sometimes when you go to URLs like this: http://itunes.apple.com/itunes-u/developing-apps-for-ios-sd/id395631522 clicking on a link that would normally open iTunes, will make FF to start opening empty tabs by itself and looping forever doing this. If you switch to another open app, it will jump back to FF and will keep opening tabs. I haven't wait to see how many tabs FF opens but I either have to quit or force-quit FF to gain control of my mac.