So you can find things by "that spicy chicken recipe" instead of having to remember what it was actually called, or slog through a gazillion chicken recipes in your history when you realise that "spicy" was nowhere in the name. Basically stemming/thesaurus search on steroids.

It's quite likely to be opt-in as I imagine ingesting the sites you're looking at is a significant computational load. The translators are also opt-in, there's enough stuff inbuilt to detect languages but not to translate, you have to download those models first. And they're quite good btw.

Another thing I could see them offering is stuff like tl;dr bot. It's probably not for everyone, but I definitely can see that it can be a useful feature for many people.

Think like Microsoft recall for your browser history. Yeah that sounds awful, it's not surprising why people would not want it. Just goes to show that Mozilla is dumb and blind like all other companies.