Idk since when, but Safari on iOS had extensions available for quite a while. I have been using an adblocker one + a few webdev ones (not that I need it often at all, but once every few months I might need to take a look at the DOM or check network requests with no access to my laptop, it comes in quite handy).
It integrates with the system browser and, I think, all embedded browsers. I only use the 'privacy-safe' subset of Wipr, that is, the passive filter list that Safari supports most efficiently. It works great. I'm sure there are other options that other iPhone users can recommend to you if you ever want to try it.
Didn't they lift the restriction on which extension you can install on mobile Firefox as well?