In-Jokes are only ever going to be funny for those within that group; that's pretty much what defines them. Since I'm not in any Mozilla hacking group I wouldn't know whether it's so, or just a bit of silliness, but either way it doesn't add more than a one-time bump.
A) You don't see any connection between "funny" and "in-joke",
B) You don't see any connection between "hip" and "showing affiliation with a high-status group".