The Firefox 4 beta has a new look, with tabs on top and reduced browser chrome space (on Windows only, for now). If you'd like an even more minimalist, Chrome-like toolbar, you can get it with a CSS tweak.
Just yesterday we came across a tweak to the userChrome.css file that de-colourised Firefox 4's menu button, and this works in the same manner. You'll create a userChrome.css file in your profile's Chrome folder, then drop in some code that the Gdgtry blog cooked up for consolidating the top toolbar with its tabs. The results give as much space as possible to your tabs and buttons, with just a little bit left to grab and drag the window with your mouse.
If you've found another good user CSS tweak or prefer another means of changing Firefox 4's appearance, do let us know in the comments.
Thinning Down FireFox 4′s Tab Bar [Gdgtry]