Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

25 files changed, 15463 insertions, 0 deletions

diff --git a/devtools/server/actors/highlighters/accessible.js b/devtools/server/actors/highlighters/accessible.js
new file mode 100644
index 0000000000..71124239f2
--- /dev/null
+++ b/devtools/server/actors/highlighters/accessible.js
@@ -0,0 +1,395 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  AutoRefreshHighlighter,
+} = require("resource://devtools/server/actors/highlighters/auto-refresh.js");
+const {
+  CanvasFrameAnonymousContentHelper,
+  isNodeValid,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+const {
+  TEXT_NODE,
+  DOCUMENT_NODE,
+} = require("resource://devtools/shared/dom-node-constants.js");
+const {
+  getCurrentZoom,
+  setIgnoreLayoutChanges,
+} = require("resource://devtools/shared/layout/utils.js");
+
+loader.lazyRequireGetter(
+  this,
+  ["getBounds", "getBoundsXUL", "Infobar"],
+  "resource://devtools/server/actors/highlighters/utils/accessibility.js",
+  true
+);
+
+/**
+ * The AccessibleHighlighter draws the bounds of an accessible object.
+ *
+ * Usage example:
+ *
+ * let h = new AccessibleHighlighter(env);
+ * h.show(node, { x, y, w, h, [duration] });
+ * h.hide();
+ * h.destroy();
+ *
+ * @param {Number} options.x
+ *        X coordinate of the top left corner of the accessible object
+ * @param {Number} options.y
+ *        Y coordinate of the top left corner of the accessible object
+ * @param {Number} options.w
+ *        Width of the the accessible object
+ * @param {Number} options.h
+ *        Height of the the accessible object
+ * @param {Number} options.duration
+ *        Duration of time that the highlighter should be shown.
+ * @param {String|null} options.name
+ *        Name of the the accessible object
+ * @param {String} options.role
+ *        Role of the the accessible object
+ *
+ * Structure:
+ * <div class="highlighter-container" aria-hidden="true">
+ *   <div class="accessible-root">
+ *     <svg class="accessible-elements" hidden="true">
+ *       <path class="accessible-bounds" points="..." />
+ *     </svg>
+ *     <div class="accessible-infobar-container">
+ *      <div class="accessible-infobar">
+ *        <div class="accessible-infobar-text">
+ *          <span class="accessible-infobar-role">Accessible Role</span>
+ *          <span class="accessible-infobar-name">Accessible Name</span>
+ *        </div>
+ *      </div>
+ *     </div>
+ *   </div>
+ * </div>
+ */
+class AccessibleHighlighter extends AutoRefreshHighlighter {
+  constructor(highlighterEnv) {
+    super(highlighterEnv);
+    this.ID_CLASS_PREFIX = "accessible-";
+    this.accessibleInfobar = new Infobar(this);
+
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      this.highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.markup.initialize();
+
+    this.onPageHide = this.onPageHide.bind(this);
+    this.onWillNavigate = this.onWillNavigate.bind(this);
+
+    this.highlighterEnv.on("will-navigate", this.onWillNavigate);
+
+    this.pageListenerTarget = highlighterEnv.pageListenerTarget;
+    this.pageListenerTarget.addEventListener("pagehide", this.onPageHide);
+  }
+
+  /**
+   * Static getter that indicates that AccessibleHighlighter supports
+   * highlighting in XUL windows.
+   */
+  static get XULSupported() {
+    return true;
+  }
+
+  get supportsSimpleHighlighters() {
+    return true;
+  }
+
+  /**
+   * Build highlighter markup.
+   *
+   * @return {Object} Container element for the highlighter markup.
+   */
+  _buildMarkup() {
+    const container = this.markup.createNode({
+      attributes: {
+        class: "highlighter-container",
+        "aria-hidden": "true",
+      },
+    });
+
+    const root = this.markup.createNode({
+      parent: container,
+      attributes: {
+        id: "root",
+        class:
+          "root" +
+          (this.highlighterEnv.useSimpleHighlightersForReducedMotion
+            ? " use-simple-highlighters"
+            : ""),
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Build the SVG element.
+    const svg = this.markup.createSVGNode({
+      nodeType: "svg",
+      parent: root,
+      attributes: {
+        id: "elements",
+        width: "100%",
+        height: "100%",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "path",
+      parent: svg,
+      attributes: {
+        class: "bounds",
+        id: "bounds",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Build the accessible's infobar markup.
+    this.accessibleInfobar.buildMarkup(root);
+
+    return container;
+  }
+
+  /**
+   * Destroy the nodes. Remove listeners.
+   */
+  destroy() {
+    if (this._highlightTimer) {
+      clearTimeout(this._highlightTimer);
+      this._highlightTimer = null;
+    }
+
+    this.highlighterEnv.off("will-navigate", this.onWillNavigate);
+    this.pageListenerTarget.removeEventListener("pagehide", this.onPageHide);
+    this.pageListenerTarget = null;
+
+    AutoRefreshHighlighter.prototype.destroy.call(this);
+
+    this.accessibleInfobar.destroy();
+    this.accessibleInfobar = null;
+    this.markup.destroy();
+  }
+
+  /**
+   * Find an element in highlighter markup.
+   *
+   * @param  {String} id
+   *         Highlighter markup elemet id attribute.
+   * @return {DOMNode} Element in the highlighter markup.
+   */
+  getElement(id) {
+    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
+  }
+
+  /**
+   * Check if node is a valid element, document or text node.
+   *
+   * @override  AutoRefreshHighlighter.prototype._isNodeValid
+   * @param  {DOMNode} node
+   *         The node to highlight.
+   * @return {Boolean} whether or not node is valid.
+   */
+  _isNodeValid(node) {
+    return (
+      super._isNodeValid(node) ||
+      isNodeValid(node, TEXT_NODE) ||
+      isNodeValid(node, DOCUMENT_NODE)
+    );
+  }
+
+  /**
+   * Show the highlighter on a given accessible.
+   *
+   * @return {Boolean} True if accessible is highlighted, false otherwise.
+   */
+  _show() {
+    if (this._highlightTimer) {
+      clearTimeout(this._highlightTimer);
+      this._highlightTimer = null;
+    }
+
+    const { duration } = this.options;
+    const shown = this._update();
+    if (shown) {
+      this.emit("highlighter-event", { options: this.options, type: "shown" });
+      if (duration) {
+        this._highlightTimer = setTimeout(() => {
+          this.hide();
+        }, duration);
+      }
+    }
+
+    return shown;
+  }
+
+  /**
+   * Update and show accessible bounds for a current accessible.
+   *
+   * @return {Boolean} True if accessible is highlighted, false otherwise.
+   */
+  _update() {
+    let shown = false;
+    setIgnoreLayoutChanges(true);
+
+    if (this._updateAccessibleBounds()) {
+      this._showAccessibleBounds();
+
+      this.accessibleInfobar.show();
+
+      shown = true;
+    } else {
+      // Nothing to highlight (0px rectangle like a <script> tag for instance)
+      this.hide();
+    }
+
+    setIgnoreLayoutChanges(
+      false,
+      this.highlighterEnv.window.document.documentElement
+    );
+
+    return shown;
+  }
+
+  /**
+   * Hide the highlighter.
+   */
+  _hide() {
+    setIgnoreLayoutChanges(true);
+    this._hideAccessibleBounds();
+    this.accessibleInfobar.hide();
+    setIgnoreLayoutChanges(
+      false,
+      this.highlighterEnv.window.document.documentElement
+    );
+  }
+
+  /**
+   * Public API method to temporarily hide accessible bounds for things like
+   * color contrast calculation.
+   */
+  hideAccessibleBounds() {
+    if (this.getElement("elements").hasAttribute("hidden")) {
+      return;
+    }
+
+    this._hideAccessibleBounds();
+    this._shouldRestoreBoundsVisibility = true;
+  }
+
+  /**
+   * Public API method to show accessible bounds in case they were temporarily
+   * hidden.
+   */
+  showAccessibleBounds() {
+    if (this._shouldRestoreBoundsVisibility) {
+      this._showAccessibleBounds();
+    }
+  }
+
+  /**
+   * Hide the accessible bounds container.
+   */
+  _hideAccessibleBounds() {
+    this._shouldRestoreBoundsVisibility = null;
+    setIgnoreLayoutChanges(true);
+    this.getElement("elements").setAttribute("hidden", "true");
+    setIgnoreLayoutChanges(
+      false,
+      this.highlighterEnv.window.document.documentElement
+    );
+  }
+
+  /**
+   * Show the accessible bounds container.
+   */
+  _showAccessibleBounds() {
+    this._shouldRestoreBoundsVisibility = null;
+    if (!this.currentNode || !this.highlighterEnv.window) {
+      return;
+    }
+
+    setIgnoreLayoutChanges(true);
+    this.getElement("elements").removeAttribute("hidden");
+    setIgnoreLayoutChanges(
+      false,
+      this.highlighterEnv.window.document.documentElement
+    );
+  }
+
+  /**
+   * Get current accessible bounds.
+   *
+   * @return {Object|null} Returns, if available, positioning and bounds
+   *                       information for the accessible object.
+   */
+  get _bounds() {
+    let { win, options } = this;
+    let getBoundsFn = getBounds;
+    if (this.options.isXUL) {
+      // Zoom level for the top level browser window does not change and only
+      // inner frames do. So we need to get the zoom level of the current node's
+      // parent window.
+      let zoom = getCurrentZoom(this.currentNode);
+      zoom *= zoom;
+      options = { ...options, zoom };
+      getBoundsFn = getBoundsXUL;
+      win = this.win.parent.ownerGlobal;
+    }
+
+    return getBoundsFn(win, options);
+  }
+
+  /**
+   * Update accessible bounds for a current accessible. Re-draw highlighter
+   * markup.
+   *
+   * @return {Boolean} True if accessible is highlighted, false otherwise.
+   */
+  _updateAccessibleBounds() {
+    const bounds = this._bounds;
+    if (!bounds) {
+      this._hide();
+      return false;
+    }
+
+    const boundsEl = this.getElement("bounds");
+    const { left, right, top, bottom } = bounds;
+    const path = `M${left},${top} L${right},${top} L${right},${bottom} L${left},${bottom} L${left},${top}`;
+    boundsEl.setAttribute("d", path);
+
+    // Un-zoom the root wrapper if the page was zoomed.
+    const rootId = this.ID_CLASS_PREFIX + "elements";
+    this.markup.scaleRootElement(this.currentNode, rootId);
+
+    return true;
+  }
+
+  /**
+   * Hide highlighter on page hide.
+   */
+  onPageHide({ target }) {
+    // If a pagehide event is triggered for current window's highlighter, hide
+    // the highlighter.
+    if (target.defaultView === this.win) {
+      this.hide();
+    }
+  }
+
+  /**
+   * Hide highlighter on navigation.
+   */
+  onWillNavigate({ isTopLevel }) {
+    if (isTopLevel) {
+      this.hide();
+    }
+  }
+}
+
+exports.AccessibleHighlighter = AccessibleHighlighter;
diff --git a/devtools/server/actors/highlighters/auto-refresh.js b/devtools/server/actors/highlighters/auto-refresh.js
new file mode 100644
index 0000000000..35e870e795
--- /dev/null
+++ b/devtools/server/actors/highlighters/auto-refresh.js
@@ -0,0 +1,368 @@
+/* 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/. */
+
+"use strict";
+
+const EventEmitter = require("resource://devtools/shared/event-emitter.js");
+const {
+  isNodeValid,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+const {
+  getAdjustedQuads,
+  getWindowDimensions,
+} = require("resource://devtools/shared/layout/utils.js");
+
+// Note that the order of items in this array is important because it is used
+// for drawing the BoxModelHighlighter's path elements correctly.
+const BOX_MODEL_REGIONS = ["margin", "border", "padding", "content"];
+const QUADS_PROPS = ["p1", "p2", "p3", "p4"];
+
+function arePointsDifferent(pointA, pointB) {
+  return (
+    Math.abs(pointA.x - pointB.x) >= 0.5 ||
+    Math.abs(pointA.y - pointB.y) >= 0.5 ||
+    Math.abs(pointA.w - pointB.w) >= 0.5
+  );
+}
+
+function areQuadsDifferent(oldQuads, newQuads) {
+  for (const region of BOX_MODEL_REGIONS) {
+    const { length } = oldQuads[region];
+
+    if (length !== newQuads[region].length) {
+      return true;
+    }
+
+    for (let i = 0; i < length; i++) {
+      for (const prop of QUADS_PROPS) {
+        const oldPoint = oldQuads[region][i][prop];
+        const newPoint = newQuads[region][i][prop];
+
+        if (arePointsDifferent(oldPoint, newPoint)) {
+          return true;
+        }
+      }
+    }
+  }
+
+  return false;
+}
+
+/**
+ * Base class for auto-refresh-on-change highlighters. Sub classes will have a
+ * chance to update whenever the current node's geometry changes.
+ *
+ * Sub classes must implement the following methods:
+ * _show: called when the highlighter should be shown,
+ * _hide: called when the highlighter should be hidden,
+ * _update: called while the highlighter is shown and the geometry of the
+ *          current node changes.
+ *
+ * Sub classes will have access to the following properties:
+ * - this.currentNode: the node to be shown
+ * - this.currentQuads: all of the node's box model region quads
+ * - this.win: the current window
+ *
+ * Emits the following events:
+ * - shown
+ * - hidden
+ * - updated
+ */
+class AutoRefreshHighlighter extends EventEmitter {
+  constructor(highlighterEnv) {
+    super();
+
+    this.highlighterEnv = highlighterEnv;
+
+    this._updateSimpleHighlighters = this._updateSimpleHighlighters.bind(this);
+    this.highlighterEnv.on(
+      "use-simple-highlighters-updated",
+      this._updateSimpleHighlighters
+    );
+
+    this.currentNode = null;
+    this.currentQuads = {};
+
+    this._winDimensions = getWindowDimensions(this.win);
+    this._scroll = { x: this.win.pageXOffset, y: this.win.pageYOffset };
+
+    this.update = this.update.bind(this);
+  }
+
+  _ignoreZoom = false;
+  _ignoreScroll = false;
+
+  /**
+   * Window corresponding to the current highlighterEnv.
+   */
+  get win() {
+    if (!this.highlighterEnv) {
+      return null;
+    }
+    return this.highlighterEnv.window;
+  }
+
+  /* Window containing the target content. */
+  get contentWindow() {
+    return this.win;
+  }
+
+  get supportsSimpleHighlighters() {
+    return false;
+  }
+
+  /**
+   * Show the highlighter on a given node
+   * @param {DOMNode} node
+   * @param {Object} options
+   *        Object used for passing options
+   */
+  show(node, options = {}) {
+    const isSameNode = node === this.currentNode;
+    const isSameOptions = this._isSameOptions(options);
+
+    if (!this._isNodeValid(node) || (isSameNode && isSameOptions)) {
+      return false;
+    }
+
+    this.options = options;
+
+    this._stopRefreshLoop();
+    this.currentNode = node;
+
+    // For offset-path, the highlighter needs to be computed from the containing block
+    // of the node, not the node itself.
+    this.useContainingBlock = this.options.mode === "cssOffsetPath";
+    this.drawingNode = this.useContainingBlock
+      ? InspectorUtils.containingBlockOf(this.currentNode)
+      : this.currentNode;
+
+    this._updateAdjustedQuads();
+    this._startRefreshLoop();
+
+    const shown = this._show();
+    if (shown) {
+      this.emit("shown");
+    }
+    return shown;
+  }
+
+  /**
+   * Hide the highlighter
+   */
+  hide() {
+    if (!this.currentNode || !this.highlighterEnv.window) {
+      return;
+    }
+
+    this._hide();
+    this._stopRefreshLoop();
+    this.currentNode = null;
+    this.currentQuads = {};
+    this.options = null;
+
+    this.emit("hidden");
+  }
+
+  /**
+   * Whether the current node is valid for this highlighter type.
+   * This is implemented by default to check if the node is an element node. Highlighter
+   * sub-classes should override this method if they want to highlight other node types.
+   * @param {DOMNode} node
+   * @return {Boolean}
+   */
+  _isNodeValid(node) {
+    return isNodeValid(node);
+  }
+
+  /**
+   * Are the provided options the same as the currently stored options?
+   * Returns false if there are no options stored currently.
+   */
+  _isSameOptions(options) {
+    if (!this.options) {
+      return false;
+    }
+
+    const keys = Object.keys(options);
+
+    if (keys.length !== Object.keys(this.options).length) {
+      return false;
+    }
+
+    for (const key of keys) {
+      if (this.options[key] !== options[key]) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  /**
+   * Update the stored box quads by reading the current node's box quads.
+   */
+  _updateAdjustedQuads() {
+    this.currentQuads = {};
+
+    // If we need to use the containing block, and if it is the <html> element,
+    // we need to use the viewport quads.
+    const useViewport =
+      this.useContainingBlock &&
+      this.drawingNode === this.currentNode.ownerDocument.documentElement;
+    const node = useViewport
+      ? this.drawingNode.ownerDocument
+      : this.drawingNode;
+
+    for (const region of BOX_MODEL_REGIONS) {
+      this.currentQuads[region] = getAdjustedQuads(
+        this.contentWindow,
+        node,
+        region,
+        { ignoreScroll: this._ignoreScroll, ignoreZoom: this._ignoreZoom }
+      );
+    }
+  }
+
+  /**
+   * Update the knowledge we have of the current node's boxquads and return true
+   * if any of the points x/y or bounds have change since.
+   * @return {Boolean}
+   */
+  _hasMoved() {
+    const oldQuads = this.currentQuads;
+    this._updateAdjustedQuads();
+
+    return areQuadsDifferent(oldQuads, this.currentQuads);
+  }
+
+  /**
+   * Update the knowledge we have of the current window's scrolling offset, both
+   * horizontal and vertical, and return `true` if they have changed since.
+   * @return {Boolean}
+   */
+  _hasWindowScrolled() {
+    if (!this.win) {
+      return false;
+    }
+
+    const { pageXOffset, pageYOffset } = this.win;
+    const hasChanged =
+      this._scroll.x !== pageXOffset || this._scroll.y !== pageYOffset;
+
+    this._scroll = { x: pageXOffset, y: pageYOffset };
+
+    return hasChanged;
+  }
+
+  /**
+   * Update the knowledge we have of the current window's dimensions and return `true`
+   * if they have changed since.
+   * @return {Boolean}
+   */
+  _haveWindowDimensionsChanged() {
+    const { width, height } = getWindowDimensions(this.win);
+    const haveChanged =
+      this._winDimensions.width !== width ||
+      this._winDimensions.height !== height;
+
+    this._winDimensions = { width, height };
+    return haveChanged;
+  }
+
+  /**
+   * Update the highlighter if the node has moved since the last update.
+   */
+  update() {
+    if (
+      !this._isNodeValid(this.currentNode) ||
+      (!this._hasMoved() && !this._haveWindowDimensionsChanged())
+    ) {
+      // At this point we're not calling the `_update` method. However, if the window has
+      // scrolled, we want to invoke `_scrollUpdate`.
+      if (this._hasWindowScrolled()) {
+        this._scrollUpdate();
+      }
+
+      return;
+    }
+
+    this._update();
+    this.emit("updated");
+  }
+
+  _show() {
+    // To be implemented by sub classes
+    // When called, sub classes should actually show the highlighter for
+    // this.currentNode, potentially using options in this.options
+    throw new Error("Custom highlighter class had to implement _show method");
+  }
+
+  _update() {
+    // To be implemented by sub classes
+    // When called, sub classes should update the highlighter shown for
+    // this.currentNode
+    // This is called as a result of a page zoom or repaint
+    throw new Error("Custom highlighter class had to implement _update method");
+  }
+
+  _scrollUpdate() {
+    // Can be implemented by sub classes
+    // When called, sub classes can upate the highlighter shown for
+    // this.currentNode
+    // This is called as a result of a page scroll
+  }
+
+  _hide() {
+    // To be implemented by sub classes
+    // When called, sub classes should actually hide the highlighter
+    throw new Error("Custom highlighter class had to implement _hide method");
+  }
+
+  _startRefreshLoop() {
+    const win = this.currentNode.ownerGlobal;
+    this.rafID = win.requestAnimationFrame(this._startRefreshLoop.bind(this));
+    this.rafWin = win;
+    this.update();
+  }
+
+  _stopRefreshLoop() {
+    if (this.rafID && !Cu.isDeadWrapper(this.rafWin)) {
+      this.rafWin.cancelAnimationFrame(this.rafID);
+    }
+    this.rafID = this.rafWin = null;
+  }
+
+  _updateSimpleHighlighters() {
+    if (!this.supportsSimpleHighlighters) {
+      return;
+    }
+
+    const root = this.getElement("root");
+    if (!root) {
+      // Highlighters which support simple highlighters are expected to use a
+      // root element with the id "root".
+      return;
+    }
+
+    // Add/remove the `user-simple-highlighters` class based on the current
+    // toolbox configuration.
+    root.classList.toggle(
+      "use-simple-highlighters",
+      this.highlighterEnv.useSimpleHighlightersForReducedMotion
+    );
+  }
+
+  destroy() {
+    this.hide();
+
+    this.highlighterEnv.off(
+      "use-simple-highlighters-updated",
+      this._updateSimpleHighlighters
+    );
+    this.highlighterEnv = null;
+    this.currentNode = null;
+  }
+}
+exports.AutoRefreshHighlighter = AutoRefreshHighlighter;
diff --git a/devtools/server/actors/highlighters/box-model.js b/devtools/server/actors/highlighters/box-model.js
new file mode 100644
index 0000000000..9368f2f292
--- /dev/null
+++ b/devtools/server/actors/highlighters/box-model.js
@@ -0,0 +1,892 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  AutoRefreshHighlighter,
+} = require("resource://devtools/server/actors/highlighters/auto-refresh.js");
+const {
+  CanvasFrameAnonymousContentHelper,
+  getBindingElementAndPseudo,
+  hasPseudoClassLock,
+  isNodeValid,
+  moveInfobar,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+const {
+  PSEUDO_CLASSES,
+} = require("resource://devtools/shared/css/constants.js");
+const {
+  getCurrentZoom,
+  setIgnoreLayoutChanges,
+} = require("resource://devtools/shared/layout/utils.js");
+const {
+  getNodeDisplayName,
+  getNodeGridFlexType,
+} = require("resource://devtools/server/actors/inspector/utils.js");
+const nodeConstants = require("resource://devtools/shared/dom-node-constants.js");
+loader.lazyGetter(this, "HighlightersBundle", () => {
+  return new Localization(["devtools/shared/highlighters.ftl"], true);
+});
+
+// Note that the order of items in this array is important because it is used
+// for drawing the BoxModelHighlighter's path elements correctly.
+const BOX_MODEL_REGIONS = ["margin", "border", "padding", "content"];
+const BOX_MODEL_SIDES = ["top", "right", "bottom", "left"];
+// Width of boxmodelhighlighter guides
+const GUIDE_STROKE_WIDTH = 1;
+
+/**
+ * The BoxModelHighlighter draws the box model regions on top of a node.
+ * If the node is a block box, then each region will be displayed as 1 polygon.
+ * If the node is an inline box though, each region may be represented by 1 or
+ * more polygons, depending on how many line boxes the inline element has.
+ *
+ * Usage example:
+ *
+ * let h = new BoxModelHighlighter(env);
+ * h.show(node, options);
+ * h.hide();
+ * h.destroy();
+ *
+ * @param {String} options.region
+ *        Specifies the region that the guides should outline:
+ *          "content" (default), "padding", "border" or "margin".
+ * @param {Boolean} options.hideGuides
+ *        Defaults to false
+ * @param {Boolean} options.hideInfoBar
+ *        Defaults to false
+ * @param {String} options.showOnly
+ *        If set, only this region will be highlighted. Use with onlyRegionArea
+ *        to only highlight the area of the region:
+ *        "content", "padding", "border" or "margin"
+ * @param {Boolean} options.onlyRegionArea
+ *        This can be set to true to make each region's box only highlight the
+ *        area of the corresponding region rather than the area of nested
+ *        regions too. This is useful when used with showOnly.
+ *
+ * Structure:
+ * <div class="highlighter-container" aria-hidden="true">
+ *   <div class="box-model-root">
+ *     <svg class="box-model-elements" hidden="true">
+ *       <g class="box-model-regions">
+ *         <path class="box-model-margin" points="..." />
+ *         <path class="box-model-border" points="..." />
+ *         <path class="box-model-padding" points="..." />
+ *         <path class="box-model-content" points="..." />
+ *       </g>
+ *       <line class="box-model-guide-top" x1="..." y1="..." x2="..." y2="..." />
+ *       <line class="box-model-guide-right" x1="..." y1="..." x2="..." y2="..." />
+ *       <line class="box-model-guide-bottom" x1="..." y1="..." x2="..." y2="..." />
+ *       <line class="box-model-guide-left" x1="..." y1="..." x2="..." y2="..." />
+ *     </svg>
+ *     <div class="box-model-infobar-container">
+ *       <div class="box-model-infobar-arrow highlighter-infobar-arrow-top" />
+ *       <div class="box-model-infobar">
+ *         <div class="box-model-infobar-text" align="center">
+ *           <span class="box-model-infobar-tagname">Node name</span>
+ *           <span class="box-model-infobar-id">Node id</span>
+ *           <span class="box-model-infobar-classes">.someClass</span>
+ *           <span class="box-model-infobar-pseudo-classes">:hover</span>
+ *           <span class="box-model-infobar-grid-type">Grid Type</span>
+ *           <span class="box-model-infobar-flex-type">Flex Type</span>
+ *         </div>
+ *       </div>
+ *       <div class="box-model-infobar-arrow box-model-infobar-arrow-bottom"/>
+ *     </div>
+ *   </div>
+ * </div>
+ */
+class BoxModelHighlighter extends AutoRefreshHighlighter {
+  constructor(highlighterEnv) {
+    super(highlighterEnv);
+
+    this.ID_CLASS_PREFIX = "box-model-";
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      this.highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.markup.initialize();
+
+    this.onPageHide = this.onPageHide.bind(this);
+    this.onWillNavigate = this.onWillNavigate.bind(this);
+
+    this.highlighterEnv.on("will-navigate", this.onWillNavigate);
+
+    const { pageListenerTarget } = highlighterEnv;
+    pageListenerTarget.addEventListener("pagehide", this.onPageHide);
+  }
+
+  /**
+   * Static getter that indicates that BoxModelHighlighter supports
+   * highlighting in XUL windows.
+   */
+  static get XULSupported() {
+    return true;
+  }
+
+  get supportsSimpleHighlighters() {
+    return true;
+  }
+
+  _buildMarkup() {
+    const highlighterContainer =
+      this.markup.anonymousContentDocument.createElement("div");
+    highlighterContainer.className = "highlighter-container box-model";
+
+    this.highlighterContainer = highlighterContainer;
+    // We need a better solution for how to handle the highlighter from the
+    // accessibility standpoint. For now, in order to avoid displaying it in the
+    // accessibility tree lets hide it altogether. See bug 1598667 for more
+    // context.
+    highlighterContainer.setAttribute("aria-hidden", "true");
+
+    // Build the root wrapper, used to adapt to the page zoom.
+    const rootWrapper = this.markup.createNode({
+      parent: highlighterContainer,
+      attributes: {
+        id: "root",
+        class:
+          "root" +
+          (this.highlighterEnv.useSimpleHighlightersForReducedMotion
+            ? " use-simple-highlighters"
+            : ""),
+        role: "presentation",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Building the SVG element with its polygons and lines
+
+    const svg = this.markup.createSVGNode({
+      nodeType: "svg",
+      parent: rootWrapper,
+      attributes: {
+        id: "elements",
+        width: "100%",
+        height: "100%",
+        hidden: "true",
+        role: "presentation",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const regions = this.markup.createSVGNode({
+      nodeType: "g",
+      parent: svg,
+      attributes: {
+        class: "regions",
+        role: "presentation",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    for (const region of BOX_MODEL_REGIONS) {
+      this.markup.createSVGNode({
+        nodeType: "path",
+        parent: regions,
+        attributes: {
+          class: region,
+          id: region,
+          role: "presentation",
+        },
+        prefix: this.ID_CLASS_PREFIX,
+      });
+    }
+
+    for (const side of BOX_MODEL_SIDES) {
+      this.markup.createSVGNode({
+        nodeType: "line",
+        parent: svg,
+        attributes: {
+          class: "guide-" + side,
+          id: "guide-" + side,
+          "stroke-width": GUIDE_STROKE_WIDTH,
+          role: "presentation",
+        },
+        prefix: this.ID_CLASS_PREFIX,
+      });
+    }
+
+    // Building the nodeinfo bar markup
+
+    const infobarContainer = this.markup.createNode({
+      parent: rootWrapper,
+      attributes: {
+        class: "infobar-container",
+        id: "infobar-container",
+        position: "top",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const infobar = this.markup.createNode({
+      parent: infobarContainer,
+      attributes: {
+        class: "infobar",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const texthbox = this.markup.createNode({
+      parent: infobar,
+      attributes: {
+        class: "infobar-text",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "span",
+      parent: texthbox,
+      attributes: {
+        class: "infobar-tagname",
+        id: "infobar-tagname",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "span",
+      parent: texthbox,
+      attributes: {
+        class: "infobar-id",
+        id: "infobar-id",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "span",
+      parent: texthbox,
+      attributes: {
+        class: "infobar-classes",
+        id: "infobar-classes",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "span",
+      parent: texthbox,
+      attributes: {
+        class: "infobar-pseudo-classes",
+        id: "infobar-pseudo-classes",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "span",
+      parent: texthbox,
+      attributes: {
+        class: "infobar-dimensions",
+        id: "infobar-dimensions",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createNode({
+      nodeType: "span",
+      parent: texthbox,
+      attributes: {
+        class: "infobar-grid-type",
+        id: "infobar-grid-type",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createNode({
+      nodeType: "span",
+      parent: texthbox,
+      attributes: {
+        class: "infobar-flex-type",
+        id: "infobar-flex-type",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    return highlighterContainer;
+  }
+
+  /**
+   * Destroy the nodes. Remove listeners.
+   */
+  destroy() {
+    this.highlighterEnv.off("will-navigate", this.onWillNavigate);
+
+    const { pageListenerTarget } = this.highlighterEnv;
+    if (pageListenerTarget) {
+      pageListenerTarget.removeEventListener("pagehide", this.onPageHide);
+    }
+
+    this.markup.destroy();
+
+    AutoRefreshHighlighter.prototype.destroy.call(this);
+  }
+
+  getElement(id) {
+    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
+  }
+
+  /**
+   * Override the AutoRefreshHighlighter's _isNodeValid method to also return true for
+   * text nodes since these can also be highlighted.
+   * @param {DOMNode} node
+   * @return {Boolean}
+   */
+  _isNodeValid(node) {
+    return (
+      node && (isNodeValid(node) || isNodeValid(node, nodeConstants.TEXT_NODE))
+    );
+  }
+
+  /**
+   * Show the highlighter on a given node
+   */
+  _show() {
+    if (!BOX_MODEL_REGIONS.includes(this.options.region)) {
+      this.options.region = "content";
+    }
+
+    const shown = this._update();
+    this._trackMutations();
+    return shown;
+  }
+
+  /**
+   * Track the current node markup mutations so that the node info bar can be
+   * updated to reflects the node's attributes
+   */
+  _trackMutations() {
+    if (isNodeValid(this.currentNode)) {
+      const win = this.currentNode.ownerGlobal;
+      this.currentNodeObserver = new win.MutationObserver(this.update);
+      this.currentNodeObserver.observe(this.currentNode, { attributes: true });
+    }
+  }
+
+  _untrackMutations() {
+    if (isNodeValid(this.currentNode) && this.currentNodeObserver) {
+      this.currentNodeObserver.disconnect();
+      this.currentNodeObserver = null;
+    }
+  }
+
+  /**
+   * Update the highlighter on the current highlighted node (the one that was
+   * passed as an argument to show(node)).
+   * Should be called whenever node size or attributes change
+   */
+  _update() {
+    const node = this.currentNode;
+    let shown = false;
+    setIgnoreLayoutChanges(true);
+
+    if (this._updateBoxModel()) {
+      // Show the infobar only if configured to do so and the node is an element or a text
+      // node.
+      if (
+        !this.options.hideInfoBar &&
+        (node.nodeType === node.ELEMENT_NODE ||
+          node.nodeType === node.TEXT_NODE)
+      ) {
+        this._showInfobar();
+      } else {
+        this._hideInfobar();
+      }
+      this._updateSimpleHighlighters();
+      this._showBoxModel();
+
+      shown = true;
+    } else {
+      // Nothing to highlight (0px rectangle like a <script> tag for instance)
+      this._hide();
+    }
+
+    setIgnoreLayoutChanges(
+      false,
+      this.highlighterEnv.window.document.documentElement
+    );
+
+    return shown;
+  }
+
+  _scrollUpdate() {
+    this._moveInfobar();
+  }
+
+  /**
+   * Hide the highlighter, the outline and the infobar.
+   */
+  _hide() {
+    setIgnoreLayoutChanges(true);
+
+    this._untrackMutations();
+    this._hideBoxModel();
+    this._hideInfobar();
+
+    setIgnoreLayoutChanges(
+      false,
+      this.highlighterEnv.window.document.documentElement
+    );
+  }
+
+  /**
+   * Hide the infobar
+   */
+  _hideInfobar() {
+    this.getElement("infobar-container").setAttribute("hidden", "true");
+  }
+
+  /**
+   * Show the infobar
+   */
+  _showInfobar() {
+    this.getElement("infobar-container").removeAttribute("hidden");
+    this._updateInfobar();
+  }
+
+  /**
+   * Hide the box model
+   */
+  _hideBoxModel() {
+    this.getElement("elements").setAttribute("hidden", "true");
+  }
+
+  /**
+   * Show the box model
+   */
+  _showBoxModel() {
+    this.getElement("elements").removeAttribute("hidden");
+  }
+
+  /**
+   * Calculate an outer quad based on the quads returned by getAdjustedQuads.
+   * The BoxModelHighlighter may highlight more than one boxes, so in this case
+   * create a new quad that "contains" all of these quads.
+   * This is useful to position the guides and infobar.
+   * This may happen if the BoxModelHighlighter is used to highlight an inline
+   * element that spans line breaks.
+   * @param {String} region The box-model region to get the outer quad for.
+   * @return {Object} A quad-like object {p1,p2,p3,p4,bounds}
+   */
+  _getOuterQuad(region) {
+    const quads = this.currentQuads[region];
+    if (!quads || !quads.length) {
+      return null;
+    }
+
+    const quad = {
+      p1: { x: Infinity, y: Infinity },
+      p2: { x: -Infinity, y: Infinity },
+      p3: { x: -Infinity, y: -Infinity },
+      p4: { x: Infinity, y: -Infinity },
+      bounds: {
+        bottom: -Infinity,
+        height: 0,
+        left: Infinity,
+        right: -Infinity,
+        top: Infinity,
+        width: 0,
+        x: 0,
+        y: 0,
+      },
+    };
+
+    for (const q of quads) {
+      quad.p1.x = Math.min(quad.p1.x, q.p1.x);
+      quad.p1.y = Math.min(quad.p1.y, q.p1.y);
+      quad.p2.x = Math.max(quad.p2.x, q.p2.x);
+      quad.p2.y = Math.min(quad.p2.y, q.p2.y);
+      quad.p3.x = Math.max(quad.p3.x, q.p3.x);
+      quad.p3.y = Math.max(quad.p3.y, q.p3.y);
+      quad.p4.x = Math.min(quad.p4.x, q.p4.x);
+      quad.p4.y = Math.max(quad.p4.y, q.p4.y);
+
+      quad.bounds.bottom = Math.max(quad.bounds.bottom, q.bounds.bottom);
+      quad.bounds.top = Math.min(quad.bounds.top, q.bounds.top);
+      quad.bounds.left = Math.min(quad.bounds.left, q.bounds.left);
+      quad.bounds.right = Math.max(quad.bounds.right, q.bounds.right);
+    }
+    quad.bounds.x = quad.bounds.left;
+    quad.bounds.y = quad.bounds.top;
+    quad.bounds.width = quad.bounds.right - quad.bounds.left;
+    quad.bounds.height = quad.bounds.bottom - quad.bounds.top;
+
+    return quad;
+  }
+
+  /**
+   * Update the box model as per the current node.
+   *
+   * @return {boolean}
+   *         True if the current node has a box model to be highlighted
+   */
+  _updateBoxModel() {
+    const options = this.options;
+    options.region = options.region || "content";
+
+    if (!this._nodeNeedsHighlighting()) {
+      this._hideBoxModel();
+      return false;
+    }
+
+    for (let i = 0; i < BOX_MODEL_REGIONS.length; i++) {
+      const boxType = BOX_MODEL_REGIONS[i];
+      const nextBoxType = BOX_MODEL_REGIONS[i + 1];
+      const box = this.getElement(boxType);
+
+      // Highlight all quads for this region by setting the "d" attribute of the
+      // corresponding <path>.
+      const path = [];
+      for (let j = 0; j < this.currentQuads[boxType].length; j++) {
+        const boxQuad = this.currentQuads[boxType][j];
+        const nextBoxQuad = this.currentQuads[nextBoxType]
+          ? this.currentQuads[nextBoxType][j]
+          : null;
+        path.push(this._getBoxPathCoordinates(boxQuad, nextBoxQuad));
+      }
+
+      box.setAttribute("d", path.join(" "));
+      box.removeAttribute("faded");
+
+      // If showOnly is defined, either hide the other regions, or fade them out
+      // if onlyRegionArea is set too.
+      if (options.showOnly && options.showOnly !== boxType) {
+        if (options.onlyRegionArea) {
+          box.setAttribute("faded", "true");
+        } else {
+          box.removeAttribute("d");
+        }
+      }
+
+      if (boxType === options.region && !options.hideGuides) {
+        this._showGuides(boxType);
+      } else if (options.hideGuides) {
+        this._hideGuides();
+      }
+    }
+
+    // Un-zoom the root wrapper if the page was zoomed.
+    const rootId = this.ID_CLASS_PREFIX + "elements";
+    this.markup.scaleRootElement(this.currentNode, rootId);
+
+    return true;
+  }
+
+  _getBoxPathCoordinates(boxQuad, nextBoxQuad) {
+    const { p1, p2, p3, p4 } = boxQuad;
+
+    let path;
+    if (!nextBoxQuad || !this.options.onlyRegionArea) {
+      // If this is the content box (inner-most box) or if we're not being asked
+      // to highlight only region areas, then draw a simple rectangle.
+      path =
+        "M" +
+        p1.x +
+        "," +
+        p1.y +
+        " " +
+        "L" +
+        p2.x +
+        "," +
+        p2.y +
+        " " +
+        "L" +
+        p3.x +
+        "," +
+        p3.y +
+        " " +
+        "L" +
+        p4.x +
+        "," +
+        p4.y +
+        " " +
+        "L" +
+        p1.x +
+        "," +
+        p1.y;
+    } else {
+      // Otherwise, just draw the region itself, not a filled rectangle.
+      const { p1: np1, p2: np2, p3: np3, p4: np4 } = nextBoxQuad;
+      path =
+        "M" +
+        p1.x +
+        "," +
+        p1.y +
+        " " +
+        "L" +
+        p2.x +
+        "," +
+        p2.y +
+        " " +
+        "L" +
+        p3.x +
+        "," +
+        p3.y +
+        " " +
+        "L" +
+        p4.x +
+        "," +
+        p4.y +
+        " " +
+        "L" +
+        p1.x +
+        "," +
+        p1.y +
+        " " +
+        "L" +
+        np1.x +
+        "," +
+        np1.y +
+        " " +
+        "L" +
+        np4.x +
+        "," +
+        np4.y +
+        " " +
+        "L" +
+        np3.x +
+        "," +
+        np3.y +
+        " " +
+        "L" +
+        np2.x +
+        "," +
+        np2.y +
+        " " +
+        "L" +
+        np1.x +
+        "," +
+        np1.y;
+    }
+
+    return path;
+  }
+
+  /**
+   * Can the current node be highlighted? Does it have quads.
+   * @return {Boolean}
+   */
+  _nodeNeedsHighlighting() {
+    return (
+      this.currentQuads.margin.length ||
+      this.currentQuads.border.length ||
+      this.currentQuads.padding.length ||
+      this.currentQuads.content.length
+    );
+  }
+
+  _getOuterBounds() {
+    for (const region of ["margin", "border", "padding", "content"]) {
+      const quad = this._getOuterQuad(region);
+
+      if (!quad) {
+        // Invisible element such as a script tag.
+        break;
+      }
+
+      const { bottom, height, left, right, top, width, x, y } = quad.bounds;
+
+      if (width > 0 || height > 0) {
+        return { bottom, height, left, right, top, width, x, y };
+      }
+    }
+
+    return {
+      bottom: 0,
+      height: 0,
+      left: 0,
+      right: 0,
+      top: 0,
+      width: 0,
+      x: 0,
+      y: 0,
+    };
+  }
+
+  /**
+   * We only want to show guides for horizontal and vertical edges as this helps
+   * to line them up. This method finds these edges and displays a guide there.
+   * @param {String} region The region around which the guides should be shown.
+   */
+  _showGuides(region) {
+    const quad = this._getOuterQuad(region);
+
+    if (!quad) {
+      // Invisible element such as a script tag.
+      return;
+    }
+
+    const { p1, p2, p3, p4 } = quad;
+
+    const allX = [p1.x, p2.x, p3.x, p4.x].sort((a, b) => a - b);
+    const allY = [p1.y, p2.y, p3.y, p4.y].sort((a, b) => a - b);
+    const toShowX = [];
+    const toShowY = [];
+
+    for (const arr of [allX, allY]) {
+      for (let i = 0; i < arr.length; i++) {
+        const val = arr[i];
+
+        if (i !== arr.lastIndexOf(val)) {
+          if (arr === allX) {
+            toShowX.push(val);
+          } else {
+            toShowY.push(val);
+          }
+          arr.splice(arr.lastIndexOf(val), 1);
+        }
+      }
+    }
+
+    // Move guide into place or hide it if no valid co-ordinate was found.
+    this._updateGuide("top", Math.round(toShowY[0]));
+    this._updateGuide("right", Math.round(toShowX[1]) - 1);
+    this._updateGuide("bottom", Math.round(toShowY[1]) - 1);
+    this._updateGuide("left", Math.round(toShowX[0]));
+  }
+
+  _hideGuides() {
+    for (const side of BOX_MODEL_SIDES) {
+      this.getElement("guide-" + side).setAttribute("hidden", "true");
+    }
+  }
+
+  /**
+   * Move a guide to the appropriate position and display it. If no point is
+   * passed then the guide is hidden.
+   *
+   * @param  {String} side
+   *         The guide to update
+   * @param  {Integer} point
+   *         x or y co-ordinate. If this is undefined we hide the guide.
+   */
+  _updateGuide(side, point) {
+    const guide = this.getElement("guide-" + side);
+
+    if (!point || point <= 0) {
+      guide.setAttribute("hidden", "true");
+      return false;
+    }
+
+    if (side === "top" || side === "bottom") {
+      guide.setAttribute("x1", "0");
+      guide.setAttribute("y1", point + "");
+      guide.setAttribute("x2", "100%");
+      guide.setAttribute("y2", point + "");
+    } else {
+      guide.setAttribute("x1", point + "");
+      guide.setAttribute("y1", "0");
+      guide.setAttribute("x2", point + "");
+      guide.setAttribute("y2", "100%");
+    }
+
+    guide.removeAttribute("hidden");
+
+    return true;
+  }
+
+  /**
+   * Update node information (displayName#id.class)
+   */
+  _updateInfobar() {
+    if (!this.currentNode) {
+      return;
+    }
+
+    const { bindingElement: node, pseudo } = getBindingElementAndPseudo(
+      this.currentNode
+    );
+
+    // Update the tag, id, classes, pseudo-classes and dimensions
+    const displayName = getNodeDisplayName(node);
+
+    const id = node.id ? "#" + node.id : "";
+
+    const classList = (node.classList || []).length
+      ? "." + [...node.classList].join(".")
+      : "";
+
+    let pseudos = this._getPseudoClasses(node).join("");
+    if (pseudo) {
+      pseudos += pseudo;
+    }
+
+    // We want to display the original `width` and `height`, instead of the ones affected
+    // by any zoom. Since the infobar can be displayed also for text nodes, we can't
+    // access the computed style for that, and this is why we recalculate them here.
+    const zoom = getCurrentZoom(this.win);
+    const quad = this._getOuterQuad("border");
+
+    if (!quad) {
+      return;
+    }
+
+    const { width, height } = quad.bounds;
+    const dim =
+      parseFloat((width / zoom).toPrecision(6)) +
+      " \u00D7 " +
+      parseFloat((height / zoom).toPrecision(6));
+
+    const { grid: gridType, flex: flexType } = getNodeGridFlexType(node);
+    const gridLayoutTextType = this._getLayoutTextType("gridtype", gridType);
+    const flexLayoutTextType = this._getLayoutTextType("flextype", flexType);
+
+    this.getElement("infobar-tagname").setTextContent(displayName);
+    this.getElement("infobar-id").setTextContent(id);
+    this.getElement("infobar-classes").setTextContent(classList);
+    this.getElement("infobar-pseudo-classes").setTextContent(pseudos);
+    this.getElement("infobar-dimensions").setTextContent(dim);
+    this.getElement("infobar-grid-type").setTextContent(gridLayoutTextType);
+    this.getElement("infobar-flex-type").setTextContent(flexLayoutTextType);
+
+    this._moveInfobar();
+  }
+
+  _getLayoutTextType(layoutTypeKey, { isContainer, isItem }) {
+    if (!isContainer && !isItem) {
+      return "";
+    }
+    if (isContainer && !isItem) {
+      return HighlightersBundle.formatValueSync(`${layoutTypeKey}-container`);
+    }
+    if (!isContainer && isItem) {
+      return HighlightersBundle.formatValueSync(`${layoutTypeKey}-item`);
+    }
+    return HighlightersBundle.formatValueSync(`${layoutTypeKey}-dual`);
+  }
+
+  _getPseudoClasses(node) {
+    if (node.nodeType !== nodeConstants.ELEMENT_NODE) {
+      // hasPseudoClassLock can only be used on Elements.
+      return [];
+    }
+
+    return PSEUDO_CLASSES.filter(pseudo => hasPseudoClassLock(node, pseudo));
+  }
+
+  /**
+   * Move the Infobar to the right place in the highlighter.
+   */
+  _moveInfobar() {
+    const bounds = this._getOuterBounds();
+    const container = this.getElement("infobar-container");
+
+    moveInfobar(container, bounds, this.win);
+  }
+
+  onPageHide({ target }) {
+    // If a pagehide event is triggered for current window's highlighter, hide the
+    // highlighter.
+    if (target.defaultView === this.win) {
+      this.hide();
+    }
+  }
+
+  onWillNavigate({ isTopLevel }) {
+    if (isTopLevel) {
+      this.hide();
+    }
+  }
+}
+
+exports.BoxModelHighlighter = BoxModelHighlighter;
diff --git a/devtools/server/actors/highlighters/css-grid.js b/devtools/server/actors/highlighters/css-grid.js
new file mode 100644
index 0000000000..04c612eb02
--- /dev/null
+++ b/devtools/server/actors/highlighters/css-grid.js
@@ -0,0 +1,1962 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  AutoRefreshHighlighter,
+} = require("resource://devtools/server/actors/highlighters/auto-refresh.js");
+const {
+  CANVAS_SIZE,
+  DEFAULT_COLOR,
+  drawBubbleRect,
+  drawLine,
+  drawRect,
+  drawRoundedRect,
+  getBoundsFromPoints,
+  getCurrentMatrix,
+  getPathDescriptionFromPoints,
+  getPointsFromDiagonal,
+  updateCanvasElement,
+  updateCanvasPosition,
+} = require("resource://devtools/server/actors/highlighters/utils/canvas.js");
+const {
+  CanvasFrameAnonymousContentHelper,
+  getComputedStyle,
+  moveInfobar,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+const { apply } = require("resource://devtools/shared/layout/dom-matrix-2d.js");
+const {
+  getCurrentZoom,
+  getDisplayPixelRatio,
+  getWindowDimensions,
+  setIgnoreLayoutChanges,
+} = require("resource://devtools/shared/layout/utils.js");
+loader.lazyGetter(this, "HighlightersBundle", () => {
+  return new Localization(["devtools/shared/highlighters.ftl"], true);
+});
+
+const COLUMNS = "cols";
+const ROWS = "rows";
+
+const GRID_FONT_SIZE = 10;
+const GRID_FONT_FAMILY = "sans-serif";
+const GRID_AREA_NAME_FONT_SIZE = "20";
+
+const GRID_LINES_PROPERTIES = {
+  edge: {
+    lineDash: [0, 0],
+    alpha: 1,
+  },
+  explicit: {
+    lineDash: [5, 3],
+    alpha: 0.75,
+  },
+  implicit: {
+    lineDash: [2, 2],
+    alpha: 0.5,
+  },
+  areaEdge: {
+    lineDash: [0, 0],
+    alpha: 1,
+    lineWidth: 3,
+  },
+};
+
+const GRID_GAP_PATTERN_WIDTH = 14; // px
+const GRID_GAP_PATTERN_HEIGHT = 14; // px
+const GRID_GAP_PATTERN_LINE_DASH = [5, 3]; // px
+const GRID_GAP_ALPHA = 0.5;
+
+// This is the minimum distance a line can be to the edge of the document under which we
+// push the line number arrow to be inside the grid. This offset is enough to fit the
+// entire arrow + a stacked arrow behind it.
+const OFFSET_FROM_EDGE = 32;
+// This is how much inside the grid we push the arrow. This a factor of the arrow size.
+// The goal here is for a row and a column arrow that have both been pushed inside the
+// grid, in a corner, not to overlap.
+const FLIP_ARROW_INSIDE_FACTOR = 2.5;
+
+/**
+ * Given an `edge` of a box, return the name of the edge one move to the right.
+ */
+function rotateEdgeRight(edge) {
+  switch (edge) {
+    case "top":
+      return "right";
+    case "right":
+      return "bottom";
+    case "bottom":
+      return "left";
+    case "left":
+      return "top";
+    default:
+      return edge;
+  }
+}
+
+/**
+ * Given an `edge` of a box, return the name of the edge one move to the left.
+ */
+function rotateEdgeLeft(edge) {
+  switch (edge) {
+    case "top":
+      return "left";
+    case "right":
+      return "top";
+    case "bottom":
+      return "right";
+    case "left":
+      return "bottom";
+    default:
+      return edge;
+  }
+}
+
+/**
+ * Given an `edge` of a box, return the name of the opposite edge.
+ */
+function reflectEdge(edge) {
+  switch (edge) {
+    case "top":
+      return "bottom";
+    case "right":
+      return "left";
+    case "bottom":
+      return "top";
+    case "left":
+      return "right";
+    default:
+      return edge;
+  }
+}
+
+/**
+ * Cached used by `CssGridHighlighter.getGridGapPattern`.
+ */
+const gCachedGridPattern = new Map();
+
+/**
+ * The CssGridHighlighter is the class that overlays a visual grid on top of
+ * display:[inline-]grid elements.
+ *
+ * Usage example:
+ * let h = new CssGridHighlighter(env);
+ * h.show(node, options);
+ * h.hide();
+ * h.destroy();
+ *
+ * @param {String} options.color
+ *        The color that should be used to draw the highlighter for this grid.
+ * @param {Number} options.globalAlpha
+ *        The alpha (transparency) value that should be used to draw the highlighter for
+ *        this grid.
+ * @param {Boolean} options.showAllGridAreas
+ *        Shows all the grid area highlights for the current grid if isShown is
+ *        true.
+ * @param {String} options.showGridArea
+ *        Shows the grid area highlight for the given area name.
+ * @param {Boolean} options.showGridAreasOverlay
+ *        Displays an overlay of all the grid areas for the current grid
+ *        container if isShown is true.
+ * @param {Object} options.showGridCell
+ *        An object containing the grid fragment index, row and column numbers
+ *        to the corresponding grid cell to highlight for the current grid.
+ * @param {Number} options.showGridCell.gridFragmentIndex
+ *        Index of the grid fragment to render the grid cell highlight.
+ * @param {Number} options.showGridCell.rowNumber
+ *        Row number of the grid cell to highlight.
+ * @param {Number} options.showGridCell.columnNumber
+ *        Column number of the grid cell to highlight.
+ * @param {Object} options.showGridLineNames
+ *        An object containing the grid fragment index and line number to the
+ *        corresponding grid line to highlight for the current grid.
+ * @param {Number} options.showGridLineNames.gridFragmentIndex
+ *        Index of the grid fragment to render the grid line highlight.
+ * @param {Number} options.showGridLineNames.lineNumber
+ *        Line number of the grid line to highlight.
+ * @param {String} options.showGridLineNames.type
+ *        The dimension type of the grid line.
+ * @param {Boolean} options.showGridLineNumbers
+ *        Displays the grid line numbers on the grid lines if isShown is true.
+ * @param {Boolean} options.showInfiniteLines
+ *        Displays an infinite line to represent the grid lines if isShown is
+ *        true.
+ * @param {Number} options.zIndex
+ *        The z-index to decide the displaying order.
+ *
+ * Structure:
+ * <div class="highlighter-container">
+ *   <canvas id="css-grid-canvas" class="css-grid-canvas">
+ *   <svg class="css-grid-elements" hidden="true">
+ *     <g class="css-grid-regions">
+ *       <path class="css-grid-areas" points="..." />
+ *       <path class="css-grid-cells" points="..." />
+ *     </g>
+ *   </svg>
+ *   <div class="css-grid-area-infobar-container">
+ *     <div class="css-grid-infobar">
+ *       <div class="css-grid-infobar-text">
+ *         <span class="css-grid-area-infobar-name">Grid Area Name</span>
+ *         <span class="css-grid-area-infobar-dimensions">Grid Area Dimensions></span>
+ *       </div>
+ *     </div>
+ *   </div>
+ *   <div class="css-grid-cell-infobar-container">
+ *     <div class="css-grid-infobar">
+ *       <div class="css-grid-infobar-text">
+ *         <span class="css-grid-cell-infobar-position">Grid Cell Position</span>
+ *         <span class="css-grid-cell-infobar-dimensions">Grid Cell Dimensions></span>
+ *       </div>
+ *     </div>
+ *   <div class="css-grid-line-infobar-container">
+ *     <div class="css-grid-infobar">
+ *       <div class="css-grid-infobar-text">
+ *         <span class="css-grid-line-infobar-number">Grid Line Number</span>
+ *         <span class="css-grid-line-infobar-names">Grid Line Names></span>
+ *       </div>
+ *     </div>
+ *   </div>
+ * </div>
+ */
+
+class CssGridHighlighter extends AutoRefreshHighlighter {
+  constructor(highlighterEnv) {
+    super(highlighterEnv);
+
+    this.ID_CLASS_PREFIX = "css-grid-";
+
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      this.highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.markup.initialize();
+
+    this.onPageHide = this.onPageHide.bind(this);
+    this.onWillNavigate = this.onWillNavigate.bind(this);
+
+    this.highlighterEnv.on("will-navigate", this.onWillNavigate);
+
+    const { pageListenerTarget } = highlighterEnv;
+    pageListenerTarget.addEventListener("pagehide", this.onPageHide);
+
+    // Initialize the <canvas> position to the top left corner of the page.
+    this._canvasPosition = {
+      x: 0,
+      y: 0,
+    };
+
+    // Calling `updateCanvasPosition` anyway since the highlighter could be initialized
+    // on a page that has scrolled already.
+    updateCanvasPosition(
+      this._canvasPosition,
+      this._scroll,
+      this.win,
+      this._winDimensions
+    );
+  }
+
+  _buildMarkup() {
+    const container = this.markup.createNode({
+      attributes: {
+        class: "highlighter-container",
+      },
+    });
+
+    const root = this.markup.createNode({
+      parent: container,
+      attributes: {
+        id: "root",
+        class: "root",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // We use a <canvas> element so that we can draw an arbitrary number of lines
+    // which wouldn't be possible with HTML or SVG without having to insert and remove
+    // the whole markup on every update.
+    this.markup.createNode({
+      parent: root,
+      nodeType: "canvas",
+      attributes: {
+        id: "canvas",
+        class: "canvas",
+        hidden: "true",
+        width: CANVAS_SIZE,
+        height: CANVAS_SIZE,
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Build the SVG element.
+    const svg = this.markup.createSVGNode({
+      nodeType: "svg",
+      parent: root,
+      attributes: {
+        id: "elements",
+        width: "100%",
+        height: "100%",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const regions = this.markup.createSVGNode({
+      nodeType: "g",
+      parent: svg,
+      attributes: {
+        class: "regions",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "path",
+      parent: regions,
+      attributes: {
+        class: "areas",
+        id: "areas",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "path",
+      parent: regions,
+      attributes: {
+        class: "cells",
+        id: "cells",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Build the grid area infobar markup.
+    const areaInfobarContainer = this.markup.createNode({
+      parent: container,
+      attributes: {
+        class: "area-infobar-container",
+        id: "area-infobar-container",
+        position: "top",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const areaInfobar = this.markup.createNode({
+      parent: areaInfobarContainer,
+      attributes: {
+        class: "infobar",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const areaTextbox = this.markup.createNode({
+      parent: areaInfobar,
+      attributes: {
+        class: "infobar-text",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "span",
+      parent: areaTextbox,
+      attributes: {
+        class: "area-infobar-name",
+        id: "area-infobar-name",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "span",
+      parent: areaTextbox,
+      attributes: {
+        class: "area-infobar-dimensions",
+        id: "area-infobar-dimensions",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Build the grid cell infobar markup.
+    const cellInfobarContainer = this.markup.createNode({
+      parent: container,
+      attributes: {
+        class: "cell-infobar-container",
+        id: "cell-infobar-container",
+        position: "top",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const cellInfobar = this.markup.createNode({
+      parent: cellInfobarContainer,
+      attributes: {
+        class: "infobar",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const cellTextbox = this.markup.createNode({
+      parent: cellInfobar,
+      attributes: {
+        class: "infobar-text",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "span",
+      parent: cellTextbox,
+      attributes: {
+        class: "cell-infobar-position",
+        id: "cell-infobar-position",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "span",
+      parent: cellTextbox,
+      attributes: {
+        class: "cell-infobar-dimensions",
+        id: "cell-infobar-dimensions",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Build the grid line infobar markup.
+    const lineInfobarContainer = this.markup.createNode({
+      parent: container,
+      attributes: {
+        class: "line-infobar-container",
+        id: "line-infobar-container",
+        position: "top",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const lineInfobar = this.markup.createNode({
+      parent: lineInfobarContainer,
+      attributes: {
+        class: "infobar",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const lineTextbox = this.markup.createNode({
+      parent: lineInfobar,
+      attributes: {
+        class: "infobar-text",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "span",
+      parent: lineTextbox,
+      attributes: {
+        class: "line-infobar-number",
+        id: "line-infobar-number",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "span",
+      parent: lineTextbox,
+      attributes: {
+        class: "line-infobar-names",
+        id: "line-infobar-names",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    return container;
+  }
+
+  clearCache() {
+    gCachedGridPattern.clear();
+  }
+
+  /**
+   * Clear the grid area highlights.
+   */
+  clearGridAreas() {
+    const areas = this.getElement("areas");
+    areas.setAttribute("d", "");
+  }
+
+  /**
+   * Clear the grid cell highlights.
+   */
+  clearGridCell() {
+    const cells = this.getElement("cells");
+    cells.setAttribute("d", "");
+  }
+
+  destroy() {
+    const { highlighterEnv } = this;
+    highlighterEnv.off("will-navigate", this.onWillNavigate);
+
+    const { pageListenerTarget } = highlighterEnv;
+    if (pageListenerTarget) {
+      pageListenerTarget.removeEventListener("pagehide", this.onPageHide);
+    }
+
+    this.markup.destroy();
+
+    // Clear the pattern cache to avoid dead object exceptions (Bug 1342051).
+    this.clearCache();
+    AutoRefreshHighlighter.prototype.destroy.call(this);
+  }
+
+  get canvas() {
+    return this.getElement("canvas");
+  }
+
+  get color() {
+    return this.options.color || DEFAULT_COLOR;
+  }
+
+  get ctx() {
+    return this.canvas.getCanvasContext("2d");
+  }
+
+  get globalAlpha() {
+    return this.options.globalAlpha || 1;
+  }
+
+  getElement(id) {
+    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
+  }
+
+  getFirstColLinePos(fragment) {
+    return fragment.cols.lines[0].start;
+  }
+
+  getFirstRowLinePos(fragment) {
+    return fragment.rows.lines[0].start;
+  }
+
+  /**
+   * Gets the grid gap pattern used to render the gap regions based on the device
+   * pixel ratio given.
