I cannot use, update, uninstall, refresh, or reinstall Firefox (and haven't for four or more years). I always get this message: "Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window." But I have (obviously) shut down the computer entirely any number of times in all those years. What can I do? I will be taking college classes and Firefox is one of the few browsers that the college supports.