diff --git a/dom/animation/Animation.cpp b/dom/animation/Animation.cpp
index 18aa340fd5b1..e7c52db5a7a6 100644
--- a/dom/animation/Animation.cpp
+++ b/dom/animation/Animation.cpp
@@ -183,11 +183,6 @@ void Animation::SetEffectNoUpdate(AnimationEffect* aEffect) {
     // Break links with the old effect and then drop it.
     RefPtr<AnimationEffect> oldEffect = mEffect;
     mEffect = nullptr;
-    if (IsPartialPrerendered()) {
-      if (KeyframeEffect* oldKeyframeEffect = oldEffect->AsKeyframeEffect()) {
-        oldKeyframeEffect->ResetPartialPrerendered();
-      }
-    }
     oldEffect->SetAnimation(nullptr);
 
     // The following will not do any notification because mEffect is null.
diff --git a/dom/animation/Animation.h b/dom/animation/Animation.h
index b5e50725e70b..503daa103f3e 100644
--- a/dom/animation/Animation.h
+++ b/dom/animation/Animation.h
@@ -421,30 +421,6 @@ class Animation : public DOMEventTargetHelper,
 
   int32_t& CachedChildIndexRef() { return mCachedChildIndex; }
 
-  void SetPartialPrerendered(uint64_t aIdOnCompositor) {
-    mIdOnCompositor = aIdOnCompositor;
-    mIsPartialPrerendered = true;
-  }
-  bool IsPartialPrerendered() const { return mIsPartialPrerendered; }
-  uint64_t IdOnCompositor() const { return mIdOnCompositor; }
-  /**
-   * Needs to be called when the pre-rendered animation is going to no longer
-   * run on the compositor.
-   */
-  void ResetPartialPrerendered() {
-    MOZ_ASSERT(mIsPartialPrerendered);
-    mIsPartialPrerendered = false;
-    mIdOnCompositor = 0;
-  }
-  /**
-   * Called via NotifyJankedAnimations IPC call from the compositor to update
-   * pre-rendered area on the main-thread.
-   */
-  void UpdatePartialPrerendered() {
-    ResetPartialPrerendered();
-    PostUpdate();
-  }
-
  protected:
   void SilentlySetCurrentTime(const TimeDuration& aNewCurrentTime);
   void CancelNoUpdate();
@@ -642,11 +618,6 @@ class Animation : public DOMEventTargetHelper,
   RefPtr<MicroTaskRunnable> mFinishNotificationTask;
 
   nsString mId;
-
- private:
-  // The id for this animaiton on the compositor.
-  uint64_t mIdOnCompositor = 0;
-  bool mIsPartialPrerendered = false;
 };
 
 }  // namespace dom
diff --git a/dom/animation/KeyframeEffect.cpp b/dom/animation/KeyframeEffect.cpp
index 243fcec60884..3a9deb3133b2 100644
--- a/dom/animation/KeyframeEffect.cpp
+++ b/dom/animation/KeyframeEffect.cpp
@@ -684,8 +684,6 @@ void KeyframeEffect::SetIsRunningOnCompositor(nsCSSPropertyID aProperty,
       // on the compositor we don't need a message.
       if (aIsRunning) {
         property.mPerformanceWarning.reset();
-      } else if (mAnimation && mAnimation->IsPartialPrerendered()) {
-        ResetPartialPrerendered();
       }
       return;
     }
@@ -709,39 +707,12 @@ void KeyframeEffect::SetIsRunningOnCompositor(
       }
     }
   }
-
-  if (!aIsRunning && mAnimation && mAnimation->IsPartialPrerendered()) {
-    ResetPartialPrerendered();
-  }
 }
 
 void KeyframeEffect::ResetIsRunningOnCompositor() {
   for (AnimationProperty& property : mProperties) {
     property.mIsRunningOnCompositor = false;
   }
-
-  if (mAnimation && mAnimation->IsPartialPrerendered()) {
-    ResetPartialPrerendered();
-  }
-}
-
-void KeyframeEffect::ResetPartialPrerendered() {
-  MOZ_ASSERT(mAnimation && mAnimation->IsPartialPrerendered());
-
-  nsIFrame* frame = GetPrimaryFrame();
-  if (!frame) {
-    return;
-  }
-
-  nsIWidget* widget = frame->GetNearestWidget();
-  if (!widget) {
-    return;
-  }
-
-  if (layers::LayerManager* layerManager = widget->GetLayerManager()) {
-    layerManager->RemovePartialPrerenderedAnimation(
-        mAnimation->IdOnCompositor(), mAnimation);
-  }
 }
 
 static bool IsSupportedPseudoForWebAnimation(PseudoStyleType aType) {
diff --git a/dom/animation/KeyframeEffect.h b/dom/animation/KeyframeEffect.h
index 2b9668781372..0d4620e9134e 100644
--- a/dom/animation/KeyframeEffect.h
+++ b/dom/animation/KeyframeEffect.h
@@ -274,8 +274,6 @@ class KeyframeEffect : public AnimationEffect {
                                 bool aIsRunning);
   void ResetIsRunningOnCompositor();
 
-  void ResetPartialPrerendered();
-
   // Returns true if this effect, applied to |aFrame|, contains properties
   // that mean we shouldn't run transform compositor animations on this element.
   //
diff --git a/dom/animation/test/mozilla/file_restyles.html b/dom/animation/test/mozilla/file_restyles.html
index ad3fbdfa713e..90544e11cca1 100644
--- a/dom/animation/test/mozilla/file_restyles.html
+++ b/dom/animation/test/mozilla/file_restyles.html
@@ -1,6 +1,5 @@
 <!doctype html>
 <head>
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
 <meta charset=utf-8>
 <title>Tests restyles caused by animations</title>
 <script>
@@ -1955,28 +1954,6 @@ waitForAllPaints(() => {
     await ensureElementRemoval(div);
   });
 
-  add_task(async function partial_prerendered_transform_animations() {
-    await SpecialPowers.pushPrefEnv({
-      set: [['layout.animation.prerender.partial', true]] });
-    const div = addDiv(null, { style: 'width: 10000px; height: 10000px;' });
-
-    const animation = div.animate(
-      // Use the same value both for `from` and `to` to avoid jank on the
-      // compositor.
-      { transform: ['rotate(0deg)', 'rotate(0deg)'] },
-      100 * MS_PER_SEC
-    );
-
-    await waitForAnimationReadyToRestyle(animation);
-
-    const markers = await observeStyling(5);
-    is(markers.length, 0,
-       'Transform animation with partial pre-rendered should never cause ' +
-       'restyles');
-
-    await ensureElementRemoval(div);
-  });
-
   add_task(async function restyling_on_create_animation() {
     const div = addDiv();
     const docShell = getDocShellForObservingRestylesForWindow(window);
diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
index 676e25b1e832..8d7fd4016d8c 100644
--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -2615,9 +2615,13 @@ nsDOMWindowUtils::ZoomToFocusedInput() {
     // Note that we only do this if the frame belongs to `presShell` (that is,
     // we still zoom in fixed elements in subdocuments, as they're not fixed to
     // the root content document).
-    if (frame->PresShell() == presShell &&
-        nsLayoutUtils::IsInPositionFixedSubtree(frame)) {
-      return true;
+    if (frame->PresShell() == presShell) {
+      for (; frame; frame = frame->GetParent()) {
+        if (frame->StyleDisplay()->mPosition == StylePositionProperty::Fixed &&
+            nsLayoutUtils::IsReallyFixedPos(frame)) {
+          return true;
+        }
+      }
     }
     return false;
   }();
diff --git a/dom/ipc/BrowserChild.cpp b/dom/ipc/BrowserChild.cpp
index 592ec8ade75a..78e4b3bde3ec 100644
--- a/dom/ipc/BrowserChild.cpp
+++ b/dom/ipc/BrowserChild.cpp
@@ -3105,14 +3105,6 @@ BrowserChild::OnHideTooltip() {
   return NS_OK;
 }
 
-void BrowserChild::NotifyJankedAnimations(
-    const nsTArray<uint64_t>& aJankedAnimations) {
-  MOZ_ASSERT(mPuppetWidget);
-  RefPtr<LayerManager> lm = mPuppetWidget->GetLayerManager();
-  MOZ_ASSERT(lm);
-  lm->UpdatePartialPrerenderedAnimations(aJankedAnimations);
-}
-
 mozilla::ipc::IPCResult BrowserChild::RecvRequestNotifyAfterRemotePaint() {
   // Get the CompositorBridgeChild instance for this content thread.
   CompositorBridgeChild* compositor = CompositorBridgeChild::Get();
diff --git a/dom/ipc/BrowserChild.h b/dom/ipc/BrowserChild.h
index 1ba50281aac7..a99eaceed1a3 100644
--- a/dom/ipc/BrowserChild.h
+++ b/dom/ipc/BrowserChild.h
@@ -509,8 +509,6 @@ class BrowserChild final : public nsMessageManagerScriptExecutor,
   void ReinitRendering();
   void ReinitRenderingForDeviceReset();
 
-  void NotifyJankedAnimations(const nsTArray<uint64_t>& aJankedAnimations);
-
   static inline BrowserChild* GetFrom(nsIDOMWindow* aWindow) {
     nsCOMPtr<nsIWebNavigation> webNav = do_GetInterface(aWindow);
     nsCOMPtr<nsIDocShell> docShell = do_QueryInterface(webNav);
diff --git a/gfx/layers/AnimationHelper.cpp b/gfx/layers/AnimationHelper.cpp
index e5221da7971e..648ac59414bc 100644
--- a/gfx/layers/AnimationHelper.cpp
+++ b/gfx/layers/AnimationHelper.cpp
@@ -5,13 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "AnimationHelper.h"
-#include "gfx2DGlue.h"                       // for ThebesRect
-#include "gfxLineSegment.h"                  // for gfxLineSegment
-#include "gfxPoint.h"                        // for gfxPoint
-#include "gfxQuad.h"                         // for gfxQuad
-#include "gfxRect.h"                         // for gfxRect
-#include "gfxUtils.h"                        // for gfxUtils::TransformToQuad
-#include "mozilla/ComputedTimingFunction.h"  // for ComputedTimingFunction
+#include "mozilla/ComputedTimingFunction.h"      // for ComputedTimingFunction
 #include "mozilla/dom/AnimationEffectBinding.h"  // for dom::FillMode
 #include "mozilla/dom/KeyframeEffectBinding.h"   // for dom::IterationComposite
 #include "mozilla/dom/KeyframeEffect.h"       // for dom::KeyFrameEffectReadOnly
@@ -321,9 +315,8 @@ static bool HasTransformLikeAnimations(const AnimationArray& aAnimations) {
 #endif
 
 AnimationStorageData AnimationHelper::ExtractAnimations(
-    const LayersId& aLayersId, const AnimationArray& aAnimations) {
+    const AnimationArray& aAnimations) {
   AnimationStorageData storageData;
-  storageData.mLayersId = aLayersId;
 
   nsCSSPropertyID prevID = eCSSProperty_UNKNOWN;
   PropertyAnimationGroup* currData = nullptr;
@@ -553,136 +546,5 @@ gfx::Matrix4x4 AnimationHelper::ServoAnimationValueToMatrix4x4(
       props, refBox, aTransformData.appUnitsPerDevPixel());
 }
 
