To locate where it is, click Help>More Troubleshooting Information and scroll down left sidebar to 'Profiles'. Click there and it will display your profile and it's location. Unless you changed it, it will appear something such as c:\(yourname)\appdata\roaming\Thunderbird\Profiles

Locate there in File Explorer, highlight the folder name, right-click and select 'send to' your USB stick.

Thank you very much. I was able to follow your instructions for backing up Thunderbird email without any problems. Work just fine. Thank you again, Larry