Although I don't think Firefox is the Privacy by Default role model, I would like to see people talking more about Privacy by Default.
Developers usualy argue that opt-out is necessary because otherwise people would not opt-in. But IMO this is just disrespecting peoples choice.
Features can be useful, developers can be trustworthy and by not opting-in people may be not using some feature that they would be missing. But still people have their reasons that should be respected even if it's: I will not opt-in because I don't feel comfortable enough or don't understand enough how it works or the consequences of opting-in
