Huh. I'm running it on a Linux machine with a Core i5 (Intel(R) Core(TM) i5-4210M CPU @ 2.60GHz according to /proc/cpuinfo), and it's a bit CPU-intensive (it makes my laptop's fan kick into gear) but it's smooth and responsive and everything obviously works the way it's supposed to. Doesn't even come close to eating a gig of RAM, out of the eight I have.

Firefox 41.0.2 on Ubuntu Vivid Vervet (3.19.0-31-generic), on a LinuxCertified.com LC2430E. (Good laptop. No Microsoft tax. Yes, that is a blatant plug. So's this WebGL demo.)