Adding upstream version 110.0.1.upstream/110.0.1upstream

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

1 files changed, 11918 insertions, 0 deletions

diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
new file mode 100644
index 0000000000..f4d42f575e
--- /dev/null
+++ b/layout/base/PresShell.cpp
@@ -0,0 +1,11918 @@
+/* -*- 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 presentation of a document, part 2 */
+
+#include "mozilla/PresShell.h"
+
+#include "Units.h"
+#include "mozilla/dom/FontFaceSet.h"
+#include "mozilla/dom/ElementBinding.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/ContentIterator.h"
+#include "mozilla/DisplayPortUtils.h"
+#include "mozilla/EventDispatcher.h"
+#include "mozilla/EventStateManager.h"
+#include "mozilla/GeckoMVMContext.h"
+#include "mozilla/IMEStateManager.h"
+#include "mozilla/IntegerRange.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/dom/BrowserChild.h"
+#include "mozilla/Likely.h"
+#include "mozilla/Logging.h"
+#include "mozilla/MouseEvents.h"
+#include "mozilla/PerfStats.h"
+#include "mozilla/PointerLockManager.h"
+#include "mozilla/PresShellInlines.h"
+#include "mozilla/RangeUtils.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/StaticAnalysisFunctions.h"
+#include "mozilla/StaticPrefs_apz.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/StaticPrefs_font.h"
+#include "mozilla/StaticPrefs_image.h"
+#include "mozilla/StaticPrefs_layout.h"
+#include "mozilla/StaticPrefs_toolkit.h"
+#include "mozilla/TextEvents.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/TouchEvents.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/ViewportUtils.h"
+#include "mozilla/gfx/Types.h"
+#include <algorithm>
+
+#ifdef XP_WIN
+#  include "winuser.h"
+#endif
+
+#include "gfxContext.h"
+#include "gfxUserFontSet.h"
+#include "nsContentList.h"
+#include "nsPresContext.h"
+#include "nsIContent.h"
+#include "mozilla/dom/BrowserBridgeChild.h"
+#include "mozilla/dom/BrowsingContext.h"
+#include "mozilla/dom/CanonicalBrowsingContext.h"
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/PointerEventHandler.h"
+#include "mozilla/dom/PopupBlocker.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/DocumentInlines.h"
+#include "mozilla/dom/UserActivation.h"
+#include "nsAnimationManager.h"
+#include "nsNameSpaceManager.h"  // for Pref-related rule management (bugs 22963,20760,31816)
+#include "nsFlexContainerFrame.h"
+#include "nsIFrame.h"
+#include "nsViewManager.h"
+#include "nsView.h"
+#include "nsCRTGlue.h"
+#include "prinrval.h"
+#include "nsTArray.h"
+#include "nsCOMArray.h"
+#include "nsContainerFrame.h"
+#include "mozilla/dom/Selection.h"
+#include "nsGkAtoms.h"
+#include "nsRange.h"
+#include "nsWindowSizes.h"
+#include "nsCOMPtr.h"
+#include "nsReadableUtils.h"
+#include "nsPageSequenceFrame.h"
+#include "nsCaret.h"
+#include "mozilla/AccessibleCaretEventHub.h"
+#include "nsFrameManager.h"
+#include "nsXPCOM.h"
+#include "nsILayoutHistoryState.h"
+#include "nsILineIterator.h"  // for ScrollContentIntoView
+#include "PLDHashTable.h"
+#include "mozilla/dom/Touch.h"
+#include "mozilla/dom/TouchEvent.h"
+#include "mozilla/dom/PointerEventBinding.h"
+#include "mozilla/dom/ShadowIncludingTreeIterator.h"
+#include "nsIObserverService.h"
+#include "nsDocShell.h"  // for reflow observation
+#include "nsIBaseWindow.h"
+#include "nsError.h"
+#include "nsLayoutUtils.h"
+#include "nsViewportInfo.h"
+#include "nsCSSRendering.h"
+// for |#ifdef DEBUG| code
+#include "prenv.h"
+#include "nsDisplayList.h"
+#include "nsRegion.h"
+#include "nsAutoLayoutPhase.h"
+#include "AutoProfilerStyleMarker.h"
+#ifdef MOZ_REFLOW_PERF
+#  include "nsFontMetrics.h"
+#endif
+#include "MobileViewportManager.h"
+#include "OverflowChangedTracker.h"
+#include "PositionedEventTargeting.h"
+
+#include "nsIReflowCallback.h"
+
+#include "nsPIDOMWindow.h"
+#include "nsFocusManager.h"
+#include "nsNetUtil.h"
+#include "nsThreadUtils.h"
+#include "nsStyleSheetService.h"
+#include "gfxUtils.h"
+#include "mozilla/SMILAnimationController.h"
+#include "mozilla/dom/SVGAnimationElement.h"
+#include "mozilla/SVGObserverUtils.h"
+#include "mozilla/SVGFragmentIdentifier.h"
+#include "nsFrameSelection.h"
+
+#include "mozilla/dom/Performance.h"
+#include "nsRefreshDriver.h"
+#include "nsDOMNavigationTiming.h"
+
+// Drag & Drop, Clipboard
+#include "nsIDocShellTreeItem.h"
+#include "nsIURI.h"
+#include "nsIScrollableFrame.h"
+#include "nsITimer.h"
+#ifdef ACCESSIBILITY
+#  include "mozilla/a11y/DocAccessible.h"
+#  ifdef DEBUG
+#    include "mozilla/a11y/Logging.h"
+#  endif
+#endif
+
+// For style data reconstruction
+#include "nsStyleChangeList.h"
+#include "nsCSSFrameConstructor.h"
+#include "nsTreeBodyFrame.h"
+#include "XULTreeElement.h"
+#include "nsMenuPopupFrame.h"
+#include "nsTreeColumns.h"
+#include "nsIDOMXULMultSelectCntrlEl.h"
+#include "nsIDOMXULSelectCntrlItemEl.h"
+#include "nsIDOMXULMenuListElement.h"
+#include "nsXULElement.h"
+
+#include "mozilla/layers/CompositorBridgeChild.h"
+#include "gfxPlatform.h"
+#include "mozilla/css/ImageLoader.h"
+#include "mozilla/dom/DocumentTimeline.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Telemetry.h"
+#include "nsCanvasFrame.h"
+#include "nsImageFrame.h"
+#include "nsIScreen.h"
+#include "nsIScreenManager.h"
+#include "nsPlaceholderFrame.h"
+#include "nsTransitionManager.h"
+#include "ChildIterator.h"
+#include "mozilla/RestyleManager.h"
+#include "nsIDragSession.h"
+#include "nsIFrameInlines.h"
+#include "mozilla/gfx/2D.h"
+#include "nsNetUtil.h"
+#include "nsSubDocumentFrame.h"
+#include "nsQueryObject.h"
+#include "mozilla/GlobalStyleSheetCache.h"
+#include "mozilla/layers/InputAPZContext.h"
+#include "mozilla/layers/FocusTarget.h"
+#include "mozilla/layers/ScrollingInteractionContext.h"
+#include "mozilla/layers/WebRenderLayerManager.h"
+#include "mozilla/layers/WebRenderUserData.h"
+#include "mozilla/layout/ScrollAnchorContainer.h"
+#include "mozilla/layers/APZPublicUtils.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/ProfilerMarkers.h"
+#include "mozilla/ScrollTimelineAnimationTracker.h"
+#include "mozilla/ScrollTypes.h"
+#include "mozilla/ServoBindings.h"
+#include "mozilla/ServoStyleSet.h"
+#include "mozilla/StyleSheet.h"
+#include "mozilla/StyleSheetInlines.h"
+#include "mozilla/InputTaskManager.h"
+#include "mozilla/dom/ImageTracker.h"
+#include "nsIDocShellTreeOwner.h"
+#include "nsClassHashtable.h"
+#include "nsHashKeys.h"
+#include "ScrollSnap.h"
+#include "VisualViewport.h"
+#include "ZoomConstraintsClient.h"
+
+// define the scalfactor of drag and drop images
+// relative to the max screen height/width
+#define RELATIVE_SCALEFACTOR 0.0925f
+
+using namespace mozilla;
+using namespace mozilla::css;
+using namespace mozilla::dom;
+using namespace mozilla::gfx;
+using namespace mozilla::layers;
+using namespace mozilla::gfx;
+using namespace mozilla::layout;
+using PaintFrameFlags = nsLayoutUtils::PaintFrameFlags;
+typedef ScrollableLayerGuid::ViewID ViewID;
+
+PresShell::CapturingContentInfo PresShell::sCapturingContentInfo;
+
+// RangePaintInfo is used to paint ranges to offscreen buffers
+struct RangePaintInfo {
+  RefPtr<nsRange> mRange;
+  nsDisplayListBuilder mBuilder;
+  nsDisplayList mList;
+
+  // offset of builder's reference frame to the root frame
+  nsPoint mRootOffset;
+
+  // Resolution at which the items are normally painted. So if we're painting
+  // these items in a range separately from the "full display list", we may want
+  // to paint them at this resolution.
+  float mResolution = 1.0;
+
+  RangePaintInfo(nsRange* aRange, nsIFrame* aFrame)
+      : mRange(aRange),
+        mBuilder(aFrame, nsDisplayListBuilderMode::Painting, false),
+        mList(&mBuilder) {
+    MOZ_COUNT_CTOR(RangePaintInfo);
+    mBuilder.BeginFrame();
+  }
+
+  ~RangePaintInfo() {
+    mList.DeleteAll(&mBuilder);
+    mBuilder.EndFrame();
+    MOZ_COUNT_DTOR(RangePaintInfo);
+  }
+};
+
+#undef NOISY
+
+// ----------------------------------------------------------------------
+
+#ifdef DEBUG
+// Set the environment variable GECKO_VERIFY_REFLOW_FLAGS to one or
+// more of the following flags (comma separated) for handy debug
+// output.
+static VerifyReflowFlags gVerifyReflowFlags;
+
+struct VerifyReflowFlagData {
+  const char* name;
+  VerifyReflowFlags bit;
+};
+
+static const VerifyReflowFlagData gFlags[] = {
+    // clang-format off
+  { "verify",                VerifyReflowFlags::On },
+  { "reflow",                VerifyReflowFlags::Noisy },
+  { "all",                   VerifyReflowFlags::All },
+  { "list-commands",         VerifyReflowFlags::DumpCommands },
+  { "noisy-commands",        VerifyReflowFlags::NoisyCommands },
+  { "really-noisy-commands", VerifyReflowFlags::ReallyNoisyCommands },
+  { "resize",                VerifyReflowFlags::DuringResizeReflow },
+    // clang-format on
+};
+
+#  define NUM_VERIFY_REFLOW_FLAGS (sizeof(gFlags) / sizeof(gFlags[0]))
+
+static void ShowVerifyReflowFlags() {
+  printf("Here are the available GECKO_VERIFY_REFLOW_FLAGS:\n");
+  const VerifyReflowFlagData* flag = gFlags;
+  const VerifyReflowFlagData* limit = gFlags + NUM_VERIFY_REFLOW_FLAGS;
+  while (flag < limit) {
+    printf("  %s\n", flag->name);
+    ++flag;
+  }
+  printf("Note: GECKO_VERIFY_REFLOW_FLAGS is a comma separated list of flag\n");
+  printf("names (no whitespace)\n");
+}
+#endif
+
+//========================================================================
+//========================================================================
+//========================================================================
+#ifdef MOZ_REFLOW_PERF
+class ReflowCountMgr;
+
+static const char kGrandTotalsStr[] = "Grand Totals";
+
+// Counting Class
+class ReflowCounter {
+ public:
+  explicit ReflowCounter(ReflowCountMgr* aMgr = nullptr);
+  ~ReflowCounter();
+
+  void ClearTotals();
+  void DisplayTotals(const char* aStr);
+  void DisplayDiffTotals(const char* aStr);
+  void DisplayHTMLTotals(const char* aStr);
+
+  void Add() { mTotal++; }
+  void Add(uint32_t aTotal) { mTotal += aTotal; }
+
+  void CalcDiffInTotals();
+  void SetTotalsCache();
+
+  void SetMgr(ReflowCountMgr* aMgr) { mMgr = aMgr; }
+
+  uint32_t GetTotal() { return mTotal; }
+
+ protected:
+  void DisplayTotals(uint32_t aTotal, const char* aTitle);
+  void DisplayHTMLTotals(uint32_t aTotal, const char* aTitle);
+
+  uint32_t mTotal;
+  uint32_t mCacheTotal;
+
+  ReflowCountMgr* mMgr;  // weak reference (don't delete)
+};
+
+// Counting Class
+class IndiReflowCounter {
+ public:
+  explicit IndiReflowCounter(ReflowCountMgr* aMgr = nullptr)
+      : mFrame(nullptr),
+        mCount(0),
+        mMgr(aMgr),
+        mCounter(aMgr),
+        mHasBeenOutput(false) {}
+  virtual ~IndiReflowCounter() = default;
+
+  nsAutoString mName;
+  nsIFrame* mFrame;  // weak reference (don't delete)
+  int32_t mCount;
+
+  ReflowCountMgr* mMgr;  // weak reference (don't delete)
+
+  ReflowCounter mCounter;
+  bool mHasBeenOutput;
+};
+
+//--------------------
+// Manager Class
+//--------------------
+class ReflowCountMgr {
+ public:
+  ReflowCountMgr();
+  virtual ~ReflowCountMgr();
+
+  void ClearTotals();
+  void ClearGrandTotals();
+  void DisplayTotals(const char* aStr);
+  void DisplayHTMLTotals(const char* aStr);
+  void DisplayDiffsInTotals();
+
+  void Add(const char* aName, nsIFrame* aFrame);
+  ReflowCounter* LookUp(const char* aName);
+
+  void PaintCount(const char* aName, gfxContext* aRenderingContext,
+                  nsPresContext* aPresContext, nsIFrame* aFrame,
+                  const nsPoint& aOffset, uint32_t aColor);
+
+  FILE* GetOutFile() { return mFD; }
+
+  void SetPresContext(nsPresContext* aPresContext) {
+    mPresContext = aPresContext;  // weak reference
+  }
+  void SetPresShell(PresShell* aPresShell) {
+    mPresShell = aPresShell;  // weak reference
+  }
+
+  void SetDumpFrameCounts(bool aVal) { mDumpFrameCounts = aVal; }
+  void SetDumpFrameByFrameCounts(bool aVal) { mDumpFrameByFrameCounts = aVal; }
+  void SetPaintFrameCounts(bool aVal) { mPaintFrameByFrameCounts = aVal; }
+
+  bool IsPaintingFrameCounts() { return mPaintFrameByFrameCounts; }
+
+ protected:
+  void DisplayTotals(uint32_t aTotal, uint32_t* aDupArray, char* aTitle);
+  void DisplayHTMLTotals(uint32_t aTotal, uint32_t* aDupArray, char* aTitle);
+
+  void DoGrandTotals();
+  void DoIndiTotalsTree();
+
+  // HTML Output Methods
+  void DoGrandHTMLTotals();
+
+  nsClassHashtable<nsCharPtrHashKey, ReflowCounter> mCounts;
+  nsClassHashtable<nsCharPtrHashKey, IndiReflowCounter> mIndiFrameCounts;
+  FILE* mFD;
+
+  bool mDumpFrameCounts;
+  bool mDumpFrameByFrameCounts;
+  bool mPaintFrameByFrameCounts;
+
+  bool mCycledOnce;
+
+  // Root Frame for Individual Tracking
+  nsPresContext* mPresContext;
+  PresShell* mPresShell;
+
+  // ReflowCountMgr gReflowCountMgr;
+};
+#endif
+//========================================================================
+
+// comment out to hide caret
+#define SHOW_CARET
+
+// The upper bound on the amount of time to spend reflowing, in
+// microseconds.  When this bound is exceeded and reflow commands are
+// still queued up, a reflow event is posted.  The idea is for reflow
+// to not hog the processor beyond the time specifed in
+// gMaxRCProcessingTime.  This data member is initialized from the
+// layout.reflow.timeslice pref.
+#define NS_MAX_REFLOW_TIME 1000000
+static int32_t gMaxRCProcessingTime = -1;
+
+struct nsCallbackEventRequest {
+  nsIReflowCallback* callback;
+  nsCallbackEventRequest* next;
+};
+
+// ----------------------------------------------------------------------------
+//
+// NOTE(emilio): It'd be nice for this to assert that our document isn't in the
+// bfcache, but font pref changes don't care about that, and maybe / probably
+// shouldn't.
+#ifdef DEBUG
+#  define ASSERT_REFLOW_SCHEDULED_STATE()                                   \
+    {                                                                       \
+      if (ObservingLayoutFlushes()) {                                       \
+        MOZ_ASSERT(                                                         \
+            mDocument->GetBFCacheEntry() ||                                 \
+                mPresContext->RefreshDriver()->IsLayoutFlushObserver(this), \
+            "Unexpected state");                                            \
+      } else {                                                              \
+        MOZ_ASSERT(                                                         \
+            !mPresContext->RefreshDriver()->IsLayoutFlushObserver(this),    \
+            "Unexpected state");                                            \
+      }                                                                     \
+    }
+#else
+#  define ASSERT_REFLOW_SCHEDULED_STATE() /* nothing */
+#endif
+
+class nsAutoCauseReflowNotifier {
+ public:
+  MOZ_CAN_RUN_SCRIPT explicit nsAutoCauseReflowNotifier(PresShell* aPresShell)
+      : mPresShell(aPresShell) {
+    mPresShell->WillCauseReflow();
+  }
+  MOZ_CAN_RUN_SCRIPT ~nsAutoCauseReflowNotifier() {
+    // This check should not be needed. Currently the only place that seem
+    // to need it is the code that deals with bug 337586.
+    if (!mPresShell->mHaveShutDown) {
+      RefPtr<PresShell> presShell(mPresShell);
+      presShell->DidCauseReflow();
+    } else {
+      nsContentUtils::RemoveScriptBlocker();
+    }
+  }
+
+  PresShell* mPresShell;
+};
+
+class MOZ_STACK_CLASS nsPresShellEventCB : public EventDispatchingCallback {
+ public:
+  explicit nsPresShellEventCB(PresShell* aPresShell) : mPresShell(aPresShell) {}
+
+  MOZ_CAN_RUN_SCRIPT
+  virtual void HandleEvent(EventChainPostVisitor& aVisitor) override {
+    if (aVisitor.mPresContext && aVisitor.mEvent->mClass != eBasicEventClass) {
+      if (aVisitor.mEvent->mMessage == eMouseDown ||
+          aVisitor.mEvent->mMessage == eMouseUp) {
+        // Mouse-up and mouse-down events call nsIFrame::HandlePress/Release
+        // which call GetContentOffsetsFromPoint which requires up-to-date
+        // layout. Bring layout up-to-date now so that GetCurrentEventFrame()
+        // below will return a real frame and we don't have to worry about
+        // destroying it by flushing later.
+        MOZ_KnownLive(mPresShell)->FlushPendingNotifications(FlushType::Layout);
+      } else if (aVisitor.mEvent->mMessage == eWheel &&
+                 aVisitor.mEventStatus != nsEventStatus_eConsumeNoDefault) {
+        nsIFrame* frame = mPresShell->GetCurrentEventFrame();
+        if (frame) {
+          // chrome (including addons) should be able to know if content
+          // handles both D3E "wheel" event and legacy mouse scroll events.
+          // We should dispatch legacy mouse events before dispatching the
+          // "wheel" event into system group.
+          RefPtr<EventStateManager> esm =
+              aVisitor.mPresContext->EventStateManager();
+          esm->DispatchLegacyMouseScrollEvents(
+              frame, aVisitor.mEvent->AsWheelEvent(), &aVisitor.mEventStatus);
+        }
+      }
+      nsIFrame* frame = mPresShell->GetCurrentEventFrame();
+      if (!frame && (aVisitor.mEvent->mMessage == eMouseUp ||
+                     aVisitor.mEvent->mMessage == eTouchEnd)) {
+        // Redirect BUTTON_UP and TOUCH_END events to the root frame to ensure
+        // that capturing is released.
+        frame = mPresShell->GetRootFrame();
+      }
+      if (frame) {
+        frame->HandleEvent(aVisitor.mPresContext, aVisitor.mEvent->AsGUIEvent(),
+                           &aVisitor.mEventStatus);
+      }
+    }
+  }
+
+  RefPtr<PresShell> mPresShell;
+};
+
+class nsBeforeFirstPaintDispatcher : public Runnable {
+ public:
+  explicit nsBeforeFirstPaintDispatcher(Document* aDocument)
+      : mozilla::Runnable("nsBeforeFirstPaintDispatcher"),
+        mDocument(aDocument) {}
+
+  // Fires the "before-first-paint" event so that interested parties (right now,
+  // the mobile browser) are aware of it.
+  NS_IMETHOD Run() override {
+    nsCOMPtr<nsIObserverService> observerService =
+        mozilla::services::GetObserverService();
+    if (observerService) {
+      observerService->NotifyObservers(ToSupports(mDocument),
+                                       "before-first-paint", nullptr);
+    }
+    return NS_OK;
+  }
+
+ private:
+  RefPtr<Document> mDocument;
+};
+
+// This is a helper class to track whether the targeted frame is destroyed after
+// dispatching pointer events. In that case, we need the original targeted
+// content so that we can dispatch the mouse events to it.
+class MOZ_STACK_CLASS AutoPointerEventTargetUpdater final {
+ public:
+  AutoPointerEventTargetUpdater(PresShell* aShell, WidgetEvent* aEvent,
+                                nsIFrame* aFrame, nsIContent** aTargetContent) {
+    MOZ_ASSERT(aEvent);
+    if (!aTargetContent || aEvent->mClass != ePointerEventClass) {
+      // Make the destructor happy.
+      mTargetContent = nullptr;
+      return;
+    }
+    MOZ_ASSERT(aShell);
+    MOZ_ASSERT(aFrame);
+    MOZ_ASSERT(!aFrame->GetContent() ||
+               aShell->GetDocument() == aFrame->GetContent()->OwnerDoc());
+
+    mShell = aShell;
+    mWeakFrame = aFrame;
+    mTargetContent = aTargetContent;
+    aShell->mPointerEventTarget = aFrame->GetContent();
+  }
+
+  ~AutoPointerEventTargetUpdater() {
+    if (!mTargetContent || !mShell || mWeakFrame.IsAlive()) {
+      return;
+    }
+    mShell->mPointerEventTarget.swap(*mTargetContent);
+  }
+
+ private:
+  RefPtr<PresShell> mShell;
+  AutoWeakFrame mWeakFrame;
+  nsIContent** mTargetContent;
+};
+
+bool PresShell::sDisableNonTestMouseEvents = false;
+
+LazyLogModule PresShell::gLog("PresShell");
+
+TimeStamp PresShell::EventHandler::sLastInputCreated;
+TimeStamp PresShell::EventHandler::sLastInputProcessed;
+StaticRefPtr<Element> PresShell::EventHandler::sLastKeyDownEventTargetElement;
+
+bool PresShell::sProcessInteractable = false;
+
+static bool gVerifyReflowEnabled;
+
+bool PresShell::GetVerifyReflowEnable() {
+#ifdef DEBUG
+  static bool firstTime = true;
+  if (firstTime) {
+    firstTime = false;
+    char* flags = PR_GetEnv("GECKO_VERIFY_REFLOW_FLAGS");
+    if (flags) {
+      bool error = false;
+
+      for (;;) {
+        char* comma = strchr(flags, ',');
+        if (comma) *comma = '\0';
+
+        bool found = false;
+        const VerifyReflowFlagData* flag = gFlags;
+        const VerifyReflowFlagData* limit = gFlags + NUM_VERIFY_REFLOW_FLAGS;
+        while (flag < limit) {
+          if (nsCRT::strcasecmp(flag->name, flags) == 0) {
+            gVerifyReflowFlags |= flag->bit;
+            found = true;
+            break;
+          }
+          ++flag;
+        }
+
+        if (!found) error = true;
+
+        if (!comma) break;
+
+        *comma = ',';
+        flags = comma + 1;
+      }
+
+      if (error) ShowVerifyReflowFlags();
+    }
+
+    if (VerifyReflowFlags::On & gVerifyReflowFlags) {
+      gVerifyReflowEnabled = true;
+
+      printf("Note: verifyreflow is enabled");
+      if (VerifyReflowFlags::Noisy & gVerifyReflowFlags) {
+        printf(" (noisy)");
+      }
+      if (VerifyReflowFlags::All & gVerifyReflowFlags) {
+        printf(" (all)");
+      }
+      if (VerifyReflowFlags::DumpCommands & gVerifyReflowFlags) {
+        printf(" (show reflow commands)");
+      }
+      if (VerifyReflowFlags::NoisyCommands & gVerifyReflowFlags) {
+        printf(" (noisy reflow commands)");
+        if (VerifyReflowFlags::ReallyNoisyCommands & gVerifyReflowFlags) {
+          printf(" (REALLY noisy reflow commands)");
+        }
+      }
+      printf("\n");
+    }
+  }
+#endif
+  return gVerifyReflowEnabled;
+}
+
+void PresShell::SetVerifyReflowEnable(bool aEnabled) {
+  gVerifyReflowEnabled = aEnabled;
+}
+
+void PresShell::AddAutoWeakFrame(AutoWeakFrame* aWeakFrame) {
+  if (aWeakFrame->GetFrame()) {
+    aWeakFrame->GetFrame()->AddStateBits(NS_FRAME_EXTERNAL_REFERENCE);
+  }
+  aWeakFrame->SetPreviousWeakFrame(mAutoWeakFrames);
+  mAutoWeakFrames = aWeakFrame;
+}
+
+void PresShell::AddWeakFrame(WeakFrame* aWeakFrame) {
+  if (aWeakFrame->GetFrame()) {
+    aWeakFrame->GetFrame()->AddStateBits(NS_FRAME_EXTERNAL_REFERENCE);
+  }
+  MOZ_ASSERT(!mWeakFrames.Contains(aWeakFrame));
+  mWeakFrames.Insert(aWeakFrame);
+}
+
+void PresShell::RemoveAutoWeakFrame(AutoWeakFrame* aWeakFrame) {
+  if (mAutoWeakFrames == aWeakFrame) {
+    mAutoWeakFrames = aWeakFrame->GetPreviousWeakFrame();
+    return;
+  }
+  AutoWeakFrame* nextWeak = mAutoWeakFrames;
+  while (nextWeak && nextWeak->GetPreviousWeakFrame() != aWeakFrame) {
+    nextWeak = nextWeak->GetPreviousWeakFrame();
+  }
+  if (nextWeak) {
+    nextWeak->SetPreviousWeakFrame(aWeakFrame->GetPreviousWeakFrame());
+  }
+}
+
+void PresShell::RemoveWeakFrame(WeakFrame* aWeakFrame) {
+  MOZ_ASSERT(mWeakFrames.Contains(aWeakFrame));
+  mWeakFrames.Remove(aWeakFrame);
+}
+
+already_AddRefed<nsFrameSelection> PresShell::FrameSelection() {
+  RefPtr<nsFrameSelection> ret = mSelection;
+  return ret.forget();
+}
+
+//----------------------------------------------------------------------
+
+static uint32_t sNextPresShellId = 0;
+
+/* static */
+bool PresShell::AccessibleCaretEnabled(nsIDocShell* aDocShell) {
+  // If the pref forces it on, then enable it.
+  if (StaticPrefs::layout_accessiblecaret_enabled()) {
+    return true;
+  }
+  // If the touch pref is on, and touch events are enabled (this depends
+  // on the specific device running), then enable it.
+  if (StaticPrefs::layout_accessiblecaret_enabled_on_touch() &&
+      dom::TouchEvent::PrefEnabled(aDocShell)) {
+    return true;
+  }
+  // Otherwise, disabled.
+  return false;
+}
+
+PresShell::PresShell(Document* aDocument)
+    : mDocument(aDocument),
+      mViewManager(nullptr),
+      mFrameManager(nullptr),
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+      mAllocatedPointers(MakeUnique<nsTHashSet<void*>>()),
+#endif  // MOZ_DIAGNOSTIC_ASSERT_ENABLED
+      mAutoWeakFrames(nullptr),
+#ifdef ACCESSIBILITY
+      mDocAccessible(nullptr),
+#endif  // ACCESSIBILITY
+      mCurrentEventFrame(nullptr),
+      mMouseLocation(NS_UNCONSTRAINEDSIZE, NS_UNCONSTRAINEDSIZE),
+      mLastResolutionChangeOrigin(ResolutionChangeOrigin::Apz),
+      mPaintCount(0),
+      mAPZFocusSequenceNumber(0),
+      mCanvasBackgroundColor(NS_RGBA(0, 0, 0, 0)),
+      mActiveSuppressDisplayport(0),
+      mPresShellId(++sNextPresShellId),
+      mFontSizeInflationEmPerLine(0),
+      mFontSizeInflationMinTwips(0),
+      mFontSizeInflationLineThreshold(0),
+      mSelectionFlags(nsISelectionDisplay::DISPLAY_TEXT |
+                      nsISelectionDisplay::DISPLAY_IMAGES),
+      mChangeNestCount(0),
+      mRenderingStateFlags(RenderingStateFlags::None),
+      mInFlush(false),
+      mCaretEnabled(false),
+      mNeedLayoutFlush(true),
+      mNeedStyleFlush(true),
+      mNeedThrottledAnimationFlush(true),
+      mVisualViewportSizeSet(false),
+      mDidInitialize(false),
+      mIsDestroying(false),
+      mIsReflowing(false),
+      mIsObservingDocument(false),
+      mForbiddenToFlush(false),
+      mIsDocumentGone(false),
+      mHaveShutDown(false),
+      mPaintingSuppressed(false),
+      mLastRootReflowHadUnconstrainedBSize(false),
+      mShouldUnsuppressPainting(false),
+      mIgnoreFrameDestruction(false),
+      mIsActive(true),
+      mIsInActiveTab(true),
+      mFrozen(false),
+      mIsFirstPaint(true),
+      mObservesMutationsForPrint(false),
+      mWasLastReflowInterrupted(false),
+      mObservingStyleFlushes(false),
+      mObservingLayoutFlushes(false),
+      mResizeEventPending(false),
+      mFontSizeInflationForceEnabled(false),
+      mFontSizeInflationDisabledInMasterProcess(false),
+      mFontSizeInflationEnabled(false),
+      mIsNeverPainting(false),
+      mResolutionUpdated(false),
+      mResolutionUpdatedByApz(false),
+      mUnderHiddenEmbedderElement(false),
+      mDocumentLoading(false),
+      mNoDelayedMouseEvents(false),
+      mNoDelayedKeyEvents(false),
+      mApproximateFrameVisibilityVisited(false),
+      mHasCSSBackgroundColor(true),
+      mIsLastChromeOnlyEscapeKeyConsumed(false),
+      mHasReceivedPaintMessage(false),
+      mIsLastKeyDownCanceled(false),
+      mHasHandledUserInput(false),
+      mForceDispatchKeyPressEventsForNonPrintableKeys(false),
+      mForceUseLegacyKeyCodeAndCharCodeValues(false),
+      mInitializedWithKeyPressEventDispatchingBlacklist(false),
+      mForceUseLegacyNonPrimaryDispatch(false),
+      mInitializedWithClickEventDispatchingBlacklist(false),
+      mMouseLocationWasSetBySynthesizedMouseEventForTests(false),
+      mHasTriedFastUnsuppress(false),
+      mProcessingReflowCommands(false),
+      mPendingDidDoReflow(false) {
+  MOZ_LOG(gLog, LogLevel::Debug, ("PresShell::PresShell this=%p", this));
+  MOZ_ASSERT(aDocument);
+
+#ifdef MOZ_REFLOW_PERF
+  mReflowCountMgr = MakeUnique<ReflowCountMgr>();
+  mReflowCountMgr->SetPresContext(mPresContext);
+  mReflowCountMgr->SetPresShell(this);
+#endif
+  mLastOSWake = mLoadBegin = TimeStamp::Now();
+}
+
+NS_INTERFACE_TABLE_HEAD(PresShell)
+  NS_INTERFACE_TABLE_BEGIN
+    // In most cases, PresShell should be treated as concrete class, but need to
+    // QI for weak reference.  Therefore, the case needed by do_QueryReferent()
+    // should be tested first.
+    NS_INTERFACE_TABLE_ENTRY(PresShell, PresShell)
+    NS_INTERFACE_TABLE_ENTRY(PresShell, nsIDocumentObserver)
+    NS_INTERFACE_TABLE_ENTRY(PresShell, nsISelectionController)
+    NS_INTERFACE_TABLE_ENTRY(PresShell, nsISelectionDisplay)
+    NS_INTERFACE_TABLE_ENTRY(PresShell, nsIObserver)
+    NS_INTERFACE_TABLE_ENTRY(PresShell, nsISupportsWeakReference)
+    NS_INTERFACE_TABLE_ENTRY(PresShell, nsIMutationObserver)
+    NS_INTERFACE_TABLE_ENTRY_AMBIGUOUS(PresShell, nsISupports, nsIObserver)
+  NS_INTERFACE_TABLE_END
+  NS_INTERFACE_TABLE_TO_MAP_SEGUE
+NS_INTERFACE_MAP_END
+
+NS_IMPL_ADDREF(PresShell)
+NS_IMPL_RELEASE(PresShell)
+
+PresShell::~PresShell() {
+  MOZ_RELEASE_ASSERT(!mForbiddenToFlush,
+                     "Flag should only be set temporarily, while doing things "
+                     "that shouldn't cause destruction");
+  MOZ_LOG(gLog, LogLevel::Debug, ("PresShell::~PresShell this=%p", this));
+
+  if (!mHaveShutDown) {
+    MOZ_ASSERT_UNREACHABLE("Someone did not call PresShell::Destroy()");
+    Destroy();
+  }
+
+  NS_ASSERTION(mCurrentEventContentStack.Count() == 0,
+               "Huh, event content left on the stack in pres shell dtor!");
+  NS_ASSERTION(mFirstCallbackEventRequest == nullptr &&
+                   mLastCallbackEventRequest == nullptr,
+               "post-reflow queues not empty.  This means we're leaking");
+
+  MOZ_ASSERT(!mAllocatedPointers || mAllocatedPointers->IsEmpty(),
+             "Some pres arena objects were not freed");
+
+  mFrameManager = nullptr;
+  mFrameConstructor = nullptr;
+
+  mCurrentEventContent = nullptr;
+}
+
+/**
+ * Initialize the presentation shell. Create view manager and style
+ * manager.
+ * Note this can't be merged into our constructor because caret initialization
+ * calls AddRef() on us.
+ */
+void PresShell::Init(nsPresContext* aPresContext, nsViewManager* aViewManager) {
+  MOZ_ASSERT(mDocument);
+  MOZ_ASSERT(aPresContext);
+  MOZ_ASSERT(aViewManager);
+  MOZ_ASSERT(!mViewManager, "already initialized");
+
+  mViewManager = aViewManager;
+
+  // mDocument is now set.  It might have a display document whose "need layout/
+  // style" flush flags are not set, but ours will be set.  To keep these
+  // consistent, call the flag setting functions to propagate those flags up
+  // to the display document.
+  SetNeedLayoutFlush();
+  SetNeedStyleFlush();
+
+  // Create our frame constructor.
+  mFrameConstructor = MakeUnique<nsCSSFrameConstructor>(mDocument, this);
+
+  mFrameManager = mFrameConstructor.get();
+
+  // The document viewer owns both view manager and pres shell.
+  mViewManager->SetPresShell(this);
+
+  // Bind the context to the presentation shell.
+  // FYI: We cannot initialize mPresContext in the constructor because we
+  //      cannot call AttachPresShell() in it and once we initialize
+  //      mPresContext, other objects may refer refresh driver or restyle
+  //      manager via mPresContext and that causes hitting MOZ_ASSERT in some
+  //      places.  Therefore, we should initialize mPresContext here with
+  //      const_cast hack since we want to guarantee that mPresContext lives
+  //      as long as the PresShell.
+  const_cast<RefPtr<nsPresContext>&>(mPresContext) = aPresContext;
+  mPresContext->AttachPresShell(this);
+
+  mPresContext->InitFontCache();
+
+  // FIXME(emilio, bug 1544185): Some Android code somehow depends on the shell
+  // being eagerly registered as a style flush observer. This shouldn't be
+  // needed otherwise.
+  EnsureStyleFlush();
+
+  // Add the preference style sheet.
+  UpdatePreferenceStyles();
+
+  bool accessibleCaretEnabled =
+      AccessibleCaretEnabled(mDocument->GetDocShell());
+  if (accessibleCaretEnabled) {
+    // Need to happen before nsFrameSelection has been set up.
+    mAccessibleCaretEventHub = new AccessibleCaretEventHub(this);
+  }
+
+  mSelection = new nsFrameSelection(this, nullptr, accessibleCaretEnabled);
+
+  // Important: this has to happen after the selection has been set up
+#ifdef SHOW_CARET
+  // make the caret
+  mCaret = new nsCaret();
+  mCaret->Init(this);
+  mOriginalCaret = mCaret;
+
+  // SetCaretEnabled(true);       // make it show in browser windows
+#endif
+  // set up selection to be displayed in document
+  // Don't enable selection for print media
+  nsPresContext::nsPresContextType type = mPresContext->Type();
+  if (type != nsPresContext::eContext_PrintPreview &&
+      type != nsPresContext::eContext_Print) {
+    SetDisplaySelection(nsISelectionController::SELECTION_DISABLED);
+  }
+
+  if (gMaxRCProcessingTime == -1) {
+    gMaxRCProcessingTime =
+        Preferences::GetInt("layout.reflow.timeslice", NS_MAX_REFLOW_TIME);
+  }
+
+  if (nsStyleSheetService* ss = nsStyleSheetService::GetInstance()) {
+    ss->RegisterPresShell(this);
+  }
+
+  {
+    nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
+    if (os) {
+      os->AddObserver(this, "memory-pressure", false);
+      os->AddObserver(this, NS_WIDGET_WAKE_OBSERVER_TOPIC, false);
+      if (XRE_IsParentProcess() && !sProcessInteractable) {
+        os->AddObserver(this, "sessionstore-one-or-no-tab-restored", false);
+      }
+      os->AddObserver(this, "font-info-updated", false);
+      os->AddObserver(this, "internal-look-and-feel-changed", false);
+    }
+  }
+
+#ifdef MOZ_REFLOW_PERF
+  if (mReflowCountMgr) {
+    bool paintFrameCounts =
+        Preferences::GetBool("layout.reflow.showframecounts");
+
+    bool dumpFrameCounts =
+        Preferences::GetBool("layout.reflow.dumpframecounts");
+
+    bool dumpFrameByFrameCounts =
+        Preferences::GetBool("layout.reflow.dumpframebyframecounts");
+
+    mReflowCountMgr->SetDumpFrameCounts(dumpFrameCounts);
+    mReflowCountMgr->SetDumpFrameByFrameCounts(dumpFrameByFrameCounts);
+    mReflowCountMgr->SetPaintFrameCounts(paintFrameCounts);
+  }
+#endif
+
+  if (mDocument->HasAnimationController()) {
+    SMILAnimationController* animCtrl = mDocument->GetAnimationController();
+    animCtrl->NotifyRefreshDriverCreated(GetPresContext()->RefreshDriver());
+  }
+
+  for (DocumentTimeline* timeline : mDocument->Timelines()) {
+    timeline->NotifyRefreshDriverCreated(GetPresContext()->RefreshDriver());
+  }
+
+  // Get our activeness from the docShell.
+  ActivenessMaybeChanged();
+
+  // Setup our font inflation preferences.
+  mFontSizeInflationEmPerLine = StaticPrefs::font_size_inflation_emPerLine();
+  mFontSizeInflationMinTwips = StaticPrefs::font_size_inflation_minTwips();
+  mFontSizeInflationLineThreshold =
+      StaticPrefs::font_size_inflation_lineThreshold();
+  mFontSizeInflationForceEnabled =
+      StaticPrefs::font_size_inflation_forceEnabled();
+  mFontSizeInflationDisabledInMasterProcess =
+      StaticPrefs::font_size_inflation_disabledInMasterProcess();
+  // We'll compute the font size inflation state in Initialize(), when we know
+  // the document type.
+
+  mTouchManager.Init(this, mDocument);
+
+  if (mPresContext->IsRootContentDocumentCrossProcess()) {
+    mZoomConstraintsClient = new ZoomConstraintsClient();
+    mZoomConstraintsClient->Init(this, mDocument);
+
+    // We call this to create mMobileViewportManager, if it is needed.
+    MaybeRecreateMobileViewportManager(false);
+  }
+
+  if (nsCOMPtr<nsIDocShell> docShell = mPresContext->GetDocShell()) {
+    BrowsingContext* bc = docShell->GetBrowsingContext();
+    bool embedderFrameIsHidden = true;
+    if (Element* embedderElement = bc->GetEmbedderElement()) {
+      if (auto embedderFrame = embedderElement->GetPrimaryFrame()) {
+        embedderFrameIsHidden = !embedderFrame->StyleVisibility()->IsVisible();
+      }
+    }
+
+    if (BrowsingContext* parent = bc->GetParent()) {
+      if (nsCOMPtr<nsIDocShell> parentDocShell = parent->GetDocShell()) {
+        if (PresShell* parentPresShell = parentDocShell->GetPresShell()) {
+          mUnderHiddenEmbedderElement =
+              parentPresShell->IsUnderHiddenEmbedderElement() ||
+              embedderFrameIsHidden;
+        }
+      }
+    }
+  }
+}
+
+enum TextPerfLogType { eLog_reflow, eLog_loaddone, eLog_totals };
+
+static void LogTextPerfStats(gfxTextPerfMetrics* aTextPerf,
+                             PresShell* aPresShell,
+                             const gfxTextPerfMetrics::TextCounts& aCounts,
+                             float aTime, TextPerfLogType aLogType,
+                             const char* aURL) {
+  LogModule* tpLog = gfxPlatform::GetLog(eGfxLog_textperf);
+
+  // ignore XUL contexts unless at debug level
+  mozilla::LogLevel logLevel = LogLevel::Warning;
+  if (aCounts.numContentTextRuns == 0) {
+    logLevel = LogLevel::Debug;
+  }
+
+  if (!MOZ_LOG_TEST(tpLog, logLevel)) {
+    return;
+  }
+
+  char prefix[256];
+
+  switch (aLogType) {
+    case eLog_reflow:
+      SprintfLiteral(prefix, "(textperf-reflow) %p time-ms: %7.0f", aPresShell,
+                     aTime);
+      break;
+    case eLog_loaddone:
+      SprintfLiteral(prefix, "(textperf-loaddone) %p time-ms: %7.0f",
+                     aPresShell, aTime);
+      break;
+    default:
+      MOZ_ASSERT(aLogType == eLog_totals, "unknown textperf log type");
+      SprintfLiteral(prefix, "(textperf-totals) %p", aPresShell);
+  }
+
+  double hitRatio = 0.0;
+  uint32_t lookups = aCounts.wordCacheHit + aCounts.wordCacheMiss;
+  if (lookups) {
+    hitRatio = double(aCounts.wordCacheHit) / double(lookups);
+  }
+
+  if (aLogType == eLog_loaddone) {
+    MOZ_LOG(
+        tpLog, logLevel,
+        ("%s reflow: %d chars: %d "
+         "[%s] "
+         "content-textruns: %d chrome-textruns: %d "
+         "max-textrun-len: %d "
+         "word-cache-lookups: %d word-cache-hit-ratio: %4.3f "
+         "word-cache-space: %d word-cache-long: %d "
+         "pref-fallbacks: %d system-fallbacks: %d "
+         "textruns-const: %d textruns-destr: %d "
+         "generic-lookups: %d "
+         "cumulative-textruns-destr: %d\n",
+         prefix, aTextPerf->reflowCount, aCounts.numChars, (aURL ? aURL : ""),
+         aCounts.numContentTextRuns, aCounts.numChromeTextRuns,
+         aCounts.maxTextRunLen, lookups, hitRatio, aCounts.wordCacheSpaceRules,
+         aCounts.wordCacheLong, aCounts.fallbackPrefs, aCounts.fallbackSystem,
+         aCounts.textrunConst, aCounts.textrunDestr, aCounts.genericLookups,
+         aTextPerf->cumulative.textrunDestr));
+  } else {
+    MOZ_LOG(
+        tpLog, logLevel,
+        ("%s reflow: %d chars: %d "
+         "content-textruns: %d chrome-textruns: %d "
+         "max-textrun-len: %d "
+         "word-cache-lookups: %d word-cache-hit-ratio: %4.3f "
+         "word-cache-space: %d word-cache-long: %d "
+         "pref-fallbacks: %d system-fallbacks: %d "
+         "textruns-const: %d textruns-destr: %d "
+         "generic-lookups: %d "
+         "cumulative-textruns-destr: %d\n",
+         prefix, aTextPerf->reflowCount, aCounts.numChars,
+         aCounts.numContentTextRuns, aCounts.numChromeTextRuns,
+         aCounts.maxTextRunLen, lookups, hitRatio, aCounts.wordCacheSpaceRules,
+         aCounts.wordCacheLong, aCounts.fallbackPrefs, aCounts.fallbackSystem,
+         aCounts.textrunConst, aCounts.textrunDestr, aCounts.genericLookups,
+         aTextPerf->cumulative.textrunDestr));
+  }
+}
+
+bool PresShell::InRDMPane() {
+  if (Document* doc = GetDocument()) {
+    if (BrowsingContext* bc = doc->GetBrowsingContext()) {
+      return bc->InRDMPane();
+    }
+  }
+  return false;
+}
+
+#if defined(MOZ_WIDGET_ANDROID)
+void PresShell::MaybeNotifyShowDynamicToolbar() {
+  const DynamicToolbarState dynToolbarState = GetDynamicToolbarState();
+  if ((dynToolbarState == DynamicToolbarState::Collapsed ||
+       dynToolbarState == DynamicToolbarState::InTransition)) {
+    MOZ_ASSERT(mPresContext &&
+               mPresContext->IsRootContentDocumentCrossProcess());
+    if (BrowserChild* browserChild = BrowserChild::GetFrom(this)) {
+      browserChild->SendShowDynamicToolbar();
+    }
+  }
+}
+#endif  // defined(MOZ_WIDGET_ANDROID)
+
+void PresShell::Destroy() {
+  // Do not add code before this line please!
+  if (mHaveShutDown) {
+    return;
+  }
+
+  NS_ASSERTION(!nsContentUtils::IsSafeToRunScript(),
+               "destroy called on presshell while scripts not blocked");
+
+  [[maybe_unused]] nsIURI* uri = mDocument->GetDocumentURI();
+  AUTO_PROFILER_LABEL_DYNAMIC_NSCSTRING_RELEVANT_FOR_JS(
+      "Layout tree destruction", LAYOUT_Destroy,
+      uri ? uri->GetSpecOrDefault() : "N/A"_ns);
+
+  // Try to determine if the page is the user had a meaningful opportunity to
+  // zoom this page. This is not 100% accurate but should be "good enough" for
+  // telemetry purposes.
+  auto isUserZoomablePage = [&]() -> bool {
+    if (mIsFirstPaint) {
+      // Page was never painted, so it wasn't zoomable by the user. We get a
+      // handful of these "transient" presShells.
+      return false;
+    }
+    if (!mPresContext->IsRootContentDocumentCrossProcess()) {
+      // Not a root content document, so APZ doesn't support zooming it.
+      return false;
+    }
+    if (InRDMPane()) {
+      // Responsive design mode is a special case that we want to ignore here.
+      return false;
+    }
+    if (mDocument && mDocument->IsInitialDocument()) {
+      // Ignore initial about:blank page loads
+      return false;
+    }
+    if (XRE_IsContentProcess() &&
+        IsExtensionRemoteType(ContentChild::GetSingleton()->GetRemoteType())) {
+      // Also omit presShells from the extension process because they sometimes
+      // can't be zoomed by the user.
+      return false;
+    }
+    // Otherwise assume the page is user-zoomable.
+    return true;
+  };
+  if (isUserZoomablePage()) {
+    Telemetry::Accumulate(Telemetry::APZ_ZOOM_ACTIVITY,
+                          IsResolutionUpdatedByApz());
+  }
+
+  // dump out cumulative text perf metrics
+  gfxTextPerfMetrics* tp;
+  if (mPresContext && (tp = mPresContext->GetTextPerfMetrics())) {
+    tp->Accumulate();
+    if (tp->cumulative.numChars > 0) {
+      LogTextPerfStats(tp, this, tp->cumulative, 0.0, eLog_totals, nullptr);
+    }
+  }
+  if (mPresContext) {
+    if (gfxUserFontSet* fs = mPresContext->GetUserFontSet()) {
+      uint32_t fontCount;
+      uint64_t fontSize;
+      fs->GetLoadStatistics(fontCount, fontSize);
+      Telemetry::Accumulate(Telemetry::WEBFONT_PER_PAGE, fontCount);
+      Telemetry::Accumulate(Telemetry::WEBFONT_SIZE_PER_PAGE,
+                            uint32_t(fontSize / 1024));
+    } else {
+      Telemetry::Accumulate(Telemetry::WEBFONT_PER_PAGE, 0);
+      Telemetry::Accumulate(Telemetry::WEBFONT_SIZE_PER_PAGE, 0);
+    }
+  }
+
+#ifdef MOZ_REFLOW_PERF
+  DumpReflows();
+  mReflowCountMgr = nullptr;
+#endif
+
+  if (mZoomConstraintsClient) {
+    mZoomConstraintsClient->Destroy();
+    mZoomConstraintsClient = nullptr;
+  }
+  if (mMobileViewportManager) {
+    mMobileViewportManager->Destroy();
+    mMobileViewportManager = nullptr;
+    mMVMContext = nullptr;
+  }
+
+#ifdef ACCESSIBILITY
+  if (mDocAccessible) {
+#  ifdef DEBUG
+    if (a11y::logging::IsEnabled(a11y::logging::eDocDestroy))
+      a11y::logging::DocDestroy("presshell destroyed", mDocument);
+#  endif
+
+    mDocAccessible->Shutdown();
+    mDocAccessible = nullptr;
+  }
+#endif  // ACCESSIBILITY
+
+  MaybeReleaseCapturingContent();
+
+  EventHandler::OnPresShellDestroy(mDocument);
+
+  if (mContentToScrollTo) {
+    mContentToScrollTo->RemoveProperty(nsGkAtoms::scrolling);
+    mContentToScrollTo = nullptr;
+  }
+
+  if (mPresContext) {
+    // We need to notify the destroying the nsPresContext to ESM for
+    // suppressing to use from ESM.
+    mPresContext->EventStateManager()->NotifyDestroyPresContext(mPresContext);
+  }
+
+  if (nsStyleSheetService* ss = nsStyleSheetService::GetInstance()) {
+    ss->UnregisterPresShell(this);
+  }
+
+  {
+    nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
+    if (os) {
+      os->RemoveObserver(this, "memory-pressure");
+      os->RemoveObserver(this, NS_WIDGET_WAKE_OBSERVER_TOPIC);
+      if (XRE_IsParentProcess()) {
+        os->RemoveObserver(this, "sessionstore-one-or-no-tab-restored");
+      }
+      os->RemoveObserver(this, "font-info-updated");
+      os->RemoveObserver(this, "internal-look-and-feel-changed");
+    }
+  }
+
+  // If our paint suppression timer is still active, kill it.
+  CancelPaintSuppressionTimer();
+
+  // Same for our reflow continuation timer
+  if (mReflowContinueTimer) {
+    mReflowContinueTimer->Cancel();
+    mReflowContinueTimer = nullptr;
+  }
+
+  mSynthMouseMoveEvent.Revoke();
+
+  mUpdateApproximateFrameVisibilityEvent.Revoke();
+
+  ClearApproximatelyVisibleFramesList(Some(OnNonvisible::DiscardImages));
+
+  if (mCaret) {
+    mCaret->Terminate();
+    mCaret = nullptr;
+  }
+
+  mFocusedFrameSelection = nullptr;
+
+  if (mSelection) {
+    RefPtr<nsFrameSelection> frameSelection = mSelection;
+    frameSelection->DisconnectFromPresShell();
+  }
+
+  // release our pref style sheet, if we have one still
+  //
+  // TODO(emilio): Should we move the preference sheet tracking to the Document?
+  RemovePreferenceStyles();
+
+  mIsDestroying = true;
+
+  // We can't release all the event content in
+  // mCurrentEventContentStack here since there might be code on the
+  // stack that will release the event content too. Double release
+  // bad!
+
+  // The frames will be torn down, so remove them from the current
+  // event frame stack (since they'd be dangling references if we'd
+  // leave them in) and null out the mCurrentEventFrame pointer as
+  // well.
+
+  mCurrentEventFrame = nullptr;
+
+  int32_t i, count = mCurrentEventFrameStack.Length();
+  for (i = 0; i < count; i++) {
+    mCurrentEventFrameStack[i] = nullptr;
+  }
+
+  mFramesToDirty.Clear();
+  mPendingScrollAnchorSelection.Clear();
+  mPendingScrollAnchorAdjustment.Clear();
+  mPendingScrollResnap.Clear();
+
+  if (mViewManager) {
+    // Clear the view manager's weak pointer back to |this| in case it
+    // was leaked.
+    mViewManager->SetPresShell(nullptr);
+    mViewManager = nullptr;
+  }
+
+  nsRefreshDriver* rd = GetPresContext()->RefreshDriver();
+
+  // This shell must be removed from the document before the frame
+  // hierarchy is torn down to avoid finding deleted frames through
+  // this presshell while the frames are being torn down
+  if (mDocument) {
+    NS_ASSERTION(mDocument->GetPresShell() == this, "Wrong shell?");
+    mDocument->ClearServoRestyleRoot();
+    mDocument->DeletePresShell();
+
+    if (mDocument->HasAnimationController()) {
+      mDocument->GetAnimationController()->NotifyRefreshDriverDestroying(rd);
+    }
+    for (DocumentTimeline* timeline : mDocument->Timelines()) {
+      timeline->NotifyRefreshDriverDestroying(rd);
+    }
+  }
+
+  if (mPresContext) {
+    rd->CancelPendingAnimationEvents(mPresContext->AnimationEventDispatcher());
+  }
+
+  // Revoke any pending events.  We need to do this and cancel pending reflows
+  // before we destroy the frame manager, since apparently frame destruction
+  // sometimes spins the event queue when plug-ins are involved(!).
+  // XXXmats is this still needed now that plugins are gone?
+  StopObservingRefreshDriver();
+
+  if (rd->GetPresContext() == GetPresContext()) {
+    rd->RevokeViewManagerFlush();
+    rd->ClearHasScheduleFlush();
+  }
+
+  CancelAllPendingReflows();
+  CancelPostedReflowCallbacks();
+
+  // Destroy the frame manager. This will destroy the frame hierarchy
+  mFrameConstructor->WillDestroyFrameTree();
+
+  NS_WARNING_ASSERTION(!mAutoWeakFrames && mWeakFrames.IsEmpty(),
+                       "Weak frames alive after destroying FrameManager");
+  while (mAutoWeakFrames) {
+    mAutoWeakFrames->Clear(this);
+  }
+  const nsTArray<WeakFrame*> weakFrames = ToArray(mWeakFrames);
+  for (WeakFrame* weakFrame : weakFrames) {
+    weakFrame->Clear(this);
+  }
+
+  // Terminate AccessibleCaretEventHub after tearing down the frame tree so that
+  // we don't need to remove caret element's frame in
+  // AccessibleCaret::RemoveCaretElement().
+  if (mAccessibleCaretEventHub) {
+    mAccessibleCaretEventHub->Terminate();
+    mAccessibleCaretEventHub = nullptr;
+  }
+
+  if (mPresContext) {
+    // We hold a reference to the pres context, and it holds a weak link back
+    // to us. To avoid the pres context having a dangling reference, set its
+    // pres shell to nullptr
+    mPresContext->DetachPresShell();
+  }
+
+  mHaveShutDown = true;
+
+  mTouchManager.Destroy();
+}
+
+void PresShell::StopObservingRefreshDriver() {
+  nsRefreshDriver* rd = mPresContext->RefreshDriver();
+  if (mResizeEventPending) {
+    rd->RemoveResizeEventFlushObserver(this);
+  }
+  if (mObservingLayoutFlushes) {
+    rd->RemoveLayoutFlushObserver(this);
+  }
+  if (mObservingStyleFlushes) {
+    rd->RemoveStyleFlushObserver(this);
+  }
+}
+
+void PresShell::StartObservingRefreshDriver() {
+  nsRefreshDriver* rd = mPresContext->RefreshDriver();
+  if (mResizeEventPending) {
+    rd->AddResizeEventFlushObserver(this);
+  }
+  if (mObservingLayoutFlushes) {
+    rd->AddLayoutFlushObserver(this);
+  }
+  if (mObservingStyleFlushes) {
+    rd->AddStyleFlushObserver(this);
+  }
+}
+
+nsRefreshDriver* PresShell::GetRefreshDriver() const {
+  return mPresContext ? mPresContext->RefreshDriver() : nullptr;
+}
+
+void PresShell::SetAuthorStyleDisabled(bool aStyleDisabled) {
+  if (aStyleDisabled != StyleSet()->GetAuthorStyleDisabled()) {
+    StyleSet()->SetAuthorStyleDisabled(aStyleDisabled);
+    mDocument->ApplicableStylesChanged();
+
+    nsCOMPtr<nsIObserverService> observerService =
+        mozilla::services::GetObserverService();
+    if (observerService) {
+      observerService->NotifyObservers(
+          ToSupports(mDocument), "author-style-disabled-changed", nullptr);
+    }
+  }
+}
+
+bool PresShell::GetAuthorStyleDisabled() const {
+  return StyleSet()->GetAuthorStyleDisabled();
+}
+
+void PresShell::UpdatePreferenceStyles() {
+  if (!mDocument) {
+    return;
+  }
+
+  // If the document doesn't have a window there's no need to notify
+  // its presshell about changes to preferences since the document is
+  // in a state where it doesn't matter any more (see
+  // nsDocumentViewer::Close()).
+  if (!mDocument->GetWindow()) {
+    return;
+  }
+
+  // Documents in chrome shells do not have any preference style rules applied.
+  if (mDocument->IsInChromeDocShell()) {
+    return;
+  }
+
+  PreferenceSheet::EnsureInitialized();
+  auto* cache = GlobalStyleSheetCache::Singleton();
+
+  RefPtr<StyleSheet> newPrefSheet =
+      PreferenceSheet::ShouldUseChromePrefs(*mDocument)
+          ? cache->ChromePreferenceSheet()
+          : cache->ContentPreferenceSheet();
+
+  if (mPrefStyleSheet == newPrefSheet) {
+    return;
+  }
+
+  RemovePreferenceStyles();
+
+  // NOTE(emilio): This sheet is added as an agent sheet, because we don't want
+  // it to be modifiable from devtools and similar, see bugs 1239336 and
+  // 1436782. I think it conceptually should be a user sheet, and could be
+  // without too much trouble I'd think.
+  StyleSet()->AppendStyleSheet(*newPrefSheet);
+  mPrefStyleSheet = newPrefSheet;
+}
+
+void PresShell::RemovePreferenceStyles() {
+  if (mPrefStyleSheet) {
+    StyleSet()->RemoveStyleSheet(*mPrefStyleSheet);
+    mPrefStyleSheet = nullptr;
+  }
+}
+
+void PresShell::AddUserSheet(StyleSheet* aSheet) {
+  // Make sure this does what nsDocumentViewer::CreateStyleSet does wrt
+  // ordering. We want this new sheet to come after all the existing stylesheet
+  // service sheets (which are at the start), but before other user sheets; see
+  // nsIStyleSheetService.idl for the ordering.
+
+  nsStyleSheetService* sheetService = nsStyleSheetService::GetInstance();
+  nsTArray<RefPtr<StyleSheet>>& userSheets = *sheetService->UserStyleSheets();
+
+  // Search for the place to insert the new user sheet. Since all of the
+  // stylesheet service provided user sheets should be at the start of the style
+  // set's list, and aSheet should be at the end of userSheets. Given that, we
+  // can find the right place to insert the new sheet based on the length of
+  // userSheets.
+  MOZ_ASSERT(aSheet);
+  MOZ_ASSERT(userSheets.LastElement() == aSheet);
+
+  size_t index = userSheets.Length() - 1;
+
+  // Assert that all of userSheets (except for the last, new element) matches up
+  // with what's in the style set.
+  for (size_t i = 0; i < index; ++i) {
+    MOZ_ASSERT(StyleSet()->SheetAt(StyleOrigin::User, i) == userSheets[i]);
+  }
+
+  if (index == static_cast<size_t>(StyleSet()->SheetCount(StyleOrigin::User))) {
+    StyleSet()->AppendStyleSheet(*aSheet);
+  } else {
+    StyleSheet* ref = StyleSet()->SheetAt(StyleOrigin::User, index);
+    StyleSet()->InsertStyleSheetBefore(*aSheet, *ref);
+  }
+
+  mDocument->ApplicableStylesChanged();
+}
+
+void PresShell::AddAgentSheet(StyleSheet* aSheet) {
+  // Make sure this does what nsDocumentViewer::CreateStyleSet does
+  // wrt ordering.
+  StyleSet()->AppendStyleSheet(*aSheet);
+  mDocument->ApplicableStylesChanged();
+}
+
+void PresShell::AddAuthorSheet(StyleSheet* aSheet) {
+  // Document specific "additional" Author sheets should be stronger than the
+  // ones added with the StyleSheetService.
