While I question the utility of having such an app integrated into Firefox, AllPeers looks like an interesting project. It's "a free extension which combines the strength of Firefox and the efficiency of BitTorrent to transform your favorite browser into a media sharing powerhouse." It looks to be a private-network P2P app, i.e. you have a buddy list and only those people can access your files, but intriguingly it also has a complete BitTorrent client included. Unfortunately AllPeers isn't yet available, but of course you can add your name to their mailing list and keep track of its development on their official blog. Check out this post for some screenshots.

[Via Zeropaid]