I suspect this is the reason; it went from FF 66 to 78, and it probably overwrote FF's profile folder. You could try this:
https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles and see if you have any luck, hopefully, you will. If and when you do, make a backup, it's as easy as copying
.mozilla's hidden folder in $HOME to a USB drive, so you can copy it back when needed. Also, as others have already recommended, you could try installing latest Mint version:
https://linuxmint.com/download.php
Linux Mint is the best Linux distribution for beginners. Learn how to install Linux Mint and make it your main and the only operating system.
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