At the moment we focus on the iOS and Android devices. This means the supported browsers are Mobile Safari, Mobile Chrome and Android Browser. I cannot tell the exact version which is required, the newer the better. Other browsers might work as well, last week I tested it the first time on IE 9 Mobile on a Windows Phone and it worked quite a lot.
But more important than the browser is the device itself: You need an up-to-date device to get a solid experience. The performance won't be sufficent with old devices.
As soon as I know the exact requirements I'll update the wiki.