Netflix on Firefox Linux: "EME has been preffed off"

Accoridng to the Netflix support pages (and I tested and confirmed it on my computer), in order for Firefox to be able to play Netflix video, you need to:

• Enable playback of HTML5 DRM media in Firefox. To do that, type about:preferences#content on the addres bar, and check "Play DRM Content".

• Try to watch the DRM-protected Netflix video again.

• Wait for Firefox to automatically install the "Widevine Content Decryption Module provided by Google, Inc" plugin (Firefox will automatically install it when you first try to watch any Netflix video).

• A dialog similar to the one below is displayed, just click "yes":

• you can check that it is installed by visiting about:addons and clicking "plugins", there will be an entry named "Widevine Content Decryption Module provided by Google, Inc"