What you mean is telemetry, that is something seperately. And it is also enabled by default( and also annoys me, but less so).
But firefox studies means, (or can mean), that firefox will track you and sell that data to ad companies, if you "allow" it. Which everyone does, by default. This behavior from a "privacy orientated" company is close to a scam by me. Because a normal user who believes the privacy promise, won't know of, nor find these settings.
And apparently now there is a third setting(on Firefox mobile, but not on desktop), that at least openly tells you they share tracking data with a ad companies.
edit: ok, that is weirdly funny. "Adjust" the ad company firefox is apparently working together with, has a website, that does not really load in firefox at all, but only in chrome