If there are problems with updating or with the permanently then best is to download the full version and trash the currently installed version to do a clean install of the new version. Download a new copy of the Firefox program and save the disk image (dmg) file to the desktop *Firefox 21.0: http://www.mozilla.org/en-US/firefox/all.html *Trash the current Firefox application (e.g. open the Applications folder in the Finder and drag the Firefox application to the Trash) to do a clean (re-)install *Install the new version that you have downloaded *https://support.mozilla.org/kb/Installing+Firefox+on+Mac Your personal data is stored elsewhere in the Firefox profile folder, so you won't lose your bookmarks and other personal data when you uninstall and (re)install Firefox. *http://kb.mozillazine.org/Profile_folder_-_Firefox