Brave has native ad-block and anti finger-printing, enabled by default, and the web works excellently as in I don't know of a single site that doesn't work with it.

Brave is based on Chromium and inherits basically all compability, that this brings.

Firefox with Gecko is a different engine entirely and that sometimes causes compatibility issues or different behaviour, that websites have to account for.

Not saying your wrong, but the number, and type, of sites you browse is going to be a very narrow slice of the sites that all Firefox users browse