And specifically about removing a single SDK, not removing ad-tracking altogether (which is kind of implied from the title). Mozilla has been trying for years to monetize Firefox through ads, so I don't think people should be reading into this change too much, especially since it happened without any kind of announcement. If it were a pro-privacy decision, the marketing people would be milking this move for all they can.
Desktop users interested in a privacy-first Firefox should try Waterfox https://www.waterfox.net/