Watching Netflix in Firefox on Ubuntu 20.04 generates error F7355

I've just set up a laptop with brand new Ubuntu 20.04 and visited Netflix in Firefox.

There was a yellow toaster underneath the address bar stating

You must enable DRM to play some audio or video on this page

So I clicked 'Enable DRM'. Then I saw "Firefox is installing components... please try again later" and after that went away I reloaded Netflix but it still would not play. When I play back video I get Netflix error F7355.

Then it points me to https://help.netflix.com where I can only find information on this error when I have trouble playing back on macOS or Windows. But I don't use those, I use Linux...

I understand that I can probably install Chrome which will Just Work - but I don't use Chrome. It seems like it could work but I'm missing something. What should I do to watch Netflix in Firefox on Linux on Ubuntu 20.04?

You don't have DRM enabled and thus you are missing Widevine plugin to decode the DRM protected Netflix content.

1. First make sure you have the media codecs installed

   sudo apt install libavcodec-extra
   

2. Then enable DRM:

   Open Firefox and type about:preferences#content in the address bar. Look for Digital Rights Management (DRM) Content field and check the box in front of Play DRM-controlled content.

   

   This will start to install the Widevine plugin from Google. Depending on your network speed it will take a few minutes to install this add-on.

3. Make sure that you have the required add-ons:

   Open a new tab in Firefox and type about:addons in the address bar. Make sure that you have Widevine and OpenH264 add-ons installed with ‘Always Active’ mode.

   

4. Restart Firefox.

You should know be able to play Netflix via the Firefox web browser.