I posted this problem virus, but the picture did not load, so I will try again. Also, it does continue to pop up, just takes longer.

I posted this problem virus,

This is neither a virus, nor related to Chromium.

It only pops up when I open Thunderbird. I UN-installed Thunderbird and downloaded the latest version

You've been wasting your time. Profile files are stored separately from the Thunderbird program files. The program files are static and do not change (except when you upgrade the Thunderbird application version). Because we store profile and program files separately, you can uninstall Thunderbird without losing your messages and settings, and if something goes wrong with a Thunderbird update your information will still be available. It also means that you don't have to reinstall Thunderbird in order to delete your information or troubleshoot a problem.

I when through the registry and deleted every instance of Chromium

I have no idea why you think it's related to Chromium.

... and got rid of it from Firefox,

It's not related to Firefox either.

... but not Thunderbird.

See https://support.mozilla.org/kb/add-security-exception

Inspect the certificate - see attached screenshot for instructions.

Who is the issuer of the cert? What's the subject field of the cert?

Please post a screenshot of the Certificate Viewer window with the information above visible.

PROBLEM SOLVED! You probably hate stupid people like me.

You probably hate stupid people like me.

Well ... For the benefit of others, you may want to share your solution.

And when your problem is fixed, can you mark the topic as 'Solved' please? Thank you.