Use MathJax with Spectacle

Question

I intend to use ox-spectacle which is a backend for using spectacle.js within emacs/orgmode.

Everything works well except that math formula are not rendered by MathJax.

You can see that with the example scratch.html although there is a call to mathjax script in the html source file.

I tried to make the script work, by making the mathjax script local and/or modifying its configuration, but nothing works.

I thought eventually you would notice bettter than I what the problem is ? or to the least could you provide a simple example with mathjax working ?

EDIT : the above linked file does work with firefox but not with chrome.

Regards