Adding upstream version 124.0.1.upstream/124.0.1

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

154 files changed, 16010 insertions, 0 deletions

diff --git a/devtools/client/responsive/actions/devices.js b/devtools/client/responsive/actions/devices.js
new file mode 100644
index 0000000000..b3f2bab982
--- /dev/null
+++ b/devtools/client/responsive/actions/devices.js
@@ -0,0 +1,254 @@
+/* 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 asyncStorage = require("resource://devtools/shared/async-storage.js");
+
+const {
+  ADD_DEVICE,
+  ADD_DEVICE_TYPE,
+  EDIT_DEVICE,
+  LOAD_DEVICE_LIST_START,
+  LOAD_DEVICE_LIST_ERROR,
+  LOAD_DEVICE_LIST_END,
+  REMOVE_DEVICE,
+  UPDATE_DEVICE_DISPLAYED,
+  UPDATE_DEVICE_MODAL,
+} = require("resource://devtools/client/responsive/actions/index.js");
+const {
+  post,
+} = require("resource://devtools/client/responsive/utils/message.js");
+
+const {
+  addDevice,
+  editDevice,
+  getDevices,
+  removeDevice,
+} = require("resource://devtools/client/shared/devices.js");
+const {
+  changeUserAgent,
+  toggleTouchSimulation,
+} = require("resource://devtools/client/responsive/actions/ui.js");
+const {
+  changeDevice,
+  changePixelRatio,
+  changeViewportAngle,
+} = require("resource://devtools/client/responsive/actions/viewports.js");
+
+const DISPLAYED_DEVICES_PREF = "devtools.responsive.html.displayedDeviceList";
+
+/**
+ * Returns an object containing the user preference of displayed devices.
+ *
+ * @return {Object} containing two Sets:
+ * - added: Names of the devices that were explicitly enabled by the user
+ * - removed: Names of the devices that were explicitly removed by the user
+ */
+function loadPreferredDevices() {
+  const preferredDevices = {
+    added: new Set(),
+    removed: new Set(),
+  };
+
+  if (Services.prefs.prefHasUserValue(DISPLAYED_DEVICES_PREF)) {
+    try {
+      let savedData = Services.prefs.getStringPref(DISPLAYED_DEVICES_PREF);
+      savedData = JSON.parse(savedData);
+      if (savedData.added && savedData.removed) {
+        preferredDevices.added = new Set(savedData.added);
+        preferredDevices.removed = new Set(savedData.removed);
+      }
+    } catch (e) {
+      console.error(e);
+    }
+  }
+
+  return preferredDevices;
+}
+
+/**
+ * Update the displayed device list preference with the given device list.
+ *
+ * @param {Object} containing two Sets:
+ * - added: Names of the devices that were explicitly enabled by the user
+ * - removed: Names of the devices that were explicitly removed by the user
+ */
+function updatePreferredDevices(devices) {
+  let devicesToSave = {
+    added: Array.from(devices.added),
+    removed: Array.from(devices.removed),
+  };
+  devicesToSave = JSON.stringify(devicesToSave);
+  Services.prefs.setStringPref(DISPLAYED_DEVICES_PREF, devicesToSave);
+}
+
+module.exports = {
+  // This function is only exported for testing purposes
+  _loadPreferredDevices: loadPreferredDevices,
+
+  updatePreferredDevices,
+
+  addCustomDevice(device) {
+    return async function ({ dispatch }) {
+      // Add custom device to device storage
+      await addDevice(device, "custom");
+      dispatch({
+        type: ADD_DEVICE,
+        device,
+        deviceType: "custom",
+      });
+    };
+  },
+
+  addDevice(device, deviceType) {
+    return {
+      type: ADD_DEVICE,
+      device,
+      deviceType,
+    };
+  },
+
+  addDeviceType(deviceType) {
+    return {
+      type: ADD_DEVICE_TYPE,
+      deviceType,
+    };
+  },
+
+  editCustomDevice(viewport, oldDevice, newDevice) {
+    return async function ({ dispatch }) {
+      // Edit custom device in storage
+      await editDevice(oldDevice, newDevice, "custom");
+      // Notify the window that the device should be updated in the device selector.
+      post(window, {
+        type: "change-device",
+        device: newDevice,
+        viewport,
+      });
+
+      // Update UI if the device is selected.
+      if (viewport) {
+        dispatch(changeUserAgent(newDevice.userAgent));
+        dispatch(toggleTouchSimulation(newDevice.touch));
+      }
+
+      dispatch({
+        type: EDIT_DEVICE,
+        deviceType: "custom",
+        viewport,
+        oldDevice,
+        newDevice,
+      });
+    };
+  },
+
+  removeCustomDevice(device) {
+    return async function ({ dispatch }) {
+      // Remove custom device from device storage
+      await removeDevice(device, "custom");
+      dispatch({
+        type: REMOVE_DEVICE,
+        device,
+        deviceType: "custom",
+      });
+    };
+  },
+
+  updateDeviceDisplayed(device, deviceType, displayed) {
+    return {
+      type: UPDATE_DEVICE_DISPLAYED,
+      device,
+      deviceType,
+      displayed,
+    };
+  },
+
+  loadDevices() {
+    return async function ({ dispatch }) {
+      dispatch({ type: LOAD_DEVICE_LIST_START });
+      const preferredDevices = loadPreferredDevices();
+      let deviceByTypes;
+
+      try {
+        deviceByTypes = await getDevices();
+      } catch (e) {
+        console.error("Could not load device list: " + e);
+        dispatch({ type: LOAD_DEVICE_LIST_ERROR });
+        return;
+      }
+
+      for (const [type, devices] of deviceByTypes.entries()) {
+        dispatch(module.exports.addDeviceType(type));
+        for (const device of devices) {
+          if (device.os == "fxos") {
+            continue;
+          }
+
+          const newDevice = Object.assign({}, device, {
+            displayed:
+              preferredDevices.added.has(device.name) ||
+              (device.featured && !preferredDevices.removed.has(device.name)),
+          });
+
+          dispatch(module.exports.addDevice(newDevice, type));
+        }
+      }
+
+      // Add an empty "custom" type if it doesn't exist in device storage
+      if (!deviceByTypes.has("custom")) {
+        dispatch(module.exports.addDeviceType("custom"));
+      }
+
+      dispatch({ type: LOAD_DEVICE_LIST_END });
+    };
+  },
+
+  restoreDeviceState() {
+    return async function ({ dispatch, getState }) {
+      const deviceState = await asyncStorage.getItem(
+        "devtools.responsive.deviceState"
+      );
+      if (!deviceState) {
+        return;
+      }
+
+      const { id, device: deviceName, deviceType } = deviceState;
+      const devices = getState().devices;
+
+      if (!devices.types.includes(deviceType)) {
+        // Can't find matching device type.
+        return;
+      }
+
+      const device = devices[deviceType].find(d => d.name === deviceName);
+      if (!device) {
+        // Can't find device with the same device name.
+        return;
+      }
+
+      const viewport = getState().viewports[0];
+
+      post(window, {
+        type: "change-device",
+        device,
+        viewport,
+      });
+
+      dispatch(changeDevice(id, device.name, deviceType));
+      dispatch(changeViewportAngle(id, viewport.angle));
+      dispatch(changePixelRatio(id, device.pixelRatio));
+      dispatch(changeUserAgent(device.userAgent));
+      dispatch(toggleTouchSimulation(device.touch));
+    };
+  },
+
+  updateDeviceModal(isOpen, modalOpenedFromViewport = null) {
+    return {
+      type: UPDATE_DEVICE_MODAL,
+      isOpen,
+      modalOpenedFromViewport,
+    };
+  },
+};
diff --git a/devtools/client/responsive/actions/index.js b/devtools/client/responsive/actions/index.js
new file mode 100644
index 0000000000..7d42c06053
--- /dev/null
+++ b/devtools/client/responsive/actions/index.js
@@ -0,0 +1,109 @@
+/* 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";
+
+// This file lists all of the actions available in responsive design. This
+// central list of constants makes it easy to see all possible action names at
+// a glance. Please add a comment with each new action type.
+
+const { createEnum } = require("resource://devtools/client/shared/enum.js");
+
+const {
+  CHANGE_NETWORK_THROTTLING,
+} = require("resource://devtools/client/shared/components/throttling/actions.js");
+
+createEnum(
+  [
+    // Add a new device.
+    "ADD_DEVICE",
+
+    // Add a new device type.
+    "ADD_DEVICE_TYPE",
+
+    // Add an additional viewport to display the document.
+    "ADD_VIEWPORT",
+
+    // Change the device displayed in the viewport.
+    "CHANGE_DEVICE",
+
+    // Change the location of the page. This may be triggered by the user
+    // directly entering a new URL, navigating with links, etc.
+    "CHANGE_LOCATION",
+
+    // The pixel ratio of the display has changed. This may be triggered by the user
+    // when changing the monitor resolution, or when the window is dragged to a different
+    // display with a different pixel ratio.
+    "CHANGE_DISPLAY_PIXEL_RATIO",
+
+    // Change the network throttling profile.
+    CHANGE_NETWORK_THROTTLING,
+
+    // Change the user agent of the viewport.
+    "CHANGE_USER_AGENT",
+
+    // The pixel ratio of the viewport has changed. This may be triggered by the user
+    // when changing the device displayed in the viewport, or when a pixel ratio is
+    // selected from the device pixel ratio dropdown.
+    "CHANGE_PIXEL_RATIO",
+
+    // Change the viewport angle.
+    "CHANGE_VIEWPORT_ANGLE",
+
+    // Edit a device.
+    "EDIT_DEVICE",
+
+    // Indicates that the device list is being loaded.
+    "LOAD_DEVICE_LIST_START",
+
+    // Indicates that the device list loading action threw an error.
+    "LOAD_DEVICE_LIST_ERROR",
+
+    // Indicates that the device list has been loaded successfully.
+    "LOAD_DEVICE_LIST_END",
+
+    // Remove a device.
+    "REMOVE_DEVICE",
+
+    // Remove the viewport's device assocation.
+    "REMOVE_DEVICE_ASSOCIATION",
+
+    // Resize the viewport.
+    "RESIZE_VIEWPORT",
+
+    // Rotate the viewport.
+    "ROTATE_VIEWPORT",
+
+    // Take a screenshot of the viewport.
+    "TAKE_SCREENSHOT_START",
+
+    // Indicates when the screenshot action ends.
+    "TAKE_SCREENSHOT_END",
+
+    // Toggles the left alignment of the viewports.
+    "TOGGLE_LEFT_ALIGNMENT",
+
+    // Toggles the reload on touch simulation changes.
+    "TOGGLE_RELOAD_ON_TOUCH_SIMULATION",
+
+    // Toggles the reload on user agent changes.
+    "TOGGLE_RELOAD_ON_USER_AGENT",
+
+    // Toggles the touch simulation state of the viewports.
+    "TOGGLE_TOUCH_SIMULATION",
+
+    // Toggles the user agent input displayed in the toolbar.
+    "TOGGLE_USER_AGENT_INPUT",
+
+    // Update the device display state in the device selector.
+    "UPDATE_DEVICE_DISPLAYED",
+
+    // Update the device modal state.
+    "UPDATE_DEVICE_MODAL",
+
+    // Zoom the viewport.
+    "ZOOM_VIEWPORT",
+  ],
+  module.exports
+);
diff --git a/devtools/client/responsive/actions/moz.build b/devtools/client/responsive/actions/moz.build
new file mode 100644
index 0000000000..d4fa0d243f
--- /dev/null
+++ b/devtools/client/responsive/actions/moz.build
@@ -0,0 +1,13 @@
+# -*- 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(
+    "devices.js",
+    "index.js",
+    "screenshot.js",
+    "ui.js",
+    "viewports.js",
+)
diff --git a/devtools/client/responsive/actions/screenshot.js b/devtools/client/responsive/actions/screenshot.js
new file mode 100644
index 0000000000..c429b41060
--- /dev/null
+++ b/devtools/client/responsive/actions/screenshot.js
@@ -0,0 +1,36 @@
+/* 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/. */
+
+/* eslint-env browser */
+
+"use strict";
+
+const {
+  TAKE_SCREENSHOT_START,
+  TAKE_SCREENSHOT_END,
+} = require("resource://devtools/client/responsive/actions/index.js");
+
+const message = require("resource://devtools/client/responsive/utils/message.js");
+
+const animationFrame = () =>
+  new Promise(resolve => {
+    window.requestAnimationFrame(resolve);
+  });
+
+module.exports = {
+  takeScreenshot() {
+    return async function ({ dispatch }) {
+      await dispatch({ type: TAKE_SCREENSHOT_START });
+
+      // Waiting the next repaint, to ensure the react components
+      // can be properly render after the action dispatched above
+      await animationFrame();
+
+      window.postMessage({ type: "screenshot" }, "*");
+      await message.wait(window, "screenshot-captured");
+
+      dispatch({ type: TAKE_SCREENSHOT_END });
+    };
+  },
+};
diff --git a/devtools/client/responsive/actions/ui.js b/devtools/client/responsive/actions/ui.js
new file mode 100644
index 0000000000..b2f05cb7c9
--- /dev/null
+++ b/devtools/client/responsive/actions/ui.js
@@ -0,0 +1,71 @@
+/* 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 {
+  CHANGE_DISPLAY_PIXEL_RATIO,
+  CHANGE_USER_AGENT,
+  TOGGLE_LEFT_ALIGNMENT,
+  TOGGLE_RELOAD_ON_TOUCH_SIMULATION,
+  TOGGLE_RELOAD_ON_USER_AGENT,
+  TOGGLE_TOUCH_SIMULATION,
+  TOGGLE_USER_AGENT_INPUT,
+} = require("resource://devtools/client/responsive/actions/index.js");
+
+module.exports = {
+  /**
+   * The pixel ratio of the display has changed. This may be triggered by the user
+   * when changing the monitor resolution, or when the window is dragged to a different
+   * display with a different pixel ratio.
+   */
+  changeDisplayPixelRatio(displayPixelRatio) {
+    return {
+      type: CHANGE_DISPLAY_PIXEL_RATIO,
+      displayPixelRatio,
+    };
+  },
+
+  changeUserAgent(userAgent) {
+    return {
+      type: CHANGE_USER_AGENT,
+      userAgent,
+    };
+  },
+
+  toggleLeftAlignment(enabled) {
+    return {
+      type: TOGGLE_LEFT_ALIGNMENT,
+      enabled,
+    };
+  },
+
+  toggleReloadOnTouchSimulation(enabled) {
+    return {
+      type: TOGGLE_RELOAD_ON_TOUCH_SIMULATION,
+      enabled,
+    };
+  },
+
+  toggleReloadOnUserAgent(enabled) {
+    return {
+      type: TOGGLE_RELOAD_ON_USER_AGENT,
+      enabled,
+    };
+  },
+
+  toggleTouchSimulation(enabled) {
+    return {
+      type: TOGGLE_TOUCH_SIMULATION,
+      enabled,
+    };
+  },
+
+  toggleUserAgentInput(enabled) {
+    return {
+      type: TOGGLE_USER_AGENT_INPUT,
+      enabled,
+    };
+  },
+};
diff --git a/devtools/client/responsive/actions/viewports.js b/devtools/client/responsive/actions/viewports.js
new file mode 100644
index 0000000000..f8fec1a8c5
--- /dev/null
+++ b/devtools/client/responsive/actions/viewports.js
@@ -0,0 +1,128 @@
+/* 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/. */
+
+/* eslint-env browser */
+
+"use strict";
+
+const asyncStorage = require("resource://devtools/shared/async-storage.js");
+
+const {
+  ADD_VIEWPORT,
+  CHANGE_DEVICE,
+  CHANGE_PIXEL_RATIO,
+  CHANGE_VIEWPORT_ANGLE,
+  REMOVE_DEVICE_ASSOCIATION,
+  RESIZE_VIEWPORT,
+  ROTATE_VIEWPORT,
+  ZOOM_VIEWPORT,
+} = require("resource://devtools/client/responsive/actions/index.js");
+
+const {
+  post,
+} = require("resource://devtools/client/responsive/utils/message.js");
+
+module.exports = {
+  /**
+   * Add an additional viewport to display the document.
+   */
+  addViewport(userContextId = 0) {
+    return {
+      type: ADD_VIEWPORT,
+      userContextId,
+    };
+  },
+
+  /**
+   * Change the viewport device.
+   */
+  changeDevice(id, device, deviceType) {
+    return async function ({ dispatch }) {
+      dispatch({
+        type: CHANGE_DEVICE,
+        id,
+        device,
+        deviceType,
+      });
+
+      try {
+        await asyncStorage.setItem("devtools.responsive.deviceState", {
+          id,
+          device,
+          deviceType,
+        });
+      } catch (e) {
+        console.error(e);
+      }
+    };
+  },
+
+  /**
+   * Change the viewport pixel ratio.
+   */
+  changePixelRatio(id, pixelRatio = 0) {
+    return {
+      type: CHANGE_PIXEL_RATIO,
+      id,
+      pixelRatio,
+    };
+  },
+
+  changeViewportAngle(id, angle) {
+    return {
+      type: CHANGE_VIEWPORT_ANGLE,
+      id,
+      angle,
+    };
+  },
+
+  /**
+   * Remove the viewport's device assocation.
+   */
+  removeDeviceAssociation(id) {
+    return async function ({ dispatch }) {
+      post(window, "remove-device-association");
+
+      dispatch({
+        type: REMOVE_DEVICE_ASSOCIATION,
+        id,
+      });
+
+      await asyncStorage.removeItem("devtools.responsive.deviceState");
+    };
+  },
+
+  /**
+   * Resize the viewport.
+   */
+  resizeViewport(id, width, height) {
+    return {
+      type: RESIZE_VIEWPORT,
+      id,
+      width,
+      height,
+    };
+  },
+
+  /**
+   * Rotate the viewport.
+   */
+  rotateViewport(id) {
+    return {
+      type: ROTATE_VIEWPORT,
+      id,
+    };
+  },
+
+  /**
+   * Zoom the viewport.
+   */
+  zoomViewport(id, zoom) {
+    return {
+      type: ZOOM_VIEWPORT,
+      id,
+      zoom,
+    };
+  },
+};
diff --git a/devtools/client/responsive/components/App.js b/devtools/client/responsive/components/App.js
new file mode 100644
index 0000000000..da9bec0527
--- /dev/null
+++ b/devtools/client/responsive/components/App.js
@@ -0,0 +1,435 @@
+/* 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/. */
+
+/* eslint-env browser */
+
+"use strict";
+
+const {
+  createFactory,
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+const {
+  connect,
+} = require("resource://devtools/client/shared/vendor/react-redux.js");
+
+const Toolbar = createFactory(
+  require("resource://devtools/client/responsive/components/Toolbar.js")
+);
+
+loader.lazyGetter(this, "DeviceModal", () =>
+  createFactory(
+    require("resource://devtools/client/responsive/components/DeviceModal.js")
+  )
+);
+
+const {
+  changeNetworkThrottling,
+} = require("resource://devtools/client/shared/components/throttling/actions.js");
+const {
+  addCustomDevice,
+  editCustomDevice,
+  removeCustomDevice,
+  updateDeviceDisplayed,
+  updateDeviceModal,
+  updatePreferredDevices,
+} = require("resource://devtools/client/responsive/actions/devices.js");
+const {
+  takeScreenshot,
+} = require("resource://devtools/client/responsive/actions/screenshot.js");
+const {
+  changeUserAgent,
+  toggleLeftAlignment,
+  toggleReloadOnTouchSimulation,
+  toggleReloadOnUserAgent,
+  toggleTouchSimulation,
+  toggleUserAgentInput,
+} = require("resource://devtools/client/responsive/actions/ui.js");
+const {
+  changeDevice,
+  changePixelRatio,
+  changeViewportAngle,
+  removeDeviceAssociation,
+  resizeViewport,
+  rotateViewport,
+} = require("resource://devtools/client/responsive/actions/viewports.js");
+const {
+  getOrientation,
+} = require("resource://devtools/client/responsive/utils/orientation.js");
+
+const Types = require("resource://devtools/client/responsive/types.js");
+
+class App extends PureComponent {
+  static get propTypes() {
+    return {
+      devices: PropTypes.shape(Types.devices).isRequired,
+      dispatch: PropTypes.func.isRequired,
+      leftAlignmentEnabled: PropTypes.bool.isRequired,
+      networkThrottling: PropTypes.shape(Types.networkThrottling).isRequired,
+      screenshot: PropTypes.shape(Types.screenshot).isRequired,
+      viewports: PropTypes.arrayOf(PropTypes.shape(Types.viewport)).isRequired,
+    };
+  }
+
+  constructor(props) {
+    super(props);
+
+    this.onAddCustomDevice = this.onAddCustomDevice.bind(this);
+    this.onChangeDevice = this.onChangeDevice.bind(this);
+    this.onChangeNetworkThrottling = this.onChangeNetworkThrottling.bind(this);
+    this.onChangePixelRatio = this.onChangePixelRatio.bind(this);
+    this.onChangeTouchSimulation = this.onChangeTouchSimulation.bind(this);
+    this.onChangeUserAgent = this.onChangeUserAgent.bind(this);
+    this.onChangeViewportOrientation =
+      this.onChangeViewportOrientation.bind(this);
+    this.onDeviceListUpdate = this.onDeviceListUpdate.bind(this);
+    this.onEditCustomDevice = this.onEditCustomDevice.bind(this);
+    this.onExit = this.onExit.bind(this);
+    this.onRemoveCustomDevice = this.onRemoveCustomDevice.bind(this);
+    this.onRemoveDeviceAssociation = this.onRemoveDeviceAssociation.bind(this);
+    this.doResizeViewport = this.doResizeViewport.bind(this);
+    this.onRotateViewport = this.onRotateViewport.bind(this);
+    this.onScreenshot = this.onScreenshot.bind(this);
+    this.onToggleLeftAlignment = this.onToggleLeftAlignment.bind(this);
+    this.onToggleReloadOnTouchSimulation =
+      this.onToggleReloadOnTouchSimulation.bind(this);
+    this.onToggleReloadOnUserAgent = this.onToggleReloadOnUserAgent.bind(this);
+    this.onToggleUserAgentInput = this.onToggleUserAgentInput.bind(this);
+    this.onUpdateDeviceDisplayed = this.onUpdateDeviceDisplayed.bind(this);
+    this.onUpdateDeviceModal = this.onUpdateDeviceModal.bind(this);
+  }
+
+  onAddCustomDevice(device) {
+    this.props.dispatch(addCustomDevice(device));
+  }
+
+  onChangeDevice(id, device, deviceType) {
+    // Resize the viewport first.
