The page at http://latex.mathoverflow.net says:

jsMath can't load one of its required components, because jsMath was not obtained from a server that is in the same domain as the page that loaded it.

The most reliable way to trigger it seems to be as follows: Click on the link to a question with quite a bit of LaTeX in the question and/or the answers. Hit the back button while it's in the process of rendering the math. The monologue pops up, not every time but quite often.

I suspect a firefox bug rather than a jsMath bug, but it is a little bothersome once in a while. Any idea why it happens, and if there might be a way to stop it from happening? (Other than browsing more slowly, of course.)