+   *
+   * @param  {Number} devicePixelRatio
+   *         The device pixel ratio we want the pattern for.
+   * @param  {Object} dimension
+   *         Refers to the Map key for the grid dimension type which is either the
+   *         constant COLUMNS or ROWS.
+   * @return {CanvasPattern} grid gap pattern.
+   */
+  getGridGapPattern(devicePixelRatio, dimension) {
+    let gridPatternMap = null;
+
+    if (gCachedGridPattern.has(devicePixelRatio)) {
+      gridPatternMap = gCachedGridPattern.get(devicePixelRatio);
+    } else {
+      gridPatternMap = new Map();
+    }
+
+    if (gridPatternMap.has(dimension)) {
+      return gridPatternMap.get(dimension);
+    }
+
+    // Create the diagonal lines pattern for the rendering the grid gaps.
+    const canvas = this.markup.createNode({ nodeType: "canvas" });
+    const width = (canvas.width = GRID_GAP_PATTERN_WIDTH * devicePixelRatio);
+    const height = (canvas.height = GRID_GAP_PATTERN_HEIGHT * devicePixelRatio);
+
+    const ctx = canvas.getContext("2d");
+    ctx.save();
+    ctx.setLineDash(GRID_GAP_PATTERN_LINE_DASH);
+    ctx.beginPath();
+    ctx.translate(0.5, 0.5);
+
+    if (dimension === COLUMNS) {
+      ctx.moveTo(0, 0);
+      ctx.lineTo(width, height);
+    } else {
+      ctx.moveTo(width, 0);
+      ctx.lineTo(0, height);
+    }
+
+    ctx.strokeStyle = this.color;
+    ctx.globalAlpha = GRID_GAP_ALPHA * this.globalAlpha;
+    ctx.stroke();
+    ctx.restore();
+
+    const pattern = ctx.createPattern(canvas, "repeat");
+
+    gridPatternMap.set(dimension, pattern);
+    gCachedGridPattern.set(devicePixelRatio, gridPatternMap);
+
+    return pattern;
+  }
+
+  getLastColLinePos(fragment) {
+    return fragment.cols.lines[fragment.cols.lines.length - 1].start;
+  }
+
+  /**
+   * Get the GridLine index of the last edge of the explicit grid for a grid dimension.
+   *
+   * @param  {GridTracks} tracks
+   *         The grid track of a given grid dimension.
+   * @return {Number} index of the last edge of the explicit grid for a grid dimension.
+   */
+  getLastEdgeLineIndex(tracks) {
+    let trackIndex = tracks.length - 1;
+
+    // Traverse the grid track backwards until we find an explicit track.
+    while (trackIndex >= 0 && tracks[trackIndex].type != "explicit") {
+      trackIndex--;
+    }
+
+    // The grid line index is the grid track index + 1.
+    return trackIndex + 1;
+  }
+
+  getLastRowLinePos(fragment) {
+    return fragment.rows.lines[fragment.rows.lines.length - 1].start;
+  }
+
+  /**
+   * The AutoRefreshHighlighter's _hasMoved method returns true only if the
+   * element's quads have changed. Override it so it also returns true if the
+   * element's grid has changed (which can happen when you change the
+   * grid-template-* CSS properties with the highlighter displayed). This
+   * check is prone to false positives, because it does a direct object
+   * comparison of the first grid fragment structure. This structure is
+   * generated by the first call to getGridFragments, and on any subsequent
+   * calls where a reflow is needed. Since a reflow is needed when the CSS
+   * changes, this will correctly detect that the grid structure has changed.
+   * However, it's possible that the reflow could generate a novel grid
+   * fragment object containing information that is unchanged -- a false
+   * positive.
+   */
+  _hasMoved() {
+    const hasMoved = AutoRefreshHighlighter.prototype._hasMoved.call(this);
+
+    const oldFirstGridFragment = this.gridData?.[0];
+    this.gridData = this.currentNode.getGridFragments();
+    const newFirstGridFragment = this.gridData[0];
+
+    return hasMoved || oldFirstGridFragment !== newFirstGridFragment;
+  }
+
+  /**
+   * Hide the highlighter, the canvas and the infobars.
+   */
+  _hide() {
+    setIgnoreLayoutChanges(true);
+    this._hideGrid();
+    this._hideGridElements();
+    this._hideGridAreaInfoBar();
+    this._hideGridCellInfoBar();
+    this._hideGridLineInfoBar();
+    setIgnoreLayoutChanges(false, this.highlighterEnv.document.documentElement);
+  }
+
+  _hideGrid() {
+    this.getElement("canvas").setAttribute("hidden", "true");
+  }
+
+  _hideGridAreaInfoBar() {
+    this.getElement("area-infobar-container").setAttribute("hidden", "true");
+  }
+
+  _hideGridCellInfoBar() {
+    this.getElement("cell-infobar-container").setAttribute("hidden", "true");
+  }
+
+  _hideGridElements() {
+    this.getElement("elements").setAttribute("hidden", "true");
+  }
+
+  _hideGridLineInfoBar() {
+    this.getElement("line-infobar-container").setAttribute("hidden", "true");
+  }
+
+  /**
+   * Checks if the current node has a CSS Grid layout.
+   *
+   * @return {Boolean} true if the current node has a CSS grid layout, false otherwise.
+   */
+  isGrid() {
+    return this.currentNode.hasGridFragments();
+  }
+
+  /**
+   * Is a given grid fragment valid? i.e. does it actually have tracks? In some cases, we
+   * may have a fragment that defines column tracks but doesn't have any rows (or vice
+   * versa). In which case we do not want to draw anything for that fragment.
+   *
+   * @param  {Object} fragment
+   * @return {Boolean}
+   */
+  isValidFragment(fragment) {
+    return fragment.cols.tracks.length && fragment.rows.tracks.length;
+  }
+
+  /**
+   * The <canvas>'s position needs to be updated if the page scrolls too much, in order
+   * to give the illusion that it always covers the viewport.
+   */
+  _scrollUpdate() {
+    const hasUpdated = updateCanvasPosition(
+      this._canvasPosition,
+      this._scroll,
+      this.win,
+      this._winDimensions
+    );
+
+    if (hasUpdated) {
+      this._update();
+    }
+  }
+
+  _show() {
+    if (!this.isGrid()) {
+      this.hide();
+      return false;
+    }
+
+    // The grid pattern cache should be cleared in case the color changed.
+    this.clearCache();
+
+    // Hide the canvas, grid element highlights and infobar.
+    this._hide();
+
+    return this._update();
+  }
+
+  _showGrid() {
+    this.getElement("canvas").removeAttribute("hidden");
+  }
+
+  _showGridAreaInfoBar() {
+    this.getElement("area-infobar-container").removeAttribute("hidden");
+  }
+
+  _showGridCellInfoBar() {
+    this.getElement("cell-infobar-container").removeAttribute("hidden");
+  }
+
+  _showGridElements() {
+    this.getElement("elements").removeAttribute("hidden");
+  }
+
+  _showGridLineInfoBar() {
+    this.getElement("line-infobar-container").removeAttribute("hidden");
+  }
+
+  /**
+   * Shows all the grid area highlights for the current grid.
+   */
+  showAllGridAreas() {
+    this.renderGridArea();
+  }
+
+  /**
+   * Shows the grid area highlight for the given area name.
+   *
+   * @param  {String} areaName
+   *         Grid area name.
+   */
+  showGridArea(areaName) {
+    this.renderGridArea(areaName);
+  }
+
+  /**
+   * Shows the grid cell highlight for the given grid cell options.
+   *
+   * @param  {Number} options.gridFragmentIndex
+   *         Index of the grid fragment to render the grid cell highlight.
+   * @param  {Number} options.rowNumber
+   *         Row number of the grid cell to highlight.
+   * @param  {Number} options.columnNumber
+   *         Column number of the grid cell to highlight.
+   */
+  showGridCell({ gridFragmentIndex, rowNumber, columnNumber }) {
+    this.renderGridCell(gridFragmentIndex, rowNumber, columnNumber);
+  }
+
+  /**
+   * Shows the grid line highlight for the given grid line options.
+   *
+   * @param  {Number} options.gridFragmentIndex
+   *         Index of the grid fragment to render the grid line highlight.
+   * @param  {Number} options.lineNumber
+   *         Line number of the grid line to highlight.
+   * @param  {String} options.type
+   *         The dimension type of the grid line.
+   */
+  showGridLineNames({ gridFragmentIndex, lineNumber, type }) {
+    this.renderGridLineNames(gridFragmentIndex, lineNumber, type);
+  }
+
+  /**
+   * If a page hide event is triggered for current window's highlighter, hide the
+   * highlighter.
+   */
+  onPageHide({ target }) {
+    if (target.defaultView === this.win) {
+      this.hide();
+    }
+  }
+
+  /**
+   * Called when the page will-navigate. Used to hide the grid highlighter and clear
+   * the cached gap patterns and avoid using DeadWrapper obejcts as gap patterns the
+   * next time.
+   */
+  onWillNavigate({ isTopLevel }) {
+    this.clearCache();
+
+    if (isTopLevel) {
+      this.hide();
+    }
+  }
+
+  renderFragment(fragment) {
+    if (!this.isValidFragment(fragment)) {
+      return;
+    }
+
+    this.renderLines(
+      fragment.cols,
+      COLUMNS,
+      this.getFirstRowLinePos(fragment),
+      this.getLastRowLinePos(fragment)
+    );
+    this.renderLines(
+      fragment.rows,
+      ROWS,
+      this.getFirstColLinePos(fragment),
+      this.getLastColLinePos(fragment)
+    );
+
+    if (this.options.showGridAreasOverlay) {
+      this.renderGridAreaOverlay();
+    }
+
+    // Line numbers are rendered in a 2nd step to avoid overlapping with existing lines.
+    if (this.options.showGridLineNumbers) {
+      this.renderLineNumbers(
+        fragment.cols,
+        COLUMNS,
+        this.getFirstRowLinePos(fragment)
+      );
+      this.renderLineNumbers(
+        fragment.rows,
+        ROWS,
+        this.getFirstColLinePos(fragment)
+      );
+      this.renderNegativeLineNumbers(
+        fragment.cols,
+        COLUMNS,
+        this.getLastRowLinePos(fragment)
+      );
+      this.renderNegativeLineNumbers(
+        fragment.rows,
+        ROWS,
+        this.getLastColLinePos(fragment)
+      );
+    }
+  }
+
+  /**
+   * Render the grid area highlight for the given area name or for all the grid areas.
+   *
+   * @param  {String} areaName
+   *         Name of the grid area to be highlighted. If no area name is provided, all
+   *         the grid areas should be highlighted.
+   */
+  renderGridArea(areaName) {
+    const { devicePixelRatio } = this.win;
+    const displayPixelRatio = getDisplayPixelRatio(this.win);
+    const paths = [];
+
+    for (let i = 0; i < this.gridData.length; i++) {
+      const fragment = this.gridData[i];
+
+      for (const area of fragment.areas) {
+        if (areaName && areaName != area.name) {
+          continue;
+        }
+
+        const rowStart = fragment.rows.lines[area.rowStart - 1];
+        const rowEnd = fragment.rows.lines[area.rowEnd - 1];
+        const columnStart = fragment.cols.lines[area.columnStart - 1];
+        const columnEnd = fragment.cols.lines[area.columnEnd - 1];
+
+        const x1 = columnStart.start + columnStart.breadth;
+        const y1 = rowStart.start + rowStart.breadth;
+        const x2 = columnEnd.start;
+        const y2 = rowEnd.start;
+
+        const points = getPointsFromDiagonal(
+          x1,
+          y1,
+          x2,
+          y2,
+          this.currentMatrix
+        );
+
+        // Scale down by `devicePixelRatio` since SVG element already take them into
+        // account.
+        const svgPoints = points.map(point => ({
+          x: Math.round(point.x / devicePixelRatio),
+          y: Math.round(point.y / devicePixelRatio),
+        }));
+
+        // Scale down by `displayPixelRatio` since infobar's HTML elements already take it
+        // into account; and the zoom scaling is handled by `moveInfobar`.
+        const bounds = getBoundsFromPoints(
+          points.map(point => ({
+            x: Math.round(point.x / displayPixelRatio),
+            y: Math.round(point.y / displayPixelRatio),
+          }))
+        );
+
+        paths.push(getPathDescriptionFromPoints(svgPoints));
+
+        // Update and show the info bar when only displaying a single grid area.
+        if (areaName) {
+          this._showGridAreaInfoBar();
+          this._updateGridAreaInfobar(area, bounds);
+        }
+      }
+    }
+
+    const areas = this.getElement("areas");
+    areas.setAttribute("d", paths.join(" "));
+  }
+
+  /**
+   * Render grid area name on the containing grid area cell.
+   *
+   * @param  {Object} fragment
+   *         The grid fragment of the grid container.
+   * @param  {Object} area
+   *         The area overlay to render on the CSS highlighter canvas.
+   */
+  renderGridAreaName(fragment, area) {
+    const { rowStart, rowEnd, columnStart, columnEnd } = area;
+    const { devicePixelRatio } = this.win;
+    const displayPixelRatio = getDisplayPixelRatio(this.win);
+    const offset = (displayPixelRatio / 2) % 1;
+    let fontSize = GRID_AREA_NAME_FONT_SIZE * displayPixelRatio;
+    const canvasX = Math.round(this._canvasPosition.x * devicePixelRatio);
+    const canvasY = Math.round(this._canvasPosition.y * devicePixelRatio);
+
+    this.ctx.save();
+    this.ctx.translate(offset - canvasX, offset - canvasY);
+    this.ctx.font = fontSize + "px " + GRID_FONT_FAMILY;
+    this.ctx.globalAlpha = this.globalAlpha;
+    this.ctx.strokeStyle = this.color;
+    this.ctx.textAlign = "center";
+    this.ctx.textBaseline = "middle";
+
+    // Draw the text for the grid area name.
+    for (let rowNumber = rowStart; rowNumber < rowEnd; rowNumber++) {
+      for (
+        let columnNumber = columnStart;
+        columnNumber < columnEnd;
+        columnNumber++
+      ) {
+        const row = fragment.rows.tracks[rowNumber - 1];
+        const column = fragment.cols.tracks[columnNumber - 1];
+
+        // If the font size exceeds the bounds of the containing grid cell, size it its
+        // row or column dimension, whichever is smallest.
+        if (
+          fontSize > column.breadth * displayPixelRatio ||
+          fontSize > row.breadth * displayPixelRatio
+        ) {
+          fontSize = Math.min([column.breadth, row.breadth]);
+          this.ctx.font = fontSize + "px " + GRID_FONT_FAMILY;
+        }
+
+        const textWidth = this.ctx.measureText(area.name).width;
+        // The width of the character 'm' approximates the height of the text.
+        const textHeight = this.ctx.measureText("m").width;
+        // Padding in pixels for the line number text inside of the line number container.
+        const padding = 3 * displayPixelRatio;
+
+        const boxWidth = textWidth + 2 * padding;
+        const boxHeight = textHeight + 2 * padding;
+
+        let x = column.start + column.breadth / 2;
+        let y = row.start + row.breadth / 2;
+
+        [x, y] = apply(this.currentMatrix, [x, y]);
+
+        const rectXPos = x - boxWidth / 2;
+        const rectYPos = y - boxHeight / 2;
+
+        // Draw a rounded rectangle with a border width of 1 pixel,
+        // a border color matching the grid color, and a white background.
+        this.ctx.lineWidth = 1 * displayPixelRatio;
+        this.ctx.strokeStyle = this.color;
+        this.ctx.fillStyle = "white";
+        const radius = 2 * displayPixelRatio;
+        drawRoundedRect(
+          this.ctx,
+          rectXPos,
+          rectYPos,
+          boxWidth,
+          boxHeight,
+          radius
+        );
+
+        this.ctx.fillStyle = this.color;
+        this.ctx.fillText(area.name, x, y + padding);
+      }
+    }
+
+    this.ctx.restore();
+  }
+
+  /**
+   * Renders the grid area overlay on the css grid highlighter canvas.
+   */
+  renderGridAreaOverlay() {
+    const padding = 1;
+
+    for (let i = 0; i < this.gridData.length; i++) {
+      const fragment = this.gridData[i];
+
+      for (const area of fragment.areas) {
+        const { rowStart, rowEnd, columnStart, columnEnd, type } = area;
+
+        if (type === "implicit") {
+          continue;
+        }
+
+        // Draw the line edges for the grid area.
+        const areaColStart = fragment.cols.lines[columnStart - 1];
+        const areaColEnd = fragment.cols.lines[columnEnd - 1];
+
+        const areaRowStart = fragment.rows.lines[rowStart - 1];
+        const areaRowEnd = fragment.rows.lines[rowEnd - 1];
+
+        const areaColStartLinePos = areaColStart.start + areaColStart.breadth;
+        const areaRowStartLinePos = areaRowStart.start + areaRowStart.breadth;
+
+        this.renderLine(
+          areaColStartLinePos + padding,
+          areaRowStartLinePos,
+          areaRowEnd.start,
+          COLUMNS,
+          "areaEdge"
+        );
+        this.renderLine(
+          areaColEnd.start - padding,
+          areaRowStartLinePos,
+          areaRowEnd.start,
+          COLUMNS,
+          "areaEdge"
+        );
+
+        this.renderLine(
+          areaRowStartLinePos + padding,
+          areaColStartLinePos,
+          areaColEnd.start,
+          ROWS,
+          "areaEdge"
+        );
+        this.renderLine(
+          areaRowEnd.start - padding,
+          areaColStartLinePos,
+          areaColEnd.start,
+          ROWS,
+          "areaEdge"
+        );
+
+        this.renderGridAreaName(fragment, area);
+      }
+    }
+  }
+
+  /**
+   * Render the grid cell highlight for the given grid fragment index, row and column
+   * number.
+   *
+   * @param  {Number} gridFragmentIndex
+   *         Index of the grid fragment to render the grid cell highlight.
+   * @param  {Number} rowNumber
+   *         Row number of the grid cell to highlight.
+   * @param  {Number} columnNumber
+   *         Column number of the grid cell to highlight.
+   */
+  renderGridCell(gridFragmentIndex, rowNumber, columnNumber) {
+    const fragment = this.gridData[gridFragmentIndex];
+
+    if (!fragment) {
+      return;
+    }
+
+    const row = fragment.rows.tracks[rowNumber - 1];
+    const column = fragment.cols.tracks[columnNumber - 1];
+
+    if (!row || !column) {
+      return;
+    }
+
+    const x1 = column.start;
+    const y1 = row.start;
+    const x2 = column.start + column.breadth;
+    const y2 = row.start + row.breadth;
+
+    const { devicePixelRatio } = this.win;
+    const displayPixelRatio = getDisplayPixelRatio(this.win);
+    const points = getPointsFromDiagonal(x1, y1, x2, y2, this.currentMatrix);
+
+    // Scale down by `devicePixelRatio` since SVG element already take them into account.
+    const svgPoints = points.map(point => ({
+      x: Math.round(point.x / devicePixelRatio),
+      y: Math.round(point.y / devicePixelRatio),
+    }));
+
+    // Scale down by `displayPixelRatio` since infobar's HTML elements already take it
+    // into account, and the zoom scaling is handled by `moveInfobar`.
+    const bounds = getBoundsFromPoints(
+      points.map(point => ({
+        x: Math.round(point.x / displayPixelRatio),
+        y: Math.round(point.y / displayPixelRatio),
+      }))
+    );
+
+    const cells = this.getElement("cells");
+    cells.setAttribute("d", getPathDescriptionFromPoints(svgPoints));
+
+    this._showGridCellInfoBar();
+    this._updateGridCellInfobar(rowNumber, columnNumber, bounds);
+  }
+
+  /**
+   * Render the grid gap area on the css grid highlighter canvas.
+   *
+   * @param  {Number} linePos
+   *         The line position along the x-axis for a column grid line and
+   *         y-axis for a row grid line.
+   * @param  {Number} startPos
+   *         The start position of the cross side of the grid line.
+   * @param  {Number} endPos
+   *         The end position of the cross side of the grid line.
+   * @param  {Number} breadth
+   *         The grid line breadth value.
+   * @param  {String} dimensionType
+   *         The grid dimension type which is either the constant COLUMNS or ROWS.
+   */
+  renderGridGap(linePos, startPos, endPos, breadth, dimensionType) {
+    const { devicePixelRatio } = this.win;
+    const displayPixelRatio = getDisplayPixelRatio(this.win);
+    const offset = (displayPixelRatio / 2) % 1;
+    const canvasX = Math.round(this._canvasPosition.x * devicePixelRatio);
+    const canvasY = Math.round(this._canvasPosition.y * devicePixelRatio);
+
+    linePos = Math.round(linePos);
+    startPos = Math.round(startPos);
+    breadth = Math.round(breadth);
+
+    this.ctx.save();
+    this.ctx.fillStyle = this.getGridGapPattern(
+      devicePixelRatio,
+      dimensionType
+    );
+    this.ctx.translate(offset - canvasX, offset - canvasY);
+
+    if (dimensionType === COLUMNS) {
+      if (isFinite(endPos)) {
+        endPos = Math.round(endPos);
+      } else {
+        endPos = this._winDimensions.height;
+        startPos = -endPos;
+      }
+      drawRect(
+        this.ctx,
+        linePos,
+        startPos,
+        linePos + breadth,
+        endPos,
+        this.currentMatrix
+      );
+    } else {
+      if (isFinite(endPos)) {
+        endPos = Math.round(endPos);
+      } else {
+        endPos = this._winDimensions.width;
+        startPos = -endPos;
+      }
+      drawRect(
+        this.ctx,
+        startPos,
+        linePos,
+        endPos,
+        linePos + breadth,
+        this.currentMatrix
+      );
+    }
+
+    // Find current angle of grid by measuring the angle of two arbitrary points,
+    // then rotate canvas, so the hash pattern stays 45deg to the gridlines.
+    const p1 = apply(this.currentMatrix, [0, 0]);
+    const p2 = apply(this.currentMatrix, [1, 0]);
+    const angleRad = Math.atan2(p2[1] - p1[1], p2[0] - p1[0]);
+    this.ctx.rotate(angleRad);
+
+    this.ctx.fill();
+    this.ctx.restore();
+  }
+
+  /**
+   * Render the grid line name highlight for the given grid fragment index, lineNumber,
+   * and dimensionType.
+   *
+   * @param  {Number} gridFragmentIndex
+   *         Index of the grid fragment to render the grid line highlight.
+   * @param  {Number} lineNumber
+   *         Line number of the grid line to highlight.
+   * @param  {String} dimensionType
+   *         The dimension type of the grid line.
+   */
+  renderGridLineNames(gridFragmentIndex, lineNumber, dimensionType) {
+    const fragment = this.gridData[gridFragmentIndex];
+
+    if (!fragment || !lineNumber || !dimensionType) {
+      return;
+    }
+
+    const { names } = fragment[dimensionType].lines[lineNumber - 1];
+    let linePos;
+
+    if (dimensionType === ROWS) {
+      linePos = fragment.rows.lines[lineNumber - 1];
+    } else if (dimensionType === COLUMNS) {
+      linePos = fragment.cols.lines[lineNumber - 1];
+    }
+
+    if (!linePos) {
+      return;
+    }
+
+    const currentZoom = getCurrentZoom(this.win);
+    const { bounds } = this.currentQuads.content[gridFragmentIndex];
+
+    const rowYPosition = fragment.rows.lines[0];
+    const colXPosition = fragment.rows.lines[0];
+
+    const x =
+      dimensionType === COLUMNS
+        ? linePos.start + bounds.left / currentZoom
+        : colXPosition.start + bounds.left / currentZoom;
+
+    const y =
+      dimensionType === ROWS
+        ? linePos.start + bounds.top / currentZoom
+        : rowYPosition.start + bounds.top / currentZoom;
+
+    this._showGridLineInfoBar();
+    this._updateGridLineInfobar(names.join(", "), lineNumber, x, y);
+  }
+
+  /**
+   * Render the grid line number on the css grid highlighter canvas.
+   *
+   * @param  {Number} lineNumber
+   *         The grid line number.
+   * @param  {Number} linePos
+   *         The line position along the x-axis for a column grid line and
+   *         y-axis for a row grid line.
+   * @param  {Number} startPos
+   *         The start position of the cross side of the grid line.
+   * @param  {Number} breadth
+   *         The grid line breadth value.
+   * @param  {String} dimensionType
+   *         The grid dimension type which is either the constant COLUMNS or ROWS.
+   * @param  {Boolean||undefined} isStackedLine
+   *         Boolean indicating if the line is stacked.
+   */
+  // eslint-disable-next-line complexity
+  renderGridLineNumber(
+    lineNumber,
+    linePos,
+    startPos,
+    breadth,
+    dimensionType,
+    isStackedLine
+  ) {
+    const displayPixelRatio = getDisplayPixelRatio(this.win);
+    const { devicePixelRatio } = this.win;
+    const offset = (displayPixelRatio / 2) % 1;
+    const fontSize = GRID_FONT_SIZE * devicePixelRatio;
+    const canvasX = Math.round(this._canvasPosition.x * devicePixelRatio);
+    const canvasY = Math.round(this._canvasPosition.y * devicePixelRatio);
+
+    linePos = Math.round(linePos);
+    startPos = Math.round(startPos);
+    breadth = Math.round(breadth);
+
+    if (linePos + breadth < 0) {
+      // Don't render the line number since the line is not visible on screen.
+      return;
+    }
+
+    this.ctx.save();
+    this.ctx.translate(offset - canvasX, offset - canvasY);
+    this.ctx.font = fontSize + "px " + GRID_FONT_FAMILY;
+
+    // For a general grid box, the height of the character "m" will be its minimum width
+    // and height. If line number's text width is greater, then use the grid box's text
+    // width instead.
+    const textHeight = this.ctx.measureText("m").width;
+    const textWidth = Math.max(
+      textHeight,
+      this.ctx.measureText(lineNumber).width
+    );
+
+    // Padding in pixels for the line number text inside of the line number container.
+    const padding = 3 * devicePixelRatio;
+    const offsetFromEdge = 2 * devicePixelRatio;
+
+    let boxWidth = textWidth + 2 * padding;
+    let boxHeight = textHeight + 2 * padding;
+
+    // Calculate the x & y coordinates for the line number container, so that its arrow
+    // tip is centered on the line (or the gap if there is one), and is offset by the
+    // calculated padding value from the grid container edge.
+    let x, y;
+
+    if (dimensionType === COLUMNS) {
+      x = linePos + breadth / 2;
+      y =
+        lineNumber > 0 ? startPos - offsetFromEdge : startPos + offsetFromEdge;
+    } else if (dimensionType === ROWS) {
+      y = linePos + breadth / 2;
+      x =
+        lineNumber > 0 ? startPos - offsetFromEdge : startPos + offsetFromEdge;
+    }
+
+    [x, y] = apply(this.currentMatrix, [x, y]);
+
+    // Draw a bubble rectangular arrow with a border width of 2 pixels, a border color
+    // matching the grid color and a white background (the line number will be written in
+    // black).
+    this.ctx.lineWidth = 2 * displayPixelRatio;
+    this.ctx.strokeStyle = this.color;
+    this.ctx.fillStyle = "white";
+    this.ctx.globalAlpha = this.globalAlpha;
+
+    // See param definitions of drawBubbleRect.
+    const radius = 2 * displayPixelRatio;
+    const margin = 2 * displayPixelRatio;
+    const arrowSize = 8 * displayPixelRatio;
+
+    const minBoxSize = arrowSize * 2 + padding;
+    boxWidth = Math.max(boxWidth, minBoxSize);
+    boxHeight = Math.max(boxHeight, minBoxSize);
+
+    // Determine which edge of the box to aim the line number arrow at.
+    const boxEdge = this.getBoxEdge(dimensionType, lineNumber);
+
+    let { width, height } = this._winDimensions;
+    width *= displayPixelRatio;
+    height *= displayPixelRatio;
+
+    // Don't draw if the line is out of the viewport.
+    if (
+      (dimensionType === ROWS && (y < 0 || y > height)) ||
+      (dimensionType === COLUMNS && (x < 0 || x > width))
+    ) {
+      this.ctx.restore();
+      return;
+    }
+
+    // If the arrow's edge (the one perpendicular to the line direction) is too close to
+    // the edge of the viewport. Push the arrow inside the grid.
+    const minOffsetFromEdge = OFFSET_FROM_EDGE * displayPixelRatio;
+    switch (boxEdge) {
+      case "left":
+        if (x < minOffsetFromEdge) {
+          x += FLIP_ARROW_INSIDE_FACTOR * boxWidth;
+        }
+        break;
+      case "right":
+        if (width - x < minOffsetFromEdge) {
+          x -= FLIP_ARROW_INSIDE_FACTOR * boxWidth;
+        }
+        break;
+      case "top":
+        if (y < minOffsetFromEdge) {
+          y += FLIP_ARROW_INSIDE_FACTOR * boxHeight;
+        }
+        break;
+      case "bottom":
+        if (height - y < minOffsetFromEdge) {
+          y -= FLIP_ARROW_INSIDE_FACTOR * boxHeight;
+        }
+        break;
+    }
+
+    // Offset stacked line numbers by a quarter of the box's width/height, so a part of
+    // them remains visible behind the number that sits at the top of the stack.
+    if (isStackedLine) {
+      const xOffset = boxWidth / 4;
+      const yOffset = boxHeight / 4;
+
+      if (lineNumber > 0) {
+        x -= xOffset;
+        y -= yOffset;
+      } else {
+        x += xOffset;
+        y += yOffset;
+      }
+    }
+
+    // If one the edges of the arrow that's parallel to the line is too close to the edge
+    // of the viewport (and therefore partly hidden), grow the arrow's size in the
+    // opposite direction.
+    // The goal is for the part that's not hidden to be exactly the size of a normal
+    // arrow and for the arrow to keep pointing at the line (keep being centered on it).
+    let grewBox = false;
+    const boxWidthBeforeGrowth = boxWidth;
+    const boxHeightBeforeGrowth = boxHeight;
+
+    if (dimensionType === ROWS && y <= boxHeight / 2) {
+      grewBox = true;
+      boxHeight = 2 * (boxHeight - y);
+    } else if (dimensionType === ROWS && y >= height - boxHeight / 2) {
+      grewBox = true;
+      boxHeight = 2 * (y - height + boxHeight);
+    } else if (dimensionType === COLUMNS && x <= boxWidth / 2) {
+      grewBox = true;
+      boxWidth = 2 * (boxWidth - x);
+    } else if (dimensionType === COLUMNS && x >= width - boxWidth / 2) {
+      grewBox = true;
+      boxWidth = 2 * (x - width + boxWidth);
+    }
+
+    // Draw the arrow box itself
+    drawBubbleRect(
+      this.ctx,
+      x,
+      y,
+      boxWidth,
+      boxHeight,
+      radius,
+      margin,
+      arrowSize,
+      boxEdge
+    );
+
+    // Determine the text position for it to be centered nicely inside the arrow box.
+    switch (boxEdge) {
+      case "left":
+        x -= boxWidth + arrowSize + radius - boxWidth / 2;
+        break;
+      case "right":
+        x += boxWidth + arrowSize + radius - boxWidth / 2;
+        break;
+      case "top":
+        y -= boxHeight + arrowSize + radius - boxHeight / 2;
+        break;
+      case "bottom":
+        y += boxHeight + arrowSize + radius - boxHeight / 2;
+        break;
+    }
+
+    // Do a second pass to adjust the position, along the other axis, if the box grew
+    // during the previous step, so the text is also centered on that axis.
+    if (grewBox) {
+      if (dimensionType === ROWS && y <= boxHeightBeforeGrowth / 2) {
+        y = boxHeightBeforeGrowth / 2;
+      } else if (
+        dimensionType === ROWS &&
+        y >= height - boxHeightBeforeGrowth / 2
+      ) {
+        y = height - boxHeightBeforeGrowth / 2;
+      } else if (dimensionType === COLUMNS && x <= boxWidthBeforeGrowth / 2) {
+        x = boxWidthBeforeGrowth / 2;
+      } else if (
+        dimensionType === COLUMNS &&
+        x >= width - boxWidthBeforeGrowth / 2
+      ) {
+        x = width - boxWidthBeforeGrowth / 2;
+      }
+    }
+
+    // Write the line number inside of the rectangle.
+    this.ctx.textAlign = "center";
+    this.ctx.textBaseline = "middle";
+    this.ctx.fillStyle = "black";
+    const numberText = isStackedLine ? "" : lineNumber;
+    this.ctx.fillText(numberText, x, y);
+    this.ctx.restore();
+  }
+
+  /**
+   * Determine which edge of a line number box to aim the line number arrow at.
+   *
+   * @param  {String} dimensionType
+   *         The grid line dimension type which is either the constant COLUMNS or ROWS.
+   * @param  {Number} lineNumber
+   *         The grid line number.
+   * @return {String} The edge of the box: top, right, bottom or left.
+   */
+  getBoxEdge(dimensionType, lineNumber) {
+    let boxEdge;
+
+    if (dimensionType === COLUMNS) {
+      boxEdge = lineNumber > 0 ? "top" : "bottom";
+    } else if (dimensionType === ROWS) {
+      boxEdge = lineNumber > 0 ? "left" : "right";
+    }
+
+    // Rotate box edge as needed for writing mode and text direction.
+    const { direction, writingMode } = getComputedStyle(this.currentNode);
+
+    switch (writingMode) {
+      case "horizontal-tb":
+        // This is the initial value.  No further adjustment needed.
+        break;
+      case "vertical-rl":
+        boxEdge = rotateEdgeRight(boxEdge);
+        break;
+      case "vertical-lr":
+        if (dimensionType === COLUMNS) {
+          boxEdge = rotateEdgeLeft(boxEdge);
+        } else {
+          boxEdge = rotateEdgeRight(boxEdge);
+        }
+        break;
+      case "sideways-rl":
+        boxEdge = rotateEdgeRight(boxEdge);
+        break;
+      case "sideways-lr":
+        boxEdge = rotateEdgeLeft(boxEdge);
+        break;
+      default:
+        console.error(`Unexpected writing-mode: ${writingMode}`);
+    }
+
+    switch (direction) {
+      case "ltr":
+        // This is the initial value.  No further adjustment needed.
+        break;
+      case "rtl":
+        if (dimensionType === ROWS) {
+          boxEdge = reflectEdge(boxEdge);
+        }
+        break;
+      default:
+        console.error(`Unexpected direction: ${direction}`);
+    }
+
+    return boxEdge;
+  }
+
+  /**
+   * Render the grid line on the css grid highlighter canvas.
+   *
+   * @param  {Number} linePos
+   *         The line position along the x-axis for a column grid line and
+   *         y-axis for a row grid line.
+   * @param  {Number} startPos
+   *         The start position of the cross side of the grid line.
+   * @param  {Number} endPos
+   *         The end position of the cross side of the grid line.
+   * @param  {String} dimensionType
+   *         The grid dimension type which is either the constant COLUMNS or ROWS.
+   * @param  {String} lineType
+   *         The grid line type - "edge", "explicit", or "implicit".
+   */
+  renderLine(linePos, startPos, endPos, dimensionType, lineType) {
+    const { devicePixelRatio } = this.win;
+    const lineWidth = getDisplayPixelRatio(this.win);
+    const offset = (lineWidth / 2) % 1;
+    const canvasX = Math.round(this._canvasPosition.x * devicePixelRatio);
+    const canvasY = Math.round(this._canvasPosition.y * devicePixelRatio);
+
+    linePos = Math.round(linePos);
+    startPos = Math.round(startPos);
+    endPos = Math.round(endPos);
+
+    this.ctx.save();
+    this.ctx.setLineDash(GRID_LINES_PROPERTIES[lineType].lineDash);
+    this.ctx.translate(offset - canvasX, offset - canvasY);
+
+    const lineOptions = {
+      matrix: this.currentMatrix,
+    };
+
+    if (this.options.showInfiniteLines) {
+      lineOptions.extendToBoundaries = [
+        canvasX,
+        canvasY,
+        canvasX + CANVAS_SIZE,
+        canvasY + CANVAS_SIZE,
+      ];
+    }
+
+    if (dimensionType === COLUMNS) {
+      drawLine(this.ctx, linePos, startPos, linePos, endPos, lineOptions);
+    } else {
+      drawLine(this.ctx, startPos, linePos, endPos, linePos, lineOptions);
+    }
+
+    this.ctx.strokeStyle = this.color;
+    this.ctx.globalAlpha =
+      GRID_LINES_PROPERTIES[lineType].alpha * this.globalAlpha;
+
+    if (GRID_LINES_PROPERTIES[lineType].lineWidth) {
+      this.ctx.lineWidth =
+        GRID_LINES_PROPERTIES[lineType].lineWidth * devicePixelRatio;
+    } else {
+      this.ctx.lineWidth = lineWidth;
+    }
+
+    this.ctx.stroke();
+    this.ctx.restore();
+  }
+
+  /**
+   * Render the grid lines given the grid dimension information of the
+   * column or row lines.
+   *
+   * @param  {GridDimension} gridDimension
+   *         Column or row grid dimension object.
+   * @param  {Object} quad.bounds
+   *         The content bounds of the box model region quads.
+   * @param  {String} dimensionType
+   *         The grid dimension type which is either the constant COLUMNS or ROWS.
+   * @param  {Number} startPos
+   *         The start position of the cross side ("left" for ROWS and "top" for COLUMNS)
+   *         of the grid dimension.
+   * @param  {Number} endPos
+   *         The end position of the cross side ("left" for ROWS and "top" for COLUMNS)
+   *         of the grid dimension.
+   */
+  renderLines(gridDimension, dimensionType, startPos, endPos) {
+    const { lines, tracks } = gridDimension;
+    const lastEdgeLineIndex = this.getLastEdgeLineIndex(tracks);
+
+    for (let i = 0; i < lines.length; i++) {
+      const line = lines[i];
+      const linePos = line.start;
+
+      if (i == 0 || i == lastEdgeLineIndex) {
+        this.renderLine(linePos, startPos, endPos, dimensionType, "edge");
+      } else {
+        this.renderLine(
+          linePos,
+          startPos,
+          endPos,
+          dimensionType,
+          tracks[i - 1].type
+        );
+      }
+
+      // Render a second line to illustrate the gutter for non-zero breadth.
+      if (line.breadth > 0) {
+        this.renderGridGap(
+          linePos,
+          startPos,
+          endPos,
+          line.breadth,
+          dimensionType
+        );
+        this.renderLine(
+          linePos + line.breadth,
+          startPos,
+          endPos,
+          dimensionType,
+          tracks[i].type
+        );
+      }
+    }
+  }
+
+  /**
+   * Render the grid lines given the grid dimension information of the
+   * column or row lines.
+   *
+   * @param  {GridDimension} gridDimension
+   *         Column or row grid dimension object.
+   * @param  {String} dimensionType
+   *         The grid dimension type which is either the constant COLUMNS or ROWS.
+   * @param  {Number} startPos
+   *         The start position of the cross side ("left" for ROWS and "top" for COLUMNS)
+   *         of the grid dimension.
+   */
+  renderLineNumbers(gridDimension, dimensionType, startPos) {
+    const { lines, tracks } = gridDimension;
+
+    for (let i = 0, line; (line = lines[i++]); ) {
+      // If you place something using negative numbers, you can trigger some implicit
+      // grid creation above and to the left of the explicit grid (assuming a
+      // horizontal-tb writing mode).
+      //
+      // The first explicit grid line gets the number of 1, and any implicit grid lines
+      // before 1 get negative numbers. Since here we're rendering only the positive line
+      // numbers, we have to skip any implicit grid lines before the first one that is
+      // explicit. The API returns a 0 as the line's number for these implicit lines that
+      // occurs before the first explicit line.
+      if (line.number === 0) {
+        continue;
+      }
+
+      // Check for overlapping lines by measuring the track width between them.
+      // We render a second box beneath the last overlapping
+      // line number to indicate there are lines beneath it.
+      const gridTrack = tracks[i - 1];
+
+      if (gridTrack) {
+        const { breadth } = gridTrack;
+
+        if (breadth === 0) {
+          this.renderGridLineNumber(
+            line.number,
+            line.start,
+            startPos,
+            line.breadth,
+            dimensionType,
+            true
+          );
+          continue;
+        }
+      }
+
+      this.renderGridLineNumber(
+        line.number,
+        line.start,
+        startPos,
+        line.breadth,
+        dimensionType
+      );
+    }
+  }
+
+  /**
+   * Render the negative grid lines given the grid dimension information of the
+   * column or row lines.
+   *
+   * @param  {GridDimension} gridDimension
+   *         Column or row grid dimension object.
+   * @param  {String} dimensionType
+   *         The grid dimension type which is either the constant COLUMNS or ROWS.
+   * @param  {Number} startPos
+   *         The start position of the cross side ("left" for ROWS and "top" for COLUMNS)
+   *         of the grid dimension.
+   */
+  renderNegativeLineNumbers(gridDimension, dimensionType, startPos) {
+    const { lines, tracks } = gridDimension;
+
+    for (let i = 0, line; (line = lines[i++]); ) {
+      const linePos = line.start;
+      const negativeLineNumber = line.negativeNumber;
+
+      // Don't render any negative line number greater than -1.
+      if (negativeLineNumber == 0) {
+        break;
+      }
+
+      // Check for overlapping lines by measuring the track width between them.
+      // We render a second box beneath the last overlapping
+      // line number to indicate there are lines beneath it.
+      const gridTrack = tracks[i - 1];
+      if (gridTrack) {
+        const { breadth } = gridTrack;
+
+        // Ensure "-1" is always visible, since it is always the largest number.
+        if (breadth === 0 && negativeLineNumber != -1) {
+          this.renderGridLineNumber(
+            negativeLineNumber,
+            linePos,
+            startPos,
+            line.breadth,
+            dimensionType,
+            true
+          );
+          continue;
+        }
+      }
+
+      this.renderGridLineNumber(
+        negativeLineNumber,
+        linePos,
+        startPos,
+        line.breadth,
+        dimensionType
+      );
+    }
+  }
+
+  /**
+   * Update the highlighter on the current highlighted node (the one that was
+   * passed as an argument to show(node)). Should be called whenever node's geometry
+   * or grid changes.
+   */
+  _update() {
+    setIgnoreLayoutChanges(true);
+
+    // Set z-index.
+    this.markup.content.root.firstElementChild.style.setProperty(
+      "z-index",
+      this.options.zIndex
+    );
+
+    const root = this.getElement("root");
+    const cells = this.getElement("cells");
+    const areas = this.getElement("areas");
+
+    // Set the grid cells and areas fill to the current grid colour.
+    cells.setAttribute("style", `fill: ${this.color}`);
+    areas.setAttribute("style", `fill: ${this.color}`);
+
+    // Hide the root element and force the reflow in order to get the proper window's
+    // dimensions without increasing them.
+    root.setAttribute("style", "display: none");
+    this.win.document.documentElement.offsetWidth;
+    this._winDimensions = getWindowDimensions(this.win);
+    const { width, height } = this._winDimensions;
+
+    // Updates the <canvas> element's position and size.
+    // It also clear the <canvas>'s drawing context.
+    updateCanvasElement(
+      this.canvas,
+      this._canvasPosition,
+      this.win.devicePixelRatio
+    );
+
+    // Clear the grid area highlights.
+    this.clearGridAreas();
+    this.clearGridCell();
+
+    // Update the current matrix used in our canvas' rendering.
+    const { currentMatrix, hasNodeTransformations } = getCurrentMatrix(
+      this.currentNode,
+      this.win
+    );
+    this.currentMatrix = currentMatrix;
+    this.hasNodeTransformations = hasNodeTransformations;
+
+    // Start drawing the grid fragments.
+    for (let i = 0; i < this.gridData.length; i++) {
+      this.renderFragment(this.gridData[i]);
+    }
+
+    // Display the grid area highlights if needed.
+    if (this.options.showAllGridAreas) {
+      this.showAllGridAreas();
+    } else if (this.options.showGridArea) {
+      this.showGridArea(this.options.showGridArea);
+    }
+
+    // Display the grid cell highlights if needed.
+    if (this.options.showGridCell) {
+      this.showGridCell(this.options.showGridCell);
+    }
+
+    // Display the grid line names if needed.
+    if (this.options.showGridLineNames) {
+      this.showGridLineNames(this.options.showGridLineNames);
+    }
+
+    this._showGrid();
+    this._showGridElements();
+
+    root.setAttribute(
+      "style",
+      `position: absolute; width: ${width}px; height: ${height}px; overflow: hidden`
+    );
+
+    setIgnoreLayoutChanges(false, this.highlighterEnv.document.documentElement);
+    return true;
+  }
+
+  /**
+   * Update the grid information displayed in the grid area info bar.
+   *
+   * @param  {GridArea} area
+   *         The grid area object.
+   * @param  {Object} bounds
+   *         A DOMRect-like object represent the grid area rectangle.
+   */
+  _updateGridAreaInfobar(area, bounds) {
+    const { width, height } = bounds;
+    const dim =
+      parseFloat(width.toPrecision(6)) +
+      " \u00D7 " +
+      parseFloat(height.toPrecision(6));
+
+    this.getElement("area-infobar-name").setTextContent(area.name);
+    this.getElement("area-infobar-dimensions").setTextContent(dim);
+
+    const container = this.getElement("area-infobar-container");
+    moveInfobar(container, bounds, this.win, {
+      position: "bottom",
+    });
+  }
+
+  /**
+   * Update the grid information displayed in the grid cell info bar.
+   *
+   * @param  {Number} rowNumber
+   *         The grid cell's row number.
+   * @param  {Number} columnNumber
+   *         The grid cell's column number.
+   * @param  {Object} bounds
+   *         A DOMRect-like object represent the grid cell rectangle.
+   */
+  _updateGridCellInfobar(rowNumber, columnNumber, bounds) {
+    const { width, height } = bounds;
+    const dim =
+      parseFloat(width.toPrecision(6)) +
+      " \u00D7 " +
+      parseFloat(height.toPrecision(6));
+    const position = HighlightersBundle.formatValueSync(
+      "grid-row-column-positions",
+      { row: rowNumber, column: columnNumber }
+    );
+
+    this.getElement("cell-infobar-position").setTextContent(position);
+    this.getElement("cell-infobar-dimensions").setTextContent(dim);
+
+    const container = this.getElement("cell-infobar-container");
+    moveInfobar(container, bounds, this.win, {
+      position: "top",
+    });
+  }
+
+  /**
+   * Update the grid information displayed in the grid line info bar.
+   *
+   * @param  {String} gridLineNames
+   *         Comma-separated string of names for the grid line.
+   * @param  {Number} gridLineNumber
+   *         The grid line number.
+   * @param  {Number} x
+   *         The x-coordinate of the grid line.
+   * @param  {Number} y
+   *         The y-coordinate of the grid line.
+   */
+  _updateGridLineInfobar(gridLineNames, gridLineNumber, x, y) {
+    this.getElement("line-infobar-number").setTextContent(gridLineNumber);
+    this.getElement("line-infobar-names").setTextContent(gridLineNames);
+
+    const container = this.getElement("line-infobar-container");
+    moveInfobar(
+      container,
+      getBoundsFromPoints([
+        { x, y },
+        { x, y },
+        { x, y },
+        { x, y },
+      ]),
+      this.win
+    );
+  }
+}
+
+exports.CssGridHighlighter = CssGridHighlighter;
diff --git a/devtools/server/actors/highlighters/css-transform.js b/devtools/server/actors/highlighters/css-transform.js
new file mode 100644
index 0000000000..c9f16b42e0
--- /dev/null
+++ b/devtools/server/actors/highlighters/css-transform.js
@@ -0,0 +1,265 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  AutoRefreshHighlighter,
+} = require("resource://devtools/server/actors/highlighters/auto-refresh.js");
+const {
+  CanvasFrameAnonymousContentHelper,
+  getComputedStyle,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+const {
+  setIgnoreLayoutChanges,
+  getNodeBounds,
+} = require("resource://devtools/shared/layout/utils.js");
+
+// The minimum distance a line should be before it has an arrow marker-end
+const ARROW_LINE_MIN_DISTANCE = 10;
+
+var MARKER_COUNTER = 1;
+
+/**
+ * The CssTransformHighlighter is the class that draws an outline around a
+ * transformed element and an outline around where it would be if untransformed
+ * as well as arrows connecting the 2 outlines' corners.
+ */
+class CssTransformHighlighter extends AutoRefreshHighlighter {
+  constructor(highlighterEnv) {
+    super(highlighterEnv);
+
+    this.ID_CLASS_PREFIX = "css-transform-";
+
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      this.highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.markup.initialize();
+  }
+
+  _buildMarkup() {
+    const container = this.markup.createNode({
+      attributes: {
+        class: "highlighter-container",
+      },
+    });
+
+    // The root wrapper is used to unzoom the highlighter when needed.
+    const rootWrapper = this.markup.createNode({
+      parent: container,
+      attributes: {
+        id: "root",
+        class: "root",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const svg = this.markup.createSVGNode({
+      nodeType: "svg",
+      parent: rootWrapper,
+      attributes: {
+        id: "elements",
+        hidden: "true",
+        width: "100%",
+        height: "100%",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Add a marker tag to the svg root for the arrow tip
+    this.markerId = "arrow-marker-" + MARKER_COUNTER;
+    MARKER_COUNTER++;
+    const marker = this.markup.createSVGNode({
+      nodeType: "marker",
+      parent: svg,
+      attributes: {
+        id: this.markerId,
+        markerWidth: "10",
+        markerHeight: "5",
+        orient: "auto",
+        markerUnits: "strokeWidth",
+        refX: "10",
+        refY: "5",
+        viewBox: "0 0 10 10",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createSVGNode({
+      nodeType: "path",
+      parent: marker,
+      attributes: {
+        d: "M 0 0 L 10 5 L 0 10 z",
+        fill: "#08C",
+      },
+    });
+
+    const shapesGroup = this.markup.createSVGNode({
+      nodeType: "g",
+      parent: svg,
+    });
+
+    // Create the 2 polygons (transformed and untransformed)
+    this.markup.createSVGNode({
+      nodeType: "polygon",
+      parent: shapesGroup,
+      attributes: {
+        id: "untransformed",
+        class: "untransformed",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createSVGNode({
+      nodeType: "polygon",
+      parent: shapesGroup,
+      attributes: {
+        id: "transformed",
+        class: "transformed",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Create the arrows
+    for (const nb of ["1", "2", "3", "4"]) {
+      this.markup.createSVGNode({
+        nodeType: "line",
+        parent: shapesGroup,
+        attributes: {
+          id: "line" + nb,
+          class: "line",
+          "marker-end": "url(#" + this.markerId + ")",
+        },
+        prefix: this.ID_CLASS_PREFIX,
+      });
+    }
+
+    return container;
+  }
+
+  /**
+   * Destroy the nodes. Remove listeners.
+   */
+  destroy() {
+    AutoRefreshHighlighter.prototype.destroy.call(this);
+    this.markup.destroy();
+  }
+
+  getElement(id) {
+    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
+  }
+
+  /**
+   * Show the highlighter on a given node
+   */
+  _show() {
+    if (!this._isTransformed(this.currentNode)) {
+      this.hide();
+      return false;
+    }
+
+    return this._update();
+  }
+
+  /**
+   * Checks if the supplied node is transformed and not inline
+   */
+  _isTransformed(node) {
+    const style = getComputedStyle(node);
+    return style && style.transform !== "none" && style.display !== "inline";
+  }
+
+  _setPolygonPoints(quad, id) {
+    const points = [];
+    for (const point of ["p1", "p2", "p3", "p4"]) {
+      points.push(quad[point].x + "," + quad[point].y);
+    }
+    this.getElement(id).setAttribute("points", points.join(" "));
+  }
+
+  _setLinePoints(p1, p2, id) {
+    const line = this.getElement(id);
+    line.setAttribute("x1", p1.x);
+    line.setAttribute("y1", p1.y);
+    line.setAttribute("x2", p2.x);
+    line.setAttribute("y2", p2.y);
+
+    const dist = Math.sqrt(Math.pow(p2.x - p1.x, 2) + Math.pow(p2.y - p1.y, 2));
+    if (dist < ARROW_LINE_MIN_DISTANCE) {
+      line.removeAttribute("marker-end");
+    } else {
+      line.setAttribute("marker-end", "url(#" + this.markerId + ")");
+    }
+  }
+
+  /**
+   * Update the highlighter on the current highlighted node (the one that was
+   * passed as an argument to show(node)).
+   * Should be called whenever node size or attributes change
+   */
+  _update() {
+    setIgnoreLayoutChanges(true);
+
+    // Getting the points for the transformed shape
+    const quads = this.currentQuads.border;
+    if (
+      !quads.length ||
+      quads[0].bounds.width <= 0 ||
+      quads[0].bounds.height <= 0
+    ) {
+      this._hideShapes();
+      return false;
+    }
+
+    const [quad] = quads;
+
+    // Getting the points for the untransformed shape
+    const untransformedQuad = getNodeBounds(this.win, this.currentNode);
+
+    this._setPolygonPoints(quad, "transformed");
+    this._setPolygonPoints(untransformedQuad, "untransformed");
+    for (const nb of ["1", "2", "3", "4"]) {
+      this._setLinePoints(
+        untransformedQuad["p" + nb],
+        quad["p" + nb],
+        "line" + nb
+      );
+    }
+
+    // Adapt to the current zoom
+    this.markup.scaleRootElement(
+      this.currentNode,
+      this.ID_CLASS_PREFIX + "root"
+    );
+
+    this._showShapes();
+
+    setIgnoreLayoutChanges(
+      false,
+      this.highlighterEnv.window.document.documentElement
+    );
+    return true;
+  }
+
+  /**
+   * Hide the highlighter, the outline and the infobar.
+   */
+  _hide() {
+    setIgnoreLayoutChanges(true);
+    this._hideShapes();
+    setIgnoreLayoutChanges(
+      false,
+      this.highlighterEnv.window.document.documentElement
+    );
+  }
+
+  _hideShapes() {
+    this.getElement("elements").setAttribute("hidden", "true");
+  }
+
+  _showShapes() {
+    this.getElement("elements").removeAttribute("hidden");
+  }
+}
+
+exports.CssTransformHighlighter = CssTransformHighlighter;
diff --git a/devtools/server/actors/highlighters/css/highlighters.css b/devtools/server/actors/highlighters/css/highlighters.css
new file mode 100644
index 0000000000..33c8a04aae
--- /dev/null
+++ b/devtools/server/actors/highlighters/css/highlighters.css
@@ -0,0 +1,1059 @@
+/* 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/. */
+
+:host { display: contents; }
+
+.highlighter-container {
+  --highlighter-accessibility-bounds-color: #6a5acd;
+  --highlighter-accessibility-bounds-opacity: 0.6;
+  --highlighter-box-border-color: #444444;
+  --highlighter-box-content-color: hsl(197, 71%, 73%);
+  --highlighter-box-margin-color: #edff64;
+  --highlighter-box-padding-color: #6a5acd;
+  --highlighter-bubble-text-color: hsl(216, 33%, 97%);
+  --highlighter-bubble-background-color: hsl(214, 13%, 24%);
+  --highlighter-bubble-border-color: rgba(255, 255, 255, 0.2);
+  --highlighter-bubble-arrow-size: 8px;
+  --highlighter-font-family: message-box;
+  --highlighter-font-size: 11px;
+  --highlighter-guide-color: hsl(200, 100%, 40%);
+  --highlighter-infobar-color: hsl(210, 30%, 85%);
+
+  --grey-40: #b1b1b3;
+  --red-40: #ff3b6b;
+  --yellow-60: #d7b600;
+  --blue-60: #0060df;
+}
+
+/**
+ * Highlighters are absolute positioned in the page by default.
+ * A single highlighter can have fixed position in its css class if needed (see below the
+ * eye dropper or rulers highlighter, for example); but if it has to handle the
+ * document's scrolling (as rulers does), it would lag a bit behind due the APZ (Async
+ * Pan/Zoom module), that performs asynchronously panning and zooming on the compositor
+ * thread rather than the main thread.
+ */
+.highlighter-container {
+  position: absolute;
+  width: 100%;
+  height: 100%;
+  /* The container for all highlighters doesn't react to pointer-events by
+     default. This is because most highlighters cover the whole viewport but
+     don't contain UIs that need to be accessed.
