Keep in mind that it's not within Google's incentives to facilitate ad-blocking and prevention of tracking. After all, that's where the lion's share of their revenue comes from. However, Mozilla is free to actively support such efforts.
The default configuration of Safari is actually protecting you better than Firefox's and most users don't have an ad blocker installed.
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.
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.
https://support.mozilla.org/en-US/kb/tracking-protection-pbm