On iOS, every browser is required by Apple to use WebKit. I just tried it again myself and FireFox on iPhone has no ublock Origin add on possibility.
Firefox Focus does work as an alternative.
Apple created a special system-level API for Safari Content Blockers. Apps like Firefox Focus, AdGuard, 1Blocker, Wipr can register filtering rules with Safari using this API. That’s why Focus can block ads/trackers inside Safari if you enable it under Safari
In EU only, and to my knowledge no mainstream browser vendor has shipped a real browser with their own engine yet. Too much work, and they need to maintain two different versions (EU and non-EU). The whole situation is a mess.
