Firefox without the add-ons would not be terribly exciting to use, however developing extensions has been the forte of experienced developers, who understand how the browser works and how they can extend it.
Jetpack is a newly formed experiment in using open Web technologies to enhance the browser, with the goal of allowing anyone who can build a Web site to participate in making the Web a better place to work, communicate and play.
In short, Jetpack is an API for allowing you to write Firefox add-ons using the web technologies you already know.
This is definitely great news for many developers who want to develop Firefox add-ons without having to break their heads learning the intricacies of Firefox.
Do expect a few useful add-ons coming your way from Techie Buzz too, we have spent sometime developing one, however we would rather use Jetpack now and get one out shortly :-).
If you are more interested in learning how to work with Jetpack, checkout this Mozilla Labs Jetpack Intro & Tutorial video.