• Start Windows in safe mode with networking enabled - https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode
• Still In Windows safe mode, start Thunderbird in Troubleshoot Mode - https://support.mozilla.org/en-US/kb/troubleshoot-mode-thunderbird

Does problem go away?

Thanks, but while in safe mode there is no message, starting normally after, at start-up while getting mail, there is a 'not responding' pause of 30 seconds.

This morning Thunderbird appears to be behaving normally. Hopefully it was a temporary issue. Thanks.

I have this problem, too. Ever since V128 Nebula, Thunderbird has been horribly slow: - startup on Win10 and Win11 machines takes more than a minute - once it has started, one needs to wait again for half a minute until messages can be read - When up and finally running, sometimes even during writing, data entry is blocked and one has to wait until mailboxes are synced.

Seems like the mailbox polling threads are blocking the user experience with the new implementation.

Definitly not the program anymore I've been using for decades...

--Juerg

I have this problem, too. Ever since V128 Nebula, Thunderbird has been horribly slow: - startup on Win10 and Win11 machines takes more than a minute ... --Juerg

If you did what was posted earlier, and you still have trouble, you will more likely get helpful response if you post your own question rather than reply in a question that has been marked "Solved".