Not sure if the UI is supposed to shake, but if you want to prevent this you should put those elements on another layer with a parallax setting of "0,0".
The game kind of doesn't contain any drift at all, seems to be based on one of the default behaviours, the car has perfect traction all the time. Also, the art style looks cheap.
Furthermore, the view distance is too low for my tastes and the fact that the timer runs in the menu makes the game seem broken.
Despite this, i kind of like it - although not exactly a great game, the music seems very relaxed and the game itself is simple and short enough. Perhaps it's just that this reminds me of times when most of the flash portals had simpler content and a bit less eyecandy, which strains the eyes and tires you out eventually... :/
Also, i didn't have any problems with running it (latest stable build of Firefox), the framerate was stable all the way through.