diff --git a/layout/base/nsDisplayList.cpp b/layout/base/nsDisplayList.cpp
index c8497535e8b9..862da3e2aedd 100644
--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -228,7 +228,8 @@ static PRUint64 RegionArea(const nsRegion& aRegion)
 
 void
 nsDisplayListBuilder::SubtractFromVisibleRegion(nsRegion* aVisibleRegion,
-                                                const nsRegion& aRegion)
+                                                const nsRegion& aRegion,
+                                                PRBool aForceSubtract)
 {
   if (aRegion.IsEmpty())
     return;
@@ -239,7 +240,8 @@ nsDisplayListBuilder::SubtractFromVisibleRegion(nsRegion* aVisibleRegion,
   // to its bounds either, which can be very bad (see bug 516740).
   // Do let aVisibleRegion get more complex if by doing so we reduce its
   // area by at least half.
-  if (GetAccurateVisibleRegions() || tmp.GetNumRects() <= 15 ||
+  if (aForceSubtract || GetAccurateVisibleRegions() ||
+      tmp.GetNumRects() <= 15 ||
       RegionArea(tmp) <= RegionArea(*aVisibleRegion)/2) {
     *aVisibleRegion = tmp;
   }
@@ -369,7 +371,9 @@ nsDisplayList::ComputeVisibilityForRoot(nsDisplayListBuilder* aBuilder,
                                         nsRegion* aVisibleRegion) {
   nsRegion r;
   r.And(*aVisibleRegion, GetBounds(aBuilder));
-  return ComputeVisibilityForSublist(aBuilder, aVisibleRegion, r.GetBounds());
+  PRBool notUsed;
+  return ComputeVisibilityForSublist(aBuilder, aVisibleRegion,
+                                     r.GetBounds(), notUsed);
 }
 
 static nsRegion
@@ -390,7 +394,8 @@ TreatAsOpaque(nsDisplayItem* aItem, nsDisplayListBuilder* aBuilder,
 PRBool
 nsDisplayList::ComputeVisibilityForSublist(nsDisplayListBuilder* aBuilder,
                                            nsRegion* aVisibleRegion,
-                                           const nsRect& aListVisibleBounds) {
+                                           const nsRect& aListVisibleBounds,
+                                           PRBool& aContainsRootContentDocBG) {
 #ifdef DEBUG
   nsRegion r;
   r.And(*aVisibleRegion, GetBounds(aBuilder));
@@ -421,12 +426,18 @@ nsDisplayList::ComputeVisibilityForSublist(nsDisplayListBuilder* aBuilder,
     itemVisible.And(*aVisibleRegion, bounds);
     item->mVisibleRect = itemVisible.GetBounds();
 
-    if (item->ComputeVisibility(aBuilder, aVisibleRegion)) {
+    PRBool containsRootContentDocBG = PR_FALSE;
+    if (item->ComputeVisibility(aBuilder, aVisibleRegion, 
+                                containsRootContentDocBG)) {
+      if (containsRootContentDocBG) {
+        aContainsRootContentDocBG = PR_TRUE;
+      }
       anyVisible = PR_TRUE;
       PRBool transparentBackground = PR_FALSE;
       nsRegion opaque = TreatAsOpaque(item, aBuilder, &transparentBackground);
       // Subtract opaque item from the visible region
-      aBuilder->SubtractFromVisibleRegion(aVisibleRegion, opaque);
+      aBuilder->SubtractFromVisibleRegion(aVisibleRegion, opaque,
+                                          containsRootContentDocBG);
       forceTransparentSurface = forceTransparentSurface || transparentBackground;
     }
     AppendToBottom(item);
@@ -731,7 +742,8 @@ PRBool nsDisplayItem::RecomputeVisibility(nsDisplayListBuilder* aBuilder,
   itemVisible.And(*aVisibleRegion, bounds);
   mVisibleRect = itemVisible.GetBounds();
 
-  if (!ComputeVisibility(aBuilder, aVisibleRegion))
+  PRBool notUsed;
+  if (!ComputeVisibility(aBuilder, aVisibleRegion, notUsed))
     return PR_FALSE;
 
