Adapt Widevine CDM from Google Chrome to work in Firefox as a GMP plugin.

Mainline version of Firefox doesn't have necessary bits of EME implemented yet, but Firefox Nightly already have them working. (January 2016). I used source snapshot 29258f59e545 from mozilla-central with firefox.patch applied. It remained unknown to me where Firefox looks up for GMP plugins, so MOZ_GMP_PATH environment variable was used instead. Note, it should point to directory path which ends with .../gmp-widevine/1. So one should create directory gmp-widevine somewhere, then directory 1 (a number, one) inside it, then copy data/widevine.info and generated libwidevine.so there. Here one can find original description of how that method works. Maybe one will have to use LD_PRELOAD to preload /opt/google/chrome/libwidevinecdm.so, since adapter can't do it itself due to sandboxing.

To test, go to [https://shaka-player-demo.appspot.com] and select a stream with "Widevine" or "multi-DRM". You could also try Netflix or Google Play, but you have to change User-Agent to Chrome.