-static uint8_t CollectOverflowedSideLines(const gfxQuad& aPrerenderedQuad,
-                                          SideBits aOverflowSides,
-                                          gfxLineSegment sideLines[4]) {
-  uint8_t count = 0;
-
-  if (aOverflowSides & SideBits::eTop) {
-    sideLines[count] = gfxLineSegment(aPrerenderedQuad.mPoints[0],
-                                      aPrerenderedQuad.mPoints[1]);
-    count++;
-  }
-  if (aOverflowSides & SideBits::eRight) {
-    sideLines[count] = gfxLineSegment(aPrerenderedQuad.mPoints[1],
-                                      aPrerenderedQuad.mPoints[2]);
-    count++;
-  }
-  if (aOverflowSides & SideBits::eBottom) {
-    sideLines[count] = gfxLineSegment(aPrerenderedQuad.mPoints[2],
-                                      aPrerenderedQuad.mPoints[3]);
-    count++;
-  }
-  if (aOverflowSides & SideBits::eLeft) {
-    sideLines[count] = gfxLineSegment(aPrerenderedQuad.mPoints[3],
-                                      aPrerenderedQuad.mPoints[0]);
-    count++;
-  }
-
-  return count;
-}
-
-enum RegionBits : uint8_t {
-  Inside = 0,
-  Left = (1 << 0),
-  Right = (1 << 1),
-  Bottom = (1 << 2),
-  Top = (1 << 3),
-};
-
-MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(RegionBits);
-
-static RegionBits GetRegionBitsForPoint(double aX, double aY,
-                                        const gfxRect& aClip) {
-  RegionBits result = RegionBits::Inside;
-  if (aX < aClip.X()) {
-    result |= RegionBits::Left;
-  } else if (aX > aClip.XMost()) {
-    result |= RegionBits::Right;
-  }
-
-  if (aY < aClip.Y()) {
-    result |= RegionBits::Bottom;
-  } else if (aY > aClip.YMost()) {
-    result |= RegionBits::Top;
-  }
-  return result;
-};
-
-// https://en.wikipedia.org/wiki/Cohen%E2%80%93Sutherland_algorithm
-static bool LineSegmentIntersectsClip(double aX0, double aY0, double aX1,
-                                      double aY1, const gfxRect& aClip) {
-  RegionBits b0 = GetRegionBitsForPoint(aX0, aY0, aClip);
-  RegionBits b1 = GetRegionBitsForPoint(aX1, aY1, aClip);
-
-  while (true) {
-    if (!(b0 | b1)) {
-      // Completely inside.
-      return true;
-    }
-
-    if (b0 & b1) {
-      // Completely outside.
-      return false;
-    }
-
-    double x, y;
-    // Choose an outside point.
-    RegionBits outsidePointBits = b1 > b0 ? b1 : b0;
-    if (outsidePointBits & RegionBits::Top) {
-      x = aX0 + (aX1 - aX0) * (aClip.YMost() - aY0) / (aY1 - aY0);
-      y = aClip.YMost();
-    } else if (outsidePointBits & RegionBits::Bottom) {
-      x = aX0 + (aX1 - aX0) * (aClip.Y() - aY0) / (aY1 - aY0);
-      y = aClip.Y();
-    } else if (outsidePointBits & RegionBits::Right) {
-      y = aY0 + (aY1 - aY0) * (aClip.XMost() - aX0) / (aX1 - aX0);
-      x = aClip.XMost();
-    } else if (outsidePointBits & RegionBits::Left) {
-      y = aY0 + (aY1 - aY0) * (aClip.X() - aX0) / (aX1 - aX0);
-      x = aClip.X();
-    }
-
-    if (outsidePointBits == b0) {
-      aX0 = x;
-      aY0 = y;
-      b0 = GetRegionBitsForPoint(aX0, aY0, aClip);
-    } else {
-      aX1 = x;
-      aY1 = y;
-      b1 = GetRegionBitsForPoint(aX1, aY1, aClip);
-    }
-  }
-  MOZ_ASSERT_UNREACHABLE();
-  return false;
-}
-
-// static
-bool AnimationHelper::ShouldBeJank(const LayoutDeviceIntRect& aPrerenderedRect,
-                                   SideBits aOverflowSides,
-                                   const gfx::Matrix4x4& aTransform,
-                                   const ParentLayerRect& aClipRect) {
-  if (aClipRect.IsEmpty()) {
-    return false;
-  }
-
-  gfxQuad prerenderedQuad = gfxUtils::TransformToQuad(
-      ThebesRect(aPrerenderedRect.ToUnknownRect()), aTransform);
-
-  gfxLineSegment sideLines[4];
-  uint8_t overflowSideCount =
-      CollectOverflowedSideLines(prerenderedQuad, aOverflowSides, sideLines);
-
-  gfxRect clipRect = ThebesRect(aClipRect.ToUnknownRect());
-  for (uint8_t j = 0; j < overflowSideCount; j++) {
-    if (LineSegmentIntersectsClip(sideLines[j].mStart.x, sideLines[j].mStart.y,
-                                  sideLines[j].mEnd.x, sideLines[j].mEnd.y,
-                                  clipRect)) {
-      return true;
-    }
-  }
-  return false;
-}
-
 }  // namespace layers
 }  // namespace mozilla
diff --git a/gfx/layers/AnimationHelper.h b/gfx/layers/AnimationHelper.h
index 224ad7106e14..df12f8d78c76 100644
--- a/gfx/layers/AnimationHelper.h
+++ b/gfx/layers/AnimationHelper.h
@@ -14,7 +14,6 @@
 #include "mozilla/webrender/WebRenderTypes.h"  // for RenderRoot
 #include "mozilla/TimeStamp.h"                 // for TimeStamp
 #include "mozilla/TimingParams.h"
-#include "mozilla/Types.h"  // for SideBits
 #include "mozilla/Variant.h"
 #include "X11UndefineNone.h"
 #include <unordered_map>
@@ -116,7 +115,7 @@ class AnimationHelper {
    * IPC boundary into something we can readily use for sampling.
    */
   static AnimationStorageData ExtractAnimations(
-      const LayersId& aLayersId, const AnimationArray& aAnimations);
+      const AnimationArray& aAnimations);
 
   /**
    * Get a unique id to represent the compositor animation between child
@@ -135,16 +134,6 @@ class AnimationHelper {
   static gfx::Matrix4x4 ServoAnimationValueToMatrix4x4(
       const nsTArray<RefPtr<RawServoAnimationValue>>& aValue,
       const TransformData& aTransformData, gfx::Path* aCachedMotionPath);
-
-  /**
-   * Returns true if |aPrerenderedRect| transformed by |aTransform| were
-   * composited in |aClipRect| there appears area which wasn't pre-rendered
-   * on the main-thread. I.e. checkerboarding.
-   */
-  static bool ShouldBeJank(const LayoutDeviceIntRect& aPrerenderedRect,
-                           SideBits aOverflowedSides,
-                           const gfx::Matrix4x4& aTransform,
-                           const ParentLayerRect& aClipRect);
 };
 
 }  // namespace layers
diff --git a/gfx/layers/AnimationInfo.cpp b/gfx/layers/AnimationInfo.cpp
index e4ae16003c4e..c0cea24c0fe8 100644
--- a/gfx/layers/AnimationInfo.cpp
+++ b/gfx/layers/AnimationInfo.cpp
@@ -81,12 +81,11 @@ void AnimationInfo::ClearAnimationsForNextTransaction() {
 }
 
 void AnimationInfo::SetCompositorAnimations(
-    const LayersId& aLayersId,
     const CompositorAnimations& aCompositorAnimations) {
   mCompositorAnimationsId = aCompositorAnimations.id();
 
-  mStorageData = AnimationHelper::ExtractAnimations(
-      aLayersId, aCompositorAnimations.animations());
+  mStorageData =
+      AnimationHelper::ExtractAnimations(aCompositorAnimations.animations());
 }
 
 bool AnimationInfo::StartPendingAnimations(const TimeStamp& aReadyTime) {
@@ -597,7 +596,7 @@ bool AnimationInfo::AddAnimationsForProperty(
     nsIFrame* aFrame, const EffectSet* aEffects,
     const nsTArray<RefPtr<dom::Animation>>& aCompositorAnimations,
     const Maybe<TransformData>& aTransformData, nsCSSPropertyID aProperty,
-    Send aSendFlag, LayerManager* aLayerManager) {
+    Send aSendFlag) {
   bool addedAny = false;
   // Add from first to last (since last overrides)
   for (dom::Animation* anim : aCompositorAnimations) {
@@ -643,94 +642,10 @@ bool AnimationInfo::AddAnimationsForProperty(
     AddAnimationForProperty(aFrame, *property, anim, aTransformData, aSendFlag);
     keyframeEffect->SetIsRunningOnCompositor(aProperty, true);
     addedAny = true;
-    if (aTransformData && aTransformData->partialPrerenderData() &&
-        aLayerManager) {
-      aLayerManager->AddPartialPrerenderedAnimation(GetCompositorAnimationsId(),
-                                                    anim);
-    }
   }
   return addedAny;
 }
 
-// Returns which pre-rendered area's sides are overflowed from the pre-rendered
-// rect.
-//
-// We don't need to make jank animations when we are going to composite the
-// area where there is no overflowed area even if it's outside of the
-// pre-rendered area.
-static SideBits GetOverflowedSides(const nsRect& aOverflow,
-                                   const nsRect& aPartialPrerenderArea) {
-  SideBits sides = SideBits::eNone;
-  if (aOverflow.X() < aPartialPrerenderArea.X()) {
-    sides |= SideBits::eLeft;
-  }
-  if (aOverflow.Y() < aPartialPrerenderArea.Y()) {
-    sides |= SideBits::eTop;
-  }
-  if (aOverflow.XMost() > aPartialPrerenderArea.XMost()) {
-    sides |= SideBits::eRight;
-  }
-  if (aOverflow.YMost() > aPartialPrerenderArea.YMost()) {
-    sides |= SideBits::eBottom;
-  }
-  return sides;
-}
-
-static ParentLayerRect GetClipRectForPartialPrerender(
-    const nsIFrame* aFrame, int32_t aDevPixelsToAppUnits) {
-  nsIScrollableFrame* scrollFrame = nsLayoutUtils::GetNearestScrollableFrame(
-      aFrame->GetParent(), nsLayoutUtils::SCROLLABLE_SAME_DOC |
-                               nsLayoutUtils::SCROLLABLE_INCLUDE_HIDDEN);
-  if (!scrollFrame) {
-    // If there is no suitable scrollable frame in the same document, use the
-    // root one.
-    scrollFrame = aFrame->PresShell()->GetRootScrollFrameAsScrollable();
-  }
-  MOZ_ASSERT(scrollFrame);
-
-  // We don't necessarily use nsLayoutUtils::CalculateCompositionSizeForFrame
-  // since this is a case where we don't use APZ at all.
-  return LayoutDeviceRect::FromAppUnits(scrollFrame->GetScrollPortRect(),
-                                        aDevPixelsToAppUnits) *
-         LayoutDeviceToLayerScale2D() * LayerToParentLayerScale();
-}
-
-static PartialPrerenderData GetPartialPrerenderData(
-    const nsIFrame* aFrame, const nsDisplayItem* aItem) {
-  const nsRect& partialPrerenderedRect = aItem->GetUntransformedPaintRect();
-  nsRect overflow = aFrame->GetVisualOverflowRectRelativeToSelf();
-
-  ScrollableLayerGuid::ViewID scrollId = ScrollableLayerGuid::NULL_SCROLL_ID;
-
-  if (nsLayoutUtils::AsyncPanZoomEnabled(const_cast<nsIFrame*>(aFrame))) {
-    const bool isInPositionFixed =
-        nsLayoutUtils::IsInPositionFixedSubtree(aFrame);
-    const ActiveScrolledRoot* asr = aItem->GetActiveScrolledRoot();
-    const nsIFrame* asrScrollableFrame =
-        asr ? do_QueryFrame(asr->mScrollableFrame) : nullptr;
-    if (!isInPositionFixed && asr &&
-        aFrame->PresContext() == asrScrollableFrame->PresContext()) {
-      scrollId = asr->GetViewId();
-    } else {
-      // Use the root scroll id in the same document if the target frame is in
-      // position:fixed subtree or there is no ASR or the ASR is in a different
-      // ancestor document.
-      scrollId =
-          nsLayoutUtils::ScrollIdForRootScrollFrame(aFrame->PresContext());
-    }
-  }
-
-  int32_t devPixelsToAppUnits = aFrame->PresContext()->AppUnitsPerDevPixel();
-
-  ParentLayerRect clipRect =
-      GetClipRectForPartialPrerender(aFrame, devPixelsToAppUnits);
-
-  return PartialPrerenderData{
-      LayoutDeviceIntRect::FromAppUnitsToInside(partialPrerenderedRect,
-                                                devPixelsToAppUnits),
-      GetOverflowedSides(overflow, partialPrerenderedRect), scrollId, clipRect};
-}
-
 enum class AnimationDataType {
   WithMotionPath,
   WithoutMotionPath,
@@ -791,14 +706,9 @@ static Maybe<TransformData> CreateAnimationData(
         motionPathOrigin, anchorAdjustment, RayReferenceData(aFrame)));
   }
 
-  Maybe<PartialPrerenderData> partialPrerenderData;
-  if (aItem && static_cast<nsDisplayTransform*>(aItem)->IsPartialPrerender()) {
-    partialPrerenderData = Some(GetPartialPrerenderData(aFrame, aItem));
-  }
-
-  return Some(TransformData(
-      origin, offsetToTransformOrigin, bounds, devPixelsToAppUnits, scaleX,
-      scaleY, hasPerspectiveParent, motionPathData, partialPrerenderData));
+  return Some(TransformData(origin, offsetToTransformOrigin, bounds,
+                            devPixelsToAppUnits, scaleX, scaleY,
+                            hasPerspectiveParent, motionPathData));
 }
 
 void AnimationInfo::AddNonAnimatingTransformLikePropertiesStyles(
@@ -876,11 +786,9 @@ void AnimationInfo::AddNonAnimatingTransformLikePropertiesStyles(
   }
 }
 
-void AnimationInfo::AddAnimationsForDisplayItem(nsIFrame* aFrame,
-                                                nsDisplayListBuilder* aBuilder,
-                                                nsDisplayItem* aItem,
-                                                DisplayItemType aType,
-                                                LayerManager* aLayerManager) {
+void AnimationInfo::AddAnimationsForDisplayItem(
+    nsIFrame* aFrame, nsDisplayListBuilder* aBuilder, nsDisplayItem* aItem,
+    DisplayItemType aType, layers::LayersBackend aLayersBackend) {
   Send sendFlag = !aBuilder ? Send::NextTransaction : Send::Immediate;
   if (sendFlag == Send::NextTransaction) {
     ClearAnimationsForNextTransaction();
@@ -925,7 +833,7 @@ void AnimationInfo::AddAnimationsForDisplayItem(nsIFrame* aFrame,
       compositorAnimations =
           GroupAnimationsByProperty(matchedAnimations, propertySet);
   Maybe<TransformData> transformData =
-      CreateAnimationData(aFrame, aItem, aType, aLayerManager->GetBackendType(),
+      CreateAnimationData(aFrame, aItem, aType, aLayersBackend,
                           compositorAnimations.has(eCSSProperty_offset_path) ||
                                   !aFrame->StyleDisplay()->mOffsetPath.IsNone()
                               ? AnimationDataType::WithMotionPath
@@ -945,9 +853,9 @@ void AnimationInfo::AddAnimationsForDisplayItem(nsIFrame* aFrame,
     // structure, 2) AddAnimationsForProperty() marks these animations as
     // running on the composiror, so CanThrottle() returns true for them, and
     // we avoid running these animations on the main thread.
-    bool added = AddAnimationsForProperty(aFrame, effects, iter.get().value(),
-                                          transformData, iter.get().key(),
-                                          sendFlag, aLayerManager);
+    bool added =
+        AddAnimationsForProperty(aFrame, effects, iter.get().value(),
+                                 transformData, iter.get().key(), sendFlag);
     if (added && transformData) {
       // Only copy TransformLikeMetaData in the first animation property.
       transformData.reset();
diff --git a/gfx/layers/AnimationInfo.h b/gfx/layers/AnimationInfo.h
index 9077834fd3aa..806de543366e 100644
--- a/gfx/layers/AnimationInfo.h
+++ b/gfx/layers/AnimationInfo.h
@@ -42,6 +42,7 @@ class Layer;
 class LayerManager;
 struct CompositorAnimationData;
 struct PropertyAnimationGroup;
+enum class LayersBackend : int8_t;
 
 class AnimationInfo final {
   typedef nsTArray<Animation> AnimationArray;
@@ -76,7 +77,6 @@ class AnimationInfo final {
   void ClearAnimations();
   void ClearAnimationsForNextTransaction();
   void SetCompositorAnimations(
-      const LayersId& aLayersId,
       const CompositorAnimations& aCompositorAnimations);
   bool StartPendingAnimations(const TimeStamp& aReadyTime);
   void TransferMutatedFlagToLayer(Layer* aLayer);
@@ -91,7 +91,6 @@ class AnimationInfo final {
   const Maybe<TransformData>& GetTransformData() const {
     return mStorageData.mTransformData;
   }
-  const LayersId& GetLayersId() const { return mStorageData.mLayersId; }
   bool ApplyPendingUpdatesForThisTransaction();
   bool HasTransformAnimation() const;
 
