Using Firefox?  Trying to watch Netflix?  Getting error message F7121-1331 for every single video?  You can probably blame Google for that.

Pardon the interruption
This title is not available to watch instantly.
Please try another title. ­– 1044
Error code F7121-1331

The above error message is what suddenly started appearing for me recently whenever I tried to watch any movie on Netflix.  Firefox was last updated over a month ago (to 94.0), so that couldn’t be the problem.  Relaunching Firefox with add-ons disabled didn’t make the problem go away, so it wasn’t anything to do with my add-ons.  My partner could watch Netflix on her machine (same OS, same browser) so it had to have something to do with my Firefox configuration.

I went into about:profiles, created a new profile, and launched it in a new window.  Navigated to Netflix, logged in, clicked ‘Play’ on a random video, and… it played.  Configuration issue confirmed.

Of course, I haven’t changed my configuration in over a year, so I know that I wasn’t responsible for breaking anything.  So what changed?

Widevine, that’s what.

You’ll find Widevine in Addons and Themes > Plugins.  This is how it describes itself:

Widevine Content Decryption Module provided by Google Inc.
This plugin enables playback of encrypted media in compliance with the Encrypted Media Extensions specification. Encrypted media is typically used by sites to protect against copying of premium media content. Visit https://www.w3.org/TR/encrypted-media/ for more information on Encrypted Media Extensions.

Basically it’s DRM garbage.

Widevine auto-updated to version 4.10.2391.0 and Netflix broke.  Strange that Google-made software would cripple video playback in a competing browser (Firefox) but not their own Chrome.  Probably just a coincidence, right?  (If you believe that then I know a Nigerian Prince who would like to talk to you about a fabulous business opportunity.)

Probably also a pure coincidence is the nature of the smallest possible change you need to make — to your Firefox about:config — to get Netflix working again:

privacy.resistFingerprinting  FALSE

Yep.  In order to watch Netflix on Firefox, you need to consent to being fingerprinted and tracked.

So, follow the bouncing ball with me:

1. Firefox introduces code that protects your privacy by resisting fingerprinting.
2. Google — an advertising company that turns people into products that are sold to anyone willing to pay — releases a Widevine update that breaks the most popular streaming service on the planet.
3. The breakage affects only competing browsers, not their own.
4. The only way to get Netflix working again is to disable the feature Firefox just introduced… and open yourself to being tracked and your privacy breached.

Google is, quite simply, evil.