+     If your highlighter has UI that needs to be interacted with, add
+     'pointer-events:auto;' on its container element. */
+  pointer-events: none;
+}
+
+.highlighter-container.box-model {
+  /* Make the box-model container have a z-index other than auto so it always sits above
+     other highlighters. */
+  z-index: 1;
+}
+
+.highlighter-container [hidden] {
+  display: none !important;
+}
+
+.highlighter-container [dragging] {
+  cursor: grabbing;
+}
+
+/* Box Model Highlighter */
+
+.box-model-regions {
+  opacity: 0.6;
+}
+
+/* Box model regions can be faded (see the onlyRegionArea option in
+   highlighters.js) in order to only display certain regions. */
+.box-model-regions [faded] {
+  display: none;
+}
+
+.box-model-content {
+  fill: var(--highlighter-box-content-color);
+}
+
+.box-model-padding {
+  fill: var(--highlighter-box-padding-color);
+}
+
+.box-model-border {
+  fill: var(--highlighter-box-border-color);
+}
+
+.box-model-margin {
+  fill: var(--highlighter-box-margin-color);
+}
+
+.box-model-content,
+.box-model-padding,
+.box-model-border,
+.box-model-margin {
+  stroke: none;
+}
+
+.box-model-guide-top,
+.box-model-guide-right,
+.box-model-guide-bottom,
+.box-model-guide-left {
+  stroke: var(--highlighter-guide-color);
+  stroke-dasharray: 5 3;
+  shape-rendering: crispEdges;
+}
+
+@media (prefers-reduced-motion) {
+  .use-simple-highlighters :is(
+     .box-model-content,
+     .box-model-padding,
+     .box-model-border,
+     .box-model-margin
+  ) {
+    fill: none;
+    stroke-width: 3;
+  }
+
+  .use-simple-highlighters .box-model-content {
+    stroke: var(--highlighter-box-content-color);
+  }
+
+  .use-simple-highlighters .box-model-padding {
+    stroke: var(--highlighter-box-padding-color);
+  }
+
+  .use-simple-highlighters .box-model-border {
+    stroke: var(--highlighter-box-border-color);
+  }
+
+  .use-simple-highlighters .box-model-margin {
+    stroke: var(--highlighter-box-margin-color);
+  }
+}
+
+/* Highlighter - Infobar */
+
+[class$="infobar-container"] {
+  position: absolute;
+  max-width: 95%;
+
+  font: var(--highlighter-font-family);
+  font-size: var(--highlighter-font-size);
+}
+
+[class$="infobar"] {
+  position: relative;
+
+  padding: 5px;
+  min-width: 75px;
+
+  border-radius: 3px;
+  background: var(--highlighter-bubble-background-color) no-repeat padding-box;
+
+  color: var(--highlighter-bubble-text-color);
+  text-shadow: none;
+
+  border: 1px solid var(--highlighter-bubble-border-color);
+}
+
+/* Arrows */
+
+[class$="infobar-container"] > [class$="infobar"]:before {
+  left: calc(50% - var(--highlighter-bubble-arrow-size));
+  border: var(--highlighter-bubble-arrow-size) solid
+    var(--highlighter-bubble-border-color);
+}
+
+[class$="infobar-container"] > [class$="infobar"]:after {
+  left: calc(50% - 7px);
+  border: 7px solid var(--highlighter-bubble-background-color);
+}
+
+[class$="infobar-container"] > [class$="infobar"]:before,
+[class$="infobar-container"] > [class$="infobar"]:after {
+  content: "";
+  display: none;
+  position: absolute;
+  height: 0;
+  width: 0;
+  border-left-color: transparent;
+  border-right-color: transparent;
+}
+
+[class$="infobar-container"][position="top"]:not([hide-arrow])
+  > [class$="infobar"]:before,
+[class$="infobar-container"][position="top"]:not([hide-arrow])
+  > [class$="infobar"]:after {
+  border-bottom: 0;
+  top: 100%;
+  display: block;
+}
+
+[class$="infobar-container"][position="bottom"]:not([hide-arrow])
+  > [class$="infobar"]:before,
+[class$="infobar-container"][position="bottom"]:not([hide-arrow])
+  > [class$="infobar"]:after {
+  border-top: 0;
+  bottom: 100%;
+  display: block;
+}
+
+/* Text Container */
+
+[class$="infobar-text"] {
+  overflow: hidden;
+  white-space: nowrap;
+  direction: ltr;
+  padding-bottom: 1px;
+  display: flex;
+  justify-content: center;
+  max-width: 768px;
+}
+
+.box-model-infobar-tagname {
+  color: hsl(285, 100%, 75%);
+}
+
+.box-model-infobar-id {
+  color: hsl(103, 46%, 54%);
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.box-model-infobar-classes,
+.box-model-infobar-pseudo-classes {
+  color: hsl(200, 74%, 57%);
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+[class$="infobar-dimensions"],
+[class$="infobar-grid-type"],
+[class$="infobar-flex-type"] {
+  border-inline-start: 1px solid #5a6169;
+  margin-inline-start: 6px;
+  padding-inline-start: 6px;
+}
+
+[class$="infobar-grid-type"]:empty,
+[class$="infobar-flex-type"]:empty {
+  display: none;
+}
+
+[class$="infobar-dimensions"] {
+  color: var(--highlighter-infobar-color);
+}
+
+[class$="infobar-grid-type"],
+[class$="infobar-flex-type"] {
+  color: var(--grey-40);
+}
+
+/* CSS Grid Highlighter */
+
+.css-grid-canvas {
+  position: absolute;
+  pointer-events: none;
+  top: 0;
+  left: 0;
+  image-rendering: -moz-crisp-edges;
+}
+
+.css-grid-regions {
+  opacity: 0.6;
+}
+
+.css-grid-areas,
+.css-grid-cells {
+  opacity: 0.5;
+  stroke: none;
+}
+
+.css-grid-area-infobar-name,
+.css-grid-cell-infobar-position,
+.css-grid-line-infobar-number {
+  color: hsl(285, 100%, 75%);
+}
+
+.css-grid-line-infobar-names:not(:empty) {
+  color: var(--highlighter-infobar-color);
+  border-inline-start: 1px solid #5a6169;
+  margin-inline-start: 6px;
+  padding-inline-start: 6px;
+}
+
+/* CSS Transform Highlighter */
+
+.css-transform-transformed {
+  fill: var(--highlighter-box-content-color);
+  opacity: 0.8;
+}
+
+.css-transform-untransformed {
+  fill: #66cc52;
+  opacity: 0.8;
+}
+
+.css-transform-transformed,
+.css-transform-untransformed,
+.css-transform-line {
+  stroke: var(--highlighter-guide-color);
+  stroke-dasharray: 5 3;
+  stroke-width: 2;
+}
+
+/* Element Geometry Highlighter */
+
+.geometry-editor-root {
+  /* The geometry editor can be interacted with, so it needs to react to
+     pointer events */
+  pointer-events: auto;
+  user-select: none;
+}
+
+.geometry-editor-offset-parent {
+  stroke: var(--highlighter-guide-color);
+  shape-rendering: crispEdges;
+  stroke-dasharray: 5 3;
+  fill: transparent;
+}
+
+.geometry-editor-current-node {
+  stroke: var(--highlighter-guide-color);
+  fill: var(--highlighter-box-content-color);
+  shape-rendering: crispEdges;
+  opacity: 0.6;
+}
+
+.geometry-editor-arrow {
+  stroke: var(--highlighter-guide-color);
+  shape-rendering: crispEdges;
+}
+
+.geometry-editor-root circle {
+  stroke: var(--highlighter-guide-color);
+  fill: var(--highlighter-box-content-color);
+}
+
+.geometry-editor-handler-top,
+.geometry-editor-handler-bottom {
+  cursor: ns-resize;
+}
+
+.geometry-editor-handler-right,
+.geometry-editor-handler-left {
+  cursor: ew-resize;
+}
+
+[dragging] .geometry-editor-handler-top,
+[dragging] .geometry-editor-handler-right,
+[dragging] .geometry-editor-handler-bottom,
+[dragging] .geometry-editor-handler-left {
+  cursor: grabbing;
+}
+
+.geometry-editor-handler-top.dragging,
+.geometry-editor-handler-right.dragging,
+.geometry-editor-handler-bottom.dragging,
+.geometry-editor-handler-left.dragging {
+  fill: var(--highlighter-guide-color);
+}
+
+.geometry-editor-label-bubble {
+  fill: var(--highlighter-bubble-background-color);
+  shape-rendering: crispEdges;
+}
+
+.geometry-editor-label-text {
+  fill: var(--highlighter-bubble-text-color);
+  font: var(--highlighter-font-family);
+  font-size: 10px;
+  text-anchor: middle;
+  dominant-baseline: middle;
+}
+
+/* Rulers Highlighter */
+
+.rulers-highlighter-elements {
+  shape-rendering: crispEdges;
+  pointer-events: none;
+  position: fixed;
+  top: 0;
+  left: 0;
+}
+
+.rulers-highlighter-elements > g {
+  opacity: 0.8;
+}
+
+.rulers-highlighter-elements > g > rect {
+  fill: #fff;
+}
+
+.rulers-highlighter-ruler-graduations {
+  stroke: #bebebe;
+}
+
+.rulers-highlighter-ruler-markers {
+  stroke: #202020;
+}
+
+.rulers-highlighter-horizontal-labels > text,
+.rulers-highlighter-vertical-labels > text {
+  stroke: none;
+  fill: #202020;
+  font: var(--highlighter-font-family);
+  font-size: 9px;
+  dominant-baseline: hanging;
+}
+
+.rulers-highlighter-horizontal-labels > text {
+  text-anchor: start;
+}
+
+.rulers-highlighter-vertical-labels > text {
+  transform: rotate(-90deg);
+  text-anchor: end;
+}
+
+.viewport-size-highlighter-viewport-infobar-container {
+  shape-rendering: crispEdges;
+  background-color: rgba(255, 255, 255, 0.7);
+  font: var(--highlighter-font-family);
+  position: fixed;
+  top: 30px;
+  right: 0px;
+  font-size: 12px;
+  padding: 4px;
+}
+
+/* Measuring Tool Highlighter */
+
+.measuring-tool-tool {
+  pointer-events: auto;
+}
+
+.measuring-tool-root {
+  position: absolute;
+  top: 0;
+  left: 0;
+  pointer-events: auto;
+  cursor: crosshair;
+}
+
+.measuring-tool-elements {
+  position: absolute;
+}
+
+.measuring-tool-root path {
+  shape-rendering: geometricPrecision;
+  pointer-events: auto;
+}
+
+.measuring-tool-root .measuring-tool-box-path,
+.measuring-tool-root .measuring-tool-diagonal-path {
+  fill: rgba(135, 206, 235, 0.6);
+  stroke: var(--highlighter-guide-color);
+}
+
+.measuring-tool-root circle {
+  stroke: var(--highlighter-guide-color);
+  stroke-width: 2px;
+  fill: #fff;
+  vector-effect: non-scaling-stroke;
+}
+
+.measuring-tool-root circle.highlight {
+  fill: var(--highlighter-guide-color);
+}
+
+.measuring-tool-handler-top,
+.measuring-tool-handler-bottom {
+  cursor: ns-resize;
+}
+
+.measuring-tool-handler-right,
+.measuring-tool-handler-left {
+  cursor: ew-resize;
+}
+
+.measuring-tool-handler-topleft,
+.measuring-tool-handler-bottomright {
+  cursor: nwse-resize;
+}
+
+.measuring-tool-handler-topright,
+.measuring-tool-handler-bottomleft {
+  cursor: nesw-resize;
+}
+
+.mirrored .measuring-tool-handler-topleft,
+.mirrored .measuring-tool-handler-bottomright {
+  cursor: nesw-resize;
+}
+
+.mirrored .measuring-tool-handler-topright,
+.mirrored .measuring-tool-handler-bottomleft {
+  cursor: nwse-resize;
+}
+
+[class^=measuring-tool-handler].dragging {
+  fill: var(--highlighter-guide-color);
+}
+
+.dragging .measuring-tool-box-path,
+.dragging .measuring-tool-diagonal-path {
+  opacity: 0.45;
+}
+
+.measuring-tool-label-size,
+.measuring-tool-label-position {
+  position: absolute;
+  top: 0;
+  left: 0;
+  display: inline-block;
+  border-radius: 4px;
+  padding: 4px;
+  white-space: pre-line;
+  font: var(--highlighter-font-family);
+  font-size: 10px;
+  pointer-events: none;
+  user-select: none;
+  box-sizing: border-box;
+}
+
+.measuring-tool-label-position {
+  color: #fff;
+  background: hsla(214, 13%, 24%, 0.8);
+}
+
+.measuring-tool-label-size {
+  color: var(--highlighter-bubble-text-color);
+  background: var(--highlighter-bubble-background-color);
+  border: 1px solid var(--highlighter-bubble-border-color);
+  line-height: 1.5em;
+}
+
+[class^=measuring-tool-guide] {
+  stroke: var(--highlighter-guide-color);
+  stroke-dasharray: 5 3;
+  shape-rendering: crispEdges;
+}
+
+/* Eye Dropper */
+
+.eye-dropper-root {
+  --magnifier-width: 96px;
+  --magnifier-height: 96px;
+  /* Width accounts for all color formats (hsl being the longest) */
+  --label-width: 160px;
+  --label-height: 23px;
+  --background-color: #e0e0e0;
+  color: #333;
+
+  position: fixed;
+  /* Tool start position. This should match the X/Y defines in JS */
+  top: 100px;
+  left: 100px;
+
+  /* Prevent interacting with the page when hovering and clicking */
+  pointer-events: auto;
+
+  /* Offset the UI so it is centered around the pointer */
+  transform: translate(
+    calc(var(--magnifier-width) / -2),
+    calc(var(--magnifier-height) / -2)
+  );
+
+  filter: drop-shadow(0 0 1px rgba(0, 0, 0, 0.4));
+
+  /* We don't need the UI to be reversed in RTL locales, otherwise the # would appear
+     to the right of the hex code. Force LTR */
+  direction: ltr;
+}
+
+.eye-dropper-canvas {
+  image-rendering: -moz-crisp-edges;
+  cursor: none;
+  width: var(--magnifier-width);
+  height: var(--magnifier-height);
+  border-radius: 50%;
+  box-shadow: 0 0 0 3px var(--background-color);
+  display: block;
+}
+
+.eye-dropper-color-container {
+  background-color: var(--background-color);
+  border-radius: 2px;
+  width: var(--label-width);
+  height: var(--label-height);
+  position: relative;
+
+  --label-horizontal-center: translateX(
+    calc((var(--magnifier-width) - var(--label-width)) / 2)
+  );
+  --label-horizontal-left: translateX(
+    calc((-1 * var(--label-width) + var(--magnifier-width) / 2))
+  );
+  --label-horizontal-right: translateX(calc(var(--magnifier-width) / 2));
+  --label-vertical-top: translateY(
+    calc((-1 * var(--magnifier-height)) - var(--label-height))
+  );
+
+  /* By default the color label container sits below the canvas.
+     Here we just center it horizontally */
+  transform: var(--label-horizontal-center);
+  transition: transform 0.1s ease-in-out;
+}
+
+/* If there isn't enough space below the canvas, we move the label container to the top */
+.eye-dropper-root[top] .eye-dropper-color-container {
+  transform: var(--label-horizontal-center) var(--label-vertical-top);
+}
+
+/* If there isn't enough space right of the canvas to horizontally center the label
+   container, offset it to the left */
+.eye-dropper-root[left] .eye-dropper-color-container {
+  transform: var(--label-horizontal-left);
+}
+
+.eye-dropper-root[left][top] .eye-dropper-color-container {
+  transform: var(--label-horizontal-left) var(--label-vertical-top);
+}
+
+/* If there isn't enough space left of the canvas to horizontally center the label
+   container, offset it to the right */
+.eye-dropper-root[right] .eye-dropper-color-container {
+  transform: var(--label-horizontal-right);
+}
+
+.eye-dropper-root[right][top] .eye-dropper-color-container {
+  transform: var(--label-horizontal-right) var(--label-vertical-top);
+}
+
+.eye-dropper-color-preview {
+  width: 16px;
+  height: 16px;
+  position: absolute;
+  inset-inline-start: 3px;
+  inset-block-start: 3px;
+  box-shadow: 0px 0px 0px black;
+  border: solid 1px #fff;
+}
+
+.eye-dropper-color-value {
+  text-shadow: 1px 1px 1px #fff;
+  font: var(--highlighter-font-family);
+  font-size: var(--highlighter-font-size);
+  text-align: center;
+  padding: 4px 0;
+}
+
+/* Paused Debugger Overlay */
+
+.paused-dbg-root {
+  position: fixed;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+
+  width: 100vw;
+  height: 100vh;
+
+  display: flex;
+  align-items: center;
+  flex-direction: column;
+
+  /* We don't have access to DevTools themes here, but some of these colors come from the
+     themes. Theme variable names are given in comments. */
+  --text-color: #585959; /* --theme-body-color-alt */
+  --toolbar-background: #fcfcfc; /* --theme-toolbar-background */
+  --toolbar-border: #dde1e4; /* --theme-splitter-color */
+  --toolbar-box-shadow: 0 2px 2px 0 rgba(155, 155, 155, 0.26); /* --rdm-box-shadow */
+  --overlay-background: #dde1e4a8;
+}
+
+.paused-dbg-root[overlay] {
+  background-color: var(--overlay-background);
+  pointer-events: auto;
+}
+
+.paused-dbg-toolbar {
+  /* Show the toolbar at the top, but not too high to prevent it overlaping OS toolbar on Android */
+  margin-top: 30px;
+  display: inline-flex;
+  user-select: none;
+
+  color: var(--text-color);
+  box-shadow: var(--toolbar-box-shadow);
+  background-color: var(--toolbar-background);
+  border: 1px solid var(--toolbar-border);
+  border-radius: 4px;
+
+  font: var(--highlighter-font-family);
+  font-size: var(--highlighter-font-size);
+}
+
+.paused-dbg-toolbar button {
+  margin: 8px 4px 6px 6px;
+  width: 16px;
+  height: 16px;
+  mask-repeat: no-repeat;
+  mask-position: center;
+  mask-size: 16px 16px;
+  background-color: var(--text-color);
+
+  border: 0px;
+  appearance: none;
+}
+
+.paused-dbg-divider {
+  width: 1px;
+  height: 16px;
+  margin-top: 10px;
+  background-color: var(--toolbar-border);
+}
+
+.paused-dbg-reason,
+.paused-dbg-step-button-wrapper,
+.paused-dbg-resume-button-wrapper {
+  margin-top: 2px;
+  margin-bottom: 2px;
+}
+
+.paused-dbg-step-button-wrapper,
+.paused-dbg-resume-button-wrapper {
+  margin-left: 2px;
+  margin-right: 2px;
+}
+
+button.paused-dbg-step-button {
+  margin-left: 6px;
+  margin-right: 6px;
+  mask-image: url(resource://devtools-shared-images/stepOver.svg);
+  padding: 0;
+}
+
+button.paused-dbg-resume-button {
+  margin-right: 6px;
+  mask-image: url(resource://devtools-shared-images/resume.svg);
+  padding: 0;
+}
+
+.paused-dbg-step-button-wrapper.hover,
+.paused-dbg-resume-button-wrapper.hover {
+  background-color: var(--toolbar-border);
+  border-radius: 2px;
+}
+
+.paused-dbg-reason {
+  padding: 3px 16px;
+  margin: 8px 0px;
+  font: var(--highlighter-font-family);
+  font-size: var(--highlighter-font-size);
+}
+
+
+/* Remote Node Picker Notice Highlighter */
+
+#node-picker-notice-root {
+  position: fixed;
+  max-width: 100vw;
+  /* Position at the bottom of the screen so it doesn't get into the user's way */
+  bottom: 0;
+  left: 0;
+  right: 0;
+
+  z-index: 2;
+
+  display: flex;
+  align-items: center;
+  flex-direction: column;
+
+  /* We don't have access to DevTools themes here, but some of these colors come from the
+     themes. Theme variable names are given in comments. */
+  --text-color: #585959; /* --theme-body-color-alt */
+  --toolbar-background: #fcfcfc; /* --theme-toolbar-background */
+  --toolbar-border: #dde1e4; /* --theme-splitter-color */
+  --toolbar-button-hover-background: rgba(12, 12, 13, 0.15); /* --theme-toolbarbutton-hover-background */
+  --toolbar-box-shadow: 0 2px 2px 0 rgba(155, 155, 155, 0.26); /* --rdm-box-shadow */
+}
+
+#node-picker-notice-root[overlay] {
+  pointer-events: auto;
+}
+
+#node-picker-notice-toolbar {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+
+  padding: 8px 16px;
+
+  color: var(--text-color);
+  box-shadow: var(--toolbar-box-shadow);
+  background-color: var(--toolbar-background);
+  border: 1px solid var(--toolbar-border);
+  border-radius: 2px;
+
+  font: var(--highlighter-font-family);
+  font-size: var(--highlighter-font-size);
+
+  user-select: none;
+}
+
+#node-picker-notice-info {
+  font: var(--highlighter-font-family);
+  font-size: var(--highlighter-font-size);
+  text-align: center;
+}
+
+#node-picker-notice-icon {
+  width: 16px;
+  height: 16px;
+
+  background-image: url(resource://devtools-shared-images/command-pick.svg);
+  -moz-context-properties: fill;
+  fill: currentColor;
+
+  background-size: contain;
+  background-repeat: no-repeat;
+}
+
+#node-picker-notice-icon.touch {
+  background-image: url(resource://devtools-shared-images/command-pick-remote-touch.svg);
+}
+
+
+#node-picker-notice-hide-button {
+  border: 0px;
+  border-radius: 2px;
+  appearance: none;
+  background-color: var(--toolbar-border);
+  color: currentColor;
+  font-size: 1em;
+  padding-inline: 4px;
+}
+
+/* We can't use :hover as it wouldn't work if the page is paused, so we add a specific class for this */
+#node-picker-notice-hide-button.hover {
+  background-color: var(--toolbar-button-hover-background);
+}
+
+/* Shapes highlighter */
+
+.shapes-root {
+  pointer-events: none;
+}
+
+.shapes-shape-container {
+  position: absolute;
+  overflow: visible;
+}
+
+.shapes-polygon,
+.shapes-ellipse,
+.shapes-rect,
+.shapes-bounding-box,
+.shapes-rotate-line,
+.shapes-quad {
+  fill: transparent;
+  stroke: var(--highlighter-guide-color);
+  shape-rendering: geometricPrecision;
+  vector-effect: non-scaling-stroke;
+}
+
+.shapes-markers {
+  fill: #fff;
+}
+
+.shapes-markers-outline {
+  fill: var(--highlighter-guide-color);
+}
+
+.shapes-marker-hover {
+  fill: var(--highlighter-guide-color);
+}
+
+/* Accessible highlighter */
+
+.accessible-infobar {
+  min-width: unset;
+}
+
+.accessible-infobar-text {
+  display: grid;
+  grid-template-areas:
+    "role name"
+    "audit audit";
+  grid-template-columns: min-content 1fr;
+}
+
+.accessible-infobar-role {
+  grid-area: role;
+  color: #9cdcfe;
+}
+
+.accessible-infobar-name {
+  grid-area: name;
+}
+
+.accessible-infobar-audit {
+  grid-area: audit;
+  padding-top: 5px;
+  padding-bottom: 2px;
+}
+
+.accessible-bounds {
+  fill: var(--highlighter-accessibility-bounds-color);
+  opacity: var(--highlighter-accessibility-bounds-opacity);
+}
+
+@media (prefers-reduced-motion) {
+  .use-simple-highlighters .accessible-bounds {
+    fill: none;
+    stroke: var(--highlighter-accessibility-bounds-color);
+    stroke-width: 3;
+  }
+}
+
+.accessible-infobar-name,
+.accessible-infobar-audit {
+  color: var(--highlighter-infobar-color);
+}
+
+.accessible-infobar-audit .accessible-contrast-ratio:empty::before,
+.accessible-infobar-audit .accessible-contrast-ratio:empty::after,
+.accessible-infobar-name:empty {
+  display: none;
+}
+
+.accessible-infobar-audit .accessible-contrast-ratio::before {
+  content: "";
+  height: 8px;
+  width: 8px;
+  display: inline-flex;
+  background-color: var(--accessibility-highlighter-contrast-ratio-color);
+  box-shadow: 0 0 0 1px var(--grey-40),
+    4px 3px var(--accessibility-highlighter-contrast-ratio-bg),
+    4px 3px 0 1px var(--grey-40);
+  margin-inline-start: 3px;
+  margin-inline-end: 9px;
+}
+
+.accessible-infobar-audit .accessible-contrast-ratio::after {
+  margin-inline-start: 2px;
+}
+
+.accessible-infobar-audit .accessible-contrast-ratio.AA::after,
+.accessible-infobar-audit .accessible-contrast-ratio.AAA::after {
+  color: #90E274;
+}
+
+.accessible-infobar-audit .accessible-audit::before,
+.accessible-infobar-audit .accessible-contrast-ratio.FAIL::after {
+  display: inline-block;
+  width: 12px;
+  height: 12px;
+  content: "";
+  vertical-align: -2px;
+  background-position: center;
+  background-repeat: no-repeat;
+  -moz-context-properties: fill;
+}
+
+.accessible-infobar-audit .accessible-contrast-ratio.FAIL:after {
+  color: #E57180;
+  margin-inline-start: 3px;
+  background-image: url(resource://devtools-shared-images/error-small.svg);
+  fill: var(--red-40);
+}
+
+.accessible-infobar-audit .accessible-contrast-ratio.AA::after {
+  content: "AA\2713";
+}
+
+.accessible-infobar-audit .accessible-contrast-ratio.AAA::after {
+  content: "AAA\2713";
+}
+
+.accessible-infobar-audit .accessible-contrast-ratio-label,
+.accessible-infobar-audit .accessible-contrast-ratio-separator::before {
+  margin-inline-end: 3px;
+}
+
+.accessible-infobar-audit .accessible-contrast-ratio-separator::before {
+  content: "-";
+  margin-inline-start: 3px;
+}
+
+.accessible-infobar-audit .accessible-audit {
+  display: block;
+  padding-block-end: 5px;
+}
+
+.accessible-infobar-audit .accessible-audit:last-child {
+  padding-block-end: 0;
+}
+
+.accessible-infobar-audit .accessible-audit::before {
+  margin-inline-end: 4px;
+  background-image: none;
+  fill: currentColor;
+}
+
+.accessible-infobar-audit .accessible-audit.FAIL::before {
+  background-image: url(resource://devtools-shared-images/error-small.svg);
+  fill: var(--red-40);
+}
+
+.accessible-infobar-audit .accessible-audit.WARNING::before {
+  background-image: url(chrome://devtools/skin/images/alert-small.svg);
+  fill: var(--yellow-60);
+}
+
+.accessible-infobar-audit .accessible-audit.BEST_PRACTICES::before {
+  background-image: url(chrome://devtools/skin/images/info-small.svg);
+}
+
+.accessible-infobar-name {
+  border-inline-start: 1px solid #5a6169;
+  margin-inline-start: 6px;
+  padding-inline-start: 6px;
+}
+
+/* Tabbing-order highlighter */
+
+.tabbing-order-infobar {
+  min-width: unset;
+}
+
+.tabbing-order .tabbing-order-infobar-container {
+  font-size:calc(var(--highlighter-font-size) + 2px);
+}
+
+.tabbing-order .tabbing-order-bounds {
+  position: absolute;
+  display: block;
+  outline: 2px solid #000;
+  outline-offset: -2px;
+}
+
+.tabbing-order.focused .tabbing-order-bounds {
+  outline-color: var(--blue-60);
+}
+
+.tabbing-order.focused .tabbing-order-infobar {
+  background-color: var(--blue-60);
+}
+
+.tabbing-order.focused .tabbing-order-infobar-text {
+  text-decoration: underline;
+}
+
+.tabbing-order.focused .tabbing-order-infobar:after {
+  border-top-color: var(--blue-60);
+  border-bottom-color: var(--blue-60);
+}
diff --git a/devtools/server/actors/highlighters/css/moz.build b/devtools/server/actors/highlighters/css/moz.build
new file mode 100644
index 0000000000..6bdf0f9579
--- /dev/null
+++ b/devtools/server/actors/highlighters/css/moz.build
@@ -0,0 +1,9 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+DevToolsModules(
+    "highlighters.css",
+)
diff --git a/devtools/server/actors/highlighters/eye-dropper.js b/devtools/server/actors/highlighters/eye-dropper.js
new file mode 100644
index 0000000000..8a206bc84f
--- /dev/null
+++ b/devtools/server/actors/highlighters/eye-dropper.js
@@ -0,0 +1,608 @@
+/* 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/. */
+"use strict";
+
+// Eye-dropper tool. This is implemented as a highlighter so it can be displayed in the
+// content page.
+// It basically displays a magnifier that tracks mouse moves and shows a magnified version
+// of the page. On click, it samples the color at the pixel being hovered.
+
+const {
+  CanvasFrameAnonymousContentHelper,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+const EventEmitter = require("resource://devtools/shared/event-emitter.js");
+const { rgbToHsl } =
+  require("resource://devtools/shared/css/color.js").colorUtils;
+const {
+  getCurrentZoom,
+  getFrameOffsets,
+} = require("resource://devtools/shared/layout/utils.js");
+
+loader.lazyGetter(this, "clipboardHelper", () =>
+  Cc["@mozilla.org/widget/clipboardhelper;1"].getService(Ci.nsIClipboardHelper)
+);
+loader.lazyGetter(this, "l10n", () =>
+  Services.strings.createBundle(
+    "chrome://devtools-shared/locale/eyedropper.properties"
+  )
+);
+
+const ZOOM_LEVEL_PREF = "devtools.eyedropper.zoom";
+const FORMAT_PREF = "devtools.defaultColorUnit";
+// Width of the canvas.
+const MAGNIFIER_WIDTH = 96;
+// Height of the canvas.
+const MAGNIFIER_HEIGHT = 96;
+// Start position, when the tool is first shown. This should match the top/left position
+// defined in CSS.
+const DEFAULT_START_POS_X = 100;
+const DEFAULT_START_POS_Y = 100;
+// How long to wait before closing after copy.
+const CLOSE_DELAY = 750;
+
+/**
+ * The EyeDropper allows the user to select a color of a pixel within the content page,
+ * showing a magnified circle and color preview while the user hover the page.
+ */
+class EyeDropper {
+  #pageEventListenersAbortController;
+  constructor(highlighterEnv) {
+    EventEmitter.decorate(this);
+
+    this.highlighterEnv = highlighterEnv;
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      this.highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.markup.initialize();
+
+    // Get a couple of settings from prefs.
+    this.format = Services.prefs.getCharPref(FORMAT_PREF);
+    this.eyeDropperZoomLevel = Services.prefs.getIntPref(ZOOM_LEVEL_PREF);
+  }
+
+  ID_CLASS_PREFIX = "eye-dropper-";
+
+  get win() {
+    return this.highlighterEnv.window;
+  }
+
+  _buildMarkup() {
+    // Highlighter main container.
+    const container = this.markup.createNode({
+      attributes: { class: "highlighter-container" },
+    });
+
+    // Wrapper element.
+    const wrapper = this.markup.createNode({
+      parent: container,
+      attributes: {
+        id: "root",
+        class: "root",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // The magnifier canvas element.
+    this.markup.createNode({
+      parent: wrapper,
+      nodeType: "canvas",
+      attributes: {
+        id: "canvas",
+        class: "canvas",
+        width: MAGNIFIER_WIDTH,
+        height: MAGNIFIER_HEIGHT,
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // The color label element.
+    const colorLabelContainer = this.markup.createNode({
+      parent: wrapper,
+      attributes: { class: "color-container" },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "div",
+      parent: colorLabelContainer,
+      attributes: { id: "color-preview", class: "color-preview" },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+    this.markup.createNode({
+      nodeType: "div",
+      parent: colorLabelContainer,
+      attributes: { id: "color-value", class: "color-value" },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    return container;
+  }
+
+  destroy() {
+    this.hide();
+    this.markup.destroy();
+  }
+
+  getElement(id) {
+    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
+  }
+
+  /**
+   * Show the eye-dropper highlighter.
+   *
+   * @param {DOMNode} node The node which document the highlighter should be inserted in.
+   * @param {Object} options The options object may contain the following properties:
+   * - {Boolean} copyOnSelect: Whether selecting a color should copy it to the clipboard.
+   * - {String|null} screenshot: a dataURL representation of the page screenshot. If null,
+   *                 the eyedropper will use `drawWindow` to get the the screenshot
+   *                 (⚠️ but it won't handle remote frames).
+   */
+  show(node, options = {}) {
+    if (this.highlighterEnv.isXUL) {
+      return false;
+    }
+
+    this.options = options;
+
+    // Get the page's current zoom level.
+    this.pageZoom = getCurrentZoom(this.win);
+
+    // Take a screenshot of the viewport. This needs to be done first otherwise the
+    // eyedropper UI will appear in the screenshot itself (since the UI is injected as
+    // native anonymous content in the page).
+    // Once the screenshot is ready, the magnified area will be drawn.
+    this.prepareImageCapture(options.screenshot);
+
+    // Start listening for user events.
+    const { pageListenerTarget } = this.highlighterEnv;
+    this.#pageEventListenersAbortController = new AbortController();
+    const signal = this.#pageEventListenersAbortController.signal;
+    pageListenerTarget.addEventListener("mousemove", this, { signal });
+    pageListenerTarget.addEventListener("click", this, {
+      signal,
+      useCapture: true,
+    });
+    pageListenerTarget.addEventListener("keydown", this, { signal });
+    pageListenerTarget.addEventListener("DOMMouseScroll", this, { signal });
+    pageListenerTarget.addEventListener("FullZoomChange", this, { signal });
+
+    // Show the eye-dropper.
+    this.getElement("root").removeAttribute("hidden");
+
+    // Prepare the canvas context on which we're drawing the magnified page portion.
+    this.ctx = this.getElement("canvas").getCanvasContext();
+    this.ctx.imageSmoothingEnabled = false;
+
+    this.magnifiedArea = {
+      width: MAGNIFIER_WIDTH,
+      height: MAGNIFIER_HEIGHT,
+      x: DEFAULT_START_POS_X,
+      y: DEFAULT_START_POS_Y,
+    };
+
+    this.moveTo(DEFAULT_START_POS_X, DEFAULT_START_POS_Y);
+
+    // Focus the content so the keyboard can be used.
+    this.win.focus();
+
+    // Make sure we receive mouse events when the debugger has paused execution
+    // in the page.
+    this.win.document.setSuppressedEventListener(this);
+
+    return true;
+  }
+
+  /**
+   * Hide the eye-dropper highlighter.
+   */
+  hide() {
+    this.pageImage = null;
+
+    if (this.#pageEventListenersAbortController) {
+      this.#pageEventListenersAbortController.abort();
+      this.#pageEventListenersAbortController = null;
+
+      const rootElement = this.getElement("root");
+      rootElement.setAttribute("hidden", "true");
+      rootElement.removeAttribute("drawn");
+
+      this.emit("hidden");
+
+      this.win.document.setSuppressedEventListener(null);
+    }
+  }
+
+  /**
+   * Convert a base64 png data-uri to raw binary data.
+   */
+  #dataURItoBlob(dataURI) {
+    const byteString = atob(dataURI.split(",")[1]);
+
+    // write the bytes of the string to an ArrayBuffer
+    const buffer = new ArrayBuffer(byteString.length);
+    // Update the buffer through a typed array.
+    const typedArray = new Uint8Array(buffer);
+    for (let i = 0; i < byteString.length; i++) {
+      typedArray[i] = byteString.charCodeAt(i);
+    }
+
+    return new Blob([buffer], { type: "image/png" });
+  }
+
+  /**
+   * Create an image bitmap from the page screenshot, draw the eyedropper and set the
+   * "drawn" attribute on the "root" element once it's done.
+   *
+   * @params {String|null} screenshot: a dataURL representation of the page screenshot.
+   *                       If null, we'll use `drawWindow` to get the the page screenshot
+   *                       (⚠️ but it won't handle remote frames).
+   */
+  async prepareImageCapture(screenshot) {
+    let imageSource;
+    if (screenshot) {
+      imageSource = this.#dataURItoBlob(screenshot);
+    } else {
+      imageSource = getWindowAsImageData(this.win);
+    }
+
+    // We need to transform the blob/imageData to something drawWindow will consume.
+    // An ImageBitmap works well. We could have used an Image, but doing so results
+    // in errors if the page defines CSP headers.
+    const image = await this.win.createImageBitmap(imageSource);
+
+    this.pageImage = image;
+    // We likely haven't drawn anything yet (no mousemove events yet), so start now.
+    this.draw();
+
+    // Set an attribute on the root element to be able to run tests after the first draw
+    // was done.
+    this.getElement("root").setAttribute("drawn", "true");
+  }
+
+  /**
+   * Get the number of cells (blown-up pixels) per direction in the grid.
+   */
+  get cellsWide() {
+    // Canvas will render whole "pixels" (cells) only, and an even number at that. Round
+    // up to the nearest even number of pixels.
+    let cellsWide = Math.ceil(
+      this.magnifiedArea.width / this.eyeDropperZoomLevel
+    );
+    cellsWide += cellsWide % 2;
+
+    return cellsWide;
+  }
+
+  /**
+   * Get the size of each cell (blown-up pixel) in the grid.
+   */
+  get cellSize() {
+    return this.magnifiedArea.width / this.cellsWide;
+  }
+
+  /**
+   * Get index of cell in the center of the grid.
+   */
+  get centerCell() {
+    return Math.floor(this.cellsWide / 2);
+  }
+
+  /**
+   * Get color of center cell in the grid.
+   */
+  get centerColor() {
+    const pos = this.centerCell * this.cellSize + this.cellSize / 2;
+    const rgb = this.ctx.getImageData(pos, pos, 1, 1).data;
+    return rgb;
+  }
+
+  draw() {
+    // If the image of the page isn't ready yet, bail out, we'll draw later on mousemove.
+    if (!this.pageImage) {
+      return;
+    }
+
+    const { width, height, x, y } = this.magnifiedArea;
+
+    const zoomedWidth = width / this.eyeDropperZoomLevel;
+    const zoomedHeight = height / this.eyeDropperZoomLevel;
+
+    const sx = x - zoomedWidth / 2;
+    const sy = y - zoomedHeight / 2;
+    const sw = zoomedWidth;
+    const sh = zoomedHeight;
+
+    this.ctx.drawImage(this.pageImage, sx, sy, sw, sh, 0, 0, width, height);
+
+    // Draw the grid on top, but only at 3x or more, otherwise it's too busy.
+    if (this.eyeDropperZoomLevel > 2) {
+      this.drawGrid();
+    }
+
+    this.drawCrosshair();
+
+    // Update the color preview and value.
+    const rgb = this.centerColor;
+    this.getElement("color-preview").setAttribute(
+      "style",
+      `background-color:${toColorString(rgb, "rgb")};`
+    );
+    this.getElement("color-value").setTextContent(
+      toColorString(rgb, this.format)
+    );
+  }
+
+  /**
+   * Draw a grid on the canvas representing pixel boundaries.
+   */
+  drawGrid() {
+    const { width, height } = this.magnifiedArea;
+
+    this.ctx.lineWidth = 1;
+    this.ctx.strokeStyle = "rgba(143, 143, 143, 0.2)";
+
+    for (let i = 0; i < width; i += this.cellSize) {
+      this.ctx.beginPath();
+      this.ctx.moveTo(i - 0.5, 0);
+      this.ctx.lineTo(i - 0.5, height);
+      this.ctx.stroke();
+
+      this.ctx.beginPath();
+      this.ctx.moveTo(0, i - 0.5);
+      this.ctx.lineTo(width, i - 0.5);
+      this.ctx.stroke();
+    }
+  }
+
+  /**
+   * Draw a box on the canvas to highlight the center cell.
+   */
+  drawCrosshair() {
+    const pos = this.centerCell * this.cellSize;
+
+    this.ctx.lineWidth = 1;
+    this.ctx.lineJoin = "miter";
+    this.ctx.strokeStyle = "rgba(0, 0, 0, 1)";
+    this.ctx.strokeRect(
+      pos - 1.5,
+      pos - 1.5,
+      this.cellSize + 2,
+      this.cellSize + 2
+    );
+
+    this.ctx.strokeStyle = "rgba(255, 255, 255, 1)";
+    this.ctx.strokeRect(pos - 0.5, pos - 0.5, this.cellSize, this.cellSize);
+  }
+
+  handleEvent(e) {
+    switch (e.type) {
+      case "mousemove":
+        // We might be getting an event from a child frame, so account for the offset.
+        const [xOffset, yOffset] = getFrameOffsets(this.win, e.target);
+        const x = xOffset + e.pageX - this.win.scrollX;
+        const y = yOffset + e.pageY - this.win.scrollY;
+        // Update the zoom area.
+        this.magnifiedArea.x = x * this.pageZoom;
+        this.magnifiedArea.y = y * this.pageZoom;
+        // Redraw the portion of the screenshot that is now under the mouse.
+        this.draw();
+        // And move the eye-dropper's UI so it follows the mouse.
+        this.moveTo(x, y);
+        break;
+      // Note: when events are suppressed we will only get mousedown/mouseup and
+      // not any click events.
+      case "click":
+      case "mouseup":
+        this.selectColor();
+        break;
+      case "keydown":
+        this.handleKeyDown(e);
+        break;
+      case "DOMMouseScroll":
+        // Prevent scrolling. That's because we only took a screenshot of the viewport, so
+        // scrolling out of the viewport wouldn't draw the expected things. In the future
+        // we can take the screenshot again on scroll, but for now it doesn't seem
+        // important.
+        e.preventDefault();
+        break;
+      case "FullZoomChange":
+        this.hide();
+        this.show();
+        break;
+    }
+  }
+
+  moveTo(x, y) {
+    const root = this.getElement("root");
+    root.setAttribute("style", `top:${y}px;left:${x}px;`);
+
+    // Move the label container to the top if the magnifier is close to the bottom edge.
+    if (y >= this.win.innerHeight - MAGNIFIER_HEIGHT) {
+      root.setAttribute("top", "");
+    } else {
+      root.removeAttribute("top");
+    }
+
+    // Also offset the label container to the right or left if the magnifier is close to
+    // the edge.
+    root.removeAttribute("left");
+    root.removeAttribute("right");
+    if (x <= MAGNIFIER_WIDTH) {
+      root.setAttribute("right", "");
+    } else if (x >= this.win.innerWidth - MAGNIFIER_WIDTH) {
+      root.setAttribute("left", "");
+    }
+  }
+
+  /**
+   * Select the current color that's being previewed. Depending on the current options,
+   * selecting might mean copying to the clipboard and closing the
+   */
+  selectColor() {
+    let onColorSelected = Promise.resolve();
+    if (this.options.copyOnSelect) {
+      onColorSelected = this.copyColor();
+    }
+
+    this.emit("selected", toColorString(this.centerColor, this.format));
+    onColorSelected.then(() => this.hide(), console.error);
+  }
+
+  /**
+   * Handler for the keydown event. Either select the color or move the panel in a
+   * direction depending on the key pressed.
+   */
+  handleKeyDown(e) {
+    // Bail out early if any unsupported modifier is used, so that we let
+    // keyboard shortcuts through.
+    if (e.metaKey || e.ctrlKey || e.altKey) {
+      return;
+    }
+
+    if (e.keyCode === e.DOM_VK_RETURN) {
+      this.selectColor();
+      e.preventDefault();
+      return;
+    }
+
+    if (e.keyCode === e.DOM_VK_ESCAPE) {
+      this.emit("canceled");
+      this.hide();
+      e.preventDefault();
+      return;
+    }
+
+    let offsetX = 0;
+    let offsetY = 0;
+    let modifier = 1;
+
+    if (e.keyCode === e.DOM_VK_LEFT) {
+      offsetX = -1;
+    } else if (e.keyCode === e.DOM_VK_RIGHT) {
+      offsetX = 1;
+    } else if (e.keyCode === e.DOM_VK_UP) {
+      offsetY = -1;
+    } else if (e.keyCode === e.DOM_VK_DOWN) {
+      offsetY = 1;
+    }
+
+    if (e.shiftKey) {
+      modifier = 10;
+    }
+
+    offsetY *= modifier;
+    offsetX *= modifier;
+
+    if (offsetX !== 0 || offsetY !== 0) {
+      this.magnifiedArea.x = cap(
+        this.magnifiedArea.x + offsetX,
+        0,
+        this.win.innerWidth * this.pageZoom
+      );
+      this.magnifiedArea.y = cap(
+        this.magnifiedArea.y + offsetY,
+        0,
+        this.win.innerHeight * this.pageZoom
+      );
+
+      this.draw();
+
+      this.moveTo(
+        this.magnifiedArea.x / this.pageZoom,
+        this.magnifiedArea.y / this.pageZoom
+      );
+
+      e.preventDefault();
+    }
+  }
+
+  /**
+   * Copy the currently inspected color to the clipboard.
+   * @return {Promise} Resolves when the copy has been done (after a delay that is used to
+   * let users know that something was copied).
+   */
+  copyColor() {
+    // Copy to the clipboard.
+    const color = toColorString(this.centerColor, this.format);
+    clipboardHelper.copyString(color);
+
+    // Provide some feedback.
+    this.getElement("color-value").setTextContent(
+      "✓ " + l10n.GetStringFromName("colorValue.copied")
+    );
+
+    // Hide the tool after a delay.
+    clearTimeout(this._copyTimeout);
+    return new Promise(resolve => {
+      this._copyTimeout = setTimeout(resolve, CLOSE_DELAY);
+    });
+  }
+}
+
+exports.EyeDropper = EyeDropper;
+
+/**
+ * Draw the visible portion of the window on a canvas and get the resulting ImageData.
+ * @param {Window} win
+ * @return {ImageData} The image data for the window.
+ */
+function getWindowAsImageData(win) {
+  const canvas = win.document.createElementNS(
+    "http://www.w3.org/1999/xhtml",
+    "canvas"
+  );
+  const scale = getCurrentZoom(win);
+  const width = win.innerWidth;
+  const height = win.innerHeight;
+  canvas.width = width * scale;
+  canvas.height = height * scale;
+  canvas.mozOpaque = true;
+
+  const ctx = canvas.getContext("2d");
+
+  ctx.scale(scale, scale);
+  ctx.drawWindow(win, win.scrollX, win.scrollY, width, height, "#fff");
+
+  return ctx.getImageData(0, 0, canvas.width, canvas.height);
+}
+
+/**
+ * Get a formatted CSS color string from a color value.
+ * @param {array} rgb Rgb values of a color to format.
+ * @param {string} format Format of string. One of "hex", "rgb", "hsl", "name".
+ * @return {string} Formatted color value, e.g. "#FFF" or "hsl(20, 10%, 10%)".
+ */
+function toColorString(rgb, format) {
+  const [r, g, b] = rgb;
+
+  switch (format) {
+    case "hex":
+      return hexString(rgb);
+    case "rgb":
+      return "rgb(" + r + ", " + g + ", " + b + ")";
+    case "hsl":
+      const [h, s, l] = rgbToHsl(rgb);
+      return "hsl(" + h + ", " + s + "%, " + l + "%)";
+    case "name":
+      const str = InspectorUtils.rgbToColorName(r, g, b) || hexString(rgb);
+      return str;
+    default:
+      return hexString(rgb);
+  }
+}
+
+/**
+ * Produce a hex-formatted color string from rgb values.
+ * @param {array} rgb Rgb values of color to stringify.
+ * @return {string} Hex formatted string for color, e.g. "#FFEE00".
+ */
+function hexString([r, g, b]) {
+  const val = (1 << 24) + (r << 16) + (g << 8) + (b << 0);
+  return "#" + val.toString(16).substr(-6);
+}
+
+function cap(value, min, max) {
+  return Math.max(min, Math.min(value, max));
+}
diff --git a/devtools/server/actors/highlighters/flexbox.js b/devtools/server/actors/highlighters/flexbox.js
new file mode 100644
index 0000000000..820e4f8a73
--- /dev/null
+++ b/devtools/server/actors/highlighters/flexbox.js
@@ -0,0 +1,1033 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  AutoRefreshHighlighter,
+} = require("resource://devtools/server/actors/highlighters/auto-refresh.js");
+const { apply } = require("resource://devtools/shared/layout/dom-matrix-2d.js");
+const {
+  CANVAS_SIZE,
+  DEFAULT_COLOR,
+  clearRect,
+  drawLine,
+  drawRect,
+  getCurrentMatrix,
+  updateCanvasElement,
+  updateCanvasPosition,
+} = require("resource://devtools/server/actors/highlighters/utils/canvas.js");
+const {
+  CanvasFrameAnonymousContentHelper,
+  getComputedStyle,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+const {
+  getAbsoluteScrollOffsetsForNode,
+  getCurrentZoom,
+  getDisplayPixelRatio,
+  getUntransformedQuad,
+  getWindowDimensions,
+  setIgnoreLayoutChanges,
+} = require("resource://devtools/shared/layout/utils.js");
+
+const FLEXBOX_LINES_PROPERTIES = {
+  edge: {
+    lineDash: [5, 3],
+  },
+  item: {
+    lineDash: [0, 0],
+  },
+  alignItems: {
+    lineDash: [0, 0],
+  },
+};
+
+const FLEXBOX_CONTAINER_PATTERN_LINE_DASH = [5, 3]; // px
+const FLEXBOX_CONTAINER_PATTERN_WIDTH = 14; // px
+const FLEXBOX_CONTAINER_PATTERN_HEIGHT = 14; // px
+const FLEXBOX_JUSTIFY_CONTENT_PATTERN_WIDTH = 7; // px
+const FLEXBOX_JUSTIFY_CONTENT_PATTERN_HEIGHT = 7; // px
+
+/**
+ * Cached used by `FlexboxHighlighter.getFlexContainerPattern`.
+ */
+const gCachedFlexboxPattern = new Map();
+
+const FLEXBOX = "flexbox";
+const JUSTIFY_CONTENT = "justify-content";
+
+/**
+ * The FlexboxHighlighter is the class that overlays a visual canvas on top of
+ * display: [inline-]flex elements.
+ *
+ * @param {String} options.color
+ *        The color that should be used to draw the highlighter for this flexbox.
+ * Structure:
+ * <div class="highlighter-container">
+ *   <div id="flexbox-root" class="flexbox-root">
+ *     <canvas id="flexbox-canvas"
+ *             class="flexbox-canvas"
+ *             width="4096"
+ *             height="4096"
+ *             hidden="true">
+ *     </canvas>
+ *   </div>
+ * </div>
+ */
+class FlexboxHighlighter extends AutoRefreshHighlighter {
+  constructor(highlighterEnv) {
+    super(highlighterEnv);
+
+    this.ID_CLASS_PREFIX = "flexbox-";
+
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      this.highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.markup.initialize();
+
+    this.onPageHide = this.onPageHide.bind(this);
+    this.onWillNavigate = this.onWillNavigate.bind(this);
+
+    this.highlighterEnv.on("will-navigate", this.onWillNavigate);
+
+    const { pageListenerTarget } = highlighterEnv;
+    pageListenerTarget.addEventListener("pagehide", this.onPageHide);
+
+    // Initialize the <canvas> position to the top left corner of the page
+    this._canvasPosition = {
+      x: 0,
+      y: 0,
+    };
+
+    this._ignoreZoom = true;
+
+    // Calling `updateCanvasPosition` anyway since the highlighter could be initialized
+    // on a page that has scrolled already.
+    updateCanvasPosition(
+      this._canvasPosition,
+      this._scroll,
+      this.win,
+      this._winDimensions
+    );
+  }
+
+  _buildMarkup() {
+    const container = this.markup.createNode({
+      attributes: {
+        class: "highlighter-container",
+      },
+    });
+
+    const root = this.markup.createNode({
+      parent: container,
+      attributes: {
+        id: "root",
+        class: "root",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // We use a <canvas> element because there is an arbitrary number of items and texts
+    // to draw which wouldn't be possible with HTML or SVG without having to insert and
+    // remove the whole markup on every update.
+    this.markup.createNode({
+      parent: root,
+      nodeType: "canvas",
+      attributes: {
+        id: "canvas",
+        class: "canvas",
+        hidden: "true",
+        width: CANVAS_SIZE,
+        height: CANVAS_SIZE,
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    return container;
+  }
+
+  clearCache() {
+    gCachedFlexboxPattern.clear();
+  }
+
+  destroy() {
+    const { highlighterEnv } = this;
+    highlighterEnv.off("will-navigate", this.onWillNavigate);
+
+    const { pageListenerTarget } = highlighterEnv;
+
+    if (pageListenerTarget) {
+      pageListenerTarget.removeEventListener("pagehide", this.onPageHide);
+    }
+
+    this.markup.destroy();
+
+    // Clear the pattern cache to avoid dead object exceptions (Bug 1342051).
+    this.clearCache();
+
+    this.axes = null;
+    this.crossAxisDirection = null;
+    this.flexData = null;
+    this.mainAxisDirection = null;
+    this.transform = null;
+
+    AutoRefreshHighlighter.prototype.destroy.call(this);
+  }
+
+  /**
+   * Draw the justify content for a given flex item (left, top, right, bottom) position.
+   */
+  drawJustifyContent(left, top, right, bottom) {
+    const { devicePixelRatio } = this.win;
+    this.ctx.fillStyle = this.getJustifyContentPattern(devicePixelRatio);
+    drawRect(this.ctx, left, top, right, bottom, this.currentMatrix);
+    this.ctx.fill();
+  }
+
+  get canvas() {
+    return this.getElement("canvas");
+  }
+
+  get color() {
+    return this.options.color || DEFAULT_COLOR;
+  }
+
+  get container() {
+    return this.currentNode;
+  }
+
+  get ctx() {
+    return this.canvas.getCanvasContext("2d");
+  }
+
+  getElement(id) {
+    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
+  }
+
+  /**
+   * Gets the flexbox container pattern used to render the container regions.
+   *
+   * @param  {Number} devicePixelRatio
+   *         The device pixel ratio we want the pattern for.
+   * @return {CanvasPattern} flex container pattern.
+   */
+  getFlexContainerPattern(devicePixelRatio) {
+    let flexboxPatternMap = null;
+
+    if (gCachedFlexboxPattern.has(devicePixelRatio)) {
+      flexboxPatternMap = gCachedFlexboxPattern.get(devicePixelRatio);
+    } else {
+      flexboxPatternMap = new Map();
+    }
+
+    if (gCachedFlexboxPattern.has(FLEXBOX)) {
+      return gCachedFlexboxPattern.get(FLEXBOX);
+    }
+
+    // Create the diagonal lines pattern for the rendering the flexbox gaps.
+    const canvas = this.markup.createNode({ nodeType: "canvas" });
+    const width = (canvas.width =
+      FLEXBOX_CONTAINER_PATTERN_WIDTH * devicePixelRatio);
+    const height = (canvas.height =
+      FLEXBOX_CONTAINER_PATTERN_HEIGHT * devicePixelRatio);
+
+    const ctx = canvas.getContext("2d");
+    ctx.save();
+    ctx.setLineDash(FLEXBOX_CONTAINER_PATTERN_LINE_DASH);
+    ctx.beginPath();
+    ctx.translate(0.5, 0.5);
+
+    ctx.moveTo(0, 0);
+    ctx.lineTo(width, height);
+
+    ctx.strokeStyle = this.color;
+    ctx.stroke();
+    ctx.restore();
+
+    const pattern = ctx.createPattern(canvas, "repeat");
+    flexboxPatternMap.set(FLEXBOX, pattern);
+    gCachedFlexboxPattern.set(devicePixelRatio, flexboxPatternMap);
+
+    return pattern;
+  }
+
+  /**
+   * Gets the flexbox justify content pattern used to render the justify content regions.
+   *
+   * @param  {Number} devicePixelRatio
+   *         The device pixel ratio we want the pattern for.
+   * @return {CanvasPattern} flex justify content pattern.
+   */
+  getJustifyContentPattern(devicePixelRatio) {
+    let flexboxPatternMap = null;
+
+    if (gCachedFlexboxPattern.has(devicePixelRatio)) {
+      flexboxPatternMap = gCachedFlexboxPattern.get(devicePixelRatio);
+    } else {
+      flexboxPatternMap = new Map();
+    }
+
+    if (flexboxPatternMap.has(JUSTIFY_CONTENT)) {
+      return flexboxPatternMap.get(JUSTIFY_CONTENT);
+    }
+
+    // Create the inversed diagonal lines pattern
+    // for the rendering the justify content gaps.
+    const canvas = this.markup.createNode({ nodeType: "canvas" });
+    const zoom = getCurrentZoom(this.win);
+    const width = (canvas.width =
+      FLEXBOX_JUSTIFY_CONTENT_PATTERN_WIDTH * devicePixelRatio * zoom);
+    const height = (canvas.height =
+      FLEXBOX_JUSTIFY_CONTENT_PATTERN_HEIGHT * devicePixelRatio * zoom);
+
+    const ctx = canvas.getContext("2d");
+    ctx.save();
+    ctx.setLineDash(FLEXBOX_CONTAINER_PATTERN_LINE_DASH);
+    ctx.beginPath();
+    ctx.translate(0.5, 0.5);
+
+    ctx.moveTo(0, height);
+    ctx.lineTo(width, 0);
+
+    ctx.strokeStyle = this.color;
+    ctx.stroke();
+    ctx.restore();
+
+    const pattern = ctx.createPattern(canvas, "repeat");
+    flexboxPatternMap.set(JUSTIFY_CONTENT, pattern);
+    gCachedFlexboxPattern.set(devicePixelRatio, flexboxPatternMap);
+
+    return pattern;
+  }
+
+  /**
+   * The AutoRefreshHighlighter's _hasMoved method returns true only if the
+   * element's quads have changed. Override it so it also returns true if the
+   * flex container and its flex items have changed.
+   */
+  _hasMoved() {
+    const hasMoved = AutoRefreshHighlighter.prototype._hasMoved.call(this);
+
+    if (!this.computedStyle) {
+      this.computedStyle = getComputedStyle(this.container);
+    }
+
+    const flex = this.container.getAsFlexContainer();
+
+    const oldCrossAxisDirection = this.crossAxisDirection;
+    this.crossAxisDirection = flex ? flex.crossAxisDirection : null;
+    const newCrossAxisDirection = this.crossAxisDirection;
+
+    const oldMainAxisDirection = this.mainAxisDirection;
+    this.mainAxisDirection = flex ? flex.mainAxisDirection : null;
+    const newMainAxisDirection = this.mainAxisDirection;
+
+    // Concatenate the axes to simplify conditionals.
+    this.axes = `${this.mainAxisDirection} ${this.crossAxisDirection}`;
+
+    const oldFlexData = this.flexData;
+    this.flexData = getFlexData(this.container);
+    const hasFlexDataChanged = compareFlexData(oldFlexData, this.flexData);
+
+    const oldAlignItems = this.alignItemsValue;
+    this.alignItemsValue = this.computedStyle.alignItems;
+    const newAlignItems = this.alignItemsValue;
+
+    const oldFlexDirection = this.flexDirection;
+    this.flexDirection = this.computedStyle.flexDirection;
+    const newFlexDirection = this.flexDirection;
+
+    const oldFlexWrap = this.flexWrap;
+    this.flexWrap = this.computedStyle.flexWrap;
+    const newFlexWrap = this.flexWrap;
+
+    const oldJustifyContent = this.justifyContentValue;
+    this.justifyContentValue = this.computedStyle.justifyContent;
+    const newJustifyContent = this.justifyContentValue;
+
+    const oldTransform = this.transformValue;
+    this.transformValue = this.computedStyle.transform;
+    const newTransform = this.transformValue;
+
+    return (
+      hasMoved ||
+      hasFlexDataChanged ||
+      oldAlignItems !== newAlignItems ||
+      oldFlexDirection !== newFlexDirection ||
+      oldFlexWrap !== newFlexWrap ||
+      oldJustifyContent !== newJustifyContent ||
+      oldCrossAxisDirection !== newCrossAxisDirection ||
+      oldMainAxisDirection !== newMainAxisDirection ||
+      oldTransform !== newTransform
+    );
+  }
+
+  _hide() {
+    this.alignItemsValue = null;
+    this.computedStyle = null;
+    this.flexData = null;
+    this.flexDirection = null;
+    this.flexWrap = null;
+    this.justifyContentValue = null;
+
+    setIgnoreLayoutChanges(true);
+    this._hideFlexbox();
+    setIgnoreLayoutChanges(false, this.highlighterEnv.document.documentElement);
+  }
+
+  _hideFlexbox() {
+    this.getElement("canvas").setAttribute("hidden", "true");
+  }
+
+  /**
+   * The <canvas>'s position needs to be updated if the page scrolls too much, in order
+   * to give the illusion that it always covers the viewport.
+   */
+  _scrollUpdate() {
+    const hasUpdated = updateCanvasPosition(
+      this._canvasPosition,
+      this._scroll,
+      this.win,
+      this._winDimensions
+    );
+
+    if (hasUpdated) {
+      this._update();
+    }
+  }
+
+  _show() {
+    this._hide();
+    return this._update();
+  }
+
+  _showFlexbox() {
+    this.getElement("canvas").removeAttribute("hidden");
+  }
+
+  /**
+   * If a page hide event is triggered for current window's highlighter, hide the
+   * highlighter.
+   */
+  onPageHide({ target }) {
+    if (target.defaultView === this.win) {
+      this.hide();
+    }
+  }
+
+  /**
+   * Called when the page will-navigate. Used to hide the flexbox highlighter and clear
+   * the cached gap patterns and avoid using DeadWrapper obejcts as gap patterns the
+   * next time.
+   */
+  onWillNavigate({ isTopLevel }) {
+    this.clearCache();
+
+    if (isTopLevel) {
+      this.hide();
+    }
+  }
+
+  renderFlexContainer() {
+    if (!this.currentQuads.content || !this.currentQuads.content[0]) {
+      return;
+    }
+
+    const { devicePixelRatio } = this.win;
+    const containerQuad = getUntransformedQuad(this.container, "content");
+    const { width, height } = containerQuad.getBounds();
+
+    this.setupCanvas({
+      lineDash: FLEXBOX_LINES_PROPERTIES.alignItems.lineDash,
+      lineWidthMultiplier: 2,
+    });
+
+    this.ctx.fillStyle = this.getFlexContainerPattern(devicePixelRatio);
+
+    drawRect(this.ctx, 0, 0, width, height, this.currentMatrix);
+
+    // Find current angle of outer flex element by measuring the angle of two arbitrary
+    // points, then rotate canvas, so the hash pattern stays 45deg to the boundary.
+    const p1 = apply(this.currentMatrix, [0, 0]);
+    const p2 = apply(this.currentMatrix, [1, 0]);
+    const angleRad = Math.atan2(p2[1] - p1[1], p2[0] - p1[0]);
+    this.ctx.rotate(angleRad);
+
+    this.ctx.fill();
+    this.ctx.stroke();
+    this.ctx.restore();
+  }
+
+  renderFlexItems() {
+    if (
+      !this.flexData ||
+      !this.currentQuads.content ||
+      !this.currentQuads.content[0]
+    ) {
+      return;
+    }
+
+    this.setupCanvas({
+      lineDash: FLEXBOX_LINES_PROPERTIES.item.lineDash,
+    });
+
+    for (const flexLine of this.flexData.lines) {
+      for (const flexItem of flexLine.items) {
+        const { left, top, right, bottom } = flexItem.rect;
+
+        clearRect(this.ctx, left, top, right, bottom, this.currentMatrix);
+        drawRect(this.ctx, left, top, right, bottom, this.currentMatrix);
+        this.ctx.stroke();
+      }
+    }
+
+    this.ctx.restore();
+  }
+
+  renderFlexLines() {
+    if (
+      !this.flexData ||
+      !this.currentQuads.content ||
+      !this.currentQuads.content[0]
+    ) {
+      return;
+    }
+
+    const lineWidth = getDisplayPixelRatio(this.win);
+    const options = { matrix: this.currentMatrix };
+    const { width: containerWidth, height: containerHeight } =
+      getUntransformedQuad(this.container, "content").getBounds();
+
+    this.setupCanvas({
+      useContainerScrollOffsets: true,
+    });
+
+    for (const flexLine of this.flexData.lines) {
+      const { crossStart, crossSize } = flexLine;
+
+      switch (this.axes) {
+        case "horizontal-lr vertical-tb":
+        case "horizontal-lr vertical-bt":
+        case "horizontal-rl vertical-tb":
+        case "horizontal-rl vertical-bt":
+          clearRect(
+            this.ctx,
+            0,
+            crossStart,
+            containerWidth,
+            crossStart + crossSize,
+            this.currentMatrix
+          );
+
+          // Avoid drawing the start flex line when they overlap with the flex container.
