Mozilla released Firefox 4 (the Final Version) today, March 22. It's been in beta so long we've mostly forgotten about it. Do we want to install it now, or wait until the initial bugs are repaired?
Install now if you like adventure and aren't disturbed by change. Wait a few days or weeks if you'd like someone else to pick out the bugs and the fixed versions to appear.
To install, open Firefox, then click on Help - Check for updates. You'll be prompted to download version 4; follow the prompts to do so. Or go directly to the web site and download fresh, then install over your current version.
Below is a link to a good early review of the major changes. For me, Firefox 4 brings new meaning to the term "minimalist". Fewer buttons, fewer toolbars (initially), fewer controls. It looks a lot more like Google's Chrome browser. Once you find your way around, it will be as simple as using whatever you're using today.
You should upgrade Firefox to version 4 at some point. Besides the new interface, there are always security improvements. Anyone who's ever been affected by malware will appreciate the efforts.