Scott Whittaker

Software engineer

Day job React | side projects Svelte

Default video controls in Firefox

Note that this tip relates to Firefox 72.0.2 at the time of writing.

Ever wondered how to inspect the default controls of a video element in the Firefox dev tools inspector? Take a look at the following DOM for the demo video Big Buck Bunny.

<body>
	<video autoplay="" controls=""></video>
</body>

We see a video element with a controls attribute but where is the DOM for the video controls?

Enable showUserAgentShadowRoots

Open a new tab and in the address bar type about:config. Search for shadow and look for devtools.inspector.showUserAgentShadowRoots and set it to true.

Now check the element inspector and note that we have a #shadow-root node that we can expand allowing us to see the elements shadow DOM.

Video Element Shadow DOM

<div class="videocontrols" xmlns="http://www.w3.org/1999/xhtml" role="none">
	<link rel="stylesheet" type="text/css" href="chrome://global/skin/media/videocontrols.css" />
	<div id="controlsContainer" class="controlsContainer" role="none">
		<div id="statusOverlay" class="statusOverlay stackItem" hidden="">
			<div id="statusIcon" class="statusIcon" type="throbber"></div>
			<bdi class="statusLabel" id="errorAborted">Video loading stopped.</bdi>
			<bdi class="statusLabel" id="errorNetwork"
				>Video playback aborted due to a network error.</bdi
			>
			<bdi class="statusLabel" id="errorDecode"
				>Video can’t be played because the file is corrupt.</bdi
			>
			<bdi class="statusLabel" id="errorSrcNotSupported"
				>Video format or MIME type is not supported.</bdi
			>
			<bdi class="statusLabel" id="errorNoSource"
				>No video with supported format and MIME type found.</bdi
			>
			<bdi class="statusLabel" id="errorGeneric"
				>Video playback aborted due to an unknown error.</bdi
			>
		</div>

		<div
			id="pictureInPictureOverlay"
			class="pictureInPictureOverlay stackItem"
			status="pictureInPicture"
			hidden="true"
		>
			<div class="statusIcon" type="pictureInPicture"></div>
			<bdi class="statusLabel" id="pictureInPicture"
				>This video is playing in Picture-in-Picture mode.</bdi
			>
		</div>

		<div id="controlsOverlay" class="controlsOverlay stackItem" role="none">
			<div class="controlsSpacerStack">
				<div id="controlsSpacer" class="controlsSpacer stackItem" role="none"></div>
				<div
					id="clickToPlay"
					class="clickToPlay"
					style="width: 61.95px; height: 61.95px;"
					hidden=""
				></div>
			</div>

			<button id="pictureInPictureToggleButton" class="pictureInPictureToggleButton">
				<div id="pictureInPictureToggleIcon" class="pictureInPictureToggleIcon"></div>
				<span class="pictureInPictureToggleLabel">Picture-in-Picture</span>
			</button>

			<div id="controlBar" class="controlBar" role="none" hidden="">
				<button
					id="playButton"
					class="button playButton"
					playlabel="Play"
					pauselabel="Pause"
					tabindex="-1"
					aria-label="Play"
					paused="true"
				></button>
				<div id="scrubberStack" class="scrubberStack progressContainer" role="none">
					<div class="progressBackgroundBar stackItem" role="none">
						<div class="progressStack" role="none">
							<progress
								id="bufferBar"
								class="bufferBar"
								value="65208"
								max="596474"
								tabindex="-1"
							></progress>
							<progress
								id="progressBar"
								class="progressBar"
								value="0.891237505742078"
								max="100"
								tabindex="-1"
							></progress>
						</div>
					</div>
					<input type="range" id="scrubber" class="scrubber" tabindex="-1" max="596474" />
				</div>
				<bdi id="positionLabel" class="positionLabel" role="presentation"></bdi>
				<bdi id="durationLabel" class="durationLabel" role="presentation"></bdi>
				<bdi id="positionDurationBox" class="positionDurationBox" aria-hidden="true">
					0:05<span class="duration" role="none" id="durationSpan"> / 9:56</span>
				</bdi>
				<div id="controlBarSpacer" class="controlBarSpacer" role="none" hidden=""></div>
				<button
					id="muteButton"
					class="button muteButton"
					mutelabel="Mute"
					unmutelabel="Unmute"
					tabindex="-1"
					aria-label="Mute"
				></button>
				<div id="volumeStack" class="volumeStack progressContainer" role="none">
					<input
						type="range"
						id="volumeControl"
						class="volumeControl"
						min="0"
						max="100"
						step="1"
						tabindex="-1"
						aria-label="Volume slider"
					/>
				</div>
				<button
					id="castingButton"
					class="button castingButton"
					aria-label="Cast to Screen"
					hidden=""
				></button>
				<button id="closedCaptionButton" class="button closedCaptionButton" hidden=""></button>
				<button
					id="fullscreenButton"
					class="button fullscreenButton"
					enterfullscreenlabel="Full Screen"
					exitfullscreenlabel="Exit Full Screen"
					aria-label="Full Screen"
				></button>
			</div>
			<div id="textTrackList" class="textTrackList" offlabel="Off" hidden="">
				<button class="textTrackItem" index="0" on="true">Off</button>
			</div>
		</div>
	</div>
</div>

