I accidentally said "Yes" a few days ago when Firefox asked me if it could be my default browser. And I only noticed it today. I really reccomend you get over to Mozilla and get yourself a copy.
http://www.mozilla.org/products/firefox/
Reasons for today:
Tabbed browsing. Instead of a new window (and icon on the Windows task bar) you can open additional pages in "tabs". This makes it very easy to switch back and forth between lots of different web pages, and also leaves space for other applications to run.
Shrink-to-fit source code printing. I know it may be old school, but lots of times I need to print code, and I hate how IE used to break long lines when you printed the source code of a page. Firefox defaulted to shrinking the type so the code fits across one printed page.