+  StyleSheet* firstAuthorSheet = mDocument->GetFirstAdditionalAuthorSheet();
+  if (firstAuthorSheet) {
+    StyleSet()->InsertStyleSheetBefore(*aSheet, *firstAuthorSheet);
+  } else {
+    StyleSet()->AppendStyleSheet(*aSheet);
+  }
+
+  mDocument->ApplicableStylesChanged();
+}
+
+bool PresShell::FixUpFocus() {
+  if (!StaticPrefs::dom_focus_fixup()) {
+    return false;
+  }
+  if (NS_WARN_IF(!mDocument)) {
+    return false;
+  }
+
+  nsIContent* currentFocus = mDocument->GetUnretargetedFocusedContent(
+      Document::IncludeChromeOnly::Yes);
+  if (!currentFocus) {
+    return false;
+  }
+
+  nsIFrame* f = currentFocus->GetPrimaryFrame();
+  if (f && f->IsFocusable()) {
+    return false;
+  }
+
+  if (currentFocus == mDocument->GetBody() ||
+      currentFocus == mDocument->GetRootElement()) {
+    return false;
+  }
+
+  RefPtr fm = nsFocusManager::GetFocusManager();
+  nsCOMPtr<nsPIDOMWindowOuter> window = mDocument->GetWindow();
+  if (NS_WARN_IF(!window)) {
+    return false;
+  }
+  fm->ClearFocus(window);
+  return true;
+}
+
+void PresShell::SelectionWillTakeFocus() {
+  if (mSelection) {
+    FrameSelectionWillTakeFocus(*mSelection);
+  }
+}
+
+void PresShell::SelectionWillLoseFocus() {
+  // Do nothing, the main selection is the default focused selection.
+}
+
+// Selection repainting code relies on selection offsets being properly
+// adjusted (see bug 1626291), so we need to wait until the DOM is finished
+// notifying.
+static void RepaintNormalSelectionWhenSafe(nsFrameSelection& aFrameSelection) {
+  if (nsContentUtils::IsSafeToRunScript()) {
+    aFrameSelection.RepaintSelection(SelectionType::eNormal);
+    return;
+  }
+
+  // Note that importantly we don't defer changing the DisplaySelection. That'd
+  // be potentially racy with other code that may change it.
+  nsContentUtils::AddScriptRunner(NS_NewRunnableFunction(
+      "RepaintNormalSelectionWhenSafe",
+      [sel = RefPtr<nsFrameSelection>(&aFrameSelection)] {
+        sel->RepaintSelection(SelectionType::eNormal);
+      }));
+}
+
+void PresShell::FrameSelectionWillLoseFocus(nsFrameSelection& aFrameSelection) {
+  if (mFocusedFrameSelection != &aFrameSelection) {
+    return;
+  }
+
+  // Do nothing, the main selection is the default focused selection.
+  if (&aFrameSelection == mSelection) {
+    return;
+  }
+
+  RefPtr<nsFrameSelection> old = std::move(mFocusedFrameSelection);
+  MOZ_ASSERT(!mFocusedFrameSelection);
+
+  if (old->GetDisplaySelection() != nsISelectionController::SELECTION_HIDDEN) {
+    old->SetDisplaySelection(nsISelectionController::SELECTION_HIDDEN);
+    RepaintNormalSelectionWhenSafe(*old);
+  }
+
+  if (mSelection) {
+    FrameSelectionWillTakeFocus(*mSelection);
+  }
+}
+
+void PresShell::FrameSelectionWillTakeFocus(nsFrameSelection& aFrameSelection) {
+  if (mFocusedFrameSelection == &aFrameSelection) {
+#ifdef XP_MACOSX
+    // FIXME: Mac needs to update the global selection cache, even if the
+    // document's focused selection doesn't change, and this is currently done
+    // from RepaintSelection. Maybe we should move part of the global selection
+    // handling here, or something of that sort, unclear.
+    RepaintNormalSelectionWhenSafe(aFrameSelection);
+#endif
+    return;
+  }
+
+  RefPtr<nsFrameSelection> old = std::move(mFocusedFrameSelection);
+  mFocusedFrameSelection = &aFrameSelection;
+
+  if (old &&
+      old->GetDisplaySelection() != nsISelectionController::SELECTION_HIDDEN) {
+    old->SetDisplaySelection(nsISelectionController::SELECTION_HIDDEN);
+    RepaintNormalSelectionWhenSafe(*old);
+  }
+
+  if (aFrameSelection.GetDisplaySelection() !=
+      nsISelectionController::SELECTION_ON) {
+    aFrameSelection.SetDisplaySelection(nsISelectionController::SELECTION_ON);
+    RepaintNormalSelectionWhenSafe(aFrameSelection);
+  }
+}
+
+NS_IMETHODIMP
+PresShell::SetDisplaySelection(int16_t aToggle) {
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  frameSelection->SetDisplaySelection(aToggle);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+PresShell::GetDisplaySelection(int16_t* aToggle) {
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  *aToggle = frameSelection->GetDisplaySelection();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+PresShell::GetSelectionFromScript(RawSelectionType aRawSelectionType,
+                                  Selection** aSelection) {
+  if (!aSelection || !mSelection) return NS_ERROR_NULL_POINTER;
+
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  RefPtr<Selection> selection =
+      frameSelection->GetSelection(ToSelectionType(aRawSelectionType));
+
+  if (!selection) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  selection.forget(aSelection);
+  return NS_OK;
+}
+
+Selection* PresShell::GetSelection(RawSelectionType aRawSelectionType) {
+  if (!mSelection) {
+    return nullptr;
+  }
+
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  return frameSelection->GetSelection(ToSelectionType(aRawSelectionType));
+}
+
+Selection* PresShell::GetCurrentSelection(SelectionType aSelectionType) {
+  if (!mSelection) {
+    return nullptr;
+  }
+
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  return frameSelection->GetSelection(aSelectionType);
+}
+
+nsFrameSelection* PresShell::GetLastFocusedFrameSelection() {
+  return mFocusedFrameSelection ? mFocusedFrameSelection : mSelection;
+}
+
+NS_IMETHODIMP
+PresShell::ScrollSelectionIntoView(RawSelectionType aRawSelectionType,
+                                   SelectionRegion aRegion, int16_t aFlags) {
+  if (!mSelection) return NS_ERROR_NULL_POINTER;
+
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  return frameSelection->ScrollSelectionIntoView(
+      ToSelectionType(aRawSelectionType), aRegion, aFlags);
+}
+
+NS_IMETHODIMP
+PresShell::RepaintSelection(RawSelectionType aRawSelectionType) {
+  if (!mSelection) {
+    return NS_ERROR_NULL_POINTER;
+  }
+
+  if (MOZ_UNLIKELY(mIsDestroying)) {
+    return NS_OK;
+  }
+
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  return frameSelection->RepaintSelection(ToSelectionType(aRawSelectionType));
+}
+
+// Make shell be a document observer
+void PresShell::BeginObservingDocument() {
+  if (mDocument && !mIsDestroying) {
+    mIsObservingDocument = true;
+    if (mIsDocumentGone) {
+      NS_WARNING(
+          "Adding a presshell that was disconnected from the document "
+          "as a document observer?  Sounds wrong...");
+      mIsDocumentGone = false;
+    }
+  }
+}
+
+// Make shell stop being a document observer
+void PresShell::EndObservingDocument() {
+  // XXXbz do we need to tell the frame constructor that the document
+  // is gone, perhaps?  Except for printing it's NOT gone, sometimes.
+  mIsDocumentGone = true;
+  mIsObservingDocument = false;
+}
+
+#ifdef DEBUG_kipp
+char* nsPresShell_ReflowStackPointerTop;
+#endif
+
+void PresShell::InitPaintSuppressionTimer() {
+  // Default to PAINTLOCK_EVENT_DELAY if we can't get the pref value.
+  Document* doc = mDocument->GetDisplayDocument()
+                      ? mDocument->GetDisplayDocument()
+                      : mDocument.get();
+  const bool inProcess = !doc->GetBrowsingContext() ||
+                         doc->GetBrowsingContext()->Top()->IsInProcess();
+  int32_t delay = inProcess
+                      ? StaticPrefs::nglayout_initialpaint_delay()
+                      : StaticPrefs::nglayout_initialpaint_delay_in_oopif();
+  mPaintSuppressionTimer->InitWithNamedFuncCallback(
+      [](nsITimer* aTimer, void* aPresShell) {
+        RefPtr<PresShell> self = static_cast<PresShell*>(aPresShell);
+        self->UnsuppressPainting();
+      },
+      this, delay, nsITimer::TYPE_ONE_SHOT,
+      "PresShell::sPaintSuppressionCallback");
+}
+
+nsresult PresShell::Initialize() {
+  if (mIsDestroying) {
+    return NS_OK;
+  }
+
+  if (!mDocument) {
+    // Nothing to do
+    return NS_OK;
+  }
+
+  MOZ_LOG(gLog, LogLevel::Debug, ("PresShell::Initialize this=%p", this));
+
+  NS_ASSERTION(!mDidInitialize, "Why are we being called?");
+
+  RefPtr<PresShell> kungFuDeathGrip(this);
+
+  RecomputeFontSizeInflationEnabled();
+  MOZ_DIAGNOSTIC_ASSERT(!mIsDestroying);
+
+  // Ensure the pres context doesn't think it has changed, since we haven't even
+  // started layout. This avoids spurious restyles / reflows afterwards.
+  //
+  // Note that this is very intentionally before setting mDidInitialize so it
+  // doesn't notify the document, or run media query change events.
+  mPresContext->FlushPendingMediaFeatureValuesChanged();
+  MOZ_DIAGNOSTIC_ASSERT(!mIsDestroying);
+
+  mDidInitialize = true;
+
+#ifdef DEBUG
+  if (VerifyReflowFlags::NoisyCommands & gVerifyReflowFlags) {
+    if (mDocument) {
+      nsIURI* uri = mDocument->GetDocumentURI();
+      if (uri) {
+        printf("*** PresShell::Initialize (this=%p, url='%s')\n", (void*)this,
+               uri->GetSpecOrDefault().get());
+      }
+    }
+  }
+#endif
+
+  // Get the root frame from the frame manager
+  // XXXbz it would be nice to move this somewhere else... like frame manager
+  // Init(), say.  But we need to make sure our views are all set up by the
+  // time we do this!
+  nsIFrame* rootFrame = mFrameConstructor->GetRootFrame();
+  NS_ASSERTION(!rootFrame, "How did that happen, exactly?");
+
+  if (!rootFrame) {
+    nsAutoScriptBlocker scriptBlocker;
+    rootFrame = mFrameConstructor->ConstructRootFrame();
+    mFrameConstructor->SetRootFrame(rootFrame);
+  }
+
+  NS_ENSURE_STATE(!mHaveShutDown);
+
+  if (!rootFrame) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  if (Element* root = mDocument->GetRootElement()) {
+    {
+      nsAutoCauseReflowNotifier reflowNotifier(this);
+      // Have the style sheet processor construct frame for the root
+      // content object down
+      mFrameConstructor->ContentInserted(
+          root, nsCSSFrameConstructor::InsertionKind::Sync);
+    }
+    // Something in mFrameConstructor->ContentInserted may have caused
+    // Destroy() to get called, bug 337586.  Or, nsAutoCauseReflowNotifier
+    // (which sets up a script blocker) going out of scope may have killed us
+    // too
+    NS_ENSURE_STATE(!mHaveShutDown);
+  }
+
+  mDocument->TriggerAutoFocus();
+
+  NS_ASSERTION(rootFrame, "How did that happen?");
+
+  // Note: when the frame was created above it had the NS_FRAME_IS_DIRTY bit
+  // set, but XBL processing could have caused a reflow which clears it.
+  if (MOZ_LIKELY(rootFrame->HasAnyStateBits(NS_FRAME_IS_DIRTY))) {
+    // Unset the DIRTY bits so that FrameNeedsReflow() will work right.
+    rootFrame->RemoveStateBits(NS_FRAME_IS_DIRTY | NS_FRAME_HAS_DIRTY_CHILDREN);
+    NS_ASSERTION(!mDirtyRoots.Contains(rootFrame),
+                 "Why is the root in mDirtyRoots already?");
+    FrameNeedsReflow(rootFrame, IntrinsicDirty::None, NS_FRAME_IS_DIRTY);
+    NS_ASSERTION(mDirtyRoots.Contains(rootFrame),
+                 "Should be in mDirtyRoots now");
+    NS_ASSERTION(mObservingLayoutFlushes, "Why no reflow scheduled?");
+  }
+
+  // Restore our root scroll position now if we're getting here after EndLoad
+  // got called, since this is our one chance to do it.  Note that we need not
+  // have reflowed for this to work; when the scrollframe is finally reflowed
+  // it'll pick up the position we store in it here.
+  if (!mDocumentLoading) {
+    RestoreRootScrollPosition();
+  }
+
+  // For printing, we just immediately unsuppress.
+  if (!mPresContext->IsPaginated()) {
+    // Kick off a one-shot timer based off our pref value.  When this timer
+    // fires, if painting is still locked down, then we will go ahead and
+    // trigger a full invalidate and allow painting to proceed normally.
+    mPaintingSuppressed = true;
+    // Don't suppress painting if the document isn't loading.
+    Document::ReadyState readyState = mDocument->GetReadyStateEnum();
+    if (readyState != Document::READYSTATE_COMPLETE) {
+      mPaintSuppressionTimer = NS_NewTimer();
+    }
+    if (!mPaintSuppressionTimer) {
+      mPaintingSuppressed = false;
+    } else {
+      // Initialize the timer.
+      mPaintSuppressionTimer->SetTarget(
+          mDocument->EventTargetFor(TaskCategory::Other));
+      InitPaintSuppressionTimer();
+      if (mHasTriedFastUnsuppress) {
+        // Someone tried to unsuppress painting before Initialize was called so
+        // unsuppress painting rather soon.
+        mHasTriedFastUnsuppress = false;
+        TryUnsuppressPaintingSoon();
+        MOZ_ASSERT(mHasTriedFastUnsuppress);
+      }
+    }
+  }
+
+  // If we get here and painting is not suppressed, we still want to run the
+  // unsuppression logic, so set mShouldUnsuppressPainting to true.
+  if (!mPaintingSuppressed) {
+    mShouldUnsuppressPainting = true;
+  }
+
+  return NS_OK;  // XXX this needs to be real. MMP
+}
+
+void PresShell::TryUnsuppressPaintingSoon() {
+  if (mHasTriedFastUnsuppress) {
+    return;
+  }
+  mHasTriedFastUnsuppress = true;
+
+  if (!mDidInitialize || !IsPaintingSuppressed() || !XRE_IsContentProcess()) {
+    return;
+  }
+
+  if (!mDocument->IsInitialDocument() &&
+      mDocument->DidHitCompleteSheetCache() &&
+      mPresContext->IsRootContentDocumentCrossProcess()) {
+    // Try to unsuppress faster on a top level page if it uses stylesheet
+    // cache, since that hints that many resources can be painted sooner than
+    // in a cold page load case.
+    NS_DispatchToCurrentThreadQueue(
+        NS_NewRunnableFunction("PresShell::TryUnsuppressPaintingSoon",
+                               [self = RefPtr{this}]() -> void {
+                                 if (self->IsPaintingSuppressed()) {
+                                   PROFILER_MARKER_UNTYPED(
+                                       "Fast paint unsuppression", GRAPHICS);
+                                   self->UnsuppressPainting();
+                                 }
+                               }),
+        EventQueuePriority::Control);
+  }
+}
+
+void PresShell::RefreshZoomConstraintsForScreenSizeChange() {
+  if (mZoomConstraintsClient) {
+    mZoomConstraintsClient->ScreenSizeChanged();
+  }
+}
+
+void PresShell::ResizeReflow(nscoord aWidth, nscoord aHeight,
+                             ResizeReflowOptions aOptions) {
+  if (mZoomConstraintsClient) {
+    // If we have a ZoomConstraintsClient and the available screen area
+    // changed, then we might need to disable double-tap-to-zoom, so notify
+    // the ZCC to update itself.
+    mZoomConstraintsClient->ScreenSizeChanged();
+  }
+  if (UsesMobileViewportSizing()) {
+    // If we are using mobile viewport sizing, request a reflow from the MVM.
+    // It can recompute the final CSS viewport and trigger a call to
+    // ResizeReflowIgnoreOverride if it changed. We don't force adjusting
+    // of resolution, because that is only necessary when we are destroying
+    // the MVM.
+    MOZ_ASSERT(mMobileViewportManager);
+    mMobileViewportManager->RequestReflow(false);
+    return;
+  }
+  ResizeReflowIgnoreOverride(aWidth, aHeight, aOptions);
+}
+
+bool PresShell::SimpleResizeReflow(nscoord aWidth, nscoord aHeight) {
+  MOZ_ASSERT(aWidth != NS_UNCONSTRAINEDSIZE);
+  MOZ_ASSERT(aHeight != NS_UNCONSTRAINEDSIZE);
+  nsSize oldSize = mPresContext->GetVisibleArea().Size();
+  mPresContext->SetVisibleArea(nsRect(0, 0, aWidth, aHeight));
+  nsIFrame* rootFrame = GetRootFrame();
+  if (!rootFrame) {
+    return false;
+  }
+  WritingMode wm = rootFrame->GetWritingMode();
+  bool isBSizeChanging =
+      wm.IsVertical() ? oldSize.width != aWidth : oldSize.height != aHeight;
+  if (isBSizeChanging) {
+    nsLayoutUtils::MarkIntrinsicISizesDirtyIfDependentOnBSize(rootFrame);
+  }
+  FrameNeedsReflow(rootFrame, IntrinsicDirty::None,
+                   NS_FRAME_HAS_DIRTY_CHILDREN);
+
+  if (mMobileViewportManager) {
+    mMobileViewportManager->UpdateSizesBeforeReflow();
+  }
+  return true;
+}
+
+void PresShell::AddResizeEventFlushObserverIfNeeded() {
+  if (!mIsDestroying && !mResizeEventPending &&
+      MOZ_LIKELY(!mDocument->GetBFCacheEntry())) {
+    mResizeEventPending = true;
+    mPresContext->RefreshDriver()->AddResizeEventFlushObserver(this);
+  }
+}
+
+bool PresShell::ResizeReflowIgnoreOverride(nscoord aWidth, nscoord aHeight,
+                                           ResizeReflowOptions aOptions) {
+  MOZ_ASSERT(!mIsReflowing, "Shouldn't be in reflow here!");
+
+  // Historically we never fired resize events if there was no root frame by the
+  // time this function got called.
+  const bool initialized = mDidInitialize;
+  RefPtr<PresShell> kungFuDeathGrip(this);
+
+  auto postResizeEventIfNeeded = [this, initialized]() {
+    if (initialized) {
+      AddResizeEventFlushObserverIfNeeded();
+    }
+  };
+
+  if (!(aOptions & ResizeReflowOptions::BSizeLimit)) {
+    nsSize oldSize = mPresContext->GetVisibleArea().Size();
+    if (oldSize == nsSize(aWidth, aHeight)) {
+      return false;
+    }
+
+    bool changed = SimpleResizeReflow(aWidth, aHeight);
+    postResizeEventIfNeeded();
+    return changed;
+  }
+
+  // Make sure that style is flushed before setting the pres context
+  // VisibleArea.
+  //
+  // Otherwise we may end up with bogus viewport units resolved against the
+  // unconstrained bsize, or restyling the whole document resolving viewport
+  // units against targetWidth, which may end up doing wasteful work.
+  mDocument->FlushPendingNotifications(FlushType::Frames);
+
+  nsIFrame* rootFrame = GetRootFrame();
+  if (mIsDestroying || !rootFrame) {
+    // If we don't have a root frame yet, that means we haven't had our initial
+    // reflow... If that's the case, and aWidth or aHeight is unconstrained,
+    // ignore them altogether.
+    if (aHeight == NS_UNCONSTRAINEDSIZE || aWidth == NS_UNCONSTRAINEDSIZE) {
+      // We can't do the work needed for SizeToContent without a root
+      // frame, and we want to return before setting the visible area.
+      return false;
+    }
+
+    mPresContext->SetVisibleArea(nsRect(0, 0, aWidth, aHeight));
+    // There isn't anything useful we can do if the initial reflow hasn't
+    // happened.
+    return true;
+  }
+
+  WritingMode wm = rootFrame->GetWritingMode();
+  MOZ_ASSERT((wm.IsVertical() ? aHeight : aWidth) != NS_UNCONSTRAINEDSIZE,
+             "unconstrained isize not allowed");
+
+  nscoord targetWidth = aWidth;
+  nscoord targetHeight = aHeight;
+  if (wm.IsVertical()) {
+    targetWidth = NS_UNCONSTRAINEDSIZE;
+  } else {
+    targetHeight = NS_UNCONSTRAINEDSIZE;
+  }
+
+  mPresContext->SetVisibleArea(nsRect(0, 0, targetWidth, targetHeight));
+  // XXX Do a full invalidate at the beginning so that invalidates along
+  // the way don't have region accumulation issues?
+
+  // For height:auto BSizes (i.e. layout-controlled), descendant
+  // intrinsic sizes can't depend on them. So the only other case is
+  // viewport-controlled BSizes which we handle here.
+  nsLayoutUtils::MarkIntrinsicISizesDirtyIfDependentOnBSize(rootFrame);
+
+  {
+    nsAutoCauseReflowNotifier crNotifier(this);
+    WillDoReflow();
+
+    // Kick off a top-down reflow
+    AUTO_LAYOUT_PHASE_ENTRY_POINT(GetPresContext(), Reflow);
+    nsViewManager::AutoDisableRefresh refreshBlocker(mViewManager);
+
+    mDirtyRoots.Remove(rootFrame);
+    DoReflow(rootFrame, true, nullptr);
+
+    const bool reflowAgain =
+        wm.IsVertical() ? mPresContext->GetVisibleArea().width > aWidth
+                        : mPresContext->GetVisibleArea().height > aHeight;
+
+    if (reflowAgain) {
+      mPresContext->SetVisibleArea(nsRect(0, 0, aWidth, aHeight));
+      DoReflow(rootFrame, true, nullptr);
+    }
+  }
+
+  // Now, we may have been destroyed by the destructor of
+  // `nsAutoCauseReflowNotifier`.
+
+  mPendingDidDoReflow = true;
+  DidDoReflow(true);
+
+  // the reflow above should've set our bsize if it was NS_UNCONSTRAINEDSIZE,
+  // and the isize shouldn't be NS_UNCONSTRAINEDSIZE anyway.
+  MOZ_DIAGNOSTIC_ASSERT(
+      mPresContext->GetVisibleArea().width != NS_UNCONSTRAINEDSIZE,
+      "width should not be NS_UNCONSTRAINEDSIZE after reflow");
+  MOZ_DIAGNOSTIC_ASSERT(
+      mPresContext->GetVisibleArea().height != NS_UNCONSTRAINEDSIZE,
+      "height should not be NS_UNCONSTRAINEDSIZE after reflow");
+
+  postResizeEventIfNeeded();
+  return true;
+}
+
+void PresShell::FireResizeEvent() {
+  if (mIsDocumentGone) {
+    return;
+  }
+
+  // If event handling is suppressed, repost the resize event to the refresh
+  // driver. The event is marked as delayed so that the refresh driver does not
+  // continue ticking.
+  if (mDocument->EventHandlingSuppressed()) {
+    if (MOZ_LIKELY(!mDocument->GetBFCacheEntry())) {
+      mDocument->SetHasDelayedRefreshEvent();
+      mPresContext->RefreshDriver()->AddResizeEventFlushObserver(
+          this, /* aDelayed = */ true);
+    }
+    return;
+  }
+
+  mResizeEventPending = false;
+  FireResizeEventSync();
+}
+
+void PresShell::FireResizeEventSync() {
+  if (mIsDocumentGone) {
+    return;
+  }
+
+  // Send resize event from here.
+  WidgetEvent event(true, mozilla::eResize);
+  nsEventStatus status = nsEventStatus_eIgnore;
+
+  if (RefPtr<nsPIDOMWindowOuter> window = mDocument->GetWindow()) {
+    EventDispatcher::Dispatch(window, mPresContext, &event, nullptr, &status);
+  }
+}
+
+static nsIContent* GetNativeAnonymousSubtreeRoot(nsIContent* aContent) {
+  if (!aContent) {
+    return nullptr;
+  }
+  return aContent->GetClosestNativeAnonymousSubtreeRoot();
+}
+
+void PresShell::NativeAnonymousContentRemoved(nsIContent* aAnonContent) {
+  MOZ_ASSERT(aAnonContent->IsRootOfNativeAnonymousSubtree());
+  if (nsIContent* root = GetNativeAnonymousSubtreeRoot(mCurrentEventContent)) {
+    if (aAnonContent == root) {
+      mCurrentEventContent = aAnonContent->GetFlattenedTreeParent();
+      mCurrentEventFrame = nullptr;
+    }
+  }
+
+  for (unsigned int i = 0; i < mCurrentEventContentStack.Length(); i++) {
+    nsIContent* anon =
+        GetNativeAnonymousSubtreeRoot(mCurrentEventContentStack.ElementAt(i));
+    if (aAnonContent == anon) {
+      mCurrentEventContentStack.ReplaceObjectAt(
+          aAnonContent->GetFlattenedTreeParent(), i);
+      mCurrentEventFrameStack[i] = nullptr;
+    }
+  }
+}
+
+void PresShell::SetIgnoreFrameDestruction(bool aIgnore) {
+  if (mDocument) {
+    // We need to tell the ImageLoader to drop all its references to frames
+    // because they're about to go away and it won't get notifications of that.
+    mDocument->StyleImageLoader()->ClearFrames(mPresContext);
+  }
+  mIgnoreFrameDestruction = aIgnore;
+}
+
+void PresShell::NotifyDestroyingFrame(nsIFrame* aFrame) {
+  // We must remove these from FrameLayerBuilder::DisplayItemData::mFrameList
+  // here, otherwise the DisplayItemData destructor will use the destroyed frame
+  // when it tries to remove it from the (array) value of this property.
+  aFrame->RemoveDisplayItemDataForDeletion();
+
+  if (!mIgnoreFrameDestruction) {
+    if (aFrame->HasImageRequest()) {
+      mDocument->StyleImageLoader()->DropRequestsForFrame(aFrame);
+    }
+
+    mFrameConstructor->NotifyDestroyingFrame(aFrame);
+
+    mDirtyRoots.Remove(aFrame);
+
+    // Remove frame properties
+    aFrame->RemoveAllProperties();
+
+    if (aFrame == mCurrentEventFrame) {
+      mCurrentEventContent = aFrame->GetContent();
+      mCurrentEventFrame = nullptr;
+    }
+
+    for (unsigned int i = 0; i < mCurrentEventFrameStack.Length(); i++) {
+      if (aFrame == mCurrentEventFrameStack.ElementAt(i)) {
+        // One of our stack frames was deleted.  Get its content so that when we
+        // pop it we can still get its new frame from its content
+        nsIContent* currentEventContent = aFrame->GetContent();
+        mCurrentEventContentStack.ReplaceObjectAt(currentEventContent, i);
+        mCurrentEventFrameStack[i] = nullptr;
+      }
+    }
+
+    mFramesToDirty.Remove(aFrame);
+
+    nsIScrollableFrame* scrollableFrame = do_QueryFrame(aFrame);
+    if (scrollableFrame) {
+      mPendingScrollAnchorSelection.Remove(scrollableFrame);
+      mPendingScrollAnchorAdjustment.Remove(scrollableFrame);
+      mPendingScrollResnap.Remove(scrollableFrame);
+    }
+
+    mContentVisibilityAutoFrames.Remove(aFrame);
+  }
+}
+
+already_AddRefed<nsCaret> PresShell::GetCaret() const {
+  RefPtr<nsCaret> caret = mCaret;
+  return caret.forget();
+}
+
+already_AddRefed<AccessibleCaretEventHub>
+PresShell::GetAccessibleCaretEventHub() const {
+  RefPtr<AccessibleCaretEventHub> eventHub = mAccessibleCaretEventHub;
+  return eventHub.forget();
+}
+
+void PresShell::SetCaret(nsCaret* aNewCaret) { mCaret = aNewCaret; }
+
+void PresShell::RestoreCaret() { mCaret = mOriginalCaret; }
+
+NS_IMETHODIMP PresShell::SetCaretEnabled(bool aInEnable) {
+  bool oldEnabled = mCaretEnabled;
+
+  mCaretEnabled = aInEnable;
+
+  if (mCaretEnabled != oldEnabled) {
+    MOZ_ASSERT(mCaret);
+    if (mCaret) {
+      mCaret->SetVisible(mCaretEnabled);
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP PresShell::SetCaretReadOnly(bool aReadOnly) {
+  if (mCaret) mCaret->SetCaretReadOnly(aReadOnly);
+  return NS_OK;
+}
+
+NS_IMETHODIMP PresShell::GetCaretEnabled(bool* aOutEnabled) {
+  NS_ENSURE_ARG_POINTER(aOutEnabled);
+  *aOutEnabled = mCaretEnabled;
+  return NS_OK;
+}
+
+NS_IMETHODIMP PresShell::SetCaretVisibilityDuringSelection(bool aVisibility) {
+  if (mCaret) mCaret->SetVisibilityDuringSelection(aVisibility);
+  return NS_OK;
+}
+
+NS_IMETHODIMP PresShell::GetCaretVisible(bool* aOutIsVisible) {
+  *aOutIsVisible = false;
+  if (mCaret) {
+    *aOutIsVisible = mCaret->IsVisible();
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP PresShell::SetSelectionFlags(int16_t aFlags) {
+  mSelectionFlags = aFlags;
+  return NS_OK;
+}
+
+NS_IMETHODIMP PresShell::GetSelectionFlags(int16_t* aFlags) {
+  if (!aFlags) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  *aFlags = mSelectionFlags;
+  return NS_OK;
+}
+
+// implementation of nsISelectionController
+
+NS_IMETHODIMP
+PresShell::PhysicalMove(int16_t aDirection, int16_t aAmount, bool aExtend) {
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  return frameSelection->PhysicalMove(aDirection, aAmount, aExtend);
+}
+
+NS_IMETHODIMP
+PresShell::CharacterMove(bool aForward, bool aExtend) {
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  return frameSelection->CharacterMove(aForward, aExtend);
+}
+
+NS_IMETHODIMP
+PresShell::WordMove(bool aForward, bool aExtend) {
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  nsresult result = frameSelection->WordMove(aForward, aExtend);
+  // if we can't go down/up any more we must then move caret completely to
+  // end/beginning respectively.
+  if (NS_FAILED(result)) result = CompleteMove(aForward, aExtend);
+  return result;
+}
+
+NS_IMETHODIMP
+PresShell::LineMove(bool aForward, bool aExtend) {
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  nsresult result = frameSelection->LineMove(aForward, aExtend);
+  // if we can't go down/up any more we must then move caret completely to
+  // end/beginning respectively.
+  if (NS_FAILED(result)) result = CompleteMove(aForward, aExtend);
+  return result;
+}
+
+NS_IMETHODIMP
+PresShell::IntraLineMove(bool aForward, bool aExtend) {
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  return frameSelection->IntraLineMove(aForward, aExtend);
+}
+
+NS_IMETHODIMP
+PresShell::PageMove(bool aForward, bool aExtend) {
+  nsIFrame* frame = nullptr;
+  if (!aExtend) {
+    frame = do_QueryFrame(GetScrollableFrameToScroll(VerticalScrollDirection));
+    // If there is no scrollable frame, get the frame to move caret instead.
+  }
+  if (!frame || frame->PresContext() != mPresContext) {
+    frame = mSelection->GetFrameToPageSelect();
+    if (!frame) {
+      return NS_OK;
+    }
+  }
+  // We may scroll parent scrollable element of current selection limiter.
+  // In such case, we don't want to scroll selection into view unless
+  // selection is changed.
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  return frameSelection->PageMove(
+      aForward, aExtend, frame, nsFrameSelection::SelectionIntoView::IfChanged);
+}
+
+NS_IMETHODIMP
+PresShell::ScrollPage(bool aForward) {
+  nsIScrollableFrame* scrollFrame =
+      GetScrollableFrameToScroll(VerticalScrollDirection);
+  ScrollMode scrollMode = apz::GetScrollModeForOrigin(ScrollOrigin::Pages);
+  if (scrollFrame) {
+    scrollFrame->ScrollBy(nsIntPoint(0, aForward ? 1 : -1), ScrollUnit::PAGES,
+                          scrollMode, nullptr,
+                          mozilla::ScrollOrigin::NotSpecified,
+                          nsIScrollableFrame::NOT_MOMENTUM,
+                          ScrollSnapFlags::IntendedDirection |
+                              ScrollSnapFlags::IntendedEndPosition);
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+PresShell::ScrollLine(bool aForward) {
+  nsIScrollableFrame* scrollFrame =
+      GetScrollableFrameToScroll(VerticalScrollDirection);
+  ScrollMode scrollMode = apz::GetScrollModeForOrigin(ScrollOrigin::Lines);
+  if (scrollFrame) {
+    nsRect scrollPort = scrollFrame->GetScrollPortRect();
+    nsSize lineSize = scrollFrame->GetLineScrollAmount();
+    int32_t lineCount = StaticPrefs::toolkit_scrollbox_verticalScrollDistance();
+    if (lineCount * lineSize.height > scrollPort.Height()) {
+      return ScrollPage(aForward);
+    }
+    scrollFrame->ScrollBy(
+        nsIntPoint(0, aForward ? lineCount : -lineCount), ScrollUnit::LINES,
+        scrollMode, nullptr, mozilla::ScrollOrigin::NotSpecified,
+        nsIScrollableFrame::NOT_MOMENTUM, ScrollSnapFlags::IntendedDirection);
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+PresShell::ScrollCharacter(bool aRight) {
+  nsIScrollableFrame* scrollFrame =
+      GetScrollableFrameToScroll(HorizontalScrollDirection);
+  ScrollMode scrollMode = apz::GetScrollModeForOrigin(ScrollOrigin::Lines);
+  if (scrollFrame) {
+    int32_t h = StaticPrefs::toolkit_scrollbox_horizontalScrollDistance();
+    scrollFrame->ScrollBy(
+        nsIntPoint(aRight ? h : -h, 0), ScrollUnit::LINES, scrollMode, nullptr,
+        mozilla::ScrollOrigin::NotSpecified, nsIScrollableFrame::NOT_MOMENTUM,
+        ScrollSnapFlags::IntendedDirection);
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+PresShell::CompleteScroll(bool aForward) {
+  nsIScrollableFrame* scrollFrame =
+      GetScrollableFrameToScroll(VerticalScrollDirection);
+  ScrollMode scrollMode = apz::GetScrollModeForOrigin(ScrollOrigin::Other);
+  if (scrollFrame) {
+    scrollFrame->ScrollBy(
+        nsIntPoint(0, aForward ? 1 : -1), ScrollUnit::WHOLE, scrollMode,
+        nullptr, mozilla::ScrollOrigin::NotSpecified,
+        nsIScrollableFrame::NOT_MOMENTUM, ScrollSnapFlags::IntendedEndPosition);
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+PresShell::CompleteMove(bool aForward, bool aExtend) {
+  // Beware! This may flush notifications via synchronous
+  // ScrollSelectionIntoView.
+  RefPtr<nsFrameSelection> frameSelection = mSelection;
+  nsIContent* limiter = frameSelection->GetAncestorLimiter();
+  nsIFrame* frame = limiter ? limiter->GetPrimaryFrame()
+                            : FrameConstructor()->GetRootElementFrame();
+  if (!frame) return NS_ERROR_FAILURE;
+  nsIFrame::CaretPosition pos = frame->GetExtremeCaretPosition(!aForward);
+
+  const nsFrameSelection::FocusMode focusMode =
+      aExtend ? nsFrameSelection::FocusMode::kExtendSelection
+              : nsFrameSelection::FocusMode::kCollapseToNewPoint;
+  frameSelection->HandleClick(
+      MOZ_KnownLive(pos.mResultContent) /* bug 1636889 */, pos.mContentOffset,
+      pos.mContentOffset, focusMode,
+      aForward ? CARET_ASSOCIATE_AFTER : CARET_ASSOCIATE_BEFORE);
+  if (limiter) {
+    // HandleClick resets ancestorLimiter, so set it again.
+    frameSelection->SetAncestorLimiter(limiter);
+  }
+
+  // After ScrollSelectionIntoView(), the pending notifications might be
+  // flushed and PresShell/PresContext/Frames may be dead. See bug 418470.
+  return ScrollSelectionIntoView(
+      nsISelectionController::SELECTION_NORMAL,
+      nsISelectionController::SELECTION_FOCUS_REGION,
+      nsISelectionController::SCROLL_SYNCHRONOUS |
+          nsISelectionController::SCROLL_FOR_CARET_MOVE);
+}
+
+// end implementations nsISelectionController
+
+nsIFrame* PresShell::GetRootScrollFrame() const {
+  nsIFrame* rootFrame = mFrameConstructor->GetRootFrame();
+  // Ensure root frame is a viewport frame
+  if (!rootFrame || !rootFrame->IsViewportFrame()) return nullptr;
+  nsIFrame* theFrame = rootFrame->PrincipalChildList().FirstChild();
+  if (!theFrame || !theFrame->IsScrollFrame()) return nullptr;
+  return theFrame;
+}
+
+nsIScrollableFrame* PresShell::GetRootScrollFrameAsScrollable() const {
+  nsIFrame* frame = GetRootScrollFrame();
+  if (!frame) return nullptr;
+  nsIScrollableFrame* scrollableFrame = do_QueryFrame(frame);
+  NS_ASSERTION(scrollableFrame,
+               "All scroll frames must implement nsIScrollableFrame");
+  return scrollableFrame;
+}
+
+nsPageSequenceFrame* PresShell::GetPageSequenceFrame() const {
+  return mFrameConstructor->GetPageSequenceFrame();
+}
+
+nsCanvasFrame* PresShell::GetCanvasFrame() const {
+  nsIFrame* frame = mFrameConstructor->GetDocElementContainingBlock();
+  return do_QueryFrame(frame);
+}
+
+void PresShell::RestoreRootScrollPosition() {
+  nsIScrollableFrame* scrollableFrame = GetRootScrollFrameAsScrollable();
+  if (scrollableFrame) {
+    scrollableFrame->ScrollToRestoredPosition();
+  }
+}
+
+void PresShell::MaybeReleaseCapturingContent() {
+  RefPtr<nsFrameSelection> frameSelection = FrameSelection();
+  if (frameSelection) {
+    frameSelection->SetDragState(false);
+  }
+  if (sCapturingContentInfo.mContent &&
+      sCapturingContentInfo.mContent->OwnerDoc() == mDocument) {
+    PresShell::ReleaseCapturingContent();
+  }
+}
+
+void PresShell::BeginLoad(Document* aDocument) {
+  mDocumentLoading = true;
+
+  gfxTextPerfMetrics* tp = nullptr;
+  if (mPresContext) {
+    tp = mPresContext->GetTextPerfMetrics();
+  }
+
+  bool shouldLog = MOZ_LOG_TEST(gLog, LogLevel::Debug);
+  if (shouldLog || tp) {
+    mLoadBegin = TimeStamp::Now();
+  }
+
+  if (shouldLog) {
+    nsIURI* uri = mDocument->GetDocumentURI();
+    MOZ_LOG(gLog, LogLevel::Debug,
+            ("(presshell) %p load begin [%s]\n", this,
+             uri ? uri->GetSpecOrDefault().get() : ""));
+  }
+}
+
+void PresShell::EndLoad(Document* aDocument) {
+  MOZ_ASSERT(aDocument == mDocument, "Wrong document");
+
+  RestoreRootScrollPosition();
+
+  mDocumentLoading = false;
+}
+
+bool PresShell::IsLayoutFlushObserver() {
+  return GetPresContext()->RefreshDriver()->IsLayoutFlushObserver(this);
+}
+
+void PresShell::LoadComplete() {
+  gfxTextPerfMetrics* tp = nullptr;
+  if (mPresContext) {
+    tp = mPresContext->GetTextPerfMetrics();
+  }
+
+  // log load
+  bool shouldLog = MOZ_LOG_TEST(gLog, LogLevel::Debug);
+  if (shouldLog || tp) {
+    TimeDuration loadTime = TimeStamp::Now() - mLoadBegin;
+    nsIURI* uri = mDocument->GetDocumentURI();
+    nsAutoCString spec;
+    if (uri) {
+      spec = uri->GetSpecOrDefault();
+    }
+    if (shouldLog) {
+      MOZ_LOG(gLog, LogLevel::Debug,
+              ("(presshell) %p load done time-ms: %9.2f [%s]\n", this,
+               loadTime.ToMilliseconds(), spec.get()));
+    }
+    if (tp) {
+      tp->Accumulate();
+      if (tp->cumulative.numChars > 0) {
+        LogTextPerfStats(tp, this, tp->cumulative, loadTime.ToMilliseconds(),
+                         eLog_loaddone, spec.get());
+      }
+    }
+  }
+}
+
+#ifdef DEBUG
+void PresShell::VerifyHasDirtyRootAncestor(nsIFrame* aFrame) {
+  // XXXbz due to bug 372769, can't actually assert anything here...
+  // XXX Since bug 372769 is now fixed, the assertion is being enabled in bug
+  //     1758104.
+#  if 0
+  // XXXbz shouldn't need this part; remove it once FrameNeedsReflow
+  // handles the root frame correctly.
+  if (!aFrame->GetParent()) {
+    return;
+  }
+
+  // Make sure that there is a reflow root ancestor of |aFrame| that's
+  // in mDirtyRoots already.
+  while (aFrame && aFrame->HasAnyStateBits(NS_FRAME_HAS_DIRTY_CHILDREN)) {
+    if ((aFrame->HasAnyStateBits(NS_FRAME_REFLOW_ROOT |
+                                 NS_FRAME_DYNAMIC_REFLOW_ROOT) ||
+         !aFrame->GetParent()) &&
+        mDirtyRoots.Contains(aFrame)) {
+      return;
+    }
+
+    aFrame = aFrame->GetParent();
+  }
+
+  MOZ_ASSERT_UNREACHABLE(
+      "Frame has dirty bits set but isn't scheduled to be "
+      "reflowed?");
+#  endif
+}
+#endif
+
+void PresShell::PostPendingScrollAnchorSelection(
+    mozilla::layout::ScrollAnchorContainer* aContainer) {
+  mPendingScrollAnchorSelection.Insert(aContainer->ScrollableFrame());
+}
+
+void PresShell::FlushPendingScrollAnchorSelections() {
+  for (nsIScrollableFrame* scroll : mPendingScrollAnchorSelection) {
+    scroll->Anchor()->SelectAnchor();
+  }
+  mPendingScrollAnchorSelection.Clear();
+}
+
+void PresShell::PostPendingScrollAnchorAdjustment(
+    ScrollAnchorContainer* aContainer) {
+  mPendingScrollAnchorAdjustment.Insert(aContainer->ScrollableFrame());
+}
+
+void PresShell::FlushPendingScrollAnchorAdjustments() {
+  for (nsIScrollableFrame* scroll : mPendingScrollAnchorAdjustment) {
+    scroll->Anchor()->ApplyAdjustments();
+  }
+  mPendingScrollAnchorAdjustment.Clear();
+}
+
+void PresShell::PostPendingScrollResnap(nsIScrollableFrame* aScrollableFrame) {
+  mPendingScrollResnap.Insert(aScrollableFrame);
+}
+
+void PresShell::FlushPendingScrollResnap() {
+  for (nsIScrollableFrame* scrollableFrame : mPendingScrollResnap) {
+    scrollableFrame->TryResnap();
+  }
+  mPendingScrollResnap.Clear();
+}
+
+void PresShell::FrameNeedsReflow(nsIFrame* aFrame,
+                                 IntrinsicDirty aIntrinsicDirty,
+                                 nsFrameState aBitToAdd,
+                                 ReflowRootHandling aRootHandling) {
+  MOZ_ASSERT(aBitToAdd == NS_FRAME_IS_DIRTY ||
+                 aBitToAdd == NS_FRAME_HAS_DIRTY_CHILDREN || !aBitToAdd,
+             "Unexpected bits being added");
+
+  // FIXME bug 478135
+  NS_ASSERTION(
+      aIntrinsicDirty != IntrinsicDirty::FrameAncestorsAndDescendants ||
+          aBitToAdd != NS_FRAME_HAS_DIRTY_CHILDREN,
+      "bits don't correspond to style change reason");
+
+  // FIXME bug 457400
+  NS_ASSERTION(!mIsReflowing, "can't mark frame dirty during reflow");
+
+  // If we've not yet done the initial reflow, then don't bother
+  // enqueuing a reflow command yet.
+  if (!mDidInitialize) return;
+
+  // If we're already destroying, don't bother with this either.
+  if (mIsDestroying) return;
+
+#ifdef DEBUG
+  // printf("gShellCounter: %d\n", gShellCounter++);
+  if (mInVerifyReflow) return;
+
+  if (VerifyReflowFlags::NoisyCommands & gVerifyReflowFlags) {
+    printf("\nPresShell@%p: frame %p needs reflow\n", (void*)this,
+           (void*)aFrame);
+    if (VerifyReflowFlags::ReallyNoisyCommands & gVerifyReflowFlags) {
+      printf("Current content model:\n");
+      Element* rootElement = mDocument->GetRootElement();
+      if (rootElement) {
+        rootElement->List(stdout, 0);
+      }
+    }
+  }
+#endif
+
+  AutoTArray<nsIFrame*, 4> subtrees;
+  subtrees.AppendElement(aFrame);
+
+  do {
+    nsIFrame* subtreeRoot = subtrees.PopLastElement();
+
+    // Grab |wasDirty| now so we can go ahead and update the bits on
+    // subtreeRoot.
+    bool wasDirty = subtreeRoot->IsSubtreeDirty();
+    subtreeRoot->AddStateBits(aBitToAdd);
+
+    // Determine whether we need to keep looking for the next ancestor
+    // reflow root if subtreeRoot itself is a reflow root.
+    bool targetNeedsReflowFromParent;
+    switch (aRootHandling) {
+      case ReflowRootHandling::PositionOrSizeChange:
+        targetNeedsReflowFromParent = true;
+        break;
+      case ReflowRootHandling::NoPositionOrSizeChange:
+        targetNeedsReflowFromParent = false;
+        break;
+      case ReflowRootHandling::InferFromBitToAdd:
+        targetNeedsReflowFromParent = (aBitToAdd == NS_FRAME_IS_DIRTY);
+        break;
+    }
+
+    auto FrameIsReflowRoot = [](const nsIFrame* aFrame) {
+      return aFrame->HasAnyStateBits(NS_FRAME_REFLOW_ROOT |
+                                     NS_FRAME_DYNAMIC_REFLOW_ROOT);
+    };
+
+    auto CanStopClearingAncestorIntrinsics = [&](const nsIFrame* aFrame) {
+      return FrameIsReflowRoot(aFrame) && aFrame != subtreeRoot;
+    };
+
+    auto IsReflowBoundary = [&](const nsIFrame* aFrame) {
+      return FrameIsReflowRoot(aFrame) &&
+             (aFrame != subtreeRoot || !targetNeedsReflowFromParent);
+    };
+
+    // Mark the intrinsic widths as dirty on the frame, all of its ancestors,
+    // and all of its descendants, if needed:
+
+    if (aIntrinsicDirty != IntrinsicDirty::None) {
+      // Mark argument and all ancestors dirty. (Unless we hit a reflow root
+      // that should contain the reflow.
+      for (nsIFrame* a = subtreeRoot;
+           a && !CanStopClearingAncestorIntrinsics(a); a = a->GetParent()) {
+        a->MarkIntrinsicISizesDirty();
+        if (a->IsAbsolutelyPositioned()) {
+          // If we get here, 'a' is abspos, so its subtree's intrinsic sizing
+          // has no effect on its ancestors' intrinsic sizing. So, don't loop
+          // upwards any further.
+          break;
+        }
+      }
+    }
+
+    const bool frameAncestorAndDescendantISizesDirty =
+        (aIntrinsicDirty == IntrinsicDirty::FrameAncestorsAndDescendants);
+    const bool dirty = (aBitToAdd == NS_FRAME_IS_DIRTY);
+    if (frameAncestorAndDescendantISizesDirty || dirty) {
+      // Mark all descendants dirty (using an nsTArray stack rather than
+      // recursion).
+      // Note that ReflowInput::InitResizeFlags has some similar
+      // code; see comments there for how and why it differs.
+      AutoTArray<nsIFrame*, 32> stack;
+      stack.AppendElement(subtreeRoot);
+
+      do {
+        nsIFrame* f = stack.PopLastElement();
+
+        if (frameAncestorAndDescendantISizesDirty && f->IsPlaceholderFrame()) {
+          // Call `GetOutOfFlowFrame` directly because we can get here from
+          // frame destruction and the placeholder might be already torn down.
+          if (nsIFrame* oof =
+                  static_cast<nsPlaceholderFrame*>(f)->GetOutOfFlowFrame()) {
+            if (!nsLayoutUtils::IsProperAncestorFrame(subtreeRoot, oof)) {
+              // We have another distinct subtree we need to mark.
+              subtrees.AppendElement(oof);
+            }
+          }
+        }
+
+        for (const auto& childList : f->ChildLists()) {
+          for (nsIFrame* kid : childList.mList) {
+            if (frameAncestorAndDescendantISizesDirty) {
+              kid->MarkIntrinsicISizesDirty();
+            }
+            if (dirty) {
+              kid->AddStateBits(NS_FRAME_IS_DIRTY);
+            }
+            stack.AppendElement(kid);
+          }
+        }
+      } while (stack.Length() != 0);
+    }
+
+    // Skip setting dirty bits up the tree if we weren't given a bit to add.
+    if (!aBitToAdd) {
+      continue;
+    }
+
+    // Set NS_FRAME_HAS_DIRTY_CHILDREN bits (via nsIFrame::ChildIsDirty)
+    // up the tree until we reach either a frame that's already dirty or
+    // a reflow root.
+    nsIFrame* f = subtreeRoot;
+    for (;;) {
+      if (IsReflowBoundary(f) || !f->GetParent()) {
+        // we've hit a reflow root or the root frame
+        if (!wasDirty) {
+          mDirtyRoots.Add(f);
+          SetNeedLayoutFlush();
+        }
+#ifdef DEBUG
+        else {
+          VerifyHasDirtyRootAncestor(f);
+        }
+#endif
+
+        break;
+      }
+
+      nsIFrame* child = f;
+      f = f->GetParent();
+      wasDirty = f->IsSubtreeDirty();
+      f->ChildIsDirty(child);
+      NS_ASSERTION(f->HasAnyStateBits(NS_FRAME_HAS_DIRTY_CHILDREN),
+                   "ChildIsDirty didn't do its job");
+      if (wasDirty) {
+        // This frame was already marked dirty.
+#ifdef DEBUG
+        VerifyHasDirtyRootAncestor(f);
+#endif
+        break;
+      }
+    }
+  } while (subtrees.Length() != 0);
+
+  MaybeScheduleReflow();
+}
+
+void PresShell::FrameNeedsToContinueReflow(nsIFrame* aFrame) {
+  NS_ASSERTION(mIsReflowing, "Must be in reflow when marking path dirty.");
+  MOZ_ASSERT(mCurrentReflowRoot, "Must have a current reflow root here");
+  NS_ASSERTION(
+      aFrame == mCurrentReflowRoot ||
+          nsLayoutUtils::IsProperAncestorFrame(mCurrentReflowRoot, aFrame),
+      "Frame passed in is not the descendant of mCurrentReflowRoot");
+  NS_ASSERTION(aFrame->HasAnyStateBits(NS_FRAME_IN_REFLOW),
+               "Frame passed in not in reflow?");
+
+  mFramesToDirty.Insert(aFrame);
+}
+
+already_AddRefed<nsIContent> PresShell::GetContentForScrolling() const {
+  if (nsCOMPtr<nsIContent> focused = GetFocusedContentInOurWindow()) {
+    return focused.forget();
+  }
+  return GetSelectedContentForScrolling();
+}
+
+already_AddRefed<nsIContent> PresShell::GetSelectedContentForScrolling() const {
+  nsCOMPtr<nsIContent> selectedContent;
+  if (mSelection) {
+    Selection* domSelection = mSelection->GetSelection(SelectionType::eNormal);
+    if (domSelection) {
+      selectedContent =
+          nsIContent::FromNodeOrNull(domSelection->GetFocusNode());
+    }
+  }
+  return selectedContent.forget();
+}
+
+nsIScrollableFrame* PresShell::GetScrollableFrameToScrollForContent(
+    nsIContent* aContent, ScrollDirections aDirections) {
+  nsIScrollableFrame* scrollFrame = nullptr;
+  if (aContent) {
+    nsIFrame* startFrame = aContent->GetPrimaryFrame();
+    if (startFrame) {
+      scrollFrame = startFrame->GetScrollTargetFrame();
+      if (scrollFrame) {
+        startFrame = scrollFrame->GetScrolledFrame();
+      }
+      scrollFrame = nsLayoutUtils::GetNearestScrollableFrameForDirection(
+          startFrame, aDirections);
+    }
+  }
+  if (!scrollFrame) {
+    scrollFrame = GetRootScrollFrameAsScrollable();
+    if (!scrollFrame || !scrollFrame->GetScrolledFrame()) {
+      return nullptr;
+    }
+    scrollFrame = nsLayoutUtils::GetNearestScrollableFrameForDirection(
+        scrollFrame->GetScrolledFrame(), aDirections);
+  }
+  return scrollFrame;
+}
+
+nsIScrollableFrame* PresShell::GetScrollableFrameToScroll(
+    ScrollDirections aDirections) {
+  nsCOMPtr<nsIContent> content = GetContentForScrolling();
+  return GetScrollableFrameToScrollForContent(content.get(), aDirections);
+}
+
+void PresShell::CancelAllPendingReflows() {
+  mDirtyRoots.Clear();
+
+  if (mObservingLayoutFlushes) {
+    GetPresContext()->RefreshDriver()->RemoveLayoutFlushObserver(this);
+    mObservingLayoutFlushes = false;
+  }
+
+  ASSERT_REFLOW_SCHEDULED_STATE();
+}
+
+static bool DestroyFramesAndStyleDataFor(
+    Element* aElement, nsPresContext& aPresContext,
+    RestyleManager::IncludeRoot aIncludeRoot) {
+  bool didReconstruct =
+      aPresContext.FrameConstructor()->DestroyFramesFor(aElement);
+  RestyleManager::ClearServoDataFromSubtree(aElement, aIncludeRoot);
+  return didReconstruct;
+}
+
+void PresShell::SlotAssignmentWillChange(Element& aElement,
+                                         HTMLSlotElement* aOldSlot,
+                                         HTMLSlotElement* aNewSlot) {
+  MOZ_ASSERT(aOldSlot != aNewSlot);
+
+  if (MOZ_UNLIKELY(!mDidInitialize)) {
+    return;
+  }
+
+  // If the old slot is about to become empty and show fallback, let layout know
+  // that it needs to do work.
+  if (aOldSlot && aOldSlot->AssignedNodes().Length() == 1 &&
+      aOldSlot->HasChildren()) {
+    DestroyFramesForAndRestyle(aOldSlot);
+  }
+
+  // Ensure the new element starts off clean.
+  DestroyFramesAndStyleDataFor(&aElement, *mPresContext,
+                               RestyleManager::IncludeRoot::Yes);
+
+  if (aNewSlot) {
+    // If the new slot will stop showing fallback content, we need to reframe it
+    // altogether.
+    if (aNewSlot->AssignedNodes().IsEmpty() && aNewSlot->HasChildren()) {
+      DestroyFramesForAndRestyle(aNewSlot);
+      // Otherwise we just care about the element, but we need to ensure that
+      // something takes care of traversing to the relevant slot, if needed.
+    } else if (aNewSlot->HasServoData() &&
+               !Servo_Element_IsDisplayNone(aNewSlot)) {
+      // Set the reframe bits...
+      aNewSlot->NoteDescendantsNeedFramesForServo();
+      aElement.SetFlags(NODE_NEEDS_FRAME);
+      // Now the style dirty bits. Note that we can't just do
+      // aElement.NoteDirtyForServo(), because the new slot is not setup yet.
+      aNewSlot->SetHasDirtyDescendantsForServo();
+      aNewSlot->NoteDirtySubtreeForServo();
+    }
+  }
+}
+
+#ifdef DEBUG
+static void AssertNoFramesOrStyleDataInDescendants(Element& aElement) {
+  for (nsINode* node : ShadowIncludingTreeIterator(aElement)) {
+    nsIContent* c = nsIContent::FromNode(node);
+    if (c == &aElement) {
+      continue;
+    }
+    // FIXME(emilio): The <area> check is needed because of bug 135040.
+    MOZ_ASSERT(!c->GetPrimaryFrame() || c->IsHTMLElement(nsGkAtoms::area));
+    MOZ_ASSERT(!c->IsElement() || !c->AsElement()->HasServoData());
+  }
+}
+#endif
+
+void PresShell::DestroyFramesForAndRestyle(Element* aElement) {
+#ifdef DEBUG
+  auto postCondition = MakeScopeExit([&]() {
+    MOZ_ASSERT(!aElement->GetPrimaryFrame());
+    AssertNoFramesOrStyleDataInDescendants(*aElement);
+  });
+#endif
+
+  MOZ_ASSERT(aElement);
+  if (!aElement->HasServoData()) {
+    // Nothing to do here, the element already is out of the flat tree or is not
+    // styled.
+    return;
+  }
+
+  // Mark ourselves as not safe to flush while we're doing frame destruction.
+  nsAutoScriptBlocker scriptBlocker;
+  ++mChangeNestCount;
+
+  const bool didReconstruct = FrameConstructor()->DestroyFramesFor(aElement);
+  // Clear the style data from all the flattened tree descendants, but _not_
+  // from us, since otherwise we wouldn't see the reframe.
+  RestyleManager::ClearServoDataFromSubtree(aElement,
+                                            RestyleManager::IncludeRoot::No);
+  auto changeHint =
+      didReconstruct ? nsChangeHint(0) : nsChangeHint_ReconstructFrame;
+  mPresContext->RestyleManager()->PostRestyleEvent(
+      aElement, RestyleHint::RestyleSubtree(), changeHint);
+
+  --mChangeNestCount;
+}
+
+void PresShell::ShadowRootWillBeAttached(Element& aElement) {
+#ifdef DEBUG
+  auto postCondition = MakeScopeExit(
+      [&]() { AssertNoFramesOrStyleDataInDescendants(aElement); });
+#endif
+
+  if (!aElement.HasServoData()) {
+    // Nothing to do here, the element already is out of the flat tree or is not
+    // styled.
+    return;
+  }
+
+  if (!aElement.HasChildren()) {
+    // The element has no children, just avoid the work.
+    return;
+  }
+
+  // Mark ourselves as not safe to flush while we're doing frame destruction.
+  nsAutoScriptBlocker scriptBlocker;
+  ++mChangeNestCount;
+
+  // NOTE(emilio): We use FlattenedChildIterator intentionally here (rather than
+  // StyleChildrenIterator), since we don't want to remove ::before / ::after
+  // content.
+  FlattenedChildIterator iter(&aElement);
+  nsCSSFrameConstructor* fc = FrameConstructor();
+  for (nsIContent* c = iter.GetNextChild(); c; c = iter.GetNextChild()) {
+    fc->DestroyFramesFor(c);
+    if (c->IsElement()) {
+      RestyleManager::ClearServoDataFromSubtree(c->AsElement());
+    }
+  }
+
+#ifdef ACCESSIBILITY
+  if (nsAccessibilityService* accService = GetAccService()) {
+    accService->ScheduleAccessibilitySubtreeUpdate(this, &aElement);
+  }
+#endif
+
+  --mChangeNestCount;
+}
+
+void PresShell::PostRecreateFramesFor(Element* aElement) {
+  if (MOZ_UNLIKELY(!mDidInitialize)) {
+    // Nothing to do here. In fact, if we proceed and aElement is the root, we
+    // will crash.
+    return;
+  }
+
+  mPresContext->RestyleManager()->PostRestyleEvent(
+      aElement, RestyleHint{0}, nsChangeHint_ReconstructFrame);
+}
+
+void PresShell::RestyleForAnimation(Element* aElement, RestyleHint aHint) {
+  // Now that we no longer have separate non-animation and animation
+  // restyles, this method having a distinct identity is less important,
+  // but it still seems useful to offer as a "more public" API and as a
+  // chokepoint for these restyles to go through.
+  mPresContext->RestyleManager()->PostRestyleEvent(aElement, aHint,
+                                                   nsChangeHint(0));
+}
+
+void PresShell::SetForwardingContainer(const WeakPtr<nsDocShell>& aContainer) {
+  mForwardingContainer = aContainer;
+}
+
+void PresShell::ClearFrameRefs(nsIFrame* aFrame) {
+  mPresContext->EventStateManager()->ClearFrameRefs(aFrame);
+
+  AutoWeakFrame* weakFrame = mAutoWeakFrames;
+  while (weakFrame) {
+    AutoWeakFrame* prev = weakFrame->GetPreviousWeakFrame();
+    if (weakFrame->GetFrame() == aFrame) {
+      // This removes weakFrame from mAutoWeakFrames.
