Technically, Firefox Focus (a separate browser for iOS) includes an adblocker feature that can be applied system wide via iOS's content blockers subsystem. This was released in the late 2010s.
Firefox including it is likely just reducing the steps required.
Yes and not only that, one can enable that as a safari extension and get an ad-free experience on safari too.
If you search the App Store and don’t find it, it’s called Firefox Klar in some markets