Space between Divs (Firefox)

Hi, I am working on a website (http://www.optimalhumidity.com/), and when I display it in Firefox, there is a gap between the header image and the nav bar. This does not occur in Internet Explorer. What's going on?
Thanks! ~Blake

P.S. I had a similar problem with spacing in Internet Explorer and solved it by opening and closing the "header" div on the same line.

The gap is there on browsers other than Firefox. It is just IE getting the defaults wrong that is the reason that it doesn't appear there.

You haven't set a margin size for the navbar so it will be using the default margin size.