User Agent: Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0 Build ID: 20170327113357 Expected results: There should be an API for music and video streaming web sites like soundcloud/spotify/youtube/... to interact with the systems media player API like MPRIS. So users are able to see the current playing track/video and control playback (pause, play, stop, forward, backward, ...) like they're used to do directly in their system.
Do you mean hooking up https://developer.mozilla.org/en-US/docs/Web/API/Media_Session_API to MPRIS?
Yes. I didn't know that there is such an API but it looks like it's the right place.