Since before version 100, I've had this happening to me on Windows 11. 1 - TB starts, with a progress bar saying "Updating, will start in a few seconds" 2 - I open Help > About menu, I see the old version number, and a "Restart to update Thunderbird" 3 - If I do, GOTO 1. 4 - The usual solutions for "Software update failed" do not work [ https://support.mozilla.org/en-US/kb/thunderbird-software-update-failed ], nor does running as Administrator, or starting in recovery mode. 5 - I completely remove Thunderbird (directories, email, every file or folder on disk that might be related to TB). 6 - I reinstall Thunderbird from a full install package. The update succeeds, but at the next upgrade, GOTO 2. 7 - I also clean the Windows registry of anything that looks TB-related and GOTO 6. My current workaround is to GOTO 6 as soon as I'm notified of an upgrade. This works as described above, so it's more of an annoyance than a true bug, but still I'd like to know why it's not working. Now I've worked with many TB installations and always had it working without troubles. This is the only installation where TB is not on my local disk, aaaaand the only one on a remote Samba 4.3 share on a Linux server (can't change that). I'm therefore pretty sure that it's something to do with permissions or ACLs on that share -- but I can't figure out the exact problem. Other programs all run (and even self-update) from the same share without any hitches.