+      weakFrame->Clear(this);
+    }
+    weakFrame = prev;
+  }
+
+  AutoTArray<WeakFrame*, 4> toRemove;
+  for (WeakFrame* weakFrame : mWeakFrames) {
+    if (weakFrame->GetFrame() == aFrame) {
+      toRemove.AppendElement(weakFrame);
+    }
+  }
+  for (WeakFrame* weakFrame : toRemove) {
+    weakFrame->Clear(this);
+  }
+}
+
+already_AddRefed<gfxContext> PresShell::CreateReferenceRenderingContext() {
+  nsDeviceContext* devCtx = mPresContext->DeviceContext();
+  RefPtr<gfxContext> rc;
+  if (mPresContext->IsScreen()) {
+    rc = gfxContext::CreateOrNull(
+        gfxPlatform::GetPlatform()->ScreenReferenceDrawTarget().get());
+  } else {
+    // We assume the devCtx has positive width and height for this call.
+    // However, width and height, may be outside of the reasonable range
+    // so rc may still be null.
+    rc = devCtx->CreateReferenceRenderingContext();
+  }
+
+  return rc ? rc.forget() : nullptr;
+}
+
+// https://html.spec.whatwg.org/#scroll-to-the-fragment-identifier
+nsresult PresShell::GoToAnchor(const nsAString& aAnchorName, bool aScroll,
+                               ScrollFlags aAdditionalScrollFlags) {
+  if (!mDocument) {
+    return NS_ERROR_FAILURE;
+  }
+
+  const Element* root = mDocument->GetRootElement();
+  if (root && root->IsSVGElement(nsGkAtoms::svg)) {
+    // We need to execute this even if there is an empty anchor name
+    // so that any existing SVG fragment identifier effect is removed
+    if (SVGFragmentIdentifier::ProcessFragmentIdentifier(mDocument,
+                                                         aAnchorName)) {
+      return NS_OK;
+    }
+  }
+
+  // Hold a reference to the ESM in case event dispatch tears us down.
+  RefPtr<EventStateManager> esm = mPresContext->EventStateManager();
+
+  // 1. If there is no indicated part of the document, set the Document's target
+  //    element to null.
+  //
+  // FIXME(emilio): Per spec empty fragment string should take the same
+  // code-path as "top"!
+  if (aAnchorName.IsEmpty()) {
+    NS_ASSERTION(!aScroll, "can't scroll to empty anchor name");
+    esm->SetContentState(nullptr, ElementState::URLTARGET);
+    return NS_OK;
+  }
+
+  // 2. If the indicated part of the document is the top of the document,
+  // then:
+  // (handled below when `target` is null, and anchor is `top`)
+
+  // 3.1. Let target be element that is the indicated part of the document.
+  //
+  // https://html.spec.whatwg.org/#target-element
+  // https://html.spec.whatwg.org/#find-a-potential-indicated-element
+  RefPtr<Element> target = [&]() -> Element* {
+    // 1. If there is an element in the document tree that has an ID equal to
+    //    fragment, then return the first such element in tree order.
+    if (Element* el = mDocument->GetElementById(aAnchorName)) {
+      return el;
+    }
+
+    // 2. If there is an a element in the document tree that has a name
+    // attribute whose value is equal to fragment, then return the first such
+    // element in tree order.
+    //
+    // FIXME(emilio): Why the different code-paths for HTML and non-HTML docs?
+    if (mDocument->IsHTMLDocument()) {
+      nsCOMPtr<nsINodeList> list = mDocument->GetElementsByName(aAnchorName);
+      // Loop through the named nodes looking for the first anchor
+      uint32_t length = list->Length();
+      for (uint32_t i = 0; i < length; i++) {
+        nsIContent* node = list->Item(i);
+        if (node->IsHTMLElement(nsGkAtoms::a)) {
+          return node->AsElement();
+        }
+      }
+    } else {
+      constexpr auto nameSpace = u"http://www.w3.org/1999/xhtml"_ns;
+      // Get the list of anchor elements
+      nsCOMPtr<nsINodeList> list =
+          mDocument->GetElementsByTagNameNS(nameSpace, u"a"_ns);
+      // Loop through the anchors looking for the first one with the given name.
+      for (uint32_t i = 0; true; i++) {
+        nsIContent* node = list->Item(i);
+        if (!node) {  // End of list
+          break;
+        }
+
+        // Compare the name attribute
+        if (node->IsElement() &&
+            node->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::name,
+                                           aAnchorName, eCaseMatters)) {
+          return node->AsElement();
+        }
+      }
+    }
+
+    // 3. Return null.
+    return nullptr;
+  }();
+
+  // 1. If there is no indicated part of the document, set the Document's
+  //    target element to null.
+  // 2.1. Set the Document's target element to null.
+  // 3.2. Set the Document's target element to target.
+  esm->SetContentState(target, ElementState::URLTARGET);
+
+  // TODO: Spec probably needs a section to account for this.
+  if (nsIScrollableFrame* rootScroll = GetRootScrollFrameAsScrollable()) {
+    if (rootScroll->DidHistoryRestore()) {
+      // Scroll position restored from history trumps scrolling to anchor.
+      aScroll = false;
+      rootScroll->ClearDidHistoryRestore();
+    }
+  }
+
+  if (target) {
+    if (aScroll) {
+      // 3.3. TODO: Run the ancestor details revealing algorithm on target.
+      // 3.4. Scroll target into view, with behavior set to "auto", block set to
+      //      "start", and inline set to "nearest".
+      // FIXME(emilio): Not all callers pass ScrollSmoothAuto (but we use auto
+      // smooth scroll for `top` regardless below, so maybe they should!).
+      ScrollingInteractionContext scrollToAnchorContext(true);
+      MOZ_TRY(ScrollContentIntoView(
+          target, ScrollAxis(WhereToScroll::Start, WhenToScroll::Always),
+          ScrollAxis(),
+          ScrollFlags::AnchorScrollFlags | aAdditionalScrollFlags));
+
+      if (nsIScrollableFrame* rootScroll = GetRootScrollFrameAsScrollable()) {
+        mLastAnchorScrolledTo = target;
+        mLastAnchorScrollPositionY = rootScroll->GetScrollPosition().y;
+      }
+    }
+
+    {
+      // 3.6. Move the sequential focus navigation starting point to target.
+      //
+      // Move the caret to the anchor. That way tabbing will start from the new
+      // location.
+      //
+      // TODO(emilio): Do we want to do this even if aScroll is false?
+      //
+      // NOTE: Intentionally out of order for now with the focus steps, see
+      // https://github.com/whatwg/html/issues/7759
+      RefPtr<nsRange> jumpToRange = nsRange::Create(mDocument);
+      nsCOMPtr<nsIContent> nodeToSelect = target.get();
+      while (nodeToSelect->GetFirstChild()) {
+        nodeToSelect = nodeToSelect->GetFirstChild();
+      }
+      jumpToRange->SelectNodeContents(*nodeToSelect, IgnoreErrors());
+      if (RefPtr sel = mSelection->GetSelection(SelectionType::eNormal)) {
+        sel->RemoveAllRanges(IgnoreErrors());
+        sel->AddRangeAndSelectFramesAndNotifyListeners(*jumpToRange,
+                                                       IgnoreErrors());
+        if (!StaticPrefs::layout_selectanchor()) {
+          // Use a caret (collapsed selection) at the start of the anchor.
+          sel->CollapseToStart(IgnoreErrors());
+        }
+      }
+    }
+
+    // 3.5. Run the focusing steps for target, with the Document's viewport as
+    // the fallback target.
+    //
+    // Note that ScrollContentIntoView flushes, so we don't need to do that
+    // again here. We also don't need to scroll again either.
+    //
+    // We intentionally focus the target only when aScroll is true, we need to
+    // sort out if the spec needs to differentiate these cases. When aScroll is
+    // false we still clear the focus unconditionally, that's legacy behavior,
+    // maybe we shouldn't do it.
+    //
+    // TODO(emilio): Do we really want to clear the focus even if aScroll is
+    // false?
+    const bool shouldFocusTarget = [&] {
+      if (!aScroll) {
+        return false;
+      }
+      nsIFrame* targetFrame = target->GetPrimaryFrame();
+      return targetFrame && targetFrame->IsFocusable();
+    }();
+
+    if (shouldFocusTarget) {
+      FocusOptions options;
+      options.mPreventScroll = true;
+      target->Focus(options, CallerType::NonSystem, IgnoreErrors());
+    } else if (RefPtr<nsIFocusManager> fm = nsFocusManager::GetFocusManager()) {
+      if (nsPIDOMWindowOuter* win = mDocument->GetWindow()) {
+        // Now focus the document itself if focus is on an element within it.
+        nsCOMPtr<mozIDOMWindowProxy> focusedWindow;
+        fm->GetFocusedWindow(getter_AddRefs(focusedWindow));
+        if (SameCOMIdentity(win, focusedWindow)) {
+          fm->ClearFocus(focusedWindow);
+        }
+      }
+    }
+
+    // If the target is an animation element, activate the animation
+    if (nsCOMPtr<SVGAnimationElement> animationElement =
+            do_QueryInterface(target)) {
+      animationElement->ActivateByHyperlink();
+    }
+
+#ifdef ACCESSIBILITY
+    if (nsAccessibilityService* accService = GetAccService()) {
+      accService->NotifyOfAnchorJumpTo(target);
+    }
+#endif
+  } else if (nsContentUtils::EqualsIgnoreASCIICase(aAnchorName, u"top"_ns)) {
+    // 2.2. Scroll to the beginning of the document for the Document.
+    nsIScrollableFrame* sf = GetRootScrollFrameAsScrollable();
+    // Check |aScroll| after setting |rv| so we set |rv| to the same
+    // thing whether or not |aScroll| is true.
+    if (aScroll && sf) {
+      ScrollMode scrollMode =
+          sf->IsSmoothScroll() ? ScrollMode::SmoothMsd : ScrollMode::Instant;
+      // Scroll to the top of the page
+      sf->ScrollTo(nsPoint(0, 0), scrollMode);
+    }
+  } else {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+nsresult PresShell::ScrollToAnchor() {
+  nsCOMPtr<nsIContent> lastAnchor = std::move(mLastAnchorScrolledTo);
+  if (!lastAnchor) {
+    return NS_OK;
+  }
+
+  NS_ASSERTION(mDidInitialize, "should have done initial reflow by now");
+  nsIScrollableFrame* rootScroll = GetRootScrollFrameAsScrollable();
+  if (!rootScroll ||
+      mLastAnchorScrollPositionY != rootScroll->GetScrollPosition().y) {
+    return NS_OK;
+  }
+  return ScrollContentIntoView(
+      lastAnchor, ScrollAxis(WhereToScroll::Start, WhenToScroll::Always),
+      ScrollAxis(), ScrollFlags::AnchorScrollFlags);
+}
+
+/*
+ * Helper (per-continuation) for ScrollContentIntoView.
+ *
+ * @param aContainerFrame [in] the frame which aRect is relative to
+ * @param aFrame [in] Frame whose bounds should be unioned
+ * @param aUseWholeLineHeightForInlines [in] if true, then for inline frames
+ * we should include the top of the line in the added rectangle
+ * @param aRect [inout] rect into which its bounds should be unioned
+ * @param aHaveRect [inout] whether aRect contains data yet
+ * @param aPrevBlock [inout] the block aLines is a line iterator for
+ * @param aLines [inout] the line iterator we're using
+ * @param aCurLine [inout] the line to start looking from in this iterator
+ */
+static void AccumulateFrameBounds(nsIFrame* aContainerFrame, nsIFrame* aFrame,
+                                  bool aUseWholeLineHeightForInlines,
+                                  nsRect& aRect, bool& aHaveRect,
+                                  nsIFrame*& aPrevBlock,
+                                  nsILineIterator*& aLines, int32_t& aCurLine) {
+  nsIFrame* frame = aFrame;
+  nsRect frameBounds = nsRect(nsPoint(0, 0), aFrame->GetSize());
+
+  // If this is an inline frame and either the bounds height is 0 (quirks
+  // layout model) or aUseWholeLineHeightForInlines is set, we need to
+  // change the top of the bounds to include the whole line.
+  if (frameBounds.height == 0 || aUseWholeLineHeightForInlines) {
+    nsIFrame* prevFrame = aFrame;
+    nsIFrame* f = aFrame;
+
+    while (f && f->IsFrameOfType(nsIFrame::eLineParticipant) &&
+           !f->IsTransformed() && !f->IsAbsPosContainingBlock()) {
+      prevFrame = f;
+      f = prevFrame->GetParent();
+    }
+
+    if (f != aFrame && f && f->IsBlockFrame()) {
+      // find the line containing aFrame and increase the top of |offset|.
+      if (f != aPrevBlock) {
+        aLines = f->GetLineIterator();
+        aPrevBlock = f;
+        aCurLine = 0;
+      }
+      if (aLines) {
+        int32_t index = aLines->FindLineContaining(prevFrame, aCurLine);
+        if (index >= 0) {
+          auto line = aLines->GetLine(index).unwrap();
+          frameBounds += frame->GetOffsetTo(f);
+          frame = f;
+          if (line.mLineBounds.y < frameBounds.y) {
+            frameBounds.height = frameBounds.YMost() - line.mLineBounds.y;
+            frameBounds.y = line.mLineBounds.y;
+          }
+        }
+      }
+    }
+  }
+
+  nsRect transformedBounds = nsLayoutUtils::TransformFrameRectToAncestor(
+      frame, frameBounds, aContainerFrame);
+
+  if (aHaveRect) {
+    // We can't use nsRect::UnionRect since it drops empty rects on
+    // the floor, and we need to include them.  (Thus we need
+    // aHaveRect to know when to drop the initial value on the floor.)
+    aRect = aRect.UnionEdges(transformedBounds);
+  } else {
+    aHaveRect = true;
+    aRect = transformedBounds;
+  }
+}
+
+static bool ComputeNeedToScroll(WhenToScroll aWhenToScroll, nscoord aLineSize,
+                                nscoord aRectMin, nscoord aRectMax,
+                                nscoord aViewMin, nscoord aViewMax) {
+  // See how the rect should be positioned in a given axis.
+  switch (aWhenToScroll) {
+    case WhenToScroll::Always:
+      // The caller wants the frame as visible as possible
+      return true;
+    case WhenToScroll::IfNotVisible:
+      // Scroll only if no part of the frame is visible in this view.
+      return aRectMax - aLineSize <= aViewMin ||
+             aRectMin + aLineSize >= aViewMax;
+    case WhenToScroll::IfNotFullyVisible:
+      // Scroll only if part of the frame is hidden and more can fit in view
+      return !(aRectMin >= aViewMin && aRectMax <= aViewMax) &&
+             std::min(aViewMax, aRectMax) - std::max(aRectMin, aViewMin) <
+                 aViewMax - aViewMin;
+  }
+  return false;
+}
+
+static nscoord ComputeWhereToScroll(WhereToScroll aWhereToScroll,
+                                    nscoord aOriginalCoord, nscoord aRectMin,
+                                    nscoord aRectMax, nscoord aViewMin,
+                                    nscoord aViewMax, nscoord* aRangeMin,
+                                    nscoord* aRangeMax) {
+  nscoord resultCoord = aOriginalCoord;
+  nscoord scrollPortLength = aViewMax - aViewMin;
+  if (!aWhereToScroll.mPercentage) {
+    // Scroll the minimum amount necessary to show as much as possible of the
+    // frame. If the frame is too large, don't hide any initially visible part
+    // of it.
+    nscoord min = std::min(aRectMin, aRectMax - scrollPortLength);
+    nscoord max = std::max(aRectMin, aRectMax - scrollPortLength);
+    resultCoord = std::min(std::max(aOriginalCoord, min), max);
+  } else {
+    float percent = aWhereToScroll.mPercentage.value() / 100.0f;
+    nscoord frameAlignCoord =
+        NSToCoordRound(aRectMin + (aRectMax - aRectMin) * percent);
+    resultCoord = NSToCoordRound(frameAlignCoord - scrollPortLength * percent);
+  }
+  // Force the scroll range to extend to include resultCoord.
+  *aRangeMin = std::min(resultCoord, aRectMax - scrollPortLength);
+  *aRangeMax = std::max(resultCoord, aRectMin);
+  return resultCoord;
+}
+
+static WhereToScroll GetApplicableWhereToScroll(
+    const nsIScrollableFrame* aFrameAsScrollable,
+    const nsIFrame* aScrollableFrame, const nsIFrame* aTarget,
+    ScrollDirection aScrollDirection, WhereToScroll aOriginal) {
+  MOZ_ASSERT(do_QueryFrame(aFrameAsScrollable) == aScrollableFrame);
+  if (aTarget == aScrollableFrame) {
+    return aOriginal;
+  }
+
+  StyleScrollSnapAlignKeyword align =
+      aScrollDirection == ScrollDirection::eHorizontal
+          ? aFrameAsScrollable->GetScrollSnapAlignFor(aTarget).first
+          : aFrameAsScrollable->GetScrollSnapAlignFor(aTarget).second;
+
+  switch (align) {
+    case StyleScrollSnapAlignKeyword::None:
+      return aOriginal;
+    case StyleScrollSnapAlignKeyword::Start:
+      return WhereToScroll::Start;
+    case StyleScrollSnapAlignKeyword::Center:
+      return WhereToScroll::Center;
+    case StyleScrollSnapAlignKeyword::End:
+      return WhereToScroll::End;
+  }
+  return aOriginal;
+}
+
+/**
+ * This function takes a scrollable frame, a rect in the coordinate system
+ * of the scrolled frame, and a desired percentage-based scroll
+ * position and attempts to scroll the rect to that position in the
+ * visual viewport.
+ *
+ * This needs to work even if aRect has a width or height of zero.
+ */
+static void ScrollToShowRect(nsIScrollableFrame* aFrameAsScrollable,
+                             const nsIFrame* aScrollableFrame,
+                             const nsIFrame* aTarget, const nsRect& aRect,
+                             const Sides aScrollPaddingSkipSides,
+                             const nsMargin& aMargin, ScrollAxis aVertical,
+                             ScrollAxis aHorizontal, ScrollFlags aScrollFlags) {
+  nsPoint scrollPt = aFrameAsScrollable->GetVisualViewportOffset();
+  const nsPoint originalScrollPt = scrollPt;
+  const nsRect visibleRect(scrollPt,
+                           aFrameAsScrollable->GetVisualViewportSize());
+
+  const nsMargin padding = [&] {
+    nsMargin p = aFrameAsScrollable->GetScrollPadding();
+    p.ApplySkipSides(aScrollPaddingSkipSides);
+    return p + aMargin;
+  }();
+
+  const nsRect rectToScrollIntoView = [&] {
+    nsRect r(aRect);
+    r.Inflate(padding);
+    return r.Intersect(aFrameAsScrollable->GetScrolledRect());
+  }();
+
+  nsSize lineSize;
+  // Don't call GetLineScrollAmount unless we actually need it. Not only
+  // does this save time, but it's not safe to call GetLineScrollAmount
+  // during reflow (because it depends on font size inflation and doesn't
+  // use the in-reflow-safe font-size inflation path). If we did call it,
+  // it would assert and possible give the wrong result.
+  if (aVertical.mWhenToScroll == WhenToScroll::IfNotVisible ||
+      aHorizontal.mWhenToScroll == WhenToScroll::IfNotVisible) {
+    lineSize = aFrameAsScrollable->GetLineScrollAmount();
+  }
+  ScrollStyles ss = aFrameAsScrollable->GetScrollStyles();
+  nsRect allowedRange(scrollPt, nsSize(0, 0));
+  ScrollDirections directions =
+      aFrameAsScrollable->GetAvailableScrollingDirections();
+
+  if (((aScrollFlags & ScrollFlags::ScrollOverflowHidden) ||
+       ss.mVertical != StyleOverflow::Hidden) &&
+      (!aVertical.mOnlyIfPerceivedScrollableDirection ||
+       (directions.contains(ScrollDirection::eVertical)))) {
+    if (ComputeNeedToScroll(aVertical.mWhenToScroll, lineSize.height, aRect.y,
+                            aRect.YMost(), visibleRect.y + padding.top,
+                            visibleRect.YMost() - padding.bottom)) {
+      // If the scroll-snap-align on the frame is valid, we need to respect it.
+      WhereToScroll whereToScroll = GetApplicableWhereToScroll(
+          aFrameAsScrollable, aScrollableFrame, aTarget,
+          ScrollDirection::eVertical, aVertical.mWhereToScroll);
+
+      nscoord maxHeight;
+      scrollPt.y = ComputeWhereToScroll(
+          whereToScroll, scrollPt.y, rectToScrollIntoView.y,
+          rectToScrollIntoView.YMost(), visibleRect.y, visibleRect.YMost(),
+          &allowedRange.y, &maxHeight);
+      allowedRange.height = maxHeight - allowedRange.y;
+    }
+  }
+
+  if (((aScrollFlags & ScrollFlags::ScrollOverflowHidden) ||
+       ss.mHorizontal != StyleOverflow::Hidden) &&
+      (!aHorizontal.mOnlyIfPerceivedScrollableDirection ||
+       (directions.contains(ScrollDirection::eHorizontal)))) {
+    if (ComputeNeedToScroll(aHorizontal.mWhenToScroll, lineSize.width, aRect.x,
+                            aRect.XMost(), visibleRect.x + padding.left,
+                            visibleRect.XMost() - padding.right)) {
+      // If the scroll-snap-align on the frame is valid, we need to respect it.
+      WhereToScroll whereToScroll = GetApplicableWhereToScroll(
+          aFrameAsScrollable, aScrollableFrame, aTarget,
+          ScrollDirection::eHorizontal, aHorizontal.mWhereToScroll);
+
+      nscoord maxWidth;
+      scrollPt.x = ComputeWhereToScroll(
+          whereToScroll, scrollPt.x, rectToScrollIntoView.x,
+          rectToScrollIntoView.XMost(), visibleRect.x, visibleRect.XMost(),
+          &allowedRange.x, &maxWidth);
+      allowedRange.width = maxWidth - allowedRange.x;
+    }
+  }
+
+  // If we don't need to scroll, then don't try since it might cancel
+  // a current smooth scroll operation.
+  if (scrollPt == originalScrollPt) {
+    return;
+  }
+
+  ScrollMode scrollMode = ScrollMode::Instant;
+  bool autoBehaviorIsSmooth = aFrameAsScrollable->IsSmoothScroll();
+  bool smoothScroll =
+      (aScrollFlags & ScrollFlags::ScrollSmooth) ||
+      ((aScrollFlags & ScrollFlags::ScrollSmoothAuto) && autoBehaviorIsSmooth);
+  if (smoothScroll) {
+    scrollMode = ScrollMode::SmoothMsd;
+  }
+  nsIFrame* frame = do_QueryFrame(aFrameAsScrollable);
+  AutoWeakFrame weakFrame(frame);
+  aFrameAsScrollable->ScrollTo(scrollPt, scrollMode, &allowedRange,
+                               ScrollSnapFlags::IntendedEndPosition,
+                               aScrollFlags & ScrollFlags::TriggeredByScript
+                                   ? ScrollTriggeredByScript::Yes
+                                   : ScrollTriggeredByScript::No);
+  if (!weakFrame.IsAlive()) {
+    return;
+  }
+
+  // If this is the RCD-RSF, also call ScrollToVisual() since we want to
+  // scroll the rect into view visually, and that may require scrolling
+  // the visual viewport in scenarios where there is not enough layout
+  // scroll range.
+  if (aFrameAsScrollable->IsRootScrollFrameOfDocument() &&
+      frame->PresContext()->IsRootContentDocumentCrossProcess()) {
+    frame->PresShell()->ScrollToVisual(scrollPt, FrameMetrics::eMainThread,
+                                       scrollMode);
+  }
+}
+
+nsresult PresShell::ScrollContentIntoView(nsIContent* aContent,
+                                          ScrollAxis aVertical,
+                                          ScrollAxis aHorizontal,
+                                          ScrollFlags aScrollFlags) {
+  NS_ENSURE_TRUE(aContent, NS_ERROR_NULL_POINTER);
+  RefPtr<Document> composedDoc = aContent->GetComposedDoc();
+  NS_ENSURE_STATE(composedDoc);
+
+  NS_ASSERTION(mDidInitialize, "should have done initial reflow by now");
+
+  if (mContentToScrollTo) {
+    mContentToScrollTo->RemoveProperty(nsGkAtoms::scrolling);
+  }
+  mContentToScrollTo = aContent;
+  ScrollIntoViewData* data = new ScrollIntoViewData();
+  data->mContentScrollVAxis = aVertical;
+  data->mContentScrollHAxis = aHorizontal;
+  data->mContentToScrollToFlags = aScrollFlags;
+  if (NS_FAILED(mContentToScrollTo->SetProperty(
+          nsGkAtoms::scrolling, data,
+          nsINode::DeleteProperty<PresShell::ScrollIntoViewData>))) {
+    mContentToScrollTo = nullptr;
+  }
+
+  // If the target frame is an ancestor of a `content-visibility: auto`
+  // element ensure that it is laid out, so that the boundary rectangle is
+  // correct.
+  if (mContentToScrollTo) {
+    if (nsIFrame* frame = mContentToScrollTo->GetPrimaryFrame()) {
+      if (frame->IsHiddenByContentVisibilityOnAnyAncestor(
+              nsIFrame::IncludeContentVisibility::Auto)) {
+        frame->PresShell()->EnsureReflowIfFrameHasHiddenContent(frame);
+      }
+    }
+  }
+
+  // Flush layout and attempt to scroll in the process.
+  if (PresShell* presShell = composedDoc->GetPresShell()) {
+    presShell->SetNeedLayoutFlush();
+  }
+  composedDoc->FlushPendingNotifications(FlushType::InterruptibleLayout);
+
+  // If mContentToScrollTo is non-null, that means we interrupted the reflow
+  // (or suppressed it altogether because we're suppressing interruptible
+  // flushes right now) and won't necessarily get the position correct, but do
+  // a best-effort scroll here.  The other option would be to do this inside
+  // FlushPendingNotifications, but I'm not sure the repeated scrolling that
+  // could trigger if reflows keep getting interrupted would be more desirable
+  // than a single best-effort scroll followed by one final scroll on the first
+  // completed reflow.
+  if (mContentToScrollTo) {
+    DoScrollContentIntoView();
+  }
+  return NS_OK;
+}
+
+static nsMargin GetScrollMargin(const nsIFrame* aFrame) {
+  MOZ_ASSERT(aFrame);
+  // If we're focusing something that can't be targeted by content, allow
+  // content to customize the margin.
+  //
+  // TODO: This is also a bit of an issue for delegated focus, see
+  // https://github.com/whatwg/html/issues/7033.
+  if (aFrame->GetContent() && aFrame->GetContent()->ChromeOnlyAccess()) {
+    if (const nsIContent* userContent =
+            aFrame->GetContent()->GetChromeOnlyAccessSubtreeRootParent()) {
+      if (const nsIFrame* frame = userContent->GetPrimaryFrame()) {
+        return frame->StyleMargin()->GetScrollMargin();
+      }
+    }
+  }
+  return aFrame->StyleMargin()->GetScrollMargin();
+}
+
+void PresShell::DoScrollContentIntoView() {
+  NS_ASSERTION(mDidInitialize, "should have done initial reflow by now");
+
+  nsIFrame* frame = mContentToScrollTo->GetPrimaryFrame();
+
+  if (!frame || frame->IsHiddenByContentVisibilityOnAnyAncestor(
+                    nsIFrame::IncludeContentVisibility::Hidden)) {
+    mContentToScrollTo->RemoveProperty(nsGkAtoms::scrolling);
+    mContentToScrollTo = nullptr;
+    return;
+  }
+
+  if (frame->HasAnyStateBits(NS_FRAME_FIRST_REFLOW)) {
+    // The reflow flush before this scroll got interrupted, and this frame's
+    // coords and size are all zero, and it has no content showing anyway.
+    // Don't bother scrolling to it.  We'll try again when we finish up layout.
+    return;
+  }
+
+  auto* data = static_cast<ScrollIntoViewData*>(
+      mContentToScrollTo->GetProperty(nsGkAtoms::scrolling));
+  if (MOZ_UNLIKELY(!data)) {
+    mContentToScrollTo = nullptr;
+    return;
+  }
+
+  ScrollFrameIntoView(frame, Nothing(), data->mContentScrollVAxis,
+                      data->mContentScrollHAxis, data->mContentToScrollToFlags);
+}
+
+bool PresShell::ScrollFrameIntoView(
+    nsIFrame* aTargetFrame, const Maybe<nsRect>& aKnownRectRelativeToTarget,
+    ScrollAxis aVertical, ScrollAxis aHorizontal, ScrollFlags aScrollFlags) {
+  // The scroll margin only applies to the whole bounds of the element, so don't
+  // apply it if we get an arbitrary rect / point to scroll to.
+  const nsMargin scrollMargin =
+      aKnownRectRelativeToTarget ? nsMargin() : GetScrollMargin(aTargetFrame);
+
+  Sides skipPaddingSides;
+  const auto MaybeSkipPaddingSides = [&](nsIFrame* aFrame) {
+    if (!aFrame->IsStickyPositioned()) {
+      return;
+    }
+    const nsPoint pos = aFrame->GetPosition();
+    const nsPoint normalPos = aFrame->GetNormalPosition();
+    if (pos == normalPos) {
+      return;  // Frame is not stuck.
+    }
+    // If we're targetting a sticky element, make sure not to apply
+    // scroll-padding on the direction we're stuck.
+    const auto& offsets = aFrame->StylePosition()->mOffset;
+    for (auto side : AllPhysicalSides()) {
+      if (offsets.Get(side).IsAuto()) {
+        continue;
+      }
+      // See if this axis is stuck.
+      const bool yAxis = side == eSideTop || side == eSideBottom;
+      const bool stuck = yAxis ? pos.y != normalPos.y : pos.x != normalPos.x;
+      if (!stuck) {
+        continue;
+      }
+      skipPaddingSides |= SideToSideBit(side);
+    }
+  };
+
+  nsIFrame* container = aTargetFrame;
+
+  // This function needs to work even if rect has a width or height of 0.
+  nsRect rect = [&] {
+    if (aKnownRectRelativeToTarget) {
+      return *aKnownRectRelativeToTarget;
+    }
+    MaybeSkipPaddingSides(aTargetFrame);
+    while (nsIFrame* parent = container->GetParent()) {
+      container = parent;
+      if (static_cast<nsIScrollableFrame*>(do_QueryFrame(container))) {
+        // We really just need a non-fragmented frame so that we can accumulate
+        // the bounds of all our continuations relative to it. We shouldn't jump
+        // out of our nearest scrollable frame, and that's an ok reference
+        // frame, so try to use that, or the root frame if there's nothing to
+        // scroll in this document.
+        break;
+      }
+      MaybeSkipPaddingSides(container);
+    }
+    MOZ_DIAGNOSTIC_ASSERT(container);
+
+    nsRect targetFrameBounds;
+    {
+      bool haveRect = false;
+      const bool useWholeLineHeightForInlines =
+          aVertical.mWhenToScroll != WhenToScroll::IfNotFullyVisible;
+      AutoAssertNoDomMutations
+          guard;  // Ensure use of nsILineIterators is safe.
+      nsIFrame* prevBlock = nullptr;
+      // Reuse the same line iterator across calls to AccumulateFrameBounds.
+      // We set it every time we detect a new block (stored in prevBlock).
+      nsILineIterator* lines = nullptr;
+      // The last line we found a continuation on in |lines|.  We assume that
+      // later continuations cannot come on earlier lines.
+      int32_t curLine = 0;
+      nsIFrame* frame = aTargetFrame;
+      do {
+        AccumulateFrameBounds(container, frame, useWholeLineHeightForInlines,
+                              targetFrameBounds, haveRect, prevBlock, lines,
+                              curLine);
+      } while ((frame = frame->GetNextContinuation()));
+    }
+
+    return targetFrameBounds;
+  }();
+
+  bool didScroll = false;
+  const nsIFrame* target = aTargetFrame;
+  // Walk up the frame hierarchy scrolling the rect into view and
+  // keeping rect relative to container
+  do {
+    if (nsIScrollableFrame* sf = do_QueryFrame(container)) {
+      nsPoint oldPosition = sf->GetScrollPosition();
+      nsRect targetRect = rect;
+      // Inflate the scrolled rect by the container's padding in each dimension,
+      // unless we have 'overflow-clip-box-*: content-box' in that dimension.
+      auto* disp = container->StyleDisplay();
+      if (disp->mOverflowClipBoxBlock == StyleOverflowClipBox::ContentBox ||
+          disp->mOverflowClipBoxInline == StyleOverflowClipBox::ContentBox) {
+        WritingMode wm = container->GetWritingMode();
+        bool cbH = (wm.IsVertical() ? disp->mOverflowClipBoxBlock
+                                    : disp->mOverflowClipBoxInline) ==
+                   StyleOverflowClipBox::ContentBox;
+        bool cbV = (wm.IsVertical() ? disp->mOverflowClipBoxInline
+                                    : disp->mOverflowClipBoxBlock) ==
+                   StyleOverflowClipBox::ContentBox;
+        nsMargin padding = container->GetUsedPadding();
+        if (!cbH) {
+          padding.left = padding.right = nscoord(0);
+        }
+        if (!cbV) {
+          padding.top = padding.bottom = nscoord(0);
+        }
+        targetRect.Inflate(padding);
+      }
+
+      targetRect -= sf->GetScrolledFrame()->GetPosition();
+
+      {
+        AutoWeakFrame wf(container);
+        ScrollToShowRect(sf, container, target, targetRect, skipPaddingSides,
+                         scrollMargin, aVertical, aHorizontal, aScrollFlags);
+        if (!wf.IsAlive()) {
+          return didScroll;
+        }
+      }
+
+      nsPoint newPosition = sf->LastScrollDestination();
+      // If the scroll position increased, that means our content moved up,
+      // so our rect's offset should decrease
+      rect += oldPosition - newPosition;
+
+      if (oldPosition != newPosition) {
+        didScroll = true;
+      }
+
+      // only scroll one container when this flag is set
+      if (aScrollFlags & ScrollFlags::ScrollFirstAncestorOnly) {
+        break;
+      }
+
+      // This scroll container will be the next target element in the nearest
+      // ancestor scroll container.
+      target = container;
+      // We found a sticky scroll container, we shouldn't skip that side
+      // anymore.
+      skipPaddingSides = {};
+    }
+
+    MaybeSkipPaddingSides(container);
+
+    nsIFrame* parent;
+    if (container->IsTransformed()) {
+      container->GetTransformMatrix(ViewportType::Layout, RelativeTo{nullptr},
+                                    &parent);
+      rect =
+          nsLayoutUtils::TransformFrameRectToAncestor(container, rect, parent);
+    } else {
+      rect += container->GetPosition();
+      parent = container->GetParent();
+    }
+    if (!parent && !(aScrollFlags & ScrollFlags::ScrollNoParentFrames)) {
+      nsPoint extraOffset(0, 0);
+      int32_t APD = container->PresContext()->AppUnitsPerDevPixel();
+      parent = nsLayoutUtils::GetCrossDocParentFrameInProcess(container,
+                                                              &extraOffset);
+      if (parent) {
+        int32_t parentAPD = parent->PresContext()->AppUnitsPerDevPixel();
+        rect = rect.ScaleToOtherAppUnitsRoundOut(APD, parentAPD);
+        rect += extraOffset;
+      } else {
+        nsCOMPtr<nsIDocShell> docShell =
+            container->PresContext()->GetDocShell();
+        if (BrowserChild* browserChild = BrowserChild::GetFrom(docShell)) {
+          // Defer to the parent document if this is an out-of-process iframe.
+          Unused << browserChild->SendScrollRectIntoView(
+              rect, aVertical, aHorizontal, aScrollFlags, APD);
+        }
+      }
+    }
+    container = parent;
+  } while (container);
+
+  return didScroll;
+}
+
+void PresShell::ScheduleViewManagerFlush() {
+  if (MOZ_UNLIKELY(mIsDestroying)) {
+    return;
+  }
+
+  nsPresContext* presContext = GetPresContext();
+  if (presContext) {
+    presContext->RefreshDriver()->ScheduleViewManagerFlush();
+  }
+  SetNeedLayoutFlush();
+}
+
+void PresShell::DispatchSynthMouseMove(WidgetGUIEvent* aEvent) {
+  AUTO_PROFILER_TRACING_MARKER_DOCSHELL("Paint", "DispatchSynthMouseMove",
+                                        GRAPHICS, mPresContext->GetDocShell());
+  nsEventStatus status = nsEventStatus_eIgnore;
+  nsView* targetView = nsView::GetViewFor(aEvent->mWidget);
+  if (!targetView) return;
+  RefPtr<nsViewManager> viewManager = targetView->GetViewManager();
+  viewManager->DispatchEvent(aEvent, targetView, &status);
+}
+
+void PresShell::ClearMouseCaptureOnView(nsView* aView) {
+  if (nsIContent* capturingContent = GetCapturingContent()) {
+    if (aView) {
+      // if a view was specified, ensure that the captured content is within
+      // this view.
+      nsIFrame* frame = capturingContent->GetPrimaryFrame();
+      if (frame) {
+        nsView* view = frame->GetClosestView();
+        // if there is no view, capturing won't be handled any more, so
+        // just release the capture.
+        if (view) {
+          do {
+            if (view == aView) {
+              ReleaseCapturingContent();
+              // the view containing the captured content likely disappeared so
+              // disable capture for now.
+              AllowMouseCapture(false);
+              break;
+            }
+
+            view = view->GetParent();
+          } while (view);
+          // return if the view wasn't found
+          return;
+        }
+      }
+    }
+
+    ReleaseCapturingContent();
+  }
+
+  // disable mouse capture until the next mousedown as a dialog has opened
+  // or a drag has started. Otherwise, someone could start capture during
+  // the modal dialog or drag.
+  AllowMouseCapture(false);
+}
+
+void PresShell::ClearMouseCapture() {
+  ReleaseCapturingContent();
+  AllowMouseCapture(false);
+}
+
+void PresShell::ClearMouseCapture(nsIFrame* aFrame) {
+  MOZ_ASSERT(aFrame);
+
+  nsIContent* capturingContent = GetCapturingContent();
+  if (!capturingContent) {
+    return;
+  }
+
+  nsIFrame* capturingFrame = capturingContent->GetPrimaryFrame();
+  const bool shouldClear =
+      !capturingFrame ||
+      nsLayoutUtils::IsAncestorFrameCrossDocInProcess(aFrame, capturingFrame);
+  if (shouldClear) {
+    ClearMouseCapture();
+  }
+}
+
+nsresult PresShell::CaptureHistoryState(nsILayoutHistoryState** aState) {
+  MOZ_ASSERT(nullptr != aState, "null state pointer");
+
+  // We actually have to mess with the docshell here, since we want to
+  // store the state back in it.
+  // XXXbz this isn't really right, since this is being called in the
+  // content viewer's Hide() method...  by that point the docshell's
+  // state could be wrong.  We should sort out a better ownership
+  // model for the layout history state.
+  nsCOMPtr<nsIDocShell> docShell(mPresContext->GetDocShell());
+  if (!docShell) return NS_ERROR_FAILURE;
+
+  nsCOMPtr<nsILayoutHistoryState> historyState;
+  docShell->GetLayoutHistoryState(getter_AddRefs(historyState));
+  if (!historyState) {
+    // Create the document state object
+    historyState = NS_NewLayoutHistoryState();
+    docShell->SetLayoutHistoryState(historyState);
+  }
+
+  *aState = historyState;
+  NS_IF_ADDREF(*aState);
+
+  // Capture frame state for the entire frame hierarchy
+  nsIFrame* rootFrame = mFrameConstructor->GetRootFrame();
+  if (!rootFrame) return NS_OK;
+
+  mFrameConstructor->CaptureFrameState(rootFrame, historyState);
+
+  return NS_OK;
+}
+
+void PresShell::ScheduleBeforeFirstPaint() {
+  if (!mDocument->IsResourceDoc()) {
+    // Notify observers that a new page is about to be drawn. Execute this
+    // as soon as it is safe to run JS, which is guaranteed to be before we
+    // go back to the event loop and actually draw the page.
+    MOZ_LOG(gLog, LogLevel::Debug,
+            ("PresShell::ScheduleBeforeFirstPaint this=%p", this));
+
+    nsContentUtils::AddScriptRunner(
+        new nsBeforeFirstPaintDispatcher(mDocument));
+  }
+}
+
+void PresShell::UnsuppressAndInvalidate() {
+  // Note: We ignore the EnsureVisible check for resource documents, because
+  // they won't have a docshell, so they'll always fail EnsureVisible.
+  if ((!mDocument->IsResourceDoc() && !mPresContext->EnsureVisible()) ||
+      mHaveShutDown) {
+    // No point; we're about to be torn down anyway.
+    return;
+  }
+
+  ScheduleBeforeFirstPaint();
+
+  PROFILER_MARKER_UNTYPED("UnsuppressAndInvalidate", GRAPHICS);
+
+  mPaintingSuppressed = false;
+  if (nsIFrame* rootFrame = mFrameConstructor->GetRootFrame()) {
+    // let's assume that outline on a root frame is not supported
+    rootFrame->InvalidateFrame();
+  }
+
+  if (mPresContext->IsRootContentDocumentCrossProcess()) {
+    if (auto* bc = BrowserChild::GetFrom(mDocument->GetDocShell())) {
+      if (mDocument->IsInitialDocument()) {
+        bc->SendDidUnsuppressPaintingNormalPriority();
+      } else {
+        bc->SendDidUnsuppressPainting();
+      }
+    }
+  }
+
+  // now that painting is unsuppressed, focus may be set on the document
+  if (nsPIDOMWindowOuter* win = mDocument->GetWindow()) {
+    win->SetReadyForFocus();
+  }
+
+  if (!mHaveShutDown) {
+    SynthesizeMouseMove(false);
+    ScheduleApproximateFrameVisibilityUpdateNow();
+  }
+}
+
+void PresShell::CancelPaintSuppressionTimer() {
+  if (mPaintSuppressionTimer) {
+    mPaintSuppressionTimer->Cancel();
+    mPaintSuppressionTimer = nullptr;
+  }
+}
+
+void PresShell::UnsuppressPainting() {
+  CancelPaintSuppressionTimer();
+
+  if (mIsDocumentGone || !mPaintingSuppressed) {
+    return;
+  }
+
+  // If we have reflows pending, just wait until we process
+  // the reflows and get all the frames where we want them
+  // before actually unlocking the painting.  Otherwise
+  // go ahead and unlock now.
+  if (!mDirtyRoots.IsEmpty())
+    mShouldUnsuppressPainting = true;
+  else
+    UnsuppressAndInvalidate();
+}
+
+// Post a request to handle an arbitrary callback after reflow has finished.
+nsresult PresShell::PostReflowCallback(nsIReflowCallback* aCallback) {
+  void* result = AllocateByObjectID(eArenaObjectID_nsCallbackEventRequest,
+                                    sizeof(nsCallbackEventRequest));
+  nsCallbackEventRequest* request = (nsCallbackEventRequest*)result;
+
+  request->callback = aCallback;
+  request->next = nullptr;
+
+  if (mLastCallbackEventRequest) {
+    mLastCallbackEventRequest = mLastCallbackEventRequest->next = request;
+  } else {
+    mFirstCallbackEventRequest = request;
+    mLastCallbackEventRequest = request;
+  }
+
+  return NS_OK;
+}
+
+void PresShell::CancelReflowCallback(nsIReflowCallback* aCallback) {
+  nsCallbackEventRequest* before = nullptr;
+  nsCallbackEventRequest* node = mFirstCallbackEventRequest;
+  while (node) {
+    nsIReflowCallback* callback = node->callback;
+
+    if (callback == aCallback) {
+      nsCallbackEventRequest* toFree = node;
+      if (node == mFirstCallbackEventRequest) {
+        node = node->next;
+        mFirstCallbackEventRequest = node;
+        NS_ASSERTION(before == nullptr, "impossible");
+      } else {
+        node = node->next;
+        before->next = node;
+      }
+
+      if (toFree == mLastCallbackEventRequest) {
+        mLastCallbackEventRequest = before;
+      }
+
+      FreeByObjectID(eArenaObjectID_nsCallbackEventRequest, toFree);
+    } else {
+      before = node;
+      node = node->next;
+    }
+  }
+}
+
+void PresShell::CancelPostedReflowCallbacks() {
+  while (mFirstCallbackEventRequest) {
+    nsCallbackEventRequest* node = mFirstCallbackEventRequest;
+    mFirstCallbackEventRequest = node->next;
+    if (!mFirstCallbackEventRequest) {
+      mLastCallbackEventRequest = nullptr;
+    }
+    nsIReflowCallback* callback = node->callback;
+    FreeByObjectID(eArenaObjectID_nsCallbackEventRequest, node);
+    if (callback) {
+      callback->ReflowCallbackCanceled();
+    }
+  }
+}
+
+void PresShell::HandlePostedReflowCallbacks(bool aInterruptible) {
+  while (true) {
+    // Call all our callbacks, tell us if we need to flush again.
+    bool shouldFlush = false;
+    while (mFirstCallbackEventRequest) {
+      nsCallbackEventRequest* node = mFirstCallbackEventRequest;
+      mFirstCallbackEventRequest = node->next;
+      if (!mFirstCallbackEventRequest) {
+        mLastCallbackEventRequest = nullptr;
+      }
+      nsIReflowCallback* callback = node->callback;
+      FreeByObjectID(eArenaObjectID_nsCallbackEventRequest, node);
+      if (callback && callback->ReflowFinished()) {
+        shouldFlush = true;
+      }
+    }
+
+    if (!shouldFlush || mIsDestroying) {
+      return;
+    }
+
+    // The flush might cause us to have more callbacks.
+    const auto flushType =
+        aInterruptible ? FlushType::InterruptibleLayout : FlushType::Layout;
+    FlushPendingNotifications(flushType);
+  }
+}
+
+bool PresShell::IsSafeToFlush() const {
+  // Not safe if we are getting torn down, reflowing, or in the middle of frame
+  // construction.
+  if (mIsReflowing || mChangeNestCount || mIsDestroying) {
+    return false;
+  }
+
+  // Not safe if we are painting
+  if (nsViewManager* viewManager = GetViewManager()) {
+    bool isPainting = false;
+    viewManager->IsPainting(isPainting);
+    if (isPainting) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+void PresShell::NotifyFontFaceSetOnRefresh() {
+  if (FontFaceSet* set = mDocument->GetFonts()) {
+    set->DidRefresh();
+  }
+}
+
+void PresShell::DoFlushPendingNotifications(FlushType aType) {
+  // by default, flush animations if aType >= FlushType::Style
+  mozilla::ChangesToFlush flush(aType, aType >= FlushType::Style);
+  FlushPendingNotifications(flush);
+}
+
+#ifdef DEBUG
+static void AssertFrameSubtreeIsSane(const nsIFrame& aRoot) {
+  if (const nsIContent* content = aRoot.GetContent()) {
+    MOZ_ASSERT(content->GetFlattenedTreeParentNodeForStyle(),
+               "Node not in the flattened tree still has a frame?");
+  }
+
+  for (const auto& childList : aRoot.ChildLists()) {
+    for (const nsIFrame* child : childList.mList) {
+      AssertFrameSubtreeIsSane(*child);
+    }
+  }
+}
+#endif
+
+static inline void AssertFrameTreeIsSane(const PresShell& aPresShell) {
+#ifdef DEBUG
+  if (const nsIFrame* root = aPresShell.GetRootFrame()) {
+    AssertFrameSubtreeIsSane(*root);
+  }
+#endif
+}
+
+static void TriggerPendingScrollTimelineAnimations(Document* aDocument) {
+  auto* tracker = aDocument->GetScrollTimelineAnimationTracker();
+  if (!tracker || !tracker->HasPendingAnimations()) {
+    return;
+  }
+  tracker->TriggerPendingAnimations();
+}
+
+void PresShell::DoFlushPendingNotifications(mozilla::ChangesToFlush aFlush) {
+  // FIXME(emilio, bug 1530177): Turn into a release assert when bug 1530188 and
+  // bug 1530190 are fixed.
+  MOZ_DIAGNOSTIC_ASSERT(!mForbiddenToFlush, "This is bad!");
+
+  // Per our API contract, hold a strong ref to ourselves until we return.
+  RefPtr<PresShell> kungFuDeathGrip = this;
+
+  /**
+   * VERY IMPORTANT: If you add some sort of new flushing to this
+   * method, make sure to add the relevant SetNeedLayoutFlush or
+   * SetNeedStyleFlush calls on the shell.
+   */
+  FlushType flushType = aFlush.mFlushType;
+
+  // If this is a layout flush, first update the relevancy of any content
+  // of elements with `content-visibility: auto` so that the values
+  // returned from script queries are up-to-date.
+  if (flushType >= mozilla::FlushType::Layout) {
+    UpdateRelevancyOfContentVisibilityAutoFrames();
+  }
+
+  MOZ_ASSERT(NeedFlush(flushType), "Why did we get called?");
+
+  AUTO_PROFILER_MARKER_TEXT(
+      "DoFlushPendingNotifications", LAYOUT,
+      MarkerOptions(MarkerStack::Capture(), MarkerInnerWindowIdFromDocShell(
+                                                mPresContext->GetDocShell())),
+      nsDependentCString(kFlushTypeNames[flushType]));
+  AUTO_PROFILER_LABEL_DYNAMIC_CSTR_NONSENSITIVE(
+      "PresShell::DoFlushPendingNotifications", LAYOUT,
+      kFlushTypeNames[flushType]);
+
+#ifdef ACCESSIBILITY
+#  ifdef DEBUG
+  if (nsAccessibilityService* accService = GetAccService()) {
+    NS_ASSERTION(!accService->IsProcessingRefreshDriverNotification(),
+                 "Flush during accessible tree update!");
+  }
+#  endif
+#endif
+
+  NS_ASSERTION(flushType >= FlushType::Style, "Why did we get called?");
+
+  mNeedStyleFlush = false;
+  mNeedThrottledAnimationFlush =
+      mNeedThrottledAnimationFlush && !aFlush.mFlushAnimations;
+  mNeedLayoutFlush =
+      mNeedLayoutFlush && (flushType < FlushType::InterruptibleLayout);
+
+  bool isSafeToFlush = IsSafeToFlush();
+
+  // If layout could possibly trigger scripts, then it's only safe to flush if
+  // it's safe to run script.
+  bool hasHadScriptObject;
+  if (mDocument->GetScriptHandlingObject(hasHadScriptObject) ||
+      hasHadScriptObject) {
+    isSafeToFlush = isSafeToFlush && nsContentUtils::IsSafeToRunScript();
+  }
+
+  // Don't flush if the doc is already in the bfcache.
+  if (MOZ_UNLIKELY(mDocument->GetPresShell() != this)) {
+    MOZ_DIAGNOSTIC_ASSERT(!mDocument->GetPresShell(),
+                          "Where did this shell come from?");
+    isSafeToFlush = false;
+  }
+
+  MOZ_DIAGNOSTIC_ASSERT(!mIsDestroying || !isSafeToFlush);
+  MOZ_DIAGNOSTIC_ASSERT(mIsDestroying || mViewManager);
+  MOZ_DIAGNOSTIC_ASSERT(mIsDestroying || mDocument->HasShellOrBFCacheEntry());
+
+  // Make sure the view manager stays alive.
+  RefPtr<nsViewManager> viewManager = mViewManager;
+  bool didStyleFlush = false;
+  bool didLayoutFlush = false;
+  if (isSafeToFlush) {
+    // Record that we are in a flush, so that our optimization in
+    // Document::FlushPendingNotifications doesn't skip any re-entrant
+    // calls to us.  Otherwise, we might miss some needed flushes, since
+    // we clear mNeedStyleFlush / mNeedLayoutFlush here at the top of
+    // the function but we might not have done the work yet.
+    AutoRestore<bool> guard(mInFlush);
+    mInFlush = true;
+
+    // We need to make sure external resource documents are flushed too (for
+    // example, svg filters that reference a filter in an external document
+    // need the frames in the external document to be constructed for the
+    // filter to work). We only need external resources to be flushed when the
+    // main document is flushing >= FlushType::Frames, so we flush external
+    // resources here instead of Document::FlushPendingNotifications.
+    mDocument->FlushExternalResources(flushType);
+
+    // Force flushing of any pending content notifications that might have
+    // queued up while our event was pending.  That will ensure that we don't
+    // construct frames for content right now that's still waiting to be
+    // notified on,
+    mDocument->FlushPendingNotifications(FlushType::ContentAndNotify);
+
+    mDocument->UpdateSVGUseElementShadowTrees();
+
+    // Ensure our preference sheets are up-to-date.
+    UpdatePreferenceStyles();
+
+    // Process pending restyles, since any flush of the presshell wants
+    // up-to-date style data.
+    if (MOZ_LIKELY(!mIsDestroying)) {
+      viewManager->FlushDelayedResize();
+      mPresContext->FlushPendingMediaFeatureValuesChanged();
+    }
+
+    if (MOZ_LIKELY(!mIsDestroying)) {
+      // Now that we have flushed media queries, update the rules before looking
+      // up @font-face / @counter-style / @font-feature-values rules.
+      StyleSet()->UpdateStylistIfNeeded();
+
+      // Flush any pending update of the user font set, since that could
+      // cause style changes (for updating ex/ch units, and to cause a
+      // reflow).
+      mDocument->FlushUserFontSet();
+
+      mPresContext->FlushCounterStyles();
+
+      mPresContext->FlushFontFeatureValues();
+
+      mPresContext->FlushFontPaletteValues();
+
+      // Flush any requested SMIL samples.
+      if (mDocument->HasAnimationController()) {
+        mDocument->GetAnimationController()->FlushResampleRequests();
+      }
+    }
+
+    // The FlushResampleRequests() above flushed style changes.
+    if (MOZ_LIKELY(!mIsDestroying) && aFlush.mFlushAnimations &&
+        mPresContext->EffectCompositor()) {
+      mPresContext->EffectCompositor()->PostRestyleForThrottledAnimations();
+    }
+
+    // The FlushResampleRequests() above flushed style changes.
+    if (MOZ_LIKELY(!mIsDestroying)) {
+      nsAutoScriptBlocker scriptBlocker;
+      Maybe<uint64_t> innerWindowID;
+      if (auto* window = mDocument->GetInnerWindow()) {
+        innerWindowID = Some(window->WindowID());
+      }
+      AutoProfilerStyleMarker tracingStyleFlush(std::move(mStyleCause),
+                                                innerWindowID);
+      PerfStats::AutoMetricRecording<PerfStats::Metric::Styling> autoRecording;
+      LAYOUT_TELEMETRY_RECORD_BASE(Restyle);
+
+      mPresContext->RestyleManager()->ProcessPendingRestyles();
+      mNeedStyleFlush = false;
+    }
+
+    AssertFrameTreeIsSane(*this);
+
+    didStyleFlush = true;
+
+    // There might be more pending constructors now, but we're not going to
+    // worry about them.  They can't be triggered during reflow, so we should
+    // be good.
+
+    if (flushType >= (SuppressInterruptibleReflows()
+                          ? FlushType::Layout
+                          : FlushType::InterruptibleLayout) &&
+        !mIsDestroying) {
+      didLayoutFlush = true;
+      if (DoFlushLayout(/* aInterruptible = */ flushType < FlushType::Layout)) {
+        if (mContentToScrollTo) {
+          DoScrollContentIntoView();
+          if (mContentToScrollTo) {
+            mContentToScrollTo->RemoveProperty(nsGkAtoms::scrolling);
+            mContentToScrollTo = nullptr;
+          }
+        }
+      }
+    }
+
+    FlushPendingScrollResnap();
+
+    if (MOZ_LIKELY(!mIsDestroying)) {
+      // Try to trigger pending scroll-driven animations after we flush
+      // style and layout (if any). If we try to trigger them after flushing
+      // style but the frame tree is not ready, we will check them again after
+      // we flush layout because the requirement to trigger scroll-driven
+      // animations is that the associated scroll containers are ready (i.e. the
+      // scroll-timeline is active), and this depends on the readiness of the
+      // scrollable frame and the primary frame of the scroll container.
+      TriggerPendingScrollTimelineAnimations(mDocument);
+    }
+
+    if (flushType >= FlushType::Layout) {
+      if (!mIsDestroying) {
+        viewManager->UpdateWidgetGeometry();
+      }
+    }
+  }
+
+  if (!didStyleFlush && flushType >= FlushType::Style && !mIsDestroying) {
+    SetNeedStyleFlush();
+    if (aFlush.mFlushAnimations) {
+      SetNeedThrottledAnimationFlush();
+    }
+  }
+
+  if (!didLayoutFlush && flushType >= FlushType::InterruptibleLayout &&
+      !mIsDestroying) {
+    // We suppressed this flush either due to it not being safe to flush,
+    // or due to SuppressInterruptibleReflows().  Either way, the
+    // mNeedLayoutFlush flag needs to be re-set.
+    SetNeedLayoutFlush();
+  }
+
+  // Update flush counters
+  if (didStyleFlush) {
+    mLayoutTelemetry.IncReqsPerFlush(FlushType::Style);
+  }
+
+  if (didLayoutFlush) {
+    mLayoutTelemetry.IncReqsPerFlush(FlushType::Layout);
+  }
+
+  // Record telemetry for the number of requests per each flush type.
+  //
+  // Flushes happen as style or style+layout. This depends upon the `flushType`
+  // where flushType >= InterruptibleLayout means flush layout and flushType >=
+  // Style means flush style. We only report if didLayoutFlush or didStyleFlush
+  // is true because we care if a flush really did take place. (Flush is guarded
+  // by `isSafeToFlush == true`.)
+  if (flushType >= FlushType::InterruptibleLayout && didLayoutFlush) {
+    MOZ_ASSERT(didLayoutFlush == didStyleFlush);
+    mLayoutTelemetry.PingReqsPerFlushTelemetry(FlushType::Layout);
+  } else if (flushType >= FlushType::Style && didStyleFlush) {
+    MOZ_ASSERT(!didLayoutFlush);
+    mLayoutTelemetry.PingReqsPerFlushTelemetry(FlushType::Style);
+  }
+}
+
+MOZ_CAN_RUN_SCRIPT_BOUNDARY void PresShell::CharacterDataChanged(
+    nsIContent* aContent, const CharacterDataChangeInfo& aInfo) {
+  MOZ_ASSERT(!nsContentUtils::IsSafeToRunScript());
+  MOZ_ASSERT(!mIsDocumentGone, "Unexpected CharacterDataChanged");
+  MOZ_ASSERT(aContent->OwnerDoc() == mDocument, "Unexpected document");
+
+  nsAutoCauseReflowNotifier crNotifier(this);
+
+  mPresContext->RestyleManager()->CharacterDataChanged(aContent, aInfo);
+  mFrameConstructor->CharacterDataChanged(aContent, aInfo);
+}
+
+MOZ_CAN_RUN_SCRIPT_BOUNDARY void PresShell::ElementStateChanged(
+    Document* aDocument, Element* aElement, ElementState aStateMask) {
+  MOZ_ASSERT(!nsContentUtils::IsSafeToRunScript());
+  MOZ_ASSERT(!mIsDocumentGone, "Unexpected ContentStateChanged");
+  MOZ_ASSERT(aDocument == mDocument, "Unexpected aDocument");
+
+  if (mDidInitialize) {
+    nsAutoCauseReflowNotifier crNotifier(this);
+    mPresContext->RestyleManager()->ElementStateChanged(aElement, aStateMask);
+  }
+}
+
+void PresShell::DocumentStatesChanged(DocumentState aStateMask) {
+  MOZ_ASSERT(!mIsDocumentGone, "Unexpected DocumentStatesChanged");
+  MOZ_ASSERT(mDocument);
+  MOZ_ASSERT(!aStateMask.IsEmpty());
+
+  if (mDidInitialize) {
+    StyleSet()->InvalidateStyleForDocumentStateChanges(aStateMask);
+  }
+
+  if (aStateMask.HasState(DocumentState::WINDOW_INACTIVE)) {
+    if (nsIFrame* root = mFrameConstructor->GetRootFrame()) {
+      root->SchedulePaint();
+    }
+  }
+}
+
+MOZ_CAN_RUN_SCRIPT_BOUNDARY void PresShell::AttributeWillChange(
+    Element* aElement, int32_t aNameSpaceID, nsAtom* aAttribute,
+    int32_t aModType) {
+  MOZ_ASSERT(!nsContentUtils::IsSafeToRunScript());
+  MOZ_ASSERT(!mIsDocumentGone, "Unexpected AttributeWillChange");
+  MOZ_ASSERT(aElement->OwnerDoc() == mDocument, "Unexpected document");
+
+  // XXXwaterson it might be more elegant to wait until after the
+  // initial reflow to begin observing the document. That would
+  // squelch any other inappropriate notifications as well.
+  if (mDidInitialize) {
+    nsAutoCauseReflowNotifier crNotifier(this);
+    mPresContext->RestyleManager()->AttributeWillChange(aElement, aNameSpaceID,
+                                                        aAttribute, aModType);
+  }
+}
+
+MOZ_CAN_RUN_SCRIPT_BOUNDARY void PresShell::AttributeChanged(
+    Element* aElement, int32_t aNameSpaceID, nsAtom* aAttribute,
+    int32_t aModType, const nsAttrValue* aOldValue) {
+  MOZ_ASSERT(!nsContentUtils::IsSafeToRunScript());
+  MOZ_ASSERT(!mIsDocumentGone, "Unexpected AttributeChanged");
+  MOZ_ASSERT(aElement->OwnerDoc() == mDocument, "Unexpected document");
+
+  // XXXwaterson it might be more elegant to wait until after the
+  // initial reflow to begin observing the document. That would
+  // squelch any other inappropriate notifications as well.
