It seems like it was May 27th when Jetpack SDK 0.4 was released – it was. Now the Mozilla Labs developers have released Jetpack SDK 0.5.
The new version of the Mozilla toolkit includes access to tabs, a request API, a localization API and something called “load/unload reasons.”
The Jetpack SDK is how future Firefox plugins will be built. What’s cool about Jetpack is that you can use HTML, CSS and JavaScript to make add-ons for Firefox.
It’s just a lot easier than the current plugin framework based on XUL.