Thunderbird update of 12/22/2020 lost all contact with my identy
Thunderbird auto-updated sometime on the 22nd of December to version 78. It now either loads to a screen that looks like it is the first-time set up screen or says that the Thunderbird profile is missing or inaccessible. I have been using Thunderbird for years and have lots of emails & accounts that are now lost. I tried some of the ideas to recover them but no luck. My default profile is about 2.11 gig. I hope that these is some way to recover this.
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I thought that this was going to fix my problem but it did not. The only other profile there had emails that ended in 2016. I switched back to the original profile and still Thunderbird thought that it was a new install.
Open the broken profile folder and see if there are files named prefs-1.js, prefs-2.js, prefs-3.js...... By replacing the current, corrupted, prefs.js with one of the most recent prefs-N.js files, you might be able to restore normal operations.
http://kb.mozillazine.org/Recovering_a_profile_that_suddenly_disappeared#Corrupt_or_empty_prefs.js
As a fallback, you can always create a new profile, add the accounts, and transfer mail, address books etc. from the old profile to the new.