From the 'Big Add-on News' files:

Mozilla's Jetpack is a new approach to deploying and building browser add-ons, but it's always had one big problem.

You first had to get users to actually install Jetpack first. In contrast every other add-on just work when you install it into Firefox. That now changes thanks to the Jetpack 0.5 bootstrap edition.

"You can now provide a one-line install link which will, if the user doesn't already have Jetpack, both install Jetpack as well as your feature," Mozilla's Jetpack site states. "With bootstrapping, the install experience for a jetpack is now easily accessible to everyday users".

It's a simple enough thing, but a big deal nonetheless. Now devs can actually write a Jetpack and add-on and have a reasonable expectation that they'll get more users than just the bleeding edge of early adopters.

Jetpack itself is also getting a real improvement in this release. It's more stable, adds audio capabilities and new twitter functions too.

With the new Twitter library, it should be trivial for someone to create their own Twitter enhanced add-on, or even just yet another Twitter client.

I still haven't seen any official word on whether or not Jetpack will be part of Firefox 3.6, but at this point I'm not sure if it matters. With the bootstrap adoption in earnest can begin now with Firefox 3.5 users.