Adding upstream version 124.0.1.upstream/124.0.1

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

43 files changed, 5224 insertions, 0 deletions

diff --git a/devtools/client/inspector/computed/computed.js b/devtools/client/inspector/computed/computed.js
new file mode 100644
index 0000000000..7d2c129c7b
--- /dev/null
+++ b/devtools/client/inspector/computed/computed.js
@@ -0,0 +1,1713 @@
+/* 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 flags = require("resource://devtools/shared/flags.js");
+const ToolDefinitions =
+  require("resource://devtools/client/definitions.js").Tools;
+const CssLogic = require("resource://devtools/shared/inspector/css-logic.js");
+const {
+  style: { ELEMENT_STYLE },
+} = require("resource://devtools/shared/constants.js");
+const OutputParser = require("resource://devtools/client/shared/output-parser.js");
+const { PrefObserver } = require("resource://devtools/client/shared/prefs.js");
+const {
+  createChild,
+} = require("resource://devtools/client/inspector/shared/utils.js");
+const {
+  VIEW_NODE_SELECTOR_TYPE,
+  VIEW_NODE_PROPERTY_TYPE,
+  VIEW_NODE_VALUE_TYPE,
+  VIEW_NODE_IMAGE_URL_TYPE,
+  VIEW_NODE_FONT_TYPE,
+} = require("resource://devtools/client/inspector/shared/node-types.js");
+const TooltipsOverlay = require("resource://devtools/client/inspector/shared/tooltips-overlay.js");
+
+loader.lazyRequireGetter(
+  this,
+  "StyleInspectorMenu",
+  "resource://devtools/client/inspector/shared/style-inspector-menu.js"
+);
+loader.lazyRequireGetter(
+  this,
+  "KeyShortcuts",
+  "resource://devtools/client/shared/key-shortcuts.js"
+);
+loader.lazyRequireGetter(
+  this,
+  "clipboardHelper",
+  "resource://devtools/shared/platform/clipboard.js"
+);
+loader.lazyRequireGetter(
+  this,
+  "openContentLink",
+  "resource://devtools/client/shared/link.js",
+  true
+);
+
+const STYLE_INSPECTOR_PROPERTIES =
+  "devtools/shared/locales/styleinspector.properties";
+const { LocalizationHelper } = require("resource://devtools/shared/l10n.js");
+const STYLE_INSPECTOR_L10N = new LocalizationHelper(STYLE_INSPECTOR_PROPERTIES);
+const L10N_TWISTY_EXPAND_LABEL = STYLE_INSPECTOR_L10N.getStr(
+  "rule.twistyExpand.label"
+);
+const L10N_TWISTY_COLLAPSE_LABEL = STYLE_INSPECTOR_L10N.getStr(
+  "rule.twistyCollapse.label"
+);
+
+const FILTER_CHANGED_TIMEOUT = 150;
+
+/**
+ * Helper for long-running processes that should yield occasionally to
+ * the mainloop.
+ *
+ * @param {Window} win
+ *        Timeouts will be set on this window when appropriate.
+ * @param {Array} array
+ *        The array of items to process.
+ * @param {Object} options
+ *        Options for the update process:
+ *          onItem {function} Will be called with the value of each iteration.
+ *          onBatch {function} Will be called after each batch of iterations,
+ *            before yielding to the main loop.
+ *          onDone {function} Will be called when iteration is complete.
+ *          onCancel {function} Will be called if the process is canceled.
+ *          threshold {int} How long to process before yielding, in ms.
+ */
+function UpdateProcess(win, array, options) {
+  this.win = win;
+  this.index = 0;
+  this.array = array;
+
+  this.onItem = options.onItem || function () {};
+  this.onBatch = options.onBatch || function () {};
+  this.onDone = options.onDone || function () {};
+  this.onCancel = options.onCancel || function () {};
+  this.threshold = options.threshold || 45;
+
+  this.canceled = false;
+}
+
+UpdateProcess.prototype = {
+  /**
+   * Error thrown when the array of items to process is empty.
+   */
+  ERROR_ITERATION_DONE: new Error("UpdateProcess iteration done"),
+
+  /**
+   * Schedule a new batch on the main loop.
+   */
+  schedule() {
+    if (this.canceled) {
+      return;
+    }
+    this._timeout = setTimeout(this._timeoutHandler.bind(this), 0);
+  },
+
+  /**
+   * Cancel the running process.  onItem will not be called again,
+   * and onCancel will be called.
+   */
+  cancel() {
+    if (this._timeout) {
+      clearTimeout(this._timeout);
+      this._timeout = 0;
+    }
+    this.canceled = true;
+    this.onCancel();
+  },
+
+  _timeoutHandler() {
+    this._timeout = null;
+    try {
+      this._runBatch();
+      this.schedule();
+    } catch (e) {
+      if (e === this.ERROR_ITERATION_DONE) {
+        this.onBatch();
+        this.onDone();
+        return;
+      }
+      console.error(e);
+      throw e;
+    }
+  },
+
+  _runBatch() {
+    const time = Date.now();
+    while (!this.canceled) {
+      const next = this._next();
+      this.onItem(next);
+      if (Date.now() - time > this.threshold) {
+        this.onBatch();
+        return;
+      }
+    }
+  },
+
+  /**
+   * Returns the item at the current index and increases the index.
+   * If all items have already been processed, will throw ERROR_ITERATION_DONE.
+   */
+  _next() {
+    if (this.index < this.array.length) {
+      return this.array[this.index++];
+    }
+    throw this.ERROR_ITERATION_DONE;
+  },
+};
+
+/**
+ * CssComputedView is a panel that manages the display of a table
+ * sorted by style. There should be one instance of CssComputedView
+ * per style display (of which there will generally only be one).
+ *
+ * @param {Inspector} inspector
+ *        Inspector toolbox panel
+ * @param {Document} document
+ *        The document that will contain the computed view.
+ */
+function CssComputedView(inspector, document) {
+  this.inspector = inspector;
+  this.styleDocument = document;
+  this.styleWindow = this.styleDocument.defaultView;
+
+  this.propertyViews = [];
+
+  this._outputParser = new OutputParser(document, inspector.cssProperties);
+
+  // Create bound methods.
+  this.focusWindow = this.focusWindow.bind(this);
+  this._onClearSearch = this._onClearSearch.bind(this);
+  this._onClick = this._onClick.bind(this);
+  this._onContextMenu = this._onContextMenu.bind(this);
+  this._onCopy = this._onCopy.bind(this);
+  this._onFilterStyles = this._onFilterStyles.bind(this);
+  this._onIncludeBrowserStyles = this._onIncludeBrowserStyles.bind(this);
+  this.refreshPanel = this.refreshPanel.bind(this);
+
+  const doc = this.styleDocument;
+  this.element = doc.getElementById("computed-property-container");
+  this.searchField = doc.getElementById("computed-searchbox");
+  this.searchClearButton = doc.getElementById("computed-searchinput-clear");
+  this.includeBrowserStylesCheckbox = doc.getElementById(
+    "browser-style-checkbox"
+  );
+
+  this.shortcuts = new KeyShortcuts({ window: this.styleWindow });
+  this._onShortcut = this._onShortcut.bind(this);
+  this.shortcuts.on("CmdOrCtrl+F", event =>
+    this._onShortcut("CmdOrCtrl+F", event)
+  );
+  this.shortcuts.on("Escape", event => this._onShortcut("Escape", event));
+  this.styleDocument.addEventListener("copy", this._onCopy);
+  this.styleDocument.addEventListener("mousedown", this.focusWindow);
+  this.element.addEventListener("click", this._onClick);
+  this.element.addEventListener("contextmenu", this._onContextMenu);
+  this.searchField.addEventListener("input", this._onFilterStyles);
+  this.searchClearButton.addEventListener("click", this._onClearSearch);
+  this.includeBrowserStylesCheckbox.addEventListener(
+    "input",
+    this._onIncludeBrowserStyles
+  );
+
+  if (flags.testing) {
+    // In tests, we start listening immediately to avoid having to simulate a mousemove.
+    this.highlighters.addToView(this);
+  } else {
+    this.element.addEventListener(
+      "mousemove",
+      () => {
+        this.highlighters.addToView(this);
+      },
+      { once: true }
+    );
+  }
+
+  if (!this.inspector.is3PaneModeEnabled) {
+    // When the rules view is added in 3 pane mode, refresh the Computed view whenever
+    // the rules are changed.
+    this.inspector.on(
+      "ruleview-added",
+      () => {
+        this.ruleView.on("ruleview-changed", this.refreshPanel);
+      },
+      { once: true }
+    );
+  }
+
+  if (this.ruleView) {
+    this.ruleView.on("ruleview-changed", this.refreshPanel);
+  }
+
+  this.searchClearButton.hidden = true;
+
+  // No results text.
+  this.noResults = this.styleDocument.getElementById("computed-no-results");
+
+  // Refresh panel when color unit changed or pref for showing
+  // original sources changes.
+  this._handlePrefChange = this._handlePrefChange.bind(this);
+  this._prefObserver = new PrefObserver("devtools.");
+  this._prefObserver.on("devtools.defaultColorUnit", this._handlePrefChange);
+
+  // The element that we're inspecting, and the document that it comes from.
+  this._viewedElement = null;
+  // The PageStyle front related to the currently selected element
+  this.viewedElementPageStyle = null;
+
+  this.createStyleViews();
+
+  // Add the tooltips and highlightersoverlay
+  this.tooltips = new TooltipsOverlay(this);
+}
+
+/**
+ * Lookup a l10n string in the shared styleinspector string bundle.
+ *
+ * @param {String} name
+ *        The key to lookup.
+ * @returns {String} localized version of the given key.
+ */
+CssComputedView.l10n = function (name) {
+  try {
+    return STYLE_INSPECTOR_L10N.getStr(name);
+  } catch (ex) {
+    console.log("Error reading '" + name + "'");
+    throw new Error("l10n error with " + name);
+  }
+};
+
+CssComputedView.prototype = {
+  // Cache the list of properties that match the selected element.
+  _matchedProperties: null,
+
+  // Used for cancelling timeouts in the style filter.
+  _filterChangedTimeout: null,
+
+  // Holds the ID of the panelRefresh timeout.
+  _panelRefreshTimeout: null,
+
+  // Number of visible properties
+  numVisibleProperties: 0,
+
+  get contextMenu() {
+    if (!this._contextMenu) {
+      this._contextMenu = new StyleInspectorMenu(this);
+    }
+
+    return this._contextMenu;
+  },
+
+  // Get the highlighters overlay from the Inspector.
+  get highlighters() {
+    if (!this._highlighters) {
+      // highlighters is a lazy getter in the inspector.
+      this._highlighters = this.inspector.highlighters;
+    }
+
+    return this._highlighters;
+  },
+
+  get includeBrowserStyles() {
+    return this.includeBrowserStylesCheckbox.checked;
+  },
+
+  get ruleView() {
+    return (
+      this.inspector.hasPanel("ruleview") &&
+      this.inspector.getPanel("ruleview").view
+    );
+  },
+
+  _handlePrefChange() {
+    if (this._computed) {
+      this.refreshPanel();
+    }
+  },
+
+  /**
+   * Update the view with a new selected element. The CssComputedView panel
+   * will show the style information for the given element.
+   *
+   * @param {NodeFront} element
+   *        The highlighted node to get styles for.
+   * @returns a promise that will be resolved when highlighting is complete.
+   */
+  selectElement(element) {
+    if (!element) {
+      if (this.viewedElementPageStyle) {
+        this.viewedElementPageStyle.off(
+          "stylesheet-updated",
+          this.refreshPanel
+        );
+        this.viewedElementPageStyle = null;
+      }
+      this._viewedElement = null;
+      this.noResults.hidden = false;
+
+      if (this._refreshProcess) {
+        this._refreshProcess.cancel();
+      }
+      // Hiding all properties
+      for (const propView of this.propertyViews) {
+        propView.refresh();
+      }
+      return Promise.resolve(undefined);
+    }
+
+    if (element === this._viewedElement) {
+      return Promise.resolve(undefined);
+    }
+
+    if (this.viewedElementPageStyle) {
+      this.viewedElementPageStyle.off("stylesheet-updated", this.refreshPanel);
+    }
+    this.viewedElementPageStyle = element.inspectorFront.pageStyle;
+    this.viewedElementPageStyle.on("stylesheet-updated", this.refreshPanel);
+
+    this._viewedElement = element;
+
+    this.refreshSourceFilter();
+
+    return this.refreshPanel();
+  },
+
+  /**
+   * Get the type of a given node in the computed-view
+   *
+   * @param {DOMNode} node
+   *        The node which we want information about
+   * @return {Object} The type information object contains the following props:
+   * - view {String} Always "computed" to indicate the computed view.
+   * - type {String} One of the VIEW_NODE_XXX_TYPE const in
+   *   client/inspector/shared/node-types
+   * - value {Object} Depends on the type of the node
+   * returns null if the node isn't anything we care about
+   */
+  // eslint-disable-next-line complexity
+  getNodeInfo(node) {
+    if (!node) {
+      return null;
+    }
+
+    const classes = node.classList;
+
+    // Check if the node isn't a selector first since this doesn't require
+    // walking the DOM
+    if (
+      classes.contains("matched") ||
+      classes.contains("bestmatch") ||
+      classes.contains("parentmatch")
+    ) {
+      let selectorText = "";
+
+      for (const child of node.childNodes[1].childNodes) {
+        if (child.nodeType === node.TEXT_NODE) {
+          selectorText += child.textContent;
+        }
+      }
+      return {
+        type: VIEW_NODE_SELECTOR_TYPE,
+        value: selectorText.trim(),
+      };
+    }
+
+    const propertyView = node.closest(".computed-property-view");
+    const propertyMatchedSelectors = node.closest(".matchedselectors");
+    const parent = propertyMatchedSelectors || propertyView;
+
+    if (!parent) {
+      return null;
+    }
+
+    let value, type;
+
+    // Get the property and value for a node that's a property name or value
+    const isHref =
+      classes.contains("theme-link") && !classes.contains("computed-link");
+
+    if (classes.contains("computed-font-family")) {
+      if (propertyMatchedSelectors) {
+        const view = propertyMatchedSelectors.closest("li");
+        value = {
+          property: view.querySelector(".computed-property-name").firstChild
+            .textContent,
+          value: node.parentNode.textContent,
+        };
+      } else if (propertyView) {
+        value = {
+          property: parent.querySelector(".computed-property-name").firstChild
+            .textContent,
+          value: node.parentNode.textContent,
+        };
+      } else {
+        return null;
+      }
+    } else if (
+      propertyMatchedSelectors &&
+      (classes.contains("computed-other-property-value") || isHref)
+    ) {
+      const view = propertyMatchedSelectors.closest("li");
+      value = {
+        property: view.querySelector(".computed-property-name").firstChild
+          .textContent,
+        value: node.textContent,
+      };
+    } else if (
+      propertyView &&
+      (classes.contains("computed-property-name") ||
+        classes.contains("computed-property-value") ||
+        isHref)
+    ) {
+      value = {
+        property: parent.querySelector(".computed-property-name").firstChild
+          .textContent,
+        value: parent.querySelector(".computed-property-value").textContent,
+      };
+    }
+
+    // Get the type
+    if (classes.contains("computed-property-name")) {
+      type = VIEW_NODE_PROPERTY_TYPE;
+    } else if (
+      classes.contains("computed-property-value") ||
+      classes.contains("computed-other-property-value")
+    ) {
+      type = VIEW_NODE_VALUE_TYPE;
+    } else if (classes.contains("computed-font-family")) {
+      type = VIEW_NODE_FONT_TYPE;
+    } else if (isHref) {
+      type = VIEW_NODE_IMAGE_URL_TYPE;
+      value.url = node.href;
+    } else {
+      return null;
+    }
+
+    return {
+      view: "computed",
+      type,
+      value,
+    };
+  },
+
+  _createPropertyViews() {
+    if (this._createViewsPromise) {
+      return this._createViewsPromise;
+    }
+
+    this.refreshSourceFilter();
+    this.numVisibleProperties = 0;
+    const fragment = this.styleDocument.createDocumentFragment();
+
+    this._createViewsPromise = new Promise((resolve, reject) => {
+      this._createViewsProcess = new UpdateProcess(
+        this.styleWindow,
+        CssComputedView.propertyNames,
+        {
+          onItem: propertyName => {
+            // Per-item callback.
+            const propView = new PropertyView(this, propertyName);
+            fragment.append(propView.createListItemElement());
+
+            if (propView.visible) {
+              this.numVisibleProperties++;
+            }
+            this.propertyViews.push(propView);
+          },
+          onCancel: () => {
+            reject("_createPropertyViews cancelled");
+          },
+          onDone: () => {
+            // Completed callback.
+            this.element.appendChild(fragment);
+            this.noResults.hidden = this.numVisibleProperties > 0;
+            resolve(undefined);
+          },
+        }
+      );
+    });
+
+    this._createViewsProcess.schedule();
+
+    return this._createViewsPromise;
+  },
+
+  isPanelVisible() {
+    return (
+      this.inspector.toolbox &&
+      this.inspector.sidebar &&
+      this.inspector.toolbox.currentToolId === "inspector" &&
+      this.inspector.sidebar.getCurrentTabID() == "computedview"
+    );
+  },
+
+  /**
+   * Refresh the panel content. This could be called by a "ruleview-changed" event, but
+   * we avoid the extra processing unless the panel is visible.
+   */
+  refreshPanel() {
+    if (!this._viewedElement || !this.isPanelVisible()) {
+      return Promise.resolve();
+    }
+
+    // Capture the current viewed element to return from the promise handler
+    // early if it changed
+    const viewedElement = this._viewedElement;
+
+    return Promise.all([
+      this._createPropertyViews(),
+      this.viewedElementPageStyle.getComputed(this._viewedElement, {
+        filter: this._sourceFilter,
+        onlyMatched: !this.includeBrowserStyles,
+        markMatched: true,
+      }),
+    ])
+      .then(([, computed]) => {
+        if (viewedElement !== this._viewedElement) {
+          return Promise.resolve();
+        }
+
+        this._computed = computed;
+        this._matchedProperties = new Set();
+        const customProperties = new Set();
+
+        for (const name in computed) {
+          if (computed[name].matched) {
+            this._matchedProperties.add(name);
+          }
+          if (name.startsWith("--")) {
+            customProperties.add(name);
+          }
+        }
+
+        // Removing custom property PropertyViews which won't be used
+        let customPropertiesStartIndex;
+        for (let i = this.propertyViews.length - 1; i >= 0; i--) {
+          const propView = this.propertyViews[i];
+
+          // custom properties are displayed at the bottom of the list, and we're looping
+          // backward through propertyViews, so if the current item does not represent
+          // a custom property, we can stop looping.
+          if (!propView.isCustomProperty) {
+            customPropertiesStartIndex = i + 1;
+            break;
+          }
+
+          // If the custom property will be used, move to the next item.
+          if (customProperties.has(propView.name)) {
+            customProperties.delete(propView.name);
+            continue;
+          }
+
+          // Otherwise remove property view element
+          if (propView.element) {
+            propView.element.remove();
+          }
+
+          propView.destroy();
+          this.propertyViews.splice(i, 1);
+        }
+
+        // At this point, `customProperties` only contains custom property names for
+        // which we don't have a PropertyView yet.
+        let insertIndex = customPropertiesStartIndex;
+        for (const customPropertyName of Array.from(customProperties).sort()) {
+          const propertyView = new PropertyView(
+            this,
+            customPropertyName,
+            // isCustomProperty
+            true
+          );
+
+          const len = this.propertyViews.length;
+          if (insertIndex !== len) {
+            for (let i = insertIndex; i <= len; i++) {
+              const existingPropView = this.propertyViews[i];
+              if (
+                !existingPropView ||
+                !existingPropView.isCustomProperty ||
+                customPropertyName < existingPropView.name
+              ) {
+                insertIndex = i;
+                break;
+              }
+            }
+          }
+          this.propertyViews.splice(insertIndex, 0, propertyView);
+
+          // Insert the custom property PropertyView at the right spot so we
+          // keep the list ordered.
