Are you trying to watch Netflix but get an error code ”F7121-1331”? It might be because you hardened Firefox against tracking by enabling the privacy.resistFingerprinting option in about:config.
To get rid of the error, enter about:config in the browser address bar, search for privacy.resistFingerprinting and set it to false. (Don’t forget to switch it back once you’re done watching).
Now if you refresh Netflix it may work as intended. (If it doesn’t you can try to disable DRM-content in Firefox, close the browser, start it again and enable DRM-content).
Tested on Linux Manjaro + Firefox 95.0 (64 bit)