Non-scrolling headers/footers break the way Page Up and Page Down work, because the visible size is no longer the size of the scrollable area. It also seems to

Non-scrolling headers/footers break the way Page Up and Page Down work, because the visible size is no longer the size of the scrollable area. It also seems to break their "Parent" links -- it ends up with the top bar partially covering the comment's header. I've yet to encounter a web site where floating title bar is a good idea.