I constantly have error F7701-1003 trying to play Netflix on Ubuntu 18.04 using FireFox 59.0.2.
I already googled the problem and tried following:
-enabled DRM in the settings, let FF download and install DRM software (widevine I suppose), restarted FF, even rebooting ubuntu completely
-not using VPN
-disabled all extensions
-disabled tracking protection
-not using private mode
-switching user agent data to mac/win and browser to chrome
Same machine on same network plays Netflix flawlessly on Windows 10 using FF as well.