+          const previousSibling = this.element.childNodes[insertIndex - 1];
+          previousSibling.insertAdjacentElement(
+            "afterend",
+            propertyView.createListItemElement()
+          );
+        }
+
+        if (this._refreshProcess) {
+          this._refreshProcess.cancel();
+        }
+
+        this.noResults.hidden = true;
+
+        // Reset visible property count
+        this.numVisibleProperties = 0;
+
+        return new Promise((resolve, reject) => {
+          this._refreshProcess = new UpdateProcess(
+            this.styleWindow,
+            this.propertyViews,
+            {
+              onItem: propView => {
+                propView.refresh();
+              },
+              onCancel: () => {
+                reject("_refreshProcess of computed view cancelled");
+              },
+              onDone: () => {
+                this._refreshProcess = null;
+                this.noResults.hidden = this.numVisibleProperties > 0;
+
+                const searchBox = this.searchField.parentNode;
+                searchBox.classList.toggle(
+                  "devtools-searchbox-no-match",
+                  !!this.searchField.value.length && !this.numVisibleProperties
+                );
+
+                this.inspector.emit("computed-view-refreshed");
+                resolve(undefined);
+              },
+            }
+          );
+          this._refreshProcess.schedule();
+        });
+      })
+      .catch(console.error);
+  },
+
+  /**
+   * Handle the shortcut events in the computed view.
+   */
+  _onShortcut(name, event) {
+    if (!event.target.closest("#sidebar-panel-computedview")) {
+      return;
+    }
+    // Handle the search box's keypress event. If the escape key is pressed,
+    // clear the search box field.
+    if (
+      name === "Escape" &&
+      event.target === this.searchField &&
+      this._onClearSearch()
+    ) {
+      event.preventDefault();
+      event.stopPropagation();
+    } else if (name === "CmdOrCtrl+F") {
+      this.searchField.focus();
+      event.preventDefault();
+    }
+  },
+
+  /**
+   * Set the filter style search value.
+   * @param {String} value
+   *        The search value.
+   */
+  setFilterStyles(value = "") {
+    this.searchField.value = value;
+    this.searchField.focus();
+    this._onFilterStyles();
+  },
+
+  /**
+   * Called when the user enters a search term in the filter style search box.
+   */
+  _onFilterStyles() {
+    if (this._filterChangedTimeout) {
+      clearTimeout(this._filterChangedTimeout);
+    }
+
+    const filterTimeout = this.searchField.value.length
+      ? FILTER_CHANGED_TIMEOUT
+      : 0;
+    this.searchClearButton.hidden = this.searchField.value.length === 0;
+
+    this._filterChangedTimeout = setTimeout(() => {
+      this.refreshPanel();
+      this._filterChangeTimeout = null;
+    }, filterTimeout);
+  },
+
+  /**
+   * Called when the user clicks on the clear button in the filter style search
+   * box. Returns true if the search box is cleared and false otherwise.
+   */
+  _onClearSearch() {
+    if (this.searchField.value) {
+      this.setFilterStyles("");
+      return true;
+    }
+
+    return false;
+  },
+
+  /**
+   * The change event handler for the includeBrowserStyles checkbox.
+   */
+  _onIncludeBrowserStyles() {
+    this.refreshSourceFilter();
+    this.refreshPanel();
+  },
+
+  /**
+   * When includeBrowserStylesCheckbox.checked is false we only display
+   * properties that have matched selectors and have been included by the
+   * document or one of thedocument's stylesheets. If .checked is false we
+   * display all properties including those that come from UA stylesheets.
+   */
+  refreshSourceFilter() {
+    this._matchedProperties = null;
+    this._sourceFilter = this.includeBrowserStyles
+      ? CssLogic.FILTER.UA
+      : CssLogic.FILTER.USER;
+  },
+
+  /**
+   * The CSS as displayed by the UI.
+   */
+  createStyleViews() {
+    if (CssComputedView.propertyNames) {
+      return;
+    }
+
+    CssComputedView.propertyNames = [];
+
+    // Here we build and cache a list of css properties supported by the browser
+    // We could use any element but let's use the main document's root element
+    const styles = this.styleWindow.getComputedStyle(
+      this.styleDocument.documentElement
+    );
+    const mozProps = [];
+    for (let i = 0, numStyles = styles.length; i < numStyles; i++) {
+      const prop = styles.item(i);
+      if (prop.startsWith("--")) {
+        // Skip any CSS variables used inside of browser CSS files
+        continue;
+      } else if (prop.startsWith("-")) {
+        mozProps.push(prop);
+      } else {
+        CssComputedView.propertyNames.push(prop);
+      }
+    }
+
+    CssComputedView.propertyNames.sort();
+    CssComputedView.propertyNames.push.apply(
+      CssComputedView.propertyNames,
+      mozProps.sort()
+    );
+
+    this._createPropertyViews().catch(e => {
+      if (!this._isDestroyed) {
+        console.warn(
+          "The creation of property views was cancelled because " +
+            "the computed-view was destroyed before it was done creating views"
+        );
+      } else {
+        console.error(e);
+      }
+    });
+  },
+
+  /**
+   * Get a set of properties that have matched selectors.
+   *
+   * @return {Set} If a property name is in the set, it has matching selectors.
+   */
+  get matchedProperties() {
+    return this._matchedProperties || new Set();
+  },
+
+  /**
+   * Focus the window on mousedown.
+   */
+  focusWindow() {
+    this.styleWindow.focus();
+  },
+
+  /**
+   * Context menu handler.
+   */
+  _onContextMenu(event) {
+    // Call stopPropagation() and preventDefault() here so that avoid to show default
+    // context menu in about:devtools-toolbox. See Bug 1515265.
+    event.stopPropagation();
+    event.preventDefault();
+    this.contextMenu.show(event);
+  },
+
+  _onClick(event) {
+    const target = event.target;
+
+    if (target.nodeName === "a") {
+      event.stopPropagation();
+      event.preventDefault();
+      openContentLink(target.href);
+    }
+  },
+
+  /**
+   * Callback for copy event. Copy selected text.
+   *
+   * @param {Event} event
+   *        copy event object.
+   */
+  _onCopy(event) {
+    const win = this.styleWindow;
+    const text = win.getSelection().toString().trim();
+    if (text !== "") {
+      this.copySelection();
+      event.preventDefault();
+    }
+  },
+
+  /**
+   * Copy the current selection to the clipboard
+   */
+  copySelection() {
+    try {
+      const win = this.styleWindow;
+      const text = win.getSelection().toString().trim();
+
+      clipboardHelper.copyString(text);
+    } catch (e) {
+      console.error(e);
+    }
+  },
+
+  /**
+   * Destructor for CssComputedView.
+   */
+  destroy() {
+    this._viewedElement = null;
+    if (this.viewedElementPageStyle) {
+      this.viewedElementPageStyle.off("stylesheet-updated", this.refreshPanel);
+      this.viewedElementPageStyle = null;
+    }
+    this._outputParser = null;
+
+    this._prefObserver.off("devtools.defaultColorUnit", this._handlePrefChange);
+    this._prefObserver.destroy();
+
+    // Cancel tree construction
+    if (this._createViewsProcess) {
+      this._createViewsProcess.cancel();
+    }
+    if (this._refreshProcess) {
+      this._refreshProcess.cancel();
+    }
+
+    if (this._contextMenu) {
+      this._contextMenu.destroy();
+      this._contextMenu = null;
+    }
+
+    if (this._highlighters) {
+      this._highlighters.removeFromView(this);
+      this._highlighters = null;
+    }
+
+    this.tooltips.destroy();
+
+    // Remove bound listeners
+    this.element.removeEventListener("click", this._onClick);
+    this.element.removeEventListener("contextmenu", this._onContextMenu);
+    this.searchField.removeEventListener("input", this._onFilterStyles);
+    this.searchClearButton.removeEventListener("click", this._onClearSearch);
+    this.styleDocument.removeEventListener("copy", this._onCopy);
+    this.styleDocument.removeEventListener("mousedown", this.focusWindow);
+    this.includeBrowserStylesCheckbox.removeEventListener(
+      "input",
+      this._onIncludeBrowserStyles
+    );
+
+    if (this.ruleView) {
+      this.ruleView.off("ruleview-changed", this.refreshPanel);
+    }
+
+    // Nodes used in templating
+    this.element = null;
+    this.searchField = null;
+    this.searchClearButton = null;
+    this.includeBrowserStylesCheckbox = null;
+
+    // Property views
+    for (const propView of this.propertyViews) {
+      propView.destroy();
+    }
+    this.propertyViews = null;
+
+    this.inspector = null;
+    this.styleDocument = null;
+    this.styleWindow = null;
+
+    this._isDestroyed = true;
+  },
+};
+
+function PropertyInfo(tree, name) {
+  this.tree = tree;
+  this.name = name;
+}
+
+PropertyInfo.prototype = {
+  get isSupported() {
+    // There can be a mismatch between the list of properties
+    // supported on the server and on the client.
+    // Ideally we should build PropertyInfo only for property names supported on
+    // the server. See Bug 1722348.
+    return this.tree._computed && this.name in this.tree._computed;
+  },
+
+  get value() {
+    if (this.isSupported) {
+      const value = this.tree._computed[this.name].value;
+      return value;
+    }
+    return null;
+  },
+};
+
+/**
+ * A container to give easy access to property data from the template engine.
+ */
+class PropertyView {
+  /*
+   * @param {CssComputedView} tree
+   *        The CssComputedView instance we are working with.
+   * @param {String} name
+   *        The CSS property name for which this PropertyView
+   *        instance will render the rules.
+   * @param {Boolean} isCustomProperty
+   *        Set to true if this will represent a custom property.
+   */
+  constructor(tree, name, isCustomProperty = false) {
+    this.tree = tree;
+    this.name = name;
+
+    this.isCustomProperty = isCustomProperty;
+
+    if (!this.isCustomProperty) {
+      this.link = "https://developer.mozilla.org/docs/Web/CSS/" + name;
+    }
+
+    this.#propertyInfo = new PropertyInfo(tree, name);
+    const win = this.tree.styleWindow;
+    this.#abortController = new win.AbortController();
+  }
+
+  // The parent element which contains the open attribute
+  element = null;
+
+  // Property header node
+  propertyHeader = null;
+
+  // Destination for property values
+  valueNode = null;
+
+  // Are matched rules expanded?
+  matchedExpanded = false;
+
+  // Matched selector container
+  matchedSelectorsContainer = null;
+
+  // Matched selector expando
+  matchedExpander = null;
+
+  // AbortController for event listeners
+  #abortController = null;
+
+  // Cache for matched selector views
+  #matchedSelectorViews = null;
+
+  // The previously selected element used for the selector view caches
+  #prevViewedElement = null;
+
+  // PropertyInfo
+  #propertyInfo = null;
+
+  /**
+   * Get the computed style for the current property.
+   *
+   * @return {String} the computed style for the current property of the
+   * currently highlighted element.
+   */
+  get value() {
+    return this.propertyInfo.value;
+  }
+
+  /**
+   * An easy way to access the CssPropertyInfo behind this PropertyView.
+   */
+  get propertyInfo() {
+    return this.#propertyInfo;
+  }
+
+  /**
+   * Does the property have any matched selectors?
+   */
+  get hasMatchedSelectors() {
+    return this.tree.matchedProperties.has(this.name);
+  }
+
+  /**
+   * Should this property be visible?
+   */
+  get visible() {
+    if (!this.tree._viewedElement) {
+      return false;
+    }
+
+    if (!this.tree.includeBrowserStyles && !this.hasMatchedSelectors) {
+      return false;
+    }
+
+    const searchTerm = this.tree.searchField.value.toLowerCase();
+    const isValidSearchTerm = !!searchTerm.trim().length;
+    if (
+      isValidSearchTerm &&
+      !this.name.toLowerCase().includes(searchTerm) &&
+      !this.value.toLowerCase().includes(searchTerm)
+    ) {
+      return false;
+    }
+
+    return this.propertyInfo.isSupported;
+  }
+
+  /**
+   * Returns the className that should be assigned to the propertyView.
+   *
+   * @return {String}
+   */
+  get propertyHeaderClassName() {
+    return this.visible ? "computed-property-view" : "computed-property-hidden";
+  }
+
+  /**
+   * Create DOM elements for a property
+   *
+   * @return {Element} The <li> element
+   */
+  createListItemElement() {
+    const doc = this.tree.styleDocument;
+    const baseEventListenerConfig = { signal: this.#abortController.signal };
+
+    // Build the container element
+    this.onMatchedToggle = this.onMatchedToggle.bind(this);
+    this.element = doc.createElement("li");
+    this.element.className = this.propertyHeaderClassName;
+    this.element.addEventListener(
+      "dblclick",
+      this.onMatchedToggle,
+      baseEventListenerConfig
+    );
+
+    // Make it keyboard navigable
+    this.element.setAttribute("tabindex", "0");
+    this.shortcuts = new KeyShortcuts({
+      window: this.tree.styleWindow,
+      target: this.element,
+    });
+    this.shortcuts.on("F1", event => {
+      this.mdnLinkClick(event);
+      // Prevent opening the options panel
+      event.preventDefault();
+      event.stopPropagation();
+    });
+    this.shortcuts.on("Return", this.onMatchedToggle);
+    this.shortcuts.on("Space", this.onMatchedToggle);
+
+    const nameContainer = doc.createElement("span");
+    nameContainer.className = "computed-property-name-container";
+
+    // Build the twisty expand/collapse
+    this.matchedExpander = doc.createElement("div");
+    this.matchedExpander.className = "computed-expander theme-twisty";
+    this.matchedExpander.setAttribute("role", "button");
+    this.matchedExpander.setAttribute("aria-label", L10N_TWISTY_EXPAND_LABEL);
+    this.matchedExpander.addEventListener(
+      "click",
+      this.onMatchedToggle,
+      baseEventListenerConfig
+    );
+
+    // Build the style name element
+    const nameNode = doc.createElement("span");
+    nameNode.classList.add("computed-property-name", "theme-fg-color3");
+
+    // Give it a heading role for screen readers.
+    nameNode.setAttribute("role", "heading");
+
+    // Reset its tabindex attribute otherwise, if an ellipsis is applied
+    // it will be reachable via TABing
+    nameNode.setAttribute("tabindex", "");
+    // Avoid english text (css properties) from being altered
+    // by RTL mode
+    nameNode.setAttribute("dir", "ltr");
+    nameNode.textContent = nameNode.title = this.name;
+    // Make it hand over the focus to the container
+    const focusElement = () => this.element.focus();
+    nameNode.addEventListener("click", focusElement, baseEventListenerConfig);
+
+    // Build the style name ":" separator
+    const nameSeparator = doc.createElement("span");
+    nameSeparator.classList.add("visually-hidden");
+    nameSeparator.textContent = ": ";
+    nameNode.appendChild(nameSeparator);
+
+    nameContainer.appendChild(nameNode);
+
+    const valueContainer = doc.createElement("span");
+    valueContainer.className = "computed-property-value-container";
+
+    // Build the style value element
+    this.valueNode = doc.createElement("span");
+    this.valueNode.classList.add("computed-property-value", "theme-fg-color1");
+    // Reset its tabindex attribute otherwise, if an ellipsis is applied
+    // it will be reachable via TABing
+    this.valueNode.setAttribute("tabindex", "");
+    this.valueNode.setAttribute("dir", "ltr");
+    // Make it hand over the focus to the container
+    this.valueNode.addEventListener(
+      "click",
+      focusElement,
+      baseEventListenerConfig
+    );
+
+    // Build the style value ";" separator
+    const valueSeparator = doc.createElement("span");
+    valueSeparator.classList.add("visually-hidden");
+    valueSeparator.textContent = ";";
+
+    // Build the matched selectors container
+    this.matchedSelectorsContainer = doc.createElement("div");
+    this.matchedSelectorsContainer.classList.add("matchedselectors");
+
+    valueContainer.append(this.valueNode, valueSeparator);
+    this.element.append(
+      this.matchedExpander,
+      nameContainer,
+      valueContainer,
+      this.matchedSelectorsContainer
+    );
+
+    return this.element;
+  }
+
+  /**
+   * Refresh the panel's CSS property value.
+   */
+  refresh() {
+    const className = this.propertyHeaderClassName;
+    if (this.element.className !== className) {
+      this.element.className = className;
+    }
+
+    if (this.#prevViewedElement !== this.tree._viewedElement) {
+      this.#matchedSelectorViews = null;
+      this.#prevViewedElement = this.tree._viewedElement;
+    }
+
+    if (!this.tree._viewedElement || !this.visible) {
+      this.valueNode.textContent = this.valueNode.title = "";
+      this.matchedSelectorsContainer.parentNode.hidden = true;
+      this.matchedSelectorsContainer.textContent = "";
+      this.matchedExpander.removeAttribute("open");
+      this.matchedExpander.setAttribute("aria-label", L10N_TWISTY_EXPAND_LABEL);
+      return;
+    }
+
+    this.tree.numVisibleProperties++;
+
+    const outputParser = this.tree._outputParser;
+    const frag = outputParser.parseCssProperty(
+      this.propertyInfo.name,
+      this.propertyInfo.value,
+      {
+        colorSwatchClass: "computed-colorswatch",
+        colorClass: "computed-color",
+        urlClass: "theme-link",
+        fontFamilyClass: "computed-font-family",
+        // No need to use baseURI here as computed URIs are never relative.
+      }
+    );
+    this.valueNode.innerHTML = "";
+    this.valueNode.appendChild(frag);
+
+    this.refreshMatchedSelectors();
+  }
+
+  /**
+   * Refresh the panel matched rules.
+   */
+  refreshMatchedSelectors() {
+    const hasMatchedSelectors = this.hasMatchedSelectors;
+    this.matchedSelectorsContainer.parentNode.hidden = !hasMatchedSelectors;
+
+    if (hasMatchedSelectors) {
+      this.matchedExpander.classList.add("computed-expandable");
+    } else {
+      this.matchedExpander.classList.remove("computed-expandable");
+    }
+
+    if (this.matchedExpanded && hasMatchedSelectors) {
+      return this.tree.viewedElementPageStyle
+        .getMatchedSelectors(this.tree._viewedElement, this.name)
+        .then(matched => {
+          if (!this.matchedExpanded) {
+            return;
+          }
+
+          this._matchedSelectorResponse = matched;
+
+          this.#buildMatchedSelectors();
+          this.matchedExpander.setAttribute("open", "");
+          this.matchedExpander.setAttribute(
+            "aria-label",
+            L10N_TWISTY_COLLAPSE_LABEL
+          );
+          this.tree.inspector.emit("computed-view-property-expanded");
+        })
+        .catch(console.error);
+    }
+
+    this.matchedSelectorsContainer.innerHTML = "";
+    this.matchedExpander.removeAttribute("open");
+    this.matchedExpander.setAttribute("aria-label", L10N_TWISTY_EXPAND_LABEL);
+    this.tree.inspector.emit("computed-view-property-collapsed");
+    return Promise.resolve(undefined);
+  }
+
+  get matchedSelectors() {
+    return this._matchedSelectorResponse;
+  }
+
+  #buildMatchedSelectors() {
+    const frag = this.element.ownerDocument.createDocumentFragment();
+
+    for (const selector of this.matchedSelectorViews) {
+      const p = createChild(frag, "p");
+      const span = createChild(p, "span", {
+        class: "rule-link",
+      });
+
+      const link = createChild(span, "a", {
+        target: "_blank",
+        class: "computed-link theme-link",
+        title: selector.longSource,
+        sourcelocation: selector.source,
+        tabindex: "0",
+        textContent: selector.source,
+      });
+      link.addEventListener("click", selector.openStyleEditor);
+      const shortcuts = new KeyShortcuts({
+        window: this.tree.styleWindow,
+        target: link,
+      });
+      shortcuts.on("Return", () => selector.openStyleEditor());
+
+      const status = createChild(p, "span", {
+        dir: "ltr",
+        class: "rule-text theme-fg-color3 " + selector.statusClass,
+        title: selector.statusText,
+      });
+
+      // Add an explicit status text span for screen readers.
+      // They won't pick up the title from the status span.
+      createChild(status, "span", {
+        dir: "ltr",
+        class: "visually-hidden",
+        textContent: selector.statusText + " ",
+      });
+
+      createChild(status, "div", {
+        class: "fix-get-selection",
+        textContent: selector.sourceText,
+      });
+
+      const valueDiv = createChild(status, "div", {
+        class:
+          "fix-get-selection computed-other-property-value theme-fg-color1",
+      });
+      valueDiv.appendChild(selector.outputFragment);
+    }
+
+    this.matchedSelectorsContainer.innerHTML = "";
+    this.matchedSelectorsContainer.appendChild(frag);
+  }
+
+  /**
+   * Provide access to the matched SelectorViews that we are currently
+   * displaying.
