diff --git a/content/canvas/src/nsCanvasRenderingContext2D.cpp b/content/canvas/src/nsCanvasRenderingContext2D.cpp
index 0887c54dc85..55fcd468791 100644
--- a/content/canvas/src/nsCanvasRenderingContext2D.cpp
+++ b/content/canvas/src/nsCanvasRenderingContext2D.cpp
@@ -3347,7 +3347,8 @@ FlushLayoutForTree(nsIDOMWindow* aWindow)
 NS_IMETHODIMP
 nsCanvasRenderingContext2D::DrawWindow(nsIDOMWindow* aWindow, PRInt32 aX, PRInt32 aY,
                                        PRInt32 aW, PRInt32 aH, 
-                                       const nsAString& aBGColor)
+                                       const nsAString& aBGColor,
+                                       PRUint32 flags)
 {
     NS_ENSURE_ARG(aWindow != nsnull);
 
@@ -3367,9 +3368,10 @@ nsCanvasRenderingContext2D::DrawWindow(nsIDOMWindow* aWindow, PRInt32 aX, PRInt3
       // XXX ERRMSG we need to report an error to developers here! (bug 329026)
         return NS_ERROR_DOM_SECURITY_ERR;
     }
-    
+
     // Flush layout updates
-    FlushLayoutForTree(aWindow);
+    if (flags & nsIDOMCanvasRenderingContext2D::DRAWWINDOW_DO_NOT_FLUSH)
+        FlushLayoutForTree(aWindow);
 
     nsCOMPtr<nsPresContext> presContext;
     nsCOMPtr<nsPIDOMWindow> win = do_QueryInterface(aWindow);
diff --git a/dom/public/idl/canvas/nsIDOMCanvasRenderingContext2D.idl b/dom/public/idl/canvas/nsIDOMCanvasRenderingContext2D.idl
index 06982872a15..65f6bd26ea5 100644
--- a/dom/public/idl/canvas/nsIDOMCanvasRenderingContext2D.idl
+++ b/dom/public/idl/canvas/nsIDOMCanvasRenderingContext2D.idl
@@ -60,7 +60,7 @@ interface nsIDOMTextMetrics : nsISupports
   readonly attribute float width;
 };
 
-[scriptable, uuid(ac35c6a9-bea7-4e5f-85f6-ed43a13c6a2b)]
+[scriptable, uuid(66e6d87c-759c-43a7-b3d3-3348180b35df)]
 interface nsIDOMCanvasRenderingContext2D : nsISupports
 {
   // back-reference to the canvas element for which
@@ -161,6 +161,12 @@ interface nsIDOMCanvasRenderingContext2D : nsISupports
   // ImageData createImageData(in float w, in float h);
   void createImageData();
 
+  // Show the caret if appropriate when drawing
+  const unsigned long DRAWWINDOW_DRAW_CARET   = 0x01;
+  // Don't flush pending layout notifications that could otherwise
+  // be batched up
+  const unsigned long DRAWWINDOW_DO_NOT_FLUSH = 0x02;
+
   /**
    * Renders a region of a window into the canvas.  The contents of
    * the window's viewport are rendered, ignoring viewport clipping
@@ -177,6 +183,9 @@ interface nsIDOMCanvasRenderingContext2D : nsISupports
    * transparent/translucent. It is given as a CSS color string
    * (e.g., rgb() or rgba()).
    *
+   * @param flags Uused to better control the drawWindow call.
+   * Flags can be ORed together.
+   *
    * Of course, the rendering obeys the current scale, transform and
    * globalAlpha values.
    *
@@ -194,5 +203,6 @@ interface nsIDOMCanvasRenderingContext2D : nsISupports
    * only.
    */
   void drawWindow(in nsIDOMWindow window, in long x, in long y,
-                  in long w, in long h, in DOMString bgColor);
+                  in long w, in long h, in DOMString bgColor,
+                  [optional] in unsigned long flags);
 };