Addon recommendations do not anonymize their input data, which I think is just what browser features and maybe sites you've used (I'm not sure). But it doesn't

Addon recommendations do not anonymize their input data, which I think is just what browser features and maybe sites you've used (I'm not sure). But it doesn't matter, since it is never sent anywhere. The data is local, the decision is local. Your browser already knows your browsing history.