diff --git a/app/javascript/mastodon/components/media_gallery.jsx b/app/javascript/mastodon/components/media_gallery.jsx
index 5be0070a3..859d16a32 100644
--- a/app/javascript/mastodon/components/media_gallery.jsx
+++ b/app/javascript/mastodon/components/media_gallery.jsx
@@ -313,7 +313,7 @@ class MediaGallery extends React.PureComponent {
   }
 
   render () {
-    const { media, lang, intl, sensitive, height, defaultWidth, standalone, autoplay } = this.props;
+    const { media, lang, intl, sensitive, defaultWidth, standalone, autoplay } = this.props;
     const { visible } = this.state;
     const width = this.state.width || defaultWidth;
 
@@ -322,13 +322,9 @@ class MediaGallery extends React.PureComponent {
     const style = {};
 
     if (this.isFullSizeEligible() && (standalone || !cropImages)) {
-      if (width) {
-        style.height = width / this.props.media.getIn([0, 'meta', 'small', 'aspect']);
-      }
-    } else if (width) {
-      style.height = width / (16/9);
+      style.aspectRatio = `${this.props.media.getIn([0, 'meta', 'small', 'aspect'])}`;
     } else {
-      style.height = height;
+      style.aspectRatio = '16 / 9';
     }
 
     const size     = media.take(4).size;
diff --git a/app/javascript/mastodon/components/picture_in_picture_placeholder.jsx b/app/javascript/mastodon/components/picture_in_picture_placeholder.jsx
index 6322b1c66..a51c97401 100644
--- a/app/javascript/mastodon/components/picture_in_picture_placeholder.jsx
+++ b/app/javascript/mastodon/components/picture_in_picture_placeholder.jsx
@@ -3,62 +3,22 @@ import PropTypes from 'prop-types';
 import Icon from 'mastodon/components/icon';
 import { removePictureInPicture } from 'mastodon/actions/picture_in_picture';
 import { connect } from 'react-redux';
-import { debounce } from 'lodash';
 import { FormattedMessage } from 'react-intl';
 
 class PictureInPicturePlaceholder extends React.PureComponent {
 
   static propTypes = {
-    width: PropTypes.number,
     dispatch: PropTypes.func.isRequired,
   };
 
-  state = {
-    width: this.props.width,
-    height: this.props.width && (this.props.width / (16/9)),
-  };
-
   handleClick = () => {
     const { dispatch } = this.props;
     dispatch(removePictureInPicture());
   };
 
-  setRef = c => {
-    this.node = c;
-
-    if (this.node) {
-      this._setDimensions();
-    }
-  };
-
-  _setDimensions () {
-    const width  = this.node.offsetWidth;
-    const height = width / (16/9);
-
-    this.setState({ width, height });
-  }
-
-  componentDidMount () {
-    window.addEventListener('resize', this.handleResize, { passive: true });
-  }
-
-  componentWillUnmount () {
-    window.removeEventListener('resize', this.handleResize);
-  }
-
-  handleResize = debounce(() => {
-    if (this.node) {
-      this._setDimensions();
-    }
-  }, 250, {
-    trailing: true,
-  });
-
   render () {
-    const { height } = this.state;
-
     return (
-      <div ref={this.setRef} className='picture-in-picture-placeholder' style={{ height }} role='button' tabIndex={0} onClick={this.handleClick}>
+      <div className='picture-in-picture-placeholder' role='button' tabIndex={0} onClick={this.handleClick}>
         <Icon id='window-restore' />
         <FormattedMessage id='picture_in_picture.restore' defaultMessage='Put it back' />
       </div>
diff --git a/app/javascript/mastodon/components/status.jsx b/app/javascript/mastodon/components/status.jsx
index cd8423b2f..b5242e769 100644
--- a/app/javascript/mastodon/components/status.jsx
+++ b/app/javascript/mastodon/components/status.jsx
@@ -411,7 +411,7 @@ class Status extends ImmutablePureComponent {
     }
 