+  if (mDidInitialize) {
+    nsAutoCauseReflowNotifier crNotifier(this);
+    mPresContext->RestyleManager()->AttributeChanged(
+        aElement, aNameSpaceID, aAttribute, aModType, aOldValue);
+  }
+}
+
+MOZ_CAN_RUN_SCRIPT_BOUNDARY void PresShell::ContentAppended(
+    nsIContent* aFirstNewContent) {
+  MOZ_ASSERT(!nsContentUtils::IsSafeToRunScript());
+  MOZ_ASSERT(!mIsDocumentGone, "Unexpected ContentAppended");
+  MOZ_ASSERT(aFirstNewContent->OwnerDoc() == mDocument, "Unexpected document");
+
+  // We never call ContentAppended with a document as the container, so we can
+  // assert that we have an nsIContent parent.
+  MOZ_ASSERT(aFirstNewContent->GetParent());
+  MOZ_ASSERT(aFirstNewContent->GetParent()->IsElement() ||
+             aFirstNewContent->GetParent()->IsShadowRoot());
+
+  if (!mDidInitialize) {
+    return;
+  }
+
+  nsAutoCauseReflowNotifier crNotifier(this);
+
+  // Call this here so it only happens for real content mutations and
+  // not cases when the frame constructor calls its own methods to force
+  // frame reconstruction.
+  mPresContext->RestyleManager()->ContentAppended(aFirstNewContent);
+
+  mFrameConstructor->ContentAppended(
+      aFirstNewContent, nsCSSFrameConstructor::InsertionKind::Async);
+}
+
+MOZ_CAN_RUN_SCRIPT_BOUNDARY void PresShell::ContentInserted(
+    nsIContent* aChild) {
+  MOZ_ASSERT(!nsContentUtils::IsSafeToRunScript());
+  MOZ_ASSERT(!mIsDocumentGone, "Unexpected ContentInserted");
+  MOZ_ASSERT(aChild->OwnerDoc() == mDocument, "Unexpected document");
+
+  if (!mDidInitialize) {
+    return;
+  }
+
+  nsAutoCauseReflowNotifier crNotifier(this);
+
+  // Call this here so it only happens for real content mutations and
+  // not cases when the frame constructor calls its own methods to force
+  // frame reconstruction.
+  mPresContext->RestyleManager()->ContentInserted(aChild);
+
+  mFrameConstructor->ContentInserted(
+      aChild, nsCSSFrameConstructor::InsertionKind::Async);
+}
+
+MOZ_CAN_RUN_SCRIPT_BOUNDARY void PresShell::ContentRemoved(
+    nsIContent* aChild, nsIContent* aPreviousSibling) {
+  MOZ_ASSERT(!nsContentUtils::IsSafeToRunScript());
+  MOZ_ASSERT(!mIsDocumentGone, "Unexpected ContentRemoved");
+  MOZ_ASSERT(aChild->OwnerDoc() == mDocument, "Unexpected document");
+  nsINode* container = aChild->GetParentNode();
+
+  // Notify the ESM that the content has been removed, so that
+  // it can clean up any state related to the content.
+
+  mPresContext->EventStateManager()->ContentRemoved(mDocument, aChild);
+
+  nsAutoCauseReflowNotifier crNotifier(this);
+
+  // Call this here so it only happens for real content mutations and
+  // not cases when the frame constructor calls its own methods to force
+  // frame reconstruction.
+  nsIContent* oldNextSibling = nullptr;
+
+  // Editor calls into here with NAC via HTMLEditor::DeleteRefToAnonymousNode.
+  // This could be asserted if that caller is fixed.
+  if (MOZ_LIKELY(!aChild->IsRootOfNativeAnonymousSubtree())) {
+    oldNextSibling = aPreviousSibling ? aPreviousSibling->GetNextSibling()
+                                      : container->GetFirstChild();
+  }
+
+  // After removing aChild from tree we should save information about live
+  // ancestor
+  if (mPointerEventTarget &&
+      mPointerEventTarget->IsInclusiveDescendantOf(aChild)) {
+    mPointerEventTarget = aChild->GetParent();
+  }
+
+  mFrameConstructor->ContentRemoved(aChild, oldNextSibling,
+                                    nsCSSFrameConstructor::REMOVE_CONTENT);
+
+  // NOTE(emilio): It's important that this goes after the frame constructor
+  // stuff, otherwise the frame constructor can't see elements which are
+  // display: contents / display: none, because we'd have cleared all the style
+  // data from there.
+  mPresContext->RestyleManager()->ContentRemoved(aChild, oldNextSibling);
+}
+
+void PresShell::NotifyCounterStylesAreDirty() {
+  // TODO: Looks like that nsFrameConstructor::NotifyCounterStylesAreDirty()
+  //       does not run script.  If so, we don't need to block script with
+  //       nsAutoCauseReflowNotifier here.  Instead, there should be methods
+  //       and stack only class which manages only mChangeNestCount for
+  //       avoiding unnecessary `MOZ_CAN_RUN_SCRIPT` marking.
+  nsAutoCauseReflowNotifier reflowNotifier(this);
+  mFrameConstructor->NotifyCounterStylesAreDirty();
+}
+
+bool PresShell::FrameIsAncestorOfDirtyRoot(nsIFrame* aFrame) const {
+  return mDirtyRoots.FrameIsAncestorOfAnyElement(aFrame);
+}
+
+void PresShell::ReconstructFrames() {
+  MOZ_ASSERT(!mFrameConstructor->GetRootFrame() || mDidInitialize,
+             "Must not have root frame before initial reflow");
+  if (!mDidInitialize || mIsDestroying) {
+    // Nothing to do here
+    return;
+  }
+
+  if (Element* root = mDocument->GetRootElement()) {
+    PostRecreateFramesFor(root);
+  }
+
+  mDocument->FlushPendingNotifications(FlushType::Frames);
+}
+
+nsresult PresShell::RenderDocument(const nsRect& aRect,
+                                   RenderDocumentFlags aFlags,
+                                   nscolor aBackgroundColor,
+                                   gfxContext* aThebesContext) {
+  NS_ENSURE_TRUE(!(aFlags & RenderDocumentFlags::IsUntrusted),
+                 NS_ERROR_NOT_IMPLEMENTED);
+
+  nsRootPresContext* rootPresContext = mPresContext->GetRootPresContext();
+  if (rootPresContext) {
+    rootPresContext->FlushWillPaintObservers();
+    if (mIsDestroying) return NS_OK;
+  }
+
+  nsAutoScriptBlocker blockScripts;
+
+  // Set up the rectangle as the path in aThebesContext
+  gfxRect r(0, 0, nsPresContext::AppUnitsToFloatCSSPixels(aRect.width),
+            nsPresContext::AppUnitsToFloatCSSPixels(aRect.height));
+  aThebesContext->NewPath();
+#ifdef MOZ_GFX_OPTIMIZE_MOBILE
+  aThebesContext->SnappedRectangle(r);
+#else
+  aThebesContext->Rectangle(r);
+#endif
+
+  nsIFrame* rootFrame = mFrameConstructor->GetRootFrame();
+  if (!rootFrame) {
+    // Nothing to paint, just fill the rect
+    aThebesContext->SetColor(sRGBColor::FromABGR(aBackgroundColor));
+    aThebesContext->Fill();
+    return NS_OK;
+  }
+
+  gfxContextAutoSaveRestore save(aThebesContext);
+
+  MOZ_ASSERT(aThebesContext->CurrentOp() == CompositionOp::OP_OVER);
+
+  aThebesContext->Clip();
+
+  nsDeviceContext* devCtx = mPresContext->DeviceContext();
+
+  gfxPoint offset(-nsPresContext::AppUnitsToFloatCSSPixels(aRect.x),
+                  -nsPresContext::AppUnitsToFloatCSSPixels(aRect.y));
+  gfxFloat scale =
+      gfxFloat(devCtx->AppUnitsPerDevPixel()) / AppUnitsPerCSSPixel();
+
+  // Since canvas APIs use floats to set up their matrices, we may have some
+  // slight rounding errors here.  We use NudgeToIntegers() here to adjust
+  // matrix components that are integers up to the accuracy of floats to be
+  // those integers.
+  gfxMatrix newTM = aThebesContext->CurrentMatrixDouble()
+                        .PreTranslate(offset)
+                        .PreScale(scale, scale)
+                        .NudgeToIntegers();
+  aThebesContext->SetMatrixDouble(newTM);
+
+  AutoSaveRestoreRenderingState _(this);
+
+  bool wouldFlushRetainedLayers = false;
+  PaintFrameFlags flags = PaintFrameFlags::IgnoreSuppression;
+  if (aThebesContext->CurrentMatrix().HasNonIntegerTranslation()) {
+    flags |= PaintFrameFlags::InTransform;
+  }
+  if (!(aFlags & RenderDocumentFlags::AsyncDecodeImages)) {
+    flags |= PaintFrameFlags::SyncDecodeImages;
+  }
+  if (aFlags & RenderDocumentFlags::UseHighQualityScaling) {
+    flags |= PaintFrameFlags::UseHighQualityScaling;
+  }
+  if (aFlags & RenderDocumentFlags::UseWidgetLayers) {
+    // We only support using widget layers on display root's with widgets.
+    nsView* view = rootFrame->GetView();
+    if (view && view->GetWidget() &&
+        nsLayoutUtils::GetDisplayRootFrame(rootFrame) == rootFrame) {
+      WindowRenderer* renderer = view->GetWidget()->GetWindowRenderer();
+      // WebRenderLayerManagers in content processes
+      // don't support taking snapshots.
+      if (renderer &&
+          (!renderer->AsKnowsCompositor() || XRE_IsParentProcess())) {
+        flags |= PaintFrameFlags::WidgetLayers;
+      }
+    }
+  }
+  if (!(aFlags & RenderDocumentFlags::DrawCaret)) {
+    wouldFlushRetainedLayers = true;
+    flags |= PaintFrameFlags::HideCaret;
+  }
+  if (aFlags & RenderDocumentFlags::IgnoreViewportScrolling) {
+    wouldFlushRetainedLayers = !IgnoringViewportScrolling();
+    mRenderingStateFlags |= RenderingStateFlags::IgnoringViewportScrolling;
+  }
+  if (aFlags & RenderDocumentFlags::ResetViewportScrolling) {
+    wouldFlushRetainedLayers = true;
+    flags |= PaintFrameFlags::ResetViewportScrolling;
+  }
+  if (aFlags & RenderDocumentFlags::DrawWindowNotFlushing) {
+    mRenderingStateFlags |= RenderingStateFlags::DrawWindowNotFlushing;
+  }
+  if (aFlags & RenderDocumentFlags::DocumentRelative) {
+    // XXX be smarter about this ... drawWindow might want a rect
+    // that's "pretty close" to what our retained layer tree covers.
+    // In that case, it wouldn't disturb normal rendering too much,
+    // and we should allow it.
+    wouldFlushRetainedLayers = true;
+    flags |= PaintFrameFlags::DocumentRelative;
+  }
+
+  // Don't let drawWindow blow away our retained layer tree
+  if ((flags & PaintFrameFlags::WidgetLayers) && wouldFlushRetainedLayers) {
+    flags &= ~PaintFrameFlags::WidgetLayers;
+  }
+
+  nsLayoutUtils::PaintFrame(aThebesContext, rootFrame, nsRegion(aRect),
+                            aBackgroundColor,
+                            nsDisplayListBuilderMode::Painting, flags);
+
+  return NS_OK;
+}
+
+/*
+ * Clip the display list aList to a range. Returns the clipped
+ * rectangle surrounding the range.
+ */
+nsRect PresShell::ClipListToRange(nsDisplayListBuilder* aBuilder,
+                                  nsDisplayList* aList, nsRange* aRange) {
+  // iterate though the display items and add up the bounding boxes of each.
+  // This will allow the total area of the frames within the range to be
+  // determined. To do this, remove an item from the bottom of the list, check
+  // whether it should be part of the range, and if so, append it to the top
+  // of the temporary list tmpList. If the item is a text frame at the end of
+  // the selection range, clip it to the portion of the text frame that is
+  // part of the selection. Then, append the wrapper to the top of the list.
+  // Otherwise, just delete the item and don't append it.
+  nsRect surfaceRect;
+
+  for (nsDisplayItem* i : aList->TakeItems()) {
+    if (i->GetType() == DisplayItemType::TYPE_CONTAINER) {
+      aList->AppendToTop(i);
+      surfaceRect.UnionRect(
+          surfaceRect, ClipListToRange(aBuilder, i->GetChildren(), aRange));
+      continue;
+    }
+
+    // itemToInsert indiciates the item that should be inserted into the
+    // temporary list. If null, no item should be inserted.
+    nsDisplayItem* itemToInsert = nullptr;
+    nsIFrame* frame = i->Frame();
+    nsIContent* content = frame->GetContent();
+    if (content) {
+      bool atStart = (content == aRange->GetStartContainer());
+      bool atEnd = (content == aRange->GetEndContainer());
+      if ((atStart || atEnd) && frame->IsTextFrame()) {
+        auto [frameStartOffset, frameEndOffset] = frame->GetOffsets();
+
+        int32_t hilightStart =
+            atStart ? std::max(static_cast<int32_t>(aRange->StartOffset()),
+                               frameStartOffset)
+                    : frameStartOffset;
+        int32_t hilightEnd =
+            atEnd ? std::min(static_cast<int32_t>(aRange->EndOffset()),
+                             frameEndOffset)
+                  : frameEndOffset;
+        if (hilightStart < hilightEnd) {
+          // determine the location of the start and end edges of the range.
+          nsPoint startPoint, endPoint;
+          frame->GetPointFromOffset(hilightStart, &startPoint);
+          frame->GetPointFromOffset(hilightEnd, &endPoint);
+
+          // The clip rectangle is determined by taking the the start and
+          // end points of the range, offset from the reference frame.
+          // Because of rtl, the end point may be to the left of (or above,
+          // in vertical mode) the start point, so x (or y) is set to the
+          // lower of the values.
+          nsRect textRect(aBuilder->ToReferenceFrame(frame), frame->GetSize());
+          if (frame->GetWritingMode().IsVertical()) {
+            nscoord y = std::min(startPoint.y, endPoint.y);
+            textRect.y += y;
+            textRect.height = std::max(startPoint.y, endPoint.y) - y;
+          } else {
+            nscoord x = std::min(startPoint.x, endPoint.x);
+            textRect.x += x;
+            textRect.width = std::max(startPoint.x, endPoint.x) - x;
+          }
+          surfaceRect.UnionRect(surfaceRect, textRect);
+
+          const ActiveScrolledRoot* asr = i->GetActiveScrolledRoot();
+
+          DisplayItemClip newClip;
+          newClip.SetTo(textRect);
+
+          const DisplayItemClipChain* newClipChain =
+              aBuilder->AllocateDisplayItemClipChain(newClip, asr, nullptr);
+
+          i->IntersectClip(aBuilder, newClipChain, true);
+          itemToInsert = i;
+        }
+      }
+      // Don't try to descend into subdocuments.
+      // If this ever changes we'd need to add handling for subdocuments with
+      // different zoom levels.
+      else if (content->GetUncomposedDoc() ==
+               aRange->GetStartContainer()->GetUncomposedDoc()) {
+        // if the node is within the range, append it to the temporary list
+        bool before, after;
+        nsresult rv =
+            RangeUtils::CompareNodeToRange(content, aRange, &before, &after);
+        if (NS_SUCCEEDED(rv) && !before && !after) {
+          itemToInsert = i;
+          bool snap;
+          surfaceRect.UnionRect(surfaceRect, i->GetBounds(aBuilder, &snap));
+        }
+      }
+    }
+
+    // insert the item into the list if necessary. If the item has a child
+    // list, insert that as well
+    nsDisplayList* sublist = i->GetSameCoordinateSystemChildren();
+    if (itemToInsert || sublist) {
+      aList->AppendToTop(itemToInsert ? itemToInsert : i);
+      // if the item is a list, iterate over it as well
+      if (sublist)
+        surfaceRect.UnionRect(surfaceRect,
+                              ClipListToRange(aBuilder, sublist, aRange));
+    } else {
+      // otherwise, just delete the item and don't readd it to the list
+      i->Destroy(aBuilder);
+    }
+  }
+
+  return surfaceRect;
+}
+
+#ifdef DEBUG
+#  include <stdio.h>
+
+static bool gDumpRangePaintList = false;
+#endif
+
+UniquePtr<RangePaintInfo> PresShell::CreateRangePaintInfo(
+    nsRange* aRange, nsRect& aSurfaceRect, bool aForPrimarySelection) {
+  nsIFrame* ancestorFrame = nullptr;
+  nsIFrame* rootFrame = GetRootFrame();
+
+  // If the start or end of the range is the document, just use the root
+  // frame, otherwise get the common ancestor of the two endpoints of the
+  // range.
+  nsINode* startContainer = aRange->GetStartContainer();
+  nsINode* endContainer = aRange->GetEndContainer();
+  Document* doc = startContainer->GetComposedDoc();
+  if (startContainer == doc || endContainer == doc) {
+    ancestorFrame = rootFrame;
+  } else {
+    nsINode* ancestor = nsContentUtils::GetClosestCommonInclusiveAncestor(
+        startContainer, endContainer);
+    NS_ASSERTION(!ancestor || ancestor->IsContent(),
+                 "common ancestor is not content");
+
+    while (ancestor && ancestor->IsContent()) {
+      ancestorFrame = ancestor->AsContent()->GetPrimaryFrame();
+      if (ancestorFrame) {
+        break;
+      }
+
+      ancestor = ancestor->GetParentOrShadowHostNode();
+    }
+
+    // use the nearest ancestor frame that includes all continuations as the
+    // root for building the display list
+    while (ancestorFrame &&
+           nsLayoutUtils::GetNextContinuationOrIBSplitSibling(ancestorFrame))
+      ancestorFrame = ancestorFrame->GetParent();
+  }
+
+  if (!ancestorFrame) {
+    return nullptr;
+  }
+
+  // get a display list containing the range
+  auto info = MakeUnique<RangePaintInfo>(aRange, ancestorFrame);
+  info->mBuilder.SetIncludeAllOutOfFlows();
+  if (aForPrimarySelection) {
+    info->mBuilder.SetSelectedFramesOnly();
+  }
+  info->mBuilder.EnterPresShell(ancestorFrame);
+
+  ContentSubtreeIterator subtreeIter;
+  nsresult rv = subtreeIter.Init(aRange);
+  if (NS_FAILED(rv)) {
+    return nullptr;
+  }
+
+  auto BuildDisplayListForNode = [&](nsINode* aNode) {
+    if (MOZ_UNLIKELY(!aNode->IsContent())) {
+      return;
+    }
+    nsIFrame* frame = aNode->AsContent()->GetPrimaryFrame();
+    // XXX deal with frame being null due to display:contents
+    for (; frame;
+         frame = nsLayoutUtils::GetNextContinuationOrIBSplitSibling(frame)) {
+      info->mBuilder.SetVisibleRect(frame->InkOverflowRect());
+      info->mBuilder.SetDirtyRect(frame->InkOverflowRect());
+      frame->BuildDisplayListForStackingContext(&info->mBuilder, &info->mList);
+    }
+  };
+  if (startContainer->NodeType() == nsINode::TEXT_NODE) {
+    BuildDisplayListForNode(startContainer);
+  }
+  for (; !subtreeIter.IsDone(); subtreeIter.Next()) {
+    nsCOMPtr<nsINode> node = subtreeIter.GetCurrentNode();
+    BuildDisplayListForNode(node);
+  }
+  if (endContainer != startContainer &&
+      endContainer->NodeType() == nsINode::TEXT_NODE) {
+    BuildDisplayListForNode(endContainer);
+  }
+
+  // If one of the ancestor presShells (including this one) has a resolution
+  // set, we may have some APZ zoom applied. That means we may want to rasterize
+  // the nodes at that zoom level. Populate `info` with the relevant information
+  // so that the caller can decide what to do. Also wrap the display list in
+  // appropriate nsDisplayAsyncZoom display items. This code handles the general
+  // case with nested async zooms (even though that never actually happens),
+  // because it fell out of the implementation for free.
+  //
+  // TODO: Do we need to do the same for ancestor transforms?
+  for (nsPresContext* ctx = GetPresContext(); ctx;
+       ctx = ctx->GetParentPresContext()) {
+    PresShell* shell = ctx->PresShell();
+    float resolution = shell->GetResolution();
+
+    // If we are at the root document in the process, try to see if documents
+    // in enclosing processes have a resolution and include that as well.
+    if (!ctx->GetParentPresContext()) {
+      // xScale is an arbitrary choice. Outside of edge cases involving CSS
+      // transforms, xScale == yScale so it doesn't matter.
+      resolution *= ViewportUtils::TryInferEnclosingResolution(shell).xScale;
+    }
+
+    if (resolution == 1.0) {
+      continue;
+    }
+
+    info->mResolution *= resolution;
+    nsIFrame* rootScrollFrame = shell->GetRootScrollFrame();
+    ViewID zoomedId =
+        nsLayoutUtils::FindOrCreateIDFor(rootScrollFrame->GetContent());
+
+    nsDisplayList wrapped(&info->mBuilder);
+    wrapped.AppendNewToTop<nsDisplayAsyncZoom>(&info->mBuilder, rootScrollFrame,
+                                               &info->mList, nullptr, zoomedId);
+    info->mList.AppendToTop(&wrapped);
+  }
+
+#ifdef DEBUG
+  if (gDumpRangePaintList) {
+    fprintf(stderr, "CreateRangePaintInfo --- before ClipListToRange:\n");
+    nsIFrame::PrintDisplayList(&(info->mBuilder), info->mList);
+  }
+#endif
+
+  nsRect rangeRect = ClipListToRange(&info->mBuilder, &info->mList, aRange);
+
+  info->mBuilder.LeavePresShell(ancestorFrame, &info->mList);
+
+#ifdef DEBUG
+  if (gDumpRangePaintList) {
+    fprintf(stderr, "CreateRangePaintInfo --- after ClipListToRange:\n");
+    nsIFrame::PrintDisplayList(&(info->mBuilder), info->mList);
+  }
+#endif
+
+  // determine the offset of the reference frame for the display list
+  // to the root frame. This will allow the coordinates used when painting
+  // to all be offset from the same point
+  info->mRootOffset = ancestorFrame->GetBoundingClientRect().TopLeft();
+  rangeRect.MoveBy(info->mRootOffset);
+  aSurfaceRect.UnionRect(aSurfaceRect, rangeRect);
+
+  return info;
+}
+
+already_AddRefed<SourceSurface> PresShell::PaintRangePaintInfo(
+    const nsTArray<UniquePtr<RangePaintInfo>>& aItems, Selection* aSelection,
+    const Maybe<CSSIntRegion>& aRegion, nsRect aArea,
+    const LayoutDeviceIntPoint aPoint, LayoutDeviceIntRect* aScreenRect,
+    RenderImageFlags aFlags) {
+  nsPresContext* pc = GetPresContext();
+  if (!pc || aArea.width == 0 || aArea.height == 0) return nullptr;
+
+  // use the rectangle to create the surface
+  LayoutDeviceIntRect pixelArea = LayoutDeviceIntRect::FromAppUnitsToOutside(
+      aArea, pc->AppUnitsPerDevPixel());
+
+  // if the image should not be resized, scale must be 1
+  float scale = 1.0;
+
+  nsRect maxSize;
+  pc->DeviceContext()->GetClientRect(maxSize);
+
+  // check if the image should be resized
+  bool resize = !!(aFlags & RenderImageFlags::AutoScale);
+
+  if (resize) {
+    // check if image-resizing-algorithm should be used
+    if (aFlags & RenderImageFlags::IsImage) {
+      // get max screensize
+      int32_t maxWidth = pc->AppUnitsToDevPixels(maxSize.width);
+      int32_t maxHeight = pc->AppUnitsToDevPixels(maxSize.height);
+      // resize image relative to the screensize
+      // get best height/width relative to screensize
+      float bestHeight = float(maxHeight) * RELATIVE_SCALEFACTOR;
+      float bestWidth = float(maxWidth) * RELATIVE_SCALEFACTOR;
+      // calculate scale for bestWidth
+      float adjustedScale = bestWidth / float(pixelArea.width);
+      // get the worst height (height when width is perfect)
+      float worstHeight = float(pixelArea.height) * adjustedScale;
+      // get the difference of best and worst height
+      float difference = bestHeight - worstHeight;
+      // halve the difference and add it to worstHeight to get
+      // the best compromise between bestHeight and bestWidth,
+      // then calculate the corresponding scale factor
+      adjustedScale = (worstHeight + difference / 2) / float(pixelArea.height);
+      // prevent upscaling
+      scale = std::min(scale, adjustedScale);
+    } else {
+      // get half of max screensize
+      int32_t maxWidth = pc->AppUnitsToDevPixels(maxSize.width >> 1);
+      int32_t maxHeight = pc->AppUnitsToDevPixels(maxSize.height >> 1);
+      if (pixelArea.width > maxWidth || pixelArea.height > maxHeight) {
+        // divide the maximum size by the image size in both directions.
+        // Whichever direction produces the smallest result determines how much
+        // should be scaled.
+        if (pixelArea.width > maxWidth)
+          scale = std::min(scale, float(maxWidth) / pixelArea.width);
+        if (pixelArea.height > maxHeight)
+          scale = std::min(scale, float(maxHeight) / pixelArea.height);
+      }
+    }
+
+    // Pick a resolution scale factor that is the highest we need for any of
+    // the items. This means some items may get rendered at a higher-than-needed
+    // resolution but at least nothing will be avoidably blurry.
+    float resolutionScale = 1.0;
+    for (const UniquePtr<RangePaintInfo>& rangeInfo : aItems) {
+      resolutionScale = std::max(resolutionScale, rangeInfo->mResolution);
+    }
+    float unclampedResolution = resolutionScale;
+    // Clamp the resolution scale so that `pixelArea` when scaled by `scale` and
+    // `resolutionScale` isn't bigger than `maxSize`. This prevents creating
+    // giant/unbounded images.
+    resolutionScale =
+        std::min(resolutionScale, maxSize.width / (scale * pixelArea.width));
+    resolutionScale =
+        std::min(resolutionScale, maxSize.height / (scale * pixelArea.height));
+    // The following assert should only get hit if pixelArea scaled by `scale`
+    // alone would already have been bigger than `maxSize`, which should never
+    // be the case. For release builds we handle gracefully by reverting
+    // resolutionScale to 1.0 to avoid unexpected consequences.
+    MOZ_ASSERT(resolutionScale >= 1.0);
+    resolutionScale = std::max(1.0f, resolutionScale);
+
+    scale *= resolutionScale;
+
+    // Now we need adjust the output screen position of the surface based on the
+    // scaling factor and any APZ zoom that may be in effect. The goal is here
+    // to set `aScreenRect`'s top-left corner (in screen-relative LD pixels)
+    // such that the scaling effect on the surface appears anchored  at `aPoint`
+    // ("anchor" here is like "transform-origin"). When this code is e.g. used
+    // to generate a drag image for dragging operations, `aPoint` refers to the
+    // position of the mouse cursor (also in screen-relative LD pixels), and the
+    // user-visible effect of doing this is that the point at which the user
+    // clicked to start the drag remains under the mouse during the drag.
+
+    // In order to do this we first compute the top-left corner of the
+    // pixelArea is screen-relative LD pixels.
+    LayoutDevicePoint visualPoint = ViewportUtils::ToScreenRelativeVisual(
+        LayoutDevicePoint(pixelArea.TopLeft()), pc);
+    // And then adjust the output screen position based on that, which we can do
+    // since everything here is screen-relative LD pixels. Note that the scale
+    // factor we use here is the effective "transform" scale applied to the
+    // content we're painting, relative to the scale at which it would normally
+    // get painted at as part of page rendering (`unclampedResolution`).
+    float scaleRelativeToNormalContent = scale / unclampedResolution;
+    aScreenRect->x =
+        NSToIntFloor(aPoint.x - float(aPoint.x.value - visualPoint.x.value) *
+                                    scaleRelativeToNormalContent);
+    aScreenRect->y =
+        NSToIntFloor(aPoint.y - float(aPoint.y.value - visualPoint.y.value) *
+                                    scaleRelativeToNormalContent);
+
+    pixelArea.width = NSToIntFloor(float(pixelArea.width) * scale);
+    pixelArea.height = NSToIntFloor(float(pixelArea.height) * scale);
+    if (!pixelArea.width || !pixelArea.height) {
+      return nullptr;
+    }
+  } else {
+    // move aScreenRect to the position of the surface in screen coordinates
+    LayoutDevicePoint visualPoint = ViewportUtils::ToScreenRelativeVisual(
+        LayoutDevicePoint(pixelArea.TopLeft()), pc);
+    aScreenRect->MoveTo(RoundedToInt(visualPoint));
+  }
+  aScreenRect->width = pixelArea.width;
+  aScreenRect->height = pixelArea.height;
+
+  RefPtr<DrawTarget> dt =
+      gfxPlatform::GetPlatform()->CreateOffscreenContentDrawTarget(
+          IntSize(pixelArea.width, pixelArea.height), SurfaceFormat::B8G8R8A8);
+  if (!dt || !dt->IsValid()) {
+    return nullptr;
+  }
+
+  RefPtr<gfxContext> ctx = gfxContext::CreateOrNull(dt);
+  MOZ_ASSERT(ctx);  // already checked the draw target above
+
+  if (aRegion) {
+    RefPtr<PathBuilder> builder = dt->CreatePathBuilder(FillRule::FILL_WINDING);
+
+    // Convert aRegion from CSS pixels to dev pixels
+    nsIntRegion region = aRegion->ToAppUnits(AppUnitsPerCSSPixel())
+                             .ToOutsidePixels(pc->AppUnitsPerDevPixel());
+    for (auto iter = region.RectIter(); !iter.Done(); iter.Next()) {
+      const IntRect& rect = iter.Get();
+
+      builder->MoveTo(rect.TopLeft());
+      builder->LineTo(rect.TopRight());
+      builder->LineTo(rect.BottomRight());
+      builder->LineTo(rect.BottomLeft());
+      builder->LineTo(rect.TopLeft());
+    }
+
+    RefPtr<Path> path = builder->Finish();
+    ctx->Clip(path);
+  }
+
+  gfxMatrix initialTM = ctx->CurrentMatrixDouble();
+
+  if (resize) {
+    initialTM.PreScale(scale, scale);
+  }
+
+  // translate so that points are relative to the surface area
+  gfxPoint surfaceOffset = nsLayoutUtils::PointToGfxPoint(
+      -aArea.TopLeft(), pc->AppUnitsPerDevPixel());
+  initialTM.PreTranslate(surfaceOffset);
+
+  // temporarily hide the selection so that text is drawn normally. If a
+  // selection is being rendered, use that, otherwise use the presshell's
+  // selection.
+  RefPtr<nsFrameSelection> frameSelection;
+  if (aSelection) {
+    frameSelection = aSelection->GetFrameSelection();
+  } else {
+    frameSelection = FrameSelection();
+  }
+  int16_t oldDisplaySelection = frameSelection->GetDisplaySelection();
+  frameSelection->SetDisplaySelection(nsISelectionController::SELECTION_HIDDEN);
+
+  // next, paint each range in the selection
+  for (const UniquePtr<RangePaintInfo>& rangeInfo : aItems) {
+    // the display lists paint relative to the offset from the reference
+    // frame, so account for that translation too:
+    gfxPoint rootOffset = nsLayoutUtils::PointToGfxPoint(
+        rangeInfo->mRootOffset, pc->AppUnitsPerDevPixel());
+    ctx->SetMatrixDouble(initialTM.PreTranslate(rootOffset));
+    aArea.MoveBy(-rangeInfo->mRootOffset.x, -rangeInfo->mRootOffset.y);
+    nsRegion visible(aArea);
+    rangeInfo->mList.PaintRoot(&rangeInfo->mBuilder, ctx,
+                               nsDisplayList::PAINT_DEFAULT, Nothing());
+    aArea.MoveBy(rangeInfo->mRootOffset.x, rangeInfo->mRootOffset.y);
+  }
+
+  // restore the old selection display state
+  frameSelection->SetDisplaySelection(oldDisplaySelection);
+
+  return dt->Snapshot();
+}
+
+already_AddRefed<SourceSurface> PresShell::RenderNode(
+    nsINode* aNode, const Maybe<CSSIntRegion>& aRegion,
+    const LayoutDeviceIntPoint aPoint, LayoutDeviceIntRect* aScreenRect,
+    RenderImageFlags aFlags) {
+  // area will hold the size of the surface needed to draw the node, measured
+  // from the root frame.
+  nsRect area;
+  nsTArray<UniquePtr<RangePaintInfo>> rangeItems;
+
+  // nothing to draw if the node isn't in a document
+  if (!aNode->IsInComposedDoc()) {
+    return nullptr;
+  }
+
+  RefPtr<nsRange> range = nsRange::Create(aNode);
+  IgnoredErrorResult rv;
+  range->SelectNode(*aNode, rv);
+  if (rv.Failed()) {
+    return nullptr;
+  }
+
+  UniquePtr<RangePaintInfo> info = CreateRangePaintInfo(range, area, false);
+  if (info) {
+    // XXX(Bug 1631371) Check if this should use a fallible operation as it
+    // pretended earlier, or change the return type to void.
+    rangeItems.AppendElement(std::move(info));
+  }
+
+  Maybe<CSSIntRegion> region = aRegion;
+  if (region) {
+    // combine the area with the supplied region
+    CSSIntRect rrectPixels = region->GetBounds();
+
+    nsRect rrect = ToAppUnits(rrectPixels, AppUnitsPerCSSPixel());
+    area.IntersectRect(area, rrect);
+
+    nsPresContext* pc = GetPresContext();
+    if (!pc) return nullptr;
+
+    // move the region so that it is offset from the topleft corner of the
+    // surface
+    region->MoveBy(-nsPresContext::AppUnitsToIntCSSPixels(area.x),
+                   -nsPresContext::AppUnitsToIntCSSPixels(area.y));
+  }
+
+  return PaintRangePaintInfo(rangeItems, nullptr, region, area, aPoint,
+                             aScreenRect, aFlags);
+}
+
+already_AddRefed<SourceSurface> PresShell::RenderSelection(
+    Selection* aSelection, const LayoutDeviceIntPoint aPoint,
+    LayoutDeviceIntRect* aScreenRect, RenderImageFlags aFlags) {
+  // area will hold the size of the surface needed to draw the selection,
+  // measured from the root frame.
+  nsRect area;
+  nsTArray<UniquePtr<RangePaintInfo>> rangeItems;
+
+  // iterate over each range and collect them into the rangeItems array.
+  // This is done so that the size of selection can be determined so as
+  // to allocate a surface area
+  const uint32_t rangeCount = aSelection->RangeCount();
+  NS_ASSERTION(rangeCount > 0, "RenderSelection called with no selection");
+  for (const uint32_t r : IntegerRange(rangeCount)) {
+    MOZ_ASSERT(aSelection->RangeCount() == rangeCount);
+    RefPtr<nsRange> range = aSelection->GetRangeAt(r);
+
+    UniquePtr<RangePaintInfo> info = CreateRangePaintInfo(range, area, true);
+    if (info) {
+      // XXX(Bug 1631371) Check if this should use a fallible operation as it
+      // pretended earlier.
+      rangeItems.AppendElement(std::move(info));
+    }
+  }
+
+  return PaintRangePaintInfo(rangeItems, aSelection, Nothing(), area, aPoint,
+                             aScreenRect, aFlags);
+}
+
+void AddDisplayItemToBottom(nsDisplayListBuilder* aBuilder,
+                            nsDisplayList* aList, nsDisplayItem* aItem) {
+  if (!aItem) {
+    return;
+  }
+
+  nsDisplayList list(aBuilder);
+  list.AppendToTop(aItem);
+  list.AppendToTop(aList);
+  aList->AppendToTop(&list);
+}
+
+void PresShell::AddPrintPreviewBackgroundItem(nsDisplayListBuilder* aBuilder,
+                                              nsDisplayList* aList,
+                                              nsIFrame* aFrame,
+                                              const nsRect& aBounds) {
+  nsDisplayItem* item = MakeDisplayItem<nsDisplaySolidColor>(
+      aBuilder, aFrame, aBounds, NS_RGB(115, 115, 115));
+  AddDisplayItemToBottom(aBuilder, aList, item);
+}
+
+static bool AddCanvasBackgroundColor(const nsDisplayList* aList,
+                                     nsIFrame* aCanvasFrame, nscolor aColor,
+                                     bool aCSSBackgroundColor) {
+  for (nsDisplayItem* i : *aList) {
+    const DisplayItemType type = i->GetType();
+
+    if (i->Frame() == aCanvasFrame &&
+        type == DisplayItemType::TYPE_CANVAS_BACKGROUND_COLOR) {
+      auto* bg = static_cast<nsDisplayCanvasBackgroundColor*>(i);
+      bg->SetExtraBackgroundColor(aColor);
+      return true;
+    }
+
+    const bool isBlendContainer =
+        type == DisplayItemType::TYPE_BLEND_CONTAINER ||
+        type == DisplayItemType::TYPE_TABLE_BLEND_CONTAINER;
+
+    nsDisplayList* sublist = i->GetSameCoordinateSystemChildren();
+    if (sublist && !(isBlendContainer && !aCSSBackgroundColor) &&
+        AddCanvasBackgroundColor(sublist, aCanvasFrame, aColor,
+                                 aCSSBackgroundColor))
+      return true;
+  }
+  return false;
+}
+
+void PresShell::AddCanvasBackgroundColorItem(
+    nsDisplayListBuilder* aBuilder, nsDisplayList* aList, nsIFrame* aFrame,
+    const nsRect& aBounds, nscolor aBackstopColor,
+    AddCanvasBackgroundColorFlags aFlags) {
+  if (aBounds.IsEmpty()) {
+    return;
+  }
+  // We don't want to add an item for the canvas background color if the frame
+  // (sub)tree we are painting doesn't include any canvas frames. There isn't
+  // an easy way to check this directly, but if we check if the root of the
+  // (sub)tree we are painting is a canvas frame that should cover us in all
+  // cases (it will usually be a viewport frame when we have a canvas frame in
+  // the (sub)tree).
+  if (!(aFlags & AddCanvasBackgroundColorFlags::ForceDraw) &&
+      !aFrame->IsViewportFrame() && !aFrame->IsPageContentFrame()) {
+    return;
+  }
+
+  nscolor bgcolor = NS_ComposeColors(aBackstopColor, mCanvasBackgroundColor);
+  if (NS_GET_A(bgcolor) == 0) return;
+
+  // To make layers work better, we want to avoid having a big non-scrolled
+  // color background behind a scrolled transparent background. Instead,
+  // we'll try to move the color background into the scrolled content
+  // by making nsDisplayCanvasBackground paint it.
+  bool addedScrollingBackgroundColor = false;
+  if (!aFrame->GetParent()) {
+    nsIScrollableFrame* sf =
+        aFrame->PresShell()->GetRootScrollFrameAsScrollable();
+    if (sf) {
+      nsCanvasFrame* canvasFrame = do_QueryFrame(sf->GetScrolledFrame());
+      if (canvasFrame && canvasFrame->IsVisibleForPainting()) {
+        // TODO: We should be able to set canvas background color during display
+        // list building to avoid calling this function.
+        addedScrollingBackgroundColor = AddCanvasBackgroundColor(
+            aList, canvasFrame, bgcolor, mHasCSSBackgroundColor);
+      }
+    }
+  }
+
+  // With async scrolling, we'd like to have two instances of the background
+  // color: one that scrolls with the content (for the reasons stated above),
+  // and one underneath which does not scroll with the content, but which can
+  // be shown during checkerboarding and overscroll.
+  // We can only do that if the color is opaque.
+  bool forceUnscrolledItem =
+      nsLayoutUtils::UsesAsyncScrolling(aFrame) && NS_GET_A(bgcolor) == 255;
+
+  if (!addedScrollingBackgroundColor || forceUnscrolledItem) {
+    nsDisplaySolidColor* item = MakeDisplayItem<nsDisplaySolidColor>(
+        aBuilder, aFrame, aBounds, bgcolor);
+    if (addedScrollingBackgroundColor &&
+        mPresContext->IsRootContentDocumentCrossProcess()) {
+      item->SetIsCheckerboardBackground();
+    }
+    AddDisplayItemToBottom(aBuilder, aList, item);
+  }
+}
+
+bool PresShell::IsTransparentContainerElement() const {
+  nsPresContext* pc = GetPresContext();
+  if (!pc->IsRootContentDocumentCrossProcess()) {
+    if (pc->IsChrome()) {
+      return true;
+    }
+    // Frames are transparent except if their used embedder color-scheme is
+    // mismatched, in which case we use an opaque background to avoid
+    // black-on-black or white-on-white text, see
+    // https://github.com/w3c/csswg-drafts/issues/4772
+    if (BrowsingContext* bc = pc->Document()->GetBrowsingContext()) {
+      switch (bc->GetEmbedderColorSchemes().mUsed) {
+        case dom::PrefersColorSchemeOverride::Light:
+          return pc->DefaultBackgroundColorScheme() == ColorScheme::Light;
+        case dom::PrefersColorSchemeOverride::Dark:
+          return pc->DefaultBackgroundColorScheme() == ColorScheme::Dark;
+        case dom::PrefersColorSchemeOverride::None:
+        case dom::PrefersColorSchemeOverride::EndGuard_:
+          break;
+      }
+    }
+    return true;
+  }
+
+  nsIDocShell* docShell = pc->GetDocShell();
+  if (!docShell) {
+    return false;
+  }
+  nsPIDOMWindowOuter* pwin = docShell->GetWindow();
+  if (!pwin) {
+    return false;
+  }
+  if (Element* containerElement = pwin->GetFrameElementInternal()) {
+    return containerElement->HasAttr(nsGkAtoms::transparent);
+  }
+  if (BrowserChild* tab = BrowserChild::GetFrom(docShell)) {
+    // Check if presShell is the top PresShell. Only the top can influence the
+    // canvas background color.
+    return this == tab->GetTopLevelPresShell() && tab->IsTransparent();
+  }
+  return false;
+}
+
+nscolor PresShell::GetDefaultBackgroundColorToDraw() const {
+  if (!mPresContext) {
+    return NS_RGB(255, 255, 255);
+  }
+  return mPresContext->DefaultBackgroundColor();
+}
+
+void PresShell::UpdateCanvasBackground() {
+  auto canvasBg = ComputeCanvasBackground();
+  mCanvasBackgroundColor = canvasBg.mColor;
+  mHasCSSBackgroundColor = canvasBg.mCSSSpecified;
+}
+
+PresShell::CanvasBackground PresShell::ComputeCanvasBackground() const {
+  // If we have a frame tree and it has style information that
+  // specifies the background color of the canvas, update our local
+  // cache of that color.
+  nsIFrame* rootStyleFrame = FrameConstructor()->GetRootElementStyleFrame();
+  if (!rootStyleFrame) {
+    // If the root element of the document (ie html) has style 'display: none'
+    // then the document's background color does not get drawn; return the color
+    // we actually draw.
+    return {GetDefaultBackgroundColorToDraw(), false};
+  }
+
+  const ComputedStyle* bgStyle =
+      nsCSSRendering::FindRootFrameBackground(rootStyleFrame);
+  // XXX We should really be passing the canvasframe, not the root element
+  // style frame but we don't have access to the canvasframe here. It isn't
+  // a problem because only a few frames can return something other than true
+  // and none of them would be a canvas frame or root element style frame.
+  nscolor color = NS_RGBA(0, 0, 0, 0);
+  bool drawBackgroundImage = false;
+  bool drawBackgroundColor = false;
+  const nsStyleDisplay* disp = rootStyleFrame->StyleDisplay();
+  StyleAppearance appearance = disp->EffectiveAppearance();
+  if (rootStyleFrame->IsThemed(disp) &&
+      appearance != StyleAppearance::MozWinBorderlessGlass) {
+    // Ignore the CSS background-color if -moz-appearance is used and it is
+    // not one of the glass values. (Windows 7 Glass has traditionally not
+    // overridden background colors, so we preserve that behavior for now.)
+  } else {
+    color = nsCSSRendering::DetermineBackgroundColor(
+        mPresContext, bgStyle, rootStyleFrame, drawBackgroundImage,
+        drawBackgroundColor);
+  }
+  if (!IsTransparentContainerElement()) {
+    color = NS_ComposeColors(GetDefaultBackgroundColorToDraw(), color);
+  }
+  return {color, drawBackgroundColor};
+}
+
+nscolor PresShell::ComputeBackstopColor(nsView* aDisplayRoot) {
+  nsIWidget* widget = aDisplayRoot->GetWidget();
+  if (widget && (widget->GetTransparencyMode() != eTransparencyOpaque ||
+                 widget->WidgetPaintsBackground())) {
+    // Within a transparent widget, so the backstop color must be
+    // totally transparent.
+    return NS_RGBA(0, 0, 0, 0);
+  }
+  // Within an opaque widget (or no widget at all), so the backstop
+  // color must be totally opaque. The user's default background
+  // as reported by the prescontext is guaranteed to be opaque.
+  return GetDefaultBackgroundColorToDraw();
+}
+
+struct PaintParams {
+  nscolor mBackgroundColor;
+};
+
+WindowRenderer* PresShell::GetWindowRenderer() {
+  NS_ASSERTION(mViewManager, "Should have view manager");
+
+  nsView* rootView = mViewManager->GetRootView();
+  if (rootView) {
+    if (nsIWidget* widget = rootView->GetWidget()) {
+      return widget->GetWindowRenderer();
+    }
+  }
+  return nullptr;
+}
+
+bool PresShell::AsyncPanZoomEnabled() {
+  NS_ASSERTION(mViewManager, "Should have view manager");
+  nsView* rootView = mViewManager->GetRootView();
+  if (rootView) {
+    if (nsIWidget* widget = rootView->GetWidget()) {
+      return widget->AsyncPanZoomEnabled();
+    }
+  }
+  return gfxPlatform::AsyncPanZoomEnabled();
+}
+
+nsresult PresShell::SetResolutionAndScaleTo(float aResolution,
+                                            ResolutionChangeOrigin aOrigin) {
+  if (!(aResolution > 0.0)) {
+    return NS_ERROR_ILLEGAL_VALUE;
+  }
+  if (aResolution == mResolution.valueOr(0.0)) {
+    MOZ_ASSERT(mResolution.isSome());
+    return NS_OK;
+  }
+
+  // GetResolution handles mResolution being nothing by returning 1 so this
+  // is checking that the resolution is actually changing.
+  bool resolutionUpdated = (aResolution != GetResolution());
+
+  mLastResolutionChangeOrigin = aOrigin;
+
+  RenderingState state(this);
+  state.mResolution = Some(aResolution);
+  SetRenderingState(state);
+  if (mMobileViewportManager) {
+    mMobileViewportManager->ResolutionUpdated(aOrigin);
+  }
+  // Changing the resolution changes the visual viewport size which may
+  // make the current visual viewport offset out-of-bounds (if the size
+  // increased). APZ will reconcile this by sending a clamped visual
+  // viewport offset on the next repaint, but to avoid main-thread code
+  // observing an out-of-bounds offset until then, reclamp it here.
+  if (IsVisualViewportOffsetSet()) {
+    SetVisualViewportOffset(GetVisualViewportOffset(),
+                            GetLayoutViewportOffset());
+  }
+  if (aOrigin == ResolutionChangeOrigin::Apz) {
+    mResolutionUpdatedByApz = true;
+  } else if (resolutionUpdated) {
+    mResolutionUpdated = true;
+  }
+
+  if (auto* window = nsGlobalWindowInner::Cast(mDocument->GetInnerWindow())) {
+    window->VisualViewport()->PostResizeEvent();
+  }
+
+  return NS_OK;
+}
+
+float PresShell::GetCumulativeResolution() const {
+  float resolution = GetResolution();
+  nsPresContext* parentCtx = GetPresContext()->GetParentPresContext();
+  if (parentCtx) {
+    resolution *= parentCtx->PresShell()->GetCumulativeResolution();
+  }
+  return resolution;
+}
+
+void PresShell::SetRestoreResolution(float aResolution,
+                                     LayoutDeviceIntSize aDisplaySize) {
+  if (mMobileViewportManager) {
+    mMobileViewportManager->SetRestoreResolution(aResolution, aDisplaySize);
+  }
+}
+
+void PresShell::SetRenderingState(const RenderingState& aState) {
+  if (GetResolution() != aState.mResolution.valueOr(1.f)) {
+    if (nsIFrame* frame = GetRootFrame()) {
+      frame->SchedulePaint();
+    }
+  }
+
+  mRenderingStateFlags = aState.mRenderingStateFlags;
+  mResolution = aState.mResolution;
+#ifdef ACCESSIBILITY
+  if (nsAccessibilityService* accService = GetAccService()) {
+    accService->NotifyOfResolutionChange(this, GetResolution());
+  }
+#endif
+}
+
+void PresShell::SynthesizeMouseMove(bool aFromScroll) {
+  if (!StaticPrefs::layout_reflow_synthMouseMove()) return;
+
+  if (mPaintingSuppressed || !mIsActive || !mPresContext) {
+    return;
+  }
+
+  if (!mPresContext->IsRoot()) {
+    if (PresShell* rootPresShell = GetRootPresShell()) {
+      rootPresShell->SynthesizeMouseMove(aFromScroll);
+    }
+    return;
+  }
+
+  if (mMouseLocation == nsPoint(NS_UNCONSTRAINEDSIZE, NS_UNCONSTRAINEDSIZE))
+    return;
+
+  if (!mSynthMouseMoveEvent.IsPending()) {
+    RefPtr<nsSynthMouseMoveEvent> ev =
+        new nsSynthMouseMoveEvent(this, aFromScroll);
+
+    GetPresContext()->RefreshDriver()->AddRefreshObserver(
+        ev, FlushType::Display, "Synthetic mouse move event");
+    mSynthMouseMoveEvent = std::move(ev);
+  }
+}
+
+static nsView* FindFloatingViewContaining(nsPresContext* aRootPresContext,
+                                          nsIWidget* aRootWidget,
+                                          const LayoutDeviceIntPoint& aPt) {
+  nsIFrame* popupFrame = nsLayoutUtils::GetPopupFrameForPoint(
+      aRootPresContext, aRootWidget, aPt,
+      nsLayoutUtils::GetPopupFrameForPointFlags::OnlyReturnFramesWithWidgets);
+  return popupFrame ? popupFrame->GetView() : nullptr;
+}
+
+/*
+ * This finds the first view with a frame that contains the given point in a
+ * postorder traversal of the view tree, assuming that the point is not in a
+ * floating view.  It assumes that only floating views extend outside the bounds
+ * of their parents.
+ *
+ * This methods should only be called if FindFloatingViewContaining returns
+ * null.
+ *
+ * aPt is relative aRelativeToView with the viewport type
+ * aRelativeToViewportType. aRelativeToView will always have a frame. If aView
+ * has a frame then aRelativeToView will be aView. (The reason aRelativeToView
+ * and aView are separate is because we need to traverse into views without
+ * frames (ie the inner view of a subdocument frame) but we can only easily
+ * transform between views using TransformPoint which takes frames.)
+ */
+static nsView* FindViewContaining(nsView* aRelativeToView,
+                                  ViewportType aRelativeToViewportType,
+                                  nsView* aView, nsPoint aPt) {
+  MOZ_ASSERT(aRelativeToView->GetFrame());
+
+  if (aView->GetVisibility() == nsViewVisibility_kHide) {
+    return nullptr;
+  }
+
+  nsIFrame* frame = aView->GetFrame();
+  if (frame) {
+    if (!frame->PresShell()->IsActive() ||
+        !frame->IsVisibleConsideringAncestors(
+            nsIFrame::VISIBILITY_CROSS_CHROME_CONTENT_BOUNDARY)) {
+      return nullptr;
+    }
+
+    // We start out in visual coords and then if we cross the zoom boundary we
+    // become in layout coords. The zoom boundary always occurs in a document
+    // with IsRootContentDocumentCrossProcess. The root view of such a document
+    // is outside the zoom boundary and any child view must be inside the zoom
+    // boundary because we only create views for certain kinds of frames and
+    // none of them can be between the root frame and the zoom boundary.
+    bool crossingZoomBoundary = false;
+    if (aRelativeToViewportType == ViewportType::Visual) {
+      if (!aRelativeToView->GetParent() ||
+          aRelativeToView->GetViewManager() !=
+              aRelativeToView->GetParent()->GetViewManager()) {
+        if (aRelativeToView->GetFrame()
+                ->PresContext()
+                ->IsRootContentDocumentCrossProcess()) {
+          crossingZoomBoundary = true;
+        }
+      }
+    }
+
+    ViewportType nextRelativeToViewportType = aRelativeToViewportType;
+    if (crossingZoomBoundary) {
+      nextRelativeToViewportType = ViewportType::Layout;
+    }
+
+    nsLayoutUtils::TransformResult result = nsLayoutUtils::TransformPoint(
+        RelativeTo{aRelativeToView->GetFrame(), aRelativeToViewportType},
+        RelativeTo{frame, nextRelativeToViewportType}, aPt);
+    if (result != nsLayoutUtils::TRANSFORM_SUCCEEDED) {
+      return nullptr;
+    }
+
+    // Even though aPt is in visual coordinates until we cross the zoom boundary
+    // it is valid to compare it to view coords (which are in layout coords)
+    // because visual coords are the same as layout coords for every view
+    // outside of the zoom boundary except for the root view of the root content
+    // document.
+    // For the root view of the root content document, its bounds don't
+    // actually correspond to what is visible when we have a
+    // MobileViewportManager. So we skip the hit test. This is okay because the
+    // point has already been hit test: 1) if we are the root view in the
+    // process then the point comes from a real mouse event so it must have been
+    // over our widget, or 2) if we are the root of a subdocument then
+    // hittesting against the view of the subdocument frame that contains us
+    // already happened and succeeded before getting here.
+    if (!crossingZoomBoundary) {
+      if (!aView->GetDimensions().Contains(aPt)) {
+        return nullptr;
+      }
+    }
+
+    aRelativeToView = aView;
+    aRelativeToViewportType = nextRelativeToViewportType;
+  }
+
+  for (nsView* v = aView->GetFirstChild(); v; v = v->GetNextSibling()) {
+    nsView* r =
+        FindViewContaining(aRelativeToView, aRelativeToViewportType, v, aPt);
+    if (r) return r;
+  }
+
+  return frame ? aView : nullptr;
+}
+
+static BrowserBridgeChild* GetChildBrowser(nsView* aView) {
+  if (!aView) {
+    return nullptr;
+  }
+  nsIFrame* frame = aView->GetFrame();
+  if (!frame && aView->GetParent()) {
+    // If frame is null then view is an anonymous inner view, and we want
+    // the frame from the corresponding outer view.
+    frame = aView->GetParent()->GetFrame();
+  }
+  if (!frame || !frame->GetContent()) {
+    return nullptr;
+  }
+  return BrowserBridgeChild::GetFrom(frame->GetContent());
+}
+
+void PresShell::ProcessSynthMouseMoveEvent(bool aFromScroll) {
+  // If drag session has started, we shouldn't synthesize mousemove event.
+  nsCOMPtr<nsIDragSession> dragSession = nsContentUtils::GetDragSession();
+  if (dragSession) {
+    mSynthMouseMoveEvent.Forget();
+    return;
+  }
+
+  // allow new event to be posted while handling this one only if the
+  // source of the event is a scroll (to prevent infinite reflow loops)
+  if (aFromScroll) {
+    mSynthMouseMoveEvent.Forget();
+  }
+
+  nsView* rootView = mViewManager ? mViewManager->GetRootView() : nullptr;
+  if (mMouseLocation == nsPoint(NS_UNCONSTRAINEDSIZE, NS_UNCONSTRAINEDSIZE) ||
+      !rootView || !rootView->HasWidget() || !mPresContext) {
+    mSynthMouseMoveEvent.Forget();
+    return;
+  }
+
+  NS_ASSERTION(mPresContext->IsRoot(), "Only a root pres shell should be here");
+
+  // Hold a ref to ourselves so DispatchEvent won't destroy us (since
+  // we need to access members after we call DispatchEvent).
+  RefPtr<PresShell> kungFuDeathGrip(this);
+
+#ifdef DEBUG_MOUSE_LOCATION
+  printf("[ps=%p]synthesizing mouse move to (%d,%d)\n", this, mMouseLocation.x,
+         mMouseLocation.y);
+#endif
+
+  int32_t APD = mPresContext->AppUnitsPerDevPixel();
+
+  // We need a widget to put in the event we are going to dispatch so we look
+  // for a view that has a widget and the mouse location is over. We first look
+  // for floating views, if there isn't one we use the root view. |view| holds
+  // that view.
+  nsView* view = nullptr;
+
+  // The appunits per devpixel ratio of |view|.
+  int32_t viewAPD;
+
+  // mRefPoint will be mMouseLocation relative to the widget of |view|, the
+  // widget we will put in the event we dispatch, in viewAPD appunits
+  nsPoint refpoint(0, 0);
+
+  // We always dispatch the event to the pres shell that contains the view that
+  // the mouse is over. pointVM is the VM of that pres shell.
+  nsViewManager* pointVM = nullptr;
+
+  if (rootView->GetFrame()) {
+    view = FindFloatingViewContaining(
+        mPresContext, rootView->GetWidget(),
+        LayoutDeviceIntPoint::FromAppUnitsToNearest(
+            mMouseLocation + rootView->ViewToWidgetOffset(), APD));
+  }
+
+  nsView* pointView = view;
+  if (!view) {
+    view = rootView;
+    if (rootView->GetFrame()) {
+      pointView = FindViewContaining(rootView, ViewportType::Visual, rootView,
+                                     mMouseLocation);
+    } else {
+      pointView = rootView;
+    }
+    // pointView can be null in situations related to mouse capture
+    pointVM = (pointView ? pointView : view)->GetViewManager();
+    refpoint = mMouseLocation + rootView->ViewToWidgetOffset();
+    viewAPD = APD;
+  } else {
+    pointVM = view->GetViewManager();
+    nsIFrame* frame = view->GetFrame();
+    NS_ASSERTION(frame, "floating views can't be anonymous");
+    viewAPD = frame->PresContext()->AppUnitsPerDevPixel();
+    refpoint = mMouseLocation;
+    DebugOnly<nsLayoutUtils::TransformResult> result =
+        nsLayoutUtils::TransformPoint(
+            RelativeTo{rootView->GetFrame(), ViewportType::Visual},
+            RelativeTo{frame, ViewportType::Layout}, refpoint);
+    MOZ_ASSERT(result == nsLayoutUtils::TRANSFORM_SUCCEEDED);
+    refpoint += view->ViewToWidgetOffset();
+  }
+  NS_ASSERTION(view->GetWidget(), "view should have a widget here");
+  WidgetMouseEvent event(true, eMouseMove, view->GetWidget(),
+                         WidgetMouseEvent::eSynthesized);
+  event.mRefPoint =
+      LayoutDeviceIntPoint::FromAppUnitsToNearest(refpoint, viewAPD);
+  // XXX set event.mModifiers ?
+  // XXX mnakano I think that we should get the latest information from widget.
+
+  if (BrowserBridgeChild* bbc = GetChildBrowser(pointView)) {
+    // If we have a BrowserBridgeChild, we're going to be dispatching this
+    // mouse event into an OOP iframe of the current document.
+    event.mLayersId = bbc->GetLayersId();
+    bbc->SendDispatchSynthesizedMouseEvent(event);
+  } else if (RefPtr<PresShell> presShell = pointVM->GetPresShell()) {
+    // Since this gets run in a refresh tick there isn't an InputAPZContext on
+    // the stack from the nsBaseWidget. We need to simulate one with at least
+    // the correct target guid, so that the correct callback transform gets
+    // applied if this event goes to a child process. The input block id is set
+    // to 0 because this is a synthetic event which doesn't really belong to any
+    // input block. Same for the APZ response field.
+    InputAPZContext apzContext(mMouseEventTargetGuid, 0, nsEventStatus_eIgnore);
+    presShell->DispatchSynthMouseMove(&event);
+  }
+
+  if (!aFromScroll) {
+    mSynthMouseMoveEvent.Forget();
+  }
+}
+
+/* static */
+void PresShell::MarkFramesInListApproximatelyVisible(
+    const nsDisplayList& aList) {
+  for (nsDisplayItem* item : aList) {
+    nsDisplayList* sublist = item->GetChildren();
+    if (sublist) {
+      MarkFramesInListApproximatelyVisible(*sublist);
+      continue;
+    }
+
+    nsIFrame* frame = item->Frame();
+    MOZ_ASSERT(frame);
+
+    if (!frame->TrackingVisibility()) {
+      continue;
+    }
+
+    // Use the presshell containing the frame.
+    PresShell* presShell = frame->PresShell();
+    MOZ_ASSERT(!presShell->AssumeAllFramesVisible());
+    if (presShell->mApproximatelyVisibleFrames.EnsureInserted(frame)) {
+      // The frame was added to mApproximatelyVisibleFrames, so increment its
+      // visible count.
