From 59203c63bb777a3bacec32fb8830fba33540e809 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Wed, 12 Jun 2024 07:35:29 +0200
Subject: Adding upstream version 127.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 layout/base/AccessibleCaretManager.cpp          |   3 +-
 layout/base/PositionedEventTargeting.cpp        |  56 ++++--
 layout/base/PresShell.cpp                       |  26 +--
 layout/base/RestyleManager.cpp                  |  46 +++--
 layout/base/ViewportUtils.cpp                   |   3 +
 layout/base/ZoomConstraintsClient.cpp           |  16 ++
 layout/base/crashtests/crashtests.list          |   8 +-
 layout/base/metrics.yaml                        |  16 ++
 layout/base/nsCSSFrameConstructor.cpp           |  28 +--
 layout/base/nsCSSFrameConstructor.h             |   3 +-
 layout/base/nsDocumentViewer.cpp                |   5 +-
 layout/base/nsGenConList.cpp                    |  13 +-
 layout/base/nsLayoutUtils.cpp                   |  82 +++++----
 layout/base/nsLayoutUtils.h                     |  55 +++---
 layout/base/nsRefreshDriver.cpp                 |  30 +---
 layout/base/tests/browser.toml                  |   6 +
 layout/base/tests/browser_animatedImageLeak.js  | 226 ++++++++++++++++++++++++
 layout/base/tests/bug1896051-ref.html           |  29 +++
 layout/base/tests/bug1896051.html               |  38 ++++
 layout/base/tests/helper_animatedImageLeak.html |  10 ++
 layout/base/tests/helper_bug1733509.html        |  30 ++++
 layout/base/tests/mochitest.toml                |   3 +
 layout/base/tests/test_event_target_radius.html |  56 +++++-
 layout/base/tests/test_reftests_with_caret.html |   1 +
 24 files changed, 619 insertions(+), 170 deletions(-)
 create mode 100644 layout/base/tests/browser_animatedImageLeak.js
 create mode 100644 layout/base/tests/bug1896051-ref.html
 create mode 100644 layout/base/tests/bug1896051.html
 create mode 100644 layout/base/tests/helper_animatedImageLeak.html
 create mode 100644 layout/base/tests/helper_bug1733509.html

(limited to 'layout/base')

diff --git a/layout/base/AccessibleCaretManager.cpp b/layout/base/AccessibleCaretManager.cpp
index 99155133cd..7c125cf023 100644
--- a/layout/base/AccessibleCaretManager.cpp
+++ b/layout/base/AccessibleCaretManager.cpp
@@ -19,6 +19,7 @@
 #include "mozilla/dom/NodeFilterBinding.h"
 #include "mozilla/dom/Selection.h"
 #include "mozilla/dom/TreeWalker.h"
+#include "mozilla/FocusModel.h"
 #include "mozilla/IMEStateManager.h"
 #include "mozilla/IntegerPrintfMacros.h"
 #include "mozilla/PresShell.h"
@@ -879,7 +880,7 @@ nsIFrame* AccessibleCaretManager::GetFocusableFrame(nsIFrame* aFrame) const {
   // Look for the nearest enclosing focusable frame.
   nsIFrame* focusableFrame = aFrame;
   while (focusableFrame) {
-    if (focusableFrame->IsFocusable(/* aWithMouse = */ true)) {
+    if (focusableFrame->IsFocusable(IsFocusableFlags::WithMouse)) {
       break;
     }
     focusableFrame = focusableFrame->GetParent();
diff --git a/layout/base/PositionedEventTargeting.cpp b/layout/base/PositionedEventTargeting.cpp
index a975372dea..9af132d96d 100644
--- a/layout/base/PositionedEventTargeting.cpp
+++ b/layout/base/PositionedEventTargeting.cpp
@@ -6,6 +6,7 @@
 
 #include "PositionedEventTargeting.h"
 
+#include "Units.h"
 #include "mozilla/EventListenerManager.h"
 #include "mozilla/MouseEvents.h"
 #include "mozilla/Preferences.h"
@@ -13,18 +14,23 @@
 #include "mozilla/StaticPrefs_dom.h"
 #include "mozilla/StaticPrefs_ui.h"
 #include "mozilla/ToString.h"
+#include "mozilla/ViewportUtils.h"
 #include "mozilla/dom/MouseEventBinding.h"
+#include "mozilla/gfx/Matrix.h"
+#include "mozilla/layers/LayersTypes.h"
 #include "nsContainerFrame.h"
+#include "nsCoord.h"
 #include "nsFrameList.h"  // for DEBUG_FRAME_DUMP
 #include "nsHTMLParts.h"
 #include "nsLayoutUtils.h"
 #include "nsGkAtoms.h"
 #include "nsFontMetrics.h"
+#include "nsIContentInlines.h"
+#include "nsPresContext.h"
 #include "nsPrintfCString.h"
 #include "mozilla/dom/Element.h"
 #include "nsRegion.h"
 #include "nsDeviceContext.h"
-#include "nsIContentInlines.h"
 #include "nsIFrame.h"
 #include <algorithm>
 
@@ -276,15 +282,40 @@ static nsIContent* GetClickableAncestor(
   return nullptr;
 }
 
-static nscoord AppUnitsFromMM(RelativeTo aFrame, uint32_t aMM) {
-  nsPresContext* pc = aFrame.mFrame->PresContext();
-  float result = float(aMM) * (pc->DeviceContext()->AppUnitsPerPhysicalInch() /
-                               MM_PER_INCH_FLOAT);
-  if (aFrame.mViewportType == ViewportType::Layout) {
+static Scale2D AppUnitsToMMScale(RelativeTo aFrame) {
+  nsPresContext* presContext = aFrame.mFrame->PresContext();
+
+  const int32_t appUnitsPerInch =
+      presContext->DeviceContext()->AppUnitsPerPhysicalInch();
+  const float appUnits =
+      static_cast<float>(appUnitsPerInch) / MM_PER_INCH_FLOAT;
+
+  // Visual coordinates are only used for quantities relative to the
+  // cross-process root content document's root frame. There should
+  // not be an enclosing resolution or transform scale above that.
+  if (aFrame.mViewportType != ViewportType::Layout) {
+    const nscoord scale = NSToCoordRound(appUnits);
+    return Scale2D{static_cast<float>(scale), static_cast<float>(scale)};
+  }
+
+  Scale2D localResolution{1.0f, 1.0f};
+  Scale2D enclosingResolution{1.0f, 1.0f};
+
+  if (auto* pc = presContext->GetInProcessRootContentDocumentPresContext()) {
     PresShell* presShell = pc->PresShell();
-    result = result / presShell->GetResolution();
+    localResolution = {presShell->GetResolution(), presShell->GetResolution()};
+    enclosingResolution = ViewportUtils::TryInferEnclosingResolution(presShell);
   }
-  return NSToCoordRound(result);
+
+  const gfx::MatrixScales parentScale =
+      nsLayoutUtils::GetTransformToAncestorScale(aFrame.mFrame);
+  const Scale2D resolution =
+      localResolution * parentScale * enclosingResolution;
+
+  const nscoord scaleX = NSToCoordRound(appUnits / resolution.xScale);
+  const nscoord scaleY = NSToCoordRound(appUnits / resolution.yScale);
+
+  return {static_cast<float>(scaleX), static_cast<float>(scaleY)};
 }
 