+          if (crossStart != 0) {
+            drawLine(
+              this.ctx,
+              0,
+              crossStart,
+              containerWidth,
+              crossStart,
+              options
+            );
+            this.ctx.stroke();
+          }
+
+          // Avoid drawing the end flex line when they overlap with the flex container.
+          if (crossStart + crossSize < containerHeight - lineWidth * 2) {
+            drawLine(
+              this.ctx,
+              0,
+              crossStart + crossSize,
+              containerWidth,
+              crossStart + crossSize,
+              options
+            );
+            this.ctx.stroke();
+          }
+          break;
+        case "vertical-tb horizontal-lr":
+        case "vertical-bt horizontal-rl":
+          clearRect(
+            this.ctx,
+            crossStart,
+            0,
+            crossStart + crossSize,
+            containerHeight,
+            this.currentMatrix
+          );
+
+          // Avoid drawing the start flex line when they overlap with the flex container.
+          if (crossStart != 0) {
+            drawLine(
+              this.ctx,
+              crossStart,
+              0,
+              crossStart,
+              containerHeight,
+              options
+            );
+            this.ctx.stroke();
+          }
+
+          // Avoid drawing the end flex line when they overlap with the flex container.
+          if (crossStart + crossSize < containerWidth - lineWidth * 2) {
+            drawLine(
+              this.ctx,
+              crossStart + crossSize,
+              0,
+              crossStart + crossSize,
+              containerHeight,
+              options
+            );
+            this.ctx.stroke();
+          }
+          break;
+        case "vertical-bt horizontal-lr":
+        case "vertical-tb horizontal-rl":
+          clearRect(
+            this.ctx,
+            containerWidth - crossStart,
+            0,
+            containerWidth - crossStart - crossSize,
+            containerHeight,
+            this.currentMatrix
+          );
+
+          // Avoid drawing the start flex line when they overlap with the flex container.
+          if (crossStart != 0) {
+            drawLine(
+              this.ctx,
+              containerWidth - crossStart,
+              0,
+              containerWidth - crossStart,
+              containerHeight,
+              options
+            );
+            this.ctx.stroke();
+          }
+
+          // Avoid drawing the end flex line when they overlap with the flex container.
+          if (crossStart + crossSize < containerWidth - lineWidth * 2) {
+            drawLine(
+              this.ctx,
+              containerWidth - crossStart - crossSize,
+              0,
+              containerWidth - crossStart - crossSize,
+              containerHeight,
+              options
+            );
+            this.ctx.stroke();
+          }
+          break;
+      }
+    }
+
+    this.ctx.restore();
+  }
+
+  /**
+   * Clear the whole alignment container along the main axis for each flex item.
+   */
+  // eslint-disable-next-line complexity
+  renderJustifyContent() {
+    if (
+      !this.flexData ||
+      !this.currentQuads.content ||
+      !this.currentQuads.content[0]
+    ) {
+      return;
+    }
+
+    const { width: containerWidth, height: containerHeight } =
+      getUntransformedQuad(this.container, "content").getBounds();
+
+    this.setupCanvas({
+      lineDash: FLEXBOX_LINES_PROPERTIES.alignItems.lineDash,
+      offset: (getDisplayPixelRatio(this.win) / 2) % 1,
+      skipLineAndStroke: true,
+      useContainerScrollOffsets: true,
+    });
+
+    for (const flexLine of this.flexData.lines) {
+      const { crossStart, crossSize } = flexLine;
+      let mainStart = 0;
+
+      // In these two situations mainStart goes from right to left so set it's
+      // value as appropriate.
+      if (
+        this.axes === "horizontal-lr vertical-bt" ||
+        this.axes === "horizontal-rl vertical-tb"
+      ) {
+        mainStart = containerWidth;
+      }
+
+      for (const flexItem of flexLine.items) {
+        const { left, top, right, bottom } = flexItem.rect;
+
+        switch (this.axes) {
+          case "horizontal-lr vertical-tb":
+          case "horizontal-rl vertical-bt":
+            this.drawJustifyContent(
+              mainStart,
+              crossStart,
+              left,
+              crossStart + crossSize
+            );
+            mainStart = right;
+            break;
+          case "horizontal-lr vertical-bt":
+          case "horizontal-rl vertical-tb":
+            this.drawJustifyContent(
+              right,
+              crossStart,
+              mainStart,
+              crossStart + crossSize
+            );
+            mainStart = left;
+            break;
+          case "vertical-tb horizontal-lr":
+          case "vertical-bt horizontal-rl":
+            this.drawJustifyContent(
+              crossStart,
+              mainStart,
+              crossStart + crossSize,
+              top
+            );
+            mainStart = bottom;
+            break;
+          case "vertical-bt horizontal-lr":
+          case "vertical-tb horizontal-rl":
+            this.drawJustifyContent(
+              containerWidth - crossStart - crossSize,
+              mainStart,
+              containerWidth - crossStart,
+              top
+            );
+            mainStart = bottom;
+            break;
+        }
+      }
+
+      // Draw the last justify-content area after the last flex item.
+      switch (this.axes) {
+        case "horizontal-lr vertical-tb":
+        case "horizontal-rl vertical-bt":
+          this.drawJustifyContent(
+            mainStart,
+            crossStart,
+            containerWidth,
+            crossStart + crossSize
+          );
+          break;
+        case "horizontal-lr vertical-bt":
+        case "horizontal-rl vertical-tb":
+          this.drawJustifyContent(
+            0,
+            crossStart,
+            mainStart,
+            crossStart + crossSize
+          );
+          break;
+        case "vertical-tb horizontal-lr":
+        case "vertical-bt horizontal-rl":
+          this.drawJustifyContent(
+            crossStart,
+            mainStart,
+            crossStart + crossSize,
+            containerHeight
+          );
+          break;
+        case "vertical-bt horizontal-lr":
+        case "vertical-tb horizontal-rl":
+          this.drawJustifyContent(
+            containerWidth - crossStart - crossSize,
+            mainStart,
+            containerWidth - crossStart,
+            containerHeight
+          );
+          break;
+      }
+    }
+
+    this.ctx.restore();
+  }
+
+  /**
+   * Set up the canvas with the given options prior to drawing.
+   *
+   * @param {String} [options.lineDash = null]
+   *        An Array of numbers that specify distances to alternately draw a
+   *        line and a gap (in coordinate space units). If the number of
+   *        elements in the array is odd, the elements of the array get copied
+   *        and concatenated. For example, [5, 15, 25] will become
+   *        [5, 15, 25, 5, 15, 25]. If the array is empty, the line dash list is
+   *        cleared and line strokes return to being solid.
+   *
+   *        We use the following constants here:
+   *          FLEXBOX_LINES_PROPERTIES.edge.lineDash,
+   *          FLEXBOX_LINES_PROPERTIES.item.lineDash
+   *          FLEXBOX_LINES_PROPERTIES.alignItems.lineDash
+   * @param {Number} [options.lineWidthMultiplier = 1]
+   *        The width of the line.
+   * @param {Number} [options.offset = `(displayPixelRatio / 2) % 1`]
+   *        The single line width used to obtain a crisp line.
+   * @param {Boolean} [options.skipLineAndStroke = false]
+   *        Skip the setting of lineWidth and strokeStyle.
+   * @param {Boolean} [options.useContainerScrollOffsets = false]
+   *        Take the flexbox container's scroll and zoom offsets into account.
+   *        This is needed for drawing flex lines and justify content when the
+   *        flexbox container itself is display:scroll.
+   */
+  setupCanvas({
+    lineDash = null,
+    lineWidthMultiplier = 1,
+    offset = (getDisplayPixelRatio(this.win) / 2) % 1,
+    skipLineAndStroke = false,
+    useContainerScrollOffsets = false,
+  }) {
+    const { devicePixelRatio } = this.win;
+    const lineWidth = getDisplayPixelRatio(this.win);
+    const zoom = getCurrentZoom(this.win);
+    const style = getComputedStyle(this.container);
+    const position = style.position;
+    let offsetX = this._canvasPosition.x;
+    let offsetY = this._canvasPosition.y;
+
+    if (useContainerScrollOffsets) {
+      offsetX += this.container.scrollLeft / zoom;
+      offsetY += this.container.scrollTop / zoom;
+    }
+
+    // If the flexbox container is position:fixed we need to subtract the scroll
+    // positions of all ancestral elements.
+    if (position === "fixed") {
+      const { scrollLeft, scrollTop } = getAbsoluteScrollOffsetsForNode(
+        this.container
+      );
+      offsetX -= scrollLeft / zoom;
+      offsetY -= scrollTop / zoom;
+    }
+
+    const canvasX = Math.round(offsetX * devicePixelRatio * zoom);
+    const canvasY = Math.round(offsetY * devicePixelRatio * zoom);
+
+    this.ctx.save();
+    this.ctx.translate(offset - canvasX, offset - canvasY);
+
+    if (lineDash) {
+      this.ctx.setLineDash(lineDash);
+    }
+
+    if (!skipLineAndStroke) {
+      this.ctx.lineWidth = lineWidth * lineWidthMultiplier;
+      this.ctx.strokeStyle = this.color;
+    }
+  }
+
+  _update() {
+    setIgnoreLayoutChanges(true);
+
+    const root = this.getElement("root");
+
+    // Hide the root element and force the reflow in order to get the proper window's
+    // dimensions without increasing them.
+    root.setAttribute("style", "display: none");
+    this.win.document.documentElement.offsetWidth;
+    this._winDimensions = getWindowDimensions(this.win);
+    const { width, height } = this._winDimensions;
+
+    // Updates the <canvas> element's position and size.
+    // It also clear the <canvas>'s drawing context.
+    updateCanvasElement(
+      this.canvas,
+      this._canvasPosition,
+      this.win.devicePixelRatio,
+      {
+        zoomWindow: this.win,
+      }
+    );
+
+    // Update the current matrix used in our canvas' rendering
+    const { currentMatrix, hasNodeTransformations } = getCurrentMatrix(
+      this.container,
+      this.win,
+      {
+        ignoreWritingModeAndTextDirection: true,
+      }
+    );
+    this.currentMatrix = currentMatrix;
+    this.hasNodeTransformations = hasNodeTransformations;
+
+    if (this.prevColor != this.color) {
+      this.clearCache();
+    }
+    this.renderFlexContainer();
+    this.renderFlexLines();
+    this.renderJustifyContent();
+    this.renderFlexItems();
+    this._showFlexbox();
+    this.prevColor = this.color;
+
+    root.setAttribute(
+      "style",
+      `position: absolute; width: ${width}px; height: ${height}px; overflow: hidden`
+    );
+
+    setIgnoreLayoutChanges(false, this.highlighterEnv.document.documentElement);
+    return true;
+  }
+}
+
+/**
+ * Returns an object representation of the Flex data object and its array of FlexLine
+ * and FlexItem objects along with the DOMRects of the flex items.
+ *
+ * @param  {DOMNode} container
+ *         The flex container.
+ * @return {Object|null} representation of the Flex data object.
+ */
+function getFlexData(container) {
+  const flex = container.getAsFlexContainer();
+
+  if (!flex) {
+    return null;
+  }
+
+  return {
+    lines: flex.getLines().map(line => {
+      return {
+        crossSize: line.crossSize,
+        crossStart: line.crossStart,
+        firstBaselineOffset: line.firstBaselineOffset,
+        growthState: line.growthState,
+        lastBaselineOffset: line.lastBaselineOffset,
+        items: line.getItems().map(item => {
+          return {
+            crossMaxSize: item.crossMaxSize,
+            crossMinSize: item.crossMinSize,
+            mainBaseSize: item.mainBaseSize,
+            mainDeltaSize: item.mainDeltaSize,
+            mainMaxSize: item.mainMaxSize,
+            mainMinSize: item.mainMinSize,
+            node: item.node,
+            rect: getRectFromFlexItemValues(item, container),
+          };
+        }),
+      };
+    }),
+  };
+}
+
+/**
+ * Given a FlexItemValues, return a DOMRect representing the flex item taking
+ * into account its flex container's border and padding.
+ *
+ * @param  {FlexItemValues} item
+ *         The FlexItemValues for which we need the DOMRect.
+ * @param  {DOMNode}
+ *         Flex container containing the flex item.
+ * @return {DOMRect} representing the flex item.
+ */
+function getRectFromFlexItemValues(item, container) {
+  const rect = item.frameRect;
+  const domRect = new DOMRect(rect.x, rect.y, rect.width, rect.height);
+  const win = container.ownerGlobal;
+  const style = win.getComputedStyle(container);
+  const borderLeftWidth = parseInt(style.borderLeftWidth, 10) || 0;
+  const borderTopWidth = parseInt(style.borderTopWidth, 10) || 0;
+  const paddingLeft = parseInt(style.paddingLeft, 10) || 0;
+  const paddingTop = parseInt(style.paddingTop, 10) || 0;
+  const scrollX = container.scrollLeft || 0;
+  const scrollY = container.scrollTop || 0;
+
+  domRect.x -= paddingLeft + scrollX;
+  domRect.y -= paddingTop + scrollY;
+
+  if (style.overflow === "visible" || style.overflow === "clip") {
+    domRect.x -= borderLeftWidth;
+    domRect.y -= borderTopWidth;
+  }
+
+  return domRect;
+}
+
+/**
+ * Returns whether or not the flex data has changed.
+ *
+ * @param  {Flex} oldFlexData
+ *         The old Flex data object.
+ * @param  {Flex} newFlexData
+ *         The new Flex data object.
+ * @return {Boolean} true if the flex data has changed and false otherwise.
+ */
+// eslint-disable-next-line complexity
+function compareFlexData(oldFlexData, newFlexData) {
+  if (!oldFlexData || !newFlexData) {
+    return true;
+  }
+
+  const oldLines = oldFlexData.lines;
+  const newLines = newFlexData.lines;
+
+  if (oldLines.length !== newLines.length) {
+    return true;
+  }
+
+  for (let i = 0; i < oldLines.length; i++) {
+    const oldLine = oldLines[i];
+    const newLine = newLines[i];
+
+    if (
+      oldLine.crossSize !== newLine.crossSize ||
+      oldLine.crossStart !== newLine.crossStart ||
+      oldLine.firstBaselineOffset !== newLine.firstBaselineOffset ||
+      oldLine.growthState !== newLine.growthState ||
+      oldLine.lastBaselineOffset !== newLine.lastBaselineOffset
+    ) {
+      return true;
+    }
+
+    const oldItems = oldLine.items;
+    const newItems = newLine.items;
+
+    if (oldItems.length !== newItems.length) {
+      return true;
+    }
+
+    for (let j = 0; j < oldItems.length; j++) {
+      const oldItem = oldItems[j];
+      const newItem = newItems[j];
+
+      if (
+        oldItem.crossMaxSize !== newItem.crossMaxSize ||
+        oldItem.crossMinSize !== newItem.crossMinSize ||
+        oldItem.mainBaseSize !== newItem.mainBaseSize ||
+        oldItem.mainDeltaSize !== newItem.mainDeltaSize ||
+        oldItem.mainMaxSize !== newItem.mainMaxSize ||
+        oldItem.mainMinSize !== newItem.mainMinSize
+      ) {
+        return true;
+      }
+
+      const oldItemRect = oldItem.rect;
+      const newItemRect = newItem.rect;
+
+      // We are using DOMRects so we only need to compare x, y, width and
+      // height (left, top, right and bottom are calculated from these values).
+      if (
+        oldItemRect.x !== newItemRect.x ||
+        oldItemRect.y !== newItemRect.y ||
+        oldItemRect.width !== newItemRect.width ||
+        oldItemRect.height !== newItemRect.height
+      ) {
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+exports.FlexboxHighlighter = FlexboxHighlighter;
diff --git a/devtools/server/actors/highlighters/fonts.js b/devtools/server/actors/highlighters/fonts.js
new file mode 100644
index 0000000000..0fe6b066c7
--- /dev/null
+++ b/devtools/server/actors/highlighters/fonts.js
@@ -0,0 +1,121 @@
+/* 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/. */
+
+"use strict";
+
+loader.lazyRequireGetter(
+  this,
+  "loadSheet",
+  "resource://devtools/shared/layout/utils.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "removeSheet",
+  "resource://devtools/shared/layout/utils.js",
+  true
+);
+
+// How many text runs are we highlighting at a time. There may be many text runs, and we
+// want to prevent performance problems.
+const MAX_TEXT_RANGES = 100;
+
+// This stylesheet is inserted into the page to customize the color of the selected text
+// runs.
+// Note that this color is defined as --highlighter-content-color in the highlighters.css
+// file, and corresponds to the box-model content color. We want to give it an opacity of
+// 0.6 here.
+const STYLESHEET_URI =
+  "data:text/css," +
+  encodeURIComponent(
+    "::selection{background-color:hsl(197,71%,73%,.6)!important;}"
+  );
+
+/**
+ * This highlighter highlights runs of text in the page that have been rendered given a
+ * certain font. The highlighting is done with window selection ranges, so no extra
+ * markup is being inserted into the content page.
+ */
+class FontsHighlighter {
+  constructor(highlighterEnv) {
+    this.env = highlighterEnv;
+  }
+
+  destroy() {
+    this.hide();
+    this.env = this.currentNode = null;
+  }
+
+  get currentNodeDocument() {
+    if (!this.currentNode) {
+      return this.env.document;
+    }
+
+    if (this.currentNode.nodeType === this.currentNode.DOCUMENT_NODE) {
+      return this.currentNode;
+    }
+
+    return this.currentNode.ownerDocument;
+  }
+
+  /**
+   * Show the highlighter for a given node.
+   * @param {DOMNode} node The node in which we want to search for text runs.
+   * @param {Object} options A bunch of options that can be set:
+   * - {String} name The actual font name to look for in the node.
+   * - {String} CSSFamilyName The CSS font-family name given to this font.
+   */
+  show(node, options) {
+    this.currentNode = node;
+    const doc = this.currentNodeDocument;
+
+    // Get all of the fonts used to render content inside the node.
+    const searchRange = doc.createRange();
+    searchRange.selectNodeContents(node);
+
+    const fonts = InspectorUtils.getUsedFontFaces(searchRange, MAX_TEXT_RANGES);
+
+    // Find the ones we want, based on the provided option.
+    const matchingFonts = fonts.filter(
+      f => f.CSSFamilyName === options.CSSFamilyName && f.name === options.name
+    );
+    if (!matchingFonts.length) {
+      return;
+    }
+
+    // Load the stylesheet that will customize the color of the highlighter (using a
+    // ::selection rule).
+    loadSheet(this.env.window, STYLESHEET_URI);
+
+    // Create a multi-selection in the page to highlight the text runs.
+    const selection = doc.defaultView.getSelection();
+    selection.removeAllRanges();
+
+    for (const matchingFont of matchingFonts) {
+      for (const range of matchingFont.ranges) {
+        selection.addRange(range);
+      }
+    }
+  }
+
+  hide() {
+    // No node was highlighted before, don't need to continue any further.
+    if (!this.currentNode) {
+      return;
+    }
+
+    try {
+      removeSheet(this.env.window, STYLESHEET_URI);
+    } catch (e) {
+      // Silently fail here as we might not have inserted the stylesheet at all.
+    }
+
+    // Simply remove all current ranges in the seletion.
+    const doc = this.currentNodeDocument;
+    const selection = doc.defaultView.getSelection();
+    selection.removeAllRanges();
+  }
+}
+
+exports.FontsHighlighter = FontsHighlighter;
diff --git a/devtools/server/actors/highlighters/geometry-editor.js b/devtools/server/actors/highlighters/geometry-editor.js
new file mode 100644
index 0000000000..ce8ec92bd5
--- /dev/null
+++ b/devtools/server/actors/highlighters/geometry-editor.js
@@ -0,0 +1,808 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  AutoRefreshHighlighter,
+} = require("resource://devtools/server/actors/highlighters/auto-refresh.js");
+const {
+  CanvasFrameAnonymousContentHelper,
+  getComputedStyle,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+const {
+  setIgnoreLayoutChanges,
+  getAdjustedQuads,
+  getCurrentZoom,
+} = require("resource://devtools/shared/layout/utils.js");
+const {
+  getCSSStyleRules,
+} = require("resource://devtools/shared/inspector/css-logic.js");
+
+const GEOMETRY_LABEL_SIZE = 6;
+
+// List of all DOM Events subscribed directly to the document from the
+// Geometry Editor highlighter
+const DOM_EVENTS = ["mousemove", "mouseup", "pagehide"];
+
+const _dragging = Symbol("geometry/dragging");
+
+/**
+ * Element geometry properties helper that gives names of position and size
+ * properties.
+ */
+var GeoProp = {
+  SIDES: ["top", "right", "bottom", "left"],
+  SIZES: ["width", "height"],
+
+  allProps() {
+    return [...this.SIDES, ...this.SIZES];
+  },
+
+  isSide(name) {
+    return this.SIDES.includes(name);
+  },
+
+  isSize(name) {
+    return this.SIZES.includes(name);
+  },
+
+  containsSide(names) {
+    return names.some(name => this.SIDES.includes(name));
+  },
+
+  containsSize(names) {
+    return names.some(name => this.SIZES.includes(name));
+  },
+
+  isHorizontal(name) {
+    return name === "left" || name === "right" || name === "width";
+  },
+
+  isInverted(name) {
+    return name === "right" || name === "bottom";
+  },
+
+  mainAxisStart(name) {
+    return this.isHorizontal(name) ? "left" : "top";
+  },
+
+  crossAxisStart(name) {
+    return this.isHorizontal(name) ? "top" : "left";
+  },
+
+  mainAxisSize(name) {
+    return this.isHorizontal(name) ? "width" : "height";
+  },
+
+  crossAxisSize(name) {
+    return this.isHorizontal(name) ? "height" : "width";
+  },
+
+  axis(name) {
+    return this.isHorizontal(name) ? "x" : "y";
+  },
+
+  crossAxis(name) {
+    return this.isHorizontal(name) ? "y" : "x";
+  },
+};
+
+/**
+ * Get the provided node's offsetParent dimensions.
+ * Returns an object with the {parent, dimension} properties.
+ * Note that the returned parent will be null if the offsetParent is the
+ * default, non-positioned, body or html node.
+ *
+ * node.offsetParent returns the nearest positioned ancestor but if it is
+ * non-positioned itself, we just return null to let consumers know the node is
+ * actually positioned relative to the viewport.
+ *
+ * @return {Object}
+ */
+function getOffsetParent(node) {
+  const win = node.ownerGlobal;
+
+  let offsetParent = node.offsetParent;
+  if (offsetParent && getComputedStyle(offsetParent).position === "static") {
+    offsetParent = null;
+  }
+
+  let width, height;
+  if (!offsetParent) {
+    height = win.innerHeight;
+    width = win.innerWidth;
+  } else {
+    height = offsetParent.offsetHeight;
+    width = offsetParent.offsetWidth;
+  }
+
+  return {
+    element: offsetParent,
+    dimension: { width, height },
+  };
+}
+
+/**
+ * Get the list of geometry properties that are actually set on the provided
+ * node.
+ *
+ * @param {Node} node The node to analyze.
+ * @return {Map} A map indexed by property name and where the value is an
+ * object having the cssRule property.
+ */
+function getDefinedGeometryProperties(node) {
+  const props = new Map();
+  if (!node) {
+    return props;
+  }
+
+  // Get the list of css rules applying to the current node.
+  const cssRules = getCSSStyleRules(node);
+  for (let i = 0; i < cssRules.length; i++) {
+    const rule = cssRules[i];
+    for (const name of GeoProp.allProps()) {
+      const value = rule.style.getPropertyValue(name);
+      if (value && value !== "auto") {
+        // getCSSStyleRules returns rules ordered from least to most specific
+        // so just override any previous properties we have set.
+        props.set(name, {
+          cssRule: rule,
+        });
+      }
+    }
+  }
+
+  // Go through the inline styles last, only if the node supports inline style
+  // (e.g. pseudo elements don't have a style property)
+  if (node.style) {
+    for (const name of GeoProp.allProps()) {
+      const value = node.style.getPropertyValue(name);
+      if (value && value !== "auto") {
+        props.set(name, {
+          // There's no cssRule to store here, so store the node instead since
+          // node.style exists.
+          cssRule: node,
+        });
+      }
+    }
+  }
+
+  // Post-process the list for invalid properties. This is done after the fact
+  // because of cases like relative positioning with both top and bottom where
+  // only top will actually be used, but both exists in css rules and computed
+  // styles.
+  const { position } = getComputedStyle(node);
+  for (const [name] of props) {
+    // Top/left/bottom/right on static positioned elements have no effect.
+    if (position === "static" && GeoProp.SIDES.includes(name)) {
+      props.delete(name);
+    }
+
+    // Bottom/right on relative positioned elements are only used if top/left
+    // are not defined.
+    const hasRightAndLeft = name === "right" && props.has("left");
+    const hasBottomAndTop = name === "bottom" && props.has("top");
+    if (position === "relative" && (hasRightAndLeft || hasBottomAndTop)) {
+      props.delete(name);
+    }
+  }
+
+  return props;
+}
+exports.getDefinedGeometryProperties = getDefinedGeometryProperties;
+
+/**
+ * The GeometryEditor highlights an elements's top, left, bottom, right, width
+ * and height dimensions, when they are set.
+ *
+ * To determine if an element has a set size and position, the highlighter lists
+ * the CSS rules that apply to the element and checks for the top, left, bottom,
+ * right, width and height properties.
+ * The highlighter won't be shown if the element doesn't have any of these
+ * properties set, but will be shown when at least 1 property is defined.
+ *
+ * The highlighter displays lines and labels for each of the defined properties
+ * in and around the element (relative to the offset parent when one exists).
+ * The highlighter also highlights the element itself and its offset parent if
+ * there is one.
+ *
+ * Note that the class name contains the word Editor because the aim is for the
+ * handles to be draggable in content to make the geometry editable.
+ */
+class GeometryEditorHighlighter extends AutoRefreshHighlighter {
+  constructor(highlighterEnv) {
+    super(highlighterEnv);
+
+    this.ID_CLASS_PREFIX = "geometry-editor-";
+
+    // The list of element geometry properties that can be set.
+    this.definedProperties = new Map();
+
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.initialize();
+
+    const { pageListenerTarget } = this.highlighterEnv;
+
+    // Register the geometry editor instance to all events we're interested in.
+    DOM_EVENTS.forEach(type => pageListenerTarget.addEventListener(type, this));
+
+    this.onWillNavigate = this.onWillNavigate.bind(this);
+
+    this.highlighterEnv.on("will-navigate", this.onWillNavigate);
+  }
+
+  async initialize() {
+    await this.markup.initialize();
+    // Register the mousedown event for each Geometry Editor's handler.
+    // Those events are automatically removed when the markup is destroyed.
+    const onMouseDown = this.handleEvent.bind(this);
+
+    for (const side of GeoProp.SIDES) {
+      this.getElement("handler-" + side).addEventListener(
+        "mousedown",
+        onMouseDown
+      );
+    }
+  }
+
+  _buildMarkup() {
+    const container = this.markup.createNode({
+      attributes: { class: "highlighter-container" },
+    });
+
+    const root = this.markup.createNode({
+      parent: container,
+      attributes: {
+        id: "root",
+        class: "root",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const svg = this.markup.createSVGNode({
+      nodeType: "svg",
+      parent: root,
+      attributes: {
+        id: "elements",
+        width: "100%",
+        height: "100%",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Offset parent node highlighter.
+    this.markup.createSVGNode({
+      nodeType: "polygon",
+      parent: svg,
+      attributes: {
+        class: "offset-parent",
+        id: "offset-parent",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Current node highlighter (margin box).
+    this.markup.createSVGNode({
+      nodeType: "polygon",
+      parent: svg,
+      attributes: {
+        class: "current-node",
+        id: "current-node",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Build the 4 side arrows, handlers and labels.
+    for (const name of GeoProp.SIDES) {
+      this.markup.createSVGNode({
+        nodeType: "line",
+        parent: svg,
+        attributes: {
+          class: "arrow " + name,
+          id: "arrow-" + name,
+          hidden: "true",
+        },
+        prefix: this.ID_CLASS_PREFIX,
+      });
+
+      this.markup.createSVGNode({
+        nodeType: "circle",
+        parent: svg,
+        attributes: {
+          class: "handler-" + name,
+          id: "handler-" + name,
+          r: "4",
+          "data-side": name,
+          hidden: "true",
+        },
+        prefix: this.ID_CLASS_PREFIX,
+      });
+
+      // Labels are positioned by using a translated <g>. This group contains
+      // a path and text that are themselves positioned using another translated
+      // <g>. This is so that the label arrow points at the 0,0 coordinates of
+      // parent <g>.
+      const labelG = this.markup.createSVGNode({
+        nodeType: "g",
+        parent: svg,
+        attributes: {
+          id: "label-" + name,
+          hidden: "true",
+        },
+        prefix: this.ID_CLASS_PREFIX,
+      });
+
+      const subG = this.markup.createSVGNode({
+        nodeType: "g",
+        parent: labelG,
+        attributes: {
+          transform: GeoProp.isHorizontal(name)
+            ? "translate(-30 -30)"
+            : "translate(5 -10)",
+        },
+      });
+
+      this.markup.createSVGNode({
+        nodeType: "path",
+        parent: subG,
+        attributes: {
+          class: "label-bubble",
+          d: GeoProp.isHorizontal(name)
+            ? "M0 0 L60 0 L60 20 L35 20 L30 25 L25 20 L0 20z"
+            : "M5 0 L65 0 L65 20 L5 20 L5 15 L0 10 L5 5z",
+        },
+        prefix: this.ID_CLASS_PREFIX,
+      });
+
+      this.markup.createSVGNode({
+        nodeType: "text",
+        parent: subG,
+        attributes: {
+          class: "label-text",
+          id: "label-text-" + name,
+          x: GeoProp.isHorizontal(name) ? "30" : "35",
+          y: "10",
+        },
+        prefix: this.ID_CLASS_PREFIX,
+      });
+    }
+
+    return container;
+  }
+
+  destroy() {
+    // Avoiding exceptions if `destroy` is called multiple times; and / or the
+    // highlighter environment was already destroyed.
+    if (!this.highlighterEnv) {
+      return;
+    }
+
+    const { pageListenerTarget } = this.highlighterEnv;
+
+    if (pageListenerTarget) {
+      DOM_EVENTS.forEach(type =>
+        pageListenerTarget.removeEventListener(type, this)
+      );
+    }
+
+    AutoRefreshHighlighter.prototype.destroy.call(this);
+
+    this.markup.destroy();
+    this.definedProperties.clear();
+    this.definedProperties = null;
+    this.offsetParent = null;
+  }
+
+  handleEvent(event, id) {
+    // No event handling if the highlighter is hidden
+    if (this.getElement("root").hasAttribute("hidden")) {
+      return;
+    }
+
+    const { target, type, pageX, pageY } = event;
+
+    switch (type) {
+      case "pagehide":
+        // If a page hide event is triggered for current window's highlighter, hide the
+        // highlighter.
+        if (target.defaultView === this.win) {
+          this.destroy();
+        }
+
+        break;
+      case "mousedown":
+        // The mousedown event is intended only for the handler
+        if (!id) {
+          return;
+        }
+
+        const handlerSide = this.markup
+          .getElement(id)
+          .getAttribute("data-side");
+
+        if (handlerSide) {
+          const side = handlerSide;
+          const sideProp = this.definedProperties.get(side);
+
+          if (!sideProp) {
+            return;
+          }
+
+          let value = sideProp.cssRule.style.getPropertyValue(side);
+          const computedValue = this.computedStyle.getPropertyValue(side);
+
+          const [unit] = value.match(/[^\d]+$/) || [""];
+
+          value = parseFloat(value);
+
+          const ratio = value / parseFloat(computedValue) || 1;
+          const dir = GeoProp.isInverted(side) ? -1 : 1;
+
+          // Store all the initial values needed for drag & drop
+          this[_dragging] = {
+            side,
+            value,
+            unit,
+            x: pageX,
+            y: pageY,
+            inc: ratio * dir,
+          };
+
+          this.getElement("handler-" + side).classList.add("dragging");
+        }
+
+        this.getElement("root").setAttribute("dragging", "true");
+        break;
+      case "mouseup":
+        // If we're dragging, drop it.
+        if (this[_dragging]) {
+          const { side } = this[_dragging];
+          this.getElement("root").removeAttribute("dragging");
+          this.getElement("handler-" + side).classList.remove("dragging");
+          this[_dragging] = null;
+        }
+        break;
+      case "mousemove":
+        if (!this[_dragging]) {
+          return;
+        }
+
+        const { side, x, y, value, unit, inc } = this[_dragging];
+        const sideProps = this.definedProperties.get(side);
+
+        if (!sideProps) {
+          return;
+        }
+
+        const delta =
+          (GeoProp.isHorizontal(side) ? pageX - x : pageY - y) * inc;
+
+        // The inline style has usually the priority over any other CSS rule
+        // set in stylesheets. However, if a rule has `!important` keyword,
+        // it will override the inline style too. To ensure Geometry Editor
+        // will always update the element, we have to add `!important` as
+        // well.
+        this.currentNode.style.setProperty(
+          side,
+          value + delta + unit,
+          "important"
+        );
+
+        break;
+    }
+  }
+
+  getElement(id) {
+    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
+  }
+
+  _show() {
+    this.computedStyle = getComputedStyle(this.currentNode);
+    const pos = this.computedStyle.position;
+    // XXX: sticky positioning is ignored for now. To be implemented next.
+    if (pos === "sticky") {
+      this.hide();
+      return false;
+    }
+
+    const hasUpdated = this._update();
+    if (!hasUpdated) {
+      this.hide();
+      return false;
+    }
+
+    this.getElement("root").removeAttribute("hidden");
+
+    return true;
+  }
+
+  _update() {
+    // At each update, the position or/and size may have changed, so get the
+    // list of defined properties, and re-position the arrows and highlighters.
+    this.definedProperties = getDefinedGeometryProperties(this.currentNode);
+    // We need the zoom factor to fix the original position of the node
+    // as well as the arrows.
+    this.zoomFactor = getCurrentZoom(this.currentNode);
+
+    if (!this.definedProperties.size) {
+      console.warn("The element does not have editable geometry properties");
+      return false;
+    }
+
+    setIgnoreLayoutChanges(true);
+
+    // Update the highlighters and arrows.
+    this.updateOffsetParent();
+    this.updateCurrentNode();
+    this.updateArrows();
+
+    // Avoid zooming the arrows when content is zoomed.
+    const node = this.currentNode;
+    this.markup.scaleRootElement(node, this.ID_CLASS_PREFIX + "root");
+
+    setIgnoreLayoutChanges(false, this.highlighterEnv.document.documentElement);
+    return true;
+  }
+
+  /**
+   * Update the offset parent rectangle.
+   * There are 3 different cases covered here:
+   * - the node is absolutely/fixed positioned, and an offsetParent is defined
+   *   (i.e. it's not just positioned in the viewport): the offsetParent node
+   *   is highlighted (i.e. the rectangle is shown),
+   * - the node is relatively positioned: the rectangle is shown where the node
+   *   would originally have been (because that's where the relative positioning
+   *   is calculated from),
+   * - the node has no offset parent at all: the offsetParent rectangle is
+   *   hidden.
+   */
+  updateOffsetParent() {
+    // Get the offsetParent, if any.
+    this.offsetParent = getOffsetParent(this.currentNode);
+    // And the offsetParent quads.
+    this.parentQuads = getAdjustedQuads(
+      this.win,
+      this.offsetParent.element,
+      "padding"
+    );
+
+    const el = this.getElement("offset-parent");
+
+    const isPositioned =
+      this.computedStyle.position === "absolute" ||
+      this.computedStyle.position === "fixed";
+    const isRelative = this.computedStyle.position === "relative";
+    let isHighlighted = false;
+
+    if (this.offsetParent.element && isPositioned) {
+      const { p1, p2, p3, p4 } = this.parentQuads[0];
+      const points =
+        p1.x +
+        "," +
+        p1.y +
+        " " +
+        p2.x +
+        "," +
+        p2.y +
+        " " +
+        p3.x +
+        "," +
+        p3.y +
+        " " +
+        p4.x +
+        "," +
+        p4.y;
+      el.setAttribute("points", points);
+      isHighlighted = true;
+    } else if (isRelative) {
+      const xDelta = parseFloat(this.computedStyle.left) * this.zoomFactor;
+      const yDelta = parseFloat(this.computedStyle.top) * this.zoomFactor;
+      if (xDelta || yDelta) {
+        const { p1, p2, p3, p4 } = this.currentQuads.margin[0];
+        const points =
+          p1.x -
+          xDelta +
+          "," +
+          (p1.y - yDelta) +
+          " " +
+          (p2.x - xDelta) +
+          "," +
+          (p2.y - yDelta) +
+          " " +
+          (p3.x - xDelta) +
+          "," +
+          (p3.y - yDelta) +
+          " " +
+          (p4.x - xDelta) +
+          "," +
+          (p4.y - yDelta);
+        el.setAttribute("points", points);
+        isHighlighted = true;
+      }
+    }
+
+    if (isHighlighted) {
+      el.removeAttribute("hidden");
+    } else {
+      el.setAttribute("hidden", "true");
+    }
+  }
+
+  updateCurrentNode() {
+    const box = this.getElement("current-node");
+    const { p1, p2, p3, p4 } = this.currentQuads.margin[0];
+    const attr =
+      p1.x +
+      "," +
+      p1.y +
+      " " +
+      p2.x +
+      "," +
+      p2.y +
+      " " +
+      p3.x +
+      "," +
+      p3.y +
+      " " +
+      p4.x +
+      "," +
+      p4.y;
+    box.setAttribute("points", attr);
+    box.removeAttribute("hidden");
+  }
+
+  _hide() {
+    setIgnoreLayoutChanges(true);
+
+    this.getElement("root").setAttribute("hidden", "true");
+    this.getElement("current-node").setAttribute("hidden", "true");
+    this.getElement("offset-parent").setAttribute("hidden", "true");
+    this.hideArrows();
+
+    this.definedProperties.clear();
+
+    setIgnoreLayoutChanges(false, this.highlighterEnv.document.documentElement);
+  }
+
+  hideArrows() {
+    for (const side of GeoProp.SIDES) {
+      this.getElement("arrow-" + side).setAttribute("hidden", "true");
+      this.getElement("label-" + side).setAttribute("hidden", "true");
+      this.getElement("handler-" + side).setAttribute("hidden", "true");
+    }
+  }
+
+  updateArrows() {
+    this.hideArrows();
+
+    // Position arrows always end at the node's margin box.
+    const marginBox = this.currentQuads.margin[0].bounds;
+
+    // Position the side arrows which need to be visible.
+    // Arrows always start at the offsetParent edge, and end at the middle
+    // position of the node's margin edge.
+    // Note that for relative positioning, the offsetParent is considered to be
+    // the node itself, where it would have been originally.
+    // +------------------+----------------+
+    // | offsetparent     | top            |
+    // | or viewport      |                |
+    // |         +--------+--------+       |
+    // |         | node            |       |
+    // +---------+                 +-------+
+    // | left    |                 | right |
+    // |         +--------+--------+       |
+    // |                  | bottom         |
+    // +------------------+----------------+
+    const getSideArrowStartPos = side => {
+      // In case of relative positioning.
+      if (this.computedStyle.position === "relative") {
+        if (GeoProp.isInverted(side)) {
+          return (
+            marginBox[side] +
+            parseFloat(this.computedStyle[side]) * this.zoomFactor
+          );
+        }
+        return (
+          marginBox[side] -
+          parseFloat(this.computedStyle[side]) * this.zoomFactor
+        );
+      }
+
+      // In case an offsetParent exists and is highlighted.
+      if (this.parentQuads && this.parentQuads.length) {
+        return this.parentQuads[0].bounds[side];
+      }
+
+      // In case the element is positioned in the viewport.
+      if (GeoProp.isInverted(side)) {
+        return this.offsetParent.dimension[GeoProp.mainAxisSize(side)];
+      }
+      return (
+        -1 *
+        this.currentNode.ownerGlobal[
+          "scroll" + GeoProp.axis(side).toUpperCase()
+        ]
+      );
+    };
+
+    for (const side of GeoProp.SIDES) {
+      const sideProp = this.definedProperties.get(side);
+      if (!sideProp) {
+        continue;
+      }
+
+      const mainAxisStartPos = getSideArrowStartPos(side);
+      const mainAxisEndPos = marginBox[side];
+      const crossAxisPos =
+        marginBox[GeoProp.crossAxisStart(side)] +
+        marginBox[GeoProp.crossAxisSize(side)] / 2;
+
+      this.updateArrow(
+        side,
+        mainAxisStartPos,
+        mainAxisEndPos,
+        crossAxisPos,
+        sideProp.cssRule.style.getPropertyValue(side)
+      );
+    }
+  }
+
+  updateArrow(side, mainStart, mainEnd, crossPos, labelValue) {
+    const arrowEl = this.getElement("arrow-" + side);
+    const labelEl = this.getElement("label-" + side);
+    const labelTextEl = this.getElement("label-text-" + side);
+    const handlerEl = this.getElement("handler-" + side);
+
+    // Position the arrow <line>.
+    arrowEl.setAttribute(GeoProp.axis(side) + "1", mainStart);
+    arrowEl.setAttribute(GeoProp.crossAxis(side) + "1", crossPos);
+    arrowEl.setAttribute(GeoProp.axis(side) + "2", mainEnd);
+    arrowEl.setAttribute(GeoProp.crossAxis(side) + "2", crossPos);
+    arrowEl.removeAttribute("hidden");
+
+    handlerEl.setAttribute("c" + GeoProp.axis(side), mainEnd);
+    handlerEl.setAttribute("c" + GeoProp.crossAxis(side), crossPos);
+    handlerEl.removeAttribute("hidden");
+
+    // Position the label <text> in the middle of the arrow (making sure it's
+    // not hidden below the fold).
+    const capitalize = str => str[0].toUpperCase() + str.substring(1);
+    const winMain = this.win["inner" + capitalize(GeoProp.mainAxisSize(side))];
+    let labelMain = mainStart + (mainEnd - mainStart) / 2;
+    if (
+      (mainStart > 0 && mainStart < winMain) ||
+      (mainEnd > 0 && mainEnd < winMain)
+    ) {
+      if (labelMain < GEOMETRY_LABEL_SIZE) {
+        labelMain = GEOMETRY_LABEL_SIZE;
+      } else if (labelMain > winMain - GEOMETRY_LABEL_SIZE) {
+        labelMain = winMain - GEOMETRY_LABEL_SIZE;
+      }
+    }
+    const labelCross = crossPos;
+    labelEl.setAttribute(
+      "transform",
+      GeoProp.isHorizontal(side)
+        ? "translate(" + labelMain + " " + labelCross + ")"
+        : "translate(" + labelCross + " " + labelMain + ")"
+    );
+    labelEl.removeAttribute("hidden");
+    labelTextEl.setTextContent(labelValue);
+  }
+
+  onWillNavigate({ isTopLevel }) {
+    if (isTopLevel) {
+      this.hide();
+    }
+  }
+}
+
+exports.GeometryEditorHighlighter = GeometryEditorHighlighter;
diff --git a/devtools/server/actors/highlighters/measuring-tool.js b/devtools/server/actors/highlighters/measuring-tool.js
new file mode 100644
index 0000000000..41c3b3098f
--- /dev/null
+++ b/devtools/server/actors/highlighters/measuring-tool.js
@@ -0,0 +1,853 @@
+/* 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/. */
+
+"use strict";
+
+const EventEmitter = require("resource://devtools/shared/event-emitter.js");
+const {
+  getCurrentZoom,
+  getWindowDimensions,
+  setIgnoreLayoutChanges,
+} = require("resource://devtools/shared/layout/utils.js");
+const {
+  CanvasFrameAnonymousContentHelper,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+
+// Hard coded value about the size of measuring tool label, in order to
+// position and flip it when is needed.
+const LABEL_SIZE_MARGIN = 8;
+const LABEL_SIZE_WIDTH = 80;
+const LABEL_SIZE_HEIGHT = 52;
+const LABEL_POS_MARGIN = 4;
+const LABEL_POS_WIDTH = 40;
+const LABEL_POS_HEIGHT = 34;
+const LABEL_TYPE_SIZE = "size";
+const LABEL_TYPE_POSITION = "position";
+
+// List of all DOM Events subscribed directly to the document from the
+// Measuring Tool highlighter
+const DOM_EVENTS = [
+  "mousedown",
+  "mousemove",
+  "mouseup",
+  "mouseleave",
+  "scroll",
+  "pagehide",
+  "keydown",
+  "keyup",
+];
+
+const SIDES = ["top", "right", "bottom", "left"];
+const HANDLERS = [...SIDES, "topleft", "topright", "bottomleft", "bottomright"];
+const HANDLER_SIZE = 6;
+const HIGHLIGHTED_HANDLER_CLASSNAME = "highlight";
+
+const IS_OSX = Services.appinfo.OS === "Darwin";
+
+/**
+ * The MeasuringToolHighlighter is used to measure distances in a content page.
+ * It allows users to click and drag with their mouse to draw an area whose
+ * dimensions will be displayed in a tooltip next to it.
+ * This allows users to measure distances between elements on a page.
+ */
+class MeasuringToolHighlighter {
+  constructor(highlighterEnv) {
+    this.env = highlighterEnv;
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.markup.initialize();
+
+    this.rect = { x: 0, y: 0, w: 0, h: 0 };
+    this.mouseCoords = { x: 0, y: 0 };
+
+    const { pageListenerTarget } = highlighterEnv;
+
+    // Register the measuring tool instance to all events we're interested in.
+    DOM_EVENTS.forEach(type => pageListenerTarget.addEventListener(type, this));
+  }
+
+  ID_CLASS_PREFIX = "measuring-tool-";
+
+  _buildMarkup() {
+    const prefix = this.ID_CLASS_PREFIX;
+
+    const container = this.markup.createNode({
+      attributes: { class: "highlighter-container" },
+    });
+
+    const root = this.markup.createNode({
+      parent: container,
+      attributes: {
+        id: "root",
+        class: "root",
+        hidden: "true",
+      },
+      prefix,
+    });
+
+    const svg = this.markup.createSVGNode({
+      nodeType: "svg",
+      parent: root,
+      attributes: {
+        id: "elements",
+        class: "elements",
+        width: "100%",
+        height: "100%",
+      },
+      prefix,
+    });
+
+    for (const side of SIDES) {
+      this.markup.createSVGNode({
+        nodeType: "line",
+        parent: svg,
+        attributes: {
+          class: `guide-${side}`,
+          id: `guide-${side}`,
+          hidden: "true",
+        },
+        prefix,
+      });
+    }
+
+    this.markup.createNode({
+      nodeType: "label",
+      attributes: {
+        id: "label-size",
+        class: "label-size",
+        hidden: "true",
+      },
+      parent: root,
+      prefix,
+    });
+
+    this.markup.createNode({
+      nodeType: "label",
+      attributes: {
+        id: "label-position",
+        class: "label-position",
+        hidden: "true",
+      },
+      parent: root,
+      prefix,
+    });
+
+    // Creating a <g> element in order to group all the paths below, that
+    // together represent the measuring tool; so that would be easier move them
+    // around
+    const g = this.markup.createSVGNode({
+      nodeType: "g",
+      attributes: {
+        id: "tool",
+      },
+      parent: svg,
+      prefix,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "path",
+      attributes: {
+        id: "box-path",
+        class: "box-path",
+      },
+      parent: g,
+      prefix,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "path",
+      attributes: {
+        id: "diagonal-path",
+        class: "diagonal-path",
+      },
+      parent: g,
+      prefix,
+    });
+
+    for (const handler of HANDLERS) {
+      this.markup.createSVGNode({
+        nodeType: "circle",
+        parent: g,
+        attributes: {
+          class: `handler-${handler}`,
+          id: `handler-${handler}`,
+          r: HANDLER_SIZE,
+          hidden: "true",
+        },
+        prefix,
+      });
+    }
+
+    return container;
+  }
+
+  _update() {
+    const { window } = this.env;
+
+    setIgnoreLayoutChanges(true);
+
+    const zoom = getCurrentZoom(window);
+
+    const { width, height } = getWindowDimensions(window);
+
+    const { rect } = this;
+
+    const isZoomChanged = zoom !== rect.zoom;
+
+    if (isZoomChanged) {
+      rect.zoom = zoom;
+      this.updateLabel();
+    }
+
+    const isDocumentSizeChanged =
+      width !== rect.documentWidth || height !== rect.documentHeight;
+
+    if (isDocumentSizeChanged) {
+      rect.documentWidth = width;
+      rect.documentHeight = height;
+    }
+
+    // If either the document's size or the zoom is changed since the last
+    // repaint, we update the tool's size as well.
+    if (isZoomChanged || isDocumentSizeChanged) {
+      this.updateViewport();
+    }
+
+    setIgnoreLayoutChanges(false, window.document.documentElement);
+
+    this._rafID = window.requestAnimationFrame(() => this._update());
+  }
+
+  _cancelUpdate() {
+    if (this._rafID) {
+      this.env.window.cancelAnimationFrame(this._rafID);
+      this._rafID = 0;
+    }
+  }
+
+  destroy() {
+    this.hide();
+
+    this._cancelUpdate();
+
+    const { pageListenerTarget } = this.env;
+
+    if (pageListenerTarget) {
+      DOM_EVENTS.forEach(type =>
+        pageListenerTarget.removeEventListener(type, this)
+      );
+    }
+
+    this.markup.destroy();
+
+    EventEmitter.emit(this, "destroy");
+  }
+
+  show() {
+    setIgnoreLayoutChanges(true);
+
+    this.getElement("root").removeAttribute("hidden");
+
+    this._update();
+
+    setIgnoreLayoutChanges(false, this.env.window.document.documentElement);
+  }
+
+  hide() {
+    setIgnoreLayoutChanges(true);
+
+    this.hideLabel(LABEL_TYPE_SIZE);
+    this.hideLabel(LABEL_TYPE_POSITION);
+
+    this.getElement("root").setAttribute("hidden", "true");
+
+    this._cancelUpdate();
+
+    setIgnoreLayoutChanges(false, this.env.window.document.documentElement);
+  }
+
+  getElement(id) {
+    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
+  }
+
+  setSize(w, h) {
+    this.setRect(undefined, undefined, w, h);
+  }
+
+  setRect(x, y, w, h) {
+    const { rect } = this;
+
+    if (typeof x !== "undefined") {
+      rect.x = x;
+    }
+
+    if (typeof y !== "undefined") {
+      rect.y = y;
+    }
+
+    if (typeof w !== "undefined") {
+      rect.w = w;
+    }
+
+    if (typeof h !== "undefined") {
+      rect.h = h;
+    }
+
+    setIgnoreLayoutChanges(true);
+
+    if (this._dragging) {
+      this.updatePaths();
+      this.updateHandlers();
+    }
+
+    this.updateLabel();
+
+    setIgnoreLayoutChanges(false, this.env.window.document.documentElement);
+  }
+
+  updatePaths() {
+    const { x, y, w, h } = this.rect;
+    const dir = `M0 0 L${w} 0 L${w} ${h} L0 ${h}z`;
+
+    // Adding correction to the line path, otherwise some pixels are drawn
+    // outside the main rectangle area.
+    const x1 = w > 0 ? 0.5 : 0;
+    const y1 = w < 0 && h < 0 ? -0.5 : 0;
+    const w1 = w + (h < 0 && w < 0 ? 0.5 : 0);
+    const h1 = h + (h > 0 && w > 0 ? -0.5 : 0);
+
+    const linedir = `M${x1} ${y1} L${w1} ${h1}`;
+
+    this.getElement("box-path").setAttribute("d", dir);
+    this.getElement("diagonal-path").setAttribute("d", linedir);
+    this.getElement("tool").setAttribute("transform", `translate(${x},${y})`);
+  }
+
+  updateLabel(type) {
+    type = type || (this._dragging ? LABEL_TYPE_SIZE : LABEL_TYPE_POSITION);
+
+    const isSizeLabel = type === LABEL_TYPE_SIZE;
+
+    const label = this.getElement(`label-${type}`);
+
+    let origin = "top left";
+
+    const { innerWidth, innerHeight, scrollX, scrollY } = this.env.window;
+    const { x: mouseX, y: mouseY } = this.mouseCoords;
+    let { x, y, w, h, zoom } = this.rect;
+    const scale = 1 / zoom;
+
+    w = w || 0;
+    h = h || 0;
+    x = x || 0;
+    y = y || 0;
+    if (type === LABEL_TYPE_SIZE) {
+      x += w;
+      y += h;
+    } else {
+      x = mouseX;
+      y = mouseY;
+    }
+
+    let labelMargin, labelHeight, labelWidth;
+
+    if (isSizeLabel) {
+      labelMargin = LABEL_SIZE_MARGIN;
+      labelWidth = LABEL_SIZE_WIDTH;
+      labelHeight = LABEL_SIZE_HEIGHT;
+
+      const d = Math.hypot(w, h).toFixed(2);
+
+      label.setTextContent(`W: ${Math.abs(w)} px
+                            H: ${Math.abs(h)} px
+                            ↘: ${d}px`);
+    } else {
+      labelMargin = LABEL_POS_MARGIN;
+      labelWidth = LABEL_POS_WIDTH;
+      labelHeight = LABEL_POS_HEIGHT;
+
+      label.setTextContent(`${mouseX}
+                            ${mouseY}`);
+    }
+
+    // Size used to position properly the label
+    const labelBoxWidth = (labelWidth + labelMargin) * scale;
+    const labelBoxHeight = (labelHeight + labelMargin) * scale;
+
+    const isGoingLeft = w < scrollX;
+    const isSizeGoingLeft = isSizeLabel && isGoingLeft;
+    const isExceedingLeftMargin = x - labelBoxWidth < scrollX;
+    const isExceedingRightMargin = x + labelBoxWidth > innerWidth + scrollX;
+    const isExceedingTopMargin = y - labelBoxHeight < scrollY;
+    const isExceedingBottomMargin = y + labelBoxHeight > innerHeight + scrollY;
+
+    if ((isSizeGoingLeft && !isExceedingLeftMargin) || isExceedingRightMargin) {
+      x -= labelBoxWidth;
+      origin = "top right";
+    } else {
+      x += labelMargin * scale;
+    }
+
+    if (isSizeLabel) {
+      y += isExceedingTopMargin ? labelMargin * scale : -labelBoxHeight;
+    } else {
+      y += isExceedingBottomMargin ? -labelBoxHeight : labelMargin * scale;
+    }
+
+    label.setAttribute(
+      "style",
+      `
+      width: ${labelWidth}px;
+      height: ${labelHeight}px;
+      transform-origin: ${origin};
+      transform: translate(${x}px,${y}px) scale(${scale})
+    `
+    );
+
+    if (!isSizeLabel) {
+      const labelSize = this.getElement("label-size");
+      const style = labelSize.getAttribute("style");
+
+      if (style) {
+        labelSize.setAttribute(
+          "style",
+          style.replace(/scale[^)]+\)/, `scale(${scale})`)
+        );
+      }
+    }
+  }
+
+  updateViewport() {
+    const { devicePixelRatio } = this.env.window;
+    const { documentWidth, documentHeight, zoom } = this.rect;
+
+    // Because `devicePixelRatio` is affected by zoom (see bug 809788),
+    // in order to get the "real" device pixel ratio, we need divide by `zoom`
+    const pixelRatio = devicePixelRatio / zoom;
+
+    // The "real" device pixel ratio is used to calculate the max stroke
+    // width we can actually assign: on retina, for instance, it would be 0.5,
+    // where on non high dpi monitor would be 1.
+    const minWidth = 1 / pixelRatio;
+    const strokeWidth = minWidth / zoom;
+
+    this.getElement("root").setAttribute(
+      "style",
+      `stroke-width:${strokeWidth};
+       width:${documentWidth}px;
+       height:${documentHeight}px;`
+    );
+  }
+
+  updateGuides() {
+    const { x, y, w, h } = this.rect;
+
+    let guide = this.getElement("guide-top");
+
+    guide.setAttribute("x1", "0");
+    guide.setAttribute("y1", y);
+    guide.setAttribute("x2", "100%");
+    guide.setAttribute("y2", y);
+
+    guide = this.getElement("guide-right");
+
+    guide.setAttribute("x1", x + w);
+    guide.setAttribute("y1", 0);
+    guide.setAttribute("x2", x + w);
+    guide.setAttribute("y2", "100%");
+
+    guide = this.getElement("guide-bottom");
+
+    guide.setAttribute("x1", "0");
+    guide.setAttribute("y1", y + h);
+    guide.setAttribute("x2", "100%");
+    guide.setAttribute("y2", y + h);
+
+    guide = this.getElement("guide-left");
+
+    guide.setAttribute("x1", x);
+    guide.setAttribute("y1", 0);
+    guide.setAttribute("x2", x);
+    guide.setAttribute("y2", "100%");
+  }
+
+  setHandlerPosition(handler, x, y) {
+    const handlerElement = this.getElement(`handler-${handler}`);
+    handlerElement.setAttribute("cx", x);
+    handlerElement.setAttribute("cy", y);
+  }
+
+  updateHandlers() {
+    const { w, h } = this.rect;
+
+    this.setHandlerPosition("top", w / 2, 0);
+    this.setHandlerPosition("topright", w, 0);
+    this.setHandlerPosition("right", w, h / 2);
+    this.setHandlerPosition("bottomright", w, h);
+    this.setHandlerPosition("bottom", w / 2, h);
+    this.setHandlerPosition("bottomleft", 0, h);
+    this.setHandlerPosition("left", 0, h / 2);
+    this.setHandlerPosition("topleft", 0, 0);
+  }
+
+  showLabel(type) {
+    setIgnoreLayoutChanges(true);
+
+    this.getElement(`label-${type}`).removeAttribute("hidden");
+
+    setIgnoreLayoutChanges(false, this.env.window.document.documentElement);
+  }
+
+  hideLabel(type) {
+    setIgnoreLayoutChanges(true);
+
+    this.getElement(`label-${type}`).setAttribute("hidden", "true");
+
+    setIgnoreLayoutChanges(false, this.env.window.document.documentElement);
+  }
+
+  showGuides() {
+    const prefix = this.ID_CLASS_PREFIX + "guide-";
+
+    for (const side of SIDES) {
+      this.markup.removeAttributeForElement(`${prefix + side}`, "hidden");
+    }
+  }
+
+  hideGuides() {
+    const prefix = this.ID_CLASS_PREFIX + "guide-";
+
+    for (const side of SIDES) {
+      this.markup.setAttributeForElement(`${prefix + side}`, "hidden", "true");
+    }
+  }
+
+  showHandler(id) {
+    const prefix = this.ID_CLASS_PREFIX + "handler-";
+    this.markup.removeAttributeForElement(prefix + id, "hidden");
+  }
+
+  showHandlers() {
+    const prefix = this.ID_CLASS_PREFIX + "handler-";
+
+    for (const handler of HANDLERS) {
+      this.markup.removeAttributeForElement(prefix + handler, "hidden");
+    }
+  }
+
+  hideAll() {
+    this.hideLabel(LABEL_TYPE_POSITION);
+    this.hideLabel(LABEL_TYPE_SIZE);
+    this.hideGuides();
+    this.hideHandlers();
+  }
+
+  showGuidesAndHandlers() {
+    // Shows the guides and handlers only if an actual area is selected
+    if (this.rect.w !== 0 && this.rect.h !== 0) {
+      this.updateGuides();
+      this.showGuides();
+      this.updateHandlers();
+      this.showHandlers();
+    }
+  }
+
+  hideHandlers() {
+    const prefix = this.ID_CLASS_PREFIX + "handler-";
+
+    for (const handler of HANDLERS) {
+      this.markup.setAttributeForElement(prefix + handler, "hidden", "true");
+    }
+  }
+
+  handleEvent(event) {
+    const { target, type } = event;
+
+    switch (type) {
+      case "mousedown":
+        if (event.button || this._dragging) {
+          return;
+        }
+
+        const isHandler = event.originalTarget.id.includes("handler");
+        if (isHandler) {
+          this.handleResizingMouseDownEvent(event);
+        } else {
+          this.handleMouseDownEvent(event);
+        }
+        break;
+      case "mousemove":
+        if (this._dragging && this._dragging.handler) {
+          this.handleResizingMouseMoveEvent(event);
+        } else {
+          this.handleMouseMoveEvent(event);
+        }
+        break;
+      case "mouseup":
+        if (this._dragging) {
+          if (this._dragging.handler) {
+            this.handleResizingMouseUpEvent();
+          } else {
+            this.handleMouseUpEvent();
+          }
+        }
+        break;
+      case "mouseleave": {
+        if (!this._dragging) {
+          this.hideLabel(LABEL_TYPE_POSITION);
+        }
+        break;
+      }
+      case "scroll": {
+        this.hideLabel(LABEL_TYPE_POSITION);
+        break;
+      }
+      case "pagehide": {
+        // If a page hide event is triggered for current window's highlighter, hide the
+        // highlighter.
