1) Small and slick

The Windows version is only 6.0 MB. That's insanely small for something this powerful. No matter what theme you choose for your Fireird -- and there are quite a handful of personalized styles out there to select from -- it just feels slicker than all the alternatives. It's extremely responsive, and just looks cool. Far more screen real estate is given to the webpage itself and less to the browser, giving it a clean and compact feel.

2) Intuitive user interface

I've watched over a dozen people pick up Firefox for the first time, and it takes them only seconds to become comfortable with its interface. All the menus are stored exactly where they should be, and although Firefox offers an abundance of features and options, it never feels as though you have to wade through an impossible labyrinth of choices and menus in order to change your settings. Firefox successfully accomplishes the difficult goal of making simple things simple and complicated things possible.

3) Tabbed browsing

Anyone currently using a browser without tabbing abilities may have difficulty comprehending exactly why tabs are such a useful feature, but those who use tabs wouldn't give them up for the world. Firefox integrates tabbed browsing seamlessly into everyday browsing life by opening tabs if a user holds Ctrl while clicking on a link. While you continue to read the current page, the background tab loads so that it's ready for you when you're ready for it. There's no confusing switching between windows, and you can open an entire folder of bookmarks as a series of tabs. Fast, efficient, and intuitive.

4) Popup blocking

You can finally laugh at all the Internet Explorer users who visit one webpage only to have fifteen popup windows jump ceaselessly on top of each other. Firefox offers a powerful solution by blocking popup windows by default but informing the user through an unobtrusive icon when popups have been blocked. If a user clicks on the icon, they can manage their popups and grant access to legitimate ones.

5) Extensions

Firefox currently has over 150 extensions (including some of the extensions mentioned in this document): from Calendar modules, to "Blog This" capabilities, to W3C checking of the current page, and mouse gestures. Extensions are remarkably easy to install in Firefox -- just a few clicks without a disruptive install screen. Whether you want to play Minesweeper in your browser, or add Word Processor functionality to text forms (including opening and saving form entries as files), Firefox has more extensions than you could possibly dream of.

source: http://www.insanecats.com/firebird