To the Mozillians that follow these threads, Shame on you for making studies like this opt-out. Look, I get that making it opt-in would reduce your sample size but this kind of thing isn't acceptable for a browser that's supposed to respect the user -- you're literally using dark patterns. Expressed consent should be the standard. You're targeting Nightly users, the very people who know enough to make an informed dec…
The article specifies that only users on Nightly who opted in previously to Nightly _Experiments_ were targeted, and were in the dataset. The first experiment you join in Firefox usually has several steps of confirmations and opt-ins.