--- a/gfx/layers/wr/WebRenderCommandBuilder.cpp
+++ b/gfx/layers/wr/WebRenderCommandBuilder.cpp
@@ -76,17 +76,17 @@ WebRenderCommandBuilder::BuildWebRenderC
       CreateWebRenderCommandsFromDisplayList(aDisplayList, aDisplayListBuilder,
                                              pageRootSc, aBuilder, aResourceUpdates);
     }
 
     // Make a "root" layer data that has everything else as descendants
     mLayerScrollData.emplace_back();
     mLayerScrollData.back().InitializeRoot(mLayerScrollData.size() - 1);
     auto callback = [&aScrollData](FrameMetrics::ViewID aScrollId) -> bool {
-      return aScrollData.HasMetadataFor(aScrollId);
+      return aScrollData.HasMetadataFor(aScrollId).isSome();
     };
     if (Maybe<ScrollMetadata> rootMetadata = nsLayoutUtils::GetRootMetadata(
           aDisplayListBuilder, mManager, ContainerLayerParameters(), callback)) {
       mLayerScrollData.back().AppendScrollMetadata(aScrollData, rootMetadata.ref());
     }
     // Append the WebRenderLayerScrollData items into WebRenderScrollData
     // in reverse order, from topmost to bottommost. This is in keeping with
     // the semantics of WebRenderScrollData.

--- a/gfx/layers/wr/WebRenderScrollData.cpp
+++ b/gfx/layers/wr/WebRenderScrollData.cpp
@@ -49,21 +49,27 @@ WebRenderLayerScrollData::Initialize(Web
   mDescendantCount = aDescendantCount;
 
   MOZ_ASSERT(aItem);
   aItem->UpdateScrollData(&aOwner, this);
   for (const ActiveScrolledRoot* asr = aItem->GetActiveScrolledRoot();
        asr && asr != aStopAtAsr;
        asr = asr->mParent) {
     MOZ_ASSERT(aOwner.GetManager());
-    Maybe<ScrollMetadata> metadata = asr->mScrollableFrame->ComputeScrollMetadata(
-        nullptr, aOwner.GetManager(), aItem->ReferenceFrame(),
-        ContainerLayerParameters(), nullptr);
-    MOZ_ASSERT(metadata);
-    mScrollIds.AppendElement(aOwner.AddMetadata(metadata.ref()));
+    FrameMetrics::ViewID scrollId = nsLayoutUtils::ViewIDForASR(asr);
+    if (Maybe<size_t> index = aOwner.HasMetadataFor(scrollId)) {
+      mScrollIds.AppendElement(index.ref());
+    } else {
+      Maybe<ScrollMetadata> metadata = asr->mScrollableFrame->ComputeScrollMetadata(
+          nullptr, aOwner.GetManager(), aItem->ReferenceFrame(),
+          ContainerLayerParameters(), nullptr);
+      MOZ_ASSERT(metadata);
+      MOZ_ASSERT(metadata->GetMetrics().GetScrollId() == scrollId);
+      mScrollIds.AppendElement(aOwner.AddMetadata(metadata.ref()));
+    }
   }
 }
 
 int32_t
 WebRenderLayerScrollData::GetDescendantCount() const
 {
   MOZ_ASSERT(mDescendantCount >= 0); // check that it was set
   return mDescendantCount;
@@ -195,20 +201,21 @@ WebRenderScrollData::GetLayerData(size_t
 
 const ScrollMetadata&
 WebRenderScrollData::GetScrollMetadata(size_t aIndex) const
 {
   MOZ_ASSERT(aIndex < mScrollMetadatas.Length());
   return mScrollMetadatas[aIndex];
 }
 
-bool
+Maybe<size_t>
 WebRenderScrollData::HasMetadataFor(const FrameMetrics::ViewID& aScrollId) const
 {
-  return mScrollIdMap.find(aScrollId) != mScrollIdMap.end();
+  auto it = mScrollIdMap.find(aScrollId);
+  return (it == mScrollIdMap.end() ? Nothing() : Some(it->second));
 }
 
 void
 WebRenderScrollData::SetFocusTarget(const FocusTarget& aFocusTarget)
 {
   mFocusTarget = aFocusTarget;
 }
 

--- a/gfx/layers/wr/WebRenderScrollData.h
+++ b/gfx/layers/wr/WebRenderScrollData.h
@@ -146,17 +146,17 @@ public:
   size_t GetLayerCount() const;
 
   // Return a pointer to the scroll data at the given index. Use with caution,
   // as the pointer may be invalidated if this WebRenderScrollData is mutated.
   WebRenderLayerScrollData* GetLayerDataMutable(size_t aIndex);
   const WebRenderLayerScrollData* GetLayerData(size_t aIndex) const;
 
   const ScrollMetadata& GetScrollMetadata(size_t aIndex) const;
-  bool HasMetadataFor(const FrameMetrics::ViewID& aScrollId) const;
+  Maybe<size_t> HasMetadataFor(const FrameMetrics::ViewID& aScrollId) const;
 
   const FocusTarget& GetFocusTarget() const { return mFocusTarget; }
   void SetFocusTarget(const FocusTarget& aFocusTarget);
 
   void SetIsFirstPaint();
   bool IsFirstPaint() const;
   void SetPaintSequenceNumber(uint32_t aPaintSequenceNumber);
   uint32_t GetPaintSequenceNumber() const;