Pocket used to be 3rd party for a moment, later Mozilla integrated it in Firefox and enabled integration for everyone by default. Some people didn't like it, but others love it. Pocket now belongs to Mozilla and is covered with the same privacy policy as other products and services from Mozilla (GDPR compliant before GDPR was a thing). There are plans to open-source Pocket the same way Firefox-sync is open-source and can be self-hosted. Some people just still think that browser is a stand-alone app that works without 3rd party code or integrations, they just never inspected network traffic of Firefox or any other browser.