They also don’t allow you to install Windows executables. They do allow you to run adblockers designed for Safari, like Wipr, and there are any number of noscript-alikes, like StopTheScript. I’m not saying that to be snarky, but to say that different platforms have different ways of doing things.
And Firefox is in the iOS App Store. I know what you meant to say, and that it’s not the same as Firefox on Android, but it’s wrong to say you’re not allowed to install Firefox.
Since Apple specifically disallows using other web engines on the App Store, I have bad news for you : Firefox on the App Store is just a reskinned safari and as such, a lot of features cannot be implemented because they depend on the web rendering engine.
That would be news to me if it wasn’t what I already said, that iOS Firefox isn’t the same as Android Firefox.