Performance tweak

Thanks for this, it's really useful and I learned a lot from it.

I'm experimenting with creating a game and have become a bit obsessed with performance. This change eliminates browser paints and layouts (at least in chrome desktop - only place I've tested): 

![comparison](https://f.cloud.github.com/assets/1655984/2139523/d5bb03f4-933f-11e3-800d-402e372dd45f.PNG)