gecko/toolkit/content/widgets/videocontrols.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

.scrubber,
.volumeControl {
  -moz-binding: url("chrome://global/content/bindings/videocontrols.xml#suppressChangeEvent");
}

.scrubber .scale-thumb {
  -moz-binding: url("chrome://global/content/bindings/videocontrols.xml#timeThumb");
}

.playButton,
.muteButton,
.scrubber .scale-slider,
.volumeControl .scale-slider {
  -moz-user-focus: none;
}

.mediaControlsFrame {
  direction: ltr;
  /* Prevent unwanted style inheritance. See bug 554717. */
  list-style-image: none !important;
  font: normal normal normal 100%/normal sans-serif !important;
  text-decoration: none !important;
}

/* CSS Transitions
 *
 * These are overriden by the default theme; the rules here just 
 * provide a fallback to drive the required transitionend event
 * (in case a 3rd party theme does not provide transitions).
 */
.controlBar:not([immediate]) {
  -moz-transition-property: opacity;
  -moz-transition-duration: 1ms;
}
.controlBar[fadeout] {
  opacity: 0;
}
.volumeStack:not([immediate]) {
  -moz-transition-property: opacity, margin-top;
  -moz-transition-duration: 1ms, 1ms;
}
.volumeStack[fadeout] {
  opacity: 0;
  margin-top: 0;
}
.statusOverlay:not([immediate]) {
  -moz-transition-property: opacity;
  -moz-transition-duration: 1ms;
  -moz-transition-delay: 750ms;
}
.statusOverlay[fadeout] {
  opacity: 0;
}

.controlBar[size="hidden"],
.controlBar[size="small"] .durationBox,
.controlBar[size="small"] .durationLabel,
.controlBar[size="small"] .positionLabel {
  visibility: collapse;
}

.controlBar[size="small"] .scrubberStack,
.controlBar[size="small"] .backgroundBar,
.controlBar[size="small"] .bufferBar,
.controlBar[size="small"] .progressBar,
.controlBar[size="small"] .scrubber {
  visibility: hidden;
}