That doesn't make it okay for an opt-out privacy invading study to suddenly be included. You shouldn't silently get less privacy protections simply because you updated.

You're right, Nightly users probably are more savvy so there's no need to decide for them. Lay out what the user's options are and force them to make a choice when the browser starts, don't have a default, and don't have an option preselected.

All this crap has to do with what's okay to do in the absence of clear user intent. If you remove the possibility you don't have to worry.