   PRBool forceTransparentBackground;
@@ -746,6 +758,19 @@ void nsDisplaySolidColor::Paint(nsDisplayListBuilder* aBuilder,
   aCtx->FillRect(mVisibleRect);
 }
 
+PRBool
+nsDisplaySolidColor::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                       nsRegion* aVisibleRegion,
+                                       PRBool& aContainsRootContentDocBG)
+{
+  PRBool retval = nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion,
+                                                   aContainsRootContentDocBG);
+  if (retval && IsRootContentDocBackground()) {
+    aContainsRootContentDocBG = PR_TRUE;
+  }
+  return retval;
+}
+
 static void
 RegisterThemeGeometry(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
 {
@@ -895,10 +920,13 @@ nsDisplayBackground::HitTest(nsDisplayListBuilder* aBuilder,
 
 PRBool
 nsDisplayBackground::ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                       nsRegion* aVisibleRegion)
+                                       nsRegion* aVisibleRegion,
+                                       PRBool& aContainsRootContentDocBG)
 {
-  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion))
+  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion,
+                                        aContainsRootContentDocBG)) {
     return PR_FALSE;
+  }
 
   // Return false if the background was propagated away from this
   // frame. We don't want this display item to show up and confuse
@@ -1167,9 +1195,12 @@ nsDisplayOutline::Paint(nsDisplayListBuilder* aBuilder,
 
 PRBool
 nsDisplayOutline::ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                    nsRegion* aVisibleRegion) {
-  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion))
+                                    nsRegion* aVisibleRegion,
+                                    PRBool& aContainsRootContentDocBG) {
+  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion,
+                                        aContainsRootContentDocBG)) {
     return PR_FALSE;
+  }
 
   const nsStyleOutline* outline = mFrame->GetStyleOutline();
   nsRect borderBox(ToReferenceFrame(), mFrame->GetSize());
@@ -1209,9 +1240,12 @@ nsDisplayCaret::Paint(nsDisplayListBuilder* aBuilder,
 
 PRBool
 nsDisplayBorder::ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion) {
-  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion))
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG) {
+  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion,
+                                        aContainsRootContentDocBG)) {
     return PR_FALSE;
+  }
 
   nsRect paddingRect = mFrame->GetPaddingRect() - mFrame->GetPosition() +
     ToReferenceFrame();
@@ -1305,9 +1339,12 @@ nsDisplayBoxShadowOuter::GetBounds(nsDisplayListBuilder* aBuilder) {
 
 PRBool
 nsDisplayBoxShadowOuter::ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                           nsRegion* aVisibleRegion) {
-  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion))
+                                           nsRegion* aVisibleRegion,
+                                           PRBool& aContainsRootContentDocBG) {
+  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion,
+                                        aContainsRootContentDocBG)) {
     return PR_FALSE;
+  }
 
   // Store the actual visible region
   mVisibleRegion.And(*aVisibleRegion, mVisibleRect);
@@ -1348,9 +1385,12 @@ nsDisplayBoxShadowInner::Paint(nsDisplayListBuilder* aBuilder,
 
 PRBool
 nsDisplayBoxShadowInner::ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                           nsRegion* aVisibleRegion) {
-  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion))
+                                           nsRegion* aVisibleRegion,
+                                           PRBool& aContainsRootContentDocBG) {
+  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion,
+                                        aContainsRootContentDocBG)) {
     return PR_FALSE;
+  }
 
   // Store the actual visible region
   mVisibleRegion.And(*aVisibleRegion, mVisibleRect);
@@ -1386,9 +1426,11 @@ nsDisplayWrapList::GetBounds(nsDisplayListBuilder* aBuilder) {
 
 PRBool
 nsDisplayWrapList::ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                     nsRegion* aVisibleRegion) {
+                                     nsRegion* aVisibleRegion,
+                                     PRBool& aContainsRootContentDocBG) {
   return mList.ComputeVisibilityForSublist(aBuilder, aVisibleRegion,
-                                           mVisibleRect);
+                                           mVisibleRect,
+                                           aContainsRootContentDocBG);
 }
 
 nsRegion
@@ -1573,7 +1615,8 @@ nsDisplayOpacity::GetLayerState(nsDisplayListBuilder* aBuilder,
 }
 
