Show me a ‘Mozilla Labs’ page on Facebook and I’ll click on that ‘Become a fan’-button immediately. ‘Labs‘ is where new and often exciting browser-functionality is being prototyped (think Prism, Weave, Ubiquity, About:tab, Personas), and where the everyone can get involved in the process. How great is that?
Aza’s demo on Vimeo is a great introduction:
It’s still early days and some important features are not implemented yet (e.g. persistent storage, access to the browser’s chrome beyond notifications and the status bar, ajax when behind a proxy), so as far as I’m concerned Jetpack doesn’t outdo Greasemonkey just yet, but looking at the draft specs and at some of the functionality that they would like to introduce in the next milestone, Jetpack could indeed bring browser extensions to a whole new level.
But don’t take my word for it, just install the Jetpack extension and see for yourself.