Found it again after a bit of googling. It’s called Browsh. Haven’t played with it yet (will report back when I do) but from the demo on that github page it seems to work pretty well.
UPDATE: I’ve tried it out and hooooly craaaaaap this is good. If I didn’t know this was running in a terminal I would never have guessed. I would’ve just assumed it was a novelty browser meant to evoke that style. Smooth scrolling works astonishingly well as does video playback.