Mathjax font errors in firefox

I started getting errors in firefox recently complaining about Math Processing Errors and problems loading imagefonts. It was sort of like this bug where a file called imagedata.js was not getting loaded.

Mathjax shouldn’t have to use imagefonts in any modern browser; mathjax was working perfectly in chrome for example. So what had happened was I’d unchecked the

Allow pages to choose their own fonts, instead of my selections above

under Preferences > Content > Advanced.

My firefox version is

Mozilla Firefox 45.0.1

It’s also interesting to note that the usual packages in ArchLinux and Ubuntu don’t package MathJax image fonts by default. These are however available in their github repository.