 PRBool nsDisplayOpacity::ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                           nsRegion* aVisibleRegion) {
+                                           nsRegion* aVisibleRegion,
+                                           PRBool& aContainsRootContentDocBG) {
   // Our children are translucent so we should not allow them to subtract
   // area from aVisibleRegion. We do need to find out what is visible under
   // our children in the temporary compositing buffer, because if our children
@@ -1582,8 +1625,12 @@ PRBool nsDisplayOpacity::ComputeVisibility(nsDisplayListBuilder* aBuilder,
   nsRect bounds = GetBounds(aBuilder);
   nsRegion visibleUnderChildren;
   visibleUnderChildren.And(*aVisibleRegion, bounds);
+  // do not pass up the aContainsRootContentDocBG value because anything under
+  // us is not opaque
+  PRBool notUsed;
   return
-    nsDisplayWrapList::ComputeVisibility(aBuilder, &visibleUnderChildren);
+    nsDisplayWrapList::ComputeVisibility(aBuilder, &visibleUnderChildren,
+                                         notUsed);
 }
 
 PRBool nsDisplayOpacity::TryMerge(nsDisplayListBuilder* aBuilder, nsDisplayItem* aItem) {
@@ -1658,7 +1705,8 @@ nsDisplayScrollLayer::BuildLayer(nsDisplayListBuilder* aBuilder,
 
 PRBool
 nsDisplayScrollLayer::ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                        nsRegion* aVisibleRegion)
+                                        nsRegion* aVisibleRegion,
+                                        PRBool& aContainsRootContentDocBG)
 {
   nsPresContext* presContext = mFrame->PresContext();
   nsIPresShell* presShell = presContext->GetPresShell();
@@ -1673,13 +1721,14 @@ nsDisplayScrollLayer::ComputeVisibility(nsDisplayListBuilder* aBuilder,
     nsRect boundedRect;
     boundedRect.IntersectRect(childVisibleRegion.GetBounds(), mList.GetBounds(aBuilder));
     PRBool visible = mList.ComputeVisibilityForSublist(
-      aBuilder, &childVisibleRegion, boundedRect);
+      aBuilder, &childVisibleRegion, boundedRect, aContainsRootContentDocBG);
     mVisibleRect = boundedRect;
 
     return visible;
 
   } else {
-    return nsDisplayOwnLayer::ComputeVisibility(aBuilder, aVisibleRegion);
+    return nsDisplayOwnLayer::ComputeVisibility(aBuilder, aVisibleRegion,
+                                                aContainsRootContentDocBG);
   }
 }
 
@@ -1728,17 +1777,20 @@ void nsDisplayClip::Paint(nsDisplayListBuilder* aBuilder,
 }
 
 PRBool nsDisplayClip::ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                        nsRegion* aVisibleRegion) {
+                                        nsRegion* aVisibleRegion,
+                                        PRBool& aContainsRootContentDocBG) {
   nsRegion clipped;
   clipped.And(*aVisibleRegion, mClip);
 
   nsRegion finalClipped(clipped);
   PRBool anyVisible =
-    nsDisplayWrapList::ComputeVisibility(aBuilder, &finalClipped);
+    nsDisplayWrapList::ComputeVisibility(aBuilder, &finalClipped,
+                                         aContainsRootContentDocBG);
 
   nsRegion removed;
   removed.Sub(clipped, finalClipped);
-  aBuilder->SubtractFromVisibleRegion(aVisibleRegion, removed);
+  aBuilder->SubtractFromVisibleRegion(aVisibleRegion, removed,
+                                      aContainsRootContentDocBG);
 
   return anyVisible;
 }
@@ -1825,12 +1877,14 @@ nsDisplayClipRoundedRect::WrapWithClone(nsDisplayListBuilder* aBuilder,
 
 PRBool nsDisplayClipRoundedRect::ComputeVisibility(
                                     nsDisplayListBuilder* aBuilder,
-                                    nsRegion* aVisibleRegion)
+                                    nsRegion* aVisibleRegion,
+                                    PRBool& aContainsRootContentDocBG)
 {
   nsRegion clipped;
   clipped.And(*aVisibleRegion, mClip);
 
