This add-on does exactly what I want it to. It makes working with math in my browser much more pleasant than waiting around for MathJax to process everything. I heavily do symbolic calculations in the Jupyter notebook, and before using this add-on some of my notebooks would take minutes to process the math when loading. With this add-on I no longer have to go make a cup of coffee every time I open up one of my old notebooks, and math-heavy online physics papers can also be loaded in a reasonable amount of time.
I just wanted a plugin to make MathJax use MathML by default on all sites. This plugin does that, plus more (such as disabling the MathJax preprocessor for sites already using MathML etc.). Excellent! Thank you!