 /**
@@ -303,10 +334,11 @@ static nsRect GetTargetRect(RelativeTo aRootFrame,
                             const nsPoint& aPointRelativeToRootFrame,
                             const nsIFrame* aRestrictToDescendants,
                             const EventRadiusPrefs& aPrefs, uint32_t aFlags) {
-  nsMargin m(AppUnitsFromMM(aRootFrame, aPrefs.mRadiusTopmm),
-             AppUnitsFromMM(aRootFrame, aPrefs.mRadiusRightmm),
-             AppUnitsFromMM(aRootFrame, aPrefs.mRadiusBottommm),
-             AppUnitsFromMM(aRootFrame, aPrefs.mRadiusLeftmm));
+  const Scale2D scale = AppUnitsToMMScale(aRootFrame);
+  nsMargin m(aPrefs.mRadiusTopmm * scale.yScale,
+             aPrefs.mRadiusRightmm * scale.xScale,
+             aPrefs.mRadiusBottommm * scale.yScale,
+             aPrefs.mRadiusLeftmm * scale.xScale);
   nsRect r(aPointRelativeToRootFrame, nsSize(0, 0));
   r.Inflate(m);
   if (!(aFlags & INPUT_IGNORE_ROOT_SCROLL_FRAME)) {
diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
index 7674abb3d0..cd41da3730 100644
--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -3931,11 +3931,9 @@ void PresShell::ScheduleViewManagerFlush() {
     return;
   }
 
-  nsPresContext* presContext = GetPresContext();
-  if (presContext) {
+  if (nsPresContext* presContext = GetPresContext()) {
     presContext->RefreshDriver()->ScheduleViewManagerFlush();
   }
-  SetNeedLayoutFlush();
 }
 
 void PresShell::DispatchSynthMouseMove(WidgetGUIEvent* aEvent) {
@@ -6566,7 +6564,7 @@ void PresShell::PaintInternal(nsView* aViewToPaint, PaintInternalFlags aFlags) {
   // We also force sync-decoding via pref for reftests.
   if (aFlags & PaintInternalFlags::PaintSyncDecodeImages ||
       mDocument->IsStaticDocument() ||
-      StaticPrefs::image_decode_sync_enabled()) {
+      StaticPrefs::image_testing_decode_sync_enabled()) {
     flags |= PaintFrameFlags::SyncDecodeImages;
   }
   if (renderer->GetBackendType() == layers::LayersBackend::LAYERS_WR) {
@@ -11260,10 +11258,8 @@ void PresShell::SetIsActive(bool aIsActive) {
 #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);
-      }
+      // Reset the dynamic toolbar offset state.
+      presContext->UpdateDynamicToolbarOffset(0);
     }
 #endif
   }
@@ -11849,10 +11845,9 @@ void PresShell::SyncWindowProperties(bool aSync) {
         canvas ? canvas : rootFrame, rootFrame);
     windowWidget->SetTransparencyMode(mode);
 
-    // For macOS, apply color scheme overrides to the top level window widget.
-    if (auto scheme = pc->GetOverriddenOrEmbedderColorScheme()) {
-      windowWidget->SetColorScheme(scheme);
-    }
+    // For macOS, apply color scheme to the top level window widget.
+    windowWidget->SetColorScheme(
+        Some(LookAndFeel::ColorSchemeForFrame(rootFrame)));
   }
 
   if (!weak.IsAlive()) {
@@ -12102,13 +12097,6 @@ void PresShell::EventHandler::EventTargetData::UpdateWheelEventTarget(
     return;
   }
 
-  // If the browsing context is no longer the same as the context of the
-  // current wheel transaction, do not override the event target.
-  if (!groupFrame->PresContext() || !groupFrame->PresShell() ||
-      groupFrame->PresContext() != GetPresContext()) {
-    return;
-  }
-
   // If dom.event.wheel-event-groups.enabled is set and whe have a stored
   // event target from the wheel transaction, override the event target.
   SetFrameAndComputePresShellAndContent(groupFrame, aGUIEvent);
diff --git a/layout/base/RestyleManager.cpp b/layout/base/RestyleManager.cpp
index 81ffebf89a..e00493467f 100644
--- a/layout/base/RestyleManager.cpp
+++ b/layout/base/RestyleManager.cpp
@@ -3246,6 +3246,12 @@ void RestyleManager::DoProcessPendingRestyles(ServoTraversalFlags aFlags) {
     // construction).
     nsTArray<RefPtr<Element>> anchorsToSuppress;
 
+    // Unfortunately, the frame constructor and ProcessPostTraversal can
+    // generate new change hints while processing existing ones. We redirect
+    // those into a secondary queue and iterate until there's nothing left.
+    ReentrantChangeList newChanges;
+    mReentrantChanges = &newChanges;
+
     {
       DocumentStyleRootIterator iter(doc->GetServoRestyleRoot());
       while (Element* root = iter.GetNextStyleRoot()) {
@@ -3271,34 +3277,26 @@ void RestyleManager::DoProcessPendingRestyles(ServoTraversalFlags aFlags) {
     doc->ClearServoRestyleRoot();
     ClearSnapshots();
 
-    // Process the change hints.
-    //
-    // Unfortunately, the frame constructor can generate new change hints while
-    // processing existing ones. We redirect those into a secondary queue and
-    // iterate until there's nothing left.
-    {
-      ReentrantChangeList newChanges;
-      mReentrantChanges = &newChanges;
-      while (!currentChanges.IsEmpty()) {
-        ProcessRestyledFrames(currentChanges);
-        MOZ_ASSERT(currentChanges.IsEmpty());
-        for (ReentrantChange& change : newChanges) {
-          if (!(change.mHint & nsChangeHint_ReconstructFrame) &&
-              !change.mContent->GetPrimaryFrame()) {
-            // SVG Elements post change hints without ensuring that the primary
-            // frame will be there after that (see bug 1366142).
-            //
-            // Just ignore those, since we can't really process them.
-            continue;
-          }
-          currentChanges.AppendChange(change.mContent->GetPrimaryFrame(),
-                                      change.mContent, change.mHint);
+    while (!currentChanges.IsEmpty()) {
+      ProcessRestyledFrames(currentChanges);
+      MOZ_ASSERT(currentChanges.IsEmpty());
+      for (ReentrantChange& change : newChanges) {
+        if (!(change.mHint & nsChangeHint_ReconstructFrame) &&
+            !change.mContent->GetPrimaryFrame()) {
+          // SVG Elements post change hints without ensuring that the primary
+          // frame will be there after that (see bug 1366142).
+          //
+          // Just ignore those, since we can't really process them.
+          continue;
         }
-        newChanges.Clear();
+        currentChanges.AppendChange(change.mContent->GetPrimaryFrame(),
+                                    change.mContent, change.mHint);
       }
-      mReentrantChanges = nullptr;
+      newChanges.Clear();
     }
 
+    mReentrantChanges = nullptr;
+
     // Suppress adjustments in the after-change scroll anchors if needed, now
     // that we're done reframing everything.
     for (Element* element : anchorsToSuppress) {
diff --git a/layout/base/ViewportUtils.cpp b/layout/base/ViewportUtils.cpp
index f0d18510bf..8b8e4a4d27 100644
--- a/layout/base/ViewportUtils.cpp
+++ b/layout/base/ViewportUtils.cpp
@@ -260,6 +260,9 @@ const nsIFrame* ViewportUtils::IsZoomedContentRoot(const nsIFrame* aFrame) {
 }
 