+    this.doResizeViewport(id, device.width, device.height);
+
+    // TODO: Bug 1332754: Move messaging and logic into the action creator so that the
+    // message is sent from the action creator and device property changes are sent from
+    // there instead of this function.
+    window.postMessage(
+      {
+        type: "change-device",
+        device,
+        viewport: device,
+      },
+      "*"
+    );
+
+    const orientation = getOrientation(device, device);
+
+    this.props.dispatch(changeViewportAngle(0, orientation.angle));
+    this.props.dispatch(changeDevice(id, device.name, deviceType));
+    this.props.dispatch(changePixelRatio(id, device.pixelRatio));
+    this.props.dispatch(changeUserAgent(device.userAgent));
+    this.props.dispatch(toggleTouchSimulation(device.touch));
+  }
+
+  onChangeNetworkThrottling(enabled, profile) {
+    window.postMessage(
+      {
+        type: "change-network-throttling",
+        enabled,
+        profile,
+      },
+      "*"
+    );
+    this.props.dispatch(changeNetworkThrottling(enabled, profile));
+  }
+
+  onChangePixelRatio(pixelRatio) {
+    window.postMessage(
+      {
+        type: "change-pixel-ratio",
+        pixelRatio,
+      },
+      "*"
+    );
+    this.props.dispatch(changePixelRatio(0, pixelRatio));
+  }
+
+  onChangeTouchSimulation(enabled) {
+    window.postMessage(
+      {
+        type: "change-touch-simulation",
+        enabled,
+      },
+      "*"
+    );
+    this.props.dispatch(toggleTouchSimulation(enabled));
+  }
+
+  onChangeUserAgent(userAgent) {
+    window.postMessage(
+      {
+        type: "change-user-agent",
+        userAgent,
+      },
+      "*"
+    );
+    this.props.dispatch(changeUserAgent(userAgent));
+  }
+
+  onChangeViewportOrientation(id, type, angle, isViewportRotated = false) {
+    window.postMessage(
+      {
+        type: "viewport-orientation-change",
+        orientationType: type,
+        angle,
+        isViewportRotated,
+      },
+      "*"
+    );
+
+    if (isViewportRotated) {
+      this.props.dispatch(changeViewportAngle(id, angle));
+    }
+  }
+
+  onDeviceListUpdate(devices) {
+    updatePreferredDevices(devices);
+  }
+
+  onEditCustomDevice(oldDevice, newDevice) {
+    // If the edited device is currently selected, then update its original association
+    // and reset UI state.
+    let viewport = this.props.viewports.find(
+      ({ device }) => device === oldDevice.name
+    );
+
+    if (viewport) {
+      viewport = {
+        ...viewport,
+        device: newDevice.name,
+        deviceType: "custom",
+        height: newDevice.height,
+        width: newDevice.width,
+        pixelRatio: newDevice.pixelRatio,
+        touch: newDevice.touch,
+        userAgent: newDevice.userAgent,
+      };
+    }
+
+    this.props.dispatch(editCustomDevice(viewport, oldDevice, newDevice));
+  }
+
+  onExit() {
+    window.postMessage({ type: "exit" }, "*");
+  }
+
+  onRemoveCustomDevice(device) {
+    // If the custom device is currently selected on any of the viewports,
+    // remove the device association and reset all the ui state.
+    for (const viewport of this.props.viewports) {
+      if (viewport.device === device.name) {
+        this.onRemoveDeviceAssociation(viewport.id);
+      }
+    }
+
+    this.props.dispatch(removeCustomDevice(device));
+  }
+
+  onRemoveDeviceAssociation(id) {
+    // TODO: Bug 1332754: Move messaging and logic into the action creator so that device
+    // property changes are sent from there instead of this function.
+    this.props.dispatch(removeDeviceAssociation(id));
+    this.props.dispatch(toggleTouchSimulation(false));
+    this.props.dispatch(changePixelRatio(id, 0));
+    this.props.dispatch(changeUserAgent(""));
+  }
+
+  doResizeViewport(id, width, height) {
+    // This is the setter function that we pass to Toolbar and Viewports
+    // so they can modify the viewport.
+    window.postMessage(
+      {
+        type: "viewport-resize",
+        width,
+        height,
+      },
+      "*"
+    );
+    this.props.dispatch(resizeViewport(id, width, height));
+  }
+
+  /**
+   * Dispatches the rotateViewport action creator. This utilized by the RDM toolbar as
+   * a prop.
+   *
+   * @param {Number} id
+   *        The viewport ID.
+   */
+  onRotateViewport(id) {
+    let currentDevice;
+    const viewport = this.props.viewports[id];
+
+    for (const type of this.props.devices.types) {
+      for (const device of this.props.devices[type]) {
+        if (viewport.device === device.name) {
+          currentDevice = device;
+        }
+      }
+    }
+
+    // If no device is selected, then assume the selected device's primary orientation is
+    // opposite of the viewport orientation.
+    if (!currentDevice) {
+      currentDevice = {
+        height: viewport.width,
+        width: viewport.height,
+      };
+    }
+
+    const currentAngle = Services.prefs.getIntPref(
+      "devtools.responsive.viewport.angle"
+    );
+    const angleToRotateTo = currentAngle === 90 ? 0 : 90;
+    const { type, angle } = getOrientation(
+      currentDevice,
+      viewport,
+      angleToRotateTo
+    );
+
+    this.onChangeViewportOrientation(id, type, angle, true);
+    this.props.dispatch(rotateViewport(id));
+
+    window.postMessage(
+      {
+        type: "viewport-resize",
+        height: viewport.width,
+        width: viewport.height,
+      },
+      "*"
+    );
+  }
+
+  onScreenshot() {
+    this.props.dispatch(takeScreenshot());
+  }
+
+  onToggleLeftAlignment() {
+    this.props.dispatch(toggleLeftAlignment());
+
+    window.postMessage(
+      {
+        type: "toggle-left-alignment",
+        leftAlignmentEnabled: this.props.leftAlignmentEnabled,
+      },
+      "*"
+    );
+  }
+
+  onToggleReloadOnTouchSimulation() {
+    this.props.dispatch(toggleReloadOnTouchSimulation());
+  }
+
+  onToggleReloadOnUserAgent() {
+    this.props.dispatch(toggleReloadOnUserAgent());
+  }
+
+  onToggleUserAgentInput() {
+    this.props.dispatch(toggleUserAgentInput());
+  }
+
+  onUpdateDeviceDisplayed(device, deviceType, displayed) {
+    this.props.dispatch(updateDeviceDisplayed(device, deviceType, displayed));
+  }
+
+  onUpdateDeviceModal(isOpen, modalOpenedFromViewport) {
+    this.props.dispatch(updateDeviceModal(isOpen, modalOpenedFromViewport));
+    window.postMessage({ type: "update-device-modal", isOpen }, "*");
+  }
+
+  render() {
+    const { devices, networkThrottling, screenshot, viewports } = this.props;
+
+    const {
+      onAddCustomDevice,
+      onChangeDevice,
+      onChangeNetworkThrottling,
+      onChangePixelRatio,
+      onChangeTouchSimulation,
+      onChangeUserAgent,
+      onDeviceListUpdate,
+      onEditCustomDevice,
+      onExit,
+      onRemoveCustomDevice,
+      onRemoveDeviceAssociation,
+      doResizeViewport,
+      onRotateViewport,
+      onScreenshot,
+      onToggleLeftAlignment,
+      onToggleReloadOnTouchSimulation,
+      onToggleReloadOnUserAgent,
+      onToggleUserAgentInput,
+      onUpdateDeviceDisplayed,
+      onUpdateDeviceModal,
+    } = this;
+
+    if (!viewports.length) {
+      return null;
+    }
+
+    const selectedDevice = viewports[0].device;
+    const selectedPixelRatio = viewports[0].pixelRatio;
+
+    let deviceAdderViewportTemplate = {};
+    if (devices.modalOpenedFromViewport !== null) {
+      deviceAdderViewportTemplate = viewports[devices.modalOpenedFromViewport];
+    }
+
+    return dom.div(
+      { id: "app" },
+      Toolbar({
+        devices,
+        networkThrottling,
+        screenshot,
+        selectedDevice,
+        selectedPixelRatio,
+        viewport: viewports[0],
+        onChangeDevice,
+        onChangeNetworkThrottling,
+        onChangePixelRatio,
+        onChangeTouchSimulation,
+        onChangeUserAgent,
+        onExit,
+        onRemoveDeviceAssociation,
+        doResizeViewport,
+        onRotateViewport,
+        onScreenshot,
+        onToggleLeftAlignment,
+        onToggleReloadOnTouchSimulation,
+        onToggleReloadOnUserAgent,
+        onToggleUserAgentInput,
+        onUpdateDeviceModal,
+      }),
+      devices.isModalOpen
+        ? DeviceModal({
+            deviceAdderViewportTemplate,
+            devices,
+            onAddCustomDevice,
+            onDeviceListUpdate,
+            onEditCustomDevice,
+            onRemoveCustomDevice,
+            onUpdateDeviceDisplayed,
+            onUpdateDeviceModal,
+          })
+        : null
+    );
+  }
+}
+
+const mapStateToProps = state => {
+  return {
+    ...state,
+    leftAlignmentEnabled: state.ui.leftAlignmentEnabled,
+  };
+};
+
+module.exports = connect(mapStateToProps)(App);
diff --git a/devtools/client/responsive/components/Device.js b/devtools/client/responsive/components/Device.js
new file mode 100644
index 0000000000..87c0845a70
--- /dev/null
+++ b/devtools/client/responsive/components/Device.js
@@ -0,0 +1,139 @@
+/* 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/. */
+
+/* eslint-env browser */
+
+"use strict";
+
+const {
+  createFactory,
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+
+const {
+  getFormatStr,
+} = require("resource://devtools/client/responsive/utils/l10n.js");
+const {
+  parseUserAgent,
+} = require("resource://devtools/client/responsive/utils/ua.js");
+const Types = require("resource://devtools/client/responsive/types.js");
+
+const DeviceInfo = createFactory(
+  require("resource://devtools/client/responsive/components/DeviceInfo.js")
+);
+
+class Device extends PureComponent {
+  static get propTypes() {
+    return {
+      // props.children are the buttons rendered as part of custom device label.
+      children: PropTypes.oneOfType([
+        PropTypes.arrayOf(PropTypes.node),
+        PropTypes.node,
+      ]),
+      device: PropTypes.shape(Types.devices).isRequired,
+      onDeviceCheckboxChange: PropTypes.func.isRequired,
+    };
+  }
+
+  constructor(props) {
+    super(props);
+
+    this.state = {
+      // Whether or not the device's input label is checked.
+      isChecked: this.props.device.isChecked,
+    };
+
+    this.onCheckboxChanged = this.onCheckboxChanged.bind(this);
+  }
+
+  onCheckboxChanged(e) {
+    this.setState(prevState => {
+      return { isChecked: !prevState.isChecked };
+    });
+
+    this.props.onDeviceCheckboxChange(e);
+  }
+
+  getBrowserOrOsTooltip(agent) {
+    if (agent) {
+      return agent.name + (agent.version ? ` ${agent.version}` : "");
+    }
+
+    return null;
+  }
+
+  getTooltip() {
+    const { device } = this.props;
+    const { browser, os } = parseUserAgent(device.userAgent);
+
+    const browserTitle = this.getBrowserOrOsTooltip(browser);
+    const osTitle = this.getBrowserOrOsTooltip(os);
+    let browserAndOsTitle = null;
+    if (browserTitle && osTitle) {
+      browserAndOsTitle = getFormatStr(
+        "responsive.deviceDetails.browserAndOS",
+        browserTitle,
+        osTitle
+      );
+    } else if (browserTitle || osTitle) {
+      browserAndOsTitle = browserTitle || osTitle;
+    }
+
+    const sizeTitle = getFormatStr(
+      "responsive.deviceDetails.size",
+      device.width,
+      device.height
+    );
+
+    const dprTitle = getFormatStr(
+      "responsive.deviceDetails.DPR",
+      device.pixelRatio
+    );
+
+    const uaTitle = getFormatStr(
+      "responsive.deviceDetails.UA",
+      device.userAgent
+    );
+
+    const touchTitle = getFormatStr(
+      "responsive.deviceDetails.touch",
+      device.touch
+    );
+
+    return (
+      `${browserAndOsTitle ? browserAndOsTitle + "\n" : ""}` +
+      `${sizeTitle}\n` +
+      `${dprTitle}\n` +
+      `${uaTitle}\n` +
+      `${touchTitle}\n`
+    );
+  }
+
+  render() {
+    const { children, device } = this.props;
+    const tooltip = this.getTooltip();
+
+    return dom.label(
+      {
+        className: "device-label",
+        key: device.name,
+        title: tooltip,
+      },
+      dom.input({
+        className: "device-input-checkbox",
+        name: device.name,
+        type: "checkbox",
+        value: device.name,
+        checked: device.isChecked,
+        onChange: this.onCheckboxChanged,
+      }),
+      DeviceInfo({ device }),
+      children
+    );
+  }
+}
+
+module.exports = Device;
diff --git a/devtools/client/responsive/components/DeviceAdder.js b/devtools/client/responsive/components/DeviceAdder.js
new file mode 100644
index 0000000000..b09da10f38
--- /dev/null
+++ b/devtools/client/responsive/components/DeviceAdder.js
@@ -0,0 +1,229 @@
+/* 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/. */
+
+/* eslint-env browser */
+
+"use strict";
+
+const {
+  createFactory,
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+
+const ViewportDimension = createFactory(
+  require("resource://devtools/client/responsive/components/ViewportDimension.js")
+);
+
+const {
+  getFormatStr,
+  getStr,
+} = require("resource://devtools/client/responsive/utils/l10n.js");
+const Types = require("resource://devtools/client/responsive/types.js");
+
+class DeviceAdder extends PureComponent {
+  static get propTypes() {
+    return {
+      devices: PropTypes.shape(Types.devices).isRequired,
+      onAddCustomDevice: PropTypes.func.isRequired,
+      viewportTemplate: PropTypes.shape(Types.viewport).isRequired,
+    };
+  }
+
+  constructor(props) {
+    super(props);
+
+    const { height, width } = this.props.viewportTemplate;
+
+    this.state = {
+      deviceAdderDisplayed: false,
+      height,
+      width,
+    };
+
+    this.onChangeSize = this.onChangeSize.bind(this);
+    this.onDeviceAdderShow = this.onDeviceAdderShow.bind(this);
+    this.onDeviceAdderSave = this.onDeviceAdderSave.bind(this);
+  }
+
+  onChangeSize(_, width, height) {
+    this.setState({
+      width,
+      height,
+    });
+  }
+
+  onDeviceAdderShow() {
+    this.setState({
+      deviceAdderDisplayed: true,
+    });
+  }
+
+  onDeviceAdderSave() {
+    const { devices, onAddCustomDevice } = this.props;
+
+    if (!this.pixelRatioInput.checkValidity()) {
+      return;
+    }
+
+    if (devices.custom.find(device => device.name == this.nameInput.value)) {
+      this.nameInput.setCustomValidity("Device name already in use");
+      return;
+    }
+
+    this.setState({
+      deviceAdderDisplayed: false,
+    });
+
+    onAddCustomDevice({
+      name: this.nameInput.value,
+      width: this.state.width,
+      height: this.state.height,
+      pixelRatio: parseFloat(this.pixelRatioInput.value),
+      userAgent: this.userAgentInput.value,
+      touch: this.touchInput.checked,
+    });
+  }
+
+  render() {
+    const { devices, viewportTemplate } = this.props;
+
+    const { deviceAdderDisplayed, height, width } = this.state;
+
+    if (!deviceAdderDisplayed) {
+      return dom.div(
+        {
+          id: "device-adder",
+        },
+        dom.button(
+          {
+            id: "device-adder-show",
+            onClick: this.onDeviceAdderShow,
+          },
+          getStr("responsive.addDevice")
+        )
+      );
+    }
+
+    // If a device is currently selected, fold its attributes into a single object for use
+    // as the starting values of the form.  If no device is selected, use the values for
+    // the current window.
+    let deviceName;
+    const normalizedViewport = Object.assign({}, viewportTemplate);
+    if (viewportTemplate.device) {
+      const device = devices[viewportTemplate.deviceType].find(d => {
+        return d.name == viewportTemplate.device;
+      });
+      deviceName = getFormatStr(
+        "responsive.customDeviceNameFromBase",
+        device.name
+      );
+      Object.assign(normalizedViewport, {
+        pixelRatio: device.pixelRatio,
+        userAgent: device.userAgent,
+        touch: device.touch,
+      });
+    } else {
+      deviceName = getStr("responsive.customDeviceName");
+      Object.assign(normalizedViewport, {
+        pixelRatio: window.devicePixelRatio,
+        userAgent: navigator.userAgent,
+        touch: false,
+      });
+    }
+
+    return dom.div(
+      { id: "device-adder" },
+      dom.div(
+        { id: "device-adder-content" },
+        dom.div(
+          { id: "device-adder-column-1" },
+          dom.label(
+            { id: "device-adder-name" },
+            dom.span(
+              { className: "device-adder-label" },
+              getStr("responsive.deviceAdderName")
+            ),
+            dom.input({
+              defaultValue: deviceName,
+              ref: input => {
+                this.nameInput = input;
+              },
+            })
+          ),
+          dom.label(
+            { id: "device-adder-size" },
+            dom.span(
+              { className: "device-adder-label" },
+              getStr("responsive.deviceAdderSize")
+            ),
+            ViewportDimension({
+              viewport: {
+                width,
+                height,
+              },
+              doResizeViewport: this.onChangeSize,
+              onRemoveDeviceAssociation: () => {},
+            })
+          ),
+          dom.label(
+            { id: "device-adder-pixel-ratio" },
+            dom.span(
+              { className: "device-adder-label" },
+              getStr("responsive.deviceAdderPixelRatio")
+            ),
+            dom.input({
+              type: "number",
+              step: "any",
+              defaultValue: normalizedViewport.pixelRatio,
+              ref: input => {
+                this.pixelRatioInput = input;
+              },
+            })
+          )
+        ),
+        dom.div(
+          { id: "device-adder-column-2" },
+          dom.label(
+            { id: "device-adder-user-agent" },
+            dom.span(
+              { className: "device-adder-label" },
+              getStr("responsive.deviceAdderUserAgent")
+            ),
+            dom.input({
+              defaultValue: normalizedViewport.userAgent,
+              ref: input => {
+                this.userAgentInput = input;
+              },
+            })
+          ),
+          dom.label(
+            { id: "device-adder-touch" },
+            dom.span(
+              { className: "device-adder-label" },
+              getStr("responsive.deviceAdderTouch")
+            ),
+            dom.input({
+              defaultChecked: normalizedViewport.touch,
+              type: "checkbox",
+              ref: input => {
+                this.touchInput = input;
+              },
+            })
+          )
+        )
+      ),
+      dom.button(
+        {
+          id: "device-adder-save",
+          onClick: this.onDeviceAdderSave,
+        },
+        getStr("responsive.deviceAdderSave")
+      )
+    );
+  }
+}
+
+module.exports = DeviceAdder;
diff --git a/devtools/client/responsive/components/DeviceForm.js b/devtools/client/responsive/components/DeviceForm.js
new file mode 100644
index 0000000000..656f846d33
--- /dev/null
+++ b/devtools/client/responsive/components/DeviceForm.js
@@ -0,0 +1,231 @@
+/* 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/. */
+
+/* eslint-env browser */
+
+"use strict";
+
+const {
+  createFactory,
+  createRef,
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+
+const ViewportDimension = createFactory(
+  require("resource://devtools/client/responsive/components/ViewportDimension.js")
+);
+
+const {
+  getStr,
+} = require("resource://devtools/client/responsive/utils/l10n.js");
+const Types = require("resource://devtools/client/responsive/types.js");
+
+class DeviceForm extends PureComponent {
+  static get propTypes() {
+    return {
+      formType: PropTypes.string.isRequired,
+      device: PropTypes.shape(Types.device).isRequired,
+      devices: PropTypes.shape(Types.devices).isRequired,
+      onSave: PropTypes.func.isRequired,
+      viewportTemplate: PropTypes.shape(Types.viewport).isRequired,
+      onDeviceFormHide: PropTypes.func.isRequired,
+    };
+  }
+
+  constructor(props) {
+    super(props);
+
+    const { height, width } = this.props.viewportTemplate;
+
+    this.state = {
+      height,
+      width,
+    };
+
+    this.nameInputRef = createRef();
+    this.pixelRatioInputRef = createRef();
+    this.touchInputRef = createRef();
+    this.userAgentInputRef = createRef();
+
+    this.onChangeSize = this.onChangeSize.bind(this);
+    this.onDeviceFormHide = this.onDeviceFormHide.bind(this);
+    this.onDeviceFormSave = this.onDeviceFormSave.bind(this);
+    this.onInputFocus = this.onInputFocus.bind(this);
+    this.validateNameField = this.validateNameField.bind(this);
+  }
+
+  onChangeSize(_, width, height) {
+    this.setState({
+      width,
+      height,
+    });
+  }
+
+  onDeviceFormSave(e) {
+    e.preventDefault();
+
+    if (!this.pixelRatioInputRef.current.checkValidity()) {
+      return;
+    }
+
+    if (
+      !this.validateNameField(
+        this.nameInputRef.current.value,
+        this.props.device
+      )
+    ) {
+      this.nameInputRef.current.setCustomValidity(
+        getStr("responsive.deviceNameAlreadyInUse")
+      );
+      return;
+    }
+
+    this.props.onSave({
+      name: this.nameInputRef.current.value.trim(),
+      width: this.state.width,
+      height: this.state.height,
+      pixelRatio: parseFloat(this.pixelRatioInputRef.current.value),
+      userAgent: this.userAgentInputRef.current.value,
+      touch: this.touchInputRef.current.checked,
+    });
+
+    this.onDeviceFormHide();
+  }
+
+  onDeviceFormHide() {
+    // Ensure that we have onDeviceFormHide before calling it.
