diff --git a/layout/base/nsDisplayList.cpp b/layout/base/nsDisplayList.cpp
index 5e05eff7a7a..1deb1893dcf 100644
--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -1469,13 +1469,11 @@ nsDisplayBackground::nsDisplayBackground(nsDisplayListBuilder* aBuilder,
                                          nsIFrame* aFrame,
                                          uint32_t aLayer,
                                          bool aIsThemed,
-                                         const nsStyleBackground* aBackgroundStyle,
-                                         bool aSkipFixedItemBoundsCheck)
+                                         const nsStyleBackground* aBackgroundStyle)
   : nsDisplayItem(aBuilder, aFrame)
   , mBackgroundStyle(aBackgroundStyle)
   , mLayer(aLayer)
   , mIsThemed(aIsThemed)
-  , mIsFixed(false)
   , mIsBottommostLayer(true)
 {
   MOZ_COUNT_CTOR(nsDisplayBackground);
@@ -1501,36 +1499,6 @@ nsDisplayBackground::nsDisplayBackground(nsDisplayListBuilder* aBuilder,
     if (!mBackgroundStyle->mLayers[mLayer].mImage.IsEmpty() &&
         mBackgroundStyle->mLayers[mLayer].mAttachment == NS_STYLE_BG_ATTACHMENT_FIXED) {
       aBuilder->SetHasFixedItems();
-
-      // Check whether we should fix to viewport scrolling
-      if (mBackgroundStyle->mLayers[mLayer].mClip == NS_STYLE_BG_CLIP_BORDER &&
-          !nsLayoutUtils::HasNonZeroCorner(mFrame->GetStyleBorder()->mBorderRadius)) {
-        if (aSkipFixedItemBoundsCheck) {
-          mIsFixed = true;
-        } else {
-          nsPresContext* presContext = mFrame->PresContext();
-          nsIFrame* rootScrollFrame = presContext->PresShell()->GetRootScrollFrame();
-          if (rootScrollFrame) {
-            bool snap;
-            nsRect bounds = GetBounds(aBuilder, &snap);
-
-            // This bounds check prevents an item fixing to the viewport unless it
-            // it encompasses the scroll-port. If a fixed background doesn't
-            // encompass the scroll-port, it usually means that scrolling will
-            // expose a new area of the fixed background and cause a lot of
-            // invalidation. This performs badly, and looks especially bad when
-            // async scrolling is being used.
-            // XXX A better check would be to see if the underlying frame is fixed to
-            //     the viewport/is the viewport.
-            nsIScrollableFrame* scrollable = do_QueryFrame(rootScrollFrame);
-            nsRect scrollport(scrollable->GetScrollPortRect().TopLeft() +
-                              aBuilder->ToReferenceFrame(rootScrollFrame),
-                              scrollable->GetScrollPositionClampingScrollPortSize());
-
-            mIsFixed = bounds.Contains(scrollport);
-          }
-        }
-      }
     }
   }
 }
@@ -2072,12 +2040,6 @@ nsDisplayBackground::RenderingMightDependOnPositioningAreaSizeChange()
   return false;
 }
 
-bool
-nsDisplayBackground::ShouldFixToViewport(nsDisplayListBuilder* aBuilder)
-{
-  return mIsFixed;
-}
-
 static void CheckForBorderItem(nsDisplayItem *aItem, uint32_t& aFlags)
 {
   nsDisplayItem* nextItem = aItem->GetAbove();
diff --git a/layout/base/nsDisplayList.h b/layout/base/nsDisplayList.h
index 436046df3f6..4b652172c4c 100644
--- a/layout/base/nsDisplayList.h
+++ b/layout/base/nsDisplayList.h
@@ -1786,17 +1786,15 @@ private:
  */
 class nsDisplayBackground : public nsDisplayItem {
 public:
-  // aLayer signifies which background layer this item represents. Normally
-  // a background layer will only be marked as fixed if it covers the scroll-
-  // port of the root scroll-frame. This check can be skipped using
-  // aSkipFixedItemBoundsCheck.
-  // aIsThemed should be the value of aFrame->IsThemed.
-  // aBackgroundStyle should be the result of
-  // nsCSSRendering::FindBackground, or null if FindBackground returned false.
+  /**
+   * aLayer signifies which background layer this item represents.
+   * aIsThemed should be the value of aFrame->IsThemed.
+   * aBackgroundStyle should be the result of
+   * nsCSSRendering::FindBackground, or null if FindBackground returned false.
+   */
   nsDisplayBackground(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
                       uint32_t aLayer, bool aIsThemed,
-                      const nsStyleBackground* aBackgroundStyle,
-                      bool aSkipFixedItemBoundsCheck = false);
+                      const nsStyleBackground* aBackgroundStyle);
   virtual ~nsDisplayBackground();
 