+   */
+  get matchedSelectorViews() {
+    if (!this.#matchedSelectorViews) {
+      this.#matchedSelectorViews = [];
+      this._matchedSelectorResponse.forEach(selectorInfo => {
+        const selectorView = new SelectorView(this.tree, selectorInfo);
+        this.#matchedSelectorViews.push(selectorView);
+      }, this);
+    }
+    return this.#matchedSelectorViews;
+  }
+
+  /**
+   * The action when a user expands matched selectors.
+   *
+   * @param {Event} event
+   *        Used to determine the class name of the targets click
+   *        event.
+   */
+  onMatchedToggle(event) {
+    if (event.shiftKey) {
+      return;
+    }
+    this.matchedExpanded = !this.matchedExpanded;
+    this.refreshMatchedSelectors();
+    event.preventDefault();
+  }
+
+  /**
+   * The action when a user clicks on the MDN help link for a property.
+   */
+  mdnLinkClick(event) {
+    if (!this.link) {
+      return;
+    }
+    openContentLink(this.link);
+  }
+
+  /**
+   * Destroy this property view, removing event listeners
+   */
+  destroy() {
+    if (this.#matchedSelectorViews) {
+      for (const view of this.#matchedSelectorViews) {
+        view.destroy();
+      }
+    }
+
+    if (this.#abortController) {
+      this.#abortController.abort();
+      this.#abortController = null;
+    }
+
+    if (this.shortcuts) {
+      this.shortcuts.destroy();
+    }
+
+    this.shortcuts = null;
+    this.element = null;
+    this.matchedExpander = null;
+    this.valueNode = null;
+  }
+}
+
+/**
+ * A container to give us easy access to display data from a CssRule
+ *
+ * @param CssComputedView tree
+ *        the owning CssComputedView
+ * @param selectorInfo
+ */
+function SelectorView(tree, selectorInfo) {
+  this.tree = tree;
+  this.selectorInfo = selectorInfo;
+  this._cacheStatusNames();
+
+  this.openStyleEditor = this.openStyleEditor.bind(this);
+  this._updateLocation = this._updateLocation.bind(this);
+
+  const rule = this.selectorInfo.rule;
+  if (!rule || !rule.parentStyleSheet || rule.type == ELEMENT_STYLE) {
+    this.source = CssLogic.l10n("rule.sourceElement");
+    this.longSource = this.source;
+  } else {
+    // This always refers to the generated location.
+    const sheet = rule.parentStyleSheet;
+    const sourceSuffix = rule.line > 0 ? ":" + rule.line : "";
+    this.source = CssLogic.shortSource(sheet) + sourceSuffix;
+    this.longSource = CssLogic.longSource(sheet) + sourceSuffix;
+
+    this.generatedLocation = {
+      sheet,
+      href: sheet.href || sheet.nodeHref,
+      line: rule.line,
+      column: rule.column,
+    };
+    this.sourceMapURLService = this.tree.inspector.toolbox.sourceMapURLService;
+    this._unsubscribeCallback = this.sourceMapURLService.subscribeByID(
+      this.generatedLocation.sheet.resourceId,
+      this.generatedLocation.line,
+      this.generatedLocation.column,
+      this._updateLocation
+    );
+  }
+}
+
+/**
+ * Decode for cssInfo.rule.status
+ * @see SelectorView.prototype._cacheStatusNames
+ * @see CssLogic.STATUS
+ */
+SelectorView.STATUS_NAMES = [
+  // "Parent Match", "Matched", "Best Match"
+];
+
+SelectorView.CLASS_NAMES = ["parentmatch", "matched", "bestmatch"];
+
+SelectorView.prototype = {
+  /**
+   * Cache localized status names.
+   *
+   * These statuses are localized inside the styleinspector.properties string
+   * bundle.
+   * @see css-logic.js - the CssLogic.STATUS array.
+   */
+  _cacheStatusNames() {
+    if (SelectorView.STATUS_NAMES.length) {
+      return;
+    }
+
+    for (const status in CssLogic.STATUS) {
+      const i = CssLogic.STATUS[status];
+      if (i > CssLogic.STATUS.UNMATCHED) {
+        const value = CssComputedView.l10n("rule.status." + status);
+        // Replace normal spaces with non-breaking spaces
+        SelectorView.STATUS_NAMES[i] = value.replace(/ /g, "\u00A0");
+      }
+    }
+  },
+
+  /**
+   * A localized version of cssRule.status
+   */
+  get statusText() {
+    return SelectorView.STATUS_NAMES[this.selectorInfo.status];
+  },
+
+  /**
+   * Get class name for selector depending on status
+   */
+  get statusClass() {
+    return SelectorView.CLASS_NAMES[this.selectorInfo.status - 1];
+  },
+
+  get href() {
+    if (this._href) {
+      return this._href;
+    }
+    const sheet = this.selectorInfo.rule.parentStyleSheet;
+    this._href = sheet ? sheet.href : "#";
+    return this._href;
+  },
+
+  get sourceText() {
+    return this.selectorInfo.sourceText;
+  },
+
+  get value() {
+    return this.selectorInfo.value;
+  },
+
+  get outputFragment() {
+    // Sadly, because this fragment is added to the template by DOM Templater
+    // we lose any events that are attached. This means that URLs will open in a
+    // new window. At some point we should fix this by stopping using the
+    // templater.
+    const outputParser = this.tree._outputParser;
+    const frag = outputParser.parseCssProperty(
+      this.selectorInfo.name,
+      this.selectorInfo.value,
+      {
+        colorSwatchClass: "computed-colorswatch",
+        colorClass: "computed-color",
+        urlClass: "theme-link",
+        fontFamilyClass: "computed-font-family",
+        baseURI: this.selectorInfo.rule.href,
+      }
+    );
+    return frag;
+  },
+
+  /**
+   * Update the text of the source link to reflect whether we're showing
+   * original sources or not.  This is a callback for
+   * SourceMapURLService.subscribe, which see.
+   *
+   * @param {Object | null} originalLocation
+   *        The original position object (url/line/column) or null.
+   */
+  _updateLocation(originalLocation) {
+    if (!this.tree.element) {
+      return;
+    }
+
+    // Update |currentLocation| to be whichever location is being
+    // displayed at the moment.
+    let currentLocation = this.generatedLocation;
+    if (originalLocation) {
+      const { url, line, column } = originalLocation;
+      currentLocation = { href: url, line, column };
+    }
+
+    const selector = '[sourcelocation="' + this.source + '"]';
+    const link = this.tree.element.querySelector(selector);
+    if (link) {
+      const text =
+        CssLogic.shortSource(currentLocation) + ":" + currentLocation.line;
+      link.textContent = text;
+    }
+
+    this.tree.inspector.emit("computed-view-sourcelinks-updated");
+  },
+
+  /**
+   * When a css link is clicked this method is called in order to either:
+   *   1. Open the link in view source (for chrome stylesheets).
+   *   2. Open the link in the style editor.
+   *
+   *   We can only view stylesheets contained in document.styleSheets inside the
+   *   style editor.
+   */
+  openStyleEditor() {
+    const inspector = this.tree.inspector;
+    const rule = this.selectorInfo.rule;
+
+    // The style editor can only display stylesheets coming from content because
+    // chrome stylesheets are not listed in the editor's stylesheet selector.
+    //
+    // If the stylesheet is a content stylesheet we send it to the style
+    // editor else we display it in the view source window.
+    const parentStyleSheet = rule.parentStyleSheet;
+    if (!parentStyleSheet || parentStyleSheet.isSystem) {
+      inspector.toolbox.viewSource(rule.href, rule.line);
+      return;
+    }
+
+    const { sheet, line, column } = this.generatedLocation;
+    if (ToolDefinitions.styleEditor.isToolSupported(inspector.toolbox)) {
+      inspector.toolbox.viewSourceInStyleEditorByResource(sheet, line, column);
+    }
+  },
+
+  /**
+   * Destroy this selector view, removing event listeners
+   */
+  destroy() {
+    if (this._unsubscribeCallback) {
+      this._unsubscribeCallback();
+    }
+  },
+};
+
+function ComputedViewTool(inspector, window) {
+  this.inspector = inspector;
+  this.document = window.document;
+
+  this.computedView = new CssComputedView(this.inspector, this.document);
+
+  this.onDetachedFront = this.onDetachedFront.bind(this);
+  this.onSelected = this.onSelected.bind(this);
+  this.refresh = this.refresh.bind(this);
+  this.onPanelSelected = this.onPanelSelected.bind(this);
+
+  this.inspector.selection.on("detached-front", this.onDetachedFront);
+  this.inspector.selection.on("new-node-front", this.onSelected);
+  this.inspector.selection.on("pseudoclass", this.refresh);
+  this.inspector.sidebar.on("computedview-selected", this.onPanelSelected);
+  this.inspector.styleChangeTracker.on("style-changed", this.refresh);
+
+  this.computedView.selectElement(null);
+
+  this.onSelected();
+}
+
+ComputedViewTool.prototype = {
+  isPanelVisible() {
+    if (!this.computedView) {
+      return false;
+    }
+    return this.computedView.isPanelVisible();
+  },
+
+  onDetachedFront() {
+    this.onSelected(false);
+  },
+
+  async onSelected(selectElement = true) {
+    // Ignore the event if the view has been destroyed, or if it's inactive.
+    // But only if the current selection isn't null. If it's been set to null,
+    // let the update go through as this is needed to empty the view on
+    // navigation.
+    if (!this.computedView) {
+      return;
+    }
+
+    const isInactive =
+      !this.isPanelVisible() && this.inspector.selection.nodeFront;
+    if (isInactive) {
+      return;
+    }
+
+    if (
+      !this.inspector.selection.isConnected() ||
+      !this.inspector.selection.isElementNode()
+    ) {
+      this.computedView.selectElement(null);
+      return;
+    }
+
+    if (selectElement) {
+      const done = this.inspector.updating("computed-view");
+      await this.computedView.selectElement(this.inspector.selection.nodeFront);
+      done();
+    }
+  },
+
+  refresh() {
+    if (this.isPanelVisible()) {
+      this.computedView.refreshPanel();
+    }
+  },
+
+  onPanelSelected() {
+    if (
+      this.inspector.selection.nodeFront === this.computedView._viewedElement
+    ) {
+      this.refresh();
+    } else {
+      this.onSelected();
+    }
+  },
+
+  destroy() {
+    this.inspector.styleChangeTracker.off("style-changed", this.refresh);
+    this.inspector.sidebar.off("computedview-selected", this.refresh);
+    this.inspector.selection.off("pseudoclass", this.refresh);
+    this.inspector.selection.off("new-node-front", this.onSelected);
+    this.inspector.selection.off("detached-front", this.onDetachedFront);
+    this.inspector.sidebar.off("computedview-selected", this.onPanelSelected);
+
+    this.computedView.destroy();
+
+    this.computedView = this.document = this.inspector = null;
+  },
+};
+
+exports.CssComputedView = CssComputedView;
+exports.ComputedViewTool = ComputedViewTool;
+exports.PropertyView = PropertyView;
diff --git a/devtools/client/inspector/computed/moz.build b/devtools/client/inspector/computed/moz.build
new file mode 100644
index 0000000000..4f84b2ebf0
--- /dev/null
+++ b/devtools/client/inspector/computed/moz.build
@@ -0,0 +1,11 @@
+# -*- 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(
+    "computed.js",
+)
+
+BROWSER_CHROME_MANIFESTS += ["test/browser.toml"]
diff --git a/devtools/client/inspector/computed/test/browser.toml b/devtools/client/inspector/computed/test/browser.toml
new file mode 100644
index 0000000000..d4ec4fc993
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser.toml
@@ -0,0 +1,86 @@
+[DEFAULT]
+tags = "devtools"
+subsuite = "devtools"
+support-files = [
+  "doc_matched_selectors_imported_1.css",
+  "doc_matched_selectors_imported_2.css",
+  "doc_matched_selectors_imported_3.css",
+  "doc_matched_selectors_imported_4.css",
+  "doc_matched_selectors_imported_5.css",
+  "doc_matched_selectors_imported_6.css",
+  "doc_matched_selectors.html",
+  "doc_media_queries.html",
+  "doc_pseudoelement.html",
+  "doc_sourcemaps.css",
+  "doc_sourcemaps.css.map",
+  "doc_sourcemaps.html",
+  "doc_sourcemaps.scss",
+  "head.js",
+  "!/devtools/client/inspector/test/head.js",
+  "!/devtools/client/inspector/test/shared-head.js",
+  "!/devtools/client/shared/test/shared-head.js",
+  "!/devtools/client/shared/test/telemetry-test-helpers.js",
+  "!/devtools/client/shared/test/highlighter-test-actor.js",
+]
+
+["browser_computed_browser-styles.js"]
+
+["browser_computed_custom_properties.js"]
+
+["browser_computed_cycle_color.js"]
+fail-if = ["a11y_checks"] # Bug 1849028 clicked element may not be focusable and/or labeled
+
+["browser_computed_default_tab.js"]
+
+["browser_computed_getNodeInfo.js"]
+skip-if = [
+  "!debug && os == 'mac'", #Bug 1559033
+  "a11y_checks", # Bugs 1849028 and 1858041 to investigate intermittent a11y_checks results
+]
+
+["browser_computed_keybindings_01.js"]
+fail-if = ["a11y_checks"] # Bug 1849028 clicked element may not be focusable and/or labeled
+
+["browser_computed_keybindings_02.js"]
+
+["browser_computed_matched-selectors-order.js"]
+
+["browser_computed_matched-selectors-toggle.js"]
+fail-if = ["a11y_checks"] # Bug 1849028 clicked element may not be focusable and/or labeled
+
+["browser_computed_matched-selectors_01.js"]
+
+["browser_computed_matched-selectors_02.js"]
+
+["browser_computed_media-queries.js"]
+
+["browser_computed_no-results-placeholder.js"]
+
+["browser_computed_original-source-link.js"]
+skip-if = ["a11y_checks"] # Bug 1858037 to investigate intermittent a11y_checks results (fails on Autoland, passes on Try)
+
+["browser_computed_pseudo-element_01.js"]
+
+["browser_computed_refresh-on-ruleview-change.js"]
+
+["browser_computed_refresh-on-style-change_01.js"]
+
+["browser_computed_search-filter.js"]
+
+["browser_computed_search-filter_clear.js"]
+
+["browser_computed_search-filter_context-menu.js"]
+
+["browser_computed_search-filter_escape-keypress.js"]
+
+["browser_computed_search-filter_noproperties.js"]
+
+["browser_computed_select-and-copy-styles-01.js"]
+
+["browser_computed_select-and-copy-styles-02.js"]
+fail-if = ["a11y_checks"] # Bug 1849028 clicked element may not be focusable and/or labeled
+
+["browser_computed_shadow_host.js"]
+
+["browser_computed_style-editor-link.js"]
+skip-if = ["true"] # bug 1307846
diff --git a/devtools/client/inspector/computed/test/browser_computed_browser-styles.js b/devtools/client/inspector/computed/test/browser_computed_browser-styles.js
new file mode 100644
index 0000000000..52477d21ed
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_browser-styles.js
@@ -0,0 +1,59 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the checkbox to include browser styles works properly.
+
+const TEST_URI = `
+  <style type="text/css">
+    .matches {
+      color: #F00;
+    }
+  </style>
+  <span id="matches" class="matches">Some styled text</span>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("#matches", inspector);
+
+  info("Checking the default styles");
+  is(
+    isPropertyVisible("color", view),
+    true,
+    "span #matches color property is visible"
+  );
+  is(
+    isPropertyVisible("background-color", view),
+    false,
+    "span #matches background-color property is hidden"
+  );
+
+  info("Toggling the browser styles");
+  const doc = view.styleDocument;
+  const checkbox = doc.querySelector(".includebrowserstyles");
+  const onRefreshed = inspector.once("computed-view-refreshed");
+  checkbox.click();
+  await onRefreshed;
+
+  info("Checking the browser styles");
+  is(isPropertyVisible("color", view), true, "span color property is visible");
+  is(
+    isPropertyVisible("background-color", view),
+    true,
+    "span background-color property is visible"
+  );
+});
+
+function isPropertyVisible(name, view) {
+  info("Checking property visibility for " + name);
+  const propertyViews = view.propertyViews;
+  for (const propView of propertyViews) {
+    if (propView.name == name) {
+      return propView.visible;
+    }
+  }
+  return false;
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_custom_properties.js b/devtools/client/inspector/computed/test/browser_computed_custom_properties.js
new file mode 100644
index 0000000000..230bffa726
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_custom_properties.js
@@ -0,0 +1,106 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that custom properties are displayed in the computed view.
+
+const TEST_URI = `
+  <style type="text/css">
+    body {
+      --global-custom-property: red;
+    }
+
+    h1 {
+      color: var(--global-custom-property);
+    }
+
+    #match-1 {
+      --global-custom-property: blue;
+      --custom-property-1: lime;
+    }
+    #match-2 {
+      --global-custom-property: gold;
+      --custom-property-2: cyan;
+    }
+  </style>
+  <h1 id="match-1">Hello</h1>
+  <h1 id="match-2">World</h1>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+
+  await assertComputedPropertiesForNode(inspector, view, "body", [
+    {
+      name: "--global-custom-property",
+      value: "red",
+    },
+  ]);
+
+  await assertComputedPropertiesForNode(inspector, view, "#match-1", [
+    {
+      name: "color",
+      value: "rgb(0, 0, 255)",
+    },
+    {
+      name: "--custom-property-1",
+      value: "lime",
+    },
+    {
+      name: "--global-custom-property",
+      value: "blue",
+    },
+  ]);
+
+  await assertComputedPropertiesForNode(inspector, view, "#match-2", [
+    {
+      name: "color",
+      value: "rgb(255, 215, 0)",
+    },
+    {
+      name: "--custom-property-2",
+      value: "cyan",
+    },
+    {
+      name: "--global-custom-property",
+      value: "gold",
+    },
+  ]);
+
+  await assertComputedPropertiesForNode(inspector, view, "html", []);
+});
+
+async function assertComputedPropertiesForNode(
+  inspector,
+  view,
+  selector,
+  expected
+) {
+  await selectNode(selector, inspector);
+
+  const computedItems = getComputedViewProperties(view);
+  is(
+    computedItems.length,
+    expected.length,
+    `Computed view has the expected number of items for "${selector}"`
+  );
+  for (let i = 0; i < computedItems.length; i++) {
+    const expectedData = expected[i];
+    const computedEl = computedItems[i];
+    const nameSpan = computedEl.querySelector(".computed-property-name");
+    const valueSpan = computedEl.querySelector(".computed-property-value");
+
+    is(
+      nameSpan.firstChild.textContent,
+      expectedData.name,
+      `computed item #${i} for "${selector}" is the expected one`
+    );
+    is(
+      valueSpan.textContent,
+      expectedData.value,
+      `computed item #${i} for "${selector}" has expected value`
+    );
+  }
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_cycle_color.js b/devtools/client/inspector/computed/test/browser_computed_cycle_color.js
new file mode 100644
index 0000000000..465c453adf
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_cycle_color.js
@@ -0,0 +1,90 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Computed view color cycling test.
+
+const TEST_URI = `
+  <style type="text/css">
+    .matches {
+      color: #f00;
+    }
+  </style>
+  <span id="matches" class="matches">Some styled text</span>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("#matches", inspector);
+
+  info("Checking the property itself");
+  let container = getComputedViewPropertyView(view, "color").valueNode;
+  await checkColorCycling(container, view);
+
+  info("Checking matched selectors");
+  container = await getComputedViewMatchedRules(view, "color");
+  await checkColorCycling(container, view);
+});
+
+async function checkColorCycling(container, view) {
+  const valueNode = container.querySelector(".computed-color");
+  const win = view.styleWindow;
+
+  // "Authored" (default; currently the computed value)
+  is(
+    valueNode.textContent,
+    "rgb(255, 0, 0)",
+    "Color displayed as an RGB value."