@@ -119,7 +118,7 @@ class AnimationInfo final {
   void AddAnimationsForDisplayItem(nsIFrame* aFrame,
                                    nsDisplayListBuilder* aBuilder,
                                    nsDisplayItem* aItem, DisplayItemType aType,
-                                   LayerManager* aLayerManager);
+                                   LayersBackend aLayersBackend);
 
  private:
   enum class Send {
@@ -136,7 +135,7 @@ class AnimationInfo final {
       nsIFrame* aFrame, const EffectSet* aEffects,
       const nsTArray<RefPtr<dom::Animation>>& aCompositorAnimations,
       const Maybe<TransformData>& aTransformData, nsCSSPropertyID aProperty,
-      Send aSendFlag, LayerManager* aLayerManager);
+      Send aSendFlag);
 
   void AddNonAnimatingTransformLikePropertiesStyles(
       const nsCSSPropertyIDSet& aNonAnimatingProperties, nsIFrame* aFrame,
diff --git a/gfx/layers/AnimationStorageData.h b/gfx/layers/AnimationStorageData.h
index 47e9981d2d3a..2d606ab87a97 100644
--- a/gfx/layers/AnimationStorageData.h
+++ b/gfx/layers/AnimationStorageData.h
@@ -10,7 +10,6 @@
 #include "mozilla/dom/Nullable.h"
 #include "mozilla/ComputedTimingFunction.h"  // for ComputedTimingFunction
 #include "mozilla/layers/LayersMessages.h"   // for TransformData, etc
-#include "mozilla/layers/LayersTypes.h"      // for LayersId
 #include "mozilla/TimeStamp.h"               // for TimeStamp
 #include "mozilla/TimingParams.h"
 #include "X11UndefineNone.h"
@@ -53,13 +52,6 @@ struct PropertyAnimation {
   float mPlaybackRate;
   dom::IterationCompositeOperation mIterationComposite;
   bool mIsNotPlaying;
-
-  void ResetLastCompositionValues() {
-    mCurrentIterationOnLastCompose = 0;
-    mSegmentIndexOnLastCompose = 0;
-    mProgressOnLastCompose.SetNull();
-    mPortionInSegmentOnLastCompose.SetNull();
-  }
 };
 
 struct PropertyAnimationGroup {
@@ -73,11 +65,6 @@ struct PropertyAnimationGroup {
     mAnimations.Clear();
     mBaseStyle = nullptr;
   }
-  void ResetLastCompositionValues() {
-    for (PropertyAnimation& animation : mAnimations) {
-      animation.ResetLastCompositionValues();
-    }
-  }
 };
 
 struct AnimationStorageData {
@@ -88,9 +75,6 @@ struct AnimationStorageData {
   Maybe<TransformData> mTransformData;
   // For motion path. We cached the gfx path for optimization.
   RefPtr<gfx::Path> mCachedMotionPath;
-  // This is used to communicate with the main-thread. E.g. to tell the fact
-  // that this animation needs to be pre-rendered again on the main-thread, etc.
-  LayersId mLayersId;
 
   AnimationStorageData() = default;
   AnimationStorageData(AnimationStorageData&& aOther) = default;
diff --git a/gfx/layers/CompositorAnimationStorage.cpp b/gfx/layers/CompositorAnimationStorage.cpp
index ee6a9bea664a..76deccb6ec1e 100644
--- a/gfx/layers/CompositorAnimationStorage.cpp
+++ b/gfx/layers/CompositorAnimationStorage.cpp
@@ -7,11 +7,8 @@
 #include "CompositorAnimationStorage.h"
 
 #include "AnimationHelper.h"
-#include "mozilla/layers/APZSampler.h"              // for APZSampler
-#include "mozilla/layers/CompositorBridgeParent.h"  // for CompositorBridgeParent
 #include "mozilla/layers/CompositorThread.h"       // for CompositorThreadHolder
 #include "mozilla/layers/LayerManagerComposite.h"  // for LayerComposite, etc
-#include "mozilla/layers/LayerMetricsWrapper.h"    // for LayerMetricsWrapper
 #include "mozilla/ServoStyleConsts.h"
 #include "mozilla/webrender/WebRenderTypes.h"  // for ToWrTransformProperty, etc
 #include "nsDeviceContext.h"                   // for AppUnitsPerCSSPixel
@@ -140,13 +137,12 @@ void CompositorAnimationStorage::SetAnimatedValue(uint64_t aId,
 }
 
 void CompositorAnimationStorage::SetAnimations(uint64_t aId,
-                                               const LayersId& aLayersId,
                                                const AnimationArray& aValue) {
   MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
   MutexAutoLock lock(mLock);
 
   mAnimations[aId] = std::make_unique<AnimationStorageData>(
-      AnimationHelper::ExtractAnimations(aLayersId, aValue));
+      AnimationHelper::ExtractAnimations(aValue));
 
   // If there is the last animated value, then we need to store the id to remove
   // the value if the new animation doesn't produce any animated data (i.e. in
@@ -289,81 +285,13 @@ static gfx::Matrix4x4 FrameTransformToTransformInDevice(
   return transformInDevice;
 }
 
-static Matrix4x4 GetTransformForPartialPrerender(
-    Layer* aLayer, const LayersId aLayersId,
-    const ScrollableLayerGuid::ViewID& aScrollId,
-    const RefPtr<APZSampler>& aSampler) {
-  MOZ_ASSERT(aLayer);
-
-  ParentLayerPoint translationByApz;
-  Matrix4x4 transform;
-
-  for (Layer* layer = aLayer; layer; layer = layer->GetParent()) {
-    if (layer->AsRefLayer()) {
-      MOZ_ASSERT(layer->AsRefLayer()->GetReferentId() == aLayersId);
-      break;
-    }
-
-    // Accumulate static transforms.
-    if (layer != aLayer) {
-      Matrix4x4 baseTransform = layer->GetBaseTransform();
-      if (ContainerLayer* container = layer->AsContainerLayer()) {
-        baseTransform.PostScale(container->GetPreXScale(),
-                                container->GetPreYScale(), 1);
-      }
-      transform *= baseTransform;
-    }
-
-    if (!layer->GetIsStickyPosition() && !layer->GetIsFixedPosition()) {
-      bool hasSameScrollId = false;
-      for (uint32_t i = 0; i < layer->GetScrollMetadataCount(); i++) {
-        // Factor APZ translation if there exists.
-        if (aSampler) {
-          LayerMetricsWrapper wrapper = LayerMetricsWrapper(layer, i);
-          AsyncTransform asyncTransform =
-              aSampler->GetCurrentAsyncTransform(wrapper, LayoutAndVisual);
-          translationByApz += asyncTransform.mTranslation;
-        }
-        if (layer->GetFrameMetrics(i).GetScrollId() == aScrollId) {
-          hasSameScrollId = true;
-        }
-      }
-
-      if (hasSameScrollId) {
-        break;
-      }
-    } else {
-      // Bug 1642547: Fix for position:sticky layers.
-    }
-  }
-
-  transform.PostTranslate(translationByApz.ToUnknownPoint());
-
-  return transform;
-}
-
-// Returns clip rect in the scroll frame's coordinate space.
-static ParentLayerRect GetClipRectForPartialPrerender(
-    const LayersId aLayersId, const PartialPrerenderData& aPartialPrerenderData,
-    const RefPtr<APZSampler>& aSampler) {
-  if (aSampler &&
-      aPartialPrerenderData.scrollId() != ScrollableLayerGuid::NULL_SCROLL_ID) {
-    return aSampler->GetCompositionBounds(aLayersId,
-                                          aPartialPrerenderData.scrollId());
-  }
-
-  return aPartialPrerenderData.clipRect();
-}
-
-bool CompositorAnimationStorage::ApplyAnimatedValue(
-    CompositorBridgeParent* aCompositorBridge, Layer* aLayer,
-    nsCSSPropertyID aProperty, AnimatedValue* aPreviousValue,
+void CompositorAnimationStorage::ApplyAnimatedValue(
+    Layer* aLayer, nsCSSPropertyID aProperty, AnimatedValue* aPreviousValue,
     const nsTArray<RefPtr<RawServoAnimationValue>>& aValues) {
   mLock.AssertCurrentThreadOwns();
 
   MOZ_ASSERT(!aValues.IsEmpty());
 
-  bool janked = false;
   HostLayer* layerCompositor = aLayer->AsHostLayer();
   switch (aProperty) {
     case eCSSProperty_background_color: {
@@ -410,31 +338,6 @@ bool CompositorAnimationStorage::ApplyAnimatedValue(
 
       gfx::Matrix4x4 transform = FrameTransformToTransformInDevice(
           frameTransform, aLayer, transformData);
-      if (const Maybe<PartialPrerenderData>& partialPrerenderData =
-              transformData.partialPrerenderData()) {
-        Matrix4x4 transformInClip = GetTransformForPartialPrerender(
-            aLayer, aLayer->GetAnimationLayersId(),
-            partialPrerenderData->scrollId(),
-            aCompositorBridge->GetAPZSampler());
-        transformInClip = transform * transformInClip;
-        ParentLayerRect clipRect = GetClipRectForPartialPrerender(
-            aLayer->GetAnimationLayersId(), *partialPrerenderData,
-            aCompositorBridge->GetAPZSampler());
-        if (AnimationHelper::ShouldBeJank(
-                partialPrerenderData->rect(),
-                partialPrerenderData->overflowedSides(), transformInClip,
-                clipRect)) {
-          // It's possible that we don't have the previous value and we don't
-          // either have enough area to composite in the first composition,
-          // e.g. a translate animation with a step timing function.  In such
-          // cases we use the base transform value which was calculated on the
-          // main-thread as a fallback value.
-          transform = aPreviousValue
-                          ? aPreviousValue->Transform().mTransformInDevSpace
-                          : aLayer->GetBaseTransform();
-          janked = true;
-        }
-      }
 
       layerCompositor->SetShadowBaseTransform(transform);
       layerCompositor->SetShadowTransformSetByAnimation(true);
@@ -449,12 +352,11 @@ bool CompositorAnimationStorage::ApplyAnimatedValue(
     default:
       MOZ_ASSERT_UNREACHABLE("Unhandled animated property");
   }
-  return !janked;
 }
 
-bool CompositorAnimationStorage::SampleAnimations(
-    Layer* aRoot, CompositorBridgeParent* aCompositorBridge,
-    TimeStamp aPreviousFrameTime, TimeStamp aCurrentFrameTime) {
+bool CompositorAnimationStorage::SampleAnimations(Layer* aRoot,
+                                                  TimeStamp aPreviousFrameTime,
+                                                  TimeStamp aCurrentFrameTime) {
   MutexAutoLock lock(mLock);
 
   bool isAnimating = false;
@@ -467,8 +369,6 @@ bool CompositorAnimationStorage::SampleAnimations(
     }
   });
 
-  std::unordered_map<LayersId, nsTArray<uint64_t>, LayersId::HashFn> janked;
-
   ForEachNode<ForwardIterator>(aRoot, [&](Layer* layer) {
     auto& propertyAnimationGroups = layer->GetPropertyAnimationGroups();
     if (propertyAnimationGroups.IsEmpty()) {
@@ -493,37 +393,8 @@ bool CompositorAnimationStorage::SampleAnimations(
         // We assume all transform like properties (on the same frame) live in
         // a single same layer, so using the transform data of the last element
         // should be fine.
-        if (!ApplyAnimatedValue(aCompositorBridge, layer,
-                                lastPropertyAnimationGroup.mProperty,
-                                previousValue, animationValues)) {
-          // Reset the last composition values in cases of jank so that we will
-          // never mis-compare in a sanity check in the case of
-          // SampleResult::Skipped below in this function.
-          //
-          // An example;
-          // a translateX(0px) -> translateX(100px) animation with step(2,start)
-          // and if the animation janked at translateX(50px) and in a later
-          // frame if the calculated transform value is going to be still
-          // translateX(50px) (i.e. at the same timing portion calculated by the
-          // step timing function), we skip sampling. That's correct ideally.
-          // But we have an assertion to do a sanity check for the skip sampling
-          // case that the check compares the calculated value translateX(50px)
-          // with the previous composited value. In this case the previous
-          // composited value is translateX(0px).
-          //
-          // NOTE: Ideally we shouldn't update the last composition values when
-          // we met janks, but it's quite hard to tell whether the jank will
-          // happen or not when we calculate each transform like properties'
-          // value (i.e. when we set the last composition value) since janks are
-          // caused by a result of the combinations of all transform like
-          // properties (e.g. `transform: translateX(50px)` and
-          // `translate: -50px` results `translateX(0px)`.
-          for (PropertyAnimationGroup& group : propertyAnimationGroups) {
-            group.ResetLastCompositionValues();
-          }
-          janked[layer->GetAnimationLayersId()].AppendElement(
-              layer->GetCompositorAnimationsId());
-        }
+        ApplyAnimatedValue(layer, lastPropertyAnimationGroup.mProperty,
+                           previousValue, animationValues);
         break;
       case AnimationHelper::SampleResult::Skipped:
         switch (lastPropertyAnimationGroup.mProperty) {
@@ -605,10 +476,6 @@ bool CompositorAnimationStorage::SampleAnimations(
     }
   });
 