+      frame->IncApproximateVisibleCount();
+    }
+  }
+}
+
+/* static */
+void PresShell::DecApproximateVisibleCount(
+    VisibleFrames& aFrames, const Maybe<OnNonvisible>& aNonvisibleAction
+    /* = Nothing() */) {
+  for (nsIFrame* frame : aFrames) {
+    // Decrement the frame's visible count if we're still tracking its
+    // visibility. (We may not be, if the frame disabled visibility tracking
+    // after we added it to the visible frames list.)
+    if (frame->TrackingVisibility()) {
+      frame->DecApproximateVisibleCount(aNonvisibleAction);
+    }
+  }
+}
+
+void PresShell::RebuildApproximateFrameVisibilityDisplayList(
+    const nsDisplayList& aList) {
+  MOZ_ASSERT(!mApproximateFrameVisibilityVisited, "already visited?");
+  mApproximateFrameVisibilityVisited = true;
+
+  // Remove the entries of the mApproximatelyVisibleFrames hashtable and put
+  // them in oldApproxVisibleFrames.
+  VisibleFrames oldApproximatelyVisibleFrames =
+      std::move(mApproximatelyVisibleFrames);
+
+  MarkFramesInListApproximatelyVisible(aList);
+
+  DecApproximateVisibleCount(oldApproximatelyVisibleFrames);
+}
+
+/* static */
+void PresShell::ClearApproximateFrameVisibilityVisited(nsView* aView,
+                                                       bool aClear) {
+  nsViewManager* vm = aView->GetViewManager();
+  if (aClear) {
+    PresShell* presShell = vm->GetPresShell();
+    if (!presShell->mApproximateFrameVisibilityVisited) {
+      presShell->ClearApproximatelyVisibleFramesList();
+    }
+    presShell->mApproximateFrameVisibilityVisited = false;
+  }
+  for (nsView* v = aView->GetFirstChild(); v; v = v->GetNextSibling()) {
+    ClearApproximateFrameVisibilityVisited(v, v->GetViewManager() != vm);
+  }
+}
+
+void PresShell::ClearApproximatelyVisibleFramesList(
+    const Maybe<OnNonvisible>& aNonvisibleAction
+    /* = Nothing() */) {
+  DecApproximateVisibleCount(mApproximatelyVisibleFrames, aNonvisibleAction);
+  mApproximatelyVisibleFrames.Clear();
+}
+
+void PresShell::MarkFramesInSubtreeApproximatelyVisible(
+    nsIFrame* aFrame, const nsRect& aRect, bool aRemoveOnly /* = false */) {
+  MOZ_DIAGNOSTIC_ASSERT(aFrame, "aFrame arg should be a valid frame pointer");
+  MOZ_ASSERT(aFrame->PresShell() == this, "wrong presshell");
+
+  if (aFrame->TrackingVisibility() && aFrame->StyleVisibility()->IsVisible() &&
+      (!aRemoveOnly ||
+       aFrame->GetVisibility() == Visibility::ApproximatelyVisible)) {
+    MOZ_ASSERT(!AssumeAllFramesVisible());
+    if (mApproximatelyVisibleFrames.EnsureInserted(aFrame)) {
+      // The frame was added to mApproximatelyVisibleFrames, so increment its
+      // visible count.
+      aFrame->IncApproximateVisibleCount();
+    }
+  }
+
+  nsSubDocumentFrame* subdocFrame = do_QueryFrame(aFrame);
+  if (subdocFrame) {
+    PresShell* presShell = subdocFrame->GetSubdocumentPresShellForPainting(
+        nsSubDocumentFrame::IGNORE_PAINT_SUPPRESSION);
+    if (presShell && !presShell->AssumeAllFramesVisible()) {
+      nsRect rect = aRect;
+      nsIFrame* root = presShell->GetRootFrame();
+      if (root) {
+        rect.MoveBy(aFrame->GetOffsetToCrossDoc(root));
+      } else {
+        rect.MoveBy(-aFrame->GetContentRectRelativeToSelf().TopLeft());
+      }
+      rect = rect.ScaleToOtherAppUnitsRoundOut(
+          aFrame->PresContext()->AppUnitsPerDevPixel(),
+          presShell->GetPresContext()->AppUnitsPerDevPixel());
+
+      presShell->RebuildApproximateFrameVisibility(&rect);
+    }
+    return;
+  }
+
+  nsRect rect = aRect;
+
+  nsIScrollableFrame* scrollFrame = do_QueryFrame(aFrame);
+  if (scrollFrame) {
+    bool ignoreDisplayPort = false;
+    if (DisplayPortUtils::IsMissingDisplayPortBaseRect(aFrame->GetContent())) {
+      // We can properly set the base rect for root scroll frames on top level
+      // and root content documents. Otherwise the base rect we compute might
+      // be way too big without the limiting that
+      // ScrollFrameHelper::DecideScrollableLayer does, so we just ignore the
+      // displayport in that case.
+      nsPresContext* pc = aFrame->PresContext();
+      if (scrollFrame->IsRootScrollFrameOfDocument() &&
+          (pc->IsRootContentDocumentCrossProcess() ||
+           (pc->IsChrome() && !pc->GetParentPresContext()))) {
+        nsRect baseRect(
+            nsPoint(), nsLayoutUtils::CalculateCompositionSizeForFrame(aFrame));
+        DisplayPortUtils::SetDisplayPortBase(aFrame->GetContent(), baseRect);
+      } else {
+        ignoreDisplayPort = true;
+      }
+    }
+
+    nsRect displayPort;
+    bool usingDisplayport =
+        !ignoreDisplayPort &&
+        DisplayPortUtils::GetDisplayPortForVisibilityTesting(
+            aFrame->GetContent(), &displayPort);
+
+    scrollFrame->NotifyApproximateFrameVisibilityUpdate(!usingDisplayport);
+
+    if (usingDisplayport) {
+      rect = displayPort;
+    } else {
+      rect = rect.Intersect(scrollFrame->GetScrollPortRect());
+    }
+    rect = scrollFrame->ExpandRectToNearlyVisible(rect);
+  }
+
+  bool preserves3DChildren = aFrame->Extend3DContext();
+
+  for (const auto& [list, listID] : aFrame->ChildLists()) {
+    if (listID == FrameChildListID::Popup) {
+      // We assume all frames in popups are visible, so we skip them here.
+      continue;
+    }
+
+    for (nsIFrame* child : list) {
+      // Note: This assert should be trivially satisfied, just by virtue of how
+      // nsFrameList and its iterator works (with nullptr being an end-of-list
+      // sentinel which should terminate the loop).  But we do somehow get
+      // crash reports inside this loop that suggest `child` is null...
+      MOZ_DIAGNOSTIC_ASSERT(child, "shouldn't have null values in child lists");
+      nsRect r = rect - child->GetPosition();
+      if (!r.IntersectRect(r, child->InkOverflowRect())) {
+        continue;
+      }
+      if (child->IsTransformed()) {
+        // for children of a preserve3d element we just pass down the same dirty
+        // rect
+        if (!preserves3DChildren ||
+            !child->Combines3DTransformWithAncestors()) {
+          const nsRect overflow = child->InkOverflowRectRelativeToSelf();
+          nsRect out;
+          if (nsDisplayTransform::UntransformRect(r, overflow, child, &out)) {
+            r = out;
+          } else {
+            r.SetEmpty();
+          }
+        }
+      }
+      MarkFramesInSubtreeApproximatelyVisible(child, r, aRemoveOnly);
+    }
+  }
+}
+
+void PresShell::RebuildApproximateFrameVisibility(
+    nsRect* aRect, bool aRemoveOnly /* = false */) {
+  MOZ_ASSERT(!mApproximateFrameVisibilityVisited, "already visited?");
+  mApproximateFrameVisibilityVisited = true;
+
+  nsIFrame* rootFrame = GetRootFrame();
+  if (!rootFrame) {
+    return;
+  }
+
+  // Remove the entries of the mApproximatelyVisibleFrames hashtable and put
+  // them in oldApproximatelyVisibleFrames.
+  VisibleFrames oldApproximatelyVisibleFrames =
+      std::move(mApproximatelyVisibleFrames);
+
+  nsRect vis(nsPoint(0, 0), rootFrame->GetSize());
+  if (aRect) {
+    vis = *aRect;
+  }
+
+  // If we are in-process root but not the top level content, we need to take
+  // the intersection with the iframe visible rect.
+  if (mPresContext->IsRootContentDocumentInProcess() &&
+      !mPresContext->IsRootContentDocumentCrossProcess()) {
+    // There are two possibilities that we can't get the iframe's visible
+    // rect other than the iframe is out side of ancestors' display ports.
+    // a) the BrowserChild is being torn down
+    // b) the visible rect hasn't been delivered the BrowserChild
+    // In both cases we consider the visible rect is empty.
+    Maybe<nsRect> visibleRect;
+    if (BrowserChild* browserChild = BrowserChild::GetFrom(this)) {
+      visibleRect = browserChild->GetVisibleRect();
+    }
+    vis = vis.Intersect(visibleRect.valueOr(nsRect()));
+  }
+
+  MarkFramesInSubtreeApproximatelyVisible(rootFrame, vis, aRemoveOnly);
+
+  DecApproximateVisibleCount(oldApproximatelyVisibleFrames);
+}
+
+void PresShell::UpdateApproximateFrameVisibility() {
+  DoUpdateApproximateFrameVisibility(/* aRemoveOnly = */ false);
+}
+
+void PresShell::DoUpdateApproximateFrameVisibility(bool aRemoveOnly) {
+  MOZ_ASSERT(
+      !mPresContext || mPresContext->IsRootContentDocumentInProcess(),
+      "Updating approximate frame visibility on a non-root content document?");
+
+  mUpdateApproximateFrameVisibilityEvent.Revoke();
+
+  if (mHaveShutDown || mIsDestroying) {
+    return;
+  }
+
+  // call update on that frame
+  nsIFrame* rootFrame = GetRootFrame();
+  if (!rootFrame) {
+    ClearApproximatelyVisibleFramesList(Some(OnNonvisible::DiscardImages));
+    return;
+  }
+
+  RebuildApproximateFrameVisibility(/* aRect = */ nullptr, aRemoveOnly);
+  ClearApproximateFrameVisibilityVisited(rootFrame->GetView(), true);
+
+#ifdef DEBUG_FRAME_VISIBILITY_DISPLAY_LIST
+  // This can be used to debug the frame walker by comparing beforeFrameList
+  // and mApproximatelyVisibleFrames in RebuildFrameVisibilityDisplayList to see
+  // if they produce the same results (mApproximatelyVisibleFrames holds the
+  // frames the display list thinks are visible, beforeFrameList holds the
+  // frames the frame walker thinks are visible).
+  nsDisplayListBuilder builder(
+      rootFrame, nsDisplayListBuilderMode::FRAME_VISIBILITY, false);
+  nsRect updateRect(nsPoint(0, 0), rootFrame->GetSize());
+  nsIFrame* rootScroll = GetRootScrollFrame();
+  if (rootScroll) {
+    nsIContent* content = rootScroll->GetContent();
+    if (content) {
+      Unused << nsLayoutUtils::GetDisplayPortForVisibilityTesting(
+          content, &updateRect, RelativeTo::ScrollFrame);
+    }
+
+    if (IgnoringViewportScrolling()) {
+      builder.SetIgnoreScrollFrame(rootScroll);
+    }
+  }
+  builder.IgnorePaintSuppression();
+  builder.EnterPresShell(rootFrame);
+  nsDisplayList list;
+  rootFrame->BuildDisplayListForStackingContext(&builder, updateRect, &list);
+  builder.LeavePresShell(rootFrame, &list);
+
+  RebuildApproximateFrameVisibilityDisplayList(list);
+
+  ClearApproximateFrameVisibilityVisited(rootFrame->GetView(), true);
+
+  list.DeleteAll(&builder);
+#endif
+}
+
+bool PresShell::AssumeAllFramesVisible() {
+  if (!StaticPrefs::layout_framevisibility_enabled() || !mPresContext ||
+      !mDocument) {
+    return true;
+  }
+
+  // We assume all frames are visible in print, print preview, chrome, and
+  // resource docs and don't keep track of them.
+  if (mPresContext->Type() == nsPresContext::eContext_PrintPreview ||
+      mPresContext->Type() == nsPresContext::eContext_Print ||
+      mPresContext->IsChrome() || mDocument->IsResourceDoc()) {
+    return true;
+  }
+
+  // If we're assuming all frames are visible in the top level content
+  // document, we need to in subdocuments as well. Otherwise we can get in a
+  // situation where things like animations won't work in subdocuments because
+  // their frames appear not to be visible, since we won't schedule an image
+  // visibility update if the top level content document is assuming all
+  // frames are visible.
+  //
+  // Note that it's not safe to call IsRootContentDocumentInProcess() if we're
+  // currently being destroyed, so we have to check that first.
+  if (!mHaveShutDown && !mIsDestroying &&
+      !mPresContext->IsRootContentDocumentInProcess()) {
+    nsPresContext* presContext =
+        mPresContext->GetInProcessRootContentDocumentPresContext();
+    if (presContext && presContext->PresShell()->AssumeAllFramesVisible()) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+void PresShell::ScheduleApproximateFrameVisibilityUpdateSoon() {
+  if (AssumeAllFramesVisible()) {
+    return;
+  }
+
+  if (!mPresContext) {
+    return;
+  }
+
+  nsRefreshDriver* refreshDriver = mPresContext->RefreshDriver();
+  if (!refreshDriver) {
+    return;
+  }
+
+  // Ask the refresh driver to update frame visibility soon.
+  refreshDriver->ScheduleFrameVisibilityUpdate();
+}
+
+void PresShell::ScheduleApproximateFrameVisibilityUpdateNow() {
+  if (AssumeAllFramesVisible()) {
+    return;
+  }
+
+  if (!mPresContext->IsRootContentDocumentInProcess()) {
+    nsPresContext* presContext =
+        mPresContext->GetInProcessRootContentDocumentPresContext();
+    if (!presContext) return;
+    MOZ_ASSERT(presContext->IsRootContentDocumentInProcess(),
+               "Didn't get a root prescontext from "
+               "GetInProcessRootContentDocumentPresContext?");
+    presContext->PresShell()->ScheduleApproximateFrameVisibilityUpdateNow();
+    return;
+  }
+
+  if (mHaveShutDown || mIsDestroying) {
+    return;
+  }
+
+  if (mUpdateApproximateFrameVisibilityEvent.IsPending()) {
+    return;
+  }
+
+  RefPtr<nsRunnableMethod<PresShell>> event =
+      NewRunnableMethod("PresShell::UpdateApproximateFrameVisibility", this,
+                        &PresShell::UpdateApproximateFrameVisibility);
+  nsresult rv = mDocument->Dispatch(TaskCategory::Other, do_AddRef(event));
+
+  if (NS_SUCCEEDED(rv)) {
+    mUpdateApproximateFrameVisibilityEvent = std::move(event);
+  }
+}
+
+void PresShell::EnsureFrameInApproximatelyVisibleList(nsIFrame* aFrame) {
+  if (!aFrame->TrackingVisibility()) {
+    return;
+  }
+
+  if (AssumeAllFramesVisible()) {
+    aFrame->IncApproximateVisibleCount();
+    return;
+  }
+
+#ifdef DEBUG
+  // Make sure it's in this pres shell.
+  nsCOMPtr<nsIContent> content = aFrame->GetContent();
+  if (content) {
+    PresShell* presShell = content->OwnerDoc()->GetPresShell();
+    MOZ_ASSERT(!presShell || presShell == this, "wrong shell");
+  }
+#endif
+
+  if (mApproximatelyVisibleFrames.EnsureInserted(aFrame)) {
+    // We inserted a new entry.
+    aFrame->IncApproximateVisibleCount();
+  }
+}
+
+void PresShell::RemoveFrameFromApproximatelyVisibleList(nsIFrame* aFrame) {
+#ifdef DEBUG
+  // Make sure it's in this pres shell.
+  nsCOMPtr<nsIContent> content = aFrame->GetContent();
+  if (content) {
+    PresShell* presShell = content->OwnerDoc()->GetPresShell();
+    MOZ_ASSERT(!presShell || presShell == this, "wrong shell");
+  }
+#endif
+
+  if (AssumeAllFramesVisible()) {
+    MOZ_ASSERT(mApproximatelyVisibleFrames.Count() == 0,
+               "Shouldn't have any frames in the table");
+    return;
+  }
+
+  if (mApproximatelyVisibleFrames.EnsureRemoved(aFrame) &&
+      aFrame->TrackingVisibility()) {
+    // aFrame was in the hashtable, and we're still tracking its visibility,
+    // so we need to decrement its visible count.
+    aFrame->DecApproximateVisibleCount();
+  }
+}
+
+void PresShell::PaintAndRequestComposite(nsView* aView, PaintFlags aFlags) {
+  if (!mIsActive) {
+    return;
+  }
+
+  WindowRenderer* renderer = aView->GetWidget()->GetWindowRenderer();
+  NS_ASSERTION(renderer, "Must be in paint event");
+  if (renderer->AsFallback()) {
+    // The fallback renderer doesn't do any retaining, so we
+    // just need to notify the view and widget that we're invalid, and
+    // we'll do a paint+composite from the PaintWindow callback.
+    GetViewManager()->InvalidateView(aView);
+    return;
+  }
+
+  // Otherwise we're a retained WebRenderLayerManager, so we want to call
+  // Paint to update with any changes and push those to WR.
+  PaintInternalFlags flags = PaintInternalFlags::None;
+  if (aFlags & PaintFlags::PaintSyncDecodeImages) {
+    flags |= PaintInternalFlags::PaintSyncDecodeImages;
+  }
+  PaintInternal(aView, flags);
+}
+
+void PresShell::SyncPaintFallback(nsView* aView) {
+  if (!mIsActive) {
+    return;
+  }
+
+  WindowRenderer* renderer = aView->GetWidget()->GetWindowRenderer();
+  NS_ASSERTION(renderer->AsFallback(),
+               "Can't do Sync paint for remote renderers");
+  if (!renderer->AsFallback()) {
+    return;
+  }
+
+  PaintInternal(aView, PaintInternalFlags::PaintComposite);
+  GetPresContext()->NotifyDidPaintForSubtree();
+}
+
+void PresShell::PaintInternal(nsView* aViewToPaint, PaintInternalFlags aFlags) {
+  nsCString url;
+  nsIURI* uri = mDocument->GetDocumentURI();
+  Document* contentRoot = GetPrimaryContentDocument();
+  if (contentRoot) {
+    uri = contentRoot->GetDocumentURI();
+  }
+  url = uri ? uri->GetSpecOrDefault() : "N/A"_ns;
+  AUTO_PROFILER_LABEL_DYNAMIC_NSCSTRING_RELEVANT_FOR_JS("Paint", GRAPHICS, url);
+
+  Maybe<js::AutoAssertNoContentJS> nojs;
+
+  // On Android, Flash can call into content JS during painting, so we can't
+  // assert there. However, we don't rely on this assertion on Android because
+  // we don't paint while JS is running.
+#if !defined(MOZ_WIDGET_ANDROID)
+  if (!(aFlags & PaintInternalFlags::PaintComposite)) {
+    // We need to allow content JS when the flag is set since we may trigger
+    // MozAfterPaint events in content in those cases.
+    nojs.emplace(dom::danger::GetJSContext());
+  }
+#endif
+
+  NS_ASSERTION(!mIsDestroying, "painting a destroyed PresShell");
+  NS_ASSERTION(aViewToPaint, "null view");
+
+  MOZ_ASSERT(!mApproximateFrameVisibilityVisited, "Should have been cleared");
+
+  if (!mIsActive) {
+    return;
+  }
+
+  if (StaticPrefs::apz_keyboard_enabled_AtStartup()) {
+    // Update the focus target for async keyboard scrolling. This will be
+    // forwarded to APZ by nsDisplayList::PaintRoot. We need to to do this
+    // before we enter the paint phase because dispatching eVoid events can
+    // cause layout to happen.
+    mAPZFocusTarget = FocusTarget(this, mAPZFocusSequenceNumber);
+  }
+
+  nsPresContext* presContext = GetPresContext();
+  AUTO_LAYOUT_PHASE_ENTRY_POINT(presContext, Paint);
+
+  nsIFrame* frame = aViewToPaint->GetFrame();
+
+  WindowRenderer* renderer = aViewToPaint->GetWidget()->GetWindowRenderer();
+  NS_ASSERTION(renderer, "Must be in paint event");
+  WebRenderLayerManager* layerManager = renderer->AsWebRender();
+
+  // Whether or not we should set first paint when painting is suppressed
+  // is debatable. For now we'll do it because B2G relied on first paint
+  // to configure the viewport and we only want to do that when we have
+  // real content to paint. See Bug 798245
+  if (mIsFirstPaint && !mPaintingSuppressed) {
+    MOZ_LOG(gLog, LogLevel::Debug,
+            ("PresShell::Paint, first paint, this=%p", this));
+
+    if (layerManager) {
+      layerManager->SetIsFirstPaint();
+    }
+    mIsFirstPaint = false;
+  }
+
+  if (!renderer->BeginTransaction(url)) {
+    return;
+  }
+
+  // Send an updated focus target with this transaction. Be sure to do this
+  // before we paint in the case this is an empty transaction.
+  if (layerManager) {
+    layerManager->SetFocusTarget(mAPZFocusTarget);
+  }
+
+  if (frame) {
+    if (!(aFlags & PaintInternalFlags::PaintSyncDecodeImages) &&
+        !frame->HasAnyStateBits(NS_FRAME_UPDATE_LAYER_TREE)) {
+      if (layerManager) {
+        layerManager->SetTransactionIdAllocator(presContext->RefreshDriver());
+      }
+
+      if (renderer->EndEmptyTransaction(
+              (aFlags & PaintInternalFlags::PaintComposite)
+                  ? WindowRenderer::END_DEFAULT
+                  : WindowRenderer::END_NO_COMPOSITE)) {
+        return;
+      }
+    }
+    frame->RemoveStateBits(NS_FRAME_UPDATE_LAYER_TREE);
+  }
+
+  nscolor bgcolor = ComputeBackstopColor(aViewToPaint);
+  PaintFrameFlags flags =
+      PaintFrameFlags::WidgetLayers | PaintFrameFlags::ExistingTransaction;
+
+  // We force sync-decode for printing / print-preview (printing already does
+  // this from nsPageSequenceFrame::PrintNextSheet).
+  // We also force sync-decoding via pref for reftests.
+  if (aFlags & PaintInternalFlags::PaintSyncDecodeImages ||
+      mDocument->IsStaticDocument() ||
+      StaticPrefs::image_decode_sync_enabled()) {
+    flags |= PaintFrameFlags::SyncDecodeImages;
+  }
+  if (renderer->GetBackendType() == layers::LayersBackend::LAYERS_WR) {
+    flags |= PaintFrameFlags::ForWebRender;
+  }
+
+  if (frame) {
+    // We can paint directly into the widget using its layer manager.
+    nsLayoutUtils::PaintFrame(nullptr, frame, nsRegion(), bgcolor,
+                              nsDisplayListBuilderMode::Painting, flags);
+    return;
+  }
+
+  bgcolor = NS_ComposeColors(bgcolor, mCanvasBackgroundColor);
+
+  if (renderer->GetBackendType() == layers::LayersBackend::LAYERS_WR) {
+    LayoutDeviceRect bounds = LayoutDeviceRect::FromAppUnits(
+        presContext->GetVisibleArea(), presContext->AppUnitsPerDevPixel());
+    WebRenderBackgroundData data(wr::ToLayoutRect(bounds),
+                                 wr::ToColorF(ToDeviceColor(bgcolor)));
+    WrFiltersHolder wrFilters;
+
+    layerManager->SetTransactionIdAllocator(presContext->RefreshDriver());
+    layerManager->EndTransactionWithoutLayer(nullptr, nullptr,
+                                             std::move(wrFilters), &data, 0);
+    return;
+  }
+
+  FallbackRenderer* fallback = renderer->AsFallback();
+  MOZ_ASSERT(fallback);
+
+  if (aFlags & PaintInternalFlags::PaintComposite) {
+    nsIntRect bounds = presContext->GetVisibleArea().ToOutsidePixels(
+        presContext->AppUnitsPerDevPixel());
+    fallback->EndTransactionWithColor(bounds, ToDeviceColor(bgcolor));
+  }
+}
+
+// static
+void PresShell::SetCapturingContent(nsIContent* aContent, CaptureFlags aFlags,
+                                    WidgetEvent* aEvent) {
+  // If capture was set for pointer lock, don't unlock unless we are coming
+  // out of pointer lock explicitly.
+  if (!aContent && sCapturingContentInfo.mPointerLock &&
+      !(aFlags & CaptureFlags::PointerLock)) {
+    return;
+  }
+
+  sCapturingContentInfo.mContent = nullptr;
+  sCapturingContentInfo.mRemoteTarget = nullptr;
+
+  // only set capturing content if allowed or the
+  // CaptureFlags::IgnoreAllowedState or CaptureFlags::PointerLock are used.
+  if ((aFlags & CaptureFlags::IgnoreAllowedState) ||
+      sCapturingContentInfo.mAllowed || (aFlags & CaptureFlags::PointerLock)) {
+    if (aContent) {
+      sCapturingContentInfo.mContent = aContent;
+    }
+    if (aEvent) {
+      MOZ_ASSERT(XRE_IsParentProcess());
+      MOZ_ASSERT(aEvent->mMessage == eMouseDown);
+      MOZ_ASSERT(aEvent->HasBeenPostedToRemoteProcess());
+      sCapturingContentInfo.mRemoteTarget =
+          BrowserParent::GetLastMouseRemoteTarget();
+      MOZ_ASSERT(sCapturingContentInfo.mRemoteTarget);
+    }
+    // CaptureFlags::PointerLock is the same as
+    // CaptureFlags::RetargetToElement & CaptureFlags::IgnoreAllowedState.
+    sCapturingContentInfo.mRetargetToElement =
+        !!(aFlags & CaptureFlags::RetargetToElement) ||
+        !!(aFlags & CaptureFlags::PointerLock);
+    sCapturingContentInfo.mPreventDrag =
+        !!(aFlags & CaptureFlags::PreventDragStart);
+    sCapturingContentInfo.mPointerLock = !!(aFlags & CaptureFlags::PointerLock);
+  }
+}
+
+nsIContent* PresShell::GetCurrentEventContent() {
+  if (mCurrentEventContent &&
+      mCurrentEventContent->GetComposedDoc() != mDocument) {
+    mCurrentEventContent = nullptr;
+    mCurrentEventFrame = nullptr;
+  }
+  return mCurrentEventContent;
+}
+
+nsIFrame* PresShell::GetCurrentEventFrame() {
+  if (MOZ_UNLIKELY(mIsDestroying)) {
+    return nullptr;
+  }
+
+  // GetCurrentEventContent() makes sure the content is still in the
+  // same document that this pres shell belongs to. If not, then the
+  // frame shouldn't get an event, nor should we even assume its safe
+  // to try and find the frame.
+  nsIContent* content = GetCurrentEventContent();
+  if (!mCurrentEventFrame && content) {
+    mCurrentEventFrame = content->GetPrimaryFrame();
+    MOZ_ASSERT(!mCurrentEventFrame ||
+               mCurrentEventFrame->PresContext()->GetPresShell() == this);
+  }
+  return mCurrentEventFrame;
+}
+
+already_AddRefed<nsIContent> PresShell::GetEventTargetContent(
+    WidgetEvent* aEvent) {
+  nsCOMPtr<nsIContent> content = GetCurrentEventContent();
+  if (!content) {
+    nsIFrame* currentEventFrame = GetCurrentEventFrame();
+    if (currentEventFrame) {
+      currentEventFrame->GetContentForEvent(aEvent, getter_AddRefs(content));
+      NS_ASSERTION(!content || content->GetComposedDoc() == mDocument,
+                   "handing out content from a different doc");
+    }
+  }
+  return content.forget();
+}
+
+void PresShell::PushCurrentEventInfo(nsIFrame* aFrame, nsIContent* aContent) {
+  if (mCurrentEventFrame || mCurrentEventContent) {
+    mCurrentEventFrameStack.InsertElementAt(0, mCurrentEventFrame);
+    mCurrentEventContentStack.InsertObjectAt(mCurrentEventContent, 0);
+  }
+  mCurrentEventFrame = aFrame;
+  mCurrentEventContent = aContent;
+}
+
+void PresShell::PopCurrentEventInfo() {
+  mCurrentEventFrame = nullptr;
+  mCurrentEventContent = nullptr;
+
+  if (0 != mCurrentEventFrameStack.Length()) {
+    mCurrentEventFrame = mCurrentEventFrameStack.ElementAt(0);
+    mCurrentEventFrameStack.RemoveElementAt(0);
+    mCurrentEventContent = mCurrentEventContentStack.ObjectAt(0);
+    mCurrentEventContentStack.RemoveObjectAt(0);
+
+    // Don't use it if it has moved to a different document.
+    if (mCurrentEventContent &&
+        mCurrentEventContent->GetComposedDoc() != mDocument) {
+      mCurrentEventContent = nullptr;
+      mCurrentEventFrame = nullptr;
+    }
+  }
+}
+
+// static
+bool PresShell::EventHandler::InZombieDocument(nsIContent* aContent) {
+  // If a content node points to a null document, or the document is not
+  // attached to a window, then it is possibly in a zombie document,
+  // about to be replaced by a newly loading document.
+  // Such documents cannot handle DOM events.
+  // It might actually be in a node not attached to any document,
+  // in which case there is not parent presshell to retarget it to.
+  Document* doc = aContent->GetComposedDoc();
+  return !doc || !doc->GetWindow();
+}
+
+already_AddRefed<nsPIDOMWindowOuter> PresShell::GetRootWindow() {
+  nsCOMPtr<nsPIDOMWindowOuter> window = mDocument->GetWindow();
+  if (window) {
+    nsCOMPtr<nsPIDOMWindowOuter> rootWindow = window->GetPrivateRoot();
+    NS_ASSERTION(rootWindow, "nsPIDOMWindow::GetPrivateRoot() returns NULL");
+    return rootWindow.forget();
+  }
+
+  // If we don't have DOM window, we're zombie, we should find the root window
+  // with our parent shell.
+  RefPtr<PresShell> parentPresShell = GetParentPresShellForEventHandling();
+  NS_ENSURE_TRUE(parentPresShell, nullptr);
+  return parentPresShell->GetRootWindow();
+}
+
+already_AddRefed<nsPIDOMWindowOuter>
+PresShell::GetFocusedDOMWindowInOurWindow() {
+  nsCOMPtr<nsPIDOMWindowOuter> rootWindow = GetRootWindow();
+  NS_ENSURE_TRUE(rootWindow, nullptr);
+  nsCOMPtr<nsPIDOMWindowOuter> focusedWindow;
+  nsFocusManager::GetFocusedDescendant(rootWindow,
+                                       nsFocusManager::eIncludeAllDescendants,
+                                       getter_AddRefs(focusedWindow));
+  return focusedWindow.forget();
+}
+
+already_AddRefed<nsIContent> PresShell::GetFocusedContentInOurWindow() const {
+  nsFocusManager* fm = nsFocusManager::GetFocusManager();
+  if (fm && mDocument) {
+    RefPtr<Element> focusedElement;
+    fm->GetFocusedElementForWindow(mDocument->GetWindow(), false, nullptr,
+                                   getter_AddRefs(focusedElement));
+    return focusedElement.forget();
+  }
+  return nullptr;
+}
+
+already_AddRefed<PresShell> PresShell::GetParentPresShellForEventHandling() {
+  if (!mPresContext) {
+    return nullptr;
+  }
+
+  // Now, find the parent pres shell and send the event there
+  RefPtr<nsDocShell> docShell = mPresContext->GetDocShell();
+  if (!docShell) {
+    docShell = mForwardingContainer.get();
+  }
+
+  // Might have gone away, or never been around to start with
+  if (!docShell) {
+    return nullptr;
+  }
+
+  BrowsingContext* bc = docShell->GetBrowsingContext();
+  if (!bc) {
+    return nullptr;
+  }
+
+  RefPtr<BrowsingContext> parentBC;
+  if (XRE_IsParentProcess()) {
+    parentBC = bc->Canonical()->GetParentCrossChromeBoundary();
+  } else {
+    parentBC = bc->GetParent();
+  }
+
+  RefPtr<nsIDocShell> parentDocShell =
+      parentBC ? parentBC->GetDocShell() : nullptr;
+  if (!parentDocShell) {
+    return nullptr;
+  }
+
+  RefPtr<PresShell> parentPresShell = parentDocShell->GetPresShell();
+  return parentPresShell.forget();
+}
+
+nsresult PresShell::EventHandler::RetargetEventToParent(
+    WidgetGUIEvent* aGUIEvent, nsEventStatus* aEventStatus) {
+  // Send this events straight up to the parent pres shell.
+  // We do this for keystroke events in zombie documents or if either a frame
+  // or a root content is not present.
+  // That way at least the UI key bindings can work.
+
+  RefPtr<PresShell> parentPresShell = GetParentPresShellForEventHandling();
+  NS_ENSURE_TRUE(parentPresShell, NS_ERROR_FAILURE);
+
+  // Fake the event as though it's from the parent pres shell's root frame.
+  return parentPresShell->HandleEvent(parentPresShell->GetRootFrame(),
+                                      aGUIEvent, true, aEventStatus);
+}
+
+void PresShell::DisableNonTestMouseEvents(bool aDisable) {
+  sDisableNonTestMouseEvents = aDisable;
+}
+
+bool PresShell::MouseLocationWasSetBySynthesizedMouseEventForTests() const {
+  if (!mPresContext) {
+    return false;
+  }
+  if (mPresContext->IsRoot()) {
+    return mMouseLocationWasSetBySynthesizedMouseEventForTests;
+  }
+  PresShell* rootPresShell = GetRootPresShell();
+  return rootPresShell &&
+         rootPresShell->mMouseLocationWasSetBySynthesizedMouseEventForTests;
+}
+
+nsPoint PresShell::GetEventLocation(const WidgetMouseEvent& aEvent) const {
+  nsIFrame* rootFrame = GetRootFrame();
+  if (rootFrame) {
+    RelativeTo relativeTo{rootFrame};
+    if (rootFrame->PresContext()->IsRootContentDocumentCrossProcess()) {
+      relativeTo.mViewportType = ViewportType::Visual;
+    }
+    return nsLayoutUtils::GetEventCoordinatesRelativeTo(&aEvent, relativeTo);
+  }
+
+  nsView* rootView = mViewManager->GetRootView();
+  return nsLayoutUtils::TranslateWidgetToView(mPresContext, aEvent.mWidget,
+                                              aEvent.mRefPoint, rootView);
+}
+
+void PresShell::RecordPointerLocation(WidgetGUIEvent* aEvent) {
+  if (!mPresContext) {
+    return;
+  }
+
+  if (!mPresContext->IsRoot()) {
+    PresShell* rootPresShell = GetRootPresShell();
+    if (rootPresShell) {
+      rootPresShell->RecordPointerLocation(aEvent);
+    }
+    return;
+  }
+
+  if ((aEvent->mMessage == eMouseMove &&
+       aEvent->AsMouseEvent()->mReason == WidgetMouseEvent::eReal) ||
+      aEvent->mMessage == eMouseEnterIntoWidget ||
+      aEvent->mMessage == eMouseDown || aEvent->mMessage == eMouseUp) {
+    mMouseLocation = GetEventLocation(*aEvent->AsMouseEvent());
+    mMouseEventTargetGuid = InputAPZContext::GetTargetLayerGuid();
+    mMouseLocationWasSetBySynthesizedMouseEventForTests =
+        aEvent->mFlags.mIsSynthesizedForTests;
+#ifdef DEBUG_MOUSE_LOCATION
+    if (aEvent->mMessage == eMouseEnterIntoWidget) {
+      printf("[ps=%p]got mouse enter for %p\n", this, aEvent->mWidget);
+    }
+    printf("[ps=%p]setting mouse location to (%d,%d)\n", this, mMouseLocation.x,
+           mMouseLocation.y);
+#endif
+    if (aEvent->mMessage == eMouseEnterIntoWidget) {
+      SynthesizeMouseMove(false);
+    }
+  } else if (aEvent->mMessage == eMouseExitFromWidget) {
+    // Although we only care about the mouse moving into an area for which this
+    // pres shell doesn't receive mouse move events, we don't check which widget
+    // the mouse exit was for since this seems to vary by platform.  Hopefully
+    // this won't matter at all since we'll get the mouse move or enter after
+    // the mouse exit when the mouse moves from one of our widgets into another.
+    mMouseLocation = nsPoint(NS_UNCONSTRAINEDSIZE, NS_UNCONSTRAINEDSIZE);
+    mMouseEventTargetGuid = InputAPZContext::GetTargetLayerGuid();
+    mMouseLocationWasSetBySynthesizedMouseEventForTests =
+        aEvent->mFlags.mIsSynthesizedForTests;
+#ifdef DEBUG_MOUSE_LOCATION
+    printf("[ps=%p]got mouse exit for %p\n", this, aEvent->mWidget);
+    printf("[ps=%p]clearing mouse location\n", this);
+#endif
+  } else if ((aEvent->mMessage == ePointerMove &&
+              aEvent->AsMouseEvent()->mReason == WidgetMouseEvent::eReal) ||
+             aEvent->mMessage == ePointerDown ||
+             aEvent->mMessage == ePointerUp) {
+    // TODO: instead, encapsulate `mMouseLocation` and
+    // `mLastOverWindowPointerLocation` in a struct.
+    mLastOverWindowPointerLocation = GetEventLocation(*aEvent->AsMouseEvent());
+  }
+}
+
+void PresShell::nsSynthMouseMoveEvent::Revoke() {
+  if (mPresShell) {
+    mPresShell->GetPresContext()->RefreshDriver()->RemoveRefreshObserver(
+        this, FlushType::Display);
+    mPresShell = nullptr;
+  }
+}
+
+// static
+nsIFrame* PresShell::EventHandler::GetNearestFrameContainingPresShell(
+    PresShell* aPresShell) {
+  nsViewManager* vm = aPresShell->GetViewManager();
+  if (!vm) {
+    return nullptr;
+  }
+  nsView* view = vm->GetRootView();
+  while (view && !view->GetFrame()) {
+    view = view->GetParent();
+  }
+
+  nsIFrame* frame = nullptr;
+  if (view) {
+    frame = view->GetFrame();
+  }
+
+  return frame;
+}
+
+static CallState FlushThrottledStyles(Document& aDocument) {
+  PresShell* presShell = aDocument.GetPresShell();
+  if (presShell && presShell->IsVisible()) {
+    if (nsPresContext* presContext = presShell->GetPresContext()) {
+      presContext->RestyleManager()->UpdateOnlyAnimationStyles();
+    }
+  }
+
+  aDocument.EnumerateSubDocuments(FlushThrottledStyles);
+  return CallState::Continue;
+}
+
+bool PresShell::CanDispatchEvent(const WidgetGUIEvent* aEvent) const {
+  bool rv =
+      mPresContext && !mHaveShutDown && nsContentUtils::IsSafeToRunScript();
+  if (aEvent) {
+    rv &= (aEvent && aEvent->mWidget && !aEvent->mWidget->Destroyed());
+  }
+  return rv;
+}
+
+/* static */
+PresShell* PresShell::GetShellForEventTarget(nsIFrame* aFrame,
+                                             nsIContent* aContent) {
+  if (aFrame) {
+    return aFrame->PresShell();
+  }
+  if (aContent) {
+    Document* doc = aContent->GetComposedDoc();
+    if (!doc) {
+      return nullptr;
+    }
+    return doc->GetPresShell();
+  }
+  return nullptr;
+}
+
+/* static */
+PresShell* PresShell::GetShellForTouchEvent(WidgetGUIEvent* aEvent) {
+  switch (aEvent->mMessage) {
+    case eTouchMove:
+    case eTouchCancel:
+    case eTouchEnd: {
+      // get the correct shell to dispatch to
+      WidgetTouchEvent* touchEvent = aEvent->AsTouchEvent();
+      for (dom::Touch* touch : touchEvent->mTouches) {
+        if (!touch) {
+          return nullptr;
+        }
+
+        RefPtr<dom::Touch> oldTouch =
+            TouchManager::GetCapturedTouch(touch->Identifier());
+        if (!oldTouch) {
+          return nullptr;
+        }
+
+        nsCOMPtr<nsIContent> content = do_QueryInterface(oldTouch->GetTarget());
+        if (!content) {
+          return nullptr;
+        }
+
+        nsIFrame* contentFrame = content->GetPrimaryFrame();
+        if (!contentFrame) {
+          return nullptr;
+        }
+
+        PresShell* presShell = contentFrame->PresContext()->GetPresShell();
+        if (presShell) {
+          return presShell;
+        }
+      }
+      return nullptr;
+    }
+    default:
+      return nullptr;
+  }
+}
+
+nsresult PresShell::HandleEvent(nsIFrame* aFrameForPresShell,
+                                WidgetGUIEvent* aGUIEvent,
+                                bool aDontRetargetEvents,
+                                nsEventStatus* aEventStatus) {
+  MOZ_ASSERT(aGUIEvent);
+  // If it's synthesized in the parent process and our mouse location was set
+  // by a mouse event which was synthesized for tests because the test does not
+  // want to change `:hover` state with the synthesized mouse event for native
+  // mouse cursor position.
+  if (aGUIEvent->mMessage == eMouseMove &&
+      aGUIEvent->CameFromAnotherProcess() && XRE_IsContentProcess() &&
+      !aGUIEvent->mFlags.mIsSynthesizedForTests &&
+      MouseLocationWasSetBySynthesizedMouseEventForTests() &&
+      aGUIEvent->AsMouseEvent()->mReason == WidgetMouseEvent::eSynthesized) {
+    return NS_OK;
+  }
+  EventHandler eventHandler(*this);
+  return eventHandler.HandleEvent(aFrameForPresShell, aGUIEvent,
+                                  aDontRetargetEvents, aEventStatus);
+}
+
+nsresult PresShell::EventHandler::HandleEvent(nsIFrame* aFrameForPresShell,
+                                              WidgetGUIEvent* aGUIEvent,
+                                              bool aDontRetargetEvents,
+                                              nsEventStatus* aEventStatus) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_DIAGNOSTIC_ASSERT(aGUIEvent->IsTrusted());
+  MOZ_ASSERT(aEventStatus);
+
+  NS_ASSERTION(aFrameForPresShell, "aFrameForPresShell should be not null");
+
+  // Update the latest focus sequence number with this new sequence number;
+  // the next transasction that gets sent to the compositor will carry this over
+  if (mPresShell->mAPZFocusSequenceNumber < aGUIEvent->mFocusSequenceNumber) {
+    mPresShell->mAPZFocusSequenceNumber = aGUIEvent->mFocusSequenceNumber;
+  }
+
+  if (mPresShell->IsDestroying() ||
+      (PresShell::sDisableNonTestMouseEvents &&
+       !aGUIEvent->mFlags.mIsSynthesizedForTests &&
+       aGUIEvent->HasMouseEventMessage())) {
+    return NS_OK;
+  }
+
+  mPresShell->RecordPointerLocation(aGUIEvent);
+
+  if (MaybeHandleEventWithAccessibleCaret(aFrameForPresShell, aGUIEvent,
+                                          aEventStatus)) {
+    // Handled by AccessibleCaretEventHub.
+    return NS_OK;
+  }
+
+  if (MaybeDiscardEvent(aGUIEvent)) {
+    // Cannot handle the event for now.
+    return NS_OK;
+  }
+
+  if (!aDontRetargetEvents) {
+    // If aGUIEvent should be handled in another PresShell, we should call its
+    // HandleEvent() and do nothing here.
+    nsresult rv = NS_OK;
+    if (MaybeHandleEventWithAnotherPresShell(aFrameForPresShell, aGUIEvent,
+                                             aEventStatus, &rv)) {
+      // Handled by another PresShell or nobody can handle the event.
+      return rv;
+    }
+  }
+
+  if (MaybeDiscardOrDelayKeyboardEvent(aGUIEvent)) {
+    // The event is discarded or put into the delayed event queue.
+    return NS_OK;
+  }
+
+  if (aGUIEvent->IsUsingCoordinates()) {
+    return HandleEventUsingCoordinates(aFrameForPresShell, aGUIEvent,
+                                       aEventStatus, aDontRetargetEvents);
+  }
+
+  // Activation events need to be dispatched even if no frame was found, since
+  // we don't want the focus to be out of sync.
+  if (!aFrameForPresShell) {
+    if (!NS_EVENT_NEEDS_FRAME(aGUIEvent)) {
+      // Push nullptr for both current event target content and frame since
+      // there is no frame but the event does not require a frame.
+      AutoCurrentEventInfoSetter eventInfoSetter(*this);
+      return HandleEventWithCurrentEventInfo(aGUIEvent, aEventStatus, true,
+                                             nullptr);
+    }
+
+    if (aGUIEvent->HasKeyEventMessage()) {
+      // Keypress events in new blank tabs should not be completely thrown away.
+      // Retarget them -- the parent chrome shell might make use of them.
+      return RetargetEventToParent(aGUIEvent, aEventStatus);
+    }
+
+    return NS_OK;
+  }
+
+  if (aGUIEvent->IsTargetedAtFocusedContent()) {
+    return HandleEventAtFocusedContent(aGUIEvent, aEventStatus);
+  }
+
+  return HandleEventWithFrameForPresShell(aFrameForPresShell, aGUIEvent,
+                                          aEventStatus);
+}
+
+nsresult PresShell::EventHandler::HandleEventUsingCoordinates(
+    nsIFrame* aFrameForPresShell, WidgetGUIEvent* aGUIEvent,
+    nsEventStatus* aEventStatus, bool aDontRetargetEvents) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aGUIEvent->IsUsingCoordinates());
+  MOZ_ASSERT(aEventStatus);
+
+  // Flush pending notifications to handle the event with the latest layout.
+  // But if it causes destroying the frame for mPresShell, stop handling the
+  // event. (why?)
+  AutoWeakFrame weakFrame(aFrameForPresShell);
+  MaybeFlushPendingNotifications(aGUIEvent);
+  if (!weakFrame.IsAlive()) {
+    *aEventStatus = nsEventStatus_eIgnore;
+    return NS_OK;
+  }
+
+  // XXX Retrieving capturing content here.  However, some of the following
+  //     methods allow to run script.  So, isn't it possible the capturing
+  //     content outdated?
+  nsCOMPtr<nsIContent> capturingContent =
+      EventHandler::GetCapturingContentFor(aGUIEvent);
+
+  if (GetDocument() && aGUIEvent->mClass == eTouchEventClass) {
+    PointerLockManager::Unlock();
+  }
+
+  nsIFrame* frameForPresShell = MaybeFlushThrottledStyles(aFrameForPresShell);
+  if (NS_WARN_IF(!frameForPresShell)) {
+    return NS_OK;
+  }
+
+  bool isCapturingContentIgnored = false;
+  bool isCaptureRetargeted = false;
+  nsIFrame* rootFrameToHandleEvent = ComputeRootFrameToHandleEvent(
+      frameForPresShell, aGUIEvent, capturingContent,
+      &isCapturingContentIgnored, &isCaptureRetargeted);
+  if (isCapturingContentIgnored) {
+    capturingContent = nullptr;
+  }
+
+  // The order to generate pointer event is
+  // 1. check pending pointer capture.
+  // 2. check if there is a capturing content.
+  // 3. hit test
+  // 4. dispatch pointer events
+  // 5. check whether the targets of all Touch instances are in the same
+  //    document and suppress invalid instances.
+  // 6. dispatch mouse or touch events.
+
+  // Try to keep frame for following check, because frame can be damaged
+  // during MaybeProcessPointerCapture.
+  {
+    AutoWeakFrame frameKeeper(rootFrameToHandleEvent);
+    PointerEventHandler::MaybeProcessPointerCapture(aGUIEvent);
+    // Prevent application crashes, in case damaged frame.
+    if (!frameKeeper.IsAlive()) {
+      NS_WARNING("Nothing to handle this event!");
+      return NS_OK;
+    }
+  }
+
+  // Only capture mouse events and pointer events.
+  RefPtr<Element> pointerCapturingElement =
+      PointerEventHandler::GetPointerCapturingElement(aGUIEvent);
+
+  if (pointerCapturingElement) {
+    rootFrameToHandleEvent = pointerCapturingElement->GetPrimaryFrame();
+    if (!rootFrameToHandleEvent) {
+      return HandleEventWithPointerCapturingContentWithoutItsFrame(
+          aFrameForPresShell, aGUIEvent, pointerCapturingElement, aEventStatus);
+    }
+  }
+
+  WidgetMouseEvent* mouseEvent = aGUIEvent->AsMouseEvent();
+  bool isWindowLevelMouseExit =
+      (aGUIEvent->mMessage == eMouseExitFromWidget) &&
+      (mouseEvent &&
+       (mouseEvent->mExitFrom.value() == WidgetMouseEvent::ePlatformTopLevel ||
+        mouseEvent->mExitFrom.value() == WidgetMouseEvent::ePuppet));
+
+  // Get the frame at the event point. However, don't do this if we're
+  // capturing and retargeting the event because the captured frame will
+  // be used instead below. Also keep using the root frame if we're dealing
+  // with a window-level mouse exit event since we want to start sending
+  // mouse out events at the root EventStateManager.
+  EventTargetData eventTargetData(rootFrameToHandleEvent);
+  if (!isCaptureRetargeted && !isWindowLevelMouseExit &&
+      !pointerCapturingElement) {
+    if (!ComputeEventTargetFrameAndPresShellAtEventPoint(
+            rootFrameToHandleEvent, aGUIEvent, &eventTargetData)) {
+      *aEventStatus = nsEventStatus_eIgnore;
+      return NS_OK;
+    }
+  }
+
+  // if a node is capturing the mouse, check if the event needs to be
+  // retargeted at the capturing content instead. This will be the case when
+  // capture retargeting is being used, no frame was found or the frame's
+  // content is not a descendant of the capturing content.
+  if (capturingContent && !pointerCapturingElement &&
+      (PresShell::sCapturingContentInfo.mRetargetToElement ||
+       !eventTargetData.mFrame->GetContent() ||
+       !nsContentUtils::ContentIsCrossDocDescendantOf(
+           eventTargetData.mFrame->GetContent(), capturingContent))) {
+    // A check was already done above to ensure that capturingContent is
+    // in this presshell.
+    NS_ASSERTION(capturingContent->OwnerDoc() == GetDocument(),
+                 "Unexpected document");
+    nsIFrame* capturingFrame = capturingContent->GetPrimaryFrame();
+    if (capturingFrame) {
+      eventTargetData.SetFrameAndComputePresShell(capturingFrame);
+    }
+  }
+
+  if (NS_WARN_IF(!eventTargetData.mFrame)) {
+    return NS_OK;
+  }
+
+  // Suppress mouse event if it's being targeted at an element inside
+  // a document which needs events suppressed
+  if (MaybeDiscardOrDelayMouseEvent(eventTargetData.mFrame, aGUIEvent)) {
+    return NS_OK;
+  }
+
+  // Check if we have an active EventStateManager which isn't the
+  // EventStateManager of the current PresContext.  If that is the case, and
+  // mouse is over some ancestor document, forward event handling to the
+  // active document.  This way content can get mouse events even when mouse
+  // is over the chrome or outside the window.
+  if (eventTargetData.MaybeRetargetToActiveDocument(aGUIEvent) &&
+      NS_WARN_IF(!eventTargetData.mFrame)) {
+    return NS_OK;
+  }
+
+  if (!eventTargetData.ComputeElementFromFrame(aGUIEvent)) {
+    return NS_OK;
+  }
+  // Note that even if ComputeElementFromFrame() returns true,
+  // eventTargetData.mContent can be nullptr here.
+
+  // Dispatch a pointer event if Pointer Events is enabled.  Note that if
+  // pointer event listeners change the layout, eventTargetData is
+  // automatically updated.
+  if (!DispatchPrecedingPointerEvent(
+          aFrameForPresShell, aGUIEvent, pointerCapturingElement,
+          aDontRetargetEvents, &eventTargetData, aEventStatus)) {
+    return NS_OK;
+  }
+
+  // frame could be null after dispatching pointer events.
+  // XXX Despite of this comment, we update the event target data outside
+  //     DispatchPrecedingPointerEvent().  Can we make it call
+  //     UpdateTouchEventTarget()?
+  eventTargetData.UpdateTouchEventTarget(aGUIEvent);
+
+  // Handle the event in the correct shell.
+  // We pass the subshell's root frame as the frame to start from. This is
+  // the only correct alternative; if the event was captured then it
+  // must have been captured by us or some ancestor shell and we
+  // now ask the subshell to dispatch it normally.
+  EventHandler eventHandler(*eventTargetData.mPresShell);
+  AutoCurrentEventInfoSetter eventInfoSetter(eventHandler, eventTargetData);
+  // eventTargetData is on the stack and is guaranteed to keep its
+  // mOverrideClickTarget alive, so we can just use MOZ_KnownLive here.
+  nsresult rv = eventHandler.HandleEventWithCurrentEventInfo(
+      aGUIEvent, aEventStatus, true,
+      MOZ_KnownLive(eventTargetData.mOverrideClickTarget));
+  return rv;
+}
+
+bool PresShell::EventHandler::MaybeFlushPendingNotifications(
+    WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(aGUIEvent);
+
+  switch (aGUIEvent->mMessage) {
+    case eMouseDown:
+    case eMouseUp: {
+      RefPtr<nsPresContext> presContext = mPresShell->GetPresContext();
+      if (NS_WARN_IF(!presContext)) {
+        return false;
+      }
+      uint64_t framesConstructedCount = presContext->FramesConstructedCount();
+      uint64_t framesReflowedCount = presContext->FramesReflowedCount();
+
+      MOZ_KnownLive(mPresShell)->FlushPendingNotifications(FlushType::Layout);
+      return framesConstructedCount != presContext->FramesConstructedCount() ||
+             framesReflowedCount != presContext->FramesReflowedCount();
+    }
+    default:
+      return false;
+  }
+}
+
+// The type of coordinates to use for hit-testing input events
+// that are relative to the RCD's viewport frame.
+// On most platforms, use visual coordinates so that scrollbars
+// can be targeted.
+// On mobile, use layout coordinates because hit-testing in
+// visual coordinates clashes with mobile viewport sizing, where
+// the ViewportFrame is sized to the initial containing block
+// (ICB) size, which is in layout coordinates. This is fine
+// because we don't need to be able to target scrollbars on mobile
+// (scrollbar dragging isn't supported).
+static ViewportType ViewportTypeForInputEventsRelativeToRoot() {
+#ifdef MOZ_WIDGET_ANDROID
+  return ViewportType::Layout;
+#else
+  return ViewportType::Visual;
+#endif
+}
+
+nsIFrame* PresShell::EventHandler::GetFrameToHandleNonTouchEvent(
+    nsIFrame* aRootFrameToHandleEvent, WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aGUIEvent->mClass != eTouchEventClass);
+
+  ViewportType viewportType = ViewportType::Layout;
+  if (aRootFrameToHandleEvent->Type() == LayoutFrameType::Viewport) {
+    nsPresContext* pc = aRootFrameToHandleEvent->PresContext();
+    if (pc->IsChrome()) {
+      viewportType = ViewportType::Visual;
+    } else if (pc->IsRootContentDocumentCrossProcess()) {
+      viewportType = ViewportTypeForInputEventsRelativeToRoot();
+    }
+  }
+  RelativeTo relativeTo{aRootFrameToHandleEvent, viewportType};
+  nsPoint eventPoint =
+      nsLayoutUtils::GetEventCoordinatesRelativeTo(aGUIEvent, relativeTo);
+
+  uint32_t flags = 0;
+  if (aGUIEvent->mClass == eMouseEventClass) {
+    WidgetMouseEvent* mouseEvent = aGUIEvent->AsMouseEvent();
+    if (mouseEvent && mouseEvent->mIgnoreRootScrollFrame) {
+      flags |= INPUT_IGNORE_ROOT_SCROLL_FRAME;
+    }
+  }
+
+  nsIFrame* targetFrame =
+      FindFrameTargetedByInputEvent(aGUIEvent, relativeTo, eventPoint, flags);
+  if (!targetFrame) {
+    return aRootFrameToHandleEvent;
+  }
+
+  if (targetFrame->PresShell() == mPresShell) {
+    // If found target is in mPresShell, we've already found it in the latest
+    // layout so that we can use it.
+    return targetFrame;
+  }
+
+  // If target is in a child document, we've not flushed its layout yet.
+  PresShell* childPresShell = targetFrame->PresShell();
+  EventHandler childEventHandler(*childPresShell);
+  AutoWeakFrame weakFrame(aRootFrameToHandleEvent);
+  bool layoutChanged =
+      childEventHandler.MaybeFlushPendingNotifications(aGUIEvent);
+  if (!weakFrame.IsAlive()) {
+    // Stop handling the event if the root frame to handle event is destroyed
+    // by the reflow. (but why?)
+    return nullptr;
+  }
+  if (!layoutChanged) {
+    // If the layout in the child PresShell hasn't been changed, we don't
+    // need to recompute the target.
+    return targetFrame;
+  }
+
+  // Finally, we need to recompute the target with the latest layout.
+  targetFrame =
+      FindFrameTargetedByInputEvent(aGUIEvent, relativeTo, eventPoint, flags);
+
+  return targetFrame ? targetFrame : aRootFrameToHandleEvent;
+}
+
+bool PresShell::EventHandler::ComputeEventTargetFrameAndPresShellAtEventPoint(
+    nsIFrame* aRootFrameToHandleEvent, WidgetGUIEvent* aGUIEvent,
+    EventTargetData* aEventTargetData) {
+  MOZ_ASSERT(aRootFrameToHandleEvent);
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aEventTargetData);
+
+  if (aGUIEvent->mClass == eTouchEventClass) {
+    nsIFrame* targetFrameAtTouchEvent = TouchManager::SetupTarget(
+        aGUIEvent->AsTouchEvent(), aRootFrameToHandleEvent);
+    aEventTargetData->SetFrameAndComputePresShell(targetFrameAtTouchEvent);
+    return true;
+  }
+
+  nsIFrame* targetFrame =
+      GetFrameToHandleNonTouchEvent(aRootFrameToHandleEvent, aGUIEvent);
+  aEventTargetData->SetFrameAndComputePresShell(targetFrame);
+  return !!aEventTargetData->mFrame;
+}
+
+bool PresShell::EventHandler::DispatchPrecedingPointerEvent(
+    nsIFrame* aFrameForPresShell, WidgetGUIEvent* aGUIEvent,
+    nsIContent* aPointerCapturingContent, bool aDontRetargetEvents,
+    EventTargetData* aEventTargetData, nsEventStatus* aEventStatus) {
+  MOZ_ASSERT(aFrameForPresShell);
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aEventTargetData);
+  MOZ_ASSERT(aEventStatus);
+
+  // Dispatch pointer events from the mouse or touch events. Regarding
+  // pointer events from mouse, we should dispatch those pointer events to
+  // the same target as the source mouse events. We pass the frame found
+  // in hit test to PointerEventHandler and dispatch pointer events to it.
+  //
+  // Regarding pointer events from touch, the behavior is different. Touch
+  // events are dispatched to the same target as the target of touchstart.
+  // Multiple touch points must be dispatched to the same document. Pointer
+  // events from touch can be dispatched to different documents. We Pass the
+  // original frame to PointerEventHandler, reentry PresShell::HandleEvent,
+  // and do hit test for each point.
+  nsIFrame* targetFrame = aGUIEvent->mClass == eTouchEventClass
+                              ? aFrameForPresShell
+                              : aEventTargetData->mFrame;
+
+  if (aPointerCapturingContent) {
+    aEventTargetData->mOverrideClickTarget =
+        GetOverrideClickTarget(aGUIEvent, aFrameForPresShell);
+    aEventTargetData->mPresShell =
+        PresShell::GetShellForEventTarget(nullptr, aPointerCapturingContent);
+    if (!aEventTargetData->mPresShell) {
+      // If we can't process event for the capturing content, release
+      // the capture.
+      PointerEventHandler::ReleaseIfCaptureByDescendant(
+          aPointerCapturingContent);
+      return false;
+    }
+
+    targetFrame = aPointerCapturingContent->GetPrimaryFrame();
+    aEventTargetData->mFrame = targetFrame;
+  }
+
+  AutoWeakFrame weakTargetFrame(targetFrame);
+  AutoWeakFrame weakFrame(aEventTargetData->mFrame);
+  nsCOMPtr<nsIContent> content(aEventTargetData->mContent);
+  RefPtr<PresShell> presShell(aEventTargetData->mPresShell);
+  nsCOMPtr<nsIContent> targetContent;
+  PointerEventHandler::DispatchPointerFromMouseOrTouch(
+      presShell, aEventTargetData->mFrame, content, aGUIEvent,
+      aDontRetargetEvents, aEventStatus, getter_AddRefs(targetContent));
+
+  // If the target frame is alive, the caller should keep handling the event
+  // unless event target frame is destroyed.
+  if (weakTargetFrame.IsAlive()) {
+    return weakFrame.IsAlive();
+  }
+
+  // If the event is not a mouse event, the caller should keep handling the
+  // event unless event target frame is destroyed.  Note that this case is
+  // not defined by the spec.
+  if (aGUIEvent->mClass != eMouseEventClass) {
+    return weakFrame.IsAlive();
+  }
+
+  // Spec defines that mouse events must be dispatched to the same target as
+  // the pointer event. If the target is no longer participating in its
+  // ownerDocument's tree, fire the event at the original target's nearest
+  // ancestor node
+  if (!targetContent) {
+    return false;
+  }
+
+  // XXX Why don't we reset aEventTargetData->mContent here?
