Here's my new version of the "Start Chatjax" bookmarklet.
javascript:(()=>{if(window.MathJax===undefined){const%20script=document.createElement("script");script.src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-AMS_HTML";script.text='MathJax.Hub.Config({extensions:["tex2jax.js"],tex2jax:{inlineMath:[["$","$"],["\\\\\\\\\\\\(","\\\\\\\\\\\\)"]],displayMath:[["$$","$$"],["\\\\[","\\\\]"]],processEscapes:true},jax:["input/TeX","output/HTML-CSS"]});MathJax.Hub.Startup.onload();';document.head.append(script);(function%20doChatJax(){setTimeout(doChatJax,1000);MathJax.Hub.Queue(["Typeset",MathJax.Hub]);})();}else{MathJax.Hub.Queue(["Typeset",MathJax.Hub]);}})();
And here's the "Render Mathjax" bookmark. It's more efficient to use this version on static pages, like the Chat transcripts.
javascript:(()=>{if(window.MathJax===undefined){const%20script=document.createElement("script");script.src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-AMS_HTML";script.text='MathJax.Hub.Config({extensions:["tex2jax.js"],tex2jax:{inlineMath:[["$","$"],["\\\\\\\\\\\\(","\\\\\\\\\\\\)"]],displayMath:[["$$","$$"],["\\\\[","\\\\]"]],processEscapes:true},jax:["input/TeX","output/HTML-CSS"]});MathJax.Hub.Startup.onload();';document.head.append(script);}else{MathJax.Hub.Queue(["Typeset",MathJax.Hub]);}})();
The original versions can be found on robjohn's site