If there are problems with updating then best is to download the full version of the Firefox installer. Download a fresh Firefox copy and save the file to the desktop. *Firefox 17.0.x: http://www.mozilla.org/en-US/firefox/all.html Uninstall your current Firefox version, if possible, to cleanup the Windows registry and settings in security software. *Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you will also lose your personal data like bookmarks and passwords from profiles of other Firefox versions. 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 in the Firefox Profile Folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox. Check that Firefox isn't set to run as Administrator. Right-click the Firefox desktop shortcut and choose "Properties". Make sure that all items are deselected in the "Compatibility" tab of the Properties window. * Privilege Level: "Run this program as Administrator" should not be selected * "Run this program in compatibility mode for:" should not be selected Also check the Properties of the firefox.exe program in the Firefox program folder (C:\Program Files\Mozilla Firefox\). ---- *http://kb.mozillazine.org/Profile_folder_-_Firefox *http://kb.mozillazine.org/Profile_backup *http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall