Page Move on Hover

I’m trying desperately to figure out why this is happening. hard to explain video: http://cl.ly/L4Re when you hover oner the navigation button, the whole page moves site: http://cl.ly/L4O4

Hm, I can’t replicate that behavior in my browsers. Have you found a solution? All I noticed is that the arrows don’t appear in Firefox … but I can’t work out why.