My testing in the past seems to indicate you're wrong. Firefox does not support setting up HTTP/3 connections without CA TLS. Unless they've changed it since version 115 esr. While the neqo lib they use for HTTP/3 does technically allow it unless you compile it yourself with all the flags required for it FF ships with neqo having CA TLS required and no support for self-signed certs when setting up HTTP/3 connections.

I'd love to be wrong or shown a newer version that does allow these things. It'd be a huge load off my mind.