--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -332,16 +332,32 @@ nsDOMWindowUtils::UpdateLayerTree()
       presShell->Paint(view, view->GetBounds(),
           nsIPresShell::PAINT_LAYERS | nsIPresShell::PAINT_SYNC_DECODE_IMAGES);
     }
   }
   return NS_OK;
 }
 
 NS_IMETHODIMP
+nsDOMWindowUtils::GetContentViewerSize(uint32_t *aDisplayWidth, uint32_t *aDisplayHeight)
+{
+  nsIPresShell* presShell = GetPresShell();
+  LayoutDeviceIntSize displaySize;
+
+  if (!presShell || !nsLayoutUtils::GetContentViewerSize(presShell->GetPresContext(), displaySize)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *aDisplayWidth = displaySize.width;
+  *aDisplayHeight = displaySize.height;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
 nsDOMWindowUtils::GetViewportInfo(uint32_t aDisplayWidth,
                                   uint32_t aDisplayHeight,
                                   double *aDefaultZoom, bool *aAllowZoom,
                                   double *aMinZoom, double *aMaxZoom,
                                   uint32_t *aWidth, uint32_t *aHeight,
                                   bool *aAutoSize)
 {
   nsIDocument* doc = GetDocument();

--- a/dom/interfaces/base/nsIDOMWindowUtils.idl
+++ b/dom/interfaces/base/nsIDOMWindowUtils.idl
@@ -117,16 +117,21 @@ interface nsIDOMWindowUtils : nsISupport
    */
   void getViewportInfo(in uint32_t aDisplayWidth, in uint32_t aDisplayHeight,
                        out double aDefaultZoom, out boolean aAllowZoom,
                        out double aMinZoom, out double aMaxZoom,
                        out uint32_t aWidth, out uint32_t aHeight,
                        out boolean aAutoSize);
 
   /**
+   * Information about the window size in device pixels.
+   */
+  void getContentViewerSize(out uint32_t aDisplayWidth, out uint32_t aDisplayHeight);
+
+  /**
    * For any scrollable element, this allows you to override the
    * visible region and draw more than what is visible, which is
    * useful for asynchronous drawing. The "displayport" will be
    * <xPx, yPx, widthPx, heightPx> in units of CSS pixels,
    * regardless of the size of the enclosing container.  This
    * will *not* trigger reflow.
    *
    * For the root scroll area, pass in the root document element.