--- a/gfx/layers/ipc/CompositorBridgeParent.cpp
+++ b/gfx/layers/ipc/CompositorBridgeParent.cpp
@@ -352,39 +352,44 @@ void
 CompositorBridgeParent::InitSameProcess(widget::CompositorWidget* aWidget,
                                         const uint64_t& aLayerTreeId)
 {
   MOZ_ASSERT(XRE_IsParentProcess());
   MOZ_ASSERT(NS_IsMainThread());
 
   mWidget = aWidget;
   mRootLayerTreeID = aLayerTreeId;
-  if (mOptions.UseAPZ()) {
-    mApzcTreeManager = new APZCTreeManager(mRootLayerTreeID);
-    mApzSampler = new APZSampler(mApzcTreeManager);
-  }
 
   Initialize();
 }
 
 mozilla::ipc::IPCResult
 CompositorBridgeParent::RecvInitialize(const uint64_t& aRootLayerTreeId)
 {
+  MOZ_ASSERT(XRE_IsGPUProcess());
+
   mRootLayerTreeID = aRootLayerTreeId;
 
   Initialize();
   return IPC_OK();
 }
 
 void
 CompositorBridgeParent::Initialize()
 {
   MOZ_ASSERT(CompositorThread(),
              "The compositor thread must be Initialized before instanciating a CompositorBridgeParent.");
 
+  if (mOptions.UseAPZ()) {
+    MOZ_ASSERT(!mApzcTreeManager);
+    MOZ_ASSERT(!mApzSampler);
+    mApzcTreeManager = new APZCTreeManager(mRootLayerTreeID);
+    mApzSampler = new APZSampler(mApzcTreeManager);
+  }
+
   mCompositorBridgeID = 0;
   // FIXME: This holds on the the fact that right now the only thing that
   // can destroy this instance is initialized on the compositor thread after
   // this task has been processed.
   MOZ_ASSERT(CompositorLoop());
   CompositorLoop()->PostTask(NewRunnableFunction("AddCompositorRunnable",
                                                  &AddCompositor,
                                                  this, &mCompositorBridgeID));
@@ -1082,28 +1087,25 @@ CompositorBridgeParent::ForceComposeToTa
   AutoRestore<bool> override(mOverrideComposeReadiness);
   mOverrideComposeReadiness = true;
   mCompositorScheduler->ForceComposeToTarget(aTarget, aRect);
 }
 
 PAPZCTreeManagerParent*
 CompositorBridgeParent::AllocPAPZCTreeManagerParent(const uint64_t& aLayersId)
 {
+  // This should only ever get called in the GPU process.
+  MOZ_ASSERT(XRE_IsGPUProcess());
   // We should only ever get this if APZ is enabled in this compositor.
   MOZ_ASSERT(mOptions.UseAPZ());
-
+  // The mApzcTreeManager should have been created via RecvInitialize()
+  MOZ_ASSERT(mApzcTreeManager);
   // The main process should pass in 0 because we assume mRootLayerTreeID
   MOZ_ASSERT(aLayersId == 0);
 
-  // This message doubles as initialization
-  MOZ_ASSERT(!mApzcTreeManager);
-
-  mApzcTreeManager = new APZCTreeManager(mRootLayerTreeID);
-  mApzSampler = new APZSampler(mApzcTreeManager);
-
   MonitorAutoLock lock(*sIndirectLayerTreesLock);
   CompositorBridgeParent::LayerTreeState& state = sIndirectLayerTrees[mRootLayerTreeID];
   MOZ_ASSERT(state.mParent.get() == this);
   MOZ_ASSERT(!state.mApzcTreeManagerParent);
   state.mApzcTreeManagerParent = new APZCTreeManagerParent(mRootLayerTreeID, mApzcTreeManager);
 
   return state.mApzcTreeManagerParent;
 }