 Scale2D ViewportUtils::TryInferEnclosingResolution(PresShell* aShell) {
+  if (!XRE_IsContentProcess()) {
+    return {1.0f, 1.0f};
+  }
   MOZ_ASSERT(aShell && aShell->GetPresContext());
   MOZ_ASSERT(!aShell->GetPresContext()->GetParentPresContext(),
              "TryInferEnclosingResolution can only be called for a root pres "
diff --git a/layout/base/ZoomConstraintsClient.cpp b/layout/base/ZoomConstraintsClient.cpp
index e695c7755e..e9be0c2073 100644
--- a/layout/base/ZoomConstraintsClient.cpp
+++ b/layout/base/ZoomConstraintsClient.cpp
@@ -53,9 +53,20 @@ static nsIWidget* GetWidget(PresShell* aPresShell) {
     return nullptr;
   }
   if (nsIFrame* rootFrame = aPresShell->GetRootFrame()) {
+#if defined(MOZ_WIDGET_ANDROID)
+    // On Android in cases of about:XX pages loaded in the browser parent
+    // process we need to return the nearest widget since it's the widget owning
+    // an IAPZCTreeManager to communicate with the APZCTreeManager for the
+    // browser.
+    // In bug 1648427 we will apply this code to desktops as well to make
+    // about pages zoomable on desktops, but it will be involving more works,
+    // see https://bugzilla.mozilla.org/show_bug.cgi?id=1648427#c7 .
+    return rootFrame->GetNearestWidget();
+#else
     if (nsView* view = rootFrame->GetView()) {
       return view->GetWidget();
     }
+#endif
   }
   return nullptr;
 }
@@ -199,6 +210,11 @@ void ZoomConstraintsClient::RefreshZoomConstraints() {
     return;
   }
 
+  // Ignore documents which has been removed from the doc shell.
+  if (!mDocument->IsActive()) {
+    return;
+  }
+
   uint32_t presShellId = 0;
   ScrollableLayerGuid::ViewID viewId = ScrollableLayerGuid::NULL_SCROLL_ID;
   bool scrollIdentifiersValid =
diff --git a/layout/base/crashtests/crashtests.list b/layout/base/crashtests/crashtests.list
index 3b1ed1e3d4..a379b981b6 100644
--- a/layout/base/crashtests/crashtests.list
+++ b/layout/base/crashtests/crashtests.list
@@ -385,11 +385,7 @@ load 836990-1.html
 load 840480.html
 load 842114.html
 load 847242.html
-# This test is slow, because it uses setTimeout a lot.
-# After bug 1875100, on windows, it times out because there's a left-over
-# window or so, and that bug causes us to throttle timers. Disable window
-# occlusion to work around this for now, see bug 1864255.
-pref(widget.windows.window_occlusion_tracking.enabled,false) skip-if(ThreadSanitizer) load 852293.html
+skip-if(ThreadSanitizer) load 852293.html
 pref(layers.force-active,true) load 859526-1.html
 pref(layers.force-active,true) load 859630-1.html
 load 860579-1.html
@@ -528,7 +524,7 @@ load 1539303.html
 load 1541679.html
 load 1547261.html
 load 1547391.html
-pref(widget.windows.window_occlusion_tracking.enabled,false) load 1548057.html # Bug 1819154
+load 1548057.html
 load 1549867.html
 load 1553874.html
 load 1560328.html
diff --git a/layout/base/metrics.yaml b/layout/base/metrics.yaml
index 856ff77965..631200bd48 100644
--- a/layout/base/metrics.yaml
+++ b/layout/base/metrics.yaml
@@ -29,6 +29,22 @@ performance.pageload:
       - perf-telemetry-alerts@mozilla.com
     expires: never
 
+  async_sheet_load:
+    type: timing_distribution
+    time_unit: millisecond
+    description: >
+      Time spent in milliseconds since a style sheet started loading async
+      until it finished.
+    bugs:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1892660
+    data_reviews:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1892660
+    data_sensitivity:
+      - technical
+    notification_emails:
+      - emilio@mozilla.com
+      - perf-telemetry-alerts@mozilla.com
+    expires: 132
 
 performance.responsiveness:
   req_anim_frame_callback:
diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index c0f35c278d..ba43eb70b9 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -1537,12 +1537,11 @@ already_AddRefed<nsIContent> nsCSSFrameConstructor::CreateGenConTextNode(
 
 void nsCSSFrameConstructor::CreateGeneratedContent(
     nsFrameConstructorState& aState, Element& aOriginatingElement,
-    ComputedStyle& aPseudoStyle, uint32_t aContentIndex,
-    const FunctionRef<void(nsIContent*)> aAddChild) {
+    ComputedStyle& aPseudoStyle, const StyleContentItem& aItem,
+    size_t aContentIndex, const FunctionRef<void(nsIContent*)> aAddChild) {
   using Type = StyleContentItem::Tag;
   // Get the content value
-  const auto& item = aPseudoStyle.StyleContent()->ContentAt(aContentIndex);
-  const Type type = item.tag;
+  const Type type = aItem.tag;
 
   switch (type) {
     case Type::Image: {
@@ -1552,7 +1551,7 @@ void nsCSSFrameConstructor::CreateGeneratedContent(
     }
 
     case Type::String: {
-      const auto string = item.AsString().AsString();
+      const auto string = aItem.AsString().AsString();
       if (string.IsEmpty()) {
         return;
       }
@@ -1563,7 +1562,7 @@ void nsCSSFrameConstructor::CreateGeneratedContent(
     }
 
     case Type::Attr: {
-      const auto& attr = item.AsAttr();
+      const auto& attr = aItem.AsAttr();
       RefPtr<nsAtom> attrName = attr.attribute.AsAtom();
       int32_t attrNameSpace = kNameSpaceID_None;
       RefPtr<nsAtom> ns = attr.namespace_url.AsAtom();
@@ -1592,11 +1591,11 @@ void nsCSSFrameConstructor::CreateGeneratedContent(
       CounterStylePtr ptr;
       nsString separator;
       if (type == Type::Counter) {
-        auto& counter = item.AsCounter();
+        auto& counter = aItem.AsCounter();
         name = counter._0.AsAtom();
         ptr = CounterStylePtr::FromStyle(counter._1);
       } else {
-        auto& counters = item.AsCounters();
+        auto& counters = aItem.AsCounters();
         name = counters._0.AsAtom();
         CopyUTF8toUTF16(counters._1.AsString(), separator);
         ptr = CounterStylePtr::FromStyle(counters._2);
@@ -1947,13 +1946,14 @@ void nsCSSFrameConstructor::CreateGeneratedContentItem(
       mPresShell->StyleSet()->StyleNewSubtree(childElement);
     }
   };
-  const uint32_t contentCount = pseudoStyle->StyleContent()->ContentCount();
-  for (uint32_t contentIndex = 0; contentIndex < contentCount; contentIndex++) {
-    CreateGeneratedContent(aState, aOriginatingElement, *pseudoStyle,
-                           contentIndex, AppendChild);
+  auto items = pseudoStyle->StyleContent()->NonAltContentItems();
+  size_t index = 0;
+  for (const auto& item : items) {
+    CreateGeneratedContent(aState, aOriginatingElement, *pseudoStyle, item,
+                           index++, AppendChild);
   }
   // If a ::marker has no 'content' then generate it from its 'list-style-*'.
-  if (contentCount == 0 && aPseudoElement == PseudoStyleType::marker) {
+  if (index == 0 && aPseudoElement == PseudoStyleType::marker) {
     CreateGeneratedContentFromListStyle(aState, aOriginatingElement,
                                         *pseudoStyle, AppendChild);
   }
@@ -5283,7 +5283,7 @@ void nsCSSFrameConstructor::AddFrameConstructionItemsInternal(
       aFlags.contains(ItemFlag::AllowPageBreak) &&
       aState.mPresContext->IsPaginated() &&
       !display.IsAbsolutelyPositionedStyle() &&
-      !(aParentFrame && aParentFrame->IsGridContainerFrame()) &&
+      !(aParentFrame && aParentFrame->IsFlexOrGridContainer()) &&
       !(bits & FCDATA_IS_TABLE_PART) && !(bits & FCDATA_IS_SVG_TEXT);
   if (canHavePageBreak && display.BreakBefore()) {
     AppendPageBreakItem(aContent, aItems);
diff --git a/layout/base/nsCSSFrameConstructor.h b/layout/base/nsCSSFrameConstructor.h
index 51d5fe32d0..5fdea315b8 100644
--- a/layout/base/nsCSSFrameConstructor.h
+++ b/layout/base/nsCSSFrameConstructor.h
@@ -477,7 +477,8 @@ class nsCSSFrameConstructor final : public nsFrameManager {
    */
   void CreateGeneratedContent(
       nsFrameConstructorState& aState, Element& aOriginatingElement,
-      ComputedStyle& aPseudoStyle, uint32_t aContentIndex,
+      ComputedStyle& aPseudoStyle, const mozilla::StyleContentItem& aItem,
+      size_t aContentIndex,
       const mozilla::FunctionRef<void(nsIContent*)> aAddChild);
 
