Good point. Mozilla made most of their money from Google, and other advertisers, iirc. "More free" might've been prudent.
You make a good observation about Safari too. Apple doesn't make much money from advertising--they still sell hardware. They can provide privacy to users at little expense to their core business.
> Mozilla made most of their money from Google, and other advertisers, iirc.
The much bigger problem is webpage owners which lose almost all incentive to support Firefox, if it blocks their ads. You'd have broken webpages all over the place.
Just like in IE/Edge, the "Do not track" setting used to be enabled by default, then it became disabled by default, and for good reason. The argument is, if it is enabled by default, sites will not bothered to support it since it was not something that the user turned on explicitly and was aware of.
The default configuration of Safari is actually protecting you better than Firefox's and most users don't have an ad blocker installed.