The problem is that this is equivocating between "selling your data" and setting Google as the default search. The former implies Firefox is harvesting your telemetry and personally identifying you and selling it off to the highest bidder. The latter is setting Google search as an optional default, where any telemetry is part of customary interactions with Google search rather than anything specific that Firefox is doing.

The sense in which you are the product on Firefox is that they want to maintain a large enough user base that search licensing is valuable enough to sell to Google.