Are you updating Firefox or downloading a file via the right-click context menu "Save Link as" or similar? ---- If you have problems with updating or with the permissions 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 DMG file to the desktop * Firefox 6.0.x: http://www.mozilla.com/en-US/firefox/all.html * Trash the current Firefox application to do a clean (re-)install * 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. * http://kb.mozillazine.org/Profile_folder_-_Firefox