For those running Ubuntu and have been wanting to run Firefox 3, it's in the repositories and can easily be installed with the following command: sudo aptitude install firefox-3.0 I was pretty happy to see this. It would be cool if there was a repo for nightlies that updated every night.
This is a development version. From the package: "This is a build of a random development version (aka trunk). It is meant for preview and not for production use."
I use Gran Paradisio on my Kubuntu desktop. It is mostly stable and has some interesting features. For instance, they have expanded the use of the warning bar at the top of the rendering window. Instead of just warning about popups and plugin failures, it now utilizes that to ask about password saving. This is nice because that popup used to interrupt page rendering and now it does not.