From the wikipedia article. linked in the ticket > Shield Studies are available on all channels. Individual studies can be opt-out or opt-in and any and all da

From the wikipedia article. linked in the ticket > Shield Studies are available on all channels. Individual studies can be opt-out or opt-in and any and all data being collected will be declared openly. After confirming willingness to participation, a self expiring add-on will be installed on the user's machine. Mozilla is only installing an experimental feature ass an add-on if they opt in.