UPDATE: Mathjax 2.2 final has been released.
We have deployed the latest Mathjax 2.2 beta on Math.SE. As with any beta release please post an answer to this question if you find any issues. We will be monitoring this thread closely along with the authors of Mathjax to ensure this release goes smoothly.
This release includes a number of new features and increased stability with over 40 bug fixes. For a list of resolved issues included in this release please check here.