+  aEventTargetData->mFrame = targetContent->GetPrimaryFrame();
+  aEventTargetData->mPresShell = PresShell::GetShellForEventTarget(
+      aEventTargetData->mFrame, targetContent);
+
+  // If new target PresShel is not found, we cannot keep handling the event.
+  return !!aEventTargetData->mPresShell;
+}
+
+bool PresShell::EventHandler::MaybeHandleEventWithAccessibleCaret(
+    nsIFrame* aFrameForPresShell, WidgetGUIEvent* aGUIEvent,
+    nsEventStatus* aEventStatus) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aEventStatus);
+
+  // Don't dispatch event to AccessibleCaretEventHub when the event status
+  // is nsEventStatus_eConsumeNoDefault. This might be happened when content
+  // preventDefault on the pointer events. In such case, we also call
+  // preventDefault on mouse events to stop default behaviors.
+  if (*aEventStatus == nsEventStatus_eConsumeNoDefault) {
+    return false;
+  }
+
+  if (!AccessibleCaretEnabled(GetDocument()->GetDocShell())) {
+    return false;
+  }
+
+  // AccessibleCaretEventHub handles only mouse, touch, and keyboard events.
+  if (aGUIEvent->mClass != eMouseEventClass &&
+      aGUIEvent->mClass != eTouchEventClass &&
+      aGUIEvent->mClass != eKeyboardEventClass) {
+    return false;
+  }
+
+  // First, try the event hub at the event point to handle a long press to
+  // select a word in an unfocused window.
+  do {
+    EventTargetData eventTargetData(nullptr);
+    if (!ComputeEventTargetFrameAndPresShellAtEventPoint(
+            aFrameForPresShell, aGUIEvent, &eventTargetData)) {
+      break;
+    }
+
+    if (!eventTargetData.mPresShell) {
+      break;
+    }
+
+    RefPtr<AccessibleCaretEventHub> eventHub =
+        eventTargetData.mPresShell->GetAccessibleCaretEventHub();
+    if (!eventHub) {
+      break;
+    }
+
+    *aEventStatus = eventHub->HandleEvent(aGUIEvent);
+    if (*aEventStatus != nsEventStatus_eConsumeNoDefault) {
+      break;
+    }
+
+    // If the event is consumed, cancel APZC panning by setting
+    // mMultipleActionsPrevented.
+    aGUIEvent->mFlags.mMultipleActionsPrevented = true;
+    return true;
+  } while (false);
+
+  // Then, we target the event to the event hub at the focused window.
+  nsCOMPtr<nsPIDOMWindowOuter> window = GetFocusedDOMWindowInOurWindow();
+  if (!window) {
+    return false;
+  }
+  RefPtr<Document> retargetEventDoc = window->GetExtantDoc();
+  if (!retargetEventDoc) {
+    return false;
+  }
+  RefPtr<PresShell> presShell = retargetEventDoc->GetPresShell();
+  if (!presShell) {
+    return false;
+  }
+
+  RefPtr<AccessibleCaretEventHub> eventHub =
+      presShell->GetAccessibleCaretEventHub();
+  if (!eventHub) {
+    return false;
+  }
+  *aEventStatus = eventHub->HandleEvent(aGUIEvent);
+  if (*aEventStatus != nsEventStatus_eConsumeNoDefault) {
+    return false;
+  }
+  // If the event is consumed, cancel APZC panning by setting
+  // mMultipleActionsPrevented.
+  aGUIEvent->mFlags.mMultipleActionsPrevented = true;
+  return true;
+}
+
+bool PresShell::EventHandler::MaybeDiscardEvent(WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(aGUIEvent);
+
+  // If it is safe to dispatch events now, don't discard the event.
+  if (nsContentUtils::IsSafeToRunScript()) {
+    return false;
+  }
+
+  // If the event does not cause dispatching DOM event (i.e., internal event),
+  // we can keep handling it even when it's not safe to run script.
+  if (!aGUIEvent->IsAllowedToDispatchDOMEvent()) {
+    return false;
+  }
+
+  // If the event is a composition event, we need to let IMEStateManager know
+  // it's discarded because it needs to listen all composition events to manage
+  // TextComposition instance.
+  if (aGUIEvent->mClass == eCompositionEventClass) {
+    IMEStateManager::OnCompositionEventDiscarded(
+        aGUIEvent->AsCompositionEvent());
+  }
+
+#ifdef DEBUG
+  if (aGUIEvent->IsIMERelatedEvent()) {
+    nsPrintfCString warning("%s event is discarded",
+                            ToChar(aGUIEvent->mMessage));
+    NS_WARNING(warning.get());
+  }
+#endif  // #ifdef DEBUG
+
+  nsContentUtils::WarnScriptWasIgnored(GetDocument());
+  return true;
+}
+
+// static
+nsIContent* PresShell::EventHandler::GetCapturingContentFor(
+    WidgetGUIEvent* aGUIEvent) {
+  return (aGUIEvent->mClass == ePointerEventClass ||
+          aGUIEvent->mClass == eWheelEventClass ||
+          aGUIEvent->HasMouseEventMessage())
+             ? PresShell::GetCapturingContent()
+             : nullptr;
+}
+
+bool PresShell::EventHandler::GetRetargetEventDocument(
+    WidgetGUIEvent* aGUIEvent, Document** aRetargetEventDocument) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aRetargetEventDocument);
+
+  *aRetargetEventDocument = nullptr;
+
+  // key and IME related events should not cross top level window boundary.
+  // Basically, such input events should be fired only on focused widget.
+  // However, some IMEs might need to clean up composition after focused
+  // window is deactivated.  And also some tests on MozMill want to test key
+  // handling on deactivated window because MozMill window can be activated
+  // during tests.  So, there is no merit the events should be redirected to
+  // active window.  So, the events should be handled on the last focused
+  // content in the last focused DOM window in same top level window.
+  // Note, if no DOM window has been focused yet, we can discard the events.
+  if (aGUIEvent->IsTargetedAtFocusedWindow()) {
+    nsCOMPtr<nsPIDOMWindowOuter> window = GetFocusedDOMWindowInOurWindow();
+    // No DOM window in same top level window has not been focused yet,
+    // discard the events.
+    if (!window) {
+      return false;
+    }
+
+    RefPtr<Document> retargetEventDoc = window->GetExtantDoc();
+    if (!retargetEventDoc) {
+      return false;
+    }
+    retargetEventDoc.forget(aRetargetEventDocument);
+    return true;
+  }
+
+  nsIContent* capturingContent =
+      EventHandler::GetCapturingContentFor(aGUIEvent);
+  if (capturingContent) {
+    // if the mouse is being captured then retarget the mouse event at the
+    // document that is being captured.
+    RefPtr<Document> retargetEventDoc = capturingContent->GetComposedDoc();
+    retargetEventDoc.forget(aRetargetEventDocument);
+    return true;
+  }
+
+#ifdef ANDROID
+  if (aGUIEvent->mClass == eTouchEventClass ||
+      aGUIEvent->mClass == eMouseEventClass ||
+      aGUIEvent->mClass == eWheelEventClass) {
+    RefPtr<Document> retargetEventDoc = mPresShell->GetPrimaryContentDocument();
+    retargetEventDoc.forget(aRetargetEventDocument);
+    return true;
+  }
+#endif  // #ifdef ANDROID
+
+  // When we don't find another document to handle the event, we need to keep
+  // handling the event by ourselves.
+  return true;
+}
+
+nsIFrame* PresShell::EventHandler::GetFrameForHandlingEventWith(
+    WidgetGUIEvent* aGUIEvent, Document* aRetargetDocument,
+    nsIFrame* aFrameForPresShell) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aRetargetDocument);
+
+  RefPtr<PresShell> retargetPresShell = aRetargetDocument->GetPresShell();
+  // Even if the document doesn't have PresShell, i.e., it's invisible, we
+  // need to dispatch only KeyboardEvent in its nearest visible document
+  // because key focus shouldn't be caught by invisible document.
+  if (!retargetPresShell) {
+    if (!aGUIEvent->HasKeyEventMessage()) {
+      return nullptr;
+    }
+    Document* retargetEventDoc = aRetargetDocument;
+    while (!retargetPresShell) {
+      retargetEventDoc = retargetEventDoc->GetInProcessParentDocument();
+      if (!retargetEventDoc) {
+        return nullptr;
+      }
+      retargetPresShell = retargetEventDoc->GetPresShell();
+    }
+  }
+
+  // If the found PresShell is this instance, caller needs to keep handling
+  // aGUIEvent by itself.  Therefore, return the given frame which was set
+  // to aFrame of HandleEvent().
+  if (retargetPresShell == mPresShell) {
+    return aFrameForPresShell;
+  }
+
+  // Use root frame of the new PresShell if there is.
+  nsIFrame* rootFrame = retargetPresShell->GetRootFrame();
+  if (rootFrame) {
+    return rootFrame;
+  }
+
+  // Otherwise, and if aGUIEvent requires content of PresShell, caller should
+  // stop handling the event.
+  if (aGUIEvent->mMessage == eQueryTextContent ||
+      aGUIEvent->IsContentCommandEvent()) {
+    return nullptr;
+  }
+
+  // Otherwise, use nearest ancestor frame which includes the PresShell.
+  return GetNearestFrameContainingPresShell(retargetPresShell);
+}
+
+bool PresShell::EventHandler::MaybeHandleEventWithAnotherPresShell(
+    nsIFrame* aFrameForPresShell, WidgetGUIEvent* aGUIEvent,
+    nsEventStatus* aEventStatus, nsresult* aRv) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aEventStatus);
+  MOZ_ASSERT(aRv);
+
+  *aRv = NS_OK;
+
+  RefPtr<Document> retargetEventDoc;
+  if (!GetRetargetEventDocument(aGUIEvent, getter_AddRefs(retargetEventDoc))) {
+    // Nobody can handle this event.  So, treat as handled by somebody to make
+    // caller do nothing anymore.
+    return true;
+  }
+
+  // If there is no proper retarget document, the caller should handle the
+  // event by itself.
+  if (!retargetEventDoc) {
+    return false;
+  }
+
+  nsIFrame* frame = GetFrameForHandlingEventWith(aGUIEvent, retargetEventDoc,
+                                                 aFrameForPresShell);
+  if (!frame) {
+    // Nobody can handle this event.  So, treat as handled by somebody to make
+    // caller do nothing anymore.
+    return true;
+  }
+
+  // If we reached same frame as set to HandleEvent(), the caller should handle
+  // the event by itself.
+  if (frame == aFrameForPresShell) {
+    return false;
+  }
+
+  // We need to handle aGUIEvent with another PresShell.
+  RefPtr<PresShell> presShell = frame->PresContext()->PresShell();
+  *aRv = presShell->HandleEvent(frame, aGUIEvent, true, aEventStatus);
+  return true;
+}
+
+bool PresShell::EventHandler::MaybeDiscardOrDelayKeyboardEvent(
+    WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(aGUIEvent);
+
+  if (aGUIEvent->mClass != eKeyboardEventClass) {
+    return false;
+  }
+
+  Document* document = GetDocument();
+  if (!document || !document->EventHandlingSuppressed()) {
+    return false;
+  }
+
+  MOZ_ASSERT_IF(InputTaskManager::CanSuspendInputEvent(),
+                !InputTaskManager::Get()->IsSuspended());
+
+  if (aGUIEvent->mMessage == eKeyDown) {
+    mPresShell->mNoDelayedKeyEvents = true;
+  } else if (!mPresShell->mNoDelayedKeyEvents) {
+    UniquePtr<DelayedKeyEvent> delayedKeyEvent =
+        MakeUnique<DelayedKeyEvent>(aGUIEvent->AsKeyboardEvent());
+    mPresShell->mDelayedEvents.AppendElement(std::move(delayedKeyEvent));
+  }
+  aGUIEvent->mFlags.mIsSuppressedOrDelayed = true;
+  return true;
+}
+
+bool PresShell::EventHandler::MaybeDiscardOrDelayMouseEvent(
+    nsIFrame* aFrameToHandleEvent, WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(aFrameToHandleEvent);
+  MOZ_ASSERT(aGUIEvent);
+
+  if (aGUIEvent->mClass != eMouseEventClass) {
+    return false;
+  }
+
+  if (!aFrameToHandleEvent->PresContext()
+           ->Document()
+           ->EventHandlingSuppressed()) {
+    return false;
+  }
+
+  MOZ_ASSERT_IF(InputTaskManager::CanSuspendInputEvent() &&
+                    aGUIEvent->mMessage != eMouseMove,
+                !InputTaskManager::Get()->IsSuspended());
+
+  RefPtr<PresShell> ps = aFrameToHandleEvent->PresShell();
+
+  if (aGUIEvent->mMessage == eMouseDown) {
+    ps->mNoDelayedMouseEvents = true;
+  } else if (!ps->mNoDelayedMouseEvents &&
+             (aGUIEvent->mMessage == eMouseUp ||
+              // contextmenu is triggered after right mouseup on Windows and
+              // right mousedown on other platforms.
+              aGUIEvent->mMessage == eContextMenu ||
+              aGUIEvent->mMessage == eMouseExitFromWidget)) {
+    UniquePtr<DelayedMouseEvent> delayedMouseEvent =
+        MakeUnique<DelayedMouseEvent>(aGUIEvent->AsMouseEvent());
+    ps->mDelayedEvents.AppendElement(std::move(delayedMouseEvent));
+  }
+
+  // If there is a suppressed event listener associated with the document,
+  // notify it about the suppressed mouse event. This allows devtools
+  // features to continue receiving mouse events even when the devtools
+  // debugger has paused execution in a page.
+  RefPtr<EventListener> suppressedListener = aFrameToHandleEvent->PresContext()
+                                                 ->Document()
+                                                 ->GetSuppressedEventListener();
+  if (!suppressedListener ||
+      aGUIEvent->AsMouseEvent()->mReason == WidgetMouseEvent::eSynthesized) {
+    return true;
+  }
+
+  nsCOMPtr<nsIContent> targetContent;
+  aFrameToHandleEvent->GetContentForEvent(aGUIEvent,
+                                          getter_AddRefs(targetContent));
+  if (targetContent) {
+    aGUIEvent->mTarget = targetContent;
+  }
+
+  nsCOMPtr<EventTarget> eventTarget = aGUIEvent->mTarget;
+  RefPtr<Event> event = EventDispatcher::CreateEvent(
+      eventTarget, aFrameToHandleEvent->PresContext(), aGUIEvent, u""_ns);
+
+  suppressedListener->HandleEvent(*event);
+  return true;
+}
+
+nsIFrame* PresShell::EventHandler::MaybeFlushThrottledStyles(
+    nsIFrame* aFrameForPresShell) {
+  if (!GetDocument()) {
+    // XXX Only when mPresShell has document, we'll try to look for a frame
+    //     containing mPresShell even if given frame is nullptr.  Does this
+    //     make sense?
+    return aFrameForPresShell;
+  }
+
+  PresShell* rootPresShell = mPresShell->GetRootPresShell();
+  if (NS_WARN_IF(!rootPresShell)) {
+    return nullptr;
+  }
+  Document* rootDocument = rootPresShell->GetDocument();
+  if (NS_WARN_IF(!rootDocument)) {
+    return nullptr;
+  }
+
+  AutoWeakFrame weakFrameForPresShell(aFrameForPresShell);
+  {  // scope for scriptBlocker.
+    nsAutoScriptBlocker scriptBlocker;
+    FlushThrottledStyles(*rootDocument);
+  }
+
+  if (weakFrameForPresShell.IsAlive()) {
+    return aFrameForPresShell;
+  }
+
+  return GetNearestFrameContainingPresShell(mPresShell);
+}
+
+nsIFrame* PresShell::EventHandler::ComputeRootFrameToHandleEvent(
+    nsIFrame* aFrameForPresShell, WidgetGUIEvent* aGUIEvent,
+    nsIContent* aCapturingContent, bool* aIsCapturingContentIgnored,
+    bool* aIsCaptureRetargeted) {
+  MOZ_ASSERT(aFrameForPresShell);
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aIsCapturingContentIgnored);
+  MOZ_ASSERT(aIsCaptureRetargeted);
+
+  nsIFrame* rootFrameToHandleEvent = ComputeRootFrameToHandleEventWithPopup(
+      aFrameForPresShell, aGUIEvent, aCapturingContent,
+      aIsCapturingContentIgnored);
+  if (*aIsCapturingContentIgnored) {
+    // If the capturing content is ignored, we don't need to respect it.
+    return rootFrameToHandleEvent;
+  }
+
+  if (!aCapturingContent) {
+    return rootFrameToHandleEvent;
+  }
+
+  // If we have capturing content, let's compute root frame with it again.
+  return ComputeRootFrameToHandleEventWithCapturingContent(
+      rootFrameToHandleEvent, aCapturingContent, aIsCapturingContentIgnored,
+      aIsCaptureRetargeted);
+}
+
+nsIFrame* PresShell::EventHandler::ComputeRootFrameToHandleEventWithPopup(
+    nsIFrame* aRootFrameToHandleEvent, WidgetGUIEvent* aGUIEvent,
+    nsIContent* aCapturingContent, bool* aIsCapturingContentIgnored) {
+  MOZ_ASSERT(aRootFrameToHandleEvent);
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aIsCapturingContentIgnored);
+
+  *aIsCapturingContentIgnored = false;
+
+  nsPresContext* framePresContext = aRootFrameToHandleEvent->PresContext();
+  nsPresContext* rootPresContext = framePresContext->GetRootPresContext();
+  NS_ASSERTION(rootPresContext == GetPresContext()->GetRootPresContext(),
+               "How did we end up outside the connected "
+               "prescontext/viewmanager hierarchy?");
+  nsIFrame* popupFrame = nsLayoutUtils::GetPopupFrameForEventCoordinates(
+      rootPresContext, aGUIEvent);
+  if (!popupFrame) {
+    return aRootFrameToHandleEvent;
+  }
+
+  // If a remote browser is currently capturing input break out if we
+  // detect a chrome generated popup.
+  // XXXedgar, do we need to check fission OOP iframe?
+  if (aCapturingContent &&
+      EventStateManager::IsTopLevelRemoteTarget(aCapturingContent)) {
+    *aIsCapturingContentIgnored = true;
+  }
+
+  // If the popupFrame is an ancestor of the 'frame', the frame should
+  // handle the event, otherwise, the popup should handle it.
+  if (nsContentUtils::ContentIsCrossDocDescendantOf(
+          framePresContext->GetPresShell()->GetDocument(),
+          popupFrame->GetContent())) {
+    return aRootFrameToHandleEvent;
+  }
+
+  // If we aren't starting our event dispatch from the root frame of the
+  // root prescontext, then someone must be capturing the mouse. In that
+  // case we only want to use the popup list if the capture is
+  // inside the popup.
+  if (framePresContext == rootPresContext &&
+      aRootFrameToHandleEvent == FrameConstructor()->GetRootFrame()) {
+    return popupFrame;
+  }
+
+  if (aCapturingContent && !*aIsCapturingContentIgnored &&
+      aCapturingContent->IsInclusiveDescendantOf(popupFrame->GetContent())) {
+    return popupFrame;
+  }
+
+  return aRootFrameToHandleEvent;
+}
+
+nsIFrame*
+PresShell::EventHandler::ComputeRootFrameToHandleEventWithCapturingContent(
+    nsIFrame* aRootFrameToHandleEvent, nsIContent* aCapturingContent,
+    bool* aIsCapturingContentIgnored, bool* aIsCaptureRetargeted) {
+  MOZ_ASSERT(aRootFrameToHandleEvent);
+  MOZ_ASSERT(aCapturingContent);
+  MOZ_ASSERT(aIsCapturingContentIgnored);
+  MOZ_ASSERT(aIsCaptureRetargeted);
+
+  *aIsCapturingContentIgnored = false;
+  *aIsCaptureRetargeted = false;
+
+  // If a capture is active, determine if the BrowsingContext is active. If
+  // not, clear the capture and target the mouse event normally instead. This
+  // would occur if the mouse button is held down while a tab change occurs.
+  // If the BrowsingContext is active, look for a scrolling container.
+  BrowsingContext* bc = GetPresContext()->Document()->GetBrowsingContext();
+  if (!bc || !bc->IsActive()) {
+    ClearMouseCapture();
+    *aIsCapturingContentIgnored = true;
+    return aRootFrameToHandleEvent;
+  }
+
+  if (PresShell::sCapturingContentInfo.mRetargetToElement) {
+    *aIsCaptureRetargeted = true;
+    return aRootFrameToHandleEvent;
+  }
+
+  // A check was already done above to ensure that aCapturingContent is
+  // in this presshell.
+  NS_ASSERTION(aCapturingContent->OwnerDoc() == GetDocument(),
+               "Unexpected document");
+  nsIFrame* captureFrame = aCapturingContent->GetPrimaryFrame();
+  if (!captureFrame) {
+    return aRootFrameToHandleEvent;
+  }
+
+  // scrollable frames should use the scrolling container as the root instead
+  // of the document
+  nsIScrollableFrame* scrollFrame = do_QueryFrame(captureFrame);
+  return scrollFrame ? scrollFrame->GetScrolledFrame()
+                     : aRootFrameToHandleEvent;
+}
+
+nsresult
+PresShell::EventHandler::HandleEventWithPointerCapturingContentWithoutItsFrame(
+    nsIFrame* aFrameForPresShell, WidgetGUIEvent* aGUIEvent,
+    nsIContent* aPointerCapturingContent, nsEventStatus* aEventStatus) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aPointerCapturingContent);
+  MOZ_ASSERT(!aPointerCapturingContent->GetPrimaryFrame(),
+             "Handle the event with frame rather than only with the content");
+  MOZ_ASSERT(aEventStatus);
+
+  RefPtr<PresShell> presShellForCapturingContent =
+      PresShell::GetShellForEventTarget(nullptr, aPointerCapturingContent);
+  if (!presShellForCapturingContent) {
+    // If we can't process event for the capturing content, release
+    // the capture.
+    PointerEventHandler::ReleaseIfCaptureByDescendant(aPointerCapturingContent);
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIContent> overrideClickTarget =
+      GetOverrideClickTarget(aGUIEvent, aFrameForPresShell);
+
+  // Dispatch events to the capturing content even it's frame is
+  // destroyed.
+  PointerEventHandler::DispatchPointerFromMouseOrTouch(
+      presShellForCapturingContent, nullptr, aPointerCapturingContent,
+      aGUIEvent, false, aEventStatus, nullptr);
+
+  if (presShellForCapturingContent == mPresShell) {
+    return HandleEventWithTarget(aGUIEvent, nullptr, aPointerCapturingContent,
+                                 aEventStatus, true, nullptr,
+                                 overrideClickTarget);
+  }
+
+  EventHandler eventHandlerForCapturingContent(
+      std::move(presShellForCapturingContent));
+  return eventHandlerForCapturingContent.HandleEventWithTarget(
+      aGUIEvent, nullptr, aPointerCapturingContent, aEventStatus, true, nullptr,
+      overrideClickTarget);
+}
+
+nsresult PresShell::EventHandler::HandleEventAtFocusedContent(
+    WidgetGUIEvent* aGUIEvent, nsEventStatus* aEventStatus) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aGUIEvent->IsTargetedAtFocusedContent());
+  MOZ_ASSERT(aEventStatus);
+
+  AutoCurrentEventInfoSetter eventInfoSetter(*this);
+
+  RefPtr<Element> eventTargetElement =
+      ComputeFocusedEventTargetElement(aGUIEvent);
+
+  mPresShell->mCurrentEventFrame = nullptr;
+  if (eventTargetElement) {
+    nsresult rv = NS_OK;
+    if (MaybeHandleEventWithAnotherPresShell(eventTargetElement, aGUIEvent,
+                                             aEventStatus, &rv)) {
+      return rv;
+    }
+  }
+
+  // If we cannot handle the event with mPresShell, let's try to handle it
+  // with parent PresShell.
+  mPresShell->mCurrentEventContent = eventTargetElement;
+  if (!mPresShell->GetCurrentEventContent() ||
+      !mPresShell->GetCurrentEventFrame() ||
+      InZombieDocument(mPresShell->mCurrentEventContent)) {
+    return RetargetEventToParent(aGUIEvent, aEventStatus);
+  }
+
+  nsresult rv =
+      HandleEventWithCurrentEventInfo(aGUIEvent, aEventStatus, true, nullptr);
+  return rv;
+}
+
+Element* PresShell::EventHandler::ComputeFocusedEventTargetElement(
+    WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aGUIEvent->IsTargetedAtFocusedContent());
+
+  // key and IME related events go to the focused frame in this DOM window.
+  nsPIDOMWindowOuter* window = GetDocument()->GetWindow();
+  nsCOMPtr<nsPIDOMWindowOuter> focusedWindow;
+  Element* eventTargetElement = nsFocusManager::GetFocusedDescendant(
+      window, nsFocusManager::eOnlyCurrentWindow,
+      getter_AddRefs(focusedWindow));
+
+  // otherwise, if there is no focused content or the focused content has
+  // no frame, just use the root content. This ensures that key events
+  // still get sent to the window properly if nothing is focused or if a
+  // frame goes away while it is focused.
+  if (!eventTargetElement || !eventTargetElement->GetPrimaryFrame()) {
+    eventTargetElement = GetDocument()->GetUnfocusedKeyEventTarget();
+  }
+
+  switch (aGUIEvent->mMessage) {
+    case eKeyDown:
+      sLastKeyDownEventTargetElement = eventTargetElement;
+      return eventTargetElement;
+    case eKeyPress:
+    case eKeyUp:
+      if (!sLastKeyDownEventTargetElement) {
+        return eventTargetElement;
+      }
+      // If a different element is now focused for the keypress/keyup event
+      // than what was focused during the keydown event, check if the new
+      // focused element is not in a chrome document any more, and if so,
+      // retarget the event back at the keydown target. This prevents a
+      // content area from grabbing the focus from chrome in-between key
+      // events.
+      if (eventTargetElement) {
+        bool keyDownIsChrome = nsContentUtils::IsChromeDoc(
+            sLastKeyDownEventTargetElement->GetComposedDoc());
+        if (keyDownIsChrome != nsContentUtils::IsChromeDoc(
+                                   eventTargetElement->GetComposedDoc()) ||
+            (keyDownIsChrome && BrowserParent::GetFrom(eventTargetElement))) {
+          eventTargetElement = sLastKeyDownEventTargetElement;
+        }
+      }
+
+      if (aGUIEvent->mMessage == eKeyUp) {
+        sLastKeyDownEventTargetElement = nullptr;
+      }
+      [[fallthrough]];
+    default:
+      return eventTargetElement;
+  }
+}
+
+bool PresShell::EventHandler::MaybeHandleEventWithAnotherPresShell(
+    Element* aEventTargetElement, WidgetGUIEvent* aGUIEvent,
+    nsEventStatus* aEventStatus, nsresult* aRv) {
+  MOZ_ASSERT(aEventTargetElement);
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(!aGUIEvent->IsUsingCoordinates());
+  MOZ_ASSERT(aEventStatus);
+  MOZ_ASSERT(aRv);
+
+  Document* eventTargetDocument = aEventTargetElement->OwnerDoc();
+  if (!eventTargetDocument || eventTargetDocument == GetDocument()) {
+    *aRv = NS_OK;
+    return false;
+  }
+
+  RefPtr<PresShell> eventTargetPresShell = eventTargetDocument->GetPresShell();
+  if (!eventTargetPresShell) {
+    *aRv = NS_OK;
+    return true;  // No PresShell can handle the event.
+  }
+
+  EventHandler eventHandler(std::move(eventTargetPresShell));
+  *aRv = eventHandler.HandleRetargetedEvent(aGUIEvent, aEventStatus,
+                                            aEventTargetElement);
+  return true;
+}
+
+nsresult PresShell::EventHandler::HandleEventWithFrameForPresShell(
+    nsIFrame* aFrameForPresShell, WidgetGUIEvent* aGUIEvent,
+    nsEventStatus* aEventStatus) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(!aGUIEvent->IsUsingCoordinates());
+  MOZ_ASSERT(!aGUIEvent->IsTargetedAtFocusedContent());
+  MOZ_ASSERT(aEventStatus);
+
+  AutoCurrentEventInfoSetter eventInfoSetter(*this, aFrameForPresShell,
+                                             nullptr);
+
+  nsresult rv = NS_OK;
+  if (mPresShell->GetCurrentEventFrame()) {
+    rv =
+        HandleEventWithCurrentEventInfo(aGUIEvent, aEventStatus, true, nullptr);
+  }
+
+  return rv;
+}
+
+Document* PresShell::GetPrimaryContentDocument() {
+  nsPresContext* context = GetPresContext();
+  if (!context || !context->IsRoot()) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIDocShellTreeItem> shellAsTreeItem = context->GetDocShell();
+  if (!shellAsTreeItem) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIDocShellTreeOwner> owner;
+  shellAsTreeItem->GetTreeOwner(getter_AddRefs(owner));
+  if (!owner) {
+    return nullptr;
+  }
+
+  // now get the primary content shell (active tab)
+  nsCOMPtr<nsIDocShellTreeItem> item;
+  owner->GetPrimaryContentShell(getter_AddRefs(item));
+  nsCOMPtr<nsIDocShell> childDocShell = do_QueryInterface(item);
+  if (!childDocShell) {
+    return nullptr;
+  }
+
+  return childDocShell->GetExtantDocument();
+}
+
+nsresult PresShell::EventHandler::HandleEventWithTarget(
+    WidgetEvent* aEvent, nsIFrame* aNewEventFrame, nsIContent* aNewEventContent,
+    nsEventStatus* aEventStatus, bool aIsHandlingNativeEvent,
+    nsIContent** aTargetContent, nsIContent* aOverrideClickTarget) {
+  MOZ_ASSERT(aEvent);
+  MOZ_DIAGNOSTIC_ASSERT(aEvent->IsTrusted());
+
+#if DEBUG
+  MOZ_ASSERT(!aNewEventFrame ||
+                 aNewEventFrame->PresContext()->GetPresShell() == mPresShell,
+             "wrong shell");
+  if (aNewEventContent) {
+    Document* doc = aNewEventContent->GetComposedDoc();
+    NS_ASSERTION(doc, "event for content that isn't in a document");
+    // NOTE: We don't require that the document still have a PresShell.
+    // See bug 1375940.
+  }
+#endif
+  NS_ENSURE_STATE(!aNewEventContent ||
+                  aNewEventContent->GetComposedDoc() == GetDocument());
+  if (aEvent->mClass == ePointerEventClass) {
+    mPresShell->RecordPointerLocation(aEvent->AsMouseEvent());
+  }
+  AutoPointerEventTargetUpdater updater(mPresShell, aEvent, aNewEventFrame,
+                                        aTargetContent);
+  AutoCurrentEventInfoSetter eventInfoSetter(*this, aNewEventFrame,
+                                             aNewEventContent);
+  nsresult rv = HandleEventWithCurrentEventInfo(aEvent, aEventStatus, false,
+                                                aOverrideClickTarget);
+  return rv;
+}
+
+namespace {
+
+class MOZ_RAII AutoEventHandler final {
+ public:
+  AutoEventHandler(WidgetEvent* aEvent, Document* aDocument) : mEvent(aEvent) {
+    MOZ_ASSERT(mEvent);
+    MOZ_ASSERT(mEvent->IsTrusted());
+
+    if (mEvent->mMessage == eMouseDown) {
+      PresShell::ReleaseCapturingContent();
+      PresShell::AllowMouseCapture(true);
+    }
+    if (NeedsToUpdateCurrentMouseBtnState()) {
+      WidgetMouseEvent* mouseEvent = mEvent->AsMouseEvent();
+      if (mouseEvent) {
+        EventStateManager::sCurrentMouseBtn = mouseEvent->mButton;
+      }
+    }
+  }
+
+  ~AutoEventHandler() {
+    if (mEvent->mMessage == eMouseDown) {
+      PresShell::AllowMouseCapture(false);
+    }
+    if (NeedsToUpdateCurrentMouseBtnState()) {
+      EventStateManager::sCurrentMouseBtn = MouseButton::eNotPressed;
+    }
+  }
+
+ protected:
+  bool NeedsToUpdateCurrentMouseBtnState() const {
+    return mEvent->mMessage == eMouseDown || mEvent->mMessage == eMouseUp ||
+           mEvent->mMessage == ePointerDown || mEvent->mMessage == ePointerUp;
+  }
+
+  WidgetEvent* mEvent;
+};
+
+}  // anonymous namespace
+
+nsresult PresShell::EventHandler::HandleEventWithCurrentEventInfo(
+    WidgetEvent* aEvent, nsEventStatus* aEventStatus,
+    bool aIsHandlingNativeEvent, nsIContent* aOverrideClickTarget) {
+  MOZ_ASSERT(aEvent);
+  MOZ_ASSERT(aEventStatus);
+
+  RefPtr<EventStateManager> manager = GetPresContext()->EventStateManager();
+
+  // If we cannot handle the event with mPresShell because of no target,
+  // just record the response time.
+  // XXX Is this intentional?  In such case, the score is really good because
+  //     of nothing to do.  So, it may make average and median better.
+  if (NS_EVENT_NEEDS_FRAME(aEvent) && !mPresShell->GetCurrentEventFrame() &&
+      !mPresShell->GetCurrentEventContent()) {
+    RecordEventHandlingResponsePerformance(aEvent);
+    return NS_OK;
+  }
+
+  if (mPresShell->mCurrentEventContent && aEvent->IsTargetedAtFocusedWindow()) {
+    if (RefPtr<nsFocusManager> fm = nsFocusManager::GetFocusManager()) {
+      // This may run script now.  So, mPresShell might be destroyed after here.
+      nsCOMPtr<nsIContent> currentEventContent =
+          mPresShell->mCurrentEventContent;
+      fm->FlushBeforeEventHandlingIfNeeded(currentEventContent);
+    }
+  }
+
+  bool touchIsNew = false;
+  if (!PrepareToDispatchEvent(aEvent, aEventStatus, &touchIsNew)) {
+    return NS_OK;
+  }
+
+  // We finished preparing to dispatch the event.  So, let's record the
+  // performance.
+  RecordEventPreparationPerformance(aEvent);
+
+  AutoHandlingUserInputStatePusher userInpStatePusher(
+      UserActivation::IsUserInteractionEvent(aEvent), aEvent);
+  AutoEventHandler eventHandler(aEvent, GetDocument());
+  AutoPopupStatePusher popupStatePusher(
+      PopupBlocker::GetEventPopupControlState(aEvent));
+
+  // FIXME. If the event was reused, we need to clear the old target,
+  // bug 329430
+  aEvent->mTarget = nullptr;
+
+  HandlingTimeAccumulator handlingTimeAccumulator(*this, aEvent);
+
+  nsresult rv = DispatchEvent(manager, aEvent, touchIsNew, aEventStatus,
+                              aOverrideClickTarget);
+
+  if (!mPresShell->IsDestroying() && aIsHandlingNativeEvent) {
+    // Ensure that notifications to IME should be sent before getting next
+    // native event from the event queue.
+    // XXX Should we check the event message or event class instead of
+    //     using aIsHandlingNativeEvent?
+    manager->TryToFlushPendingNotificationsToIME();
+  }
+
+  FinalizeHandlingEvent(aEvent);
+
+  RecordEventHandlingResponsePerformance(aEvent);
+
+  return rv;  // Result of DispatchEvent()
+}
+
+nsresult PresShell::EventHandler::DispatchEvent(
+    EventStateManager* aEventStateManager, WidgetEvent* aEvent,
+    bool aTouchIsNew, nsEventStatus* aEventStatus,
+    nsIContent* aOverrideClickTarget) {
+  MOZ_ASSERT(aEventStateManager);
+  MOZ_ASSERT(aEvent);
+  MOZ_ASSERT(aEventStatus);
+
+  // 1. Give event to event manager for pre event state changes and
+  //    generation of synthetic events.
+  {  // Scope for presContext
+    RefPtr<nsPresContext> presContext = GetPresContext();
+    nsCOMPtr<nsIContent> eventContent = mPresShell->mCurrentEventContent;
+    nsresult rv = aEventStateManager->PreHandleEvent(
+        presContext, aEvent, mPresShell->mCurrentEventFrame, eventContent,
+        aEventStatus, aOverrideClickTarget);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  // 2. Give event to the DOM for third party and JS use.
+  bool wasHandlingKeyBoardEvent = nsContentUtils::IsHandlingKeyBoardEvent();
+  if (aEvent->mClass == eKeyboardEventClass) {
+    nsContentUtils::SetIsHandlingKeyBoardEvent(true);
+  }
+  // If EventStateManager or something wants reply from remote process and
+  // needs to win any other event listeners in chrome, the event is both
+  // stopped its propagation and marked as "waiting reply from remote
+  // process".  In this case, PresShell shouldn't dispatch the event into
+  // the DOM tree because they don't have a chance to stop propagation in
+  // the system event group.  On the other hand, if its propagation is not
+  // stopped, that means that the event may be reserved by chrome.  If it's
+  // reserved by chrome, the event shouldn't be sent to any remote
+  // processes.  In this case, PresShell needs to dispatch the event to
+  // the DOM tree for checking if it's reserved.
+  if (aEvent->IsAllowedToDispatchDOMEvent() &&
+      !(aEvent->PropagationStopped() &&
+        aEvent->IsWaitingReplyFromRemoteProcess())) {
+    MOZ_ASSERT(nsContentUtils::IsSafeToRunScript(),
+               "Somebody changed aEvent to cause a DOM event!");
+    nsPresShellEventCB eventCB(mPresShell);
+    if (nsIFrame* target = mPresShell->GetCurrentEventFrame()) {
+      if (target->OnlySystemGroupDispatch(aEvent->mMessage)) {
+        aEvent->StopPropagation();
+      }
+    }
+    if (aEvent->mClass == eTouchEventClass) {
+      DispatchTouchEventToDOM(aEvent, aEventStatus, &eventCB, aTouchIsNew);
+    } else {
+      DispatchEventToDOM(aEvent, aEventStatus, &eventCB);
+    }
+  }
+
+  nsContentUtils::SetIsHandlingKeyBoardEvent(wasHandlingKeyBoardEvent);
+
+  if (mPresShell->IsDestroying()) {
+    return NS_OK;
+  }
+
+  // 3. Give event to event manager for post event state changes and
+  //    generation of synthetic events.
+  // Refetch the prescontext, in case it changed.
+  RefPtr<nsPresContext> presContext = GetPresContext();
+  return aEventStateManager->PostHandleEvent(
+      presContext, aEvent, mPresShell->GetCurrentEventFrame(), aEventStatus,
+      aOverrideClickTarget);
+}
+
+bool PresShell::EventHandler::PrepareToDispatchEvent(
+    WidgetEvent* aEvent, nsEventStatus* aEventStatus, bool* aTouchIsNew) {
+  MOZ_ASSERT(aEvent->IsTrusted());
+  MOZ_ASSERT(aEventStatus);
+  MOZ_ASSERT(aTouchIsNew);
+
+  *aTouchIsNew = false;
+  if (aEvent->IsUserAction()) {
+    mPresShell->mHasHandledUserInput = true;
+  }
+
+  switch (aEvent->mMessage) {
+    case eKeyPress:
+    case eKeyDown:
+    case eKeyUp: {
+      WidgetKeyboardEvent* keyboardEvent = aEvent->AsKeyboardEvent();
+      MaybeHandleKeyboardEventBeforeDispatch(keyboardEvent);
+      return true;
+    }
+    case eMouseMove: {
+      bool allowCapture = EventStateManager::GetActiveEventStateManager() &&
+                          GetPresContext() &&
+                          GetPresContext()->EventStateManager() ==
+                              EventStateManager::GetActiveEventStateManager();
+      PresShell::AllowMouseCapture(allowCapture);
+      return true;
+    }
+    case eDrop: {
+      nsCOMPtr<nsIDragSession> session = nsContentUtils::GetDragSession();
+      if (session) {
+        bool onlyChromeDrop = false;
+        session->GetOnlyChromeDrop(&onlyChromeDrop);
+        if (onlyChromeDrop) {
+          aEvent->mFlags.mOnlyChromeDispatch = true;
+        }
+      }
+      return true;
+    }
+    case eDragExit: {
+      if (!StaticPrefs::dom_event_dragexit_enabled()) {
+        aEvent->mFlags.mOnlyChromeDispatch = true;
+      }
+      return true;
+    }
+    case eContextMenu: {
+      // If we cannot open context menu even though eContextMenu is fired, we
+      // should stop dispatching it into the DOM.
+      WidgetMouseEvent* mouseEvent = aEvent->AsMouseEvent();
+      if (mouseEvent->IsContextMenuKeyEvent() &&
+          !AdjustContextMenuKeyEvent(mouseEvent)) {
+        return false;
+      }
+
+      // If "Shift" state is active, context menu should be forcibly opened even
+      // if web apps want to prevent it since we respect our users' intention.
+      // In this case, we don't fire "contextmenu" event on web content because
+      // of not cancelable.
+      if (mouseEvent->IsShift()) {
+        aEvent->mFlags.mOnlyChromeDispatch = true;
+        aEvent->mFlags.mRetargetToNonNativeAnonymous = true;
+      }
+      return true;
+    }
+    case eTouchStart:
+    case eTouchMove:
+    case eTouchEnd:
+    case eTouchCancel:
+    case eTouchPointerCancel:
+      return mPresShell->mTouchManager.PreHandleEvent(
+          aEvent, aEventStatus, *aTouchIsNew, mPresShell->mCurrentEventContent);
+    default:
+      return true;
+  }
+}
+
+void PresShell::EventHandler::FinalizeHandlingEvent(WidgetEvent* aEvent) {
+  switch (aEvent->mMessage) {
+    case eKeyPress:
+    case eKeyDown:
+    case eKeyUp: {
+      if (aEvent->AsKeyboardEvent()->mKeyCode == NS_VK_ESCAPE) {
+        if (aEvent->mMessage == eKeyUp) {
+          // Reset this flag after key up is handled.
+          mPresShell->mIsLastChromeOnlyEscapeKeyConsumed = false;
+        } else {
+          if (aEvent->mFlags.mOnlyChromeDispatch &&
+              aEvent->mFlags.mDefaultPreventedByChrome) {
+            mPresShell->mIsLastChromeOnlyEscapeKeyConsumed = true;
+          }
+          if (aEvent->mMessage == eKeyDown &&
+              !aEvent->mFlags.mDefaultPrevented) {
+            if (Document* doc = GetDocument()) {
+              doc->TryCancelDialog();
+            }
+          }
+        }
+      }
+      if (aEvent->mMessage == eKeyDown) {
+        mPresShell->mIsLastKeyDownCanceled = aEvent->mFlags.mDefaultPrevented;
+      }
+      return;
+    }
+    case eMouseUp:
+      // reset the capturing content now that the mouse button is up
+      PresShell::ReleaseCapturingContent();
+      return;
+    case eMouseMove:
+      PresShell::AllowMouseCapture(false);
+      return;
+    case eDrag:
+    case eDragEnd:
+    case eDragEnter:
+    case eDragExit:
+    case eDragLeave:
+    case eDragOver:
+    case eDrop: {
+      // After any drag event other than dragstart (which is handled
+      // separately, as we need to collect the data first), the DataTransfer
+      // needs to be made protected, and then disconnected.
+      DataTransfer* dataTransfer = aEvent->AsDragEvent()->mDataTransfer;
+      if (dataTransfer) {
+        dataTransfer->Disconnect();
+      }
+      return;
+    }
+    default:
+      return;
+  }
+}
+
+void PresShell::EventHandler::MaybeHandleKeyboardEventBeforeDispatch(
+    WidgetKeyboardEvent* aKeyboardEvent) {
+  MOZ_ASSERT(aKeyboardEvent);
+
+  if (aKeyboardEvent->mKeyCode != NS_VK_ESCAPE) {
+    return;
+  }
+
+  // If we're in fullscreen mode, exit from it forcibly when Escape key is
+  // pressed.
+  Document* doc = mPresShell->GetCurrentEventContent()
+                      ? mPresShell->mCurrentEventContent->OwnerDoc()
+                      : nullptr;
+  Document* root = nsContentUtils::GetInProcessSubtreeRootDocument(doc);
+  if (root && root->GetFullscreenElement()) {
+    // Prevent default action on ESC key press when exiting
+    // DOM fullscreen mode. This prevents the browser ESC key
+    // handler from stopping all loads in the document, which
+    // would cause <video> loads to stop.
+    // XXX We need to claim the Escape key event which will be
+    //     dispatched only into chrome is already consumed by
+    //     content because we need to prevent its default here
+    //     for some reasons (not sure) but we need to detect
+    //     if a chrome event handler will call PreventDefault()
+    //     again and check it later.
+    aKeyboardEvent->PreventDefaultBeforeDispatch(CrossProcessForwarding::eStop);
+    aKeyboardEvent->mFlags.mOnlyChromeDispatch = true;
+
+    // The event listeners in chrome can prevent this ESC behavior by
+    // calling prevent default on the preceding keydown/press events.
+    if (!mPresShell->mIsLastChromeOnlyEscapeKeyConsumed &&
+        aKeyboardEvent->mMessage == eKeyUp) {
+      // ESC key released while in DOM fullscreen mode.
+      // Fully exit all browser windows and documents from
+      // fullscreen mode.
+      Document::AsyncExitFullscreen(nullptr);
+    }
+  }
+
+  nsCOMPtr<Document> pointerLockedDoc = PointerLockManager::GetLockedDocument();
+  if (!mPresShell->mIsLastChromeOnlyEscapeKeyConsumed && pointerLockedDoc) {
+    // XXX See above comment to understand the reason why this needs
+    //     to claim that the Escape key event is consumed by content
+    //     even though it will be dispatched only into chrome.
+    aKeyboardEvent->PreventDefaultBeforeDispatch(CrossProcessForwarding::eStop);
+    aKeyboardEvent->mFlags.mOnlyChromeDispatch = true;
+    if (aKeyboardEvent->mMessage == eKeyUp) {
+      PointerLockManager::Unlock();
+    }
+  }
+}
+
+void PresShell::EventHandler::RecordEventPreparationPerformance(
+    const WidgetEvent* aEvent) {
+  MOZ_ASSERT(aEvent);
+
+  switch (aEvent->mMessage) {
+    case eKeyPress:
+    case eKeyDown:
+    case eKeyUp:
+      if (aEvent->AsKeyboardEvent()->ShouldInteractionTimeRecorded()) {
+        GetPresContext()->RecordInteractionTime(
+            nsPresContext::InteractionType::KeyInteraction, aEvent->mTimeStamp);
+      }
+      Telemetry::AccumulateTimeDelta(Telemetry::INPUT_EVENT_QUEUED_KEYBOARD_MS,
+                                     aEvent->mTimeStamp);
+      return;
+
+    case eMouseDown:
+    case eMouseUp:
+      Telemetry::AccumulateTimeDelta(Telemetry::INPUT_EVENT_QUEUED_CLICK_MS,
+                                     aEvent->mTimeStamp);
+      [[fallthrough]];
+    case ePointerDown:
+    case ePointerUp:
+      GetPresContext()->RecordInteractionTime(
+          nsPresContext::InteractionType::ClickInteraction, aEvent->mTimeStamp);
+      return;
+
+    case eMouseMove:
+      if (aEvent->mFlags.mHandledByAPZ) {
+        Telemetry::AccumulateTimeDelta(
+            Telemetry::INPUT_EVENT_QUEUED_APZ_MOUSE_MOVE_MS,
+            aEvent->mTimeStamp);
+      }
+      GetPresContext()->RecordInteractionTime(
+          nsPresContext::InteractionType::MouseMoveInteraction,
+          aEvent->mTimeStamp);
+      return;
+
+    case eWheel:
+      if (aEvent->mFlags.mHandledByAPZ) {
+        Telemetry::AccumulateTimeDelta(
+            Telemetry::INPUT_EVENT_QUEUED_APZ_WHEEL_MS, aEvent->mTimeStamp);
+      }
+      return;
+
+    case eTouchMove:
+      if (aEvent->mFlags.mHandledByAPZ) {
+        Telemetry::AccumulateTimeDelta(
+            Telemetry::INPUT_EVENT_QUEUED_APZ_TOUCH_MOVE_MS,
+            aEvent->mTimeStamp);
+      }
+      return;
+
+    default:
+      return;
+  }
+}
+
+void PresShell::EventHandler::RecordEventHandlingResponsePerformance(
+    const WidgetEvent* aEvent) {
+  if (!Telemetry::CanRecordBase() || aEvent->mTimeStamp.IsNull() ||
+      aEvent->mTimeStamp <= mPresShell->mLastOSWake ||
+      !aEvent->AsInputEvent()) {
+    return;
+  }
+
+  TimeStamp now = TimeStamp::Now();
+  double millis = (now - aEvent->mTimeStamp).ToMilliseconds();
+  Telemetry::Accumulate(Telemetry::INPUT_EVENT_RESPONSE_MS, millis);
+  if (GetDocument() &&
+      GetDocument()->GetReadyStateEnum() != Document::READYSTATE_COMPLETE) {
+    Telemetry::Accumulate(Telemetry::LOAD_INPUT_EVENT_RESPONSE_MS, millis);
+  }
+
+  if (!sLastInputProcessed || sLastInputProcessed < aEvent->mTimeStamp) {
+    if (sLastInputProcessed) {
+      // This input event was created after we handled the last one.
+      // Accumulate the previous events' coalesced duration.
+      double lastMillis =
+          (sLastInputProcessed - sLastInputCreated).ToMilliseconds();
+      Telemetry::Accumulate(Telemetry::INPUT_EVENT_RESPONSE_COALESCED_MS,
+                            lastMillis);
+
+      if (MOZ_UNLIKELY(!PresShell::sProcessInteractable)) {
+        // For content process, we use the ready state of
+        // top-level-content-document to know if the process has finished the
+        // start-up.
+        // For parent process, see the topic
+        // 'sessionstore-one-or-no-tab-restored' in PresShell::Observe.
+        if (XRE_IsContentProcess() && GetDocument() &&
+            GetDocument()->IsTopLevelContentDocument()) {
+          switch (GetDocument()->GetReadyStateEnum()) {
+            case Document::READYSTATE_INTERACTIVE:
+            case Document::READYSTATE_COMPLETE:
+              PresShell::sProcessInteractable = true;
+              break;
+            default:
+              break;
+          }
+        }
+      }
+      if (MOZ_LIKELY(PresShell::sProcessInteractable)) {
+        Telemetry::Accumulate(Telemetry::INPUT_EVENT_RESPONSE_POST_STARTUP_MS,
+                              lastMillis);
+      } else {
+        Telemetry::Accumulate(Telemetry::INPUT_EVENT_RESPONSE_STARTUP_MS,
+                              lastMillis);
+      }
+    }
+    sLastInputCreated = aEvent->mTimeStamp;
+  } else if (aEvent->mTimeStamp < sLastInputCreated) {
+    // This event was created before the last input. May be processing out
+    // of order, so coalesce backwards, too.
+    sLastInputCreated = aEvent->mTimeStamp;
+  }
+  sLastInputProcessed = now;
+}
+
+// static
+nsIPrincipal*
+PresShell::EventHandler::GetDocumentPrincipalToCompareWithBlacklist(
+    PresShell& aPresShell) {
+  nsPresContext* presContext = aPresShell.GetPresContext();
+  if (NS_WARN_IF(!presContext)) {
+    return nullptr;
+  }
+  return presContext->Document()->GetPrincipalForPrefBasedHacks();
+}
+
+nsresult PresShell::EventHandler::DispatchEventToDOM(
+    WidgetEvent* aEvent, nsEventStatus* aEventStatus,
+    nsPresShellEventCB* aEventCB) {
+  nsresult rv = NS_OK;
+  nsCOMPtr<nsINode> eventTarget = mPresShell->mCurrentEventContent;
+  nsPresShellEventCB* eventCBPtr = aEventCB;
+  if (!eventTarget) {
+    nsCOMPtr<nsIContent> targetContent;
+    if (mPresShell->mCurrentEventFrame) {
+      rv = mPresShell->mCurrentEventFrame->GetContentForEvent(
+          aEvent, getter_AddRefs(targetContent));
+    }
+    if (NS_SUCCEEDED(rv) && targetContent) {
+      eventTarget = targetContent;
+    } else if (GetDocument()) {
+      eventTarget = GetDocument();
+      // If we don't have any content, the callback wouldn't probably
+      // do nothing.
+      eventCBPtr = nullptr;
+    }
+  }
+  if (eventTarget) {
+    if (aEvent->IsBlockedForFingerprintingResistance()) {
+      aEvent->mFlags.mOnlySystemGroupDispatchInContent = true;
+    } else if (aEvent->mMessage == eKeyPress) {
+      // If eKeyPress event is marked as not dispatched in the default event
+      // group in web content, it's caused by non-printable key or key
+      // combination.  In this case, UI Events declares that browsers
+      // shouldn't dispatch keypress event.  However, some web apps may be
+      // broken with this strict behavior due to historical issue.
+      // Therefore, we need to keep dispatching keypress event for such keys
+      // even with breaking the standard.
+      // Similarly, the other browsers sets non-zero value of keyCode or
+      // charCode of keypress event to the other.  Therefore, we should
+      // behave so, however, some web apps may be broken.  On such web apps,
+      // we should keep using legacy our behavior.
+      if (!mPresShell->mInitializedWithKeyPressEventDispatchingBlacklist) {
+        mPresShell->mInitializedWithKeyPressEventDispatchingBlacklist = true;
+        nsCOMPtr<nsIPrincipal> principal =
+            GetDocumentPrincipalToCompareWithBlacklist(*mPresShell);
+        if (principal) {
+          mPresShell->mForceDispatchKeyPressEventsForNonPrintableKeys =
+              principal->IsURIInPrefList(
+                  "dom.keyboardevent.keypress.hack.dispatch_non_printable_"
+                  "keys") ||
+              principal->IsURIInPrefList(
+                  "dom.keyboardevent.keypress.hack."
+                  "dispatch_non_printable_keys.addl");
+
+          mPresShell->mForceUseLegacyKeyCodeAndCharCodeValues |=
+              principal->IsURIInPrefList(
+                  "dom.keyboardevent.keypress.hack."
+                  "use_legacy_keycode_and_charcode") ||
+              principal->IsURIInPrefList(
+                  "dom.keyboardevent.keypress.hack."
+                  "use_legacy_keycode_and_charcode.addl");
+        }
+      }
+      if (mPresShell->mForceDispatchKeyPressEventsForNonPrintableKeys) {
+        aEvent->mFlags.mOnlySystemGroupDispatchInContent = false;
+      }
+      if (mPresShell->mForceUseLegacyKeyCodeAndCharCodeValues) {
+        aEvent->AsKeyboardEvent()->mUseLegacyKeyCodeAndCharCodeValues = true;
+      }
+    } else if (aEvent->mMessage == eMouseUp) {
+      // Historically Firefox has dispatched click events for non-primary
+      // buttons, but only on window and document (and inside input/textarea),
+      // not on elements in general. The UI events spec forbids click (and
+      // dblclick) for non-primary mouse buttons, and specifies auxclick
+      // instead. In case of some websites that rely on non-primary click to
+      // prevent new tab etc. and don't have auxclick code to do the same, we
+      // need to revert to the historial non-standard behaviour
+      if (!mPresShell->mInitializedWithClickEventDispatchingBlacklist) {
+        mPresShell->mInitializedWithClickEventDispatchingBlacklist = true;
+
+        nsCOMPtr<nsIPrincipal> principal =
+            GetDocumentPrincipalToCompareWithBlacklist(*mPresShell);
+
+        if (principal) {
+          mPresShell->mForceUseLegacyNonPrimaryDispatch =
+              principal->IsURIInPrefList(
+                  "dom.mouseevent.click.hack.use_legacy_non-primary_dispatch");
+        }
+      }
+      if (mPresShell->mForceUseLegacyNonPrimaryDispatch) {
+        aEvent->AsMouseEvent()->mUseLegacyNonPrimaryDispatch = true;
+      }
+    }
+
+    if (aEvent->mClass == eCompositionEventClass) {
+      RefPtr<nsPresContext> presContext = GetPresContext();
+      RefPtr<BrowserParent> browserParent =
+          IMEStateManager::GetActiveBrowserParent();
+      IMEStateManager::DispatchCompositionEvent(
+          eventTarget, presContext, browserParent, aEvent->AsCompositionEvent(),
+          aEventStatus, eventCBPtr);
+    } else {
+      RefPtr<nsPresContext> presContext = GetPresContext();
+      EventDispatcher::Dispatch(eventTarget, presContext, aEvent, nullptr,
+                                aEventStatus, eventCBPtr);
+    }
+  }
+  return rv;
+}
+
+void PresShell::EventHandler::DispatchTouchEventToDOM(
+    WidgetEvent* aEvent, nsEventStatus* aEventStatus,
+    nsPresShellEventCB* aEventCB, bool aTouchIsNew) {
+  // calling preventDefault on touchstart or the first touchmove for a
+  // point prevents mouse events. calling it on the touchend should
+  // prevent click dispatching.
+  bool canPrevent = (aEvent->mMessage == eTouchStart) ||
+                    (aEvent->mMessage == eTouchMove && aTouchIsNew) ||
+                    (aEvent->mMessage == eTouchEnd);
+  bool preventDefault = false;
+  nsEventStatus tmpStatus = nsEventStatus_eIgnore;
+  WidgetTouchEvent* touchEvent = aEvent->AsTouchEvent();
+
+  // loop over all touches and dispatch events on any that have changed
+  for (dom::Touch* touch : touchEvent->mTouches) {
+    // We should remove all suppressed touch instances in
+    // TouchManager::PreHandleEvent.
+    MOZ_ASSERT(!touch->mIsTouchEventSuppressed);
+
+    if (!touch || !touch->mChanged) {
+      continue;
+    }
+
+    nsCOMPtr<EventTarget> targetPtr = touch->mTarget;
+    nsCOMPtr<nsIContent> content = do_QueryInterface(targetPtr);
+    if (!content) {
+      continue;
+    }
+
+    Document* doc = content->OwnerDoc();
+    nsIContent* capturingContent = PresShell::GetCapturingContent();
+    if (capturingContent) {
+      if (capturingContent->OwnerDoc() != doc) {
+        // Wrong document, don't dispatch anything.
+        continue;
+      }
+      content = capturingContent;
+    }
+    // copy the event
+    MOZ_ASSERT(touchEvent->IsTrusted());
+    WidgetTouchEvent newEvent(true, touchEvent->mMessage, touchEvent->mWidget);
+    newEvent.AssignTouchEventData(*touchEvent, false);
+    newEvent.mTarget = targetPtr;
+    newEvent.mFlags.mHandledByAPZ = touchEvent->mFlags.mHandledByAPZ;
+
+    RefPtr<PresShell> contentPresShell;
+    if (doc == GetDocument()) {
+      contentPresShell = doc->GetPresShell();
+      if (contentPresShell) {
+        // XXXsmaug huge hack. Pushing possibly capturing content,
+        //         even though event target is something else.
+        contentPresShell->PushCurrentEventInfo(content->GetPrimaryFrame(),
+                                               content);
+      }
+    }
+
+    RefPtr<nsPresContext> presContext = doc->GetPresContext();
+    if (!presContext) {
+      if (contentPresShell) {
+        contentPresShell->PopCurrentEventInfo();
+      }
+      continue;
+    }
+
+    tmpStatus = nsEventStatus_eIgnore;
+    EventDispatcher::Dispatch(targetPtr, presContext, &newEvent, nullptr,
+                              &tmpStatus, aEventCB);
+    if (nsEventStatus_eConsumeNoDefault == tmpStatus ||
+        newEvent.mFlags.mMultipleActionsPrevented) {
+      preventDefault = true;
+    }
+
+    if (newEvent.mFlags.mMultipleActionsPrevented) {
+      touchEvent->mFlags.mMultipleActionsPrevented = true;
+    }
+
+    if (contentPresShell) {
+      contentPresShell->PopCurrentEventInfo();
+    }
+  }
+
+  if (preventDefault && canPrevent) {
+    *aEventStatus = nsEventStatus_eConsumeNoDefault;
+  } else {
+    *aEventStatus = nsEventStatus_eIgnore;
+  }
+}
+
+// Dispatch event to content only (NOT full processing)
+// See also HandleEventWithTarget which does full event processing.
+nsresult PresShell::HandleDOMEventWithTarget(nsIContent* aTargetContent,
+                                             WidgetEvent* aEvent,
+                                             nsEventStatus* aStatus) {
+  nsresult rv = NS_OK;
+
+  PushCurrentEventInfo(nullptr, aTargetContent);
+
+  // Bug 41013: Check if the event should be dispatched to content.
+  // It's possible that we are in the middle of destroying the window
+  // and the js context is out of date. This check detects the case
+  // that caused a crash in bug 41013, but there may be a better way
+  // to handle this situation!
+  nsCOMPtr<nsISupports> container = mPresContext->GetContainerWeak();
+  if (container) {
+    // Dispatch event to content
+    rv = EventDispatcher::Dispatch(aTargetContent, mPresContext, aEvent,
+                                   nullptr, aStatus);
+  }
+
+  PopCurrentEventInfo();
+  return rv;
+}
+
+// See the method above.
