Comment 21 for bug 1830096

For those who come here and can't wait until this fix is released (thanks for your hard work, people fixing this!) you can find workarounds here (I can't say if the workarounds are safe or not):

https://old.reddit.com/r/firefox/comments/brjj82/firefox_67_thinks_its_an_old_version_and_wont/

Running
MOZ_ALLOW_DOWNGRADE=1 firefox --ProfileManager
from bash worked for me, since I accidentally created a new profile when exploring my options, and had to switch back to my original profile. I now have access to my session, bookmarks and containers again.