diff --git a/gfx/layers/composite/CompositableHost.h b/gfx/layers/composite/CompositableHost.h
index 10df6c8435e6..257c6885eee8 100644
--- a/gfx/layers/composite/CompositableHost.h
+++ b/gfx/layers/composite/CompositableHost.h
@@ -78,7 +78,7 @@ protected:
   virtual ~CompositableHost();
 
 public:
-  NS_INLINE_DECL_REFCOUNTING(CompositableHost)
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(CompositableHost)
   explicit CompositableHost(const TextureInfo& aTextureInfo);
 
   static already_AddRefed<CompositableHost> Create(const TextureInfo& aTextureInfo);
diff --git a/gfx/layers/ipc/ImageBridgeChild.cpp b/gfx/layers/ipc/ImageBridgeChild.cpp
index 8b8ff296834f..dc77a96d007a 100644
--- a/gfx/layers/ipc/ImageBridgeChild.cpp
+++ b/gfx/layers/ipc/ImageBridgeChild.cpp
@@ -295,18 +295,17 @@ ImageBridgeChild::ShutdownStep2(SynchronousTask* aTask)
 
   MOZ_ASSERT(InImageBridgeChildThread(),
              "Should be in ImageBridgeChild thread.");
-
-  if (!mCalledClose) {
-    Close();
-    mCalledClose = true;
-  }
+  Close();
 }
 
 void
 ImageBridgeChild::ActorDestroy(ActorDestroyReason aWhy)
 {
   mCanSend = false;
-  mCalledClose = true;
+  {
+    MutexAutoLock lock(mContainerMapLock);
+    mImageContainers.Clear();
+  }
 }
 
 void
@@ -338,7 +337,7 @@ ImageBridgeChild::CreateCanvasClientSync(SynchronousTask* aTask,
 
 ImageBridgeChild::ImageBridgeChild()
   : mCanSend(false)
-  , mCalledClose(false)
+  , mDestroyed(false)
   , mFwdTransactionId(0)
   , mContainerMapLock("ImageBridgeChild.mContainerMapLock")
 {
@@ -736,6 +735,8 @@ ImageBridgeChild::WillShutdown()
 
     task.Wait();
   }
+
+  mDestroyed = true;
 }
 
 void
@@ -998,6 +999,12 @@ ImageBridgeChild::DeallocShmem(ipc::Shmem& aShmem)
     return PImageBridgeChild::DeallocShmem(aShmem);
   }
 
+  // If we can't post a task, then we definitely cannot send, so there's
+  // no reason to queue up this send.
+  if (!CanPostTask()) {
+    return false;
+  }
+
   SynchronousTask task("AllocatorProxy Dealloc");
   bool result = false;
 
@@ -1150,10 +1157,32 @@ bool ImageBridgeChild::IsSameProcess() const
   return OtherPid() == base::GetCurrentProcId();
 }
 
+bool
+ImageBridgeChild::CanPostTask() const
+{
+  // During shutdown, the cycle collector may free objects that are holding a
+  // reference to ImageBridgeChild. Since this happens on the main thread,
+  // ImageBridgeChild will attempt to post a task to the ImageBridge thread.
+  // However the thread manager has already been shut down, so the task cannot
+  // post.
+  //
+  // It's okay if this races. We only care about the shutdown case where
+  // everything's happening on the main thread. Even if it races outside of
+  // shutdown, it's still harmless to post the task, since the task must
+  // check CanSend().
+  return !mDestroyed;
+}
+
 void
 ImageBridgeChild::ReleaseCompositable(const CompositableHandle& aHandle)
 {
   if (!InImageBridgeChildThread()) {
+    // If we can't post a task, then we definitely cannot send, so there's
+    // no reason to queue up this send.
+    if (!CanPostTask()) {
+      return;
+    }
+
     RefPtr<Runnable> runnable = WrapRunnable(
       RefPtr<ImageBridgeChild>(this),
       &ImageBridgeChild::ReleaseCompositable,
diff --git a/gfx/layers/ipc/ImageBridgeChild.h b/gfx/layers/ipc/ImageBridgeChild.h
index 46ad683ddfa7..82ca193ff481 100644
--- a/gfx/layers/ipc/ImageBridgeChild.h
+++ b/gfx/layers/ipc/ImageBridgeChild.h
@@ -360,6 +360,7 @@ protected:
   void DeallocPImageBridgeChild() override;
 
   bool CanSend() const;
+  bool CanPostTask() const;
 
   static void ShutdownSingleton();
 
@@ -367,7 +368,7 @@ private:
   CompositableTransaction* mTxn;
 
   bool mCanSend;
-  bool mCalledClose;
+  mozilla::Atomic<bool> mDestroyed;
 
   /**
    * Transaction id of CompositableForwarder.
diff --git a/gfx/layers/ipc/ImageBridgeParent.cpp b/gfx/layers/ipc/ImageBridgeParent.cpp
index 50fb1ce49235..ddd168a167bb 100644
--- a/gfx/layers/ipc/ImageBridgeParent.cpp
+++ b/gfx/layers/ipc/ImageBridgeParent.cpp
@@ -104,6 +104,7 @@ ImageBridgeParent::ActorDestroy(ActorDestroyReason aWhy)
 {
   // Can't alloc/dealloc shmems from now on.
   mClosed = true;
+  mCompositables.clear();
 
   MessageLoop::current()->PostTask(NewRunnableMethod(this, &ImageBridgeParent::DeferredDestroy));
 
diff --git a/gfx/layers/ipc/LayerTransactionParent.cpp b/gfx/layers/ipc/LayerTransactionParent.cpp
index 5e97c5326017..ce6cfd882d9d 100644
--- a/gfx/layers/ipc/LayerTransactionParent.cpp
+++ b/gfx/layers/ipc/LayerTransactionParent.cpp
@@ -94,6 +94,7 @@ void
 LayerTransactionParent::Destroy()
 {
   mDestroyed = true;
+  mCompositables.clear();
 }
 
 mozilla::ipc::IPCResult