Firefox 4 RC release candidate is out and the final version will be available in a couple days. I downloaded the MX3 skin which cleans things up a little. Below are some screen shots and a link where to download it. Overall, it feels very fast and responsive. Developers are in the process of updating their plug-ins for the new platform, so keep checking the Mozilla add-ons page for your favorite plug-ins.
You can get Firefox 4 RC here: