When mozdev.org was started several years ago, there was no big vision for the site—it was created because a few people wanted a place to work on their Mozilla-related projects and there was a thought that other people might also find this useful. This is a pretty typical open source type of story in the sense that some people had an itch that they scratched and then things went from there.
Another thing that happened with mozdev that also typically happens with open source projects is that it became whatever the community of people interacting with the site made it. Looking back at how the site has been used by the community, it seems that one of mozdev’s functions has been to act as an incubator for new ideas for applications, extensions and features.
As an example, Camino started out as a mozdev project called Chimera. The project soon moved off of the site since it got very popular, but hopefully mozdev helped get this project to the point where it was big enough that it needed more than we could offer. This same thing has happened with extensions such as Greasemonkey and Firefox features such as session restore (I don’t think the Total Recall project directly contributed to this feature, but it was an early working implementation of the idea).
There have been several other extensions and applications that started on mozdev that then matured and left the site. I think it would be interesting to get a list together of these projects, so I’ve created a wiki page where we can start working on this. If you know of other examples of projects that have started out and then moved on from mozdev, feel free to edit the wiki or add a comment on the page.