See https://support.mozilla.org/en-US/questions/1161878

This did not work. I just updated Thunderbird and my system did a restart.

Restarts are required when files that are in use need to be updated. In these cases windows institutes a restart to force the files out of use so they can be updated.

Matt: Thanks for the reply but I doubt that is the problem. Thunderbird would update without restarting Windows until a few months ago. I don't see this problem on my laptop. I will close Thunderbird the next time I update my desktop and hope you are right and a Windows restart does not happen.

This did not work. I just updated Thunderbird and my system did a restart.

You'd need to be a little more specific about what you did.

christ1: I followed the instructions in the link you referred me to. That is I deleted the Mozilla Thunderbird folder in Files(x86) and reinstalled Thunderbird. I did this from my standard user account. My standard user account profiles.ini is not relative but points to my administrative account profiles.ini. This has worked for years.

That is I deleted the Mozilla Thunderbird folder in Files(x86) and reinstalled Thunderbird. I did this from my standard user account.

Did you shut down Thunderbird first? I'd expect you get a UAC prompt for both of these actions. Did you?

My standard user account profiles.ini is not relative but points to my administrative account profiles.ini.

I don't understand what that means, and what this is good for. There is a profiles.ini file for each Windows user account where Thunderbird has been started at least once.

Christ1: I did delete the directories suggested and it seems to have worked. It escaped me that when the directories were missing Thunderbird thinks it is a completely new installation and of course would need to restart Windows. I was able to update to the latest version without a Windows restart so the problem seems to be solved.

Just a not. If you look at a profiles.ini file you will see a line such as: IsRelative=1 Path=Profiles/nmwpbuc6.default Path shows the location of the desired profile. If IsRelative is changed to 0 then Thunderbird expects a full path to the desired profile. I have my preferred profile in my administrative account Thunderbird directory which I leave as relative. I change IsRelative to 0 in my standard user account and put the complete path to the profile in my administrative account so Thunderbird is the same whether I am in either account. I do the same with my Firefox ini profiles.

Ok It turn out the problem is not solved. I did delete the x86 Thunderbird folders and reasonably had to reboot/restart Windows 10. The next time I was alerted to a update for Thunderbird it updated as expected without requiring a Windows 10 reboot. I just got a alert that there was a new version of Thunderbird and proceeded to download the new version as directed. Low and behold I had to reboot/restart Windows this time. It sure seems like there is something in the registry or the profile that causes Thunderbird to think the update needs a reboot.

I have been using Thunderbird for decades so the profile file has been updated through I don't know how many revisions and versions of Thunderbird.

I have included a screenshot of the update section of Thunderbird Options. I would note that the Automatically install updates is selected but that does not seem to be happening.