-  if (!janked.empty()) {
-    aCompositorBridge->NotifyJankedAnimations(janked);
-  }
-
   return isAnimating;
 }
 
diff --git a/gfx/layers/CompositorAnimationStorage.h b/gfx/layers/CompositorAnimationStorage.h
index c04754b81871..87ad500dd41c 100644
--- a/gfx/layers/CompositorAnimationStorage.h
+++ b/gfx/layers/CompositorAnimationStorage.h
@@ -18,7 +18,6 @@ namespace mozilla {
 namespace layers {
 class Animation;
 class Layers;
-class CompositorBridgeParent;
 
 typedef nsTArray<layers::Animation> AnimationArray;
 
@@ -123,8 +122,7 @@ class CompositorAnimationStorage final {
   /**
    * Set the animations based on the unique id
    */
-  void SetAnimations(uint64_t aId, const LayersId& aLayersId,
-                     const AnimationArray& aAnimations);
+  void SetAnimations(uint64_t aId, const AnimationArray& aAnimations);
 
   /**
    * Sample animation based the given timestamps and store them in this
@@ -146,8 +144,7 @@ class CompositorAnimationStorage final {
    *
    * Note: This is called only by non WebRender.
    */
-  bool SampleAnimations(Layer* aRoot, CompositorBridgeParent* aCompositorBridge,
-                        TimeStamp aPreviousFrameTime,
+  bool SampleAnimations(Layer* aRoot, TimeStamp aPreviousFrameTime,
                         TimeStamp aCurrentFrameTime);
 
   bool HasAnimations() const;
@@ -189,9 +186,8 @@ class CompositorAnimationStorage final {
   void SetAnimatedValue(uint64_t aId, AnimatedValue* aPreviousValue,
                         nscolor aColor);
 
-  bool ApplyAnimatedValue(
-      CompositorBridgeParent* aCompositorBridge, Layer* aLayer,
-      nsCSSPropertyID aProperty, AnimatedValue* aPreviousValue,
+  void ApplyAnimatedValue(
+      Layer* aLayer, nsCSSPropertyID aProperty, AnimatedValue* aPreviousValue,
       const nsTArray<RefPtr<RawServoAnimationValue>>& aValues);
 
   void Clear();
diff --git a/gfx/layers/Layers.cpp b/gfx/layers/Layers.cpp
index ded24ce95354..152345671d80 100644
--- a/gfx/layers/Layers.cpp
+++ b/gfx/layers/Layers.cpp
@@ -24,7 +24,6 @@
 #include "mozilla/StaticPrefs_layers.h"
 #include "mozilla/Telemetry.h"  // for Accumulate
 #include "mozilla/ToString.h"
-#include "mozilla/dom/Animation.h"              // for dom::Animation
 #include "mozilla/gfx/2D.h"                     // for DrawTarget
 #include "mozilla/gfx/BaseSize.h"               // for BaseSize
 #include "mozilla/gfx/Matrix.h"                 // for Matrix4x4
@@ -168,37 +167,6 @@ void LayerManager::PayloadPresented() {
   RecordCompositionPayloadsPresented(mPayload);
 }
 
-void LayerManager::AddPartialPrerenderedAnimation(
-    uint64_t aCompositorAnimationId, dom::Animation* aAnimation) {
-  mPartialPrerenderedAnimations.Put(aCompositorAnimationId, RefPtr{aAnimation});
-  aAnimation->SetPartialPrerendered(aCompositorAnimationId);
-}
-
-void LayerManager::RemovePartialPrerenderedAnimation(
-    uint64_t aCompositorAnimationId, dom::Animation* aAnimation) {
-  MOZ_ASSERT(aAnimation);
-#ifdef DEBUG
-  RefPtr<dom::Animation> animation;
-  if (mPartialPrerenderedAnimations.Remove(aCompositorAnimationId,
-                                           getter_AddRefs(animation))) {
-    MOZ_ASSERT(aAnimation == animation.get());
-  }
-#else
-  mPartialPrerenderedAnimations.Remove(aCompositorAnimationId);
-#endif
-  aAnimation->ResetPartialPrerendered();
-}
-
-void LayerManager::UpdatePartialPrerenderedAnimations(
-    const nsTArray<uint64_t>& aJankedAnimations) {
-  for (uint64_t id : aJankedAnimations) {
-    RefPtr<dom::Animation> animation;
-    if (mPartialPrerenderedAnimations.Remove(id, getter_AddRefs(animation))) {
-      animation->UpdatePartialPrerendered();
-    }
-  }
-}
-
 //--------------------------------------------------
 // Layer
 
@@ -219,13 +187,12 @@ Layer::Layer(LayerManager* aManager, void* aImplData)
 Layer::~Layer() = default;
 
 void Layer::SetCompositorAnimations(
-    const LayersId& aLayersId,
     const CompositorAnimations& aCompositorAnimations) {
   MOZ_LAYERS_LOG_IF_SHADOWABLE(
       this, ("Layer::Mutated(%p) SetCompositorAnimations with id=%" PRIu64,
              this, mAnimationInfo.GetCompositorAnimationsId()));
 
-  mAnimationInfo.SetCompositorAnimations(aLayersId, aCompositorAnimations);
+  mAnimationInfo.SetCompositorAnimations(aCompositorAnimations);
 
   Mutated();
 }
diff --git a/gfx/layers/Layers.h b/gfx/layers/Layers.h
index 7e16f21e8d73..f3cf60504c1a 100644
--- a/gfx/layers/Layers.h
+++ b/gfx/layers/Layers.h
@@ -28,7 +28,6 @@
 #include "mozilla/RefPtr.h"                // for already_AddRefed
 #include "mozilla/TimeStamp.h"             // for TimeStamp, TimeDuration
 #include "mozilla/UniquePtr.h"             // for UniquePtr
-#include "mozilla/dom/Animation.h"         // for dom::Animation
 #include "mozilla/gfx/BaseMargin.h"        // for BaseMargin
 #include "mozilla/gfx/BasePoint.h"         // for BasePoint
 #include "mozilla/gfx/Point.h"             // for IntSize
@@ -47,7 +46,6 @@
 #include "nsDebug.h"                 // for NS_ASSERTION
 #include "nsISupportsImpl.h"         // for Layer::Release, etc
 #include "nsRect.h"                  // for mozilla::gfx::IntRect
-#include "nsRefPtrHashtable.h"       // for nsRefPtrHashtable
 #include "nsRegion.h"                // for nsIntRegion
 #include "nsString.h"                // for nsCString
 #include "nsTArray.h"                // for nsTArray
@@ -258,7 +256,6 @@ class LayerManager : public FrameRecorder {
     mDestroyed = true;
     mUserData.Destroy();
     mRoot = nullptr;
-    mPartialPrerenderedAnimations.Clear();
   }
   bool IsDestroyed() { return mDestroyed; }
 
@@ -756,13 +753,6 @@ class LayerManager : public FrameRecorder {
 
   void SetContainsSVG(bool aContainsSVG) { mContainsSVG = aContainsSVG; }
 
-  void AddPartialPrerenderedAnimation(uint64_t aCompositorAnimationId,
-                                      dom::Animation* aAnimation);
-  void RemovePartialPrerenderedAnimation(uint64_t aCompositorAnimationId,
-                                         dom::Animation* aAnimation);
-  void UpdatePartialPrerenderedAnimations(
-      const nsTArray<uint64_t>& aJankedAnimations);
-
  protected:
   RefPtr<Layer> mRoot;
   gfx::UserData mUserData;
@@ -800,12 +790,6 @@ class LayerManager : public FrameRecorder {
   // IMPORTANT: Clients should take care to clear this or risk it slowly
   // growing out of control.
   nsTArray<CompositionPayload> mPayload;
-  // Transform animations which are not fully pre-rendered because it's on a
-  // large frame.  We need to update the pre-rendered area once after we tried
-  // to composite area which is outside of the pre-rendered area on the
-  // compositor.
-  nsRefPtrHashtable<nsUint64HashKey, dom::Animation>
-      mPartialPrerenderedAnimations;
 
  public:
   /*
@@ -832,7 +816,7 @@ class LayerManager : public FrameRecorder {
 class Layer {
   NS_INLINE_DECL_REFCOUNTING(Layer)
 
-  using AnimationArray = nsTArray<layers::Animation>;
+  typedef nsTArray<Animation> AnimationArray;
 
  public:
   // Keep these in alphabetical order
@@ -1270,7 +1254,6 @@ class Layer {
   // This is only called when the layer tree is updated. Do not call this from
   // layout code.  To add an animation to this layer, use AddAnimation.
   void SetCompositorAnimations(
-      const LayersId& aLayersId,
       const CompositorAnimations& aCompositorAnimations);
   // Go through all animations in this layer and its children and, for
   // any animations with a null start time, update their start time such
@@ -1369,7 +1352,7 @@ class Layer {
   bool HasScrollableFrameMetrics() const;
   bool IsScrollableWithoutContent() const;
   const EventRegions& GetEventRegions() const { return mEventRegions; }
-  ContainerLayer* GetParent() const { return mParent; }
+  ContainerLayer* GetParent() { return mParent; }
   Layer* GetNextSibling() {
     if (mNextSibling) {
       mNextSibling->CheckCanary();
@@ -1485,9 +1468,6 @@ class Layer {
   const Maybe<TransformData>& GetTransformData() const {
     return mAnimationInfo.GetTransformData();
   }
-  const LayersId& GetAnimationLayersId() const {
-    return mAnimationInfo.GetLayersId();
-  }
 
   Maybe<uint64_t> GetAnimationGeneration() const {
     return mAnimationInfo.GetAnimationGeneration();
diff --git a/gfx/layers/apz/public/APZSampler.h b/gfx/layers/apz/public/APZSampler.h
index bad0e051ae15..565590e4a336 100644
--- a/gfx/layers/apz/public/APZSampler.h
+++ b/gfx/layers/apz/public/APZSampler.h
@@ -98,14 +98,6 @@ class APZSampler {
   void MarkAsyncTransformAppliedToContent(const LayerMetricsWrapper& aLayer);
   bool HasUnusedAsyncTransform(const LayerMetricsWrapper& aLayer);
 
-  /**
-   * Returns the composition bounds of the APZC correspoinding to the pair of
-   * |aLayersId| and |aScrollId|.
-   */
-  ParentLayerRect GetCompositionBounds(
-      const LayersId& aLayersId,
-      const ScrollableLayerGuid::ViewID& aScrollId) const;
-
   ScrollableLayerGuid GetGuid(const LayerMetricsWrapper& aLayer);
 
   ScreenMargin GetGeckoFixedLayerMargins() const;
diff --git a/gfx/layers/apz/src/APZSampler.cpp b/gfx/layers/apz/src/APZSampler.cpp
index db6d0f26a016..d38e1c095a8d 100644
--- a/gfx/layers/apz/src/APZSampler.cpp
+++ b/gfx/layers/apz/src/APZSampler.cpp
@@ -212,28 +212,6 @@ ScreenMargin APZSampler::GetGeckoFixedLayerMargins() const {
   return mApz->GetGeckoFixedLayerMargins();
 }
 
-ParentLayerRect APZSampler::GetCompositionBounds(
-    const LayersId& aLayersId,
-    const ScrollableLayerGuid::ViewID& aScrollId) const {
-  // This function can get called on the compositor in case of non WebRender
-  // get called on the sampler thread in case of WebRender.
-  AssertOnSamplerThread();
-
-  RefPtr<AsyncPanZoomController> apzc =
-      mApz->GetTargetAPZC(aLayersId, aScrollId);
-  if (!apzc) {
-    // On WebRender it's possible that this function can get called even after
-    // the target APZC has been already destroyed because destroying the
-    // animation which triggers this function call is basically processed later
-    // than the APZC one, i.e. queue mCompositorAnimationsToDelete in
-    // WebRenderBridgeParent and then remove them in
-    // WebRenderBridgeParent::RemoveEpochDataPriorTo.
-    return ParentLayerRect();
-  }
-
-  return apzc->GetCompositionBounds();
-}
-
 void APZSampler::AssertOnSamplerThread() const {
   if (APZThreadUtils::GetThreadAssertionsEnabled()) {
     MOZ_ASSERT(IsSamplerThread());
diff --git a/gfx/layers/composite/AsyncCompositionManager.cpp b/gfx/layers/composite/AsyncCompositionManager.cpp
index 80c51781e92b..1f83384c55ac 100644
--- a/gfx/layers/composite/AsyncCompositionManager.cpp
+++ b/gfx/layers/composite/AsyncCompositionManager.cpp
@@ -560,8 +560,8 @@ bool AsyncCompositionManager::SampleAnimations(Layer* aLayer,
       mCompositorBridge->GetAnimationStorage();
   MOZ_ASSERT(storage);
 
