I already posted on Google+ the results, so I'm now summarizing the steps you need.
- First things first, you need the Adwaita Theme[en] that, as usual, you can find on addons.mozilla.org.
- Then you need the HTitle extension, from the same source. Big warning! The extension hides the titlebar, so if you use the same Firefox profile in other desktop environments, you could loose the titlebar when Firefox is maximized!
- Next you want also the Movable Firefox Button. This is optional but very convenient as you can move the FF button (which contains all the menus and such other things) in the url bar or in the tab bar, in the position you want it. In the original article it's just after the url bar, I prefer to have it as the first item in the tab bar.
- Install the OmniBar which let you merge the url bar and the search bar as Chrome do, but without losing functionality.
- Now you can move the tab bar on top of the url bar if you like, just type the usual about:config into the url bar and set the property browser.tabs.onTop to True.
- Now you can install the Status Titlebar Gnome Shell extension. This is also optional but it may be very useful in case you have similar windows open.
