The best theme that I found from AMO... Check this out! ^0^
ANTHEM is a take on originality and recent UI trends for Firefox web browsing. It was built on the original Mac theme that comes OOB with the FF3 install.
A Green and black coat of Chrome for Firefox. Chromifox is a dark and deep green theme for Firefox on Windows, Linux, and Mac OS X, inspired by the appearance of the Google Chrome browser. This theme is a fork of Chromifox Extreme Blade by Triton
Go Green Firefox theme for Green Ecology enthusiasts. Modifications to this theme can be found here http://www.zamaansoft.com/firefox/hacks.htm
It's simple sky blue theme with simple, cool interface as like summer sea.
Chromifox Extreme BLADE is a Crimson and Black coat of Chrome for Firefox 3.5.
RulerDark is a simple to use and install dark theme for your Firefox browser.
A monochrome version of the default windows firefox 3-3.6.* theme, Strata.
The new HEAVEN.CUBE for Firefox 3.5. This is a dark modern theme recommended for those with a correspondingly dark OS visual style. I have updated this theme to be Windows-compatible only. I will be releasing another theme specifically for the Mac.