You can’t use ad blocker apps if you use any browser other than Safari. I use Firefox because I want to sync it with my desktop, which is not a Mac, so I have to choose between syncing and ad blocking.
You can even install Firefox Focus and use it's ad-blocking in Safari. Focus installs their ad-blocking as a system-level blocker (I assume due to iOS rules/requirements) which allows you to just toggle it on for "all browsers" (aka Safari and the Safari based browsers, which is all of them).