+  );
+
+  const tests = [
+    {
+      value: "hwb(0 0% 0%)",
+      comment: "Color displayed as an HWB value.",
+    },
+    {
+      value: "red",
+      comment: "Color displayed as a color name.",
+    },
+    {
+      value: "#f00",
+      comment: "Color displayed as a HEX value.",
+    },
+    {
+      value: "hsl(0, 100%, 50%)",
+      comment: "Color displayed as an HSL value.",
+    },
+    {
+      value: "rgb(255, 0, 0)",
+      comment: "Color displayed as an RGB value again.",
+    },
+  ];
+
+  for (const test of tests) {
+    await checkSwatchShiftClick(container, win, test.value, test.comment);
+  }
+}
+
+async function checkSwatchShiftClick(container, win, expectedValue, comment) {
+  const swatch = container.querySelector(".computed-colorswatch");
+  const valueNode = container.querySelector(".computed-color");
+  swatch.scrollIntoView();
+
+  const onUnitChange = once(swatch, "unit-change");
+  EventUtils.synthesizeMouseAtCenter(
+    swatch,
+    {
+      type: "mousedown",
+      shiftKey: true,
+    },
+    win
+  );
+  // we need to have the mouse up event in order to make sure that the platform
+  // lets go of the last container, and is not waiting for something to happen.
+  // Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1442153
+  EventUtils.synthesizeMouseAtCenter(swatch, { type: "mouseup" }, win);
+  await onUnitChange;
+  is(valueNode.textContent, expectedValue, comment);
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_default_tab.js b/devtools/client/inspector/computed/test/browser_computed_default_tab.js
new file mode 100644
index 0000000000..1a485a7cc7
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_default_tab.js
@@ -0,0 +1,39 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that the computed view is initialized when the computed view is the default tab
+// for the inspector.
+
+const TEST_URI = `
+  <style type="text/css">
+    #matches {
+      color: #F00;
+    }
+  </style>
+  <span id="matches">Some styled text</span>
+`;
+
+add_task(async function () {
+  await pushPref("devtools.inspector.activeSidebar", "computedview");
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("#matches", inspector);
+  is(
+    isPropertyVisible("color", view),
+    true,
+    "span #matches color property is visible"
+  );
+});
+
+function isPropertyVisible(name, view) {
+  info("Checking property visibility for " + name);
+  const propertyViews = view.propertyViews;
+  for (const propView of propertyViews) {
+    if (propView.name == name) {
+      return propView.visible;
+    }
+  }
+  return false;
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_getNodeInfo.js b/devtools/client/inspector/computed/test/browser_computed_getNodeInfo.js
new file mode 100644
index 0000000000..0aa1c85ff2
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_getNodeInfo.js
@@ -0,0 +1,176 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests various output of the computed-view's getNodeInfo method.
+// This method is used by the HighlightersOverlay and TooltipsOverlay on mouseover to
+// decide which highlighter or tooltip to show when hovering over a value/name/selector
+// if any.
+//
+// For instance, browser_ruleview_selector-highlighter_01.js and
+// browser_ruleview_selector-highlighter_02.js test that the selector
+// highlighter appear when hovering over a selector in the rule-view.
+// Since the code to make this work for the computed-view is 90% the same,
+// there is no need for testing it again here.
+// This test however serves as a unit test for getNodeInfo.
+
+const {
+  VIEW_NODE_SELECTOR_TYPE,
+  VIEW_NODE_PROPERTY_TYPE,
+  VIEW_NODE_VALUE_TYPE,
+  VIEW_NODE_IMAGE_URL_TYPE,
+} = require("resource://devtools/client/inspector/shared/node-types.js");
+
+const TEST_URI = `
+  <style type="text/css">
+    body {
+      background: red;
+      color: white;
+    }
+    div {
+      background: green;
+    }
+    div div {
+      background-color: yellow;
+      background-image: url(chrome://branding/content/icon64.png);
+      color: red;
+    }
+  </style>
+  <div><div id="testElement">Test element</div></div>
+`;
+
+// Each item in this array must have the following properties:
+// - desc {String} will be logged for information
+// - getHoveredNode {Generator Function} received the computed-view instance as
+//   argument and must return the node to be tested
+// - assertNodeInfo {Function} should check the validity of the nodeInfo
+//   argument it receives
+const TEST_DATA = [
+  {
+    desc: "Testing a null node",
+    getHoveredNode() {
+      return null;
+    },
+    assertNodeInfo(nodeInfo) {
+      is(nodeInfo, null);
+    },
+  },
+  {
+    desc: "Testing a useless node",
+    getHoveredNode(view) {
+      return view.element;
+    },
+    assertNodeInfo(nodeInfo) {
+      is(nodeInfo, null);
+    },
+  },
+  {
+    desc: "Testing a property name",
+    getHoveredNode(view) {
+      return getComputedViewProperty(view, "color").nameSpan;
+    },
+    assertNodeInfo(nodeInfo) {
+      is(nodeInfo.type, VIEW_NODE_PROPERTY_TYPE);
+      ok("property" in nodeInfo.value);
+      ok("value" in nodeInfo.value);
+      is(nodeInfo.value.property, "color");
+      is(nodeInfo.value.value, "rgb(255, 0, 0)");
+    },
+  },
+  {
+    desc: "Testing a property value",
+    getHoveredNode(view) {
+      return getComputedViewProperty(view, "color").valueSpan;
+    },
+    assertNodeInfo(nodeInfo) {
+      is(nodeInfo.type, VIEW_NODE_VALUE_TYPE);
+      ok("property" in nodeInfo.value);
+      ok("value" in nodeInfo.value);
+      is(nodeInfo.value.property, "color");
+      is(nodeInfo.value.value, "rgb(255, 0, 0)");
+    },
+  },
+  {
+    desc: "Testing an image url",
+    getHoveredNode(view) {
+      const { valueSpan } = getComputedViewProperty(view, "background-image");
+      return valueSpan.querySelector(".theme-link");
+    },
+    assertNodeInfo(nodeInfo) {
+      is(nodeInfo.type, VIEW_NODE_IMAGE_URL_TYPE);
+      ok("property" in nodeInfo.value);
+      ok("value" in nodeInfo.value);
+      is(nodeInfo.value.property, "background-image");
+      is(nodeInfo.value.value, 'url("chrome://branding/content/icon64.png")');
+      is(nodeInfo.value.url, "chrome://branding/content/icon64.png");
+    },
+  },
+  {
+    desc: "Testing a matched rule selector (bestmatch)",
+    async getHoveredNode(view) {
+      const el = await getComputedViewMatchedRules(view, "background-color");
+      return el.querySelector(".bestmatch");
+    },
+    assertNodeInfo(nodeInfo) {
+      is(nodeInfo.type, VIEW_NODE_SELECTOR_TYPE);
+      is(nodeInfo.value, "div div");
+    },
+  },
+  {
+    desc: "Testing a matched rule selector (matched)",
+    async getHoveredNode(view) {
+      const el = await getComputedViewMatchedRules(view, "background-color");
+      return el.querySelector(".matched");
+    },
+    assertNodeInfo(nodeInfo) {
+      is(nodeInfo.type, VIEW_NODE_SELECTOR_TYPE);
+      is(nodeInfo.value, "div");
+    },
+  },
+  {
+    desc: "Testing a matched rule selector (parentmatch)",
+    async getHoveredNode(view) {
+      const el = await getComputedViewMatchedRules(view, "color");
+      return el.querySelector(".parentmatch");
+    },
+    assertNodeInfo(nodeInfo) {
+      is(nodeInfo.type, VIEW_NODE_SELECTOR_TYPE);
+      is(nodeInfo.value, "body");
+    },
+  },
+  {
+    desc: "Testing a matched rule value",
+    async getHoveredNode(view) {
+      const el = await getComputedViewMatchedRules(view, "color");
+      return el.querySelector(".computed-other-property-value");
+    },
+    assertNodeInfo(nodeInfo) {
+      is(nodeInfo.type, VIEW_NODE_VALUE_TYPE);
+      is(nodeInfo.value.property, "color");
+      is(nodeInfo.value.value, "red");
+    },
+  },
+  {
+    desc: "Testing a matched rule stylesheet link",
+    async getHoveredNode(view) {
+      const el = await getComputedViewMatchedRules(view, "color");
+      return el.querySelector(".rule-link .theme-link");
+    },
+    assertNodeInfo(nodeInfo) {
+      is(nodeInfo, null);
+    },
+  },
+];
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("#testElement", inspector);
+
+  for (const { desc, getHoveredNode, assertNodeInfo } of TEST_DATA) {
+    info(desc);
+    const nodeInfo = view.getNodeInfo(await getHoveredNode(view));
+    assertNodeInfo(nodeInfo);
+  }
+});
diff --git a/devtools/client/inspector/computed/test/browser_computed_keybindings_01.js b/devtools/client/inspector/computed/test/browser_computed_keybindings_01.js
new file mode 100644
index 0000000000..5a6681f139
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_keybindings_01.js
@@ -0,0 +1,92 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests computed view key bindings.
+
+const TEST_URI = `
+  <style type="text/css">
+    .matches {
+      color: #F00;
+    }
+  </style>
+  <span class="matches">Some styled text</span>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode(".matches", inspector);
+
+  const propView = getFirstVisiblePropertyView(view);
+  const rulesTable = propView.matchedSelectorsContainer;
+  const matchedExpander = propView.element;
+
+  info("Focusing the property");
+  matchedExpander.scrollIntoView();
+  const onMatchedExpanderFocus = once(matchedExpander, "focus", true);
+  EventUtils.synthesizeMouseAtCenter(matchedExpander, {}, view.styleWindow);
+  await onMatchedExpanderFocus;
+
+  await checkToggleKeyBinding(
+    view.styleWindow,
+    "VK_SPACE",
+    rulesTable,
+    inspector
+  );
+  await checkToggleKeyBinding(
+    view.styleWindow,
+    "VK_RETURN",
+    rulesTable,
+    inspector
+  );
+  await checkHelpLinkKeybinding(view);
+});
+
+function getFirstVisiblePropertyView(view) {
+  let propView = null;
+  view.propertyViews.some(p => {
+    if (p.visible) {
+      propView = p;
+      return true;
+    }
+    return false;
+  });
+
+  return propView;
+}
+
+async function checkToggleKeyBinding(win, key, rulesTable, inspector) {
+  info(
+    "Pressing " +
+      key +
+      " key a couple of times to check that the " +
+      "property gets expanded/collapsed"
+  );
+
+  const onExpand = inspector.once("computed-view-property-expanded");
+  const onCollapse = inspector.once("computed-view-property-collapsed");
+
+  info("Expanding the property");
+  EventUtils.synthesizeKey(key, {}, win);
+  await onExpand;
+  isnot(rulesTable.innerHTML, "", "The property has been expanded");
+
+  info("Collapsing the property");
+  EventUtils.synthesizeKey(key, {}, win);
+  await onCollapse;
+  is(rulesTable.innerHTML, "", "The property has been collapsed");
+}
+
+function checkHelpLinkKeybinding(view) {
+  info('Check that MDN link is opened on "F1"');
+  const propView = getFirstVisiblePropertyView(view);
+  return new Promise(resolve => {
+    propView.mdnLinkClick = function (event) {
+      ok(true, "Pressing F1 opened the MDN link");
+      resolve();
+    };
+    EventUtils.synthesizeKey("VK_F1", {}, view.styleWindow);
+  });
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_keybindings_02.js b/devtools/client/inspector/computed/test/browser_computed_keybindings_02.js
new file mode 100644
index 0000000000..46434f0660
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_keybindings_02.js
@@ -0,0 +1,69 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests the computed-view keyboard navigation.
+
+const TEST_URI = `
+  <style type="text/css">
+    span {
+      font-variant: small-caps;
+      color: #000000;
+    }
+    .nomatches {
+      color: #ff0000;
+    }
+  </style>
+  <div id="first" style="margin: 10em;
+    font-size: 14pt; font-family: helvetica, sans-serif; color: #AAA">
+    <h1>Some header text</h1>
+    <p id="salutation" style="font-size: 12pt">hi.</p>
+    <p id="body" style="font-size: 12pt">I am a test-case. This text exists
+    solely to provide some things to <span style="color: yellow">
+    highlight</span> and <span style="font-weight: bold">count</span>
+    style list-items in the box at right. If you are reading this,
+    you should go do something else instead. Maybe read a book. Or better
+    yet, write some test-cases for another bit of code.
+    <span style="font-style: italic">some text</span></p>
+    <p id="closing">more text</p>
+    <p>even more text</p>
+  </div>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("span", inspector);
+
+  info("Selecting the first computed style in the list");
+  const firstStyle = view.styleDocument.querySelector(
+    "#computed-container .computed-property-view"
+  );
+  ok(firstStyle, "First computed style found in panel");
+  firstStyle.focus();
+
+  info("Tab to select the 2nd style and press return");
+  let onExpanded = inspector.once("computed-view-property-expanded");
+  EventUtils.synthesizeKey("KEY_Tab");
+  EventUtils.synthesizeKey("KEY_Enter");
+  await onExpanded;
+
+  info("Verify the 2nd style has been expanded");
+  const secondStyleSelectors = view.styleDocument.querySelectorAll(
+    ".computed-property-view .matchedselectors"
+  )[1];
+  ok(!!secondStyleSelectors.childNodes.length, "Matched selectors expanded");
+
+  info("Tab back up and test the same thing, with space");
+  onExpanded = inspector.once("computed-view-property-expanded");
+  EventUtils.synthesizeKey("KEY_Tab", { shiftKey: true });
+  EventUtils.synthesizeKey(" ");
+  await onExpanded;
+
+  info("Verify the 1st style has been expanded too");
+  const firstStyleSelectors = view.styleDocument.querySelectorAll(
+    ".computed-property-view .matchedselectors"
+  )[0];
+  ok(!!firstStyleSelectors.childNodes.length, "Matched selectors expanded");
+});
diff --git a/devtools/client/inspector/computed/test/browser_computed_matched-selectors-order.js b/devtools/client/inspector/computed/test/browser_computed_matched-selectors-order.js
new file mode 100644
index 0000000000..b90e86a295
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_matched-selectors-order.js
@@ -0,0 +1,889 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests for the order of matched selector in the computed view.
+const TEST_URI = URL_ROOT + "doc_matched_selectors.html";
+
+add_task(async function () {
+  await addTab(TEST_URI);
+  const { inspector, view } = await openComputedView();
+
+  const checkMatchedSelectors = options =>
+    checkBackgroundColorMatchedSelectors(inspector, view, options);
+
+  info("matching rules with different specificity");
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "specificity",
+      class: "mySection",
+    },
+    style: `
+      #specificity.mySection {
+        --spec_highest: var(--winning-color);
+        background-color: var(--spec_highest);
+      }
+      #specificity {
+        background-color: var(--spec_lowest);
+      }`,
+    expectedMatchedSelectors: [
+      // Higher specificity wins
+      { selector: "#specificity.mySection", value: "var(--spec_highest)" },
+      { selector: "#specificity", value: "var(--spec_lowest)" },
+    ],
+  });
+
+  info("matching rules with same specificity");
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "order-of-appearance",
+    },
+    style: `
+      #order-of-appearance {
+        background-color: var(--appearance-order_first);
+      }
+      #order-of-appearance {
+        --appearance-order_second: var(--winning-color);
+        background-color: var(--appearance-order_second);
+      }`,
+    expectedMatchedSelectors: [
+      // Last rule in stylesheet wins
+      {
+        selector: "#order-of-appearance",
+        value: "var(--appearance-order_second)",
+      },
+      {
+        selector: "#order-of-appearance",
+        value: "var(--appearance-order_first)",
+      },
+    ],
+  });
+
+  info("matching rules on element with style attribute");
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "style-attr",
+      style: "background-color: var(--style-attr_in-attr)",
+    },
+    style: `
+      main {
+        --style-attr_in-attr: var(--winning-color);
+      }
+
+      #style-attr {
+        background-color: var(--style-attr_in-rule);
+      }
+    `,
+    expectedMatchedSelectors: [
+      // style attribute wins
+      { selector: "this.style", value: "var(--style-attr_in-attr)" },
+      { selector: "#style-attr", value: "var(--style-attr_in-rule)" },
+    ],
+  });
+
+  info("matching rules on different layers");
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "layers",
+      class: "layers",
+    },
+    style: `
+      @layer second {
+        .layers {
+          --layers_in-second: var(--winning-color);
+          background-color: var(--layers_in-second);
+        }
+      }
+      @layer first {
+        #layers {
+          background-color: var(--layers_in-first);
+        }
+      }
+    `,
+    expectedMatchedSelectors: [
+      // rule in last declared layer wins
+      { selector: ".layers", value: "var(--layers_in-second)" },
+      { selector: "#layers", value: "var(--layers_in-first)" },
+    ],
+  });
+
+  info("matching rules on same layer, with same specificity");
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "same-layers-order-of-appearance",
+    },
+    style: `
+      @layer second {
+        #same-layers-order-of-appearance {
+          background-color: var(--same-layers-appearance-order_first);
+        }
+
+        #same-layers-order-of-appearance {
+          --same-layers-appearance-order_second: var(--winning-color);
+          background-color: var(--same-layers-appearance-order_second);
+        }
+      }
+    `,
+    expectedMatchedSelectors: [
+      // last rule in the layer wins
+      {
+        selector: "#same-layers-order-of-appearance",
+        value: "var(--same-layers-appearance-order_second)",
+      },
+      {
+        selector: "#same-layers-order-of-appearance",
+        value: "var(--same-layers-appearance-order_first)",
+      },
+    ],
+  });
+
+  info("matching rules some in layers, some not");
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "in-layer-and-no-layer",
+    },
+    style: `
+      @layer second {
+        #in-layer-and-no-layer {
+          background-color: var(--in-layer-and-no-layer_in-second);
+        }
+      }
+
+      @layer first {
+        #in-layer-and-no-layer {
+          background-color: var(--in-layer-and-no-layer_in-first);
+        }
+      }
+
+      #in-layer-and-no-layer {
+        --in-layer-and-no-layer_no-layer: var(--winning-color);
+        background-color: var(--in-layer-and-no-layer_no-layer);
+      }`,
+    expectedMatchedSelectors: [
+      // rule not in layer wins
+      {
+        selector: "#in-layer-and-no-layer",
+        value: "var(--in-layer-and-no-layer_no-layer)",
+      },
+      {
+        selector: "#in-layer-and-no-layer",
+        value: "var(--in-layer-and-no-layer_in-second)",
+      },
+      {
+        selector: "#in-layer-and-no-layer",
+        value: "var(--in-layer-and-no-layer_in-first)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules with different specificity and one property declared with !important"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "important-specificity",
+      class: "myImportantSection",
+    },
+    style: `
+      #important-specificity.myImportantSection {
+        background-color: var(--important-spec_highest);
+      }
+      #important-specificity {
+        --important-spec_lowest-important: var(--winning-color);
+        background-color: var(--important-spec_lowest-important) !important;
+      }`,
+    expectedMatchedSelectors: [
+      // lesser specificity, but value was set with !important
+      {
+        selector: "#important-specificity",
+        value: "var(--important-spec_lowest-important)",
+      },
+      {
+        selector: "#important-specificity.myImportantSection",
+        value: "var(--important-spec_highest)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules with different specificity and all properties declared with !important"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "all-important-specificity",
+      class: "myAllImportantSection",
+    },
+    style: `
+      #all-important-specificity.myAllImportantSection {
+        --all-important-spec_highest-important: var(--winning-color);
+        background-color: var(--all-important-spec_highest-important) !important;
+      }
+      #all-important-specificity {
+        background-color: var(--all-important-spec_lowest-important) !important;
+      }`,
+    expectedMatchedSelectors: [
+      // all values !important, so highest specificity rule wins
+      {
+        selector: "#all-important-specificity.myAllImportantSection",
+        value: "var(--all-important-spec_highest-important)",
+      },
+      {
+        selector: "#all-important-specificity",
+        value: "var(--all-important-spec_lowest-important)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules with same specificity and one property declared with !important"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "important-order-of-appearance",
+    },
+    style: `
+      #important-order-of-appearance {
+        --important-appearance-order_first-important: var(--winning-color);
+        background-color: var(--important-appearance-order_first-important) !important;
+      }
+      #important-order-of-appearance {
+        background-color: var(--important-appearance-order_second);
+      }`,
+    expectedMatchedSelectors: [
+      // same specificity, but this value was set with !important
+      {
+        selector: "#important-order-of-appearance",
+        value: "var(--important-appearance-order_first-important)",
+      },
+      {
+        selector: "#important-order-of-appearance",
+        value: "var(--important-appearance-order_second)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules with same specificity and all properties declared with !important"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "all-important-order-of-appearance",
+    },
+    style: `
+      #all-important-order-of-appearance {
+        background-color: var(--all-important-appearance-order_first-important) !important;
+      }
+      #all-important-order-of-appearance {
+        --all-important-appearance-order_second-important: var(--winning-color);
+        background-color: var(--all-important-appearance-order_second-important) !important;
+      }`,
+    expectedMatchedSelectors: [
+      // all values !important, so latest rule in stylesheet wins
+      {
+        selector: "#all-important-order-of-appearance",
+        value: "var(--all-important-appearance-order_second-important)",
+      },
+      {
+        selector: "#all-important-order-of-appearance",
+        value: "var(--all-important-appearance-order_first-important)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules with important property on element with style attribute"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "important-style-attr",
+      style: "background-color: var(--important-style-attr_in-attr);",
+    },
+    style: `
+      #important-style-attr {
+        --important-style-attr_in-rule-important: var(--winning-color);
+        background-color: var(--important-style-attr_in-rule-important) !important;
+      }`,
+    expectedMatchedSelectors: [
+      // important property wins over style attribute
+      {
+        selector: "#important-style-attr",
+        value: "var(--important-style-attr_in-rule-important)",
+      },
+      { selector: "this.style", value: "var(--important-style-attr_in-attr)" },
+    ],
+  });
+
+  info(
