I accidentally turned off MathJax on a comment so I could see the LaTex source, and I don't know how to turn it back on again. I turned it off by right clicking in my browser, but now when I right click, I get a Firefox menu instead of a MathJax menu. Please help!
Perhaps someone else will find this useful some day.
I noticed that, for a split second, MathJax was rendering type-set equations before it was rendering the source. I was able to very quickly reload the page with Cmd-R (on the Mac) while quickly right clicking. That gave me the menu I was missing.
Was this a coincidence? Perhaps. I was also trying bookmarklets from this web page, which indeed caused proper rendering, but did not seem to affect pages on this web site. It may also be the case that I was not right clicking exactly on top of the LaTex source.