-  return nsDisplayWrapList::ComputeVisibility(aBuilder, &clipped);
+  PRBool notUsed;
+  return nsDisplayWrapList::ComputeVisibility(aBuilder, &clipped, notUsed);
   // FIXME: Remove a *conservative* opaque region from aVisibleRegion
   // (like in nsDisplayClip::ComputeVisibility).
 }
@@ -1892,7 +1946,8 @@ void nsDisplayZoom::Paint(nsDisplayListBuilder* aBuilder,
 }
 
 PRBool nsDisplayZoom::ComputeVisibility(nsDisplayListBuilder *aBuilder,
-                                        nsRegion *aVisibleRegion)
+                                        nsRegion *aVisibleRegion,
+                                        PRBool& aContainsRootContentDocBG)
 {
   // Convert the passed in visible region to our appunits.
   nsRegion visibleRegion =
@@ -1903,7 +1958,8 @@ PRBool nsDisplayZoom::ComputeVisibility(nsDisplayListBuilder *aBuilder,
     mVisibleRect.ConvertAppUnitsRoundOut(mParentAPD, mAPD);
   PRBool retval =
     mList.ComputeVisibilityForSublist(aBuilder, &visibleRegion,
-                                      transformedVisibleRect);
+                                      transformedVisibleRect,
+                                      aContainsRootContentDocBG);
 
   nsRegion removed;
   // removed = originalVisibleRegion - visibleRegion
@@ -1912,7 +1968,8 @@ PRBool nsDisplayZoom::ComputeVisibility(nsDisplayListBuilder *aBuilder,
   removed = removed.ConvertAppUnitsRoundIn(mAPD, mParentAPD);
   // aVisibleRegion = aVisibleRegion - removed (modulo any simplifications
   // SubtractFromVisibleRegion does)
-  aBuilder->SubtractFromVisibleRegion(aVisibleRegion, removed);
+  aBuilder->SubtractFromVisibleRegion(aVisibleRegion, removed,
+                                      aContainsRootContentDocBG);
 
   return retval;
 }
@@ -2098,7 +2155,8 @@ nsDisplayTransform::GetLayerState(nsDisplayListBuilder* aBuilder,
 }
 
 PRBool nsDisplayTransform::ComputeVisibility(nsDisplayListBuilder *aBuilder,
-                                             nsRegion *aVisibleRegion)
+                                             nsRegion *aVisibleRegion,
+                                             PRBool& aContainsRootContentDocBG)
 {
   /* As we do this, we need to be sure to
    * untransform the visible rect, since we want everything that's painting to
@@ -2379,7 +2437,8 @@ void nsDisplaySVGEffects::Paint(nsDisplayListBuilder* aBuilder,
 }
 
 PRBool nsDisplaySVGEffects::ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                              nsRegion* aVisibleRegion) {
+                                              nsRegion* aVisibleRegion,
+                                              PRBool& aContainsRootContentDocBG) {
   nsPoint offset = aBuilder->ToReferenceFrame(mEffectsFrame);
   nsRect dirtyRect =
     nsSVGIntegrationUtils::GetRequiredSourceForInvalidArea(mEffectsFrame,
@@ -2391,7 +2450,8 @@ PRBool nsDisplaySVGEffects::ComputeVisibility(nsDisplayListBuilder* aBuilder,
   nsRegion childrenVisible(dirtyRect);
   nsRect r;
   r.IntersectRect(dirtyRect, mList.GetBounds(aBuilder));
-  mList.ComputeVisibilityForSublist(aBuilder, &childrenVisible, r);
+  PRBool notUsed;
+  mList.ComputeVisibilityForSublist(aBuilder, &childrenVisible, r, notUsed);
   return PR_TRUE;
 }
 
diff --git a/layout/base/nsDisplayList.h b/layout/base/nsDisplayList.h
index 315953f7a61d..3db58a21a78d 100644
--- a/layout/base/nsDisplayList.h
+++ b/layout/base/nsDisplayList.h
@@ -327,10 +327,12 @@ public:
    * Subtracts aRegion from *aVisibleRegion. We avoid letting
    * aVisibleRegion become overcomplex by simplifying it if necessary ---
    * unless mAccurateVisibleRegions is set, in which case we let it
-   * get arbitrarily complex.
+   * get arbitrarily complex. If aForceSubtract is true then we subtract
+   * aRegion even if it makes the visible region more complex.
    */
   void SubtractFromVisibleRegion(nsRegion* aVisibleRegion,
-                                 const nsRegion& aRegion);
+                                 const nsRegion& aRegion,
+                                 PRBool aForceSubtract = PR_FALSE);
 
