I updated to Firefox 4.0.1 recently, since the update when I open Firefox the window does not fill the screen even though the window is maximised. If I then reduce the window and maximise it again it appears full size but about a minute later it will reduce itself to about 2/3rds of the screen size again. When maximised the window never lasts for more than 1 minute or so before reducing itself again... Anybody have any idea why??