Looks like the marget share for Firefox is growing steadily but 95% of UK web users still use Internet Explorer.
Mozilla Firefox global usage share is still growing
Why do I think you should give Firefox a try?
Internet Explorer is one of the reasons why Windows is so prone to spyware and malware due to ActiveX. ActiveX does a lot of good things but it also allows a lot of access to your pc, access that leaves your PC open to attack. Firefox does not support ActiveX.
Pop-up blocking is built in.
Firefox supports tabbed browsing, a feature that once you use you'll never go back. Also since Firefox is open source it can be customised very easily. This gives you the power to change the look and feel to suit your needs.
FREEDOM OF CHOICE:
If you run Windows you don't have a choice whether to install IE. You can install Firefox and run it alongside IE with no problems at all. I suggest running Firefox for 99% of browsing, locking down IE for essential ActiveX sites only (Windows Update for example).
Firefox can be downloaded in a wide variety of languages. It's not dependant on your OS.
Firefox runs the same on Windows, OS X & Linux. Ideal if you use multiple platforms.
Give Firefox a try today: Get Firefox!
While you're at it you might like to check out Opera or if you're using OS X check out Camino.