Wahou, first , thank's a lot for this so rapid response
Hum, hum , I was afraid of this, sadly it's a browser render problem .... well I was hoping that I've missed some important code to get my animation smoother, but not....
As I come from the Flash platform, it's very very hard to see so simple animation rendered no very well, but as i read somewhere in this forum , i'll use Canvas ot SVG for smoother more or less complex animations.
I Wish FireFox get better very soon, and wish that the whole internet user in the world get the latest browser for nice animation render made by GSAP the next week , what a wish ......
thank's again
Larry