Comment by acqq

Your link in edit part is the answer to your question before the edit:

https://normandy.readthedocs.io/en/latest/user/actions/opt-o...

"opt-out-study: Install a Study Add-on Without Prompting

The opt-out-study action installs an add-on, typically one that implements a feature experiment by changing Firefox and measuring how it affects the user."

They are obviously the topic of:

app.shield.optoutstudies.enabled=true

That I mentioned.

I see a lot of commenters trying to excuse them. The problem is, people allowed the "studies" because Mozilla claimed that they are "measuring" whatever "to make Firefox better." They never told anybody that they are selling the "studies" functionality which silently installs ("opt-out" not opt in!) to the advertisers.

I don't know how anybody can defend such an approach.