+    "matching rules with important property on element with style attribute and important value"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "all-important-style-attr",
+      style:
+        "background-color: var(--all-important-style-attr_in-attr-important) !important;",
+    },
+    style: `
+      main {
+        --all-important-style-attr_in-attr-important: var(--winning-color);
+      }
+      #all-important-style-attr {
+        background-color: var(--all-important-style-attr_in-rule-important);
+      }`,
+    expectedMatchedSelectors: [
+      // both values are important, so style attribute wins
+      {
+        selector: "this.style",
+        value: "var(--all-important-style-attr_in-attr-important)",
+      },
+      {
+        selector: "#all-important-style-attr",
+        value: "var(--all-important-style-attr_in-rule-important)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules on different layer, with same specificity and important values"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "important-layers",
+    },
+    style: `
+      @layer second {
+        #important-layers {
+          background-color: var(--important-layers_in-second);
+        }
+      }
+      @layer first {
+        #important-layers {
+          --important-layers_in-first-important: var(--winning-color);
+          background-color: var(--important-layers_in-first-important) !important;
+        }
+      }`,
+    expectedMatchedSelectors: [
+      // rule with important property wins
+      {
+        selector: "#important-layers",
+        value: "var(--important-layers_in-first-important)",
+      },
+      {
+        selector: "#important-layers",
+        value: "var(--important-layers_in-second)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules on different layer, with same specificity and all important values"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "all-important-layers",
+    },
+    style: `
+      @layer second {
+        #all-important-layers {
+          background-color: var(--all-important-layers_in-second-important) !important;
+        }
+      }
+      @layer first {
+        #all-important-layers {
+          --all-important-layers_in-first-important: var(--winning-color);
+          background-color: var(--all-important-layers_in-first-important) !important;
+        }
+      }`,
+    expectedMatchedSelectors: [
+      // all properties are important, rule from first declared layer wins
+      {
+        selector: "#all-important-layers",
+        value: "var(--all-important-layers_in-first-important)",
+      },
+      {
+        selector: "#all-important-layers",
+        value: "var(--all-important-layers_in-second-important)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules on same layer, with same specificity and important values"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "important-same-layers-order-of-appearance",
+    },
+    style: `
+      @layer second {
+        #important-same-layers-order-of-appearance {
+          --important-same-layers-appearance-order_first-important: var(--winning-color);
+          background-color: var(--important-same-layers-appearance-order_first-important) !important;
+        }
+
+        #important-same-layers-order-of-appearance {
+          background-color: var(--important-same-layers-appearance-order_second);
+        }
+      }`,
+    expectedMatchedSelectors: [
+      // rule with important property wins
+      {
+        selector: "#important-same-layers-order-of-appearance",
+        value: "var(--important-same-layers-appearance-order_first-important)",
+      },
+      {
+        selector: "#important-same-layers-order-of-appearance",
+        value: "var(--important-same-layers-appearance-order_second)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules on same layer, with same specificity and all important values"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "all-important-same-layers-order-of-appearance",
+    },
+    style: `
+      @layer second {
+        #all-important-same-layers-order-of-appearance {
+          background-color: var(--all-important-same-layers-appearance-order_first-important) !important;
+        }
+
+        #all-important-same-layers-order-of-appearance {
+          --all-important-same-layers-appearance-order_second-important: var(--winning-color);
+          background-color: var(--all-important-same-layers-appearance-order_second-important) !important;
+        }
+      }`,
+    expectedMatchedSelectors: [
+      // last rule with important property wins
+      {
+        selector: "#all-important-same-layers-order-of-appearance",
+        value:
+          "var(--all-important-same-layers-appearance-order_second-important)",
+      },
+      {
+        selector: "#all-important-same-layers-order-of-appearance",
+        value:
+          "var(--all-important-same-layers-appearance-order_first-important)",
+      },
+    ],
+  });
+
+  info("matching rules ,some in layers, some not, important values in layers");
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "important-in-layer-and-no-layer",
+    },
+    style: `
+      @layer second {
+        #important-in-layer-and-no-layer {
+          background-color: var(--important-in-layer-and-no-layer_in-second);
+        }
+      }
+
+      @layer first {
+        #important-in-layer-and-no-layer {
+          --important-in-layer-and-no-layer_in-first-important: var(--winning-color);
+          background-color: var(--important-in-layer-and-no-layer_in-first-important) !important;
+        }
+      }
+
+      #important-in-layer-and-no-layer {
+        background-color: var(--important-in-layer-and-no-layer_no-layer);
+      }`,
+    expectedMatchedSelectors: [
+      // rule with important property wins
+      {
+        selector: "#important-in-layer-and-no-layer",
+        value: "var(--important-in-layer-and-no-layer_in-first-important)",
+      },
+      // then rule not in layer
+      {
+        selector: "#important-in-layer-and-no-layer",
+        value: "var(--important-in-layer-and-no-layer_no-layer)",
+      },
+      {
+        selector: "#important-in-layer-and-no-layer",
+        value: "var(--important-in-layer-and-no-layer_in-second)",
+      },
+    ],
+  });
+
+  info("matching rules ,some in layers, some not, all important values");
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "all-important-in-layer-and-no-layer",
+    },
+    style: `
+      @layer second {
+        #all-important-in-layer-and-no-layer {
+          background-color: var(--all-important-in-layer-and-no-layer_in-second-important) !important;
+        }
+      }
+
+      @layer first {
+        #all-important-in-layer-and-no-layer {
+          --all-important-in-layer-and-no-layer_in-first-important: var(--winning-color);
+          background-color: var(--all-important-in-layer-and-no-layer_in-first-important) !important;
+        }
+      }
+
+      #all-important-in-layer-and-no-layer {
+        background-color: var(--all-important-in-layer-and-no-layer_no-layer-important) !important;
+      }`,
+    expectedMatchedSelectors: [
+      // important properties in first declared layer wins
+      {
+        selector: "#all-important-in-layer-and-no-layer",
+        value: "var(--all-important-in-layer-and-no-layer_in-first-important)",
+      },
+      // then following important rules in layers
+      {
+        selector: "#all-important-in-layer-and-no-layer",
+        value: "var(--all-important-in-layer-and-no-layer_in-second-important)",
+      },
+      // then important rules not in layers
+      {
+        selector: "#all-important-in-layer-and-no-layer",
+        value: "var(--all-important-in-layer-and-no-layer_no-layer-important)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules ,some in layers, some not, and style attribute all important values"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "all-important-in-layer-no-layer-style-attr",
+      style:
+        "background-color: var(--all-important-in-layer-no-layer-style-attr_in-attr-important) !important",
+    },
+    style: `
+      main {
+        --all-important-in-layer-no-layer-style-attr_in-attr-important: var(--winning-color);
+      }
+
+      @layer second {
+        #all-important-in-layer-no-layer-style-attr {
+          background-color: var(--all-important-in-layer-no-layer-style-attr_in-second-important) !important;
+        }
+      }
+
+      @layer first {
+        #all-important-in-layer-no-layer-style-attr {
+          background-color: var(--all-important-in-layer-no-layer-style-attr_in-first-important) !important;
+        }
+      }
+
+      #all-important-in-layer-no-layer-style-attr {
+        background-color: var(--all-important-in-layer-no-layer-style-attr_no-layer-important) !important;
+      }`,
+    expectedMatchedSelectors: [
+      // important properties in style attribute wins
+      {
+        selector: "this.style",
+        value:
+          "var(--all-important-in-layer-no-layer-style-attr_in-attr-important)",
+      },
+      // then important property in first declared layer
+      {
+        selector: "#all-important-in-layer-no-layer-style-attr",
+        value:
+          "var(--all-important-in-layer-no-layer-style-attr_in-first-important)",
+      },
+      // then following important property in layers
+      {
+        selector: "#all-important-in-layer-no-layer-style-attr",
+        value:
+          "var(--all-important-in-layer-no-layer-style-attr_in-second-important)",
+      },
+      // then important property not in layers
+      {
+        selector: "#all-important-in-layer-no-layer-style-attr",
+        value:
+          "var(--all-important-in-layer-no-layer-style-attr_no-layer-important)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules on same layer but different rules and all important values"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "all-important-same-layer-different-rule",
+    },
+    style: `
+      @layer first {
+        #all-important-same-layer-different-rule {
+          background-color: var(--all-important-same-layer-different-rule_first-important) !important;
+        }
+      }
+
+      @layer first {
+        #all-important-same-layer-different-rule {
+          --all-important-same-layer-different-rule_second-important: var(--winning-color);
+          background-color: var(--all-important-same-layer-different-rule_second-important) !important;
+        }
+      }`,
+    expectedMatchedSelectors: [
+      // last rule for the layer with important property wins
+      {
+        selector: "#all-important-same-layer-different-rule",
+        value:
+          "var(--all-important-same-layer-different-rule_second-important)",
+      },
+      {
+        selector: "#all-important-same-layer-different-rule",
+        value: "var(--all-important-same-layer-different-rule_first-important)",
+      },
+    ],
+  });
+
+  info(
+    "matching rules on same layer but different nested rules and all important values"
+  );
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "all-important-same-nested-layer-different-rule",
+    },
+    style: `
+      @layer first {
+        @layer {
+          @layer second {
+            #all-important-same-nested-layer-different-rule {
+              background-color: var(--all-important-same-nested-layer-different-rule_first-important) !important;
+            }
+          }
+
+          @layer second {
+            #all-important-same-nested-layer-different-rule {
+              --all-important-same-nested-layer-different-rule_second-important: var(--winning-color);
+              background-color: var(--all-important-same-nested-layer-different-rule_second-important) !important;
+            }
+          }
+        }
+      }`,
+    expectedMatchedSelectors: [
+      // last rule for the layer with important property wins
+      {
+        selector: "#all-important-same-nested-layer-different-rule",
+        value:
+          "var(--all-important-same-nested-layer-different-rule_second-important)",
+      },
+      {
+        selector: "#all-important-same-nested-layer-different-rule",
+        value:
+          "var(--all-important-same-nested-layer-different-rule_first-important)",
+      },
+    ],
+  });
+
+  info("matching rules on different nameless layers and all important values");
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "all-important-different-nameless-layers",
+    },
+    style: `
+      @layer {
+        @layer first {
+          #all-important-different-nameless-layers {
+            --all-important-different-nameless-layers_first-important: var(--winning-color);
+            background-color: var(--all-important-different-nameless-layers_first-important) !important;
+          }
+        }
+      }
+      @layer {
+        @layer first {
+          #all-important-different-nameless-layers {
+            background-color: var(--all-important-different-nameless-layers_second-important) !important;
+          }
+        }
+      }`,
+    expectedMatchedSelectors: [
+      // rule with important property in first declared layer wins
+      {
+        selector: "#all-important-different-nameless-layers",
+        value: "var(--all-important-different-nameless-layers_first-important)",
+      },
+      {
+        selector: "#all-important-different-nameless-layers",
+        value:
+          "var(--all-important-different-nameless-layers_second-important)",
+      },
+    ],
+  });
+
+  info("matching rules on different imported layers");
+  // no provided style as rules are defined in doc_matched_selectors_imported_*.css
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "imported-layers",
+    },
+    expectedMatchedSelectors: [
+      // rule in last declared layer wins
+      {
+        selector: "#imported-layers",
+        value: "var(--imported-layers_in-anonymous-second)",
+      },
+      {
+        selector: "#imported-layers",
+        value: "var(--imported-layers_in-nested-importedSecond)",
+      },
+      {
+        selector: "#imported-layers",
+        value: "var(--imported-layers_in-anonymous-first)",
+      },
+      {
+        selector: "#imported-layers",
+        value: "var(--imported-layers_in-importedSecond)",
+      },
+      {
+        selector: "#imported-layers",
+        value: "var(--imported-layers_in-importedFirst-second)",
+      },
+      {
+        selector: "#imported-layers",
+        value: "var(--imported-layers_in-importedFirst-first)",
+      },
+    ],
+  });
+
+  info("matching rules on different imported layers all with important values");
+  // no provided style as rules are defined in doc_matched_selectors_imported_*.css
+  await checkMatchedSelectors({
+    elementAttributes: {
+      id: "all-important-imported-layers",
+    },
+    expectedMatchedSelectors: [
+      // last important property in first declared layer wins
+      {
+        selector: "#all-important-imported-layers",
+        value:
+          "var(--all-important-imported-layers_in-importedFirst-second-important)",
+      },
+      // then earlier important property for first declared layer
+      {
+        selector: "#all-important-imported-layers",
+        value:
+          "var(--all-important-imported-layers_in-importedFirst-first-important)",
+      },
+      {
+        selector: "#all-important-imported-layers",
+        value:
+          "var(--all-important-imported-layers_in-importedSecond-important)",
+      },
+      {
+        selector: "#all-important-imported-layers",
+        value:
+          "var(--all-important-imported-layers_in-anonymous-first-important)",
+      },
+      {
+        selector: "#all-important-imported-layers",
+        value:
+          "var(--all-important-imported-layers_in-nested-importedSecond-important)",
+      },
+      {
+        selector: "#all-important-imported-layers",
+        value:
+          "var(--all-important-imported-layers_in-anonymous-second-important)",
+      },
+    ],
+  });
+});
+
+async function checkBackgroundColorMatchedSelectors(
+  inspector,
+  view,
+  { elementAttributes, style, expectedMatchedSelectors }
+) {
+  const elementId = await SpecialPowers.spawn(
+    gBrowser.selectedBrowser,
+    [elementAttributes, style],
+    (attr, _style) => {
+      const sectionEl = content.document.createElement("section");
+      for (const [name, value] of Object.entries(attr)) {
+        sectionEl.setAttribute(name, value);
+      }
+
+      if (_style) {
+        const styleEl = content.document.createElement("style");
+        styleEl.innerText = _style;
+        styleEl.setAttribute("id", `style-${sectionEl.id}`);
+        content.document.head.append(styleEl);
+      }
+      content.document.querySelector("main").append(sectionEl);
+
+      return sectionEl.id;
+    }
+  );
+  const selector = `#${elementId}`;
+  await selectNode(selector, inspector);
+
+  const bgColorComputedValue = await getComputedStyleProperty(
+    selector,
+    null,
+    "background-color"
+  );
+  is(
+    bgColorComputedValue,
+    "rgb(0, 0, 255)",
+    `The created element does have a "blue" background-color`
+  );
+
+  const propertyView = getPropertyView(view, "background-color");
+  ok(propertyView, "found PropertyView for background-color");
+  const valueNode = propertyView.valueNode.querySelector(".computed-color");
+  is(
+    valueNode.textContent,
+    "rgb(0, 0, 255)",
+    `The displayed computed value is the expected "blue"`
+  );
+
+  is(propertyView.hasMatchedSelectors, true, "hasMatchedSelectors is true");
+
+  info("Expanding the matched selectors");
+  propertyView.matchedExpanded = true;
+  await propertyView.refreshMatchedSelectors();
+
+  const selectorsEl =
+    propertyView.matchedSelectorsContainer.querySelectorAll(".rule-text");
+  is(
+    selectorsEl.length,
+    expectedMatchedSelectors.length,
+    "Expected number of selectors are displayed"
+  );
+
+  selectorsEl.forEach((selectorEl, index) => {
+    is(
+      selectorEl.querySelector(".fix-get-selection").innerText,
+      expectedMatchedSelectors[index].selector,
+      `Selector #${index} is the expected one`
+    );
+    is(
+      selectorEl.querySelector(".computed-other-property-value").innerText,
+      expectedMatchedSelectors[index].value,
+      `Selector #${index} has the expected background color`
+    );
+    const classToMatch = index === 0 ? "bestmatch" : "matched";
+    ok(
+      selectorEl.classList.contains(classToMatch),
+      `selector element has expected "${classToMatch}" class`
+    );
+  });
+
+  // cleanup
+  await SpecialPowers.spawn(gBrowser.selectedBrowser, [elementId], id => {
+    // Remove added element and stylesheet
+    content.document.getElementById(id).remove();
+    // Some test cases don't insert a style element
+    content.document.getElementById(`style-${id}`)?.remove();
+  });
+}
+
+function getPropertyView(computedView, name) {
+  return computedView.propertyViews.find(view => view.name === name);
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_matched-selectors-toggle.js b/devtools/client/inspector/computed/test/browser_computed_matched-selectors-toggle.js
new file mode 100644
index 0000000000..2de29c2607
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_matched-selectors-toggle.js
@@ -0,0 +1,125 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the computed view properties can be expanded and collapsed with
+// either the twisty or by dbl-clicking on the container.
+
+const TEST_URI = `
+  <style type="text/css"> ,
+    html { color: #000000; font-size: 15pt; }
+    h1 { color: red; }
+  </style>
+  <h1>Some header text</h1>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("h1", inspector);
+
+  await testExpandOnTwistyClick(view, inspector);
+  await testCollapseOnTwistyClick(view, inspector);
+  await testExpandOnDblClick(view, inspector);
+  await testCollapseOnDblClick(view, inspector);
+});
+
+async function testExpandOnTwistyClick({ styleDocument }, inspector) {
+  info("Testing that a property expands on twisty click");
+
+  info("Getting twisty element");
+  const twisty = styleDocument.querySelector(".computed-expandable");
+  ok(twisty, "Twisty found");
+
+  const onExpand = inspector.once("computed-view-property-expanded");
+  info("Clicking on the twisty element");
+  twisty.click();
+
+  await onExpand;
+
+  // Expanded means the matchedselectors div is not empty
+  const matchedSelectorsEl = twisty
+    .closest(".computed-property-view")
+    .querySelector(".matchedselectors");
+  ok(
+    !!matchedSelectorsEl.childNodes.length,
+    "Matched selectors are expanded on twisty click"
+  );
+}
+
+async function testCollapseOnTwistyClick({ styleDocument }, inspector) {
+  info("Testing that a property collapses on twisty click");
+
+  info("Getting twisty element");
+  const twisty = styleDocument.querySelector(".computed-expandable");
+  ok(twisty, "Twisty found");
+
+  const onCollapse = inspector.once("computed-view-property-collapsed");
+  info("Clicking on the twisty element");
+  twisty.click();
+
+  await onCollapse;
+
+  // Collapsed means the matchedselectors div is empty
+  const matchedSelectorsEl = twisty
+    .closest(".computed-property-view")
+    .querySelector(".matchedselectors");
+  is(
+    matchedSelectorsEl.childNodes.length,
+    0,
+    "Matched selectors are collapsed on twisty click"
+  );
+}
+
+async function testExpandOnDblClick({ styleDocument, styleWindow }, inspector) {
+  info("Testing that a property expands on container dbl-click");
+
+  info("Getting computed property container");
+  const container = styleDocument.querySelector(
+    "#computed-container .computed-property-view"
+  );
+  ok(container, "Container found");
+
+  container.scrollIntoView();
+
+  const onExpand = inspector.once("computed-view-property-expanded");
+  info("Dbl-clicking on the container");
+  EventUtils.synthesizeMouseAtCenter(container, { clickCount: 2 }, styleWindow);
+
+  await onExpand;
+
+  // Expanded means the matchedselectors div is not empty
+  const matchedSelectorsEl = container.querySelector(".matchedselectors");
+  ok(
+    !!matchedSelectorsEl.childNodes.length,
+    "Matched selectors are expanded on dblclick"
+  );
+}
+
+async function testCollapseOnDblClick(
+  { styleDocument, styleWindow },
+  inspector
+) {
+  info("Testing that a property collapses on container dbl-click");
+
+  info("Getting computed property container");
+  const container = styleDocument.querySelector(
+    "#computed-container .computed-property-view"
+  );
+  ok(container, "Container found");
+
+  const onCollapse = inspector.once("computed-view-property-collapsed");
+  info("Dbl-clicking on the container");
+  EventUtils.synthesizeMouseAtCenter(container, { clickCount: 2 }, styleWindow);
+
+  await onCollapse;
+
+  // Collapsed means the matchedselectors div is empty
+  const matchedSelectorsEl = container.querySelector(".matchedselectors");
+  is(
+    matchedSelectorsEl.childNodes.length,
+    0,
+    "Matched selectors are collapsed on dblclick"
+  );
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_matched-selectors_01.js b/devtools/client/inspector/computed/test/browser_computed_matched-selectors_01.js
new file mode 100644
index 0000000000..bb90dfb4ea
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_matched-selectors_01.js
@@ -0,0 +1,48 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Checking selector counts, matched rules and titles in the computed-view.
