diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -1461,32 +1461,39 @@ nsIFrame::BuildDisplayListForChild(nsDis
       dirty = *savedDirty;
     } else {
       // The out-of-flow frame did not intersect the dirty area. We may still
       // need to traverse into it, since it may contain placeholders we need
       // to enter to reach other out-of-flow frames that are visible.
       dirty.Empty();
     }
     pseudoStackingContext = PR_TRUE;
-  } else {
-    dirty.IntersectRect(dirty, aChild->GetOverflowRect());
   }
 
   if (aBuilder->GetPaintAllFrames()) {
     dirty = aChild->GetOverflowRect();
   } else if (!(aChild->GetStateBits() & NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO)) {
     // No need to descend into aChild to catch placeholders for visible
     // positioned stuff. So see if we can short-circuit frame traversal here.
 
-    // We can stop if aChild's intersection with the dirty area ended up empty.
+    // We can stop if aChild's frame subtree's intersection with the
+    // dirty area is empty.
     // If the child is a scrollframe that we want to ignore, then we need
     // to descend into it because its scrolled child may intersect the dirty
     // area even if the scrollframe itself doesn't.
-    if (dirty.IsEmpty() && aChild != aBuilder->GetIgnoreScrollFrame())
-      return NS_OK;
+    if (aChild != aBuilder->GetIgnoreScrollFrame()) {
+      nsRect childDirty;
+      if (!childDirty.IntersectRect(dirty, aChild->GetOverflowRect()))
+        return NS_OK;
+      // Usually we could set dirty to childDirty now but there's no
+      // benefit, and it can be confusing. It can especially confuse
+      // situations where we're going to ignore a scrollframe's clipping;
+      // we wouldn't want to clip the dirty area to the scrollframe's
+      // bounds in that case.
+    }
 
     // Note that aBuilder->GetRootMovingFrame() is non-null only if we're doing
     // ComputeRepaintRegionForCopy.
     if (aBuilder->GetRootMovingFrame() == this &&
         !PresContext()->GetRenderedPositionVaryingContent()) {
       // No position-varying content has been rendered in this prescontext.
       // Therefore there is no need to descend into analyzing the moving frame's
       // descendants looking for such content, because any bitblit will
diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -1310,22 +1310,19 @@ nsGfxScrollFrameInner::BuildDisplayList(
                                         const nsDisplayListSet& aLists)
 {
   nsresult rv = mOuter->DisplayBorderBackgroundOutline(aBuilder, aLists);
   NS_ENSURE_SUCCESS(rv, rv);
   
   if (aBuilder->GetIgnoreScrollFrame() == mOuter) {
     // Don't clip the scrolled child, and don't paint scrollbars/scrollcorner.
     // The scrolled frame shouldn't have its own background/border, so we
-    // can just pass aLists directly. We do need to replace aDirtyRect with
-    // the scrolled area though, since callers may have restricted aDirtyRect
-    // to our bounds.
-    nsRect newDirty = GetScrolledRect(GetScrollPortSize()) +
-        aBuilder->ToReferenceFrame(mScrolledFrame);
-    return mOuter->BuildDisplayListForChild(aBuilder, mScrolledFrame, newDirty, aLists);
+    // can just pass aLists directly.
+    return mOuter->BuildDisplayListForChild(aBuilder, mScrolledFrame,
+                                            aDirtyRect, aLists);
   }
 
   // Now display the scrollbars and scrollcorner. These parts are drawn
   // in the border-background layer, on top of our own background and
   // borders and underneath borders and backgrounds of later elements
   // in the tree.
   nsIFrame* kid = mOuter->GetFirstChild(nsnull);
   while (kid) {