Because Mozilla takes a metric shitload of your data via fakespot such as (but not limited to)
Internet or other electronic network activity (e.g., browsing history, search history, information regarding an individual’s interaction with an internet website, application, or advertisement, and online viewing activities)
https://www.fakespot.com/privacy-policy
And then sells it to advertisers
Read the Pocket and Mozilla FakeSpot privacy policies. They collect a lot if data, including browsing history, and do so via Google Analytics. They then share that data with advertisers.