Firefox generating extra space after a div, clears on reload

I notice on 2 pages from my site (http://blazingoctopuss.com/about.html and http://blazingoctopuss.com/donate.html) firefox adds a large amount of space that clears on page reload. The other 2 main pages don't have this issue but I can't figure out what I did in the markup that would cause this.

I can't replicate the problem in any other browser. Any ide开发者_开发百科as?

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The Navcontainer height changes from

550px to 800px

This is probably in javascript/jquery, somewhere that you dont know.

It occurs when you load the page the first time.