   /**
diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index 8ae0e001b8..bbd43a830e 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -2426,7 +2426,7 @@ NS_IMETHODIMP nsDocumentViewer::CopyLinkLocation() {
   NS_ENSURE_SUCCESS(rv, rv);
 
   // copy the href onto the clipboard
-  return clipboard->CopyString(locationText);
+  return clipboard->CopyString(locationText, mDocument->GetWindowContext());
 }
 
 NS_IMETHODIMP nsDocumentViewer::CopyImage(int32_t aCopyFlags) {
@@ -2436,7 +2436,8 @@ NS_IMETHODIMP nsDocumentViewer::CopyImage(int32_t aCopyFlags) {
   NS_ENSURE_TRUE(node, NS_ERROR_FAILURE);
 
   nsCOMPtr<nsILoadContext> loadContext(mContainer);
-  return nsCopySupport::ImageCopy(node, loadContext, aCopyFlags);
+  return nsCopySupport::ImageCopy(node, loadContext, aCopyFlags,
+                                  mDocument->GetWindowContext());
 }
 
 NS_IMETHODIMP nsDocumentViewer::GetCopyable(bool* aCopyable) {
diff --git a/layout/base/nsGenConList.cpp b/layout/base/nsGenConList.cpp
index b770ee539a..175e6fe7d5 100644
--- a/layout/base/nsGenConList.cpp
+++ b/layout/base/nsGenConList.cpp
@@ -12,12 +12,13 @@
 #include "nsIFrame.h"
 
 void nsGenConNode::CheckFrameAssertions() {
-  NS_ASSERTION(
-      mContentIndex < int32_t(mPseudoFrame->StyleContent()->ContentCount()) ||
-          // Special-case for the USE node created for the legacy markers,
-          // which don't use the content property.
-          mContentIndex == 0,
-      "index out of range");
+  NS_ASSERTION(mContentIndex < int32_t(mPseudoFrame->StyleContent()
+                                           ->NonAltContentItems()
+                                           .Length()) ||
+                   // Special-case for the USE node created for the legacy
+                   // markers, which don't use the content property.
+                   mContentIndex == 0,
+               "index out of range");
   // We allow negative values of mContentIndex for 'counter-reset' and
   // 'counter-increment'.
 
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 429ad335cc..3f84a97250 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -900,7 +900,7 @@ void nsLayoutUtils::GetMarkerSpokenText(const nsIContent* aContent,
     return;
   }
 
-  if (frame->StyleContent()->ContentCount() > 0) {
+  if (!frame->StyleContent()->NonAltContentItems().IsEmpty()) {
     for (nsIFrame* child : frame->PrincipalChildList()) {
       nsIFrame::RenderedText text = child->GetRenderedText();
       aText += text.mString;
@@ -2131,6 +2131,7 @@ const nsIFrame* nsLayoutUtils::FindNearestCommonAncestorFrameWithinBlock(
 bool nsLayoutUtils::AuthorSpecifiedBorderBackgroundDisablesTheming(
     StyleAppearance aAppearance) {
   return aAppearance == StyleAppearance::NumberInput ||
+         aAppearance == StyleAppearance::PasswordInput ||
          aAppearance == StyleAppearance::Button ||
          aAppearance == StyleAppearance::Textfield ||
          aAppearance == StyleAppearance::Textarea ||
@@ -3498,7 +3499,7 @@ nsIFrame* nsLayoutUtils::GetFirstNonAnonymousFrame(nsIFrame* aFrame) {
 struct BoxToRect : public nsLayoutUtils::BoxCallback {
   const nsIFrame* mRelativeTo;
   RectCallback* mCallback;
-  uint32_t mFlags;
+  nsLayoutUtils::GetAllInFlowRectsFlags mFlags;
   // If the frame we're measuring relative to is the root, we know all frames
   // are descendants of it, so we don't need to compute the common ancestor
   // between a frame and mRelativeTo.
@@ -3510,7 +3511,8 @@ struct BoxToRect : public nsLayoutUtils::BoxCallback {
   bool mRelativeToIsTarget;
 
   BoxToRect(const nsIFrame* aTargetFrame, const nsIFrame* aRelativeTo,
-            RectCallback* aCallback, uint32_t aFlags)
+            RectCallback* aCallback,
+            nsLayoutUtils::GetAllInFlowRectsFlags aFlags)
       : mRelativeTo(aRelativeTo),
         mCallback(aCallback),
         mFlags(aFlags),
@@ -3523,21 +3525,34 @@ struct BoxToRect : public nsLayoutUtils::BoxCallback {
     const bool usingSVGOuterFrame = !!outer;
     if (!outer) {
       outer = aFrame;
-      switch (mFlags & nsLayoutUtils::RECTS_WHICH_BOX_MASK) {
-        case nsLayoutUtils::RECTS_USE_CONTENT_BOX:
-          r = aFrame->GetContentRectRelativeToSelf();
-          break;
-        case nsLayoutUtils::RECTS_USE_PADDING_BOX:
-          r = aFrame->GetPaddingRectRelativeToSelf();
-          break;
-        case nsLayoutUtils::RECTS_USE_MARGIN_BOX:
-          r = aFrame->GetMarginRectRelativeToSelf();
-          break;
-        default:  // Use the border box
-          r = aFrame->GetRectRelativeToSelf();
+      if (mFlags.contains(
+              nsLayoutUtils::GetAllInFlowRectsFlag::UseContentBox)) {
+        r = aFrame->GetContentRectRelativeToSelf();
+      } else if (mFlags.contains(
+                     nsLayoutUtils::GetAllInFlowRectsFlag::UsePaddingBox)) {
+        r = aFrame->GetPaddingRectRelativeToSelf();
+      } else if (mFlags.contains(
+                     nsLayoutUtils::GetAllInFlowRectsFlag::UseMarginBox)) {
+        r = aFrame->GetMarginRectRelativeToSelf();
+      } else if (mFlags.contains(nsLayoutUtils::GetAllInFlowRectsFlag::
+                                     UseMarginBoxWithAutoResolvedAsZero)) {
+        r = aFrame->GetRectRelativeToSelf();
+        const auto& styleMargin = aFrame->StyleMargin()->mMargin;
+        nsMargin usedMargin =
+            aFrame->GetUsedMargin().ApplySkipSides(aFrame->GetSkipSides());
+        for (const Side side : AllPhysicalSides()) {
+          if (styleMargin.Get(side).IsAuto()) {
+            usedMargin.Side(side) = 0;
+          }
+        }
+        r.Inflate(usedMargin);
+      } else {
+        // Use the border-box.
+        r = aFrame->GetRectRelativeToSelf();
       }
     }
-    if (mFlags & nsLayoutUtils::RECTS_ACCOUNT_FOR_TRANSFORMS) {
+    if (mFlags.contains(
+            nsLayoutUtils::GetAllInFlowRectsFlag::AccountForTransforms)) {
       const bool isAncestorKnown = [&] {
         if (mRelativeToIsRoot) {
           return true;
@@ -3568,7 +3583,7 @@ struct MOZ_RAII BoxToRectAndText : public BoxToRect {
 
   BoxToRectAndText(const nsIFrame* aTargetFrame, const nsIFrame* aRelativeTo,
                    RectCallback* aCallback, Sequence<nsString>* aTextList,
-                   uint32_t aFlags)
+                   nsLayoutUtils::GetAllInFlowRectsFlags aFlags)
       : BoxToRect(aTargetFrame, aRelativeTo, aCallback, aFlags),
         mTextList(aTextList) {}
 