+nsresult PresShell::HandleDOMEventWithTarget(nsIContent* aTargetContent,
+                                             Event* aEvent,
+                                             nsEventStatus* aStatus) {
+  nsresult rv = NS_OK;
+
+  PushCurrentEventInfo(nullptr, aTargetContent);
+  nsCOMPtr<nsISupports> container = mPresContext->GetContainerWeak();
+  if (container) {
+    rv = EventDispatcher::DispatchDOMEvent(aTargetContent, nullptr, aEvent,
+                                           mPresContext, aStatus);
+  }
+
+  PopCurrentEventInfo();
+  return rv;
+}
+
+bool PresShell::EventHandler::AdjustContextMenuKeyEvent(
+    WidgetMouseEvent* aMouseEvent) {
+  // if a menu is open, open the context menu relative to the active item on the
+  // menu.
+  if (nsXULPopupManager* pm = nsXULPopupManager::GetInstance()) {
+    nsIFrame* popupFrame = pm->GetTopPopup(ePopupTypeMenu);
+    if (popupFrame) {
+      nsIFrame* itemFrame = (static_cast<nsMenuPopupFrame*>(popupFrame))
+                                ->GetCurrentMenuItemFrame();
+      if (!itemFrame) itemFrame = popupFrame;
+
+      nsCOMPtr<nsIWidget> widget = popupFrame->GetNearestWidget();
+      aMouseEvent->mWidget = widget;
+      LayoutDeviceIntPoint widgetPoint = widget->WidgetToScreenOffset();
+      aMouseEvent->mRefPoint =
+          LayoutDeviceIntPoint::FromAppUnitsToNearest(
+              itemFrame->GetScreenRectInAppUnits().BottomLeft(),
+              itemFrame->PresContext()->AppUnitsPerDevPixel()) -
+          widgetPoint;
+
+      mPresShell->mCurrentEventContent = itemFrame->GetContent();
+      mPresShell->mCurrentEventFrame = itemFrame;
+
+      return true;
+    }
+  }
+
+  // If we're here because of the key-equiv for showing context menus, we
+  // have to twiddle with the NS event to make sure the context menu comes
+  // up in the upper left of the relevant content area before we create
+  // the DOM event. Since we never call InitMouseEvent() on the event,
+  // the client X/Y will be 0,0. We can make use of that if the widget is null.
+  // Use the root view manager's widget since it's most likely to have one,
+  // and the coordinates returned by GetCurrentItemAndPositionForElement
+  // are relative to the widget of the root of the root view manager.
+  nsRootPresContext* rootPC = GetPresContext()->GetRootPresContext();
+  aMouseEvent->mRefPoint = LayoutDeviceIntPoint(0, 0);
+  if (rootPC) {
+    aMouseEvent->mWidget =
+        rootPC->PresShell()->GetViewManager()->GetRootWidget();
+    if (aMouseEvent->mWidget) {
+      // default the refpoint to the topleft of our document
+      nsPoint offset(0, 0);
+      nsIFrame* rootFrame = FrameConstructor()->GetRootFrame();
+      if (rootFrame) {
+        nsView* view = rootFrame->GetClosestView(&offset);
+        offset += view->GetOffsetToWidget(aMouseEvent->mWidget);
+        aMouseEvent->mRefPoint = LayoutDeviceIntPoint::FromAppUnitsToNearest(
+            offset, GetPresContext()->AppUnitsPerDevPixel());
+      }
+    }
+  } else {
+    aMouseEvent->mWidget = nullptr;
+  }
+
+  // see if we should use the caret position for the popup
+  LayoutDeviceIntPoint caretPoint;
+  // Beware! This may flush notifications via synchronous
+  // ScrollSelectionIntoView.
+  if (PrepareToUseCaretPosition(MOZ_KnownLive(aMouseEvent->mWidget),
+                                caretPoint)) {
+    // caret position is good
+    int32_t devPixelRatio = GetPresContext()->AppUnitsPerDevPixel();
+    caretPoint = LayoutDeviceIntPoint::FromAppUnitsToNearest(
+        ViewportUtils::LayoutToVisual(
+            LayoutDeviceIntPoint::ToAppUnits(caretPoint, devPixelRatio),
+            GetPresContext()->PresShell()),
+        devPixelRatio);
+    aMouseEvent->mRefPoint = caretPoint;
+    return true;
+  }
+
+  // If we're here because of the key-equiv for showing context menus, we
+  // have to reset the event target to the currently focused element. Get it
+  // from the focus controller.
+  RefPtr<Element> currentFocus;
+  nsFocusManager* fm = nsFocusManager::GetFocusManager();
+  if (fm) {
+    currentFocus = fm->GetFocusedElement();
+  }
+
+  // Reset event coordinates relative to focused frame in view
+  if (currentFocus) {
+    nsCOMPtr<nsIContent> currentPointElement;
+    GetCurrentItemAndPositionForElement(
+        currentFocus, getter_AddRefs(currentPointElement),
+        aMouseEvent->mRefPoint, MOZ_KnownLive(aMouseEvent->mWidget));
+    if (currentPointElement) {
+      mPresShell->mCurrentEventContent = currentPointElement;
+      mPresShell->mCurrentEventFrame = nullptr;
+      mPresShell->GetCurrentEventFrame();
+    }
+  }
+
+  return true;
+}
+
+// PresShell::EventHandler::PrepareToUseCaretPosition
+//
+//    This checks to see if we should use the caret position for popup context
+//    menus. Returns true if the caret position should be used, and the
+//    coordinates of that position is returned in aTargetPt. This function
+//    will also scroll the window as needed to make the caret visible.
+//
+//    The event widget should be the widget that generated the event, and
+//    whose coordinate system the resulting event's mRefPoint should be
+//    relative to.  The returned point is in device pixels realtive to the
+//    widget passed in.
+bool PresShell::EventHandler::PrepareToUseCaretPosition(
+    nsIWidget* aEventWidget, LayoutDeviceIntPoint& aTargetPt) {
+  nsresult rv;
+
+  // check caret visibility
+  RefPtr<nsCaret> caret = mPresShell->GetCaret();
+  NS_ENSURE_TRUE(caret, false);
+
+  bool caretVisible = caret->IsVisible();
+  if (!caretVisible) return false;
+
+  // caret selection, this is a temporary weak reference, so no refcounting is
+  // needed
+  Selection* domSelection = caret->GetSelection();
+  NS_ENSURE_TRUE(domSelection, false);
+
+  // since the match could be an anonymous textnode inside a
+  // <textarea> or text <input>, we need to get the outer frame
+  // note: frames are not refcounted
+  nsIFrame* frame = nullptr;  // may be nullptr
+  nsINode* node = domSelection->GetFocusNode();
+  NS_ENSURE_TRUE(node, false);
+  nsCOMPtr<nsIContent> content = nsIContent::FromNode(node);
+  if (content) {
+    nsIContent* nonNative = content->FindFirstNonChromeOnlyAccessContent();
+    content = nonNative;
+  }
+
+  if (content) {
+    // It seems like ScrollSelectionIntoView should be enough, but it's
+    // not. The problem is that scrolling the selection into view when it is
+    // below the current viewport will align the top line of the frame exactly
+    // with the bottom of the window. This is fine, BUT, the popup event causes
+    // the control to be re-focused which does this exact call to
+    // ScrollContentIntoView, which has a one-pixel disagreement of whether the
+    // frame is actually in view. The result is that the frame is aligned with
+    // the top of the window, but the menu is still at the bottom.
+    //
+    // Doing this call first forces the frame to be in view, eliminating the
+    // problem. The only difference in the result is that if your cursor is in
+    // an edit box below the current view, you'll get the edit box aligned with
+    // the top of the window. This is arguably better behavior anyway.
+    rv = MOZ_KnownLive(mPresShell)
+             ->ScrollContentIntoView(
+                 content,
+                 ScrollAxis(WhereToScroll::Nearest, WhenToScroll::IfNotVisible),
+                 ScrollAxis(WhereToScroll::Nearest, WhenToScroll::IfNotVisible),
+                 ScrollFlags::ScrollOverflowHidden);
+    NS_ENSURE_SUCCESS(rv, false);
+    frame = content->GetPrimaryFrame();
+    NS_WARNING_ASSERTION(frame, "No frame for focused content?");
+  }
+
+  // Actually scroll the selection (ie caret) into view. Note that this must
+  // be synchronous since we will be checking the caret position on the screen.
+  //
+  // Be easy about errors, and just don't scroll in those cases. Better to have
+  // the correct menu at a weird place than the wrong menu.
+  // After ScrollSelectionIntoView(), the pending notifications might be
+  // flushed and PresShell/PresContext/Frames may be dead. See bug 418470.
+  nsCOMPtr<nsISelectionController> selCon;
+  if (frame)
+    frame->GetSelectionController(GetPresContext(), getter_AddRefs(selCon));
+  else
+    selCon = static_cast<nsISelectionController*>(mPresShell);
+  if (selCon) {
+    rv = selCon->ScrollSelectionIntoView(
+        nsISelectionController::SELECTION_NORMAL,
+        nsISelectionController::SELECTION_FOCUS_REGION,
+        nsISelectionController::SCROLL_SYNCHRONOUS);
+    NS_ENSURE_SUCCESS(rv, false);
+  }
+
+  nsPresContext* presContext = GetPresContext();
+
+  // get caret position relative to the closest view
+  nsRect caretCoords;
+  nsIFrame* caretFrame = caret->GetGeometry(&caretCoords);
+  if (!caretFrame) return false;
+  nsPoint viewOffset;
+  nsView* view = caretFrame->GetClosestView(&viewOffset);
+  if (!view) return false;
+  // and then get the caret coords relative to the event widget
+  if (aEventWidget) {
+    viewOffset += view->GetOffsetToWidget(aEventWidget);
+  }
+  caretCoords.MoveBy(viewOffset);
+
+  // caret coordinates are in app units, convert to pixels
+  aTargetPt.x =
+      presContext->AppUnitsToDevPixels(caretCoords.x + caretCoords.width);
+  aTargetPt.y =
+      presContext->AppUnitsToDevPixels(caretCoords.y + caretCoords.height);
+
+  // make sure rounding doesn't return a pixel which is outside the caret
+  // (e.g. one line lower)
+  aTargetPt.y -= 1;
+
+  return true;
+}
+
+void PresShell::EventHandler::GetCurrentItemAndPositionForElement(
+    Element* aFocusedElement, nsIContent** aTargetToUse,
+    LayoutDeviceIntPoint& aTargetPt, nsIWidget* aRootWidget) {
+  nsCOMPtr<nsIContent> focusedContent = aFocusedElement;
+  MOZ_KnownLive(mPresShell)
+      ->ScrollContentIntoView(focusedContent, ScrollAxis(), ScrollAxis(),
+                              ScrollFlags::ScrollOverflowHidden);
+
+  nsPresContext* presContext = GetPresContext();
+
+  bool istree = false, checkLineHeight = true;
+  nscoord extraTreeY = 0;
+
+  // Set the position to just underneath the current item for multi-select
+  // lists or just underneath the selected item for single-select lists. If
+  // the element is not a list, or there is no selection, leave the position
+  // as is.
+  nsCOMPtr<Element> item;
+  nsCOMPtr<nsIDOMXULMultiSelectControlElement> multiSelect =
+      aFocusedElement->AsXULMultiSelectControl();
+  if (multiSelect) {
+    checkLineHeight = false;
+
+    int32_t currentIndex;
+    multiSelect->GetCurrentIndex(&currentIndex);
+    if (currentIndex >= 0) {
+      RefPtr<XULTreeElement> tree = XULTreeElement::FromNode(focusedContent);
+      // Tree view special case (tree items have no frames)
+      // Get the focused row and add its coordinates, which are already in
+      // pixels
+      // XXX Boris, should we create a new interface so that this doesn't
+      // need to know about trees? Something like nsINodelessChildCreator
+      // which could provide the current focus coordinates?
+      if (tree) {
+        tree->EnsureRowIsVisible(currentIndex);
+        int32_t firstVisibleRow = tree->GetFirstVisibleRow();
+        int32_t rowHeight = tree->RowHeight();
+
+        extraTreeY += nsPresContext::CSSPixelsToAppUnits(
+            (currentIndex - firstVisibleRow + 1) * rowHeight);
+        istree = true;
+
+        RefPtr<nsTreeColumns> cols = tree->GetColumns();
+        if (cols) {
+          nsTreeColumn* col = cols->GetFirstColumn();
+          if (col) {
+            RefPtr<Element> colElement = col->Element();
+            nsIFrame* frame = colElement->GetPrimaryFrame();
+            if (frame) {
+              extraTreeY += frame->GetSize().height;
+            }
+          }
+        }
+      } else {
+        multiSelect->GetCurrentItem(getter_AddRefs(item));
+      }
+    }
+  } else {
+    // don't check menulists as the selected item will be inside a popup.
+    nsCOMPtr<nsIDOMXULMenuListElement> menulist =
+        aFocusedElement->AsXULMenuList();
+    if (!menulist) {
+      nsCOMPtr<nsIDOMXULSelectControlElement> select =
+          aFocusedElement->AsXULSelectControl();
+      if (select) {
+        checkLineHeight = false;
+        select->GetSelectedItem(getter_AddRefs(item));
+      }
+    }
+  }
+
+  if (item) {
+    focusedContent = item;
+  }
+
+  nsIFrame* frame = focusedContent->GetPrimaryFrame();
+  if (frame) {
+    NS_ASSERTION(
+        frame->PresContext() == GetPresContext(),
+        "handling event for focused content that is not in our document?");
+
+    nsPoint frameOrigin(0, 0);
+
+    // Get the frame's origin within its view
+    nsView* view = frame->GetClosestView(&frameOrigin);
+    NS_ASSERTION(view, "No view for frame");
+
+    // View's origin relative the widget
+    if (aRootWidget) {
+      frameOrigin += view->GetOffsetToWidget(aRootWidget);
+    }
+
+    // Start context menu down and to the right from top left of frame
+    // use the lineheight. This is a good distance to move the context
+    // menu away from the top left corner of the frame. If we always
+    // used the frame height, the context menu could end up far away,
+    // for example when we're focused on linked images.
+    // On the other hand, we want to use the frame height if it's less
+    // than the current line height, so that the context menu appears
+    // associated with the correct frame.
+    nscoord extra = 0;
+    if (!istree) {
+      extra = frame->GetSize().height;
+      if (checkLineHeight) {
+        nsIScrollableFrame* scrollFrame =
+            nsLayoutUtils::GetNearestScrollableFrame(
+                frame, nsLayoutUtils::SCROLLABLE_INCLUDE_HIDDEN |
+                           nsLayoutUtils::SCROLLABLE_FIXEDPOS_FINDS_ROOT);
+        if (scrollFrame) {
+          nsSize scrollAmount = scrollFrame->GetLineScrollAmount();
+          nsIFrame* f = do_QueryFrame(scrollFrame);
+          int32_t APD = presContext->AppUnitsPerDevPixel();
+          int32_t scrollAPD = f->PresContext()->AppUnitsPerDevPixel();
+          scrollAmount = scrollAmount.ScaleToOtherAppUnits(scrollAPD, APD);
+          if (extra > scrollAmount.height) {
+            extra = scrollAmount.height;
+          }
+        }
+      }
+    }
+
+    aTargetPt.x = presContext->AppUnitsToDevPixels(frameOrigin.x);
+    aTargetPt.y =
+        presContext->AppUnitsToDevPixels(frameOrigin.y + extra + extraTreeY);
+  }
+
+  NS_IF_ADDREF(*aTargetToUse = focusedContent);
+}
+
+bool PresShell::ShouldIgnoreInvalidation() {
+  return mPaintingSuppressed || !mIsActive || mIsNeverPainting;
+}
+
+void PresShell::WillPaint() {
+  // Check the simplest things first.  In particular, it's important to
+  // check mIsActive before making any of the more expensive calls such
+  // as GetRootPresContext, for the case of a browser with a large
+  // number of tabs.
+  // Don't bother doing anything if some viewmanager in our tree is painting
+  // while we still have painting suppressed or we are not active.
+  if (!mIsActive || mPaintingSuppressed || !IsVisible()) {
+    return;
+  }
+
+  nsRootPresContext* rootPresContext = mPresContext->GetRootPresContext();
+  if (!rootPresContext) {
+    // In some edge cases, such as when we don't have a root frame yet,
+    // we can't find the root prescontext. There's nothing to do in that
+    // case.
+    return;
+  }
+
+  rootPresContext->FlushWillPaintObservers();
+  if (mIsDestroying) return;
+
+  // Process reflows, if we have them, to reduce flicker due to invalidates and
+  // reflow being interspersed.  Note that we _do_ allow this to be
+  // interruptible; if we can't do all the reflows it's better to flicker a bit
+  // than to freeze up.
+  FlushPendingNotifications(
+      ChangesToFlush(FlushType::InterruptibleLayout, false));
+}
+
+void PresShell::DidPaintWindow() {
+  nsRootPresContext* rootPresContext = mPresContext->GetRootPresContext();
+  if (rootPresContext != mPresContext) {
+    // This could be a popup's presshell. No point in notifying XPConnect
+    // about compositing of popups.
+    return;
+  }
+
+  if (!mHasReceivedPaintMessage) {
+    mHasReceivedPaintMessage = true;
+
+    nsCOMPtr<nsIObserverService> obsvc = services::GetObserverService();
+    if (obsvc && mDocument) {
+      nsPIDOMWindowOuter* window = mDocument->GetWindow();
+      nsCOMPtr<nsIDOMChromeWindow> chromeWin(do_QueryInterface(window));
+      if (chromeWin) {
+        obsvc->NotifyObservers(chromeWin, "widget-first-paint", nullptr);
+      }
+    }
+  }
+}
+
+bool PresShell::IsVisible() const {
+  if (!mIsActive || !mViewManager) return false;
+
+  nsView* view = mViewManager->GetRootView();
+  if (!view) return true;
+
+  // inner view of subdoc frame
+  view = view->GetParent();
+  if (!view) return true;
+
+  // subdoc view
+  view = view->GetParent();
+  if (!view) return true;
+
+  nsIFrame* frame = view->GetFrame();
+  if (!frame) return true;
+
+  return frame->IsVisibleConsideringAncestors(
+      nsIFrame::VISIBILITY_CROSS_CHROME_CONTENT_BOUNDARY);
+}
+
+void PresShell::SuppressDisplayport(bool aEnabled) {
+  if (aEnabled) {
+    mActiveSuppressDisplayport++;
+  } else if (mActiveSuppressDisplayport > 0) {
+    bool isSuppressed = IsDisplayportSuppressed();
+    mActiveSuppressDisplayport--;
+    if (isSuppressed && !IsDisplayportSuppressed()) {
+      // We unsuppressed the displayport, trigger a paint
+      if (nsIFrame* rootFrame = mFrameConstructor->GetRootFrame()) {
+        rootFrame->SchedulePaint();
+      }
+    }
+  }
+}
+
+static bool sDisplayPortSuppressionRespected = true;
+
+void PresShell::RespectDisplayportSuppression(bool aEnabled) {
+  bool isSuppressed = IsDisplayportSuppressed();
+  sDisplayPortSuppressionRespected = aEnabled;
+  if (isSuppressed && !IsDisplayportSuppressed()) {
+    // We unsuppressed the displayport, trigger a paint
+    if (nsIFrame* rootFrame = mFrameConstructor->GetRootFrame()) {
+      rootFrame->SchedulePaint();
+    }
+  }
+}
+
+bool PresShell::IsDisplayportSuppressed() {
+  return sDisplayPortSuppressionRespected && mActiveSuppressDisplayport > 0;
+}
+
+static CallState FreezeSubDocument(Document& aDocument) {
+  if (PresShell* presShell = aDocument.GetPresShell()) {
+    presShell->Freeze();
+  }
+  return CallState::Continue;
+}
+
+void PresShell::Freeze(bool aIncludeSubDocuments) {
+  mUpdateApproximateFrameVisibilityEvent.Revoke();
+
+  MaybeReleaseCapturingContent();
+
+  if (mCaret) {
+    SetCaretEnabled(false);
+  }
+
+  mPaintingSuppressed = true;
+
+  if (aIncludeSubDocuments && mDocument) {
+    mDocument->EnumerateSubDocuments(FreezeSubDocument);
+  }
+
+  nsPresContext* presContext = GetPresContext();
+  if (presContext) {
+    presContext->DisableInteractionTimeRecording();
+    if (presContext->RefreshDriver()->GetPresContext() == presContext) {
+      presContext->RefreshDriver()->Freeze();
+    }
+  }
+
+  mFrozen = true;
+  if (mDocument) {
+    UpdateImageLockingState();
+  }
+}
+
+void PresShell::FireOrClearDelayedEvents(bool aFireEvents) {
+  mNoDelayedMouseEvents = false;
+  mNoDelayedKeyEvents = false;
+  if (!aFireEvents) {
+    mDelayedEvents.Clear();
+    return;
+  }
+
+  if (mDocument) {
+    RefPtr<Document> doc = mDocument;
+    while (!mIsDestroying && mDelayedEvents.Length() &&
+           !doc->EventHandlingSuppressed()) {
+      UniquePtr<DelayedEvent> ev = std::move(mDelayedEvents[0]);
+      mDelayedEvents.RemoveElementAt(0);
+      if (ev->IsKeyPressEvent() && mIsLastKeyDownCanceled) {
+        continue;
+      }
+      ev->Dispatch();
+    }
+    if (!doc->EventHandlingSuppressed()) {
+      mDelayedEvents.Clear();
+    }
+  }
+}
+
+void PresShell::Thaw(bool aIncludeSubDocuments) {
+  nsPresContext* presContext = GetPresContext();
+  if (presContext &&
+      presContext->RefreshDriver()->GetPresContext() == presContext) {
+    presContext->RefreshDriver()->Thaw();
+  }
+
+  if (aIncludeSubDocuments && mDocument) {
+    mDocument->EnumerateSubDocuments([](Document& aSubDoc) {
+      if (PresShell* presShell = aSubDoc.GetPresShell()) {
+        presShell->Thaw();
+      }
+      return CallState::Continue;
+    });
+  }
+
+  // Get the activeness of our presshell, as this might have changed
+  // while we were in the bfcache
+  ActivenessMaybeChanged();
+
+  // We're now unfrozen
+  mFrozen = false;
+  UpdateImageLockingState();
+
+  UnsuppressPainting();
+}
+
+//--------------------------------------------------------
+// Start of protected and private methods on the PresShell
+//--------------------------------------------------------
+
+void PresShell::MaybeScheduleReflow() {
+  ASSERT_REFLOW_SCHEDULED_STATE();
+  if (mObservingLayoutFlushes || mIsDestroying || mIsReflowing ||
+      mDirtyRoots.IsEmpty())
+    return;
+
+  if (!mPresContext->HasPendingInterrupt() || !ScheduleReflowOffTimer()) {
+    ScheduleReflow();
+  }
+
+  ASSERT_REFLOW_SCHEDULED_STATE();
+}
+
+void PresShell::ScheduleReflow() {
+  ASSERT_REFLOW_SCHEDULED_STATE();
+  DoObserveLayoutFlushes();
+  ASSERT_REFLOW_SCHEDULED_STATE();
+}
+
+void PresShell::WillCauseReflow() {
+  nsContentUtils::AddScriptBlocker();
+  ++mChangeNestCount;
+}
+
+void PresShell::DidCauseReflow() {
+  NS_ASSERTION(mChangeNestCount != 0, "Unexpected call to DidCauseReflow()");
+  --mChangeNestCount;
+  nsContentUtils::RemoveScriptBlocker();
+}
+
+void PresShell::WillDoReflow() {
+  mDocument->FlushUserFontSet();
+
+  mPresContext->FlushCounterStyles();
+
+  mPresContext->FlushFontFeatureValues();
+
+  mPresContext->FlushFontPaletteValues();
+
+  mLastReflowStart = GetPerformanceNowUnclamped();
+}
+
+void PresShell::DidDoReflow(bool aInterruptible) {
+  MOZ_ASSERT(mPendingDidDoReflow);
+  if (!nsContentUtils::IsSafeToRunScript()) {
+    // If we're reflowing while script-blocked (e.g. from container query
+    // updates), defer our reflow callbacks until the end of our next layout
+    // flush.
+    SetNeedLayoutFlush();
+    return;
+  }
+
+  auto clearPendingDidDoReflow =
+      MakeScopeExit([&] { mPendingDidDoReflow = false; });
+
+  mHiddenContentInForcedLayout.Clear();
+
+  HandlePostedReflowCallbacks(aInterruptible);
+
+  if (mIsDestroying) {
+    return;
+  }
+
+  nsAutoScriptBlocker scriptBlocker;
+  AutoAssertNoFlush noReentrantFlush(*this);
+  if (nsCOMPtr<nsIDocShell> docShell = mPresContext->GetDocShell()) {
+    DOMHighResTimeStamp now = GetPerformanceNowUnclamped();
+    docShell->NotifyReflowObservers(aInterruptible, mLastReflowStart, now);
+  }
+
+  if (!mPresContext->HasPendingInterrupt()) {
+    // The ResizeObserver object may exist in the outer documents (e.g. observe
+    // an element in the in-process iframe) or any other documents which can
+    // access |mDocument|, so we have to schedule the resize observers for all
+    // possible documents via browsing context tree.
+    if (RefPtr<BrowsingContext> bc = mDocument->GetBrowsingContext()) {
+      bc->Top()->PreOrderWalk([](BrowsingContext* aCur) {
+        // Use extant document because we only want to schedule the observer to
+        // its refresh driver and so don't need to ensure the content viewer.
+        if (const Document* doc = aCur->GetExtantDocument()) {
+          doc->ScheduleResizeObserversNotification();
+        }
+      });
+    }
+  }
+
+  if (StaticPrefs::layout_reflow_synthMouseMove()) {
+    SynthesizeMouseMove(false);
+  }
+
+  mPresContext->NotifyMissingFonts();
+}
+
+DOMHighResTimeStamp PresShell::GetPerformanceNowUnclamped() {
+  DOMHighResTimeStamp now = 0;
+
+  if (nsPIDOMWindowInner* window = mDocument->GetInnerWindow()) {
+    Performance* perf = window->GetPerformance();
+
+    if (perf) {
+      now = perf->NowUnclamped();
+    }
+  }
+
+  return now;
+}
+
+void PresShell::sReflowContinueCallback(nsITimer* aTimer, void* aPresShell) {
+  RefPtr<PresShell> self = static_cast<PresShell*>(aPresShell);
+
+  MOZ_ASSERT(aTimer == self->mReflowContinueTimer, "Unexpected timer");
+  self->mReflowContinueTimer = nullptr;
+  self->ScheduleReflow();
+}
+
+bool PresShell::ScheduleReflowOffTimer() {
+  MOZ_ASSERT(!mObservingLayoutFlushes, "Shouldn't get here");
+  ASSERT_REFLOW_SCHEDULED_STATE();
+
+  if (!mReflowContinueTimer) {
+    nsresult rv = NS_NewTimerWithFuncCallback(
+        getter_AddRefs(mReflowContinueTimer), sReflowContinueCallback, this, 30,
+        nsITimer::TYPE_ONE_SHOT, "sReflowContinueCallback",
+        mDocument->EventTargetFor(TaskCategory::Other));
+    return NS_SUCCEEDED(rv);
+  }
+  return true;
+}
+
+bool PresShell::DoReflow(nsIFrame* target, bool aInterruptible,
+                         OverflowChangedTracker* aOverflowTracker) {
+  [[maybe_unused]] nsIURI* uri = mDocument->GetDocumentURI();
+  AUTO_PROFILER_LABEL_DYNAMIC_NSCSTRING_RELEVANT_FOR_JS(
+      "Reflow", LAYOUT_Reflow, uri ? uri->GetSpecOrDefault() : "N/A"_ns);
+
+  LAYOUT_TELEMETRY_RECORD_BASE(Reflow);
+
+  PerfStats::AutoMetricRecording<PerfStats::Metric::Reflowing> autoRecording;
+
+  gfxTextPerfMetrics* tp = mPresContext->GetTextPerfMetrics();
+  TimeStamp timeStart;
+  if (tp) {
+    tp->Accumulate();
+    tp->reflowCount++;
+    timeStart = TimeStamp::Now();
+  }
+
+  // Schedule a paint, but don't actually mark this frame as changed for
+  // retained DL building purposes. If any child frames get moved, then
+  // they will schedule paint again. We could probaby skip this, and just
+  // schedule a similar paint when a frame is deleted.
+  target->SchedulePaint(nsIFrame::PAINT_DEFAULT, false);
+
+  nsDocShell* docShell =
+      static_cast<nsDocShell*>(GetPresContext()->GetDocShell());
+  bool isTimelineRecording = TimelineConsumers::HasConsumer(docShell);
+
+  if (isTimelineRecording) {
+    TimelineConsumers::AddMarkerForDocShell(docShell, "Reflow",
+                                            MarkerTracingType::START);
+  }
+
+  Maybe<uint64_t> innerWindowID;
+  if (auto* window = mDocument->GetInnerWindow()) {
+    innerWindowID = Some(window->WindowID());
+  }
+  AutoProfilerTracing tracingLayoutFlush(
+      "Paint", "Reflow", geckoprofiler::category::LAYOUT,
+      std::move(mReflowCause), innerWindowID);
+  mReflowCause = nullptr;
+
+  FlushPendingScrollAnchorSelections();
+
+  if (mReflowContinueTimer) {
+    mReflowContinueTimer->Cancel();
+    mReflowContinueTimer = nullptr;
+  }
+
+  const bool isRoot = target == mFrameConstructor->GetRootFrame();
+
+  MOZ_ASSERT(isRoot || aOverflowTracker,
+             "caller must provide overflow tracker when reflowing "
+             "non-root frames");
+
+  // CreateReferenceRenderingContext can return nullptr
+  RefPtr<gfxContext> rcx(CreateReferenceRenderingContext());
+
+#ifdef DEBUG
+  mCurrentReflowRoot = target;
+#endif
+
+  // If the target frame is the root of the frame hierarchy, then
+  // use all the available space. If it's simply a `reflow root',
+  // then use the target frame's size as the available space.
+  WritingMode wm = target->GetWritingMode();
+  LogicalSize size(wm);
+  if (isRoot) {
+    size = LogicalSize(wm, mPresContext->GetVisibleArea().Size());
+  } else {
+    size = target->GetLogicalSize();
+  }
+
+  OverflowAreas oldOverflow;  // initialized and used only when !isRoot
+  if (!isRoot) {
+    oldOverflow = target->GetOverflowAreas();
+  }
+
+  NS_ASSERTION(!target->GetNextInFlow() && !target->GetPrevInFlow(),
+               "reflow roots should never split");
+
+  // Don't pass size directly to the reflow input, since a
+  // constrained height implies page/column breaking.
+  LogicalSize reflowSize(wm, size.ISize(wm), NS_UNCONSTRAINEDSIZE);
+  ReflowInput reflowInput(mPresContext, target, rcx, reflowSize,
+                          ReflowInput::InitFlag::CallerWillInit);
+  reflowInput.mOrthogonalLimit = size.BSize(wm);
+
+  if (isRoot) {
+    reflowInput.Init(mPresContext);
+
+    // When the root frame is being reflowed with unconstrained block-size
+    // (which happens when we're called from
+    // nsDocumentViewer::SizeToContent), we're effectively doing a
+    // resize in the block direction, since it changes the meaning of
+    // percentage block-sizes even if no block-sizes actually changed.
+    // The same applies when we reflow again after that computation. This is
+    // an unusual case, and isn't caught by ReflowInput::InitResizeFlags.
+    bool hasUnconstrainedBSize = size.BSize(wm) == NS_UNCONSTRAINEDSIZE;
+
+    if (hasUnconstrainedBSize || mLastRootReflowHadUnconstrainedBSize) {
+      reflowInput.SetBResize(true);
+    }
+
+    mLastRootReflowHadUnconstrainedBSize = hasUnconstrainedBSize;
+  } else {
+    // Initialize reflow input with current used border and padding,
+    // in case this was set specially by the parent frame when the reflow root
+    // was reflowed by its parent.
+    reflowInput.Init(mPresContext, Nothing(),
+                     Some(target->GetLogicalUsedBorder(wm)),
+                     Some(target->GetLogicalUsedPadding(wm)));
+  }
+
+  // fix the computed height
+  NS_ASSERTION(reflowInput.ComputedPhysicalMargin() == nsMargin(0, 0, 0, 0),
+               "reflow input should not set margin for reflow roots");
+  if (size.BSize(wm) != NS_UNCONSTRAINEDSIZE) {
+    nscoord computedBSize =
+        size.BSize(wm) -
+        reflowInput.ComputedLogicalBorderPadding(wm).BStartEnd(wm);
+    computedBSize = std::max(computedBSize, 0);
+    reflowInput.SetComputedBSize(computedBSize);
+  }
+  NS_ASSERTION(
+      reflowInput.ComputedISize() ==
+          size.ISize(wm) -
+              reflowInput.ComputedLogicalBorderPadding(wm).IStartEnd(wm),
+      "reflow input computed incorrect inline size");
+
+  mPresContext->ReflowStarted(aInterruptible);
+  mIsReflowing = true;
+
+  nsReflowStatus status;
+  ReflowOutput desiredSize(reflowInput);
+  target->Reflow(mPresContext, desiredSize, reflowInput, status);
+
+  // If an incremental reflow is initiated at a frame other than the
+  // root frame, then its desired size had better not change!  If it's
+  // initiated at the root, then the size better not change unless its
+  // height was unconstrained to start with.
+  nsRect boundsRelativeToTarget =
+      nsRect(0, 0, desiredSize.Width(), desiredSize.Height());
+  NS_ASSERTION((isRoot && size.BSize(wm) == NS_UNCONSTRAINEDSIZE) ||
+                   (desiredSize.ISize(wm) == size.ISize(wm) &&
+                    desiredSize.BSize(wm) == size.BSize(wm)),
+               "non-root frame's desired size changed during an "
+               "incremental reflow");
+  NS_ASSERTION(status.IsEmpty(), "reflow roots should never split");
+
+  target->SetSize(boundsRelativeToTarget.Size());
+
+  // Always use boundsRelativeToTarget here, not
+  // desiredSize.InkOverflowRect(), because for root frames (where they
+  // could be different, since root frames are allowed to have overflow) the
+  // root view bounds need to match the viewport bounds; the view manager
+  // "window dimensions" code depends on it.
+  nsContainerFrame::SyncFrameViewAfterReflow(
+      mPresContext, target, target->GetView(), boundsRelativeToTarget);
+  nsContainerFrame::SyncWindowProperties(mPresContext, target,
+                                         target->GetView(), rcx,
+                                         nsContainerFrame::SET_ASYNC);
+
+  target->DidReflow(mPresContext, nullptr);
+  if (target->IsInScrollAnchorChain()) {
+    ScrollAnchorContainer* container = ScrollAnchorContainer::FindFor(target);
+    PostPendingScrollAnchorAdjustment(container);
+  }
+  if (isRoot && size.BSize(wm) == NS_UNCONSTRAINEDSIZE) {
+    mPresContext->SetVisibleArea(boundsRelativeToTarget);
+  }
+
+#ifdef DEBUG
+  mCurrentReflowRoot = nullptr;
+#endif
+
+  if (!isRoot && oldOverflow != target->GetOverflowAreas()) {
+    // The overflow area changed.  Propagate this change to ancestors.
+    aOverflowTracker->AddFrame(target->GetParent(),
+                               OverflowChangedTracker::CHILDREN_CHANGED);
+  }
+
+  NS_ASSERTION(
+      mPresContext->HasPendingInterrupt() || mFramesToDirty.Count() == 0,
+      "Why do we need to dirty anything if not interrupted?");
+
+  mIsReflowing = false;
+  bool interrupted = mPresContext->HasPendingInterrupt();
+  if (interrupted) {
+    // Make sure target gets reflowed again.
+    for (const auto& key : mFramesToDirty) {
+      // Mark frames dirty until target frame.
+      for (nsIFrame* f = key; f && !f->IsSubtreeDirty(); f = f->GetParent()) {
+        f->AddStateBits(NS_FRAME_HAS_DIRTY_CHILDREN);
+        if (f->IsFlexItem()) {
+          nsFlexContainerFrame::MarkCachedFlexMeasurementsDirty(f);
+        }
+
+        if (f == target) {
+          break;
+        }
+      }
+    }
+
+    NS_ASSERTION(target->IsSubtreeDirty(), "Why is the target not dirty?");
+    mDirtyRoots.Add(target);
+    SetNeedLayoutFlush();
+
+    // Clear mFramesToDirty after we've done the target->IsSubtreeDirty()
+    // assertion so that if it fails it's easier to see what's going on.
+#ifdef NOISY_INTERRUPTIBLE_REFLOW
+    printf("mFramesToDirty.Count() == %u\n", mFramesToDirty.Count());
+#endif /* NOISY_INTERRUPTIBLE_REFLOW */
+    mFramesToDirty.Clear();
+
+    // Any FlushPendingNotifications with interruptible reflows
+    // should be suppressed now. We don't want to do extra reflow work
+    // before our reflow event happens.
+    mWasLastReflowInterrupted = true;
+    MaybeScheduleReflow();
+  }
+
+  // dump text perf metrics for reflows with significant text processing
+  if (tp) {
+    if (tp->current.numChars > 100) {
+      TimeDuration reflowTime = TimeStamp::Now() - timeStart;
+      LogTextPerfStats(tp, this, tp->current, reflowTime.ToMilliseconds(),
+                       eLog_reflow, nullptr);
+    }
+    tp->Accumulate();
+  }
+
+  if (isTimelineRecording) {
+    TimelineConsumers::AddMarkerForDocShell(docShell, "Reflow",
+                                            MarkerTracingType::END);
+  }
+
+  return !interrupted;
+}
+
+#ifdef DEBUG
+void PresShell::DoVerifyReflow() {
+  if (GetVerifyReflowEnable()) {
+    // First synchronously render what we have so far so that we can
+    // see it.
+    nsView* rootView = mViewManager->GetRootView();
+    mViewManager->InvalidateView(rootView);
+
+    FlushPendingNotifications(FlushType::Layout);
+    mInVerifyReflow = true;
+    bool ok = VerifyIncrementalReflow();
+    mInVerifyReflow = false;
+    if (VerifyReflowFlags::All & gVerifyReflowFlags) {
+      printf("ProcessReflowCommands: finished (%s)\n", ok ? "ok" : "failed");
+    }
+
+    if (!mDirtyRoots.IsEmpty()) {
+      printf("XXX yikes! reflow commands queued during verify-reflow\n");
+    }
+  }
+}
+#endif
+
+// used with Telemetry metrics
+#define NS_LONG_REFLOW_TIME_MS 5000
+
+bool PresShell::ProcessReflowCommands(bool aInterruptible) {
+  if (mDirtyRoots.IsEmpty() && !mShouldUnsuppressPainting &&
+      !mPendingDidDoReflow) {
+    // Nothing to do; bail out
+    return true;
+  }
+
+  const bool wasProcessingReflowCommands = mProcessingReflowCommands;
+  auto restoreProcessingReflowCommands = MakeScopeExit(
+      [&] { mProcessingReflowCommands = wasProcessingReflowCommands; });
+  mProcessingReflowCommands = true;
+
+  auto timerStart = mozilla::TimeStamp::Now();
+  bool interrupted = false;
+  if (!mDirtyRoots.IsEmpty()) {
+#ifdef DEBUG
+    if (VerifyReflowFlags::DumpCommands & gVerifyReflowFlags) {
+      printf("ProcessReflowCommands: begin incremental reflow\n");
+    }
+#endif
+
+    // If reflow is interruptible, then make a note of our deadline.
+    const PRIntervalTime deadline =
+        aInterruptible
+            ? PR_IntervalNow() + PR_MicrosecondsToInterval(gMaxRCProcessingTime)
+            : (PRIntervalTime)0;
+
+    // Scope for the reflow entry point
+    nsAutoScriptBlocker scriptBlocker;
+    WillDoReflow();
+    AUTO_LAYOUT_PHASE_ENTRY_POINT(GetPresContext(), Reflow);
+    nsViewManager::AutoDisableRefresh refreshBlocker(mViewManager);
+
+    OverflowChangedTracker overflowTracker;
+
+    do {
+      // Send an incremental reflow notification to the target frame.
+      nsIFrame* target = mDirtyRoots.PopShallowestRoot();
+
+      if (!target->IsSubtreeDirty()) {
+        // It's not dirty anymore, which probably means the notification
+        // was posted in the middle of a reflow (perhaps with a reflow
+        // root in the middle).  Don't do anything.
+        continue;
+      }
+
+      interrupted = !DoReflow(target, aInterruptible, &overflowTracker);
+
+      // Keep going until we're out of reflow commands, or we've run
+      // past our deadline, or we're interrupted.
+    } while (!interrupted && !mDirtyRoots.IsEmpty() &&
+             (!aInterruptible || PR_IntervalNow() < deadline));
+
+    interrupted = !mDirtyRoots.IsEmpty();
+
+    overflowTracker.Flush();
+
+    if (!interrupted) {
+      // We didn't get interrupted. Go ahead and perform scroll anchor
+      // adjustments.
+      FlushPendingScrollAnchorAdjustments();
+    }
+    mPendingDidDoReflow = true;
+  }
+
+  // Exiting the scriptblocker might have killed us. If we were processing
+  // scroll commands, let the outermost call deal with it.
+  if (!mIsDestroying && mPendingDidDoReflow && !wasProcessingReflowCommands) {
+    DidDoReflow(aInterruptible);
+  }
+
+  // DidDoReflow might have killed us
+  if (!mIsDestroying) {
+#ifdef DEBUG
+    if (VerifyReflowFlags::DumpCommands & gVerifyReflowFlags) {
+      printf("\nPresShell::ProcessReflowCommands() finished: this=%p\n",
+             (void*)this);
+    }
+    DoVerifyReflow();
+#endif
+
+    // If any new reflow commands were enqueued during the reflow, schedule
+    // another reflow event to process them.  Note that we want to do this
+    // after DidDoReflow(), since that method can change whether there are
+    // dirty roots around by flushing, and there's no point in posting a
+    // reflow event just to have the flush revoke it.
+    if (!mDirtyRoots.IsEmpty()) {
+      MaybeScheduleReflow();
+      // And record that we might need flushing
+      SetNeedLayoutFlush();
+    }
+  }
+
+  if (!mIsDestroying && mShouldUnsuppressPainting && mDirtyRoots.IsEmpty()) {
+    // We only unlock if we're out of reflows.  It's pointless
+    // to unlock if reflows are still pending, since reflows
+    // are just going to thrash the frames around some more.  By
+    // waiting we avoid an overeager "jitter" effect.
+    mShouldUnsuppressPainting = false;
+    UnsuppressAndInvalidate();
+  }
+
+  if (mDocument->GetRootElement()) {
+    TimeDuration elapsed = TimeStamp::Now() - timerStart;
+    int32_t intElapsed = int32_t(elapsed.ToMilliseconds());
+
+    if (intElapsed > NS_LONG_REFLOW_TIME_MS) {
+      Telemetry::Accumulate(Telemetry::LONG_REFLOW_INTERRUPTIBLE,
+                            aInterruptible ? 1 : 0);
+    }
+  }
+
+  return !interrupted;
+}
+
+bool PresShell::DoFlushLayout(bool aInterruptible) {
+  mFrameConstructor->RecalcQuotesAndCounters();
+  return ProcessReflowCommands(aInterruptible);
+}
+
+void PresShell::WindowSizeMoveDone() {
+  if (mPresContext) {
+    EventStateManager::ClearGlobalActiveContent(nullptr);
+    ClearMouseCapture();
+  }
+}
+
+NS_IMETHODIMP
+PresShell::Observe(nsISupports* aSubject, const char* aTopic,
+                   const char16_t* aData) {
+  if (mIsDestroying) {
+    NS_WARNING("our observers should have been unregistered by now");
+    return NS_OK;
+  }
+
+  if (!nsCRT::strcmp(aTopic, "memory-pressure")) {
+    if (!AssumeAllFramesVisible() &&
+        mPresContext->IsRootContentDocumentInProcess()) {
+      DoUpdateApproximateFrameVisibility(/* aRemoveOnly = */ true);
+    }
+    return NS_OK;
+  }
+
+  if (!nsCRT::strcmp(aTopic, NS_WIDGET_WAKE_OBSERVER_TOPIC)) {
+    mLastOSWake = TimeStamp::Now();
+    return NS_OK;
+  }
+
+  // For parent process, user may expect the UI is interactable after a
+  // tab (previously opened page or home page) has restored.
+  if (!nsCRT::strcmp(aTopic, "sessionstore-one-or-no-tab-restored")) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+    sProcessInteractable = true;
+
+    nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
+    if (os) {
+      os->RemoveObserver(this, "sessionstore-one-or-no-tab-restored");
+    }
+    return NS_OK;
+  }
+
+  if (!nsCRT::strcmp(aTopic, "font-info-updated")) {
+    // See how gfxPlatform::ForceGlobalReflow encodes this.
+    bool needsReframe = aData && !!aData[0];
+    mPresContext->ForceReflowForFontInfoUpdate(needsReframe);
+    return NS_OK;
+  }
+
+  // The "look-and-feel-changed" notification for JS observers will be
+  // dispatched HandleGlobalThemeChange once LookAndFeel caches are cleared.
+  if (!nsCRT::strcmp(aTopic, "internal-look-and-feel-changed")) {
+    // See how LookAndFeel::NotifyChangedAllWindows encodes this.
+    auto kind = widget::ThemeChangeKind(aData[0]);
+    mPresContext->ThemeChanged(kind);
+    return NS_OK;
+  }
+
+  NS_WARNING("unrecognized topic in PresShell::Observe");
+  return NS_ERROR_FAILURE;
+}
+
+bool PresShell::AddRefreshObserver(nsARefreshObserver* aObserver,
+                                   FlushType aFlushType,
+                                   const char* aObserverDescription) {
+  nsPresContext* presContext = GetPresContext();
+  if (MOZ_UNLIKELY(!presContext)) {
+    return false;
+  }
+  presContext->RefreshDriver()->AddRefreshObserver(aObserver, aFlushType,
+                                                   aObserverDescription);
+  return true;
+}
+
+bool PresShell::RemoveRefreshObserver(nsARefreshObserver* aObserver,
+                                      FlushType aFlushType) {
+  nsPresContext* presContext = GetPresContext();
+  return presContext && presContext->RefreshDriver()->RemoveRefreshObserver(
+                            aObserver, aFlushType);
+}
+
+bool PresShell::AddPostRefreshObserver(nsAPostRefreshObserver* aObserver) {
+  nsPresContext* presContext = GetPresContext();
+  if (!presContext) {
+    return false;
+  }
+  presContext->RefreshDriver()->AddPostRefreshObserver(aObserver);
+  return true;
+}
+
+bool PresShell::RemovePostRefreshObserver(nsAPostRefreshObserver* aObserver) {
+  nsPresContext* presContext = GetPresContext();
+  if (!presContext) {
+    return false;
+  }
+  presContext->RefreshDriver()->RemovePostRefreshObserver(aObserver);
+  return true;
+}
+
+void PresShell::DoObserveStyleFlushes() {
+  MOZ_ASSERT(!ObservingStyleFlushes());
+  mObservingStyleFlushes = true;
+
+  if (MOZ_LIKELY(!mDocument->GetBFCacheEntry())) {
+    mPresContext->RefreshDriver()->AddStyleFlushObserver(this);
+  }
+}
+
+void PresShell::DoObserveLayoutFlushes() {
+  MOZ_ASSERT(!ObservingLayoutFlushes());
+  mObservingLayoutFlushes = true;
+
+  if (MOZ_LIKELY(!mDocument->GetBFCacheEntry())) {
+    mPresContext->RefreshDriver()->AddLayoutFlushObserver(this);
+  }
+}
+
+//------------------------------------------------------
+// End of protected and private methods on the PresShell
+//------------------------------------------------------
+
+//------------------------------------------------------------------
+//-- Delayed event Classes Impls
+//------------------------------------------------------------------
+
+PresShell::DelayedInputEvent::DelayedInputEvent()
+    : DelayedEvent(), mEvent(nullptr) {}
+
+PresShell::DelayedInputEvent::~DelayedInputEvent() { delete mEvent; }
+
+void PresShell::DelayedInputEvent::Dispatch() {
+  if (!mEvent || !mEvent->mWidget) {
+    return;
+  }
+  nsCOMPtr<nsIWidget> widget = mEvent->mWidget;
+  nsEventStatus status;
+  widget->DispatchEvent(mEvent, status);
+}
+
+PresShell::DelayedMouseEvent::DelayedMouseEvent(WidgetMouseEvent* aEvent)
+    : DelayedInputEvent() {
+  MOZ_DIAGNOSTIC_ASSERT(aEvent->IsTrusted());
+  WidgetMouseEvent* mouseEvent =
+      new WidgetMouseEvent(true, aEvent->mMessage, aEvent->mWidget,
+                           aEvent->mReason, aEvent->mContextMenuTrigger);
+  mouseEvent->AssignMouseEventData(*aEvent, false);
+  mEvent = mouseEvent;
+}
+
+PresShell::DelayedKeyEvent::DelayedKeyEvent(WidgetKeyboardEvent* aEvent)
+    : DelayedInputEvent() {
+  MOZ_DIAGNOSTIC_ASSERT(aEvent->IsTrusted());
+  WidgetKeyboardEvent* keyEvent =
+      new WidgetKeyboardEvent(true, aEvent->mMessage, aEvent->mWidget);
+  keyEvent->AssignKeyEventData(*aEvent, false);
+  keyEvent->mFlags.mIsSynthesizedForTests =
+      aEvent->mFlags.mIsSynthesizedForTests;
+  keyEvent->mFlags.mIsSuppressedOrDelayed = true;
+  mEvent = keyEvent;
+}
+
+bool PresShell::DelayedKeyEvent::IsKeyPressEvent() {
+  return mEvent->mMessage == eKeyPress;
+}
+
+// Start of DEBUG only code
+
+#ifdef DEBUG
+
+static void LogVerifyMessage(nsIFrame* k1, nsIFrame* k2, const char* aMsg) {
+  nsAutoString n1, n2;
+  if (k1) {
+    k1->GetFrameName(n1);
+  } else {
+    n1.AssignLiteral(u"(null)");
+  }
+
+  if (k2) {
+    k2->GetFrameName(n2);
+  } else {
+    n2.AssignLiteral(u"(null)");
+  }
+
+  printf("verifyreflow: %s %p != %s %p  %s\n",
+         NS_LossyConvertUTF16toASCII(n1).get(), (void*)k1,
+         NS_LossyConvertUTF16toASCII(n2).get(), (void*)k2, aMsg);
+}
+
+static void LogVerifyMessage(nsIFrame* k1, nsIFrame* k2, const char* aMsg,
+                             const nsRect& r1, const nsRect& r2) {
+  printf("VerifyReflow Error:\n");
+  nsAutoString name;
+
+  if (k1) {
+    k1->GetFrameName(name);
+    printf("  %s %p ", NS_LossyConvertUTF16toASCII(name).get(), (void*)k1);
+  }
+  printf("{%d, %d, %d, %d} != \n", r1.x, r1.y, r1.width, r1.height);
+
+  if (k2) {
+    k2->GetFrameName(name);
+    printf("  %s %p ", NS_LossyConvertUTF16toASCII(name).get(), (void*)k2);
+  }
+  printf("{%d, %d, %d, %d}\n  %s\n", r2.x, r2.y, r2.width, r2.height, aMsg);
+}
+
+static void LogVerifyMessage(nsIFrame* k1, nsIFrame* k2, const char* aMsg,
+                             const nsIntRect& r1, const nsIntRect& r2) {
+  printf("VerifyReflow Error:\n");
+  nsAutoString name;
+
+  if (k1) {
+    k1->GetFrameName(name);
+    printf("  %s %p ", NS_LossyConvertUTF16toASCII(name).get(), (void*)k1);
+  }
+  printf("{%d, %d, %d, %d} != \n", r1.x, r1.y, r1.width, r1.height);
+
+  if (k2) {
+    k2->GetFrameName(name);
+    printf("  %s %p ", NS_LossyConvertUTF16toASCII(name).get(), (void*)k2);
+  }
+  printf("{%d, %d, %d, %d}\n  %s\n", r2.x, r2.y, r2.width, r2.height, aMsg);
+}
+
+static bool CompareTrees(nsPresContext* aFirstPresContext,
+                         nsIFrame* aFirstFrame,
+                         nsPresContext* aSecondPresContext,
+                         nsIFrame* aSecondFrame) {
+  if (!aFirstPresContext || !aFirstFrame || !aSecondPresContext ||
+      !aSecondFrame)
+    return true;
+  // XXX Evil hack to reduce false positives; I can't seem to figure
+  // out how to flush scrollbar changes correctly
+  // if (aFirstFrame->IsScrollbarFrame())
+  //  return true;
+  bool ok = true;
+  const auto& childLists1 = aFirstFrame->ChildLists();
+  const auto& childLists2 = aSecondFrame->ChildLists();
+  auto iterLists1 = childLists1.begin();
+  auto iterLists2 = childLists2.begin();
+  do {
+    const nsFrameList& kids1 = iterLists1 != childLists1.end()
+                                   ? iterLists1->mList
+                                   : nsFrameList::EmptyList();
+    const nsFrameList& kids2 = iterLists2 != childLists2.end()
+                                   ? iterLists2->mList
+                                   : nsFrameList::EmptyList();
+    int32_t l1 = kids1.GetLength();
+    int32_t l2 = kids2.GetLength();
+    if (l1 != l2) {
+      ok = false;
+      LogVerifyMessage(kids1.FirstChild(), kids2.FirstChild(),
+                       "child counts don't match: ");
+      printf("%d != %d\n", l1, l2);
+      if (!(VerifyReflowFlags::All & gVerifyReflowFlags)) {
+        break;
+      }
+    }
+
+    LayoutDeviceIntRect r1, r2;
+    nsView* v1;
+    nsView* v2;
+    for (auto kids1Iter = kids1.begin(), kids2Iter = kids2.begin();;
+         ++kids1Iter, ++kids2Iter) {
+      nsIFrame* k1 = *kids1Iter;
+      nsIFrame* k2 = *kids2Iter;
+      if (((nullptr == k1) && (nullptr != k2)) ||
+          ((nullptr != k1) && (nullptr == k2))) {
+        ok = false;
+        LogVerifyMessage(k1, k2, "child lists are different\n");
+        break;
+      } else if (nullptr != k1) {
+        // Verify that the frames are the same size
+        if (!k1->GetRect().IsEqualInterior(k2->GetRect())) {
+          ok = false;
+          LogVerifyMessage(k1, k2, "(frame rects)", k1->GetRect(),
+                           k2->GetRect());
+        }
+
+        // Make sure either both have views or neither have views; if they
+        // do have views, make sure the views are the same size. If the
+        // views have widgets, make sure they both do or neither does. If
+        // they do, make sure the widgets are the same size.
+        v1 = k1->GetView();
+        v2 = k2->GetView();
+        if (((nullptr == v1) && (nullptr != v2)) ||
+            ((nullptr != v1) && (nullptr == v2))) {
+          ok = false;
+          LogVerifyMessage(k1, k2, "child views are not matched\n");
+        } else if (nullptr != v1) {
+          if (!v1->GetBounds().IsEqualInterior(v2->GetBounds())) {
+            LogVerifyMessage(k1, k2, "(view rects)", v1->GetBounds(),
+                             v2->GetBounds());
+          }
+
+          nsIWidget* w1 = v1->GetWidget();
+          nsIWidget* w2 = v2->GetWidget();
+          if (((nullptr == w1) && (nullptr != w2)) ||
+              ((nullptr != w1) && (nullptr == w2))) {
+            ok = false;
+            LogVerifyMessage(k1, k2, "child widgets are not matched\n");
+          } else if (nullptr != w1) {
+            r1 = w1->GetBounds();
+            r2 = w2->GetBounds();
+            if (!r1.IsEqualEdges(r2)) {
+              LogVerifyMessage(k1, k2, "(widget rects)", r1.ToUnknownRect(),
+                               r2.ToUnknownRect());
+            }
+          }
+        }
+        if (!ok && !(VerifyReflowFlags::All & gVerifyReflowFlags)) {
+          break;
+        }
+
+        // XXX Should perhaps compare their float managers.
+
+        // Compare the sub-trees too
+        if (!CompareTrees(aFirstPresContext, k1, aSecondPresContext, k2)) {
+          ok = false;
+          if (!(VerifyReflowFlags::All & gVerifyReflowFlags)) {
+            break;
+          }
+        }
+      } else {
+        break;
+      }
+    }
+    if (!ok && (!(VerifyReflowFlags::All & gVerifyReflowFlags))) {
+      break;
+    }
+
+    ++iterLists1;
+    ++iterLists2;
+    const bool lists1Done = iterLists1 == childLists1.end();
+    const bool lists2Done = iterLists2 == childLists2.end();
+    if (lists1Done != lists2Done ||
+        (!lists1Done && iterLists1->mID != iterLists2->mID)) {
+      if (!(VerifyReflowFlags::All & gVerifyReflowFlags)) {
+        ok = false;
+      }
+      LogVerifyMessage(kids1.FirstChild(), kids2.FirstChild(),
+                       "child list names are not matched: ");
+      fprintf(stdout, "%s != %s\n",
+              !lists1Done ? ChildListName(iterLists1->mID) : "(null)",
+              !lists2Done ? ChildListName(iterLists2->mID) : "(null)");
+      break;
+    }
+  } while (ok && iterLists1 != childLists1.end());
+
+  return ok;
+}
+#endif
+
+#if 0
+static nsIFrame*
+FindTopFrame(nsIFrame* aRoot)
+{
+  if (aRoot) {
+    nsIContent* content = aRoot->GetContent();
+    if (content) {
+      nsAtom* tag;
+      content->GetTag(tag);
+      if (nullptr != tag) {
+        NS_RELEASE(tag);
+        return aRoot;
+      }
+    }
+
+    // Try one of the children
+    for (nsIFrame* kid : aRoot->PrincipalChildList()) {
+      nsIFrame* result = FindTopFrame(kid);
+      if (nullptr != result) {
+        return result;
+      }
+    }
+  }
+  return nullptr;
+}
+#endif
+
+#ifdef DEBUG
+
+// After an incremental reflow, we verify the correctness by doing a
+// full reflow into a fresh frame tree.
+bool PresShell::VerifyIncrementalReflow() {
+  if (VerifyReflowFlags::Noisy & gVerifyReflowFlags) {
+    printf("Building Verification Tree...\n");
+  }
+
+  // Create a presentation context to view the new frame tree
+  RefPtr<nsPresContext> cx = new nsRootPresContext(
+      mDocument, mPresContext->IsPaginated()
+                     ? nsPresContext::eContext_PrintPreview
+                     : nsPresContext::eContext_Galley);
+  NS_ENSURE_TRUE(cx, false);
+
+  nsDeviceContext* dc = mPresContext->DeviceContext();
+  nsresult rv = cx->Init(dc);
+  NS_ENSURE_SUCCESS(rv, false);
+
+  // Get our scrolling preference
+  nsView* rootView = mViewManager->GetRootView();
+  NS_ENSURE_TRUE(rootView->HasWidget(), false);
+  nsIWidget* parentWidget = rootView->GetWidget();
+
+  // Create a new view manager.
+  RefPtr<nsViewManager> vm = new nsViewManager();
+  NS_ENSURE_TRUE(vm, false);
+  rv = vm->Init(dc);
+  NS_ENSURE_SUCCESS(rv, false);
+
+  // Create a child window of the parent that is our "root view/window"
+  // Create a view
+  nsRect tbounds = mPresContext->GetVisibleArea();
+  nsView* view = vm->CreateView(tbounds, nullptr);
+  NS_ENSURE_TRUE(view, false);
+
+  // now create the widget for the view
+  rv = view->CreateWidgetForParent(parentWidget, nullptr, true);
+  NS_ENSURE_SUCCESS(rv, false);
+
+  // Setup hierarchical relationship in view manager
+  vm->SetRootView(view);
+
+  // Make the new presentation context the same size as our
+  // presentation context.
+  cx->SetVisibleArea(mPresContext->GetVisibleArea());
+
+  RefPtr<PresShell> presShell = mDocument->CreatePresShell(cx, vm);
+  NS_ENSURE_TRUE(presShell, false);
+
+  // Note that after we create the shell, we must make sure to destroy it
+  presShell->SetVerifyReflowEnable(
+      false);  // turn off verify reflow while we're
+               // reflowing the test frame tree
+  vm->SetPresShell(presShell);
+  {
+    nsAutoCauseReflowNotifier crNotifier(this);
+    presShell->Initialize();
+  }
+  presShell->FlushPendingNotifications(FlushType::Layout);
+  presShell->SetVerifyReflowEnable(
+      true);  // turn on verify reflow again now that
+              // we're done reflowing the test frame tree
+  // Force the non-primary presshell to unsuppress; it doesn't want to normally
+  // because it thinks it's hidden
+  presShell->mPaintingSuppressed = false;
+  if (VerifyReflowFlags::Noisy & gVerifyReflowFlags) {
+    printf("Verification Tree built, comparing...\n");
+  }
+
+  // Now that the document has been reflowed, use its frame tree to
+  // compare against our frame tree.
