Hello thank you very much for your answers.
My performance problem is not due to my PC (powerful enough, I play Battlefield 3 smoothly, Batman AC ...) but for some reason I feel my square :) lightly not walk, sometimes I feel certain pauses and delays I do not understand why?
About the HD as if I'd do it in HD because I think of a PC game with the best graphics possible.
Another problem I've discovered is that my character does not jump with the same force Firefox to display if I use that if I use Opera ... ie physics behave different. Is this normal?
regards