Download a fresh Firefox copy and save the file to the desktop. * Firefox 3.6.x: http://www.mozilla.com/en-US/firefox/all-older.html * Uninstall your current Firefox version. * Do not remove personal data if you uninstall the current version. * Remove the Firefox program folder before installing that downloaded copy of the Firefox installer. Your bookmarks and other profile data are stored elsewhere in the [http://kb.mozillazine.org/Profile_folder_-_Firefox Firefox Profile Folder] and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.