I just posted this on Reddit as well, here is my Reddit message. thanks!! =================== Very weird situation. I'm a professor, and have used Thunderbird for like ~15 years, and generally love it. I have 1000s of messages archived in local folders, which I have been doing forever. I was using Thunderbird 143.0.1, on a reliable Windows 11 system. Yesterday I noticed about ~50 folders just randomly missing, and panicked thinking maybe my hard drive was corrupt. My subsequent troubleshooting was: [a] I fortunately made a Paragon Hard Drive Backup from earlier in September, and restored it. That backup was using Thunderbird 142.0. All of ~50 folders were back to life!!! (minus messages that I archived over the last month, of course). [b] Thunderbird then did an un-solicited auto-update back to 143.0.1. Now the same ~50 folders are gone again !?! WTF. [c] I did another Paragon Restore back to the same early September time point, but unplugged my ethernet cable. Then I started again, and turned Thunderbird Auto Updates to "off", keeping me at 142.0. [d] Now everything is fine, Thunderbird works, and my folders are intact. Conclusion: at least on my computer, Thunderbird 143.0.1 is bad and deletes a massive number of my important work folders. It doesn't look like they were archived, just completely lost. For now, I will keep "auto updates" off., and only consider updating after I do future Paragon backups. I will also maybe transition to IMAP folder storage. (I've been doing local folder storage for the last ~15 years).