You can already use any player or program you like to open the m3u8/mpd files. This is chosen under 'Applications' in Firefox 'General' settings and also your default operating system file handler.

If you set MPV player as the default application in Firefox for m3u8/mpd files and, if using Windows (or Mac or Linux), then set the default file handler for m3u8/mpd files as MPV, then when you click the icon in VideoController, MPV player will open and play the video.