@namespace url(http://www.w3.org/1999/xhtml);

@-moz-document url-prefix("http://www.youtube.com/watch") {

#watch-video.medium #watch-player {
    width: 1280px !important;
    height: 750px !important;
}

#watch-video.medium {
    margin: auto !important;
    width: 100% !important;
}

}