+    if (this.props.onDeviceFormHide) {
+      this.props.onDeviceFormHide();
+    }
+  }
+
+  onInputFocus(e) {
+    // If the formType is "add", select all text in input field when focused.
+    if (this.props.formType === "add") {
+      e.target.select();
+    }
+  }
+
+  /**
+   * Validates the name field's value.
+   *
+   * @param  {String} value
+   *         The input field value for the device name.
+   * @return {Boolean} true if device name is valid, false otherwise.
+   */
+  validateNameField(value) {
+    const nameFieldValue = value.trim();
+    let isValidDeviceName = false;
+
+    // If the formType is "add", then we just need to check if a custom device with that
+    // same name exists.
+    if (this.props.formType === "add") {
+      isValidDeviceName = !this.props.devices.custom.find(
+        device => device.name == nameFieldValue
+      );
+    } else {
+      // Otherwise, the formType is "edit". We'd have to find another device that
+      // already has the same name, but not itself, so:
+      // Find the index of the device being edited. Use this index value to distinguish
+      // between the device being edited from other devices in the list.
+      const deviceIndex = this.props.devices.custom.findIndex(({ name }) => {
+        return name === this.props.device.name;
+      });
+
+      isValidDeviceName = !this.props.devices.custom.find((d, index) => {
+        return d.name === nameFieldValue && index !== deviceIndex;
+      });
+    }
+
+    return isValidDeviceName;
+  }
+
+  render() {
+    const { device, formType } = this.props;
+    const { width, height } = this.state;
+
+    return dom.form(
+      { id: "device-form" },
+      dom.label(
+        { id: "device-form-name" },
+        dom.span(
+          { className: "device-form-label" },
+          getStr("responsive.deviceAdderName")
+        ),
+        dom.input({
+          defaultValue: device.name,
+          ref: this.nameInputRef,
+          onFocus: this.onInputFocus,
+        })
+      ),
+      dom.label(
+        { id: "device-form-size" },
+        dom.span(
+          { className: "device-form-label" },
+          getStr("responsive.deviceAdderSize")
+        ),
+        ViewportDimension({
+          viewport: { width, height },
+          doResizeViewport: this.onChangeSize,
+          onRemoveDeviceAssociation: () => {},
+        })
+      ),
+      dom.label(
+        { id: "device-form-pixel-ratio" },
+        dom.span(
+          { className: "device-form-label" },
+          getStr("responsive.deviceAdderPixelRatio2")
+        ),
+        dom.input({
+          type: "number",
+          step: "any",
+          defaultValue: device.pixelRatio,
+          ref: this.pixelRatioInputRef,
+          onFocus: this.onInputFocus,
+        })
+      ),
+      dom.label(
+        { id: "device-form-user-agent" },
+        dom.span(
+          { className: "device-form-label" },
+          getStr("responsive.deviceAdderUserAgent2")
+        ),
+        dom.input({
+          defaultValue: device.userAgent,
+          ref: this.userAgentInputRef,
+          onFocus: this.onInputFocus,
+        })
+      ),
+      dom.label(
+        { id: "device-form-touch" },
+        dom.input({
+          defaultChecked: device.touch,
+          type: "checkbox",
+          ref: this.touchInputRef,
+        }),
+        dom.span(
+          { className: "device-form-label" },
+          getStr("responsive.deviceAdderTouch2")
+        )
+      ),
+      dom.div(
+        { className: "device-form-buttons" },
+        dom.button(
+          { id: "device-form-save", onClick: this.onDeviceFormSave },
+          formType === "add"
+            ? getStr("responsive.deviceAdderSave")
+            : getStr("responsive.deviceFormUpdate")
+        ),
+        dom.button(
+          { id: "device-form-cancel", onClick: this.onDeviceFormHide },
+          getStr("responsive.deviceAdderCancel")
+        )
+      )
+    );
+  }
+}
+
+module.exports = DeviceForm;
diff --git a/devtools/client/responsive/components/DeviceInfo.js b/devtools/client/responsive/components/DeviceInfo.js
new file mode 100644
index 0000000000..2dc53bb603
--- /dev/null
+++ b/devtools/client/responsive/components/DeviceInfo.js
@@ -0,0 +1,52 @@
+/* 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 {
+  createElement,
+  Fragment,
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+
+const {
+  parseUserAgent,
+} = require("resource://devtools/client/responsive/utils/ua.js");
+const Types = require("resource://devtools/client/responsive/types.js");
+
+class DeviceInfo extends PureComponent {
+  static get propTypes() {
+    return {
+      device: PropTypes.shape(Types.devices).isRequired,
+    };
+  }
+
+  renderBrowser({ name }) {
+    return dom.span({
+      className: `device-browser ${name.toLowerCase()}`,
+    });
+  }
+
+  renderOS({ name, version }) {
+    const text = version ? `${name} ${version}` : name;
+    return dom.span({ className: "device-os" }, text);
+  }
+
+  render() {
+    const { device } = this.props;
+    const { browser, os } = parseUserAgent(device.userAgent);
+
+    return createElement(
+      Fragment,
+      null,
+      browser ? this.renderBrowser(browser) : dom.span(),
+      dom.span({ className: "device-name" }, device.name),
+      os ? this.renderOS(os) : dom.span()
+    );
+  }
+}
+
+module.exports = DeviceInfo;
diff --git a/devtools/client/responsive/components/DeviceList.js b/devtools/client/responsive/components/DeviceList.js
new file mode 100644
index 0000000000..3cf44f0e2e
--- /dev/null
+++ b/devtools/client/responsive/components/DeviceList.js
@@ -0,0 +1,97 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* eslint-env browser */
+
+"use strict";
+
+const {
+  createFactory,
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+
+const Types = require("resource://devtools/client/responsive/types.js");
+
+const Device = createFactory(
+  require("resource://devtools/client/responsive/components/Device.js")
+);
+
+class DeviceList extends PureComponent {
+  static get propTypes() {
+    return {
+      // Whether or not to show the custom device edit/remove buttons.
+      devices: PropTypes.shape(Types.devices).isRequired,
+      isDeviceFormShown: PropTypes.bool.isRequired,
+      onDeviceCheckboxChange: PropTypes.func.isRequired,
+      onDeviceFormHide: PropTypes.func.isRequired,
+      onDeviceFormShow: PropTypes.func.isRequired,
+      onRemoveCustomDevice: PropTypes.func.isRequired,
+      type: PropTypes.string.isRequired,
+    };
+  }
+
+  renderCustomDevice(device) {
+    const {
+      isDeviceFormShown,
+      type,
+      onDeviceCheckboxChange,
+      onRemoveCustomDevice,
+    } = this.props;
+
+    // Show a remove button for custom devices.
+    const removeDeviceButton = dom.button({
+      id: "device-edit-remove",
+      className: "device-remove-button devtools-button",
+      onClick: () => {
+        onRemoveCustomDevice(device);
+        this.props.onDeviceFormHide();
+      },
+    });
+
+    // Show an edit button for custom devices
+    const editButton = dom.button({
+      id: "device-edit-button",
+      className: "devtools-button",
+      onClick: () => {
+        this.props.onDeviceFormShow("edit", device);
+      },
+    });
+
+    return Device(
+      {
+        device,
+        key: device.name,
+        type,
+        onDeviceCheckboxChange,
+      },
+      // Don't show the remove/edit buttons for a custom device if the form is open.
+      !isDeviceFormShown ? editButton : null,
+      !isDeviceFormShown ? removeDeviceButton : null
+    );
+  }
+
+  render() {
+    const { devices, type, onDeviceCheckboxChange } = this.props;
+
+    return dom.div(
+      { className: "device-list" },
+      devices[type].map(device => {
+        if (type === "custom") {
+          return this.renderCustomDevice(device);
+        }
+
+        return Device({
+          device,
+          key: device.name,
+          type,
+          onDeviceCheckboxChange,
+        });
+      })
+    );
+  }
+}
+
+module.exports = DeviceList;
diff --git a/devtools/client/responsive/components/DeviceModal.js b/devtools/client/responsive/components/DeviceModal.js
new file mode 100644
index 0000000000..1cd21951e3
--- /dev/null
+++ b/devtools/client/responsive/components/DeviceModal.js
@@ -0,0 +1,303 @@
+/* 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/. */
+
+/* eslint-env browser */
+
+"use strict";
+
+const {
+  createFactory,
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+
+const DeviceForm = createFactory(
+  require("resource://devtools/client/responsive/components/DeviceForm.js")
+);
+const DeviceList = createFactory(
+  require("resource://devtools/client/responsive/components/DeviceList.js")
+);
+
+const {
+  getFormatStr,
+  getStr,
+} = require("resource://devtools/client/responsive/utils/l10n.js");
+const {
+  getDeviceString,
+} = require("resource://devtools/client/shared/devices.js");
+const Types = require("resource://devtools/client/responsive/types.js");
+
+class DeviceModal extends PureComponent {
+  static get propTypes() {
+    return {
+      deviceAdderViewportTemplate: PropTypes.shape(Types.viewport).isRequired,
+      devices: PropTypes.shape(Types.devices).isRequired,
+      onAddCustomDevice: PropTypes.func.isRequired,
+      onDeviceListUpdate: PropTypes.func.isRequired,
+      onEditCustomDevice: PropTypes.func.isRequired,
+      onRemoveCustomDevice: PropTypes.func.isRequired,
+      onUpdateDeviceDisplayed: PropTypes.func.isRequired,
+      onUpdateDeviceModal: PropTypes.func.isRequired,
+    };
+  }
+
+  constructor(props) {
+    super(props);
+
+    this.state = {
+      // The device form type can be 3 states: "add", "edit", or "".
+      // "add"  - The form shown is adding a new device.
+      // "edit" - The form shown is editing an existing custom device.
+      // ""     - The form is closed.
+      deviceFormType: "",
+      // The device being edited from the edit form.
+      editingDevice: null,
+    };
+    for (const type of this.props.devices.types) {
+      for (const device of this.props.devices[type]) {
+        this.state[device.name] = device.displayed;
+      }
+    }
+
+    this.onAddCustomDevice = this.onAddCustomDevice.bind(this);
+    this.onDeviceCheckboxChange = this.onDeviceCheckboxChange.bind(this);
+    this.onDeviceFormShow = this.onDeviceFormShow.bind(this);
+    this.onDeviceFormHide = this.onDeviceFormHide.bind(this);
+    this.onDeviceModalSubmit = this.onDeviceModalSubmit.bind(this);
+    this.onEditCustomDevice = this.onEditCustomDevice.bind(this);
+    this.onKeyDown = this.onKeyDown.bind(this);
+  }
+
+  componentDidMount() {
+    window.addEventListener("keydown", this.onKeyDown, true);
+  }
+
+  componentWillUnmount() {
+    this.onDeviceModalSubmit();
+    window.removeEventListener("keydown", this.onKeyDown, true);
+  }
+
+  onAddCustomDevice(device) {
+    this.props.onAddCustomDevice(device);
+    // Default custom devices to enabled
+    this.setState({
+      [device.name]: true,
+    });
+  }
+
+  onDeviceCheckboxChange({ nativeEvent: { button }, target }) {
+    if (button !== 0) {
+      return;
+    }
+    this.setState({
+      [target.value]: !this.state[target.value],
+    });
+  }
+
+  onDeviceFormShow(type, device) {
+    this.setState({
+      deviceFormType: type,
+      editingDevice: device,
+    });
+  }
+
+  onDeviceFormHide() {
+    this.setState({
+      deviceFormType: "",
+      editingDevice: null,
+    });
+  }
+
+  onDeviceModalSubmit() {
+    const { devices, onDeviceListUpdate, onUpdateDeviceDisplayed } = this.props;
+
+    const preferredDevices = {
+      added: new Set(),
+      removed: new Set(),
+    };
+
+    for (const type of devices.types) {
+      for (const device of devices[type]) {
+        const newState = this.state[device.name];
+
+        if (device.featured && !newState) {
+          preferredDevices.removed.add(device.name);
+        } else if (!device.featured && newState) {
+          preferredDevices.added.add(device.name);
+        }
+
+        if (this.state[device.name] != device.displayed) {
+          onUpdateDeviceDisplayed(device, type, this.state[device.name]);
+        }
+      }
+    }
+
+    onDeviceListUpdate(preferredDevices);
+  }
+
+  onEditCustomDevice(newDevice) {
+    this.props.onEditCustomDevice(this.state.editingDevice, newDevice);
+
+    // We want to remove the original device name from state after editing, so create a
+    // new state setting the old key to null and the new one to true.
+    this.setState({
+      [this.state.editingDevice.name]: null,
+      [newDevice.name]: true,
+    });
+  }
+
+  onKeyDown(event) {
+    if (!this.props.devices.isModalOpen) {
+      return;
+    }
+    // Escape keycode
+    if (event.keyCode === 27) {
+      const { onUpdateDeviceModal } = this.props;
+      onUpdateDeviceModal(false);
+    }
+  }
+
+  renderAddForm() {
+    // If a device is currently selected, fold its attributes into a single object for use
+    // as the starting values of the form.  If no device is selected, use the values for
+    // the current window.
