User blog comment:Unknown95387/I need help/@comment-3427444-20171008130231

MathJax was implemented by adding some code to MediaWiki:Common.js. Specifically, these lines of code make it work:

// MathJax is disabled in the Special and MediaWiki namespaces var enableMathJax = (wgCanonicalNamespace !== "Special") && (wgCanonicalNamespace !== "MediaWiki"); // Enable MathJax when viewing deleted revisions enableMathJax = enableMathJax || (wgCanonicalSpecialPageName === "Undelete"); addOnloadHook(function {    if (enableMathJax) {        importScriptURI("http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML,Safe");    } });

Note that if you add custom JavaScript on your wiki's common.js, it may require approval before being activated.