   /**
    * Mark the frames in aFrames to be displayed if they intersect aDirtyRect
@@ -705,10 +707,12 @@ public:
    * nsDisplayList::ComputeVisibility or nsDisplayItem::RecomputeVisibility.
    * 
    * @return PR_TRUE if the item is visible, PR_FALSE if no part of the item
-   * is visible
+   * is visible. aContainsRootContentDocBG is set to true if this item contains
+   * the background for the root content document.
    */
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion)
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG)
   { return !mVisibleRect.IsEmpty(); }
 
   /**
@@ -982,11 +986,14 @@ public:
    * I.e., opaque contents of this list are subtracted from aVisibleRegion.
    * @param aListVisibleBounds must be equal to the bounds of the intersection
    * of aVisibleRegion and GetBounds() for this list.
-   * @return true if any item in the list is visible
+   * @return true if any item in the list is visible. aContainsRootContentDocBG
+   * is set to true if the list contains the background for a root content
+   * document.
    */
   PRBool ComputeVisibilityForSublist(nsDisplayListBuilder* aBuilder,
                                      nsRegion* aVisibleRegion,
-                                     const nsRect& aListVisibleBounds);
+                                     const nsRect& aListVisibleBounds,
+                                     PRBool& aContainsRootContentDocBG);
 
   /**
    * As ComputeVisibilityForSublist, but computes visibility for a root
@@ -1391,7 +1398,8 @@ public:
   virtual nsRect GetBounds(nsDisplayListBuilder* aBuilder);
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
   NS_DISPLAY_DECL_NAME("Border", TYPE_BORDER)
 
 protected:
@@ -1412,8 +1420,10 @@ protected:
 class nsDisplaySolidColor : public nsDisplayItem {
 public:
   nsDisplaySolidColor(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
-                      const nsRect& aBounds, nscolor aColor)
-    : nsDisplayItem(aBuilder, aFrame), mBounds(aBounds), mColor(aColor) {
+                      const nsRect& aBounds, nscolor aColor,
+                      PRBool aIsRootContentDocBackground = PR_FALSE)
+    : nsDisplayItem(aBuilder, aFrame), mBounds(aBounds), mColor(aColor),
+      mIsRootContentDocBackground(aIsRootContentDocBackground) {
     NS_ASSERTION(NS_GET_A(aColor) > 0, "Don't create invisible nsDisplaySolidColors!");
     MOZ_COUNT_CTOR(nsDisplaySolidColor);
   }
@@ -1445,12 +1455,20 @@ public:
 
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
 
+  virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
+
+  PRBool IsRootContentDocBackground() {
+    return mIsRootContentDocBackground;
+  }
+
   NS_DISPLAY_DECL_NAME("SolidColor", TYPE_SOLID_COLOR)
 
 private:
   nsRect  mBounds;
   nscolor mColor;
-  PRBool  mTransparentBackground;
+  PRPackedBool mIsRootContentDocBackground;
 };
 
 /**
@@ -1468,7 +1486,8 @@ public:
   virtual void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
                        HitTestState* aState, nsTArray<nsIFrame*> *aOutFrames);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
   virtual nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
                                    PRBool* aForceTransparentSurface = nsnull);
   virtual PRBool IsVaryingRelativeToMovingFrame(nsDisplayListBuilder* aBuilder,
@@ -1506,7 +1525,8 @@ public:
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   virtual nsRect GetBounds(nsDisplayListBuilder* aBuilder);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
   NS_DISPLAY_DECL_NAME("BoxShadowOuter", TYPE_BOX_SHADOW_OUTER)
 
 private:
@@ -1530,7 +1550,8 @@ public:
 
