Some projects building on Mozilla based technologies are now part of the Google Summer of Code initiative. mozdev.org - summer: projects. Nothing that will have a big impact on end users (i.e. mass exodus to Firefox), but could still be useful and encourage more development on Mozilla technologies. The BitTorrent client built using XUL may prove useful, especially if it will be able to integrate with Firefox.
Would be interesting to see how Summer of Code goes at what comes out and is improved by the time the summer ends. Hopefully the code will be good and not have too many (or have no) bugs.