Restyle the web with Stylish, a user styles manager. Stylish lets you easily install themes and skins for Google, Facebook, YouTube, Orkut, and many, many other sites. You can even customize Firefox and other programs themselves.
Displays a country flag depicting the location of the current website's server and provides a multitude of tools such as site safety checks, whois, translation, similar sites, validation, URL shortening, and more...
Xmarks is the #1 bookmarking and open tab add-on. Keep your bookmarks, and open tabs backed up and synchronized across computers and browsers. Mobile phones with Premium access. Utilize LastPass to sync passwords!
Personas are free, easy-to-install "skins" for Firefox. Personas Plus extends that built-in functionality to give you even more control and easier access to new, popular, and your own favorite Personas.
Stratiform is the ultimate user friendly customization add-on for Firefox. It puts the power in the average user's hands to customize the browser's look.
Personalize Firefox Button in Firefox 4 and change it to your personal and powerful one!
Create your personalized menu to replace Menu Bar in Firefox 3.
It enables user to change some default FF options and gain more out of firefox. It increases user's ability to manage FF the way he wants.User can change many features which are not in Tools -> options menu . (^_^). Now tweak NETWORK settings, too.