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
   NS_DISPLAY_DECL_NAME("BoxShadowInner", TYPE_BOX_SHADOW_INNER)
 
 private:
@@ -1555,7 +1576,8 @@ public:
   virtual nsRect GetBounds(nsDisplayListBuilder* aBuilder);
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
   NS_DISPLAY_DECL_NAME("Outline", TYPE_OUTLINE)
 };
 
@@ -1616,7 +1638,8 @@ public:
                                                 nsIFrame* aFrame);
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
   virtual PRBool TryMerge(nsDisplayListBuilder* aBuilder, nsDisplayItem* aItem) {
     NS_WARNING("This list should already have been flattened!!!");
     return PR_FALSE;
@@ -1700,7 +1723,8 @@ public:
   virtual LayerState GetLayerState(nsDisplayListBuilder* aBuilder,
                                    LayerManager* aManager);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);  
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);  
   virtual PRBool TryMerge(nsDisplayListBuilder* aBuilder, nsDisplayItem* aItem);
   NS_DISPLAY_DECL_NAME("Opacity", TYPE_OPACITY)
 };
@@ -1766,7 +1790,8 @@ public:
                                              LayerManager* aManager);
 
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
 
 private:
   nsIFrame* mViewportFrame;
@@ -1796,7 +1821,8 @@ public:
   virtual nsRect GetBounds(nsDisplayListBuilder* aBuilder);
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
   virtual PRBool TryMerge(nsDisplayListBuilder* aBuilder, nsDisplayItem* aItem);
   NS_DISPLAY_DECL_NAME("Clip", TYPE_CLIP)
   virtual PRUint32 GetPerFrameKey() { return 0; }
@@ -1837,7 +1863,8 @@ public:
   virtual void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
                        HitTestState* aState, nsTArray<nsIFrame*> *aOutFrames);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
   virtual PRBool TryMerge(nsDisplayListBuilder* aBuilder, nsDisplayItem* aItem);
   NS_DISPLAY_DECL_NAME("ClipRoundedRect", TYPE_CLIP_ROUNDED_RECT)
 
@@ -1877,7 +1904,8 @@ public:
   virtual void HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
                        HitTestState* aState, nsTArray<nsIFrame*> *aOutFrames);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
   NS_DISPLAY_DECL_NAME("Zoom", TYPE_ZOOM)
 
   // Get the app units per dev pixel ratio of the child document.
@@ -1911,7 +1939,8 @@ public:
   }
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);  
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);  
   virtual PRBool TryMerge(nsDisplayListBuilder* aBuilder, nsDisplayItem* aItem);
   NS_DISPLAY_DECL_NAME("SVGEffects", TYPE_SVG_EFFECTS)
 
@@ -1974,7 +2003,8 @@ public:
   virtual already_AddRefed<Layer> BuildLayer(nsDisplayListBuilder* aBuilder,
                                              LayerManager* aManager);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder *aBuilder,
-                                   nsRegion *aVisibleRegion);
+                                   nsRegion *aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
   virtual PRBool TryMerge(nsDisplayListBuilder *aBuilder, nsDisplayItem *aItem);
 
   /**
diff --git a/layout/base/nsIPresShell.h b/layout/base/nsIPresShell.h
index 19857a33b3aa..f0e60568f66f 100644
--- a/layout/base/nsIPresShell.h
+++ b/layout/base/nsIPresShell.h
@@ -140,8 +140,8 @@ typedef struct CapturingContentInfo {
     { 0x95, 0x47, 0x85, 0x06, 0x5e, 0x02, 0xec, 0xb4 } }
 
 #define NS_IPRESSHELL_MOZILLA_2_0_BRANCH_IID     \
- { 0x5e445910, 0xfbee, 0x11df, \
-    { 0x8c, 0xff, 0x08, 0x00, 0x20, 0x0c, 0x9a, 0x66 } }
+ { 0x4abb9970, 0xd7ce, 0x4c02, \
+    { 0x8a, 0xdb, 0x42, 0xc6, 0xbd, 0xa8, 0x95, 0xb7 } }
 
