A third party company (funded by venture capital) created something called "Pocket", which allowed you to save any article you were reading to their service. Pocket had an extension that you could choose to download & enable on your Firefox browser.
For apparently no reason at all, in June 2015, Mozilla integrated the proprietary Pocket into their open source browser, not just as an optional extension but as part of the default installation. The only way to disable Pocket was to go into "about:config", as the option was not available in the "Extensions" toolbar. (Later, Mozilla Corporation purchased the company Pocket, though at the time Pocket was introduced as an inextricable part of Firefox, Pocket was a separate company.)
The Mr. Robot addon had some similarities with the Pocket fiasco:
1. it was pushed to users without their knowledge or consent
2. it was integration of a plugin for a private company into an open-source project
3. it was a decision by marketing, and not development
I am not quite sure how or when we can begin to trust Mozilla Firefox, and what they would need to do to regain that trust.