Bug 926706. When nsGfxScrollFrameInner::UpdateOverflow decides we need to update the scrollbars, don't reflow the scrollframe with NS_FRAME_IS_DIRTY since that reflows all descendants. Just reflow the frame itself and don't dirty anything else. r=tn a=lsblakk
Bug 928607. Ensure that nsGfxScrollFrameInner::UpdatePosition clips the overflow area of its children. r=tn a=lsblakk