Although it's still under development and you can only use them with the Dev channel version, I find them very promising! oh, and you can install, activate and use them without restarting the browser.
In my case I installed Google Wave, GMail, Facebook and Google Reader notifiers, and here's how you can do it:
I must say that the first Avatar trailer I saw was a little disappointing for me, it gave me a bad first taste (lack of epic moments/music/speeches, etc...), but then when I saw the second one, it changed completely my opinion, now I really know that James Cameron has made a very special film, and I also think that's gonna be better than we expect.
Theatrical release date is December 18, and in order to make the wait, ironically, a little bit shorter... here is a new 4min featurette with some new scenes.