 #define NS_IPRESSHELL_MOZILLA_2_0_BRANCH2_IID     \
  { 0x5ff6fd00, 0x1ba9, 0x11e0, \
@@ -180,6 +180,26 @@ public:
   NS_DECLARE_STATIC_IID_ACCESSOR(NS_IPRESSHELL_MOZILLA_2_0_BRANCH_IID)
 
   virtual PRBool GetIsViewportOverridden() = 0;
+
+  /**
+   * Add a solid color item to the bottom of aList with frame aFrame and bounds
+   * aBounds. Checks first if this needs to be done by checking if aFrame is a
+   * canvas frame (if the FORCE_DRAW flag is passed then this check is skipped).
+   * aBackstopColor is composed behind the background color of the canvas, it is
+   * transparent by default. The ROOT_CONTENT_DOC_BG flag indicates that this is
+   * the background for the root content document.
+   */
+  enum {
+    FORCE_DRAW = 0x01,
+    ROOT_CONTENT_DOC_BG = 0x02
+  };
+  virtual nsresult AddCanvasBackgroundColorItem2(nsDisplayListBuilder& aBuilder,
+                                                nsDisplayList& aList,
+                                                nsIFrame* aFrame,
+                                                const nsRect& aBounds,
+                                                nscolor aBackstopColor = NS_RGBA(0,0,0,0),
+                                                PRUint32 aFlags = 0) = 0;
+
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(nsIPresShell_MOZILLA_2_0_BRANCH,
diff --git a/layout/base/nsPresShell.cpp b/layout/base/nsPresShell.cpp
index 8b6ee87501d6..15eac91d02a6 100644
--- a/layout/base/nsPresShell.cpp
+++ b/layout/base/nsPresShell.cpp
@@ -954,6 +954,13 @@ public:
 
   virtual void UpdateCanvasBackground();
 
+  virtual nsresult AddCanvasBackgroundColorItem2(nsDisplayListBuilder& aBuilder,
+                                                nsDisplayList& aList,
+                                                nsIFrame* aFrame,
+                                                const nsRect& aBounds,
+                                                nscolor aBackstopColor,
+                                                PRUint32 aFlags);
+
   virtual nsresult AddCanvasBackgroundColorItem(nsDisplayListBuilder& aBuilder,
                                                 nsDisplayList& aList,
                                                 nsIFrame* aFrame,
@@ -5850,6 +5857,18 @@ nsresult PresShell::AddCanvasBackgroundColorItem(nsDisplayListBuilder& aBuilder,
                                                  const nsRect&         aBounds,
                                                  nscolor               aBackstopColor,
                                                  PRBool                aForceDraw)
+{
+  return AddCanvasBackgroundColorItem2(aBuilder, aList, aFrame, aBounds,
+    aBackstopColor,
+    aForceDraw ? nsIPresShell_MOZILLA_2_0_BRANCH::FORCE_DRAW : 0);
+}
+
+nsresult PresShell::AddCanvasBackgroundColorItem2(nsDisplayListBuilder& aBuilder,
+                                                 nsDisplayList&        aList,
+                                                 nsIFrame*             aFrame,
+                                                 const nsRect&         aBounds,
+                                                 nscolor               aBackstopColor,
+                                                 PRUint32              aFlags)
 {
   // We don't want to add an item for the canvas background color if the frame
   // (sub)tree we are painting doesn't include any canvas frames. There isn't
@@ -5857,8 +5876,10 @@ nsresult PresShell::AddCanvasBackgroundColorItem(nsDisplayListBuilder& aBuilder,
   // (sub)tree we are painting is a canvas frame that should cover us in all
   // cases (it will usually be a viewport frame when we have a canvas frame in
   // the (sub)tree).
-  if (!aForceDraw && !nsCSSRendering::IsCanvasFrame(aFrame))
+  if (!(aFlags & nsIPresShell_MOZILLA_2_0_BRANCH::FORCE_DRAW) &&
+      !nsCSSRendering::IsCanvasFrame(aFrame)) {
     return NS_OK;
+  }
 
   nscolor bgcolor = NS_ComposeColors(aBackstopColor, mCanvasBackgroundColor);
   if (NS_GET_A(bgcolor) == 0)
@@ -5881,7 +5902,8 @@ nsresult PresShell::AddCanvasBackgroundColorItem(nsDisplayListBuilder& aBuilder,
   }
 
