My Firefox sync key no longr works. I have Windows 7 on both of my desktops and each has both Firefox 3.6.xx and Firefox 4. Does my having used Firefox 4 count as an upgrade that prevents my sync key from working? Would it solve my problem if I replace the profiles on the firefox browsers that have never synced with profiles from the ones that have synced in the past? Does it matter that I have Linux operating systems dual or triple-booting with the Windows operating systems on both computers?