If you have problem with updating Firefox then easiest is to 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 3.6.x: http://www.mozilla.com/en-US/firefox/all-older.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 [http://kb.mozillazine.org/Profile_folder_-_Firefox Firefox Profile Folder], so you won't lose your bookmarks and other personal data. ---- Firefox 4 doesn't run on a PowerPC Mac.<br /> Firefox 4 requires at least OS X 10.5 and an Intel Mac. * http://www.mozilla.com/firefox/4.0/system-requirements/ For a Firefox 4 compatible version that runs on Mac OS X 10.4.11 or Mac OS X 10.5.8 (PowerPC) you can look at: * http://www.floodgap.com/software/tenfourfox/