Does it launch when you right click it and Run as Administrator? You can also try to run it as an admin through the actual executable to see if that helps. Firefox is usually installed at *C:/Program Files/Mozilla Firefox (32-bit systems) *C:/Program Files (x86)/Mozilla Firefox (64-bit systems) You can then right click "firefox.exe" and click Run As Administrator ---- If that doesn't work, you can Do a clean reinstall and delete the Firefox program before (re)installing a fresh copy of the current Firefox release. Download a fresh Firefox copy and save the file to the desktop. *Firefox 30: http://www.mozilla.org/en-US/firefox/all.html If possible uninstall your current Firefox version to cleanup the Windows registry and settings in security software. *Do NOT remove "personal data" when you uninstall your current Firefox version, because this will remove all profile folders and you lose personal data like bookmarks and passwords including data in profiles created by other Firefox versions. Remove the Firefox program before installing that newly downloaded copy of the Firefox installer. *(32 bit Windows) "C:\Program Files\Mozilla Firefox\" *(64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\" *It is important to delete the Firefox program to remove all the files and make sure that there are no problems with files that were leftover after uninstalling. *http://kb.mozillazine.org/Uninstalling_Firefox Your bookmarks and other personal data are stored in the Firefox profile folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox.