ajbw: We have that too, but playback does not work, and they state that linux is not supported.

They have disabled the specific CDM used for Firefox on Linux

Widevine uses individual CDM's for different platforms and browsers.  Eg for Chrome (Windows), Firefox (Windows), Firefox (Linux), Android (unique per device), Each of the TV manufactures has CDM's that are unique to each TV.  Apple uses PlayReady.

The content provider can restrict their DRM content to specific browsers on different platforms if they wish.