I've used just about every computer operating system under the Sun (no pun intended....OK, maybe a small one). DOS. Desqview, OS/2, Linux, Windows 3.1, Windows95, WindowsNT, Windows2000, Windows XP and now there’s Windows Vista. I’ve even installed and checked out BeOS - not many will have heard of that one.

Maturity

I've used Firefox since the early days of it's release. I love it, along with all it's extensions.

Extensions such as Firebug, Web Developer, MeasureIt and Colour Picker - to name but a few. And now there's the social networking extensions like Digg, Delicious and StumbleUpon. These have been an enormous benefit to Firefox's success as well as kicking the ass out of IE.