This is an offshoot of [ChatJax][1], which enables MathJax along with mhchem on chat.

Copy the text below:

    javascript:(function(){if(window.MathJax===undefined){var script=document.createElement("script");script.type="text/javascript";script.src="https://d3eoax9i5htok0.cloudfront.net/mathjax/latest/MathJax.js?config=TeX-AMS_HTML";var config='MathJax.Hub.Config({"HTML-CSS": { preferredFont: "TeX", availableFonts: ["STIX","TeX"], linebreaks: { automatic:true }, EqnChunk: (MathJax.Hub.Browser.isMobile ? 10 : 50) },                                    tex2jax: { inlineMath: [ ["$", "$"], ["\\\\(","\\\\)"] ], displayMath: [ ["$$","$$"], ["\\[", "\\]"] ], processEscapes: true, ignoreClass: "tex2jax_ignore|dno" },                                    TeX: { extensions: ["mhchem.js"], noUndefined: { attributes: { mathcolor: "red", mathbackground: "#FFEEEE", mathsize: "90%" } } },                                    messageStyle: "none"                });            '+'MathJax.Hub.Startup.onload();';if(window.opera){script.innerHTML=config}else{script.text=config}document.getElementsByTagName("head")[0].appendChild(script)}else{MathJax.Hub.Queue(["Typeset",MathJax.Hub])}$('html').ajaxComplete(function(){MathJax.Hub.Queue(["Typeset",MathJax.Hub])})})();


Then simply create a bookmark or bookmarklet with the copied text as the "Location".

Once installed, activating the bookmark or bookmarklet (choosing it from a menu or clicking on its button) will render most $\LaTeX$ on the current page. Rendering is now automatic, so if new $\LaTeX$ appears on the chat page, the bookmark does not need to be activated again. Note that refreshing the page will lose the code, so the bookmark will need to be reactivated after refreshing.


Enjoy!

  [1]: http://meta.math.stackexchange.com/a/3297/24293