Strange, my little 2.4 Core Duo was fine with it (~30fps) and typically does very badly with these games. For contrast Minecraft can cause this laptop to overheat and shut down if not using an additional cooling stand. Perhaps I don't need to upgrade after all!
In my experience it's basically impossible for a demo like this to run well without both a good GPU and a good CPU. Even when you use WebGL, rendering code uses a vast amount of CPU time compared with native alternatives.
Crashed my Firefox and in Chrome it clips and moves worse than similar games on my 133MHz machine back in the day.
Now can you port it to pure CSS? How about ASCII art in streaming JSON?
i5/4GB MacBook Air