+
+const {
+  PropertyView,
+} = require("resource://devtools/client/inspector/computed/computed.js");
+const TEST_URI = URL_ROOT + "doc_matched_selectors.html";
+
+add_task(async function () {
+  await addTab(TEST_URI);
+  const { inspector, view } = await openComputedView();
+
+  await selectNode("#test", inspector);
+  await testMatchedSelectors(view, inspector);
+});
+
+async function testMatchedSelectors(view, inspector) {
+  info("checking selector counts, matched rules and titles");
+
+  const nodeFront = await getNodeFront("#test", inspector);
+  is(
+    nodeFront,
+    view._viewedElement,
+    "style inspector node matches the selected node"
+  );
+
+  const propertyView = new PropertyView(view, "color");
+  propertyView.createListItemElement();
+  propertyView.matchedExpanded = true;
+
+  await propertyView.refreshMatchedSelectors();
+
+  const numMatchedSelectors = propertyView.matchedSelectors.length;
+  is(
+    numMatchedSelectors,
+    7,
+    "CssLogic returns the correct number of matched selectors for div"
+  );
+  is(
+    propertyView.hasMatchedSelectors,
+    true,
+    "hasMatchedSelectors returns true"
+  );
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_matched-selectors_02.js b/devtools/client/inspector/computed/test/browser_computed_matched-selectors_02.js
new file mode 100644
index 0000000000..b0327a30cf
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_matched-selectors_02.js
@@ -0,0 +1,40 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests for matched selector texts in the computed view.
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8,<div style='color:blue;'></div>");
+  const { inspector, view } = await openComputedView();
+  await selectNode("div", inspector);
+
+  info("Checking the color property view");
+  const propertyView = getPropertyView(view, "color");
+  ok(propertyView, "found PropertyView for color");
+  is(propertyView.hasMatchedSelectors, true, "hasMatchedSelectors is true");
+
+  info("Expanding the matched selectors");
+  propertyView.matchedExpanded = true;
+  await propertyView.refreshMatchedSelectors();
+
+  const span =
+    propertyView.matchedSelectorsContainer.querySelector("span.rule-text");
+  ok(span, "Found the first table row");
+
+  const selector = propertyView.matchedSelectorViews[0];
+  ok(selector, "Found the first matched selector view");
+});
+
+function getPropertyView(computedView, name) {
+  let propertyView = null;
+  computedView.propertyViews.some(function (view) {
+    if (view.name == name) {
+      propertyView = view;
+      return true;
+    }
+    return false;
+  });
+  return propertyView;
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_media-queries.js b/devtools/client/inspector/computed/test/browser_computed_media-queries.js
new file mode 100644
index 0000000000..9f09fc7e3c
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_media-queries.js
@@ -0,0 +1,42 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that we correctly display appropriate media query titles in the
+// property view.
+
+const TEST_URI = URL_ROOT + "doc_media_queries.html";
+
+var {
+  PropertyView,
+} = require("resource://devtools/client/inspector/computed/computed.js");
+
+add_task(async function () {
+  await addTab(TEST_URI);
+  const { inspector, view } = await openComputedView();
+  await selectNode("div", inspector);
+  await checkPropertyView(view);
+});
+
+function checkPropertyView(view) {
+  const propertyView = new PropertyView(view, "width");
+  propertyView.createListItemElement();
+  propertyView.matchedExpanded = true;
+
+  return propertyView.refreshMatchedSelectors().then(() => {
+    const numMatchedSelectors = propertyView.matchedSelectors.length;
+
+    is(
+      numMatchedSelectors,
+      2,
+      "Property view has the correct number of matched selectors for div"
+    );
+
+    is(
+      propertyView.hasMatchedSelectors,
+      true,
+      "hasMatchedSelectors returns true"
+    );
+  });
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_no-results-placeholder.js b/devtools/client/inspector/computed/test/browser_computed_no-results-placeholder.js
new file mode 100644
index 0000000000..3e63bfb9b3
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_no-results-placeholder.js
@@ -0,0 +1,69 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the no results placeholder works properly.
+
+const TEST_URI = `
+  <style type="text/css">
+    .matches {
+      color: #F00;
+    }
+  </style>
+  <span id="matches" class="matches">Some styled text</span>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("#matches", inspector);
+
+  await enterInvalidFilter(inspector, view);
+  checkNoResultsPlaceholderShown(view);
+
+  await clearFilterText(inspector, view);
+  checkNoResultsPlaceholderHidden(view);
+});
+
+async function enterInvalidFilter(inspector, computedView) {
+  const searchbar = computedView.searchField;
+  const searchTerm = "xxxxx";
+
+  info('setting filter text to "' + searchTerm + '"');
+
+  const onRefreshed = inspector.once("computed-view-refreshed");
+  searchbar.focus();
+  synthesizeKeys(searchTerm, computedView.styleWindow);
+  await onRefreshed;
+}
+
+function checkNoResultsPlaceholderShown(computedView) {
+  info("Checking that the no results placeholder is shown");
+
+  const placeholder = computedView.noResults;
+  const win = computedView.styleWindow;
+  const display = win.getComputedStyle(placeholder).display;
+  is(display, "block", "placeholder is visible");
+}
+
+async function clearFilterText(inspector, computedView) {
+  info("Clearing the filter text");
+
+  const searchbar = computedView.searchField;
+
+  const onRefreshed = inspector.once("computed-view-refreshed");
+  searchbar.focus();
+  searchbar.value = "";
+  EventUtils.synthesizeKey("c", {}, computedView.styleWindow);
+  await onRefreshed;
+}
+
+function checkNoResultsPlaceholderHidden(computedView) {
+  info("Checking that the no results placeholder is hidden");
+
+  const placeholder = computedView.noResults;
+  const win = computedView.styleWindow;
+  const display = win.getComputedStyle(placeholder).display;
+  is(display, "none", "placeholder is hidden");
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_original-source-link.js b/devtools/client/inspector/computed/test/browser_computed_original-source-link.js
new file mode 100644
index 0000000000..771d349b3b
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_original-source-link.js
@@ -0,0 +1,71 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the computed view shows the original source link when source maps
+// are enabled.
+
+const TESTCASE_URI = URL_ROOT_SSL + "doc_sourcemaps.html";
+const PREF = "devtools.source-map.client-service.enabled";
+const SCSS_LOC = "doc_sourcemaps.scss:4";
+const CSS_LOC = "doc_sourcemaps.css:1";
+
+add_task(async function () {
+  info("Turning the pref " + PREF + " on");
+  Services.prefs.setBoolPref(PREF, true);
+
+  await addTab(TESTCASE_URI);
+  const { toolbox, inspector, view } = await openComputedView();
+  let onLinksUpdated = inspector.once("computed-view-sourcelinks-updated");
+  await selectNode("div", inspector);
+
+  info("Expanding the first property");
+  await expandComputedViewPropertyByIndex(view, 0);
+
+  info("Verifying the link text");
+  await onLinksUpdated;
+  verifyLinkText(view, SCSS_LOC);
+
+  info("Toggling the pref");
+  onLinksUpdated = inspector.once("computed-view-sourcelinks-updated");
+  Services.prefs.setBoolPref(PREF, false);
+  await onLinksUpdated;
+
+  info("Verifying that the link text has changed after the pref change");
+  await verifyLinkText(view, CSS_LOC);
+
+  info("Toggling the pref again");
+  onLinksUpdated = inspector.once("computed-view-sourcelinks-updated");
+  Services.prefs.setBoolPref(PREF, true);
+  await onLinksUpdated;
+
+  info("Testing that clicking on the link works");
+  await testClickingLink(toolbox, view);
+
+  info("Turning the pref " + PREF + " off");
+  Services.prefs.clearUserPref(PREF);
+});
+
+async function testClickingLink(toolbox, view) {
+  const onEditor = waitForStyleEditor(toolbox, "doc_sourcemaps.scss");
+
+  info("Clicking the computedview stylesheet link");
+  const link = getComputedViewLinkByIndex(view, 0);
+  link.scrollIntoView();
+  link.click();
+
+  const editor = await onEditor;
+
+  const { line } = editor.sourceEditor.getCursor();
+  is(line, 3, "cursor is at correct line number in original source");
+}
+
+function verifyLinkText(view, text) {
+  const link = getComputedViewLinkByIndex(view, 0);
+  is(
+    link.textContent,
+    text,
+    "Linked text changed to display the correct location"
+  );
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_pseudo-element_01.js b/devtools/client/inspector/computed/test/browser_computed_pseudo-element_01.js
new file mode 100644
index 0000000000..e972a0257a
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_pseudo-element_01.js
@@ -0,0 +1,38 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that pseudoelements are displayed correctly in the rule view.
+
+const TEST_URI = URL_ROOT + "doc_pseudoelement.html";
+
+add_task(async function () {
+  await addTab(TEST_URI);
+  const { inspector, view } = await openComputedView();
+  await testTopLeft(inspector, view);
+});
+
+async function testTopLeft(inspector, view) {
+  const node = await getNodeFront("#topleft", inspector.markup);
+  await selectNode(node, inspector);
+  const float = getComputedViewPropertyValue(view, "float");
+  is(float, "left", "The computed view shows the correct float");
+
+  const children = await inspector.markup.walker.children(node);
+  is(children.nodes.length, 3, "Element has correct number of children");
+
+  const beforeElement = children.nodes[0];
+  await selectNode(beforeElement, inspector);
+  let top = getComputedViewPropertyValue(view, "top");
+  is(top, "0px", "The computed view shows the correct top");
+  let left = getComputedViewPropertyValue(view, "left");
+  is(left, "0px", "The computed view shows the correct left");
+
+  const afterElement = children.nodes[children.nodes.length - 1];
+  await selectNode(afterElement, inspector);
+  top = getComputedViewPropertyValue(view, "top");
+  is(top, "96px", "The computed view shows the correct top");
+  left = getComputedViewPropertyValue(view, "left");
+  is(left, "96px", "The computed view shows the correct left");
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_refresh-on-ruleview-change.js b/devtools/client/inspector/computed/test/browser_computed_refresh-on-ruleview-change.js
new file mode 100644
index 0000000000..12b7901970
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_refresh-on-ruleview-change.js
@@ -0,0 +1,93 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the computed view refreshes when the rule view is updated in 3 pane mode.
+
+const TEST_URI = "<div id='target' style='color: rgb(255, 0, 0);'>test</div>";
+
+add_task(async function () {
+  info(
+    "Check whether the color as well in computed view is updated " +
+      "when the rule in rule view is changed in case of 3 pane mode"
+  );
+  await pushPref("devtools.inspector.three-pane-enabled", true);
+
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("#target", inspector);
+
+  is(
+    getComputedViewPropertyValue(view, "color"),
+    "rgb(255, 0, 0)",
+    "The computed view shows the right color"
+  );
+
+  info("Change the value in the ruleview");
+  const ruleView = inspector.getPanel("ruleview").view;
+  const editor = await getValueEditor(ruleView);
+  const onRuleViewChanged = ruleView.once("ruleview-changed");
+  const onComputedViewRefreshed = inspector.once("computed-view-refreshed");
+  editor.input.value = "rgb(0, 255, 0)";
+  EventUtils.synthesizeKey("VK_RETURN", {}, ruleView.styleWindow);
+  await Promise.all([onRuleViewChanged, onComputedViewRefreshed]);
+
+  info("Check the value in the computed view");
+  is(
+    getComputedViewPropertyValue(view, "color"),
+    "rgb(0, 255, 0)",
+    "The computed value is updated when the rule in ruleview is changed"
+  );
+});
+
+add_task(async function () {
+  info(
+    "Check that the computed view is not updated " +
+      "if the rule view is changed in 2 pane mode."
+  );
+  await pushPref("devtools.inspector.three-pane-enabled", false);
+
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector } = await openComputedView();
+  await selectNode("#target", inspector);
+
+  info("Select the rule view");
+  const ruleView = inspector.getPanel("ruleview").view;
+  const onRuleViewReady = ruleView.once("ruleview-refreshed");
+  const onSidebarSelect = inspector.sidebar.once("select");
+  inspector.sidebar.select("ruleview");
+  await Promise.all([onSidebarSelect, onRuleViewReady]);
+
+  info(
+    "Prepare the counter which counts how many times computed view is refreshed"
+  );
+  let computedViewRefreshCount = 0;
+  const computedViewRefreshListener = () => {
+    computedViewRefreshCount += 1;
+  };
+  inspector.on("computed-view-refreshed", computedViewRefreshListener);
+
+  info("Change the value in the rule view");
+  const editor = await getValueEditor(ruleView);
+  const onRuleViewChanged = ruleView.once("ruleview-changed");
+  editor.input.value = "rgb(0, 255, 0)";
+  EventUtils.synthesizeKey("VK_RETURN", {}, ruleView.styleWindow);
+  await onRuleViewChanged;
+
+  info(
+    "Wait for time enough to check whether the computed value is updated or not"
+  );
+  await wait(1000);
+
+  info("Check the counter");
+  is(computedViewRefreshCount, 0, "The computed view is not updated");
+
+  inspector.off("computed-view-refreshed", computedViewRefreshListener);
+});
+
+async function getValueEditor(ruleView) {
+  const ruleEditor = ruleView.element.children[0]._ruleEditor;
+  const propEditor = ruleEditor.rule.textProps[0].editor;
+  return focusEditableField(ruleView, propEditor.valueSpan);
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_refresh-on-style-change_01.js b/devtools/client/inspector/computed/test/browser_computed_refresh-on-style-change_01.js
new file mode 100644
index 0000000000..190593497b
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_refresh-on-style-change_01.js
@@ -0,0 +1,32 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the computed view refreshes when the current node has its style
+// changed.
+
+const TEST_URI = "<div id='testdiv' style='font-size:10px;'>Test div!</div>";
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("#testdiv", inspector);
+
+  let fontSize = getComputedViewPropertyValue(view, "font-size");
+  is(fontSize, "10px", "The computed view shows the right font-size");
+
+  info("Changing the node's style and waiting for the update");
+  const onUpdated = inspector.once("computed-view-refreshed");
+  await setContentPageElementAttribute(
+    "#testdiv",
+    "style",
+    "font-size: 15px; color: red;"
+  );
+  await onUpdated;
+
+  fontSize = getComputedViewPropertyValue(view, "font-size");
+  is(fontSize, "15px", "The computed view shows the updated font-size");
+  const color = getComputedViewPropertyValue(view, "color");
+  is(color, "rgb(255, 0, 0)", "The computed view also shows the color now");
+});
diff --git a/devtools/client/inspector/computed/test/browser_computed_search-filter.js b/devtools/client/inspector/computed/test/browser_computed_search-filter.js
new file mode 100644
index 0000000000..a22cdb4038
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_search-filter.js
@@ -0,0 +1,67 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the search filter works properly.
+
+const TEST_URI = `
+  <style type="text/css">
+    .matches {
+      color: #F00;
+    }
+  </style>
+  <span id="matches" class="matches">Some styled text</span>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("#matches", inspector);
+  await testToggleDefaultStyles(inspector, view);
+  await testAddTextInFilter(inspector, view);
+});
+
+async function testToggleDefaultStyles(inspector, computedView) {
+  info('checking "Browser styles" checkbox');
+  const checkbox = computedView.includeBrowserStylesCheckbox;
+  const onRefreshed = inspector.once("computed-view-refreshed");
+  checkbox.click();
+  await onRefreshed;
+}
+
+async function testAddTextInFilter(inspector, computedView) {
+  info('setting filter text to "color"');
+  const searchField = computedView.searchField;
+  const onRefreshed = inspector.once("computed-view-refreshed");
+  const win = computedView.styleWindow;
+
+  // First check to make sure that accel + F doesn't focus search if the
+  // container isn't focused
+  inspector.panelWin.focus();
+  EventUtils.synthesizeKey("f", { accelKey: true });
+  isnot(
+    inspector.panelDoc.activeElement,
+    searchField,
+    "Search field isn't focused"
+  );
+
+  computedView.element.focus();
+  EventUtils.synthesizeKey("f", { accelKey: true });
+  is(inspector.panelDoc.activeElement, searchField, "Search field is focused");
+
+  synthesizeKeys("color", win);
+  await onRefreshed;
+
+  info("check that the correct properties are visible");
+
+  const propertyViews = computedView.propertyViews;
+  propertyViews.forEach(propView => {
+    const name = propView.name;
+    is(
+      propView.visible,
+      name.indexOf("color") > -1,
+      "span " + name + " property visibility check"
+    );
+  });
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_search-filter_clear.js b/devtools/client/inspector/computed/test/browser_computed_search-filter_clear.js
new file mode 100644
index 0000000000..f77a71cc18
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_search-filter_clear.js
@@ -0,0 +1,72 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the search filter clear button works properly.
+
+const TEST_URI = `
+  <style type="text/css">
+    .matches {
+      color: #F00;
+      background-color: #00F;
+      border-color: #0F0;
+    }
+  </style>
+  <span id="matches" class="matches">Some styled text</span>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("#matches", inspector);
+  await testAddTextInFilter(inspector, view);
+  await testClearSearchFilter(inspector, view);
+});
+
+async function testAddTextInFilter(inspector, computedView) {
+  info('Setting filter text to "background-color"');
+
+  const win = computedView.styleWindow;
+  const propertyViews = computedView.propertyViews;
+  const searchField = computedView.searchField;
+
+  searchField.focus();
+  synthesizeKeys("background-color", win);
+  await inspector.once("computed-view-refreshed");
+
+  info("Check that the correct properties are visible");
+
+  propertyViews.forEach(propView => {
+    const name = propView.name;
+    is(
+      propView.visible,
+      name.indexOf("background-color") > -1,
+      "span " + name + " property visibility check"
+    );
+  });
+}
+
+async function testClearSearchFilter(inspector, computedView) {
+  info("Clearing the search filter");
+
+  const win = computedView.styleWindow;
+  const propertyViews = computedView.propertyViews;
+  const searchField = computedView.searchField;
+  const searchClearButton = computedView.searchClearButton;
+  const onRefreshed = inspector.once("computed-view-refreshed");
+
+  EventUtils.synthesizeMouseAtCenter(searchClearButton, {}, win);
+  await onRefreshed;
+
+  info("Check that the correct properties are visible");
+
+  ok(!searchField.value, "Search filter is cleared");
+  propertyViews.forEach(propView => {
+    is(
+      propView.visible,
+      propView.hasMatchedSelectors,
+      "span " + propView.name + " property visibility check"
+    );
+  });
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_search-filter_context-menu.js b/devtools/client/inspector/computed/test/browser_computed_search-filter_context-menu.js
new file mode 100644
index 0000000000..0069d644c7
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_search-filter_context-menu.js
@@ -0,0 +1,101 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests computed view search filter context menu works properly.
