Run the Firefox program once as Administrator (right-click: Run as Administrator).<br /> If that doesn't help then do a clean (re)install.<br /> Download a fresh copy of Firefox ([http://www.mozilla.com/firefox/all.html]) and do a reinstall of Firefox on top of the current version.<br /> If that still causes the same problem then do a clean reinstall and remove the Firefox program folder. See also: * http://kb.mozillazine.org/Software_Update (Software Update not working properly)