if you are being asked to restart there is truly a problem, as Thunderbird does not update any of the windows system files that would require a restart.

Hi Matt, yes there truly was a problem ... it is solved now, with the help of my computer guy and this info from a former poster on another thread:

Try uninstalling aka 'deleting' the 'Mozilla Thunderbird' folder directly from the following location. [Attempts to uninstall the regular way just sent me back into the same restart loop.]

On a Windows OS 64bit computer: A win32 version of Thunderbird will be here:

   C:\Program Files (86) \Mozilla Thunderbird\ 

A win64 version of Thunderbird will be here:

   C:\Program Files \Mozilla Thunderbird\ 

Delete the 'Mozilla Thunderbird' folder. check both locations just in case there are two versions. Then empty the 'Recycle bin' on computer.

Then get a fresh download from here and install. https://www.thunderbird.net/en-US/thunderbird/all/#E