--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -1415,17 +1415,17 @@ nsDisplayListBuilder::GetDirtyRectForScr
     return nsRect();
   }
   return result;
 }
 
 bool
 nsDisplayListBuilder::IsBuildingLayerEventRegions()
 {
-  if (mMode == PAINTING) {
+  if (IsPaintingToWindow()) {
     // Note: this function and LayerEventRegionsEnabled are the only places
     // that get to query LayoutEventRegionsEnabled 'directly' - other code
     // should call this function.
     return gfxPrefs::LayoutEventRegionsEnabledDoNotUseDirectly() ||
            mAsyncPanZoomEnabled;
   }
   return false;
 }