Jquery animation in Firefox only displayed after window resize

Jquery animation in Firefox only displayed after window resize

(I hope it is ok to post the whole page..) Ok I deleted the website url in this post. Here is my code more simple:

The problem only appears in Firefox (Firefox 33.0.1, OS X Yosemite 10.10), Google Chrome and Safari are working fine!

So if you click on the navigation icon in the top right corner, you can see in Firebug that the animation is executed and the div (#navWrapper) is animated from -70px to 0px. But it is not displayed in Firefox. Only if you resize the browser.

I really don't understand it! I've been wasting hours on that problem..