A lot of this is the same kind of things amazon do to make purchase suggestions. It is fairly invasive but also effective. There are even some customers who appreciate this kind of thing. I will say though that the name is misleading. It dosen't just spot fakes, it seems to be designed as a shopping assitant or search engine who's stand out feature is pointing out fakes. I think there is a place in the market for such a thing, but they need to be careful of how they market that and what data is actually needed to be collected. Ideally they should put in a system where you can opt in to personalised recommendations and collect data for only those people who require that feature. It also needs to be spelled out clearly what this involves in terms of data collected and who sees the data. Regardless I don't think it should be enabled by default in Firefox. Including it in the browser isn't so bad provided they don't get up to microsoft-like shenanigans pushing people to use it.