I have been using firefox on linux for a little more than a decade now and haven't realize I was missing on anything so I guess it's probably not a real problem.
Netflix et al work on Linux but are limited to 480p.
Without the propietary Widevine, maybe.
720p
Which is not a big deal when you are watching on a laptop screen.or via a projector.
and yet ~some devices are constantly pwned, and pristine UHD WEB-DL's are being ripped automatically.