Since I started this thread it has stopped. I haven't seen it again, here or any other site. I did not change a thing, browser or anything else.
It would sometimes show up on other sites but the worst was this chicken forum. It was showing up am few times a day every day, the only way to unlock the computer was to close out Explorer. Then suddenly it stopped.
If it happens again I'll view the certificate and see what I can capture on a screenshot.