Firefox 4, with the release of Beta 7, is as good as finished. From now until its release in early 2011, no new features will be added, no significant changes will be made -- Beta 7 is, for all intents and purposes, Firefox 4.
Unlike Firefox 3.5 (private browsing) and 3.6 (personas!!), version 4 has a significant number of new in-your-face features -- features that will take a little getting used to... like tabs-on-top! There are tons of neat little additions that improve your surfing experience, too. Many of these will exist in the background, under the hood, but it still helps to know exactly what your new browser is capable of; did you know that Firefox 4 is as fast as Chrome, for example?
This guide will fully prepare you for Firefox 4. It will teach you how to work with the big-hitters Panorama and Sync, and also introduce some other features you might not have heard about. If you're already using the Beta, this guide might teach you some new tricks. If you're holding off until the official launch in 2011, that's fine too -- bookmark this page and check back later!
You might find, after reading this guide, that you suddenly feel compelled to try out Firefox 4. It really is rather good.