Can you share a screenshot of that message, and the "copy text to clipboard" output from about:support? Feel free to send me the details in private via email to email@example.com if you don't want to have this information public.
DRM was not enabled, and enabling it resolved it. 🙂
Hmm, I think Firefox would normally display an infobar in that situation making it easy to fix the setting, but I haven't tested recently to confirm that. Maybe the bar is only for installing Widevine?