+        if (target.defaultView === this.env.window) {
+          this.destroy();
+        }
+        break;
+      }
+      case "keydown": {
+        this.handleKeyDown(event);
+        break;
+      }
+      case "keyup": {
+        if (MeasuringToolHighlighter.#isResizeModifierPressed(event)) {
+          this.getElement("handler-topleft").classList.remove(
+            HIGHLIGHTED_HANDLER_CLASSNAME
+          );
+        }
+        break;
+      }
+    }
+  }
+
+  handleMouseDownEvent(event) {
+    const { pageX, pageY } = event;
+    const { window } = this.env;
+    const elementId = `${this.ID_CLASS_PREFIX}tool`;
+
+    setIgnoreLayoutChanges(true);
+
+    this.markup.getElement(elementId).classList.add("dragging");
+
+    this.hideAll();
+
+    setIgnoreLayoutChanges(false, window.document.documentElement);
+
+    // Store all the initial values needed for drag & drop
+    this._dragging = {
+      handler: null,
+      x: pageX,
+      y: pageY,
+    };
+
+    this.setRect(pageX, pageY, 0, 0);
+  }
+
+  handleMouseMoveEvent(event) {
+    const { pageX, pageY } = event;
+    const { mouseCoords } = this;
+    let { x, y, w, h } = this.rect;
+    let labelType;
+
+    if (this._dragging) {
+      w = pageX - x;
+      h = pageY - y;
+
+      this.setRect(x, y, w, h);
+
+      labelType = LABEL_TYPE_SIZE;
+    } else {
+      mouseCoords.x = pageX;
+      mouseCoords.y = pageY;
+      this.updateLabel(LABEL_TYPE_POSITION);
+
+      labelType = LABEL_TYPE_POSITION;
+    }
+
+    this.showLabel(labelType);
+  }
+
+  handleMouseUpEvent() {
+    setIgnoreLayoutChanges(true);
+
+    this.getElement("tool").classList.remove("dragging");
+
+    this.showGuidesAndHandlers();
+
+    setIgnoreLayoutChanges(false, this.env.window.document.documentElement);
+    this._dragging = null;
+  }
+
+  handleResizingMouseDownEvent(event) {
+    const { originalTarget, pageX, pageY } = event;
+    const { window } = this.env;
+    const prefix = this.ID_CLASS_PREFIX + "handler-";
+    const handler = originalTarget.id.replace(prefix, "");
+
+    setIgnoreLayoutChanges(true);
+
+    this.markup.getElement(originalTarget.id).classList.add("dragging");
+
+    this.hideAll();
+    this.showHandler(handler);
+
+    // Set coordinates to the current measurement area's position
+    const [, x, y] = this.getElement("tool")
+      .getAttribute("transform")
+      .match(/(\d+),(\d+)/);
+    this.setRect(Number(x), Number(y));
+
+    setIgnoreLayoutChanges(false, window.document.documentElement);
+
+    // Store all the initial values needed for drag & drop
+    this._dragging = {
+      handler,
+      x: pageX,
+      y: pageY,
+    };
+  }
+
+  handleResizingMouseMoveEvent(event) {
+    const { pageX, pageY } = event;
+    const { rect } = this;
+    let { x, y, w, h } = rect;
+
+    const { handler } = this._dragging;
+
+    switch (handler) {
+      case "top":
+        y = pageY;
+        h = rect.y + rect.h - pageY;
+        break;
+      case "topright":
+        y = pageY;
+        w = pageX - rect.x;
+        h = rect.y + rect.h - pageY;
+        break;
+      case "right":
+        w = pageX - rect.x;
+        break;
+      case "bottomright":
+        w = pageX - rect.x;
+        h = pageY - rect.y;
+        break;
+      case "bottom":
+        h = pageY - rect.y;
+        break;
+      case "bottomleft":
+        x = pageX;
+        w = rect.x + rect.w - pageX;
+        h = pageY - rect.y;
+        break;
+      case "left":
+        x = pageX;
+        w = rect.x + rect.w - pageX;
+        break;
+      case "topleft":
+        x = pageX;
+        y = pageY;
+        w = rect.x + rect.w - pageX;
+        h = rect.y + rect.h - pageY;
+        break;
+    }
+
+    this.setRect(x, y, w, h);
+
+    // Changes the resizing cursors in case the measuring box is mirrored
+    const isMirrored =
+      (rect.w < 0 || rect.h < 0) && !(rect.w < 0 && rect.h < 0);
+    this.getElement("tool").classList.toggle("mirrored", isMirrored);
+
+    this.showLabel("size");
+  }
+
+  handleResizingMouseUpEvent() {
+    const { handler } = this._dragging;
+
+    setIgnoreLayoutChanges(true);
+
+    this.getElement(`handler-${handler}`).classList.remove("dragging");
+    this.showHandlers();
+
+    this.showGuidesAndHandlers();
+
+    setIgnoreLayoutChanges(false, this.env.window.document.documentElement);
+    this._dragging = null;
+  }
+
+  handleKeyDown(event) {
+    if (MeasuringToolHighlighter.#isResizeModifierPressed(event)) {
+      this.getElement("handler-topleft").classList.add(
+        HIGHLIGHTED_HANDLER_CLASSNAME
+      );
+    }
+
+    if (
+      !["ArrowUp", "ArrowDown", "ArrowLeft", "ArrowRight"].includes(event.key)
+    ) {
+      return;
+    }
+
+    const { x, y, w, h } = this.rect;
+    const modifier = event.shiftKey ? 10 : 1;
+
+    event.preventDefault();
+    if (MeasuringToolHighlighter.#isResizeModifierHeld(event)) {
+      // If Ctrl (or Command on OS X) is held, resize the tool
+      switch (event.key) {
+        case "ArrowUp":
+          this.setSize(undefined, h - modifier);
+          break;
+        case "ArrowDown":
+          this.setSize(undefined, h + modifier);
+          break;
+        case "ArrowLeft":
+          this.setSize(w - modifier, undefined);
+          break;
+        case "ArrowRight":
+          this.setSize(w + modifier, undefined);
+          break;
+      }
+    } else {
+      // Arrow keys with no modifier move the tool
+      switch (event.key) {
+        case "ArrowUp":
+          this.setRect(undefined, y - modifier);
+          break;
+        case "ArrowDown":
+          this.setRect(undefined, y + modifier);
+          break;
+        case "ArrowLeft":
+          this.setRect(x - modifier, undefined);
+          break;
+        case "ArrowRight":
+          this.setRect(x + modifier, undefined);
+          break;
+      }
+    }
+
+    this.updatePaths();
+    this.updateGuides();
+    this.updateHandlers();
+    this.updateLabel(LABEL_TYPE_SIZE);
+  }
+
+  static #isResizeModifierPressed(event) {
+    return (
+      (!IS_OSX && event.key === "Control") || (IS_OSX && event.key === "Meta")
+    );
+  }
+
+  static #isResizeModifierHeld(event) {
+    return (!IS_OSX && event.ctrlKey) || (IS_OSX && event.metaKey);
+  }
+}
+exports.MeasuringToolHighlighter = MeasuringToolHighlighter;
diff --git a/devtools/server/actors/highlighters/moz.build b/devtools/server/actors/highlighters/moz.build
new file mode 100644
index 0000000000..eeaca89992
--- /dev/null
+++ b/devtools/server/actors/highlighters/moz.build
@@ -0,0 +1,31 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+DIRS += [
+    "utils",
+    "css",
+]
+
+DevToolsModules(
+    "accessible.js",
+    "auto-refresh.js",
+    "box-model.js",
+    "css-grid.js",
+    "css-transform.js",
+    "eye-dropper.js",
+    "flexbox.js",
+    "fonts.js",
+    "geometry-editor.js",
+    "measuring-tool.js",
+    "node-tabbing-order.js",
+    "paused-debugger.js",
+    "remote-node-picker-notice.js",
+    "rulers.js",
+    "selector.js",
+    "shapes.js",
+    "tabbing-order.js",
+    "viewport-size.js",
+)
diff --git a/devtools/server/actors/highlighters/node-tabbing-order.js b/devtools/server/actors/highlighters/node-tabbing-order.js
new file mode 100644
index 0000000000..229342ee98
--- /dev/null
+++ b/devtools/server/actors/highlighters/node-tabbing-order.js
@@ -0,0 +1,399 @@
+/* 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/. */
+
+"use strict";
+
+loader.lazyRequireGetter(
+  this,
+  ["setIgnoreLayoutChanges", "getCurrentZoom"],
+  "resource://devtools/shared/layout/utils.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "AutoRefreshHighlighter",
+  "resource://devtools/server/actors/highlighters/auto-refresh.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  ["CanvasFrameAnonymousContentHelper"],
+  "resource://devtools/server/actors/highlighters/utils/markup.js",
+  true
+);
+
+/**
+ * The NodeTabbingOrderHighlighter draws an outline around a node (based on its
+ * border bounds).
+ *
+ * Usage example:
+ *
+ * const h = new NodeTabbingOrderHighlighter(env);
+ * await h.isReady();
+ * h.show(node, options);
+ * h.hide();
+ * h.destroy();
+ *
+ * @param {Number} options.index
+ *        Tabbing index value to be displayed in the highlighter info bar.
+ */
+class NodeTabbingOrderHighlighter extends AutoRefreshHighlighter {
+  constructor(highlighterEnv) {
+    super(highlighterEnv);
+
+    this._doNotStartRefreshLoop = true;
+    this.ID_CLASS_PREFIX = "tabbing-order-";
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      this.highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.markup.initialize();
+  }
+
+  _buildMarkup() {
+    const root = this.markup.createNode({
+      attributes: {
+        id: "root",
+        class: "root highlighter-container tabbing-order",
+        "aria-hidden": "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const container = this.markup.createNode({
+      parent: root,
+      attributes: {
+        id: "container",
+        width: "100%",
+        height: "100%",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Building the SVG element
+    this.markup.createNode({
+      parent: container,
+      attributes: {
+        class: "bounds",
+        id: "bounds",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Building the nodeinfo bar markup
+
+    const infobarContainer = this.markup.createNode({
+      parent: root,
+      attributes: {
+        class: "infobar-container",
+        id: "infobar-container",
+        position: "top",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const infobar = this.markup.createNode({
+      parent: infobarContainer,
+      attributes: {
+        class: "infobar",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createNode({
+      parent: infobar,
+      attributes: {
+        class: "infobar-text",
+        id: "infobar-text",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    return root;
+  }
+
+  /**
+   * Destroy the nodes. Remove listeners.
+   */
+  destroy() {
+    this.markup.destroy();
+
+    AutoRefreshHighlighter.prototype.destroy.call(this);
+  }
+
+  getElement(id) {
+    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
+  }
+
+  /**
+   * Update focused styling for a node tabbing index highlight.
+   *
+   * @param {Boolean} focused
+   *        Indicates if the highlighted node needs to be focused.
+   */
+  updateFocus(focused) {
+    const root = this.getElement("root");
+    root.classList.toggle("focused", focused);
+  }
+
+  /**
+   * Show the highlighter on a given node
+   */
+  _show() {
+    return this._update();
+  }
+
+  /**
+   * Update the highlighter on the current highlighted node (the one that was
+   * passed as an argument to show(node)).
+   * Should be called whenever node size or attributes change
+   */
+  _update() {
+    let shown = false;
+    setIgnoreLayoutChanges(true);
+
+    if (this._updateTabbingOrder()) {
+      this._showInfobar();
+      this._showTabbingOrder();
+      shown = true;
+      setIgnoreLayoutChanges(
+        false,
+        this.highlighterEnv.window.document.documentElement
+      );
+    } else {
+      // Nothing to highlight (0px rectangle like a <script> tag for instance)
+      this._hide();
+    }
+
+    return shown;
+  }
+
+  /**
+   * Hide the highlighter, the outline and the infobar.
+   */
+  _hide() {
+    setIgnoreLayoutChanges(true);
+
+    this._hideTabbingOrder();
+    this._hideInfobar();
+
+    setIgnoreLayoutChanges(
+      false,
+      this.highlighterEnv.window.document.documentElement
+    );
+  }
+
+  /**
+   * Hide the infobar
+   */
+  _hideInfobar() {
+    this.getElement("infobar-container").setAttribute("hidden", "true");
+  }
+
+  /**
+   * Show the infobar
+   */
+  _showInfobar() {
+    if (!this.currentNode) {
+      return;
+    }
+
+    this.getElement("infobar-container").removeAttribute("hidden");
+    this.getElement("infobar-text").setTextContent(this.options.index);
+    const bounds = this._getBounds();
+    const container = this.getElement("infobar-container");
+
+    moveInfobar(container, bounds, this.win);
+  }
+
+  /**
+   * Hide the tabbing order highlighter
+   */
+  _hideTabbingOrder() {
+    this.getElement("container").setAttribute("hidden", "true");
+  }
+
+  /**
+   * Show the tabbing order highlighter
+   */
+  _showTabbingOrder() {
+    this.getElement("container").removeAttribute("hidden");
+  }
+
+  /**
+   * Calculate border bounds based on the quads returned by getAdjustedQuads.
+   * @return {Object} A bounds object {bottom,height,left,right,top,width,x,y}
+   */
+  _getBorderBounds() {
+    const quads = this.currentQuads.border;
+    if (!quads || !quads.length) {
+      return null;
+    }
+
+    const bounds = {
+      bottom: -Infinity,
+      height: 0,
+      left: Infinity,
+      right: -Infinity,
+      top: Infinity,
+      width: 0,
+      x: 0,
+      y: 0,
+    };
+
+    for (const q of quads) {
+      bounds.bottom = Math.max(bounds.bottom, q.bounds.bottom);
+      bounds.top = Math.min(bounds.top, q.bounds.top);
+      bounds.left = Math.min(bounds.left, q.bounds.left);
+      bounds.right = Math.max(bounds.right, q.bounds.right);
+    }
+    bounds.x = bounds.left;
+    bounds.y = bounds.top;
+    bounds.width = bounds.right - bounds.left;
+    bounds.height = bounds.bottom - bounds.top;
+
+    return bounds;
+  }
+
+  /**
+   * Update the tabbing order index as per the current node.
+   *
+   * @return {boolean}
+   *         True if the current node has a tabbing order index to be
+   *         highlighted
+   */
+  _updateTabbingOrder() {
+    if (!this._nodeNeedsHighlighting()) {
+      this._hideTabbingOrder();
+      return false;
+    }
+
+    const boundsEl = this.getElement("bounds");
+    const { left, top, width, height } = this._getBounds();
+    boundsEl.setAttribute(
+      "style",
+      `top: ${top}px; left: ${left}px; width: ${width}px; height: ${height}px;`
+    );
+
+    // Un-zoom the root wrapper if the page was zoomed.
+    const rootId = this.ID_CLASS_PREFIX + "container";
+    this.markup.scaleRootElement(this.currentNode, rootId);
+
+    return true;
+  }
+
+  /**
+   * Can the current node be highlighted? Does it have quads.
+   * @return {Boolean}
+   */
+  _nodeNeedsHighlighting() {
+    return (
+      this.currentQuads.margin.length ||
+      this.currentQuads.border.length ||
+      this.currentQuads.padding.length ||
+      this.currentQuads.content.length
+    );
+  }
+
+  _getBounds() {
+    const borderBounds = this._getBorderBounds();
+    let bounds = {
+      bottom: 0,
+      height: 0,
+      left: 0,
+      right: 0,
+      top: 0,
+      width: 0,
+      x: 0,
+      y: 0,
+    };
+
+    if (!borderBounds) {
+      // Invisible element such as a script tag.
+      return bounds;
+    }
+
+    const { bottom, height, left, right, top, width, x, y } = borderBounds;
+    if (width > 0 || height > 0) {
+      bounds = { bottom, height, left, right, top, width, x, y };
+    }
+
+    return bounds;
+  }
+}
+
+/**
+ * Move the infobar to the right place in the highlighter. The infobar is used
+ * to display element's tabbing order index.
+ *
+ * @param  {DOMNode} container
+ *         The container element which will be used to position the infobar.
+ * @param  {Object} bounds
+ *         The content bounds of the container element.
+ * @param  {Window} win
+ *         The window object.
+ */
+function moveInfobar(container, bounds, win) {
+  const zoom = getCurrentZoom(win);
+  const { computedStyle } = container;
+  const margin = 2;
+  const arrowSize =
+    parseFloat(
+      computedStyle.getPropertyValue("--highlighter-bubble-arrow-size")
+    ) - 2;
+  const containerHeight = parseFloat(computedStyle.getPropertyValue("height"));
+  const containerWidth = parseFloat(computedStyle.getPropertyValue("width"));
+
+  const topBoundary = margin;
+  const bottomBoundary =
+    win.document.scrollingElement.scrollHeight - containerHeight - margin - 1;
+  const leftBoundary = containerWidth / 2 + margin;
+
+  let top = bounds.y - containerHeight - arrowSize;
+  let left = bounds.x + bounds.width / 2;
+  const bottom = bounds.bottom + arrowSize;
+  let positionAttribute = "top";
+
+  const canBePlacedOnTop = top >= topBoundary;
+  const canBePlacedOnBottom = bottomBoundary - bottom > 0;
+
+  if (!canBePlacedOnTop && canBePlacedOnBottom) {
+    top = bottom;
+    positionAttribute = "bottom";
+  }
+
+  let hideArrow = false;
+  if (top < topBoundary) {
+    hideArrow = true;
+    top = topBoundary;
+  } else if (top > bottomBoundary) {
+    hideArrow = true;
+    top = bottomBoundary;
+  }
+
+  if (left < leftBoundary) {
+    hideArrow = true;
+    left = leftBoundary;
+  }
+
+  if (hideArrow) {
+    container.setAttribute("hide-arrow", "true");
+  } else {
+    container.removeAttribute("hide-arrow");
+  }
+
+  container.setAttribute(
+    "style",
+    `
+     position: absolute;
+     transform-origin: 0 0;
+     transform: scale(${1 / zoom}) translate(calc(${left}px - 50%), ${top}px)`
+  );
+
+  container.setAttribute("position", positionAttribute);
+}
+
+exports.NodeTabbingOrderHighlighter = NodeTabbingOrderHighlighter;
diff --git a/devtools/server/actors/highlighters/paused-debugger.js b/devtools/server/actors/highlighters/paused-debugger.js
new file mode 100644
index 0000000000..5035ab04c2
--- /dev/null
+++ b/devtools/server/actors/highlighters/paused-debugger.js
@@ -0,0 +1,260 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  CanvasFrameAnonymousContentHelper,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+
+loader.lazyGetter(this, "PausedReasonsBundle", () => {
+  return new Localization(
+    ["devtools/shared/debugger-paused-reasons.ftl"],
+    true
+  );
+});
+
+loader.lazyRequireGetter(
+  this,
+  "DEBUGGER_PAUSED_REASONS_L10N_MAPPING",
+  "resource://devtools/shared/constants.js",
+  true
+);
+
+/**
+ * The PausedDebuggerOverlay is a class that displays a semi-transparent mask on top of
+ * the whole page and a toolbar at the top of the page.
+ * This is used to signal to users that script execution is current paused.
+ * The toolbar is used to display the reason for the pause in script execution as well as
+ * buttons to resume or step through the program.
+ */
+class PausedDebuggerOverlay {
+  constructor(highlighterEnv, options = {}) {
+    this.env = highlighterEnv;
+    this.resume = options.resume;
+    this.stepOver = options.stepOver;
+
+    this.lastTarget = null;
+
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      highlighterEnv,
+      this._buildMarkup.bind(this),
+      { waitForDocumentToLoad: false }
+    );
+    this.isReady = this.markup.initialize();
+  }
+
+  ID_CLASS_PREFIX = "paused-dbg-";
+
+  _buildMarkup() {
+    const prefix = this.ID_CLASS_PREFIX;
+
+    const container = this.markup.createNode({
+      attributes: { class: "highlighter-container" },
+    });
+
+    // Wrapper element.
+    const wrapper = this.markup.createNode({
+      parent: container,
+      attributes: {
+        id: "root",
+        class: "root",
+        hidden: "true",
+        overlay: "true",
+      },
+      prefix,
+    });
+
+    const toolbar = this.markup.createNode({
+      parent: wrapper,
+      attributes: {
+        id: "toolbar",
+        class: "toolbar",
+      },
+      prefix,
+    });
+
+    this.markup.createNode({
+      nodeType: "span",
+      parent: toolbar,
+      attributes: {
+        id: "reason",
+        class: "reason",
+      },
+      prefix,
+    });
+
+    this.markup.createNode({
+      parent: toolbar,
+      attributes: {
+        id: "divider",
+        class: "divider",
+      },
+      prefix,
+    });
+
+    const stepWrapper = this.markup.createNode({
+      parent: toolbar,
+      attributes: {
+        id: "step-button-wrapper",
+        class: "step-button-wrapper",
+      },
+      prefix,
+    });
+
+    this.markup.createNode({
+      nodeType: "button",
+      parent: stepWrapper,
+      attributes: {
+        id: "step-button",
+        class: "step-button",
+      },
+      prefix,
+    });
+
+    const resumeWrapper = this.markup.createNode({
+      parent: toolbar,
+      attributes: {
+        id: "resume-button-wrapper",
+        class: "resume-button-wrapper",
+      },
+      prefix,
+    });
+
+    this.markup.createNode({
+      nodeType: "button",
+      parent: resumeWrapper,
+      attributes: {
+        id: "resume-button",
+        class: "resume-button",
+      },
+      prefix,
+    });
+
+    return container;
+  }
+
+  destroy() {
+    this.hide();
+    this.markup.destroy();
+    this.env = null;
+    this.lastTarget = null;
+  }
+
+  onClick(target) {
+    const { id } = target;
+    if (!id) {
+      return;
+    }
+
+    if (id.includes("paused-dbg-step-button")) {
+      this.stepOver();
+    } else if (id.includes("paused-dbg-resume-button")) {
+      this.resume();
+    }
+  }
+
+  onMouseMove(target) {
+    // Not an element we care about
+    if (!target || !target.id) {
+      return;
+    }
+
+    // If the user didn't change targets, do nothing
+    if (this.lastTarget && this.lastTarget.id === target.id) {
+      return;
+    }
+
+    if (
+      target.id.includes("step-button") ||
+      target.id.includes("resume-button")
+    ) {
+      // The hover should be applied to the wrapper (icon's parent node)
+      const newTarget = target.parentNode.id.includes("wrapper")
+        ? target.parentNode
+        : target;
+
+      // Remove the hover class if the user has changed buttons
+      if (this.lastTarget && this.lastTarget != newTarget) {
+        this.lastTarget.classList.remove("hover");
+      }
+      newTarget.classList.add("hover");
+      this.lastTarget = newTarget;
+    } else if (this.lastTarget) {
+      // Remove the hover class if the user isn't on a button
+      this.lastTarget.classList.remove("hover");
+    }
+  }
+
+  handleEvent(e) {
+    switch (e.type) {
+      case "mousedown":
+        this.onClick(e.target);
+        break;
+      case "DOMMouseScroll":
+        // Prevent scrolling. That's because we only took a screenshot of the viewport, so
+        // scrolling out of the viewport wouldn't draw the expected things. In the future
+        // we can take the screenshot again on scroll, but for now it doesn't seem
+        // important.
+        e.preventDefault();
+        break;
+
+      case "mousemove":
+        this.onMouseMove(e.target);
+        break;
+    }
+  }
+
+  getElement(id) {
+    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
+  }
+
+  show(reason) {
+    if (this.env.isXUL || !reason) {
+      return false;
+    }
+
+    // Only track mouse movement when the the overlay is shown
+    // Prevents mouse tracking when the user isn't paused
+    const { pageListenerTarget } = this.env;
+    pageListenerTarget.addEventListener("mousemove", this);
+
+    // Show the highlighter's root element.
+    const root = this.getElement("root");
+    root.removeAttribute("hidden");
+    root.setAttribute("overlay", "true");
+
+    // Set the text to appear in the toolbar.
+    const toolbar = this.getElement("toolbar");
+    this.getElement("reason").setTextContent(
+      PausedReasonsBundle.formatValueSync(
+        DEBUGGER_PAUSED_REASONS_L10N_MAPPING[reason]
+      )
+    );
+    toolbar.removeAttribute("hidden");
+
+    // When the debugger pauses execution in a page, events will not be delivered
+    // to any handlers added to elements on that page. So here we use the
+    // document's setSuppressedEventListener interface to still be able to act on mouse
+    // events (they'll be handled by the `handleEvent` method)
+    this.env.window.document.setSuppressedEventListener(this);
+    return true;
+  }
+
+  hide() {
+    if (this.env.isXUL) {
+      return;
+    }
+
+    const { pageListenerTarget } = this.env;
+    pageListenerTarget.removeEventListener("mousemove", this);
+
+    // Hide the overlay.
+    this.getElement("root").setAttribute("hidden", "true");
+    // Remove the hover state
+    this.getElement("step-button-wrapper").classList.remove("hover");
+    this.getElement("resume-button-wrapper").classList.remove("hover");
+  }
+}
+exports.PausedDebuggerOverlay = PausedDebuggerOverlay;
diff --git a/devtools/server/actors/highlighters/remote-node-picker-notice.js b/devtools/server/actors/highlighters/remote-node-picker-notice.js
new file mode 100644
index 0000000000..64b131d2a2
--- /dev/null
+++ b/devtools/server/actors/highlighters/remote-node-picker-notice.js
@@ -0,0 +1,188 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  CanvasFrameAnonymousContentHelper,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+
+loader.lazyGetter(this, "HighlightersBundle", () => {
+  return new Localization(["devtools/shared/highlighters.ftl"], true);
+});
+
+loader.lazyGetter(this, "isAndroid", () => {
+  return Services.appinfo.OS === "Android";
+});
+
+/**
+ * The RemoteNodePickerNotice is a class that displays a notice in a remote debugged page.
+ * This is used to signal to users they can click/tap an element to select it in the
+ * about:devtools-toolbox toolbox inspector.
+ */
+class RemoteNodePickerNotice {
+  #highlighterEnvironment;
+  #previousHoveredElement;
+
+  rootElementId = "node-picker-notice-root";
+  hideButtonId = "node-picker-notice-hide-button";
+  infoNoticeElementId = "node-picker-notice-info";
+
+  /**
+   * @param {highlighterEnvironment} highlighterEnvironment
+   */
+  constructor(highlighterEnvironment) {
+    this.#highlighterEnvironment = highlighterEnvironment;
+
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      this.#highlighterEnvironment,
+      this.#buildMarkup
+    );
+    this.isReady = this.markup.initialize();
+  }
+
+  #buildMarkup = () => {
+    const container = this.markup.createNode({
+      attributes: { class: "highlighter-container" },
+    });
+
+    // Wrapper element.
+    const wrapper = this.markup.createNode({
+      parent: container,
+      attributes: {
+        id: this.rootElementId,
+        hidden: "true",
+        overlay: "true",
+      },
+    });
+
+    const toolbar = this.markup.createNode({
+      parent: wrapper,
+      attributes: {
+        id: "node-picker-notice-toolbar",
+        class: "toolbar",
+      },
+    });
+
+    this.markup.createNode({
+      parent: toolbar,
+      attributes: {
+        id: "node-picker-notice-icon",
+        class: isAndroid ? "touch" : "",
+      },
+    });
+
+    const actionStr = HighlightersBundle.formatValueSync(
+      isAndroid
+        ? "remote-node-picker-notice-action-touch"
+        : "remote-node-picker-notice-action-desktop"
+    );
+
+    this.markup.createNode({
+      nodeType: "span",
+      parent: toolbar,
+      text: HighlightersBundle.formatValueSync("remote-node-picker-notice", {
+        action: actionStr,
+      }),
+      attributes: {
+        id: this.infoNoticeElementId,
+      },
+    });
+
+    this.markup.createNode({
+      nodeType: "button",
+      parent: toolbar,
+      text: HighlightersBundle.formatValueSync(
+        "remote-node-picker-notice-hide-button"
+      ),
+      attributes: {
+        id: this.hideButtonId,
+      },
+    });
+
+    return container;
+  };
+
+  destroy() {
+    // hide will nullify take care of this.#abortController.
+    this.hide();
+    this.markup.destroy();
+    this.#highlighterEnvironment = null;
+    this.#previousHoveredElement = null;
+  }
+
+  /**
+   * We can't use event listener directly on the anonymous content because they aren't
+   * working while the page is paused.
+   * This is called from the NodePicker instance for easier events management.
+   *
+   * @param {ClickEvent}
+   */
+  onClick(e) {
+    const target = e.originalTarget || e.target;
+    const targetId = target?.id;
+
+    if (targetId === this.hideButtonId) {
+      this.hide();
+    }
+  }
+
+  /**
+   * Since we can't use :hover in the CSS for the anonymous content as it wouldn't work
+   * when the page is paused, we have to roll our own implementation, adding a `.hover`
+   * class for the element we want to style on hover (e.g. the close button).
+   * This is called from the NodePicker instance for easier events management.
+   *
+   * @param {MouseMoveEvent}
+   */
+  handleHoveredElement(e) {
+    const hideButton = this.markup.getElement(this.hideButtonId);
+
+    const target = e.originalTarget || e.target;
+    const targetId = target?.id;
+
+    // If the user didn't change targets, do nothing
+    if (this.#previousHoveredElement?.id === targetId) {
+      return;
+    }
+
+    if (targetId === this.hideButtonId) {
+      hideButton.classList.add("hover");
+    } else {
+      hideButton.classList.remove("hover");
+    }
+    this.#previousHoveredElement = target;
+  }
+
+  getMarkupRootElement() {
+    return this.markup.getElement(this.rootElementId);
+  }
+
+  async show() {
+    if (this.#highlighterEnvironment.isXUL) {
+      return false;
+    }
+    await this.isReady;
+
+    // Show the highlighter's root element.
+    const root = this.getMarkupRootElement();
+    root.removeAttribute("hidden");
+    root.setAttribute("overlay", "true");
+
+    return true;
+  }
+
+  hide() {
+    if (this.#highlighterEnvironment.isXUL) {
+      return;
+    }
+
+    // Hide the overlay.
+    this.getMarkupRootElement().setAttribute("hidden", "true");
+    // Reset the hover state
+    this.markup.getElement(this.hideButtonId).classList.remove("hover");
+    this.#previousHoveredElement = null;
+  }
+}
+exports.RemoteNodePickerNotice = RemoteNodePickerNotice;
diff --git a/devtools/server/actors/highlighters/rulers.js b/devtools/server/actors/highlighters/rulers.js
new file mode 100644
index 0000000000..b201757d8c
--- /dev/null
+++ b/devtools/server/actors/highlighters/rulers.js
@@ -0,0 +1,312 @@
+/* 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/. */
+
+"use strict";
+
+const EventEmitter = require("resource://devtools/shared/event-emitter.js");
+const {
+  getCurrentZoom,
+  setIgnoreLayoutChanges,
+} = require("resource://devtools/shared/layout/utils.js");
+const {
+  CanvasFrameAnonymousContentHelper,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+
+// Maximum size, in pixel, for the horizontal ruler and vertical ruler
+// used by RulersHighlighter
+const RULERS_MAX_X_AXIS = 10000;
+const RULERS_MAX_Y_AXIS = 15000;
+// Number of steps after we add a graduation, marker and text in
+// RulersHighliter; currently the unit is in pixel.
+const RULERS_GRADUATION_STEP = 5;
+const RULERS_MARKER_STEP = 50;
+const RULERS_TEXT_STEP = 100;
+
+/**
+ * The RulersHighlighter is a class that displays both horizontal and
+ * vertical rules on the page, along the top and left edges, with pixel
+ * graduations, useful for users to quickly check distances
+ */
+class RulersHighlighter {
+  constructor(highlighterEnv) {
+    this.env = highlighterEnv;
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.markup.initialize();
+
+    const { pageListenerTarget } = highlighterEnv;
+    pageListenerTarget.addEventListener("scroll", this);
+    pageListenerTarget.addEventListener("pagehide", this);
+  }
+
+  ID_CLASS_PREFIX = "rulers-highlighter-";
+
+  _buildMarkup() {
+    const prefix = this.ID_CLASS_PREFIX;
+
+    const createRuler = (axis, size) => {
+      let width, height;
+      let isHorizontal = true;
+
+      if (axis === "x") {
+        width = size;
+        height = 16;
+      } else if (axis === "y") {
+        width = 16;
+        height = size;
+        isHorizontal = false;
+      } else {
+        throw new Error(
+          `Invalid type of axis given; expected "x" or "y" but got "${axis}"`
+        );
+      }
+
+      const g = this.markup.createSVGNode({
+        nodeType: "g",
+        attributes: {
+          id: `${axis}-axis`,
+        },
+        parent: svg,
+        prefix,
+      });
+
+      this.markup.createSVGNode({
+        nodeType: "rect",
+        attributes: {
+          y: isHorizontal ? 0 : 16,
+          width,
+          height,
+        },
+        parent: g,
+      });
+
+      const gRule = this.markup.createSVGNode({
+        nodeType: "g",
+        attributes: {
+          id: `${axis}-axis-ruler`,
+        },
+        parent: g,
+        prefix,
+      });
+
+      const pathGraduations = this.markup.createSVGNode({
+        nodeType: "path",
+        attributes: {
+          class: "ruler-graduations",
+          width,
+          height,
+        },
+        parent: gRule,
+        prefix,
+      });
+
+      const pathMarkers = this.markup.createSVGNode({
+        nodeType: "path",
+        attributes: {
+          class: "ruler-markers",
+          width,
+          height,
+        },
+        parent: gRule,
+        prefix,
+      });
+
+      const gText = this.markup.createSVGNode({
+        nodeType: "g",
+        attributes: {
+          id: `${axis}-axis-text`,
+          class: (isHorizontal ? "horizontal" : "vertical") + "-labels",
+        },
+        parent: g,
+        prefix,
+      });
+
+      let dGraduations = "";
+      let dMarkers = "";
+      let graduationLength;
+
+      for (let i = 0; i < size; i += RULERS_GRADUATION_STEP) {
+        if (i === 0) {
+          continue;
+        }
+
+        graduationLength = i % 2 === 0 ? 6 : 4;
+
+        if (i % RULERS_TEXT_STEP === 0) {
+          graduationLength = 8;
+          this.markup.createSVGNode({
+            nodeType: "text",
+            parent: gText,
+            attributes: {
+              x: isHorizontal ? 2 + i : -i - 1,
+              y: 5,
+            },
+          }).textContent = i;
+        }
+
+        if (isHorizontal) {
+          if (i % RULERS_MARKER_STEP === 0) {
+            dMarkers += `M${i} 0 L${i} ${graduationLength}`;
+          } else {
+            dGraduations += `M${i} 0 L${i} ${graduationLength} `;
+          }
+        } else if (i % 50 === 0) {
+          dMarkers += `M0 ${i} L${graduationLength} ${i}`;
+        } else {
+          dGraduations += `M0 ${i} L${graduationLength} ${i}`;
+        }
+      }
+
+      pathGraduations.setAttribute("d", dGraduations);
+      pathMarkers.setAttribute("d", dMarkers);
+
+      return g;
+    };
+
+    const container = this.markup.createNode({
+      attributes: { class: "highlighter-container" },
+    });
+
+    const root = this.markup.createNode({
+      parent: container,
+      attributes: {
+        id: "root",
+        class: "root",
+      },
+      prefix,
+    });
+
+    const svg = this.markup.createSVGNode({
+      nodeType: "svg",
+      parent: root,
+      attributes: {
+        id: "elements",
+        class: "elements",
+        width: "100%",
+        height: "100%",
+        hidden: "true",
+      },
+      prefix,
+    });
+
+    createRuler("x", RULERS_MAX_X_AXIS);
+    createRuler("y", RULERS_MAX_Y_AXIS);
+
+    return container;
+  }
+
+  handleEvent(event) {
+    switch (event.type) {
+      case "scroll":
+        this._onScroll(event);
+        break;
+      case "pagehide":
+        // If a page hide event is triggered for current window's highlighter, hide the
+        // highlighter.
+        if (event.target.defaultView === this.env.window) {
+          this.destroy();
+        }
+        break;
+    }
+  }
+
+  _onScroll(event) {
+    const prefix = this.ID_CLASS_PREFIX;
+    const { scrollX, scrollY } = event.view;
+
+    this.markup
+      .getElement(`${prefix}x-axis-ruler`)
+      .setAttribute("transform", `translate(${-scrollX})`);
+    this.markup
+      .getElement(`${prefix}x-axis-text`)
+      .setAttribute("transform", `translate(${-scrollX})`);
+    this.markup
+      .getElement(`${prefix}y-axis-ruler`)
+      .setAttribute("transform", `translate(0, ${-scrollY})`);
+    this.markup
+      .getElement(`${prefix}y-axis-text`)
+      .setAttribute("transform", `translate(0, ${-scrollY})`);
+  }
+
+  _update() {
+    const { window } = this.env;
+
+    setIgnoreLayoutChanges(true);
+
+    const zoom = getCurrentZoom(window);
+    const isZoomChanged = zoom !== this._zoom;
+
+    if (isZoomChanged) {
+      this._zoom = zoom;
+      this.updateViewport();
+    }
+
+    setIgnoreLayoutChanges(false, window.document.documentElement);
+
+    this._rafID = window.requestAnimationFrame(() => this._update());
+  }
+
+  _cancelUpdate() {
+    if (this._rafID) {
+      this.env.window.cancelAnimationFrame(this._rafID);
+      this._rafID = 0;
+    }
+  }
+  updateViewport() {
+    const { devicePixelRatio } = this.env.window;
+
+    // Because `devicePixelRatio` is affected by zoom (see bug 809788),
+    // in order to get the "real" device pixel ratio, we need divide by `zoom`
+    const pixelRatio = devicePixelRatio / this._zoom;
+
+    // The "real" device pixel ratio is used to calculate the max stroke
+    // width we can actually assign: on retina, for instance, it would be 0.5,
+    // where on non high dpi monitor would be 1.
+    const minWidth = 1 / pixelRatio;
+    const strokeWidth = Math.min(minWidth, minWidth / this._zoom);
+
+    this.markup
+      .getElement(this.ID_CLASS_PREFIX + "root")
+      .setAttribute("style", `stroke-width:${strokeWidth};`);
+  }
+
+  destroy() {
+    this.hide();
+
+    const { pageListenerTarget } = this.env;
+
+    if (pageListenerTarget) {
+      pageListenerTarget.removeEventListener("scroll", this);
+      pageListenerTarget.removeEventListener("pagehide", this);
+    }
+
+    this.markup.destroy();
+
+    EventEmitter.emit(this, "destroy");
+  }
+
+  show() {
+    this.markup.removeAttributeForElement(
+      this.ID_CLASS_PREFIX + "elements",
+      "hidden"
+    );
+
+    this._update();
+
+    return true;
+  }
+
+  hide() {
+    this.markup.setAttributeForElement(
+      this.ID_CLASS_PREFIX + "elements",
+      "hidden",
+      "true"
+    );
+
+    this._cancelUpdate();
+  }
+}
+exports.RulersHighlighter = RulersHighlighter;
diff --git a/devtools/server/actors/highlighters/selector.js b/devtools/server/actors/highlighters/selector.js
new file mode 100644
index 0000000000..249060fd3b
--- /dev/null
+++ b/devtools/server/actors/highlighters/selector.js
@@ -0,0 +1,97 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  isNodeValid,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+const {
+  BoxModelHighlighter,
+} = require("resource://devtools/server/actors/highlighters/box-model.js");
+
+// How many maximum nodes can be highlighted at the same time by the SelectorHighlighter
+const MAX_HIGHLIGHTED_ELEMENTS = 100;
+
+/**
+ * The SelectorHighlighter runs a given selector through querySelectorAll on the
+ * document of the provided context node and then uses the BoxModelHighlighter
+ * to highlight the matching nodes
+ */
+class SelectorHighlighter {
+  constructor(highlighterEnv) {
+    this.highlighterEnv = highlighterEnv;
+    this._highlighters = [];
+  }
+
+  /**
+   * Show a BoxModelHighlighter on each node that matches a given selector.
+   *
+   * @param {DOMNode} node
+   *        A context node used to get the document element on which to run
+   *        querySelectorAll(). This node will not be highlighted.
+   * @param {Object} options
+   *        Configuration options for SelectorHighlighter.
+   *        All of the options for BoxModelHighlighter.show() are also valid here.
+   * @param {String} options.selector
+   *        Required. CSS selector used with querySelectorAll() to find matching elements.
+   */
+  async show(node, options = {}) {
+    this.hide();
+
+    if (!isNodeValid(node) || !options.selector) {
+      return false;
+    }
+
+    let nodes = [];
+    try {
+      nodes = [...node.ownerDocument.querySelectorAll(options.selector)];
+    } catch (e) {
+      // It's fine if the provided selector is invalid, `nodes` will be an empty array.
+    }
+
+    // Prevent passing the `selector` option to BoxModelHighlighter
+    delete options.selector;
+
+    const promises = [];
+    for (let i = 0; i < Math.min(nodes.length, MAX_HIGHLIGHTED_ELEMENTS); i++) {
+      promises.push(this._showHighlighter(nodes[i], options));
+    }
+
+    await Promise.all(promises);
+    return true;
+  }
+
+  /**
+   * Create an instance of BoxModelHighlighter, wait for it to be ready
+   * (see CanvasFrameAnonymousContentHelper.initialize()),
+   * then show the highlighter on the given node with the given configuration options.
+   *
+   * @param  {DOMNode} node
+   *         Node to be highlighted
+   * @param  {Object} options
+   *         Configuration options for the BoxModelHighlighter
+   * @return {Promise} Promise that resolves when the BoxModelHighlighter is ready
+   */
+  async _showHighlighter(node, options) {
+    const highlighter = new BoxModelHighlighter(this.highlighterEnv);
+    await highlighter.isReady;
+
+    highlighter.show(node, options);
+    this._highlighters.push(highlighter);
+  }
+
+  hide() {
+    for (const highlighter of this._highlighters) {
+      highlighter.destroy();
+    }
+    this._highlighters = [];
+  }
+
+  destroy() {
+    this.hide();
+    this.highlighterEnv = null;
+  }
+}
+exports.SelectorHighlighter = SelectorHighlighter;
diff --git a/devtools/server/actors/highlighters/shapes.js b/devtools/server/actors/highlighters/shapes.js
new file mode 100644
index 0000000000..a77e8c31be
--- /dev/null
+++ b/devtools/server/actors/highlighters/shapes.js
@@ -0,0 +1,3263 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  CanvasFrameAnonymousContentHelper,
+  getComputedStyle,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+const {
+  setIgnoreLayoutChanges,
+  getCurrentZoom,
+  getAdjustedQuads,
+  getFrameOffsets,
+} = require("resource://devtools/shared/layout/utils.js");
+const {
+  AutoRefreshHighlighter,
+} = require("resource://devtools/server/actors/highlighters/auto-refresh.js");
+const {
+  getDistance,
+  clickedOnEllipseEdge,
+  distanceToLine,
+  projection,
+  clickedOnPoint,
+} = require("resource://devtools/server/actors/utils/shapes-utils.js");
+const {
+  identity,
+  apply,
+  translate,
+  multiply,
+  scale,
+  rotate,
+  changeMatrixBase,
+  getBasis,
+} = require("resource://devtools/shared/layout/dom-matrix-2d.js");
+const EventEmitter = require("resource://devtools/shared/event-emitter.js");
+const {
+  getCSSStyleRules,
+} = require("resource://devtools/shared/inspector/css-logic.js");
+
+const BASE_MARKER_SIZE = 5;
+// the width of the area around highlighter lines that can be clicked, in px
+const LINE_CLICK_WIDTH = 5;
+const ROTATE_LINE_LENGTH = 50;
+const DOM_EVENTS = ["mousedown", "mousemove", "mouseup", "dblclick"];
+const _dragging = Symbol("shapes/dragging");
+
+/**
+ * The ShapesHighlighter draws an outline shapes in the page.
+ * The idea is to have something that is able to wrap complex shapes for css properties
+ * such as shape-outside/inside, clip-path but also SVG elements.
+ *
+ * Notes on shape transformation:
+ *
+ * When using transform mode to translate, scale, and rotate shapes, a transformation
+ * matrix keeps track of the transformations done to the original shape. When the
+ * highlighter is toggled on/off or between transform mode and point editing mode,
+ * the transformations applied to the shape become permanent.
+ *
+ * While transformations are being performed on a shape, there is an "original" and
+ * a "transformed" coordinate system. This is used when scaling or rotating a rotated
+ * shape.
+ *
+ * The "original" coordinate system is the one where (0,0) is at the top left corner
+ * of the page, the x axis is horizontal, and the y axis is vertical.
+ *
+ * The "transformed" coordinate system is the one where (0,0) is at the top left
+ * corner of the current shape. The x axis follows the north edge of the shape
+ * (from the northwest corner to the northeast corner) and the y axis follows
+ * the west edge of the shape (from the northwest corner to the southwest corner).
+ *
+ * Because of rotation, the "north" and "west" edges might not actually be at the
+ * top and left of the transformed shape. Imagine that the compass directions are
+ * also rotated along with the shape.
+ *
+ * A refresher for coordinates and change of basis that may be helpful:
+ * https://www.math.ubc.ca/~behrend/math221/Coords.pdf
+ *
+ * @param {String} options.hoverPoint
+ *        The point to highlight.
+ * @param {Boolean} options.transformMode
+ *        Whether to show the highlighter in transforms mode.
+ * @param {} options.mode
+ */
+class ShapesHighlighter extends AutoRefreshHighlighter {
+  constructor(highlighterEnv) {
+    super(highlighterEnv);
+    EventEmitter.decorate(this);
+
+    this.ID_CLASS_PREFIX = "shapes-";
+
+    this.referenceBox = "border";
+    this.useStrokeBox = false;
+    this.geometryBox = "";
+    this.hoveredPoint = null;
+    this.fillRule = "";
+    this.numInsetPoints = 0;
+    this.transformMode = false;
+    this.viewport = {};
+
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      this.highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.markup.initialize();
+    this.onPageHide = this.onPageHide.bind(this);
+
+    const { pageListenerTarget } = this.highlighterEnv;
+    DOM_EVENTS.forEach(event =>
+      pageListenerTarget.addEventListener(event, this)
+    );
+    pageListenerTarget.addEventListener("pagehide", this.onPageHide);
+  }
+
+  _buildMarkup() {
+    const container = this.markup.createNode({
+      attributes: {
+        class: "highlighter-container",
+      },
+    });
+
+    // The root wrapper is used to unzoom the highlighter when needed.
+    const rootWrapper = this.markup.createNode({
+      parent: container,
+      attributes: {
+        id: "root",
+        class: "root",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const mainSvg = this.markup.createSVGNode({
+      nodeType: "svg",
+      parent: rootWrapper,
+      attributes: {
+        id: "shape-container",
+        class: "shape-container",
+        viewBox: "0 0 100 100",
+        preserveAspectRatio: "none",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // This clipPath and its children make sure the element quad outline
+    // is only shown when the shape extends past the element quads.
+    const clipSvg = this.markup.createSVGNode({
+      nodeType: "clipPath",
+      parent: mainSvg,
+      attributes: {
+        id: "clip-path",
+        class: "clip-path",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "polygon",
+      parent: clipSvg,
+      attributes: {
+        id: "clip-polygon",
+        class: "clip-polygon",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "ellipse",
+      parent: clipSvg,
+      attributes: {
+        id: "clip-ellipse",
+        class: "clip-ellipse",
+        hidden: true,
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "rect",
+      parent: clipSvg,
+      attributes: {
+        id: "clip-rect",
+        class: "clip-rect",
+        hidden: true,
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Rectangle that displays the element quads. Only shown for shape-outside.
+    // Only the parts of the rectangle's outline that overlap with the shape is shown.
+    this.markup.createSVGNode({
+      nodeType: "rect",
+      parent: mainSvg,
+      attributes: {
+        id: "quad",
+        class: "quad",
+        hidden: "true",
+        "clip-path": "url(#shapes-clip-path)",
+        x: 0,
+        y: 0,
+        width: 100,
+        height: 100,
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // clipPath that corresponds to the element's quads. Only applied for shape-outside.
+    // This ensures only the parts of the shape that are within the element's quads are
+    // outlined by a solid line.
+    const shapeClipSvg = this.markup.createSVGNode({
+      nodeType: "clipPath",
+      parent: mainSvg,
+      attributes: {
+        id: "quad-clip-path",
+        class: "quad-clip-path",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "rect",
+      parent: shapeClipSvg,
+      attributes: {
+        id: "quad-clip",
+        class: "quad-clip",
+        x: -1,
+        y: -1,
+        width: 102,
+        height: 102,
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    const mainGroup = this.markup.createSVGNode({
+      nodeType: "g",
+      parent: mainSvg,
+      attributes: {
+        id: "group",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Append a polygon for polygon shapes.
+    this.markup.createSVGNode({
+      nodeType: "polygon",
+      parent: mainGroup,
+      attributes: {
+        id: "polygon",
+        class: "polygon",
+        hidden: "true",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Append an ellipse for circle/ellipse shapes.
+    this.markup.createSVGNode({
+      nodeType: "ellipse",
+      parent: mainGroup,
+      attributes: {
+        id: "ellipse",
+        class: "ellipse",
+        hidden: true,
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Append a rect for inset().
+    this.markup.createSVGNode({
+      nodeType: "rect",
+      parent: mainGroup,
+      attributes: {
+        id: "rect",
+        class: "rect",
+        hidden: true,
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Dashed versions of each shape. Only shown for the parts of the shape
+    // that extends past the element's quads.
+    this.markup.createSVGNode({
+      nodeType: "polygon",
+      parent: mainGroup,
+      attributes: {
+        id: "dashed-polygon",
+        class: "polygon",
+        hidden: "true",
+        "stroke-dasharray": "5, 5",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "ellipse",
+      parent: mainGroup,
+      attributes: {
+        id: "dashed-ellipse",
+        class: "ellipse",
+        hidden: "true",
+        "stroke-dasharray": "5, 5",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "rect",
+      parent: mainGroup,
+      attributes: {
+        id: "dashed-rect",
+        class: "rect",
+        hidden: "true",
+        "stroke-dasharray": "5, 5",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "path",
+      parent: mainGroup,
+      attributes: {
+        id: "bounding-box",
+        class: "bounding-box",
+        "stroke-dasharray": "5, 5",
+        hidden: true,
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "path",
+      parent: mainGroup,
+      attributes: {
+        id: "rotate-line",
+        class: "rotate-line",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    // Append a path to display the markers for the shape.
+    this.markup.createSVGNode({
+      nodeType: "path",
+      parent: mainGroup,
+      attributes: {
+        id: "markers-outline",
+        class: "markers-outline",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "path",
+      parent: mainGroup,
+      attributes: {
+        id: "markers",
+        class: "markers",
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    this.markup.createSVGNode({
+      nodeType: "path",
+      parent: mainGroup,
+      attributes: {
+        id: "marker-hover",
+        class: "marker-hover",
+        hidden: true,
+      },
+      prefix: this.ID_CLASS_PREFIX,
+    });
+
+    return container;
+  }
+
+  get currentDimensions() {
+    let dims = this.currentQuads[this.referenceBox][0].bounds;
+    const zoom = getCurrentZoom(this.win);
+
+    // If an SVG element has a stroke, currentQuads will return the stroke bounding box.
+    // However, clip-path always uses the object bounding box unless "stroke-box" is
+    // specified. So, we must calculate the object bounding box if there is a stroke
+    // and "stroke-box" is not specified. stroke only applies to SVG elements, so use
+    // getBBox, which only exists for SVG, to check if currentNode is an SVG element.
+    if (
+      this.drawingNode.getBBox &&
+      getComputedStyle(this.drawingNode).stroke !== "none" &&
+      !this.useStrokeBox
+    ) {
+      dims = getObjectBoundingBox(
+        dims.top,
+        dims.left,
+        dims.width,
+        dims.height,
+        this.drawingNode
+      );
+    }
+
+    return {
+      top: dims.top / zoom,
+      left: dims.left / zoom,
+      width: dims.width / zoom,
+      height: dims.height / zoom,
+    };
+  }
+
+  get frameDimensions() {
+    // In an iframe, we get the node's quads relative to the frame, instead of the parent
+    // document.
+    let dims =
+      this.highlighterEnv.window.document === this.drawingNode.ownerDocument
+        ? this.currentQuads[this.referenceBox][0].bounds
+        : getAdjustedQuads(
+            this.drawingNode.ownerGlobal,
+            this.drawingNode,
+            this.referenceBox
+          )[0].bounds;
+    const zoom = getCurrentZoom(this.win);
+
+    // If an SVG element has a stroke, currentQuads will return the stroke bounding box.
+    // However, clip-path always uses the object bounding box unless "stroke-box" is
+    // specified. So, we must calculate the object bounding box if there is a stroke
+    // and "stroke-box" is not specified. stroke only applies to SVG elements, so use
+    // getBBox, which only exists for SVG, to check if currentNode is an SVG element.
+    if (
+      this.drawingNode.getBBox &&
+      getComputedStyle(this.drawingNode).stroke !== "none" &&
+      !this.useStrokeBox
+    ) {
+      dims = getObjectBoundingBox(
+        dims.top,
+        dims.left,
+        dims.width,
+        dims.height,
+        this.drawingNode
+      );
+    }
+
+    return {
+      top: dims.top / zoom,
+      left: dims.left / zoom,
+      width: dims.width / zoom,
+      height: dims.height / zoom,
+    };
+  }
+
+  /**
+   * Changes the appearance of the mouse cursor on the highlighter.
+   *
+   * Because we can't attach event handlers to individual elements in the
+   * highlighter, we determine if the mouse is hovering over a point by seeing if
+   * it's within 5 pixels of it. This creates a square hitbox that doesn't match
+   * perfectly with the circular markers. So if we were to use the :hover
+   * pseudo-class to apply changes to the mouse cursor, the cursor change would not
+   * always accurately reflect whether you can interact with the point. This is
+   * also the reason we have the hidden marker-hover element instead of using CSS
+   * to fill in the marker.
+   *
+   * In addition, the cursor CSS property is applied to .shapes-root because if
+   * it were attached to .shapes-marker, the cursor change no longer applies if
+   * you are for example resizing the shape and your mouse goes off the point.
+   * Also, if you are dragging a polygon point, the marker plays catch up to your
+   * mouse position, resulting in an undesirable visual effect where the cursor
+   * rapidly flickers between "grab" and "auto".
+   *
+   * @param {String} cursorType the name of the cursor to display
+   */
+  setCursor(cursorType) {
+    const container = this.getElement("root");
+    let style = container.getAttribute("style");
+    // remove existing cursor definitions in the style
+    style = style.replace(/cursor:.*?;/g, "");
+    style = style.replace(/pointer-events:.*?;/g, "");
+    const pointerEvents = cursorType === "auto" ? "none" : "auto";
+    container.setAttribute(
+      "style",
+      `${style}pointer-events:${pointerEvents};cursor:${cursorType};`
+    );
+  }
+
+  /**
+   * Set the absolute pixel offsets which define the current viewport in relation to
+   * the full page size.
+   *
+   * If a padding value is given, inset the viewport by this value. This is used to define
+   * a virtual viewport which ensures some element remains visible even when at the edges
+   * of the actual viewport.
+   *
+   * @param {Number} padding
+   *        Optional. Amount by which to inset the viewport in all directions.
+   */
+  setViewport(padding = 0) {
+    let xOffset = 0;
+    let yOffset = 0;
+
+    // If the node exists within an iframe, get offsets for the virtual viewport so that
+    // points can be dragged to the extent of the global window, outside of the iframe
+    // window.
+    if (this.currentNode.ownerGlobal !== this.win) {
+      const win = this.win;
+      const nodeWin = this.currentNode.ownerGlobal;
+      // Get bounding box of iframe document relative to global document.
+      const bounds = nodeWin.document
+        .getBoxQuads({
+          relativeTo: win.document,
+          createFramesForSuppressedWhitespace: false,
+        })[0]
+        .getBounds();
+      xOffset = bounds.left - nodeWin.scrollX + win.scrollX;
+      yOffset = bounds.top - nodeWin.scrollY + win.scrollY;
+    }
+
+    const { pageXOffset, pageYOffset } = this.win;
+    const { clientHeight, clientWidth } = this.win.document.documentElement;
+    const left = pageXOffset + padding - xOffset;
+    const right = clientWidth + pageXOffset - padding - xOffset;
+    const top = pageYOffset + padding - yOffset;
+    const bottom = clientHeight + pageYOffset - padding - yOffset;
+    this.viewport = { left, right, top, bottom, padding };
+  }
+
+  // eslint-disable-next-line complexity
+  handleEvent(event, id) {
+    // No event handling if the highlighter is hidden
+    if (this.areShapesHidden()) {
+      return;
+    }
+
+    let { target, type, pageX, pageY } = event;
+
+    // For events on highlighted nodes in an iframe, when the event takes place
+    // outside the iframe. Check if event target belongs to the iframe. If it doesn't,
+    // adjust pageX/pageY to be relative to the iframe rather than the parent.
+    const nodeDocument = this.currentNode.ownerDocument;
+    if (target !== nodeDocument && target.ownerDocument !== nodeDocument) {
+      const [xOffset, yOffset] = getFrameOffsets(
+        target.ownerGlobal,
+        this.currentNode
+      );
+      const zoom = getCurrentZoom(this.win);
+      // xOffset/yOffset are relative to the viewport, so first find the top/left
+      // edges of the viewport relative to the page.
+      const viewportLeft = pageX - event.clientX;
+      const viewportTop = pageY - event.clientY;
+      // Also adjust for scrolling in the iframe.
+      const { scrollTop, scrollLeft } = nodeDocument.documentElement;
+      pageX -= viewportLeft + xOffset / zoom - scrollLeft;
+      pageY -= viewportTop + yOffset / zoom - scrollTop;
+    }
+
+    switch (type) {
+      case "pagehide":
+        // If a page hide event is triggered for current window's highlighter, hide the
+        // highlighter.
+        if (target.defaultView === this.win) {
+          this.destroy();
+        }
+
+        break;
+      case "mousedown":
+        if (this.transformMode) {
+          this._handleTransformClick(pageX, pageY);
+        } else if (this.shapeType === "polygon") {
+          this._handlePolygonClick(pageX, pageY);
+        } else if (this.shapeType === "circle") {
+          this._handleCircleClick(pageX, pageY);
+        } else if (this.shapeType === "ellipse") {
+          this._handleEllipseClick(pageX, pageY);
+        } else if (this.shapeType === "inset") {
+          this._handleInsetClick(pageX, pageY);
+        }
+        event.stopPropagation();
+        event.preventDefault();
+
+        // Calculate constraints for a virtual viewport which ensures that a dragged
+        // marker remains visible even at the edges of the actual viewport.
+        this.setViewport(BASE_MARKER_SIZE);
+        break;
+      case "mouseup":
+        if (this[_dragging]) {
+          this[_dragging] = null;
+          this._handleMarkerHover(this.hoveredPoint);
+        }
+        break;
+      case "mousemove":
+        if (!this[_dragging]) {
+          this._handleMouseMoveNotDragging(pageX, pageY);
+          return;
+        }
+        event.stopPropagation();
+        event.preventDefault();
+
+        // Set constraints for mouse position to ensure dragged marker stays in viewport.
