diff --git a/layout/base/nsDisplayList.h b/layout/base/nsDisplayList.h
index 8aca154cb401..2bdc5e422f59 100644
--- a/layout/base/nsDisplayList.h
+++ b/layout/base/nsDisplayList.h
@@ -470,6 +470,18 @@ public:
     return CurrentPresShellState()->mPresShell->GetPresContext();
   }
 
+  /**
+   * Accumulates the bounds of box frames that have moz-appearance
+   * -moz-win-exclude-glass style. Used in setting glass margins on
+   * Windows.
+   */  
+  void AddExcludedGlassRegion(nsRect &bounds) {
+    mExcludedGlassRegion.Or(mExcludedGlassRegion, bounds);
+  }
+  const nsRegion& GetExcludedGlassRegion() {
+    return mExcludedGlassRegion;
+  }
+
 private:
   void MarkOutOfFlowFrameForDisplay(nsIFrame* aDirtyFrame, nsIFrame* aFrame,
                                     const nsRect& aDirtyRect);
@@ -496,6 +508,7 @@ private:
   nsAutoTArray<ThemeGeometry,2>  mThemeGeometries;
   nsDisplayTableItem*            mCurrentTableItem;
   const nsRegion*                mFinalTransparentRegion;
+  nsRegion                       mExcludedGlassRegion;
   Mode                           mMode;
   PRPackedBool                   mBuildCaret;
   PRPackedBool                   mIgnoreSuppression;
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index f000f258ad73..04714ba28bf4 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -1636,16 +1636,17 @@ nsLayoutUtils::PaintFrame(nsRenderingContext* aRenderingContext, nsIFrame* aFram
 
   list.PaintRoot(&builder, aRenderingContext, flags);
 
-  // Update the widget's transparent region information. This sets
+  // Update the widget's opaque region information. This sets
   // glass boundaries on Windows.
   if ((aFlags & PAINT_WIDGET_LAYERS) &&
       !willFlushRetainedLayers &&
       !(aFlags & PAINT_DOCUMENT_RELATIVE)) {
     nsIWidget *widget = aFrame->GetNearestWidget();
     if (widget) {
-      PRInt32 pixelRatio = presContext->AppUnitsPerDevPixel();
-      nsIntRegion visibleWindowRegion(visibleRegion.ToOutsidePixels(pixelRatio));
-      widget->UpdateTransparentRegion(visibleWindowRegion);
+      nsRegion excludedRegion = builder.GetExcludedGlassRegion();
+      excludedRegion.Sub(excludedRegion, visibleRegion);
+      nsIntRegion windowRegion(excludedRegion.ToNearestPixels(presContext->AppUnitsPerDevPixel()));
+      widget->UpdateOpaqueRegion(windowRegion);
     }
   }
 
diff --git a/layout/xul/base/src/nsBoxFrame.cpp b/layout/xul/base/src/nsBoxFrame.cpp
index 03a7dab2df5c..bba01f858eda 100644
--- a/layout/xul/base/src/nsBoxFrame.cpp
+++ b/layout/xul/base/src/nsBoxFrame.cpp
@@ -1299,6 +1299,16 @@ nsBoxFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
     GetContent()->HasAttr(kNameSpaceID_None, nsGkAtoms::layer) &&
     GetContent()->IsXUL();
 
+  // Check for frames that are marked as a part of the region used
+  // in calculating glass margins on Windows.
+  if (GetContent()->IsXUL()) {
+      const nsStyleDisplay* styles = mStyleContext->GetStyleDisplay();
+      if (styles && styles->mAppearance == NS_THEME_WIN_EXCLUDE_GLASS) {
+        nsRect rect = mRect + aBuilder->ToReferenceFrame(this);
+        aBuilder->AddExcludedGlassRegion(rect);
+      }
+  }
+
   nsDisplayListCollection tempLists;
   const nsDisplayListSet& destination = forceLayer ? tempLists : aLists;