I found out about this last night from a tweet sent out by the jQuery Twitter account (which is probably a good indication that they like the idea).
You can learn more about Jetpack via the following URLs:
...the tutorials in the final link give you a good idea of the kinds of things Jetpack will allow you to do: the last example is a Jetpack add-on that will count and display the number of unread e-mails in your Gmail Inbox.
I want to give Jetpack a whirl, but I honestly can't think of any functionality I want to add to Firefox that I can't get from an existing plugin. Anyone have any suggestions for something to try with Jetpack?
It's interesting how web technologies keep being repurposed as a development option in other technologies (Adobe AIR, the upcoming Palm Pre's WebOS, and now Jetpack). Even though I'm not particularly interested in delving into all these different areas, I must say that I like the trend. :)