Also, after importing the settings, Thunderbird would disappear as expected when I quit, but when trying to start it again, the system reported that it was still running. I checked with System Monitor, and it was still there. The first time, I terminated Thunderbird. The next time I exited Thunderbird, the same thing happened, only I waited longer. A Thunderbird Crash message appeared. This crash message appeared after each time I quit, for the next two or three times I quit. After that, the crashing stopped.

I don't know if these matters are related.

If thunderbird is still on the win 11 machine, try this:

1. click help>troubleshootinginformation on the win 11 pc
2. scroll to 'profile folder' and click 'open folder'
3. exit thunderbird
4. you are now in the profile folder. copy ALL of it and save to external media **
5. start thunderbird on the linux PC
6. repeat steps 1 through 3 above
7. delete the contents of the profile
8. paste the contents of the profile you copied from other PC
9. restart thunderbird

• • TIP: Following step 3 above, if external media cannot contain the full size of profile, you can delete the message folders for IMAP accounts (such as inbox, inbox.msf, sent, sent,msf) as thunderbird will automatically repopulate the folders on restart

In the Linux system, I opened the file Thunderbird_profile_backup.zip that I got from the Windows system, with the Archive Manager. In the file /ugeuay9c.default-release/prefs.js I found these:

user_pref("mail.root.imap", "C:\\Users\\muh2l\\AppData\\Roaming\\thunderbird\\Profiles\\ugeuay9c.default-release\\ImapMail"); user_pref("mail.root.none", "C:\\Users\\muh2l\\AppData\\Roaming\\thunderbird\\Profiles\\ugeuay9c.default-release\\Mail");

These directories are used in the Windows Thunderbird. Could that be causing problems?

I have never been comfortable with the Thunderbird exported zip file. That is why I proposed another approach. Maybe someone else seeing this thread can assist in using the zip file.

I found the problem. I scrolled down further and found the duplicate accounts, and deleted them. Just out of curiosity, if you don't use the zip file, what do you do?

You do as I posted. Those steps are especially good when switching operating systems as those steps focus solely on Thunderbird. This approach also retains 100% of the settings, including passwords. I have no argument with the zip process, but it causes its share of problems. I am happy you resolved the problem.