--- a/gfx/layers/wr/WebRenderLayerManager.cpp
+++ b/gfx/layers/wr/WebRenderLayerManager.cpp
@@ -28,16 +28,17 @@ namespace mozilla {
 
 using namespace gfx;
 
 namespace layers {
 
 WebRenderLayerManager::WebRenderLayerManager(nsIWidget* aWidget)
   : mWidget(aWidget)
   , mLatestTransactionId(0)
+  , mLastAsr(nullptr)
   , mNeedsComposite(false)
   , mIsFirstPaint(false)
   , mEndTransactionWithoutLayers(false)
   , mTarget(nullptr)
   , mPaintSequenceNumber(0)
 {
   MOZ_COUNT_CTOR(WebRenderLayerManager);
 }
@@ -193,17 +194,16 @@ PopulateScrollData(WebRenderScrollData& 
 
 void
 WebRenderLayerManager::CreateWebRenderCommandsFromDisplayList(nsDisplayList* aDisplayList,
                                                               nsDisplayListBuilder* aDisplayListBuilder,
                                                               const StackingContextHelper& aSc,
                                                               wr::DisplayListBuilder& aBuilder)
 {
   bool apzEnabled = AsyncPanZoomEnabled();
-  const ActiveScrolledRoot* lastAsr = nullptr;
 
   nsDisplayList savedItems;
   nsDisplayItem* item;
   while ((item = aDisplayList->RemoveBottom()) != nullptr) {
     DisplayItemType itemType = item->GetType();
 
     // If the item is a event regions item, but is empty (has no regions in it)
     // then we should just throw it out
@@ -248,18 +248,18 @@ WebRenderLayerManager::CreateWebRenderCo
       // data that is in the display item.
       forceNewLayerData = item->UpdateScrollData(nullptr, nullptr);
 
       // Anytime the ASR changes we also want to force a new layer data because
       // the stack of scroll metadata is going to be different for this
       // display item than previously, so we can't squash the display items
       // into the same "layer".
       const ActiveScrolledRoot* asr = item->GetActiveScrolledRoot();
-      if (asr != lastAsr) {
-        lastAsr = asr;
+      if (asr != mLastAsr) {
+        mLastAsr = asr;
         forceNewLayerData = true;
       }
 
       // If we're going to create a new layer data for this item, stash the
       // ASR so that if we recurse into a sublist they will know where to stop
       // walking up their ASR chain when building scroll metadata.
       if (forceNewLayerData) {
         mAsrStack.push_back(asr);
@@ -610,16 +610,17 @@ WebRenderLayerManager::EndTransactionInt
     // transaction, so we reuse the previously built displaylist and scroll
     // metadata information
     if (aDisplayList && aDisplayListBuilder) {
       StackingContextHelper sc;
       mParentCommands.Clear();
       mScrollData = WebRenderScrollData();
       MOZ_ASSERT(mLayerScrollData.empty());
       mLastCanvasDatas.Clear();
+      mLastAsr = nullptr;
 
       CreateWebRenderCommandsFromDisplayList(aDisplayList, aDisplayListBuilder, sc, builder);
 
       builder.Finalize(contentSize, mBuiltDisplayList);
 
       // Make a "root" layer data that has everything else as descendants
       mLayerScrollData.emplace_back();
       mLayerScrollData.back().InitializeRoot(mLayerScrollData.size() - 1);

--- a/gfx/layers/wr/WebRenderLayerManager.h
+++ b/gfx/layers/wr/WebRenderLayerManager.h
@@ -267,16 +267,17 @@ private:
   // We use this as a temporary data structure while building the mScrollData
   // inside a layers-free transaction.
   std::vector<WebRenderLayerScrollData> mLayerScrollData;
   // We use this as a temporary data structure to track the current display
   // item's ASR as we recurse in CreateWebRenderCommandsFromDisplayList. We
   // need this so that WebRenderLayerScrollData items that deeper in the
   // tree don't duplicate scroll metadata that their ancestors already have.
   std::vector<const ActiveScrolledRoot*> mAsrStack;
+  const ActiveScrolledRoot* mLastAsr;
 
 public:
   // Note: two DisplayItemClipChain* A and B might actually be "equal" (as per
   // DisplayItemClipChain::Equal(A, B)) even though they are not the same pointer
   // (A != B). In this hopefully-rare case, they will get separate entries
   // in this map when in fact we could collapse them. However, to collapse
   // them involves writing a custom hash function for the pointer type such that
   // A and B hash to the same things whenever DisplayItemClipChain::Equal(A, B)