include "MacHelpers.h"
+#endif
+
+#ifdef MOZ_WIDGET_GTK
+#  include <gtk/gtk.h>
+#  include <dlfcn.h>
+#  include "mozilla/WidgetUtilsGtk.h"
+#endif
+
+#if defined(XP_LINUX) && !defined(ANDROID)
+#  include <unistd.h>
+#  include <fstream>
+#  include "mozilla/Tokenizer.h"
+#  include "mozilla/widget/LSBUtils.h"
+#  include "nsCharSeparatedTokenizer.h"
+
+#  include <map>
+#  include <string>
+#endif
+
+#ifdef MOZ_WIDGET_ANDROID
+#  include "AndroidBuild.h"
+#  include "mozilla/java/GeckoAppShellWrappers.h"
+#  include "mozilla/jni/Utils.h"
+#endif
+
+#ifdef XP_MACOSX
+#  include <sys/sysctl.h>
+#endif
+
+#if defined(XP_LINUX) && defined(MOZ_SANDBOX)
+#  include "mozilla/SandboxInfo.h"
+#endif
+
+// Slot for NS_InitXPCOM to pass information to nsSystemInfo::Init.
+// Only set to nonzero (potentially) if XP_UNIX.  On such systems, the
+// system call to discover the appropriate value is not thread-safe,
+// so we must call it before going multithreaded, but nsSystemInfo::Init
+// only happens well after that point.
+uint32_t nsSystemInfo::gUserUmask = 0;
+
+using namespace mozilla::dom;
+
+#if defined(XP_WIN)
+#  define RuntimeClass_Windows_System_Profile_WindowsIntegrityPolicy \
+    L"Windows.System.Profile.WindowsIntegrityPolicy"
+#  ifndef __MINGW32__
+using namespace Microsoft::WRL;
+using namespace Microsoft::WRL::Wrappers;
+using namespace ABI::Windows::Foundation;
+#  endif  // __MINGW32__
+#endif
+
+#if defined(XP_LINUX) && !defined(ANDROID)
+static void SimpleParseKeyValuePairs(
+    const std::string& aFilename,
+    std::map<nsCString, nsCString>& aKeyValuePairs) {
+  std::ifstream input(aFilename.c_str());
+  for (std::string line; std::getline(input, line);) {
+    nsAutoCString key, value;
+
+    nsCCharSeparatedTokenizer tokens(nsDependentCString(line.c_str()), ':');
+    if (tokens.hasMoreTokens()) {
+      key = tokens.nextToken();
+      if (tokens.hasMoreTokens()) {
+        value = tokens.nextToken();
+      }
+      // We want the value even if there was just one token, to cover the
+      // case where we had the key, and the value was blank (seems to be
+      // a valid scenario some files.)
+      aKeyValuePairs[key] = value;
+    }
+  }
+}
+#endif
+
+#ifdef XP_WIN
+// Lifted from media/webrtc/trunk/webrtc/base/systeminfo.cc,
+// so keeping the _ instead of switching to camel case for now.
+static void GetProcessorInformation(int* physical_cpus, int* cache_size_L2,
+                                    int* cache_size_L3) {
+  MOZ_ASSERT(physical_cpus && cache_size_L2 && cache_size_L3);
+
+  *physical_cpus = 0;
+  *cache_size_L2 = 0;  // This will be in kbytes
+  *cache_size_L3 = 0;  // This will be in kbytes
+
+  // Determine buffer size, allocate and get processor information.
+  // Size can change between calls (unlikely), so a loop is done.
+  SYSTEM_LOGICAL_PROCESSOR_INFORMATION info_buffer[32];
+  SYSTEM_LOGICAL_PROCESSOR_INFORMATION* infos = &info_buffer[0];
+  DWORD return_length = sizeof(info_buffer);
+  while (!::GetLogicalProcessorInformation(infos, &return_length)) {
+    if (GetLastError() == ERROR_INSUFFICIENT_BUFFER &&
+        infos == &info_buffer[0]) {
+      infos = new SYSTEM_LOGICAL_PROCESSOR_INFORMATION
+          [return_length / sizeof(SYSTEM_LOGICAL_PROCESSOR_INFORMATION)];
+    } else {
+      return;
+    }
+  }
+
+  for (size_t i = 0;
+       i < return_length / sizeof(SYSTEM_LOGICAL_PROCESSOR_INFORMATION); ++i) {
+    if (infos[i].Relationship == RelationProcessorCore) {
+      ++*physical_cpus;
+    } else if (infos[i].Relationship == RelationCache) {
+      // Only care about L2 and L3 cache
+      switch (infos[i].Cache.Level) {
+        case 2:
+          *cache_size_L2 = static_cast<int>(infos[i].Cache.Size / 1024);
+          break;
+        case 3:
+          *cache_size_L3 = static_cast<int>(infos[i].Cache.Size / 1024);
+          break;
+        default:
+          break;
+      }
+    }
+  }
+  if (infos != &info_buffer[0]) {
+    delete[] infos;
+  }
+  return;
+}
+#endif
+
+#if defined(XP_WIN)
+namespace {
+static nsresult GetFolderDiskInfo(nsIFile* file, FolderDiskInfo& info) {
+  info.model.Truncate();
+  info.revision.Truncate();
+  info.isSSD = false;
+
+  nsAutoString filePath;
+  nsresult rv = file->GetPath(filePath);
+  NS_ENSURE_SUCCESS(rv, rv);
+  wchar_t volumeMountPoint[MAX_PATH] = {L'\\', L'\\', L'.', L'\\'};
+  const size_t PREFIX_LEN = 4;
+  if (!::GetVolumePathNameW(
+          filePath.get(), volumeMountPoint + PREFIX_LEN,
+          mozilla::ArrayLength(volumeMountPoint) - PREFIX_LEN)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  size_t volumeMountPointLen = wcslen(volumeMountPoint);
+  // Since we would like to open a drive and not a directory, we need to
+  // remove any trailing backslash. A drive handle is valid for
+  // DeviceIoControl calls, a directory handle is not.
+  if (volumeMountPoint[volumeMountPointLen - 1] == L'\\') {
+    volumeMountPoint[volumeMountPointLen - 1] = L'\0';
+  }
+  ScopedHandle handle(::CreateFileW(volumeMountPoint, 0,
+                                    FILE_SHARE_READ | FILE_SHARE_WRITE, nullptr,
+                                    OPEN_EXISTING, 0, nullptr));
+  if (!handle.IsValid()) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  STORAGE_PROPERTY_QUERY queryParameters = {StorageDeviceProperty,
+                                            PropertyStandardQuery};
+  STORAGE_DEVICE_DESCRIPTOR outputHeader = {sizeof(STORAGE_DEVICE_DESCRIPTOR)};
+  DWORD bytesRead = 0;
+  if (!::DeviceIoControl(handle, IOCTL_STORAGE_QUERY_PROPERTY, &queryParameters,
+                         sizeof(queryParameters), &outputHeader,
+                         sizeof(outputHeader), &bytesRead, nullptr)) {
+    return NS_ERROR_FAILURE;
+  }
+  PSTORAGE_DEVICE_DESCRIPTOR deviceOutput =
+      (PSTORAGE_DEVICE_DESCRIPTOR)malloc(outputHeader.Size);
+  if (!::DeviceIoControl(handle, IOCTL_STORAGE_QUERY_PROPERTY, &queryParameters,
+                         sizeof(queryParameters), deviceOutput,
+                         outputHeader.Size, &bytesRead, nullptr)) {
+    free(deviceOutput);
+    return NS_ERROR_FAILURE;
+  }
+
+  queryParameters.PropertyId = StorageDeviceTrimProperty;
+  bytesRead = 0;
+  bool isSSD = false;
+  DEVICE_TRIM_DESCRIPTOR trimDescriptor = {sizeof(DEVICE_TRIM_DESCRIPTOR)};
+  if (::DeviceIoControl(handle, IOCTL_STORAGE_QUERY_PROPERTY, &queryParameters,
+                        sizeof(queryParameters), &trimDescriptor,
+                        sizeof(trimDescriptor), &bytesRead, nullptr)) {
+    if (trimDescriptor.TrimEnabled) {
+      isSSD = true;
+    }
+  }
+
+  if (isSSD) {
+    // Get Seek Penalty
+    queryParameters.PropertyId = StorageDeviceSeekPenaltyProperty;
+    bytesRead = 0;
+    DEVICE_SEEK_PENALTY_DESCRIPTOR seekPenaltyDescriptor = {
+        sizeof(DEVICE_SEEK_PENALTY_DESCRIPTOR)};
+    if (::DeviceIoControl(handle, IOCTL_STORAGE_QUERY_PROPERTY,
+                          &queryParameters, sizeof(queryParameters),
+                          &seekPenaltyDescriptor, sizeof(seekPenaltyDescriptor),
+                          &bytesRead, nullptr)) {
+      // It is possible that the disk has TrimEnabled, but also
+      // IncursSeekPenalty; In this case, this is an HDD
+      if (seekPenaltyDescriptor.IncursSeekPenalty) {
+        isSSD = false;
+      }
+    }
+  }
+
+  // Some HDDs are including product ID info in the vendor field. Since PNP
+  // IDs include vendor info and product ID concatenated together, we'll do
+  // that here and interpret the result as a unique ID for the HDD model.
+  if (deviceOutput->VendorIdOffset) {
+    info.model =
+        reinterpret_cast<char*>(deviceOutput) + deviceOutput->VendorIdOffset;
+  }
+  if (deviceOutput->ProductIdOffset) {
+    info.model +=
+        reinterpret_cast<char*>(deviceOutput) + deviceOutput->ProductIdOffset;
+  }
+  info.model.CompressWhitespace();
+  if (deviceOutput->ProductRevisionOffset) {
+    info.revision = reinterpret_cast<char*>(deviceOutput) +
+                    deviceOutput->ProductRevisionOffset;
+    info.revision.CompressWhitespace();
+  }
+  info.isSSD = isSSD;
+  free(deviceOutput);
+  return NS_OK;
+}
+
+static nsresult CollectDiskInfo(nsIFile* greDir, nsIFile* winDir,
+                                nsIFile* profDir, DiskInfo& info) {
+  nsresult rv = GetFolderDiskInfo(greDir, info.binary);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  rv = GetFolderDiskInfo(winDir, info.system);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  return GetFolderDiskInfo(profDir, info.profile);
+}
+
+static nsresult CollectOSInfo(OSInfo& info) {
+  HKEY installYearHKey;
+  LONG status = RegOpenKeyExW(
+      HKEY_LOCAL_MACHINE, L"SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion", 0,
+      KEY_READ | KEY_WOW64_64KEY, &installYearHKey);
+
+  if (status != ERROR_SUCCESS) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  nsAutoRegKey installYearKey(installYearHKey);
+
+  DWORD type = 0;
+  time_t raw_time = 0;
+  DWORD time_size = sizeof(time_t);
+
+  status = RegQueryValueExW(installYearHKey, L"InstallDate", nullptr, &type,
+                            (LPBYTE)&raw_time, &time_size);
+
+  if (status != ERROR_SUCCESS) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  if (type != REG_DWORD) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  tm time;
+  if (localtime_s(&time, &raw_time) != 0) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  info.installYear = 1900UL + time.tm_year;
+
+  nsAutoServiceHandle scm(
+      OpenSCManager(nullptr, SERVICES_ACTIVE_DATABASE, SC_MANAGER_CONNECT));
+
+  if (!scm) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  bool superfetchServiceRunning = false;
+
+  // Superfetch was introduced in Windows Vista as a service with the name
+  // SysMain. The service display name was also renamed to SysMain after Windows
+  // 10 build 1809.
+  nsAutoServiceHandle hService(OpenService(scm, L"SysMain", GENERIC_READ));
+
+  if (hService) {
+    SERVICE_STATUS superfetchStatus;
+    LPSERVICE_STATUS pSuperfetchStatus = &superfetchStatus;
+
+    if (!QueryServiceStatus(hService, pSuperfetchStatus)) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    superfetchServiceRunning =
+        superfetchStatus.dwCurrentState == SERVICE_RUNNING;
+  }
+
+  // If the SysMain (Superfetch) service is available, but not configured using
+  // the defaults, then it's disabled for our purposes, since it's not going to
+  // be operating as expected.
+  bool superfetchUsingDefaultParams = true;
+  bool prefetchUsingDefaultParams = true;
+
+  static const WCHAR prefetchParamsKeyName[] =
+      L"SYSTEM\\CurrentControlSet\\Control\\Session Manager\\Memory "
+      L"Management\\PrefetchParameters";
+  static const DWORD SUPERFETCH_DEFAULT_PARAM = 3;
+  static const DWORD PREFETCH_DEFAULT_PARAM = 3;
+
+  HKEY prefetchParamsHKey;
+
+  LONG prefetchParamsStatus =
+      RegOpenKeyExW(HKEY_LOCAL_MACHINE, prefetchParamsKeyName, 0,
+                    KEY_READ | KEY_WOW64_64KEY, &prefetchParamsHKey);
+
+  if (prefetchParamsStatus == ERROR_SUCCESS) {
+    DWORD valueSize = sizeof(DWORD);
+    DWORD superfetchValue = 0;
+    nsAutoRegKey prefetchParamsKey(prefetchParamsHKey);
+    LONG superfetchParamStatus = RegQueryValueExW(
+        prefetchParamsHKey, L"EnableSuperfetch", nullptr, &type,
+        reinterpret_cast<LPBYTE>(&superfetchValue), &valueSize);
+
+    // If the EnableSuperfetch registry key doesn't exist, then it's using the
+    // default configuration.
+    if (superfetchParamStatus == ERROR_SUCCESS &&
+        superfetchValue != SUPERFETCH_DEFAULT_PARAM) {
+      superfetchUsingDefaultParams = false;
+    }
+
+    DWORD prefetchValue = 0;
+
+    LONG prefetchParamStatus = RegQueryValueExW(
+        prefetchParamsHKey, L"EnablePrefetcher", nullptr, &type,
+        reinterpret_cast<LPBYTE>(&prefetchValue), &valueSize);
+
+    // If the EnablePrefetcher registry key doesn't exist, then we interpret
+    // that as the Prefetcher being disabled (since Prefetch behaviour when
+    // the key is not available appears to be undefined).
+    if (prefetchParamStatus != ERROR_SUCCESS ||
+        prefetchValue != PREFETCH_DEFAULT_PARAM) {
+      prefetchUsingDefaultParams = false;
+    }
+  }
+
+  info.hasSuperfetch = superfetchServiceRunning && superfetchUsingDefaultParams;
+  info.hasPrefetch = prefetchUsingDefaultParams;
+
+  return NS_OK;
+}
+
+nsresult CollectCountryCode(nsAString& aCountryCode) {
+  GEOID geoid = GetUserGeoID(GEOCLASS_NATION);
+  if (geoid == GEOID_NOT_AVAILABLE) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+  // Get required length
+  int numChars = GetGeoInfoW(geoid, GEO_ISO2, nullptr, 0, 0);
+  if (!numChars) {
+    return NS_ERROR_FAILURE;
+  }
+  // Now get the string for real
+  aCountryCode.SetLength(numChars);
+  numChars =
+      GetGeoInfoW(geoid, GEO_ISO2, char16ptr_t(aCountryCode.BeginWriting()),
+                  aCountryCode.Length(), 0);
+  if (!numChars) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // numChars includes null terminator
+  aCountryCode.Truncate(numChars - 1);
+  return NS_OK;
+}
+
+}  // namespace
+
+#  ifndef __MINGW32__
+
+static HRESULT EnumWSCProductList(
+    nsAString& aOutput, mozilla::NotNull<IWSCProductList*> aProdList) {
+  MOZ_ASSERT(aOutput.IsEmpty());
+
+  LONG count;
+  HRESULT hr = aProdList->get_Count(&count);
+  if (FAILED(hr)) {
+    return hr;
+  }
+
+  for (LONG index = 0; index < count; ++index) {
+    RefPtr<IWscProduct> product;
+    hr = aProdList->get_Item(index, getter_AddRefs(product));
+    if (FAILED(hr)) {
+      return hr;
+    }
+
+    WSC_SECURITY_PRODUCT_STATE state;
+    hr = product->get_ProductState(&state);
+    if (FAILED(hr)) {
+      return hr;
+    }
+
+    // We only care about products that are active
+    if (state == WSC_SECURITY_PRODUCT_STATE_OFF ||
+        state == WSC_SECURITY_PRODUCT_STATE_SNOOZED) {
+      continue;
+    }
+
+    _bstr_t bName;
+    hr = product->get_ProductName(bName.GetAddress());
+    if (FAILED(hr)) {
+      return hr;
+    }
+
+    if (!aOutput.IsEmpty()) {
+      aOutput.AppendLiteral(u";");
+    }
+
+    aOutput.Append((wchar_t*)bName, bName.length());
+  }
+
+  return S_OK;
+}
+
+static nsresult GetWindowsSecurityCenterInfo(nsAString& aAVInfo,
+                                             nsAString& aAntiSpyInfo,
+                                             nsAString& aFirewallInfo) {
+  aAVInfo.Truncate();
+  aAntiSpyInfo.Truncate();
+  aFirewallInfo.Truncate();
+
+  if (!XRE_IsParentProcess()) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  const CLSID clsid = __uuidof(WSCProductList);
+  const IID iid = __uuidof(IWSCProductList);
+
+  // NB: A separate instance of IWSCProductList is needed for each distinct
+  // security provider type; MSDN says that we cannot reuse the same object
+  // and call Initialize() to pave over the previous data.
+
+  WSC_SECURITY_PROVIDER providerTypes[] = {WSC_SECURITY_PROVIDER_ANTIVIRUS,
+                                           WSC_SECURITY_PROVIDER_ANTISPYWARE,
+                                           WSC_SECURITY_PROVIDER_FIREWALL};
+
+  // Each output must match the corresponding entry in providerTypes.
+  nsAString* outputs[] = {&aAVInfo, &aAntiSpyInfo, &aFirewallInfo};
+
+  static_assert(
+      mozilla::ArrayLength(providerTypes) == mozilla::ArrayLength(outputs),
+      "Length of providerTypes and outputs arrays must match");
+
+  for (uint32_t index = 0; index < mozilla::ArrayLength(providerTypes);
+       ++index) {
+    RefPtr<IWSCProductList> prodList;
+    HRESULT hr = ::CoCreateInstance(clsid, nullptr, CLSCTX_INPROC_SERVER, iid,
+                                    getter_AddRefs(prodList));
+    if (FAILED(hr)) {
+      return NS_ERROR_NOT_AVAILABLE;
+    }
+
+    hr = prodList->Initialize(providerTypes[index]);
+    if (FAILED(hr)) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    hr = EnumWSCProductList(*outputs[index],
+                            mozilla::WrapNotNull(prodList.get()));
+    if (FAILED(hr)) {
+      return NS_ERROR_UNEXPECTED;
+    }
+  }
+
+  return NS_OK;
+}
+
+#  endif  // __MINGW32__
+
+#endif  // defined(XP_WIN)
+
+#ifdef XP_MACOSX
+static nsresult GetAppleModelId(nsAutoCString& aModelId) {
+  size_t numChars = 0;
+  size_t result = sysctlbyname("hw.model", nullptr, &numChars, nullptr, 0);
+  if (result != 0 || !numChars) {
+    return NS_ERROR_FAILURE;
+  }
+  aModelId.SetLength(numChars);
+  result =
+      sysctlbyname("hw.model", aModelId.BeginWriting(), &numChars, nullptr, 0);
+  if (result != 0) {
+    return NS_ERROR_FAILURE;
+  }
+  // numChars includes null terminator
+  aModelId.Truncate(numChars - 1);
+  return NS_OK;
+}
+
+static nsresult ProcessIsRosettaTranslated(bool& isRosetta) {
+#  if defined(__aarch64__)
+  // There is no need to call sysctlbyname() if we are running as arm64.
+  isRosetta = false;
+#  else
+  int ret = 0;
+  size_t size = sizeof(ret);
+  if (sysctlbyname("sysctl.proc_translated", &ret, &size, NULL, 0) == -1) {
+    if (errno != ENOENT) {
+      fprintf(stderr, "Failed to check for translation environment\n");
+    }
+    isRosetta = false;
+  } else {
+    isRosetta = (ret == 1);
+  }
+#  endif
+  return NS_OK;
+}
+#endif
+
+using namespace mozilla;
+
+nsSystemInfo::nsSystemInfo() = default;
+
+nsSystemInfo::~nsSystemInfo() = default;
+
+// CPU-specific information.
+static const struct PropItems {
+  const char* name;
+  bool (*propfun)(void);
+} cpuPropItems[] = {
+    // x86-specific bits.
+    {"hasMMX", mozilla::supports_mmx},
+    {"hasSSE", mozilla::supports_sse},
+    {"hasSSE2", mozilla::supports_sse2},
+    {"hasSSE3", mozilla::supports_sse3},
+    {"hasSSSE3", mozilla::supports_ssse3},
+    {"hasSSE4A", mozilla::supports_sse4a},
+    {"hasSSE4_1", mozilla::supports_sse4_1},
+    {"hasSSE4_2", mozilla::supports_sse4_2},
+    {"hasAVX", mozilla::supports_avx},
+    {"hasAVX2", mozilla::supports_avx2},
+    {"hasAES", mozilla::supports_aes},
+    // ARM-specific bits.
