Most people don't think about this stuff and are simply uninformed. Referring to what "most people think" is a cop-out from their side.
But I think the sense Mozilla are referring to is the more obvious and over-the-top things like selling your name, phone number, email, postal address, your Amazon purchasing history, or to ramp it up more, your passwords, your credit card info etc.
Just saying that you can stretch it pretty far with vague language like "we aren't doing [bad thing] in the sense that most people would understand [bad thing]".
But I think the sense Mozilla are referring to is the more obvious and over-the-top things like selling your name, phone number, email, postal address, your Amazon purchasing history, or to ramp it up more, your passwords, your credit card info etc.