The production release of the Firestorm Viewer is here. It has taken 15 months from the preview to this production viewer. The team has essentially combined the features from the Phoenix Viewer with the new Linden Lab Viewer and technology while giving it a custom user interface.
Significant portions of the Lab’s technology have been changing while the team was working. The team had a changing foundation to deal with as they built. For now, the team feels they have caught up with the Lab. Check it out. The following is what I found.

In February of this year we saw the first previews of the Firestorm viewer in a video, see: Firestorm Viewer Preview, and a preview version of the viewer. Since then releases of the Firestorm Viewer have been few and far between. I think that phase of Firestorm’s development is over. I expect to see the release cycle speed up.
We are promised another release of Phoenix. I doubt we will see any more development in Phoenix once it gets mesh. Once that release is out we will see all of the team’s effort placed into Firestorm. There will probably be some bug fixes on Phoenix, but Firestorm is the replacement for Phoenix.