gistfile1.txt

diff --git a/gfx/layers/apz/src/APZCTreeManager.cpp b/gfx/layers/apz/src/APZCTreeManager.cpp
index d6757151b7f0..8919e03eef4b 100644
--- a/gfx/layers/apz/src/APZCTreeManager.cpp
+++ b/gfx/layers/apz/src/APZCTreeManager.cpp
@@ -2507,17 +2507,19 @@ already_AddRefed<AsyncPanZoomController> APZCTreeManager::GetAPZCAtPointWR(
     return result.forget();
   }

   LayersId layersId = wr::AsLayersId(pipelineId);
   result = GetTargetAPZC(layersId, scrollId);
   if (!result) {
     // It falls back to the root
     MOZ_ASSERT(scrollId == ScrollableLayerGuid::NULL_SCROLL_ID);
-    result = FindRootApzcForLayersId(layersId);
+    HitTestingTreeNode* httn = FindRootHitTestingTreeNodeForLayersId(layersId);
+    CSSTransformMatrix theMatrixHenriWants = httn->GetCSSTransformToContent();
+    result = httn->GetNearestContainingApzc();
     MOZ_ASSERT(result);
   }

   const bool isScrollbar =
       hitInfo.contains(gfx::CompositorHitTestFlags::eScrollbar);
   const bool isScrollbarThumb =
       hitInfo.contains(gfx::CompositorHitTestFlags::eScrollbarThumb);
   const ScrollDirection direction =
@@ -2730,26 +2732,32 @@ AsyncPanZoomController* APZCTreeManager::GetAPZCAtPoint(
     APZCTM_LOG("Successfully matched APZC %p via node %p (hit result 0x%x)\n",
                result, resultNode, aOutHitResult->serialize());
     return result;
   }

   return nullptr;
 }

-AsyncPanZoomController* APZCTreeManager::FindRootApzcForLayersId(
+HitTestingTreeNode* APZCTreeManager::FindRootHitTestingTreeNodeForLayersId(
     LayersId aLayersId) const {
   mTreeLock.AssertCurrentThreadIn();

   HitTestingTreeNode* resultNode = BreadthFirstSearch<ReverseIterator>(
       mRootNode.get(), [aLayersId](HitTestingTreeNode* aNode) {
         AsyncPanZoomController* apzc = aNode->GetApzc();
         return apzc && apzc->GetLayersId() == aLayersId &&
                apzc->IsRootForLayersId();
       });
+  return resultNode;
+}
+
+AsyncPanZoomController* APZCTreeManager::FindRootApzcForLayersId(
+    LayersId aLayersId) const {
+  HitTestingTreeNode* resultNode = FindRootHitTestingTreeNodeForLayersId(aLayersId);
   return resultNode ? resultNode->GetApzc() : nullptr;
 }

 AsyncPanZoomController* APZCTreeManager::FindRootContentApzcForLayersId(
     LayersId aLayersId) const {
   mTreeLock.AssertCurrentThreadIn();

   HitTestingTreeNode* resultNode = BreadthFirstSearch<ReverseIterator>(
diff --git a/gfx/layers/apz/src/HitTestingTreeNode.cpp b/gfx/layers/apz/src/HitTestingTreeNode.cpp
index 44d547d8faca..958acaf19b20 100644
--- a/gfx/layers/apz/src/HitTestingTreeNode.cpp
+++ b/gfx/layers/apz/src/HitTestingTreeNode.cpp
@@ -305,16 +305,23 @@ CompositorHitTestInfo HitTestingTreeNode::HitTest(
 EventRegionsOverride HitTestingTreeNode::GetEventRegionsOverride() const {
   return mOverride;
 }

 const CSSTransformMatrix& HitTestingTreeNode::GetTransform() const {
   return mTransform;
 }

+const CSSTransformMatrix& HitTestingTreeNode::GetCSSTransformToContent() const {
+  if (mParent) {
+    return mParent->GetCSSTransformToContent() * mTransform;
+  }
+  return mTransform;
+}
+
 const LayerIntRegion& HitTestingTreeNode::GetVisibleRegion() const {
   return mVisibleRegion;
 }

 bool HitTestingTreeNode::IsAsyncZoomContainer() const {
   return mIsAsyncZoomContainer;
 }

diff --git a/gfx/layers/apz/src/HitTestingTreeNode.h b/gfx/layers/apz/src/HitTestingTreeNode.h
index 7c27b462b4cf..16b7dee842fd 100644
--- a/gfx/layers/apz/src/HitTestingTreeNode.h
+++ b/gfx/layers/apz/src/HitTestingTreeNode.h
@@ -134,16 +134,17 @@ class HitTestingTreeNode {
       const ParentLayerPoint& aPoint,
       const LayerToParentLayerMatrix4x4& aTransform) const;
   /* Assuming aPoint is inside the clip region for this node, check which of the
    * event region spaces it falls inside. */
   gfx::CompositorHitTestInfo HitTest(const LayerPoint& aPoint) const;
   /* Returns the mOverride flag. */
   EventRegionsOverride GetEventRegionsOverride() const;
   const CSSTransformMatrix& GetTransform() const;
+  const CSSTransformMatrix& GetCSSTransformToContent() const;
   const LayerIntRegion& GetVisibleRegion() const;

   bool IsAsyncZoomContainer() const;

   /* Debug helpers */
   void Dump(const char* aPrefix = "") const;

  private: