Umm .. get with the program
A majority of spyware doesn't work and virus your PC in FireFox
FireFox stores your user/pass right on the input fields on a page so all you have to do is click to gain access
Supports tabbed browsing straight out the box.
Unless your really gay, it actually loads 3-4x faster than IE
And its not MS
Why would you not use it? And comes with a dope Email client Thunderbird that actually supports IMAP mail accounts correctly storing sent messages in the sent folder of the IMAP rather than your local sent folder.