Styles

Note that we see a link to the css too.

<link rel="stylesheet" type="text/css" href="chrome://global/skin/media/videocontrols.css" />

Throw that link into a new browser tab in Firefox to see it.

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

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

.videocontrols {
	writing-mode: horizontal-tb;
	width: 100%;
	height: 100%;
	display: inline-block;
	overflow: hidden;

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

.controlsContainer {
	--clickToPlay-size: 48px;
	--button-size: 30px;
	--timer-size: 40px;
	--timer-long-size: 60px;
	--track-size: 5px;
	--thumb-size: 13px;
	--label-font-size: 13px;
	--pip-toggle-bgcolor: rgb(0, 96, 223);
	--pip-toggle-text-and-icon-color: rgb(255, 255, 255);
	--pip-toggle-padding: 5px;
	--pip-toggle-icon-width-height: 16px;
}
.controlsContainer.touch {
	--clickToPlay-size: 64px;
	--button-size: 40px;
	--timer-size: 52px;
	--timer-long-size: 78px;
	--track-size: 7px;
	--thumb-size: 16px;
	--label-font-size: 16px;
}

/* Some CSS custom properties defined here are referenced by videocontrols.js */
.controlBar {
	/* Do not delete: these variables are accessed by JavaScript directly.
     see videocontrols.js and search for |-width|. */
	--clickToPlay-width: var(--clickToPlay-size);
	--playButton-width: var(--button-size);
	--scrubberStack-width: 64px;
	--muteButton-width: var(--button-size);
	--volumeStack-width: 48px;
	--castingButton-width: var(--button-size);
	--closedCaptionButton-width: var(--button-size);
	--fullscreenButton-width: var(--button-size);
	--positionDurationBox-width: var(--timer-size);
	--durationSpan-width: var(--timer-size);
	--positionDurationBox-width-long: var(--timer-long-size);
	--durationSpan-width-long: var(--timer-long-size);
}

.touch .controlBar {
	/* Do not delete: these variables are accessed by JavaScript directly.
     see videocontrols.js and search for |-width|. */
	--scrubberStack-width: 84px;
	--volumeStack-width: 64px;
}

.controlsContainer [hidden],
.controlBar[hidden],
.pictureInPictureToggleButton[hidden],
.videocontrols[inDOMFullscreen]
	> .controlsContainer
	> .controlsOverlay
	> .pictureInPictureToggleButton {
	display: none;
}

.controlBar[size='hidden'] {
	display: none;
}

.controlsSpacer[hideCursor] {
	cursor: none;
}

.controlsContainer,
.progressContainer {
	position: relative;
	height: 100%;
}

.stackItem {
	position: absolute;
	left: 0;
	bottom: 0;
	width: 100%;
	height: 100%;
}

.statusOverlay {
	display: flex;
	flex-direction: column;
	justify-content: center;
	align-items: center;
	background-color: rgb(80, 80, 80, 0.85);
}