+
+const TEST_INPUT = "h1";
+
+const TEST_URI = "<h1>test filter context menu</h1>";
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { toolbox, inspector, view } = await openComputedView();
+  await selectNode("h1", inspector);
+
+  const searchField = view.searchField;
+
+  info("Opening context menu");
+
+  emptyClipboard();
+
+  const onFocus = once(searchField, "focus");
+  searchField.focus();
+  await onFocus;
+
+  let onContextMenuOpen = toolbox.once("menu-open");
+  synthesizeContextMenuEvent(searchField);
+  await onContextMenuOpen;
+
+  let searchContextMenu = toolbox.getTextBoxContextMenu();
+  ok(
+    searchContextMenu,
+    "The search filter context menu is loaded in the computed view"
+  );
+
+  let cmdUndo = searchContextMenu.querySelector("#editmenu-undo");
+  let cmdDelete = searchContextMenu.querySelector("#editmenu-delete");
+  let cmdSelectAll = searchContextMenu.querySelector("#editmenu-selectAll");
+  let cmdCut = searchContextMenu.querySelector("#editmenu-cut");
+  let cmdCopy = searchContextMenu.querySelector("#editmenu-copy");
+  let cmdPaste = searchContextMenu.querySelector("#editmenu-paste");
+
+  is(cmdUndo.getAttribute("disabled"), "true", "cmdUndo is disabled");
+  is(cmdDelete.getAttribute("disabled"), "true", "cmdDelete is disabled");
+  is(cmdSelectAll.getAttribute("disabled"), "true", "cmdSelectAll is disabled");
+
+  is(cmdCut.getAttribute("disabled"), "true", "cmdCut is disabled");
+  is(cmdCopy.getAttribute("disabled"), "true", "cmdCopy is disabled");
+  if (isWindows()) {
+    // emptyClipboard only works on Windows (666254), assert paste only for this OS.
+    is(cmdPaste.getAttribute("disabled"), "true", "cmdPaste is disabled");
+  }
+
+  info("Closing context menu");
+  let onContextMenuClose = toolbox.once("menu-close");
+  searchContextMenu.hidePopup();
+  await onContextMenuClose;
+
+  info("Copy text in search field using the context menu");
+  searchField.setUserInput(TEST_INPUT);
+  searchField.select();
+
+  onContextMenuOpen = toolbox.once("menu-open");
+  synthesizeContextMenuEvent(searchField);
+  await onContextMenuOpen;
+
+  searchContextMenu = toolbox.getTextBoxContextMenu();
+  cmdCopy = searchContextMenu.querySelector("#editmenu-copy");
+  onContextMenuClose = toolbox.once("menu-close");
+  await waitForClipboardPromise(
+    () => searchContextMenu.activateItem(cmdCopy),
+    TEST_INPUT
+  );
+  await onContextMenuClose;
+
+  info("Reopen context menu and check command properties");
+
+  onContextMenuOpen = toolbox.once("menu-open");
+  synthesizeContextMenuEvent(searchField);
+  await onContextMenuOpen;
+
+  searchContextMenu = toolbox.getTextBoxContextMenu();
+  cmdUndo = searchContextMenu.querySelector("#editmenu-undo");
+  cmdDelete = searchContextMenu.querySelector("#editmenu-delete");
+  cmdSelectAll = searchContextMenu.querySelector("#editmenu-selectAll");
+  cmdCut = searchContextMenu.querySelector("#editmenu-cut");
+  cmdCopy = searchContextMenu.querySelector("#editmenu-copy");
+  cmdPaste = searchContextMenu.querySelector("#editmenu-paste");
+
+  is(cmdUndo.getAttribute("disabled"), "", "cmdUndo is enabled");
+  is(cmdDelete.getAttribute("disabled"), "", "cmdDelete is enabled");
+  is(cmdSelectAll.getAttribute("disabled"), "", "cmdSelectAll is enabled");
+  is(cmdCut.getAttribute("disabled"), "", "cmdCut is enabled");
+  is(cmdCopy.getAttribute("disabled"), "", "cmdCopy is enabled");
+  is(cmdPaste.getAttribute("disabled"), "", "cmdPaste is enabled");
+
+  onContextMenuClose = toolbox.once("menu-close");
+  searchContextMenu.hidePopup();
+  await onContextMenuClose;
+});
diff --git a/devtools/client/inspector/computed/test/browser_computed_search-filter_escape-keypress.js b/devtools/client/inspector/computed/test/browser_computed_search-filter_escape-keypress.js
new file mode 100644
index 0000000000..59c71d01fe
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_search-filter_escape-keypress.js
@@ -0,0 +1,76 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Avoid test timeouts on Linux debug builds where the test takes just a bit too long to
+// run (see bug 1258081).
+requestLongerTimeout(2);
+
+// Tests that search filter escape keypress will clear the search field.
+
+const TEST_URI = `
+  <style type="text/css">
+    .matches {
+      color: #F00;
+    }
+  </style>
+  <span id="matches" class="matches">Some styled text</span>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("#matches", inspector);
+  await testAddTextInFilter(inspector, view);
+  await testEscapeKeypress(inspector, view);
+});
+
+async function testAddTextInFilter(inspector, computedView) {
+  info('Setting filter text to "background-color"');
+
+  const win = computedView.styleWindow;
+  const propertyViews = computedView.propertyViews;
+  const searchField = computedView.searchField;
+  const checkbox = computedView.includeBrowserStylesCheckbox;
+
+  info("Include browser styles");
+  checkbox.click();
+  await inspector.once("computed-view-refreshed");
+
+  searchField.focus();
+  synthesizeKeys("background-color", win);
+  await inspector.once("computed-view-refreshed");
+
+  info("Check that the correct properties are visible");
+
+  propertyViews.forEach(propView => {
+    const name = propView.name;
+    is(
+      propView.visible,
+      name.indexOf("background-color") > -1,
+      "span " + name + " property visibility check"
+    );
+  });
+}
+
+async function testEscapeKeypress(inspector, computedView) {
+  info("Pressing the escape key on search filter");
+
+  const win = computedView.styleWindow;
+  const propertyViews = computedView.propertyViews;
+  const searchField = computedView.searchField;
+  const onRefreshed = inspector.once("computed-view-refreshed");
+
+  searchField.focus();
+  EventUtils.synthesizeKey("VK_ESCAPE", {}, win);
+  await onRefreshed;
+
+  info("Check that the correct properties are visible");
+
+  ok(!searchField.value, "Search filter is cleared");
+  propertyViews.forEach(propView => {
+    const name = propView.name;
+    is(propView.visible, true, "span " + name + " property is visible");
+  });
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_search-filter_noproperties.js b/devtools/client/inspector/computed/test/browser_computed_search-filter_noproperties.js
new file mode 100644
index 0000000000..b24722e237
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_search-filter_noproperties.js
@@ -0,0 +1,68 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the "no-results" message is displayed when selecting an invalid element or
+// when all properties have been filtered out.
+
+const TEST_URI = `
+  <style type="text/css">
+    .matches {
+      color: #F00;
+      background-color: #00F;
+      border-color: #0F0;
+    }
+  </style>
+  <div>
+    <!-- comment node -->
+    <span id="matches" class="matches">Some styled text</span>
+  </div>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  const propertyViews = view.propertyViews;
+
+  info("Select the #matches node");
+  const matchesNode = await getNodeFront("#matches", inspector);
+  let onRefresh = inspector.once("computed-view-refreshed");
+  await selectNode(matchesNode, inspector);
+  await onRefresh;
+
+  ok(
+    !!propertyViews.filter(p => p.visible).length,
+    "CSS properties are displayed"
+  );
+  ok(view.noResults.hasAttribute("hidden"), "no-results message is hidden");
+
+  info("Select a comment node");
+  const commentNode = await inspector.walker.previousSibling(matchesNode);
+  await selectNode(commentNode, inspector);
+
+  is(propertyViews.filter(p => p.visible).length, 0, "No properties displayed");
+  ok(!view.noResults.hasAttribute("hidden"), "no-results message is displayed");
+
+  info("Select the #matches node again");
+  onRefresh = inspector.once("computed-view-refreshed");
+  await selectNode(matchesNode, inspector);
+  await onRefresh;
+
+  ok(
+    !!propertyViews.filter(p => p.visible).length,
+    "CSS properties are displayed"
+  );
+  ok(view.noResults.hasAttribute("hidden"), "no-results message is hidden");
+
+  info(
+    "Filter by 'will-not-match' and check the no-results message is displayed"
+  );
+  const searchField = view.searchField;
+  searchField.focus();
+  synthesizeKeys("will-not-match", view.styleWindow);
+  await inspector.once("computed-view-refreshed");
+
+  is(propertyViews.filter(p => p.visible).length, 0, "No properties displayed");
+  ok(!view.noResults.hasAttribute("hidden"), "no-results message is displayed");
+});
diff --git a/devtools/client/inspector/computed/test/browser_computed_select-and-copy-styles-01.js b/devtools/client/inspector/computed/test/browser_computed_select-and-copy-styles-01.js
new file mode 100644
index 0000000000..4c75d2885e
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_select-and-copy-styles-01.js
@@ -0,0 +1,67 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that properties can be selected and copied from the computed view.
+
+const TEST_URI = `
+  <style type="text/css">
+    span {
+      font-variant-caps: small-caps;
+      color: #000000;
+    }
+    .nomatches {
+      color: #ff0000;
+    }
+  </style>
+  <div id="first" style="margin: 10em;
+    font-size: 14pt; font-family: helvetica, sans-serif; color: #AAA">
+    <h1>Some header text</h1>
+    <p id="salutation" style="font-size: 12pt">hi.</p>
+    <p id="body" style="font-size: 12pt">I am a test-case. This text exists
+    solely to provide some things to <span style="color: yellow">
+    highlight</span> and <span style="font-weight: bold">count</span>
+    style list-items in the box at right. If you are reading this,
+    you should go do something else instead. Maybe read a book. Or better
+    yet, write some test-cases for another bit of code.
+    <span style="font-style: italic">some text</span></p>
+    <p id="closing">more text</p>
+    <p>even more text</p>
+  </div>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("span", inspector);
+
+  await testCopySome(view);
+  await testCopyAll(view);
+});
+
+async function testCopySome(view) {
+  const expectedPattern =
+    "font-family: helvetica, sans-serif;[\\r\\n]+" +
+    "font-size: 16px;[\\r\\n]+" +
+    "font-variant-caps: small-caps;[\\r\\n]*";
+
+  await copySomeTextAndCheckClipboard(
+    view,
+    {
+      start: { prop: 1, offset: 0 },
+      end: { prop: 3, offset: 3 },
+    },
+    expectedPattern
+  );
+}
+
+async function testCopyAll(view) {
+  const expectedPattern =
+    "color: rgb\\(255, 255, 0\\);[\\r\\n]+" +
+    "font-family: helvetica, sans-serif;[\\r\\n]+" +
+    "font-size: 16px;[\\r\\n]+" +
+    "font-variant-caps: small-caps;[\\r\\n]*";
+
+  await copyAllAndCheckClipboard(view, expectedPattern);
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_select-and-copy-styles-02.js b/devtools/client/inspector/computed/test/browser_computed_select-and-copy-styles-02.js
new file mode 100644
index 0000000000..87fe1d9629
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_select-and-copy-styles-02.js
@@ -0,0 +1,35 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that properties can be selected and copied from the computed view.
+
+const TEST_URI = `<div style="text-align:left;width:25px;">Hello world</div>`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view } = await openComputedView();
+  await selectNode("div", inspector);
+
+  let expectedPattern = "text-align: left;[\\r\\n]+" + "width: 25px;[\\r\\n]*";
+  await copyAllAndCheckClipboard(view, expectedPattern);
+
+  info("Testing expand then select all copy");
+
+  expectedPattern =
+    "text-align: left;[\\r\\n]+" +
+    "element[\\r\\n]+" +
+    "Best Match this.style[\\r\\n]+" +
+    "left[\\r\\n]+" +
+    "width: 25px;[\\r\\n]+" +
+    "element[\\r\\n]+" +
+    "Best Match this.style[\\r\\n]+" +
+    "25px[\\r\\n]*";
+
+  info("Expanding computed view properties");
+  await expandComputedViewPropertyByIndex(view, 0);
+  await expandComputedViewPropertyByIndex(view, 1);
+
+  await copyAllAndCheckClipboard(view, expectedPattern);
+});
diff --git a/devtools/client/inspector/computed/test/browser_computed_shadow_host.js b/devtools/client/inspector/computed/test/browser_computed_shadow_host.js
new file mode 100644
index 0000000000..19562eb1ed
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_shadow_host.js
@@ -0,0 +1,74 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const {
+  PropertyView,
+} = require("resource://devtools/client/inspector/computed/computed.js");
+
+// Test matched selectors for a :host selector in the computed view.
+
+const SHADOW_DOM = `<style>
+  :host {
+    color: red;
+  }
+
+  .test-span {
+    color: blue;
+  }
+</style>
+<span class="test-span">test</span>`;
+
+const TEST_PAGE = `
+  <div id="host"></div>
+  <script>
+    const div = document.querySelector("div");
+    div.attachShadow({ mode: "open" }).innerHTML = \`${SHADOW_DOM}\`;
+  </script>`;
+
+const TEST_URI = `https://example.com/document-builder.sjs?html=${encodeURIComponent(
+  TEST_PAGE
+)}`;
+
+add_task(async function () {
+  await addTab(TEST_URI);
+  const { inspector, view } = await openComputedView();
+
+  {
+    await selectNode("#host", inspector);
+    const propertyView = await getPropertyViewWithSelectors(view, "color");
+    const selectors = propertyView.matchedSelectors.map(s => s.selector);
+    Assert.deepEqual(
+      selectors,
+      [":host", ":root"],
+      "host has the expected selectors for color"
+    );
+  }
+
+  {
+    const nodeFront = await getNodeFrontInShadowDom(
+      ".test-span",
+      "#host",
+      inspector
+    );
+    await selectNode(nodeFront, inspector);
+    const propertyView = await getPropertyViewWithSelectors(view, "color");
+    const selectors = propertyView.matchedSelectors.map(s => s.selector);
+    Assert.deepEqual(
+      selectors,
+      [".test-span", ":host", ":root"],
+      "shadow host child has the expected selectors for color"
+    );
+  }
+});
+
+async function getPropertyViewWithSelectors(view, property) {
+  const propertyView = new PropertyView(view, property);
+  propertyView.createListItemElement();
+  propertyView.matchedExpanded = true;
+
+  await propertyView.refreshMatchedSelectors();
+
+  return propertyView;
+}
diff --git a/devtools/client/inspector/computed/test/browser_computed_style-editor-link.js b/devtools/client/inspector/computed/test/browser_computed_style-editor-link.js
new file mode 100644
index 0000000000..832c1658a5
--- /dev/null
+++ b/devtools/client/inspector/computed/test/browser_computed_style-editor-link.js
@@ -0,0 +1,210 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests the links from the computed view to the style editor.
+
+const STYLESHEET_URL =
+  "data:text/css," + encodeURIComponent(".highlight {color: blue}");
+
+const DOCUMENT_URL =
+  "data:text/html;charset=utf-8," +
+  encodeURIComponent(
+    `<html>
+   <head>
+   <title>Computed view style editor link test</title>
+   <style type="text/css">
+   html { color: #000000; }
+   span { font-variant: small-caps; color: #000000; }
+   .nomatches {color: #ff0000;}</style> <div id="first" style="margin: 10em;
+   font-size: 14pt; font-family: helvetica, sans-serif; color: #AAA">
+   </style>
+   <style>
+   div { color: #f06; }
+   </style>
+   <link rel="stylesheet" type="text/css" href="${STYLESHEET_URL}">
+   <script>
+     const sheet = new CSSStyleSheet();
+     sheet.replaceSync(".highlight { color: tomato; }");
+     document.adoptedStyleSheets.push(sheet);
+   </script>
+   </head>
+   <body>
+   <h1>Some header text</h1>
+   <p id="salutation" style="font-size: 12pt">hi.</p>
+   <p id="body" style="font-size: 12pt">I am a test-case. This text exists
+   solely to provide some things to
+   <span style="color: yellow" class="highlight">
+   highlight</span> and <span style="font-weight: bold">count</span>
+   style list-items in the box at right. If you are reading this,
+   you should go do something else instead. Maybe read a book. Or better
+   yet, write some test-cases for another bit of code.
+   <span style="font-style: italic">some text</span></p>
+   <p id="closing">more text</p>
+   <p>even more text</p>
+   </div>
+   </body>
+   </html>`
+  );
+
+add_task(async function () {
+  await addTab(DOCUMENT_URL);
+  const { toolbox, inspector, view } = await openComputedView();
+  await selectNode("span", inspector);
+
+  await testInlineStyle(view);
+  await testFirstInlineStyleSheet(view, toolbox);
+  await testSecondInlineStyleSheet(view, toolbox);
+  await testExternalStyleSheet(view, toolbox);
+  await testConstructedStyleSheet(view, toolbox);
+});
+
+async function testInlineStyle(view) {
+  info("Testing inline style");
+
+  await expandComputedViewPropertyByIndex(view, 0);
+
+  const onTab = waitForTab();
+  info("Clicking on the first rule-link in the computed-view");
+  checkComputedViewLink(view, {
+    index: 0,
+    expectedText: "element",
+    expectedTitle: "element",
+  });
+
+  const tab = await onTab;
+
+  const tabURI = tab.linkedBrowser.documentURI.spec;
+  ok(tabURI.startsWith("view-source:"), "View source tab is open");
+  info("Closing tab");
+  gBrowser.removeTab(tab);
+}
+
+async function testFirstInlineStyleSheet(view, toolbox) {
+  info("Testing inline stylesheet");
+
+  info("Listening for toolbox switch to the styleeditor");
+  const onSwitch = waitForStyleEditor(toolbox);
+
+  info("Clicking an inline stylesheet");
+  checkComputedViewLink(view, {
+    index: 3,
+    expectedText: "inline:3",
+    expectedTitle: "inline:3",
+  });
+  const editor = await onSwitch;
+
+  ok(true, "Switched to the style-editor panel in the toolbox");
+
+  await validateStyleEditorSheet(editor, 0);
+}
+
+async function testSecondInlineStyleSheet(view, toolbox) {
+  info("Testing second inline stylesheet");
+
+  const panel = toolbox.getCurrentPanel();
+  const onSelected = panel.UI.once("editor-selected");
+
+  info("Switching back to the inspector panel in the toolbox");
+  await toolbox.selectTool("inspector");
+
+  info("Clicking on second inline stylesheet link");
+  checkComputedViewLink(view, {
+    index: 5,
+    expectedText: "inline:2",
+    expectedTitle: "inline:2",
+  });
+
+  info("Waiting for an editor to be selected in StyleEditor");
+  const editor = await onSelected;
+
+  is(
+    toolbox.currentToolId,
+    "styleeditor",
+    "The style editor is selected again"
+  );
+  await validateStyleEditorSheet(editor, 1);
+}
+
+async function testExternalStyleSheet(view, toolbox) {
+  info("Testing external stylesheet");
+
+  const panel = toolbox.getCurrentPanel();
+  const onSelected = panel.UI.once("editor-selected");
+
+  info("Switching back to the inspector panel in the toolbox");
+  await toolbox.selectTool("inspector");
+
+  info("Clicking on an external stylesheet link");
+  checkComputedViewLink(view, {
+    index: 2,
+    expectedText: `${STYLESHEET_URL.replace("data:text/css,", "")}:1`,
+    expectedTitle: `${STYLESHEET_URL}:1`,
+  });
+
+  info("Waiting for an editor to be selected in StyleEditor");
+  const editor = await onSelected;
+
+  is(
+    toolbox.currentToolId,
+    "styleeditor",
+    "The style editor is selected again"
+  );
+  await validateStyleEditorSheet(editor, 2);
+}
+
+async function testConstructedStyleSheet(view, toolbox) {
+  info("Testing constructed stylesheet");
+
+  const panel = toolbox.getCurrentPanel();
+  const onSelected = panel.UI.once("editor-selected");
+
+  info("Switching back to the inspector panel in the toolbox");
+  await toolbox.selectTool("inspector");
+
+  info("Clicking on an constructed stylesheet link");
+
+  checkComputedViewLink(view, {
+    index: 1,
+    expectedText: "constructed",
+    expectedTitle: "constructed",
+  });
+
+  info("Waiting for an editor to be selected in StyleEditor");
+  const editor = await onSelected;
+
+  is(
+    toolbox.currentToolId,
+    "styleeditor",
+    "The style editor is selected again"
+  );
+  ok(editor.styleSheet.constructed, "The constructed stylesheet is selected");
+}
+
+async function validateStyleEditorSheet(editor, expectedSheetIndex) {
+  info("Validating style editor stylesheet");
+  const expectedHref = await SpecialPowers.spawn(
+    gBrowser.selectedBrowser,
+    [expectedSheetIndex],
+    _expectedSheetIndex =>
+      content.document.styleSheets[_expectedSheetIndex].href
+  );
+  is(
+    editor.styleSheet.href,
+    expectedHref,
+    "loaded stylesheet matches document stylesheet"
+  );
+}
+
+function checkComputedViewLink(view, { index, expectedText, expectedTitle }) {
+  const link = getComputedViewLinkByIndex(view, index);
+  is(link.innerText, expectedText, `Link #${index} has expected label`);
+  is(
+    link.getAttribute("title"),
+    expectedTitle,
+    `Link #${index} has expected title attribute`
+  );
+  link.scrollIntoView();
+  link.click();
+}
diff --git a/devtools/client/inspector/computed/test/doc_matched_selectors.html b/devtools/client/inspector/computed/test/doc_matched_selectors.html
new file mode 100644
index 0000000000..41abe48826
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_matched_selectors.html
@@ -0,0 +1,54 @@
+<!-- Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf8">
+    <style>
+      @import url(./doc_matched_selectors_imported_1.css) layer(importedFirst);
+      @import url(./doc_matched_selectors_imported_2.css) layer(importedSecond);
+      @import url(./doc_matched_selectors_imported_3.css) layer(importedFirst);
+      @import url(./doc_matched_selectors_imported_4.css) layer;
+      @import url(./doc_matched_selectors_imported_5.css) layer;
+
+      @layer first, second;
+
+      .matched1, .matched2, .matched3, .matched4, .matched5 {
+        color: #000;
+      }
+
+      div {
+        position: absolute;
+        top: 40px;
+        left: 20px;
+        border: 1px solid #000;
+        color: #111;
+        width: 100px;
+        height: 50px;
+      }
+
+      main {
+        /*
+         * Set "winning" custom properties values to "blue" so we can check in the
+         * test that the best matching rule/property is actually what is applied by
+         * the engine.
