Mozilla was developing a private Reading List feature that used Firefox Sync. They suddenly replaced it with Pocket, which sent users' bookmarks to a third party that engaged in data mining. (The acquisition came later.)
Users suspected money was involved. Mozilla employees insisted that Pocket hadn't paid for the integration. Months later, it came out that there was a referral deal.
Pocket was and is an extension. It just gets special treatment.
Mozilla acquired Pocket in early 2017 and said they would release the source code. That still hasn't happened.
It's just a bundled extension inside Firefox. You can't uninstall bundled extensions, and you can bundle yours in your custom Firefox installation if you want.
Did a similar thing for a project, rolled out customer's own Firefox extensions (for office workflow) to employee desktops. Extensions were bundled because the employers sometimes uninstall them and freak out because they can't work anymore.
Users suspected money was involved. Mozilla employees insisted that Pocket hadn't paid for the integration. Months later, it came out that there was a referral deal.
Pocket was and is an extension. It just gets special treatment.
Mozilla acquired Pocket in early 2017 and said they would release the source code. That still hasn't happened.