     if (pictureInPicture.get('inUse')) {
-      media = <PictureInPicturePlaceholder width={this.props.cachedMediaWidth} />;
+      media = <PictureInPicturePlaceholder />;
     } else if (status.get('media_attachments').size > 0) {
       if (this.props.muted) {
         media = (
@@ -460,12 +460,9 @@ class Status extends ImmutablePureComponent {
                 src={attachment.get('url')}
                 alt={attachment.get('description')}
                 lang={status.get('language')}
-                width={this.props.cachedMediaWidth}
-                height={110}
                 inline
                 sensitive={status.get('sensitive')}
                 onOpenVideo={this.handleOpenVideo}
-                cacheWidth={this.props.cacheMediaWidth}
                 deployPictureInPicture={pictureInPicture.get('available') ? this.handleDeployPictureInPicture : undefined}
                 visible={this.state.showMedia}
                 onToggleVisibility={this.handleToggleMediaVisibility}
@@ -498,8 +495,6 @@ class Status extends ImmutablePureComponent {
           onOpenMedia={this.handleOpenMedia}
           card={status.get('card')}
           compact
-          cacheWidth={this.props.cacheMediaWidth}
-          defaultWidth={this.props.cachedMediaWidth}
           sensitive={status.get('sensitive')}
         />
       );
diff --git a/app/javascript/mastodon/features/audio/index.jsx b/app/javascript/mastodon/features/audio/index.jsx
index 53f24c6a3..e8fe2c4d9 100644
--- a/app/javascript/mastodon/features/audio/index.jsx
+++ b/app/javascript/mastodon/features/audio/index.jsx
@@ -384,7 +384,7 @@ class Audio extends React.PureComponent {
   }
 
   _getRadius () {
-    return parseInt(((this.state.height || this.props.height) - (PADDING * this._getScaleCoefficient()) * 2) / 2);
+    return parseInt((this.state.height || this.props.height) / 2 - PADDING * this._getScaleCoefficient());
   }
 
   _getScaleCoefficient () {
@@ -396,7 +396,7 @@ class Audio extends React.PureComponent {
   }
 
   _getCY() {
-    return Math.floor(this._getRadius() + (PADDING * this._getScaleCoefficient()));
+    return Math.floor((this.state.height || this.props.height) / 2);
   }
 
   _getAccentColor () {
@@ -470,7 +470,7 @@ class Audio extends React.PureComponent {
     }
 
     return (
-      <div className={classNames('audio-player', { editable, inactive: !revealed })} ref={this.setPlayerRef} style={{ backgroundColor: this._getBackgroundColor(), color: this._getForegroundColor(), height: this.props.fullscreen ? '100%' : (this.state.height || this.props.height) }} onMouseEnter={this.handleMouseEnter} onMouseLeave={this.handleMouseLeave} tabIndex={0} onKeyDown={this.handleKeyDown}>
+      <div className={classNames('audio-player', { editable, inactive: !revealed })} ref={this.setPlayerRef} style={{ backgroundColor: this._getBackgroundColor(), color: this._getForegroundColor(), aspectRatio: '16 / 9' }} onMouseEnter={this.handleMouseEnter} onMouseLeave={this.handleMouseLeave} tabIndex={0} onKeyDown={this.handleKeyDown}>
 
         <Blurhash
           hash={blurhash}
@@ -515,9 +515,16 @@ class Audio extends React.PureComponent {
         {(revealed || editable) && <img
           src={this.props.poster}
           alt=''
-          width={(this._getRadius() - TICK_SIZE) * 2}
-          height={(this._getRadius() - TICK_SIZE) * 2}
-          style={{ position: 'absolute', left: this._getCX(), top: this._getCY(), transform: 'translate(-50%, -50%)', borderRadius: '50%', pointerEvents: 'none' }}
+          style={{
+            position: 'absolute',
+            left: '50%',
+            top: '50%',
+            height: `calc(${(100 - 2 * 100 * PADDING / 982)}% - ${TICK_SIZE * 2}px)`,
+            aspectRatio: '1',
+            transform: 'translate(-50%, -50%)',
+            borderRadius: '50%',
+            pointerEvents: 'none',
+          }}
         />}
 
         <div className='video-player__seek' onMouseDown={this.handleMouseDown} ref={this.setSeekRef}>
diff --git a/app/javascript/mastodon/features/status/components/card.jsx b/app/javascript/mastodon/features/status/components/card.jsx
index b67f671c5..88b38c65a 100644
--- a/app/javascript/mastodon/features/status/components/card.jsx
+++ b/app/javascript/mastodon/features/status/components/card.jsx
@@ -8,7 +8,6 @@ import classnames from 'classnames';
 import Icon from 'mastodon/components/icon';
 import { useBlurhash } from 'mastodon/initial_state';
 import Blurhash from 'mastodon/components/blurhash';
-import { debounce } from 'lodash';
 
 const IDNA_PREFIX = 'xn--';
 
@@ -54,8 +53,6 @@ export default class Card extends React.PureComponent {
     card: ImmutablePropTypes.map,
     onOpenMedia: PropTypes.func.isRequired,
     compact: PropTypes.bool,
-    defaultWidth: PropTypes.number,
-    cacheWidth: PropTypes.func,
     sensitive: PropTypes.bool,
   };
 
@@ -64,7 +61,6 @@ export default class Card extends React.PureComponent {
   };
 
   state = {
-    width: this.props.defaultWidth || 280,
     previewLoaded: false,
     embedded: false,
     revealed: !this.props.sensitive,
@@ -87,24 +83,6 @@ export default class Card extends React.PureComponent {
     window.removeEventListener('resize', this.handleResize);
   }
 
