Page centering messes up

I'm making a website and it is here: http://animactions.ca/Animactions/accueil.php

My problem is when I go from accueil to contact, I notice the page shifts 开发者_StackOverflowa bit. I cant figure out why though, the body is supposed to be a fixed width.Thanks *Bear in mind my resolution is 1680x1050, it doesn't do this on 1280x800

It's just because the scrollbar appears when you go to Contact, since the page isn't long enough with your resolution to need one on Accueil.

Edit : mais pourquoi je parle en anglais moi ? :) Bref c'est juste la présence ou non de l'ascenceur de Firefox qui fait que la page semble bouger, c'est normal.