@@ -3609,7 +3624,7 @@ struct MOZ_RAII BoxToRectAndText : public BoxToRect {
 void nsLayoutUtils::GetAllInFlowRects(nsIFrame* aFrame,
                                       const nsIFrame* aRelativeTo,
                                       RectCallback* aCallback,
-                                      uint32_t aFlags) {
+                                      GetAllInFlowRectsFlags aFlags) {
   BoxToRect converter(aFrame, aRelativeTo, aCallback, aFlags);
   GetAllInFlowBoxes(aFrame, &converter);
 }
@@ -3618,7 +3633,7 @@ void nsLayoutUtils::GetAllInFlowRectsAndTexts(nsIFrame* aFrame,
                                               const nsIFrame* aRelativeTo,
                                               RectCallback* aCallback,
                                               Sequence<nsString>* aTextList,
-                                              uint32_t aFlags) {
+                                              GetAllInFlowRectsFlags aFlags) {
   BoxToRectAndText converter(aFrame, aRelativeTo, aCallback, aTextList, aFlags);
   GetAllInFlowBoxes(aFrame, &converter);
 }
@@ -3649,7 +3664,7 @@ nsIFrame* nsLayoutUtils::GetContainingBlockForClientRect(nsIFrame* aFrame) {
 
 nsRect nsLayoutUtils::GetAllInFlowRectsUnion(nsIFrame* aFrame,
                                              const nsIFrame* aRelativeTo,
-                                             uint32_t aFlags) {
+                                             GetAllInFlowRectsFlags aFlags) {
   RectAccumulator accumulator;
   GetAllInFlowRects(aFrame, aRelativeTo, &accumulator, aFlags);
   return accumulator.mResultRect.IsEmpty() ? accumulator.mFirstRect
@@ -4610,7 +4625,7 @@ static nscoord AddIntrinsicSizeOffset(
     LayoutDeviceIntSize devSize = pc->Theme()->GetMinimumWidgetSize(
         pc, aFrame, disp->EffectiveAppearance());
     nscoord themeSize = pc->DevPixelsToAppUnits(
-        aAxis == eAxisVertical ? devSize.height : devSize.width);
+        aAxis == PhysicalAxis::Vertical ? devSize.height : devSize.width);
     // GetMinimumWidgetSize() returns a border-box width.
     themeSize += aOffsets.margin;
     if (themeSize > result) {
@@ -4641,7 +4656,7 @@ nscoord nsLayoutUtils::IntrinsicForAxis(
                  aPercentageBasis.isSome(),
              "grid layout should always pass a percentage basis");
 
-  const bool horizontalAxis = MOZ_LIKELY(aAxis == eAxisHorizontal);
+  const bool horizontalAxis = MOZ_LIKELY(aAxis == PhysicalAxis::Horizontal);
 #ifdef DEBUG_INTRINSIC_WIDTH
   nsIFrame::IndentBy(stderr, gNoiseIndent);
   aFrame->ListTag(stderr);
@@ -5048,10 +5063,11 @@ nscoord nsLayoutUtils::MinSizeContributionForAxis(
 
   // Note: this method is only meant for grid/flex items.
   const nsStylePosition* const stylePos = aFrame->StylePosition();
-  StyleSize size =
-      aAxis == eAxisHorizontal ? stylePos->mMinWidth : stylePos->mMinHeight;
-  StyleMaxSize maxSize =
-      aAxis == eAxisHorizontal ? stylePos->mMaxWidth : stylePos->mMaxHeight;
+  StyleSize size = aAxis == PhysicalAxis::Horizontal ? stylePos->mMinWidth
+                                                     : stylePos->mMinHeight;
+  StyleMaxSize maxSize = aAxis == PhysicalAxis::Horizontal
+                             ? stylePos->mMaxWidth
+                             : stylePos->mMaxHeight;
   auto childWM = aFrame->GetWritingMode();
   PhysicalAxis ourInlineAxis = childWM.PhysicalAxis(LogicalAxis::Inline);
   // According to the spec, max-content and min-content should behave as the
@@ -5077,7 +5093,8 @@ nscoord nsLayoutUtils::MinSizeContributionForAxis(
       minSize = 0;
       fixedMinSize = &minSize;
     } else {
-      size = aAxis == eAxisHorizontal ? stylePos->mWidth : stylePos->mHeight;
+      size = aAxis == PhysicalAxis::Horizontal ? stylePos->mWidth
+                                               : stylePos->mHeight;
       // This is same as above: keywords should behaves as property's initial
       // values in block axis.
       if (aAxis != ourInlineAxis && size.BehavesLikeInitialValueOnBlockAxis()) {
@@ -8896,13 +8913,7 @@ ScrollMetadata nsLayoutUtils::ComputeScrollMetadata(
   }
   if (primaryFrame) {
     WritingMode writingModeOfRootScrollFrame = primaryFrame->GetWritingMode();
-    WritingMode::BlockDir blockDirOfRootScrollFrame =
-        writingModeOfRootScrollFrame.GetBlockDir();
-    WritingMode::InlineDir inlineDirOfRootScrollFrame =
-        writingModeOfRootScrollFrame.GetInlineDir();
-    if (blockDirOfRootScrollFrame == WritingMode::BlockDir::eBlockRL ||
-        (blockDirOfRootScrollFrame == WritingMode::BlockDir::eBlockTB &&
-         inlineDirOfRootScrollFrame == WritingMode::InlineDir::eInlineRTL)) {
+    if (writingModeOfRootScrollFrame.IsPhysicalRTL()) {
       metadata.SetIsAutoDirRootContentRTL(true);
     }
   }
@@ -9223,7 +9234,8 @@ CSSRect nsLayoutUtils::GetBoundingFrameRect(
   CSSRect result;
   nsIFrame* relativeTo = aRootScrollFrame->GetScrolledFrame();
   result = CSSRect::FromAppUnits(nsLayoutUtils::GetAllInFlowRectsUnion(
-      aFrame, relativeTo, nsLayoutUtils::RECTS_ACCOUNT_FOR_TRANSFORMS));
+      aFrame, relativeTo,
+      nsLayoutUtils::GetAllInFlowRectsFlag::AccountForTransforms));
 
   // If the element is contained in a scrollable frame that is not
   // the root scroll frame, make sure to clip the result so that it is
diff --git a/layout/base/nsLayoutUtils.h b/layout/base/nsLayoutUtils.h
index 135a9ad9ab..6b6e45b3e4 100644
--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -1241,52 +1241,57 @@ class nsLayoutUtils {
 
   static nsIFrame* GetContainingBlockForClientRect(nsIFrame* aFrame);
 
