It sounds as if it's your lack of knowledge/experience that is the issue there.
There's no reason as to why you have to use Firefox as a browser on your phone if it doesn't work for you.
If you don't like Ads and Paywalls, choose a Browser that is suitable to that purpose. A couple of examples might be Brave and Snowhaze.
I don't see what a small screen has to do with playing music and due to the phone being close to your eyes when watching videos, the size isn't really an issue. But of course there is the option to connect to a TV or monitor.