According to Mozilla Links (via Lifehacker) the latest nightly build of Firefox has a customizable tab bar. This new function, which was previously only available through third-party add-ons and CSS tweaks, allows a user to take full control over the way Firefox looks and feels. Buttons in the tab bar can be removed, added, and moved around.
If someone wanted, they could maximize web site viewing space by moving everything, tabs and all, onto a single row of chrome. There are still some kinks to be worked out (read quote below), but the implementation of this new feature goes to show you how serious Mozilla is about giving users what they want.
"Right now there is no way to set a minimum size for the location or search bars and they are just compressed as you open more tabs, becoming unusable when working with more than 7 tabs (in a 1280px wide screen)."
You can grab the latest nightly builds of Firefox from Mozilla's FTP server.
Image taken from Mozilla Links.