.controlsOverlay {
	display: flex;
	flex-direction: column;
	justify-content: center;
	position: relative;
}

.controlsSpacerStack {
	display: flex;
	flex-direction: column;
	flex-grow: 1;
	justify-content: center;
	align-items: center;
}

.controlBar {
	position: relative;
	display: flex;
	box-sizing: border-box;
	justify-content: center;
	align-items: center;
	overflow: hidden;
	height: 40px;
	padding: 0 9px;
	background-color: rgba(26, 26, 26, 0.8);
}

.touch .controlBar {
	height: 52px;
}

.controlBar > .button {
	height: 100%;
	min-width: var(--button-size);
	min-height: var(--button-size);
	padding: 6px;
	border: 0;
	margin: 0;
	background-color: transparent;
	background-repeat: no-repeat;
	background-position: center;
	background-origin: content-box;
	background-clip: content-box;
	-moz-context-properties: fill;
	fill: #ffffff;
}

.touch .controlBar > .button {
	background-size: 24px 24px;
}

.controlBar > .button:hover {
	fill: #48a0f7;
}

.controlBar > .button:hover:active {
	fill: #2d89e6;
}

.playButton {
	background-image: url(chrome://global/skin/media/pauseButton.svg);
}
.playButton[paused] {
	background-image: url(chrome://global/skin/media/playButton.svg);
}

.muteButton {
	background-image: url(chrome://global/skin/media/audioUnmutedButton.svg);
}
.muteButton[muted] {
	background-image: url(chrome://global/skin/media/audioMutedButton.svg);
}
.muteButton[noAudio],
.muteButton[noAudio]:hover,
.muteButton[noAudio]:hover:active {
	background-image: url(chrome://global/skin/media/audioNoAudioButton.svg);
	fill: white;
}
.muteButton[noAudio] + .volumeStack {
	display: none;
}

.castingButton {
	background-image: url(chrome://global/skin/media/castingButton-ready.svg);
}

.castingButton[enabled] {
	background-image: url(chrome://global/skin/media/castingButton-active.svg);
}

.closedCaptionButton {
	background-image: url(chrome://global/skin/media/closedCaptionButton-cc-off.svg);
}
.closedCaptionButton[enabled] {
	background-image: url(chrome://global/skin/media/closedCaptionButton-cc-on.svg);
}

.fullscreenButton {
	background-image: url(chrome://global/skin/media/fullscreenEnterButton.svg);
}
.fullscreenButton[fullscreened] {
	background-image: url(chrome://global/skin/media/fullscreenExitButton.svg);
}

.controlBarSpacer {
	flex-grow: 1;
}

.volumeControl::-moz-range-thumb,
.scrubber::-moz-range-thumb {
	height: var(--thumb-size);
	width: var(--thumb-size);
	border: none;
	border-radius: 50%;
	background-color: #ffffff;
	filter: drop-shadow(0px 0px 2px rgba(0, 0, 0, 0.65));
}

.volumeControl::-moz-focus-outer,
.scrubber::-moz-focus-outer {
	border: 0;
}

.progressBackgroundBar {
	display: flex;
	flex-direction: column;
	justify-content: center;
	align-items: center;
}

.progressStack {
	position: relative;
	width: 100%;
	height: var(--track-size);
}

.scrubberStack {
	/* minus margin to get basis of required width */
	min-width: calc(var(--scrubberStack-width) - 18px);
	flex-basis: calc(var(--scrubberStack-width) - 18px);
	flex-grow: 2;
	flex-shrink: 0;
	margin: 0 9px;
}

.volumeStack {
	max-width: 60px;
	min-width: var(--volumeStack-width);
	flex-grow: 1;
	flex-shrink: 0;
	margin-right: 6px;
	margin-left: 4px;
}

.bufferBar,
.progressBar,
.scrubber,
.volumeBackground,
.volumeControl {
	bottom: 0;
	left: 0;
	position: absolute;
	width: 100%;
	height: 100%;
	padding: 0;
	border: 0;
	border-radius: calc(var(--track-size) / 2);
	margin: 0;
	background: none;
	background-color: transparent;
}

