community/firefox: plug-and-play widevine support

I got widevine to run on alpine natively (would be nicer without DRM but some things require it unfortunately):

Start firefox with MOZ_DISABLE_GMP_SANDBOX=1 firefox. Open about:config and enable media.gmp-widevinecdm.enabled and media.gmp-widevinecdm.visible. Then open a webpage that triggers a widevine install (eg. https://shaka-player-demo.appspot.com). In a terminal run:

apk add gcompat
patchelf --add-needed libgcompat.so.0 ~/.mozilla/firefox/*/gmp-widevinecdm/*/libwidevinecdm.so

Reload the tab and it should be able to Widevine DRM media.

It would be nice if we could patch firefox a bit to have widevine work without manual patching (as long as gcompat is installed). For example before libwidevinecdm.so is loaded also load libgcompat.so.0 (which ether needs to be done before the sandbox is set up or we need to allow libgcompat.so.0 to be opened in the sandbox).

changed the description

CC @ptrcnull

MOZ_DISABLE_GMP_SANDBOX=1

ooh, that's nasty :/

i'm not sure if i want to encourage disabling the sandbox, and the effort it takes to patch the .so would hopefully weed out people who don't know what they're doing; nonetheless, i'll think if there's some more elegant solution here

I used MOZ_DISABLE_GMP_SANDBOX=1 for now to avoid recompiling firefox. I will try to create a proper patch which loads libgcompat.so.0 before starting the sandbox.