I recently bought a new laptop and I am seeing very poor MathJax rendering. I now see the ugly beast below, rather than the beautifully rendered equations that I saw previously. Is there a simple fix?
This is a bug caused by an interaction between MathJax and Mac OS X Lion.
A workaround is to open Font Book (hit Cmd-Space and type "Font Book") and search for "stix" in the search box. Select all of the STIX fonts, and hit the checkbox (circled in red in the image below) to disable them. This will cause MathJax to ignore those fonts when rendering TeX.