Doesn't sync encrypt the data sent out with keys only known by you? So in that case the main loss in privacy seems to be that others learn that someone from you

Doesn't sync encrypt the data sent out with keys only known by you? So in that case the main loss in privacy seems to be that others learn that someone from your IP uses Firefox sync. Are there other privacy-oriented reasons to avoid it? edit: Now that I think about it, it does also seem to force you to use a functioning email address as opposed to say an arbitrary username. That is something I never liked.