+  nsIFrame* root1 = mFrameConstructor->GetRootFrame();
+  nsIFrame* root2 = presShell->GetRootFrame();
+  bool ok = CompareTrees(mPresContext, root1, cx, root2);
+  if (!ok && (VerifyReflowFlags::Noisy & gVerifyReflowFlags)) {
+    printf("Verify reflow failed, primary tree:\n");
+    root1->List(stdout);
+    printf("Verification tree:\n");
+    root2->List(stdout);
+  }
+
+#  if 0
+  // Sample code for dumping page to png
+  // XXX Needs to be made more flexible
+  if (!ok) {
+    nsString stra;
+    static int num = 0;
+    stra.AppendLiteral("C:\\mozilla\\mozilla\\debug\\filea");
+    stra.AppendInt(num);
+    stra.AppendLiteral(".png");
+    gfxUtils::WriteAsPNG(presShell, stra);
+    nsString strb;
+    strb.AppendLiteral("C:\\mozilla\\mozilla\\debug\\fileb");
+    strb.AppendInt(num);
+    strb.AppendLiteral(".png");
+    gfxUtils::WriteAsPNG(presShell, strb);
+    ++num;
+  }
+#  endif
+
+  presShell->EndObservingDocument();
+  presShell->Destroy();
+  if (VerifyReflowFlags::Noisy & gVerifyReflowFlags) {
+    printf("Finished Verifying Reflow...\n");
+  }
+
+  return ok;
+}
+
+// Layout debugging hooks
+void PresShell::ListComputedStyles(FILE* out, int32_t aIndent) {
+  nsIFrame* rootFrame = GetRootFrame();
+  if (rootFrame) {
+    rootFrame->Style()->List(out, aIndent);
+  }
+
+  // The root element's frame's ComputedStyle is the root of a separate tree.
+  Element* rootElement = mDocument->GetRootElement();
+  if (rootElement) {
+    nsIFrame* rootElementFrame = rootElement->GetPrimaryFrame();
+    if (rootElementFrame) {
+      rootElementFrame->Style()->List(out, aIndent);
+    }
+  }
+}
+#endif
+
+#if defined(DEBUG) || defined(MOZ_LAYOUT_DEBUGGER)
+void PresShell::ListStyleSheets(FILE* out, int32_t aIndent) {
+  auto ListStyleSheetsAtOrigin = [this, out, aIndent](StyleOrigin origin) {
+    int32_t sheetCount = StyleSet()->SheetCount(origin);
+    for (int32_t i = 0; i < sheetCount; ++i) {
+      StyleSet()->SheetAt(origin, i)->List(out, aIndent);
+    }
+  };
+
+  ListStyleSheetsAtOrigin(StyleOrigin::UserAgent);
+  ListStyleSheetsAtOrigin(StyleOrigin::User);
+  ListStyleSheetsAtOrigin(StyleOrigin::Author);
+}
+#endif
+
+//=============================================================
+//=============================================================
+//-- Debug Reflow Counts
+//=============================================================
+//=============================================================
+#ifdef MOZ_REFLOW_PERF
+//-------------------------------------------------------------
+void PresShell::DumpReflows() {
+  if (mReflowCountMgr) {
+    nsAutoCString uriStr;
+    if (mDocument) {
+      nsIURI* uri = mDocument->GetDocumentURI();
+      if (uri) {
+        uri->GetPathQueryRef(uriStr);
+      }
+    }
+    mReflowCountMgr->DisplayTotals(uriStr.get());
+    mReflowCountMgr->DisplayHTMLTotals(uriStr.get());
+    mReflowCountMgr->DisplayDiffsInTotals();
+  }
+}
+
+//-------------------------------------------------------------
+void PresShell::CountReflows(const char* aName, nsIFrame* aFrame) {
+  if (mReflowCountMgr) {
+    mReflowCountMgr->Add(aName, aFrame);
+  }
+}
+
+//-------------------------------------------------------------
+void PresShell::PaintCount(const char* aName, gfxContext* aRenderingContext,
+                           nsPresContext* aPresContext, nsIFrame* aFrame,
+                           const nsPoint& aOffset, uint32_t aColor) {
+  if (mReflowCountMgr) {
+    mReflowCountMgr->PaintCount(aName, aRenderingContext, aPresContext, aFrame,
+                                aOffset, aColor);
+  }
+}
+
+//-------------------------------------------------------------
+void PresShell::SetPaintFrameCount(bool aPaintFrameCounts) {
+  if (mReflowCountMgr) {
+    mReflowCountMgr->SetPaintFrameCounts(aPaintFrameCounts);
+  }
+}
+
+bool PresShell::IsPaintingFrameCounts() {
+  if (mReflowCountMgr) return mReflowCountMgr->IsPaintingFrameCounts();
+  return false;
+}
+
+//------------------------------------------------------------------
+//-- Reflow Counter Classes Impls
+//------------------------------------------------------------------
+
+//------------------------------------------------------------------
+ReflowCounter::ReflowCounter(ReflowCountMgr* aMgr) : mMgr(aMgr) {
+  ClearTotals();
+  SetTotalsCache();
+}
+
+//------------------------------------------------------------------
+ReflowCounter::~ReflowCounter() = default;
+
+//------------------------------------------------------------------
+void ReflowCounter::ClearTotals() { mTotal = 0; }
+
+//------------------------------------------------------------------
+void ReflowCounter::SetTotalsCache() { mCacheTotal = mTotal; }
+
+//------------------------------------------------------------------
+void ReflowCounter::CalcDiffInTotals() { mCacheTotal = mTotal - mCacheTotal; }
+
+//------------------------------------------------------------------
+void ReflowCounter::DisplayTotals(const char* aStr) {
+  DisplayTotals(mTotal, aStr ? aStr : "Totals");
+}
+
+//------------------------------------------------------------------
+void ReflowCounter::DisplayDiffTotals(const char* aStr) {
+  DisplayTotals(mCacheTotal, aStr ? aStr : "Diff Totals");
+}
+
+//------------------------------------------------------------------
+void ReflowCounter::DisplayHTMLTotals(const char* aStr) {
+  DisplayHTMLTotals(mTotal, aStr ? aStr : "Totals");
+}
+
+//------------------------------------------------------------------
+void ReflowCounter::DisplayTotals(uint32_t aTotal, const char* aTitle) {
+  // figure total
+  if (aTotal == 0) {
+    return;
+  }
+  ReflowCounter* gTots = (ReflowCounter*)mMgr->LookUp(kGrandTotalsStr);
+
+  printf("%25s\t", aTitle);
+  printf("%d\t", aTotal);
+  if (gTots != this && aTotal > 0) {
+    gTots->Add(aTotal);
+  }
+}
+
+//------------------------------------------------------------------
+void ReflowCounter::DisplayHTMLTotals(uint32_t aTotal, const char* aTitle) {
+  if (aTotal == 0) {
+    return;
+  }
+
+  ReflowCounter* gTots = (ReflowCounter*)mMgr->LookUp(kGrandTotalsStr);
+  FILE* fd = mMgr->GetOutFile();
+  if (!fd) {
+    return;
+  }
+
+  fprintf(fd, "<tr><td><center>%s</center></td>", aTitle);
+  fprintf(fd, "<td><center>%d</center></td></tr>\n", aTotal);
+
+  if (gTots != this && aTotal > 0) {
+    gTots->Add(aTotal);
+  }
+}
+
+//------------------------------------------------------------------
+//-- ReflowCountMgr
+//------------------------------------------------------------------
+
+#  define KEY_BUF_SIZE_FOR_PTR \
+    24  // adequate char[] buffer to sprintf a pointer
+
+ReflowCountMgr::ReflowCountMgr() : mCounts(10), mIndiFrameCounts(10) {
+  mCycledOnce = false;
+  mDumpFrameCounts = false;
+  mDumpFrameByFrameCounts = false;
+  mPaintFrameByFrameCounts = false;
+}
+
+//------------------------------------------------------------------
+ReflowCountMgr::~ReflowCountMgr() = default;
+
+//------------------------------------------------------------------
+ReflowCounter* ReflowCountMgr::LookUp(const char* aName) {
+  return mCounts.Get(aName);
+}
+
+//------------------------------------------------------------------
+void ReflowCountMgr::Add(const char* aName, nsIFrame* aFrame) {
+  NS_ASSERTION(aName != nullptr, "Name shouldn't be null!");
+
+  if (mDumpFrameCounts) {
+    auto* const counter = mCounts.GetOrInsertNew(aName, this);
+    counter->Add();
+  }
+
+  if ((mDumpFrameByFrameCounts || mPaintFrameByFrameCounts) &&
+      aFrame != nullptr) {
+    char key[KEY_BUF_SIZE_FOR_PTR];
+    SprintfLiteral(key, "%p", (void*)aFrame);
+    auto* const counter =
+        mIndiFrameCounts
+            .LookupOrInsertWith(key,
+                                [&aName, &aFrame, this]() {
+                                  auto counter =
+                                      MakeUnique<IndiReflowCounter>(this);
+                                  counter->mFrame = aFrame;
+                                  counter->mName.AssignASCII(aName);
+                                  return counter;
+                                })
+            .get();
+    // this eliminates extra counts from super classes
+    if (counter && counter->mName.EqualsASCII(aName)) {
+      counter->mCount++;
+      counter->mCounter.Add(1);
+    }
+  }
+}
+
+//------------------------------------------------------------------
+void ReflowCountMgr::PaintCount(const char* aName,
+                                gfxContext* aRenderingContext,
+                                nsPresContext* aPresContext, nsIFrame* aFrame,
+                                const nsPoint& aOffset, uint32_t aColor) {
+  if (mPaintFrameByFrameCounts && aFrame != nullptr) {
+    char key[KEY_BUF_SIZE_FOR_PTR];
+    SprintfLiteral(key, "%p", (void*)aFrame);
+    IndiReflowCounter* counter = mIndiFrameCounts.Get(key);
+    if (counter != nullptr && counter->mName.EqualsASCII(aName)) {
+      DrawTarget* drawTarget = aRenderingContext->GetDrawTarget();
+      int32_t appUnitsPerDevPixel = aPresContext->AppUnitsPerDevPixel();
+
+      aRenderingContext->Save();
+      gfxPoint devPixelOffset =
+          nsLayoutUtils::PointToGfxPoint(aOffset, appUnitsPerDevPixel);
+      aRenderingContext->SetMatrixDouble(
+          aRenderingContext->CurrentMatrixDouble().PreTranslate(
+              devPixelOffset));
+
+      // We don't care about the document language or user fonts here;
+      // just get a default Latin font.
+      nsFont font(StyleGenericFontFamily::Serif, Length::FromPixels(11));
+      nsFontMetrics::Params params;
+      params.language = nsGkAtoms::x_western;
+      params.textPerf = aPresContext->GetTextPerfMetrics();
+      params.featureValueLookup = aPresContext->GetFontFeatureValuesLookup();
+      RefPtr<nsFontMetrics> fm = aPresContext->GetMetricsFor(font, params);
+
+      char buf[16];
+      int len = SprintfLiteral(buf, "%d", counter->mCount);
+      nscoord x = 0, y = fm->MaxAscent();
+      nscoord width, height = fm->MaxHeight();
+      fm->SetTextRunRTL(false);
+      width = fm->GetWidth(buf, len, drawTarget);
+
+      sRGBColor color;
+      sRGBColor color2;
+      if (aColor != 0) {
+        color = sRGBColor::FromABGR(aColor);
+        color2 = sRGBColor(0.f, 0.f, 0.f);
+      } else {
+        gfx::Float rc = 0.f, gc = 0.f, bc = 0.f;
+        if (counter->mCount < 5) {
+          rc = 1.f;
+          gc = 1.f;
+        } else if (counter->mCount < 11) {
+          gc = 1.f;
+        } else {
+          rc = 1.f;
+        }
+        color = sRGBColor(rc, gc, bc);
+        color2 = sRGBColor(rc / 2, gc / 2, bc / 2);
+      }
+
+      nsRect rect(0, 0, width + 15, height + 15);
+      Rect devPxRect =
+          NSRectToSnappedRect(rect, appUnitsPerDevPixel, *drawTarget);
+      ColorPattern black(ToDeviceColor(sRGBColor::OpaqueBlack()));
+      drawTarget->FillRect(devPxRect, black);
+
+      aRenderingContext->SetColor(color2);
+      fm->DrawString(buf, len, x + 15, y + 15, aRenderingContext);
+      aRenderingContext->SetColor(color);
+      fm->DrawString(buf, len, x, y, aRenderingContext);
+
+      aRenderingContext->Restore();
+    }
+  }
+}
+
+//------------------------------------------------------------------
+void ReflowCountMgr::DoGrandTotals() {
+  mCounts.WithEntryHandle(kGrandTotalsStr, [this](auto&& entry) {
+    if (!entry) {
+      entry.Insert(MakeUnique<ReflowCounter>(this));
+    } else {
+      entry.Data()->ClearTotals();
+    }
+  });
+
+  printf("\t\t\t\tTotal\n");
+  for (uint32_t i = 0; i < 78; i++) {
+    printf("-");
+  }
+  printf("\n");
+  for (const auto& entry : mCounts) {
+    entry.GetData()->DisplayTotals(entry.GetKey());
+  }
+}
+
+static void RecurseIndiTotals(
+    nsPresContext* aPresContext,
+    nsClassHashtable<nsCharPtrHashKey, IndiReflowCounter>& aHT,
+    nsIFrame* aParentFrame, int32_t aLevel) {
+  if (aParentFrame == nullptr) {
+    return;
+  }
+
+  char key[KEY_BUF_SIZE_FOR_PTR];
+  SprintfLiteral(key, "%p", (void*)aParentFrame);
+  IndiReflowCounter* counter = aHT.Get(key);
+  if (counter) {
+    counter->mHasBeenOutput = true;
+    char* name = ToNewCString(counter->mName);
+    for (int32_t i = 0; i < aLevel; i++) printf(" ");
+    printf("%s - %p   [%d][", name, (void*)aParentFrame, counter->mCount);
+    printf("%d", counter->mCounter.GetTotal());
+    printf("]\n");
+    free(name);
+  }
+
+  for (nsIFrame* child : aParentFrame->PrincipalChildList()) {
+    RecurseIndiTotals(aPresContext, aHT, child, aLevel + 1);
+  }
+}
+
+//------------------------------------------------------------------
+void ReflowCountMgr::DoIndiTotalsTree() {
+  printf("\n------------------------------------------------\n");
+  printf("-- Individual Frame Counts\n");
+  printf("------------------------------------------------\n");
+
+  if (mPresShell) {
+    nsIFrame* rootFrame = mPresShell->GetRootFrame();
+    RecurseIndiTotals(mPresContext, mIndiFrameCounts, rootFrame, 0);
+    printf("------------------------------------------------\n");
+    printf("-- Individual Counts of Frames not in Root Tree\n");
+    printf("------------------------------------------------\n");
+    for (const auto& counter : mIndiFrameCounts.Values()) {
+      if (!counter->mHasBeenOutput) {
+        char* name = ToNewCString(counter->mName);
+        printf("%s - %p   [%d][", name, (void*)counter->mFrame,
+               counter->mCount);
+        printf("%d", counter->mCounter.GetTotal());
+        printf("]\n");
+        free(name);
+      }
+    }
+  }
+}
+
+//------------------------------------------------------------------
+void ReflowCountMgr::DoGrandHTMLTotals() {
+  mCounts.WithEntryHandle(kGrandTotalsStr, [this](auto&& entry) {
+    if (!entry) {
+      entry.Insert(MakeUnique<ReflowCounter>(this));
+    } else {
+      entry.Data()->ClearTotals();
+    }
+  });
+
+  static const char* title[] = {"Class", "Reflows"};
+  fprintf(mFD, "<tr>");
+  for (uint32_t i = 0; i < ArrayLength(title); i++) {
+    fprintf(mFD, "<td><center><b>%s<b></center></td>", title[i]);
+  }
+  fprintf(mFD, "</tr>\n");
+
+  for (const auto& entry : mCounts) {
+    entry.GetData()->DisplayHTMLTotals(entry.GetKey());
+  }
+}
+
+//------------------------------------
+void ReflowCountMgr::DisplayTotals(const char* aStr) {
+#  ifdef DEBUG_rods
+  printf("%s\n", aStr ? aStr : "No name");
+#  endif
+  if (mDumpFrameCounts) {
+    DoGrandTotals();
+  }
+  if (mDumpFrameByFrameCounts) {
+    DoIndiTotalsTree();
+  }
+}
+//------------------------------------
+void ReflowCountMgr::DisplayHTMLTotals(const char* aStr) {
+#  ifdef WIN32x  // XXX NOT XP!
+  char name[1024];
+
+  char* sptr = strrchr(aStr, '/');
+  if (sptr) {
+    sptr++;
+    strcpy(name, sptr);
+    char* eptr = strrchr(name, '.');
+    if (eptr) {
+      *eptr = 0;
+    }
+    strcat(name, "_stats.html");
+  }
+  mFD = fopen(name, "w");
+  if (mFD) {
+    fprintf(mFD, "<html><head><title>Reflow Stats</title></head><body>\n");
+    const char* title = aStr ? aStr : "No name";
+    fprintf(mFD,
+            "<center><b>%s</b><br><table border=1 "
+            "style=\"background-color:#e0e0e0\">",
+            title);
+    DoGrandHTMLTotals();
+    fprintf(mFD, "</center></table>\n");
+    fprintf(mFD, "</body></html>\n");
+    fclose(mFD);
+    mFD = nullptr;
+  }
+#  endif  // not XP!
+}
+
+//------------------------------------------------------------------
+void ReflowCountMgr::ClearTotals() {
+  for (const auto& data : mCounts.Values()) {
+    data->ClearTotals();
+  }
+}
+
+//------------------------------------------------------------------
+void ReflowCountMgr::ClearGrandTotals() {
+  mCounts.WithEntryHandle(kGrandTotalsStr, [&](auto&& entry) {
+    if (!entry) {
+      entry.Insert(MakeUnique<ReflowCounter>(this));
+    } else {
+      entry.Data()->ClearTotals();
+      entry.Data()->SetTotalsCache();
+    }
+  });
+}
+
+//------------------------------------------------------------------
+void ReflowCountMgr::DisplayDiffsInTotals() {
+  if (mCycledOnce) {
+    printf("Differences\n");
+    for (int32_t i = 0; i < 78; i++) {
+      printf("-");
+    }
+    printf("\n");
+    ClearGrandTotals();
+  }
+
+  for (const auto& entry : mCounts) {
+    if (mCycledOnce) {
+      entry.GetData()->CalcDiffInTotals();
+      entry.GetData()->DisplayDiffTotals(entry.GetKey());
+    }
+    entry.GetData()->SetTotalsCache();
+  }
+
+  mCycledOnce = true;
+}
+
+#endif  // MOZ_REFLOW_PERF
+
+nsIFrame* PresShell::GetAbsoluteContainingBlock(nsIFrame* aFrame) {
+  return FrameConstructor()->GetAbsoluteContainingBlock(
+      aFrame, nsCSSFrameConstructor::ABS_POS);
+}
+
+void PresShell::ActivenessMaybeChanged() {
+  if (!mDocument) {
+    return;
+  }
+  auto activeness = ComputeActiveness();
+  SetIsActive(activeness.mShouldBeActive, activeness.mIsInActiveTab);
+}
+
+// A PresShell being active means that it is visible (or close to be visible, if
+// the front-end is warming it). That means that when it is active we always
+// tick its refresh driver at full speed if needed.
+//
+// However we also want to track whether we're in the active tab (represented by
+// the browsing context activeness) for the refresh driver to be able to treat
+// invisible-but-in-the-active-tab frames slightly differently in some
+// circumstances (give them a throttled or unthrottled refresh driver after a
+// while). mIsInActiveTab should ~always be GetBrowsingContext()->IsActive().
+//
+// Image documents behave specially in the sense that they are always "active"
+// and never "in the active tab". However these documents tick manually so
+// there's not much to worry about there.
+auto PresShell::ComputeActiveness() const -> Activeness {
+  MOZ_LOG(gLog, LogLevel::Debug,
+          ("PresShell::ShouldBeActive(%s, %d, %d)\n",
+           mDocument->GetDocumentURI()
+               ? mDocument->GetDocumentURI()->GetSpecOrDefault().get()
+               : "(no uri)",
+           mIsActive, mIsInActiveTab));
+
+  Document* doc = mDocument;
+
+  if (doc->IsBeingUsedAsImage()) {
+    // Documents used as an image can remain active. They do not tick their
+    // refresh driver if not painted, and they can't run script or such so they
+    // can't really observe much else.
+    //
+    // Image docs can be displayed in multiple docs at the same time so the "in
+    // active tab" bool doesn't make much sense for them.
+    return {true, false};
+  }
+
+  if (Document* displayDoc = doc->GetDisplayDocument()) {
+    // Ok, we're an external resource document -- we need to use our display
+    // document's docshell to determine "IsActive" status, since we lack
+    // a browsing context of our own.
+    MOZ_ASSERT(!doc->GetBrowsingContext(),
+               "external resource doc shouldn't have its own BC");
+    doc = displayDoc;
+  }
+
+  BrowsingContext* bc = doc->GetBrowsingContext();
+  const bool inActiveTab = bc && bc->IsActive();
+
+  MOZ_LOG(gLog, LogLevel::Debug,
+          (" > BrowsingContext %p  active: %d", bc, inActiveTab));
+
+  Document* root = nsContentUtils::GetInProcessSubtreeRootDocument(doc);
+  if (auto* browserChild = BrowserChild::GetFrom(root->GetDocShell())) {
+    // We might want to activate a tab even though the browsing-context is not
+    // active if the BrowserChild is considered visible. This serves two
+    // purposes:
+    //
+    //  * For top-level tabs, we use this for tab warming. The browsing-context
+    //    might still be inactive, but we want to activate the pres shell and
+    //    the refresh driver.
+    //
+    //  * For oop iframes, we do want to throttle them if they're not visible.
+    //
+    // TODO(emilio): Consider unifying the in-process vs. fission iframe
+    // throttling code (in-process throttling for non-visible iframes lives
+    // right now in Document::ShouldThrottleFrameRequests(), but that only
+    // throttles rAF).
+    if (!browserChild->IsVisible()) {
+      MOZ_LOG(gLog, LogLevel::Debug,
+              (" > BrowserChild %p is not visible", browserChild));
+      return {false, inActiveTab};
+    }
+
+    // If the browser is visible but just due to be preserving layers
+    // artificially, we do want to fall back to the browsing context activeness
+    // instead. Otherwise we do want to be active for the use cases above.
+    if (!browserChild->IsPreservingLayers()) {
+      MOZ_LOG(gLog, LogLevel::Debug,
+              (" > BrowserChild %p is visible and not preserving layers",
+               browserChild));
+      return {true, inActiveTab};
+    }
+    MOZ_LOG(
+        gLog, LogLevel::Debug,
+        (" > BrowserChild %p is visible and preserving layers", browserChild));
+  }
+  return {inActiveTab, inActiveTab};
+}
+
+void PresShell::SetIsActive(bool aIsActive, bool aIsInActiveTab) {
+  MOZ_ASSERT(mDocument, "should only be called with a document");
+
+  const bool activityChanged = mIsActive != aIsActive;
+  const bool inActiveTabChanged = mIsInActiveTab != aIsInActiveTab;
+
+  mIsActive = aIsActive;
+  mIsInActiveTab = aIsInActiveTab;
+
+  nsPresContext* presContext = GetPresContext();
+  if (presContext &&
+      presContext->RefreshDriver()->GetPresContext() == presContext) {
+    presContext->RefreshDriver()->SetActivity(aIsActive, aIsInActiveTab);
+  }
+
+  if (activityChanged || inActiveTabChanged) {
+    // Propagate state-change to my resource documents' PresShells and other
+    // subdocuments.
+    //
+    // Note that it is fine to not propagate to fission iframes. Those will
+    // become active / inactive as needed as a result of they getting painted /
+    // not painted eventually.
+    auto recurse = [aIsActive, aIsInActiveTab](Document& aSubDoc) {
+      if (PresShell* presShell = aSubDoc.GetPresShell()) {
+        presShell->SetIsActive(aIsActive, aIsInActiveTab);
+      }
+      return CallState::Continue;
+    };
+    mDocument->EnumerateExternalResources(recurse);
+    mDocument->EnumerateSubDocuments(recurse);
+  }
+
+  UpdateImageLockingState();
+
+  if (activityChanged) {
+#if defined(MOZ_WIDGET_ANDROID)
+    if (!aIsActive && presContext &&
+        presContext->IsRootContentDocumentCrossProcess()) {
+      if (BrowserChild* browserChild = BrowserChild::GetFrom(this)) {
+        // Reset the dynamic toolbar offset state.
+        presContext->UpdateDynamicToolbarOffset(0);
+      }
+    }
+#endif
+  }
+
+  if (aIsActive) {
+#ifdef ACCESSIBILITY
+    if (nsAccessibilityService* accService = GetAccService()) {
+      accService->PresShellActivated(this);
+    }
+#endif
+    if (nsIFrame* rootFrame = GetRootFrame()) {
+      rootFrame->SchedulePaint();
+    }
+  }
+}
+
+RefPtr<MobileViewportManager> PresShell::GetMobileViewportManager() const {
+  return mMobileViewportManager;
+}
+
+Maybe<MobileViewportManager::ManagerType> UseMobileViewportManager(
+    PresShell* aPresShell, Document* aDocument) {
+  // If we're not using APZ, we won't be able to zoom, so there is no
+  // point in having an MVM.
+  if (nsPresContext* presContext = aPresShell->GetPresContext()) {
+    if (nsIWidget* widget = presContext->GetNearestWidget()) {
+      if (!widget->AsyncPanZoomEnabled()) {
+        return Nothing();
+      }
+    }
+  }
+  if (nsLayoutUtils::ShouldHandleMetaViewport(aDocument)) {
+    return Some(MobileViewportManager::ManagerType::VisualAndMetaViewport);
+  }
+  if (StaticPrefs::apz_mvm_force_enabled() ||
+      nsLayoutUtils::AllowZoomingForDocument(aDocument)) {
+    return Some(MobileViewportManager::ManagerType::VisualViewportOnly);
+  }
+  return Nothing();
+}
+
+void PresShell::MaybeRecreateMobileViewportManager(bool aAfterInitialization) {
+  // Determine if we require a MobileViewportManager, and what kind if so. We
+  // need one any time we allow resolution zooming for a document, and any time
+  // we want to obey <meta name="viewport"> tags for it.
+  Maybe<MobileViewportManager::ManagerType> mvmType =
+      UseMobileViewportManager(this, mDocument);
+
+  if (mvmType.isNothing() && !mMobileViewportManager) {
+    // We don't need one and don't have it. So we're done.
+    return;
+  }
+  if (mvmType && mMobileViewportManager &&
+      *mvmType == mMobileViewportManager->GetManagerType()) {
+    // We need one and we have one of the correct type, so we're done.
+    return;
+  }
+
+  if (mMobileViewportManager) {
+    // We have one, but we need to either destroy it completely to replace it
+    // with another one of the correct type. So either way, let's destroy the
+    // one we have.
+    mMobileViewportManager->Destroy();
+    mMobileViewportManager = nullptr;
+    mMVMContext = nullptr;
+
+    ResetVisualViewportSize();
+
+    // After we clear out the MVM and the MVMContext, also reset the
+    // resolution to its pre-MVM value.
+    SetResolutionAndScaleTo(mDocument->GetSavedResolutionBeforeMVM(),
+                            ResolutionChangeOrigin::MainThreadRestore);
+
+    if (aAfterInitialization) {
+      // Force a reflow to our correct size by going back to the docShell
+      // and asking it to reassert its size. This is necessary because
+      // everything underneath the docShell, like the ViewManager, has been
+      // altered by the MobileViewportManager in an irreversible way.
+      nsDocShell* docShell =
+          static_cast<nsDocShell*>(GetPresContext()->GetDocShell());
+      int32_t width, height;
+      docShell->GetSize(&width, &height);
+      docShell->SetSize(width, height, false);
+    }
+  }
+
+  if (mvmType) {
+    // Let's create the MVM of the type that we need. At this point we shouldn't
+    // have one.
+    MOZ_ASSERT(!mMobileViewportManager);
+
+    if (mPresContext->IsRootContentDocumentCrossProcess()) {
+      // Store the resolution so we can restore to this resolution when
+      // the MVM is destroyed.
+      mDocument->SetSavedResolutionBeforeMVM(mResolution.valueOr(1.0f));
+
+      mMVMContext = new GeckoMVMContext(mDocument, this);
+      mMobileViewportManager = new MobileViewportManager(mMVMContext, *mvmType);
+      if (MOZ_UNLIKELY(
+              MOZ_LOG_TEST(MobileViewportManager::gLog, LogLevel::Debug))) {
+        nsIURI* uri = mDocument->GetDocumentURI();
+        MOZ_LOG(MobileViewportManager::gLog, LogLevel::Debug,
+                ("Created MVM %p (type %d) for URI %s",
+                 mMobileViewportManager.get(), (int)*mvmType,
+                 uri ? uri->GetSpecOrDefault().get() : "(null)"));
+      }
+
+      if (aAfterInitialization) {
+        // Setting the initial viewport will trigger a reflow.
+        mMobileViewportManager->SetInitialViewport();
+      }
+    }
+  }
+}
+
+bool PresShell::UsesMobileViewportSizing() const {
+  return mMobileViewportManager != nullptr &&
+         nsLayoutUtils::ShouldHandleMetaViewport(mDocument);
+}
+
+/*
+ * Determines the current image locking state. Called when one of the
+ * dependent factors changes.
+ */
+void PresShell::UpdateImageLockingState() {
+  // We're locked if we're both thawed and active.
+  const bool locked = !mFrozen && mIsActive;
+  auto* tracker = mDocument->ImageTracker();
+  if (locked == tracker->GetLockingState()) {
+    return;
+  }
+
+  tracker->SetLockingState(locked);
+  if (locked) {
+    // Request decodes for visible image frames; we want to start decoding as
+    // quickly as possible when we get foregrounded to minimize flashing.
+    for (const auto& key : mApproximatelyVisibleFrames) {
+      if (nsImageFrame* imageFrame = do_QueryFrame(key)) {
+        imageFrame->MaybeDecodeForPredictedSize();
+      }
+    }
+  }
+}
+
+PresShell* PresShell::GetRootPresShell() const {
+  if (mPresContext) {
+    nsPresContext* rootPresContext = mPresContext->GetRootPresContext();
+    if (rootPresContext) {
+      return rootPresContext->PresShell();
+    }
+  }
+  return nullptr;
+}
+
+void PresShell::AddSizeOfIncludingThis(nsWindowSizes& aSizes) const {
+  MallocSizeOf mallocSizeOf = aSizes.mState.mMallocSizeOf;
+  mFrameArena.AddSizeOfExcludingThis(aSizes, Arena::ArenaKind::PresShell);
+  aSizes.mLayoutPresShellSize += mallocSizeOf(this);
+  if (mCaret) {
+    aSizes.mLayoutPresShellSize += mCaret->SizeOfIncludingThis(mallocSizeOf);
+  }
+  aSizes.mLayoutPresShellSize +=
+      mApproximatelyVisibleFrames.ShallowSizeOfExcludingThis(mallocSizeOf) +
+      mFramesToDirty.ShallowSizeOfExcludingThis(mallocSizeOf) +
+      mPendingScrollAnchorSelection.ShallowSizeOfExcludingThis(mallocSizeOf) +
+      mPendingScrollAnchorAdjustment.ShallowSizeOfExcludingThis(mallocSizeOf);
+
+  aSizes.mLayoutTextRunsSize += SizeOfTextRuns(mallocSizeOf);
+
+  aSizes.mLayoutPresContextSize +=
+      mPresContext->SizeOfIncludingThis(mallocSizeOf);
+
+  mFrameConstructor->AddSizeOfIncludingThis(aSizes);
+}
+
+size_t PresShell::SizeOfTextRuns(MallocSizeOf aMallocSizeOf) const {
+  nsIFrame* rootFrame = mFrameConstructor->GetRootFrame();
+  if (!rootFrame) {
+    return 0;
+  }
+
+  // clear the TEXT_RUN_MEMORY_ACCOUNTED flags
+  nsLayoutUtils::SizeOfTextRunsForFrames(rootFrame, nullptr,
+                                         /* clear = */ true);
+
+  // collect the total memory in use for textruns
+  return nsLayoutUtils::SizeOfTextRunsForFrames(rootFrame, aMallocSizeOf,
+                                                /* clear = */ false);
+}
+
+void PresShell::MarkFixedFramesForReflow(IntrinsicDirty aIntrinsicDirty) {
+  nsIFrame* rootFrame = mFrameConstructor->GetRootFrame();
+  if (rootFrame) {
+    const nsFrameList& childList =
+        rootFrame->GetChildList(FrameChildListID::Fixed);
+    for (nsIFrame* childFrame : childList) {
+      FrameNeedsReflow(childFrame, aIntrinsicDirty, NS_FRAME_IS_DIRTY);
+    }
+  }
+}
+
+static void AppendSubtree(nsIDocShell* aDocShell,
+                          nsTArray<nsCOMPtr<nsIContentViewer>>& aArray) {
+  if (nsCOMPtr<nsIContentViewer> cv = aDocShell->GetContentViewer()) {
+    aArray.AppendElement(cv);
+  }
+
+  int32_t n = aDocShell->GetInProcessChildCount();
+  for (int32_t i = 0; i < n; i++) {
+    nsCOMPtr<nsIDocShellTreeItem> childItem;
+    aDocShell->GetInProcessChildAt(i, getter_AddRefs(childItem));
+    if (childItem) {
+      nsCOMPtr<nsIDocShell> child(do_QueryInterface(childItem));
+      AppendSubtree(child, aArray);
+    }
+  }
+}
+
+void PresShell::MaybeReflowForInflationScreenSizeChange() {
+  nsPresContext* pc = GetPresContext();
+  const bool fontInflationWasEnabled = FontSizeInflationEnabled();
+  RecomputeFontSizeInflationEnabled();
+  bool changed = false;
+  if (FontSizeInflationEnabled() && FontSizeInflationMinTwips() != 0) {
+    pc->ScreenSizeInchesForFontInflation(&changed);
+  }
+
+  changed = changed || fontInflationWasEnabled != FontSizeInflationEnabled();
+  if (!changed) {
+    return;
+  }
+  if (nsCOMPtr<nsIDocShell> docShell = pc->GetDocShell()) {
+    nsTArray<nsCOMPtr<nsIContentViewer>> array;
+    AppendSubtree(docShell, array);
+    for (uint32_t i = 0, iEnd = array.Length(); i < iEnd; ++i) {
+      nsCOMPtr<nsIContentViewer> cv = array[i];
+      if (RefPtr<PresShell> descendantPresShell = cv->GetPresShell()) {
+        nsIFrame* rootFrame = descendantPresShell->GetRootFrame();
+        if (rootFrame) {
+          descendantPresShell->FrameNeedsReflow(
+              rootFrame, IntrinsicDirty::FrameAncestorsAndDescendants,
+              NS_FRAME_IS_DIRTY);
+        }
+      }
+    }
+  }
+}
+
+void PresShell::CompleteChangeToVisualViewportSize() {
+  // This can get called during reflow, if the caller wants to get the latest
+  // visual viewport size after scrollbars have been added/removed. In such a
+  // case, we don't need to mark things as dirty because the things that we
+  // would mark dirty either just got updated (the root scrollframe's
+  // scrollbars), or will be laid out later during this reflow cycle (fixed-pos
+  // items). Callers that update the visual viewport during a reflow are
+  // responsible for maintaining these invariants.
+  if (!mIsReflowing) {
+    if (nsIScrollableFrame* rootScrollFrame =
+            GetRootScrollFrameAsScrollable()) {
+      rootScrollFrame->MarkScrollbarsDirtyForReflow();
+    }
+    MarkFixedFramesForReflow(IntrinsicDirty::None);
+  }
+
+  MaybeReflowForInflationScreenSizeChange();
+
+  if (auto* window = nsGlobalWindowInner::Cast(mDocument->GetInnerWindow())) {
+    window->VisualViewport()->PostResizeEvent();
+  }
+}
+
+void PresShell::SetVisualViewportSize(nscoord aWidth, nscoord aHeight) {
+  MOZ_ASSERT(aWidth >= 0.0 && aHeight >= 0.0);
+
+  if (!mVisualViewportSizeSet || mVisualViewportSize.width != aWidth ||
+      mVisualViewportSize.height != aHeight) {
+    mVisualViewportSizeSet = true;
+    mVisualViewportSize.width = aWidth;
+    mVisualViewportSize.height = aHeight;
+
+    CompleteChangeToVisualViewportSize();
+  }
+}
+
+void PresShell::ResetVisualViewportSize() {
+  if (mVisualViewportSizeSet) {
+    mVisualViewportSizeSet = false;
+    mVisualViewportSize.width = 0;
+    mVisualViewportSize.height = 0;
+
+    CompleteChangeToVisualViewportSize();
+  }
+}
+
+bool PresShell::SetVisualViewportOffset(const nsPoint& aScrollOffset,
+                                        const nsPoint& aPrevLayoutScrollPos) {
+  nsPoint newOffset = aScrollOffset;
+  nsIScrollableFrame* rootScrollFrame = GetRootScrollFrameAsScrollable();
+  if (rootScrollFrame) {
+    // See the comment in nsHTMLScrollFrame::Reflow above the call to
+    // SetVisualViewportOffset for why we need to do this.
+    nsRect scrollRange = rootScrollFrame->GetScrollRangeForUserInputEvents();
+    if (!scrollRange.Contains(newOffset)) {
+      newOffset.x = std::min(newOffset.x, scrollRange.XMost());
+      newOffset.x = std::max(newOffset.x, scrollRange.x);
+      newOffset.y = std::min(newOffset.y, scrollRange.YMost());
+      newOffset.y = std::max(newOffset.y, scrollRange.y);
+    }
+  }
+
+  // Careful here not to call GetVisualViewportOffset to get the previous visual
+  // viewport offset because if mVisualViewportOffset is nothing then we'll get
+  // the layout scroll position directly from the scroll frame and it has likely
+  // already been updated.
+  nsPoint prevOffset = aPrevLayoutScrollPos;
+  if (mVisualViewportOffset.isSome()) {
+    prevOffset = *mVisualViewportOffset;
+  }
+  if (prevOffset == newOffset) {
+    return false;
+  }
+
+  mVisualViewportOffset = Some(newOffset);
+
+  if (auto* window = nsGlobalWindowInner::Cast(mDocument->GetInnerWindow())) {
+    window->VisualViewport()->PostScrollEvent(prevOffset, aPrevLayoutScrollPos);
+  }
+
+  if (IsVisualViewportSizeSet() && rootScrollFrame) {
+    rootScrollFrame->Anchor()->UserScrolled();
+  }
+
+  if (gfxPlatform::UseDesktopZoomingScrollbars()) {
+    if (nsIScrollableFrame* rootScrollFrame =
+            GetRootScrollFrameAsScrollable()) {
+      rootScrollFrame->UpdateScrollbarPosition();
+    }
+  }
+
+  return true;
+}
+
+void PresShell::ResetVisualViewportOffset() { mVisualViewportOffset.reset(); }
+
+void PresShell::ScrollToVisual(const nsPoint& aVisualViewportOffset,
+                               FrameMetrics::ScrollOffsetUpdateType aUpdateType,
+                               ScrollMode aMode) {
+  MOZ_ASSERT(aMode == ScrollMode::Instant || aMode == ScrollMode::SmoothMsd);
+
+  if (aMode == ScrollMode::SmoothMsd) {
+    if (nsIScrollableFrame* sf = GetRootScrollFrameAsScrollable()) {
+      if (sf->SmoothScrollVisual(aVisualViewportOffset, aUpdateType)) {
+        return;
+      }
+    }
+  }
+
+  // If the caller asked for instant scroll, or if we failed
+  // to do a smooth scroll, do an instant scroll.
+  SetPendingVisualScrollUpdate(aVisualViewportOffset, aUpdateType);
+}
+
+void PresShell::SetPendingVisualScrollUpdate(
+    const nsPoint& aVisualViewportOffset,
+    FrameMetrics::ScrollOffsetUpdateType aUpdateType) {
+  mPendingVisualScrollUpdate =
+      Some(VisualScrollUpdate{aVisualViewportOffset, aUpdateType});
+
+  // The pending update is picked up during the next paint.
+  // Schedule a paint to make sure one will happen.
+  if (nsIFrame* rootFrame = GetRootFrame()) {
+    rootFrame->SchedulePaint();
+  }
+}
+
+void PresShell::ClearPendingVisualScrollUpdate() {
+  if (mPendingVisualScrollUpdate && mPendingVisualScrollUpdate->mAcknowledged) {
+    mPendingVisualScrollUpdate = mozilla::Nothing();
+  }
+}
+
+void PresShell::AcknowledgePendingVisualScrollUpdate() {
+  MOZ_ASSERT(mPendingVisualScrollUpdate);
+  mPendingVisualScrollUpdate->mAcknowledged = true;
+}
+
+nsPoint PresShell::GetVisualViewportOffsetRelativeToLayoutViewport() const {
+  return GetVisualViewportOffset() - GetLayoutViewportOffset();
+}
+
+nsPoint PresShell::GetLayoutViewportOffset() const {
+  nsPoint result;
+  if (nsIScrollableFrame* sf = GetRootScrollFrameAsScrollable()) {
+    result = sf->GetScrollPosition();
+  }
+  return result;
+}
+
+nsSize PresShell::GetLayoutViewportSize() const {
+  nsSize result;
+  if (nsIScrollableFrame* sf = GetRootScrollFrameAsScrollable()) {
+    result = sf->GetScrollPortRect().Size();
+  }
+  return result;
+}
+
+nsSize PresShell::GetVisualViewportSizeUpdatedByDynamicToolbar() const {
+  NS_ASSERTION(mVisualViewportSizeSet,
+               "asking for visual viewport size when its not set?");
+  if (!mMobileViewportManager) {
+    return mVisualViewportSize;
+  }
+
+  MOZ_ASSERT(GetDynamicToolbarState() == DynamicToolbarState::InTransition ||
+             GetDynamicToolbarState() == DynamicToolbarState::Collapsed);
+
+  nsSize sizeUpdatedByDynamicToolbar =
+      mMobileViewportManager->GetVisualViewportSizeUpdatedByDynamicToolbar();
+  return sizeUpdatedByDynamicToolbar == nsSize() ? mVisualViewportSize
+                                                 : sizeUpdatedByDynamicToolbar;
+}
+
+void PresShell::RecomputeFontSizeInflationEnabled() {
+  mFontSizeInflationEnabled = DetermineFontSizeInflationState();
+
+  // Divide by 100 to convert the pref from a percentage to a fraction.
+  float fontScale = StaticPrefs::font_size_systemFontScale() / 100.0f;
+  if (fontScale == 0.0f) {
+    return;
+  }
+
+  MOZ_ASSERT(mDocument);
+  MOZ_ASSERT(mPresContext);
+  if (mFontSizeInflationEnabled || mDocument->IsSyntheticDocument()) {
+    mPresContext->SetSystemFontScale(1.0f);
+  } else {
+    mPresContext->SetSystemFontScale(fontScale);
+  }
+}
+
+bool PresShell::DetermineFontSizeInflationState() {
+  MOZ_ASSERT(mPresContext, "our pres context should not be null");
+  if (mPresContext->IsChrome()) {
+    return false;
+  }
+
+  if (FontSizeInflationEmPerLine() == 0 && FontSizeInflationMinTwips() == 0) {
+    return false;
+  }
+
+  // Force-enabling font inflation always trumps the heuristics here.
+  if (!FontSizeInflationForceEnabled()) {
+    if (BrowserChild* tab = BrowserChild::GetFrom(this)) {
+      // We're in a child process.  Cancel inflation if we're not
+      // async-pan zoomed.
+      if (!tab->AsyncPanZoomEnabled()) {
+        return false;
+      }
+    } else if (XRE_IsParentProcess()) {
+      // We're in the master process.  Cancel inflation if it's been
+      // explicitly disabled.
+      if (FontSizeInflationDisabledInMasterProcess()) {
+        return false;
+      }
+    }
+  }
+
+  Maybe<LayoutDeviceIntSize> displaySize;
+  // The MVM already caches the top-level content viewer size and is therefore
+  // the fastest way of getting that data.
+  if (mPresContext->IsRootContentDocumentCrossProcess()) {
+    if (mMobileViewportManager) {
+      displaySize = Some(mMobileViewportManager->DisplaySize());
+    }
+  } else if (PresShell* rootPresShell = GetRootPresShell()) {
+    // With any luck, we can get at the root content document without any cross-
+    // process shenanigans.
+    if (auto mvm = rootPresShell->GetMobileViewportManager()) {
+      displaySize = Some(mvm->DisplaySize());
+    }
+  }
+
+  if (!displaySize) {
+    // Unfortunately, it looks like the root content document lives in a
+    // different process. For consistency's sake it would be best to always use
+    // the content viewer size of the root content document, but it's not worth
+    // the effort, because this only makes a difference in the case of pages
+    // with an explicitly sized viewport (neither "width=device-width" nor a
+    // completely missing viewport tag) being loaded within a frame, which is
+    // hopefully a relatively exotic case.
+    // More to the point, these viewport size and zoom-based calculations don't
+    // really make sense for frames anyway, so instead of creating a way to
+    // access the content viewer size of the top level document cross-process,
+    // we probably rather want frames to simply inherit the font inflation state
+    // of their top-level parent and should therefore invest any time spent on
+    // getting things to work cross-process into that (bug 1724311).
+
+    // Until we get around to that though, we just use the content viewer size
+    // of however high we can get within the same process.
+
+    // (This also serves as a fallback code path if the MVM isn't available,
+    // e.g. when debugging in non-e10s mode on Desktop.)
+    nsPresContext* topContext =
+        mPresContext->GetInProcessRootContentDocumentPresContext();
+    LayoutDeviceIntSize result;
+    if (!nsLayoutUtils::GetContentViewerSize(topContext, result)) {
+      return false;
+    }
+    displaySize = Some(result);
+  }
+
+  ScreenIntSize screenSize = ViewAs<ScreenPixel>(
+      displaySize.value(),
+      PixelCastJustification::LayoutDeviceIsScreenForBounds);
+  nsViewportInfo vInf = GetDocument()->GetViewportInfo(screenSize);
+
+  CSSToScreenScale defaultScale =
+      mPresContext->CSSToDevPixelScale() * LayoutDeviceToScreenScale(1.0);
+
+  if (vInf.GetDefaultZoom() >= defaultScale || vInf.IsAutoSizeEnabled()) {
+    return false;
+  }
+
+  return true;
+}
+
+void PresShell::SyncWindowProperties(nsView* aView) {
+  nsIFrame* frame = aView->GetFrame();
+  if (frame && mPresContext) {
+    // CreateReferenceRenderingContext can return nullptr
+    RefPtr<gfxContext> rcx(CreateReferenceRenderingContext());
+    nsContainerFrame::SyncWindowProperties(mPresContext, frame, aView, rcx, 0);
+  }
+}
+
+nsresult PresShell::HasRuleProcessorUsedByMultipleStyleSets(uint32_t aSheetType,
+                                                            bool* aRetVal) {
+  *aRetVal = false;
+  return NS_OK;
+}
+
+void PresShell::NotifyStyleSheetServiceSheetAdded(StyleSheet* aSheet,
+                                                  uint32_t aSheetType) {
+  switch (aSheetType) {
+    case nsIStyleSheetService::AGENT_SHEET:
+      AddAgentSheet(aSheet);
+      break;
+    case nsIStyleSheetService::USER_SHEET:
+      AddUserSheet(aSheet);
+      break;
+    case nsIStyleSheetService::AUTHOR_SHEET:
+      AddAuthorSheet(aSheet);
+      break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("unexpected aSheetType value");
+      break;
+  }
+}
+
+void PresShell::NotifyStyleSheetServiceSheetRemoved(StyleSheet* aSheet,
+                                                    uint32_t aSheetType) {
+  StyleSet()->RemoveStyleSheet(*aSheet);
+  mDocument->ApplicableStylesChanged();
+}
+
+void PresShell::SetIsUnderHiddenEmbedderElement(
+    bool aUnderHiddenEmbedderElement) {
+  if (mUnderHiddenEmbedderElement == aUnderHiddenEmbedderElement) {
+    return;
+  }
+
+  mUnderHiddenEmbedderElement = aUnderHiddenEmbedderElement;
+
+  if (nsCOMPtr<nsIDocShell> docShell = mPresContext->GetDocShell()) {
+    BrowsingContext* bc = docShell->GetBrowsingContext();
+
+    // Propagate to children.
+    for (BrowsingContext* child : bc->Children()) {
+      Element* embedderElement = child->GetEmbedderElement();
+      if (!embedderElement) {
+        // TODO: We shouldn't need to null check here since `child` and the
+        // element returned by `child->GetEmbedderElement()` are in our
+        // process (the actual browsing context represented by `child` may not
+        // be, but that doesn't matter).  However, there are currently a very
+        // small number of crashes due to `embedderElement` being null, somehow
+        // - see bug 1551241.  For now we wallpaper the crash.
+        continue;
+      }
+
+      bool embedderFrameIsHidden = true;
+      if (auto embedderFrame = embedderElement->GetPrimaryFrame()) {
+        embedderFrameIsHidden = !embedderFrame->StyleVisibility()->IsVisible();
+      }
+
+      if (nsIDocShell* childDocShell = child->GetDocShell()) {
+        PresShell* presShell = childDocShell->GetPresShell();
+        if (!presShell) {
+          continue;
+        }
+        presShell->SetIsUnderHiddenEmbedderElement(
+            aUnderHiddenEmbedderElement || embedderFrameIsHidden);
+      } else {
+        BrowserBridgeChild* bridgeChild =
+            BrowserBridgeChild::GetFrom(embedderElement);
+        bridgeChild->SetIsUnderHiddenEmbedderElement(
+            aUnderHiddenEmbedderElement || embedderFrameIsHidden);
+      }
+    }
+  }
+}
+
+nsIContent* PresShell::EventHandler::GetOverrideClickTarget(
+    WidgetGUIEvent* aGUIEvent, nsIFrame* aFrame) {
+  if (aGUIEvent->mMessage != eMouseUp) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(aGUIEvent->mClass == eMouseEventClass);
+  WidgetMouseEvent* mouseEvent = aGUIEvent->AsMouseEvent();
+
+  uint32_t flags = 0;
+  RelativeTo relativeTo{aFrame};
+  nsPoint eventPoint =
+      nsLayoutUtils::GetEventCoordinatesRelativeTo(aGUIEvent, relativeTo);
+  if (mouseEvent->mIgnoreRootScrollFrame) {
+    flags |= INPUT_IGNORE_ROOT_SCROLL_FRAME;
+  }
+
+  nsIFrame* target =
+      FindFrameTargetedByInputEvent(aGUIEvent, relativeTo, eventPoint, flags);
+  if (!target) {
+    return nullptr;
+  }
+
+  nsIContent* overrideClickTarget = target->GetContent();
+  while (overrideClickTarget && !overrideClickTarget->IsElement()) {
+    overrideClickTarget = overrideClickTarget->GetFlattenedTreeParent();
+  }
+  return overrideClickTarget;
+}
+
+/******************************************************************************
+ * PresShell::EventHandler::EventTargetData
+ ******************************************************************************/
+
+void PresShell::EventHandler::EventTargetData::SetFrameAndComputePresShell(
+    nsIFrame* aFrameToHandleEvent) {
+  if (aFrameToHandleEvent) {
+    mFrame = aFrameToHandleEvent;
+    mPresShell = aFrameToHandleEvent->PresShell();
+  } else {
+    mFrame = nullptr;
+    mPresShell = nullptr;
+  }
+}
+
+void PresShell::EventHandler::EventTargetData::
+    SetFrameAndComputePresShellAndContent(nsIFrame* aFrameToHandleEvent,
+                                          WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(aFrameToHandleEvent);
+  MOZ_ASSERT(aGUIEvent);
+
+  SetFrameAndComputePresShell(aFrameToHandleEvent);
+  SetContentForEventFromFrame(aGUIEvent);
+}
+
+void PresShell::EventHandler::EventTargetData::SetContentForEventFromFrame(
+    WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(mFrame);
+  mContent = nullptr;
+  mFrame->GetContentForEvent(aGUIEvent, getter_AddRefs(mContent));
+}
+
+nsIContent* PresShell::EventHandler::EventTargetData::GetFrameContent() const {
+  return mFrame ? mFrame->GetContent() : nullptr;
+}
+
+bool PresShell::EventHandler::EventTargetData::MaybeRetargetToActiveDocument(
+    WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(mFrame);
+  MOZ_ASSERT(mPresShell);
+  MOZ_ASSERT(!mContent, "Doesn't support to retarget the content");
+
+  EventStateManager* activeESM =
+      EventStateManager::GetActiveEventStateManager();
+  if (!activeESM) {
+    return false;
+  }
+
+  if (aGUIEvent->mClass != ePointerEventClass &&
+      !aGUIEvent->HasMouseEventMessage()) {
+    return false;
+  }
+
+  if (activeESM == GetEventStateManager()) {
+    return false;
+  }
+
+  nsPresContext* activePresContext = activeESM->GetPresContext();
+  if (!activePresContext) {
+    return false;
+  }
+
+  PresShell* activePresShell = activePresContext->GetPresShell();
+  if (!activePresShell) {
+    return false;
+  }
+
+  // Note, currently for backwards compatibility we don't forward mouse events
+  // to the active document when mouse is over some subdocument.
+  if (!nsContentUtils::ContentIsCrossDocDescendantOf(
+          activePresShell->GetDocument(), GetDocument())) {
+    return false;
+  }
+
+  SetFrameAndComputePresShell(activePresShell->GetRootFrame());
+  return true;
+}
+
+bool PresShell::EventHandler::EventTargetData::ComputeElementFromFrame(
+    WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(aGUIEvent);
+  MOZ_ASSERT(aGUIEvent->IsUsingCoordinates());
+  MOZ_ASSERT(mPresShell);
+  MOZ_ASSERT(mFrame);
+
+  SetContentForEventFromFrame(aGUIEvent);
+
+  // If there is no content for this frame, target it anyway.  Some frames can
+  // be targeted but do not have content, particularly windows with scrolling
+  // off.
+  if (!mContent) {
+    return true;
+  }
+
+  // Bug 103055, bug 185889: mouse events apply to *elements*, not all nodes.
+  // Thus we get the nearest element parent here.
+  // XXX we leave the frame the same even if we find an element parent, so that
+  // the text frame will receive the event (selection and friends are the ones
+  // who care about that anyway)
+  //
+  // We use weak pointers because during this tight loop, the node
+  // will *not* go away.  And this happens on every mousemove.
+  nsIContent* content = mContent;
+  while (content && !content->IsElement()) {
+    content = content->GetFlattenedTreeParent();
+  }
+  mContent = content;
+
+  // If we found an element, target it.  Otherwise, target *nothing*.
+  return !!mContent;
+}
+
+void PresShell::EventHandler::EventTargetData::UpdateTouchEventTarget(
+    WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(aGUIEvent);
+
+  if (aGUIEvent->mClass != eTouchEventClass) {
+    return;
+  }
+
+  if (aGUIEvent->mMessage == eTouchStart) {
+    WidgetTouchEvent* touchEvent = aGUIEvent->AsTouchEvent();
+    nsIFrame* newFrame =
+        TouchManager::SuppressInvalidPointsAndGetTargetedFrame(touchEvent);
+    if (!newFrame) {
+      return;  // XXX Why don't we stop handling the event in this case?
+    }
+    SetFrameAndComputePresShellAndContent(newFrame, aGUIEvent);
+    return;
+  }
+
+  PresShell* newPresShell = PresShell::GetShellForTouchEvent(aGUIEvent);
+  if (!newPresShell) {
+    return;  // XXX Why don't we stop handling the event in this case?
+  }
+
+  // Touch events (except touchstart) are dispatching to the captured
+  // element. Get correct shell from it.
+  mPresShell = newPresShell;
+}
+
+/******************************************************************************
+ * PresShell::EventHandler::HandlingTimeAccumulator
+ ******************************************************************************/
+
+PresShell::EventHandler::HandlingTimeAccumulator::HandlingTimeAccumulator(
+    const PresShell::EventHandler& aEventHandler, const WidgetEvent* aEvent)
+    : mEventHandler(aEventHandler),
+      mEvent(aEvent),
+      mHandlingStartTime(TimeStamp::Now()) {
+  MOZ_ASSERT(mEvent);
+  MOZ_ASSERT(mEvent->IsTrusted());
+}
+
+PresShell::EventHandler::HandlingTimeAccumulator::~HandlingTimeAccumulator() {
+  if (mEvent->mTimeStamp <= mEventHandler.mPresShell->mLastOSWake) {
+    return;
+  }
+
+  switch (mEvent->mMessage) {
+    case eKeyPress:
+    case eKeyDown:
+    case eKeyUp:
+      Telemetry::AccumulateTimeDelta(Telemetry::INPUT_EVENT_HANDLED_KEYBOARD_MS,
+                                     mHandlingStartTime);
+      return;
+    case eMouseDown:
+      Telemetry::AccumulateTimeDelta(
+          Telemetry::INPUT_EVENT_HANDLED_MOUSE_DOWN_MS, mHandlingStartTime);
+      return;
+    case eMouseUp:
+      Telemetry::AccumulateTimeDelta(Telemetry::INPUT_EVENT_HANDLED_MOUSE_UP_MS,
+                                     mHandlingStartTime);
+      return;
+    case eMouseMove:
+      if (mEvent->mFlags.mHandledByAPZ) {
+        Telemetry::AccumulateTimeDelta(
+            Telemetry::INPUT_EVENT_HANDLED_APZ_MOUSE_MOVE_MS,
+            mHandlingStartTime);
+      }
+      return;
+    case eWheel:
+      if (mEvent->mFlags.mHandledByAPZ) {
+        Telemetry::AccumulateTimeDelta(
+            Telemetry::INPUT_EVENT_HANDLED_APZ_WHEEL_MS, mHandlingStartTime);
+      }
+      return;
+    case eTouchMove:
+      if (mEvent->mFlags.mHandledByAPZ) {
+        Telemetry::AccumulateTimeDelta(
+            Telemetry::INPUT_EVENT_HANDLED_APZ_TOUCH_MOVE_MS,
+            mHandlingStartTime);
+      }
+      return;
+    default:
+      return;
+  }
+}
+
+void PresShell::EndPaint() {
+  ClearPendingVisualScrollUpdate();
+
+  if (mDocument) {
+    mDocument->EnumerateSubDocuments([](Document& aSubDoc) {
+      if (PresShell* presShell = aSubDoc.GetPresShell()) {
+        presShell->EndPaint();
+      }
+      return CallState::Continue;
+    });
+  }
+}
+
+void PresShell::PingPerTickTelemetry(FlushType aFlushType) {
+  mLayoutTelemetry.PingPerTickTelemetry(aFlushType);
+}
+
+bool PresShell::GetZoomableByAPZ() const {
+  return mZoomConstraintsClient && mZoomConstraintsClient->GetAllowZoom();
+}
+
+void PresShell::EnsureReflowIfFrameHasHiddenContent(nsIFrame* aFrame) {
+  if (!aFrame || !aFrame->IsSubtreeDirty() ||
+      !StaticPrefs::layout_css_content_visibility_enabled()) {
+    return;
+  }
+
+  // Flushing notifications below might trigger more layouts, which might,
+  // in turn, trigger layout of other hidden content. We keep a local set
+  // of hidden content we are laying out to handle recursive calls.
+  nsTHashSet<nsIContent*> hiddenContentInForcedLayout;
+
+  MOZ_ASSERT(mHiddenContentInForcedLayout.IsEmpty());
+  nsIFrame* topmostFrameWithContentHidden = nullptr;
+  for (nsIFrame* cur = aFrame->GetInFlowParent(); cur;
+       cur = cur->GetInFlowParent()) {
+    if (cur->HidesContent()) {
+      topmostFrameWithContentHidden = cur;
+      mHiddenContentInForcedLayout.Insert(cur->GetContent());
+    }
+  }
+
+  if (mHiddenContentInForcedLayout.IsEmpty()) {
+    return;
+  }
+
+  // Queue and immediately flush a reflow for this node.
+  MOZ_ASSERT(topmostFrameWithContentHidden);
+  FrameNeedsReflow(topmostFrameWithContentHidden, IntrinsicDirty::None,
+                   NS_FRAME_IS_DIRTY);
+  mDocument->FlushPendingNotifications(FlushType::Layout);
+
+  mHiddenContentInForcedLayout.Clear();
+}
+
+bool PresShell::IsForcingLayoutForHiddenContent(const nsIFrame* aFrame) const {
+  return mHiddenContentInForcedLayout.Contains(aFrame->GetContent());
+}
+
+void PresShell::UpdateRelevancyOfContentVisibilityAutoFrames() {
+  if (mContentVisibilityRelevancyToUpdate.isEmpty()) {
+    return;
+  }
+
+  for (nsIFrame* frame : mContentVisibilityAutoFrames) {
+    frame->UpdateIsRelevantContent(mContentVisibilityRelevancyToUpdate);
+  }
+
+  mContentVisibilityRelevancyToUpdate.clear();
+}
+
+void PresShell::ScheduleContentRelevancyUpdate(ContentRelevancyReason aReason) {
+  if (MOZ_UNLIKELY(mIsDestroying)) {
+    return;
+  }
+
+  mContentVisibilityRelevancyToUpdate += aReason;
+
+  SetNeedLayoutFlush();
+  if (nsPresContext* presContext = GetPresContext()) {
+    presContext->RefreshDriver()->EnsureContentRelevancyUpdateHappens();
+  }
+}