With Firefox 3.0 when I log in to the admin pages the dashboard keeps loading and loading and loading... and nothing happens for ages. On the other hand when I look at it from Opera it works fine. When I was using 2.3 everything was perfect. But I don't want to downgrade since I like the new 2.5.1 admin pages look. ;]
Edit: Oh I almost forgot. There are problems with it in Opera as well. The problem is that you cannot click on any button. With IE7 it works well.