Okay, FF3 is now availible in Alpha.  Final release is the final release, with bugs fixed, and kinks worked out.  Beta is sort of a mass test, where you see how a program reacts in the real world, on computers more vastly different than the developers could ever hope to simulate in a lab.  Alpha is when a program is barely ready to be called a complete program.  So, don’t get your hopes up yet, unless you’re a serious developer or web page scripter.

FF3 looks like it’s got some good changes : A possible bookmark re-vamp that got cut from FF2, a new download manager that can pause downloads and resume them across different sessions, and some better extension handling that might minimize some compatibility issues.  FF3 has also passed the Acid 2 Test, a rigorous test designed to use every aspect of a browsers scripting capabilities, to see how well it reads and handles various types of scripts and graphics.

To read more about FF3 (not my extremely shortened summary)
http://arstechnica.com/news.ars/post/20061212-8409.html