Firefox doesn't pause on org.mpris.MediaPlayer2.Player.PlayPause

Whenever I press play/pause button on my keyboard, the firefox can start playing, but cannot stop playing. I tried to follow the error as far as I can, and it seems firefox ignores direct dbus message

dbus-send --print-reply --dest=org.mpris.MediaPlayer2.firefox.instance3155 /org/mpris/MediaPlayer2 org.mpris.MediaPlayer2.Player.PlayPause

So how can I solve it? Is there some config to change or a patched firefox version or something?