+         */
+        --winning-color: blue;
+      }
+
+      section {
+        min-width: 10px;
+        min-height: 10px;
+        display: inline-block;
+      }
+      </style>
+  </head>
+  <body>
+    inspectstyle($("test"));
+    <div id="test" class="matched1 matched2 matched3 matched4 matched5">Test div</div>
+    <div id="dummy">
+      <div></div>
+    </div>
+    <main></main>
+  </body>
+</html>
diff --git a/devtools/client/inspector/computed/test/doc_matched_selectors_imported_1.css b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_1.css
new file mode 100644
index 0000000000..3eca2e8086
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_1.css
@@ -0,0 +1,7 @@
+#imported-layers {
+  background-color: var(--imported-layers_in-importedFirst-first);
+}
+
+#all-important-imported-layers {
+  background-color: var(--all-important-imported-layers_in-importedFirst-first-important) !important;
+}
diff --git a/devtools/client/inspector/computed/test/doc_matched_selectors_imported_2.css b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_2.css
new file mode 100644
index 0000000000..035d9e0ff5
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_2.css
@@ -0,0 +1,7 @@
+#imported-layers {
+  background-color: var(--imported-layers_in-importedSecond);
+}
+
+#all-important-imported-layers {
+  background-color: var(--all-important-imported-layers_in-importedSecond-important) !important;
+}
diff --git a/devtools/client/inspector/computed/test/doc_matched_selectors_imported_3.css b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_3.css
new file mode 100644
index 0000000000..1139d7e107
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_3.css
@@ -0,0 +1,8 @@
+#imported-layers {
+  background-color: var(--imported-layers_in-importedFirst-second);
+}
+
+#all-important-imported-layers {
+  --all-important-imported-layers_in-importedFirst-second-important: var(--winning-color);
+  background-color: var(--all-important-imported-layers_in-importedFirst-second-important) !important;
+}
diff --git a/devtools/client/inspector/computed/test/doc_matched_selectors_imported_4.css b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_4.css
new file mode 100644
index 0000000000..abee8206b6
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_4.css
@@ -0,0 +1,7 @@
+#imported-layers {
+  background-color: var(--imported-layers_in-anonymous-first);
+}
+
+#all-important-imported-layers {
+  background-color: var(--all-important-imported-layers_in-anonymous-first-important) !important;
+}
diff --git a/devtools/client/inspector/computed/test/doc_matched_selectors_imported_5.css b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_5.css
new file mode 100644
index 0000000000..26fb567293
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_5.css
@@ -0,0 +1,10 @@
+@import url(./doc_matched_selectors_imported_6.css) layer(importedSecond);
+
+#imported-layers {
+  --imported-layers_in-anonymous-second: var(--winning-color);
+  background-color: var(--imported-layers_in-anonymous-second);
+}
+
+#all-important-imported-layers {
+  background-color: var(--all-important-imported-layers_in-anonymous-second-important) !important;
+}
diff --git a/devtools/client/inspector/computed/test/doc_matched_selectors_imported_6.css b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_6.css
new file mode 100644
index 0000000000..63b1cf0dc9
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_matched_selectors_imported_6.css
@@ -0,0 +1,7 @@
+#imported-layers {
+  background-color: var(--imported-layers_in-nested-importedSecond);
+}
+
+#all-important-imported-layers {
+  background-color: var(--all-important-imported-layers_in-nested-importedSecond-important) !important;
+}
diff --git a/devtools/client/inspector/computed/test/doc_media_queries.html b/devtools/client/inspector/computed/test/doc_media_queries.html
new file mode 100644
index 0000000000..819e1ea7aa
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_media_queries.html
@@ -0,0 +1,21 @@
+<html>
+<head>
+  <title>test</title>
+  <style>
+    div {
+      width: 1000px;
+      height: 100px;
+      background-color: #f00;
+    }
+
+    @media screen and (min-width: 1px) {
+      div {
+        width: 200px;
+      }
+    }
+  </style>
+</head>
+<body>
+<div></div>
+</body>
+</html>
diff --git a/devtools/client/inspector/computed/test/doc_pseudoelement.html b/devtools/client/inspector/computed/test/doc_pseudoelement.html
new file mode 100644
index 0000000000..6145d4bf1b
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_pseudoelement.html
@@ -0,0 +1,131 @@
+<!-- Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/ -->
+<html>
+  <head>
+    <style>
+
+body {
+    color: #333;
+}
+
+.box {
+    float:left;
+    width: 128px;
+    height: 128px;
+    background: #ddd;
+    padding: 32px;
+    margin: 32px;
+    position:relative;
+}
+
+.box:first-line {
+    color: orange;
+    background: red;
+}
+
+.box:first-letter {
+    color: green;
+}
+
+* {
+    cursor: default;
+}
+
+nothing {
+    cursor: pointer;
+}
+
+p::-moz-selection {
+    color: white;
+    background: black;
+}
+p::selection {
+    color: white;
+    background: black;
+}
+
+p:first-line {
+   background: blue;
+}
+p:first-letter {
+  color: red;
+  font-size: 130%;
+}
+
+.box:before {
+    background: green;
+    content: " ";
+    position: absolute;
+    height:32px;
+    width:32px;
+}
+
+.box:after {
+    background: red;
+    content: " ";
+    position: absolute;
+    border-radius: 50%;
+    height:32px;
+    width:32px;
+    top: 50%;
+    left: 50%;
+    margin-top: -16px;
+    margin-left: -16px;
+}
+
+.topleft:before {
+    top:0;
+    left:0;
+}
+
+.topleft:first-line {
+    color: orange;
+}
+.topleft::selection {
+    color: orange;
+}
+
+.topright:before {
+    top:0;
+    right:0;
+}
+
+.bottomright:before {
+    bottom:10px;
+    right:10px;
+    color: red;
+}
+
+.bottomright:before {
+    bottom:0;
+    right:0;
+}
+
+.bottomleft:before {
+    bottom:0;
+    left:0;
+}
+
+    </style>
+  </head>
+  <body>
+    <h1>ruleview pseudoelement($("test"));</h1>
+
+    <div id="topleft" class="box topleft">
+        <p>Top Left<br />Position</p>
+    </div>
+
+    <div id="topright" class="box topright">
+        <p>Top Right<br />Position</p>
+    </div>
+
+    <div id="bottomright" class="box bottomright">
+        <p>Bottom Right<br />Position</p>
+    </div>
+
+    <div id="bottomleft" class="box bottomleft">
+        <p>Bottom Left<br />Position</p>
+    </div>
+
+  </body>
+</html>
diff --git a/devtools/client/inspector/computed/test/doc_sourcemaps.css b/devtools/client/inspector/computed/test/doc_sourcemaps.css
new file mode 100644
index 0000000000..f62fbda21e
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_sourcemaps.css
@@ -0,0 +1,7 @@
+div {
+  color: #ff0066; }
+
+span {
+  background-color: #EEE; }
+
+/*# sourceMappingURL=doc_sourcemaps.css.map */
diff --git a/devtools/client/inspector/computed/test/doc_sourcemaps.css.map b/devtools/client/inspector/computed/test/doc_sourcemaps.css.map
new file mode 100644
index 0000000000..0f7486fd91
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_sourcemaps.css.map
@@ -0,0 +1,7 @@
+{
+"version": 3,
+"mappings": "AAGA,GAAI;EACF,KAAK,EAHU,OAAI;;AAMrB,IAAK;EACH,gBAAgB,EAAE,IAAI",
+"sources": ["doc_sourcemaps.scss"],
+"names": [],
+"file": "doc_sourcemaps.css"
+}
diff --git a/devtools/client/inspector/computed/test/doc_sourcemaps.html b/devtools/client/inspector/computed/test/doc_sourcemaps.html
new file mode 100644
index 0000000000..0014e55fe9
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_sourcemaps.html
@@ -0,0 +1,11 @@
+<!doctype html>
+<html>
+<head>
+  <title>testcase for testing CSS source maps</title>
+  <link rel="stylesheet" type="text/css" href="simple.css"/>
+  <link rel="stylesheet" type="text/css" href="doc_sourcemaps.css"/>
+</head>
+<body>
+	<div>source maps <span>testcase</span></div>
+</body>
+</html>
diff --git a/devtools/client/inspector/computed/test/doc_sourcemaps.scss b/devtools/client/inspector/computed/test/doc_sourcemaps.scss
new file mode 100644
index 0000000000..0ff6c471bb
--- /dev/null
+++ b/devtools/client/inspector/computed/test/doc_sourcemaps.scss
@@ -0,0 +1,10 @@
+
+$paulrougetpink: #f06;
+
+div {
+  color: $paulrougetpink;
+}
+
+span {
+  background-color: #EEE;
+}
\ No newline at end of file
diff --git a/devtools/client/inspector/computed/test/head.js b/devtools/client/inspector/computed/test/head.js
new file mode 100644
index 0000000000..dfa1f87e9c
--- /dev/null
+++ b/devtools/client/inspector/computed/test/head.js
@@ -0,0 +1,279 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+/* eslint no-unused-vars: [2, {"vars": "local"}] */
+
+"use strict";
+
+// Import the inspector's head.js first (which itself imports shared-head.js).
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/devtools/client/inspector/test/head.js",
+  this
+);
+
+registerCleanupFunction(() => {
+  Services.prefs.clearUserPref("devtools.defaultColorUnit");
+});
+
+/**
+ * Dispatch the copy event on the given element
+ */
+function fireCopyEvent(element) {
+  const evt = element.ownerDocument.createEvent("Event");
+  evt.initEvent("copy", true, true);
+  element.dispatchEvent(evt);
+}
+
+/**
+ * Return all the computed items in the computed view
+ *
+ * @param {CssComputedView} view
+ *        The instance of the computed view panel
+ * @returns {Array<Element>}
+ */
+function getComputedViewProperties(view) {
+  return Array.from(
+    view.styleDocument.querySelectorAll(
+      "#computed-container .computed-property-view"
+    )
+  );
+}
+
+/**
+ * Get references to the name and value span nodes corresponding to a given
+ * property name in the computed-view
+ *
+ * @param {CssComputedView} view
+ *        The instance of the computed view panel
+ * @param {String} name
+ *        The name of the property to retrieve
+ * @return an object {nameSpan, valueSpan}
+ */
+function getComputedViewProperty(view, name) {
+  let prop;
+  for (const property of getComputedViewProperties(view)) {
+    const nameSpan = property.querySelector(".computed-property-name");
+    const valueSpan = property.querySelector(".computed-property-value");
+
+    if (nameSpan.firstChild.textContent === name) {
+      prop = { nameSpan, valueSpan };
+      break;
+    }
+  }
+  return prop;
+}
+
+/**
+ * Get an instance of PropertyView from the computed-view.
+ *
+ * @param {CssComputedView} view
+ *        The instance of the computed view panel
+ * @param {String} name
+ *        The name of the property to retrieve
+ * @return {PropertyView}
+ */
+function getComputedViewPropertyView(view, name) {
+  let propView;
+  for (const propertyView of view.propertyViews) {
+    if (propertyView.propertyInfo.name === name) {
+      propView = propertyView;
+      break;
+    }
+  }
+  return propView;
+}
+
+/**
+ * Get a reference to the matched rules element for a given property name in
+ * the computed-view.
+ * A matched rule element is inside the property element (<li>) itself
+ * and is only shown when the twisty icon is expanded on the property.
+ * It contains matched rules, with selectors, properties, values and stylesheet links.
+ *
+ * @param {CssComputedView} view
+ *        The instance of the computed view panel
+ * @param {String} name
+ *        The name of the property to retrieve
+ * @return {Promise} A promise that resolves to the property matched rules
+ * container
+ */
+var getComputedViewMatchedRules = async function (view, name) {
+  let expander;
+  let matchedRulesEl;
+  for (const property of view.styleDocument.querySelectorAll(
+    "#computed-container .computed-property-view"
+  )) {
+    const nameSpan = property.querySelector(".computed-property-name");
+    if (nameSpan.firstChild.textContent === name) {
+      expander = property.querySelector(".computed-expandable");
+      matchedRulesEl = property.querySelector(".matchedselectors");
+
+      break;
+    }
+  }
+
+  if (!expander.hasAttribute("open")) {
+    // Need to expand the property
+    const onExpand = view.inspector.once("computed-view-property-expanded");
+    expander.click();
+    await onExpand;
+
+    await waitFor(() => expander.hasAttribute("open"));
+  }
+
+  return matchedRulesEl;
+};
+
+/**
+ * Get the text value of the property corresponding to a given name in the
+ * computed-view
+ *
+ * @param {CssComputedView} view
+ *        The instance of the computed view panel
+ * @param {String} name
+ *        The name of the property to retrieve
+ * @return {String} The property value
+ */
+function getComputedViewPropertyValue(view, name) {
+  return getComputedViewProperty(view, name).valueSpan.textContent;
+}
+
+/**
+ * Expand a given property, given its index in the current property list of
+ * the computed view
+ *
+ * @param {CssComputedView} view
+ *        The instance of the computed view panel
+ * @param {Number} index
+ *        The index of the property to be expanded
+ * @return a promise that resolves when the property has been expanded, or
+ * rejects if the property was not found
+ */
+function expandComputedViewPropertyByIndex(view, index) {
+  info("Expanding property " + index + " in the computed view");
+  const expandos = view.styleDocument.querySelectorAll(".computed-expandable");
+  if (!expandos.length || !expandos[index]) {
+    return Promise.reject();
+  }
+
+  const onExpand = view.inspector.once("computed-view-property-expanded");
+  expandos[index].click();
+  return onExpand;
+}
+
+/**
+ * Get a rule-link from the computed-view given its index
+ *
+ * @param {CssComputedView} view
+ *        The instance of the computed view panel
+ * @param {Number} index
+ *        The index of the link to be retrieved
+ * @return {DOMNode} The link at the given index, if one exists, null otherwise
+ */
+function getComputedViewLinkByIndex(view, index) {
+  const links = view.styleDocument.querySelectorAll(
+    ".rule-link .computed-link"
+  );
+  return links[index];
+}
+
+/**
+ * Trigger the select all action in the computed view.
+ *
+ * @param {CssComputedView} view
+ *        The instance of the computed view panel
+ */
+function selectAllText(view) {
+  info("Selecting all the text");
+  view.contextMenu._onSelectAll();
+}
+
+/**
+ * Select all the text, copy it, and check the content in the clipboard.
+ *
+ * @param {CssComputedView} view
+ *        The instance of the computed view panel
+ * @param {String} expectedPattern
+ *        A regular expression used to check the content of the clipboard
+ */
+async function copyAllAndCheckClipboard(view, expectedPattern) {
+  selectAllText(view);
+  const contentDoc = view.styleDocument;
+  const prop = contentDoc.querySelector(
+    "#computed-container .computed-property-view"
+  );
+
+  try {
+    info("Trigger a copy event and wait for the clipboard content");
+    await waitForClipboardPromise(
+      () => fireCopyEvent(prop),
+      () => checkClipboard(expectedPattern)
+    );
+  } catch (e) {
+    failClipboardCheck(expectedPattern);
+  }
+}
+
+/**
+ * Select some text, copy it, and check the content in the clipboard.
+ *
+ * @param {CssComputedView} view
+ *        The instance of the computed view panel
+ * @param {Object} positions
+ *        The start and end positions of the text to be selected. This must be an object
+ *        like this:
+ *        { start: {prop: 1, offset: 0}, end: {prop: 3, offset: 5} }
+ * @param {String} expectedPattern
+ *        A regular expression used to check the content of the clipboard
+ */
+async function copySomeTextAndCheckClipboard(view, positions, expectedPattern) {
+  info("Testing selection copy");
+
+  const contentDocument = view.styleDocument;
+  const props = contentDocument.querySelectorAll(
+    "#computed-container .computed-property-view"
+  );
+
+  info("Create the text selection range");
+  const range = contentDocument.createRange();
+  range.setStart(props[positions.start.prop], positions.start.offset);
+  range.setEnd(props[positions.end.prop], positions.end.offset);
+  contentDocument.defaultView.getSelection().addRange(range);
+
+  try {
+    info("Trigger a copy event and wait for the clipboard content");
+    await waitForClipboardPromise(
+      () => fireCopyEvent(props[0]),
+      () => checkClipboard(expectedPattern)
+    );
+  } catch (e) {
+    failClipboardCheck(expectedPattern);
+  }
+}
+
+function checkClipboard(expectedPattern) {
+  const actual = SpecialPowers.getClipboardData("text/plain");
+  const expectedRegExp = new RegExp(expectedPattern, "g");
+  return expectedRegExp.test(actual);
+}
+
+function failClipboardCheck(expectedPattern) {
+  // Format expected text for comparison
+  const terminator = Services.appinfo.OS == "WINNT" ? "\r\n" : "\n";
+  expectedPattern = expectedPattern.replace(/\[\\r\\n\][+*]/g, terminator);
+  expectedPattern = expectedPattern.replace(/\\\(/g, "(");
+  expectedPattern = expectedPattern.replace(/\\\)/g, ")");
+
+  let actual = SpecialPowers.getClipboardData("text/plain");
+
+  // Trim the right hand side of our strings. This is because expectedPattern
+  // accounts for windows sometimes adding a newline to our copied data.
+  expectedPattern = expectedPattern.trimRight();
+  actual = actual.trimRight();
+
+  dump(
+    "TEST-UNEXPECTED-FAIL | Clipboard text does not match expected ... " +
+      "results (escaped for accurate comparison):\n"
+  );
+  info("Actual: " + escape(actual));
+  info("Expected: " + escape(expectedPattern));
+}