User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:92.0) Gecko/20100101 Firefox/92.0

Steps to reproduce:

1. 4 months ago I changed hosting and updated server name in my mail account settings in Thunderbird. Old was let's say mail.server1.com, new is mail.server2.com
2. Today hosting certificate was updated. Initially all worked well.
3. I accessed my mail server through Firefox as https://mail.server2.com Just out of curiosity. Not sure whether it affected somethings, but who knows? I use TB 78.13.0 64-bit on Ubuntu 20.

Actual results:

4. After that Thunderbird started showing popup that server name in certificate does not match accessed server name and in edited field in this popup rendered mail.server1.com:995 (old server!)
5. Accepting it as exception did not help. I deleted my Thunderbird accounts and recreated them with entering mail.server2.com in settings (So, in prefs file realhostname and hostname are the same now!)
6. After that all started working. But in some time the same popup as in step 4 was rendered again but with new servername mail.server2.com:995. Accepting exception worked in this case and I can access mail again.

I checked Certificates settings in Thunderbird. And what I have found? Instead of certificate of mail.server2.com, I see there certificate for server.hostingcompany.com It is correct certificate of my hosting server, but it is not certificate of my domain. That's why I suppose that accessing https://mail.server2.com in Firefox could create such mess.

But why? Is there any way to resolve such mess and remove exceptions?