The newest version of the Mozilla Firefox browser, which I highly recommend for superior interface and security in comparison with other browsers, is now available:
http://www.mozilla.org/products/firefox/
It should just install over your previous version without changing anything (except the appearance of a few icons). Unless, of course, you don't have a previous version... In that case, now's a great time to start.

You can also find the Linux version here, and the Mac OS X version here