-  enum {
-    RECTS_ACCOUNT_FOR_TRANSFORMS = 0x01,
-    // Two bits for specifying which box type to use.
-    // With neither bit set (default), use the border box.
-    RECTS_USE_CONTENT_BOX = 0x02,
-    RECTS_USE_PADDING_BOX = 0x04,
-    RECTS_USE_MARGIN_BOX = 0x06,  // both bits set
-    RECTS_WHICH_BOX_MASK = 0x06   // bitmask for these two bits
-  };
   /**
    * Collect all CSS boxes (content, padding, border, or margin) associated
    * with aFrame and its continuations, "drilling down" through table wrapper
    * frames and some anonymous blocks since they're not real CSS boxes.
+   *
    * The boxes are positioned relative to aRelativeTo (taking scrolling
    * into account) and passed to the callback in frame-tree order.
    * If aFrame is null, no boxes are returned.
+   *
    * For SVG frames, returns one rectangle, the bounding box.
-   * If aFlags includes RECTS_ACCOUNT_FOR_TRANSFORMS, then when converting
-   * the boxes into aRelativeTo coordinates, transforms (including CSS
-   * and SVG transforms) are taken into account.
-   * If aFlags includes one of RECTS_USE_CONTENT_BOX, RECTS_USE_PADDING_BOX,
-   * or RECTS_USE_MARGIN_BOX, the corresponding type of box is used.
-   * Otherwise (by default), the border box is used.
-   */
+   *
+   * If aFlags includes 'AccountForTransforms', then when converting the boxes
+   * into aRelativeTo coordinates, transforms (including CSS and SVG transforms)
+   * are taken into account.
+   *
+   * If aFlags includes one of 'UseContentBox', 'UsePaddingBox', 'UseMarginBox',
+   * or 'UseMarginBoxWithAutoResolvedAsZero', the corresponding type of box is
+   * used. Otherwise (by default), the border box is used. Note that these "Box"
+   * flags are meant to be mutually exclusive, though we don't enforce that. If
+   * multiple "Box" flags are used, we'll gracefully just use the first one in
+   * the order of the enum.
+   */
+  enum class GetAllInFlowRectsFlag : uint8_t {
+    AccountForTransforms,
+    UseContentBox,
+    UsePaddingBox,
+    UseMarginBox,
+    // Similar to UseMarginBox, but the 'auto' margins are resolved as zero.
+    UseMarginBoxWithAutoResolvedAsZero,
+  };
+  using GetAllInFlowRectsFlags = mozilla::EnumSet<GetAllInFlowRectsFlag>;
   static void GetAllInFlowRects(nsIFrame* aFrame, const nsIFrame* aRelativeTo,
                                 mozilla::RectCallback* aCallback,
-                                uint32_t aFlags = 0);
+                                GetAllInFlowRectsFlags aFlags = {});
 
   static void GetAllInFlowRectsAndTexts(
       nsIFrame* aFrame, const nsIFrame* aRelativeTo,
       mozilla::RectCallback* aCallback,
-      mozilla::dom::Sequence<nsString>* aTextList, uint32_t aFlags = 0);
+      mozilla::dom::Sequence<nsString>* aTextList,
+      GetAllInFlowRectsFlags aFlags = {});
 
   /**
    * Computes the union of all rects returned by GetAllInFlowRects. If
    * the union is empty, returns the first rect.
-   * If aFlags includes RECTS_ACCOUNT_FOR_TRANSFORMS, then when converting
-   * the boxes into aRelativeTo coordinates, transforms (including CSS
-   * and SVG transforms) are taken into account.
-   * If aFlags includes one of RECTS_USE_CONTENT_BOX, RECTS_USE_PADDING_BOX,
-   * or RECTS_USE_MARGIN_BOX, the corresponding type of box is used.
-   * Otherwise (by default), the border box is used.
+   *
+   * See GetAllInFlowRects() documentation for the meaning of aRelativeTo and
+   * aFlags.
    */
   static nsRect GetAllInFlowRectsUnion(nsIFrame* aFrame,
                                        const nsIFrame* aRelativeTo,
-                                       uint32_t aFlags = 0);
+                                       GetAllInFlowRectsFlags aFlags = {});
 
   enum { EXCLUDE_BLUR_SHADOWS = 0x01 };
   /**
diff --git a/layout/base/nsRefreshDriver.cpp b/layout/base/nsRefreshDriver.cpp
index 7885d6b8db..218d158a47 100644
--- a/layout/base/nsRefreshDriver.cpp
+++ b/layout/base/nsRefreshDriver.cpp
@@ -831,11 +831,11 @@ class VsyncRefreshDriverTimer : public RefreshDriverTimer {
     const TimeDuration previousRate = mVsyncRate;
     const TimeDuration rate = GetTimerRate();
 
-    hal::PerformanceHintSession* const performanceHintSession =
-        GetPerformanceHintSession();
-    if (performanceHintSession && rate != previousRate) {
-      performanceHintSession->UpdateTargetWorkDuration(
-          ContentChild::GetPerformanceHintTarget(rate));
+    if (rate != previousRate) {
+      if (auto* const performanceHintSession = GetPerformanceHintSession()) {
+        performanceHintSession->UpdateTargetWorkDuration(
+            ContentChild::GetPerformanceHintTarget(rate));
+      }
     }
 
     if (TimeDuration::FromMilliseconds(nsRefreshDriver::DefaultInterval()) >
@@ -862,7 +862,7 @@ class VsyncRefreshDriverTimer : public RefreshDriverTimer {
 
     TimeStamp tickEnd = TimeStamp::Now();
 
-    if (performanceHintSession) {
+    if (auto* const performanceHintSession = GetPerformanceHintSession()) {
       performanceHintSession->ReportActualWorkDuration(tickEnd - tickStart);
     }
 
@@ -2228,23 +2228,7 @@ void nsRefreshDriver::RunFullscreenSteps() {
 
 void nsRefreshDriver::UpdateIntersectionObservations(TimeStamp aNowTime) {
   AUTO_PROFILER_LABEL_RELEVANT_FOR_JS("Compute intersections", LAYOUT);
-
-  AutoTArray<RefPtr<Document>, 32> documents;
-
-  if (mPresContext->Document()->HasIntersectionObservers()) {
-    documents.AppendElement(mPresContext->Document());
-  }
-
-  mPresContext->Document()->CollectDescendantDocuments(
-      documents, [](const Document* document) -> bool {
-        return document->HasIntersectionObservers();
-      });
-
-  for (const auto& doc : documents) {
-    doc->UpdateIntersectionObservations(aNowTime);
-    doc->ScheduleIntersectionObserverNotification();
-  }
-
+  mPresContext->Document()->UpdateIntersections(aNowTime);
   mNeedToUpdateIntersectionObservations = false;
 }
 
diff --git a/layout/base/tests/browser.toml b/layout/base/tests/browser.toml
index a5b279145f..cc8df52306 100644
--- a/layout/base/tests/browser.toml
+++ b/layout/base/tests/browser.toml
@@ -3,6 +3,12 @@ prefs = [
   "layout.css.properties-and-values.enabled=true",
 ]
 
+["browser_animatedImageLeak.js"]
+skip-if = ["!debug"]
+support-files = [
+  "helper_animatedImageLeak.html"
+]
+
 ["browser_bug617076.js"]
 
