The typesetting of this looks very broken on firefox with extreme gaps between lines of text. Seems to render fine on chromium.

It renders fine for me, but I've also had the "extreme gaps between lines" thing happen before on Firefox, and in my case it was caused by a bad font fallback - I forget the precise details but I think it had something to do with having Arabic fonts installed, which were erroneously taking preference for certain non-arabic glyphs. (Check the Fonts tab in dev tools)

Thank you for letting me now, but I cannot replicate the issue on Firefox. There are some issues with math and the animations not breaking on mobile, which I am working on repairing. (fixed)

EDIT: I have added a different fallback font so it should work on your Firefox now.

I believe this is a missing font issue, whereupon Firefox chooses very poor substitutes. I ran into this recently on one of my machines and solved it by installing the Microsoft fonts package (or possibly another one… I can’t remember now exactly which one did the trick).

I use firefox and it renders approximately the same as Chrome for me.

Assuming OP didn't patch something, you may have a misbehaving extension.