+    {"hasEDSP", mozilla::supports_edsp},
+    {"hasARMv6", mozilla::supports_armv6},
+    {"hasARMv7", mozilla::supports_armv7},
+    {"hasNEON", mozilla::supports_neon}};
+
+nsresult CollectProcessInfo(ProcessInfo& info) {
+  nsAutoCString cpuVendor;
+  nsAutoCString cpuName;
+  int cpuSpeed = -1;
+  int cpuFamily = -1;
+  int cpuModel = -1;
+  int cpuStepping = -1;
+  int logicalCPUs = -1;
+  int physicalCPUs = -1;
+  int cacheSizeL2 = -1;
+  int cacheSizeL3 = -1;
+
+#if defined(XP_WIN)
+  // IsWow64Process2 is only available on Windows 10+, so we have to dynamically
+  // check for its existence.
+  typedef BOOL(WINAPI * LPFN_IWP2)(HANDLE, USHORT*, USHORT*);
+  LPFN_IWP2 iwp2 = reinterpret_cast<LPFN_IWP2>(
+      GetProcAddress(GetModuleHandle(L"kernel32"), "IsWow64Process2"));
+  BOOL isWow64 = FALSE;
+  USHORT processMachine = IMAGE_FILE_MACHINE_UNKNOWN;
+  USHORT nativeMachine = IMAGE_FILE_MACHINE_UNKNOWN;
+  BOOL gotWow64Value;
+  if (iwp2) {
+    gotWow64Value = iwp2(GetCurrentProcess(), &processMachine, &nativeMachine);
+    if (gotWow64Value) {
+      isWow64 = (processMachine != IMAGE_FILE_MACHINE_UNKNOWN);
+    }
+  } else {
+    gotWow64Value = IsWow64Process(GetCurrentProcess(), &isWow64);
+    // The function only indicates a WOW64 environment if it's 32-bit x86
+    // running on x86-64, so emulate what IsWow64Process2 would have given.
+    if (gotWow64Value && isWow64) {
+      processMachine = IMAGE_FILE_MACHINE_I386;
+      nativeMachine = IMAGE_FILE_MACHINE_AMD64;
+    }
+  }
+  NS_WARNING_ASSERTION(gotWow64Value, "IsWow64Process failed");
+  if (gotWow64Value) {
+    // Set this always, even for the x86-on-arm64 case.
+    info.isWow64 = !!isWow64;
+    // Additional information if we're running x86-on-arm64
+    info.isWowARM64 = (processMachine == IMAGE_FILE_MACHINE_I386 &&
+                       nativeMachine == IMAGE_FILE_MACHINE_ARM64);
+  }
+
+  // S Mode
+
+#  ifndef __MINGW32__
+  // WindowsIntegrityPolicy is only available on newer versions
+  // of Windows 10, so there's no point in trying to check this
+  // on earlier versions. We know GetActivationFactory crashes on
+  // Windows 7 when trying to retrieve this class, and may also
+  // crash on very old versions of Windows 10.
+  if (IsWin10Sep2018UpdateOrLater()) {
+    ComPtr<IWindowsIntegrityPolicyStatics> wip;
+    HRESULT hr = GetActivationFactory(
+        HStringReference(
+            RuntimeClass_Windows_System_Profile_WindowsIntegrityPolicy)
+            .Get(),
+        &wip);
+    if (SUCCEEDED(hr)) {
+      // info.isWindowsSMode ends up true if Windows is in S mode, otherwise
+      // false
+      // https://docs.microsoft.com/en-us/uwp/api/windows.system.profile.windowsintegritypolicy.isenabled?view=winrt-22000
+      hr = wip->get_IsEnabled(&info.isWindowsSMode);
+      NS_WARNING_ASSERTION(SUCCEEDED(hr),
+                           "WindowsIntegrityPolicy.IsEnabled failed");
+    }
+  }
+#  endif  // __MINGW32__
+
+  // CPU speed
+  HKEY key;
+  static const WCHAR keyName[] =
+      L"HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0";
+
+  if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, keyName, 0, KEY_QUERY_VALUE, &key) ==
+      ERROR_SUCCESS) {
+    DWORD data, len, vtype;
+    len = sizeof(data);
+
+    if (RegQueryValueEx(key, L"~Mhz", 0, 0, reinterpret_cast<LPBYTE>(&data),
+                        &len) == ERROR_SUCCESS) {
+      cpuSpeed = static_cast<int>(data);
+    }
+
+    // Limit to 64 double byte characters, should be plenty, but create
+    // a buffer one larger as the result may not be null terminated. If
+    // it is more than 64, we will not get the value.
+    wchar_t cpuVendorStr[64 + 1];
+    len = sizeof(cpuVendorStr) - 2;
+    if (RegQueryValueExW(key, L"VendorIdentifier", 0, &vtype,
+                         reinterpret_cast<LPBYTE>(cpuVendorStr),
+                         &len) == ERROR_SUCCESS &&
+        vtype == REG_SZ && len % 2 == 0 && len > 1) {
+      cpuVendorStr[len / 2] = 0;  // In case it isn't null terminated
+      CopyUTF16toUTF8(nsDependentString(cpuVendorStr), cpuVendor);
+    }
+
+    // Limit to 64 double byte characters, should be plenty, but create
+    // a buffer one larger as the result may not be null terminated. If
+    // it is more than 64, we will not get the value.
+    // The expected string size is 48 characters or less.
+    wchar_t cpuNameStr[64 + 1];
+    len = sizeof(cpuNameStr) - 2;
+    if (RegQueryValueExW(key, L"ProcessorNameString", 0, &vtype,
+                         reinterpret_cast<LPBYTE>(cpuNameStr),
+                         &len) == ERROR_SUCCESS &&
+        vtype == REG_SZ && len % 2 == 0 && len > 1) {
+      cpuNameStr[len / 2] = 0;  // In case it isn't null terminated
+      CopyUTF16toUTF8(nsDependentString(cpuNameStr), cpuName);
+    }
+
+    RegCloseKey(key);
+  }
+
+  // Other CPU attributes:
+  SYSTEM_INFO si;
+  GetNativeSystemInfo(&si);
+  logicalCPUs = si.dwNumberOfProcessors;
+  GetProcessorInformation(&physicalCPUs, &cacheSizeL2, &cacheSizeL3);
+  if (physicalCPUs <= 0) {
+    physicalCPUs = logicalCPUs;
+  }
+  cpuFamily = si.wProcessorLevel;
+  cpuModel = si.wProcessorRevision >> 8;
+  cpuStepping = si.wProcessorRevision & 0xFF;
+#elif defined(XP_MACOSX)
+  // CPU speed
+  uint64_t sysctlValue64 = 0;
+  uint32_t sysctlValue32 = 0;
+  size_t len = 0;
+  len = sizeof(sysctlValue64);
+  if (!sysctlbyname("hw.cpufrequency_max", &sysctlValue64, &len, NULL, 0)) {
+    cpuSpeed = static_cast<int>(sysctlValue64 / 1000000);
+  }
+  MOZ_ASSERT(sizeof(sysctlValue64) == len);
+
+  len = sizeof(sysctlValue32);
+  if (!sysctlbyname("hw.physicalcpu_max", &sysctlValue32, &len, NULL, 0)) {
+    physicalCPUs = static_cast<int>(sysctlValue32);
+  }
+  MOZ_ASSERT(sizeof(sysctlValue32) == len);
+
+  len = sizeof(sysctlValue32);
+  if (!sysctlbyname("hw.logicalcpu_max", &sysctlValue32, &len, NULL, 0)) {
+    logicalCPUs = static_cast<int>(sysctlValue32);
+  }
+  MOZ_ASSERT(sizeof(sysctlValue32) == len);
+
+  len = sizeof(sysctlValue64);
+  if (!sysctlbyname("hw.l2cachesize", &sysctlValue64, &len, NULL, 0)) {
+    cacheSizeL2 = static_cast<int>(sysctlValue64 / 1024);
+  }
+  MOZ_ASSERT(sizeof(sysctlValue64) == len);
+
+  len = sizeof(sysctlValue64);
+  if (!sysctlbyname("hw.l3cachesize", &sysctlValue64, &len, NULL, 0)) {
+    cacheSizeL3 = static_cast<int>(sysctlValue64 / 1024);
+  }
+  MOZ_ASSERT(sizeof(sysctlValue64) == len);
+
+  if (!sysctlbyname("machdep.cpu.vendor", NULL, &len, NULL, 0)) {
+    char* cpuVendorStr = new char[len];
+    if (!sysctlbyname("machdep.cpu.vendor", cpuVendorStr, &len, NULL, 0)) {
+      cpuVendor = cpuVendorStr;
+    }
+    delete[] cpuVendorStr;
+  }
+
+  if (!sysctlbyname("machdep.cpu.brand_string", NULL, &len, NULL, 0)) {
+    char* cpuNameStr = new char[len];
+    if (!sysctlbyname("machdep.cpu.brand_string", cpuNameStr, &len, NULL, 0)) {
+      cpuName = cpuNameStr;
+    }
+    delete[] cpuNameStr;
+  }
+
+  len = sizeof(sysctlValue32);
+  if (!sysctlbyname("machdep.cpu.family", &sysctlValue32, &len, NULL, 0)) {
+    cpuFamily = static_cast<int>(sysctlValue32);
+  }
+  MOZ_ASSERT(sizeof(sysctlValue32) == len);
+
+  len = sizeof(sysctlValue32);
+  if (!sysctlbyname("machdep.cpu.model", &sysctlValue32, &len, NULL, 0)) {
+    cpuModel = static_cast<int>(sysctlValue32);
+  }
+  MOZ_ASSERT(sizeof(sysctlValue32) == len);
+
+  len = sizeof(sysctlValue32);
+  if (!sysctlbyname("machdep.cpu.stepping", &sysctlValue32, &len, NULL, 0)) {
+    cpuStepping = static_cast<int>(sysctlValue32);
+  }
+  MOZ_ASSERT(sizeof(sysctlValue32) == len);
+
+#elif defined(XP_LINUX) && !defined(ANDROID)
+  // Get vendor, family, model, stepping, physical cores
+  // from /proc/cpuinfo file
+  {
+    std::map<nsCString, nsCString> keyValuePairs;
+    SimpleParseKeyValuePairs("/proc/cpuinfo", keyValuePairs);
+
+    // cpuVendor from "vendor_id"
+    info.cpuVendor.Assign(keyValuePairs["vendor_id"_ns]);
+
+    // cpuName from "model name"
+    info.cpuName.Assign(keyValuePairs["model name"_ns]);
+
+    {
+      // cpuFamily from "cpu family"
+      Tokenizer::Token t;
+      Tokenizer p(keyValuePairs["cpu family"_ns]);
+      if (p.Next(t) && t.Type() == Tokenizer::TOKEN_INTEGER &&
+          t.AsInteger() <= INT32_MAX) {
+        cpuFamily = static_cast<int32_t>(t.AsInteger());
+      }
+    }
+
+    {
+      // cpuModel from "model"
+      Tokenizer::Token t;
+      Tokenizer p(keyValuePairs["model"_ns]);
+      if (p.Next(t) && t.Type() == Tokenizer::TOKEN_INTEGER &&
+          t.AsInteger() <= INT32_MAX) {
+        cpuModel = static_cast<int32_t>(t.AsInteger());
+      }
+    }
+
+    {
+      // cpuStepping from "stepping"
+      Tokenizer::Token t;
+      Tokenizer p(keyValuePairs["stepping"_ns]);
+      if (p.Next(t) && t.Type() == Tokenizer::TOKEN_INTEGER &&
+          t.AsInteger() <= INT32_MAX) {
+        cpuStepping = static_cast<int32_t>(t.AsInteger());
+      }
+    }
+
+    {
+      // physicalCPUs from "cpu cores"
+      Tokenizer::Token t;
+      Tokenizer p(keyValuePairs["cpu cores"_ns]);
+      if (p.Next(t) && t.Type() == Tokenizer::TOKEN_INTEGER &&
+          t.AsInteger() <= INT32_MAX) {
+        physicalCPUs = static_cast<int32_t>(t.AsInteger());
+      }
+    }
+  }
+
+  {
+    // Get cpuSpeed from another file.
+    std::ifstream input(
+        "/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq");
+    std::string line;
+    if (getline(input, line)) {
+      Tokenizer::Token t;
+      Tokenizer p(line.c_str());
+      if (p.Next(t) && t.Type() == Tokenizer::TOKEN_INTEGER &&
+          t.AsInteger() <= INT32_MAX) {
+        cpuSpeed = static_cast<int32_t>(t.AsInteger() / 1000);
+      }
+    }
+  }
+
+  {
+    // Get cacheSizeL2 from yet another file
+    std::ifstream input("/sys/devices/system/cpu/cpu0/cache/index2/size");
+    std::string line;
+    if (getline(input, line)) {
+      Tokenizer::Token t;
+      Tokenizer p(line.c_str(), nullptr, "K");
+      if (p.Next(t) && t.Type() == Tokenizer::TOKEN_INTEGER &&
+          t.AsInteger() <= INT32_MAX) {
+        cacheSizeL2 = static_cast<int32_t>(t.AsInteger());
+      }
+    }
+  }
+
+  {
+    // Get cacheSizeL3 from yet another file
+    std::ifstream input("/sys/devices/system/cpu/cpu0/cache/index3/size");
+    std::string line;
+    if (getline(input, line)) {
+      Tokenizer::Token t;
+      Tokenizer p(line.c_str(), nullptr, "K");
+      if (p.Next(t) && t.Type() == Tokenizer::TOKEN_INTEGER &&
+          t.AsInteger() <= INT32_MAX) {
+        cacheSizeL3 = static_cast<int32_t>(t.AsInteger());
+      }
+    }
+  }
+
+  info.cpuCount = PR_GetNumberOfProcessors();
+#else
+  info.cpuCount = PR_GetNumberOfProcessors();
+#endif
+
+  if (cpuSpeed >= 0) {
+    info.cpuSpeed = cpuSpeed;
+  } else {
+    info.cpuSpeed = 0;
+  }
+  if (!cpuVendor.IsEmpty()) {
+    info.cpuVendor = cpuVendor;
+  }
+  if (!cpuName.IsEmpty()) {
+    info.cpuName = cpuName;
+  }
+  if (cpuFamily >= 0) {
+    info.cpuFamily = cpuFamily;
+  }
+  if (cpuModel >= 0) {
+    info.cpuModel = cpuModel;
+  }
+  if (cpuStepping >= 0) {
+    info.cpuStepping = cpuStepping;
+  }
+
+  if (logicalCPUs >= 0) {
+    info.cpuCount = logicalCPUs;
+  }
+  if (physicalCPUs >= 0) {
+    info.cpuCores = physicalCPUs;
+  }
+
+  if (cacheSizeL2 >= 0) {
+    info.l2cacheKB = cacheSizeL2;
+  }
+  if (cacheSizeL3 >= 0) {
+    info.l3cacheKB = cacheSizeL3;
+  }
+
+  return NS_OK;
+}
+
+#if defined(XP_WIN) && (_WIN32_WINNT < 0x0A00)
+WINBASEAPI
+BOOL WINAPI IsUserCetAvailableInEnvironment(_In_ DWORD UserCetEnvironment);
+
+#  define USER_CET_ENVIRONMENT_WIN32_PROCESS 0x00000000
+#endif
+
+nsresult nsSystemInfo::Init() {
+  // check that it is called from the main thread on all platforms.
+  MOZ_ASSERT(NS_IsMainThread());
+
+  nsresult rv;
+
+  static const struct {
+    PRSysInfo cmd;
+    const char* name;
+  } items[] = {{PR_SI_SYSNAME, "name"},
+               {PR_SI_ARCHITECTURE, "arch"},
+               {PR_SI_RELEASE, "version"},
+               {PR_SI_RELEASE_BUILD, "build"}};
+
+  for (uint32_t i = 0; i < (sizeof(items) / sizeof(items[0])); i++) {
+    char buf[SYS_INFO_BUFFER_LENGTH];
+    if (PR_GetSystemInfo(items[i].cmd, buf, sizeof(buf)) == PR_SUCCESS) {
+      rv = SetPropertyAsACString(NS_ConvertASCIItoUTF16(items[i].name),
+                                 nsDependentCString(buf));
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+    } else {
+      NS_WARNING("PR_GetSystemInfo failed");
+    }
+  }
+
+  SetPropertyAsBool(u"isPackagedApp"_ns, false);
+
+  // Additional informations not available through PR_GetSystemInfo.
+  SetInt32Property(u"pagesize"_ns, PR_GetPageSize());
+  SetInt32Property(u"pageshift"_ns, PR_GetPageShift());
+  SetInt32Property(u"memmapalign"_ns, PR_GetMemMapAlignment());
+  SetUint64Property(u"memsize"_ns, PR_GetPhysicalMemorySize());
+  SetUint32Property(u"umask"_ns, nsSystemInfo::gUserUmask);
+
+  uint64_t virtualMem = 0;
+
+#if defined(XP_WIN)
+  // Virtual memory:
+  MEMORYSTATUSEX memStat;
+  memStat.dwLength = sizeof(memStat);
+  if (GlobalMemoryStatusEx(&memStat)) {
+    virtualMem = memStat.ullTotalVirtual;
+  }
+#endif
+  if (virtualMem) SetUint64Property(u"virtualmemsize"_ns, virtualMem);
+
+  for (uint32_t i = 0; i < ArrayLength(cpuPropItems); i++) {
+    rv = SetPropertyAsBool(NS_ConvertASCIItoUTF16(cpuPropItems[i].name),
+                           cpuPropItems[i].propfun());
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+#ifdef XP_WIN
+  bool isMinGW =
+#  ifdef __MINGW32__
+      true;
+#  else
+      false;
+#  endif
+  rv = SetPropertyAsBool(u"isMinGW"_ns, !!isMinGW);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  boolean hasPackageIdentity = widget::WinUtils::HasPackageIdentity();
+
+  rv = SetPropertyAsBool(u"hasWinPackageId"_ns, hasPackageIdentity);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = SetPropertyAsAString(u"winPackageFamilyName"_ns,
+                            widget::WinUtils::GetPackageFamilyName());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = SetPropertyAsBool(u"isPackagedApp"_ns, hasPackageIdentity);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+#  ifndef __MINGW32__
+  nsAutoString avInfo, antiSpyInfo, firewallInfo;
+  if (NS_SUCCEEDED(
+          GetWindowsSecurityCenterInfo(avInfo, antiSpyInfo, firewallInfo))) {
+    if (!avInfo.IsEmpty()) {
+      rv = SetPropertyAsAString(u"registeredAntiVirus"_ns, avInfo);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+    }
+
+    if (!antiSpyInfo.IsEmpty()) {
+      rv = SetPropertyAsAString(u"registeredAntiSpyware"_ns, antiSpyInfo);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+    }
+
+    if (!firewallInfo.IsEmpty()) {
+      rv = SetPropertyAsAString(u"registeredFirewall"_ns, firewallInfo);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+    }
+  }
+#  endif  // __MINGW32__
+
+  mozilla::DynamicallyLinkedFunctionPtr<
+      decltype(&IsUserCetAvailableInEnvironment)>
+      isUserCetAvailable(L"api-ms-win-core-sysinfo-l1-2-6.dll",
+                         "IsUserCetAvailableInEnvironment");
+  bool hasUserCET = isUserCetAvailable &&
+                    isUserCetAvailable(USER_CET_ENVIRONMENT_WIN32_PROCESS);
+  rv = SetPropertyAsBool(u"hasUserCET"_ns, hasUserCET);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+#endif
+
+#if defined(XP_MACOSX)
+  nsAutoCString modelId;
+  if (NS_SUCCEEDED(GetAppleModelId(modelId))) {
+    rv = SetPropertyAsACString(u"appleModelId"_ns, modelId);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  bool isRosetta;
+  if (NS_SUCCEEDED(ProcessIsRosettaTranslated(isRosetta))) {
+    rv = SetPropertyAsBool(u"rosettaStatus"_ns, isRosetta);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+#endif
+
+  {
+    nsAutoCString themeInfo;
+    LookAndFeel::GetThemeInfo(themeInfo);
+    MOZ_TRY(SetPropertyAsACString(u"osThemeInfo"_ns, themeInfo));
+  }
+
+#if defined(MOZ_WIDGET_GTK)
+  // This must be done here because NSPR can only separate OS's when compiled,
+  // not libraries. 64 bytes is going to be well enough for "GTK " followed by 3
+  // integers separated with dots.
+  char gtkver[64];
+  ssize_t gtkver_len = 0;
+
+  if (gtkver_len <= 0) {
+    gtkver_len = SprintfLiteral(gtkver, "GTK %u.%u.%u", gtk_major_version,
+                                gtk_minor_version, gtk_micro_version);
+  }
+
+  nsAutoCString secondaryLibrary;
+  if (gtkver_len > 0 && gtkver_len < int(sizeof(gtkver))) {
+    secondaryLibrary.Append(nsDependentCSubstring(gtkver, gtkver_len));
+  }
+
+#  ifndef MOZ_TSAN
+  // With TSan, avoid loading libpulse here because we cannot unload it
+  // afterwards due to restrictions from TSan about unloading libraries
+  // matched by the suppression list.
