Mozilla JetPack: Lowering the Bar to Extend Firefox

Bears more than a passing similarity to Greasemonkey (which is awesome). Looks like it would let you do things in that gray area between stuff Greasemonkey can do and stuff you really don't want to start messing around with XUL to do.

My big gripe with Firefox extension development was that getting started there were like 20 different source files and a dozen configuration files just to get something on the screen. With that said, the extension API is pretty robust and lets you play pretty deep into the core of FF.

There's a video over here: http://www.sitepoint.com/blogs/2009/05/21/mozilla-jetpack-fi...

Previous announcement http://news.ycombinator.com/item?id=625958 and short tutorial http://news.ycombinator.com/item?id=619548