Firefox should come with GPC (Global Privacy Control) and DNT (Do Not Track) setting toggled on and not opt is as of now.
To my understanding changing the browser settings makes you easier to track with fingerprinting, hence why in terms of privacy it's better to not opt in on these privacy features. This makes the whole opt in for privacy settings as GPC and DNT sort of a toggle that defeats it own purpose. Privacy should be by default and not the other way around.
If it where shipped with this settings on, then most firefox browsers would have this settings and would not stand out as a fingerprintable datapoint. That would increase privacy for all users of firefox and its forks.