-  return storage->SampleAnimations(aLayer, mCompositorBridge,
-                                   mPreviousFrameTimeStamp, aCurrentFrameTime);
+  return storage->SampleAnimations(aLayer, mPreviousFrameTimeStamp,
+                                   aCurrentFrameTime);
 }
 
 void AsyncCompositionManager::RecordShadowTransforms(Layer* aLayer) {
diff --git a/gfx/layers/ipc/CompositorBridgeChild.cpp b/gfx/layers/ipc/CompositorBridgeChild.cpp
index 331b4f15bf31..717d3d213d15 100644
--- a/gfx/layers/ipc/CompositorBridgeChild.cpp
+++ b/gfx/layers/ipc/CompositorBridgeChild.cpp
@@ -847,21 +847,6 @@ mozilla::ipc::IPCResult CompositorBridgeChild::RecvCompositorOptionsChanged(
   return IPC_OK();
 }
 
-mozilla::ipc::IPCResult CompositorBridgeChild::RecvNotifyJankedAnimations(
-    const LayersId& aLayersId, nsTArray<uint64_t>&& aJankedAnimations) {
-  if (mLayerManager) {
-    MOZ_ASSERT(!aLayersId.IsValid());
-    mLayerManager->UpdatePartialPrerenderedAnimations(aJankedAnimations);
-  } else if (aLayersId.IsValid()) {
-    RefPtr<dom::BrowserChild> child = dom::BrowserChild::GetFrom(aLayersId);
-    if (child) {
-      child->NotifyJankedAnimations(aJankedAnimations);
-    }
-  }
-
-  return IPC_OK();
-}
-
 void CompositorBridgeChild::HoldUntilCompositableRefReleasedIfNecessary(
     TextureClient* aClient) {
   if (!aClient) {
diff --git a/gfx/layers/ipc/CompositorBridgeChild.h b/gfx/layers/ipc/CompositorBridgeChild.h
index 1eac9c6d4a8d..f8d9f0fdfebb 100644
--- a/gfx/layers/ipc/CompositorBridgeChild.h
+++ b/gfx/layers/ipc/CompositorBridgeChild.h
@@ -111,9 +111,6 @@ class CompositorBridgeChild final : public PCompositorBridgeChild,
 
   mozilla::ipc::IPCResult RecvHideAllPlugins(const uintptr_t& aParentWidget);
 
-  mozilla::ipc::IPCResult RecvNotifyJankedAnimations(
-      const LayersId& aLayersId, nsTArray<uint64_t>&& aJankedAnimations);
-
   PTextureChild* AllocPTextureChild(
       const SurfaceDescriptor& aSharedData, const ReadLockDescriptor& aReadLock,
       const LayersBackend& aLayersBackend, const TextureFlags& aFlags,
diff --git a/gfx/layers/ipc/CompositorBridgeParent.cpp b/gfx/layers/ipc/CompositorBridgeParent.cpp
index 05d147c75b39..446d341ca8b7 100644
--- a/gfx/layers/ipc/CompositorBridgeParent.cpp
+++ b/gfx/layers/ipc/CompositorBridgeParent.cpp
@@ -1375,33 +1375,6 @@ CompositorAnimationStorage* CompositorBridgeParent::GetAnimationStorage() {
   return mAnimationStorage;
 }
 
-void CompositorBridgeParent::NotifyJankedAnimations(
-    const JankedAnimations& aJankedAnimations) {
-  MOZ_ASSERT(!aJankedAnimations.empty());
-
-  if (StaticPrefs::layout_animation_prerender_partial_jank()) {
-    return;
-  }
-
-  for (const auto& entry : aJankedAnimations) {
-    const LayersId& layersId = entry.first;
-    const nsTArray<uint64_t>& animations = entry.second;
-    if (layersId == mRootLayerTreeID) {
-      if (mLayerManager) {
-        Unused << SendNotifyJankedAnimations(LayersId{0}, animations);
-      }
-      // It unlikely happens multiple processes have janked animations at same
-      // time, so it should be fine with enumerating sIndirectLayerTrees every
-      // time.
-    } else if (const LayerTreeState* state = GetIndirectShadowTree(layersId)) {
-      if (ContentCompositorBridgeParent* cpcp =
-              state->mContentCompositorBridgeParent) {
-        Unused << cpcp->SendNotifyJankedAnimations(layersId, animations);
-      }
-    }
-  }
-}
-
 mozilla::ipc::IPCResult CompositorBridgeParent::RecvGetFrameUniformity(
     FrameUniformityData* aOutData) {
   mCompositionManager->GetFrameUniformity(aOutData);
diff --git a/gfx/layers/ipc/CompositorBridgeParent.h b/gfx/layers/ipc/CompositorBridgeParent.h
index 96d6cfa0229e..f83517b07668 100644
--- a/gfx/layers/ipc/CompositorBridgeParent.h
+++ b/gfx/layers/ipc/CompositorBridgeParent.h
@@ -408,9 +408,6 @@ class CompositorBridgeParent final : public CompositorBridgeParentBase,
   void ApplyAsyncProperties(LayerTransactionParent* aLayerTree,
                             TransformsToSkip aSkip) override;
   CompositorAnimationStorage* GetAnimationStorage();
-  using JankedAnimations =
-      std::unordered_map<LayersId, nsTArray<uint64_t>, LayersId::HashFn>;
-  void NotifyJankedAnimations(const JankedAnimations& aJankedAnimations);
   void SetTestAsyncScrollOffset(const LayersId& aLayersId,
                                 const ScrollableLayerGuid::ViewID& aScrollId,
                                 const CSSPoint& aPoint) override;
diff --git a/gfx/layers/ipc/LayerTransactionParent.cpp b/gfx/layers/ipc/LayerTransactionParent.cpp
index d9213a339497..0739bce90435 100644
--- a/gfx/layers/ipc/LayerTransactionParent.cpp
+++ b/gfx/layers/ipc/LayerTransactionParent.cpp
@@ -524,7 +524,7 @@ bool LayerTransactionParent::SetLayerAttributes(
   } else {
     layer->SetMaskLayer(nullptr);
   }
-  layer->SetCompositorAnimations(mId, common.compositorAnimations());
+  layer->SetCompositorAnimations(common.compositorAnimations());
   // Clean up the Animations by id in the CompositorAnimationStorage
   // if there are no active animations on the layer
   if (mAnimStorage && layer->GetCompositorAnimationsId() &&
diff --git a/gfx/layers/ipc/LayersMessages.ipdlh b/gfx/layers/ipc/LayersMessages.ipdlh
index 44ca36e644fa..feae4abdd9dc 100644
--- a/gfx/layers/ipc/LayersMessages.ipdlh
+++ b/gfx/layers/ipc/LayersMessages.ipdlh
@@ -20,7 +20,6 @@ using struct mozilla::gfx::Point from "mozilla/gfx/Point.h";
 using struct mozilla::gfx::Point3D from "mozilla/gfx/Point.h";
 using mozilla::gfx::IntPoint from "mozilla/gfx/Point.h";
 using class mozilla::gfx::Matrix4x4 from "mozilla/gfx/Matrix.h";
-using class mozilla::SideBits from "mozilla/gfx/Types.h";
 using nscolor from "nsColor.h";
 using nscoord from "nsCoord.h";
 using struct nsRect from "nsRect.h";
@@ -39,10 +38,8 @@ using mozilla::LayerCoord from "Units.h";
 using mozilla::LayerSize from "Units.h";
 using mozilla::LayerRect from "Units.h";
 using mozilla::LayerIntSize from "Units.h";
-using mozilla::LayerIntRect from "Units.h";
 using mozilla::LayerIntRegion from "Units.h";
 using mozilla::ParentLayerIntRect from "Units.h";
-using mozilla::ParentLayerRect from "Units.h";
 using mozilla::LayoutDeviceIntRect from "Units.h";
 using mozilla::layers::ScaleMode from "mozilla/layers/LayersTypes.h";
 using mozilla::layers::EventRegions from "mozilla/layers/LayersTypes.h";
@@ -156,17 +153,6 @@ struct MotionPathData {
   RayReferenceData rayReferenceData;
 };
 
-struct PartialPrerenderData {
-  LayoutDeviceIntRect rect;
-  SideBits overflowedSides;
-  // the scroll id of the nearest scrollable frame of this partial prerender
-  // data.
-  ViewID scrollId;
-  // The clip rectangle of the nearest scrollable frame.
-  // NOTE: This should be used only for fallback cases where APZ is not enabled.
-  ParentLayerRect clipRect;
-};
-
 // Transforms need extra information to correctly convert the list of transform
 // functions to a Matrix4x4 that can be applied directly to the layer.
 struct TransformData {
@@ -182,7 +168,6 @@ struct TransformData {
   // True if the parent has perspective transform
   bool hasPerspectiveParent;
   MotionPathData? motionPathData;
-  PartialPrerenderData? partialPrerenderData;
 };
 
 struct Animation {
diff --git a/gfx/layers/ipc/PCompositorBridge.ipdl b/gfx/layers/ipc/PCompositorBridge.ipdl
index 9d4021e99a63..2a730d8a65c7 100644
--- a/gfx/layers/ipc/PCompositorBridge.ipdl
+++ b/gfx/layers/ipc/PCompositorBridge.ipdl
@@ -161,8 +161,6 @@ child:
 
   async CompositorOptionsChanged(LayersId id, CompositorOptions newOptions);
 
-  async NotifyJankedAnimations(LayersId id, uint64_t[] aJankedAnimations);
-
 parent:
   async __delete__();
 
diff --git a/gfx/layers/wr/OMTASampler.cpp b/gfx/layers/wr/OMTASampler.cpp
index 7f44b6a41267..71543bbcc046 100644
--- a/gfx/layers/wr/OMTASampler.cpp
+++ b/gfx/layers/wr/OMTASampler.cpp
@@ -154,12 +154,11 @@ void OMTASampler::SampleForTesting(const Maybe<TimeStamp>& aTestingSampleTime) {
 }
 
 void OMTASampler::SetAnimations(
-    uint64_t aId, const LayersId& aLayersId,
-    const nsTArray<layers::Animation>& aAnimations) {
+    uint64_t aId, const nsTArray<layers::Animation>& aAnimations) {
   MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
   MutexAutoLock lock(mStorageLock);
 
-  mAnimStorage->SetAnimations(aId, aLayersId, aAnimations);
+  mAnimStorage->SetAnimations(aId, aAnimations);
 }
 
 bool OMTASampler::HasAnimations() const {
diff --git a/gfx/layers/wr/OMTASampler.h b/gfx/layers/wr/OMTASampler.h
index 5e30a6e63f48..657ba4039337 100644
--- a/gfx/layers/wr/OMTASampler.h
+++ b/gfx/layers/wr/OMTASampler.h
@@ -66,7 +66,7 @@ class OMTASampler final {
    */
   void SetSampleTime(const TimeStamp& aSampleTime);
   void ResetPreviousSampleTime();
-  void SetAnimations(uint64_t aId, const LayersId& aLayersId,
+  void SetAnimations(uint64_t aId,
                      const nsTArray<layers::Animation>& aAnimations);
   bool HasAnimations() const;
 
diff --git a/gfx/layers/wr/WebRenderBridgeParent.cpp b/gfx/layers/wr/WebRenderBridgeParent.cpp
index 48f120768be8..9e5bd9c96012 100644
--- a/gfx/layers/wr/WebRenderBridgeParent.cpp
+++ b/gfx/layers/wr/WebRenderBridgeParent.cpp
@@ -1387,7 +1387,7 @@ bool WebRenderBridgeParent::ProcessWebRenderParentCommands(
         }
         if (data.animations().Length()) {
           if (RefPtr<OMTASampler> sampler = GetOMTASampler()) {
-            sampler->SetAnimations(data.id(), GetLayersId(), data.animations());
+            sampler->SetAnimations(data.id(), data.animations());
             const auto activeAnim = mActiveAnimations.find(data.id());
             if (activeAnim == mActiveAnimations.end()) {
               mActiveAnimations.emplace(data.id(), mWrEpoch);
diff --git a/gfx/thebes/gfxLineSegment.h b/gfx/thebes/gfxLineSegment.h
index b54d3097f2eb..e3e83910b262 100644
--- a/gfx/thebes/gfxLineSegment.h
+++ b/gfx/thebes/gfxLineSegment.h
@@ -10,7 +10,6 @@
 #include "gfxPoint.h"
 
 struct gfxLineSegment {
-  gfxLineSegment() : mStart(gfxPoint()), mEnd(gfxPoint()) {}
   gfxLineSegment(const gfxPoint& aStart, const gfxPoint& aEnd)
       : mStart(aStart), mEnd(aEnd) {}
 
diff --git a/layout/base/AccessibleCaret.cpp b/layout/base/AccessibleCaret.cpp
index 8bff1ef9d9a2..af0613cc3a97 100644
--- a/layout/base/AccessibleCaret.cpp
+++ b/layout/base/AccessibleCaret.cpp
@@ -174,8 +174,14 @@ void AccessibleCaret::EnsureApzAware() {
 }
 
 bool AccessibleCaret::IsInPositionFixedSubtree() const {
-  return nsLayoutUtils::IsInPositionFixedSubtree(
-      mImaginaryCaretReferenceFrame.GetFrame());
+  for (nsIFrame* f = mImaginaryCaretReferenceFrame.GetFrame(); f;
+       f = f->GetParent()) {
+    if (f->StyleDisplay()->mPosition == StylePositionProperty::Fixed &&
+        nsLayoutUtils::IsReallyFixedPos(f)) {
+      return true;
+    }
+  }
+  return false;
 }
 
 void AccessibleCaret::InjectCaretElement(Document* aDocument) {
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 0222880258a1..3826392f05b5 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -7653,17 +7653,6 @@ bool nsLayoutUtils::MayBeReallyFixedPos(const nsIFrame* aFrame) {
          parentType == LayoutFrameType::PageContent;
 }
 
