Try to run the Firefox program once as Administrator (right-click firefox.exe: Run as Administrator).<br /> If that doesn't solve the problem then remove the Firefox program folder (C:\Program Files\Mozilla Firefox\) to do a clean reinstall. Download a fresh Firefox copy and save the file to the desktop. *Firefox 10.0.x: http://www.mozilla.org/en-US/firefox/all.html Uninstall your current Firefox version, if possible. *Do NOT remove personal data when you uninstall the current version or you lose your bookmarks and other data because all profile folders will be removed. 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. *http://kb.mozillazine.org/Uninstalling_Firefox 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. ---- *http://kb.mozillazine.org/Profile_folder_-_Firefox *http://kb.mozillazine.org/Profile_backup *http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall