I've never had this problem closing thunderbird using the File->Exit menu. However, when you quit the program, the instance of this one takes a few seconds before closing completely as a process. You must therefore wait a few seconds before restarting Thunderbird (or Firefox) otherwise the program does not restart and freezes the instance in the Windows tasks, as you describe it and you have to go through the tasks manager to close it and be able to restart it.

I had Thunderbird start normally. I checked the task manager and have three instances of thunderbird. I then closed thunderbird with the X and timed to see how long it takes them to disspapear from the task manager and it was almost 3 minutes.

When I try to close Thunderbird with File> Exit...the Thunderbird window stays open...and I see the three instances in task manager. When I waited close to 3 minutes the Thunderbird window closed as well as the three instances in the task manager.

So what would cause this long delay in closing? It should be seconds....not minutes...right?

I have found that if I uncheck "Clean up ("Expunge") Inbox on Exit" that Thunderbird closes and opens normally. Not sure why this would be? Recently upgraded to Thunderbird 115 and have always had this checked with no issues. Anything I can do to get this working as it was before the upgrade?

Unfortunately, I have no idea about your problem. But I guess that's one of the probable bugs in this brand new version. As for me, I have a problem with the "Unified Folder" option, which hasn't been activated since this last update. Hopefully all these bugs are only temporary...

Created a new profile for testing and downloaded all my messages. Thunderbird opened and closed quickly as expected. The setting "Clean up ("Expunge") Inbox on Exit" was not enabled by default. Enabled the setting and tried File>Exit. Thunderbird closed in about 2 minutes. Is this a bug?

Have you ever tried this ? https://support.mozilla.org/en-US/kb/rebuilding-global-database#

I did try rebuilding the global database. No change.

What is the size of your Inbox? What is your anti-virus software?

My inbox is 504MB. I use Windows Defender as well as Malwarebytes Pro. I have made excpetions for both of them.

I use Windows Defender as well as Malwarebytes Pro.

Not sure if this is what you're doing, but running two real-time scanners at the same time would be a bad idea.

I have made excpetions for both of them.

Exceptions for what exactly?

I have use Malwarebytes Pro and Windows Defender for a couple of years now and have not had issues. The exceptions for both of these programs are for ImapMail and Mail folders , which are located in my Thunderbird profile folder.

Thunderbird just updated to 115.1.0 (64-bit), and now closes in about 2 seconds, and opens fine now.