Mozilla is developing a social network tool that will be integrated into Firefox. The project is available for testing and it is still in the early development stages therefore has flaws which has to be fixed.
Mozilla Labs are working on the project called "The Coop" that will be a part
of your Firefox browser and it will allow you to interact with your friends
in a way that should have been introduced to the internet users long time ago. Mozilla Lab lad claim in its log that “when people think of tools for social
interaction, email and instant messenger are at the top of their list, not web
browsers”. Mozilla wants to change it.
This tool in development should allow users to keep track of their friends, share links, jokes, Flicker photos, Myspace updates etc.
You can find more information on the Mozilla Lab site here