YASTM by fazekmar

This is a yet another Firefox add-on that try to play URLs with mpv player.

The extension creates an address bar button and a context menu item. Hit the button if you want to play the current URL, or use the context menu in links, media files, etc.

Keyboard shortcut also added to play the current URL, default set to alt+m (you can change it: Manage extension shortcuts in Firefox)

Its need to install a native host application to work this add-on properly. Follow the install instructions Here.