I'm on my desktop computer with an RTX 2060 in it. I tried the game in Microsoft Edge and it ran much better. I have several add-ons installed in Firefox, so I don't know if any of those may be interfering.
I even tried disabling all my add-ons and forcing on hardware accelerated rendering, but no change. Apparently Firefox and p5.js have a history of not working well together. Still, I really like the game, so I don't mind using Edge to play it. Really great job from all developers/artists involved!