diff --git a/dom/plugins/base/nsPluginInstanceOwner.cpp b/dom/plugins/base/nsPluginInstanceOwner.cpp
index e108c41f6af..dc856427b8e 100644
--- a/dom/plugins/base/nsPluginInstanceOwner.cpp
+++ b/dom/plugins/base/nsPluginInstanceOwner.cpp
@@ -173,9 +173,8 @@ nsPluginInstanceOwner::GetImageContainer()
 
   // NotifySize() causes Flash to do a bunch of stuff like ask for surfaces to render
   // into, set y-flip flags, etc, so we do this at the beginning.
-  float xResolution = mObjectFrame->PresContext()->GetRootPresContext()->PresShell()->GetXResolution();
-  float yResolution = mObjectFrame->PresContext()->GetRootPresContext()->PresShell()->GetYResolution();
-  ScreenSize screenSize = (r * LayoutDeviceToScreenScale(xResolution, yResolution)).Size();
+  gfxSize resolution = mObjectFrame->PresContext()->PresShell()->GetCumulativeResolution();
+  ScreenSize screenSize = (r * LayoutDeviceToScreenScale(resolution.width, resolution.height)).Size();
   mInstance->NotifySize(nsIntSize(screenSize.width, screenSize.height));
   
   container = LayerManager::CreateImageContainer();