That’s correct: https://help.netflix.com/en/node/13444

> Netflix is available in Ultra HD on Windows and Mac computers with:

> - Microsoft Edge for Windows

> - Windows 10 App

> - Safari for MacOS 11.0 or later

I believe this is for DRM reasons — Firefox is open-source, so they don’t want you modifying your copy of Firefox to bypass DRM or whatever.

Does spoofing your user-agent bypass that?

You probably can't spoof the DRM.

I think that is because there is actually DRM technology in the browser that communicates with Netflix when on their site. So it's definitely a lot more than just checking a UA. But it would be nice if it were that easy.