The end user chose to use Firefox. The service provider is free to do as they please, it's their infrastructure and your access to it is at their discretion.

Don't like it? Use Privacy Pass or pick another set of compromises.

With that said, when I was still willing to subject myself to Mozilla in any form, I never found CloudFlare to be a problem, and I've used it since it launched. If people use Firefox, they're probably a privacy wonk LARPing an imagined threat model, and are using a shitty cheap VPN used by countless attackers, it's unlikely to be the browser itself unless they're doing something weird with extensions.