I use plasma-browser-integration (not using KDE) to get firefox websites (like youtube, netflix..) to respond to mpris commands like play/pause, and to get the playback status (playing/paused) so I can control media using my media keys and so I can display what's currently playing in polybar.
export QT_QPA_PLATFORMTHEME="qt5ct" in my
.xinitrc, the dbus service
org.mpris.MediaPlayer2.plasma-browser-integration that controls the browser doesn't load.
I need that environment variable because some qt apps like VLC look like shit when I don't have it set.