+        const { left, right, top, bottom } = this.viewport;
+        pageX = Math.min(Math.max(left, pageX), right);
+        pageY = Math.min(Math.max(top, pageY), bottom);
+
+        const { point } = this[_dragging];
+        if (this.transformMode) {
+          this._handleTransformMove(pageX, pageY);
+        } else if (this.shapeType === "polygon") {
+          this._handlePolygonMove(pageX, pageY);
+        } else if (this.shapeType === "circle") {
+          this._handleCircleMove(point, pageX, pageY);
+        } else if (this.shapeType === "ellipse") {
+          this._handleEllipseMove(point, pageX, pageY);
+        } else if (this.shapeType === "inset") {
+          this._handleInsetMove(point, pageX, pageY);
+        }
+        break;
+      case "dblclick":
+        if (this.shapeType === "polygon" && !this.transformMode) {
+          const { percentX, percentY } = this.convertPageCoordsToPercent(
+            pageX,
+            pageY
+          );
+          const index = this.getPolygonPointAt(percentX, percentY);
+          if (index === -1) {
+            this.getPolygonClickedLine(percentX, percentY);
+            return;
+          }
+
+          this._deletePolygonPoint(index);
+        }
+        break;
+    }
+  }
+
+  /**
+   * Handle a mouse click in transform mode.
+   * @param {Number} pageX the x coordinate of the mouse
+   * @param {Number} pageY the y coordinate of the mouse
+   */
+  _handleTransformClick(pageX, pageY) {
+    const { percentX, percentY } = this.convertPageCoordsToPercent(
+      pageX,
+      pageY
+    );
+    const type = this.getTransformPointAt(percentX, percentY);
+    if (!type) {
+      return;
+    }
+
+    if (this.shapeType === "polygon") {
+      this._handlePolygonTransformClick(pageX, pageY, type);
+    } else if (this.shapeType === "circle") {
+      this._handleCircleTransformClick(pageX, pageY, type);
+    } else if (this.shapeType === "ellipse") {
+      this._handleEllipseTransformClick(pageX, pageY, type);
+    } else if (this.shapeType === "inset") {
+      this._handleInsetTransformClick(pageX, pageY, type);
+    }
+  }
+
+  /**
+   * Handle a click in transform mode while highlighting a polygon.
+   * @param {Number} pageX the x coordinate of the mouse.
+   * @param {Number} pageY the y coordinate of the mouse.
+   * @param {String} type the type of transform handle that was clicked.
+   */
+  _handlePolygonTransformClick(pageX, pageY, type) {
+    const { width, height } = this.currentDimensions;
+    const pointsInfo = this.origCoordUnits.map(([x, y], i) => {
+      const xComputed = (this.origCoordinates[i][0] / 100) * width;
+      const yComputed = (this.origCoordinates[i][1] / 100) * height;
+      const unitX = getUnit(x);
+      const unitY = getUnit(y);
+      const valueX = isUnitless(x) ? xComputed : parseFloat(x);
+      const valueY = isUnitless(y) ? yComputed : parseFloat(y);
+
+      const ratioX = this.getUnitToPixelRatio(unitX, width);
+      const ratioY = this.getUnitToPixelRatio(unitY, height);
+      return { unitX, unitY, valueX, valueY, ratioX, ratioY };
+    });
+    this[_dragging] = {
+      type,
+      pointsInfo,
+      x: pageX,
+      y: pageY,
+      bb: this.boundingBox,
+      matrix: this.transformMatrix,
+      transformedBB: this.transformedBoundingBox,
+    };
+    this._handleMarkerHover(this.hoveredPoint);
+  }
+
+  /**
+   * Handle a click in transform mode while highlighting a circle.
+   * @param {Number} pageX the x coordinate of the mouse.
+   * @param {Number} pageY the y coordinate of the mouse.
+   * @param {String} type the type of transform handle that was clicked.
+   */
+  _handleCircleTransformClick(pageX, pageY, type) {
+    const { width, height } = this.currentDimensions;
+    const { cx, cy } = this.origCoordUnits;
+    const cxComputed = (this.origCoordinates.cx / 100) * width;
+    const cyComputed = (this.origCoordinates.cy / 100) * height;
+    const unitX = getUnit(cx);
+    const unitY = getUnit(cy);
+    const valueX = isUnitless(cx) ? cxComputed : parseFloat(cx);
+    const valueY = isUnitless(cy) ? cyComputed : parseFloat(cy);
+
+    const ratioX = this.getUnitToPixelRatio(unitX, width);
+    const ratioY = this.getUnitToPixelRatio(unitY, height);
+
+    let { radius } = this.origCoordinates;
+    const computedSize = Math.sqrt(width ** 2 + height ** 2) / Math.sqrt(2);
+    radius = (radius / 100) * computedSize;
+    let valueRad = this.origCoordUnits.radius;
+    const unitRad = getUnit(valueRad);
+    valueRad = isUnitless(valueRad) ? radius : parseFloat(valueRad);
+    const ratioRad = this.getUnitToPixelRatio(unitRad, computedSize);
+
+    this[_dragging] = {
+      type,
+      unitX,
+      unitY,
+      unitRad,
+      valueX,
+      valueY,
+      ratioX,
+      ratioY,
+      ratioRad,
+      x: pageX,
+      y: pageY,
+      bb: this.boundingBox,
+      matrix: this.transformMatrix,
+      transformedBB: this.transformedBoundingBox,
+    };
+  }
+
+  /**
+   * Handle a click in transform mode while highlighting an ellipse.
+   * @param {Number} pageX the x coordinate of the mouse.
+   * @param {Number} pageY the y coordinate of the mouse.
+   * @param {String} type the type of transform handle that was clicked.
+   */
+  _handleEllipseTransformClick(pageX, pageY, type) {
+    const { width, height } = this.currentDimensions;
+    const { cx, cy } = this.origCoordUnits;
+    const cxComputed = (this.origCoordinates.cx / 100) * width;
+    const cyComputed = (this.origCoordinates.cy / 100) * height;
+    const unitX = getUnit(cx);
+    const unitY = getUnit(cy);
+    const valueX = isUnitless(cx) ? cxComputed : parseFloat(cx);
+    const valueY = isUnitless(cy) ? cyComputed : parseFloat(cy);
+
+    const ratioX = this.getUnitToPixelRatio(unitX, width);
+    const ratioY = this.getUnitToPixelRatio(unitY, height);
+
+    let { rx, ry } = this.origCoordinates;
+    rx = (rx / 100) * width;
+    let valueRX = this.origCoordUnits.rx;
+    const unitRX = getUnit(valueRX);
+    valueRX = isUnitless(valueRX) ? rx : parseFloat(valueRX);
+    const ratioRX = valueRX / rx || 1;
+    ry = (ry / 100) * height;
+    let valueRY = this.origCoordUnits.ry;
+    const unitRY = getUnit(valueRY);
+    valueRY = isUnitless(valueRY) ? ry : parseFloat(valueRY);
+    const ratioRY = valueRY / ry || 1;
+
+    this[_dragging] = {
+      type,
+      unitX,
+      unitY,
+      unitRX,
+      unitRY,
+      valueX,
+      valueY,
+      ratioX,
+      ratioY,
+      ratioRX,
+      ratioRY,
+      x: pageX,
+      y: pageY,
+      bb: this.boundingBox,
+      matrix: this.transformMatrix,
+      transformedBB: this.transformedBoundingBox,
+    };
+  }
+
+  /**
+   * Handle a click in transform mode while highlighting an inset.
+   * @param {Number} pageX the x coordinate of the mouse.
+   * @param {Number} pageY the y coordinate of the mouse.
+   * @param {String} type the type of transform handle that was clicked.
+   */
+  _handleInsetTransformClick(pageX, pageY, type) {
+    const { width, height } = this.currentDimensions;
+    const pointsInfo = {};
+    ["top", "right", "bottom", "left"].forEach(point => {
+      let value = this.origCoordUnits[point];
+      const size = point === "left" || point === "right" ? width : height;
+      const computedValue = (this.origCoordinates[point] / 100) * size;
+      const unit = getUnit(value);
+      value = isUnitless(value) ? computedValue : parseFloat(value);
+      const ratio = this.getUnitToPixelRatio(unit, size);
+
+      pointsInfo[point] = { value, unit, ratio };
+    });
+    this[_dragging] = {
+      type,
+      pointsInfo,
+      x: pageX,
+      y: pageY,
+      bb: this.boundingBox,
+      matrix: this.transformMatrix,
+      transformedBB: this.transformedBoundingBox,
+    };
+  }
+
+  /**
+   * Handle mouse movement after a click on a handle in transform mode.
+   * @param {Number} pageX the x coordinate of the mouse
+   * @param {Number} pageY the y coordinate of the mouse
+   */
+  _handleTransformMove(pageX, pageY) {
+    const { type } = this[_dragging];
+    if (type === "translate") {
+      this._translateShape(pageX, pageY);
+    } else if (type.includes("scale")) {
+      this._scaleShape(pageX, pageY);
+    } else if (type === "rotate" && this.shapeType === "polygon") {
+      this._rotateShape(pageX, pageY);
+    }
+
+    this.transformedBoundingBox = this.calculateTransformedBoundingBox();
+  }
+
+  /**
+   * Translates a shape based on the current mouse position.
+   * @param {Number} pageX the x coordinate of the mouse.
+   * @param {Number} pageY the y coordinate of the mouse.
+   */
+  _translateShape(pageX, pageY) {
+    const { x, y, matrix } = this[_dragging];
+    const deltaX = pageX - x;
+    const deltaY = pageY - y;
+    this.transformMatrix = multiply(translate(deltaX, deltaY), matrix);
+
+    if (this.shapeType === "polygon") {
+      this._transformPolygon();
+    } else if (this.shapeType === "circle") {
+      this._transformCircle();
+    } else if (this.shapeType === "ellipse") {
+      this._transformEllipse();
+    } else if (this.shapeType === "inset") {
+      this._transformInset();
+    }
+  }
+
+  /**
+   * Scales a shape according to the current mouse position.
+   * @param {Number} pageX the x coordinate of the mouse.
+   * @param {Number} pageY the y coordinate of the mouse.
+   */
+  _scaleShape(pageX, pageY) {
+    /**
+     * To scale a shape:
+     * 1) Get the change of basis matrix corresponding to the current transformation
+     *    matrix of the shape.
+     * 2) Convert the mouse x/y deltas to the "transformed" coordinate system, using
+     *    the change of base matrix.
+     * 3) Calculate the proportion to which the shape should be scaled to, using the
+     *    mouse x/y deltas and the width/height of the transformed shape.
+     * 4) Translate the shape such that the anchor (the point opposite to the one
+     *    being dragged) is at the top left of the element.
+     * 5) Scale each point by multiplying by the scaling proportion.
+     * 6) Translate the shape back such that the anchor is in its original position.
+     */
+    const { type, x, y, matrix } = this[_dragging];
+    const { width, height } = this.currentDimensions;
+    // The point opposite to the one being dragged
+    const anchor = getAnchorPoint(type);
+
+    const { ne, nw, sw } = this[_dragging].transformedBB;
+    // u/v are the basis vectors of the transformed coordinate system.
+    const u = [
+      ((ne[0] - nw[0]) / 100) * width,
+      ((ne[1] - nw[1]) / 100) * height,
+    ];
+    const v = [
+      ((sw[0] - nw[0]) / 100) * width,
+      ((sw[1] - nw[1]) / 100) * height,
+    ];
+    // uLength/vLength represent the width/height of the shape in the
+    // transformed coordinate system.
+    const { basis, invertedBasis, uLength, vLength } = getBasis(u, v);
+
+    // How much points on each axis should be translated before scaling
+    const transX = (this[_dragging].transformedBB[anchor][0] / 100) * width;
+    const transY = (this[_dragging].transformedBB[anchor][1] / 100) * height;
+
+    // Distance from original click to current mouse position
+    const distanceX = pageX - x;
+    const distanceY = pageY - y;
+    // Convert from original coordinate system to transformed coordinate system
+    const tDistanceX =
+      invertedBasis[0] * distanceX + invertedBasis[1] * distanceY;
+    const tDistanceY =
+      invertedBasis[3] * distanceX + invertedBasis[4] * distanceY;
+
+    // Proportion of distance to bounding box width/height of shape
+    const proportionX = tDistanceX / uLength;
+    const proportionY = tDistanceY / vLength;
+    // proportionX is positive for size reductions dragging on w/nw/sw,
+    // negative for e/ne/se.
+    const scaleX = type.includes("w") ? 1 - proportionX : 1 + proportionX;
+    // proportionT is positive for size reductions dragging on n/nw/ne,
+    // negative for s/sw/se.
+    const scaleY = type.includes("n") ? 1 - proportionY : 1 + proportionY;
+    // Take the average of scaleX/scaleY for scaling on two axes
+    const scaleXY = (scaleX + scaleY) / 2;
+
+    const translateMatrix = translate(-transX, -transY);
+    let scaleMatrix = identity();
+    // The scale matrices are in the transformed coordinate system. We must convert
+    // them to the original coordinate system before applying it to the transformation
+    // matrix.
+    if (type === "scale-e" || type === "scale-w") {
+      scaleMatrix = changeMatrixBase(scale(scaleX, 1), invertedBasis, basis);
+    } else if (type === "scale-n" || type === "scale-s") {
+      scaleMatrix = changeMatrixBase(scale(1, scaleY), invertedBasis, basis);
+    } else {
+      scaleMatrix = changeMatrixBase(
+        scale(scaleXY, scaleXY),
+        invertedBasis,
+        basis
+      );
+    }
+    const translateBackMatrix = translate(transX, transY);
+    this.transformMatrix = multiply(
+      translateBackMatrix,
+      multiply(scaleMatrix, multiply(translateMatrix, matrix))
+    );
+
+    if (this.shapeType === "polygon") {
+      this._transformPolygon();
+    } else if (this.shapeType === "circle") {
+      this._transformCircle(transX);
+    } else if (this.shapeType === "ellipse") {
+      this._transformEllipse(transX, transY);
+    } else if (this.shapeType === "inset") {
+      this._transformInset();
+    }
+  }
+
+  /**
+   * Rotates a polygon based on the current mouse position.
+   * @param {Number} pageX the x coordinate of the mouse.
+   * @param {Number} pageY the y coordinate of the mouse.
+   */
+  _rotateShape(pageX, pageY) {
+    const { matrix } = this[_dragging];
+    const { center, ne, nw, sw } = this[_dragging].transformedBB;
+    const { width, height } = this.currentDimensions;
+    const centerX = (center[0] / 100) * width;
+    const centerY = (center[1] / 100) * height;
+    const { x: pageCenterX, y: pageCenterY } = this.convertPercentToPageCoords(
+      ...center
+    );
+
+    const dx = pageCenterX - pageX;
+    const dy = pageCenterY - pageY;
+
+    const u = [
+      ((ne[0] - nw[0]) / 100) * width,
+      ((ne[1] - nw[1]) / 100) * height,
+    ];
+    const v = [
+      ((sw[0] - nw[0]) / 100) * width,
+      ((sw[1] - nw[1]) / 100) * height,
+    ];
+    const { invertedBasis } = getBasis(u, v);
+
+    const tdx = invertedBasis[0] * dx + invertedBasis[1] * dy;
+    const tdy = invertedBasis[3] * dx + invertedBasis[4] * dy;
+    const angle = Math.atan2(tdx, tdy);
+    const translateMatrix = translate(-centerX, -centerY);
+    const rotateMatrix = rotate(angle);
+    const translateBackMatrix = translate(centerX, centerY);
+    this.transformMatrix = multiply(
+      translateBackMatrix,
+      multiply(rotateMatrix, multiply(translateMatrix, matrix))
+    );
+
+    this._transformPolygon();
+  }
+
+  /**
+   * Transform a polygon depending on the current transformation matrix.
+   */
+  _transformPolygon() {
+    const { pointsInfo } = this[_dragging];
+
+    let polygonDef = this.fillRule ? `${this.fillRule}, ` : "";
+    polygonDef += pointsInfo
+      .map(point => {
+        const { unitX, unitY, valueX, valueY, ratioX, ratioY } = point;
+        const vector = [valueX / ratioX, valueY / ratioY];
+        let [newX, newY] = apply(this.transformMatrix, vector);
+        newX = round(newX * ratioX, unitX);
+        newY = round(newY * ratioY, unitY);
+
+        return `${newX}${unitX} ${newY}${unitY}`;
+      })
+      .join(", ");
+    polygonDef = `polygon(${polygonDef}) ${this.geometryBox}`.trim();
+
+    this.emit("highlighter-event", { type: "shape-change", value: polygonDef });
+  }
+
+  /**
+   * Transform a circle depending on the current transformation matrix.
+   * @param {Number} transX the number of pixels the shape is translated on the x axis
+   *                 before scaling
+   */
+  _transformCircle(transX = null) {
+    const { unitX, unitY, unitRad, valueX, valueY, ratioX, ratioY, ratioRad } =
+      this[_dragging];
+    let { radius } = this.coordUnits;
+
+    let [newCx, newCy] = apply(this.transformMatrix, [
+      valueX / ratioX,
+      valueY / ratioY,
+    ]);
+    if (transX !== null) {
+      // As part of scaling, the shape is translated to be tangent to the line y=0.
+      // To get the new radius, we translate the new cx back to that point and get
+      // the distance to the line y=0.
+      radius = round(Math.abs((newCx - transX) * ratioRad), unitRad);
+      radius = `${radius}${unitRad}`;
+    }
+
+    newCx = round(newCx * ratioX, unitX);
+    newCy = round(newCy * ratioY, unitY);
+    const circleDef =
+      `circle(${radius} at ${newCx}${unitX} ${newCy}${unitY})` +
+      ` ${this.geometryBox}`.trim();
+    this.emit("highlighter-event", { type: "shape-change", value: circleDef });
+  }
+
+  /**
+   * Transform an ellipse depending on the current transformation matrix.
+   * @param {Number} transX the number of pixels the shape is translated on the x axis
+   *                 before scaling
+   * @param {Number} transY the number of pixels the shape is translated on the y axis
+   *                 before scaling
+   */
+  _transformEllipse(transX = null, transY = null) {
+    const {
+      unitX,
+      unitY,
+      unitRX,
+      unitRY,
+      valueX,
+      valueY,
+      ratioX,
+      ratioY,
+      ratioRX,
+      ratioRY,
+    } = this[_dragging];
+    let { rx, ry } = this.coordUnits;
+
+    let [newCx, newCy] = apply(this.transformMatrix, [
+      valueX / ratioX,
+      valueY / ratioY,
+    ]);
+    if (transX !== null && transY !== null) {
+      // As part of scaling, the shape is translated to be tangent to the lines y=0 & x=0.
+      // To get the new radii, we translate the new center back to that point and get the
+      // distances to the line x=0 and y=0.
+      rx = round(Math.abs((newCx - transX) * ratioRX), unitRX);
+      rx = `${rx}${unitRX}`;
+      ry = round(Math.abs((newCy - transY) * ratioRY), unitRY);
+      ry = `${ry}${unitRY}`;
+    }
+
+    newCx = round(newCx * ratioX, unitX);
+    newCy = round(newCy * ratioY, unitY);
+
+    const centerStr = `${newCx}${unitX} ${newCy}${unitY}`;
+    const ellipseDef =
+      `ellipse(${rx} ${ry} at ${centerStr}) ${this.geometryBox}`.trim();
+    this.emit("highlighter-event", { type: "shape-change", value: ellipseDef });
+  }
+
+  /**
+   * Transform an inset depending on the current transformation matrix.
+   */
+  _transformInset() {
+    const { top, left, right, bottom } = this[_dragging].pointsInfo;
+    const { width, height } = this.currentDimensions;
+
+    const topLeft = [left.value / left.ratio, top.value / top.ratio];
+    let [newLeft, newTop] = apply(this.transformMatrix, topLeft);
+    newLeft = round(newLeft * left.ratio, left.unit);
+    newLeft = `${newLeft}${left.unit}`;
+    newTop = round(newTop * top.ratio, top.unit);
+    newTop = `${newTop}${top.unit}`;
+
+    // Right and bottom values are relative to the right and bottom edges of the
+    // element, so convert to the value relative to the left/top edges before scaling
+    // and convert back.
+    const bottomRight = [
+      width - right.value / right.ratio,
+      height - bottom.value / bottom.ratio,
+    ];
+    let [newRight, newBottom] = apply(this.transformMatrix, bottomRight);
+    newRight = round((width - newRight) * right.ratio, right.unit);
+    newRight = `${newRight}${right.unit}`;
+    newBottom = round((height - newBottom) * bottom.ratio, bottom.unit);
+    newBottom = `${newBottom}${bottom.unit}`;
+
+    let insetDef = this.insetRound
+      ? `inset(${newTop} ${newRight} ${newBottom} ${newLeft} round ${this.insetRound})`
+      : `inset(${newTop} ${newRight} ${newBottom} ${newLeft})`;
+    insetDef += this.geometryBox ? this.geometryBox : "";
+
+    this.emit("highlighter-event", { type: "shape-change", value: insetDef });
+  }
+
+  /**
+   * Handle a click when highlighting a polygon.
+   * @param {Number} pageX the x coordinate of the click
+   * @param {Number} pageY the y coordinate of the click
+   */
+  _handlePolygonClick(pageX, pageY) {
+    const { width, height } = this.currentDimensions;
+    const { percentX, percentY } = this.convertPageCoordsToPercent(
+      pageX,
+      pageY
+    );
+    const point = this.getPolygonPointAt(percentX, percentY);
+    if (point === -1) {
+      return;
+    }
+
+    const [x, y] = this.coordUnits[point];
+    const xComputed = (this.coordinates[point][0] / 100) * width;
+    const yComputed = (this.coordinates[point][1] / 100) * height;
+    const unitX = getUnit(x);
+    const unitY = getUnit(y);
+    const valueX = isUnitless(x) ? xComputed : parseFloat(x);
+    const valueY = isUnitless(y) ? yComputed : parseFloat(y);
+
+    const ratioX = this.getUnitToPixelRatio(unitX, width);
+    const ratioY = this.getUnitToPixelRatio(unitY, height);
+
+    this.setCursor("grabbing");
+    this[_dragging] = {
+      point,
+      unitX,
+      unitY,
+      valueX,
+      valueY,
+      ratioX,
+      ratioY,
+      x: pageX,
+      y: pageY,
+    };
+  }
+
+  /**
+   * Update the dragged polygon point with the given x/y coords and update
+   * the element style.
+   * @param {Number} pageX the new x coordinate of the point
+   * @param {Number} pageY the new y coordinate of the point
+   */
+  _handlePolygonMove(pageX, pageY) {
+    const { point, unitX, unitY, valueX, valueY, ratioX, ratioY, x, y } =
+      this[_dragging];
+    const deltaX = (pageX - x) * ratioX;
+    const deltaY = (pageY - y) * ratioY;
+    const newX = round(valueX + deltaX, unitX);
+    const newY = round(valueY + deltaY, unitY);
+
+    let polygonDef = this.fillRule ? `${this.fillRule}, ` : "";
+    polygonDef += this.coordUnits
+      .map((coords, i) => {
+        return i === point
+          ? `${newX}${unitX} ${newY}${unitY}`
+          : `${coords[0]} ${coords[1]}`;
+      })
+      .join(", ");
+    polygonDef = `polygon(${polygonDef}) ${this.geometryBox}`.trim();
+
+    this.emit("highlighter-event", { type: "shape-change", value: polygonDef });
+  }
+
+  /**
+   * Add new point to the polygon defintion and update element style.
+   * TODO: Bug 1436054 - Do not default to percentage unit when inserting new point.
+   * https://bugzilla.mozilla.org/show_bug.cgi?id=1436054
+   *
+   * @param {Number} after the index of the point that the new point should be added after
+   * @param {Number} x the x coordinate of the new point
+   * @param {Number} y the y coordinate of the new point
+   */
+  _addPolygonPoint(after, x, y) {
+    let polygonDef = this.fillRule ? `${this.fillRule}, ` : "";
+    polygonDef += this.coordUnits
+      .map((coords, i) => {
+        return i === after
+          ? `${coords[0]} ${coords[1]}, ${x}% ${y}%`
+          : `${coords[0]} ${coords[1]}`;
+      })
+      .join(", ");
+    polygonDef = `polygon(${polygonDef}) ${this.geometryBox}`.trim();
+
+    this.hoveredPoint = after + 1;
+    this._emitHoverEvent(this.hoveredPoint);
+    this.emit("highlighter-event", { type: "shape-change", value: polygonDef });
+  }
+
+  /**
+   * Remove point from polygon defintion and update the element style.
+   * @param {Number} point the index of the point to delete
+   */
+  _deletePolygonPoint(point) {
+    const coordinates = this.coordUnits.slice();
+    coordinates.splice(point, 1);
+    let polygonDef = this.fillRule ? `${this.fillRule}, ` : "";
+    polygonDef += coordinates
+      .map((coords, i) => {
+        return `${coords[0]} ${coords[1]}`;
+      })
+      .join(", ");
+    polygonDef = `polygon(${polygonDef}) ${this.geometryBox}`.trim();
+
+    this.hoveredPoint = null;
+    this._emitHoverEvent(this.hoveredPoint);
+    this.emit("highlighter-event", { type: "shape-change", value: polygonDef });
+  }
+  /**
+   * Handle a click when highlighting a circle.
+   * @param {Number} pageX the x coordinate of the click
+   * @param {Number} pageY the y coordinate of the click
+   */
+  _handleCircleClick(pageX, pageY) {
+    const { width, height } = this.currentDimensions;
+    const { percentX, percentY } = this.convertPageCoordsToPercent(
+      pageX,
+      pageY
+    );
+    const point = this.getCirclePointAt(percentX, percentY);
+    if (!point) {
+      return;
+    }
+
+    this.setCursor("grabbing");
+    if (point === "center") {
+      const { cx, cy } = this.coordUnits;
+      const cxComputed = (this.coordinates.cx / 100) * width;
+      const cyComputed = (this.coordinates.cy / 100) * height;
+      const unitX = getUnit(cx);
+      const unitY = getUnit(cy);
+      const valueX = isUnitless(cx) ? cxComputed : parseFloat(cx);
+      const valueY = isUnitless(cy) ? cyComputed : parseFloat(cy);
+
+      const ratioX = this.getUnitToPixelRatio(unitX, width);
+      const ratioY = this.getUnitToPixelRatio(unitY, height);
+
+      this[_dragging] = {
+        point,
+        unitX,
+        unitY,
+        valueX,
+        valueY,
+        ratioX,
+        ratioY,
+        x: pageX,
+        y: pageY,
+      };
+    } else if (point === "radius") {
+      let { radius } = this.coordinates;
+      const computedSize = Math.sqrt(width ** 2 + height ** 2) / Math.sqrt(2);
+      radius = (radius / 100) * computedSize;
+      let value = this.coordUnits.radius;
+      const unit = getUnit(value);
+      value = isUnitless(value) ? radius : parseFloat(value);
+      const ratio = this.getUnitToPixelRatio(unit, computedSize);
+
+      this[_dragging] = { point, value, origRadius: radius, unit, ratio };
+    }
+  }
+
+  /**
+   * Set the center/radius of the circle according to the mouse position and
+   * update the element style.
+   * @param {String} point either "center" or "radius"
+   * @param {Number} pageX the x coordinate of the mouse position, in terms of %
+   *        relative to the element
+   * @param {Number} pageY the y coordinate of the mouse position, in terms of %
+   *        relative to the element
+   */
+  _handleCircleMove(point, pageX, pageY) {
+    const { radius, cx, cy } = this.coordUnits;
+
+    if (point === "center") {
+      const { unitX, unitY, valueX, valueY, ratioX, ratioY, x, y } =
+        this[_dragging];
+      const deltaX = (pageX - x) * ratioX;
+      const deltaY = (pageY - y) * ratioY;
+      const newCx = `${round(valueX + deltaX, unitX)}${unitX}`;
+      const newCy = `${round(valueY + deltaY, unitY)}${unitY}`;
+      // if not defined by the user, geometryBox will be an empty string; trim() cleans up
+      const circleDef =
+        `circle(${radius} at ${newCx} ${newCy}) ${this.geometryBox}`.trim();
+
+      this.emit("highlighter-event", {
+        type: "shape-change",
+        value: circleDef,
+      });
+    } else if (point === "radius") {
+      const { value, unit, origRadius, ratio } = this[_dragging];
+      // convert center point to px, then get distance between center and mouse.
+      const { x: pageCx, y: pageCy } = this.convertPercentToPageCoords(
+        this.coordinates.cx,
+        this.coordinates.cy
+      );
+      const newRadiusPx = getDistance(pageCx, pageCy, pageX, pageY);
+
+      const delta = (newRadiusPx - origRadius) * ratio;
+      const newRadius = `${round(value + delta, unit)}${unit}`;
+
+      const position = cx !== "" ? ` at ${cx} ${cy}` : "";
+      const circleDef =
+        `circle(${newRadius}${position}) ${this.geometryBox}`.trim();
+
+      this.emit("highlighter-event", {
+        type: "shape-change",
+        value: circleDef,
+      });
+    }
+  }
+
+  /**
+   * Handle a click when highlighting an ellipse.
+   * @param {Number} pageX the x coordinate of the click
+   * @param {Number} pageY the y coordinate of the click
+   */
+  _handleEllipseClick(pageX, pageY) {
+    const { width, height } = this.currentDimensions;
+    const { percentX, percentY } = this.convertPageCoordsToPercent(
+      pageX,
+      pageY
+    );
+    const point = this.getEllipsePointAt(percentX, percentY);
+    if (!point) {
+      return;
+    }
+
+    this.setCursor("grabbing");
+    if (point === "center") {
+      const { cx, cy } = this.coordUnits;
+      const cxComputed = (this.coordinates.cx / 100) * width;
+      const cyComputed = (this.coordinates.cy / 100) * height;
+      const unitX = getUnit(cx);
+      const unitY = getUnit(cy);
+      const valueX = isUnitless(cx) ? cxComputed : parseFloat(cx);
+      const valueY = isUnitless(cy) ? cyComputed : parseFloat(cy);
+
+      const ratioX = this.getUnitToPixelRatio(unitX, width);
+      const ratioY = this.getUnitToPixelRatio(unitY, height);
+
+      this[_dragging] = {
+        point,
+        unitX,
+        unitY,
+        valueX,
+        valueY,
+        ratioX,
+        ratioY,
+        x: pageX,
+        y: pageY,
+      };
+    } else if (point === "rx") {
+      let { rx } = this.coordinates;
+      rx = (rx / 100) * width;
+      let value = this.coordUnits.rx;
+      const unit = getUnit(value);
+      value = isUnitless(value) ? rx : parseFloat(value);
+      const ratio = this.getUnitToPixelRatio(unit, width);
+
+      this[_dragging] = { point, value, origRadius: rx, unit, ratio };
+    } else if (point === "ry") {
+      let { ry } = this.coordinates;
+      ry = (ry / 100) * height;
+      let value = this.coordUnits.ry;
+      const unit = getUnit(value);
+      value = isUnitless(value) ? ry : parseFloat(value);
+      const ratio = this.getUnitToPixelRatio(unit, height);
+
+      this[_dragging] = { point, value, origRadius: ry, unit, ratio };
+    }
+  }
+
+  /**
+   * Set center/rx/ry of the ellispe according to the mouse position and update the
+   * element style.
+   * @param {String} point "center", "rx", or "ry"
+   * @param {Number} pageX the x coordinate of the mouse position, in terms of %
+   *        relative to the element
+   * @param {Number} pageY the y coordinate of the mouse position, in terms of %
+   *        relative to the element
+   */
+  _handleEllipseMove(point, pageX, pageY) {
+    const { percentX, percentY } = this.convertPageCoordsToPercent(
+      pageX,
+      pageY
+    );
+    const { rx, ry, cx, cy } = this.coordUnits;
+    const position = cx !== "" ? ` at ${cx} ${cy}` : "";
+
+    if (point === "center") {
+      const { unitX, unitY, valueX, valueY, ratioX, ratioY, x, y } =
+        this[_dragging];
+      const deltaX = (pageX - x) * ratioX;
+      const deltaY = (pageY - y) * ratioY;
+      const newCx = `${round(valueX + deltaX, unitX)}${unitX}`;
+      const newCy = `${round(valueY + deltaY, unitY)}${unitY}`;
+      const ellipseDef =
+        `ellipse(${rx} ${ry} at ${newCx} ${newCy}) ${this.geometryBox}`.trim();
+
+      this.emit("highlighter-event", {
+        type: "shape-change",
+        value: ellipseDef,
+      });
+    } else if (point === "rx") {
+      const { value, unit, origRadius, ratio } = this[_dragging];
+      const newRadiusPercent = Math.abs(percentX - this.coordinates.cx);
+      const { width } = this.currentDimensions;
+      const delta = ((newRadiusPercent / 100) * width - origRadius) * ratio;
+      const newRadius = `${round(value + delta, unit)}${unit}`;
+
+      const ellipseDef =
+        `ellipse(${newRadius} ${ry}${position}) ${this.geometryBox}`.trim();
+
+      this.emit("highlighter-event", {
+        type: "shape-change",
+        value: ellipseDef,
+      });
+    } else if (point === "ry") {
+      const { value, unit, origRadius, ratio } = this[_dragging];
+      const newRadiusPercent = Math.abs(percentY - this.coordinates.cy);
+      const { height } = this.currentDimensions;
+      const delta = ((newRadiusPercent / 100) * height - origRadius) * ratio;
+      const newRadius = `${round(value + delta, unit)}${unit}`;
+
+      const ellipseDef =
+        `ellipse(${rx} ${newRadius}${position}) ${this.geometryBox}`.trim();
+
+      this.emit("highlighter-event", {
+        type: "shape-change",
+        value: ellipseDef,
+      });
+    }
+  }
+
+  /**
+   * Handle a click when highlighting an inset.
+   * @param {Number} pageX the x coordinate of the click
+   * @param {Number} pageY the y coordinate of the click
+   */
+  _handleInsetClick(pageX, pageY) {
+    const { width, height } = this.currentDimensions;
+    const { percentX, percentY } = this.convertPageCoordsToPercent(
+      pageX,
+      pageY
+    );
+    const point = this.getInsetPointAt(percentX, percentY);
+    if (!point) {
+      return;
+    }
+
+    this.setCursor("grabbing");
+    let value = this.coordUnits[point];
+    const size = point === "left" || point === "right" ? width : height;
+    const computedValue = (this.coordinates[point] / 100) * size;
+    const unit = getUnit(value);
+    value = isUnitless(value) ? computedValue : parseFloat(value);
+    const ratio = this.getUnitToPixelRatio(unit, size);
+    const origValue = point === "left" || point === "right" ? pageX : pageY;
+
+    this[_dragging] = { point, value, origValue, unit, ratio };
+  }
+
+  /**
+   * Set the top/left/right/bottom of the inset shape according to the mouse position
+   * and update the element style.
+   * @param {String} point "top", "left", "right", or "bottom"
+   * @param {Number} pageX the x coordinate of the mouse position, in terms of %
+   *        relative to the element
+   * @param {Number} pageY the y coordinate of the mouse position, in terms of %
+   *        relative to the element
+   * @memberof ShapesHighlighter
+   */
+  _handleInsetMove(point, pageX, pageY) {
+    let { top, left, right, bottom } = this.coordUnits;
+    const { value, origValue, unit, ratio } = this[_dragging];
+
+    if (point === "left") {
+      const delta = (pageX - origValue) * ratio;
+      left = `${round(value + delta, unit)}${unit}`;
+    } else if (point === "right") {
+      const delta = (pageX - origValue) * ratio;
+      right = `${round(value - delta, unit)}${unit}`;
+    } else if (point === "top") {
+      const delta = (pageY - origValue) * ratio;
+      top = `${round(value + delta, unit)}${unit}`;
+    } else if (point === "bottom") {
+      const delta = (pageY - origValue) * ratio;
+      bottom = `${round(value - delta, unit)}${unit}`;
+    }
+
+    let insetDef = this.insetRound
+      ? `inset(${top} ${right} ${bottom} ${left} round ${this.insetRound})`
+      : `inset(${top} ${right} ${bottom} ${left})`;
+
+    insetDef += this.geometryBox ? this.geometryBox : "";
+
+    this.emit("highlighter-event", { type: "shape-change", value: insetDef });
+  }
+
+  _handleMouseMoveNotDragging(pageX, pageY) {
+    const { percentX, percentY } = this.convertPageCoordsToPercent(
+      pageX,
+      pageY
+    );
+    if (this.transformMode) {
+      const point = this.getTransformPointAt(percentX, percentY);
+      this.hoveredPoint = point;
+      this._handleMarkerHover(point);
+    } else if (this.shapeType === "polygon") {
+      const point = this.getPolygonPointAt(percentX, percentY);
+      const oldHoveredPoint = this.hoveredPoint;
+      this.hoveredPoint = point !== -1 ? point : null;
+      if (this.hoveredPoint !== oldHoveredPoint) {
+        this._emitHoverEvent(this.hoveredPoint);
+      }
+      this._handleMarkerHover(point);
+    } else if (this.shapeType === "circle") {
+      const point = this.getCirclePointAt(percentX, percentY);
+      const oldHoveredPoint = this.hoveredPoint;
+      this.hoveredPoint = point ? point : null;
+      if (this.hoveredPoint !== oldHoveredPoint) {
+        this._emitHoverEvent(this.hoveredPoint);
+      }
+      this._handleMarkerHover(point);
+    } else if (this.shapeType === "ellipse") {
+      const point = this.getEllipsePointAt(percentX, percentY);
+      const oldHoveredPoint = this.hoveredPoint;
+      this.hoveredPoint = point ? point : null;
+      if (this.hoveredPoint !== oldHoveredPoint) {
+        this._emitHoverEvent(this.hoveredPoint);
+      }
+      this._handleMarkerHover(point);
+    } else if (this.shapeType === "inset") {
+      const point = this.getInsetPointAt(percentX, percentY);
+      const oldHoveredPoint = this.hoveredPoint;
+      this.hoveredPoint = point ? point : null;
+      if (this.hoveredPoint !== oldHoveredPoint) {
+        this._emitHoverEvent(this.hoveredPoint);
+      }
+      this._handleMarkerHover(point);
+    }
+  }
+
+  /**
+   * Change the appearance of the given marker when the mouse hovers over it.
+   * @param {String|Number} point if the shape is a polygon, the integer index of the
+   *        point being hovered. Otherwise, a string identifying the point being hovered.
+   *        Integers < 0 and falsey values excluding 0 indicate no point is being hovered.
+   */
+  _handleMarkerHover(point) {
+    // Hide hover marker for now, will be shown if point is a valid hover target
+    this.getElement("marker-hover").setAttribute("hidden", true);
+    // Catch all falsey values except when point === 0, as that's a valid point
+    if (!point && point !== 0) {
+      this.setCursor("auto");
+      return;
+    }
+    const hoverCursor = this[_dragging] ? "grabbing" : "grab";
+
+    if (this.transformMode) {
+      if (!point) {
+        this.setCursor("auto");
+        return;
+      }
+      const { nw, ne, sw, se, n, w, s, e, rotatePoint, center } =
+        this.transformedBoundingBox;
+
+      const points = [
+        {
+          pointName: "translate",
+          x: center[0],
+          y: center[1],
+          cursor: hoverCursor,
+        },
+        { pointName: "scale-se", x: se[0], y: se[1], anchor: "nw" },
+        { pointName: "scale-ne", x: ne[0], y: ne[1], anchor: "sw" },
+        { pointName: "scale-sw", x: sw[0], y: sw[1], anchor: "ne" },
+        { pointName: "scale-nw", x: nw[0], y: nw[1], anchor: "se" },
+        { pointName: "scale-n", x: n[0], y: n[1], anchor: "s" },
+        { pointName: "scale-s", x: s[0], y: s[1], anchor: "n" },
+        { pointName: "scale-e", x: e[0], y: e[1], anchor: "w" },
+        { pointName: "scale-w", x: w[0], y: w[1], anchor: "e" },
+        {
+          pointName: "rotate",
+          x: rotatePoint[0],
+          y: rotatePoint[1],
+          cursor: hoverCursor,
+        },
+      ];
+
+      for (const { pointName, x, y, cursor, anchor } of points) {
+        if (point === pointName) {
+          this._drawHoverMarker([[x, y]]);
+
+          // If the point is a scale handle, we will need to determine the direction
+          // of the resize cursor based on the position of the handle relative to its
+          // "anchor" (the handle opposite to it).
+          if (pointName.includes("scale")) {
+            const direction = this.getRoughDirection(pointName, anchor);
+            this.setCursor(`${direction}-resize`);
+          } else {
+            this.setCursor(cursor);
+          }
+        }
+      }
+    } else if (this.shapeType === "polygon") {
+      if (point === -1) {
+        this.setCursor("auto");
+        return;
+      }
+      this.setCursor(hoverCursor);
+      this._drawHoverMarker([this.coordinates[point]]);
+    } else if (this.shapeType === "circle") {
+      this.setCursor(hoverCursor);
+
+      const { cx, cy, rx } = this.coordinates;
+      if (point === "radius") {
+        this._drawHoverMarker([[cx + rx, cy]]);
+      } else if (point === "center") {
+        this._drawHoverMarker([[cx, cy]]);
+      }
+    } else if (this.shapeType === "ellipse") {
+      this.setCursor(hoverCursor);
+
+      if (point === "center") {
+        const { cx, cy } = this.coordinates;
+        this._drawHoverMarker([[cx, cy]]);
+      } else if (point === "rx") {
+        const { cx, cy, rx } = this.coordinates;
+        this._drawHoverMarker([[cx + rx, cy]]);
+      } else if (point === "ry") {
+        const { cx, cy, ry } = this.coordinates;
+        this._drawHoverMarker([[cx, cy + ry]]);
+      }
+    } else if (this.shapeType === "inset") {
+      this.setCursor(hoverCursor);
+
+      const { top, right, bottom, left } = this.coordinates;
+      const centerX = (left + (100 - right)) / 2;
+      const centerY = (top + (100 - bottom)) / 2;
+      const points = point.split(",");
+      const coords = points.map(side => {
+        if (side === "top") {
+          return [centerX, top];
+        } else if (side === "right") {
+          return [100 - right, centerY];
+        } else if (side === "bottom") {
+          return [centerX, 100 - bottom];
+        } else if (side === "left") {
+          return [left, centerY];
+        }
+        return null;
+      });
+
+      this._drawHoverMarker(coords);
+    }
+  }
+
+  _drawHoverMarker(points) {
+    const { width, height } = this.currentDimensions;
+    const zoom = getCurrentZoom(this.win);
+    const path = points
+      .map(([x, y]) => {
+        return getCirclePath(BASE_MARKER_SIZE, x, y, width, height, zoom);
+      })
+      .join(" ");
+
+    const markerHover = this.getElement("marker-hover");
+    markerHover.setAttribute("d", path);
+    markerHover.removeAttribute("hidden");
+  }
+
+  _emitHoverEvent(point) {
+    if (point === null || point === undefined) {
+      this.emit("highlighter-event", {
+        type: "shape-hover-off",
+      });
+    } else {
+      this.emit("highlighter-event", {
+        type: "shape-hover-on",
+        point: point.toString(),
+      });
+    }
+  }
+
+  /**
+   * Convert the given coordinates on the page to percentages relative to the current
+   * element.
+   * @param {Number} pageX the x coordinate on the page
+   * @param {Number} pageY the y coordinate on the page
+   * @returns {Object} object of form {percentX, percentY}, which are the x/y coords
+   *          in percentages relative to the element.
+   */
+  convertPageCoordsToPercent(pageX, pageY) {
+    // If the current node is in an iframe, we get dimensions relative to the frame.
+    const dims = this.frameDimensions;
+    const { top, left, width, height } = dims;
+    pageX -= left;
+    pageY -= top;
+    const percentX = (pageX * 100) / width;
+    const percentY = (pageY * 100) / height;
+    return { percentX, percentY };
+  }
+
+  /**
+   * Convert the given x/y coordinates, in percentages relative to the current element,
+   * to pixel coordinates relative to the page
+   * @param {Number} x the x coordinate
+   * @param {Number} y the y coordinate
+   * @returns {Object} object of form {x, y}, which are the x/y coords in pixels
+   *          relative to the page
+   *
+   * @memberof ShapesHighlighter
+   */
+  convertPercentToPageCoords(x, y) {
+    const dims = this.frameDimensions;
+    const { top, left, width, height } = dims;
+    x = (x * width) / 100;
+    y = (y * height) / 100;
+    x += left;
+    y += top;
+    return { x, y };
+  }
+
+  /**
+   * Get which transformation should be applied based on the mouse position.
+   * @param {Number} pageX the x coordinate of the mouse.
+   * @param {Number} pageY the y coordinate of the mouse.
+   * @returns {String} a string describing the transformation that should be applied
+   *          to the shape.
+   */
+  getTransformPointAt(pageX, pageY) {
+    const { nw, ne, sw, se, n, w, s, e, rotatePoint, center } =
+      this.transformedBoundingBox;
+    const { width, height } = this.currentDimensions;
+    const zoom = getCurrentZoom(this.win);
+    const clickRadiusX = ((BASE_MARKER_SIZE / zoom) * 100) / width;
+    const clickRadiusY = ((BASE_MARKER_SIZE / zoom) * 100) / height;
+
+    const points = [
+      { pointName: "translate", x: center[0], y: center[1] },
+      { pointName: "scale-se", x: se[0], y: se[1] },
+      { pointName: "scale-ne", x: ne[0], y: ne[1] },
+      { pointName: "scale-sw", x: sw[0], y: sw[1] },
+      { pointName: "scale-nw", x: nw[0], y: nw[1] },
+    ];
+
+    if (this.shapeType === "polygon" || this.shapeType === "ellipse") {
+      points.push(
+        { pointName: "scale-n", x: n[0], y: n[1] },
+        { pointName: "scale-s", x: s[0], y: s[1] },
+        { pointName: "scale-e", x: e[0], y: e[1] },
+        { pointName: "scale-w", x: w[0], y: w[1] }
+      );
+    }
+
+    if (this.shapeType === "polygon") {
+      const x = rotatePoint[0];
+      const y = rotatePoint[1];
+      if (
+        pageX >= x - clickRadiusX &&
+        pageX <= x + clickRadiusX &&
+        pageY >= y - clickRadiusY &&
+        pageY <= y + clickRadiusY
+      ) {
+        return "rotate";
+      }
+    }
+
+    for (const { pointName, x, y } of points) {
+      if (
+        pageX >= x - clickRadiusX &&
+        pageX <= x + clickRadiusX &&
+        pageY >= y - clickRadiusY &&
+        pageY <= y + clickRadiusY
+      ) {
+        return pointName;
+      }
+    }
+
+    return "";
+  }
+
+  /**
+   * Get the id of the point on the polygon highlighter at the given coordinate.
+   * @param {Number} pageX the x coordinate on the page, in % relative to the element
+   * @param {Number} pageY the y coordinate on the page, in % relative to the element
+   * @returns {Number} the index of the point that was clicked on in this.coordinates,
+   *          or -1 if none of the points were clicked on.
+   */
+  getPolygonPointAt(pageX, pageY) {
+    const { coordinates } = this;
+    const { width, height } = this.currentDimensions;
+    const zoom = getCurrentZoom(this.win);
+    const clickRadiusX = ((BASE_MARKER_SIZE / zoom) * 100) / width;
+    const clickRadiusY = ((BASE_MARKER_SIZE / zoom) * 100) / height;
+
+    for (const [index, coord] of coordinates.entries()) {
+      const [x, y] = coord;
+      if (
+        pageX >= x - clickRadiusX &&
+        pageX <= x + clickRadiusX &&
+        pageY >= y - clickRadiusY &&
+        pageY <= y + clickRadiusY
+      ) {
+        return index;
+      }
+    }
+
+    return -1;
+  }
+
+  /**
+   * Check if the mouse clicked on a line of the polygon, and if so, add a point near
+   * the click.
+   * @param {Number} pageX the x coordinate on the page, in % relative to the element
+   * @param {Number} pageY the y coordinate on the page, in % relative to the element
+   */
+  getPolygonClickedLine(pageX, pageY) {
+    const { coordinates } = this;
+    const { width } = this.currentDimensions;
+    const clickWidth = (LINE_CLICK_WIDTH * 100) / width;
+
+    for (let i = 0; i < coordinates.length; i++) {
+      const [x1, y1] = coordinates[i];
+      const [x2, y2] =
+        i === coordinates.length - 1 ? coordinates[0] : coordinates[i + 1];
+      // Get the distance between clicked point and line drawn between points 1 and 2
+      // to check if the click was on the line between those two points.
+      const distance = distanceToLine(x1, y1, x2, y2, pageX, pageY);
+      if (
+        distance <= clickWidth &&
+        Math.min(x1, x2) - clickWidth <= pageX &&
+        pageX <= Math.max(x1, x2) + clickWidth &&
+        Math.min(y1, y2) - clickWidth <= pageY &&
+        pageY <= Math.max(y1, y2) + clickWidth
+      ) {
+        // Get the point on the line closest to the clicked point.
+        const [newX, newY] = projection(x1, y1, x2, y2, pageX, pageY);
+        // Default unit for new points is percentages
+        this._addPolygonPoint(i, round(newX, "%"), round(newY, "%"));
+        return;
+      }
+    }
+  }
+
+  /**
+   * Check if the center point or radius of the circle highlighter is at given coords
+   * @param {Number} pageX the x coordinate on the page, in % relative to the element
+   * @param {Number} pageY the y coordinate on the page, in % relative to the element
+   * @returns {String} "center" if the center point was clicked, "radius" if the radius
+   *          was clicked, "" if neither was clicked.
+   */
+  getCirclePointAt(pageX, pageY) {
+    const { cx, cy, rx, ry } = this.coordinates;
+    const { width, height } = this.currentDimensions;
+    const zoom = getCurrentZoom(this.win);
+    const clickRadiusX = ((BASE_MARKER_SIZE / zoom) * 100) / width;
+    const clickRadiusY = ((BASE_MARKER_SIZE / zoom) * 100) / height;
+
+    if (clickedOnPoint(pageX, pageY, cx, cy, clickRadiusX, clickRadiusY)) {
+      return "center";
+    }
+
+    const clickWidthX = (LINE_CLICK_WIDTH * 100) / width;
+    const clickWidthY = (LINE_CLICK_WIDTH * 100) / height;
+    if (
+      clickedOnEllipseEdge(
+        pageX,
+        pageY,
+        cx,
+        cy,
+        rx,
+        ry,
+        clickWidthX,
+        clickWidthY
+      ) ||
+      clickedOnPoint(pageX, pageY, cx + rx, cy, clickRadiusX, clickRadiusY)
+    ) {
+      return "radius";
+    }
+
+    return "";
+  }
+
+  /**
+   * Check if the center or rx/ry points of the ellipse highlighter is at given point
+   * @param {Number} pageX the x coordinate on the page, in % relative to the element
+   * @param {Number} pageY the y coordinate on the page, in % relative to the element
+   * @returns {String} "center" if the center point was clicked, "rx" if the x-radius
+   *          point was clicked, "ry" if the y-radius point was clicked,
+   *          "" if none was clicked.
+   */
+  getEllipsePointAt(pageX, pageY) {
+    const { cx, cy, rx, ry } = this.coordinates;
+    const { width, height } = this.currentDimensions;
+    const zoom = getCurrentZoom(this.win);
+    const clickRadiusX = ((BASE_MARKER_SIZE / zoom) * 100) / width;
+    const clickRadiusY = ((BASE_MARKER_SIZE / zoom) * 100) / height;
+
+    if (clickedOnPoint(pageX, pageY, cx, cy, clickRadiusX, clickRadiusY)) {
+      return "center";
+    }
+
+    if (clickedOnPoint(pageX, pageY, cx + rx, cy, clickRadiusX, clickRadiusY)) {
+      return "rx";
+    }
+
+    if (clickedOnPoint(pageX, pageY, cx, cy + ry, clickRadiusX, clickRadiusY)) {
+      return "ry";
+    }
+
+    return "";
+  }
+
+  /**
+   * Check if the edges of the inset highlighter is at given coords
+   * @param {Number} pageX the x coordinate on the page, in % relative to the element
+   * @param {Number} pageY the y coordinate on the page, in % relative to the element
+   * @returns {String} "top", "left", "right", or "bottom" if any of those edges were
+   *          clicked. "" if none were clicked.
+   */
+  // eslint-disable-next-line complexity
+  getInsetPointAt(pageX, pageY) {
+    const { top, left, right, bottom } = this.coordinates;
+    const zoom = getCurrentZoom(this.win);
+    const { width, height } = this.currentDimensions;
+    const clickWidthX = (LINE_CLICK_WIDTH * 100) / width;
+    const clickWidthY = (LINE_CLICK_WIDTH * 100) / height;
+    const clickRadiusX = ((BASE_MARKER_SIZE / zoom) * 100) / width;
+    const clickRadiusY = ((BASE_MARKER_SIZE / zoom) * 100) / height;
+    const centerX = (left + (100 - right)) / 2;
+    const centerY = (top + (100 - bottom)) / 2;
+
+    if (
+      (pageX >= left - clickWidthX &&
+        pageX <= left + clickWidthX &&
+        pageY >= top &&
+        pageY <= 100 - bottom) ||
+      clickedOnPoint(pageX, pageY, left, centerY, clickRadiusX, clickRadiusY)
+    ) {
+      return "left";
+    }
+
+    if (
+      (pageX >= 100 - right - clickWidthX &&
+        pageX <= 100 - right + clickWidthX &&
+        pageY >= top &&
+        pageY <= 100 - bottom) ||
+      clickedOnPoint(
+        pageX,
+        pageY,
+        100 - right,
+        centerY,
+        clickRadiusX,
+        clickRadiusY
+      )
+    ) {
+      return "right";
+    }
+
+    if (
+      (pageY >= top - clickWidthY &&
+        pageY <= top + clickWidthY &&
+        pageX >= left &&
+        pageX <= 100 - right) ||
+      clickedOnPoint(pageX, pageY, centerX, top, clickRadiusX, clickRadiusY)
+    ) {
+      return "top";
+    }
+
+    if (
+      (pageY >= 100 - bottom - clickWidthY &&
+        pageY <= 100 - bottom + clickWidthY &&
+        pageX >= left &&
+        pageX <= 100 - right) ||
+      clickedOnPoint(
+        pageX,
+        pageY,
+        centerX,
+        100 - bottom,
+        clickRadiusX,
+        clickRadiusY
+      )
+    ) {
+      return "bottom";
+    }
+
+    return "";
+  }
+
+  /**
+   * Parses the CSS definition given and returns the shape type associated
+   * with the definition and the coordinates necessary to draw the shape.
+   * @param {String} definition the input CSS definition
+   * @returns {Object} null if the definition is not of a known shape type,
+   *          or an object of the type { shapeType, coordinates }, where
+   *          shapeType is the name of the shape and coordinates are an array
+   *          or object of the coordinates needed to draw the shape.
+   */
+  _parseCSSShapeValue(definition) {
+    const shapeTypes = [
+      {
+        name: "polygon",
+        prefix: "polygon(",
+        coordParser: this.polygonPoints.bind(this),
+      },
+      {
+        name: "circle",
+        prefix: "circle(",
+        coordParser: this.circlePoints.bind(this),
+      },
+      {
+        name: "ellipse",
+        prefix: "ellipse(",
+        coordParser: this.ellipsePoints.bind(this),
+      },
+      {
+        name: "inset",
+        prefix: "inset(",
+        coordParser: this.insetPoints.bind(this),
+      },
+    ];
+    const geometryTypes = ["margin", "border", "padding", "content"];
+    // default to border for clip-path and offset-path, and margin for shape-outside
+    const defaultGeometryTypesByProperty = new Map([
+      ["clip-path", "border"],
+      ["offset-path", "border"],
+      ["shape-outside", "margin"],
+    ]);
+
+    let referenceBox = defaultGeometryTypesByProperty.get(this.property);
+    for (const geometry of geometryTypes) {
+      if (definition.includes(geometry)) {
+        referenceBox = geometry;
+      }
+    }
+    this.referenceBox = referenceBox;
+
+    this.useStrokeBox = definition.includes("stroke-box");
+    this.geometryBox = definition
+      .substring(definition.lastIndexOf(")") + 1)
+      .trim();
+
+    for (const { name, prefix, coordParser } of shapeTypes) {
+      if (definition.includes(prefix)) {
+        // the closing paren of the shape function is always the last one in definition.
+        definition = definition.substring(
+          prefix.length,
+          definition.lastIndexOf(")")
+        );
+        return {
+          shapeType: name,
+          coordinates: coordParser(definition),
+        };
+      }
+    }
+
+    return null;
+  }
+
+  /**
+   * Parses the definition of the CSS polygon() function and returns its points,
+   * converted to percentages.
+   * @param {String} definition the arguments of the polygon() function
+   * @returns {Array} an array of the points of the polygon, with all values
+   *          evaluated and converted to percentages
+   */
+  polygonPoints(definition) {
+    this.coordUnits = this.polygonRawPoints();
+    if (!this.origCoordUnits) {
+      this.origCoordUnits = this.coordUnits;
+    }
+    const splitDef = definition.split(", ");
+    if (splitDef[0] === "evenodd" || splitDef[0] === "nonzero") {
+      splitDef.shift();
+    }
+    let minX = Number.MAX_SAFE_INTEGER;
+    let minY = Number.MAX_SAFE_INTEGER;
+    let maxX = Number.MIN_SAFE_INTEGER;
+    let maxY = Number.MIN_SAFE_INTEGER;
+    const coordinates = splitDef.map(coords => {
+      const [x, y] = splitCoords(coords).map(
+        this.convertCoordsToPercent.bind(this)
+      );
+      if (x < minX) {
+        minX = x;
+      }
+      if (y < minY) {
+        minY = y;
+      }
+      if (x > maxX) {
+        maxX = x;
+      }
+      if (y > maxY) {
+        maxY = y;
+      }
+      return [x, y];
+    });
+    this.boundingBox = { minX, minY, maxX, maxY };
+    if (!this.origBoundingBox) {
+      this.origBoundingBox = this.boundingBox;
+    }
+    return coordinates;
+  }
+
+  /**
+   * Parse the raw (non-computed) definition of the CSS polygon.
+   * @returns {Array} an array of the points of the polygon, with units preserved.
+   */
+  polygonRawPoints() {
+    let definition = getDefinedShapeProperties(this.currentNode, this.property);
+    if (definition === this.rawDefinition && this.coordUnits) {
+      return this.coordUnits;
+    }
+    this.rawDefinition = definition;
+    definition = definition.substring(8, definition.lastIndexOf(")"));
+    const splitDef = definition.split(", ");
+    if (splitDef[0].includes("evenodd") || splitDef[0].includes("nonzero")) {
+      this.fillRule = splitDef[0].trim();
+      splitDef.shift();
+    } else {
+      this.fillRule = "";
+    }
+    return splitDef.map(coords => {
+      return splitCoords(coords).map(coord => {
+        // Undo the insertion of &nbsp; that was done in splitCoords.
+        return coord.replace(/\u00a0/g, " ");
+      });
+    });
+  }
+
+  /**
+   * Parses the definition of the CSS circle() function and returns the x/y radiuses and
+   * center coordinates, converted to percentages.
+   * @param {String} definition the arguments of the circle() function
+   * @returns {Object} an object of the form { rx, ry, cx, cy }, where rx and ry are the
+   *          radiuses for the x and y axes, and cx and cy are the x/y coordinates for the
+   *          center of the circle. All values are evaluated and converted to percentages.
+   */
+  circlePoints(definition) {
+    this.coordUnits = this.circleRawPoints();
+    if (!this.origCoordUnits) {
+      this.origCoordUnits = this.coordUnits;
+    }
+
+    const values = definition.split("at");
+    let radius = values[0] ? values[0].trim() : "closest-side";
+    const { width, height } = this.currentDimensions;
+    // This defaults to center if omitted.
+    const position = values[1] || "50% 50%";
+    const center = splitCoords(position).map(
+      this.convertCoordsToPercent.bind(this)
+    );
+
+    // Percentage values for circle() are resolved from the
+    // used width and height of the reference box as sqrt(width^2+height^2)/sqrt(2).
+    const computedSize = Math.sqrt(width ** 2 + height ** 2) / Math.sqrt(2);
+
+    // Position coordinates for circle center in pixels.
+    const cxPx = (width * center[0]) / 100;
+    const cyPx = (height * center[1]) / 100;
+
+    if (radius === "closest-side") {
+      // radius is the distance from center to closest side of reference box
+      radius = Math.min(cxPx, cyPx, width - cxPx, height - cyPx);
+      radius = coordToPercent(`${radius}px`, computedSize);
+    } else if (radius === "farthest-side") {
+      // radius is the distance from center to farthest side of reference box
+      radius = Math.max(cxPx, cyPx, width - cxPx, height - cyPx);
+      radius = coordToPercent(`${radius}px`, computedSize);
+    } else if (radius.includes("calc(")) {
+      radius = evalCalcExpression(
+        radius.substring(5, radius.length - 1),
+        computedSize
+      );
+    } else {
+      radius = coordToPercent(radius, computedSize);
+    }
+
+    // Scale both radiusX and radiusY to match the radius computed
+    // using the above equation.