-/* static */
-bool nsLayoutUtils::IsInPositionFixedSubtree(const nsIFrame* aFrame) {
-  for (const nsIFrame* f = aFrame; f; f = f->GetParent()) {
-    if (f->StyleDisplay()->mPosition == StylePositionProperty::Fixed &&
-        nsLayoutUtils::IsReallyFixedPos(f)) {
-      return true;
-    }
-  }
-  return false;
-}
-
 nsLayoutUtils::SurfaceFromElementResult
 nsLayoutUtils::SurfaceFromOffscreenCanvas(OffscreenCanvas* aOffscreenCanvas,
                                           uint32_t aSurfaceFlags,
diff --git a/layout/base/nsLayoutUtils.h b/layout/base/nsLayoutUtils.h
index 28eb76efe405..46c7d61988b4 100644
--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -2186,11 +2186,6 @@ class nsLayoutUtils {
    */
   static bool MayBeReallyFixedPos(const nsIFrame* aFrame);
 
-  /**
-   * Returns true if |aFrame| is inside position:fixed subtree.
-   */
-  static bool IsInPositionFixedSubtree(const nsIFrame* aFrame);
-
   /**
    * Obtain a SourceSurface from the given DOM element, if possible.
    * This obtains the most natural surface from the element; that
diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index cbe5bec893ea..21d1caf9560f 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -3260,15 +3260,17 @@ void nsIFrame::BuildDisplayListForStackingContext(
   aBuilder->SetContainsBackdropFilter(false);
 
   nsRect visibleRectOutsideTransform = visibleRect;
-  nsDisplayTransform::PrerenderInfo prerenderInfo;
+  bool allowAsyncAnimation = false;
   bool inTransform = aBuilder->IsInTransform();
   if (isTransformed) {
-    prerenderInfo = nsDisplayTransform::ShouldPrerenderTransformedContent(
-        aBuilder, this, &dirtyRect);
+    nsDisplayTransform::PrerenderInfo decision =
+        nsDisplayTransform::ShouldPrerenderTransformedContent(aBuilder, this,
+                                                              &dirtyRect);
 
-    switch (prerenderInfo.mDecision) {
+    switch (decision.mDecision) {
       case nsDisplayTransform::PrerenderDecision::Full:
       case nsDisplayTransform::PrerenderDecision::Partial:
+        allowAsyncAnimation = true;
         visibleRect = dirtyRect;
         break;
       case nsDisplayTransform::PrerenderDecision::No: {
@@ -3276,7 +3278,7 @@ void nsIFrame::BuildDisplayListForStackingContext(
         // then we want disable async animations for the rest of the preserve-3d
         // (especially ancestors).
         if ((extend3DContext || combines3DTransformWithAncestors) &&
-            prerenderInfo.mHasAnimations) {
+            decision.mHasAnimations) {
           aBuilder->SavePreserves3DAllowAsyncAnimation(false);
         }
 
@@ -3766,15 +3768,14 @@ void nsIFrame::BuildDisplayListForStackingContext(
     // Alternatively we could not block animations for later siblings, and only
     // block them for ancestors of a blocked one.
     if ((extend3DContext || combines3DTransformWithAncestors) &&
-        prerenderInfo.CanUseAsyncAnimations() &&
-        !aBuilder->GetPreserves3DAllowAsyncAnimation()) {
+        allowAsyncAnimation) {
       // aBuilder->GetPreserves3DAllowAsyncAnimation() means the inner or
       // previous silbing frames are allowed/disallowed for async animations.
-      prerenderInfo.mDecision = nsDisplayTransform::PrerenderDecision::No;
+      allowAsyncAnimation = aBuilder->GetPreserves3DAllowAsyncAnimation();
     }
 
     nsDisplayTransform* transformItem = MakeDisplayItem<nsDisplayTransform>(
-        aBuilder, this, &resultList, visibleRect, prerenderInfo.mDecision);
+        aBuilder, this, &resultList, visibleRect, allowAsyncAnimation);
     if (transformItem) {
       resultList.AppendToTop(transformItem);
       ct.TrackContainer(transformItem);
diff --git a/layout/painting/nsDisplayList.cpp b/layout/painting/nsDisplayList.cpp
index 285638ead754..1c8ad17c2f8c 100644
--- a/layout/painting/nsDisplayList.cpp
+++ b/layout/painting/nsDisplayList.cpp
@@ -229,7 +229,7 @@ static uint64_t AddAnimationsForWebRender(
   AnimationInfo& animationInfo = animationData->GetAnimationInfo();
   animationInfo.AddAnimationsForDisplayItem(aItem->Frame(), aDisplayListBuilder,
                                             aItem, aItem->GetType(),
-                                            aManager->LayerManager());
+                                            layers::LayersBackend::LAYERS_WR);
   animationInfo.StartPendingAnimations(
       aManager->LayerManager()->GetAnimationReadyTime());
 
@@ -321,8 +321,8 @@ void nsDisplayListBuilder::AddAnimationsAndTransitionsToLayer(
   }
 
   AnimationInfo& animationInfo = aLayer->GetAnimationInfo();
-  animationInfo.AddAnimationsForDisplayItem(aFrame, aBuilder, aItem, aType,
-                                            aLayer->Manager());
+  animationInfo.AddAnimationsForDisplayItem(
+      aFrame, aBuilder, aItem, aType, layers::LayersBackend::LAYERS_CLIENT);
   animationInfo.TransferMutatedFlagToLayer(aLayer);
 }
 
@@ -7287,8 +7287,8 @@ nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
       mAnimatedGeometryRootForChildren(mAnimatedGeometryRoot),
       mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot),
       mChildrenBuildingRect(aChildrenBuildingRect),
-      mPrerenderDecision(PrerenderDecision::No),
-      mIsTransformSeparator(true) {
+      mIsTransformSeparator(true),
+      mAllowAsyncAnimation(false) {
   MOZ_COUNT_CTOR(nsDisplayTransform);
   MOZ_ASSERT(aFrame, "Must have a frame!");
   Init(aBuilder, aList);
@@ -7297,14 +7297,14 @@ nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
 nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
                                        nsIFrame* aFrame, nsDisplayList* aList,
                                        const nsRect& aChildrenBuildingRect,
-                                       PrerenderDecision aPrerenderDecision)
+                                       bool aAllowAsyncAnimation)
     : nsDisplayHitTestInfoBase(aBuilder, aFrame),
       mTransformGetter(nullptr),
       mAnimatedGeometryRootForChildren(mAnimatedGeometryRoot),
       mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot),
       mChildrenBuildingRect(aChildrenBuildingRect),
-      mPrerenderDecision(aPrerenderDecision),
-      mIsTransformSeparator(false) {
+      mIsTransformSeparator(false),
+      mAllowAsyncAnimation(aAllowAsyncAnimation) {
   MOZ_COUNT_CTOR(nsDisplayTransform);
   MOZ_ASSERT(aFrame, "Must have a frame!");
   SetReferenceFrameToAncestor(aBuilder);
@@ -7320,8 +7320,8 @@ nsDisplayTransform::nsDisplayTransform(
       mAnimatedGeometryRootForChildren(mAnimatedGeometryRoot),
       mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot),
       mChildrenBuildingRect(aChildrenBuildingRect),
-      mPrerenderDecision(PrerenderDecision::No),
-      mIsTransformSeparator(false) {
+      mIsTransformSeparator(false),
+      mAllowAsyncAnimation(false) {
   MOZ_COUNT_CTOR(nsDisplayTransform);
   MOZ_ASSERT(aFrame, "Must have a frame!");
   Init(aBuilder, aList);
@@ -7640,7 +7640,7 @@ bool nsDisplayOpacity::CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) {
 }
 
 bool nsDisplayTransform::CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) {
-  return mPrerenderDecision != PrerenderDecision::No;
+  return mAllowAsyncAnimation;
 }
 
 bool nsDisplayBackgroundColor::CanUseAsyncAnimations(
@@ -7648,22 +7648,6 @@ bool nsDisplayBackgroundColor::CanUseAsyncAnimations(
   return StaticPrefs::gfx_omta_background_color();
 }
 
-static bool IsInStickyPositionedSubtree(const nsIFrame* aFrame) {
-  for (const nsIFrame* frame = aFrame; frame;
-       frame = nsLayoutUtils::GetCrossDocParentFrame(frame)) {
-    if (frame->IsStickyPositioned()) {
-      return true;
-    }
-  }
-  return false;
-}
-
-static bool ShouldUsePartialPrerender(const nsIFrame* aFrame) {
-  return StaticPrefs::layout_animation_prerender_partial() &&
-         // Bug 1642547: Support partial prerender for position:sticky elements.
-         !IsInStickyPositionedSubtree(aFrame);
-}
-
 /* static */
 auto nsDisplayTransform::ShouldPrerenderTransformedContent(
     nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsRect* aDirtyRect)
@@ -7785,7 +7769,7 @@ auto nsDisplayTransform::ShouldPrerenderTransformedContent(
     return result;
   }
 
-  if (ShouldUsePartialPrerender(aFrame)) {
+  if (StaticPrefs::layout_animation_prerender_partial()) {
     *aDirtyRect = nsLayoutUtils::ComputePartialPrerenderArea(
         aFrame, untransformedDirtyRect, overflow, maxSize);
     result.mDecision = PrerenderDecision::Partial;
@@ -8069,7 +8053,7 @@ already_AddRefed<Layer> nsDisplayTransform::BuildLayer(
                                ~Layer::CONTENT_EXTEND_3D_CONTEXT);
   }
 
-  if (CanUseAsyncAnimations(aBuilder)) {
+  if (mAllowAsyncAnimation) {
     mFrame->SetProperty(nsIFrame::RefusedAsyncAnimationProperty(), false);
   }
 
@@ -8079,7 +8063,7 @@ already_AddRefed<Layer> nsDisplayTransform::BuildLayer(
         container, aBuilder, this, mFrame, GetType());
   }
 
-  if (CanUseAsyncAnimations(aBuilder) && MayBeAnimated(aBuilder)) {
+  if (mAllowAsyncAnimation && MayBeAnimated(aBuilder)) {
     // Only allow async updates to the transform if we're an animated layer,
     // since that's what triggers us to set the correct AGR in the constructor
     // and makes sure FrameLayerBuilder won't compute occlusions for this layer.
@@ -8556,19 +8540,7 @@ void nsDisplayTransform::WriteDebugInfo(std::stringstream& aStream) {
     aStream << " combines-3d-with-ancestors";
   }
 
-  aStream << " prerender(";
-  switch (mPrerenderDecision) {
-    case PrerenderDecision::No:
-      aStream << "no";
-      break;
-    case PrerenderDecision::Partial:
-      aStream << "partial";
-      break;
-    case PrerenderDecision::Full:
-      aStream << "full";
-      break;
-  }
-  aStream << ")";
+  aStream << " allowAsync(" << (mAllowAsyncAnimation ? "true" : "false") << ")";
   aStream << " childrenBuildingRect" << mChildrenBuildingRect;
 }
 
diff --git a/layout/painting/nsDisplayList.h b/layout/painting/nsDisplayList.h
index 0bcd8b9c8bd1..8e338e5a178a 100644
--- a/layout/painting/nsDisplayList.h
+++ b/layout/painting/nsDisplayList.h
@@ -6727,7 +6727,7 @@ class nsDisplayTransform : public nsDisplayHitTestInfoBase {
   using TransformReferenceBox = nsStyleTransformMatrix::TransformReferenceBox;
 
  public:
-  enum class PrerenderDecision : uint8_t { No, Full, Partial };
+  enum class PrerenderDecision { No, Full, Partial };
 
   /**
    * Returns a matrix (in pixels) for the current frame. The matrix should be
@@ -6747,7 +6747,7 @@ class nsDisplayTransform : public nsDisplayHitTestInfoBase {
 
   nsDisplayTransform(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
                      nsDisplayList* aList, const nsRect& aChildrenBuildingRect,
-                     PrerenderDecision aPrerenderDecision);
+                     bool aAllowAsyncAnimation);
 
   nsDisplayTransform(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
                      nsDisplayList* aList, const nsRect& aChildrenBuildingRect,
@@ -7006,9 +7006,6 @@ class nsDisplayTransform : public nsDisplayHitTestInfoBase {
       float aAppUnitsPerPixel);
 
   struct PrerenderInfo {
-    bool CanUseAsyncAnimations() const {
-      return mDecision != PrerenderDecision::No && mHasAnimations;
-    }
     PrerenderDecision mDecision = PrerenderDecision::No;
     bool mHasAnimations = true;
   };
@@ -7055,10 +7052,6 @@ class nsDisplayTransform : public nsDisplayHitTestInfoBase {
     return mFrame->Extend3DContext() || Combines3DTransformWithAncestors();
   }
 
