css - How to center the Firefox #urlbar? -

in firefox navigationbar have back/forward buttons on 1 side
, menu button on other side of urlbar.
i'd horizontally center urlbar on remaining space of navigationbar custom userstyle.

in css, i've added following code:

#urlbar {  width: 800px;  margin: 0 auto !important; } 

but doesn't work. can maybe point me in right direction?

thanks!

i think right way make urlbar fixed width (it's how have set on profile):

#urlbar, #urlbar-container { min-width: 250px !important; max-width: 550px !important; } 

don't know how make urlbar centered in navbar through userchrome.css, can achieve same result classic theme restorer extension (or other lets customize navbar flexible spaces).