.bufferBar,
.volumeBackground {
	background-color: rgba(0, 0, 0, 0.7);
}

.bufferBar::-moz-progress-bar,
.progressBar::-moz-progress-bar,
.volumeBackground::-moz-meter-bar {
	height: 100%;
	padding: 0;
	margin: 0;
	border: 0;
	border-radius: calc(var(--track-size) / 2);
	background: none;
}

.scrubber:hover::-moz-range-thumb,
.volumeControl:hover::-moz-range-thumb {
	background-color: #48a0f7;
}

.scrubber:active::-moz-range-thumb,
.volumeControl:active::-moz-range-thumb {
	background-color: #2d89e6;
}

.scrubber::-moz-range-track,
.scrubber::-moz-range-progress {
	background-color: transparent;
}

.volumeControl::-moz-range-progress,
.volumeControl::-moz-range-track {
	height: var(--track-size);
	border-radius: calc(var(--track-size) / 2);
}

.volumeControl::-moz-range-progress {
	background-color: #ffffff;
}

.volumeControl::-moz-range-track {
	background-color: rgba(0, 0, 0, 0.7);
}

.bufferBar::-moz-progress-bar {
	background-color: rgba(255, 255, 255, 0.3);
	border-radius: calc(var(--track-size) / 2);
}

.progressBar::-moz-progress-bar {
	background-color: #00b6f0;
}

.textTrackList {
	position: absolute;
	right: 5px;
	bottom: 45px;
	max-width: 80%;
	border: 1px solid #000000;
	border-radius: 2.5px;
	padding: 5px 0;
	vertical-align: middle;
	background-color: #000000;
	opacity: 0.7;
}

.touch .textTrackList {
	bottom: 58px;
}

.textTrackList > .textTrackItem {
	display: block;
	width: 100%;
	height: var(--button-size);
	font-size: var(--label-font-size);
	padding: 2px 10px;
	border: none;
	margin: 0;
	white-space: nowrap;
	overflow: hidden;
	text-align: left;
	text-overflow: ellipsis;
	color: #ffffff;
	background-color: transparent;
}

.textTrackList > .textTrackItem:hover {
	background-color: #444444;
}

.textTrackList > .textTrackItem[on] {
	color: #48a0f7;
}

.positionLabel,
.durationLabel {
	display: none;
}

.positionDurationBox {
	text-align: center;
	padding-inline-start: 1px;
	padding-inline-end: 9px;
	white-space: nowrap;
	font: message-box;
	font-size: var(--label-font-size);
	font-size-adjust: 0.55;
	color: #ffffff;
}

.positionDurationBox {
	font-size-adjust: unset;
	font-family: 'Helvetica Neue', 'Helvetica', sans-serif;
}

.duration {
	display: inline-block;
	white-space: pre;
	color: #929292;
}

.statusIcon {
	width: 36px;
	height: 36px;
	margin-bottom: 20px;
}

/* Not showing the throbber on mobile because of conflict with m.youtube.com (see bug 1289412) */
.controlsContainer:not(.mobile) .statusIcon[type='throbber'] {
	background: url(chrome://global/skin/media/throbber.png) no-repeat center;
}

.controlsContainer:not(.mobile) .statusIcon[type='throbber'][stalled] {
	background: url(chrome://global/skin/media/stalled.png) no-repeat center;
}

.statusIcon[type='error'],
.statusIcon[type='pictureInPicture'] {
	background-size: contain;
	background-repeat: no-repeat;
	background-position: center;
}

.statusIcon[type='error'] {
	min-width: 70px;
	min-height: 60px;
	background-image: url(chrome://global/skin/media/error.png);
}

.statusIcon[type='pictureInPicture'] {
	min-width: 84px;
	min-height: 84px;
	background-image: url(chrome://global/skin/media/pictureinpicture.svg);
	-moz-context-properties: fill, stroke;
	fill: #fff;
	stroke: #fff;
}