   return aList.AppendNewToBottom(
-      new (&aBuilder) nsDisplaySolidColor(&aBuilder, aFrame, aBounds, bgcolor));
+      new (&aBuilder) nsDisplaySolidColor(&aBuilder, aFrame, aBounds, bgcolor,
+        !!(aFlags & nsIPresShell_MOZILLA_2_0_BRANCH::ROOT_CONTENT_DOC_BG)));
 }
 
 static PRBool IsTransparentContainerElement(nsPresContext* aPresContext)
diff --git a/layout/generic/nsCanvasFrame.h b/layout/generic/nsCanvasFrame.h
index 9f5d7e77c0e0..b644cf30ebdc 100644
--- a/layout/generic/nsCanvasFrame.h
+++ b/layout/generic/nsCanvasFrame.h
@@ -172,10 +172,16 @@ public:
   }
 
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion)
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG)
   {
-    return NS_GET_A(mExtraBackgroundColor) > 0 ||
-           nsDisplayBackground::ComputeVisibility(aBuilder, aVisibleRegion);
+    PRBool retval = NS_GET_A(mExtraBackgroundColor) > 0 ||
+           nsDisplayBackground::ComputeVisibility(aBuilder, aVisibleRegion,
+                                                  aContainsRootContentDocBG);
+    if (retval && mFrame->PresContext()->IsRootContentDocument()) {
+      aContainsRootContentDocBG = PR_TRUE;
+    }
+    return retval;
   }
   virtual nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
                                    PRBool* aForceTransparentSurface = nsnull)
diff --git a/layout/generic/nsObjectFrame.cpp b/layout/generic/nsObjectFrame.cpp
index 1afd53069f06..3e9d2027f0c8 100644
--- a/layout/generic/nsObjectFrame.cpp
+++ b/layout/generic/nsObjectFrame.cpp
@@ -1284,10 +1284,12 @@ nsDisplayPlugin::Paint(nsDisplayListBuilder* aBuilder,
 
 PRBool
 nsDisplayPlugin::ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion)
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG)
 {
   mVisibleRegion.And(*aVisibleRegion, GetBounds(aBuilder));  
-  return nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion);
+  return nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion,
+                                          aContainsRootContentDocBG);
 }
 
 nsRegion
diff --git a/layout/generic/nsObjectFrame.h b/layout/generic/nsObjectFrame.h
index 2cf122ced835..05d579d54aaf 100644
--- a/layout/generic/nsObjectFrame.h
+++ b/layout/generic/nsObjectFrame.h
@@ -321,7 +321,8 @@ public:
   virtual void Paint(nsDisplayListBuilder* aBuilder,
                      nsIRenderingContext* aCtx);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
-                                   nsRegion* aVisibleRegion);
+                                   nsRegion* aVisibleRegion,
+                                   PRBool& aContainsRootContentDocBG);
 
   NS_DISPLAY_DECL_NAME("Plugin", TYPE_PLUGIN)
 
diff --git a/layout/generic/nsSubDocumentFrame.cpp b/layout/generic/nsSubDocumentFrame.cpp
index e5d8acd0f430..ab79c85444bc 100644
--- a/layout/generic/nsSubDocumentFrame.cpp
+++ b/layout/generic/nsSubDocumentFrame.cpp
@@ -411,9 +411,13 @@ nsSubDocumentFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
       // Add the canvas background color to the bottom of the list. This
       // happens after we've built the list so that AddCanvasBackgroundColorItem
       // can monkey with the contents if necessary.
+      PRUint32 flags = nsIPresShell_MOZILLA_2_0_BRANCH::FORCE_DRAW;
+      if (presContext->IsRootContentDocument()) {
+        flags |= nsIPresShell_MOZILLA_2_0_BRANCH::ROOT_CONTENT_DOC_BG;
+      }
       rv = presShell->AddCanvasBackgroundColorItem(
              *aBuilder, childItems, subdocRootFrame ? subdocRootFrame : this,
-             bounds, NS_RGBA(0,0,0,0), PR_TRUE);
+             bounds, NS_RGBA(0,0,0,0), flags);
     }
   }