+  void* libpulse = dlopen("libpulse.so.0", RTLD_LAZY);
+  const char* libpulseVersion = "not-available";
+  if (libpulse) {
+    auto pa_get_library_version = reinterpret_cast<const char* (*)()>(
+        dlsym(libpulse, "pa_get_library_version"));
+
+    if (pa_get_library_version) {
+      libpulseVersion = pa_get_library_version();
+    }
+  }
+
+  secondaryLibrary.AppendPrintf(",libpulse %s", libpulseVersion);
+
+  if (libpulse) {
+    dlclose(libpulse);
+  }
+#  endif
+
+  rv = SetPropertyAsACString(u"secondaryLibrary"_ns, secondaryLibrary);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  rv = SetPropertyAsBool(u"isPackagedApp"_ns,
+                         widget::IsRunningUnderFlatpakOrSnap() ||
+                             widget::IsPackagedAppFileExists());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+#endif
+
+#ifdef MOZ_WIDGET_ANDROID
+  AndroidSystemInfo info;
+  GetAndroidSystemInfo(&info);
+  SetupAndroidInfo(info);
+#endif
+
+#if defined(XP_LINUX) && !defined(ANDROID)
+  nsCString dist, desc, release, codename;
+  if (widget::lsb::GetLSBRelease(dist, desc, release, codename)) {
+    SetPropertyAsACString(u"distro"_ns, dist);
+    SetPropertyAsACString(u"distroVersion"_ns, release);
+  }
+#endif
+
+#if defined(XP_LINUX) && defined(MOZ_SANDBOX)
+  SandboxInfo sandInfo = SandboxInfo::Get();
+
+  SetPropertyAsBool(u"hasSeccompBPF"_ns,
+                    sandInfo.Test(SandboxInfo::kHasSeccompBPF));
+  SetPropertyAsBool(u"hasSeccompTSync"_ns,
+                    sandInfo.Test(SandboxInfo::kHasSeccompTSync));
+  SetPropertyAsBool(u"hasUserNamespaces"_ns,
+                    sandInfo.Test(SandboxInfo::kHasUserNamespaces));
+  SetPropertyAsBool(u"hasPrivilegedUserNamespaces"_ns,
+                    sandInfo.Test(SandboxInfo::kHasPrivilegedUserNamespaces));
+
+  if (sandInfo.Test(SandboxInfo::kEnabledForContent)) {
+    SetPropertyAsBool(u"canSandboxContent"_ns, sandInfo.CanSandboxContent());
+  }
+
+  if (sandInfo.Test(SandboxInfo::kEnabledForMedia)) {
+    SetPropertyAsBool(u"canSandboxMedia"_ns, sandInfo.CanSandboxMedia());
+  }
+#endif  // XP_LINUX && MOZ_SANDBOX
+
+  return NS_OK;
+}
+
+#ifdef MOZ_WIDGET_ANDROID
+// Prerelease versions of Android use a letter instead of version numbers.
+// Unfortunately this breaks websites due to the user agent.
+// Chrome works around this by hardcoding an Android version when a
+// numeric version can't be obtained. We're doing the same.
+// This version will need to be updated whenever there is a new official
+// Android release. Search for "kDefaultAndroidMajorVersion" in:
+// https://source.chromium.org/chromium/chromium/src/+/master:base/system/sys_info_android.cc
+#  define DEFAULT_ANDROID_VERSION u"10.0.99"
+
+/* static */
+void nsSystemInfo::GetAndroidSystemInfo(AndroidSystemInfo* aInfo) {
+  if (!jni::IsAvailable()) {
+    // called from xpcshell etc.
+    aInfo->sdk_version() = 0;
+    return;
+  }
+
+  jni::String::LocalRef model = java::sdk::Build::MODEL();
+  aInfo->device() = model->ToString();
+
+  jni::String::LocalRef manufacturer =
+      mozilla::java::sdk::Build::MANUFACTURER();
+  aInfo->manufacturer() = manufacturer->ToString();
+
+  jni::String::LocalRef hardware = java::sdk::Build::HARDWARE();
+  aInfo->hardware() = hardware->ToString();
+
+  jni::String::LocalRef release = java::sdk::Build::VERSION::RELEASE();
+  nsString str(release->ToString());
+  int major_version;
+  int minor_version;
+  int bugfix_version;
+  int num_read = sscanf(NS_ConvertUTF16toUTF8(str).get(), "%d.%d.%d",
+                        &major_version, &minor_version, &bugfix_version);
+  if (num_read == 0) {
+    aInfo->release_version() = nsLiteralString(DEFAULT_ANDROID_VERSION);
+  } else {
+    aInfo->release_version() = str;
+  }
+
+  aInfo->sdk_version() = jni::GetAPIVersion();
+  aInfo->isTablet() = java::GeckoAppShell::IsTablet();
+}
+
+void nsSystemInfo::SetupAndroidInfo(const AndroidSystemInfo& aInfo) {
+  if (!aInfo.device().IsEmpty()) {
+    SetPropertyAsAString(u"device"_ns, aInfo.device());
+  }
+  if (!aInfo.manufacturer().IsEmpty()) {
+    SetPropertyAsAString(u"manufacturer"_ns, aInfo.manufacturer());
+  }
+  if (!aInfo.release_version().IsEmpty()) {
+    SetPropertyAsAString(u"release_version"_ns, aInfo.release_version());
+  }
+  SetPropertyAsBool(u"tablet"_ns, aInfo.isTablet());
+  // NSPR "version" is the kernel version. For Android we want the Android
+  // version. Rename SDK version to version and put the kernel version into
+  // kernel_version.
+  nsAutoString str;
+  nsresult rv = GetPropertyAsAString(u"version"_ns, str);
+  if (NS_SUCCEEDED(rv)) {
+    SetPropertyAsAString(u"kernel_version"_ns, str);
+  }
+  // When JNI is not available (eg. in xpcshell tests), sdk_version is 0.
+  if (aInfo.sdk_version() != 0) {
+    if (!aInfo.hardware().IsEmpty()) {
+      SetPropertyAsAString(u"hardware"_ns, aInfo.hardware());
+    }
+    SetPropertyAsInt32(u"version"_ns, aInfo.sdk_version());
+  }
+}
+#endif  // MOZ_WIDGET_ANDROID
+
+void nsSystemInfo::SetInt32Property(const nsAString& aPropertyName,
+                                    const int32_t aValue) {
+  NS_WARNING_ASSERTION(aValue > 0, "Unable to read system value");
+  if (aValue > 0) {
+#ifdef DEBUG
+    nsresult rv =
+#endif
+        SetPropertyAsInt32(aPropertyName, aValue);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "Unable to set property");
+  }
+}
+
+void nsSystemInfo::SetUint32Property(const nsAString& aPropertyName,
+                                     const uint32_t aValue) {
+  // Only one property is currently set via this function.
+  // It may legitimately be zero.
+#ifdef DEBUG
+  nsresult rv =
+#endif
+      SetPropertyAsUint32(aPropertyName, aValue);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "Unable to set property");
+}
+
+void nsSystemInfo::SetUint64Property(const nsAString& aPropertyName,
+                                     const uint64_t aValue) {
+  NS_WARNING_ASSERTION(aValue > 0, "Unable to read system value");
+  if (aValue > 0) {
+#ifdef DEBUG
+    nsresult rv =
+#endif
+        SetPropertyAsUint64(aPropertyName, aValue);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "Unable to set property");
+  }
+}
+
+#ifdef XP_WIN
+
+static bool GetJSObjForDiskInfo(JSContext* aCx, JS::Handle<JSObject*> aParent,
+                                const FolderDiskInfo& info,
+                                const char* propName) {
+  JS::Rooted<JSObject*> jsInfo(aCx, JS_NewPlainObject(aCx));
+  if (!jsInfo) {
+    return false;
+  }
+
+  JSString* strModel =
+      JS_NewStringCopyN(aCx, info.model.get(), info.model.Length());
+  if (!strModel) {
+    return false;
+  }
+  JS::Rooted<JS::Value> valModel(aCx, JS::StringValue(strModel));
+  if (!JS_SetProperty(aCx, jsInfo, "model", valModel)) {
+    return false;
+  }
+
+  JSString* strRevision =
+      JS_NewStringCopyN(aCx, info.revision.get(), info.revision.Length());
+  if (!strRevision) {
+    return false;
+  }
+  JS::Rooted<JS::Value> valRevision(aCx, JS::StringValue(strRevision));
+  if (!JS_SetProperty(aCx, jsInfo, "revision", valRevision)) {
+    return false;
+  }
+
+  JSString* strSSD = JS_NewStringCopyZ(aCx, info.isSSD ? "SSD" : "HDD");
+  if (!strSSD) {
+    return false;
+  }
+  JS::Rooted<JS::Value> valSSD(aCx, JS::StringValue(strSSD));
+  if (!JS_SetProperty(aCx, jsInfo, "type", valSSD)) {
+    return false;
+  }
+
+  JS::Rooted<JS::Value> val(aCx, JS::ObjectValue(*jsInfo));
+  return JS_SetProperty(aCx, aParent, propName, val);
+}
+
+JSObject* GetJSObjForOSInfo(JSContext* aCx, const OSInfo& info) {
+  JS::Rooted<JSObject*> jsInfo(aCx, JS_NewPlainObject(aCx));
+
+  JS::Rooted<JS::Value> valInstallYear(aCx, JS::Int32Value(info.installYear));
+  JS_SetProperty(aCx, jsInfo, "installYear", valInstallYear);
+
+  JS::Rooted<JS::Value> valHasSuperfetch(aCx,
+                                         JS::BooleanValue(info.hasSuperfetch));
+  JS_SetProperty(aCx, jsInfo, "hasSuperfetch", valHasSuperfetch);
+
+  JS::Rooted<JS::Value> valHasPrefetch(aCx, JS::BooleanValue(info.hasPrefetch));
+  JS_SetProperty(aCx, jsInfo, "hasPrefetch", valHasPrefetch);
+
+  return jsInfo;
+}
+
+#endif
+
+JSObject* GetJSObjForProcessInfo(JSContext* aCx, const ProcessInfo& info) {
+  JS::Rooted<JSObject*> jsInfo(aCx, JS_NewPlainObject(aCx));
+
+#if defined(XP_WIN)
+  JS::Rooted<JS::Value> valisWow64(aCx, JS::BooleanValue(info.isWow64));
+  JS_SetProperty(aCx, jsInfo, "isWow64", valisWow64);
+
+  JS::Rooted<JS::Value> valisWowARM64(aCx, JS::BooleanValue(info.isWowARM64));
+  JS_SetProperty(aCx, jsInfo, "isWowARM64", valisWowARM64);
+
+  JS::Rooted<JS::Value> valisWindowsSMode(
+      aCx, JS::BooleanValue(info.isWindowsSMode));
+  JS_SetProperty(aCx, jsInfo, "isWindowsSMode", valisWindowsSMode);
+#endif
+
+  JS::Rooted<JS::Value> valCountInfo(aCx, JS::Int32Value(info.cpuCount));
+  JS_SetProperty(aCx, jsInfo, "count", valCountInfo);
+
+  JS::Rooted<JS::Value> valCoreInfo(aCx, JS::Int32Value(info.cpuCores));
+  JS_SetProperty(aCx, jsInfo, "cores", valCoreInfo);
+
+  JSString* strVendor =
+      JS_NewStringCopyN(aCx, info.cpuVendor.get(), info.cpuVendor.Length());
+  JS::Rooted<JS::Value> valVendor(aCx, JS::StringValue(strVendor));
+  JS_SetProperty(aCx, jsInfo, "vendor", valVendor);
+
+  JSString* strName =
+      JS_NewStringCopyN(aCx, info.cpuName.get(), info.cpuName.Length());
+  JS::Rooted<JS::Value> valName(aCx, JS::StringValue(strName));
+  JS_SetProperty(aCx, jsInfo, "name", valName);
+
+  JS::Rooted<JS::Value> valFamilyInfo(aCx, JS::Int32Value(info.cpuFamily));
+  JS_SetProperty(aCx, jsInfo, "family", valFamilyInfo);
+
+  JS::Rooted<JS::Value> valModelInfo(aCx, JS::Int32Value(info.cpuModel));
+  JS_SetProperty(aCx, jsInfo, "model", valModelInfo);
+
+  JS::Rooted<JS::Value> valSteppingInfo(aCx, JS::Int32Value(info.cpuStepping));
+  JS_SetProperty(aCx, jsInfo, "stepping", valSteppingInfo);
+
+  JS::Rooted<JS::Value> valL2CacheInfo(aCx, JS::Int32Value(info.l2cacheKB));
+  JS_SetProperty(aCx, jsInfo, "l2cacheKB", valL2CacheInfo);
+
+  JS::Rooted<JS::Value> valL3CacheInfo(aCx, JS::Int32Value(info.l3cacheKB));
+  JS_SetProperty(aCx, jsInfo, "l3cacheKB", valL3CacheInfo);
+
+  JS::Rooted<JS::Value> valSpeedInfo(aCx, JS::Int32Value(info.cpuSpeed));
+  JS_SetProperty(aCx, jsInfo, "speedMHz", valSpeedInfo);
+
+  return jsInfo;
+}
+
+RefPtr<nsISerialEventTarget> nsSystemInfo::GetBackgroundTarget() {
+  if (!mBackgroundET) {
+    MOZ_ALWAYS_SUCCEEDS(NS_CreateBackgroundTaskQueue(
+        "SystemInfoThread", getter_AddRefs(mBackgroundET)));
+  }
+  return mBackgroundET;
+}
+
+NS_IMETHODIMP
+nsSystemInfo::GetOsInfo(JSContext* aCx, Promise** aResult) {
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = nullptr;
+  if (!XRE_IsParentProcess()) {
+    return NS_ERROR_FAILURE;
+  }
+#if defined(XP_WIN)
+  nsIGlobalObject* global = xpc::CurrentNativeGlobal(aCx);
+  if (NS_WARN_IF(!global)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  ErrorResult erv;
+  RefPtr<Promise> promise = Promise::Create(global, erv);
+  if (NS_WARN_IF(erv.Failed())) {
+    return erv.StealNSResult();
+  }
+
+  if (!mOSInfoPromise) {
+    RefPtr<nsISerialEventTarget> backgroundET = GetBackgroundTarget();
+
+    mOSInfoPromise = InvokeAsync(backgroundET, __func__, []() {
+      OSInfo info;
+      nsresult rv = CollectOSInfo(info);
+      if (NS_SUCCEEDED(rv)) {
+        return OSInfoPromise::CreateAndResolve(info, __func__);
+      }
+      return OSInfoPromise::CreateAndReject(rv, __func__);
+    });
+  };
+
+  // Chain the new promise to the extant mozpromise
+  RefPtr<Promise> capturedPromise = promise;
+  mOSInfoPromise->Then(
+      GetMainThreadSerialEventTarget(), __func__,
+      [capturedPromise](const OSInfo& info) {
+        AutoJSAPI jsapi;
+        if (NS_WARN_IF(!jsapi.Init(capturedPromise->GetGlobalObject()))) {
+          capturedPromise->MaybeReject(NS_ERROR_UNEXPECTED);
+          return;
+        }
+        JSContext* cx = jsapi.cx();
+        JS::Rooted<JS::Value> val(
+            cx, JS::ObjectValue(*GetJSObjForOSInfo(cx, info)));
+        capturedPromise->MaybeResolve(val);
+      },
+      [capturedPromise](const nsresult rv) {
+        // Resolve with null when installYear is not available from the system
+        capturedPromise->MaybeResolve(JS::NullHandleValue);
+      });
+
+  promise.forget(aResult);
+#endif
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSystemInfo::GetDiskInfo(JSContext* aCx, Promise** aResult) {
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = nullptr;
+  if (!XRE_IsParentProcess()) {
+    return NS_ERROR_FAILURE;
+  }
+#ifdef XP_WIN
+  nsIGlobalObject* global = xpc::CurrentNativeGlobal(aCx);
+  if (NS_WARN_IF(!global)) {
+    return NS_ERROR_FAILURE;
+  }
+  ErrorResult erv;
+  RefPtr<Promise> promise = Promise::Create(global, erv);
+  if (NS_WARN_IF(erv.Failed())) {
+    return erv.StealNSResult();
+  }
+
+  if (!mDiskInfoPromise) {
+    RefPtr<nsISerialEventTarget> backgroundET = GetBackgroundTarget();
+    nsCOMPtr<nsIFile> greDir;
+    nsCOMPtr<nsIFile> winDir;
+    nsCOMPtr<nsIFile> profDir;
+    nsresult rv = NS_GetSpecialDirectory(NS_GRE_DIR, getter_AddRefs(greDir));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+    rv = NS_GetSpecialDirectory(NS_WIN_WINDOWS_DIR, getter_AddRefs(winDir));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+    rv = NS_GetSpecialDirectory(NS_APP_USER_PROFILE_50_DIR,
+                                getter_AddRefs(profDir));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    mDiskInfoPromise =
+        InvokeAsync(backgroundET, __func__, [greDir, winDir, profDir]() {
+          DiskInfo info;
+          nsresult rv = CollectDiskInfo(greDir, winDir, profDir, info);
+          if (NS_SUCCEEDED(rv)) {
+            return DiskInfoPromise::CreateAndResolve(info, __func__);
+          }
+          return DiskInfoPromise::CreateAndReject(rv, __func__);
+        });
+  }
+
+  // Chain the new promise to the extant mozpromise.
