Unclear from this article is how they determine what is a "tracker"? I assume there'll be a curated block list, maybe based on anonymously collected data. But that detail is key to whether this is a success or not.
Apple's Intelligent Tracking Prevention (version 2 of which will ship in Safari/iOS 12 in September[0]) uses some sort of ML-based solution to decide what is and what is not a tracker, blocks cookies from being sent to domains that haven't been visited in a first party context, and has an explicit way for the user to opt-in to cookies being sent upon interaction in an iframe (e.g. the FB "like" button). Unclear how this Mozilla version stacks up.
0: https://webkit.org/blog/8311/intelligent-tracking-prevention...