When first starting Firefox accessing the bookmark menu is fine and highlighting an item by mouse over is almost instantaneous (although not as instantaneous as either Opera or IE8). After Firefox has been open for a while >1hour the menus and mouse over responses becomes progressively slower to respond until it becomes almost unusable, each mouse over taking nearly four seconds to highlight a bookmark. It is about this time that I have to close firefox and use Opera or IE8 which is a bind if the bookmark is not known to these clients.