Yeah it sucks, to have it work you need to enable DRM in Firefox settings, I would recommend having a separate Firefox profile (type in about:profiles) so that you isolate your DRM sites from others.
It was bought up by Kape recently its not recommended anymore. It would be good to switch to mullvad they are quite trusted so far. Video from mental outlaw. piped.video/watch?v=hfjCB_oPIuo