I found the following on that error message here: http://kb.mozillazine.org/Browser_will_not_start_up#Computer_must_be_restarted_message_after_Firefox_upgrade ----- '''Computer must be restarted message after Firefox upgrade''' If you see a message similar to ''Your computer must be restarted to complete a previous upgrade of Firefox'' after a major update (e.g., from Firefox 3.6 to 8.0) and restarting the computer doesn't help: On Windows, open the Mozilla Firefox installation directory (e.g., C:\Program Files\Mozilla Firefox or, on 64-bit Windows, C:\Program Files (x86)\Mozilla Firefox) and delete the file "firefox.exe.moz-upgrade". If you still can't start Firefox, do a clean reinstall (use another browser to download the Firefox installer from www.mozilla.org/firefox and, after first removing the Mozilla Firefox installation directory, reinstall Firefox). ----- The above refers to an error attempting to start Firefox but the same solution might work for errors when attempting to uninstall Firefox (delete the file '''firefox.exe.moz-upgrade''' from the folder where Firefox is installed, then run the uninstaller.) See also [[Uninstalling Firefox]].