If there are problems with updating then easiest 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 from: http://www.mozilla.org/en-US/firefox/all.html (latest stable Firefox 10.0.1) '''then''' trash the current Firefox application to do a clean (re-) install, '''then''' install the new version that you have downloaded Your profile data is stored elsewhere in the Firefox Profile Folder, so you won't lose your bookmarks and other personal data if you uninstall and (re) install Firefox. http://kb.mozillazine.org/Profile_folder_-_Firefox see also : [https://support.mozilla.org/en-US/kb/Installing%20Firefox%20on%20Mac Installing Firefox on Mac] thank you Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.