So I tried playing a video on Netflix in Firefox and while everything worked including the previews while hovering over a title, the actual movie/TV episode failed to play and resulted in the following error:
Playback Error Code: F7701-1003
The main thing that needs to be done is to enabled DRM support in Firefox's preferences section. (Look for a checkbox titled "Play DRM-controlled content".)
If you already have that enabled and the video still doesn't play, then you're doing one of two things. You're either doing all this when you're in Private/incognito mode or your Firefox preferences is set up so as to never save history. Netflix does not like either of these. So the fix is to watch Firefox in normal mode with history enabled.
If you are still having trouble, you should consider refreshing Firefox via
about:support or setting up a fresh profile via
about:profiles. You can also close Firefox and restart it using
firefox -P --new-instance
This was all on Linux for me with Firefox 63. I suspect that much of this will also be applicable for Chrome.