.pictureInPictureToggleButton {
	display: flex;
	-moz-appearance: none;
	position: absolute;
	background-color: var(--pip-toggle-bgcolor);
	color: var(--pip-toggle-text-and-icon-color);
	border: 0;
	padding: var(--pip-toggle-padding);
	right: 0;
	top: 50%;
	transform: translateY(-50%) translateX(
			calc(100% - var(--pip-toggle-icon-width-height) - 2 * var(--pip-toggle-padding))
		);
	transition: opacity 160ms linear, transform 160ms linear;
	min-width: max-content;
	pointer-events: auto;
	opacity: 0;
}

.pictureInPictureToggleIcon {
	display: inline-block;
	background-image: url(chrome://global/skin/media/pictureinpicture.svg);
	background-position: center left;
	background-repeat: no-repeat;
	-moz-context-properties: fill, stroke;
	fill: var(--pip-toggle-text-and-icon-color);
	stroke: var(--pip-toggle-text-and-icon-color);
	width: var(--pip-toggle-icon-width-height);
	height: var(--pip-toggle-icon-width-height);
	min-width: max-content;
}

.statusIcon[type='pictureInPicture']:dir(rtl),
.pictureInPictureToggleIcon:dir(rtl) {
	transform: scaleX(-1);
}

.pictureInPictureToggleLabel {
	margin-inline-start: var(--pip-toggle-padding);
}

/**
 * For the Picture-in-Picture toggle, we don't use the built-in :hover
 * pseudoclass because there are many sites where the arrangement of the DOM
 * or the CSS will conspire to prevent :hover from matching on the <video>
 * itself. PictureInPictureToggleChild takes care of punching through those
 * barriers, and manually sets a .hovering class.
 */

.controlsOverlay.hovering > .pictureInPictureToggleButton {
	opacity: 0.8;
}

.controlsOverlay[hidetoggle='true'].hovering > .pictureInPictureToggleButton:not(.hovering) {
	opacity: 0;
}

.controlsOverlay.hovering > .pictureInPictureToggleButton.hovering {
	opacity: 1;
	transform: translateY(-50%) translateX(0);
}

@supports -moz-bool-pref('media.videocontrols.picture-in-picture.video-toggle.testing') {
	/**
   * To make automated tests faster, we drop the transition duration in
   * testing mode.
   */
	.pictureInPictureToggleButton {
		transition-duration: 10ms;
	}
}

/* Overlay Play button */
.clickToPlay {
	min-width: var(--clickToPlay-size);
	min-height: var(--clickToPlay-size);
	border-radius: 50%;
	background-image: url(chrome://global/skin/media/playButton.svg);
	background-repeat: no-repeat;
	background-position: 54% 50%;
	background-size: 40% 40%;
	background-color: #1a1a1a;
	-moz-context-properties: fill;
	fill: #ffffff;
	opacity: 0.8;
	position: relative;
	top: 20px;
}

.controlsSpacerStack:hover > .clickToPlay,
.clickToPlay:hover {
	opacity: 0.55;
}

.controlsSpacerStack:hover > .clickToPlay[fadeout] {
	opacity: 0;
}

.controlBar[fullscreen-unavailable] .fullscreenButton {
	display: none;
}

.statusOverlay[fadeout],
.statusOverlay[error] + .controlsOverlay > .controlsSpacerStack {
	opacity: 0;
}

.pictureInPictureOverlay {
	display: flex;
	flex-direction: column;
	justify-content: center;
	align-items: center;
	opacity: 1;
	background-color: rgb(12, 12, 13);
}

/* Status description formatting */
.statusLabel {
	padding: 0 10px;
	text-align: center;
	font: message-box;
	font-size: 14px;
	color: #ffffff;
}

.statusLabel {
	display: none;
}

[status='errorAborted'] > [id='errorAborted'],
[status='errorNetwork'] > [id='errorNetwork'],
[status='errorDecode'] > [id='errorDecode'],
[status='errorSrcNotSupported'] > [id='errorSrcNotSupported'],
[status='errorNoSource'] > [id='errorNoSource'],
[status='errorGeneric'] > [id='errorGeneric'],
[status='pictureInPicture'] > [id='pictureInPicture'] {
	display: inline;
}

Summary

If you ever need to build your own video controls this is a great reference. What better way to get started than seeing how the browser builds the UI for its own default video controls.