You got this error after *downloading* it?! Huh well... that's new. Sorry about that! Yeah, the game lags a lot in browser, although apparently some browsers are worse than others for web games.
BTW, have you played any other downloadable Godot games on that system? I'd be interested to know if it's my game only or if it's all Godot games. Wiggly Candy Hand is another one that's made in Godot. give it a try and let me know if you get a similar bug... it'd help me narrow it down to if it's an engine thing or specifically just my one!