-  _setDimensions () {
-    const width = this.node.offsetWidth;
-
-    if (this.props.cacheWidth) {
-      this.props.cacheWidth(width);
-    }
-
-    this.setState({ width });
-  }
-
-  handleResize = debounce(() => {
-    if (this.node) {
-      this._setDimensions();
-    }
-  }, 250, {
-    trailing: true,
-  });
-
   handlePhotoClick = () => {
     const { card, onOpenMedia } = this.props;
 
@@ -138,10 +116,6 @@ export default class Card extends React.PureComponent {
 
   setRef = c => {
     this.node = c;
-
-    if (this.node) {
-      this._setDimensions();
-    }
   };
 
   handleImageLoad = () => {
@@ -157,36 +131,31 @@ export default class Card extends React.PureComponent {
   renderVideo () {
     const { card }  = this.props;
     const content   = { __html: addAutoPlay(card.get('html')) };
-    const { width } = this.state;
-    const ratio     = card.get('width') / card.get('height');
-    const height    = width / ratio;
 
     return (
       <div
         ref={this.setRef}
         className='status-card__image status-card-video'
         dangerouslySetInnerHTML={content}
-        style={{ height }}
+        style={{ aspectRatio: `${card.get('width')} / ${card.get('height')}` }}
       />
     );
   }
 
   render () {
     const { card, compact } = this.props;
-    const { width, embedded, revealed } = this.state;
+    const { embedded, revealed } = this.state;
 
     if (card === null) {
       return null;
     }
 
     const provider    = card.get('provider_name').length === 0 ? decodeIDNA(getHostname(card.get('url'))) : card.get('provider_name');
-    const horizontal  = (!compact && card.get('width') > card.get('height') && (card.get('width') + 100 >= width)) || card.get('type') !== 'link' || embedded;
+    const horizontal  = (!compact && card.get('width') > card.get('height')) || card.get('type') !== 'link' || embedded;
     const interactive = card.get('type') !== 'link';
     const className   = classnames('status-card', { horizontal, compact, interactive });
     const title       = interactive ? <a className='status-card__title' href={card.get('url')} title={card.get('title')} rel='noopener noreferrer' target='_blank'><strong>{card.get('title')}</strong></a> : <strong className='status-card__title' title={card.get('title')}>{card.get('title')}</strong>;
     const language    = card.get('language') || '';
-    const ratio       = card.get('width') / card.get('height');
-    const height      = (compact && !embedded) ? (width / (16 / 9)) : (width / ratio);
 
     const description = (
       <div className='status-card__content' lang={language}>
@@ -196,6 +165,14 @@ export default class Card extends React.PureComponent {
       </div>
     );
 
+    const thumbnailStyle = {
+      visibility: revealed? null : 'hidden',
+    };
+
+    if (horizontal) {
+      thumbnailStyle.aspectRatio = (compact && !embedded) ? '16 / 9' : `${card.get('width')} / ${card.get('height')}`;
+    }
+
     let embed     = '';
     let canvas = (
       <Blurhash
@@ -206,7 +183,7 @@ export default class Card extends React.PureComponent {
         dummy={!useBlurhash}
       />
     );
-    let thumbnail = <img src={card.get('image')} alt='' style={{ width: horizontal ? width : null, height: horizontal ? height : null, visibility: revealed ? null : 'hidden' }} onLoad={this.handleImageLoad} className='status-card__image-image' />;
+    let thumbnail = <img src={card.get('image')} alt='' style={thumbnailStyle} onLoad={this.handleImageLoad} className='status-card__image-image' />;
     let spoilerButton = (
       <button type='button' onClick={this.handleReveal} className='spoiler-button__overlay'>
         <span className='spoiler-button__overlay__label'><FormattedMessage id='status.sensitive_warning' defaultMessage='Sensitive content' /></span>
diff --git a/app/javascript/mastodon/features/video/index.jsx b/app/javascript/mastodon/features/video/index.jsx
index e2637e0be..d76d34546 100644
--- a/app/javascript/mastodon/features/video/index.jsx
+++ b/app/javascript/mastodon/features/video/index.jsx
@@ -2,7 +2,7 @@ import React from 'react';
 import PropTypes from 'prop-types';
 import { defineMessages, injectIntl, FormattedMessage } from 'react-intl';
 import { is } from 'immutable';
-import { throttle, debounce } from 'lodash';
+import { throttle } from 'lodash';
 import classNames from 'classnames';
 import { isFullscreen, requestFullscreen, exitFullscreen } from '../ui/util/fullscreen';
 import { displayMedia, useBlurhash } from '../../initial_state';
@@ -102,8 +102,6 @@ class Video extends React.PureComponent {
     src: PropTypes.string.isRequired,
     alt: PropTypes.string,
     lang: PropTypes.string,
-    width: PropTypes.number,
-    height: PropTypes.number,
     sensitive: PropTypes.bool,
     currentTime: PropTypes.number,
     onOpenVideo: PropTypes.func,
@@ -112,7 +110,6 @@ class Video extends React.PureComponent {
     inline: PropTypes.bool,
     editable: PropTypes.bool,
     alwaysVisible: PropTypes.bool,
-    cacheWidth: PropTypes.func,
     visible: PropTypes.bool,
     onToggleVisibility: PropTypes.func,
     deployPictureInPicture: PropTypes.func,
@@ -135,7 +132,6 @@ class Video extends React.PureComponent {
     volume: 0.5,
     paused: true,
     dragging: false,
-    containerWidth: this.props.width,
     fullscreen: false,
     hovered: false,
     muted: false,
@@ -144,24 +140,8 @@ class Video extends React.PureComponent {
 
