Start *Windows'* 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 safe mode - https://support.mozilla.org/kb/safe-mode-thunderbird

Does problem go away? Please reply to let me know results.

Thanks for the response...!

I ultimately discovered that none of my applications, other than Chrome, would launch after the Microsoft 6/14/2017 update push. A check of the update log revealed that many failures occurred during the process.

I contacted Microsoft support. After 4+ hours of effort, including a complete reinstall of Windows 10 and patches, the only solution was to roll back to the previous version. I'm scheduled to work with the next level of tech support on Friday.

Meanwhile, since Windows 10 has been rolled back, I can't conduct the experiment you suggest. At this point, I believe the update problems are solely a Microsoft issue.