+  RefPtr<Promise> capturedPromise = promise;
+  mDiskInfoPromise->Then(
+      GetMainThreadSerialEventTarget(), __func__,
+      [capturedPromise](const DiskInfo& info) {
+        AutoJSAPI jsapi;
+        if (NS_WARN_IF(!jsapi.Init(capturedPromise->GetGlobalObject()))) {
+          capturedPromise->MaybeReject(NS_ERROR_UNEXPECTED);
+          return;
+        }
+        JSContext* cx = jsapi.cx();
+        JS::Rooted<JSObject*> jsInfo(cx, JS_NewPlainObject(cx));
+        // Store data in the rv:
+        bool succeededSettingAllObjects =
+            jsInfo && GetJSObjForDiskInfo(cx, jsInfo, info.binary, "binary") &&
+            GetJSObjForDiskInfo(cx, jsInfo, info.profile, "profile") &&
+            GetJSObjForDiskInfo(cx, jsInfo, info.system, "system");
+        // The above can fail due to OOM
+        if (!succeededSettingAllObjects) {
+          JS_ClearPendingException(cx);
+          capturedPromise->MaybeReject(NS_ERROR_FAILURE);
+          return;
+        }
+
+        JS::Rooted<JS::Value> val(cx, JS::ObjectValue(*jsInfo));
+        capturedPromise->MaybeResolve(val);
+      },
+      [capturedPromise](const nsresult rv) {
+        capturedPromise->MaybeReject(rv);
+      });
+
+  promise.forget(aResult);
+#endif
+  return NS_OK;
+}
+
+NS_IMPL_ISUPPORTS_INHERITED(nsSystemInfo, nsHashPropertyBag, nsISystemInfo)
+
+NS_IMETHODIMP
+nsSystemInfo::GetCountryCode(JSContext* aCx, Promise** aResult) {
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = nullptr;
+
+  if (!XRE_IsParentProcess()) {
+    return NS_ERROR_FAILURE;
+  }
+#if defined(XP_MACOSX) || defined(XP_WIN)
+  nsIGlobalObject* global = xpc::CurrentNativeGlobal(aCx);
+  if (NS_WARN_IF(!global)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  ErrorResult erv;
+  RefPtr<Promise> promise = Promise::Create(global, erv);
+  if (NS_WARN_IF(erv.Failed())) {
+    return erv.StealNSResult();
+  }
+
+  if (!mCountryCodePromise) {
+    RefPtr<nsISerialEventTarget> backgroundET = GetBackgroundTarget();
+
+    mCountryCodePromise = InvokeAsync(backgroundET, __func__, []() {
+      nsAutoString countryCode;
+#  ifdef XP_MACOSX
+      nsresult rv = GetSelectedCityInfo(countryCode);
+#  endif
+#  ifdef XP_WIN
+      nsresult rv = CollectCountryCode(countryCode);
+#  endif
+
+      if (NS_SUCCEEDED(rv)) {
+        return CountryCodePromise::CreateAndResolve(countryCode, __func__);
+      }
+      return CountryCodePromise::CreateAndReject(rv, __func__);
+    });
+  }
+
+  RefPtr<Promise> capturedPromise = promise;
+  mCountryCodePromise->Then(
+      GetMainThreadSerialEventTarget(), __func__,
+      [capturedPromise](const nsString& countryCode) {
+        AutoJSAPI jsapi;
+        if (NS_WARN_IF(!jsapi.Init(capturedPromise->GetGlobalObject()))) {
+          capturedPromise->MaybeReject(NS_ERROR_UNEXPECTED);
+          return;
+        }
+        JSContext* cx = jsapi.cx();
+        JS::Rooted<JSString*> jsCountryCode(
+            cx, JS_NewUCStringCopyZ(cx, countryCode.get()));
+
+        JS::Rooted<JS::Value> val(cx, JS::StringValue(jsCountryCode));
+        capturedPromise->MaybeResolve(val);
+      },
+      [capturedPromise](const nsresult rv) {
+        // Resolve with null when countryCode is not available from the system
+        capturedPromise->MaybeResolve(JS::NullHandleValue);
+      });
+
+  promise.forget(aResult);
+#endif
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSystemInfo::GetProcessInfo(JSContext* aCx, Promise** aResult) {
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = nullptr;
+
+  if (!XRE_IsParentProcess()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsIGlobalObject* global = xpc::CurrentNativeGlobal(aCx);
+  if (NS_WARN_IF(!global)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  ErrorResult erv;
+  RefPtr<Promise> promise = Promise::Create(global, erv);
+  if (NS_WARN_IF(erv.Failed())) {
+    return erv.StealNSResult();
+  }
+
+  if (!mProcessInfoPromise) {
+    RefPtr<nsISerialEventTarget> backgroundET = GetBackgroundTarget();
+
+    mProcessInfoPromise = InvokeAsync(backgroundET, __func__, []() {
+      ProcessInfo info;
+      nsresult rv = CollectProcessInfo(info);
+      if (NS_SUCCEEDED(rv)) {
+        return ProcessInfoPromise::CreateAndResolve(info, __func__);
+      }
+      return ProcessInfoPromise::CreateAndReject(rv, __func__);
+    });
+  };
+
+  // Chain the new promise to the extant mozpromise
+  RefPtr<Promise> capturedPromise = promise;
+  mProcessInfoPromise->Then(
+      GetMainThreadSerialEventTarget(), __func__,
+      [capturedPromise](const ProcessInfo& info) {
+        AutoJSAPI jsapi;
+        if (NS_WARN_IF(!jsapi.Init(capturedPromise->GetGlobalObject()))) {
+          capturedPromise->MaybeReject(NS_ERROR_UNEXPECTED);
+          return;
+        }
+        JSContext* cx = jsapi.cx();
+        JS::Rooted<JS::Value> val(
+            cx, JS::ObjectValue(*GetJSObjForProcessInfo(cx, info)));
+        capturedPromise->MaybeResolve(val);
+      },
+      [capturedPromise](const nsresult rv) {
+        // Resolve with null when installYear is not available from the system
+        capturedPromise->MaybeResolve(JS::NullHandleValue);
+      });
+
+  promise.forget(aResult);
+
+  return NS_OK;
+}
diff --git a/xpcom/base/nsSystemInfo.h b/xpcom/base/nsSystemInfo.h
new file mode 100644
index 0000000000..9d47b5d4f6
--- /dev/null
+++ b/xpcom/base/nsSystemInfo.h
@@ -0,0 +1,130 @@
+/* -*- 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/. */
+
+#ifndef _NSSYSTEMINFO_H_
+#define _NSSYSTEMINFO_H_
+
+#include "nsHashPropertyBag.h"
+#include "nsISystemInfo.h"
+#include "mozilla/MozPromise.h"
+
+#ifdef MOZ_WIDGET_ANDROID
+#  include "mozilla/dom/PContent.h"
+#endif  // MOZ_WIDGET_ANDROID
+
+#if defined(XP_WIN)
+#  include <inspectable.h>
+
+// The UUID comes from winrt/windows.system.profile.idl
+// in the Windows SDK
+MIDL_INTERFACE("7D1D81DB-8D63-4789-9EA5-DDCF65A94F3C")
+IWindowsIntegrityPolicyStatics : public IInspectable {
+ public:
+  virtual HRESULT STDMETHODCALLTYPE get_IsEnabled(bool* value) = 0;
+};
+#endif
+
+class nsISerialEventTarget;
+
+struct FolderDiskInfo {
+  nsCString model;
+  nsCString revision;
+  bool isSSD;
+};
+
+struct DiskInfo {
+  FolderDiskInfo binary;
+  FolderDiskInfo profile;
+  FolderDiskInfo system;
+};
+
+struct OSInfo {
+  uint32_t installYear;
+  bool hasSuperfetch;
+  bool hasPrefetch;
+};
+
+struct ProcessInfo {
+  bool isWow64 = false;
+  bool isWowARM64 = false;
+  // Whether or not the system is Windows 10 or 11 in S Mode.
+  // S Mode existed prior to us being able to query it, so this
+  // is unreliable on Windows versions prior to 1810.
+  bool isWindowsSMode = false;
+  int32_t cpuCount = 0;
+  int32_t cpuCores = 0;
+  nsCString cpuVendor;
+  nsCString cpuName;
+  int32_t cpuFamily = 0;
+  int32_t cpuModel = 0;
+  int32_t cpuStepping = 0;
+  int32_t l2cacheKB = 0;
+  int32_t l3cacheKB = 0;
+  int32_t cpuSpeed = 0;
+};
+
+typedef mozilla::MozPromise<DiskInfo, nsresult, /* IsExclusive */ false>
+    DiskInfoPromise;
+
+typedef mozilla::MozPromise<nsAutoString, nsresult, /* IsExclusive */ false>
+    CountryCodePromise;
+
+typedef mozilla::MozPromise<OSInfo, nsresult, /* IsExclusive */ false>
+    OSInfoPromise;
+
+typedef mozilla::MozPromise<ProcessInfo, nsresult, /* IsExclusive */ false>
+    ProcessInfoPromise;
+
+// Synchronous info collection, avoid calling it from the main thread, consider
+// using the promise-based `nsISystemInfo::GetProcessInfo()` instead.
+// Note that only known fields will be written.
+nsresult CollectProcessInfo(ProcessInfo& info);
+
+class nsSystemInfo final : public nsISystemInfo, public nsHashPropertyBag {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_NSISYSTEMINFO
+
+  nsSystemInfo();
+
+  nsresult Init();
+
+  // Slot for NS_InitXPCOM to pass information to nsSystemInfo::Init.
+  // See comments above the variable definition and in NS_InitXPCOM.
+  static uint32_t gUserUmask;
+
+#ifdef MOZ_WIDGET_ANDROID
+  static void GetAndroidSystemInfo(mozilla::dom::AndroidSystemInfo* aInfo);
+
+ protected:
+  void SetupAndroidInfo(const mozilla::dom::AndroidSystemInfo&);
+#endif
+
+ protected:
+  void SetInt32Property(const nsAString& aPropertyName, const int32_t aValue);
+  void SetUint32Property(const nsAString& aPropertyName, const uint32_t aValue);
+  void SetUint64Property(const nsAString& aPropertyName, const uint64_t aValue);
+
+ private:
+  ~nsSystemInfo();
+
+  RefPtr<DiskInfoPromise> mDiskInfoPromise;
+  RefPtr<CountryCodePromise> mCountryCodePromise;
+  RefPtr<OSInfoPromise> mOSInfoPromise;
+  RefPtr<ProcessInfoPromise> mProcessInfoPromise;
+  RefPtr<nsISerialEventTarget> mBackgroundET;
+  RefPtr<nsISerialEventTarget> GetBackgroundTarget();
+};
+
+#define NS_SYSTEMINFO_CONTRACTID "@mozilla.org/system-info;1"
+#define NS_SYSTEMINFO_CID                            \
+  {                                                  \
+    0xd962398a, 0x99e5, 0x49b2, {                    \
+      0x85, 0x7a, 0xc1, 0x59, 0x04, 0x9c, 0x7f, 0x6c \
+    }                                                \
+  }
+
+#endif /* _NSSYSTEMINFO_H_ */
diff --git a/xpcom/base/nsTraceRefcnt.cpp b/xpcom/base/nsTraceRefcnt.cpp
new file mode 100644
index 0000000000..1da0f6b647
--- /dev/null
+++ b/xpcom/base/nsTraceRefcnt.cpp
@@ -0,0 +1,1219 @@
+/* -*- 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 "nsTraceRefcnt.h"
+
+#include "base/process_util.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/IntegerPrintfMacros.h"
+#include "mozilla/Path.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/StaticPtr.h"
+#include "nsXPCOMPrivate.h"
+#include "nscore.h"
+#include "nsClassHashtable.h"
+#include "nsContentUtils.h"
+#include "nsISupports.h"
+#include "nsHashKeys.h"
+#include "nsPrintfCString.h"
+#include "nsTArray.h"
+#include "nsTHashtable.h"
+#include "prenv.h"
+#include "prlink.h"
+#include "nsCRT.h"
+#include <math.h>
+#include "nsHashKeys.h"
+#include "mozilla/StackWalk.h"
+#include "nsThreadUtils.h"
+#include "CodeAddressService.h"
+
+#include "nsXULAppAPI.h"
+#ifdef XP_WIN
+#  include <io.h>
+#  include <process.h>
+#  define getpid _getpid
+#else
+#  include <unistd.h>
+#endif
+
+#include "mozilla/Atomics.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/BlockingResourceBase.h"
+#include "mozilla/PoisonIOInterposer.h"
+#include "mozilla/UniquePtr.h"
+
+#include <string>
+#include <vector>
+
+#ifdef HAVE_DLOPEN
+#  include <dlfcn.h>
+#endif
+
+#ifdef MOZ_DMD
+#  include "nsMemoryInfoDumper.h"
+#endif
+
+// dynamic_cast<void*> is not supported on Windows without RTTI.
+#ifndef _WIN32
+#  define HAVE_CPP_DYNAMIC_CAST_TO_VOID_PTR
+#endif
+
+////////////////////////////////////////////////////////////////////////////////
+
+#include "prthread.h"
+
+class MOZ_CAPABILITY("mutex") TraceLogMutex
+    : private mozilla::detail::MutexImpl {
+ public:
+  explicit TraceLogMutex() : ::mozilla::detail::MutexImpl(){};
+
+ private:
+  friend class AutoTraceLogLock;
+
+  void Lock() MOZ_CAPABILITY_ACQUIRE() { ::mozilla::detail::MutexImpl::lock(); }
+  void Unlock() MOZ_CAPABILITY_RELEASE() {
+    ::mozilla::detail::MutexImpl::unlock();
+  }
+};
+
+static TraceLogMutex gTraceLog;
+
+class MOZ_RAII AutoTraceLogLock {
+ public:
+  explicit AutoTraceLogLock(TraceLogMutex& aMutex) : mMutex(aMutex) {
+    mMutex.Lock();
+  }
+
+  AutoTraceLogLock(const AutoTraceLogLock&) = delete;
+  AutoTraceLogLock& operator=(const AutoTraceLogLock&) = delete;
+  AutoTraceLogLock(AutoTraceLogLock&&) = delete;
+  AutoTraceLogLock& operator=(AutoTraceLogLock&&) = delete;
+
+  ~AutoTraceLogLock() { mMutex.Unlock(); }
+
+ private:
+  TraceLogMutex& mMutex;
+};
+
+class BloatEntry;
+struct SerialNumberRecord;
+
+using mozilla::AutoRestore;
+using mozilla::CodeAddressService;
+using mozilla::CycleCollectedJSContext;
+using mozilla::StaticAutoPtr;
+
+using BloatHash = nsClassHashtable<nsDepCharHashKey, BloatEntry>;
+using CharPtrSet = nsTHashtable<nsCharPtrHashKey>;
+using IntPtrSet = nsTHashtable<IntPtrHashKey>;
+using SerialHash = nsClassHashtable<nsVoidPtrHashKey, SerialNumberRecord>;
+
+static StaticAutoPtr<BloatHash> gBloatView;
+static StaticAutoPtr<CharPtrSet> gTypesToLog;
+static StaticAutoPtr<IntPtrSet> gObjectsToLog;
+static StaticAutoPtr<SerialHash> gSerialNumbers;
+
+static intptr_t gNextSerialNumber;
+static bool gDumpedStatistics = false;
+static bool gLogJSStacks = false;
+
+// By default, debug builds only do bloat logging. Bloat logging
+// only tries to record when an object is created or destroyed, so we
+// optimize the common case in NS_LogAddRef and NS_LogRelease where
+// only bloat logging is enabled and no logging needs to be done.
+enum LoggingType { NoLogging, OnlyBloatLogging, FullLogging };
+
+static LoggingType gLogging;
+
+static bool gLogLeaksOnly;
+
+#define BAD_TLS_INDEX ((unsigned)-1)
+
+// if gActivityTLS == BAD_TLS_INDEX, then we're
+// unitialized... otherwise this points to a NSPR TLS thread index
+// indicating whether addref activity is legal. If the PTR_TO_INT32 is 0 then
+// activity is ok, otherwise not!
+static unsigned gActivityTLS = BAD_TLS_INDEX;
+
+static bool gInitialized;
+static nsrefcnt gInitCount;
+
+static FILE* gBloatLog = nullptr;
+static FILE* gRefcntsLog = nullptr;
+static FILE* gAllocLog = nullptr;
+static FILE* gCOMPtrLog = nullptr;
+
+static void WalkTheStackSavingLocations(std::vector<void*>& aLocations,
+                                        const void* aFirstFramePC);
+
+struct SerialNumberRecord {
+  SerialNumberRecord()
+      : serialNumber(++gNextSerialNumber), refCount(0), COMPtrCount(0) {}
+
+  intptr_t serialNumber;
+  int32_t refCount;
+  int32_t COMPtrCount;
+  // We use std:: classes here rather than the XPCOM equivalents because the
+  // XPCOM equivalents do leak-checking, and if you try to leak-check while
+  // leak-checking, you're gonna have a bad time.
+  std::vector<void*> allocationStack;
+  mozilla::UniquePtr<char[]> jsStack;
+
+  void SaveJSStack() {
+    // If this thread isn't running JS, there's nothing to do.
+    if (!CycleCollectedJSContext::Get()) {
+      return;
+    }
+
+    if (!nsContentUtils::IsInitialized()) {
+      return;
+    }
+
+    JSContext* cx = nsContentUtils::GetCurrentJSContext();
+    if (!cx) {
+      return;
+    }
+
+    JS::UniqueChars chars = xpc_PrintJSStack(cx,
+                                             /*showArgs=*/false,
+                                             /*showLocals=*/false,
+                                             /*showThisProps=*/false);
+    size_t len = strlen(chars.get());
+    jsStack = mozilla::MakeUnique<char[]>(len + 1);
+    memcpy(jsStack.get(), chars.get(), len + 1);
+  }
+};
+
+struct nsTraceRefcntStats {
+  uint64_t mCreates;
+  uint64_t mDestroys;
+
+  bool HaveLeaks() const { return mCreates != mDestroys; }
+
+  void Clear() {
+    mCreates = 0;
+    mDestroys = 0;
+  }
+
+  int64_t NumLeaked() const { return (int64_t)(mCreates - mDestroys); }
+};
+
+#ifdef DEBUG
+static void AssertActivityIsLegal(const char* aType, const char* aAction) {
+  if (gActivityTLS == BAD_TLS_INDEX || PR_GetThreadPrivate(gActivityTLS)) {
+    char buf[1024];
+    SprintfLiteral(buf, "XPCOM object %s %s from static ctor/dtor", aType,
+                   aAction);
+
+    if (PR_GetEnv("MOZ_FATAL_STATIC_XPCOM_CTORS_DTORS")) {
+      MOZ_CRASH_UNSAFE_PRINTF("%s", buf);
+    } else {
+      NS_WARNING(buf);
+    }
+  }
+}
+#  define ASSERT_ACTIVITY_IS_LEGAL(type_, action_) \
+    do {                                           \
+      AssertActivityIsLegal(type_, action_);       \
+    } while (0)
+#else
+#  define ASSERT_ACTIVITY_IS_LEGAL(type_, action_) \
+    do {                                           \
+    } while (0)
+#endif  // DEBUG
+
+////////////////////////////////////////////////////////////////////////////////
+
+mozilla::StaticAutoPtr<CodeAddressService<>> gCodeAddressService;
+
+////////////////////////////////////////////////////////////////////////////////
+
+class BloatEntry {
+ public:
+  BloatEntry(const char* aClassName, uint32_t aClassSize)
+      : mClassSize(aClassSize), mStats() {
+    MOZ_ASSERT(strlen(aClassName) > 0, "BloatEntry name must be non-empty");
+    mClassName = aClassName;
+    mStats.Clear();
+    mTotalLeaked = 0;
+  }
+
+  ~BloatEntry() = default;
+
+  uint32_t GetClassSize() { return (uint32_t)mClassSize; }
+  const char* GetClassName() { return mClassName; }
+
+  void Ctor() { mStats.mCreates++; }
+
+  void Dtor() { mStats.mDestroys++; }
+
+  void Total(BloatEntry* aTotal) {
+    aTotal->mStats.mCreates += mStats.mCreates;
+    aTotal->mStats.mDestroys += mStats.mDestroys;
+    aTotal->mClassSize +=
+        mClassSize * mStats.mCreates;  // adjust for average in DumpTotal
+    aTotal->mTotalLeaked += mClassSize * mStats.NumLeaked();
+  }
+
+  void DumpTotal(FILE* aOut) {
+    mClassSize /= mStats.mCreates;
+    Dump(-1, aOut);
+  }
+
+  bool PrintDumpHeader(FILE* aOut, const char* aMsg) {
+    fprintf(aOut, "\n== BloatView: %s, %s process %d\n", aMsg,
+            XRE_GetProcessTypeString(), getpid());
+    if (gLogLeaksOnly && !mStats.HaveLeaks()) {
+      return false;
+    }
+
+    // clang-format off
+    fprintf(aOut,
+            "\n" \
+            "     |<----------------Class--------------->|<-----Bytes------>|<----Objects---->|\n" \
+            "     |                                      | Per-Inst   Leaked|   Total      Rem|\n");
+    // clang-format on
+
+    this->DumpTotal(aOut);
+
+    return true;
+  }
+
+  void Dump(int aIndex, FILE* aOut) {
+    if (gLogLeaksOnly && !mStats.HaveLeaks()) {
+      return;
+    }
+
+    if (mStats.HaveLeaks() || mStats.mCreates != 0) {
+      fprintf(aOut,
+              "%4d |%-38.38s| %8d %8" PRId64 "|%8" PRIu64 " %8" PRId64 "|\n",
+              aIndex + 1, mClassName, GetClassSize(),
+              nsCRT::strcmp(mClassName, "TOTAL")
+                  ? (mStats.NumLeaked() * GetClassSize())
+                  : mTotalLeaked,
+              mStats.mCreates, mStats.NumLeaked());
+    }
+  }
+
+ protected:
+  const char* mClassName;
+  // mClassSize is stored as a double because of the way we compute the avg
+  // class size for total bloat.
+  double mClassSize;
+  // mTotalLeaked is only used for the TOTAL entry.
+  int64_t mTotalLeaked;
+  nsTraceRefcntStats mStats;
+};
+
+static void EnsureBloatView() {
+  if (!gBloatView) {
+    gBloatView = new BloatHash(256);
+  }
+}
+
+static BloatEntry* GetBloatEntry(const char* aTypeName,
+                                 uint32_t aInstanceSize) {
+  EnsureBloatView();
+  BloatEntry* entry = gBloatView->Get(aTypeName);
+  if (!entry && aInstanceSize > 0) {
+    entry = gBloatView
+                ->InsertOrUpdate(aTypeName, mozilla::MakeUnique<BloatEntry>(
+                                                aTypeName, aInstanceSize))
+                .get();
+  } else {
+    MOZ_ASSERT(
+        aInstanceSize == 0 || entry->GetClassSize() == aInstanceSize,
+        "Mismatched sizes were recorded in the memory leak logging table. "
+        "The usual cause of this is having a templated class that uses "
+        "MOZ_COUNT_{C,D}TOR in the constructor or destructor, respectively. "
+        "As a workaround, the MOZ_COUNT_{C,D}TOR calls can be moved to a "
+        "non-templated base class. Another possible cause is a runnable with "
+        "an mName that matches another refcounted class, or two refcounted "
+        "classes with the same class name in different C++ namespaces.");
+  }
+  return entry;
+}
+
+static void DumpSerialNumbers(const SerialHash::ConstIterator& aHashEntry,
+                              FILE* aFd, bool aDumpAsStringBuffer) {
+  SerialNumberRecord* record = aHashEntry.UserData();
+  auto* outputFile = aFd;
+#ifdef HAVE_CPP_DYNAMIC_CAST_TO_VOID_PTR
+  fprintf(outputFile, "%" PRIdPTR " @%p (%d references; %d from COMPtrs)\n",
+          record->serialNumber, aHashEntry.Key(), record->refCount,
+          record->COMPtrCount);
+#else
+  fprintf(outputFile, "%" PRIdPTR " @%p (%d references)\n",
+          record->serialNumber, aHashEntry.Key(), record->refCount);
+#endif
+
+  if (aDumpAsStringBuffer) {
+    // This output will be wrong if the nsStringBuffer was used to
+    // store a char16_t string.
