Earlier quoted context omitted.
Same for me (Firefox 27.1, Ubuntu 12.04). The game loads, then nothing at all happen. Doesn't react to clicks, keyboard, anything. Some game complains when out of focus, I click on the canvas, then nothing.
What games did you try? Do you get any errors on the JavaScript console?
Sorry for the late reply, I've tried a couple of games with similar results, but POlycraft works at least.