I find the first reply rather troublesome - Firefox is free, completely and totally. The download is free, the add-ons are free, the help forums are free.
Internet Explorer is the actual name of Microsoft's browser, so I think you're looking for the best "browser" out there.
Opinions vary, but the vast majority of reviewers have found that Firefox is much better than even IE7. It's smaller, safer, more up to date, shows pages correctly, is constantly improving, has very few flaws and any security flaws found are fixed much, much faster.
The reason I like it? The add-ons:
Adblock Plus blocks ads - banner ads, flash ads, iframe ads.
Adblock Plus: Element Hiding Helper - allows you to get rid of text ads, boxes that contained ads that were blocked and other annoyances.
FoxyTunes - control your music player without switching to it.
CookieSafe - block cookies until you ok them. Sites use cookies to track what you're doing, etc. Increases privacy.
NoScript - block javascripts (and more) until you ok them. Increases privacy and security.
And there are literally about a thousand more... all free.