Report: My old daily user machine Linux Mint Cinnamon 17 - 64bit received the notice to upgrade Firefox. This Firefox was a download from mozlla and install Firefox many years ago. To upgrade I went to open application menu HELP then ABOUT FIREFOX and clicked the update to 123.0 box and then clicked the Reboot to upgrade. Firefox never came back, it disappeared.
Solution is to restore my system from a backup and try again. It failed again. The solution for me now is to restore the backup and not upgrade.
Hope this helps someone - Mike
(edit was to add 17)
