Apart from being free, fast, secure and web standard compliant, fire fox is also favored by many web surfers and developers because of its extensive range of add ons which extend the functionality of the browser.
FireFTP - FTP Interface - Upload/download directly to server via firefox.
ColorZilla - Colour Picker - Sample exact colour of anything within browser.
Delicious Bookmarks - Online Book Mark Manager - Synchronise bookmarks across computers.
MeasureIt - Ruler - Measure exact dimension of anything within browser.
Download Statusbar - Download Manager - Displays Firefox downloads at bottom of browser.
Speed Dial - Browser Launch Pad - Access your favourite / frequented websites much faster.
BetterSearch - Search Engine Extender - See thumbnail previews of Google and Yahoo pages, remove sponsored links.
FEBE - Firefox Backup - Backup and transfer Fire fire settings and Add-ons.
Web Developer - WEb Development - Huge bundle of web development tools.
There are thousand more plug ins available Firefox all conveniently categorised for improved security, convenient twitter and news feeds or whatever your need may be, so visit the Firefox plug in website and see what you find.