Basic summary from a CNET Review on the products.
Despite its many improvements, Firefox 2, like Internet Explorer 7, still does not pass the Acid2 Web Standards test, although, unlike Microsoft, Mozilla says it is working toward full compliance.
Security enhancements within Firefox 2 continue. New is a dialog box informing you of cross-domain scripting, a tactic used by criminal hackers to link nonrelated sites to sites you think may be legit. And
Mozilla remains very responsive to fixing its vulnerabilities, pushing out updates within a few days of public notice.
IE 7 was Microsoft's one chance to leapfrog ahead of the competition, but the company has only barely caught sight of the current front-runners. For more features and greater security,
switch to Mozilla Firefox.
- LOL, their words not mine 
Bottom line, for security, safe browsing and quickness of fixes released, stick with the Fox 