+    const ratioX = width / computedSize;
+    const ratioY = height / computedSize;
+    const radiusX = radius / ratioX;
+    const radiusY = radius / ratioY;
+
+    this.boundingBox = {
+      minX: center[0] - radiusX,
+      maxX: center[0] + radiusX,
+      minY: center[1] - radiusY,
+      maxY: center[1] + radiusY,
+    };
+    if (!this.origBoundingBox) {
+      this.origBoundingBox = this.boundingBox;
+    }
+    return { radius, rx: radiusX, ry: radiusY, cx: center[0], cy: center[1] };
+  }
+
+  /**
+   * Parse the raw (non-computed) definition of the CSS circle.
+   * @returns {Object} an object of the points of the circle (cx, cy, radius),
+   *          with units preserved.
+   */
+  circleRawPoints() {
+    let definition = getDefinedShapeProperties(this.currentNode, this.property);
+    if (definition === this.rawDefinition && this.coordUnits) {
+      return this.coordUnits;
+    }
+    this.rawDefinition = definition;
+    definition = definition.substring(7, definition.lastIndexOf(")"));
+
+    const values = definition.split("at");
+    const [cx = "", cy = ""] = values[1]
+      ? splitCoords(values[1]).map(coord => {
+          // Undo the insertion of &nbsp; that was done in splitCoords.
+          return coord.replace(/\u00a0/g, " ");
+        })
+      : [];
+    const radius = values[0] ? values[0].trim() : "closest-side";
+    return { cx, cy, radius };
+  }
+
+  /**
+   * Parses the computed style definition of the CSS ellipse() function and returns the
+   * x/y radii and center coordinates, converted to percentages.
+   * @param {String} definition the arguments of the ellipse() function
+   * @returns {Object} an object of the form { rx, ry, cx, cy }, where rx and ry are the
+   *          radiuses for the x and y axes, and cx and cy are the x/y coordinates for the
+   *          center of the ellipse. All values are evaluated and converted to percentages
+   */
+  ellipsePoints(definition) {
+    this.coordUnits = this.ellipseRawPoints();
+    if (!this.origCoordUnits) {
+      this.origCoordUnits = this.coordUnits;
+    }
+
+    const values = definition.split("at");
+    // This defaults to center if omitted.
+    const position = values[1] || "50% 50%";
+    const center = splitCoords(position).map(
+      this.convertCoordsToPercent.bind(this)
+    );
+
+    let radii = values[0] ? values[0].trim() : "closest-side closest-side";
+    radii = splitCoords(radii).map((radius, i) => {
+      if (radius === "closest-side") {
+        // radius is the distance from center to closest x/y side of reference box
+        return i % 2 === 0
+          ? Math.min(center[0], 100 - center[0])
+          : Math.min(center[1], 100 - center[1]);
+      } else if (radius === "farthest-side") {
+        // radius is the distance from center to farthest x/y side of reference box
+        return i % 2 === 0
+          ? Math.max(center[0], 100 - center[0])
+          : Math.max(center[1], 100 - center[1]);
+      }
+      return this.convertCoordsToPercent(radius, i);
+    });
+
+    this.boundingBox = {
+      minX: center[0] - radii[0],
+      maxX: center[0] + radii[0],
+      minY: center[1] - radii[1],
+      maxY: center[1] + radii[1],
+    };
+    if (!this.origBoundingBox) {
+      this.origBoundingBox = this.boundingBox;
+    }
+    return { rx: radii[0], ry: radii[1], cx: center[0], cy: center[1] };
+  }
+
+  /**
+   * Parse the raw (non-computed) definition of the CSS ellipse.
+   * @returns {Object} an object of the points of the ellipse (cx, cy, rx, ry),
+   *          with units preserved.
+   */
+  ellipseRawPoints() {
+    let definition = getDefinedShapeProperties(this.currentNode, this.property);
+    if (definition === this.rawDefinition && this.coordUnits) {
+      return this.coordUnits;
+    }
+    this.rawDefinition = definition;
+    definition = definition.substring(8, definition.lastIndexOf(")"));
+
+    const values = definition.split("at");
+    const [rx = "closest-side", ry = "closest-side"] = values[0]
+      ? splitCoords(values[0]).map(coord => {
+          // Undo the insertion of &nbsp; that was done in splitCoords.
+          return coord.replace(/\u00a0/g, " ");
+        })
+      : [];
+    const [cx = "", cy = ""] = values[1]
+      ? splitCoords(values[1]).map(coord => {
+          return coord.replace(/\u00a0/g, " ");
+        })
+      : [];
+    return { rx, ry, cx, cy };
+  }
+
+  /**
+   * Parses the definition of the CSS inset() function and returns the x/y offsets and
+   * width/height of the shape, converted to percentages. Border radiuses (given after
+   * "round" in the definition) are currently ignored.
+   * @param {String} definition the arguments of the inset() function
+   * @returns {Object} an object of the form { x, y, width, height }, which are the top/
+   *          left positions and width/height of the shape.
+   */
+  insetPoints(definition) {
+    this.coordUnits = this.insetRawPoints();
+    if (!this.origCoordUnits) {
+      this.origCoordUnits = this.coordUnits;
+    }
+    const values = definition.split(" round ");
+    const offsets = splitCoords(values[0]);
+
+    let top, left, right, bottom;
+    // The offsets, like margin/padding/border, are in order: top, right, bottom, left.
+    if (offsets.length === 1) {
+      top = left = right = bottom = offsets[0];
+    } else if (offsets.length === 2) {
+      top = bottom = offsets[0];
+      left = right = offsets[1];
+    } else if (offsets.length === 3) {
+      top = offsets[0];
+      left = right = offsets[1];
+      bottom = offsets[2];
+    } else if (offsets.length === 4) {
+      top = offsets[0];
+      right = offsets[1];
+      bottom = offsets[2];
+      left = offsets[3];
+    }
+
+    top = this.convertCoordsToPercentFromCurrentDimension(top, "height");
+    bottom = this.convertCoordsToPercentFromCurrentDimension(bottom, "height");
+    left = this.convertCoordsToPercentFromCurrentDimension(left, "width");
+    right = this.convertCoordsToPercentFromCurrentDimension(right, "width");
+
+    // maxX/maxY are found by subtracting the right/bottom edges from 100
+    // (the width/height of the element in %)
+    this.boundingBox = {
+      minX: left,
+      maxX: 100 - right,
+      minY: top,
+      maxY: 100 - bottom,
+    };
+    if (!this.origBoundingBox) {
+      this.origBoundingBox = this.boundingBox;
+    }
+    return { top, left, right, bottom };
+  }
+
+  /**
+   * Parse the raw (non-computed) definition of the CSS inset.
+   * @returns {Object} an object of the points of the inset (top, right, bottom, left),
+   *          with units preserved.
+   */
+  insetRawPoints() {
+    let definition = getDefinedShapeProperties(this.currentNode, this.property);
+    if (definition === this.rawDefinition && this.coordUnits) {
+      return this.coordUnits;
+    }
+    this.rawDefinition = definition;
+    definition = definition.substring(6, definition.lastIndexOf(")"));
+
+    const values = definition.split(" round ");
+    this.insetRound = values[1];
+    const offsets = splitCoords(values[0]).map(coord => {
+      // Undo the insertion of &nbsp; that was done in splitCoords.
+      return coord.replace(/\u00a0/g, " ");
+    });
+
+    let top,
+      left,
+      right,
+      bottom = 0;
+
+    if (offsets.length === 1) {
+      top = left = right = bottom = offsets[0];
+    } else if (offsets.length === 2) {
+      top = bottom = offsets[0];
+      left = right = offsets[1];
+    } else if (offsets.length === 3) {
+      top = offsets[0];
+      left = right = offsets[1];
+      bottom = offsets[2];
+    } else if (offsets.length === 4) {
+      top = offsets[0];
+      right = offsets[1];
+      bottom = offsets[2];
+      left = offsets[3];
+    }
+
+    return { top, left, right, bottom };
+  }
+
+  /**
+   * This uses the index to decide whether to use width or height for the
+   * computation. See `convertCoordsToPercentFromCurrentDimension()` if you
+   * need to specify width or height.
+   * @param {Number} coord a single coordinate
+   * @param {Number} i the index of its position in the function
+   * @returns {Number} the coordinate as a percentage value
+   */
+  convertCoordsToPercent(coord, i) {
+    const { width, height } = this.currentDimensions;
+    const size = i % 2 === 0 ? width : height;
+    if (coord.includes("calc(")) {
+      return evalCalcExpression(coord.substring(5, coord.length - 1), size);
+    }
+    return coordToPercent(coord, size);
+  }
+
+  /**
+   * Converts a value to percent based on the specified dimension.
+   * @param {Number} coord a single coordinate
+   * @param {Number} currentDimensionProperty the dimension ("width" or
+   *        "height") to base the calculation off of
+   * @returns {Number} the coordinate as a percentage value
+   */
+  convertCoordsToPercentFromCurrentDimension(coord, currentDimensionProperty) {
+    const size = this.currentDimensions[currentDimensionProperty];
+    if (coord.includes("calc(")) {
+      return evalCalcExpression(coord.substring(5, coord.length - 1), size);
+    }
+    return coordToPercent(coord, size);
+  }
+
+  /**
+   * Destroy the nodes. Remove listeners.
+   */
+  destroy() {
+    const { pageListenerTarget } = this.highlighterEnv;
+    if (pageListenerTarget) {
+      DOM_EVENTS.forEach(type =>
+        pageListenerTarget.removeEventListener(type, this)
+      );
+    }
+    super.destroy(this);
+    this.markup.destroy();
+  }
+
+  /**
+   * Get the element in the highlighter markup with the given id
+   * @param {String} id
+   * @returns {Object} the element with the given id
+   */
+  getElement(id) {
+    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
+  }
+
+  /**
+   * Return whether all the elements used to draw shapes are hidden.
+   * @returns {Boolean}
+   */
+  areShapesHidden() {
+    return (
+      this.getElement("ellipse").hasAttribute("hidden") &&
+      this.getElement("polygon").hasAttribute("hidden") &&
+      this.getElement("rect").hasAttribute("hidden") &&
+      this.getElement("bounding-box").hasAttribute("hidden")
+    );
+  }
+
+  /**
+   * Show the highlighter on a given node
+   */
+  _show() {
+    this.hoveredPoint = this.options.hoverPoint;
+    this.transformMode = this.options.transformMode;
+    this.coordinates = null;
+    this.coordUnits = null;
+    this.origBoundingBox = null;
+    this.origCoordUnits = null;
+    this.origCoordinates = null;
+    this.transformedBoundingBox = null;
+    if (this.transformMode) {
+      this.transformMatrix = identity();
+    }
+    if (this._hasMoved() && this.transformMode) {
+      this.transformedBoundingBox = this.calculateTransformedBoundingBox();
+    }
+    return this._update();
+  }
+
+  /**
+   * The AutoRefreshHighlighter's _hasMoved method returns true only if the element's
+   * quads have changed. Override it so it also returns true if the element's shape has
+   * changed (which can happen when you change a CSS properties for instance).
+   */
+  _hasMoved() {
+    let hasMoved = AutoRefreshHighlighter.prototype._hasMoved.call(this);
+
+    if (hasMoved) {
+      this.origBoundingBox = null;
+      this.origCoordUnits = null;
+      this.origCoordinates = null;
+      if (this.transformMode) {
+        this.transformMatrix = identity();
+      }
+    }
+
+    const oldShapeCoordinates = JSON.stringify(this.coordinates);
+
+    // TODO: need other modes too.
+    if (this.options.mode.startsWith("css")) {
+      const property = shapeModeToCssPropertyName(this.options.mode);
+      // change camelCase to kebab-case
+      this.property = property.replace(/([a-z][A-Z])/g, g => {
+        return g[0] + "-" + g[1].toLowerCase();
+      });
+      const style = getComputedStyle(this.currentNode)[property];
+
+      if (!style || style === "none") {
+        this.coordinates = [];
+        this.shapeType = "none";
+      } else {
+        const { coordinates, shapeType } = this._parseCSSShapeValue(style);
+        this.coordinates = coordinates;
+        if (!this.origCoordinates) {
+          this.origCoordinates = coordinates;
+        }
+        this.shapeType = shapeType;
+      }
+    }
+
+    const newShapeCoordinates = JSON.stringify(this.coordinates);
+    hasMoved = hasMoved || oldShapeCoordinates !== newShapeCoordinates;
+    if (this.transformMode && hasMoved) {
+      this.transformedBoundingBox = this.calculateTransformedBoundingBox();
+    }
+
+    return hasMoved;
+  }
+
+  /**
+   * Hide all elements used to highlight CSS different shapes.
+   */
+  _hideShapes() {
+    this.getElement("ellipse").setAttribute("hidden", true);
+    this.getElement("polygon").setAttribute("hidden", true);
+    this.getElement("rect").setAttribute("hidden", true);
+    this.getElement("bounding-box").setAttribute("hidden", true);
+    this.getElement("markers").setAttribute("d", "");
+    this.getElement("markers-outline").setAttribute("d", "");
+    this.getElement("rotate-line").setAttribute("d", "");
+    this.getElement("quad").setAttribute("hidden", true);
+    this.getElement("clip-ellipse").setAttribute("hidden", true);
+    this.getElement("clip-polygon").setAttribute("hidden", true);
+    this.getElement("clip-rect").setAttribute("hidden", true);
+    this.getElement("dashed-polygon").setAttribute("hidden", true);
+    this.getElement("dashed-ellipse").setAttribute("hidden", true);
+    this.getElement("dashed-rect").setAttribute("hidden", true);
+  }
+
+  /**
+   * Update the highlighter for the current node. Called whenever the element's quads
+   * or CSS shape has changed.
+   * @returns {Boolean} whether the highlighter was successfully updated
+   */
+  _update() {
+    setIgnoreLayoutChanges(true);
+    this.getElement("group").setAttribute("transform", "");
+    const root = this.getElement("root");
+    root.setAttribute("hidden", true);
+
+    const { top, left, width, height } = this.currentDimensions;
+    const zoom = getCurrentZoom(this.win);
+
+    // Size the SVG like the current node.
+    this.getElement("shape-container").setAttribute(
+      "style",
+      `top:${top}px;left:${left}px;width:${width}px;height:${height}px;`
+    );
+
+    this._hideShapes();
+    this._updateShapes(width, height, zoom);
+
+    // For both shape-outside and clip-path the element's quads are displayed for the
+    // parts that overlap with the shape. The parts of the shape that extend past the
+    // element's quads are shown with a dashed line.
+    const quadRect = this.getElement("quad");
+    quadRect.removeAttribute("hidden");
+
+    this.getElement("polygon").setAttribute(
+      "clip-path",
+      "url(#shapes-quad-clip-path)"
+    );
+    this.getElement("ellipse").setAttribute(
+      "clip-path",
+      "url(#shapes-quad-clip-path)"
+    );
+    this.getElement("rect").setAttribute(
+      "clip-path",
+      "url(#shapes-quad-clip-path)"
+    );
+
+    const { width: winWidth, height: winHeight } = this._winDimensions;
+    root.removeAttribute("hidden");
+    root.setAttribute(
+      "style",
+      `position:absolute; width:${winWidth}px;height:${winHeight}px; overflow:hidden;`
+    );
+
+    this._handleMarkerHover(this.hoveredPoint);
+
+    setIgnoreLayoutChanges(
+      false,
+      this.highlighterEnv.window.document.documentElement
+    );
+
+    return true;
+  }
+
+  /**
+   * Update the SVGs to render the current CSS shape and add markers depending on shape
+   * type and transform mode.
+   * @param {Number} width the width of the element quads
+   * @param {Number} height the height of the element quads
+   * @param {Number} zoom the zoom level of the window
+   */
+  _updateShapes(width, height, zoom) {
+    if (this.transformMode && this.shapeType !== "none") {
+      this._updateTransformMode(width, height, zoom);
+    } else if (this.shapeType === "polygon") {
+      this._updatePolygonShape(width, height, zoom);
+      // Draw markers for each of the polygon's points.
+      this._drawMarkers(this.coordinates, width, height, zoom);
+    } else if (this.shapeType === "circle") {
+      const { rx, cx, cy } = this.coordinates;
+      // Shape renders for "circle()" and "ellipse()" use the same SVG nodes.
+      this._updateEllipseShape(width, height, zoom);
+      // Draw markers for center and radius points.
+      this._drawMarkers(
+        [
+          [cx, cy],
+          [cx + rx, cy],
+        ],
+        width,
+        height,
+        zoom
+      );
+    } else if (this.shapeType === "ellipse") {
+      const { rx, ry, cx, cy } = this.coordinates;
+      this._updateEllipseShape(width, height, zoom);
+      // Draw markers for center, horizontal radius and vertical radius points.
+      this._drawMarkers(
+        [
+          [cx, cy],
+          [cx + rx, cy],
+          [cx, cy + ry],
+        ],
+        width,
+        height,
+        zoom
+      );
+    } else if (this.shapeType === "inset") {
+      const { top, left, right, bottom } = this.coordinates;
+      const centerX = (left + (100 - right)) / 2;
+      const centerY = (top + (100 - bottom)) / 2;
+      const markerCoords = [
+        [centerX, top],
+        [100 - right, centerY],
+        [centerX, 100 - bottom],
+        [left, centerY],
+      ];
+      this._updateInsetShape(width, height, zoom);
+      // Draw markers for each of the inset's sides.
+      this._drawMarkers(markerCoords, width, height, zoom);
+    }
+  }
+
+  /**
+   * Update the SVGs for transform mode to fit the new shape.
+   * @param {Number} width the width of the element quads
+   * @param {Number} height the height of the element quads
+   * @param {Number} zoom the zoom level of the window
+   */
+  _updateTransformMode(width, height, zoom) {
+    const { nw, ne, sw, se, n, w, s, e, rotatePoint, center } =
+      this.transformedBoundingBox;
+    const boundingBox = this.getElement("bounding-box");
+    const path = `M${nw.join(" ")} L${ne.join(" ")} L${se.join(" ")} L${sw.join(
+      " "
+    )} Z`;
+    boundingBox.setAttribute("d", path);
+    boundingBox.removeAttribute("hidden");
+
+    const markerPoints = [center, nw, ne, se, sw];
+    if (this.shapeType === "polygon" || this.shapeType === "ellipse") {
+      markerPoints.push(n, s, w, e);
+    }
+
+    if (this.shapeType === "polygon") {
+      this._updatePolygonShape(width, height, zoom);
+      markerPoints.push(rotatePoint);
+      const rotateLine = `M ${center.join(" ")} L ${rotatePoint.join(" ")}`;
+      this.getElement("rotate-line").setAttribute("d", rotateLine);
+    } else if (this.shapeType === "circle" || this.shapeType === "ellipse") {
+      // Shape renders for "circle()" and "ellipse()" use the same SVG nodes.
+      this._updateEllipseShape(width, height, zoom);
+    } else if (this.shapeType === "inset") {
+      this._updateInsetShape(width, height, zoom);
+    }
+
+    this._drawMarkers(markerPoints, width, height, zoom);
+  }
+
+  /**
+   * Update the SVG polygon to fit the CSS polygon.
+   * @param {Number} width the width of the element quads
+   * @param {Number} height the height of the element quads
+   * @param {Number} zoom the zoom level of the window
+   */
+  _updatePolygonShape(width, height, zoom) {
+    // Draw and show the polygon.
+    const points = this.coordinates.map(point => point.join(",")).join(" ");
+
+    const polygonEl = this.getElement("polygon");
+    polygonEl.setAttribute("points", points);
+    polygonEl.removeAttribute("hidden");
+
+    const clipPolygon = this.getElement("clip-polygon");
+    clipPolygon.setAttribute("points", points);
+    clipPolygon.removeAttribute("hidden");
+
+    const dashedPolygon = this.getElement("dashed-polygon");
+    dashedPolygon.setAttribute("points", points);
+    dashedPolygon.removeAttribute("hidden");
+  }
+
+  /**
+   * Update the SVG ellipse to fit the CSS circle or ellipse.
+   * @param {Number} width the width of the element quads
+   * @param {Number} height the height of the element quads
+   * @param {Number} zoom the zoom level of the window
+   */
+  _updateEllipseShape(width, height, zoom) {
+    const { rx, ry, cx, cy } = this.coordinates;
+    const ellipseEl = this.getElement("ellipse");
+    ellipseEl.setAttribute("rx", rx);
+    ellipseEl.setAttribute("ry", ry);
+    ellipseEl.setAttribute("cx", cx);
+    ellipseEl.setAttribute("cy", cy);
+    ellipseEl.removeAttribute("hidden");
+
+    const clipEllipse = this.getElement("clip-ellipse");
+    clipEllipse.setAttribute("rx", rx);
+    clipEllipse.setAttribute("ry", ry);
+    clipEllipse.setAttribute("cx", cx);
+    clipEllipse.setAttribute("cy", cy);
+    clipEllipse.removeAttribute("hidden");
+
+    const dashedEllipse = this.getElement("dashed-ellipse");
+    dashedEllipse.setAttribute("rx", rx);
+    dashedEllipse.setAttribute("ry", ry);
+    dashedEllipse.setAttribute("cx", cx);
+    dashedEllipse.setAttribute("cy", cy);
+    dashedEllipse.removeAttribute("hidden");
+  }
+
+  /**
+   * Update the SVG rect to fit the CSS inset.
+   * @param {Number} width the width of the element quads
+   * @param {Number} height the height of the element quads
+   * @param {Number} zoom the zoom level of the window
+   */
+  _updateInsetShape(width, height, zoom) {
+    const { top, left, right, bottom } = this.coordinates;
+    const rectEl = this.getElement("rect");
+    rectEl.setAttribute("x", left);
+    rectEl.setAttribute("y", top);
+    rectEl.setAttribute("width", 100 - left - right);
+    rectEl.setAttribute("height", 100 - top - bottom);
+    rectEl.removeAttribute("hidden");
+
+    const clipRect = this.getElement("clip-rect");
+    clipRect.setAttribute("x", left);
+    clipRect.setAttribute("y", top);
+    clipRect.setAttribute("width", 100 - left - right);
+    clipRect.setAttribute("height", 100 - top - bottom);
+    clipRect.removeAttribute("hidden");
+
+    const dashedRect = this.getElement("dashed-rect");
+    dashedRect.setAttribute("x", left);
+    dashedRect.setAttribute("y", top);
+    dashedRect.setAttribute("width", 100 - left - right);
+    dashedRect.setAttribute("height", 100 - top - bottom);
+    dashedRect.removeAttribute("hidden");
+  }
+
+  /**
+   * Draw markers for the given coordinates.
+   * @param {Array} coords an array of coordinate arrays, of form [[x, y] ...]
+   * @param {Number} width the width of the element markers are being drawn for
+   * @param {Number} height the height of the element markers are being drawn for
+   * @param {Number} zoom the zoom level of the window
+   */
+  _drawMarkers(coords, width, height, zoom) {
+    const markers = coords
+      .map(([x, y]) => {
+        return getCirclePath(BASE_MARKER_SIZE, x, y, width, height, zoom);
+      })
+      .join(" ");
+    const outline = coords
+      .map(([x, y]) => {
+        return getCirclePath(BASE_MARKER_SIZE + 2, x, y, width, height, zoom);
+      })
+      .join(" ");
+
+    this.getElement("markers").setAttribute("d", markers);
+    this.getElement("markers-outline").setAttribute("d", outline);
+  }
+
+  /**
+   * Calculate the bounding box of the shape after it is transformed according to
+   * the transformation matrix.
+   * @returns {Object} of form { nw, ne, sw, se, n, s, w, e, rotatePoint, center }.
+   *          Each element in the object is an array of form [x,y], denoting the x/y
+   *          coordinates of the given point.
+   */
+  calculateTransformedBoundingBox() {
+    const { minX, minY, maxX, maxY } = this.origBoundingBox;
+    const { width, height } = this.currentDimensions;
+    const toPixel = scale(width / 100, height / 100);
+    const toPercent = scale(100 / width, 100 / height);
+    const matrix = multiply(toPercent, multiply(this.transformMatrix, toPixel));
+    const centerX = (minX + maxX) / 2;
+    const centerY = (minY + maxY) / 2;
+    const nw = apply(matrix, [minX, minY]);
+    const ne = apply(matrix, [maxX, minY]);
+    const sw = apply(matrix, [minX, maxY]);
+    const se = apply(matrix, [maxX, maxY]);
+    const n = apply(matrix, [centerX, minY]);
+    const s = apply(matrix, [centerX, maxY]);
+    const w = apply(matrix, [minX, centerY]);
+    const e = apply(matrix, [maxX, centerY]);
+    const center = apply(matrix, [centerX, centerY]);
+
+    const u = [
+      ((ne[0] - nw[0]) / 100) * width,
+      ((ne[1] - nw[1]) / 100) * height,
+    ];
+    const v = [
+      ((sw[0] - nw[0]) / 100) * width,
+      ((sw[1] - nw[1]) / 100) * height,
+    ];
+    const { basis, invertedBasis } = getBasis(u, v);
+    let rotatePointMatrix = changeMatrixBase(
+      translate(0, -ROTATE_LINE_LENGTH),
+      invertedBasis,
+      basis
+    );
+    rotatePointMatrix = multiply(
+      toPercent,
+      multiply(rotatePointMatrix, multiply(this.transformMatrix, toPixel))
+    );
+    const rotatePoint = apply(rotatePointMatrix, [centerX, centerY]);
+    return { nw, ne, sw, se, n, s, w, e, rotatePoint, center };
+  }
+
+  /**
+   * Hide the highlighter, the outline and the infobar.
+   */
+  _hide() {
+    setIgnoreLayoutChanges(true);
+
+    this._hideShapes();
+    this.getElement("markers").setAttribute("d", "");
+    this.getElement("root").setAttribute("style", "");
+
+    setIgnoreLayoutChanges(
+      false,
+      this.highlighterEnv.window.document.documentElement
+    );
+  }
+
+  onPageHide({ target }) {
+    // If a page hide event is triggered for current window's highlighter, hide the
+    // highlighter.
+    if (target.defaultView === this.win) {
+      this.hide();
+    }
+  }
+
+  /**
+   * Get the rough direction of the point relative to the anchor.
+   * If the handle is roughly horizontal relative to the anchor, return "ew".
+   * If the handle is roughly vertical relative to the anchor, return "ns"
+   * If the handle is roughly above/right or below/left, return "nesw"
+   * If the handle is roughly above/left or below/right, return "nwse"
+   * @param {String} pointName the name of the point being hovered
+   * @param {String} anchor the name of the anchor point
+   * @returns {String} The rough direction of the point relative to the anchor
+   */
+  getRoughDirection(pointName, anchor) {
+    const scalePoint = pointName.split("-")[1];
+    const anchorPos = this.transformedBoundingBox[anchor];
+    const scalePos = this.transformedBoundingBox[scalePoint];
+    const { minX, minY, maxX, maxY } = this.boundingBox;
+    const width = maxX - minX;
+    const height = maxY - minY;
+    const dx = (scalePos[0] - anchorPos[0]) / width;
+    const dy = (scalePos[1] - anchorPos[1]) / height;
+    if (dx >= -0.33 && dx <= 0.33) {
+      return "ns";
+    } else if (dy >= -0.33 && dy <= 0.33) {
+      return "ew";
+    } else if ((dx > 0.33 && dy < -0.33) || (dx < -0.33 && dy > 0.33)) {
+      return "nesw";
+    }
+    return "nwse";
+  }
+
+  /**
+   * Given a unit type, get the ratio by which to multiply a pixel value in order to
+   * convert pixels to that unit.
+   *
+   * Percentage units (%) are relative to a size. This must be provided when requesting
+   * a ratio for converting from pixels to percentages.
+   *
+   * @param {String} unit
+   *        One of: %, em, rem, vw, vh
+   * @param {Number} size
+   *        Size to which percentage values are relative to.
+   * @return {Number}
+   */
+  getUnitToPixelRatio(unit, size) {
+    let ratio;
+    const windowHeight = this.currentNode.ownerGlobal.innerHeight;
+    const windowWidth = this.currentNode.ownerGlobal.innerWidth;
+    switch (unit) {
+      case "%":
+        ratio = 100 / size;
+        break;
+      case "em":
+        ratio = 1 / parseFloat(getComputedStyle(this.currentNode).fontSize);
+        break;
+      case "rem":
+        const root = this.currentNode.ownerDocument.documentElement;
+        ratio = 1 / parseFloat(getComputedStyle(root).fontSize);
+        break;
+      case "vw":
+        ratio = 100 / windowWidth;
+        break;
+      case "vh":
+        ratio = 100 / windowHeight;
+        break;
+      case "vmin":
+        ratio = 100 / Math.min(windowHeight, windowWidth);
+        break;
+      case "vmax":
+        ratio = 100 / Math.max(windowHeight, windowWidth);
+        break;
+      default:
+        // If unit is not recognized, peg ratio 1:1 to pixels.
+        ratio = 1;
+    }
+
+    return ratio;
+  }
+}
+
+/**
+ * Get the "raw" (i.e. non-computed) shape definition on the given node.
+ * @param {Node} node the node to analyze
+ * @param {String} property the CSS property for which a value should be retrieved.
+ * @returns {String} the value of the given CSS property on the given node.
+ */
+function getDefinedShapeProperties(node, property) {
+  let prop = "";
+  if (!node) {
+    return prop;
+  }
+
+  const cssRules = getCSSStyleRules(node);
+  for (let i = 0; i < cssRules.length; i++) {
+    const rule = cssRules[i];
+    const value = rule.style.getPropertyValue(property);
+    if (value && value !== "auto") {
+      prop = value;
+    }
+  }
+
+  if (node.style) {
+    const value = node.style.getPropertyValue(property);
+    if (value && value !== "auto") {
+      prop = value;
+    }
+  }
+
+  return prop.trim();
+}
+
+/**
+ * Split coordinate pairs separated by a space and return an array.
+ * @param {String} coords the coordinate pair, where each coord is separated by a space.
+ * @returns {Array} a 2 element array containing the coordinates.
+ */
+function splitCoords(coords) {
+  // All coordinate pairs are of the form "x y" where x and y are values or
+  // calc() expressions. calc() expressions have spaces around operators, so
+  // replace those spaces with \u00a0 (non-breaking space) so they will not be
+  // split later.
+  return coords
+    .trim()
+    .replace(/ [\+\-\*\/] /g, match => {
+      return `\u00a0${match.trim()}\u00a0`;
+    })
+    .split(" ");
+}
+exports.splitCoords = splitCoords;
+
+/**
+ * Convert a coordinate to a percentage value.
+ * @param {String} coord a single coordinate
+ * @param {Number} size the size of the element (width or height) that the percentages
+ *        are relative to
+ * @returns {Number} the coordinate as a percentage value
+ */
+function coordToPercent(coord, size) {
+  if (coord.includes("%")) {
+    // Just remove the % sign, nothing else to do, we're in a viewBox that's 100%
+    // worth.
+    return parseFloat(coord.replace("%", ""));
+  } else if (coord.includes("px")) {
+    // Convert the px value to a % value.
+    const px = parseFloat(coord.replace("px", ""));
+    return (px * 100) / size;
+  }
+
+  // Unit-less value, so 0.
+  return 0;
+}
+exports.coordToPercent = coordToPercent;
+
+/**
+ * Evaluates a CSS calc() expression (only handles addition)
+ * @param {String} expression the arguments to the calc() function
+ * @param {Number} size the size of the element (width or height) that percentage values
+ *        are relative to
+ * @returns {Number} the result of the expression as a percentage value
+ */
+function evalCalcExpression(expression, size) {
+  // the calc() values returned by getComputedStyle only have addition, as it
+  // computes calc() expressions as much as possible without resolving percentages,
+  // leaving only addition.
+  const values = expression.split("+").map(v => v.trim());
+
+  return values.reduce((prev, curr) => {
+    return prev + coordToPercent(curr, size);
+  }, 0);
+}
+exports.evalCalcExpression = evalCalcExpression;
+
+/**
+ * Converts a shape mode to the proper CSS property name.
+ * @param {String} mode the mode of the CSS shape
+ * @returns the equivalent CSS property name
+ */
+const shapeModeToCssPropertyName = mode => {
+  const property = mode.substring(3);
+  return property.substring(0, 1).toLowerCase() + property.substring(1);
+};
+exports.shapeModeToCssPropertyName = shapeModeToCssPropertyName;
+
+/**
+ * Get the SVG path definition for a circle with given attributes.
+ * @param {Number} size the radius of the circle in pixels
+ * @param {Number} cx the x coordinate of the centre of the circle
+ * @param {Number} cy the y coordinate of the centre of the circle
+ * @param {Number} width the width of the element the circle is being drawn for
+ * @param {Number} height the height of the element the circle is being drawn for
+ * @param {Number} zoom the zoom level of the window the circle is drawn in
+ * @returns {String} the definition of the circle in SVG path description format.
+ */
+const getCirclePath = (size, cx, cy, width, height, zoom) => {
+  // We use a viewBox of 100x100 for shape-container so it's easy to position things
+  // based on their percentage, but this makes it more difficult to create circles.
+  // Therefor, 100px is the base size of shape-container. In order to make the markers'
+  // size scale properly, we must adjust the radius based on zoom and the width/height of
+  // the element being highlighted, then calculate a radius for both x/y axes based
+  // on the aspect ratio of the element.
+  const radius = (size * (100 / Math.max(width, height))) / zoom;
+  const ratio = width / height;
+  const rx = ratio > 1 ? radius : radius / ratio;
+  const ry = ratio > 1 ? radius * ratio : radius;
+  // a circle is drawn as two arc lines, starting at the leftmost point of the circle.
+  return (
+    `M${cx - rx},${cy}a${rx},${ry} 0 1,0 ${rx * 2},0` +
+    `a${rx},${ry} 0 1,0 ${rx * -2},0`
+  );
+};
+exports.getCirclePath = getCirclePath;
+
+/**
+ * Calculates the object bounding box for a node given its stroke bounding box.
+ * @param {Number} top the y coord of the top edge of the stroke bounding box
+ * @param {Number} left the x coord of the left edge of the stroke bounding box
+ * @param {Number} width the width of the stroke bounding box
+ * @param {Number} height the height of the stroke bounding box
+ * @param {Object} node the node object
+ * @returns {Object} an object of the form { top, left, width, height }, which
+ *          are the top/left/width/height of the object bounding box for the node.
+ */
+const getObjectBoundingBox = (top, left, width, height, node) => {
+  // See https://drafts.fxtf.org/css-masking-1/#stroke-bounding-box for details
+  // on this algorithm. Note that we intentionally do not check "stroke-linecap".
+  const strokeWidth = parseFloat(getComputedStyle(node).strokeWidth);
+  let delta = strokeWidth / 2;
+  const tagName = node.tagName;
+
+  if (
+    tagName !== "rect" &&
+    tagName !== "ellipse" &&
+    tagName !== "circle" &&
+    tagName !== "image"
+  ) {
+    if (getComputedStyle(node).strokeLinejoin === "miter") {
+      const miter = getComputedStyle(node).strokeMiterlimit;
+      if (miter < Math.SQRT2) {
+        delta *= Math.SQRT2;
+      } else {
+        delta *= miter;
+      }
+    } else {
+      delta *= Math.SQRT2;
+    }
+  }
+
+  return {
+    top: top + delta,
+    left: left + delta,
+    width: width - 2 * delta,
+    height: height - 2 * delta,
+  };
+};
+
+/**
+ * Get the unit (e.g. px, %, em) for the given point value.
+ * @param {any} point a point value for which a unit should be retrieved.
+ * @returns {String} the unit.
+ */
+const getUnit = point => {
+  // If the point has no unit, default to px.
+  if (isUnitless(point)) {
+    return "px";
+  }
+  const [unit] = point.match(/[^\d]+$/) || ["px"];
+  return unit;
+};
+exports.getUnit = getUnit;
+
+/**
+ * Check if the given point value has a unit.
+ * @param {any} point a point value.
+ * @returns {Boolean} whether the given value has a unit.
+ */
+const isUnitless = point => {
+  return (
+    !point ||
+    !point.match(/[^\d]+$/) ||
+    // If zero doesn't have a unit, its numeric and string forms should be equal.
+    (parseFloat(point) === 0 && parseFloat(point).toString() === point) ||
+    point.includes("(") ||
+    point === "center" ||
+    point === "closest-side" ||
+    point === "farthest-side"
+  );
+};
+
+/**
+ * Return the anchor corresponding to the given scale type.
+ * @param {String} type a scale type, of form "scale-[direction]"
+ * @returns {String} a string describing the anchor, one of the 8 cardinal directions.
+ */
+const getAnchorPoint = type => {
+  let anchor = type.split("-")[1];
+  if (anchor.includes("n")) {
+    anchor = anchor.replace("n", "s");
+  } else if (anchor.includes("s")) {
+    anchor = anchor.replace("s", "n");
+  }
+  if (anchor.includes("w")) {
+    anchor = anchor.replace("w", "e");
+  } else if (anchor.includes("e")) {
+    anchor = anchor.replace("e", "w");
+  }
+
+  if (anchor === "e" || anchor === "w") {
+    anchor = "n" + anchor;
+  } else if (anchor === "n" || anchor === "s") {
+    anchor = anchor + "w";
+  }
+
+  return anchor;
+};
+
+/**
+ * Get the decimal point precision for values depending on unit type.
+ * Only handle pixels and falsy values for now. Round them to the nearest integer value.
+ * All other unit types round to two decimal points.
+ *
+ * @param {String|undefined} unitType any one of the accepted CSS unit types for position.
+ * @return {Number} decimal precision when rounding a value
+ */
+function getDecimalPrecision(unitType) {
+  switch (unitType) {
+    case "px":
+    case "":
+    case undefined:
+      return 0;
+    default:
+      return 2;
+  }
+}
+exports.getDecimalPrecision = getDecimalPrecision;
+
+/**
+ * Round up a numeric value to a fixed number of decimals depending on CSS unit type.
+ * Used when generating output shape values when:
+ * - transforming shapes
+ * - inserting new points on a polygon.
+ *
+ * @param {Number} number
+ *        Value to round up.
+ * @param {String} unitType
+ *        CSS unit type, like "px", "%", "em", "vh", etc.
+ * @return {Number}
+ *         Rounded value
+ */
+function round(number, unitType) {
+  return number.toFixed(getDecimalPrecision(unitType));
+}
+
+exports.ShapesHighlighter = ShapesHighlighter;
diff --git a/devtools/server/actors/highlighters/tabbing-order.js b/devtools/server/actors/highlighters/tabbing-order.js
new file mode 100644
index 0000000000..ab96d30fe6
--- /dev/null
+++ b/devtools/server/actors/highlighters/tabbing-order.js
@@ -0,0 +1,247 @@
+/* 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/. */
+
+"use strict";
+
+const lazy = {};
+loader.lazyGetter(
+  lazy,
+  "ContentDOMReference",
+  () =>
+    ChromeUtils.importESModule(
+      "resource://gre/modules/ContentDOMReference.sys.mjs",
+      {
+        // ContentDOMReference needs to be retrieved from the shared global
+        // since it is a shared singleton.
+        loadInDevToolsLoader: false,
+      }
+    ).ContentDOMReference
+);
+loader.lazyRequireGetter(
+  this,
+  ["isFrameWithChildTarget", "isWindowIncluded"],
+  "resource://devtools/shared/layout/utils.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "NodeTabbingOrderHighlighter",
+  "resource://devtools/server/actors/highlighters/node-tabbing-order.js",
+  true
+);
+
+const DEFAULT_FOCUS_FLAGS = Services.focus.FLAG_NOSCROLL;
+
+/**
+ * The TabbingOrderHighlighter uses focus manager to traverse all focusable
+ * nodes on the page and then uses the NodeTabbingOrderHighlighter to highlight
+ * these nodes.
+ */
+class TabbingOrderHighlighter {
+  constructor(highlighterEnv) {
+    this.highlighterEnv = highlighterEnv;
+    this._highlighters = new Map();
+
+    this.onMutation = this.onMutation.bind(this);
+    this.onPageHide = this.onPageHide.bind(this);
+    this.onWillNavigate = this.onWillNavigate.bind(this);
+
+    this.highlighterEnv.on("will-navigate", this.onWillNavigate);
+
+    const { pageListenerTarget } = highlighterEnv;
+    pageListenerTarget.addEventListener("pagehide", this.onPageHide);
+  }
+
+  /**
+   * Static getter that indicates that TabbingOrderHighlighter supports
+   * highlighting in XUL windows.
+   */
+  static get XULSupported() {
+    return true;
+  }
+
+  get win() {
+    return this.highlighterEnv.window;
+  }
+
+  get focusedElement() {
+    return Services.focus.getFocusedElementForWindow(this.win, true, {});
+  }
+
+  set focusedElement(element) {
+    Services.focus.setFocus(element, DEFAULT_FOCUS_FLAGS);
+  }
+
+  moveFocus(startElement) {
+    return Services.focus.moveFocus(
+      this.win,
+      startElement.nodeType === Node.DOCUMENT_NODE
+        ? startElement.documentElement
+        : startElement,
+      Services.focus.MOVEFOCUS_FORWARD,
+      DEFAULT_FOCUS_FLAGS
+    );
+  }
+
+  /**
+   * Show NodeTabbingOrderHighlighter on each node that belongs to the keyboard
+   * tabbing order.
+   *
+   * @param  {DOMNode} startElm
+   *         Starting element to calculate tabbing order from.
+   *
+   * @param  {JSON} options
+   *         - options.index
+   *           Start index for the tabbing order. Starting index will be 0 at
+   *           the start of the tabbing order highlighting; in remote frames
+   *           starting index will, typically, be greater than 0 (unless there
+   *           was nothing to focus in the top level content document prior to
+   *           the remote frame).
+   */
+  async show(startElm, { index }) {
+    const focusableElements = [];
+    const originalFocusedElement = this.focusedElement;
+    let currentFocusedElement = this.moveFocus(startElm);
+    while (
+      currentFocusedElement &&
+      isWindowIncluded(this.win, currentFocusedElement.ownerGlobal)
+    ) {
+      focusableElements.push(currentFocusedElement);
+      currentFocusedElement = this.moveFocus(currentFocusedElement);
+    }
+
+    // Allow to flush pending notifications to ensure the PresShell and frames
+    // are updated.
+    await new Promise(resolve => Services.tm.dispatchToMainThread(resolve));
+    let endElm = this.focusedElement;
+    if (
+      currentFocusedElement &&
+      !isWindowIncluded(this.win, currentFocusedElement.ownerGlobal)
+    ) {
+      endElm = null;
+    }
+
+    if (
+      !endElm &&
+      !!focusableElements.length &&
+      isFrameWithChildTarget(
+        this.highlighterEnv.targetActor,
+        focusableElements[focusableElements.length - 1]
+      )
+    ) {
+      endElm = focusableElements[focusableElements.length - 1];
+    }
+
+    if (originalFocusedElement && originalFocusedElement !== endElm) {
+      this.focusedElement = originalFocusedElement;
+    }
+
+    const highlighters = [];
+    for (let i = 0; i < focusableElements.length; i++) {
+      highlighters.push(
+        this._accumulateHighlighter(focusableElements[i], index++)
+      );
+    }
+    await Promise.all(highlighters);
+
+    this._trackMutations();
+
+    return {
+      contentDOMReference: endElm && lazy.ContentDOMReference.get(endElm),
+      index,
+    };
+  }
+
+  async _accumulateHighlighter(node, index) {
+    const highlighter = new NodeTabbingOrderHighlighter(this.highlighterEnv);
+    await highlighter.isReady;
+
+    highlighter.show(node, { index: index + 1 });
+    this._highlighters.set(node, highlighter);
+  }
+
+  hide() {
+    this._untrackMutations();
+    for (const highlighter of this._highlighters.values()) {
+      highlighter.destroy();
+    }
+
+    this._highlighters.clear();
+  }
+
+  /**
+   * Track mutations in the top level document subtree so that the appropriate
+   * NodeTabbingOrderHighlighter infobar's could be updated to reflect the
+   * attribute mutations on relevant nodes.
+   */
+  _trackMutations() {
+    const { win } = this;
+    this.currentMutationObserver = new win.MutationObserver(this.onMutation);
+    this.currentMutationObserver.observe(win.document.documentElement, {
+      subtree: true,
+      attributes: true,
+    });
+  }
+
+  _untrackMutations() {
+    if (!this.currentMutationObserver) {
+      return;
+    }
+
+    this.currentMutationObserver.disconnect();
+    this.currentMutationObserver = null;
+  }
+
+  onMutation(mutationList) {
+    for (const { target } of mutationList) {
+      const highlighter = this._highlighters.get(target);
+      if (highlighter) {
+        highlighter.update();
+      }
+    }
+  }
+
+  /**
+   * Update NodeTabbingOrderHighlighter focus styling for a node that,
+   * potentially, belongs to the tabbing order.
+   * @param {Object} options
+   *        Options specifying the node and its focused state.
+   */
+  updateFocus({ node, focused }) {
+    const highlighter = this._highlighters.get(node);
+    if (!highlighter) {
+      return;
+    }
+
+    highlighter.updateFocus(focused);
+  }
+
+  destroy() {
+    this.highlighterEnv.off("will-navigate", this.onWillNavigate);
+
+    const { pageListenerTarget } = this.highlighterEnv;
+    if (pageListenerTarget) {
+      pageListenerTarget.removeEventListener("pagehide", this.onPageHide);
+    }
+
+    this.hide();
+    this.highlighterEnv = null;
+  }
+
+  onPageHide({ target }) {
+    // If a pagehide event is triggered for current window's highlighter, hide
+    // the highlighter.
+    if (target.defaultView === this.win) {
+      this.hide();
+    }
+  }
+
+  onWillNavigate({ isTopLevel }) {
+    if (isTopLevel) {
+      this.hide();
+    }
+  }
+}
+
+exports.TabbingOrderHighlighter = TabbingOrderHighlighter;
diff --git a/devtools/server/actors/highlighters/utils/accessibility.js b/devtools/server/actors/highlighters/utils/accessibility.js
new file mode 100644
index 0000000000..23c4210a65
--- /dev/null
+++ b/devtools/server/actors/highlighters/utils/accessibility.js
@@ -0,0 +1,774 @@
+/* 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/. */
+
+"use strict";
+
+const DevToolsUtils = require("resource://devtools/shared/DevToolsUtils.js");
+const {
+  getCurrentZoom,
+} = require("resource://devtools/shared/layout/utils.js");
+const {
+  moveInfobar,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+const {
+  truncateString,
+} = require("resource://devtools/shared/inspector/utils.js");
+
+const STRINGS_URI = "devtools/shared/locales/accessibility.properties";
+loader.lazyRequireGetter(
+  this,
+  "LocalizationHelper",
+  "resource://devtools/shared/l10n.js",
+  true
+);
+DevToolsUtils.defineLazyGetter(
+  this,
+  "L10N",
+  () => new LocalizationHelper(STRINGS_URI)
+);
+
+const {
+  accessibility: {
+    AUDIT_TYPE,
+    ISSUE_TYPE: {
+      [AUDIT_TYPE.KEYBOARD]: {
+        FOCUSABLE_NO_SEMANTICS,
+        FOCUSABLE_POSITIVE_TABINDEX,
+        INTERACTIVE_NO_ACTION,
+        INTERACTIVE_NOT_FOCUSABLE,
+        MOUSE_INTERACTIVE_ONLY,
+        NO_FOCUS_VISIBLE,
+      },
+      [AUDIT_TYPE.TEXT_LABEL]: {
+        AREA_NO_NAME_FROM_ALT,
+        DIALOG_NO_NAME,
+        DOCUMENT_NO_TITLE,
+        EMBED_NO_NAME,
+        FIGURE_NO_NAME,
+        FORM_FIELDSET_NO_NAME,
+        FORM_FIELDSET_NO_NAME_FROM_LEGEND,
+        FORM_NO_NAME,
+        FORM_NO_VISIBLE_NAME,
+        FORM_OPTGROUP_NO_NAME_FROM_LABEL,
+        FRAME_NO_NAME,
+        HEADING_NO_CONTENT,
+        HEADING_NO_NAME,
+        IFRAME_NO_NAME_FROM_TITLE,
+        IMAGE_NO_NAME,
+        INTERACTIVE_NO_NAME,
+        MATHML_GLYPH_NO_NAME,
+        TOOLBAR_NO_NAME,
+      },
+    },
+    SCORES,
+  },
+} = require("resource://devtools/shared/constants.js");
+
+// Max string length for truncating accessible name values.
+const MAX_STRING_LENGTH = 50;
+
+/**
+ * The AccessibleInfobar is a class responsible for creating the markup for the
+ * accessible highlighter. It is also reponsible for updating content within the
+ * infobar such as role and name values.
+ */
+class Infobar {
+  constructor(highlighter) {
+    this.highlighter = highlighter;
+    this.audit = new Audit(this);
+  }
+
+  get markup() {
+    return this.highlighter.markup;
+  }
+
+  get document() {
+    return this.highlighter.win.document;
+  }
+
+  get bounds() {
+    return this.highlighter._bounds;
+  }
+
+  get options() {
+    return this.highlighter.options;
+  }
+
+  get prefix() {
+    return this.highlighter.ID_CLASS_PREFIX;
+  }
+
+  get win() {
+    return this.highlighter.win;
+  }
+
+  /**
+   * Move the Infobar to the right place in the highlighter.
+   *
+   * @param  {Element} container
+   *         Container of infobar.
+   */
+  _moveInfobar(container) {
+    // Position the infobar using accessible's bounds
+    const { left: x, top: y, bottom, width } = this.bounds;
+    const infobarBounds = { x, y, bottom, width };
+
+    moveInfobar(container, infobarBounds, this.win);
+  }
+
+  /**
+   * Build markup for infobar.
+   *
+   * @param  {Element} root
+   *         Root element to build infobar with.
+   */
+  buildMarkup(root) {
+    const container = this.markup.createNode({
+      parent: root,
+      attributes: {
+        class: "infobar-container",
+        id: "infobar-container",
+        "aria-hidden": "true",
+        hidden: "true",
+      },
+      prefix: this.prefix,
+    });
+
+    const infobar = this.markup.createNode({
+      parent: container,
+      attributes: {
+        class: "infobar",
+        id: "infobar",
+      },
+      prefix: this.prefix,
+    });
+
+    const infobarText = this.markup.createNode({
+      parent: infobar,
+      attributes: {
+        class: "infobar-text",
+        id: "infobar-text",
+      },
+      prefix: this.prefix,
+    });
+
+    this.markup.createNode({
+      nodeType: "span",
+      parent: infobarText,
+      attributes: {
+        class: "infobar-role",
+        id: "infobar-role",
+      },
+      prefix: this.prefix,
+    });
+
+    this.markup.createNode({
+      nodeType: "span",
+      parent: infobarText,
+      attributes: {
+        class: "infobar-name",
+        id: "infobar-name",
+      },
+      prefix: this.prefix,
+    });
+
+    this.audit.buildMarkup(infobarText);
+  }
+
+  /**
+   * Destroy the Infobar's highlighter.
+   */
+  destroy() {
+    this.highlighter = null;
+    this.audit.destroy();
+    this.audit = null;
+  }
+
+  /**
+   * Gets the element with the specified ID.
+   *
+   * @param  {String} id
+   *         Element ID.
+   * @return {Element} The element with specified ID.
+   */
+  getElement(id) {
+    return this.highlighter.getElement(id);
+  }
+
+  /**
+   * Gets the text content of element.
+   *
+   * @param  {String} id
+   *          Element ID to retrieve text content from.
+   * @return {String} The text content of the element.
+   */
+  getTextContent(id) {
+    const anonymousContent = this.markup.content;
+    return anonymousContent.root.getElementById(`${this.prefix}${id}`)
+      .textContent;
+  }
+
+  /**
+   * Hide the accessible infobar.
+   */
+  hide() {
+    const container = this.getElement("infobar-container");
+    container.setAttribute("hidden", "true");
+  }
+
+  /**
+   * Show the accessible infobar highlighter.
+   */
+  show() {
+    const container = this.getElement("infobar-container");
+
+    // Remove accessible's infobar "hidden" attribute. We do this first to get the
+    // computed styles of the infobar container.
+    container.removeAttribute("hidden");
+
+    // Update the infobar's position and content.
+    this.update(container);
+  }
+
+  /**
+   * Update content of the infobar.
+   */
+  update(container) {
+    const { audit, name, role } = this.options;
+
+    this.updateRole(role, this.getElement("infobar-role"));
+    this.updateName(name, this.getElement("infobar-name"));
+    this.audit.update(audit);
+
+    // Position the infobar.
+    this._moveInfobar(container);
+  }
+
+  /**
+   * Sets the text content of the specified element.
+   *
+   * @param  {Element} el
+   *         Element to set text content on.
+   * @param  {String} text
+   *         Text for content.
+   */
+  setTextContent(el, text) {
+    el.setTextContent(text);
+  }
+
+  /**
+   * Show the accessible's name message.
+   *
+   * @param  {String} name
+   *         Accessible's name value.
+   * @param  {Element} el
+   *         Element to set text content on.
+   */
+  updateName(name, el) {
+    const nameText = name ? `"${truncateString(name, MAX_STRING_LENGTH)}"` : "";
+    this.setTextContent(el, nameText);
+  }
+
+  /**
+   * Show the accessible's role.
+   *
+   * @param  {String} role
+   *         Accessible's role value.
+   * @param  {Element} el
+   *         Element to set text content on.
+   */
+  updateRole(role, el) {
+    this.setTextContent(el, role);
+  }
+}
+
+/**
+ * Audit component used within the accessible highlighter infobar. This component is
+ * responsible for rendering and updating its containing AuditReport components that
+ * display various audit information such as contrast ratio score.
+ */
+class Audit {
+  constructor(infobar) {
+    this.infobar = infobar;
+
+    // A list of audit reports to be shown on the fly when highlighting an accessible
+    // object.
+    this.reports = {
+      [AUDIT_TYPE.CONTRAST]: new ContrastRatio(this),
+      [AUDIT_TYPE.KEYBOARD]: new Keyboard(this),
+      [AUDIT_TYPE.TEXT_LABEL]: new TextLabel(this),
+    };
+  }
+
+  get prefix() {
+    return this.infobar.prefix;
+  }
+
+  get markup() {
+    return this.infobar.markup;
+  }
+
+  buildMarkup(root) {
+    const audit = this.markup.createNode({
+      nodeType: "span",
+      parent: root,
+      attributes: {
+        class: "infobar-audit",
+        id: "infobar-audit",
+      },
+      prefix: this.prefix,
+    });
+
+    Object.values(this.reports).forEach(report => report.buildMarkup(audit));
+  }
+
+  update(audit = {}) {
+    const el = this.getElement("infobar-audit");
+    el.setAttribute("hidden", true);
+
+    let updated = false;
+    Object.values(this.reports).forEach(report => {
+      if (report.update(audit)) {
+        updated = true;
+      }
+    });
+
+    if (updated) {
+      el.removeAttribute("hidden");
+    }
+  }
+
+  getElement(id) {
+    return this.infobar.getElement(id);
+  }
+
+  setTextContent(el, text) {
+    return this.infobar.setTextContent(el, text);
+  }
+
+  destroy() {
+    this.infobar = null;
+    Object.values(this.reports).forEach(report => report.destroy());
+    this.reports = null;
+  }
+}
+
+/**
+ * A common interface between audit report components used to render accessibility audit
+ * information for the currently highlighted accessible object.
+ */
+class AuditReport {
+  constructor(audit) {
+    this.audit = audit;
+  }
+
+  get prefix() {
+    return this.audit.prefix;
+  }
+
+  get markup() {
+    return this.audit.markup;
+  }
+
+  getElement(id) {
+    return this.audit.getElement(id);
+  }
+
+  setTextContent(el, text) {
+    return this.audit.setTextContent(el, text);
+  }
+
+  destroy() {
+    this.audit = null;
+  }
+}
+
+/**
+ * Contrast ratio audit report that is used to display contrast ratio score as part of the
+ * inforbar,
+ */
+class ContrastRatio extends AuditReport {
+  buildMarkup(root) {
+    this.markup.createNode({
+      nodeType: "span",
+      parent: root,
+      attributes: {
+        class: "contrast-ratio-label",
+        id: "contrast-ratio-label",
+      },
+      prefix: this.prefix,
+    });
+
+    this.markup.createNode({
+      nodeType: "span",
+      parent: root,
+      attributes: {
+        class: "contrast-ratio-error",
+        id: "contrast-ratio-error",
+      },
+      prefix: this.prefix,
+      text: L10N.getStr("accessibility.contrast.ratio.error"),
+    });
+
+    this.markup.createNode({
+      nodeType: "span",
+      parent: root,
+      attributes: {
+        class: "contrast-ratio",
+        id: "contrast-ratio-min",
+      },
+      prefix: this.prefix,
+    });
+
+    this.markup.createNode({
+      nodeType: "span",
+      parent: root,
+      attributes: {
+        class: "contrast-ratio-separator",
+        id: "contrast-ratio-separator",
+      },
+      prefix: this.prefix,
+    });
+
+    this.markup.createNode({
+      nodeType: "span",
+      parent: root,
+      attributes: {
+        class: "contrast-ratio",
+        id: "contrast-ratio-max",
+      },
+      prefix: this.prefix,
+    });
+  }
+
+  _fillAndStyleContrastValue(el, { value, className, color, backgroundColor }) {
+    value = value.toFixed(2);
+    this.setTextContent(el, value);
+    el.classList.add(className);
+    el.setAttribute(
+      "style",
+      `--accessibility-highlighter-contrast-ratio-color: rgba(${color});` +
+        `--accessibility-highlighter-contrast-ratio-bg: rgba(${backgroundColor});`
+    );
+    el.removeAttribute("hidden");
+  }
+
+  /**
+   * Update contrast ratio score infobar markup.
+   * @param  {Object}
+   *         Audit report for a given highlighted accessible.
+   * @return {Boolean}
+   *         True if the contrast ratio markup was updated correctly and infobar audit
+   *         block should be visible.
+   */
+  update(audit) {
+    const els = {};
+    for (const key of ["label", "min", "max", "error", "separator"]) {
+      const el = (els[key] = this.getElement(`contrast-ratio-${key}`));
+      if (["min", "max"].includes(key)) {
+        Object.values(SCORES).forEach(className =>
+          el.classList.remove(className)
+        );
+        this.setTextContent(el, "");
+      }
+
+      el.setAttribute("hidden", true);
+      el.removeAttribute("style");
+    }
+
+    if (!audit) {
+      return false;
+    }
+
+    const contrastRatio = audit[AUDIT_TYPE.CONTRAST];
+    if (!contrastRatio) {
+      return false;
+    }
+
+    const { isLargeText, error } = contrastRatio;
+    this.setTextContent(
+      els.label,
+      L10N.getStr(
+        `accessibility.contrast.ratio.label${isLargeText ? ".large" : ""}`
+      )
+    );
+    els.label.removeAttribute("hidden");
+    if (error) {
+      els.error.removeAttribute("hidden");
+      return true;
+    }
+
+    if (contrastRatio.value) {
+      const { value, color, score, backgroundColor } = contrastRatio;
+      this._fillAndStyleContrastValue(els.min, {
+        value,
+        className: score,
+        color,
+        backgroundColor,
+      });
+      return true;
+    }
+
+    const {
+      min,
+      max,
+      color,
+      backgroundColorMin,
+      backgroundColorMax,
+      scoreMin,
+      scoreMax,
+    } = contrastRatio;
+    this._fillAndStyleContrastValue(els.min, {
+      value: min,
+      className: scoreMin,
+      color,
+      backgroundColor: backgroundColorMin,
+    });
+    els.separator.removeAttribute("hidden");
+    this._fillAndStyleContrastValue(els.max, {
+      value: max,
+      className: scoreMax,
+      color,
+      backgroundColor: backgroundColorMax,
+    });
+
+    return true;
+  }
+}
+
+/**
+ * Keyboard audit report that is used to display a problem with keyboard
+ * accessibility as part of the inforbar.
+ */
+class Keyboard extends AuditReport {
+  /**
+   * A map from keyboard issues to annotation component properties.
