--- a/gfx/layers/ImageLayers.h
+++ b/gfx/layers/ImageLayers.h
@@ -167,16 +167,23 @@ public:
     return mManager;
   }
 
   /**
    * Returns the size of the image in pixels.
    */
   virtual gfxIntSize GetCurrentSize() = 0;
 
+  /**
+   * Set a new layer manager for this image container.  It must be
+   * either of the same type as the container's current layer manager,
+   * or null.  TRUE is returned on success.
+   */
+  virtual PRBool SetLayerManager(LayerManager *aManager) = 0;
+
 protected:
   LayerManager* mManager;
 
   ImageContainer(LayerManager* aManager) : mManager(aManager) {}
 };
 
 /**
  * A Layer which renders an Image.

--- a/gfx/layers/Layers.h
+++ b/gfx/layers/Layers.h
@@ -137,23 +137,32 @@ class THEBES_API LayerManager {
 
 public:
   enum LayersBackend {
     LAYERS_BASIC = 0,
     LAYERS_OPENGL,
     LAYERS_D3D9
   };
 
-  LayerManager() : mUserData(nsnull)
+  LayerManager() : mUserData(nsnull), mDestroyed(PR_FALSE)
   {
     InitLog();
   }
   virtual ~LayerManager() {}
 
   /**
+   * Release layers and resources held by this layer manager, and mark
+   * it as destroyed.  Should do any cleanup necessary in preparation
+   * for its widget going away.  After this call, only user data calls
+   * are valid on the layer manager.
+   */
+  virtual void Destroy() { mDestroyed = PR_TRUE; }
+  PRBool IsDestroyed() { return mDestroyed; }
+
+  /**
    * Start a new transaction. Nested transactions are not allowed so
    * there must be no transaction currently in progress.
    * This transaction will update the state of the window from which
    * this LayerManager was obtained.
    */
   virtual void BeginTransaction() = 0;
   /**
    * Start a new transaction. Nested transactions are not allowed so
@@ -292,16 +301,17 @@ public:
   void LogSelf(const char* aPrefix="");
 
   static bool IsLogEnabled();
   static PRLogModuleInfo* GetLog() { return sLog; }
 
 protected:
   nsRefPtr<Layer> mRoot;
   void* mUserData;
+  PRPackedBool mDestroyed;
 
   // Print interesting information about this into aTo.  Internally
   // used to implement Dump*() and Log*().
   virtual nsACString& PrintInfo(nsACString& aTo, const char* aPrefix);
 
   static void InitLog();
   static PRLogModuleInfo* sLog;
 };
@@ -323,17 +333,19 @@ public:
     TYPE_COLOR,
     TYPE_CANVAS,
     TYPE_SHADOW
   };
 
   virtual ~Layer() {}
 
   /**
-   * Returns the LayoutManager this Layer belongs to. Cannot be null.
+   * Returns the LayerManager this Layer belongs to. Note that the layer
+   * manager might be in a destroyed state, at which point it's only
+   * valid to set/get user data from it.
    */
   LayerManager* Manager() { return mManager; }
 
   /**
    * CONSTRUCTION PHASE ONLY
    * If this is called with aOpaque set to true, the caller is promising
    * that by the end of this transaction the entire visible region
    * (as specified by SetVisibleRegion) will be filled with opaque
@@ -382,16 +394,17 @@ public:
   void SetClipRect(const nsIntRect* aRect)
   {
     mUseClipRect = aRect != nsnull;
     if (aRect) {
       mClipRect = *aRect;
     }
     Mutated();
   }
+
   /**
    * CONSTRUCTION PHASE ONLY
    * Set a clip rect which will be applied to this layer as it is
    * composited to the destination. The coordinates are relative to
    * the parent layer (i.e. the contents of this layer
    * are transformed before this clip rect is applied).
    * For the root layer, the coordinates are relative to the widget,
    * in device pixels.