   setPlayerRef = c => {
     this.player = c;
-
-    if (this.player) {
-      this._setDimensions();
-    }
   };
 
-  _setDimensions () {
-    const width = this.player.offsetWidth;
-
-    if (this.props.cacheWidth) {
-      this.props.cacheWidth(width);
-    }
-
-    this.setState({
-      containerWidth: width,
-    });
-  }
-
   setVideoRef = c => {
     this.video = c;
 
@@ -370,12 +350,10 @@ class Video extends React.PureComponent {
     document.addEventListener('MSFullscreenChange', this.handleFullscreenChange, true);
 
     window.addEventListener('scroll', this.handleScroll);
-    window.addEventListener('resize', this.handleResize, { passive: true });
   }
 
   componentWillUnmount () {
     window.removeEventListener('scroll', this.handleScroll);
-    window.removeEventListener('resize', this.handleResize);
 
     document.removeEventListener('fullscreenchange', this.handleFullscreenChange, true);
     document.removeEventListener('webkitfullscreenchange', this.handleFullscreenChange, true);
@@ -404,14 +382,6 @@ class Video extends React.PureComponent {
     }
   }
 
-  handleResize = debounce(() => {
-    if (this.player) {
-      this._setDimensions();
-    }
-  }, 250, {
-    trailing: true,
-  });
-
   handleScroll = throttle(() => {
     if (!this.video) {
       return;
@@ -525,17 +495,12 @@ class Video extends React.PureComponent {
 
   render () {
     const { preview, src, inline, onOpenVideo, onCloseVideo, intl, alt, lang, detailed, sensitive, editable, blurhash, autoFocus } = this.props;
-    const { containerWidth, currentTime, duration, volume, buffer, dragging, paused, fullscreen, hovered, muted, revealed } = this.state;
+    const { currentTime, duration, volume, buffer, dragging, paused, fullscreen, hovered, muted, revealed } = this.state;
     const progress = Math.min((currentTime / duration) * 100, 100);
     const playerStyle = {};
 
-    let { width, height } = this.props;
-
-    if (inline && containerWidth) {
-      width  = containerWidth;
-      height = containerWidth / (16/9);
-
-      playerStyle.height = height;
+    if (inline) {
+      playerStyle.aspectRatio = '16 / 9';
     }
 
     let preload;
@@ -586,8 +551,6 @@ class Video extends React.PureComponent {
           aria-label={alt}
           title={alt}
           lang={lang}
-          width={width}
-          height={height}
           volume={volume}
           onClick={this.togglePlay}
           onKeyDown={this.handleVideoKeyDown}
@@ -596,6 +559,7 @@ class Video extends React.PureComponent {
           onLoadedData={this.handleLoadedData}
           onProgress={this.handleProgress}
           onVolumeChange={this.handleVolumeChange}
+          style={{ ...playerStyle, width: '100%' }}
         />}
 
         <div className={classNames('spoiler-button', { 'spoiler-button--hidden': revealed || editable })}>
diff --git a/app/javascript/styles/mastodon/components.scss b/app/javascript/styles/mastodon/components.scss
index df3330316..3710695e0 100644
--- a/app/javascript/styles/mastodon/components.scss
+++ b/app/javascript/styles/mastodon/components.scss
@@ -3804,6 +3804,10 @@ a.status-card {
 }
 
 .status-card-video {
+  // Firefox has a bug where frameborder=0 iframes add some extra blank space
+  // see https://bugzilla.mozilla.org/show_bug.cgi?id=155174
+  overflow: hidden;
+
   iframe {
     width: 100%;
     height: 100%;
@@ -8332,6 +8336,7 @@ noscript {
   font-weight: 500;
   cursor: pointer;
   color: $darker-text-color;
+  aspect-ratio: 16 / 9;
 
   i {
     display: block;