 ["browser_bug1701027-1.js"]
diff --git a/layout/base/tests/browser_animatedImageLeak.js b/layout/base/tests/browser_animatedImageLeak.js
new file mode 100644
index 0000000000..2c34ed9d89
--- /dev/null
+++ b/layout/base/tests/browser_animatedImageLeak.js
@@ -0,0 +1,226 @@
+/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set sts=2 sw=2 et tw=80: */
+"use strict";
+
+requestLongerTimeout(4);
+
+/*
+ * This tests that when we have an animated image in a minimized window we
+ * don't leak.
+ * We've encountered this bug in 3 different ways:
+ * -bug 1830753 - images in top level chrome processes
+ *  (we avoid processing them due to their CompositorBridgeChild being paused)
+ * -bug 1839109 - images in content processes
+ *  (we avoid processing them due to their refresh driver being throttled, this
+ *   would also fix the above case)
+ * -bug 1875100 - images that are in a content iframe that is not the content
+ *  of a tab, so something like an extension iframe in the sidebar
+ *  (this was fixed by making the content of a tab declare that it manually
+ *   manages its activeness and having all other iframes inherit their
+ *   activeness from their parent)
+ * In order to hit this bug we require
+ * -the same image to be in a minimized window and in a non-mininmized window
+ *  so that the image is animated.
+ * -the animated image to go over the
+ *  image.animated.decode-on-demand.threshold-kb threshold so that we do not
+ *  keep all of its frames around (if we keep all its frame around then we
+ *  don't try to keep allocating frames and not freeing the old ones)
+ * -it has to be the same Image object in memory, not just the same uri
+ * Then the visible copy of the image keeps generating new frames, those frames
+ * get sent to the minimized copies of the image but they never get processed
+ * or marked displayed so they can never be freed/reused.
+ *
+ * Note that due to bug 1889840, in order to test this we can't use an image
+ * loaded at the top level (see the last point above). We must use an html page
+ * that contains the image.
+ */
+
+// this test is based in part on https://searchfox.org/mozilla-central/rev/c09764753ea40725eb50decad2c51edecbd33308/browser/components/extensions/test/browser/browser_ext_sidebarAction.js
+
+async function pushPrefs1() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["image.animated.decode-on-demand.threshold-kb", 1],
+      ["image.animated.decode-on-demand.batch-size", 2],
+    ],
+  });
+}
+
+async function openWindowsAndMinimize(taskToPerformBeforeMinimize) {
+  let wins = [null, null, null, null];
+  for (let i = 0; i < wins.length; i++) {
+    let win = await BrowserTestUtils.openNewBrowserWindow();
+    await win.delayedStartupPromise;
+    await taskToPerformBeforeMinimize(win);
+
+    // Leave the last window un-minimized.
+    if (i < wins.length - 1) {
+      let promiseSizeModeChange = BrowserTestUtils.waitForEvent(
+        win,
+        "sizemodechange"
+      );
+      win.minimize();
+      await promiseSizeModeChange;
+    }
+
+    wins[i] = win;
+  }
+  return wins;
+}
+
+async function pushPrefs2() {
+  // wait so that at least one frame of the animation has been shown while the
+  // below pref is not set so that the counter gets reset.
+  await new Promise(resolve => setTimeout(resolve, 500));
+
+  await SpecialPowers.pushPrefEnv({
+    set: [["gfx.testing.assert-render-textures-increase", 75]],
+  });
+}
+
+async function waitForEnoughFrames() {
+  // we want to wait for over 75 frames of the image, it has a delay of 200ms
+  // Windows debug test machines seem to animate at about 10 fps though
+  await new Promise(resolve => setTimeout(resolve, 20000));
+}
+
+async function closeWindows(wins) {
+  for (let i = 0; i < wins.length; i++) {
+    await BrowserTestUtils.closeWindow(wins[i]);
+  }
+}
+
+async function popPrefs() {
+  await SpecialPowers.popPrefEnv();
+  await SpecialPowers.popPrefEnv();
+}
+
+add_task(async () => {
+  async function runTest(theTestPath) {
+    await pushPrefs1();
+
+    let wins = await openWindowsAndMinimize(async function (win) {
+      let tab = await BrowserTestUtils.openNewForegroundTab(
+        win.gBrowser,
+        theTestPath
+      );
+    });
+
+    await pushPrefs2();
+
+    await waitForEnoughFrames();
+
+    await closeWindows(wins);
+
+    await popPrefs();
+
+    ok(true, "got here without assserting");
+  }
+
+  function fileURL(filename) {
+    let ifile = getChromeDir(getResolvedURI(gTestPath));
+    ifile.append(filename);
+    return Services.io.newFileURI(ifile).spec;
+  }
+
+  // This tests the image in content process case
+  await runTest(fileURL("helper_animatedImageLeak.html"));
+  // This tests the image in chrome process case
+  await runTest(getRootDirectory(gTestPath) + "helper_animatedImageLeak.html");
+});
+
+// Now we test the image in a sidebar loaded via an extension case.
+
+/*
+ * The data uri below is a 2kb apng that is 3000x200 with 22 frames with delay
+ * of 200ms, it just toggles the color of one pixel from black to red so it's
+ * tiny. We use the same data uri (although that is not important to this test)
+ * in helper_animatedImageLeak.html.
+ */
+
+/*
+ * This is just data to create a simple extension that creates a sidebar with
+ * an image in it.
+ */
+let extData = {
+  manifest: {
+    sidebar_action: {
+      default_panel: "sidebar.html",
+    },
+  },
+  useAddonManager: "temporary",
+
+  files: {
+    "sidebar.html": `
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="UTF-8">
+    <script src="sidebar.js"></script>
+  </head>
+  <body><p>Sidebar</p>
+  <img src="data:image/png;base64,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"/>
+  </body>
+</html>
+    `,
+
+    "sidebar.js": function () {
+      window.onload = () => {
+        browser.test.sendMessage("sidebar");
+      };
+    },
+  },
+};
+
+function getExtData(manifestUpdates = {}) {
+  return {
+    ...extData,
+    manifest: {
+      ...extData.manifest,
+      ...manifestUpdates,
+    },
+  };
+}
+
+async function sendMessage(ext, msg, data = undefined) {
+  ext.sendMessage({ msg, data });
+  await ext.awaitMessage("done");
+}
+
+add_task(async function sidebar_initial_install() {
+  await pushPrefs1();
+
+  ok(
+    document.getElementById("sidebar-box").hidden,
+    "sidebar box is not visible"
+  );
+
+  let extension = ExtensionTestUtils.loadExtension(getExtData());
+  await extension.startup();
+  await extension.awaitMessage("sidebar");
+
+  // Test sidebar is opened on install
+  ok(!document.getElementById("sidebar-box").hidden, "sidebar box is visible");
+
+  // the sidebar appears on all new windows automatically.
+  let wins = await openWindowsAndMinimize(async function (win) {
+    await extension.awaitMessage("sidebar");
+  });
+
+  await pushPrefs2();
+
+  await waitForEnoughFrames();
+
+  await extension.unload();
+  // Test that the sidebar was closed on unload.
+  ok(
+    document.getElementById("sidebar-box").hidden,
+    "sidebar box is not visible"
+  );
+
+  await closeWindows(wins);
+
+  await popPrefs();
+
+  ok(true, "got here without assserting");
+});
diff --git a/layout/base/tests/bug1896051-ref.html b/layout/base/tests/bug1896051-ref.html
new file mode 100644
index 0000000000..39b26f148d
--- /dev/null
+++ b/layout/base/tests/bug1896051-ref.html
@@ -0,0 +1,29 @@
+<!doctype html>
+<html class="reftest-wait">
+<script src="/tests/SimpleTest/EventUtils.js"></script>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<style>
+  textarea {
+    font: 13px / 1 monospace;
+    border: 1px solid;
+    padding: 0;
+    overflow: hidden;
+    resize: none;
+  }
+</style>
+<textarea rows=5>
+a
+b
+c
+d
+</textarea>
+<script>
+SimpleTest.waitForFocus(function() {
+  let textarea = document.querySelector("textarea");
+  textarea.focus();
+  textarea.selectionStart = textarea.selectionEnd = textarea.value.length;
+  setTimeout(() => {
+    document.documentElement.removeAttribute("class");
+  }, 0);
+});
+</script>
diff --git a/layout/base/tests/bug1896051.html b/layout/base/tests/bug1896051.html
new file mode 100644
index 0000000000..ba35339475
--- /dev/null
+++ b/layout/base/tests/bug1896051.html
@@ -0,0 +1,38 @@
+<!doctype html>
+<html class="reftest-wait">
+<script src="/tests/SimpleTest/EventUtils.js"></script>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<style>
+  textarea {
+    font: 13px / 1 monospace;
+    border: 1px solid;
+    padding: 0;
+    overflow: hidden;
+    resize: none;
+  }
+</style>
+<textarea rows=5>
+a
+b
+c
+d
+</textarea>
+<script>
+SimpleTest.waitForFocus(function() {
+  let textarea = document.querySelector("textarea");
+  textarea.focus();
+  if (navigator.platform.startsWith("Mac")) {
+    // On mac there is no page down key that moves the selection, afaict.
+    // (Fn+Arrow moves the scroll position but not selection).
+    // Do the next thing which would be something like Cmd+Down to move to the
+    // end. That tests a different code-path altogether, but for this test it
+    // doesn't matter.
+    synthesizeKey("KEY_ArrowDown", { metaKey: true });
+  } else {
+    synthesizeKey("KEY_PageDown");
+  }
+  setTimeout(() => {
+    document.documentElement.removeAttribute("class")
+  }, 0);
+});
+</script>
diff --git a/layout/base/tests/helper_animatedImageLeak.html b/layout/base/tests/helper_animatedImageLeak.html
new file mode 100644
index 0000000000..a5555f1fbb
--- /dev/null
+++ b/layout/base/tests/helper_animatedImageLeak.html
@@ -0,0 +1,10 @@
+<html>
+<!--
+ The data uri below is a 2kb apng that is 3000x200 with 22 frames with delay
+ of 200ms, it just toggles the color of one pixel from black to red so it's
+ tiny. We use the same data uri (although that is not important to this test)
+ in browser_animatedImageLeak.js.
+-->
+
+<img src="data:image/png;base64,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"/>
+</html>
diff --git a/layout/base/tests/helper_bug1733509.html b/layout/base/tests/helper_bug1733509.html
new file mode 100644
index 0000000000..4fbdacdb46
--- /dev/null
+++ b/layout/base/tests/helper_bug1733509.html
@@ -0,0 +1,30 @@
+<html>
+<script src="/tests/SimpleTest/EventUtils.js"></script>
+<script src="/tests/SimpleTest/paint_listener.js"></script>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<script type="text/javascript" src="/tests/gfx/layers/apz/test/mochitest/apz_test_utils.js"></script>
+<style>
+    body {
+        margin: 0;
+        padding: 20;
+        background-color: blueviolet;
+    }
+
+    button {
+        margin: 0;
+    }
+</style>
+
+<body>
+    <button id="btn">Click me</button>
+</body>
+
+<script>
+    // Silence SimpleTest warning about missing assertions by having it wait
+    // indefinitely. We don't need to give it an explicit finish because the
+    // entire window this test runs in will be closed after the main browser test
+    // finished.
+    SimpleTest.waitForExplicitFinish();
+</script>
+
+</html>
diff --git a/layout/base/tests/mochitest.toml b/layout/base/tests/mochitest.toml
index 24924809c0..f74c6b030d 100644
--- a/layout/base/tests/mochitest.toml
+++ b/layout/base/tests/mochitest.toml
@@ -247,6 +247,7 @@ support-files = ["file_dynamic_toolbar_max_height.html"]
 ["test_emulate_color_scheme.html"]
 
