User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:86.0) Gecko/20100101 Firefox/86.0

Steps to reproduce:

Windows 10 will sometimes (by itself) perform a forced re-start, for example if it feels that critical updates must be applied.
When this happens you'll notice that certain applications automatically come up again after the re-boot .. while others don't.

Actual results:

Some applications come up again after a Windows10-Restart-Inititiated-by-Windows-Update while others don't. For example my Firefox, Chrome, MS Word and so on are automatically restarted.

Thunderbird ain't one of these applications! (unfortunately)

Expected results:

I would have expected Thunderbird to be restarted automatically.

For this to work the application, Thunderbird, must "register for restart". Ref:
https://docs.microsoft.com/en-us/windows/win32/recovery/registering-for-application-restart
I'm betting that Thunderbird doesn't use this Win32 function at the moment, while FF does. This is the possible explanation of the missing restart.

Note that a forced re-boot like those initiated by the Windows Update process can be simulated from command line with the command:

shutdown /g /d p:2:16 /c "My shutdown test" /t 5

Therefore, a test can be performed like this:

1. On a Windows 10 system start a few applications, Thunderbird included.
2. Issue from command line: shutdown /g /d p:2:16 /c "My shutdown test" /t 5
3. Wait for re-boot. On my Windows 10 there's no auto-sign-in so after the re-boot I have to sign-in again.
4. After sign-in to Windows wait 1-2 minutes.
5. Notice which applications have automatically restarted themselves.

I've noticed my TB is still 32-bit. I don't know if the 64-bit version would help in this respect?

(In reply to Lars Bruun-Hansen from comment #1)

I've noticed my TB is still 32-bit. I don't know if the 64-bit version would help in this respect?

no

Why the link to issue #899913 ? (which is about having a convenience feature in the UI to allow TB to always start itself on Windows boot). Perhaps the concern is this? : if the user has enabled such feature as described in #899913 and at the same time TB has been made WER-aware [1] and Windows experiences a forced re-boot, will two instances of TB then be started? My answer is "no" as Thunderbird is a singleton. You cannot start two instances. With this in mind I don't see how the two tickets are related?

[1] The current ticket is basically about making sure that Thunderbird registers itself for restart following an unintended reboot (or an application crash .. but luckily TB is IMO very stable so this fact is less important to me). This feature is handled by the Windows Error Reporting subsystem, so I like to call it making the application "WER aware".

I guess more accurately my concern is bug 487832