'Twitching' Mozzila Firefox...?

[Runescapian321]

When I open Mozzila Firefox, it starts doing somethin that I guess I'll describe as twitching. It's rapidly moving up and down but only a bit. It doesn't 'twitch' on the desktop nor on the toolbar or menu bar at the top, just the actual internet screen. It seems to stop twitching on a few sites (didn't test much but SI.com works fine but Runescape, Sythe, SRL don't). If I use internet explorer it doesn't have these effects. Whats wrong?

Oh and I was just playing runescape when it started, I don't think I pressed anything. Maybe having one guy logged in on ScapeRune and another on runescape.com have something to do with it?


EDIT: Figured it out, it is a vista bug where if you delete all the 'Bookmarks' that are under the web adress it starts twitching.