This has been ruining my reading experience on the web for years. I remember fondly an old Opera version (10-15 years ago) that would briefly display a dotted line on page up/down to mark the boundary between pages. It was such an amazingly useful little addition. I don't recall whether it was built-in or an extension, I just remember the disappointment when I couldn't use it any more (either they disabled or it was the time I switched to Firefox).