+   */
+  static get ISSUE_TO_INFOBAR_LABEL_MAP() {
+    return {
+      [FOCUSABLE_NO_SEMANTICS]: "accessibility.keyboard.issue.semantics",
+      [FOCUSABLE_POSITIVE_TABINDEX]: "accessibility.keyboard.issue.tabindex",
+      [INTERACTIVE_NO_ACTION]: "accessibility.keyboard.issue.action",
+      [INTERACTIVE_NOT_FOCUSABLE]: "accessibility.keyboard.issue.focusable",
+      [MOUSE_INTERACTIVE_ONLY]: "accessibility.keyboard.issue.mouse.only",
+      [NO_FOCUS_VISIBLE]: "accessibility.keyboard.issue.focus.visible",
+    };
+  }
+
+  buildMarkup(root) {
+    this.markup.createNode({
+      nodeType: "span",
+      parent: root,
+      attributes: {
+        class: "audit",
+        id: "keyboard",
+      },
+      prefix: this.prefix,
+    });
+  }
+
+  /**
+   * Update keyboard audit infobar markup.
+   * @param  {Object}
+   *         Audit report for a given highlighted accessible.
+   * @return {Boolean}
+   *         True if the keyboard markup was updated correctly and infobar audit
+   *         block should be visible.
+   */
+  update(audit) {
+    const el = this.getElement("keyboard");
+    el.setAttribute("hidden", true);
+    Object.values(SCORES).forEach(className => el.classList.remove(className));
+
+    if (!audit) {
+      return false;
+    }
+
+    const keyboardAudit = audit[AUDIT_TYPE.KEYBOARD];
+    if (!keyboardAudit) {
+      return false;
+    }
+
+    const { issue, score } = keyboardAudit;
+    this.setTextContent(
+      el,
+      L10N.getStr(Keyboard.ISSUE_TO_INFOBAR_LABEL_MAP[issue])
+    );
+    el.classList.add(score);
+    el.removeAttribute("hidden");
+
+    return true;
+  }
+}
+
+/**
+ * Text label audit report that is used to display a problem with text alternatives
+ * as part of the inforbar.
+ */
+class TextLabel extends AuditReport {
+  /**
+   * A map from text label issues to annotation component properties.
+   */
+  static get ISSUE_TO_INFOBAR_LABEL_MAP() {
+    return {
+      [AREA_NO_NAME_FROM_ALT]: "accessibility.text.label.issue.area",
+      [DIALOG_NO_NAME]: "accessibility.text.label.issue.dialog",
+      [DOCUMENT_NO_TITLE]: "accessibility.text.label.issue.document.title",
+      [EMBED_NO_NAME]: "accessibility.text.label.issue.embed",
+      [FIGURE_NO_NAME]: "accessibility.text.label.issue.figure",
+      [FORM_FIELDSET_NO_NAME]: "accessibility.text.label.issue.fieldset",
+      [FORM_FIELDSET_NO_NAME_FROM_LEGEND]:
+        "accessibility.text.label.issue.fieldset.legend2",
+      [FORM_NO_NAME]: "accessibility.text.label.issue.form",
+      [FORM_NO_VISIBLE_NAME]: "accessibility.text.label.issue.form.visible",
+      [FORM_OPTGROUP_NO_NAME_FROM_LABEL]:
+        "accessibility.text.label.issue.optgroup.label2",
+      [FRAME_NO_NAME]: "accessibility.text.label.issue.frame",
+      [HEADING_NO_CONTENT]: "accessibility.text.label.issue.heading.content",
+      [HEADING_NO_NAME]: "accessibility.text.label.issue.heading",
+      [IFRAME_NO_NAME_FROM_TITLE]: "accessibility.text.label.issue.iframe",
+      [IMAGE_NO_NAME]: "accessibility.text.label.issue.image",
+      [INTERACTIVE_NO_NAME]: "accessibility.text.label.issue.interactive",
+      [MATHML_GLYPH_NO_NAME]: "accessibility.text.label.issue.glyph",
+      [TOOLBAR_NO_NAME]: "accessibility.text.label.issue.toolbar",
+    };
+  }
+
+  buildMarkup(root) {
+    this.markup.createNode({
+      nodeType: "span",
+      parent: root,
+      attributes: {
+        class: "audit",
+        id: "text-label",
+      },
+      prefix: this.prefix,
+    });
+  }
+
+  /**
+   * Update text label audit infobar markup.
+   * @param  {Object}
+   *         Audit report for a given highlighted accessible.
+   * @return {Boolean}
+   *         True if the text label markup was updated correctly and infobar
+   *         audit block should be visible.
+   */
+  update(audit) {
+    const el = this.getElement("text-label");
+    el.setAttribute("hidden", true);
+    Object.values(SCORES).forEach(className => el.classList.remove(className));
+
+    if (!audit) {
+      return false;
+    }
+
+    const textLabelAudit = audit[AUDIT_TYPE.TEXT_LABEL];
+    if (!textLabelAudit) {
+      return false;
+    }
+
+    const { issue, score } = textLabelAudit;
+    this.setTextContent(
+      el,
+      L10N.getStr(TextLabel.ISSUE_TO_INFOBAR_LABEL_MAP[issue])
+    );
+    el.classList.add(score);
+    el.removeAttribute("hidden");
+
+    return true;
+  }
+}
+
+/**
+ * A helper function that calculate accessible object bounds and positioning to
+ * be used for highlighting.
+ *
+ * @param  {Object} win
+ *         window that contains accessible object.
+ * @param  {Object} options
+ *         Object used for passing options:
+ *         - {Number} x
+ *           x coordinate of the top left corner of the accessible object
+ *         - {Number} y
+ *           y coordinate of the top left corner of the accessible object
+ *         - {Number} w
+ *           width of the the accessible object
+ *         - {Number} h
+ *           height of the the accessible object
+ * @return {Object|null} Returns, if available, positioning and bounds information for
+ *                 the accessible object.
+ */
+function getBounds(win, { x, y, w, h }) {
+  const { mozInnerScreenX, mozInnerScreenY, scrollX, scrollY } = win;
+  const zoom = getCurrentZoom(win);
+  let left = x;
+  let right = x + w;
+  let top = y;
+  let bottom = y + h;
+
+  left -= mozInnerScreenX - scrollX;
+  right -= mozInnerScreenX - scrollX;
+  top -= mozInnerScreenY - scrollY;
+  bottom -= mozInnerScreenY - scrollY;
+
+  left *= zoom;
+  right *= zoom;
+  top *= zoom;
+  bottom *= zoom;
+
+  const width = right - left;
+  const height = bottom - top;
+
+  return { left, right, top, bottom, width, height };
+}
+
+/**
+ * A helper function that calculate accessible object bounds and positioning to
+ * be used for highlighting in browser toolbox.
+ *
+ * @param  {Object} win
+ *         window that contains accessible object.
+ * @param  {Object} options
+ *         Object used for passing options:
+ *         - {Number} x
+ *           x coordinate of the top left corner of the accessible object
+ *         - {Number} y
+ *           y coordinate of the top left corner of the accessible object
+ *         - {Number} w
+ *           width of the the accessible object
+ *         - {Number} h
+ *           height of the the accessible object
+ *         - {Number} zoom
+ *           zoom level of the accessible object's parent window
+ * @return {Object|null} Returns, if available, positioning and bounds information for
+ *                 the accessible object.
+ */
+function getBoundsXUL(win, { x, y, w, h, zoom }) {
+  const { mozInnerScreenX, mozInnerScreenY } = win;
+  let left = x;
+  let right = x + w;
+  let top = y;
+  let bottom = y + h;
+
+  left *= zoom;
+  right *= zoom;
+  top *= zoom;
+  bottom *= zoom;
+
+  left -= mozInnerScreenX;
+  right -= mozInnerScreenX;
+  top -= mozInnerScreenY;
+  bottom -= mozInnerScreenY;
+
+  const width = right - left;
+  const height = bottom - top;
+
+  return { left, right, top, bottom, width, height };
+}
+
+exports.MAX_STRING_LENGTH = MAX_STRING_LENGTH;
+exports.getBounds = getBounds;
+exports.getBoundsXUL = getBoundsXUL;
+exports.Infobar = Infobar;
diff --git a/devtools/server/actors/highlighters/utils/canvas.js b/devtools/server/actors/highlighters/utils/canvas.js
new file mode 100644
index 0000000000..24285f02e0
--- /dev/null
+++ b/devtools/server/actors/highlighters/utils/canvas.js
@@ -0,0 +1,596 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  apply,
+  getNodeTransformationMatrix,
+  getWritingModeMatrix,
+  identity,
+  isIdentity,
+  multiply,
+  scale,
+  translate,
+} = require("resource://devtools/shared/layout/dom-matrix-2d.js");
+const {
+  getCurrentZoom,
+  getViewportDimensions,
+} = require("resource://devtools/shared/layout/utils.js");
+const {
+  getComputedStyle,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+
+// A set of utility functions for highlighters that render their content to a <canvas>
+// element.
+
+// We create a <canvas> element that has always 4096x4096 physical pixels, to displays
+// our grid's overlay.
+// Then, we move the element around when needed, to give the perception that it always
+// covers the screen (See bug 1345434).
+//
+// This canvas size value is the safest we can use because most GPUs can handle it.
+// It's also far from the maximum canvas memory allocation limit (4096x4096x4 is
+// 67.108.864 bytes, where the limit is 500.000.000 bytes, see
+// gfx_max_alloc_size in modules/libpref/init/StaticPrefList.yaml.
+//
+// Note:
+// Once bug 1232491 lands, we could try to refactor this code to use the values from
+// the displayport API instead.
+//
+// Using a fixed value should also solve bug 1348293.
+const CANVAS_SIZE = 4096;
+
+// The default color used for the canvas' font, fill and stroke colors.
+const DEFAULT_COLOR = "#9400FF";
+
+/**
+ * Draws a rect to the context given and applies a transformation matrix if passed.
+ * The coordinates are the start and end points of the rectangle's diagonal.
+ *
+ * @param  {CanvasRenderingContext2D} ctx
+ *         The 2D canvas context.
+ * @param  {Number} x1
+ *         The x-axis coordinate of the rectangle's diagonal start point.
+ * @param  {Number} y1
+ *         The y-axis coordinate of the rectangle's diagonal start point.
+ * @param  {Number} x2
+ *         The x-axis coordinate of the rectangle's diagonal end point.
+ * @param  {Number} y2
+ *         The y-axis coordinate of the rectangle's diagonal end point.
+ * @param  {Array} [matrix=identity()]
+ *         The transformation matrix to apply.
+ */
+function clearRect(ctx, x1, y1, x2, y2, matrix = identity()) {
+  const p = getPointsFromDiagonal(x1, y1, x2, y2, matrix);
+
+  // We are creating a clipping path and want it removed after we clear it's
+  // contents so we need to save the context.
+  ctx.save();
+
+  // Create a path to be cleared.
+  ctx.beginPath();
+  ctx.moveTo(Math.round(p[0].x), Math.round(p[0].y));
+  ctx.lineTo(Math.round(p[1].x), Math.round(p[1].y));
+  ctx.lineTo(Math.round(p[2].x), Math.round(p[2].y));
+  ctx.lineTo(Math.round(p[3].x), Math.round(p[3].y));
+  ctx.closePath();
+
+  // Restrict future drawing to the inside of the path.
+  ctx.clip();
+
+  // Clear any transforms applied to the canvas so that clearRect() really does
+  // clear everything.
+  ctx.setTransform(1, 0, 0, 1, 0, 0);
+
+  // Clear the contents of our clipped path by attempting to clear the canvas.
+  ctx.clearRect(0, 0, CANVAS_SIZE, CANVAS_SIZE);
+
+  // Restore the context to the state it was before changing transforms and
+  // adding clipping paths.
+  ctx.restore();
+}
+
+/**
+ * Draws an arrow-bubble rectangle in the provided canvas context.
+ *
+ * @param  {CanvasRenderingContext2D} ctx
+ *         The 2D canvas context.
+ * @param  {Number} x
+ *         The x-axis origin of the rectangle.
+ * @param  {Number} y
+ *         The y-axis origin of the rectangle.
+ * @param  {Number} width
+ *         The width of the rectangle.
+ * @param  {Number} height
+ *         The height of the rectangle.
+ * @param  {Number} radius
+ *         The radius of the rounding.
+ * @param  {Number} margin
+ *         The distance of the origin point from the pointer.
+ * @param  {Number} arrowSize
+ *         The size of the arrow.
+ * @param  {String} alignment
+ *         The alignment of the rectangle in relation to its position to the grid.
+ */
+function drawBubbleRect(
+  ctx,
+  x,
+  y,
+  width,
+  height,
+  radius,
+  margin,
+  arrowSize,
+  alignment
+) {
+  let angle = 0;
+
+  if (alignment === "bottom") {
+    angle = 180;
+  } else if (alignment === "right") {
+    angle = 90;
+    [width, height] = [height, width];
+  } else if (alignment === "left") {
+    [width, height] = [height, width];
+    angle = 270;
+  }
+
+  const originX = x;
+  const originY = y;
+
+  ctx.save();
+  ctx.translate(originX, originY);
+  ctx.rotate(angle * (Math.PI / 180));
+  ctx.translate(-originX, -originY);
+  ctx.translate(-width / 2, -height - arrowSize - margin);
+
+  // The contour of the bubble is drawn with a path. The canvas context will have taken
+  // care of transforming the coordinates before calling the function, so we just always
+  // draw with the arrow pointing down. The top edge has rounded corners too.
+  ctx.beginPath();
+  // Start at the top/left corner (below the rounded corner).
+  ctx.moveTo(x, y + radius);
+  // Go down.
+  ctx.lineTo(x, y + height);
+  // Go down and the right, to draw the first half of the arrow tip.
+  ctx.lineTo(x + width / 2, y + height + arrowSize);
+  // Go back up and to the right, to draw the second half of the arrow tip.
+  ctx.lineTo(x + width, y + height);
+  // Go up to just below the top/right rounded corner.
+  ctx.lineTo(x + width, y + radius);
+  // Draw the top/right rounded corner.
+  ctx.arcTo(x + width, y, x + width - radius, y, radius);
+  // Go to the left.
+  ctx.lineTo(x + radius, y);
+  // Draw the top/left rounded corner.
+  ctx.arcTo(x, y, x, y + radius, radius);
+
+  ctx.stroke();
+  ctx.fill();
+
+  ctx.restore();
+}
+
+/**
+ * Draws a line to the context given and applies a transformation matrix if passed.
+ *
+ * @param  {CanvasRenderingContext2D} ctx
+ *         The 2D canvas context.
+ * @param  {Number} x1
+ *         The x-axis of the coordinate for the begin of the line.
+ * @param  {Number} y1
+ *         The y-axis of the coordinate for the begin of the line.
+ * @param  {Number} x2
+ *         The x-axis of the coordinate for the end of the line.
+ * @param  {Number} y2
+ *         The y-axis of the coordinate for the end of the line.
+ * @param  {Object} [options]
+ *         The options object.
+ * @param  {Array} [options.matrix=identity()]
+ *         The transformation matrix to apply.
+ * @param  {Array} [options.extendToBoundaries]
+ *         If set, the line will be extended to reach the boundaries specified.
+ */
+function drawLine(ctx, x1, y1, x2, y2, options) {
+  const matrix = options.matrix || identity();
+
+  const p1 = apply(matrix, [x1, y1]);
+  const p2 = apply(matrix, [x2, y2]);
+
+  x1 = p1[0];
+  y1 = p1[1];
+  x2 = p2[0];
+  y2 = p2[1];
+
+  if (options.extendToBoundaries) {
+    if (p1[1] === p2[1]) {
+      x1 = options.extendToBoundaries[0];
+      x2 = options.extendToBoundaries[2];
+    } else {
+      y1 = options.extendToBoundaries[1];
+      x1 = ((p2[0] - p1[0]) * (y1 - p1[1])) / (p2[1] - p1[1]) + p1[0];
+      y2 = options.extendToBoundaries[3];
+      x2 = ((p2[0] - p1[0]) * (y2 - p1[1])) / (p2[1] - p1[1]) + p1[0];
+    }
+  }
+
+  ctx.beginPath();
+  ctx.moveTo(Math.round(x1), Math.round(y1));
+  ctx.lineTo(Math.round(x2), Math.round(y2));
+}
+
+/**
+ * Draws a rect to the context given and applies a transformation matrix if passed.
+ * The coordinates are the start and end points of the rectangle's diagonal.
+ *
+ * @param  {CanvasRenderingContext2D} ctx
+ *         The 2D canvas context.
+ * @param  {Number} x1
+ *         The x-axis coordinate of the rectangle's diagonal start point.
+ * @param  {Number} y1
+ *         The y-axis coordinate of the rectangle's diagonal start point.
+ * @param  {Number} x2
+ *         The x-axis coordinate of the rectangle's diagonal end point.
+ * @param  {Number} y2
+ *         The y-axis coordinate of the rectangle's diagonal end point.
+ * @param  {Array} [matrix=identity()]
+ *         The transformation matrix to apply.
+ */
+function drawRect(ctx, x1, y1, x2, y2, matrix = identity()) {
+  const p = getPointsFromDiagonal(x1, y1, x2, y2, matrix);
+
+  ctx.beginPath();
+  ctx.moveTo(Math.round(p[0].x), Math.round(p[0].y));
+  ctx.lineTo(Math.round(p[1].x), Math.round(p[1].y));
+  ctx.lineTo(Math.round(p[2].x), Math.round(p[2].y));
+  ctx.lineTo(Math.round(p[3].x), Math.round(p[3].y));
+  ctx.closePath();
+}
+
+/**
+ * Draws a rounded rectangle in the provided canvas context.
+ *
+ * @param  {CanvasRenderingContext2D} ctx
+ *         The 2D canvas context.
+ * @param  {Number} x
+ *         The x-axis origin of the rectangle.
+ * @param  {Number} y
+ *         The y-axis origin of the rectangle.
+ * @param  {Number} width
+ *         The width of the rectangle.
+ * @param  {Number} height
+ *         The height of the rectangle.
+ * @param  {Number} radius
+ *         The radius of the rounding.
+ */
+function drawRoundedRect(ctx, x, y, width, height, radius) {
+  ctx.beginPath();
+  ctx.moveTo(x, y + radius);
+  ctx.lineTo(x, y + height - radius);
+  ctx.arcTo(x, y + height, x + radius, y + height, radius);
+  ctx.lineTo(x + width - radius, y + height);
+  ctx.arcTo(x + width, y + height, x + width, y + height - radius, radius);
+  ctx.lineTo(x + width, y + radius);
+  ctx.arcTo(x + width, y, x + width - radius, y, radius);
+  ctx.lineTo(x + radius, y);
+  ctx.arcTo(x, y, x, y + radius, radius);
+  ctx.stroke();
+  ctx.fill();
+}
+
+/**
+ * Given an array of four points and returns a DOMRect-like object representing the
+ * boundaries defined by the four points.
+ *
+ * @param  {Array} points
+ *         An array with 4 pointer objects {x, y} representing the box quads.
+ * @return {Object} DOMRect-like object of the 4 points.
+ */
+function getBoundsFromPoints(points) {
+  const bounds = {};
+
+  bounds.left = Math.min(points[0].x, points[1].x, points[2].x, points[3].x);
+  bounds.right = Math.max(points[0].x, points[1].x, points[2].x, points[3].x);
+  bounds.top = Math.min(points[0].y, points[1].y, points[2].y, points[3].y);
+  bounds.bottom = Math.max(points[0].y, points[1].y, points[2].y, points[3].y);
+
+  bounds.x = bounds.left;
+  bounds.y = bounds.top;
+  bounds.width = bounds.right - bounds.left;
+  bounds.height = bounds.bottom - bounds.top;
+
+  return bounds;
+}
+
+/**
+ * Returns the current matrices for both canvas drawing and SVG taking into account the
+ * following transformations, in this order:
+ *   1. The scale given by the display pixel ratio.
+ *   2. The translation to the top left corner of the element.
+ *   3. The scale given by the current zoom.
+ *   4. The translation given by the top and left padding of the element.
+ *   5. Any CSS transformation applied directly to the element (only 2D
+ *      transformation; the 3D transformation are flattened, see `dom-matrix-2d` module
+ *      for further details.)
+ *   6. Rotate, translate, and reflect as needed to match the writing mode and text
+ *      direction of the element.
+ *
+ *  The transformations of the element's ancestors are not currently computed (see
+ *  bug 1355675).
+ *
+ * @param  {Element} element
+ *         The current element.
+ * @param  {Window} window
+ *         The window object.
+ * @param  {Object} [options.ignoreWritingModeAndTextDirection=false]
+ *                  Avoid transforming the current matrix to match the text direction
+ *                  and writing mode.
+ * @return {Object} An object with the following properties:
+ *         - {Array} currentMatrix
+ *           The current matrix.
+ *         - {Boolean} hasNodeTransformations
+ *           true if the node has transformed and false otherwise.
+ */
+function getCurrentMatrix(
+  element,
+  window,
+  { ignoreWritingModeAndTextDirection } = {}
+) {
+  const computedStyle = getComputedStyle(element);
+
+  const paddingTop = parseFloat(computedStyle.paddingTop);
+  const paddingRight = parseFloat(computedStyle.paddingRight);
+  const paddingBottom = parseFloat(computedStyle.paddingBottom);
+  const paddingLeft = parseFloat(computedStyle.paddingLeft);
+  const borderTop = parseFloat(computedStyle.borderTopWidth);
+  const borderRight = parseFloat(computedStyle.borderRightWidth);
+  const borderBottom = parseFloat(computedStyle.borderBottomWidth);
+  const borderLeft = parseFloat(computedStyle.borderLeftWidth);
+
+  const nodeMatrix = getNodeTransformationMatrix(
+    element,
+    window.document.documentElement
+  );
+
+  let currentMatrix = identity();
+  let hasNodeTransformations = false;
+
+  // Scale based on the device pixel ratio.
+  currentMatrix = multiply(currentMatrix, scale(window.devicePixelRatio));
+
+  // Apply the current node's transformation matrix, relative to the inspected window's
+  // root element, but only if it's not a identity matrix.
+  if (isIdentity(nodeMatrix)) {
+    hasNodeTransformations = false;
+  } else {
+    currentMatrix = multiply(currentMatrix, nodeMatrix);
+    hasNodeTransformations = true;
+  }
+
+  // Translate the origin based on the node's padding and border values.
+  currentMatrix = multiply(
+    currentMatrix,
+    translate(paddingLeft + borderLeft, paddingTop + borderTop)
+  );
+
+  // Adjust as needed to match the writing mode and text direction of the element.
+  const size = {
+    width:
+      element.offsetWidth -
+      borderLeft -
+      borderRight -
+      paddingLeft -
+      paddingRight,
+    height:
+      element.offsetHeight -
+      borderTop -
+      borderBottom -
+      paddingTop -
+      paddingBottom,
+  };
+
+  if (!ignoreWritingModeAndTextDirection) {
+    const writingModeMatrix = getWritingModeMatrix(size, computedStyle);
+    if (!isIdentity(writingModeMatrix)) {
+      currentMatrix = multiply(currentMatrix, writingModeMatrix);
+    }
+  }
+
+  return { currentMatrix, hasNodeTransformations };
+}
+
+/**
+ * Given an array of four points, returns a string represent a path description.
+ *
+ * @param  {Array} points
+ *         An array with 4 pointer objects {x, y} representing the box quads.
+ * @return {String} a Path Description that can be used in svg's <path> element.
+ */
+function getPathDescriptionFromPoints(points) {
+  return (
+    "M" +
+    points[0].x +
+    "," +
+    points[0].y +
+    " " +
+    "L" +
+    points[1].x +
+    "," +
+    points[1].y +
+    " " +
+    "L" +
+    points[2].x +
+    "," +
+    points[2].y +
+    " " +
+    "L" +
+    points[3].x +
+    "," +
+    points[3].y
+  );
+}
+
+/**
+ * Given the rectangle's diagonal start and end coordinates, returns an array containing
+ * the four coordinates of a rectangle. If a matrix is provided, applies the matrix
+ * function to each of the coordinates' value.
+ *
+ * @param  {Number} x1
+ *         The x-axis coordinate of the rectangle's diagonal start point.
+ * @param  {Number} y1
+ *         The y-axis coordinate of the rectangle's diagonal start point.
+ * @param  {Number} x2
+ *         The x-axis coordinate of the rectangle's diagonal end point.
+ * @param  {Number} y2
+ *         The y-axis coordinate of the rectangle's diagonal end point.
+ * @param  {Array} [matrix=identity()]
+ *         A transformation matrix to apply.
+ * @return {Array} the four coordinate points of the given rectangle transformed by the
+ * matrix given.
+ */
+function getPointsFromDiagonal(x1, y1, x2, y2, matrix = identity()) {
+  return [
+    [x1, y1],
+    [x2, y1],
+    [x2, y2],
+    [x1, y2],
+  ].map(point => {
+    const transformedPoint = apply(matrix, point);
+
+    return { x: transformedPoint[0], y: transformedPoint[1] };
+  });
+}
+
+/**
+ * Updates the <canvas> element's style in accordance with the current window's
+ * device pixel ratio, and the position calculated in `getCanvasPosition`. It also
+ * clears the drawing context. This is called on canvas update after a scroll event where
+ * `getCanvasPosition` updates the new canvasPosition.
+ *
+ * @param  {Canvas} canvas
+ *         The <canvas> element.
+ * @param  {Object} canvasPosition
+ *         A pointer object {x, y} representing the <canvas> position to the top left
+ *         corner of the page.
+ * @param  {Number} devicePixelRatio
+ *         The device pixel ratio.
+ * @param  {Window} [options.zoomWindow]
+ *         Optional window object used to calculate zoom (default = undefined).
+ */
+function updateCanvasElement(
+  canvas,
+  canvasPosition,
+  devicePixelRatio,
+  { zoomWindow } = {}
+) {
+  let { x, y } = canvasPosition;
+  const size = CANVAS_SIZE / devicePixelRatio;
+
+  if (zoomWindow) {
+    const zoom = getCurrentZoom(zoomWindow);
+    x *= zoom;
+    y *= zoom;
+  }
+
+  // Resize the canvas taking the dpr into account so as to have crisp lines, and
+  // translating it to give the perception that it always covers the viewport.
+  canvas.setAttribute(
+    "style",
+    `width: ${size}px; height: ${size}px; transform: translate(${x}px, ${y}px);`
+  );
+  canvas.getCanvasContext("2d").clearRect(0, 0, CANVAS_SIZE, CANVAS_SIZE);
+}
+
+/**
+ * Calculates and returns the <canvas>'s position in accordance with the page's scroll,
+ * document's size, canvas size, and viewport's size. This is called when a page's scroll
+ * is detected.
+ *
+ * @param  {Object} canvasPosition
+ *         A pointer object {x, y} representing the <canvas> position to the top left
+ *         corner of the page.
+ * @param  {Object} scrollPosition
+ *         A pointer object {x, y} representing the window's pageXOffset and pageYOffset.
+ * @param  {Window} window
+ *         The window object.
+ * @param  {Object} windowDimensions
+ *         An object {width, height} representing the window's dimensions for the
+ *         `window` given.
+ * @return {Boolean} true if the <canvas> position was updated and false otherwise.
+ */
+function updateCanvasPosition(
+  canvasPosition,
+  scrollPosition,
+  window,
+  windowDimensions
+) {
+  let { x: canvasX, y: canvasY } = canvasPosition;
+  const { x: scrollX, y: scrollY } = scrollPosition;
+  const cssCanvasSize = CANVAS_SIZE / window.devicePixelRatio;
+  const viewportSize = getViewportDimensions(window);
+  const { height, width } = windowDimensions;
+  const canvasWidth = cssCanvasSize;
+  const canvasHeight = cssCanvasSize;
+  let hasUpdated = false;
+
+  // Those values indicates the relative horizontal and vertical space the page can
+  // scroll before we have to reposition the <canvas>; they're 1/4 of the delta between
+  // the canvas' size and the viewport's size: that's because we want to consider both
+  // sides (top/bottom, left/right; so 1/2 for each side) and also we don't want to
+  // shown the edges of the canvas in case of fast scrolling (to avoid showing undraw
+  // areas, therefore another 1/2 here).
+  const bufferSizeX = (canvasWidth - viewportSize.width) >> 2;
+  const bufferSizeY = (canvasHeight - viewportSize.height) >> 2;
+
+  // Defines the boundaries for the canvas.
+  const leftBoundary = 0;
+  const rightBoundary = width - canvasWidth;
+  const topBoundary = 0;
+  const bottomBoundary = height - canvasHeight;
+
+  // Defines the thresholds that triggers the canvas' position to be updated.
+  const leftThreshold = scrollX - bufferSizeX;
+  const rightThreshold =
+    scrollX - canvasWidth + viewportSize.width + bufferSizeX;
+  const topThreshold = scrollY - bufferSizeY;
+  const bottomThreshold =
+    scrollY - canvasHeight + viewportSize.height + bufferSizeY;
+
+  if (canvasX < rightBoundary && canvasX < rightThreshold) {
+    canvasX = Math.min(leftThreshold, rightBoundary);
+    hasUpdated = true;
+  } else if (canvasX > leftBoundary && canvasX > leftThreshold) {
+    canvasX = Math.max(rightThreshold, leftBoundary);
+    hasUpdated = true;
+  }
+
+  if (canvasY < bottomBoundary && canvasY < bottomThreshold) {
+    canvasY = Math.min(topThreshold, bottomBoundary);
+    hasUpdated = true;
+  } else if (canvasY > topBoundary && canvasY > topThreshold) {
+    canvasY = Math.max(bottomThreshold, topBoundary);
+    hasUpdated = true;
+  }
+
+  // Update the canvas position with the calculated canvasX and canvasY positions.
+  canvasPosition.x = canvasX;
+  canvasPosition.y = canvasY;
+
+  return hasUpdated;
+}
+
+exports.CANVAS_SIZE = CANVAS_SIZE;
+exports.DEFAULT_COLOR = DEFAULT_COLOR;
+exports.clearRect = clearRect;
+exports.drawBubbleRect = drawBubbleRect;
+exports.drawLine = drawLine;
+exports.drawRect = drawRect;
+exports.drawRoundedRect = drawRoundedRect;
+exports.getBoundsFromPoints = getBoundsFromPoints;
+exports.getCurrentMatrix = getCurrentMatrix;
+exports.getPathDescriptionFromPoints = getPathDescriptionFromPoints;
+exports.getPointsFromDiagonal = getPointsFromDiagonal;
+exports.updateCanvasElement = updateCanvasElement;
+exports.updateCanvasPosition = updateCanvasPosition;
diff --git a/devtools/server/actors/highlighters/utils/markup.js b/devtools/server/actors/highlighters/utils/markup.js
new file mode 100644
index 0000000000..a550ca0076
--- /dev/null
+++ b/devtools/server/actors/highlighters/utils/markup.js
@@ -0,0 +1,787 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  getCurrentZoom,
+  getWindowDimensions,
+  getViewportDimensions,
+} = require("resource://devtools/shared/layout/utils.js");
+const EventEmitter = require("resource://devtools/shared/event-emitter.js");
+
+const lazyContainer = {};
+
+loader.lazyRequireGetter(
+  lazyContainer,
+  "CssLogic",
+  "resource://devtools/server/actors/inspector/css-logic.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "isDocumentReady",
+  "resource://devtools/server/actors/inspector/utils.js",
+  true
+);
+
+exports.getComputedStyle = node =>
+  lazyContainer.CssLogic.getComputedStyle(node);
+
+exports.getBindingElementAndPseudo = node =>
+  lazyContainer.CssLogic.getBindingElementAndPseudo(node);
+
+exports.hasPseudoClassLock = (...args) =>
+  InspectorUtils.hasPseudoClassLock(...args);
+
+exports.addPseudoClassLock = (...args) =>
+  InspectorUtils.addPseudoClassLock(...args);
+
+exports.removePseudoClassLock = (...args) =>
+  InspectorUtils.removePseudoClassLock(...args);
+
+const SVG_NS = "http://www.w3.org/2000/svg";
+const XHTML_NS = "http://www.w3.org/1999/xhtml";
+const XUL_NS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
+const STYLESHEET_URI =
+  "resource://devtools-highlighter-styles/highlighters.css";
+
+const _tokens = Symbol("classList/tokens");
+
+/**
+ * Shims the element's `classList` for anonymous content elements; used
+ * internally by `CanvasFrameAnonymousContentHelper.getElement()` method.
+ */
+function ClassList(className) {
+  const trimmed = (className || "").trim();
+  this[_tokens] = trimmed ? trimmed.split(/\s+/) : [];
+}
+
+ClassList.prototype = {
+  item(index) {
+    return this[_tokens][index];
+  },
+  contains(token) {
+    return this[_tokens].includes(token);
+  },
+  add(token) {
+    if (!this.contains(token)) {
+      this[_tokens].push(token);
+    }
+    EventEmitter.emit(this, "update");
+  },
+  remove(token) {
+    const index = this[_tokens].indexOf(token);
+
+    if (index > -1) {
+      this[_tokens].splice(index, 1);
+    }
+    EventEmitter.emit(this, "update");
+  },
+  toggle(token, force) {
+    // If force parameter undefined retain the toggle behavior
+    if (force === undefined) {
+      if (this.contains(token)) {
+        this.remove(token);
+      } else {
+        this.add(token);
+      }
+    } else if (force) {
+      // If force is true, enforce token addition
+      this.add(token);
+    } else {
+      // If force is falsy value, enforce token removal
+      this.remove(token);
+    }
+  },
+  get length() {
+    return this[_tokens].length;
+  },
+  *[Symbol.iterator]() {
+    for (let i = 0; i < this.tokens.length; i++) {
+      yield this[_tokens][i];
+    }
+  },
+  toString() {
+    return this[_tokens].join(" ");
+  },
+};
+
+/**
+ * Is this content window a XUL window?
+ * @param {Window} window
+ * @return {Boolean}
+ */
+function isXUL(window) {
+  return window.document.documentElement.namespaceURI === XUL_NS;
+}
+exports.isXUL = isXUL;
+
+/**
+ * Returns true if a DOM node is "valid", where "valid" means that the node isn't a dead
+ * object wrapper, is still attached to a document, and is of a given type.
+ * @param {DOMNode} node
+ * @param {Number} nodeType Optional, defaults to ELEMENT_NODE
+ * @return {Boolean}
+ */
+function isNodeValid(node, nodeType = Node.ELEMENT_NODE) {
+  // Is it still alive?
+  if (!node || Cu.isDeadWrapper(node)) {
+    return false;
+  }
+
+  // Is it of the right type?
+  if (node.nodeType !== nodeType) {
+    return false;
+  }
+
+  // Is its document accessible?
+  const doc = node.nodeType === Node.DOCUMENT_NODE ? node : node.ownerDocument;
+  if (!doc || !doc.defaultView) {
+    return false;
+  }
+
+  // Is the node connected to the document?
+  if (!node.isConnected) {
+    return false;
+  }
+
+  return true;
+}
+exports.isNodeValid = isNodeValid;
+
+/**
+ * Every highlighters should insert their markup content into the document's
+ * canvasFrame anonymous content container (see dom/webidl/Document.webidl).
+ *
+ * Since this container gets cleared when the document navigates, highlighters
+ * should use this helper to have their markup content automatically re-inserted
+ * in the new document.
+ *
+ * Since the markup content is inserted in the canvasFrame using
+ * insertAnonymousContent, this means that it can be modified using the API
+ * described in AnonymousContent.webidl.
+ * To retrieve the AnonymousContent instance, use the content getter.
+ *
+ * @param {HighlighterEnv} highlighterEnv
+ *        The environemnt which windows will be used to insert the node.
+ * @param {Function} nodeBuilder
+ *        A function that, when executed, returns a DOM node to be inserted into
+ *        the canvasFrame.
+ * @param {Object} options
+ * @param {Boolean} options.waitForDocumentToLoad
+ *        Set to false to try to insert the anonymous content even if the document
+ *        isn't loaded yet. Defaults to true.
+ */
+function CanvasFrameAnonymousContentHelper(
+  highlighterEnv,
+  nodeBuilder,
+  { waitForDocumentToLoad = true } = {}
+) {
+  this.highlighterEnv = highlighterEnv;
+  this.nodeBuilder = nodeBuilder;
+  this.waitForDocumentToLoad = !!waitForDocumentToLoad;
+
+  this._onWindowReady = this._onWindowReady.bind(this);
+  this.highlighterEnv.on("window-ready", this._onWindowReady);
+
+  this.listeners = new Map();
+  this.elements = new Map();
+}
+
+CanvasFrameAnonymousContentHelper.prototype = {
+  initialize() {
+    // _insert will resolve this promise once the markup is displayed
+    const onInitialized = new Promise(resolve => {
+      this._initialized = resolve;
+    });
+    // Only try to create the highlighter when the document is loaded,
+    // otherwise, wait for the window-ready event to fire.
+    const doc = this.highlighterEnv.document;
+    if (
+      doc.documentElement &&
+      (!this.waitForDocumentToLoad ||
+        isDocumentReady(doc) ||
+        doc.readyState !== "uninitialized")
+    ) {
+      this._insert();
+    }
+
+    return onInitialized;
+  },
+
+  destroy() {
+    this._remove();
+
+    this.highlighterEnv.off("window-ready", this._onWindowReady);
+    this.highlighterEnv = this.nodeBuilder = this._content = null;
+    this.anonymousContentDocument = null;
+    this.anonymousContentWindow = null;
+    this.pageListenerTarget = null;
+
+    this._removeAllListeners();
+    this.elements.clear();
+  },
+
+  async _insert() {
+    if (this.waitForDocumentToLoad) {
+      await waitForContentLoaded(this.highlighterEnv.window);
+    }
+    if (!this.highlighterEnv) {
+      // CanvasFrameAnonymousContentHelper was already destroyed.
+      return;
+    }
+
+    // Highlighters are drawn inside the anonymous content of the
+    // highlighter environment document.
+    this.anonymousContentDocument = this.highlighterEnv.document;
+    this.anonymousContentWindow = this.highlighterEnv.window;
+    this.pageListenerTarget = this.highlighterEnv.pageListenerTarget;
+
+    // It was stated that hidden documents don't accept
+    // `insertAnonymousContent` calls yet. That doesn't seems the case anymore,
+    // at least on desktop. Therefore, removing the code that was dealing with
+    // that scenario, fixes when we're adding anonymous content in a tab that
+    // is not the active one (see bug 1260043 and bug 1260044)
+    try {
+      // If we didn't wait for the document to load, we want to force a layout update
+      // to ensure the anonymous content will be rendered (see Bug 1580394).
+      const forceSynchronousLayoutUpdate = !this.waitForDocumentToLoad;
+      this._content = this.anonymousContentDocument.insertAnonymousContent(
+        forceSynchronousLayoutUpdate
+      );
+    } catch (e) {
+      // If the `insertAnonymousContent` fails throwing a `NS_ERROR_UNEXPECTED`, it means
+      // we don't have access to a `CustomContentContainer` yet (see bug 1365075).
+      // At this point, it could only happen on document's interactive state, and we
+      // need to wait until the `complete` state before inserting the anonymous content
+      // again.
+      if (
+        e.result === Cr.NS_ERROR_UNEXPECTED &&
+        this.anonymousContentDocument.readyState === "interactive"
+      ) {
+        // The next state change will be "complete" since the current is "interactive"
+        await new Promise(resolve => {
+          this.anonymousContentDocument.addEventListener(
+            "readystatechange",
+            resolve,
+            { once: true }
+          );
+        });
+        this._content = this.anonymousContentDocument.insertAnonymousContent();
+      } else {
+        throw e;
+      }
+    }
+
+    // Use createElementNS to make sure this is an HTML element.
+    // Document.createElement's behavior is different between SVG and HTML
+    // documents, see bug 1850007.
+    const link = this.anonymousContentDocument.createElementNS(
+      XHTML_NS,
+      "link"
+    );
+    link.href = STYLESHEET_URI;
+    link.rel = "stylesheet";
+    this._content.root.appendChild(link);
+    this._content.root.appendChild(this.nodeBuilder());
+
+    this._initialized();
+  },
+
+  _remove() {
+    try {
+      this.anonymousContentDocument.removeAnonymousContent(this._content);
+    } catch (e) {
+      // If the current window isn't the one the content was inserted into, this
+      // will fail, but that's fine.
+    }
+  },
+
+  /**
+   * The "window-ready" event can be triggered when:
+   *   - a new window is created
+   *   - a window is unfrozen from bfcache
+   *   - when first attaching to a page
+   *   - when swapping frame loaders (moving tabs, toggling RDM)
+   */
+  _onWindowReady({ isTopLevel }) {
+    if (isTopLevel) {
+      this._removeAllListeners();
+      this.elements.clear();
+      this._insert();
+    }
+  },
+
+  _getNodeById(id) {
+    return this.content?.root.getElementById(id);
+  },
+
+  getBoundingClientRect(id) {
+    const node = this._getNodeById(id);
+    if (!node) {
+      return null;
+    }
+    return node.getBoundingClientRect();
+  },
+
+  getComputedStylePropertyValue(id, property) {
+    const node = this._getNodeById(id);
+    if (!node) {
+      return null;
+    }
+    return this.anonymousContentWindow
+      .getComputedStyle(node)
+      .getPropertyValue(property);
+  },
+
+  getTextContentForElement(id) {
+    return this._getNodeById(id)?.textContent;
+  },
+
+  setTextContentForElement(id, text) {
+    const node = this._getNodeById(id);
+    if (!node) {
+      return;
+    }
+    node.textContent = text;
+  },
+
+  setAttributeForElement(id, name, value) {
+    this._getNodeById(id)?.setAttribute(name, value);
+  },
+
+  getAttributeForElement(id, name) {
+    return this._getNodeById(id)?.getAttribute(name);
+  },
+
+  removeAttributeForElement(id, name) {
+    this._getNodeById(id)?.removeAttribute(name);
+  },
+
+  hasAttributeForElement(id, name) {
+    return typeof this.getAttributeForElement(id, name) === "string";
+  },
+
+  getCanvasContext(id, type = "2d") {
+    return this._getNodeById(id)?.getContext(type);
+  },
+
+  /**
+   * Add an event listener to one of the elements inserted in the canvasFrame
+   * native anonymous container.
+   * Like other methods in this helper, this requires the ID of the element to
+   * be passed in.
+   *
+   * Note that if the content page navigates, the event listeners won't be
+   * added again.
+   *
+   * Also note that unlike traditional DOM events, the events handled by
+   * listeners added here will propagate through the document only through
+   * bubbling phase, so the useCapture parameter isn't supported.
+   * It is possible however to call e.stopPropagation() to stop the bubbling.
+   *
+   * IMPORTANT: the chrome-only canvasFrame insertion API takes great care of
+   * not leaking references to inserted elements to chrome JS code. That's
+   * because otherwise, chrome JS code could freely modify native anon elements
+   * inside the canvasFrame and probably change things that are assumed not to
+   * change by the C++ code managing this frame.
+   * See https://wiki.mozilla.org/DevTools/Highlighter#The_AnonymousContent_API
+   * Unfortunately, the inserted nodes are still available via
+   * event.originalTarget, and that's what the event handler here uses to check
+   * that the event actually occured on the right element, but that also means
+   * consumers of this code would be able to access the inserted elements.
+   * Therefore, the originalTarget property will be nullified before the event
+   * is passed to your handler.
+   *
+   * IMPL DETAIL: A single event listener is added per event types only, at
+   * browser level and if the event originalTarget is found to have the provided
+   * ID, the callback is executed (and then IDs of parent nodes of the
+   * originalTarget are checked too).
+   *
+   * @param {String} id
+   * @param {String} type
+   * @param {Function} handler
+   */
+  addEventListenerForElement(id, type, handler) {
+    if (typeof id !== "string") {
+      throw new Error(
+        "Expected a string ID in addEventListenerForElement but" + " got: " + id
+      );
+    }
+
+    // If no one is listening for this type of event yet, add one listener.
+    if (!this.listeners.has(type)) {
+      const target = this.pageListenerTarget;
+      target.addEventListener(type, this, true);
+      // Each type entry in the map is a map of ids:handlers.
+      this.listeners.set(type, new Map());
+    }
+
+    const listeners = this.listeners.get(type);
+    listeners.set(id, handler);
+  },
+
+  /**
+   * Remove an event listener from one of the elements inserted in the
+   * canvasFrame native anonymous container.
+   * @param {String} id
+   * @param {String} type
+   */
+  removeEventListenerForElement(id, type) {
+    const listeners = this.listeners.get(type);
+    if (!listeners) {
+      return;
+    }
+    listeners.delete(id);
+
+    // If no one is listening for event type anymore, remove the listener.
+    if (!this.listeners.has(type)) {
+      const target = this.pageListenerTarget;
+      target.removeEventListener(type, this, true);
+    }
+  },
+
+  handleEvent(event) {
+    const listeners = this.listeners.get(event.type);
+    if (!listeners) {
+      return;
+    }
+
+    // Hide the originalTarget property to avoid exposing references to native
+    // anonymous elements. See addEventListenerForElement's comment.
+    let isPropagationStopped = false;
+    const eventProxy = new Proxy(event, {
+      get: (obj, name) => {
+        if (name === "originalTarget") {
+          return null;
+        } else if (name === "stopPropagation") {
+          return () => {
+            isPropagationStopped = true;
+          };
+        }
+        return obj[name];
+      },
+    });
+
+    // Start at originalTarget, bubble through ancestors and call handlers when
+    // needed.
+    let node = event.originalTarget;
+    while (node) {
+      const handler = listeners.get(node.id);
+      if (handler) {
+        handler(eventProxy, node.id);
+        if (isPropagationStopped) {
+          break;
+        }
+      }
+      node = node.parentNode;
+    }
+  },
+
+  _removeAllListeners() {
+    if (this.pageListenerTarget) {
+      const target = this.pageListenerTarget;
+      for (const [type] of this.listeners) {
+        target.removeEventListener(type, this, true);
+      }
+    }
+    this.listeners.clear();
+  },
+
+  getElement(id) {
+    if (this.elements.has(id)) {
+      return this.elements.get(id);
+    }
+
+    const classList = new ClassList(this.getAttributeForElement(id, "class"));
+
+    EventEmitter.on(classList, "update", () => {
+      this.setAttributeForElement(id, "class", classList.toString());
+    });
+
+    const element = {
+      getTextContent: () => this.getTextContentForElement(id),
+      setTextContent: text => this.setTextContentForElement(id, text),
+      setAttribute: (name, val) => this.setAttributeForElement(id, name, val),
+      getAttribute: name => this.getAttributeForElement(id, name),
+      removeAttribute: name => this.removeAttributeForElement(id, name),
+      hasAttribute: name => this.hasAttributeForElement(id, name),
+      getCanvasContext: type => this.getCanvasContext(id, type),
+      addEventListener: (type, handler) => {
+        return this.addEventListenerForElement(id, type, handler);
+      },
+      removeEventListener: (type, handler) => {
+        return this.removeEventListenerForElement(id, type, handler);
+      },
+      computedStyle: {
+        getPropertyValue: property =>
+          this.getComputedStylePropertyValue(id, property),
+      },
+      classList,
+    };
+
+    this.elements.set(id, element);
+
+    return element;
+  },
+
+  get content() {
+    if (!this._content || Cu.isDeadWrapper(this._content)) {
+      return null;
+    }
+    return this._content;
+  },
+
+  /**
+   * The canvasFrame anonymous content container gets zoomed in/out with the
+   * page. If this is unwanted, i.e. if you want the inserted element to remain
+   * unzoomed, then this method can be used.
+   *
+   * Consumers of the CanvasFrameAnonymousContentHelper should call this method,
+   * it isn't executed automatically. Typically, AutoRefreshHighlighter can call
+   * it when _update is executed.
+   *
+   * The matching element will be scaled down or up by 1/zoomLevel (using css
+   * transform) to cancel the current zoom. The element's width and height
+   * styles will also be set according to the scale. Finally, the element's
+   * position will be set as absolute.
+   *
+   * Note that if the matching element already has an inline style attribute, it
+   * *won't* be preserved.
+   *
+   * @param {DOMNode} node This node is used to determine which container window
+   * should be used to read the current zoom value.
+   * @param {String} id The ID of the root element inserted with this API.
+   */
+  scaleRootElement(node, id) {
+    const boundaryWindow = this.highlighterEnv.window;
+    const zoom = getCurrentZoom(node);
+    // Hide the root element and force the reflow in order to get the proper window's
+    // dimensions without increasing them.
+    const root = this._getNodeById(id);
+    root.style.display = "none";
+    node.offsetWidth;
+
+    let { width, height } = getWindowDimensions(boundaryWindow);
+    let value = "";
+
+    if (zoom !== 1) {
+      value = `transform-origin:top left; transform:scale(${1 / zoom}); `;
+      width *= zoom;
+      height *= zoom;
+    }
+
+    value += `position:absolute; width:${width}px;height:${height}px; overflow:hidden;`;
+    root.style = value;
+  },
+
+  /**
+   * Helper function that creates SVG DOM nodes.
+   * @param {Object} Options for the node include:
+   * - nodeType: the type of node, defaults to "box".
+   * - attributes: a {name:value} object to be used as attributes for the node.
+   * - prefix: a string that will be used to prefix the values of the id and class
+   *   attributes.
+   * - parent: if provided, the newly created element will be appended to this
+   *   node.
+   */
+  createSVGNode(options) {
+    if (!options.nodeType) {
+      options.nodeType = "box";
+    }
+
+    options.namespace = SVG_NS;
+
+    return this.createNode(options);
+  },
+
+  /**
+   * Helper function that creates DOM nodes.
+   * @param {Object} Options for the node include:
+   * - nodeType: the type of node, defaults to "div".
+   * - namespace: the namespace to use to create the node, defaults to XHTML namespace.
+   * - attributes: a {name:value} object to be used as attributes for the node.
+   * - prefix: a string that will be used to prefix the values of the id and class
+   *   attributes.
+   * - parent: if provided, the newly created element will be appended to this
+   *   node.
+   * - text: if provided, set the text content of the element.
+   */
+  createNode(options) {
+    const type = options.nodeType || "div";
+    const namespace = options.namespace || XHTML_NS;
+    const doc = this.anonymousContentDocument;
+
+    const node = doc.createElementNS(namespace, type);
+
+    for (const name in options.attributes || {}) {
+      let value = options.attributes[name];
+      if (options.prefix && (name === "class" || name === "id")) {
+        value = options.prefix + value;
+      }
+      node.setAttribute(name, value);
+    }
+
+    if (options.parent) {
+      options.parent.appendChild(node);
+    }
+
+    if (options.text) {
+      node.appendChild(doc.createTextNode(options.text));
+    }
+
+    return node;
+  },
+};
+exports.CanvasFrameAnonymousContentHelper = CanvasFrameAnonymousContentHelper;
+
+/**
+ * Wait for document readyness.
+ * @param {Object} iframeOrWindow
+ *        IFrame or Window for which the content should be loaded.
+ */
+function waitForContentLoaded(iframeOrWindow) {
+  let loadEvent = "DOMContentLoaded";
+  // If we are waiting for an iframe to load and it is for a XUL window
+  // highlighter that is not browser toolbox, we must wait for IFRAME's "load".
+  if (
+    iframeOrWindow.contentWindow &&
+    iframeOrWindow.ownerGlobal !==
+      iframeOrWindow.contentWindow.browsingContext.topChromeWindow
+  ) {
+    loadEvent = "load";
+  }
+
+  const doc = iframeOrWindow.contentDocument || iframeOrWindow.document;
+  if (isDocumentReady(doc)) {
+    return Promise.resolve();
+  }
+
+  return new Promise(resolve => {
+    iframeOrWindow.addEventListener(loadEvent, resolve, { once: true });
+  });
+}
+
+/**
+ * Move the infobar to the right place in the highlighter. This helper method is utilized
+ * in both css-grid.js and box-model.js to help position the infobar in an appropriate
+ * space over the highlighted node element or grid area. The infobar is used to display
+ * relevant information about the highlighted item (ex, node or grid name and dimensions).
+ *
+ * This method will first try to position the infobar to top or bottom of the container
+ * such that it has enough space for the height of the infobar. Afterwards, it will try
+ * to horizontally center align with the container element if possible.
+ *
+ * @param  {DOMNode} container
+ *         The container element which will be used to position the infobar.
+ * @param  {Object} bounds
+ *         The content bounds of the container element.
+ * @param  {Window} win
+ *         The window object.
+ * @param  {Object} [options={}]
+ *         Advanced options for the infobar.
+ * @param  {String} options.position
+ *         Force the infobar to be displayed either on "top" or "bottom". Any other value
+ *         will be ingnored.
+ */
+function moveInfobar(container, bounds, win, options = {}) {
+  const zoom = getCurrentZoom(win);
+  const viewport = getViewportDimensions(win);
+
+  const { computedStyle } = container;
+
+  const margin = 2;
+  const arrowSize = parseFloat(
+    computedStyle.getPropertyValue("--highlighter-bubble-arrow-size")
+  );
+  const containerHeight = parseFloat(computedStyle.getPropertyValue("height"));
+  const containerWidth = parseFloat(computedStyle.getPropertyValue("width"));
+  const containerHalfWidth = containerWidth / 2;
+
+  const viewportWidth = viewport.width * zoom;
+  const viewportHeight = viewport.height * zoom;
+  let { pageXOffset, pageYOffset } = win;
+
+  pageYOffset *= zoom;
+  pageXOffset *= zoom;
+
+  // Defines the boundaries for the infobar.
+  const topBoundary = margin;
+  const bottomBoundary = viewportHeight - containerHeight - margin - 1;
+  const leftBoundary = containerHalfWidth + margin;
+  const rightBoundary = viewportWidth - containerHalfWidth - margin;
+
+  // Set the default values.
+  let top = bounds.y - containerHeight - arrowSize;
+  const bottom = bounds.bottom + margin + arrowSize;
+  let left = bounds.x + bounds.width / 2;
+  let isOverlapTheNode = false;
+  let positionAttribute = "top";
+  let position = "absolute";
+
+  // Here we start the math.
+  // We basically want to position absolutely the infobar, except when is pointing to a
+  // node that is offscreen or partially offscreen, in a way that the infobar can't
+  // be placed neither on top nor on bottom.
+  // In such cases, the infobar will overlap the node, and to limit the latency given
+  // by APZ (See Bug 1312103) it will be positioned as "fixed".
+  // It's a sort of "position: sticky" (but positioned as absolute instead of relative).
+  const canBePlacedOnTop = top >= pageYOffset;
+  const canBePlacedOnBottom = bottomBoundary + pageYOffset - bottom > 0;
+  const forcedOnTop = options.position === "top";
+  const forcedOnBottom = options.position === "bottom";
+
+  if (
+    (!canBePlacedOnTop && canBePlacedOnBottom && !forcedOnTop) ||
+    forcedOnBottom
+  ) {
+    top = bottom;
+    positionAttribute = "bottom";
+  }
+
+  const isOffscreenOnTop = top < topBoundary + pageYOffset;
+  const isOffscreenOnBottom = top > bottomBoundary + pageYOffset;
+  const isOffscreenOnLeft = left < leftBoundary + pageXOffset;
+  const isOffscreenOnRight = left > rightBoundary + pageXOffset;
+
+  if (isOffscreenOnTop) {
+    top = topBoundary;
+    isOverlapTheNode = true;
+  } else if (isOffscreenOnBottom) {
+    top = bottomBoundary;
+    isOverlapTheNode = true;
+  } else if (isOffscreenOnLeft || isOffscreenOnRight) {
+    isOverlapTheNode = true;
+    top -= pageYOffset;
+  }
+
+  if (isOverlapTheNode) {
+    left = Math.min(Math.max(leftBoundary, left - pageXOffset), rightBoundary);
+
+    position = "fixed";
+    container.setAttribute("hide-arrow", "true");
+  } else {
+    position = "absolute";
+    container.removeAttribute("hide-arrow");
+  }
+
+  // We need to scale the infobar Independently from the highlighter's container;
+  // otherwise the `position: fixed` won't work, since "any value other than `none` for
+  // the transform, results in the creation of both a stacking context and a containing
+  // block. The object acts as a containing block for fixed positioned descendants."
+  // (See https://www.w3.org/TR/css-transforms-1/#transform-rendering)
+  // We also need to shift the infobar 50% to the left in order for it to appear centered
+  // on the element it points to.
+  container.setAttribute(
+    "style",
+    `
+    position:${position};
+    transform-origin: 0 0;
+    transform: scale(${1 / zoom}) translate(calc(${left}px - 50%), ${top}px)`
+  );
+
+  container.setAttribute("position", positionAttribute);
+}
+exports.moveInfobar = moveInfobar;
diff --git a/devtools/server/actors/highlighters/utils/moz.build b/devtools/server/actors/highlighters/utils/moz.build
new file mode 100644
index 0000000000..ab4f96912d
--- /dev/null
+++ b/devtools/server/actors/highlighters/utils/moz.build
@@ -0,0 +1,7 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+DevToolsModules("accessibility.js", "canvas.js", "markup.js")
diff --git a/devtools/server/actors/highlighters/viewport-size.js b/devtools/server/actors/highlighters/viewport-size.js
new file mode 100644
index 0000000000..4c85a305ca
--- /dev/null
+++ b/devtools/server/actors/highlighters/viewport-size.js
@@ -0,0 +1,129 @@
+/* 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/. */
+
+"use strict";
+
+const EventEmitter = require("resource://devtools/shared/event-emitter.js");
+const {
+  setIgnoreLayoutChanges,
+} = require("resource://devtools/shared/layout/utils.js");
+const {
+  CanvasFrameAnonymousContentHelper,
+} = require("resource://devtools/server/actors/highlighters/utils/markup.js");
+
+/**
+ * The ViewportSizeHighlighter is a class that displays the viewport
+ * width and height on a small overlay on the top right edge of the page
+ * while the rulers are turned on.
+ */
+class ViewportSizeHighlighter {
+  constructor(highlighterEnv) {
+    this.env = highlighterEnv;
+    this.markup = new CanvasFrameAnonymousContentHelper(
+      highlighterEnv,
+      this._buildMarkup.bind(this)
+    );
+    this.isReady = this.markup.initialize();
+
+    const { pageListenerTarget } = highlighterEnv;
+    pageListenerTarget.addEventListener("pagehide", this);
+  }
+
+  ID_CLASS_PREFIX = "viewport-size-highlighter-";
+
+  _buildMarkup() {
+    const prefix = this.ID_CLASS_PREFIX;
+
+    const container = this.markup.createNode({
+      attributes: { class: "highlighter-container" },
+    });
+
+    this.markup.createNode({
+      parent: container,
+      attributes: {
+        class: "viewport-infobar-container",
+        id: "viewport-infobar-container",
+        position: "top",
+      },
+      prefix,
+    });
+
+    return container;
+  }
+
+  handleEvent(event) {
+    switch (event.type) {
+      case "pagehide":
+        // If a page hide event is triggered for current window's highlighter, hide the
+        // highlighter.
+        if (event.target.defaultView === this.env.window) {
+          this.destroy();
+        }
+        break;
+    }
+  }
+
+  _update() {
+    const { window } = this.env;
+
+    setIgnoreLayoutChanges(true);
+
+    this.updateViewportInfobar();
+
+    setIgnoreLayoutChanges(false, window.document.documentElement);
+
+    this._rafID = window.requestAnimationFrame(() => this._update());
+  }
+
+  _cancelUpdate() {
+    if (this._rafID) {
+      this.env.window.cancelAnimationFrame(this._rafID);
+      this._rafID = 0;
+    }
+  }
+
+  updateViewportInfobar() {
+    const { window } = this.env;
+    const { innerHeight, innerWidth } = window;
+    const infobarId = this.ID_CLASS_PREFIX + "viewport-infobar-container";
+    const textContent = innerWidth + "px \u00D7 " + innerHeight + "px";
+    this.markup.getElement(infobarId).setTextContent(textContent);
+  }
+
+  destroy() {
+    this.hide();
+
+    const { pageListenerTarget } = this.env;
+
+    if (pageListenerTarget) {
+      pageListenerTarget.removeEventListener("pagehide", this);
+    }
+
+    this.markup.destroy();
+
+    EventEmitter.emit(this, "destroy");
+  }
+
+  show() {
+    this.markup.removeAttributeForElement(
+      this.ID_CLASS_PREFIX + "viewport-infobar-container",
+      "hidden"
+    );
+
+    this._update();
+
+    return true;
+  }
+
+  hide() {
+    this.markup.setAttributeForElement(
+      this.ID_CLASS_PREFIX + "viewport-infobar-container",
+      "hidden",
+      "true"
+    );
+
+    this._cancelUpdate();
+  }
+}
+exports.ViewportSizeHighlighter = ViewportSizeHighlighter;