I tried the demo on both Chrome and Firefox (both the very latest as of the date of this post.
I am using Windows 7 Ultimate 64-bit with 16 Gigabytes of ram DDR3 1600 with Intel 3770k Ivy Bridge Processor and Nvidia Geforce 670 2 Gigabytes of ram with the latest drivers from August.
In Chrome everything was perfect and it was fully playable.
In Firefox it was slow as heck and when I would move my object with the arrow keys it would move the entire window (this did not happen with chrome).
Firefox should not be slow with the top of the line CPU, and high end GPU with 16 Gigs of DDR3 1600 RAM. Nothing under-clocked and nothing over-clocked. Only ONE TAB Open in in Firefox (which was the game). NO wonder I never use that browser anymore. Horrible.
App Game Kit (A.G.K.) - Want to be creative on many platforms at once? This is the tool you need.