To enhance the browser using open Web technologies JetPack is a newly formed experiment for Firefox. It has the ability to allow anyone to build a Web site to participate in making the Web a better place to work, communicate and play.
Click to use some more Firefox Addons
In a simple way, you can say that Jetpack is an API for allowing you to write Firefox addons using the web technologies you know already.
Moreover, it is a Labs experiments, it is an open source project, and it can be easily developed and redesigned by everyone.
Click to SOURCE and DOWNLOAD
[ More ]