What is your anti-virus software?

I use Webroot and Spybot S & D. I used them before with XP and Wiindows 7 with no issues.

Try to start *Windows* in safe mode with networking enabled. - Win10 http://windows.microsoft.com/en-us/windows-10/change-startup-settings-in-windows-10#v1h=tab01

Still in Windows safe mode, start Thunderbird in safe mode. - https://support.mozilla.org/en-US/kb/safe-mode

Does the problem go away?

Did this before and the issue doesn't go away. My thought is that it is an issue with T-Bird and something new in Windows 10. Have you received questions about this from others?

Then the cause may be a Thunderbird add-on - eliminate them by disabling one at a time in Tools (Alt-T) | Add-ons | Extensions and restarting.

Only have one add-on and disabling it did not fix the issue.

jbacinti,

Another possibility, is delete the Thunderbird PROGRAM directory (NOT your profile data), and reinstall from https://www.mozilla.org/en-US/thunderbird/ --- one of the several ideas you can try at https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems

Let us know what works?

Problem fixed.

jbacinti said

Problem fixed.

OK. But the question is - what specific step/change solved it?

Can you share with us what fixed it?

Frankly I am not exactly sure but my first guess is an update last month to Windows 10. By the time I got your latest suggestion about deleting T-Bird, the problem was solved.