There are recent reports that the following may be causing a crash on shut down.

Addon extension: Bitdefender AntiSpam toolbar Note Bitdefender says: “IMAP is not supported with Bitdefender Anti-Spam, therefore it won't work with it. The server type that is supported by the Bitdefender feature is POP3." report says: With the Bitdefender Anti-Spam add-on removed, Thunderbird no longer crashes on shut-down.

If using this addon, disable it and restart Thunderbird to see if it is responsible. Addon extension: Addon Compatibility Check for TB 91 1.5

I've also just seen a couple of reports which relates to people who also installed Language Pack extensions. (I'm not talking about 'dictionaries', but some people have installed 'Language Packs' thinking they were dictionaries) If you have installed a 'Language Pack' - it will be mentioned in Addons - uninstall it and restart Thunderbird.

Thanks for the answer, but unfortunately it doesn't work. I don't have Bitdefender installed (or the add-on). I did have a language pack installed. I removed it, restarted everything twice (both Thunderbird and Windows), but I still have the same problem. I close Thunderbird, but see in Task Manager that it is still active, using about 30% of CPU. After about 100 seconds it disappears, and I a pop-up "Thunderbird had a problem and crashed".

Also when I go into "Troubleshoot Mode", the same happens.

When Thunderbird is "active" it is shown under apps - see screen shot Active. When closed it is shown under Background processes - see screen shot Closed.

Can you update to 91.3.1 In bugzilla there is some mention of fixing for shut down crashes, I'm not sure if they got into that version, so it would be good to know if this sorts out your problem.

I had updated to 91.3.1 when it came out a day or two ago. And yes, I no longer get an error message when closing Thunderbird. So the problem seems to be fixed. Thank you for the message.

I spoke too soon. The error message was not there when I closed TB. But then after opening it again and a bit later closing it, I get the error message again. Now the error seems to appear fairly consistently again. Also TB keeps opening with the same series of mails open. I close some of these before closing and open others, but that makes no difference. The same set of mails is always opened (one mail per tab) whenever I start TB, irrespective of the situation when I closed the program.

Have you tried a complete new installation of 91.3.1 ?

Exit Thunderbird - make sure it is not running.

Access where Thunderbird is installed - check both locations: Windows:

• C:\Program Files\Mozilla Thunderbird\
• C:\Program Files (x86)\Mozilla Thunderbird\

Delete the 'Mozilla Thunderbird' folder.

Empty the computer 'Recycle Bin'.

Get a fresh download from this link: https://www.thunderbird.net/en-US/thunderbird/all/

Run Thunderbird.

If still issue, please create a new profile, set as default and add accounts.

Test running. If ok, then we can discuss getting address books etc moved over to new profile.

Thank you for your advise. I did remove Thunderbird and completely reinstall (I had to reinstall Firefox as well). Unfortunately it did not help. But I have decided just to live with this issue. It only occurs when I close Thunderbird. The effort to create a new profile and transfer a lot is greater than is worth it for this issue. So thanks again, but I will leave it as is.

The idea of creating a new profile - set as default and add one mail account was to test whether the problem was lurking in a profile setting or in Thunderbird. Not everyone is having the same issue, but you did mention you had downloaded a Language Pack and that has been shown to cause issues. So it is possible some setting may still be lurking.

But if you do not want to go down that route then it's up to you.

Thanks for the explanation.

I have created a new profile and added one mail account. I have also added a few dictionaries, but not language packs. This profile works properly. When I exit Thunderbird it is immediately closed. The tabs (mails) which are open when I close it are also there when I start Thunderbird again. No crashes, everything works properly. When I then switch back to my old profile, the problems are there. So the problem would seem to be in the profile. But transferring everything to a new profile seems a bit too much hastle.

It might not be as daunting as you think.

If you use IMAP mail accounts then everything is stored on the server, so it's just a question of creating imap mail accounts and all is up and running again.

