--- a/gfx/layers/wr/WebRenderBridgeParent.cpp
+++ b/gfx/layers/wr/WebRenderBridgeParent.cpp
@@ -6,16 +6,17 @@
 
 #include "mozilla/layers/WebRenderBridgeParent.h"
 
 #include "CompositableHost.h"
 #include "GLContext.h"
 #include "GLContextProvider.h"
 #include "mozilla/Range.h"
 #include "mozilla/layers/AnimationHelper.h"
+#include "mozilla/layers/APZCTreeManager.h"
 #include "mozilla/layers/Compositor.h"
 #include "mozilla/layers/CompositorBridgeParent.h"
 #include "mozilla/layers/CompositorThread.h"
 #include "mozilla/layers/CompositorVsyncScheduler.h"
 #include "mozilla/layers/ImageBridgeParent.h"
 #include "mozilla/layers/ImageDataSerializer.h"
 #include "mozilla/layers/TextureHost.h"
 #include "mozilla/layers/WebRenderCompositableHolder.h"
@@ -303,18 +304,59 @@ WebRenderBridgeParent::HandleDPEnd(const
   AutoWebRenderBridgeParentAsyncMessageSender autoAsyncMessageSender(this, &aToDestroy);
 
   ++mWrEpoch; // Update webrender epoch
   ProcessWebRenderCommands(aSize, aCommands, wr::NewEpoch(mWrEpoch),
                            dl, dlDesc, aux, auxDesc);
   HoldPendingTransactionId(mWrEpoch, aTransactionId);
 
   mScrollData = aScrollData;
-  // TODO: pass the WebRenderScrollData to APZ (this will happen in a future
-  // patch)
+  UpdateAPZ();
+}
+
+void
+WebRenderBridgeParent::UpdateAPZ()
+{
+  if (!mCompositorBridge) {
+    return;
+  }
+
+  CompositorBridgeParent* cbp;
+  uint64_t rootLayersId;
+  WebRenderBridgeParent* rootWrbp;
+  if (mWidget) {
+    // This WebRenderBridgeParent is attached to the root
+    // CompositorBridgeParent.
+    cbp = static_cast<CompositorBridgeParent*>(mCompositorBridge);
+    rootLayersId = wr::AsUint64(mPipelineId);
+    rootWrbp = this;
+  } else {
+    // This WebRenderBridgeParent is attached to a
+    // CrossProcessCompositorBridgeParent so we have an extra level of
+    // indirection to unravel.
+    uint64_t layersId = wr::AsUint64(mPipelineId);
+    CompositorBridgeParent::LayerTreeState* lts =
+        CompositorBridgeParent::GetIndirectShadowTree(layersId);
+    MOZ_ASSERT(lts);
+    cbp = lts->mParent;
+    rootLayersId = cbp->RootLayerTreeId();
+    lts = CompositorBridgeParent::GetIndirectShadowTree(rootLayersId);
+    MOZ_ASSERT(lts);
+    rootWrbp = lts->mWrBridge.get();
+  }
+
+  MOZ_ASSERT(cbp);
+  if (!rootWrbp) {
+    return;
+  }
+  if (RefPtr<APZCTreeManager> apzc = cbp->GetAPZCTreeManager()) {
+    apzc->UpdateHitTestingTree(rootLayersId, rootWrbp->GetScrollData(),
+        mScrollData.IsFirstPaint(), wr::AsUint64(mPipelineId),
+        /* TODO: propagate paint sequence number */ 0);
+  }
 }
 
 const WebRenderScrollData&
 WebRenderBridgeParent::GetScrollData() const
 {
   MOZ_ASSERT(mozilla::layers::CompositorThreadHolder::IsInCompositorThread());
   return mScrollData;
 }

--- a/gfx/layers/wr/WebRenderBridgeParent.h
+++ b/gfx/layers/wr/WebRenderBridgeParent.h
@@ -155,16 +155,17 @@ public:
     aNotifications->AppendElements(Move(mImageCompositeNotifications));
   }
 
   uint32_t GetIdNameSpace()
   {
     return mIdNameSpace;
   }
 
+  void UpdateAPZ();
   const WebRenderScrollData& GetScrollData() const;
 
 private:
   virtual ~WebRenderBridgeParent();
 
   void DeleteOldImages();
   void ProcessWebRenderCommands(const gfx::IntSize &aSize, InfallibleTArray<WebRenderParentCommand>& commands, const wr::Epoch& aEpoch,
                                     const ByteBuffer& dl,