This plugin configures MathJax and Google Code Pretiffy URLs and enables them by default on Question Pages. There is also a widget which you can add on Page bottom of any other page- like Question List- if you want MathJax to be used there.
The above plugin is only one part as we also need editor support for it. You can just download and use the ckeditor which I have configured for both. Also, do copy the qa-question.js and replace the one in qa-include - this is the only core hack but can't be avoided as of now if you want to render mathjax immediately upon submit of a comment or answer or when the expand All comments button is clicked.
The "fx" button in ckeditor is for Latex and while typing equations are replaced with $-$ and on submit rendered by MathJax without any conversion to image.