--- a/layout/xul/nsScrollbarFrame.cpp
+++ b/layout/xul/nsScrollbarFrame.cpp
@@ -164,25 +164,24 @@ nsresult
 nsScrollbarFrame::GetXULMargin(nsMargin& aMargin)
 {
   nsresult rv = NS_ERROR_FAILURE;
   aMargin.SizeTo(0,0,0,0);
 
   if (LookAndFeel::GetInt(LookAndFeel::eIntID_UseOverlayScrollbars) != 0) {
     nsPresContext* presContext = PresContext();
     nsITheme* theme = presContext->GetTheme();
-    if (theme) {
+    if (theme && theme->ThemeSupportsWidget(presContext, this, NS_THEME_SCROLLBAR)) {
       LayoutDeviceIntSize size;
       bool isOverridable;
       theme->GetMinimumWidgetSize(presContext, this, NS_THEME_SCROLLBAR, &size,
                                   &isOverridable);
       if (IsXULHorizontal()) {
         aMargin.top = -presContext->DevPixelsToAppUnits(size.height);
-      }
-      else {
+      } else {
         aMargin.left = -presContext->DevPixelsToAppUnits(size.width);
       }
       rv = NS_OK;
     }
   }
 
   if (NS_FAILED(rv)) {
     rv = nsBox::GetXULMargin(aMargin);