You can downgrade to the previous secure version which is 3.6.16 like this. * Go to [http://www.mozilla.com/en-US/firefox/all-older.html Download Firefox v3.6.16] and download it to the desktop. If necessary, download the file with IE8 and choose to save it to your desktop when you see the prompt. * Then go to Add/Remove Programs, scroll down to Mozilla Firefox and remove it, choosing to keep your bookmarks, customizations etc., (don't checkmark the box). * Then reboot and delete the folder called Mozilla Firefox at this location: C:\Program Files\Mozilla Firefox * Finally run the installation file you downloaded to the desktop earlier.