-  bool IsPartialPrerender() const {
-    return mPrerenderDecision == PrerenderDecision::Partial;
-  }
-
   void AddSizeOfExcludingThis(nsWindowSizes&) const override;
 
  private:
@@ -7089,7 +7082,6 @@ class nsDisplayTransform : public nsDisplayHitTestInfoBase {
   nsRect mChildBounds;
   // The transformed bounds of this display item.
   nsRect mBounds;
-  PrerenderDecision mPrerenderDecision : 2;
   // This item is a separator between 3D rendering contexts, and
   // mTransform have been presetted by the constructor.
   // This also forces us not to extend the 3D context.  Since we don't create a
@@ -7097,9 +7089,11 @@ class nsDisplayTransform : public nsDisplayHitTestInfoBase {
   // context, the transform items of a child preserves3d context may extend the
   // parent context unintendedly if the root of the child preserves3d context
   // doesn't create a transform item.
-  bool mIsTransformSeparator : 1;
+  bool mIsTransformSeparator;
+  // True if async animation of the transform is allowed.
+  bool mAllowAsyncAnimation;
   // True if this nsDisplayTransform should get flattened
-  bool mShouldFlatten : 1;
+  bool mShouldFlatten;
 };
 
 /* A display item that applies a perspective transformation to a single
diff --git a/layout/reftests/transform/partial-prerender-translate-1.html b/layout/reftests/transform/partial-prerender-translate-1.html
deleted file mode 100644
index 1ee7dacd8f10..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-1.html
+++ /dev/null
@@ -1,57 +0,0 @@
-<!DOCTYPE html>
-<html class="reftest-wait reftest-no-flush">
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<!--
-  A test for a partial pre-rendered transform animation moves to a place where
-  the whole area of the transform animation is out of the viewport.
-  If we mis-recognize it as a jank, the last visible composited area will
-  remain.
-  -->
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-@keyframes anim {
-  /* translate to a position the element is completely outside of the */
-  /* viewport                                                         */
-  to { transform: translateX(-300vw); }
-}
-#target {
-  width: 200vw;
-  height: 200vh;
-  position: absolute;
-  /* Some part of this element needs to be visible initially so that  */
-  /* a display item for this element is generated, thus the transform */
-  /* animation runs on the compositor.                                */
-  transform: translateX(-110vw);
-}
-</style>
-<div id="target">
-  <!--
-    Put an SVG element so that the transform display item has a blob on
-    WebRender which means this test properly fails without the proper fix.
-    -->
-  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16">
-    <rect fill="green" width="16" height="16"></rect>
-  </svg>
-</div>
-<script>
-document.addEventListener("MozReftestInvalidate", () => {
-  target.style.animation = "anim 100s 1s step-start";
-  target.addEventListener("animationstart", () => {
-    // animtionstart event is fired just before requestAnimationFrame callbacks,
-    // so we need to wait two rAF to make sure the initial animation value is
-    // composited on the compositor.
-    requestAnimationFrame(() => {
-      requestAnimationFrame(() => {
-        document.documentElement.classList.remove("reftest-wait");
-      });
-    });
-  });
-}, { once: true });
-</script>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-2-ref.html b/layout/reftests/transform/partial-prerender-translate-2-ref.html
deleted file mode 100644
index 98ee6a1f140b..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-2-ref.html
+++ /dev/null
@@ -1,29 +0,0 @@
-<!DOCTYPE html>
-<html>
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-#target {
-  width: 2000px;
-  height: 2000px;
-  position: absolute;
-  transform: translateX(-325px);
-}
-</style>
-<div id="target">
-  <!--
-    Put an SVG element so that the transform display item has a blob on
-    WebRender which means this test properly fails without the proper fix.
-    -->
-  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16">
-    <rect fill="green" x="0" width="1125" height="2000"></rect>
-    <rect fill="red" x="1125" width="875" height="2000"></rect>
-  </svg>
-</div>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-2.html b/layout/reftests/transform/partial-prerender-translate-2.html
deleted file mode 100644
index 550a74084adb..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-2.html
+++ /dev/null
@@ -1,56 +0,0 @@
-<!DOCTYPE html>
-<html class="reftest-wait reftest-no-flush">
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<!--
-  A test for a partial pre-rendered transform animation moves to a place where
-  jank happens.
-  -->
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-@keyframes anim {
-  /* The reftest window size is (800x1000), which means the partial prerender */
-  /* area is (1125x1125). Thus -325px(= 800 - 1125) is the boundary where     */
-  /* jank happens, so we choose a value close to -325px so that within a next */
-  /* couple of frames jank should happen. */
-  0% { transform: translateX(-324px); }
-  100% { transform: translateX(-2000px); }
-}
-#target {
-  width: 2000px;
-  height: 2000px;
-  position: absolute;
-  transform: translateX(0px);
-}
-</style>
-<div id="target">
-  <!--
-    Put an SVG element so that the transform display item has a blob on
-    WebRender which means this test properly fails without the proper fix.
-    -->
-  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 2000 2000">
-    <!-- green on the pre-render area -->
-    <rect fill="green" x="0" width="1125" height="2000"></rect>
-    <rect fill="red" x="1125" width="875" height="2000"></rect>
-  </svg>
-</div>
-<script>
-document.addEventListener("MozReftestInvalidate", () => {
-  // A shorter animation-duration than we normally use (100s) because if we used
-  // the longer duration it may NOT fail this test even if any jank happens.
-  target.style.animation = "anim 10s 1s";
-  target.addEventListener("animationstart", () => {
-    // Wait a second to make sure the animation gets stucked (i.e. jank) at the
-    // boundary (325px).
-    setTimeout(() => {
-      document.documentElement.classList.remove("reftest-wait");
-    }, 1000);
-  });
-}, { once: true });
-</script>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-3-ref.html b/layout/reftests/transform/partial-prerender-translate-3-ref.html
deleted file mode 100644
index d4941007bdf7..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-3-ref.html
+++ /dev/null
@@ -1,20 +0,0 @@
-<!DOCTYPE html>
-<html>
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-#target {
-  background-color: green;
-  width: 50vw;
-  height: 100vh;
-  position: absolute;
-}
-</style>
-<div id="target"></div>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-3.html b/layout/reftests/transform/partial-prerender-translate-3.html
deleted file mode 100644
index 6e4ad202b11c..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-3.html
+++ /dev/null
@@ -1,54 +0,0 @@
-<!DOCTYPE html>
-<html class="reftest-wait reftest-no-flush">
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<!--
-  A test for a partial pre-rendered transform animation moves to a place where
-  the partial pre-rendered area is completely out of the viewport but still
-  there remains some amount of area of the entire transform element.
-  If we mis-recognize it as NOT a jank, checkerboading will happen.
-  -->
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-@keyframes anim {
-  /* translate to a position the partial pre-rendered area is outside of the */
-  /* viewport but still there should remain visible area. */
-  to { transform: translateX(-150vw); }
-}
-#target {
-  width: 200vw;
-  height: 200vh;
-  position: absolute;
-  transform: translateX(0vw);
-}
-</style>
-<div id="target">
-  <!--
-    Put an SVG element so that the transform display item has a blob on
-    WebRender which means this test properly fails without the proper fix.
-    -->
-  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16">
-    <rect fill="green" width="16" height="16"></rect>
-  </svg>
-</div>
-<script>
-document.addEventListener("MozReftestInvalidate", () => {
-  target.style.animation = "anim 100s 1s step-start";
-  target.addEventListener("animationstart", () => {
-    // animtionstart event is fired just before requestAnimationFrame callbacks,
-    // so we need to wait two rAF to make sure the initial animation value is
-    // composited on the compositor.
-    requestAnimationFrame(() => {
-      requestAnimationFrame(() => {
-        document.documentElement.classList.remove("reftest-wait");
-      });
-    });
-  });
-}, { once: true });
-</script>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-4.html b/layout/reftests/transform/partial-prerender-translate-4.html
deleted file mode 100644
index 11ff491b8701..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-4.html
+++ /dev/null
@@ -1,56 +0,0 @@
-<!DOCTYPE html>
-<html class="reftest-wait reftest-no-flush">
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<!--
-  A test that a partial pre-rendered transform animation is transformed by an
-  ancestor transform value.
-  If we don't factor the ancestor's transform, we mis-recognize janks, which
-  means janked at the initial translateX(0vw) position, thus white blank area
-  will appears.
-  -->
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-@keyframes anim {
-  /* translate to a position where the left edge of partial pre-rendered on */
-  /* the left edge of the viewport. */
-  to { transform: translateX(-50vw); }
-}
-#target {
-  width: 300vw;
-  height: 300vh;
-  transform: translateX(0vw);
-}
-</style>
-<div style="transform: translateX(50vw);">
-  <div id="target">
-    <!--
-      Put an SVG element so that the transform display item has a blob on
-      WebRender which means this test properly fails without the proper fix.
-      -->
-    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16">
-      <rect fill="green" width="16" height="16"></rect>
-    </svg>
-  </div>
-</div>
-<script>
-document.addEventListener("MozReftestInvalidate", () => {
-  target.style.animation = "anim 100s 1s step-start";
-  target.addEventListener("animationstart", () => {
-    // animtionstart event is fired just before requestAnimationFrame callbacks,
-    // so we need to wait two rAF to make sure the initial animation value is
-    // composited on the compositor.
-    requestAnimationFrame(() => {
-      requestAnimationFrame(() => {
-        document.documentElement.classList.remove("reftest-wait");
-      });
-    });
-  });
-}, { once: true });
-</script>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-5-ref.html b/layout/reftests/transform/partial-prerender-translate-5-ref.html
deleted file mode 100644
index c2047502af41..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-5-ref.html
+++ /dev/null
@@ -1,35 +0,0 @@
-<!DOCTYPE html>
-<html reftest-async-scroll
-      reftest-displayport-x="0" reftest-displayport-y="0"
-      reftest-displayport-w="800" reftest-displayport-h="2000"
-      reftest-async-scroll-x="0" reftest-async-scroll-y="1000">
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<style>
-html {
-  overflow-x: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-#target {
-  width: 800px;
-  height: 1600px;
-  transform: translateY(-500px);
-}
-</style>
-<div style="width: 800px; height: 2000px"><!-- spacer --></div>
-<div style="position: fixed; top: 400px">
-  <div id="target">
-    <!--
-      Put an SVG element so that the transform display item has a blob on
-      WebRender which means this test properly fails without the proper fix.
-      -->
-    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 800 1600">
-      <rect fill="green" y="0"    width="800" height="1000"></rect>
-      <rect fill="blue"  y="1000" width="800" height="125"></rect>
-      <rect fill="red"   y="1125" width="800" height="875"></rect>
-    </svg>
-  </div>
-</div>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-5.html b/layout/reftests/transform/partial-prerender-translate-5.html
deleted file mode 100644
index 6225b7de251c..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-5.html
+++ /dev/null
@@ -1,58 +0,0 @@
-<!DOCTYPE html>
-<html class="reftest-wait reftest-no-flush"
-      reftest-async-scroll
-      reftest-displayport-x="0" reftest-displayport-y="0"
-      reftest-displayport-w="800" reftest-displayport-h="2000"
-      reftest-async-scroll-x="0" reftest-async-scroll-y="1000">
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<!--
-  A test that a partial pre-rendered transform animation is in a position:fixed
-  layer.
-  -->
-<style>
-html {
-  overflow-x: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-@keyframes anim {
-  to { transform: translateY(-500px); }
-}
-#target {
-  width: 800px;
-  height: 1600px;
-  transform: translateY(-400px);
-}
-</style>
-<div style="width: 800px; height: 2000px"><!-- spacer --></div>
-<div style="position: fixed; top: 400px">
-  <div id="target">
-    <!--
-      Put an SVG element so that the transform display item has a blob on
-      WebRender which means this test properly fails without the proper fix.
-      -->
-    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 800 1600">
-      <rect fill="green" y="0"    width="800" height="1000"></rect>
-      <rect fill="blue"  y="1000" width="800" height="125"></rect>
-      <rect fill="red"   y="1125" width="800" height="875"></rect>
-    </svg>
-  </div>
-</div>
-<script>
-document.addEventListener("MozReftestInvalidate", () => {
-  target.style.animation = "anim 100s 1s step-start";
-  target.addEventListener("animationstart", () => {
-    // animtionstart event is fired just before requestAnimationFrame callbacks,
-    // so we need to wait two rAF to make sure the initial animation value is
-    // composited on the compositor.
-    requestAnimationFrame(() => {
-      requestAnimationFrame(() => {
-        document.documentElement.classList.remove("reftest-wait");
-      });
-    });
-  });
-}, { once: true });
-</script>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-6-ref.html b/layout/reftests/transform/partial-prerender-translate-6-ref.html
deleted file mode 100644
index dece645afb4f..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-6-ref.html
+++ /dev/null
@@ -1,29 +0,0 @@
-<!DOCTYPE html>
-<html>
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-#target {
-  width: 1600px;
-  height: 900px;
-  position: absolute;
-  transform: translateX(-325px);
-}
-</style>
-<div id="target">
-  <!--
-    Put an SVG element so that the transform display item has a blob on
-    WebRender which means this test properly fails without the proper fix.
-    -->
-  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1600 900">
-    <rect fill="green" x="0" width="1125" height="900"></rect>
-    <rect fill="red" x="1125" width="875" height="900"></rect>
-  </svg>
-</div>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-6.html b/layout/reftests/transform/partial-prerender-translate-6.html
deleted file mode 100644
index 1ec13f44d77d..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-6.html
+++ /dev/null
@@ -1,54 +0,0 @@
-<!DOCTYPE html>
-<html class="reftest-wait reftest-no-flush">
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-@keyframes anim {
-  /* The reftest window size is (800x1000), which means the partial prerender */
-  /* area is (1125x900). Thus -325px(= 800 - 1125) is the boundary where jank */
-  /* happens, so we choose a value close to -325px so that within a next      */
-  /* couple of frames jank should happen. */
-  0% { transform: translateX(-324px); }
-  100% { transform: translateX(-2000px); }
-}
-#target {
-  width: 1600px;
-  /* Use a smallar value than the reftest window height to avoid bloating up  */
-  /* svg inside this element beyond the window height */
-  height: 900px;
-  position: absolute;
-  transform: translateX(0px);
-}
-</style>
-<div id="target">
-  <!--
-    Put an SVG element so that the transform display item has a blob on
-    WebRender which means this test properly fails without the proper fix.
-    -->
-  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1600 900">
-    <!-- green on the pre-render area -->
-    <rect fill="green" x="0" width="1125" height="900"></rect>
-    <rect fill="red" x="1125" width="875" height="900"></rect>
-  </svg>
-</div>
-<script>
-document.addEventListener("MozReftestInvalidate", () => {
-  // A shorter animation-duration than we normally use (100s) because if we used
-  // the longer duration it may NOT fail this test even if any jank happens.
-  target.style.animation = "anim 10s 1s";
-  target.addEventListener("animationstart", () => {
-    // Wait a second to make sure the animation gets stucked (i.e. jank) at the
-    // boundary (325px).
-    setTimeout(() => {
-      document.documentElement.classList.remove("reftest-wait");
-    }, 1000);
-  });
-}, { once: true });
-</script>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-7.html b/layout/reftests/transform/partial-prerender-translate-7.html
deleted file mode 100644
index 06c26c66fbf5..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-7.html
+++ /dev/null
@@ -1,53 +0,0 @@
-<!DOCTYPE html>
-<html class="reftest-wait reftest-no-flush">
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<!--
-  Another variant of partial-prerender-translate-2.html, but the transform
-  animation is scaled by the parent element.
-  -->
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-@keyframes anim {
-  /* translate to a position where the left edge of partial pre-rendered on */
-  /* the left edge of the viewport. */
-  0% { transform: translateX(-649px); }
-  100% { transform: translateX(-2000px); }
-}
-#target {
-  width: 4000px;
-  height: 2000px;
-  position: absolute;
-  transform: translateX(0);
-}
-</style>
-<div style="transform: scale(0.5); transform-origin: 0 0">
-  <div id="target">
-    <!--
-      Put an SVG element so that the transform display item has a blob on
-      WebRender which means this test properly fails without the proper fix.
-      -->
-    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 4000 2000">
-      <rect fill="green" x="0" width="2250" height="2000"></rect>
-      <rect fill="red" x="2250" width="1750" height="2000"></rect>
-    </svg>
-  </div>
-</div>
-<script>
-document.addEventListener("MozReftestInvalidate", () => {
-  target.style.animation = "anim 10s 1s";
-  target.addEventListener("animationstart", () => {
-    // Wait a second to make sure the animation gets stucked (i.e. jank) at the
-    // boundary (650px).
-    setTimeout(() => {
-      document.documentElement.classList.remove("reftest-wait");
-    }, 1000);
-  });
-}, { once: true });
-</script>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-8-ref.html b/layout/reftests/transform/partial-prerender-translate-8-ref.html
deleted file mode 100644
index ddf5bda1722e..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-8-ref.html
+++ /dev/null
@@ -1,44 +0,0 @@
-<!DOCTYPE html>
-<html>
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<!--
-  A variant test of partial-prerender-translate-5.html but in this test the
-  position:fixed element is inside an iframe.
-  -->
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-</style>
-<iframe style="width:400px; height:1000px; border: 0"
-        srcdoc="<!DOCTYPE HTML>
-                <html>
-                <style>
-                html {
-                  overflow-x: hidden;
-                  scrollbar-width: none;
-                }
-                html, body {
-                  margin: 0;
-                  padding: 0;
-                }
-                #target {
-                  width: 1600px;
-                  height: 1000px;
-                  transform: translateX(-725px);
-                }
-                </style>
-                <div id='target'>
-                  <svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1600 1000'>
-                    <rect fill='green' x='0'   width='800' height='1000'></rect>
-                    <rect fill='blue'  x='800' width='325' height='1000'></rect>
-                    <rect fill='red'   x='1125' width='675' height='1000'></rect>
-                  </svg>
-                </div>
-                </html>">
-</iframe>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-8.html b/layout/reftests/transform/partial-prerender-translate-8.html
deleted file mode 100644
index 0fc633a532d5..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-8.html
+++ /dev/null
@@ -1,73 +0,0 @@
-<!DOCTYPE html>
-<html class="reftest-wait reftest-no-flush">
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<!--
-  A test for a partial pre-rendered transform in an iframe, if the clip
-  rectangle of the transform animation were wrong, e.g. (800, 1000), the
-  transform animation janks at the initial position.
-  -->
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-</style>
-              <!-- a half width of the view port -->
-<iframe style="width:400px; height:1000px; border: 0"
-        srcdoc="<!DOCTYPE HTML>
-                <html>
-                <style>
-                html {
-                  overflow: hidden;
-                  scrollbar-width: none;
-                }
-                html, body {
-                  margin: 0;
-                  padding: 0;
-                }
-                @keyframes anim {
-                  /* the partial prerender area is (1125, 1000), thus         */
-                  /* translateX(-725px) is the position where the right edge  */
-                  /* of the partial prerender is positioned at the right edge */
-                  /* of the clip rect (400, 1000).                            */
-                  to { transform: translateX(-725px); }
-                }
-                #target {
-                  width: 1600px;
-                  height: 1000px;
-                  transform: translateX(0px);
-                }
-                </style>
-                <div id='target'>
-                  <svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1600 1000'>
-                    <rect fill='green' x='0'   width='800' height='1000'></rect>
-                    <rect fill='blue'  x='800' width='325' height='1000'></rect>
-                    <rect fill='red'   x='1125' width='675' height='1000'></rect>
-                  </svg>
-                </div>
-                <script>
-                window.addEventListener('message', () => {
-                  if (event.data == 'start') {
-                    target.style.animation = 'anim 100s 1s step-start';
-                    target.addEventListener('animationstart', () => {
-                      parent.postMessage('animationstart', '*');
-                    });
-                  }
-                });
-                </script></html>">
-</iframe>
-<script>
-document.addEventListener("MozReftestInvalidate", () => {
-  document.querySelector("iframe").contentWindow.postMessage("start", "*");
-}, { once: true });
-
-window.addEventListener("message", event => {
-  if (event.data == "animationstart") {
-    document.documentElement.classList.remove('reftest-wait');
-  }
-});
-</script>
-</html>
diff --git a/layout/reftests/transform/partial-prerender-translate-9.html b/layout/reftests/transform/partial-prerender-translate-9.html
deleted file mode 100644
index 2c6af406cb32..000000000000
--- a/layout/reftests/transform/partial-prerender-translate-9.html
+++ /dev/null
@@ -1,76 +0,0 @@
-<!DOCTYPE html>
-<html reftest-async-scroll class="reftest-wait reftest-no-flush">
-<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
-<!--
-  A variant test of partial-prerender-translate-5.html but in this test the
-  position:fixed element is inside an iframe.
-  -->
-<style>
-html {
-  overflow: hidden;
-}
-body {
-  margin: 0px;
-  padding: 0px;
-}
-</style>
-<iframe style="width:800px; height:1000px; border: 0"
-        srcdoc="<!DOCTYPE HTML>
-                <html reftest-displayport-x='0' reftest-displayport-y='0'
-                      reftest-displayport-w='800' reftest-displayport-h='2000'
-                      reftest-async-scroll-x='0' reftest-async-scroll-y='1000'>
-                <style>
-                html {
-                  overflow-x: hidden;
-                }
-                html, body {
-                  margin: 0;
-                  padding: 0;
-                }
-                @keyframes anim {
-                  to { transform: translateY(-500px); }
-                }
-                #target {
-                  width: 800px;
-                  height: 1600px;
-                  transform: translateY(-400px);
-                }
-                </style>
-                <div style='width: 800px; height: 2000px'><!-- spacer --></div>
-                <div style='position: fixed; top: 400px'>
-                  <div id='target'>
-                    <!--
-                      Put an SVG element so that the transform display item has
-                      a blob on WebRender which means this test properly fails
-                      without the proper fix.
-                      -->
-                    <svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 800 1600'>
-                      <rect fill='green' y='0'    width='800' height='1000'></rect>
-                      <rect fill='blue'  y='1000' width='800' height='125'></rect>
-                      <rect fill='red'   y='1125' width='800' height='875'></rect>
-                    </svg>
-                  </div>
-                </div>
-                <script>
-                window.addEventListener('message', () => {
-                  if (event.data == 'start') {
-                    target.style.animation = 'anim 100s 1s step-start';
-                    target.addEventListener('animationstart', () => {
-                      parent.postMessage('animationstart', '*');
-                    });
-                  }
-                });
-                </script></html>">
-</iframe>
-<script>
-document.addEventListener("MozReftestInvalidate", () => {
-  document.querySelector("iframe").contentWindow.postMessage("start", "*");
-}, { once: true });
-
-window.addEventListener("message", event => {
-  if (event.data == "animationstart") {
-    document.documentElement.classList.remove('reftest-wait');
-  }
-});
-</script>
-</html>
diff --git a/layout/reftests/transform/reftest.list b/layout/reftests/transform/reftest.list
index 68f8e89e6dad..fa58a8020b7e 100644
--- a/layout/reftests/transform/reftest.list
+++ b/layout/reftests/transform/reftest.list
@@ -156,20 +156,7 @@ test-pref(layout.css.zoom-transform-hack.enabled,false) != zoom-hack-1.html zoom
 test-pref(layout.css.zoom-transform-hack.enabled,true) == zoom-hack-2.html zoom-hack-ref.html
 
