Can't find something on my iphone (default browser)?

Ok I wasn't really paying attention and I guess I clicked something on my iphone & when I looked (i guess I was in the "Settings") there was an option to change my web browser from Safari to Mozilla. It was weird because I've been using Apple for years never knew iphone could do that & I never saw that option until now. So I switched it. And then just got out of it because like I said I was only half paying attention. But now I'm trying to go back to that option under settings but I can't find it anywhere! Its so weird
Does anyone know what i'm talking about

(it wasn't "change the search engine" it was "change default browser)

I don't use Apple Iphone but try updating your software or something like that. Don't use mozilla.use google chrome