If this turns out to be true, I might leave #Firefox for the first time.

Firefox is on a slippery slope
For a long time, it was just setting the default search provider to Google in exchange for a beefy stipend. Later, paid links in your new tab page were added. Then, a proprietary service, Pocket, was bundled into the browser - not as an addon, but a hardcoded feature. In the past few days, we’ve discovered an advertisement in the form of browser extension was sideloaded into user browsers. Whoever is leading these decisions at Mozilla needs to be stopped.
 via Diaspora
It's part of the Firefox "data collection and use" settings; specifically, "Allow Firefox to install and run studies". It's not forced nor hidden.
  
Is it off by default and won't turn itself on? (I can't check since I'm using the FF LTS that comes with #Slackware)