 == transform-anon-block-1.html transform-anon-block-1-ref.html
-test-pref(layout.animation.prerender.partial.jank,true) test-pref(layout.animation.prerender.partial,true) == partial-prerender-expansion-translate.html partial-prerender-expansion-ref.html
-test-pref(layout.animation.prerender.partial.jank,true) test-pref(layout.animation.prerender.partial,true) == partial-prerender-translate-1.html about:blank
-skip-if(webrender) test-pref(layout.animation.prerender.partial.jank,true) test-pref(layout.animation.prerender.partial,true) test-pref(layout.animation.prerender.viewport-ratio-limit,"1.125") == partial-prerender-translate-2.html partial-prerender-translate-2-ref.html # bug 1638152 for WebRender
-fails test-pref(layout.animation.prerender.partial.jank,true) test-pref(layout.animation.prerender.partial,true) test-pref(layout.animation.prerender.viewport-ratio-limit,"1.125") == partial-prerender-translate-3.html partial-prerender-translate-3-ref.html # bug 1642575
-# This reftest doesn't fail on WebRender, this reftest fails only if there is a jank mechanism and the mechanism doesn't properly handle ancestor's transform values
-test-pref(layout.animation.prerender.partial.jank,true) test-pref(layout.animation.prerender.partial,true) test-pref(layout.animation.prerender.viewport-ratio-limit,"1.125") == partial-prerender-translate-4.html partial-prerender-expansion-ref.html
-# This reftest doesn't fail on WebRender, this reftest fails only if there is a jank mechanism and the mechanism does inproperly handle position:fixed scroll target
-test-pref(layout.animation.prerender.partial.jank,true) test-pref(layout.animation.prerender.partial,true) test-pref(layout.animation.prerender.viewport-ratio-limit,"1.125") == partial-prerender-translate-5.html partial-prerender-translate-5-ref.html
-fails-if(webrender) test-pref(layout.animation.prerender.partial.jank,true) test-pref(layout.animation.prerender.partial,true) test-pref(layout.animation.prerender.viewport-ratio-limit,"1.125") == partial-prerender-translate-6.html partial-prerender-translate-6-ref.html # bug 1638152 for WebRender
-fails-if(webrender) test-pref(layout.animation.prerender.partial.jank,true) test-pref(layout.animation.prerender.partial,true) test-pref(layout.animation.prerender.viewport-ratio-limit,"1.125") == partial-prerender-translate-7.html partial-prerender-translate-2-ref.html # bug 1638152 for WebRender
-# This reftest doesn't fail on WebRender, this reftest fails only if there is a jank mechanism and the mechanism doesn't properly clip transform in iframes.
-test-pref(layout.animation.prerender.partial.jank,true) test-pref(layout.animation.prerender.partial,true) test-pref(layout.animation.prerender.viewport-ratio-limit,"1.125") == partial-prerender-translate-8.html partial-prerender-translate-8-ref.html
-# This reftest doesn't fail on WebRender, this reftest fails only if there is a jank mechanism and the mechanism does inproperly handle position:fixed scroll target
-test-pref(layout.animation.prerender.partial.jank,true) test-pref(layout.animation.prerender.partial,true) test-pref(layout.animation.prerender.viewport-ratio-limit,"1.125") == partial-prerender-translate-9.html partial-prerender-translate-5-ref.html
+test-pref(layout.animation.prerender.partial,true) == partial-prerender-expansion-translate.html partial-prerender-expansion-ref.html
 # This reftest heavily depends on layout.animation.prerender.viewport-ratio-limit
 # and reftest viewport size (800, 1000).
 skip-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)||Android) test-pref(layout.animation.prerender.partial,true) test-pref(layout.animation.prerender.viewport-ratio-limit,"1.125") == partial-prerender-expansion-rotate.html partial-prerender-expansion-ref.html
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index ccaba430d12b..ed4c0cf4a99b 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -5601,14 +5601,6 @@
   value: 4096
   mirror: always
 
-# Test-only pref, if this is true, partial pre-rendered transform animations
-# get stuck when it reaches to the pre-rendered boundaries and the pre-render
-# region is never updated.
-- name: layout.animation.prerender.partial.jank
-  type: RelaxedAtomicBool
-  value: false
-  mirror: always
-
 # Whether Constructable Stylesheets are enabled in script.
 - name: layout.css.constructable-stylesheets.enabled
   type: bool