However, the replies on that thread did give me something to look for. I found "Test Your memory! 1.2 true email@example.com" in my FF profile and removed it.
To the extent that one data point is proof; it seems to have solved the problem. I posted the new info on that thread and would delete this one entirely but that doesn't seem possible. So . . . I've included my apparent solution and links to the other thread to tie them together in case someone finds one and not the other.