+    auto* buffer = static_cast<const nsStringBuffer*>(aHashEntry.Key());
+    nsDependentCString bufferString(static_cast<char*>(buffer->Data()));
+    fprintf(outputFile,
+            "Contents of leaked nsStringBuffer with storage size %d as a "
+            "char*: %s\n",
+            buffer->StorageSize(), bufferString.get());
+  }
+
+  if (!record->allocationStack.empty()) {
+    static const size_t bufLen = 1024;
+    char buf[bufLen];
+    fprintf(outputFile, "allocation stack:\n");
+    for (size_t i = 0, length = record->allocationStack.size(); i < length;
+         ++i) {
+      gCodeAddressService->GetLocation(i, record->allocationStack[i], buf,
+                                       bufLen);
+      fprintf(outputFile, "%s\n", buf);
+    }
+  }
+
+  if (gLogJSStacks) {
+    if (record->jsStack) {
+      fprintf(outputFile, "JS allocation stack:\n%s\n", record->jsStack.get());
+    } else {
+      fprintf(outputFile, "There is no JS context on the stack.\n");
+    }
+  }
+}
+
+template <>
+class nsDefaultComparator<BloatEntry*, BloatEntry*> {
+ public:
+  bool Equals(BloatEntry* const& aEntry1, BloatEntry* const& aEntry2) const {
+    return strcmp(aEntry1->GetClassName(), aEntry2->GetClassName()) == 0;
+  }
+  bool LessThan(BloatEntry* const& aEntry1, BloatEntry* const& aEntry2) const {
+    return strcmp(aEntry1->GetClassName(), aEntry2->GetClassName()) < 0;
+  }
+};
+
+nsresult nsTraceRefcnt::DumpStatistics() {
+  if (!gBloatLog || !gBloatView) {
+    return NS_ERROR_FAILURE;
+  }
+
+  AutoTraceLogLock lock(gTraceLog);
+
+  MOZ_ASSERT(!gDumpedStatistics,
+             "Calling DumpStatistics more than once may result in "
+             "bogus positive or negative leaks being reported");
+  gDumpedStatistics = true;
+
+  // Don't try to log while we hold the lock, we'd deadlock.
+  AutoRestore<LoggingType> saveLogging(gLogging);
+  gLogging = NoLogging;
+
+  BloatEntry total("TOTAL", 0);
+  for (const auto& data : gBloatView->Values()) {
+    if (nsCRT::strcmp(data->GetClassName(), "TOTAL") != 0) {
+      data->Total(&total);
+    }
+  }
+
+  const char* msg;
+  if (gLogLeaksOnly) {
+    msg = "ALL (cumulative) LEAK STATISTICS";
+  } else {
+    msg = "ALL (cumulative) LEAK AND BLOAT STATISTICS";
+  }
+  const bool leaked = total.PrintDumpHeader(gBloatLog, msg);
+
+  nsTArray<BloatEntry*> entries(gBloatView->Count());
+  for (const auto& data : gBloatView->Values()) {
+    entries.AppendElement(data.get());
+  }
+
+  const uint32_t count = entries.Length();
+
+  if (!gLogLeaksOnly || leaked) {
+    // Sort the entries alphabetically by classname.
+    entries.Sort();
+
+    for (uint32_t i = 0; i < count; ++i) {
+      BloatEntry* entry = entries[i];
+      entry->Dump(i, gBloatLog);
+    }
+
+    fprintf(gBloatLog, "\n");
+  }
+
+  fprintf(gBloatLog, "nsTraceRefcnt::DumpStatistics: %d entries\n", count);
+
+  if (gSerialNumbers) {
+    bool onlyLoggingStringBuffers = gTypesToLog && gTypesToLog->Count() == 1 &&
+                                    gTypesToLog->Contains("nsStringBuffer");
+
+    fprintf(gBloatLog, "\nSerial Numbers of Leaked Objects:\n");
+    for (auto iter = gSerialNumbers->ConstIter(); !iter.Done(); iter.Next()) {
+      DumpSerialNumbers(iter, gBloatLog, onlyLoggingStringBuffers);
+    }
+  }
+
+  return NS_OK;
+}
+
+void nsTraceRefcnt::ResetStatistics() {
+  AutoTraceLogLock lock(gTraceLog);
+  gBloatView = nullptr;
+}
+
+static intptr_t GetSerialNumber(void* aPtr, bool aCreate, void* aFirstFramePC) {
+  if (!aCreate) {
+    auto record = gSerialNumbers->Get(aPtr);
+    return record ? record->serialNumber : 0;
+  }
+
+  gSerialNumbers->WithEntryHandle(aPtr, [aFirstFramePC](auto&& entry) {
+    if (entry) {
+      MOZ_CRASH(
+          "If an object already has a serial number, we should be destroying "
+          "it.");
+    }
+
+    auto& record = entry.Insert(mozilla::MakeUnique<SerialNumberRecord>());
+    WalkTheStackSavingLocations(record->allocationStack, aFirstFramePC);
+    if (gLogJSStacks) {
+      record->SaveJSStack();
+    }
+  });
+  return gNextSerialNumber;
+}
+
+static void RecycleSerialNumberPtr(void* aPtr) { gSerialNumbers->Remove(aPtr); }
+
+static bool LogThisObj(intptr_t aSerialNumber) {
+  return gObjectsToLog->Contains(aSerialNumber);
+}
+
+using EnvCharType = mozilla::filesystem::Path::value_type;
+
+static bool InitLog(const EnvCharType* aEnvVar, const char* aMsg,
+                    FILE** aResult, const char* aProcType) {
+#ifdef XP_WIN
+  // This is gross, I know.
+  const wchar_t* envvar = reinterpret_cast<const wchar_t*>(aEnvVar);
+  const char16_t* value = reinterpret_cast<const char16_t*>(::_wgetenv(envvar));
+#  define ENVVAR_PRINTF "%S"
+#else
+  const char* envvar = aEnvVar;
+  const char* value = ::getenv(aEnvVar);
+#  define ENVVAR_PRINTF "%s"
+#endif
+
+  if (value) {
+    nsTDependentString<EnvCharType> fname(value);
+    if (fname.EqualsLiteral("1")) {
+      *aResult = stdout;
+      fprintf(stdout, "### " ENVVAR_PRINTF " defined -- logging %s to stdout\n",
+              envvar, aMsg);
+      return true;
+    }
+    if (fname.EqualsLiteral("2")) {
+      *aResult = stderr;
+      fprintf(stdout, "### " ENVVAR_PRINTF " defined -- logging %s to stderr\n",
+              envvar, aMsg);
+      return true;
+    }
+    if (!XRE_IsParentProcess()) {
+      nsTString<EnvCharType> extension;
+      extension.AssignLiteral(".log");
+      bool hasLogExtension = StringEndsWith(fname, extension);
+      if (hasLogExtension) {
+        fname.Cut(fname.Length() - 4, 4);
+      }
+      fname.Append('_');
+      fname.AppendASCII(aProcType);
+      fname.AppendLiteral("_pid");
+      fname.AppendInt((uint32_t)getpid());
+      if (hasLogExtension) {
+        fname.AppendLiteral(".log");
+      }
+    }
+#ifdef XP_WIN
+    FILE* stream = ::_wfopen(fname.get(), L"wN");
+    const wchar_t* fp = (const wchar_t*)fname.get();
+#else
+    FILE* stream = ::fopen(fname.get(), "w");
+    const char* fp = fname.get();
+#endif
+    if (stream) {
+      MozillaRegisterDebugFD(fileno(stream));
+#ifdef MOZ_ENABLE_FORKSERVER
+      base::RegisterForkServerNoCloseFD(fileno(stream));
+#endif
+      *aResult = stream;
+      fprintf(stderr,
+              "### " ENVVAR_PRINTF " defined -- logging %s to " ENVVAR_PRINTF
+              "\n",
+              envvar, aMsg, fp);
+
+      return true;
+    }
+
+    fprintf(stderr,
+            "### " ENVVAR_PRINTF
+            " defined -- unable to log %s to " ENVVAR_PRINTF "\n",
+            envvar, aMsg, fp);
+    MOZ_ASSERT(false, "Tried and failed to create an XPCOM log");
+
+#undef ENVVAR_PRINTF
+  }
+  return false;
+}
+
+static void maybeUnregisterAndCloseFile(FILE*& aFile) {
+  if (!aFile) {
+    return;
+  }
+
+  MozillaUnRegisterDebugFILE(aFile);
+  fclose(aFile);
+  aFile = nullptr;
+}
+
+static void DoInitTraceLog(const char* aProcType) {
+#ifdef XP_WIN
+#  define ENVVAR(x) u"" x
+#else
+#  define ENVVAR(x) x
+#endif
+
+  bool defined = InitLog(ENVVAR("XPCOM_MEM_BLOAT_LOG"), "bloat/leaks",
+                         &gBloatLog, aProcType);
+  if (!defined) {
+    gLogLeaksOnly =
+        InitLog(ENVVAR("XPCOM_MEM_LEAK_LOG"), "leaks", &gBloatLog, aProcType);
+  }
+  if (defined || gLogLeaksOnly) {
+    // Use the same bloat view, if there is one, to keep it consistent
+    // between the fork server and content processes.
+    EnsureBloatView();
+  } else if (gBloatView) {
+    nsTraceRefcnt::ResetStatistics();
+  }
+
+  InitLog(ENVVAR("XPCOM_MEM_REFCNT_LOG"), "refcounts", &gRefcntsLog, aProcType);
+
+  InitLog(ENVVAR("XPCOM_MEM_ALLOC_LOG"), "new/delete", &gAllocLog, aProcType);
+
+  const char* classes = getenv("XPCOM_MEM_LOG_CLASSES");
+
+#ifdef HAVE_CPP_DYNAMIC_CAST_TO_VOID_PTR
+  if (classes) {
+    InitLog(ENVVAR("XPCOM_MEM_COMPTR_LOG"), "nsCOMPtr", &gCOMPtrLog, aProcType);
+  } else {
+    if (getenv("XPCOM_MEM_COMPTR_LOG")) {
+      fprintf(stdout,
+              "### XPCOM_MEM_COMPTR_LOG defined -- "
+              "but XPCOM_MEM_LOG_CLASSES is not defined\n");
+    }
+  }
+#else
+  const char* comptr_log = getenv("XPCOM_MEM_COMPTR_LOG");
+  if (comptr_log) {
+    fprintf(stdout,
+            "### XPCOM_MEM_COMPTR_LOG defined -- "
+            "but it will not work without dynamic_cast\n");
+  }
+#endif  // HAVE_CPP_DYNAMIC_CAST_TO_VOID_PTR
+
+#undef ENVVAR
+
+  if (classes) {
+    // if XPCOM_MEM_LOG_CLASSES was set to some value, the value is interpreted
+    // as a list of class names to track
+    //
+    // Use the same |gTypesToLog| and |gSerialNumbers| to keep them
+    // consistent through the fork server and content processes.
+    // Without this, counters will be incorrect.
+    if (!gTypesToLog) {
+      gTypesToLog = new CharPtrSet(256);
+    }
+
+    fprintf(stdout,
+            "### XPCOM_MEM_LOG_CLASSES defined -- "
+            "only logging these classes: ");
+    const char* cp = classes;
+    for (;;) {
+      char* cm = (char*)strchr(cp, ',');
+      if (cm) {
+        *cm = '\0';
+      }
+      if (!gTypesToLog->Contains(cp)) {
+        gTypesToLog->PutEntry(cp);
+      }
+      fprintf(stdout, "%s ", cp);
+      if (!cm) {
+        break;
+      }
+      *cm = ',';
+      cp = cm + 1;
+    }
+    fprintf(stdout, "\n");
+
+    if (!gSerialNumbers) {
+      gSerialNumbers = new SerialHash(256);
+    }
+  } else {
+    gTypesToLog = nullptr;
+    gSerialNumbers = nullptr;
+  }
+
+  const char* objects = getenv("XPCOM_MEM_LOG_OBJECTS");
+  if (objects) {
+    gObjectsToLog = new IntPtrSet(256);
+
+    if (!(gRefcntsLog || gAllocLog || gCOMPtrLog)) {
+      fprintf(stdout,
+              "### XPCOM_MEM_LOG_OBJECTS defined -- "
+              "but none of XPCOM_MEM_(REFCNT|ALLOC|COMPTR)_LOG is defined\n");
+    } else {
+      fprintf(stdout,
+              "### XPCOM_MEM_LOG_OBJECTS defined -- "
+              "only logging these objects: ");
+      const char* cp = objects;
+      for (;;) {
+        char* cm = (char*)strchr(cp, ',');
+        if (cm) {
+          *cm = '\0';
+        }
+        intptr_t top = 0;
+        intptr_t bottom = 0;
+        while (*cp) {
+          if (*cp == '-') {
+            bottom = top;
+            top = 0;
+            ++cp;
+          }
+          top *= 10;
+          top += *cp - '0';
+          ++cp;
+        }
+        if (!bottom) {
+          bottom = top;
+        }
+        for (intptr_t serialno = bottom; serialno <= top; serialno++) {
+          gObjectsToLog->PutEntry(serialno);
+          fprintf(stdout, "%" PRIdPTR " ", serialno);
+        }
+        if (!cm) {
+          break;
+        }
+        *cm = ',';
+        cp = cm + 1;
+      }
+      fprintf(stdout, "\n");
+    }
+  }
+
+  if (getenv("XPCOM_MEM_LOG_JS_STACK")) {
+    fprintf(stdout, "### XPCOM_MEM_LOG_JS_STACK defined\n");
+    gLogJSStacks = true;
+  }
+
+  if (gBloatLog) {
+    gLogging = OnlyBloatLogging;
+  }
+
+  if (gRefcntsLog || gAllocLog || gCOMPtrLog) {
+    gLogging = FullLogging;
+  }
+}
+
+static void InitTraceLog() {
+  if (gInitialized) {
+    return;
+  }
+  gInitialized = true;
+
+  DoInitTraceLog(XRE_GetProcessTypeString());
+}
+
+extern "C" {
+
+static void EnsureWrite(FILE* aStream, const char* aBuf, size_t aLen) {
+#ifdef XP_WIN
+  int fd = _fileno(aStream);
+#else
+  int fd = fileno(aStream);
+#endif
+  while (aLen > 0) {
+#ifdef XP_WIN
+    auto written = _write(fd, aBuf, aLen);
+#else
+    auto written = write(fd, aBuf, aLen);
+#endif
+    if (written <= 0 || size_t(written) > aLen) {
+      break;
+    }
+    aBuf += written;
+    aLen -= written;
+  }
+}
+
+static void PrintStackFrameCached(uint32_t aFrameNumber, void* aPC, void* aSP,
+                                  void* aClosure) {
+  auto stream = static_cast<FILE*>(aClosure);
+  static const int buflen = 1024;
+  char buf[buflen + 5] = "    ";  // 5 for leading "    " and trailing '\n'
+  int len =
+      gCodeAddressService->GetLocation(aFrameNumber, aPC, buf + 4, buflen);
+  len = std::min(len, buflen + 1 - 2) + 4;
+  buf[len++] = '\n';
+  buf[len] = '\0';
+  fflush(stream);
+  EnsureWrite(stream, buf, len);
+}
+
+static void RecordStackFrame(uint32_t /*aFrameNumber*/, void* aPC,
+                             void* /*aSP*/, void* aClosure) {
+  auto locations = static_cast<std::vector<void*>*>(aClosure);
+  locations->push_back(aPC);
+}
+}
+
+/**
+ * This is a variant of |MozWalkTheStack| that uses |CodeAddressService| to
+ * cache the results of |NS_DescribeCodeAddress|. If |WalkTheStackCached| is
+ * being called frequently, it will be a few orders of magnitude faster than
+ * |MozWalkTheStack|. However, the cache uses a lot of memory, which can cause
+ * OOM crashes. Therefore, this should only be used for things like refcount
+ * logging which walk the stack extremely frequently.
+ */
+static void WalkTheStackCached(FILE* aStream, const void* aFirstFramePC) {
+  if (!gCodeAddressService) {
+    gCodeAddressService = new CodeAddressService<>();
+  }
+  MozStackWalk(PrintStackFrameCached, aFirstFramePC, /* maxFrames */ 0,
+               aStream);
+}
+
+static void WalkTheStackSavingLocations(std::vector<void*>& aLocations,
+                                        const void* aFirstFramePC) {
+  if (!gCodeAddressService) {
+    gCodeAddressService = new CodeAddressService<>();
+  }
+  MozStackWalk(RecordStackFrame, aFirstFramePC, /* maxFrames */ 0, &aLocations);
+}
+
+//----------------------------------------------------------------------
+
+EXPORT_XPCOM_API(void)
+NS_LogInit() {
+  NS_SetMainThread();
+
+  // FIXME: This is called multiple times, we should probably not allow that.
+  if (++gInitCount) {
+    nsTraceRefcnt::SetActivityIsLegal(true);
+  }
+}
+
+EXPORT_XPCOM_API(void)
+NS_LogTerm() { mozilla::LogTerm(); }
+
+#ifdef MOZ_DMD
+// If MOZ_DMD_SHUTDOWN_LOG is set, dump a DMD report to a file.
+// The value of this environment variable is used as the prefix
+// of the file name, so you probably want something like "/tmp/".
+// By default, this is run in all processes, but you can record a
+// log only for a specific process type by setting MOZ_DMD_LOG_PROCESS
+// to the process type you want to log, such as "default" or "tab".
+// This method can't use the higher level XPCOM file utilities
+// because it is run very late in shutdown to avoid recording
+// information about refcount logging entries.
+static void LogDMDFile() {
+  const char* dmdFilePrefix = PR_GetEnv("MOZ_DMD_SHUTDOWN_LOG");
+  if (!dmdFilePrefix) {
+    return;
+  }
+
+  const char* logProcessEnv = PR_GetEnv("MOZ_DMD_LOG_PROCESS");
+  if (logProcessEnv && !!strcmp(logProcessEnv, XRE_GetProcessTypeString())) {
+    return;
+  }
+
+  nsPrintfCString fileName("%sdmd-%" PRIPID ".log.gz", dmdFilePrefix,
+                           base::GetCurrentProcId());
+  FILE* logFile = fopen(fileName.get(), "w");
+  if (NS_WARN_IF(!logFile)) {
+    return;
+  }
+
+  nsMemoryInfoDumper::DumpDMDToFile(logFile);
+}
+#endif  // MOZ_DMD
+
+namespace mozilla {
+void LogTerm() {
+  NS_ASSERTION(gInitCount > 0, "NS_LogTerm without matching NS_LogInit");
+
+  if (--gInitCount == 0) {
+#ifdef DEBUG
+    /* FIXME bug 491977: This is only going to operate on the
+     * BlockingResourceBase which is compiled into
+     * libxul/libxpcom_core.so. Anyone using external linkage will
+     * have their own copy of BlockingResourceBase statics which will
+     * not be freed by this method.
+     *
+     * It sounds like what we really want is to be able to register a
+     * callback function to call at XPCOM shutdown.  Note that with
+     * this solution, however, we need to guarantee that
+     * BlockingResourceBase::Shutdown() runs after all other shutdown
+     * functions.
