My blog doesn’t display properly in Firefox.

My blog displays fine in IE. However, in Firefox, the colors get messed up and the sidebar goes all the way to the end. I am using Alternate O Theme. I have two blogs, both using this theme. One is working fine in FF the other is not.
I know it isn’t a problem with the stylesheet.css, because I copied and pasted the stylesheet.css from the blog that works to the one that doesn’t and it still looks wrong in FF. I think it is something wrong with my header maybe.
The address is http://guigece.com
Any help will be appreciated.

Thanks