Ever since I installed Firefox 24.0 on my computer, it hangs when I close it, either using X or File->Exit. The only way to stop it is to use the Task Manager to kill the process. Windows tries to find a solution to the problem and it also hangs, although it responds when I click "Cancel." I've tried restarting my computer and resetting Firefox. When Firefox hangs, it also prevents Internet Explorer from opening up.
Thanks, getting Firefox into safe mode did the trick. It was tricky getting into Safe mode, because it was one of the add-ons causing the problem, but I couldn't disable add-ons and restart in Safe Mode, because I couldn't close Firefox in a normal way. I had to use pressing Shift while starting Firefox to get into Safe Mode.
It was the Norton Family add-on, which I had seen in one of my search results. I had to uninstall Norton Family to disable the add-on. I hope that they fix Norton Family, because I do rely on it.