Yeah, it works for me and all my other players... I'm not sure what's happening for you? Try reloading the page, and click inside the view for the iframe to recognize your input; if all else fails just download the local Windows build.
Hmm... I've reloaded the page, and I've clicked on it. None of the keys appear to do anything except R, which causes it to tear down and reload. And I'm not sure what it's supposed to look like, but all I see is a pattern of white blocks on a gray background. So strange!
(Unfortunately the local Windows build won't run on my Mac.)
EDIT: But don't worry about it — what I can see of the game looks really awesome. Clearly this is some sort of bug in the engine, and not your fault.
Gotcha! Duh, I should have asked that first... I've heard of Firefox not liking to run web games correctly but I totally forgot about that aspect. Thank you for letting me know!
And thanks! Yeah, this concept of negative space collision environments where two characters / systems exist in each other's negative space is something I've been obsessed with for some ten years. For white, white is the foreground and black is the background, and for black, black is the foreground and white is the background. I've made several games in this vein:https://itch.io/c/713576/negative-space-games