   // This will create and append new items for all the layers of the
@@ -1825,7 +1823,6 @@ public:
   virtual bool IsVaryingRelativeToMovingFrame(nsDisplayListBuilder* aBuilder,
                                                 nsIFrame* aFrame) MOZ_OVERRIDE;
   virtual bool IsUniform(nsDisplayListBuilder* aBuilder, nscolor* aColor) MOZ_OVERRIDE;
-  virtual bool ShouldFixToViewport(nsDisplayListBuilder* aBuilder) MOZ_OVERRIDE;
   /**
    * GetBounds() returns the background painting area.
    */
@@ -1883,9 +1880,6 @@ protected:
   nsITheme::Transparency mThemeTransparency;
   /* Used to cache mFrame->IsThemed() since it isn't a cheap call */
   bool mIsThemed;
-  /* true if this item represents a background-attachment:fixed layer and
-   * should fix to the viewport. */
-  bool mIsFixed;
   /* true if this item represents the bottom-most background layer */
   bool mIsBottommostLayer;
 };
diff --git a/layout/generic/nsCanvasFrame.h b/layout/generic/nsCanvasFrame.h
index 4197dca9da7..02382203dd8 100644
--- a/layout/generic/nsCanvasFrame.h
+++ b/layout/generic/nsCanvasFrame.h
@@ -127,10 +127,9 @@ public:
   nsDisplayCanvasBackground(nsDisplayListBuilder* aBuilder, nsIFrame *aFrame,
                             uint32_t aLayer, bool aIsThemed,
                             const nsStyleBackground* aBackgroundStyle)
-    : nsDisplayBackground(aBuilder, aFrame, aLayer,
-                          aIsThemed, aBackgroundStyle, true)
+    : nsDisplayBackground(aBuilder, aFrame, aLayer, aIsThemed, aBackgroundStyle),
+      mExtraBackgroundColor(NS_RGBA(0,0,0,0))
   {
-    mExtraBackgroundColor = NS_RGBA(0,0,0,0);
   }
 
   virtual bool ComputeVisibility(nsDisplayListBuilder* aBuilder,
@@ -172,7 +171,17 @@ public:
     // We need to override so we don't consider border-radius.
     aOutFrames->AppendElement(mFrame);
   }
-  
+  virtual bool ShouldFixToViewport(nsDisplayListBuilder* aBuilder) MOZ_OVERRIDE
+  {
+    // Put background-attachment:fixed canvas background images in their own
+    // compositing layer. Since we know their background painting area can't
+    // change (unless the viewport size itself changes), async scrolling
+    // will work well.
+    return mBackgroundStyle &&
+      mBackgroundStyle->mLayers[mLayer].mAttachment == NS_STYLE_BG_ATTACHMENT_FIXED &&
+      !mBackgroundStyle->mLayers[mLayer].mImage.IsEmpty();
+  }
+
   virtual void Paint(nsDisplayListBuilder* aBuilder,
                      nsRenderingContext* aCtx) MOZ_OVERRIDE;
 
@@ -187,5 +196,4 @@ private:
   nscolor mExtraBackgroundColor;
 };
 
-
 #endif /* nsCanvasFrame_h___ */