 ["test_event_target_radius.html"]
+support-files = ["helper_bug1733509.html"]
 skip-if = ["xorigin"] # JavaScript error: resource://specialpowers/SpecialPowersChild.sys.mjs, line 73: SecurityError: Permission denied to access property "windowUtils" on cross-origin object
 
 ["test_frame_reconstruction_body_table.html"]
@@ -558,6 +559,8 @@ support-files = [
   "bug1518339-2-ref.html",
   "bug1529492-1.html",
   "bug1529492-1-ref.html",
+  "bug1896051.html",
+  "bug1896051-ref.html",
   "chrome/blue-32x32.png",
 ]
 
diff --git a/layout/base/tests/test_event_target_radius.html b/layout/base/tests/test_event_target_radius.html
index caf046cf99..a1e8d9c16c 100644
--- a/layout/base/tests/test_event_target_radius.html
+++ b/layout/base/tests/test_event_target_radius.html
@@ -2,14 +2,19 @@
 <html id="html" style="height:100%">
 <!--
 https://bugzilla.mozilla.org/show_bug.cgi?id=780847
+https://bugzilla.mozilla.org/show_bug.cgi?id=1733509
 -->
 <head>
   <title>Test radii for mouse events</title>
-  <script src="/tests/SimpleTest/SimpleTest.js"></script>
   <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <script src="/tests/SimpleTest/paint_listener.js"></script>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="/tests/gfx/layers/apz/test/mochitest/apz_test_utils.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
   <style>
   .target { position:absolute; left:100px; top:100px; width:100px; height:100px; background:blue; }
+  .scaled { background: green; transform: scale(0.5); }
+  iframe { margin:0; padding:0; width:50; height:50; border:1px solid black; background:yellowgreen; }
   </style>
 </head>
 <body id="body" onload="setTimeout(startTest, 0)" style="margin:0; width:100%; height:100%; overflow:hidden">
@@ -73,6 +78,10 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=780847
    <div id="t13_touchlistener" style="width: 50px; height: 50px; background:red" ontouchend="x=1"></div>
    <div id="t13_notouchlistener" style="width: 50px; height: 50px; background:green"></div>
   </div>
+
+  <div id="t14" class="target scaled" hidden>
+    <iframe id="t14iframe"></iframe>
+  </div>
 </div>
 <pre id="test">
 <script type="application/javascript">
@@ -414,7 +423,50 @@ function testTouchable() {
   testTouch("t13", 10, 50 - (2*mm), "t13_touchlistener", "touch inside t13_touchlistener bottom edge");
   setShowing("t13", false);
 
-  endTest();
+  test4();
+}
+
+// https://bugzilla.mozilla.org/show_bug.cgi?id=1733509
+function test4() {
+  // Skip non-Fission for now because of bug 1890522
+  if (SpecialPowers.Services.appinfo.fissionAutostart) {
+    waitUntilApzStable().then(async () => doTest4()).then(endTest);
+  } else {
+    endTest();
+  }
+}
+
+async function doTest4() {
+  setShowing("t14", true);
+
+  let iframeURL = SimpleTest.getTestFileURL("helper_bug1733509.html");
+  // todo: Also perform this test for an in-process iframe
+  // once bug 1890522 is fixed.
+  const iframe = document.querySelector("#t14iframe");
+  iframeURL = iframeURL.replace(window.location.origin, "https://example.com");
+  await setupIframe(iframe, iframeURL);
+
+  var result = await SpecialPowers.spawn(iframe, [], async () => {
+    await content.wrappedJSObject.waitUntilApzStable();
+    var iframeEventTarget = null;
+    content.window.onmousedown = function (event) { iframeEventTarget = event.target; };
+    content.wrappedJSObject.synthesizeMouse(content.document.documentElement, 2, 2, {});
+    return iframeEventTarget && iframeEventTarget.id === "btn";
+  });
+
+  ok(result, "Failed to target button inside iframe");
+  setShowing("t14", false);
+}
+
+async function setupIframe(aIFrame, aURL) {
+  const iframeLoadPromise = promiseOneEvent(aIFrame, "load", null);
+  aIFrame.src = aURL;
+  await iframeLoadPromise;
+
+  await SpecialPowers.spawn(aIFrame, [], async () => {
+    await content.wrappedJSObject.waitUntilApzStable();
+    await SpecialPowers.contentTransformsReceived(content);
+  });
 }
 </script>
 </pre>
diff --git a/layout/base/tests/test_reftests_with_caret.html b/layout/base/tests/test_reftests_with_caret.html
index 3935380e5d..d134bd2eb9 100644
--- a/layout/base/tests/test_reftests_with_caret.html
+++ b/layout/base/tests/test_reftests_with_caret.html
@@ -112,6 +112,7 @@ var tests = [
     [ 'bug613807-1.html' , 'bug613807-1-ref.html' ] ,
     [ 'bug1082486-1.html', 'bug1082486-1-ref.html'] ,
     [ 'bug1082486-2.html', 'bug1082486-2-ref.html'] ,
+    [ 'bug1896051.html', 'bug1896051-ref.html'],
     // The following test cases uses mouse events. We need to make
     // AccessibleCaret unhide for them.
     function() {SpecialPowers.pushPrefEnv({'set': [['layout.accessiblecaret.hide_carets_for_mouse_input', false]]}, nextTest);} ,
-- 
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