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

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

body {
-webkit-transition-property: opacity, background !important;
-webkit-transition-duration: 0.5s !important;
-webkit-transition-timing-function: linear !important;
opacity: 0.0 !important;
background: #000 !important;
}

body:hover {
opacity: 1.0 !important;
background: #fff !important;
}

}