Firefox fixed header jumping

Firefox fixed header jumping

Hi All!

I have such a code: http://jsfiddle.net/twEJ4/2/
When I test it with my firefox in my test page I see the fixed header of page1 jumping after the back slide animation from page2. It is ok when I test in jsfiddle, also it is ok with webkit browsers.
Why the header jumps to its place at the end of slide animation with back link?And it appears in the same place.