Last I saw was January 2014:
https://github.com/josdejong/mathjs/issues/131#issuecomment-33103607
ES5 requirement. Is that still the only requirement? - Do you support IE9 and above?
That's correct, math.js works on IE9 and newer.
Cool. Might be worth advertising this in the README.
That's a good point. I've added a section in the readme (only in the develop branch right now), and on the download page.
There was already a bit of text on the getting started page, and there was already an example old_browsers.html though I can't test right now if that still works.