What happened? I came back to the site, and TeX is no longer being rendered. Is anybody else having this problem? I didn't make any updates to my browser or other changes that might explain the problem at my end.
As of 14:20 UTC, MathJax.org is down, hence all MathJax requests fail.
Edit From Pierre-Yves' comment: there was an issue with DNS propagation (IP address for the server changed but the DNS didn't update fast enough). The hole is gradually healing itself. As of 16:15 UTC people have reported being about to connect to the mathjax.org domain (though it is still not connecting where I am physically).