+     */
+    BlockingResourceBase::Shutdown();
+#endif
+
+    if (gInitialized) {
+      nsTraceRefcnt::DumpStatistics();
+      nsTraceRefcnt::ResetStatistics();
+    }
+    nsTraceRefcnt::Shutdown();
+    nsTraceRefcnt::SetActivityIsLegal(false);
+    gActivityTLS = BAD_TLS_INDEX;
+
+#ifdef MOZ_DMD
+    LogDMDFile();
+#endif
+  }
+}
+
+}  // namespace mozilla
+
+EXPORT_XPCOM_API(MOZ_NEVER_INLINE void)
+NS_LogAddRef(void* aPtr, nsrefcnt aRefcnt, const char* aClass,
+             uint32_t aClassSize) {
+  ASSERT_ACTIVITY_IS_LEGAL(aClass, "addrefed");
+  if (!gInitialized) {
+    InitTraceLog();
+  }
+  if (gLogging == NoLogging) {
+    return;
+  }
+  if (aRefcnt == 1 || gLogging == FullLogging) {
+    AutoTraceLogLock lock(gTraceLog);
+
+    if (aRefcnt == 1 && gBloatLog) {
+      BloatEntry* entry = GetBloatEntry(aClass, aClassSize);
+      if (entry) {
+        entry->Ctor();
+      }
+    }
+
+    // Here's the case where MOZ_COUNT_CTOR was not used,
+    // yet we still want to see creation information:
+
+    bool loggingThisType = (!gTypesToLog || gTypesToLog->Contains(aClass));
+    intptr_t serialno = 0;
+    if (gSerialNumbers && loggingThisType) {
+      serialno = GetSerialNumber(aPtr, aRefcnt == 1, CallerPC());
+      MOZ_ASSERT(serialno != 0,
+                 "Serial number requested for unrecognized pointer!  "
+                 "Are you memmoving a refcounted object?");
+      auto record = gSerialNumbers->Get(aPtr);
+      if (record) {
+        ++record->refCount;
+      }
+    }
+
+    bool loggingThisObject = (!gObjectsToLog || LogThisObj(serialno));
+    if (aRefcnt == 1 && gAllocLog && loggingThisType && loggingThisObject) {
+      fprintf(gAllocLog, "\n<%s> %p %" PRIdPTR " Create [thread %p]\n", aClass,
+              aPtr, serialno, PR_GetCurrentThread());
+      WalkTheStackCached(gAllocLog, CallerPC());
+    }
+
+    if (gRefcntsLog && loggingThisType && loggingThisObject) {
+      // Can't use MOZ_LOG(), b/c it truncates the line
+      fprintf(gRefcntsLog,
+              "\n<%s> %p %" PRIuPTR " AddRef %" PRIuPTR " [thread %p]\n",
+              aClass, aPtr, serialno, aRefcnt, PR_GetCurrentThread());
+      WalkTheStackCached(gRefcntsLog, CallerPC());
+      fflush(gRefcntsLog);
+    }
+  }
+}
+
+EXPORT_XPCOM_API(MOZ_NEVER_INLINE void)
+NS_LogRelease(void* aPtr, nsrefcnt aRefcnt, const char* aClass) {
+  ASSERT_ACTIVITY_IS_LEGAL(aClass, "released");
+  if (!gInitialized) {
+    InitTraceLog();
+  }
+  if (gLogging == NoLogging) {
+    return;
+  }
+  if (aRefcnt == 0 || gLogging == FullLogging) {
+    AutoTraceLogLock lock(gTraceLog);
+
+    if (aRefcnt == 0 && gBloatLog) {
+      BloatEntry* entry = GetBloatEntry(aClass, 0);
+      if (entry) {
+        entry->Dtor();
+      }
+    }
+
+    bool loggingThisType = (!gTypesToLog || gTypesToLog->Contains(aClass));
+    intptr_t serialno = 0;
+    if (gSerialNumbers && loggingThisType) {
+      serialno = GetSerialNumber(aPtr, false, CallerPC());
+      MOZ_ASSERT(serialno != 0,
+                 "Serial number requested for unrecognized pointer!  "
+                 "Are you memmoving a refcounted object?");
+      auto record = gSerialNumbers->Get(aPtr);
+      if (record) {
+        --record->refCount;
+      }
+    }
+
+    bool loggingThisObject = (!gObjectsToLog || LogThisObj(serialno));
+    if (gRefcntsLog && loggingThisType && loggingThisObject) {
+      // Can't use MOZ_LOG(), b/c it truncates the line
+      fprintf(gRefcntsLog,
+              "\n<%s> %p %" PRIuPTR " Release %" PRIuPTR " [thread %p]\n",
+              aClass, aPtr, serialno, aRefcnt, PR_GetCurrentThread());
+      WalkTheStackCached(gRefcntsLog, CallerPC());
+      fflush(gRefcntsLog);
+    }
+
+    // Here's the case where MOZ_COUNT_DTOR was not used,
+    // yet we still want to see deletion information:
+
+    if (aRefcnt == 0 && gAllocLog && loggingThisType && loggingThisObject) {
+      fprintf(gAllocLog, "\n<%s> %p %" PRIdPTR " Destroy [thread %p]\n", aClass,
+              aPtr, serialno, PR_GetCurrentThread());
+      WalkTheStackCached(gAllocLog, CallerPC());
+    }
+
+    if (aRefcnt == 0 && gSerialNumbers && loggingThisType) {
+      RecycleSerialNumberPtr(aPtr);
+    }
+  }
+}
+
+EXPORT_XPCOM_API(MOZ_NEVER_INLINE void)
+NS_LogCtor(void* aPtr, const char* aType, uint32_t aInstanceSize) {
+  ASSERT_ACTIVITY_IS_LEGAL(aType, "constructed");
+  if (!gInitialized) {
+    InitTraceLog();
+  }
+
+  if (gLogging == NoLogging) {
+    return;
+  }
+
+  AutoTraceLogLock lock(gTraceLog);
+
+  if (gBloatLog) {
+    BloatEntry* entry = GetBloatEntry(aType, aInstanceSize);
+    if (entry) {
+      entry->Ctor();
+    }
+  }
+
+  bool loggingThisType = (!gTypesToLog || gTypesToLog->Contains(aType));
+  intptr_t serialno = 0;
+  if (gSerialNumbers && loggingThisType) {
+    serialno = GetSerialNumber(aPtr, true, CallerPC());
+    MOZ_ASSERT(serialno != 0,
+               "GetSerialNumber should never return 0 when passed true");
+  }
+
+  bool loggingThisObject = (!gObjectsToLog || LogThisObj(serialno));
+  if (gAllocLog && loggingThisType && loggingThisObject) {
+    fprintf(gAllocLog, "\n<%s> %p %" PRIdPTR " Ctor (%d)\n", aType, aPtr,
+            serialno, aInstanceSize);
+    WalkTheStackCached(gAllocLog, CallerPC());
+  }
+}
+
+EXPORT_XPCOM_API(MOZ_NEVER_INLINE void)
+NS_LogDtor(void* aPtr, const char* aType, uint32_t aInstanceSize) {
+  ASSERT_ACTIVITY_IS_LEGAL(aType, "destroyed");
+  if (!gInitialized) {
+    InitTraceLog();
+  }
+
+  if (gLogging == NoLogging) {
+    return;
+  }
+
+  AutoTraceLogLock lock(gTraceLog);
+
+  if (gBloatLog) {
+    BloatEntry* entry = GetBloatEntry(aType, aInstanceSize);
+    if (entry) {
+      entry->Dtor();
+    }
+  }
+
+  bool loggingThisType = (!gTypesToLog || gTypesToLog->Contains(aType));
+  intptr_t serialno = 0;
+  if (gSerialNumbers && loggingThisType) {
+    serialno = GetSerialNumber(aPtr, false, CallerPC());
+    MOZ_ASSERT(serialno != 0,
+               "Serial number requested for unrecognized pointer!  "
+               "Are you memmoving a MOZ_COUNT_CTOR-tracked object?");
+    RecycleSerialNumberPtr(aPtr);
+  }
+
+  bool loggingThisObject = (!gObjectsToLog || LogThisObj(serialno));
+
+  // (If we're on a losing architecture, don't do this because we'll be
+  // using LogDeleteXPCOM instead to get file and line numbers.)
+  if (gAllocLog && loggingThisType && loggingThisObject) {
+    fprintf(gAllocLog, "\n<%s> %p %" PRIdPTR " Dtor (%d)\n", aType, aPtr,
+            serialno, aInstanceSize);
+    WalkTheStackCached(gAllocLog, CallerPC());
+  }
+}
+
+EXPORT_XPCOM_API(MOZ_NEVER_INLINE void)
+NS_LogCOMPtrAddRef(void* aCOMPtr, nsISupports* aObject) {
+#ifdef HAVE_CPP_DYNAMIC_CAST_TO_VOID_PTR
+  // Get the most-derived object.
+  void* object = dynamic_cast<void*>(aObject);
+
+  // This is a very indirect way of finding out what the class is
+  // of the object being logged.  If we're logging a specific type,
+  // then
+  if (!gTypesToLog || !gSerialNumbers) {
+    return;
+  }
+  if (!gInitialized) {
+    InitTraceLog();
+  }
+  if (gLogging == FullLogging) {
+    AutoTraceLogLock lock(gTraceLog);
+
+    intptr_t serialno = GetSerialNumber(object, false, CallerPC());
+    if (serialno == 0) {
+      return;
+    }
+
+    auto record = gSerialNumbers->Get(object);
+    int32_t count = record ? ++record->COMPtrCount : -1;
+    bool loggingThisObject = (!gObjectsToLog || LogThisObj(serialno));
+
+    if (gCOMPtrLog && loggingThisObject) {
+      fprintf(gCOMPtrLog, "\n<?> %p %" PRIdPTR " nsCOMPtrAddRef %d %p\n",
+              object, serialno, count, aCOMPtr);
+      WalkTheStackCached(gCOMPtrLog, CallerPC());
+    }
+  }
+#endif  // HAVE_CPP_DYNAMIC_CAST_TO_VOID_PTR
+}
+
+EXPORT_XPCOM_API(MOZ_NEVER_INLINE void)
+NS_LogCOMPtrRelease(void* aCOMPtr, nsISupports* aObject) {
+#ifdef HAVE_CPP_DYNAMIC_CAST_TO_VOID_PTR
+  // Get the most-derived object.
+  void* object = dynamic_cast<void*>(aObject);
+
+  // This is a very indirect way of finding out what the class is
+  // of the object being logged.  If we're logging a specific type,
+  // then
+  if (!gTypesToLog || !gSerialNumbers) {
+    return;
+  }
+  if (!gInitialized) {
+    InitTraceLog();
+  }
+  if (gLogging == FullLogging) {
+    AutoTraceLogLock lock(gTraceLog);
+
+    intptr_t serialno = GetSerialNumber(object, false, CallerPC());
+    if (serialno == 0) {
+      return;
+    }
+
+    auto record = gSerialNumbers->Get(object);
+    int32_t count = record ? --record->COMPtrCount : -1;
+    bool loggingThisObject = (!gObjectsToLog || LogThisObj(serialno));
+
+    if (gCOMPtrLog && loggingThisObject) {
+      fprintf(gCOMPtrLog, "\n<?> %p %" PRIdPTR " nsCOMPtrRelease %d %p\n",
+              object, serialno, count, aCOMPtr);
+      WalkTheStackCached(gCOMPtrLog, CallerPC());
+    }
+  }
+#endif  // HAVE_CPP_DYNAMIC_CAST_TO_VOID_PTR
+}
+
+static void ClearLogs(bool aKeepCounters) {
+  gCodeAddressService = nullptr;
+  // These counters from the fork server process will be preserved
+  // for the content processes to keep them consistent.
+  if (!aKeepCounters) {
+    gBloatView = nullptr;
+    gTypesToLog = nullptr;
+    gSerialNumbers = nullptr;
+  }
+  gObjectsToLog = nullptr;
+  gLogJSStacks = false;
+  gLogLeaksOnly = false;
+  maybeUnregisterAndCloseFile(gBloatLog);
+  maybeUnregisterAndCloseFile(gRefcntsLog);
+  maybeUnregisterAndCloseFile(gAllocLog);
+  maybeUnregisterAndCloseFile(gCOMPtrLog);
+}
+
+void nsTraceRefcnt::Shutdown() { ClearLogs(false); }
+
+void nsTraceRefcnt::SetActivityIsLegal(bool aLegal) {
+  if (gActivityTLS == BAD_TLS_INDEX) {
+    PR_NewThreadPrivateIndex(&gActivityTLS, nullptr);
+  }
+
+  PR_SetThreadPrivate(gActivityTLS, reinterpret_cast<void*>(!aLegal));
+}
+
+void nsTraceRefcnt::StartLoggingClass(const char* aClass) {
+  gLogging = FullLogging;
+
+  if (!gTypesToLog) {
+    gTypesToLog = new CharPtrSet(256);
+  }
+
+  fprintf(stdout, "### StartLoggingClass %s\n", aClass);
+  if (!gTypesToLog->Contains(aClass)) {
+    gTypesToLog->PutEntry(aClass);
+  }
+
+  // We are deliberately not initializing gSerialNumbers here, because
+  // it would cause assertions. gObjectsToLog can't be used because it
+  // relies on serial numbers.
+
+#ifdef XP_WIN
+#  define ENVVAR(x) u"" x
+#else
+#  define ENVVAR(x) x
+#endif
+
+  if (!gRefcntsLog) {
+    InitLog(ENVVAR("XPCOM_MEM_LATE_REFCNT_LOG"), "refcounts", &gRefcntsLog,
+            XRE_GetProcessTypeString());
+  }
+
+#undef ENVVAR
+}
+
+#ifdef MOZ_ENABLE_FORKSERVER
+void nsTraceRefcnt::ResetLogFiles(const char* aProcType) {
+  AutoRestore<LoggingType> saveLogging(gLogging);
+  gLogging = NoLogging;
+
+  ClearLogs(true);
+
+  // Create log files with the correct process type in the name.
+  DoInitTraceLog(aProcType);
+}
+#endif
diff --git a/xpcom/base/nsTraceRefcnt.h b/xpcom/base/nsTraceRefcnt.h
new file mode 100644
index 0000000000..23eeec0bdf
--- /dev/null
+++ b/xpcom/base/nsTraceRefcnt.h
@@ -0,0 +1,38 @@
+/* -*- 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/. */
+#ifndef nsTraceRefcnt_h
+#define nsTraceRefcnt_h
+
+#include "nscore.h"
+
+class nsTraceRefcnt {
+ public:
+  static void Shutdown();
+
+  static nsresult DumpStatistics();
+
+  static void ResetStatistics();
+
+  /**
+   * Tell nsTraceRefcnt whether refcounting, allocation, and destruction
+   * activity is legal.  This is used to trigger assertions for any such
+   * activity that occurs because of static constructors or destructors.
+   */
+  static void SetActivityIsLegal(bool aLegal);
+
+  /**
+   * Start refcount logging aClass. If refcount logging has not already begun,
+   * it will use the environment variable XPCOM_MEM_LATE_REFCNT_LOG to decide
+   * where to make the log, in a similar way as the other nsTraceRefcnt logs.
+   */
+  static void StartLoggingClass(const char* aClass);
+
+#ifdef MOZ_ENABLE_FORKSERVER
+  static void ResetLogFiles(const char* aProcType = nullptr);
+#endif
+};
+
+#endif  // nsTraceRefcnt_h
diff --git a/xpcom/base/nsUUIDGenerator.cpp b/xpcom/base/nsUUIDGenerator.cpp
new file mode 100644
index 0000000000..f00437ada7
--- /dev/null
+++ b/xpcom/base/nsUUIDGenerator.cpp
@@ -0,0 +1,30 @@
+/* -*- 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 "nsUUIDGenerator.h"
+
+NS_IMPL_ISUPPORTS(nsUUIDGenerator, nsIUUIDGenerator)
+
+nsUUIDGenerator::~nsUUIDGenerator() = default;
+
+NS_IMETHODIMP
+nsUUIDGenerator::GenerateUUID(nsID** aRet) {
+  nsID* id = static_cast<nsID*>(moz_xmalloc(sizeof(nsID)));
+
+  nsresult rv = GenerateUUIDInPlace(id);
+  if (NS_FAILED(rv)) {
+    free(id);
+    return rv;
+  }
+
+  *aRet = id;
+  return rv;
+}
+
+NS_IMETHODIMP
+nsUUIDGenerator::GenerateUUIDInPlace(nsID* aId) {
+  return nsID::GenerateUUIDInPlace(*aId);
+}
diff --git a/xpcom/base/nsUUIDGenerator.h b/xpcom/base/nsUUIDGenerator.h
new file mode 100644
index 0000000000..b1b2921a3b
--- /dev/null
+++ b/xpcom/base/nsUUIDGenerator.h
@@ -0,0 +1,30 @@
+/* -*- 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/. */
+
+#ifndef _NSUUIDGENERATOR_H_
+#define _NSUUIDGENERATOR_H_
+
+#include "nsIUUIDGenerator.h"
+
+class nsUUIDGenerator final : public nsIUUIDGenerator {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  NS_DECL_NSIUUIDGENERATOR
+
+ private:
+  ~nsUUIDGenerator();
+};
+
+#define NS_UUID_GENERATOR_CONTRACTID "@mozilla.org/uuid-generator;1"
+#define NS_UUID_GENERATOR_CID                        \
+  {                                                  \
+    0x706d36bb, 0xbf79, 0x4293, {                    \
+      0x81, 0xf2, 0x8f, 0x68, 0x28, 0xc1, 0x8f, 0x9d \
+    }                                                \
+  }
+
+#endif /* _NSUUIDGENERATOR_H_ */
diff --git a/xpcom/base/nsVersionComparator.cpp b/xpcom/base/nsVersionComparator.cpp
new file mode 100644
index 0000000000..f12e54272a
--- /dev/null
+++ b/xpcom/base/nsVersionComparator.cpp
@@ -0,0 +1,401 @@
+/* -*- 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 "nsVersionComparator.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <errno.h>
+#include "mozilla/CheckedInt.h"
+#if defined(XP_WIN) && !defined(UPDATER_NO_STRING_GLUE_STL)
+#  include <wchar.h>
+#  include "nsString.h"
+#endif
+
+struct VersionPart {
+  int32_t numA;
+
+  const char* strB;  // NOT null-terminated, can be a null pointer
+  uint32_t strBlen;
+
+  int32_t numC;
+
+  char* extraD;  // null-terminated
+};
+
+#ifdef XP_WIN
+struct VersionPartW {
+  int32_t numA;
+
+  wchar_t* strB;  // NOT null-terminated, can be a null pointer
+  uint32_t strBlen;
+
+  int32_t numC;
+
+  wchar_t* extraD;  // null-terminated
+};
+#endif
+
+static int32_t ns_strtol(const char* aPart, char** aNext) {
+  errno = 0;
+  long result_long = strtol(aPart, aNext, 10);
+
+  // Different platforms seem to disagree on what to return when the value
+  // is out of range so we ensure that it is always what we want it to be.
+  // We choose 0 firstly because that is the default when the number doesn't
+  // exist at all and also because it would be easier to recover from should
+  // you somehow end up in a situation where an old version is invalid. It is
+  // much easier to create a version either larger or smaller than 0, much
+  // harder to do the same with INT_MAX.
+  if (errno != 0) {
+    return 0;
+  }
+
+  mozilla::CheckedInt<int32_t> result = result_long;
+  if (!result.isValid()) {
+    return 0;
+  }
+
+  return result.value();
+}
+
+/**
+ * Parse a version part into a number and "extra text".
+ *
+ * @returns A pointer to the next versionpart, or null if none.
+ */
+static char* ParseVP(char* aPart, VersionPart& aResult) {
+  char* dot;
+
+  aResult.numA = 0;
+  aResult.strB = nullptr;
+  aResult.strBlen = 0;
+  aResult.numC = 0;
+  aResult.extraD = nullptr;
+
+  if (!aPart) {
+    return aPart;
+  }
+
+  dot = strchr(aPart, '.');
+  if (dot) {
+    *dot = '\0';
+  }
+
+  if (aPart[0] == '*' && aPart[1] == '\0') {
+    aResult.numA = INT32_MAX;
+    aResult.strB = "";
+  } else {
+    aResult.numA = ns_strtol(aPart, const_cast<char**>(&aResult.strB));
+  }
+
+  if (!*aResult.strB) {
+    aResult.strB = nullptr;
+    aResult.strBlen = 0;
+  } else {
+    if (aResult.strB[0] == '+') {
+      static const char kPre[] = "pre";
+
+      ++aResult.numA;
+      aResult.strB = kPre;
+      aResult.strBlen = sizeof(kPre) - 1;
+    } else {
+      const char* numstart = strpbrk(aResult.strB, "0123456789+-");
+      if (!numstart) {
+        aResult.strBlen = strlen(aResult.strB);
+      } else {
+        aResult.strBlen = numstart - aResult.strB;
+        aResult.numC = ns_strtol(numstart, const_cast<char**>(&aResult.extraD));
+
+        if (!*aResult.extraD) {
+          aResult.extraD = nullptr;
+        }
+      }
+    }
+  }
+
+  if (dot) {
+    ++dot;
+
+    if (!*dot) {
+      dot = nullptr;
+    }
+  }
+
+  return dot;
+}
+
+/**
+ * Parse a version part into a number and "extra text".
+ *
+ * @returns A pointer to the next versionpart, or null if none.
+ */
+#ifdef XP_WIN
+
+static int32_t ns_wcstol(const wchar_t* aPart, wchar_t** aNext) {
+  errno = 0;
+  long result_long = wcstol(aPart, aNext, 10);
+
+  // See above for the rationale for using 0 here.
