[right click] -> Open With -> mpv https://addons.mozilla.org/en-US/firefox/addon/open-with/ https://addons.mozilla.org/en-US/firefox/addon/open-with/ (If your

[right click] -> Open With -> mpv https://addons.mozilla.org/en-US/firefox/addon/open-with/ https://addons.mozilla.org/en-US/firefox/addon/open-with/ (If your desktop environment supports drag and drop, you can also drag and drop vimeo or youtube URLs into mpv.)