First of all, DRM must be enabled in Firefox. Usually Firefox asks to do that once you enter a DRM page, but you can also change the setting in the preferences:
Preferences -> General -> Play DRM-controlled contentMost importantly you have to have the correct video coded installed on your system. It usually comes down to installing the proper ffmpeg/libavcodec version support h.264. In OpenSuse, use the packman repository and change the version of libavcodec to the packman version (H.264_Video_Support).
An easy way to check if your browser supports all the important codecs is to go to https://www.youtube.com/html5 and check if H.264 and MSE & H.264 is available. If so, Netflix should just work.
tags: netflix1
newer (2019-01-07): YouTube video subscriptions via RSS
older (2019-01-02): Updating OpenSuse 42.3 to Leap 15