+  if (errno != 0) {
+    return 0;
+  }
+
+  mozilla::CheckedInt<int32_t> result = result_long;
+  if (!result.isValid()) {
+    return 0;
+  }
+
+  return result.value();
+}
+
+static wchar_t* ParseVP(wchar_t* aPart, VersionPartW& aResult) {
+  wchar_t* dot;
+
+  aResult.numA = 0;
+  aResult.strB = nullptr;
+  aResult.strBlen = 0;
+  aResult.numC = 0;
+  aResult.extraD = nullptr;
+
+  if (!aPart) {
+    return aPart;
+  }
+
+  dot = wcschr(aPart, '.');
+  if (dot) {
+    *dot = '\0';
+  }
+
+  if (aPart[0] == '*' && aPart[1] == '\0') {
+    static wchar_t kEmpty[] = L"";
+
+    aResult.numA = INT32_MAX;
+    aResult.strB = kEmpty;
+  } else {
+    aResult.numA = ns_wcstol(aPart, const_cast<wchar_t**>(&aResult.strB));
+  }
+
+  if (!*aResult.strB) {
+    aResult.strB = nullptr;
+    aResult.strBlen = 0;
+  } else {
+    if (aResult.strB[0] == '+') {
+      static wchar_t kPre[] = L"pre";
+
+      ++aResult.numA;
+      aResult.strB = kPre;
+      aResult.strBlen = sizeof(kPre) - 1;
+    } else {
+      const wchar_t* numstart = wcspbrk(aResult.strB, L"0123456789+-");
+      if (!numstart) {
+        aResult.strBlen = wcslen(aResult.strB);
+      } else {
+        aResult.strBlen = numstart - aResult.strB;
+        aResult.numC =
+            ns_wcstol(numstart, const_cast<wchar_t**>(&aResult.extraD));
+
+        if (!*aResult.extraD) {
+          aResult.extraD = nullptr;
+        }
+      }
+    }
+  }
+
+  if (dot) {
+    ++dot;
+
+    if (!*dot) {
+      dot = nullptr;
+    }
+  }
+
+  return dot;
+}
+#endif
+
+// compare two null-terminated strings, which may be null pointers
+static int32_t ns_strcmp(const char* aStr1, const char* aStr2) {
+  // any string is *before* no string
+  if (!aStr1) {
+    return aStr2 != 0;
+  }
+
+  if (!aStr2) {
+    return -1;
+  }
+
+  return strcmp(aStr1, aStr2);
+}
+
+// compare two length-specified string, which may be null pointers
+static int32_t ns_strnncmp(const char* aStr1, uint32_t aLen1, const char* aStr2,
+                           uint32_t aLen2) {
+  // any string is *before* no string
+  if (!aStr1) {
+    return aStr2 != 0;
+  }
+
+  if (!aStr2) {
+    return -1;
+  }
+
+  for (; aLen1 && aLen2; --aLen1, --aLen2, ++aStr1, ++aStr2) {
+    if (*aStr1 < *aStr2) {
+      return -1;
+    }
+
+    if (*aStr1 > *aStr2) {
+      return 1;
+    }
+  }
+
+  if (aLen1 == 0) {
+    return aLen2 == 0 ? 0 : -1;
+  }
+
+  return 1;
+}
+
+// compare two int32_t
+static int32_t ns_cmp(int32_t aNum1, int32_t aNum2) {
+  if (aNum1 < aNum2) {
+    return -1;
+  }
+
+  return aNum1 != aNum2;
+}
+
+/**
+ * Compares two VersionParts
+ */
+static int32_t CompareVP(VersionPart& aVer1, VersionPart& aVer2) {
+  int32_t r = ns_cmp(aVer1.numA, aVer2.numA);
+  if (r) {
+    return r;
+  }
+
+  r = ns_strnncmp(aVer1.strB, aVer1.strBlen, aVer2.strB, aVer2.strBlen);
+  if (r) {
+    return r;
+  }
+
+  r = ns_cmp(aVer1.numC, aVer2.numC);
+  if (r) {
+    return r;
+  }
+
+  return ns_strcmp(aVer1.extraD, aVer2.extraD);
+}
+
+/**
+ * Compares two VersionParts
+ */
+#ifdef XP_WIN
+static int32_t CompareVP(VersionPartW& aVer1, VersionPartW& aVer2) {
+  int32_t r = ns_cmp(aVer1.numA, aVer2.numA);
+  if (r) {
+    return r;
+  }
+
+  r = wcsncmp(aVer1.strB, aVer2.strB, XPCOM_MIN(aVer1.strBlen, aVer2.strBlen));
+  if (r) {
+    return r;
+  }
+
+  r = ns_cmp(aVer1.numC, aVer2.numC);
+  if (r) {
+    return r;
+  }
+
+  if (!aVer1.extraD) {
+    return aVer2.extraD != 0;
+  }
+
+  if (!aVer2.extraD) {
+    return -1;
+  }
+
+  return wcscmp(aVer1.extraD, aVer2.extraD);
+}
+#endif
+
+namespace mozilla {
+
+#ifdef XP_WIN
+int32_t CompareVersions(const char16_t* aStrA, const char16_t* aStrB) {
+  wchar_t* A2 = wcsdup(char16ptr_t(aStrA));
+  if (!A2) {
+    return 1;
+  }
+
+  wchar_t* B2 = wcsdup(char16ptr_t(aStrB));
+  if (!B2) {
+    free(A2);
+    return 1;
+  }
+
+  int32_t result;
+  wchar_t* a = A2;
+  wchar_t* b = B2;
+
+  do {
+    VersionPartW va, vb;
+
+    a = ParseVP(a, va);
+    b = ParseVP(b, vb);
+
+    result = CompareVP(va, vb);
+    if (result) {
+      break;
+    }
+
+  } while (a || b);
+
+  free(A2);
+  free(B2);
+
+  return result;
+}
+#endif
+
+int32_t CompareVersions(const char* aStrA, const char* aStrB) {
+  char* A2 = strdup(aStrA);
+  if (!A2) {
+    return 1;
+  }
+
+  char* B2 = strdup(aStrB);
+  if (!B2) {
+    free(A2);
+    return 1;
+  }
+
+  int32_t result;
+  char* a = A2;
+  char* b = B2;
+
+  do {
+    VersionPart va, vb;
+
+    a = ParseVP(a, va);
+    b = ParseVP(b, vb);
+
+    result = CompareVP(va, vb);
+    if (result) {
+      break;
+    }
+
+  } while (a || b);
+
+  free(A2);
+  free(B2);
+
+  return result;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/base/nsVersionComparator.h b/xpcom/base/nsVersionComparator.h
new file mode 100644
index 0000000000..32ea620583
--- /dev/null
+++ b/xpcom/base/nsVersionComparator.h
@@ -0,0 +1,112 @@
+/* -*- 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/. */
+
+// NB: This code may be used from non-XPCOM code, in particular, the
+// standalone updater executable.
+
+#ifndef nsVersionComparator_h__
+#define nsVersionComparator_h__
+
+#include "mozilla/Char16.h"
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#if defined(XP_WIN) && !defined(UPDATER_NO_STRING_GLUE_STL)
+#  include <wchar.h>
+#  include "nsString.h"
+#endif
+
+/**
+ * In order to compare version numbers in Mozilla, you need to use the
+ * mozilla::Version class.  You can construct an object of this type by passing
+ * in a string version number to the constructor.  Objects of this type can be
+ * compared using the standard comparison operators.
+ *
+ * For example, let's say that you want to make sure that a given version
+ * number is not older than 15.a2.  Here's how you would write a function to
+ * do that.
+ *
+ * bool IsVersionValid(const char* version) {
+ *   return mozilla::Version("15.a2") <= mozilla::Version(version);
+ * }
+ *
+ * Or, since Version's constructor is implicit, you can simplify this code:
+ *
+ * bool IsVersionValid(const char* version) {
+ *   return mozilla::Version("15.a2") <= version;
+ * }
+ */
+
+namespace mozilla {
+
+/**
+ * Compares the version strings provided.
+ *
+ * Returns 0 if the versions match, < 0 if aStrB > aStrA and > 0 if
+ * aStrA > aStrB.
+ */
+int32_t CompareVersions(const char* aStrA, const char* aStrB);
+
+#ifdef XP_WIN
+/**
+ * As above but for wide character strings.
+ */
+int32_t CompareVersions(const char16_t* aStrA, const char16_t* aStrB);
+#endif
+
+struct Version {
+  explicit Version(const char* aVersionString) {
+    versionContent = strdup(aVersionString);
+  }
+
+  const char* ReadContent() const { return versionContent; }
+
+  ~Version() { free(versionContent); }
+
+  bool operator<(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) < 0;
+  }
+  bool operator<=(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) < 1;
+  }
+  bool operator>(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) > 0;
+  }
+  bool operator>=(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) > -1;
+  }
+  bool operator==(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) == 0;
+  }
+  bool operator!=(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) != 0;
+  }
+  bool operator<(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) < 0;
+  }
+  bool operator<=(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) < 1;
+  }
+  bool operator>(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) > 0;
+  }
+  bool operator>=(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) > -1;
+  }
+  bool operator==(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) == 0;
+  }
+  bool operator!=(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) != 0;
+  }
+
+ private:
+  char* versionContent;
+};
+
+}  // namespace mozilla
+
+#endif  // nsVersionComparator_h__
diff --git a/xpcom/base/nsVersionComparatorImpl.cpp b/xpcom/base/nsVersionComparatorImpl.cpp
new file mode 100644
index 0000000000..b52395bbac
--- /dev/null
+++ b/xpcom/base/nsVersionComparatorImpl.cpp
@@ -0,0 +1,20 @@
+/* -*- 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 "nsVersionComparatorImpl.h"
+#include "nsVersionComparator.h"
+#include "nsString.h"
+
+NS_IMPL_ISUPPORTS(nsVersionComparatorImpl, nsIVersionComparator)
+
+NS_IMETHODIMP
+nsVersionComparatorImpl::Compare(const nsACString& aStr1,
+                                 const nsACString& aStr2, int32_t* aResult) {
+  *aResult = mozilla::CompareVersions(PromiseFlatCString(aStr1).get(),
+                                      PromiseFlatCString(aStr2).get());
+
+  return NS_OK;
+}
diff --git a/xpcom/base/nsVersionComparatorImpl.h b/xpcom/base/nsVersionComparatorImpl.h
new file mode 100644
index 0000000000..49b6f157a1
--- /dev/null
+++ b/xpcom/base/nsVersionComparatorImpl.h
@@ -0,0 +1,28 @@
+/* -*- 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 "mozilla/Attributes.h"
+
+#include "nsIVersionComparator.h"
+
+class nsVersionComparatorImpl final : public nsIVersionComparator {
+  ~nsVersionComparatorImpl() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIVERSIONCOMPARATOR
+};
+
+#define NS_VERSIONCOMPARATOR_CONTRACTID \
+  "@mozilla.org/xpcom/version-comparator;1"
+
+// c6e47036-ca94-4be3-963a-9abd8705f7a8
+#define NS_VERSIONCOMPARATOR_CID                     \
+  {                                                  \
+    0xc6e47036, 0xca94, 0x4be3, {                    \
+      0x96, 0x3a, 0x9a, 0xbd, 0x87, 0x05, 0xf7, 0xa8 \
+    }                                                \
+  }
diff --git a/xpcom/base/nsWeakReference.cpp b/xpcom/base/nsWeakReference.cpp
new file mode 100644
index 0000000000..958ef08451
--- /dev/null
+++ b/xpcom/base/nsWeakReference.cpp
@@ -0,0 +1,151 @@
+/* -*- 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/. */
+
+// nsWeakReference.cpp
+
+#include "mozilla/Attributes.h"
+
+#include "nsWeakReference.h"
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+
+class nsWeakReference final : public nsIWeakReference {
+ public:
+  // nsISupports...
+  NS_DECL_ISUPPORTS
+
+  // nsIWeakReference...
+  NS_DECL_NSIWEAKREFERENCE
+
+ private:
+  friend class nsSupportsWeakReference;
+
+  explicit nsWeakReference(nsSupportsWeakReference* aReferent)
+      : nsIWeakReference(aReferent)
+  // ...I can only be constructed by an |nsSupportsWeakReference|
+  {}
+
+  ~nsWeakReference()
+  // ...I will only be destroyed by calling |delete| myself.
+  {
+    MOZ_WEAKREF_ASSERT_OWNINGTHREAD;
+    if (mObject) {
+      static_cast<nsSupportsWeakReference*>(mObject)->NoticeProxyDestruction();
+    }
+  }
+
+  void NoticeReferentDestruction()
+  // ...called (only) by an |nsSupportsWeakReference| from _its_ dtor.
+  {
+    MOZ_WEAKREF_ASSERT_OWNINGTHREAD;
+    mObject = nullptr;
+  }
+};
+
+nsresult nsQueryReferent::operator()(const nsIID& aIID, void** aAnswer) const {
+  nsresult status;
+  if (mWeakPtr) {
+    if (NS_FAILED(status = mWeakPtr->QueryReferent(aIID, aAnswer))) {
+      *aAnswer = 0;
+    }
+  } else {
+    status = NS_ERROR_NULL_POINTER;
+  }
+
+  if (mErrorPtr) {
+    *mErrorPtr = status;
+  }
+  return status;
+}
+
+nsIWeakReference* NS_GetWeakReference(nsISupportsWeakReference* aInstancePtr,
+                                      nsresult* aErrorPtr) {
+  nsresult status;
+
+  nsIWeakReference* result = nullptr;
+
+  if (aInstancePtr) {
+    status = aInstancePtr->GetWeakReference(&result);
+  } else {
+    status = NS_ERROR_NULL_POINTER;
+  }
+
+  if (aErrorPtr) {
+    *aErrorPtr = status;
+  }
+
+  return result;
+}
+
+nsIWeakReference*  // or else |already_AddRefed<nsIWeakReference>|
+NS_GetWeakReference(nsISupports* aInstancePtr, nsresult* aErrorPtr) {
+  nsresult status;
+
+  nsIWeakReference* result = nullptr;
+
+  if (aInstancePtr) {
+    nsCOMPtr<nsISupportsWeakReference> factoryPtr =
+        do_QueryInterface(aInstancePtr, &status);
+    if (factoryPtr) {
+      status = factoryPtr->GetWeakReference(&result);
+    }
+    // else, |status| has already been set by |do_QueryInterface|
+  } else {
+    status = NS_ERROR_NULL_POINTER;
+  }
+
+  if (aErrorPtr) {
+    *aErrorPtr = status;
+  }
+  return result;
+}
+
+nsresult nsSupportsWeakReference::GetWeakReference(
+    nsIWeakReference** aInstancePtr) {
+  if (!aInstancePtr) {
+    return NS_ERROR_NULL_POINTER;
+  }
+
+  if (!mProxy) {
+    mProxy = new nsWeakReference(this);
+  } else {
+    MOZ_WEAKREF_ASSERT_OWNINGTHREAD_DELEGATED(mProxy);
+  }
+  RefPtr<nsWeakReference> rval = mProxy;
+  rval.forget(aInstancePtr);
+
+  return NS_OK;
+}
+
+NS_IMPL_ISUPPORTS(nsWeakReference, nsIWeakReference)
+
+NS_IMETHODIMP
+nsWeakReference::QueryReferentFromScript(const nsIID& aIID,
+                                         void** aInstancePtr) {
+  return QueryReferent(aIID, aInstancePtr);
+}
+
+nsresult nsIWeakReference::QueryReferent(const nsIID& aIID,
+                                         void** aInstancePtr) {
+  MOZ_WEAKREF_ASSERT_OWNINGTHREAD;
+
+  if (!mObject) {
+    return NS_ERROR_NULL_POINTER;
+  }
+
+  return mObject->QueryInterface(aIID, aInstancePtr);
+}
+
+size_t nsWeakReference::SizeOfOnlyThis(mozilla::MallocSizeOf aMallocSizeOf) {
+  return aMallocSizeOf(this);
+}
+
+void nsSupportsWeakReference::ClearWeakReferences() {
+  if (mProxy) {
+    mProxy->NoticeReferentDestruction();
+    mProxy = nullptr;
+  }
+}
diff --git a/xpcom/base/nsWeakReference.h b/xpcom/base/nsWeakReference.h
new file mode 100644
index 0000000000..5303f2d2ea
--- /dev/null
+++ b/xpcom/base/nsWeakReference.h
@@ -0,0 +1,68 @@
+/* -*- 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/. */
+
+#ifndef nsWeakReference_h__
+#define nsWeakReference_h__
+
+// nsWeakReference.h
+
+// See mfbt/WeakPtr.h for a more typesafe C++ implementation of weak references
+
+#include "nsIWeakReferenceUtils.h"
+
+class nsWeakReference;
+
+class nsSupportsWeakReference : public nsISupportsWeakReference {
+ public:
+  nsSupportsWeakReference() : mProxy(0) {}
+
+  NS_DECL_NSISUPPORTSWEAKREFERENCE
+
+ protected:
+  inline ~nsSupportsWeakReference();
+
+ private:
+  friend class nsWeakReference;
+
+  // Called (only) by an |nsWeakReference| from _its_ dtor.
+  // The thread safety check is made by the caller.
+  void NoticeProxyDestruction() { mProxy = nullptr; }
+
+  nsWeakReference* MOZ_NON_OWNING_REF mProxy;
+
+ protected:
+  void ClearWeakReferences();
+  bool HasWeakReferences() const { return !!mProxy; }
+};
+
+inline nsSupportsWeakReference::~nsSupportsWeakReference() {
+  ClearWeakReferences();
+}
+
+#define NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_REFERENCE \
+  tmp->ClearWeakReferences();
+
+#define NS_IMPL_CYCLE_COLLECTION_WEAK(class_, ...) \
+  NS_IMPL_CYCLE_COLLECTION_CLASS(class_)           \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(class_)    \
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)   \
+    NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_REFERENCE \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_END              \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(class_)  \
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__) \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+#define NS_IMPL_CYCLE_COLLECTION_WEAK_INHERITED(class_, super_, ...) \
+  NS_IMPL_CYCLE_COLLECTION_CLASS(class_)                             \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(class_, super_)    \
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)                     \
+    NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_REFERENCE                   \
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_END                                \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(class_, super_)  \
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__)                   \
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+#endif
diff --git a/xpcom/base/nsWindowsHelpers.h b/xpcom/base/nsWindowsHelpers.h
new file mode 100644
index 0000000000..c99c7ed08d
--- /dev/null
+++ b/xpcom/base/nsWindowsHelpers.h
@@ -0,0 +1,348 @@
+/* -*- 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/. */
+
+// NB: This code may be used from non-XPCOM code, in particular, the
+// Windows Default Browser Agent.
+
+#ifndef nsWindowsHelpers_h
+#define nsWindowsHelpers_h
+
+#include <windows.h>
+#include <msi.h>
+#include "nsAutoRef.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/UniquePtr.h"
+
+// ----------------------------------------------------------------------------
+// Critical Section helper class
+// ----------------------------------------------------------------------------
+
+class AutoCriticalSection {
+ public:
+  explicit AutoCriticalSection(LPCRITICAL_SECTION aSection)
+      : mSection(aSection) {
+    ::EnterCriticalSection(mSection);
+  }
+  ~AutoCriticalSection() { ::LeaveCriticalSection(mSection); }
+
+ private:
+  LPCRITICAL_SECTION mSection;
+};
+
+template <>
+class nsAutoRefTraits<HKEY> {
+ public:
+  typedef HKEY RawRef;
+  static HKEY Void() { return nullptr; }
+
+  static void Release(RawRef aFD) {
+    if (aFD != Void()) {
+      RegCloseKey(aFD);
+    }
+  }
+};
+
+template <>
+class nsAutoRefTraits<HDC> {
+ public:
+  typedef HDC RawRef;
+  static HDC Void() { return nullptr; }
+
+  static void Release(RawRef aFD) {
+    if (aFD != Void()) {
+      ::DeleteDC(aFD);
+    }
+  }
+};
+
+template <>
+class nsAutoRefTraits<HFONT> {
+ public:
+  typedef HFONT RawRef;
+  static HFONT Void() { return nullptr; }
+
+  static void Release(RawRef aFD) {
+    if (aFD != Void()) {
+      ::DeleteObject(aFD);
+    }
+  }
+};
+
+template <>
+class nsAutoRefTraits<HBRUSH> {
+ public:
+  typedef HBRUSH RawRef;
+  static HBRUSH Void() { return nullptr; }
+
+  static void Release(RawRef aFD) {
+    if (aFD != Void()) {
+      ::DeleteObject(aFD);
+    }
+  }
+};
+
+template <>
+class nsAutoRefTraits<HRGN> {
+ public:
+  typedef HRGN RawRef;
+  static HRGN Void() { return nullptr; }
+
+  static void Release(RawRef aFD) {
+    if (aFD != Void()) {
+      ::DeleteObject(aFD);
+    }
+  }
+};
+
+template <>
+class nsAutoRefTraits<HBITMAP> {
+ public:
+  typedef HBITMAP RawRef;
+  static HBITMAP Void() { return nullptr; }
+
+  static void Release(RawRef aFD) {
+    if (aFD != Void()) {
+      ::DeleteObject(aFD);
+    }
+  }
+};
+
+template <>
+class nsAutoRefTraits<SC_HANDLE> {
+ public:
+  typedef SC_HANDLE RawRef;
+  static SC_HANDLE Void() { return nullptr; }
+
+  static void Release(RawRef aFD) {
+    if (aFD != Void()) {
+      CloseServiceHandle(aFD);
+    }
+  }
+};
+
+template <>
+class nsSimpleRef<HANDLE> {
+ protected:
+  typedef HANDLE RawRef;
+
+  nsSimpleRef() : mRawRef(nullptr) {}
+
+  explicit nsSimpleRef(RawRef aRawRef) : mRawRef(aRawRef) {}
+
+  bool HaveResource() const {
+    return mRawRef && mRawRef != INVALID_HANDLE_VALUE;
+  }
+
+ public:
+  RawRef get() const { return mRawRef; }
+
+  static void Release(RawRef aRawRef) {
+    if (aRawRef && aRawRef != INVALID_HANDLE_VALUE) {
+      CloseHandle(aRawRef);
+    }
+  }
+  RawRef mRawRef;
+};
+
+template <>
+class nsAutoRefTraits<HMODULE> {
+ public:
+  typedef HMODULE RawRef;
+  static RawRef Void() { return nullptr; }
+
+  static void Release(RawRef aFD) {
+    if (aFD != Void()) {
+      FreeLibrary(aFD);
+    }
+  }
+};
+
+template <>
+class nsAutoRefTraits<DEVMODEW*> {
+ public:
+  typedef DEVMODEW* RawRef;
+  static RawRef Void() { return nullptr; }
+
+  static void Release(RawRef aDevMode) {
+    if (aDevMode != Void()) {
+      ::HeapFree(::GetProcessHeap(), 0, aDevMode);
+    }
+  }
+};
+
+template <>
+class nsAutoRefTraits<MSIHANDLE> {
+ public:
+  typedef MSIHANDLE RawRef;
+  static RawRef Void() { return 0; }
+
+  static void Release(RawRef aHandle) {
+    if (aHandle != Void()) {
+      ::MsiCloseHandle(aHandle);
+    }
+  }
+};
+
+// HGLOBAL is just a typedef of HANDLE which nsSimpleRef has a specialization
+// of, that means having a nsAutoRefTraits specialization for HGLOBAL is
+// useless. Therefore we create a wrapper class for HGLOBAL to make
+// nsAutoRefTraits and nsAutoRef work as intention.