The following copy paste procedures would have to be done with Thunderbird not running - TB must be exited first. If you have emails in POP accounts - create the pop account before exiting Thunderbird - but do not download anything. Then simple copy and paste of pop account folder assuming it has been created using same name from old to new profile or copy paste of that accounts files. I can offer much more details if you provide images of contents of 'Mail' folders which are located in the two profile name folders.

If you have emails stored in 'Local Folders' mail account, it is a simple process to delete the default empty 'Local Folders' folder from new profile and copy and paste the 'Local Folders' folder from old profile to new.

If you only use the default address books - Personal Address Book and Collected Addresses - again it's simple copy and paste procedure of abook.sqlite and history.sqlite from old profile to new - having previously deleted the empty default abook.sqlite and history.sqlite from the new profile.

For other address books you created - export address books as LDIF or .csv files and then import to new profile.

If you need to know info in more detail I can offer help. I'll ask you post specific images and then I'll guide you on the process. Just let me know when you feel ready to do it.

Thanks for the offer of help. I have been using Thunderbird for a long time, and I think a lot is quite old. I have the old and new profiles both in Appdata\Local\Thunderbird\Profiles and in Appdata\Roaming\Thunderbird\Profiles. I have added a screen print of the file structure of the old profile in both locations, but Local is quite limited.

Apart from the folders, the profile in Roaming contains 10,102 files. Most of these are prefs-1.js to prefs-9999.js, the -1 file last modified in May 2019 and the -9999 file in November 2020. No idea what these are. The mail folder is about 6.5 Gb (most of it in Archives.

You shouldn't have 9999 prefs.js files

In the old profile that crashes, which problems go away after doing...

• Please start *Windows'* in safe mode with networking enabled

win10 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

You shouldn't have 9999 prefs.js files

Yes, I did realise that, but does that mean I can go in and delete prefs.js, prefs-1 .js all the way to prefs-9999.js and prefs.zal when Thunderbird is closed?

In the old profile that crashes, which problems go away after doing...

• Please start *Windows'* in safe mode with networking enabled
• Still in Windows safe mode, start Thunderbird in Troubleshoot mode

In safe mode and troubleshoot mode: Thunderbird does not crash after closing. But the open tabs don't reflect the status at time of closing. I.e. closing tabs and opening new mails has no impact on what is shown next time Thunderbird is opened. So the crash problem does not occur.

re :Yes, I did realise that, but does that mean I can go in and delete prefs.js, prefs-1 .js all the way to prefs-9999.js and prefs.zal when Thunderbird is closed?

With Thunderbird closed and make sure it is not running in the Task Manager - Please note: Do not delete the 'prefs.js' file as Thunderbird is using it. This is important.

Providing that 'prefs.js' file has a size - not zero then: Delete all the 'prefs-n.js' files where 'n' is a number.

Also - delete these files so new ones get created when you restart Thunderbird:

• session.json file
• xulstore.json

re :'prefs.zal'

I believe this is something Mozbackup uses, have you used Mozbackup in the past? I would suggest you do not use Mozbackup as it has not been maintained since 2012. The author says: MozBackup is not being developed anymore. There are known issues and there is no time on my side to fix all issues and develop new features. Use MozBackup only on your risk. Thanks for understanding.

Providing that 'prefs.js' file has a size - not zero then: Delete all the 'prefs-n.js' files where 'n' is a number. Also - delete these files so new ones get created when you restart Thunderbird:

• session.json file
• xulstore.json

Thank you very much. This seems to have done the trick. Thunderbird no longer crashes. Also the tabs work exactly as expected. I opened and closed the program several times, and the time stamp on file prefs.js is changed, but no others are created.

re :'prefs.zal' Have you used Mozbackup in the past? I would suggest you do not use Mozbackup as it has not been maintained since 2012.

I did use Mozbackup years ago, but stopped when I heard is was not being maintained, and probably the restore also would not work.