Leaking what? Your publicly available JS libraries? or is this a more general Mozilla bashing comment?
The service itself looks great, and the versioning is exactly what I'm after.
I guess, browsers could provide a separate cache for CDN domains that's _really_ long lived (there's a certain guarantee that files won't change there) and also send requests there with no referer at all times.
Requesting assets from third-party websites leaks that I have been visiting your site to the third-party. Now imagine having a big CDN that many websites use and you can spy on a lot of unsuspecting users.
If you don't want someone to have this information, the sensible thing is not to offer it. I cannot conceive of any way in which sending the information and then yelling at the recipient for receiving it is "more correct" than just not telling people things you don't want them to know.
Web developers have a responsibility to protect their users from threats they don't even know exist.