+class nsHGLOBAL {
+ public:
+  MOZ_IMPLICIT nsHGLOBAL(HGLOBAL hGlobal) : m_hGlobal(hGlobal) {}
+
+  operator HGLOBAL() const { return m_hGlobal; }
+
+ private:
+  HGLOBAL m_hGlobal;
+};
+
+template <>
+class nsAutoRefTraits<nsHGLOBAL> {
+ public:
+  typedef nsHGLOBAL RawRef;
+  static RawRef Void() { return nullptr; }
+
+  static void Release(RawRef hGlobal) { ::GlobalFree(hGlobal); }
+};
+
+// Because Printer's HANDLE uses ClosePrinter and we already have
+// nsAutoRef<HANDLE> which uses CloseHandle so we need to create a wrapper class
+// for HANDLE to have another specialization for nsAutoRefTraits.
+class nsHPRINTER {
+ public:
+  MOZ_IMPLICIT nsHPRINTER(HANDLE hPrinter) : m_hPrinter(hPrinter) {}
+
+  operator HANDLE() const { return m_hPrinter; }
+
+  HANDLE* operator&() { return &m_hPrinter; }
+
+ private:
+  HANDLE m_hPrinter;
+};
+
+// winspool.h header has AddMonitor macro, it conflicts with AddMonitor member
+// function in TaskbarPreview.cpp and TaskbarTabPreview.cpp. Beside, we only
+// need ClosePrinter here for Release function, so having its prototype is
+// enough.
+extern "C" BOOL WINAPI ClosePrinter(HANDLE hPrinter);
+
+template <>
+class nsAutoRefTraits<nsHPRINTER> {
+ public:
+  typedef nsHPRINTER RawRef;
+  static RawRef Void() { return nullptr; }
+
+  static void Release(RawRef hPrinter) { ::ClosePrinter(hPrinter); }
+};
+
+typedef nsAutoRef<HKEY> nsAutoRegKey;
+typedef nsAutoRef<HDC> nsAutoHDC;
+typedef nsAutoRef<HFONT> nsAutoFont;
+typedef nsAutoRef<HBRUSH> nsAutoBrush;
+typedef nsAutoRef<HRGN> nsAutoRegion;
+typedef nsAutoRef<HBITMAP> nsAutoBitmap;
+typedef nsAutoRef<SC_HANDLE> nsAutoServiceHandle;
+typedef nsAutoRef<HANDLE> nsAutoHandle;
+typedef nsAutoRef<HMODULE> nsModuleHandle;
+typedef nsAutoRef<DEVMODEW*> nsAutoDevMode;
+typedef nsAutoRef<nsHGLOBAL> nsAutoGlobalMem;
+typedef nsAutoRef<nsHPRINTER> nsAutoPrinter;
+typedef nsAutoRef<MSIHANDLE> nsAutoMsiHandle;
+
+// Construct a path "<system32>\<aModule>". return false if the output buffer
+// is too small.
+// Note: If the system path cannot be found, or doesn't fit in the output buffer
+// with the module name, we will just ignore the system path and output the
+// module name alone;
+// this may mean using a normal search path wherever the output is used.
+bool inline ConstructSystem32Path(LPCWSTR aModule, WCHAR* aSystemPath,
+                                  UINT aSize) {
+  MOZ_ASSERT(aSystemPath);
+
+  size_t fileLen = wcslen(aModule);
+  if (fileLen >= aSize) {
+    // The module name alone cannot even fit!
+    return false;
+  }
+
+  size_t systemDirLen = GetSystemDirectoryW(aSystemPath, aSize);
+
+  if (systemDirLen) {
+    if (systemDirLen < aSize - fileLen) {
+      // Make the system directory path terminate with a slash.
+      if (aSystemPath[systemDirLen - 1] != L'\\') {
+        if (systemDirLen + 1 < aSize - fileLen) {
+          aSystemPath[systemDirLen] = L'\\';
+          ++systemDirLen;
+          // No need to re-nullptr terminate.
+        } else {
+          // Couldn't fit the system path with added slash.
+          systemDirLen = 0;
+        }
+      }
+    } else {
+      // Couldn't fit the system path.
+      systemDirLen = 0;
+    }
+  }
+
+  MOZ_ASSERT(systemDirLen + fileLen < aSize);
+
+  wcsncpy(aSystemPath + systemDirLen, aModule, fileLen);
+  aSystemPath[systemDirLen + fileLen] = L'\0';
+  return true;
+}
+
+HMODULE inline LoadLibrarySystem32(LPCWSTR aModule) {
+  static const auto setDefaultDllDirectories =
+      GetProcAddress(GetModuleHandleW(L"kernel32"), "SetDefaultDllDirectories");
+  if (setDefaultDllDirectories) {
+    return LoadLibraryExW(aModule, nullptr, LOAD_LIBRARY_SEARCH_SYSTEM32);
+  }
+  WCHAR systemPath[MAX_PATH + 1];
+  if (!ConstructSystem32Path(aModule, systemPath, MAX_PATH + 1)) {
+    return NULL;
+  }
+  return LoadLibraryExW(systemPath, nullptr, LOAD_WITH_ALTERED_SEARCH_PATH);
+}
+
+// for UniquePtr
+struct LocalFreeDeleter {
+  void operator()(void* aPtr) { ::LocalFree(aPtr); }
+};
+
+struct VirtualFreeDeleter {
+  void operator()(void* aPtr) { ::VirtualFree(aPtr, 0, MEM_RELEASE); }
+};
+
+// for UniquePtr to store a PSID
+struct FreeSidDeleter {
+  void operator()(void* aPtr) { ::FreeSid(aPtr); }
+};
+// Unfortunately, although SID is a struct, PSID is a void*
+// This typedef will work for storing a PSID in a UniquePtr and should make
+// things a bit more readable.
+typedef mozilla::UniquePtr<void, FreeSidDeleter> UniqueSidPtr;
+
+struct CloseHandleDeleter {
+  typedef HANDLE pointer;
+  void operator()(pointer aHandle) {
+    if (aHandle != INVALID_HANDLE_VALUE) {
+      ::CloseHandle(aHandle);
+    }
+  }
+};
+
+// One caller of this function is early in startup and several others are not,
+// so they have different ways of determining the two parameters. This function
+// exists just so any future code that needs to determine whether the dynamic
+// blocklist is disabled remembers to check whether safe mode is active.
+inline bool IsDynamicBlocklistDisabled(bool isSafeMode,
+                                       bool hasCommandLineDisableArgument) {
+  return isSafeMode || hasCommandLineDisableArgument;
+}
+#endif
diff --git a/xpcom/base/nscore.h b/xpcom/base/nscore.h
new file mode 100644
index 0000000000..498853983e
--- /dev/null
+++ b/xpcom/base/nscore.h
@@ -0,0 +1,265 @@
+/* -*- 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/. */
+
+#ifndef nscore_h___
+#define nscore_h___
+
+/**
+ * Make sure that we have the proper platform specific
+ * c++ definitions needed by nscore.h
+ */
+#ifndef _XPCOM_CONFIG_H_
+#  include "xpcom-config.h"  // IWYU pragma: export
+#endif
+
+/* Definitions of functions and operators that allocate memory. */
+#if !defined(NS_NO_XPCOM) && !defined(MOZ_NO_MOZALLOC)
+#  include "mozilla/mozalloc.h"
+#endif
+
+/**
+ * Incorporate the integer data types which XPCOM uses.
+ */
+#include <stddef.h>  // IWYU pragma: export
+#include <stdint.h>  // IWYU pragma: export
+
+#include "mozilla/HelperMacros.h"  // IWYU pragma: export
+#include "mozilla/RefCountType.h"
+
+/* Core XPCOM declarations. */
+
+/*----------------------------------------------------------------------*/
+/* Import/export defines */
+
+#ifdef HAVE_VISIBILITY_HIDDEN_ATTRIBUTE
+#  define NS_VISIBILITY_HIDDEN __attribute__((visibility("hidden")))
+#else
+#  define NS_VISIBILITY_HIDDEN
+#endif
+
+#if defined(HAVE_VISIBILITY_ATTRIBUTE)
+#  define NS_VISIBILITY_DEFAULT __attribute__((visibility("default")))
+#elif defined(__SUNPRO_C) || defined(__SUNPRO_CC)
+#  define NS_VISIBILITY_DEFAULT __global
+#else
+#  define NS_VISIBILITY_DEFAULT
+#endif
+
+#define NS_HIDDEN_(type) NS_VISIBILITY_HIDDEN type
+#define NS_EXTERNAL_VIS_(type) NS_VISIBILITY_DEFAULT type
+
+#define NS_HIDDEN NS_VISIBILITY_HIDDEN
+#define NS_EXTERNAL_VIS NS_VISIBILITY_DEFAULT
+
+/**
+ * Mark a function as using a potentially non-standard function calling
+ * convention.  This can be used on functions that are called very
+ * frequently, to reduce the overhead of the function call.  It is still worth
+ * using the macro for C++ functions which take no parameters since it allows
+ * passing |this| in a register.
+ *
+ *  - Do not use this on any scriptable interface method since xptcall won't be
+ *    aware of the different calling convention.
+ *  - This must appear on the declaration, not the definition.
+ *  - Adding this to a public function _will_ break binary compatibility.
+ *  - This may be used on virtual functions but you must ensure it is applied
+ *    to all implementations - the compiler will _not_ warn but it will crash.
+ *  - This has no effect for functions which take a variable number of
+ *    arguments.
+ *  - __fastcall on windows should not be applied to class
+ *    constructors/destructors - use the NS_CONSTRUCTOR_FASTCALL macro for
+ *    constructors/destructors.
+ *
+ * Examples: int NS_FASTCALL func1(char *foo);
+ *           NS_HIDDEN_(int) NS_FASTCALL func2(char *foo);
+ */
+
+#if defined(__i386__) && defined(__GNUC__)
+#  define NS_FASTCALL __attribute__((regparm(3), stdcall))
+#  define NS_CONSTRUCTOR_FASTCALL __attribute__((regparm(3), stdcall))
+#elif defined(XP_WIN) && !defined(_WIN64)
+#  define NS_FASTCALL __fastcall
+#  define NS_CONSTRUCTOR_FASTCALL
+#else
+#  define NS_FASTCALL
+#  define NS_CONSTRUCTOR_FASTCALL
+#endif
+
+/**
+ * Various API modifiers.
+ *
+ * - NS_IMETHOD/NS_IMETHOD_: use for in-class declarations and definitions.
+ * - NS_IMETHODIMP/NS_IMETHODIMP_: use for out-of-class definitions.
+ * - NS_METHOD_: usually used in conjunction with NS_CALLBACK_. Best avoided.
+ * - NS_CALLBACK_: used in some legacy situations. Best avoided.
+ */
+
+#ifdef XP_WIN
+
+#  define NS_IMPORT __declspec(dllimport)
+#  define NS_IMPORT_(type) __declspec(dllimport) type __stdcall
+#  define NS_EXPORT __declspec(dllexport)
+#  define NS_EXPORT_(type) __declspec(dllexport) type __stdcall
+#  define NS_IMETHOD_(type) virtual type __stdcall
+#  define NS_IMETHODIMP_(type) type __stdcall
+#  define NS_METHOD_(type) type __stdcall
+#  define NS_CALLBACK_(_type, _name) _type(__stdcall* _name)
+#  ifndef _WIN64
+// Win64 has only one calling convention.  __stdcall will be ignored by the
+// compiler.
+#    define NS_STDCALL __stdcall
+#    define NS_HAVE_STDCALL
+#  else
+#    define NS_STDCALL
+#  endif
+#  define NS_FROZENCALL __cdecl
+
+#else
+
+#  define NS_IMPORT NS_EXTERNAL_VIS
+#  define NS_IMPORT_(type) NS_EXTERNAL_VIS_(type)
+#  define NS_EXPORT NS_EXTERNAL_VIS
+#  define NS_EXPORT_(type) NS_EXTERNAL_VIS_(type)
+#  define NS_IMETHOD_(type) virtual type
+#  define NS_IMETHODIMP_(type) type
+#  define NS_METHOD_(type) type
+#  define NS_CALLBACK_(_type, _name) _type(*_name)
+#  define NS_STDCALL
+#  define NS_FROZENCALL
+
+#endif
+
+#define NS_IMETHOD NS_IMETHOD_(nsresult)
+#define NS_IMETHODIMP NS_IMETHODIMP_(nsresult)
+
+/**
+ * Import/Export macros for XPCOM APIs
+ */
+
+#define EXPORT_XPCOM_API(type) type
+#define IMPORT_XPCOM_API(type) type
+#define GLUE_XPCOM_API(type) type
+
+#ifdef __cplusplus
+#  define NS_EXTERN_C extern "C"
+#else
+#  define NS_EXTERN_C
+#endif
+
+#define XPCOM_API(type) NS_EXTERN_C type
+
+/* If a program allocates memory for the lifetime of the app, it doesn't make
+ * sense to touch memory pages and free that memory at shutdown,
+ * unless we are running leak stats.
+ *
+ * Note that we're also setting this for code coverage and pgo profile
+ * generation, because both of those require atexit hooks, which won't fire
+ * if we're using _exit. Bug 1555974 covers improving this.
+ *
+ */
+#ifndef NS_FREE_PERMANENT_DATA
+#  if defined(NS_BUILD_REFCNT_LOGGING) || defined(MOZ_VALGRIND) ||            \
+      defined(MOZ_ASAN) || defined(MOZ_TSAN) || defined(MOZ_CODE_COVERAGE) || \
+      defined(MOZ_PROFILE_GENERATE) || defined(JS_STRUCTURED_SPEW)
+#    define NS_FREE_PERMANENT_DATA
+#  endif
+#endif
+
+/**
+ * NS_NO_VTABLE is emitted by xpidl in interface declarations whenever
+ * xpidl can determine that the interface can't contain a constructor.
+ * This results in some space savings and possible runtime savings -
+ * see bug 49416.  We undefine it first, as xpidl-generated headers
+ * define it for IDL uses that don't include this file.
+ */
+#ifdef NS_NO_VTABLE
+#  undef NS_NO_VTABLE
+#endif
+#if defined(_MSC_VER)
+#  define NS_NO_VTABLE __declspec(novtable)
+#else
+#  define NS_NO_VTABLE
+#endif
+
+/**
+ * Generic XPCOM result data type
+ */
+#include "nsError.h"  // IWYU pragma: export
+
+typedef MozRefCountType nsrefcnt;
+
+namespace mozilla {
+// Extensions to the mozilla::Result type for handling of nsresult values.
+//
+// Note that these specializations need to be defined before Result.h is
+// included, or we run into explicit specialization after instantiation errors,
+// especially if Result.h is used in multiple sources in a unified compile.
+
+namespace detail {
+// When used as an error value, nsresult should never be NS_OK.
+// This specialization allows us to pack Result<Ok, nsresult> into a
+// nsresult-sized value.
+template <typename T>
+struct UnusedZero;
+template <>
+struct UnusedZero<nsresult> {
+  using StorageType = nsresult;
+
+  static constexpr bool value = true;
+  static constexpr StorageType nullValue = NS_OK;
+
+  static constexpr void AssertValid(StorageType aValue) {}
+  static constexpr const nsresult& Inspect(const StorageType& aValue) {
+    return aValue;
+  }
+  static constexpr nsresult Unwrap(StorageType aValue) { return aValue; }
+  static constexpr StorageType Store(nsresult aValue) { return aValue; }
+};
+}  // namespace detail
+
+template <typename T>
+class GenericErrorResult;
+template <>
+class GenericErrorResult<nsresult>;
+
+struct Ok;
+template <typename V, typename E>
+class Result;
+
+// Allow MOZ_TRY to handle `nsresult` values.
+template <typename E = nsresult>
+inline Result<Ok, E> ToResult(nsresult aValue);
+}  // namespace mozilla
+
+/*
+ * Use these macros to do 64bit safe pointer conversions.
+ */
+
+#define NS_PTR_TO_INT32(x) ((int32_t)(intptr_t)(x))
+#define NS_PTR_TO_UINT32(x) ((uint32_t)(intptr_t)(x))
+#define NS_INT32_TO_PTR(x) ((void*)(intptr_t)(x))
+
+/*
+ * If we're being linked as standalone glue, we don't want a dynamic
+ * dependency on NSPR libs, so we skip the debug thread-safety
+ * checks, and we cannot use the THREADSAFE_ISUPPORTS macros.
+ */
+#if defined(XPCOM_GLUE) && !defined(XPCOM_GLUE_USE_NSPR)
+#  define XPCOM_GLUE_AVOID_NSPR
+#endif
+
+/*
+ * SEH exception macros.
+ */
+#ifdef HAVE_SEH_EXCEPTIONS
+#  define MOZ_SEH_TRY __try
+#  define MOZ_SEH_EXCEPT(expr) __except (expr)
+#else
+#  define MOZ_SEH_TRY if (true)
+#  define MOZ_SEH_EXCEPT(expr) else
+#endif
+
+#endif /* nscore_h___ */
diff --git a/xpcom/base/nsrootidl.idl b/xpcom/base/nsrootidl.idl
new file mode 100644
index 0000000000..28e643e312
--- /dev/null
+++ b/xpcom/base/nsrootidl.idl
@@ -0,0 +1,105 @@
+/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* 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/. */
+
+/**
+ * Root idl declarations to be used by all.
+ */
+
+%{C++
+
+#include "nscore.h"
+#include "nsID.h"
+typedef int64_t PRTime;
+
+/*
+ * Forward declarations for new string types
+ */
+#include "nsStringFwd.h"
+
+struct JSContext;
+
+/*
+ * Forward declaration of mozilla::dom::Promise
+ */
+namespace mozilla {
+namespace dom {
+class Promise;
+} // namespace dom
+} // namespace mozilla
+
+/*
+ * Start commenting out the C++ versions of the below in the output header
+ */
+#if 0
+%}
+
+typedef boolean             bool   ;
+typedef octet               uint8_t  ;
+typedef unsigned short      uint16_t ;
+typedef unsigned short      char16_t;
+typedef unsigned long       uint32_t ;
+typedef unsigned long long  uint64_t ;
+typedef long long           PRTime   ;
+typedef short               int16_t  ;
+typedef long                int32_t  ;
+typedef long long           int64_t  ;
+
+typedef unsigned long       nsresult ;
+
+// If we ever want to use `size_t` in scriptable interfaces, this will need to
+// be built into the xpidl compiler, as the size varies based on platform.
+              native size_t(size_t);
+
+[ptr]         native voidPtr(void);
+[ptr]         native charPtr(char);
+[ptr]         native unicharPtr(char16_t);
+
+[ref, nsid]   native nsIDRef(nsID);
+[ref, nsid]   native nsIIDRef(nsIID);
+[ref, nsid]   native nsCIDRef(nsCID);
+
+[ptr, nsid]   native nsIDPtr(nsID);
+[ptr, nsid]   native nsIIDPtr(nsIID);
+[ptr, nsid]   native nsCIDPtr(nsCID);
+
+// NOTE: Be careful in using the following 3 types. The *Ref and *Ptr variants
+// are more commonly used (and better supported). Those variants require
+// nsMemory alloc'd copies when used as 'out' params while these types do not.
+// However, currently these types can not be used for 'in' params. And, methods
+// that use them as 'out' params *must* be declared [notxpcom] (with an explicit
+// return type of nsresult). This makes such methods implicitly not scriptable.
+// Use of these types in methods without a [notxpcom] declaration will cause
+// the xpidl compiler to raise an error.
+// See: http://bugzilla.mozilla.org/show_bug.cgi?id=93792
+
+[nsid]        native nsIID(nsIID);
+[nsid]        native nsID(nsID);
+[nsid]        native nsCID(nsCID);
+
+[ptr]         native nsQIResult(void);
+
+[ref, utf8string] native AUTF8String(ignored);
+[ref, utf8string] native AUTF8StringRef(ignored);
+[ptr, utf8string] native AUTF8StringPtr(ignored);
+
+[ref, cstring] native ACString(ignored);
+[ref, cstring] native ACStringRef(ignored);
+[ptr, cstring] native ACStringPtr(ignored);
+
+[ref, astring] native AString(ignored);
+[ref, astring] native AStringRef(ignored);
+[ptr, astring] native AStringPtr(ignored);
+
+[ref, jsval]  native jsval(jsval);
+              native jsid(jsid);
+
+[ptr, promise] native Promise(ignored);
+
+%{C++
+/*
+ * End commenting out the C++ versions of the above in the output header
+ */
+#endif
+%}