The updater wasn't able to update all the files and some were left as older versions.<br /> You need to do a clean reinstall. Download a fresh Firefox copy and save the file to the desktop. * Firefox 5.0.x: http://www.mozilla.com/en-US/firefox/all.html * Uninstall your current Firefox version. * Do not remove personal data when you uninstall the current version. Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer. * It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling. <i>Your bookmarks and other profile data are stored elsewhere in the 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.</i>