--- a/gfx/layers/wr/WebRenderScrollData.cpp
+++ b/gfx/layers/wr/WebRenderScrollData.cpp
@@ -1,16 +1,17 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/layers/WebRenderScrollData.h"
 
 #include "Layers.h"
+#include "LayersLogging.h"
 #include "mozilla/layout/RenderFrameParent.h"
 #include "mozilla/Unused.h"
 #include "nsTArray.h"
 #include "UnitTransforms.h"
 
 namespace mozilla {
 namespace layers {
 
@@ -123,16 +124,37 @@ WebRenderLayerScrollData::GetScrollMetad
 }
 
 CSSTransformMatrix
 WebRenderLayerScrollData::GetTransformTyped() const
 {
   return ViewAs<CSSTransformMatrix>(GetTransform());
 }
 
+void
+WebRenderLayerScrollData::Dump(const WebRenderScrollData& aOwner) const
+{
+  printf_stderr("LayerScrollData(%p) descendants %d\n", this, mDescendantCount);
+  for (size_t i : mScrollIds) {
+    printf_stderr("  metadata: %s\n", Stringify(aOwner.GetScrollMetadata(i)).c_str());
+  }
+  printf_stderr("  transform: %s perspective: %d visible: %s\n",
+    Stringify(mTransform).c_str(), mTransformIsPerspective,
+    Stringify(mVisibleRegion).c_str());
+  printf_stderr("  event regions: %s override: 0x%x\n",
+    Stringify(mEventRegions).c_str(), mEventRegionsOverride);
+  printf_stderr("  ref layers id: %" PRIu64 "\n", mReferentId.valueOr(0));
+  //printf_stderr("  scroll thumb: %s animation: %" PRIu64 "\n",
+  //  Stringify(mScrollThumbData).c_str(), mScrollbarAnimationId);
+  printf_stderr("  scroll container: %d target: %" PRIu64 "\n",
+    mIsScrollbarContainer, mScrollbarTargetContainerId);
+  printf_stderr("  fixed pos container: %" PRIu64 "\n",
+    mFixedPosScrollContainerId);
+}
+
 WebRenderScrollData::WebRenderScrollData()
   : mIsFirstPaint(false)
   , mPaintSequenceNumber(0)
 {
 }
 
 WebRenderScrollData::~WebRenderScrollData()
 {
@@ -222,10 +244,20 @@ WebRenderScrollData::SetPaintSequenceNum
 }
 
 uint32_t
 WebRenderScrollData::GetPaintSequenceNumber() const
 {
   return mPaintSequenceNumber;
 }
 
+void
+WebRenderScrollData::Dump() const
+{
+  printf_stderr("WebRenderScrollData with %zu layers firstpaint: %d\n",
+      mLayerScrollData.Length(), mIsFirstPaint);
+  for (size_t i = 0; i < mLayerScrollData.Length(); i++) {
+    mLayerScrollData.ElementAt(i).Dump(*this);
+  }
+}
+
 } // namespace layers
 } // namespace mozilla

--- a/gfx/layers/wr/WebRenderScrollData.h
+++ b/gfx/layers/wr/WebRenderScrollData.h
@@ -63,16 +63,18 @@ public:
   Maybe<uint64_t> GetReferentId() const { return mReferentId; }
   EventRegionsOverride GetEventRegionsOverride() const { return mEventRegionsOverride; }
   const ScrollThumbData& GetScrollThumbData() const { return mScrollThumbData; }
   const uint64_t& GetScrollbarAnimationId() const { return mScrollbarAnimationId; }
   FrameMetrics::ViewID GetScrollbarTargetContainerId() const { return mScrollbarTargetContainerId; }
   bool IsScrollbarContainer() const { return mIsScrollbarContainer; }
   FrameMetrics::ViewID GetFixedPositionScrollContainerId() const { return mFixedPosScrollContainerId; }
 
+  void Dump(const WebRenderScrollData& aOwner) const;
+
   friend struct IPC::ParamTraits<WebRenderLayerScrollData>;
 
 private:
   // The number of descendants this layer has (not including the layer itself).
   // This is needed to reconstruct the depth-first layer tree traversal
   // efficiently. Leaf layers should always have 0 descendants.
   int32_t mDescendantCount;
 
@@ -133,16 +135,18 @@ public:
 
   void SetIsFirstPaint();
   bool IsFirstPaint() const;
   void SetPaintSequenceNumber(uint32_t aPaintSequenceNumber);
   uint32_t GetPaintSequenceNumber() const;
 
   friend struct IPC::ParamTraits<WebRenderScrollData>;
 
+  void Dump() const;
+
 private:
   // Internal data structure used to maintain uniqueness of mScrollMetadatas.
   // This is not serialized/deserialized over IPC because there's no need for it,
   // as the parent side doesn't need this at all. Also because we don't have any
   // IPC-friendly hashtable implementation lying around.
   // The key into this map is the scrollId of a ScrollMetadata, and the value is
   // an index into the mScrollMetadatas array.
   std::map<FrameMetrics::ViewID, size_t> mScrollIdMap;