I had no problem playing Netflix videos before FF 66. I'm now on FF 66.0.1. I disabled all add-ons, restarted FF to no avail. This issue MIGHT be DRM related since preview vids play correctly in Netflix. They aren't DRM controlled. The full videos, which are DRM controlled, do not play. 'Play DRM-Controlled Content' is checked in my FF settings. I can play full videos as expected in Chrome. I prefer not to for obvious reasons. The NF error code is F7701-1003. The msg is 'There appears to be a problem with Firefox which is preventing Netflix from starting playback'. I've gone through the steps that NF suggest for this issue. Doing that doesn't resolve the issue.