+    const { deviceAdderViewportTemplate: viewportTemplate } = this.props;
+    const deviceTemplate = this.props.deviceAdderViewportTemplate;
+    if (viewportTemplate.device) {
+      const device = this.props.devices[viewportTemplate.deviceType].find(d => {
+        return d.name == viewportTemplate.device;
+      });
+      Object.assign(deviceTemplate, {
+        pixelRatio: device.pixelRatio,
+        userAgent: device.userAgent,
+        touch: device.touch,
+        name: getFormatStr("responsive.customDeviceNameFromBase", device.name),
+      });
+    } else {
+      Object.assign(deviceTemplate, {
+        pixelRatio: window.devicePixelRatio,
+        userAgent: navigator.userAgent,
+        touch: false,
+        name: getStr("responsive.customDeviceName"),
+      });
+    }
+
+    return DeviceForm({
+      formType: "add",
+      device: deviceTemplate,
+      devices: this.props.devices,
+      onDeviceFormHide: this.onDeviceFormHide,
+      onSave: this.onAddCustomDevice,
+      viewportTemplate,
+    });
+  }
+
+  renderDevices() {
+    const sortedDevices = {};
+    for (const type of this.props.devices.types) {
+      sortedDevices[type] = this.props.devices[type].sort((a, b) =>
+        a.name.localeCompare(b.name)
+      );
+
+      sortedDevices[type].forEach(device => {
+        device.isChecked = this.state[device.name];
+      });
+    }
+
+    return this.props.devices.types.map(type => {
+      return sortedDevices[type].length
+        ? dom.div(
+            {
+              className: `device-type device-type-${type}`,
+              key: type,
+            },
+            dom.header({ className: "device-header" }, getDeviceString(type)),
+            DeviceList({
+              devices: sortedDevices,
+              isDeviceFormShown: this.state.deviceFormType,
+              type,
+              onDeviceCheckboxChange: this.onDeviceCheckboxChange,
+              onDeviceFormHide: this.onDeviceFormHide,
+              onDeviceFormShow: this.onDeviceFormShow,
+              onEditCustomDevice: this.onEditCustomDevice,
+              onRemoveCustomDevice: this.props.onRemoveCustomDevice,
+            })
+          )
+        : null;
+    });
+  }
+
+  renderEditForm() {
+    return DeviceForm({
+      formType: "edit",
+      device: this.state.editingDevice,
+      devices: this.props.devices,
+      onDeviceFormHide: this.onDeviceFormHide,
+      onSave: this.onEditCustomDevice,
+      viewportTemplate: {
+        width: this.state.editingDevice.width,
+        height: this.state.editingDevice.height,
+      },
+    });
+  }
+
+  renderForm() {
+    let form = null;
+
+    if (this.state.deviceFormType === "add") {
+      form = this.renderAddForm();
+    } else if (this.state.deviceFormType === "edit") {
+      form = this.renderEditForm();
+    }
+
+    return form;
+  }
+
+  render() {
+    const { onUpdateDeviceModal } = this.props;
+    const isDeviceFormShown = this.state.deviceFormType;
+
+    return dom.div(
+      {
+        id: "device-modal-wrapper",
+        className: this.props.devices.isModalOpen ? "opened" : "closed",
+      },
+      dom.div(
+        { className: "device-modal" },
+        dom.div(
+          { className: "device-modal-header" },
+          !isDeviceFormShown
+            ? dom.header(
+                { className: "device-modal-title" },
+                getStr("responsive.deviceSettings"),
+                dom.button({
+                  id: "device-close-button",
+                  className: "devtools-button",
+                  onClick: () => onUpdateDeviceModal(false),
+                })
+              )
+            : null,
+          !isDeviceFormShown
+            ? dom.button(
+                {
+                  id: "device-add-button",
+                  onClick: () => this.onDeviceFormShow("add"),
+                },
+                getStr("responsive.addDevice2")
+              )
+            : null,
+          this.renderForm()
+        ),
+        dom.div({ className: "device-modal-content" }, this.renderDevices())
+      ),
+      dom.div({
+        className: "modal-overlay",
+        onClick: () => onUpdateDeviceModal(false),
+      })
+    );
+  }
+}
+
+module.exports = DeviceModal;
diff --git a/devtools/client/responsive/components/DevicePixelRatioMenu.js b/devtools/client/responsive/components/DevicePixelRatioMenu.js
new file mode 100644
index 0000000000..7ad37b8e03
--- /dev/null
+++ b/devtools/client/responsive/components/DevicePixelRatioMenu.js
@@ -0,0 +1,100 @@
+/* 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/. */
+
+/* eslint-env browser */
+
+"use strict";
+
+const {
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+
+const {
+  getStr,
+  getFormatStr,
+} = require("resource://devtools/client/responsive/utils/l10n.js");
+const Types = require("resource://devtools/client/responsive/types.js");
+
+loader.lazyRequireGetter(
+  this,
+  "showMenu",
+  "resource://devtools/client/shared/components/menu/utils.js",
+  true
+);
+
+const PIXEL_RATIO_PRESET = [1, 2, 3];
+
+class DevicePixelRatioMenu extends PureComponent {
+  static get propTypes() {
+    return {
+      devices: PropTypes.shape(Types.devices).isRequired,
+      displayPixelRatio: PropTypes.number.isRequired,
+      onChangePixelRatio: PropTypes.func.isRequired,
+      selectedDevice: PropTypes.string.isRequired,
+      selectedPixelRatio: PropTypes.number.isRequired,
+    };
+  }
+
+  constructor(props) {
+    super(props);
+    this.onShowDevicePixelMenu = this.onShowDevicePixelMenu.bind(this);
+  }
+
+  onShowDevicePixelMenu(event) {
+    const { displayPixelRatio, onChangePixelRatio, selectedPixelRatio } =
+      this.props;
+
+    const menuItems = PIXEL_RATIO_PRESET.map(value => {
+      return {
+        label: getFormatStr("responsive.devicePixelRatioOption", value),
+        type: "checkbox",
+        checked:
+          selectedPixelRatio > 0
+            ? selectedPixelRatio === value
+            : displayPixelRatio === value,
+        click: () => onChangePixelRatio(+value),
+      };
+    });
+
+    showMenu(menuItems, {
+      button: event.target,
+    });
+  }
+
+  render() {
+    const { devices, displayPixelRatio, selectedDevice, selectedPixelRatio } =
+      this.props;
+
+    const isDisabled =
+      devices.listState !== Types.loadableState.LOADED || selectedDevice !== "";
+
+    let title;
+    if (isDisabled) {
+      title = getFormatStr("responsive.devicePixelRatio.auto", selectedDevice);
+    } else {
+      title = getStr("responsive.changeDevicePixelRatio");
+    }
+
+    return dom.button(
+      {
+        id: "device-pixel-ratio-menu",
+        className: "devtools-button devtools-dropdown-button",
+        disabled: isDisabled,
+        title,
+        onClick: this.onShowDevicePixelMenu,
+      },
+      dom.span(
+        { className: "title" },
+        getFormatStr(
+          "responsive.devicePixelRatioOption",
+          selectedPixelRatio || displayPixelRatio
+        )
+      )
+    );
+  }
+}
+
+module.exports = DevicePixelRatioMenu;
diff --git a/devtools/client/responsive/components/DeviceSelector.js b/devtools/client/responsive/components/DeviceSelector.js
new file mode 100644
index 0000000000..3028f2fa42
--- /dev/null
+++ b/devtools/client/responsive/components/DeviceSelector.js
@@ -0,0 +1,173 @@
+/* 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 {
+  createFactory,
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const { hr } = dom;
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+
+const {
+  getStr,
+} = require("resource://devtools/client/responsive/utils/l10n.js");
+const {
+  parseUserAgent,
+} = require("resource://devtools/client/responsive/utils/ua.js");
+const Types = require("resource://devtools/client/responsive/types.js");
+
+const MenuButton = createFactory(
+  require("resource://devtools/client/shared/components/menu/MenuButton.js")
+);
+
+loader.lazyGetter(this, "MenuItem", () => {
+  const menuItemClass = require("resource://devtools/client/shared/components/menu/MenuItem.js");
+  const menuItem = createFactory(menuItemClass);
+  menuItem.DUMMY_ICON = menuItemClass.DUMMY_ICON;
+  return menuItem;
+});
+
+loader.lazyGetter(this, "MenuList", () => {
+  return createFactory(
+    require("resource://devtools/client/shared/components/menu/MenuList.js")
+  );
+});
+
+class DeviceSelector extends PureComponent {
+  static get propTypes() {
+    return {
+      devices: PropTypes.shape(Types.devices).isRequired,
+      onChangeDevice: PropTypes.func.isRequired,
+      onUpdateDeviceModal: PropTypes.func.isRequired,
+      selectedDevice: PropTypes.string.isRequired,
+      viewportId: PropTypes.number.isRequired,
+    };
+  }
+
+  getMenuProps(device) {
+    if (!device) {
+      return { icon: null, label: null, tooltip: null };
+    }
+
+    const { browser, os } = parseUserAgent(device.userAgent);
+    let label = device.name;
+    if (os) {
+      label += ` ${os.name}`;
+      if (os.version) {
+        label += ` ${os.version}`;
+      }
+    }
+
+    let icon = null;
+    let tooltip = label;
+    if (browser) {
+      icon = `chrome://devtools/skin/images/browsers/${browser.name.toLowerCase()}.svg`;
+      tooltip += ` ${browser.name} ${browser.version}`;
+    }
+
+    return { icon, label, tooltip };
+  }
+
+  getSelectedDevice() {
+    const { devices, selectedDevice } = this.props;
+
+    if (!selectedDevice) {
+      return null;
+    }
+
+    for (const type of devices.types) {
+      for (const device of devices[type]) {
+        if (selectedDevice === device.name) {
+          return device;
+        }
+      }
+    }
+
+    return null;
+  }
+
+  renderMenuList() {
+    const {
+      devices,
+      onChangeDevice,
+      onUpdateDeviceModal,
+      selectedDevice,
+      viewportId,
+    } = this.props;
+
+    const menuItems = [];
+
+    for (const type of devices.types) {
+      for (const device of devices[type]) {
+        if (device.displayed) {
+          const { icon, label, tooltip } = this.getMenuProps(device);
+
+          menuItems.push(
+            MenuItem({
+              key: label,
+              className: "device-selector-item",
+              checked: selectedDevice === device.name,
+              label,
+              icon: icon || MenuItem.DUMMY_ICON,
+              tooltip,
+              onClick: () => onChangeDevice(viewportId, device, type),
+            })
+          );
+        }
+      }
+    }
+
+    menuItems.sort(function (a, b) {
+      return a.props.label.localeCompare(b.props.label);
+    });
+
+    if (menuItems.length) {
+      menuItems.push(hr({ key: "separator" }));
+    }
+
+    menuItems.push(
+      MenuItem({
+        key: "edit-device",
+        label: getStr("responsive.editDeviceList2"),
+        onClick: () => onUpdateDeviceModal(true, viewportId),
+      })
+    );
+
+    return MenuList({}, menuItems);
+  }
+
+  render() {
+    const { devices } = this.props;
+    const selectedDevice = this.getSelectedDevice();
+    let { icon, label, tooltip } = this.getMenuProps(selectedDevice);
+
+    if (!selectedDevice) {
+      label = getStr("responsive.responsiveMode");
+    }
+
+    // MenuButton is expected to be used in the toolbox document usually,
+    // but since RDM's frame also loads theme-switching.js, we can create
+    // MenuButtons (& HTMLTooltips) in the RDM frame document.
+    const toolboxDoc = window.document;
+
+    return MenuButton(
+      {
+        id: "device-selector",
+        menuId: "device-selector-menu",
+        toolboxDoc,
+        className: "devtools-button devtools-dropdown-button",
+        label,
+        icon,
+        title: tooltip,
+        disabled: devices.listState !== Types.loadableState.LOADED,
+      },
+      () => this.renderMenuList()
+    );
+  }
+}
+
+module.exports = DeviceSelector;
diff --git a/devtools/client/responsive/components/SettingsMenu.js b/devtools/client/responsive/components/SettingsMenu.js
new file mode 100644
index 0000000000..a221ce39ec
--- /dev/null
+++ b/devtools/client/responsive/components/SettingsMenu.js
@@ -0,0 +1,122 @@
+/* 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 {
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+const {
+  connect,
+} = require("resource://devtools/client/shared/vendor/react-redux.js");
+
+const {
+  getStr,
+} = require("resource://devtools/client/responsive/utils/l10n.js");
+
+loader.lazyRequireGetter(
+  this,
+  "showMenu",
+  "resource://devtools/client/shared/components/menu/utils.js",
+  true
+);
+
+class SettingsMenu extends PureComponent {
+  static get propTypes() {
+    return {
+      leftAlignmentEnabled: PropTypes.bool.isRequired,
+      onToggleLeftAlignment: PropTypes.func.isRequired,
+      onToggleReloadOnTouchSimulation: PropTypes.func.isRequired,
+      onToggleReloadOnUserAgent: PropTypes.func.isRequired,
+      onToggleUserAgentInput: PropTypes.func.isRequired,
+      reloadOnTouchSimulation: PropTypes.bool.isRequired,
+      reloadOnUserAgent: PropTypes.bool.isRequired,
+      showUserAgentInput: PropTypes.bool.isRequired,
+    };
+  }
+
+  constructor(props) {
+    super(props);
+    this.onToggleSettingMenu = this.onToggleSettingMenu.bind(this);
+  }
+
+  onToggleSettingMenu(event) {
+    const {
+      leftAlignmentEnabled,
+      onToggleLeftAlignment,
+      onToggleReloadOnTouchSimulation,
+      onToggleReloadOnUserAgent,
+      onToggleUserAgentInput,
+      reloadOnTouchSimulation,
+      reloadOnUserAgent,
+      showUserAgentInput,
+    } = this.props;
+
+    const menuItems = [
+      {
+        id: "toggleLeftAlignment",
+        checked: leftAlignmentEnabled,
+        label: getStr("responsive.leftAlignViewport"),
+        type: "checkbox",
+        click: () => {
+          onToggleLeftAlignment();
+        },
+      },
+      "-",
+      {
+        id: "toggleUserAgentInput",
+        checked: showUserAgentInput,
+        label: getStr("responsive.showUserAgentInput"),
+        type: "checkbox",
+        click: () => {
+          onToggleUserAgentInput();
+        },
+      },
+      "-",
+      {
+        id: "touchSimulation",
+        checked: reloadOnTouchSimulation,
+        label: getStr("responsive.reloadConditions.touchSimulation"),
+        type: "checkbox",
+        click: () => {
+          onToggleReloadOnTouchSimulation();
+        },
+      },
+      {
+        id: "userAgent",
+        checked: reloadOnUserAgent,
+        label: getStr("responsive.reloadConditions.userAgent"),
+        type: "checkbox",
+        click: () => {
+          onToggleReloadOnUserAgent();
+        },
+      },
+    ];
+
+    showMenu(menuItems, {
+      button: event.target,
+    });
+  }
+
+  render() {
+    return dom.button({
+      id: "settings-button",
+      className: "devtools-button",
+      onClick: this.onToggleSettingMenu,
+    });
+  }
+}
+
+const mapStateToProps = state => {
+  return {
+    leftAlignmentEnabled: state.ui.leftAlignmentEnabled,
+    reloadOnTouchSimulation: state.ui.reloadOnTouchSimulation,
+    reloadOnUserAgent: state.ui.reloadOnUserAgent,
+    showUserAgentInput: state.ui.showUserAgentInput,
+  };
+};
+
+module.exports = connect(mapStateToProps)(SettingsMenu);
diff --git a/devtools/client/responsive/components/Toolbar.js b/devtools/client/responsive/components/Toolbar.js
new file mode 100644
index 0000000000..a9a75dc9b3
--- /dev/null
+++ b/devtools/client/responsive/components/Toolbar.js
@@ -0,0 +1,216 @@
+/* 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 {
+  createElement,
+  createFactory,
+  Fragment,
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+const {
+  connect,
+} = require("resource://devtools/client/shared/vendor/react-redux.js");
+
+const DevicePixelRatioMenu = createFactory(
+  require("resource://devtools/client/responsive/components/DevicePixelRatioMenu.js")
+);
+const DeviceSelector = createFactory(
+  require("resource://devtools/client/responsive/components/DeviceSelector.js")
+);
+const NetworkThrottlingMenu = createFactory(
+  require("resource://devtools/client/shared/components/throttling/NetworkThrottlingMenu.js")
+);
+const SettingsMenu = createFactory(
+  require("resource://devtools/client/responsive/components/SettingsMenu.js")
+);
+const ViewportDimension = createFactory(
+  require("resource://devtools/client/responsive/components/ViewportDimension.js")
+);
+
+loader.lazyGetter(this, "UserAgentInput", function () {
+  return createFactory(
+    require("resource://devtools/client/responsive/components/UserAgentInput.js")
+  );
+});
+
+const {
+  getStr,
+} = require("resource://devtools/client/responsive/utils/l10n.js");
+const Types = require("resource://devtools/client/responsive/types.js");
+
+class Toolbar extends PureComponent {
+  static get propTypes() {
+    return {
+      devices: PropTypes.shape(Types.devices).isRequired,
+      displayPixelRatio: PropTypes.number.isRequired,
+      leftAlignmentEnabled: PropTypes.bool.isRequired,
+      networkThrottling: PropTypes.shape(Types.networkThrottling).isRequired,
+      onChangeDevice: PropTypes.func.isRequired,
+      onChangeNetworkThrottling: PropTypes.func.isRequired,
+      onChangePixelRatio: PropTypes.func.isRequired,
+      onChangeTouchSimulation: PropTypes.func.isRequired,
+      onChangeUserAgent: PropTypes.func.isRequired,
+      onExit: PropTypes.func.isRequired,
+      onRemoveDeviceAssociation: PropTypes.func.isRequired,
+      doResizeViewport: PropTypes.func.isRequired,
+      onRotateViewport: PropTypes.func.isRequired,
+      onScreenshot: PropTypes.func.isRequired,
+      onToggleLeftAlignment: PropTypes.func.isRequired,
+      onToggleReloadOnTouchSimulation: PropTypes.func.isRequired,
+      onToggleReloadOnUserAgent: PropTypes.func.isRequired,
+      onToggleUserAgentInput: PropTypes.func.isRequired,
+      onUpdateDeviceModal: PropTypes.func.isRequired,
+      screenshot: PropTypes.shape(Types.screenshot).isRequired,
+      selectedDevice: PropTypes.string.isRequired,
+      selectedPixelRatio: PropTypes.number.isRequired,
+      showUserAgentInput: PropTypes.bool.isRequired,
+      touchSimulationEnabled: PropTypes.bool.isRequired,
+      viewport: PropTypes.shape(Types.viewport).isRequired,
+    };
+  }
+
+  renderUserAgent() {
+    const { onChangeUserAgent, showUserAgentInput } = this.props;
+
+    if (!showUserAgentInput) {
+      return null;
+    }
+
+    return createElement(
+      Fragment,
+      null,
+      UserAgentInput({
+        onChangeUserAgent,
+      }),
+      dom.div({ className: "devtools-separator" })
+    );
+  }
+
+  render() {
+    const {
+      devices,
+      displayPixelRatio,
+      leftAlignmentEnabled,
+      networkThrottling,
+      onChangeDevice,
+      onChangeNetworkThrottling,
+      onChangePixelRatio,
+      onChangeTouchSimulation,
+      onExit,
+      onRemoveDeviceAssociation,
+      doResizeViewport,
+      onRotateViewport,
+      onScreenshot,
+      onToggleLeftAlignment,
+      onToggleReloadOnTouchSimulation,
+      onToggleReloadOnUserAgent,
+      onToggleUserAgentInput,
+      onUpdateDeviceModal,
+      screenshot,
+      selectedDevice,
+      selectedPixelRatio,
+      showUserAgentInput,
+      touchSimulationEnabled,
+      viewport,
+    } = this.props;
+
+    return dom.header(
+      {
+        id: "toolbar",
+        className: [
+          leftAlignmentEnabled ? "left-aligned" : "",
+          showUserAgentInput ? "user-agent" : "",
+        ]
+          .join(" ")
+          .trim(),
+      },
+      dom.div(
+        { id: "toolbar-center-controls" },
+        DeviceSelector({
+          devices,
+          onChangeDevice,
+          onUpdateDeviceModal,
+          selectedDevice,
+          viewportId: viewport.id,
+        }),
+        dom.div({ className: "devtools-separator" }),
+        ViewportDimension({
+          onRemoveDeviceAssociation,
+          doResizeViewport,
+          viewport,
+        }),
+        dom.button({
+          id: "rotate-button",
+          className: `devtools-button viewport-orientation-${
+            viewport.width > viewport.height ? "landscape" : "portrait"
+          }`,
+          onClick: () => onRotateViewport(viewport.id),
+          title: getStr("responsive.rotate"),
+        }),
+        dom.div({ className: "devtools-separator" }),
+        DevicePixelRatioMenu({
+          devices,
+          displayPixelRatio,
+          onChangePixelRatio,
+          selectedDevice,
+          selectedPixelRatio,
+        }),
+        dom.div({ className: "devtools-separator" }),
+        NetworkThrottlingMenu({
+          networkThrottling,
+          onChangeNetworkThrottling,
+        }),
+        dom.div({ className: "devtools-separator" }),
+        this.renderUserAgent(),
+        dom.button({
+          id: "touch-simulation-button",
+          className:
+            "devtools-button" + (touchSimulationEnabled ? " checked" : ""),
+          title: touchSimulationEnabled
+            ? getStr("responsive.disableTouch")
+            : getStr("responsive.enableTouch"),
+          onClick: () => onChangeTouchSimulation(!touchSimulationEnabled),
+        })
+      ),
+      dom.div(
+        { id: "toolbar-end-controls" },
+        dom.button({
+          id: "screenshot-button",
+          className: "devtools-button",
+          title: getStr("responsive.screenshot"),
+          onClick: onScreenshot,
+          disabled: screenshot.isCapturing,
+        }),
+        SettingsMenu({
+          onToggleLeftAlignment,
+          onToggleReloadOnTouchSimulation,
+          onToggleReloadOnUserAgent,
+          onToggleUserAgentInput,
+        }),
+        dom.div({ className: "devtools-separator" }),
+        dom.button({
+          id: "exit-button",
+          className: "devtools-button",
+          title: getStr("responsive.exit"),
+          onClick: onExit,
+        })
+      )
+    );
+  }
+}
+
+const mapStateToProps = state => {
+  return {
+    displayPixelRatio: state.ui.displayPixelRatio,
+    leftAlignmentEnabled: state.ui.leftAlignmentEnabled,
+    showUserAgentInput: state.ui.showUserAgentInput,
+    touchSimulationEnabled: state.ui.touchSimulationEnabled,
+  };
+};
+
+module.exports = connect(mapStateToProps)(Toolbar);
diff --git a/devtools/client/responsive/components/UserAgentInput.js b/devtools/client/responsive/components/UserAgentInput.js
new file mode 100644
index 0000000000..d24fc99c6f
--- /dev/null
+++ b/devtools/client/responsive/components/UserAgentInput.js
@@ -0,0 +1,103 @@
+/* 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 {
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+const {
+  connect,
+} = require("resource://devtools/client/shared/vendor/react-redux.js");
+const { KeyCodes } = require("resource://devtools/client/shared/keycodes.js");
+
+const {
+  getStr,
+} = require("resource://devtools/client/responsive/utils/l10n.js");
+
+class UserAgentInput extends PureComponent {
+  static get propTypes() {
+    return {
+      onChangeUserAgent: PropTypes.func.isRequired,
+      userAgent: PropTypes.string.isRequired,
+    };
+  }
+
+  constructor(props) {
+    super(props);
+
+    this.state = {
+      // The user agent input value.
+      value: this.props.userAgent,
+    };
+
+    this.onChange = this.onChange.bind(this);
+    this.onKeyUp = this.onKeyUp.bind(this);
+  }
+
+  // FIXME: https://bugzilla.mozilla.org/show_bug.cgi?id=1774507
+  UNSAFE_componentWillReceiveProps(nextProps) {
+    if (this.props.userAgent !== nextProps.userAgent) {
+      this.setState({ value: nextProps.userAgent });
+    }
+  }
+
+  /**
+   * Input change handler.
+   *
+   * @param  {Event} event
+   */
+  onChange({ target }) {
+    const value = target.value;
+
+    this.setState(prevState => {
+      return {
+        ...prevState,
+        value,
+      };
+    });
+  }
+
+  /**
+   * Input key up handler.
+   *
+   * @param  {Event} event
+   */
+  onKeyUp({ target, keyCode }) {
+    if (keyCode == KeyCodes.DOM_VK_RETURN) {
+      this.props.onChangeUserAgent(target.value);
+      target.blur();
+    }
+
+    if (keyCode == KeyCodes.DOM_VK_ESCAPE) {
+      target.blur();
+    }
+  }
+
+  render() {
+    return dom.label(
+      { id: "user-agent-label" },
+      "UA:",
+      dom.input({
+        id: "user-agent-input",
+        className: "text-input",
+        onChange: this.onChange,
+        onKeyUp: this.onKeyUp,
+        placeholder: getStr("responsive.customUserAgent"),
+        type: "text",
+        value: this.state.value,
+      })
+    );
+  }
+}
+
+const mapStateToProps = state => {
+  return {
+    userAgent: state.ui.userAgent,
+  };
+};
+
+module.exports = connect(mapStateToProps)(UserAgentInput);
diff --git a/devtools/client/responsive/components/ViewportDimension.js b/devtools/client/responsive/components/ViewportDimension.js
new file mode 100644
index 0000000000..988b690e21
--- /dev/null
+++ b/devtools/client/responsive/components/ViewportDimension.js
@@ -0,0 +1,251 @@
+/* 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 {
+  PureComponent,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const dom = require("resource://devtools/client/shared/vendor/react-dom-factories.js");
+const PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+
+const {
+  isKeyIn,
+} = require("resource://devtools/client/responsive/utils/key.js");
+const {
+  MIN_VIEWPORT_DIMENSION,
+} = require("resource://devtools/client/responsive/constants.js");
+const Types = require("resource://devtools/client/responsive/types.js");
+
+class ViewportDimension extends PureComponent {
+  static get propTypes() {
+    return {
+      doResizeViewport: PropTypes.func.isRequired,
+      onRemoveDeviceAssociation: PropTypes.func.isRequired,
+      viewport: PropTypes.shape(Types.viewport).isRequired,
+    };
+  }
+
+  constructor(props) {
+    super(props);
+
+    const { width, height } = props.viewport;
+
+    this.state = {
+      width,
+      height,
+      isEditing: false,
+      isWidthValid: true,
+      isHeightValid: true,
+    };
+
+    this.isInputValid = this.isInputValid.bind(this);
+    this.onInputBlur = this.onInputBlur.bind(this);
+    this.onInputChange = this.onInputChange.bind(this);
+    this.onInputFocus = this.onInputFocus.bind(this);
+    this.onInputKeyDown = this.onInputKeyDown.bind(this);
+    this.onInputKeyUp = this.onInputKeyUp.bind(this);
+    this.onInputSubmit = this.onInputSubmit.bind(this);
+  }
+
+  // FIXME: https://bugzilla.mozilla.org/show_bug.cgi?id=1774507
+  UNSAFE_componentWillReceiveProps(nextProps) {
+    const { width, height } = nextProps.viewport;
+
+    this.setState({
+      width,
+      height,
+    });
+  }
+
+  /**
+   * Return true if the given value is a number and greater than MIN_VIEWPORT_DIMENSION
+   * and false otherwise.
+   */
+  isInputValid(value) {
+    return (
+      /^\d{2,4}$/.test(value) && parseInt(value, 10) >= MIN_VIEWPORT_DIMENSION
+    );
+  }
+
+  onInputBlur() {
+    const { width, height } = this.props.viewport;
+
+    if (this.state.width != width || this.state.height != height) {
+      this.onInputSubmit();
+    }
+
+    this.setState({ isEditing: false });
+  }
+
+  onInputChange({ target }, callback) {
+    if (target.value.length > 4) {
+      return;
+    }
+
+    if (this.widthInput == target) {
+      this.setState(
+        {
+          width: target.value,
+          isWidthValid: this.isInputValid(target.value),
+        },
+        callback
+      );
+    }
+
+    if (this.heightInput == target) {
+      this.setState(
+        {
+          height: target.value,
+          isHeightValid: this.isInputValid(target.value),
+        },
+        callback
+      );
+    }
+  }
+
+  onInputFocus(e) {
+    this.setState({ isEditing: true });
+    e.target.select();
+  }
+
+  onInputKeyDown(event) {
+    const increment = getIncrement(event);
+    if (!increment) {
+      return;
+    }
+
+    const { target } = event;
+    target.value = parseInt(target.value, 10) + increment;
+    this.onInputChange(event, this.onInputSubmit);
+
+    // Keep this event from having default processing. Since the field is a
+    // number field, default processing would trigger additional manipulations
+    // of the value, and we've already applied the desired amount.
+    event.preventDefault();
+  }
+
+  onInputKeyUp({ target, keyCode }) {
+    // On Enter, submit the input
+    if (keyCode == 13) {
+      this.onInputSubmit();
+    }
+
+    // On Esc, blur the target
+    if (keyCode == 27) {
+      target.blur();
+    }
+  }
+
+  onInputSubmit() {
+    const { viewport, onRemoveDeviceAssociation, doResizeViewport } =
+      this.props;
+
+    if (!this.state.isWidthValid || !this.state.isHeightValid) {
+      const { width, height } = viewport;
+
+      this.setState({
+        width,
+        height,
+        isWidthValid: true,
+        isHeightValid: true,
+      });
+
+      return;
+    }
+
+    // Change the device selector back to an unselected device
+    // TODO: Bug 1332754: Logic like this probably belongs in the action creator.
+    if (viewport.device) {
+      onRemoveDeviceAssociation(viewport.id);
+    }
+
+    doResizeViewport(
+      viewport.id,
+      parseInt(this.state.width, 10),
+      parseInt(this.state.height, 10)
+    );
+  }
+
+  render() {
+    return dom.div(
+      {
+        className:
+          "viewport-dimension" +
+          (this.state.isEditing ? " editing" : "") +
+          (!this.state.isWidthValid || !this.state.isHeightValid
+            ? " invalid"
+            : ""),
+      },
+      dom.input({
+        ref: input => {
+          this.widthInput = input;
+        },
+        className:
+          "text-input viewport-dimension-input" +
+          (this.state.isWidthValid ? "" : " invalid"),
+        size: 4,
+        type: "number",
+        value: this.state.width,
+        onBlur: this.onInputBlur,
+        onChange: this.onInputChange,
+        onFocus: this.onInputFocus,
+        onKeyDown: this.onInputKeyDown,
+        onKeyUp: this.onInputKeyUp,
+      }),
+      dom.span(
+        {
+          className: "viewport-dimension-separator",
+        },
+        "×"
+      ),
+      dom.input({
+        ref: input => {
+          this.heightInput = input;
+        },
+        className:
+          "text-input viewport-dimension-input" +
+          (this.state.isHeightValid ? "" : " invalid"),
+        size: 4,
+        type: "number",
+        value: this.state.height,
+        onBlur: this.onInputBlur,
+        onChange: this.onInputChange,
+        onFocus: this.onInputFocus,
+        onKeyDown: this.onInputKeyDown,
+        onKeyUp: this.onInputKeyUp,
+      })
+    );
+  }
+}
+
+/**
+ * Get the increment/decrement step to use for the provided key event.
+ */
+function getIncrement(event) {
+  const defaultIncrement = 1;
+  const largeIncrement = 100;
+  const mediumIncrement = 10;
+
+  let increment = 0;
+  const key = event.keyCode;
+
+  if (isKeyIn(key, "UP", "PAGE_UP")) {
+    increment = 1 * defaultIncrement;
+  } else if (isKeyIn(key, "DOWN", "PAGE_DOWN")) {
+    increment = -1 * defaultIncrement;
+  }
+
+  if (event.shiftKey) {
+    if (isKeyIn(key, "PAGE_UP", "PAGE_DOWN")) {
+      increment *= largeIncrement;
+    } else {
+      increment *= mediumIncrement;
+    }
+  }
+
+  return increment;
+}
+
+module.exports = ViewportDimension;
diff --git a/devtools/client/responsive/components/moz.build b/devtools/client/responsive/components/moz.build
new file mode 100644
index 0000000000..04ef642afc
--- /dev/null
+++ b/devtools/client/responsive/components/moz.build
@@ -0,0 +1,20 @@
+# -*- 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(
+    "App.js",
+    "Device.js",
+    "DeviceForm.js",
+    "DeviceInfo.js",
+    "DeviceList.js",
+    "DeviceModal.js",
+    "DevicePixelRatioMenu.js",
+    "DeviceSelector.js",
+    "SettingsMenu.js",
+    "Toolbar.js",
+    "UserAgentInput.js",
+    "ViewportDimension.js",
+)
diff --git a/devtools/client/responsive/constants.js b/devtools/client/responsive/constants.js
new file mode 100644
index 0000000000..a01cd69f51
--- /dev/null
+++ b/devtools/client/responsive/constants.js
@@ -0,0 +1,14 @@
+/* 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";
+
+// The minimum viewport width and height
+exports.MIN_VIEWPORT_DIMENSION = 50;
+
+// Orientation types
+exports.PORTRAIT_PRIMARY = "portrait-primary";
+exports.PORTRAIT_SECONDARY = "portrait-secondary";
+exports.LANDSCAPE_PRIMARY = "landscape-primary";
+exports.LANDSCAPE_SECONDARY = "landscape-secondary";
diff --git a/devtools/client/responsive/docs/devices.md b/devtools/client/responsive/docs/devices.md
new file mode 100644
index 0000000000..ba54428638
--- /dev/null
+++ b/devtools/client/responsive/docs/devices.md
@@ -0,0 +1,37 @@
+# Updating List of Devices for RDM
+
+## Where to locate the list
+
+The devices list is a [RemoteSettings](https://firefox-source-docs.mozilla.org/services/settings/index.html) collection named `devtools-devices`.
+A dump of the list can be found in [services/settings/dumps/main/devtools-devices.json](https://searchfox.org/mozilla-central/source/services/settings/dumps/main/devtools-devices.json).
+
+## Adding and removing devices
+
+There is no set criteria for which devices should be added or removed from the list. However, we can take this into account:
+
+- Adding the latest iPhone and iPad models from Apple.
+- Adding the latest Galaxy series from Samsung.
+- Checking out what devices Google Chrome supports in its DevTools. They keep the list hardcoded in [source](https://github.com/ChromeDevTools/devtools-frontend/blob/79095c6c14d96582806982b63e99ef936a6cd74c/front_end/models/emulation/EmulatedDevices.ts#L645)
+
+## Data format
+
+An important field is `featured`, which is a boolean. When set to `true`, the device will appear in the RDM dropdown. If it's set to `false`, the device will not appear in the dropdown, but can be enabled in the `Edit list` modal.
+Each device has a user agent specified. We can get this value by:
+
+- At `https://developers.whatismybrowser.com/useragents/explore/`
+- With a real device, open its default browser, and google "my user agent" will display a Google widget with the user agent string.
+- Looking at Google's own list of devices (they also specify the user agent)
+
+## Releasing the changes
+
+First, make sure you can have access to RemoteSettings (see https://remote-settings.readthedocs.io/en/latest/getting-started.html#getting-started).
+
+You should then be able to add the device to the [RemoteSettings Stage instance](https://remote-settings.allizom.org/v1/admin/#/buckets/main-workspace/collections/devtools-devices/) using the interface.
+Then use the RemoteSettings DevTools to make Firefox pull the devices list from the Stage instance (see https://remote-settings.readthedocs.io/en/latest/support.html?highlight=devtools#how-do-i-setup-firefox-to-pull-data-from-stage)
+Once that is done, open RDM and make sure you can see the new addition in the Devices modal.
+
+If everything is good, you can then ask for review on the data change. Once this get approved, you can replicate the same changes to the [RemoteSettings Prod instance](https://remote-settings.mozilla.org/v1/admin/#/buckets/main-workspace/collections/devtools-devices/), reset the RemoteSettings DevTools settings, check RDM again just to be sure and finally ask for review on the data change.
+
+## Things to consider in the future
+
+- Galaxy Fold has two screens, how do we handle that?
diff --git a/devtools/client/responsive/images/grippers.svg b/devtools/client/responsive/images/grippers.svg
new file mode 100644
index 0000000000..91db83af9d
--- /dev/null
+++ b/devtools/client/responsive/images/grippers.svg
@@ -0,0 +1,6 @@
+<!-- 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/. -->
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16" fill="#A5A5A5">
+  <path d="M16 3.2L3.1 16h1.7L16 4.9zM16 7.2L7.1 16h1.8L16 8.9zM16 11.1L11.1 16h1.8l3.1-3.1z" />
+</svg>
diff --git a/devtools/client/responsive/images/rotate-viewport.svg b/devtools/client/responsive/images/rotate-viewport.svg
new file mode 100644
index 0000000000..2a9fd2f6a8
--- /dev/null
+++ b/devtools/client/responsive/images/rotate-viewport.svg
@@ -0,0 +1,7 @@
+<!-- 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/. -->
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
+  <path fill="context-fill" fill-rule="evenodd" d="M2 1a1 1 0 0 0-1 1v12a1 1 0 0 0 1 1h6a1 1 0 0 0 1-1V2a1 1 0 0 0-1-1H2zm6 2H2v10h6V3z"/>
+  <path fill="context-fill" d="M10.5 4c.62 0 1.07.03 1.4.11.34.08.53.2.66.34.14.16.25.4.33.83.08.42.11.98.11 1.72h-1.43a.2.2 0 0 0-.15.33l1.93 2.33c.08.1.22.1.3 0l1.93-2.33a.2.2 0 0 0-.15-.33H14c0-.76-.03-1.39-.13-1.9-.09-.52-.26-.96-.56-1.3-.3-.35-.7-.55-1.17-.66-.46-.1-1-.14-1.64-.14v1z"/>
+</svg>
diff --git a/devtools/client/responsive/images/touch-events.svg b/devtools/client/responsive/images/touch-events.svg
new file mode 100644
index 0000000000..42de2d8e04
--- /dev/null
+++ b/devtools/client/responsive/images/touch-events.svg
@@ -0,0 +1,6 @@
+<!-- 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/. -->
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
+  <path fill="context-fill" d="M3.174 6.222A3.99 3.99 0 0 1 2.5 4a4 4 0 1 1 7.326 2.222l-.83-.556A2.99 2.99 0 0 0 9.5 4a3 3 0 1 0-5.495 1.666l-.831.556zM5 9.4V3.5a1.5 1.5 0 1 1 3 0v3.085a1.499 1.499 0 0 1 1.764.607 1.499 1.499 0 0 1 2 .5A1.5 1.5 0 0 1 14 9h-.004c0 .155-.023.313-.074.468l-1.791 5.494A1.5 1.5 0 0 1 10.739 16V16H6.695a2.5 2.5 0 0 1-2.202-1.315L1.975 10.01a1.5 1.5 0 0 1 .443-1.927l.04-.029c.04-.029.04-.029.083-.056a1.36 1.36 0 0 1 1.87.446L5 9.4zm6.18 5.253L12.97 9.16a.5.5 0 0 0-.847-.488A.498.498 0 0 0 12 9a.5.5 0 1 1-1 0v-.5a.5.5 0 1 0-1 0 .5.5 0 1 1-1 0V8a.5.5 0 1 0-1 0 .5.5 0 0 1-1 0V3.5a.5.5 0 0 0-1 0v7.667c0 .504-.662.691-.926.262L3.56 8.967a.36.36 0 0 0-.494-.118l-.007.004-.008.006-.007.005-.04.028a.5.5 0 0 0-.147.643l2.518 4.676a1.5 1.5 0 0 0 1.32.789h4.013v-.001a.5.5 0 0 0 .473-.346z"/>
+</svg>
diff --git a/devtools/client/responsive/index.css b/devtools/client/responsive/index.css
new file mode 100644
index 0000000000..c8342bc8ea
--- /dev/null
+++ b/devtools/client/responsive/index.css
@@ -0,0 +1,750 @@
+/* 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/. */
+
+/* TODO: May break up into component local CSS.  Pending future discussions by
+ * React component group on how to best handle CSS. */
+
+/**
+ * CSS Variables specific to the responsive design mode
+ */
+
+:root {
+  --toolbar-row-height: 28px;
+  --rdm-box-shadow: 0 4px 4px 0 rgba(155, 155, 155, 0.26);
+  --viewport-active-color: #3b3b3b;
+  --input-invalid-border-color: var(--red-60);
+  --custom-device-button-hover: var(--grey-30);
+  --device-list-grid-template-columns: auto auto max-content 1fr;
+}
+
+:root.theme-dark {
+  --rdm-box-shadow: 0 4px 4px 0 rgba(105, 105, 105, 0.26);
+  --viewport-active-color: #fcfcfc;
+  --input-invalid-border-color: var(--red-50);
+  --custom-device-button-hover: var(--grey-70);
+}
+
+* {
+  box-sizing: border-box;
+}
+
+:root,
+input,
+button {
+  font-size: 12px;
+}
+
+input,
+button {
+  color: var(--theme-toolbar-color);
+  background-color: var(--theme-tab-toolbar-background);
+}
+
+html,
+body,
+#root {
+  height: 100%;
+  overflow: hidden;
+  color: var(--theme-body-color);
+}
+
+.text-input {
+  border: 1px solid var(--theme-splitter-color);
+  margin: 0 1px;
+  padding: 2px;
+  font-size: 12px;
+  line-height: 16px;
+}
+
+.text-input.invalid {
+  outline-color: var(--input-invalid-border-color);
+}
+
+#app {
+  display: flex;
+  flex-direction: column;
+  width: 100%;
+  height: 100%;
+}
+
+/**
+ * Common styles for shared components
+ */
+
+.devtools-separator {
+  height: 100%;
+  margin: 0 1px;
+}
+
+/**
+ * Toolbar
+ */
+
+#toolbar {
+  background-color: var(--theme-tab-toolbar-background);
+  border-bottom: 1px solid var(--theme-splitter-color);
+  display: grid;
+  grid-template-columns: auto min-content;
+  width: 100%;
+  user-select: none;
+}
+
+#toolbar :is(select, button):focus-visible {
+  /* Adjust the outline otherwise it's clipped at the top */
+  outline-offset: -1px
+}
+
+#toolbar-center-controls,
+#toolbar-end-controls {
+  display: grid;
+  grid-auto-flow: column;
+  grid-auto-rows: var(--toolbar-row-height);
+  grid-row-gap: 1px;
+  padding: 0 1px;
+}
+
+#toolbar-center-controls {
+  grid-gap: 2px;
+  grid-template-columns:
+    [device-selector]
+    minmax(auto, 120px)
+    [separator]
+    max-content
+    [size-selector]
+    max-content
+    [rotate-icon]
+    max-content
+    [separator]
+    max-content
+    [dpr]
+    minmax(auto, 60px)
+    [separator]
+    max-content
+    [throttling]
+    minmax(auto, max-content)
+    [separator]
+    max-content
+    [touch-simulation]
+    max-content;
+}
+
+#toolbar.user-agent #toolbar-center-controls {
+  grid-template-columns:
+    [device-selector]
+    minmax(auto, 120px)
+    [separator]
+    max-content
+    [size-selector]
+    max-content
+    [rotate-icon]
+    max-content
+    [separator]
+    max-content
+    [dpr]
+    minmax(auto, 60px)
+    [separator]
+    max-content
+    [throttling]
+    minmax(auto, max-content)
+    [separator]
+    max-content
+    [ua]
+    minmax(auto, 300px)
+    [separator]
+    max-content
+    [touch-simulation]
+    max-content;
+}
+
+#toolbar:not(.left-aligned) {
+  grid-template-columns: 1fr auto 1fr min-content;
+  justify-content: center;
+}
+
+#toolbar:not(.left-aligned) #toolbar-center-controls {
+  grid-column-start: 2;
+}
+
+#toolbar:not(.left-aligned) #toolbar-end-controls {
+  justify-content: end;
+}
+
+#user-agent-label {
+  display: flex;
+  align-items: center;
+  margin-inline-start: 3px;
+  margin-inline-end: 3px;
+}
+
+#user-agent-input {
+  margin-inline-start: 3px;
+  flex: 1;
+}
+
+@media (max-width: 520px) {
+  /* When room becomes scarce, no need to constrain the selectors with a minmax like we
+     do in larger viewports, here they can occupy 1fr */
+  #toolbar.user-agent #toolbar-center-controls {
+    grid-template-columns:
+      [device-selector]
+      .8fr
+      [separator]
+      max-content
+      [size-selector]
+      max-content
+      [rotate-icon]
+      max-content
+      [separator]
+      max-content
+      [dpr]
+      .6fr
+      [separator]
+      max-content
+      [throttling]
+      1fr
+      [separator]
+      max-content
+      [touch-simulation]
+      max-content;
+  }
+
+  /* Drop the user agent label to the next line if there isn't enough space */
+  #user-agent-label {
+    grid-column: 1 / -1;
+    grid-row: 2;
+    margin-inline-start: 9px;
+  }
+
+  /* Since the UA is hidden, no need for a separator after it */
+  #user-agent-label + .devtools-separator {
+    display: none;
+  }
+
+  /* When the UA label is here and it's on a second line, draw a separator between the
+     2 lines*/
+  #toolbar.user-agent {
+    background-image: linear-gradient(to bottom,
+      transparent var(--toolbar-row-height),
+      var(--theme-splitter-color) var(--toolbar-row-height),
+      var(--theme-splitter-color) calc(var(--toolbar-row-height) + 1px),
+      transparent 0);
+  }
+}
+
+#rotate-button::before {
+  background-image: url("chrome://devtools/content/responsive/images/rotate-viewport.svg");
+}
+
+#rotate-button.viewport-orientation-landscape::before {
+  transform: rotate(90deg) scaleX(-1);
+}
+
+#touch-simulation-button::before {
+  background-image: url("chrome://devtools/content/responsive/images/touch-events.svg");
+}
+
+#screenshot-button::before {
+  background-image: url("chrome://devtools/skin/images/command-screenshot.svg");
+}
+
+#settings-button::before {
+  background-image: url("chrome://devtools/skin/images/settings.svg");
+}
+
+#exit-button::before {
+  background-image: url("chrome://devtools/skin/images/close.svg");
+}
+
+/* Briefly animate screenshot button when clicked */
+#screenshot-button:disabled {
+  opacity: 1 !important;
+}
+
+#screenshot-button:disabled::before {
+  fill: var(--theme-icon-checked-color);
+}
+
+#device-selector {
+  justify-self: end;
+  max-width: 100%;
+  margin-inline-start: 4px;
+}
+
+#device-selector .title {
+  display: grid;
+  grid-template-columns: var(--device-list-grid-template-columns);
+}
+
+#device-selector .title .device-name,
+#device-selector .title .device-os {
+  margin-inline-start: 6px;
+}
+
+#device-selector::before {
+  fill: var(--theme-icon-dimmed-color);
+}
+
+/* Override the style defined in tooltips.css */
+.tooltip-container[type="doorhanger"] .menuitem > .command.iconic.device-selector-item > .label::before {
+  fill: var(--theme-icon-dimmed-color);
+}
+
+/**
+ * Viewport Dimension Input
+ */
+
+.viewport-dimension {
+  display: flex;
+  align-items: center;
+  margin: 1px;
+}
+
+.viewport-dimension-input {
+  text-align: center;
+  width: 3em;
+  appearance: textfield;
+}
+
+.viewport-dimension-separator {
+  user-select: none;
+  padding: 0 0.2em;
+}
+
+/**
+ * Device Modal
+ */
+
+@keyframes fade-in-and-up {
+  0% {
+    opacity: 0;
+    transform: translateY(5px);
+  }
+  100% {
+    opacity: 1;
+    transform: translateY(0px);
+  }
+}
+
+@keyframes fade-down-and-out {
+  0% {
+    opacity: 1;
+    transform: translateY(0px);
+  }
+  100% {
+    opacity: 0;
+    transform: translateY(5px);
+    visibility: hidden;
+  }
+}
+
+.device-modal {
+  display: grid;
+  grid-template-rows: minmax(80px, auto) auto;
+  background-color: var(--theme-toolbar-background);
+  border: 1px solid var(--theme-splitter-color);
+  border-radius: 2px;
+  box-shadow: var(--rdm-box-shadow);
+  position: absolute;
+  margin: auto;
+  top: 0;
+  bottom: 0;
+  left: 0;
+  right: 0;
+  width: 90%;
+  height: 90%;
+  max-width: 750px;
+  max-height: 730px;
+  z-index: 1;
+  overflow: hidden;
+}
+
+/* Handles the opening/closing of the modal */
+#device-modal-wrapper.opened .device-modal {
+  animation: fade-in-and-up 0.3s ease forwards;
+}
+
+#device-modal-wrapper.closed .device-modal {
+  animation: fade-down-and-out 0.3s ease forwards;
+}
+
+#device-modal-wrapper.opened .modal-overlay {
+  background-color: var(--theme-splitter-color);
+  position: absolute;
+  top: 0;
+  left: 0;
+  height: 100%;
+  width: 100%;
+  z-index: 0;
+  opacity: 0.5;
+}
+
+.device-modal-content {
+  display: grid;
+  grid-row-gap: 30px;
+  overflow: auto;
+  height: 100%;
+  padding: 10px 32px 50px 32px;
+}
+
+/* On screens that are >750px*/
+@media (min-width: 750px) {
+  #device-form {
+    grid-template-areas: "name size dpr"
+                         "user-agent touch buttons";
+  }
+
+  #device-form-name input,
+  #device-form-user-agent input {
+    width: 350px;
+  }
+
+  .device-modal-content {
+    grid-template-columns: 1fr 1fr;
+    grid-template-areas: "phone phone"
+                         "tablet laptop"
+                         "tv custom";
+  }
+
+  .device-type-phones .device-list {
+    grid-template-columns: repeat(2, var(--device-list-grid-template-columns));
+  }
+}
+
+/* On screens that are between 450px and 749px */
+@media (min-width: 450px) and (max-width: 749px) {
+  #device-form {
+    grid-template-areas: "name size"
+                         "user-agent dpr"
+                         "touch buttons";
+    grid-template-columns: 2fr 1fr;
+  }
+
+  #device-form-name {
+    grid-area: name;
+  }
+
+  #device-form-name input,
+  #device-form-user-agent input {
+    width: 100%;
+  }
+}
+
+/* On screens that are <450px */
+@media (max-width: 449px) {
+  #device-form {
+    grid-template-areas: "name"
+                         "size"
+                         "dpr"
+                         "user-agent"
+                         "touch"
+                         "buttons";
+  }
+
+  #device-form-name input,
+  #device-form-user-agent input {
+    width: 90%;
+  }
+
+  #device-form-size {
+    justify-self: unset;
+  }
+}
+
+@media (max-width: 749px) {
+  .device-modal-content {
+    grid-template-areas: "phone"
+                         "phone"
+                         "tablet"
+                         "laptop"
+                         "tv"
+                         "custom";
+  }
+
+  .device-modal-header {
+    flex-direction: column;
+  }
+}
+
+#device-close-button {
+  position: absolute;
+  top: 5px;
+  right: 2px;
+}
+
+#device-close-button::before {
+  background-image: url("chrome://devtools/skin/images/close.svg");
+}
+
+.device-type {
+  display: flex;
+  flex-direction: column;
+}
+
+.device-header {
+  font-size: 17px;
+  margin-bottom: 7px;
+  height: 20px;
+  text-transform: capitalize;
+}
+
+.device-label {
+  color: var(--theme-body-color);
+  padding-bottom: 5px;
+  padding-top: 5px;
+  align-items: center;
+  display: grid;
+  grid-column: span 4;
+  grid-template-columns: subgrid;
+}
+
+.device-label > button {
+  visibility: hidden;
+}
+
+.device-label > span {
+  margin-right: 6px;
+}
+
+.device-label:focus-within > button,
+.device-label:hover > button {
+  visibility: visible;
+}
+
+.device-label:focus-within,
+.device-label:hover {
+  background-color: var(--toolbarbutton-hover-background);
+}
+
+.device-modal-header {
+  display: flex;
+  justify-content: space-between;
+}
+
+.device-modal-header > #device-add-button {
+  margin: 30px 75px 0 30px;
+}
+
+.device-list {
+  display: grid;
+  font-size: 13px;
+  grid-template-columns: var(--device-list-grid-template-columns);
+}
+
+.device-input-checkbox {
+  margin-right: 8px;
+}
+
+.device-modal-title {
+  font-size: 22px;
+  margin: 30px 0 0px 30px;
+}
+
+.device-browser {
+  width: 16px;
+  height: 16px;
+  background-size: cover;
+  -moz-context-properties: fill;
+  fill: var(--theme-icon-dimmed-color);
+}
+
+.device-browser.chrome {
+  background-image: url("chrome://devtools/skin/images/browsers/chrome.svg");
+}
+
+.device-browser.edge {
+  background-image: url("chrome://devtools/skin/images/browsers/edge.svg");
+}
+
+.device-browser.firefox {
+  background-image: url("chrome://devtools/skin/images/browsers/firefox.svg");
+}
+
+.device-browser.ie {
+  background-image: url("chrome://devtools/skin/images/browsers/ie.svg");
+}
+
+.device-browser.opera {
+  background-image: url("chrome://devtools/skin/images/browsers/opera.svg");
+}
+
+.device-browser.safari {
+  background-image: url("chrome://devtools/skin/images/browsers/safari.svg");
+}
+
+.device-remove-button:empty::before {
+  background-image: url("chrome://devtools/skin/images/close.svg");
+}
+
+/**
+ * Device Form
+ */
+
+#device-form {
+  display: grid;
+  width: 100%;
+  background-color: var(--theme-toolbar-background);
+  min-height: 150px;
+  padding: 15px 20px 10px;
+  border-bottom: 1px solid var(--theme-splitter-color);
+  overflow: auto;
+  z-index: 1;
+}
+
+#device-add-button,
+#device-form button {
+  background-color: rgba(12, 12, 13, 0.1);
+  border: 1px solid var(--theme-splitter-color);
+  border-radius: 2px;
+  cursor: pointer;
+  width: 167px;
+  height: 32px;
+}
+
+#device-edit-button::before {
+  background: url("chrome://devtools/skin/images/pencil-icon.svg") no-repeat 0 0;
+}
+
+#device-edit-button,
+#device-edit-remove {
+  cursor: pointer;
+}
+
+#device-edit-button:focus-within,
+#device-edit-button:hover,
+#device-edit-remove.device-remove-button:focus-within,
+#device-edit-remove.device-remove-button:hover {
+  background-color: var(--custom-device-button-hover);
+}
+
+#device-form label {
+  display: flex;
+  flex-direction: column;
+  margin: 5px;
+}
+
+#device-form label > .viewport-dimension {
+  color: var(--theme-body-color);
+  display: flex;
+  align-items: center;
+}
+
+#device-form input {
+  background: transparent;
+  border: 1px solid var(--theme-toolbarbutton-active-background);
+  border-radius: 2px;
+  text-align: center;
+  color: var(--theme-body-color);
+  transition: all 0.25s ease;
+}
+
+#device-form #device-form-name input,
+#device-form #device-form-user-agent input {
+  text-align: left;
+  padding-left: 12px;
+  padding-right: 12px;
+}
+
+#device-form input:focus {
+  color: var(--viewport-active-color);
+}
+
+#device-form-pixel-ratio {
+  grid-area: dpr;
+}
+
+#device-form-pixel-ratio input {
+  appearance: textfield;
+}
+
+#device-form-user-agent {
+  grid-area: user-agent;
+}
+
+#device-form-name input,
+#device-form-pixel-ratio input,
+#device-form-user-agent input,
+#device-form-size input {
+  height: 35px;
+}
+
+#device-form #device-form-touch {
+  flex-direction: row;
+  grid-area: touch;
+}
+
+#device-form-touch .device-form-label {
+  align-self: center;
+  margin-left: 5px;
+}
+
+#device-form #device-form-save {
+  background-color: #0060DF;
+  color: #fff;
+  border: 1px solid #0060DF;
+  width: 60px;
+
+  &:focus-visible {
+    /* Adjust outline so it's separated from the background color */
+    outline-offset: 2px;
+  }
+}
+
+#device-form-size {
+  grid-area: size;
+}
+
+#device-form-size input,
+#device-form #device-form-cancel {
+  width: 60px;
+}
+
+#device-form-save,
+#device-form-cancel {
+  align-self: center;
+}
+
+.device-form-buttons {
+  display: flex;
+  grid-area: buttons;
+  justify-content: space-evenly;
+  width: 154px;
+}
+
+.device-form-label {
+  display: inline-block;
+  margin: 0 5px 5px 0;
+  min-width: 35px;
+  font-size: 13px;
+}
+
+/* Device Types */
+
+.device-type-phones {
+  grid-area: phone;
+}
+
+.device-type-custom {
+  grid-area: custom;
+  align-self: start;
+}
+
+.device-type-custom .device-list {
+  grid-template-columns: var(--device-list-grid-template-columns) auto auto;
+}
+
+.device-type-custom .device-label {
+  grid-column: span 6;
+}
+
+.device-type-tablets {
+  grid-area: tablet;
+}
+
+.device-type-laptops {
+  grid-area: laptop;
+}
+
+.device-type-televisions {
+  grid-area: tv;
+}
diff --git a/devtools/client/responsive/index.js b/devtools/client/responsive/index.js
new file mode 100644
index 0000000000..84bdf16e12
--- /dev/null
+++ b/devtools/client/responsive/index.js
@@ -0,0 +1,227 @@
+/* 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/. */
+
+/* eslint-env browser */
+
+"use strict";
+
+const { BrowserLoader } = ChromeUtils.import(
+  "resource://devtools/shared/loader/browser-loader.js"
+);
+const { require } = BrowserLoader({
+  baseURI: "resource://devtools/client/responsive/",
+  window,
+});
+const Telemetry = require("resource://devtools/client/shared/telemetry.js");
+
+const {
+  createFactory,
+  createElement,
+} = require("resource://devtools/client/shared/vendor/react.js");
+const ReactDOM = require("resource://devtools/client/shared/vendor/react-dom.js");
+const {
+  Provider,
+} = require("resource://devtools/client/shared/vendor/react-redux.js");
+
+const message = require("resource://devtools/client/responsive/utils/message.js");
+const App = createFactory(
+  require("resource://devtools/client/responsive/components/App.js")
+);
+const Store = require("resource://devtools/client/responsive/store.js");
+const {
+  loadDevices,
+  restoreDeviceState,
+} = require("resource://devtools/client/responsive/actions/devices.js");
+const {
+  addViewport,
+  changePixelRatio,
+  removeDeviceAssociation,
+  resizeViewport,
+  zoomViewport,
+} = require("resource://devtools/client/responsive/actions/viewports.js");
+const {
+  changeDisplayPixelRatio,
+  changeUserAgent,
+  toggleTouchSimulation,
+} = require("resource://devtools/client/responsive/actions/ui.js");
+
+// Exposed for use by tests
+window.require = require;
+
+// Tell the ResponsiveUIManager that the frame script has begun initializing.
+message.post(window, "script-init");
+
+const bootstrap = {
+  telemetry: new Telemetry(),
+
+  store: null,
+
+  async init() {
+    this.telemetry.toolOpened("responsive", this);
+
+    const store = (this.store = Store());
+    const provider = createElement(Provider, { store }, App());
+    this._root = document.querySelector("#root");
+    ReactDOM.render(provider, this._root);
+    message.post(window, "init:done");
+
+    this.destroy = this.destroy.bind(this);
+    window.addEventListener("unload", this.destroy, { once: true });
+  },
+
+  destroy() {
+    window.removeEventListener("unload", this.destroy, { once: true });
+
+    // unmount to stop async action and renders after destroy
+    ReactDOM.unmountComponentAtNode(this._root);
+
+    this.store = null;
+
+    this.telemetry.toolClosed("responsive", this);
+    this.telemetry = null;
+  },
+
+  /**
+   * While most actions will be dispatched by React components, some external
+   * APIs that coordinate with the larger browser UI may also have actions to
+   * to dispatch.  They can do so here.
+   */
+  dispatch(action) {
+    if (!this.store) {
+      // If actions are dispatched after store is destroyed, ignore them.  This
+      // can happen in tests that close the tool quickly while async tasks like
+      // initDevices() below are still pending.
+      return Promise.resolve();
+    }
+    return this.store.dispatch(action);
+  },
+};
+
+// manager.js sends a message to signal init
+message.wait(window, "init").then(() => bootstrap.init());
+
+// manager.js sends a message to signal init is done, which can be used for delayed
+// startup work that shouldn't block initial load
+message.wait(window, "post-init").then(() => {
+  bootstrap.dispatch(loadDevices()).then(() => {
+    bootstrap.dispatch(restoreDeviceState());
+  });
+});
+
+window.destroy = () => bootstrap.destroy();
+// Allows quick testing of actions from the console
+window.dispatch = action => bootstrap.dispatch(action);
+
+// Expose the store on window for testing
+Object.defineProperty(window, "store", {
+  get: () => bootstrap.store,
+  enumerable: true,
+});
+
+// Dispatch a `changeDisplayPixelRatio` action when the browser's pixel ratio is changing.
+// This is usually triggered when the user changes the monitor resolution, or when the
+// browser's window is dragged to a different display with a different pixel ratio.
+// TODO: It would be better to move this watching into the actor, so that it can be
+// better synchronized with any overrides that might be applied.  Also, reading a single
+// value like this makes less sense with multiple viewports.
+function onDevicePixelRatioChange() {
+  const dpr = window.devicePixelRatio;
+  const mql = window.matchMedia(`(resolution: ${dpr}dppx)`);
+
+  function listener() {
+    bootstrap.dispatch(changeDisplayPixelRatio(window.devicePixelRatio));
+    mql.removeListener(listener);
+    onDevicePixelRatioChange();
+  }
+
+  mql.addListener(listener);
+}
+
+/**
+ * Called by manager.js to add the initial viewport based on the original page.
+ */
+window.addInitialViewport = ({ userContextId }) => {
+  try {
+    onDevicePixelRatioChange();
+    bootstrap.dispatch(changeDisplayPixelRatio(window.devicePixelRatio));
+    bootstrap.dispatch(addViewport(userContextId));
+  } catch (e) {
+    console.error(e);
+  }
+};
+
+window.getAssociatedDevice = () => {
+  const { viewports } = bootstrap.store.getState();
+  if (!viewports.length) {
+    return null;
+  }
+
+  return viewports[0].device;
+};
+
+/**
+ * Called by manager.js when tests want to check the viewport size.
+ */
+window.getViewportSize = () => {
+  const { viewports } = bootstrap.store.getState();
+  if (!viewports.length) {
+    return null;
+  }
+
+  const { width, height } = viewports[0];
+  return { width, height };
+};
+
+/**
+ * Called by manager.js to set viewport size from tests, etc.
+ */
+window.setViewportSize = ({ width, height }) => {
+  try {
+    bootstrap.dispatch(resizeViewport(0, width, height));
+  } catch (e) {
+    console.error(e);
+  }
+};
+
+window.clearDeviceAssociation = () => {
+  try {
+    bootstrap.dispatch(removeDeviceAssociation(0));
+    bootstrap.dispatch(toggleTouchSimulation(false));
+    bootstrap.dispatch(changePixelRatio(0, 0));
+    bootstrap.dispatch(changeUserAgent(""));
+  } catch (e) {
+    console.error(e);
+  }
+};
+
+/**
+ * Called by manager.js to access the viewport's browser, either for testing
+ * purposes or to reload it when touch simulation is enabled.
+ * A messageManager getter is added on the object to provide an easy access
+ * to the message manager without pulling the frame loader.
+ */
+window.getViewportBrowser = () => {
+  const browser = document.querySelector("iframe.browser");
+  if (browser && !browser.messageManager) {
+    Object.defineProperty(browser, "messageManager", {
+      get() {
+        return this.frameLoader.messageManager;
+      },
+      configurable: true,
+      enumerable: true,
+    });
+  }
+  return browser;
+};
+
+/**
+ * Called by manager.js to zoom the viewport.
+ */
+window.setViewportZoom = zoom => {
+  try {
+    bootstrap.dispatch(zoomViewport(0, zoom));
+  } catch (e) {
+    console.error(e);
+  }
+};
diff --git a/devtools/client/responsive/manager.js b/devtools/client/responsive/manager.js
new file mode 100644
index 0000000000..2491b7c67f
--- /dev/null
+++ b/devtools/client/responsive/manager.js
@@ -0,0 +1,292 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+const EventEmitter = require("resource://devtools/shared/event-emitter.js");
+
+loader.lazyRequireGetter(
+  this,
+  "ResponsiveUI",
+  "resource://devtools/client/responsive/ui.js"
+);
+loader.lazyRequireGetter(
+  this,
+  "startup",
+  "resource://devtools/client/responsive/utils/window.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "showNotification",
+  "resource://devtools/client/responsive/utils/notification.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "l10n",
+  "resource://devtools/client/responsive/utils/l10n.js"
+);
+loader.lazyRequireGetter(
+  this,
+  "PriorityLevels",
+  "resource://devtools/client/shared/components/NotificationBox.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "gDevTools",
+  "resource://devtools/client/framework/devtools.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "gDevToolsBrowser",
+  "resource://devtools/client/framework/devtools-browser.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "Telemetry",
+  "resource://devtools/client/shared/telemetry.js"
+);
+
+/**
+ * ResponsiveUIManager is the external API for the browser UI, etc. to use when
+ * opening and closing the responsive UI.
+ */
+class ResponsiveUIManager {
+  constructor() {
+    this.activeTabs = new Map();
+
+    this.handleMenuCheck = this.handleMenuCheck.bind(this);
+
+    EventEmitter.decorate(this);
+  }
+
+  get telemetry() {
+    if (!this._telemetry) {
+      this._telemetry = new Telemetry();
+    }
+
+    return this._telemetry;
+  }
+
+  /**
+   * Toggle the responsive UI for a tab.
+   *
+   * @param window
+   *        The main browser chrome window.
+   * @param tab
+   *        The browser tab.
+   * @param options
+   *        Other options associated with toggling.  Currently includes:
+   *        - `trigger`: String denoting the UI entry point, such as:
+   *          - `toolbox`:  Toolbox Button
+   *          - `menu`:     Browser Tools menu item
+   *          - `shortcut`: Keyboard shortcut
+   * @return Promise
+   *         Resolved when the toggling has completed.  If the UI has opened,
+   *         it is resolved to the ResponsiveUI instance for this tab.  If the
+   *         the UI has closed, there is no resolution value.
+   */
+  toggle(window, tab, options = {}) {
+    const completed = this._toggleForTab(window, tab, options);
+    completed.catch(console.error);
+    return completed;
+  }
+
+  _toggleForTab(window, tab, options) {
+    if (this.isActiveForTab(tab)) {
+      return this.closeIfNeeded(window, tab, options);
+    }
+
+    return this.openIfNeeded(window, tab, options);
+  }
+
+  /**
+   * Opens the responsive UI, if not already open.
+   *
+   * @param window
+   *        The main browser chrome window.
+   * @param tab
+   *        The browser tab.
+   * @param options
+   *        Other options associated with opening.  Currently includes:
+   *        - `trigger`: String denoting the UI entry point, such as:
+   *          - `toolbox`:  Toolbox Button
+   *          - `menu`:     Browser Tools menu item
+   *          - `shortcut`: Keyboard shortcut
+   * @return Promise
+   *         Resolved to the ResponsiveUI instance for this tab when opening is
+   *         complete.
+   */
+  async openIfNeeded(window, tab, options = {}) {
+    if (!this.isActiveForTab(tab)) {
+      this.initMenuCheckListenerFor(window);
+
+      const ui = new ResponsiveUI(this, window, tab);
+      this.activeTabs.set(tab, ui);
+
+      // Explicitly not await on telemetry to avoid delaying RDM opening
+      this.recordTelemetryOpen(window, tab, options);
+
+      await gDevToolsBrowser.loadBrowserStyleSheet(window);
+      await this.setMenuCheckFor(tab, window);
+      await ui.inited;
+      this.emit("on", { tab });
+    }
+
+    return this.getResponsiveUIForTab(tab);
+  }
+
+  /**
+   * Record all telemetry probes related to RDM opening.
+   */
+  recordTelemetryOpen(window, tab, options) {
+    // Track whether a toolbox was opened before RDM was opened.
+    const toolbox = gDevTools.getToolboxForTab(tab);
+    const hostType = toolbox ? toolbox.hostType : "none";
+    const hasToolbox = !!toolbox;
+
+    if (hasToolbox) {
+      this.telemetry.scalarAdd("devtools.responsive.toolbox_opened_first", 1);
+    }
+
+    this.telemetry.recordEvent("activate", "responsive_design", null, {
+      host: hostType,
+      width: Math.ceil(window.outerWidth / 50) * 50,
+    });
+
+    // Track opens keyed by the UI entry point used.
+    let { trigger } = options;
+    if (!trigger) {
+      trigger = "unknown";
+    }
+    this.telemetry.keyedScalarAdd(
+      "devtools.responsive.open_trigger",
+      trigger,
+      1
+    );
+  }
+
+  /**
+   * Closes the responsive UI, if not already closed.
+   *
+   * @param window
+   *        The main browser chrome window.
+   * @param tab
+   *        The browser tab.
+   * @param options
+   *        Other options associated with closing.  Currently includes:
+   *        - `trigger`: String denoting the UI entry point, such as:
+   *          - `toolbox`:  Toolbox Button
+   *          - `menu`:     Browser Tools menu item
+   *          - `shortcut`: Keyboard shortcut
+   *        - `reason`: String detailing the specific cause for closing
+   * @return Promise
+   *         Resolved (with no value) when closing is complete.
+   */
+  async closeIfNeeded(window, tab, options = {}) {
+    if (this.isActiveForTab(tab)) {
+      const ui = this.activeTabs.get(tab);
+      const destroyed = await ui.destroy(options);
+      if (!destroyed) {
+        // Already in the process of destroying, abort.
+        return;
+      }
+
+      this.activeTabs.delete(tab);
+
+      if (!this.isActiveForWindow(window)) {
+        this.removeMenuCheckListenerFor(window);
+      }
+      this.emit("off", { tab });
+      await this.setMenuCheckFor(tab, window);
+
+      // Explicitly not await on telemetry to avoid delaying RDM closing
+      this.recordTelemetryClose(window, tab);
+    }
+  }
+
+  recordTelemetryClose(window, tab) {
+    const toolbox = gDevTools.getToolboxForTab(tab);
+
+    const hostType = toolbox ? toolbox.hostType : "none";
+
+    this.telemetry.recordEvent("deactivate", "responsive_design", null, {
+      host: hostType,
+      width: Math.ceil(window.outerWidth / 50) * 50,
+    });
+  }
+
+  /**
+   * Returns true if responsive UI is active for a given tab.
+   *
+   * @param tab
+   *        The browser tab.
+   * @return boolean
+   */
+  isActiveForTab(tab) {
+    return this.activeTabs.has(tab);
+  }
+
+  /**
+   * Returns true if responsive UI is active in any tab in the given window.
+   *
+   * @param window
+   *        The main browser chrome window.
+   * @return boolean
+   */
+  isActiveForWindow(window) {
+    return [...this.activeTabs.keys()].some(t => t.ownerGlobal === window);
+  }
+
+  /**
+   * Return the responsive UI controller for a tab.
+   *
+   * @param tab
+   *        The browser tab.
+   * @return ResponsiveUI
+   *         The UI instance for this tab.
+   */
+  getResponsiveUIForTab(tab) {
+    return this.activeTabs.get(tab);
+  }
+
+  handleMenuCheck({ target }) {
+    this.setMenuCheckFor(target);
+  }
+
+  initMenuCheckListenerFor(window) {
+    const { tabContainer } = window.gBrowser;
+    tabContainer.addEventListener("TabSelect", this.handleMenuCheck);
+  }
+
+  removeMenuCheckListenerFor(window) {
+    if (window?.gBrowser?.tabContainer) {
+      const { tabContainer } = window.gBrowser;
+      tabContainer.removeEventListener("TabSelect", this.handleMenuCheck);
+    }
+  }
+
+  async setMenuCheckFor(tab, window = tab.ownerGlobal) {
+    await startup(window);
+
+    const menu = window.document.getElementById("menu_responsiveUI");
+    if (menu) {
+      menu.setAttribute("checked", this.isActiveForTab(tab));
+    }
+  }
+
+  showRemoteOnlyNotification(window, tab, { trigger } = {}) {
+    return showNotification(window, tab, {
+      toolboxButton: trigger == "toolbox",
+      msg: l10n.getStr("responsive.remoteOnly"),
+      priority: PriorityLevels.PRIORITY_CRITICAL_MEDIUM,
+    });
+  }
+}
+
+module.exports = new ResponsiveUIManager();
diff --git a/devtools/client/responsive/moz.build b/devtools/client/responsive/moz.build
new file mode 100644
index 0000000000..d10333a350
--- /dev/null
+++ b/devtools/client/responsive/moz.build
@@ -0,0 +1,30 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DIRS += [
+    "actions",
+    "components",
+    "reducers",
+    "utils",
+]
+
+DevToolsModules(
+    "constants.js",
+    "index.js",
+    "manager.js",
+    "reducers.js",
+    "store.js",
+    "types.js",
+    "ui.js",
+)
+
+XPCSHELL_TESTS_MANIFESTS += ["test/xpcshell/xpcshell.toml"]
+BROWSER_CHROME_MANIFESTS += ["test/browser/browser.toml"]
+
+with Files("**"):
+    BUG_COMPONENT = ("DevTools", "Responsive Design Mode")
+
+SPHINX_TREES["/devtools/responsive"] = "docs"
diff --git a/devtools/client/responsive/reducers.js b/devtools/client/responsive/reducers.js
new file mode 100644
index 0000000000..434ef7a7ed
--- /dev/null
+++ b/devtools/client/responsive/reducers.js
@@ -0,0 +1,11 @@
+/* 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";
+
+exports.devices = require("resource://devtools/client/responsive/reducers/devices.js");
+exports.networkThrottling = require("resource://devtools/client/shared/components/throttling/reducer.js");
+exports.screenshot = require("resource://devtools/client/responsive/reducers/screenshot.js");
+exports.ui = require("resource://devtools/client/responsive/reducers/ui.js");
+exports.viewports = require("resource://devtools/client/responsive/reducers/viewports.js");
diff --git a/devtools/client/responsive/reducers/devices.js b/devtools/client/responsive/reducers/devices.js
new file mode 100644
index 0000000000..98f0602175
--- /dev/null
+++ b/devtools/client/responsive/reducers/devices.js
@@ -0,0 +1,124 @@
+/* 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 {
+  ADD_DEVICE,
+  ADD_DEVICE_TYPE,
+  EDIT_DEVICE,
+  LOAD_DEVICE_LIST_START,
+  LOAD_DEVICE_LIST_ERROR,
+  LOAD_DEVICE_LIST_END,
+  REMOVE_DEVICE,
+  UPDATE_DEVICE_DISPLAYED,
+  UPDATE_DEVICE_MODAL,
+} = require("resource://devtools/client/responsive/actions/index.js");
+
+const Types = require("resource://devtools/client/responsive/types.js");
+
+const INITIAL_DEVICES = {
+  isModalOpen: false,
+  listState: Types.loadableState.INITIALIZED,
+  modalOpenedFromViewport: null,
+  types: [],
+};
+
+const reducers = {
+  [ADD_DEVICE](devices, { device, deviceType }) {
+    return {
+      ...devices,
+      [deviceType]: [...devices[deviceType], device],
+    };
+  },
+
+  [ADD_DEVICE_TYPE](devices, { deviceType }) {
+    return {
+      ...devices,
+      types: [...devices.types, deviceType],
+      [deviceType]: [],
+    };
+  },
+
+  [EDIT_DEVICE](devices, { oldDevice, newDevice, deviceType }) {
+    const index = devices[deviceType].indexOf(oldDevice);
+    if (index < 0) {
+      return devices;
+    }
+
+    devices[deviceType].splice(index, 1, newDevice);
+
+    return {
+      ...devices,
+      [deviceType]: [...devices[deviceType]],
+    };
+  },
+
+  [UPDATE_DEVICE_DISPLAYED](devices, { device, deviceType, displayed }) {
+    const newDevices = devices[deviceType].map(d => {
+      if (d == device) {
+        d.displayed = displayed;
+      }
+
+      return d;
+    });
+
+    return {
+      ...devices,
+      [deviceType]: newDevices,
+    };
+  },
+
+  [LOAD_DEVICE_LIST_START](devices, action) {
+    return {
+      ...devices,
+      listState: Types.loadableState.LOADING,
+    };
+  },
+
+  [LOAD_DEVICE_LIST_ERROR](devices, action) {
+    return {
+      ...devices,
+      listState: Types.loadableState.ERROR,
+    };
+  },
+
+  [LOAD_DEVICE_LIST_END](devices, action) {
+    return {
+      ...devices,
+      listState: Types.loadableState.LOADED,
+    };
+  },
+
+  [REMOVE_DEVICE](devices, { device, deviceType }) {
+    const index = devices[deviceType].indexOf(device);
+    if (index < 0) {
+      return devices;
+    }
+
+    const list = [...devices[deviceType]];
+    list.splice(index, 1);
+
+    return {
+      ...devices,
+      [deviceType]: list,
+    };
+  },
+
+  [UPDATE_DEVICE_MODAL](devices, { isOpen, modalOpenedFromViewport }) {
+    return {
+      ...devices,
+      isModalOpen: isOpen,
+      modalOpenedFromViewport,
+    };
+  },
+};
+
+module.exports = function (devices = INITIAL_DEVICES, action) {
+  const reducer = reducers[action.type];
+  if (!reducer) {
+    return devices;
+  }
+  return reducer(devices, action);
+};
diff --git a/devtools/client/responsive/reducers/moz.build b/devtools/client/responsive/reducers/moz.build
new file mode 100644
index 0000000000..9f2fb54e16
--- /dev/null
+++ b/devtools/client/responsive/reducers/moz.build
@@ -0,0 +1,12 @@
+# -*- 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(
+    "devices.js",
+    "screenshot.js",
+    "ui.js",
+    "viewports.js",
+)
diff --git a/devtools/client/responsive/reducers/screenshot.js b/devtools/client/responsive/reducers/screenshot.js
new file mode 100644
index 0000000000..67f26f1f9a
--- /dev/null
+++ b/devtools/client/responsive/reducers/screenshot.js
@@ -0,0 +1,38 @@
+/* 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 {
+  TAKE_SCREENSHOT_END,
+  TAKE_SCREENSHOT_START,
+} = require("resource://devtools/client/responsive/actions/index.js");
+
+const INITIAL_SCREENSHOT = {
+  isCapturing: false,
+};
+
+const reducers = {
+  [TAKE_SCREENSHOT_END](screenshot, action) {
+    return {
+      ...screenshot,
+      isCapturing: false,
+    };
+  },
+
+  [TAKE_SCREENSHOT_START](screenshot, action) {
+    return {
+      ...screenshot,
+      isCapturing: true,
+    };
+  },
+};
+
+module.exports = function (screenshot = INITIAL_SCREENSHOT, action) {
+  const reducer = reducers[action.type];
+  if (!reducer) {
+    return screenshot;
+  }
+  return reducer(screenshot, action);
+};
diff --git a/devtools/client/responsive/reducers/ui.js b/devtools/client/responsive/reducers/ui.js
new file mode 100644
index 0000000000..bf03353bf3
--- /dev/null
+++ b/devtools/client/responsive/reducers/ui.js
@@ -0,0 +1,135 @@
+/* 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 {
+  CHANGE_DISPLAY_PIXEL_RATIO,
+  CHANGE_USER_AGENT,
+  TOGGLE_LEFT_ALIGNMENT,
+  TOGGLE_RELOAD_ON_TOUCH_SIMULATION,
+  TOGGLE_RELOAD_ON_USER_AGENT,
+  TOGGLE_TOUCH_SIMULATION,
+  TOGGLE_USER_AGENT_INPUT,
+} = require("resource://devtools/client/responsive/actions/index.js");
+
+const LEFT_ALIGNMENT_ENABLED = "devtools.responsive.leftAlignViewport.enabled";
+const RELOAD_ON_TOUCH_SIMULATION =
+  "devtools.responsive.reloadConditions.touchSimulation";
+const RELOAD_ON_USER_AGENT = "devtools.responsive.reloadConditions.userAgent";
+const SHOW_USER_AGENT_INPUT = "devtools.responsive.showUserAgentInput";
+const TOUCH_SIMULATION_ENABLED = "devtools.responsive.touchSimulation.enabled";
+const USER_AGENT = "devtools.responsive.userAgent";
+
+const INITIAL_UI = {
+  // The pixel ratio of the display.
+  displayPixelRatio: 0,
+  // Whether or not the viewports are left aligned.
+  leftAlignmentEnabled: Services.prefs.getBoolPref(
+    LEFT_ALIGNMENT_ENABLED,
+    false
+  ),
+  // Whether or not to reload when touch simulation is toggled.
+  reloadOnTouchSimulation: Services.prefs.getBoolPref(
+    RELOAD_ON_TOUCH_SIMULATION,
+    false
+  ),
+  // Whether or not to reload when user agent is changed.
+  reloadOnUserAgent: Services.prefs.getBoolPref(RELOAD_ON_USER_AGENT, false),
+  // Whether or not to show the user agent input in the toolbar.
+  showUserAgentInput: Services.prefs.getBoolPref(SHOW_USER_AGENT_INPUT, false),
+  // Whether or not touch simulation is enabled.
+  touchSimulationEnabled: Services.prefs.getBoolPref(
+    TOUCH_SIMULATION_ENABLED,
+    false
+  ),
+  // The user agent of the viewport.
+  userAgent: Services.prefs.getCharPref(USER_AGENT, ""),
+};
+
+const reducers = {
+  [CHANGE_DISPLAY_PIXEL_RATIO](ui, { displayPixelRatio }) {
+    return {
+      ...ui,
+      displayPixelRatio,
+    };
+  },
+
+  [CHANGE_USER_AGENT](ui, { userAgent }) {
+    Services.prefs.setCharPref(USER_AGENT, userAgent);
+
+    return {
+      ...ui,
+      userAgent,
+    };
+  },
+
+  [TOGGLE_LEFT_ALIGNMENT](ui, { enabled }) {
+    const leftAlignmentEnabled =
+      enabled !== undefined ? enabled : !ui.leftAlignmentEnabled;
+
+    Services.prefs.setBoolPref(LEFT_ALIGNMENT_ENABLED, leftAlignmentEnabled);
+
+    return {
+      ...ui,
+      leftAlignmentEnabled,
+    };
+  },
+
+  [TOGGLE_RELOAD_ON_TOUCH_SIMULATION](ui, { enabled }) {
+    const reloadOnTouchSimulation =
+      enabled !== undefined ? enabled : !ui.reloadOnTouchSimulation;
+
+    Services.prefs.setBoolPref(
+      RELOAD_ON_TOUCH_SIMULATION,
+      reloadOnTouchSimulation
+    );
+
+    return {
+      ...ui,
+      reloadOnTouchSimulation,
+    };
+  },
+
+  [TOGGLE_RELOAD_ON_USER_AGENT](ui, { enabled }) {
+    const reloadOnUserAgent =
+      enabled !== undefined ? enabled : !ui.reloadOnUserAgent;
+
+    Services.prefs.setBoolPref(RELOAD_ON_USER_AGENT, reloadOnUserAgent);
+
+    return {
+      ...ui,
+      reloadOnUserAgent,
+    };
+  },
+
+  [TOGGLE_TOUCH_SIMULATION](ui, { enabled }) {
+    Services.prefs.setBoolPref(TOUCH_SIMULATION_ENABLED, enabled);
+
+    return {
+      ...ui,
+      touchSimulationEnabled: enabled,
+    };
+  },
+
+  [TOGGLE_USER_AGENT_INPUT](ui, { enabled }) {
+    const showUserAgentInput =
+      enabled !== undefined ? enabled : !ui.showUserAgentInput;
+
+    Services.prefs.setBoolPref(SHOW_USER_AGENT_INPUT, showUserAgentInput);
+
+    return {
+      ...ui,
+      showUserAgentInput,
+    };
+  },
+};
+
+module.exports = function (ui = INITIAL_UI, action) {
+  const reducer = reducers[action.type];
+  if (!reducer) {
+    return ui;
+  }
+  return reducer(ui, action);
+};
diff --git a/devtools/client/responsive/reducers/viewports.js b/devtools/client/responsive/reducers/viewports.js
new file mode 100644
index 0000000000..71ced90975
--- /dev/null
+++ b/devtools/client/responsive/reducers/viewports.js
@@ -0,0 +1,212 @@
+/* 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 {
+  ADD_VIEWPORT,
+  CHANGE_DEVICE,
+  CHANGE_PIXEL_RATIO,
+  CHANGE_VIEWPORT_ANGLE,
+  EDIT_DEVICE,
+  REMOVE_DEVICE_ASSOCIATION,
+  RESIZE_VIEWPORT,
+  ROTATE_VIEWPORT,
+  ZOOM_VIEWPORT,
+} = require("resource://devtools/client/responsive/actions/index.js");
+
+const VIEWPORT_WIDTH_PREF = "devtools.responsive.viewport.width";
+const VIEWPORT_HEIGHT_PREF = "devtools.responsive.viewport.height";
+const VIEWPORT_PIXEL_RATIO_PREF = "devtools.responsive.viewport.pixelRatio";
+const VIEWPORT_ANGLE_PREF = "devtools.responsive.viewport.angle";
+
+let nextViewportId = 0;
+
+const INITIAL_VIEWPORTS = [];
+const INITIAL_VIEWPORT = {
+  id: nextViewportId++,
+  angle: Services.prefs.getIntPref(VIEWPORT_ANGLE_PREF, 0),
+  device: "",
+  deviceType: "",
+  height: Services.prefs.getIntPref(VIEWPORT_HEIGHT_PREF, 480),
+  width: Services.prefs.getIntPref(VIEWPORT_WIDTH_PREF, 320),
+  pixelRatio: Services.prefs.getIntPref(VIEWPORT_PIXEL_RATIO_PREF, 0),
+  userContextId: 0,
+  zoom: 1,
+};
+
+const reducers = {
+  [ADD_VIEWPORT](viewports, { userContextId }) {
+    // For the moment, there can be at most one viewport.
+    if (viewports.length === 1) {
+      return viewports;
+    }
+
+    return [
+      ...viewports,
+      {
+        ...INITIAL_VIEWPORT,
+        userContextId,
+      },
+    ];
+  },
+
+  [CHANGE_DEVICE](viewports, { id, device, deviceType }) {
+    return viewports.map(viewport => {
+      if (viewport.id !== id) {
+        return viewport;
+      }
+
+      return {
+        ...viewport,
+        device,
+        deviceType,
+      };
+    });
+  },
+
+  [CHANGE_PIXEL_RATIO](viewports, { id, pixelRatio }) {
+    return viewports.map(viewport => {
+      if (viewport.id !== id) {
+        return viewport;
+      }
+
+      Services.prefs.setIntPref(VIEWPORT_PIXEL_RATIO_PREF, pixelRatio);
+
+      return {
+        ...viewport,
+        pixelRatio,
+      };
+    });
+  },
+
+  [CHANGE_VIEWPORT_ANGLE](viewports, { id, angle }) {
+    return viewports.map(viewport => {
+      if (viewport.id !== id) {
+        return viewport;
+      }
+
+      Services.prefs.setIntPref(VIEWPORT_ANGLE_PREF, angle);
+
+      return {
+        ...viewport,
+        angle,
+      };
+    });
+  },
+
+  [EDIT_DEVICE](viewports, { viewport, newDevice, deviceType }) {
+    if (!viewport) {
+      return viewports;
+    }
+
+    return viewports.map(v => {
+      if (v.id !== viewport.id) {
+        return viewport;
+      }
+
+      Services.prefs.setIntPref(VIEWPORT_WIDTH_PREF, newDevice.width);
+      Services.prefs.setIntPref(VIEWPORT_HEIGHT_PREF, newDevice.height);
+      Services.prefs.setIntPref(
+        VIEWPORT_PIXEL_RATIO_PREF,
+        newDevice.pixelRatio
+      );
+
+      return {
+        ...viewport,
+        device: newDevice.name,
+        deviceType,
+        height: newDevice.height,
+        width: newDevice.width,
+        pixelRatio: newDevice.pixelRatio,
+        userAgent: newDevice.userAgent,
+        touch: newDevice.touch,
+      };
+    });
+  },
+
+  [REMOVE_DEVICE_ASSOCIATION](viewports, { id }) {
+    return viewports.map(viewport => {
+      if (viewport.id !== id) {
+        return viewport;
+      }
+
+      return {
+        ...viewport,
+        device: "",
+        deviceType: "",
+      };
+    });
+  },
+
+  [RESIZE_VIEWPORT](viewports, { id, width, height }) {
+    return viewports.map(viewport => {
+      if (viewport.id !== id) {
+        return viewport;
+      }
+
+      if (!height) {
+        height = viewport.height;
+      }
+
+      if (!width) {
+        width = viewport.width;
+      }
+
+      Services.prefs.setIntPref(VIEWPORT_WIDTH_PREF, width);
+      Services.prefs.setIntPref(VIEWPORT_HEIGHT_PREF, height);
+
+      return {
+        ...viewport,
+        height,
+        width,
+      };
+    });
+  },
+
+  [ROTATE_VIEWPORT](viewports, { id }) {
+    return viewports.map(viewport => {
+      if (viewport.id !== id) {
+        return viewport;
+      }
+
+      const height = viewport.width;
+      const width = viewport.height;
+
+      Services.prefs.setIntPref(VIEWPORT_WIDTH_PREF, width);
+      Services.prefs.setIntPref(VIEWPORT_HEIGHT_PREF, height);
+
+      return {
+        ...viewport,
+        height,
+        width,
+      };
+    });
+  },
+
+  [ZOOM_VIEWPORT](viewports, { id, zoom }) {
+    return viewports.map(viewport => {
+      if (viewport.id !== id) {
+        return viewport;
+      }
+
+      if (!zoom) {
+        zoom = viewport.zoom;
+      }
+
+      return {
+        ...viewport,
+        zoom,
+      };
+    });
+  },
+};
+
+module.exports = function (viewports = INITIAL_VIEWPORTS, action) {
+  const reducer = reducers[action.type];
+  if (!reducer) {
+    return viewports;
+  }
+  return reducer(viewports, action);
+};
diff --git a/devtools/client/responsive/responsive-browser.css b/devtools/client/responsive/responsive-browser.css
new file mode 100644
index 0000000000..86aa689e71
--- /dev/null
+++ b/devtools/client/responsive/responsive-browser.css
@@ -0,0 +1,132 @@
+/* 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/. */
+
+#appcontent[devtoolstheme="light"] {
+  --rdm-browser-container-background: #F5F5F6;
+  --rdm-browser-box-shadow: 0 4px 4px 0 rgba(155, 155, 155, 0.26);
+}
+
+#appcontent[devtoolstheme="dark"] {
+  --rdm-browser-container-background: #18181a; /* This should map to --theme-toolbar-background. */
+  --rdm-browser-box-shadow: 0 4px 4px 0 rgba(105, 105, 105, 0.26);
+}
+
+.browserContainer.responsive-mode {
+  background-color: var(--rdm-browser-container-background);
+}
+
+.browserContainer.responsive-mode > .rdm-toolbar {
+  border: none;
+  position: absolute;
+  z-index: var(--browser-stack-z-index-rdm-toolbar);
+  height: 30px;
+  top: 0;
+  left: 0;
+  width: 100%;
+}
+
+.browserContainer.responsive-mode > .rdm-toolbar.accomodate-ua {
+  height: 60px;
+}
+
+.browserContainer.responsive-mode > .rdm-toolbar.device-modal-opened {
+  height: 100%;
+}
+
+.browserContainer.responsive-mode > .browserStack {
+  --resizer-offset: 4px;
+  --browser-viewport-width: calc(var(--rdm-width) + var(--resizer-offset));
+  --browser-viewport-height: calc(var(--rdm-height) + var(--resizer-offset));
+  --rdm-zoomed-width: calc(var(--rdm-width) * var(--rdm-zoom));
+  --rdm-zoomed-height: calc(var(--rdm-height) * var(--rdm-zoom));
+  min-height: 0;
+  min-width: 0;
+  overflow: auto;
+  contain: size;
+  grid-template-columns: 15px 1fr [center-align] var(--browser-viewport-width) 1fr;
+  grid-template-rows: 65px [margin-top-offset] var(--browser-viewport-height);
+}
+
+.browserContainer.responsive-mode > .browserStack > :is(browser, .rdm-viewport-resize-handle) {
+  grid-column: center-align;
+  grid-row: margin-top-offset;
+}
+
+.browserContainer.responsive-mode.left-aligned > .browserStack > :is(browser, .rdm-viewport-resize-handle) {
+  grid-column: left-align;
+}
+
+.browserContainer.responsive-mode.left-aligned > .browserStack {
+  grid-template-columns: 15px [left-align] var(--browser-viewport-width) 1fr;
+}
+
+html[dir="rtl"] .browserContainer.responsive-mode.left-aligned > .browserStack {
+  grid-template-columns: 1fr [left-align] var(--browser-viewport-width) 15px
+}
+
+.browserContainer.responsive-mode > .browserStack > browser {
+  border: 1px solid var(--devtools-splitter-color);
+  box-shadow: var(--rdm-browser-box-shadow);
+  transform-origin: 50% 0;
+  transform: scale(var(--rdm-zoom), var(--rdm-zoom));
+
+  box-sizing: content-box; /* This is important to ensure that the pane has the
+                              precise number of pixels defined by --rdm-width
+                              and --rdm-height. */
+  height: var(--rdm-height);
+  width: var(--rdm-width);
+}
+
+.browserContainer.responsive-mode.left-aligned > .browserStack > browser {
+  transform-origin: 0 0;
+}
+
+/* Resize handles */
+
+.browserContainer.responsive-mode > .browserStack > .viewport-resize-handle {
+  width: 16px;
+  height: 16px;
+  background-image: url("./images/grippers.svg");
+  margin-inline-end: var(--resizer-offset);
+  margin-block-end: var(--resizer-offset);
+  background-repeat: no-repeat;
+  background-origin: content-box;
+  cursor: nwse-resize;
+  align-self: end;
+  justify-self: right;
+  position: relative;
+  left: calc((var(--rdm-zoomed-width) - var(--rdm-width)) / 2);
+  top: calc(var(--rdm-zoomed-height) - var(--rdm-height));
+}
+
+.browserContainer.responsive-mode.left-aligned > .browserStack > .viewport-resize-handle {
+  left: calc(var(--rdm-zoomed-width) - var(--rdm-width));
+}
+
+.browserContainer.responsive-mode > .browserStack > .viewport-horizontal-resize-handle {
+  width: 5px;
+  height: calc(var(--rdm-zoomed-height) - 16px);
+  cursor: ew-resize;
+  justify-self: right;
+  position: relative;
+  left: calc((var(--rdm-zoomed-width) - var(--rdm-width)) / 2);
+}
+
+.browserContainer.responsive-mode.left-aligned > .browserStack > .viewport-horizontal-resize-handle {
+  left: calc(var(--rdm-zoomed-width) - var(--rdm-width));
+}
+
+.browserContainer.responsive-mode > .browserStack > .viewport-vertical-resize-handle {
+  width: calc(var(--rdm-zoomed-width) - 16px);
+  height: 5px;
+  cursor: ns-resize;
+  align-self: end;
+  position: relative;
+  top: calc(var(--rdm-zoomed-height) - var(--rdm-height));
+  left: calc((-1 * (var(--rdm-zoomed-width) - var(--rdm-width)) / 2));
+}
+
+.browserContainer.responsive-mode.left-aligned > .browserStack > .viewport-vertical-resize-handle {
+  left: 0;
+}
diff --git a/devtools/client/responsive/store.js b/devtools/client/responsive/store.js
new file mode 100644
index 0000000000..10b283a56a
--- /dev/null
+++ b/devtools/client/responsive/store.js
@@ -0,0 +1,14 @@
+/* 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 createStore = require("resource://devtools/client/shared/redux/create-store.js");
+const reducers = require("resource://devtools/client/responsive/reducers.js");
+
+module.exports = () =>
+  createStore(reducers, {
+    // Uncomment this for logging in tests.
+    shouldLog: true,
+  });
diff --git a/devtools/client/responsive/test/browser/browser.toml b/devtools/client/responsive/test/browser/browser.toml
new file mode 100644
index 0000000000..d71267d360
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser.toml
@@ -0,0 +1,207 @@
+[DEFAULT]
+tags = "devtools"
+subsuite = "devtools"
+skip-if = ["os == 'win'"] # Win: Bug 1319248
+support-files = [
+  "contextual_identity.html",
+  "doc_contextmenu_inspect.html",
+  "doc_page_state.html",
+  "doc_picker_link.html",
+  "doc_toolbox_rule_view.css",
+  "doc_toolbox_rule_view.html",
+  "doc_with_remote_iframe_and_isolated_cross_origin_capabilities.sjs",
+  "favicon.html",
+  "favicon.ico",
+  "geolocation.html",
+  "head.js",
+  "hover.html",
+  "page_style.html",
+  "sjs_redirection.sjs",
+  "touch_event_bubbles.html",
+  "touch_event_target.html",
+  "touch.html",
+  "!/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",
+  "!/gfx/layers/apz/test/mochitest/apz_test_utils.js",
+  "!/testing/mochitest/tests/SimpleTest/paint_listener.js",
+]
+
+
+["browser_cmd_click.js"]
+https_first_disabled = true
+
+["browser_container_tab.js"]
+skip-if = ["os == 'linux'"] # Bug 1625501, bug 1629729
+
+["browser_contextmenu_inspect.js"]
+
+["browser_device_change.js"]
+fail-if = ["a11y_checks"] # Bug 1849028 clicked element may not be focusable and/or labeled
+
+["browser_device_custom.js"]
+skip-if = ["a11y_checks"] # Bug 1858041 and 1849028 intermittent a11y_checks results (fails on Try, passes on Autoland)
+
+["browser_device_custom_edit.js"]
+fail-if = ["a11y_checks"] # Bug 1849028 clicked element may not be focusable and/or labeled
+
+["browser_device_custom_remove.js"]
+skip-if = ["a11y_checks"] # Bug 1849028, 1858041 to investigate intermittent a11y_checks results (fails on Try, passes on Autoland)
+
+["browser_device_modal_exit.js"]
+
+["browser_device_modal_items.js"]
+
+["browser_device_modal_submit.js"]
+skip-if = ["a11y_checks"] # Bug 1858041 and 1849028 intermittent a11y_checks results (fails on Autoland, passes on Try)
+
+["browser_device_pixel_ratio_change.js"]
+fail-if = ["a11y_checks"] # Bug 1849028 clicked element may not be focusable and/or labeled
+
+["browser_device_selector_items.js"]
+
+["browser_device_state_restore.js"]
+
+["browser_device_width.js"]
+
+["browser_exit_button.js"]
+
+["browser_ext_messaging.js"]
+https_first_disabled = true
+tags = "devtools webextensions"
+
+["browser_in_rdm_pane.js"]
+
+["browser_many_toggles.js"]
+skip-if = ["verify"] # Too many exceptions happening on test teardown
+
+["browser_max_touchpoints.js"]
+
+["browser_menu_item_01.js"]
+
+["browser_menu_item_02.js"]
+
+["browser_mouse_resize.js"]
+fail-if = ["a11y_checks"] # Bug 1849028 clicked element may not be focusable and/or labeled
+
+["browser_navigation.js"]
+https_first_disabled = true
+
+["browser_network_throttling.js"]
+
+["browser_orientationchange_event.js"]
+
+["browser_page_redirection.js"]
+
+["browser_page_state.js"]
+https_first_disabled = true
+
+["browser_page_style.js"]
+
+["browser_permission_doorhanger.js"]
+tags = "devtools geolocation"
+skip-if = [
+  "http3", # Bug 1829298
+  "http2",
+]
+
+["browser_picker_link.js"]
+
+["browser_preloaded_newtab.js"]
+
+["browser_screenshot_button.js"]
+
+["browser_screenshot_button_warning.js"]
+https_first_disabled = true
+
+["browser_scroll.js"]
+skip-if = [
+  "http3", # Bug 1829298
+  "http2",
+]
+
+["browser_state_restore.js"]
+
+["browser_tab_close.js"]
+
+["browser_tab_not_selected.js"]
+fail-if = ["a11y_checks"] # Bug 1849028 clicked button#device-pixel-ratio-menu element may not be focusable
+
+["browser_tab_remoteness_change.js"]
+
+["browser_tab_remoteness_change_fission_switch_target.js"]
+
+["browser_target_blank.js"]
+https_first_disabled = true
+
+["browser_telemetry_activate_rdm.js"]
+
+["browser_toolbox_computed_view.js"]
+
+["browser_toolbox_rule_view.js"]
+
+["browser_toolbox_rule_view_reload.js"]
+
+["browser_toolbox_swap_browsers.js"]
+
+["browser_toolbox_swap_inspector.js"]
+
+["browser_tooltip.js"]
+
+["browser_touch_device.js"]
+fail-if = ["a11y_checks"] # Bug 1849028 clicked element may not be focusable and/or labeled
+
+["browser_touch_does_not_trigger_hover_states.js"]
+
+["browser_touch_event_iframes.js"]
+fail-if = ["a11y_checks"] # Bug 1849028 clicked element may not be focusable and/or labeled
+skip-if = [
+  "http3", # Bug 1829298
+  "http2",
+  "os == 'linux' && os_version == '18.04' && debug", # Bug 1717330
+]
+
+["browser_touch_event_should_bubble.js"]
+
+["browser_touch_pointerevents.js"]
+
+["browser_touch_simulation.js"]
+https_first_disabled = true
+skip-if = ["debug"] # timing-senstive tests should only run on optimized builds
+
+["browser_typeahead_find.js"]
+
+["browser_user_agent_input.js"]
+
+["browser_viewport_basics.js"]
+https_first_disabled = true
+
+["browser_viewport_changed_meta.js"]
+skip-if = ["a11y_checks"] # Bug 1849028 and 1824058 for causing intermittent crashes
+
+["browser_viewport_fallback_width.js"]
+
+["browser_viewport_resizing_after_reload.js"]
+
+["browser_viewport_resizing_fixed_width.js"]
+
+["browser_viewport_resizing_fixed_width_and_zoom.js"]
+
+["browser_viewport_resizing_minimum_scale.js"]
+
+["browser_viewport_resizing_scrollbar.js"]
+
+["browser_viewport_resolution_restore.js"]
+
+["browser_viewport_state_after_close.js"]
+
+["browser_viewport_zoom_resolution_invariant.js"]
+
+["browser_viewport_zoom_toggle.js"]
+
+["browser_window_close.js"]
+
+["browser_window_sizing.js"]
+
+["browser_zoom.js"]
diff --git a/devtools/client/responsive/test/browser/browser_cmd_click.js b/devtools/client/responsive/test/browser/browser_cmd_click.js
new file mode 100644
index 0000000000..25cdca20a4
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_cmd_click.js
@@ -0,0 +1,33 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Ensure Cmd/Ctrl-clicking link opens a new tab
+
+const TAB_URL = "https://example.com/";
+const TEST_URL = `data:text/html,<a href="${TAB_URL}">Click me</a>`.replace(
+  / /g,
+  "%20"
+);
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    // Cmd-click the link and wait for a new tab
+    await waitForFrameLoad(ui, TEST_URL);
+    const newTabPromise = BrowserTestUtils.waitForNewTab(gBrowser, TAB_URL);
+    BrowserTestUtils.synthesizeMouseAtCenter(
+      "a",
+      {
+        ctrlKey: true,
+        metaKey: true,
+      },
+      ui.getViewportBrowser()
+    );
+    const newTab = await newTabPromise;
+    ok(newTab, "New tab opened from link");
+    await removeTab(newTab);
+  },
+  { waitForDeviceList: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_container_tab.js b/devtools/client/responsive/test/browser/browser_container_tab.js
new file mode 100644
index 0000000000..7be60207b8
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_container_tab.js
@@ -0,0 +1,30 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Verify RDM opens for a container tab.
+
+const TEST_URL = "https://example.com/";
+
+addRDMTask(
+  null,
+  async function () {
+    // Open a tab with about:newtab in a container.
+    const tab = await addTab(BROWSER_NEW_TAB_URL, {
+      userContextId: 2,
+    });
+    is(tab.userContextId, 2, "Tab's container ID is correct");
+
+    // Open RDM and try to navigate
+    const { ui } = await openRDM(tab);
+    await waitForDeviceAndViewportState(ui);
+
+    await navigateTo(TEST_URL);
+    ok(true, "Test URL navigated successfully");
+
+    await closeRDM(tab);
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_contextmenu_inspect.js b/devtools/client/responsive/test/browser/browser_contextmenu_inspect.js
new file mode 100644
index 0000000000..6d02a61917
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_contextmenu_inspect.js
@@ -0,0 +1,55 @@
+"use strict";
+
+// Check that Inspect Element works in Responsive Design Mode.
+
+const TEST_URI = `${URL_ROOT}doc_contextmenu_inspect.html`;
+
+addRDMTask(TEST_URI, async function ({ ui, manager }) {
+  info("Open the responsive design mode and set its size to 500x500 to start");
+  await setViewportSize(ui, manager, 500, 500);
+
+  info("Open the inspector, rule-view and select the test node");
+  const { inspector } = await openRuleView();
+
+  const startNodeFront = inspector.selection.nodeFront;
+  is(startNodeFront.displayName, "body", "body element is selected by default");
+
+  const onSelected = inspector.once("inspector-updated");
+
+  const contentAreaContextMenu = document.querySelector(
+    "#contentAreaContextMenu"
+  );
+  const contextOpened = once(contentAreaContextMenu, "popupshown");
+
+  info("Simulate a context menu event from the top browser.");
+  BrowserTestUtils.synthesizeMouse(
+    ui.getViewportBrowser(),
+    250,
+    100,
+    {
+      type: "contextmenu",
+      button: 2,
+    },
+    ui.tab.linkedBrowser
+  );
+
+  await contextOpened;
+
+  info("Triggering the inspect action");
+  await gContextMenu.inspectNode();
+
+  info("Hiding the menu");
+  const contextClosed = once(contentAreaContextMenu, "popuphidden");
+  contentAreaContextMenu.hidePopup();
+  await contextClosed;
+
+  await onSelected;
+  const newNodeFront = inspector.selection.nodeFront;
+  is(
+    newNodeFront.displayName,
+    "div",
+    "div element is selected after using Inspect Element"
+  );
+
+  await closeToolbox();
+});
diff --git a/devtools/client/responsive/test/browser/browser_device_change.js b/devtools/client/responsive/test/browser/browser_device_change.js
new file mode 100644
index 0000000000..6a3fe643af
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_device_change.js
@@ -0,0 +1,129 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests changing viewport device (need HTTP load for proper UA testing)
+
+const TEST_URL = `${URL_ROOT}doc_page_state.html`;
+const DEFAULT_DPPX = window.devicePixelRatio;
+
+const Types = require("resource://devtools/client/responsive/types.js");
+
+const testDevice = {
+  name: "Fake Phone RDM Test",
+  width: 320,
+  height: 570,
+  pixelRatio: 5.5,
+  userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+  touch: true,
+  firefoxOS: true,
+  os: "custom",
+  featured: true,
+};
+
+// Add the new device to the list
+addDeviceForTest(testDevice);
+
+// Add the laptop to the device list
+const {
+  updatePreferredDevices,
+} = require("resource://devtools/client/responsive/actions/devices.js");
+updatePreferredDevices({
+  added: ["Laptop with MDPI screen"],
+  removed: [],
+});
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    reloadOnUAChange(true);
+
+    // Test defaults
+    testViewportDimensions(ui, 320, 480);
+    info("Should have default UA at the start of the test");
+    await testUserAgent(ui, DEFAULT_UA);
+    await testDevicePixelRatio(ui, DEFAULT_DPPX);
+    await testTouchEventsOverride(ui, false);
+    testViewportDeviceMenuLabel(ui, "Responsive");
+
+    // Test device with custom properties
+    await selectDevice(ui, "Fake Phone RDM Test");
+    await waitForViewportResizeTo(ui, testDevice.width, testDevice.height);
+    info("Should have device UA now that device is applied");
+    await testUserAgent(ui, testDevice.userAgent);
+    await testDevicePixelRatio(ui, testDevice.pixelRatio);
+    await testTouchEventsOverride(ui, true);
+
+    // Test resetting device when resizing viewport
+    await testViewportResize(
+      ui,
+      ".viewport-vertical-resize-handle",
+      [-10, -10],
+      [0, -10],
+      {
+        hasDevice: true,
+      }
+    );
+
+    info("Should have default UA after resizing viewport");
+    await testUserAgent(ui, DEFAULT_UA);
+    await testDevicePixelRatio(ui, DEFAULT_DPPX);
+    await testTouchEventsOverride(ui, false);
+    testViewportDeviceMenuLabel(ui, "Responsive");
+
+    // Test device with generic properties
+    await selectDevice(ui, "Laptop with MDPI screen");
+    await waitForViewportResizeTo(ui, 1280, 800);
+    info("Should have default UA when using device without specific UA");
+    await testUserAgent(ui, DEFAULT_UA);
+    await testDevicePixelRatio(ui, 1);
+    await testTouchEventsOverride(ui, false);
+
+    reloadOnUAChange(false);
+  },
+  { waitForDeviceList: true }
+);
+
+addRDMTask(
+  null,
+  async function () {
+    const tab = await addTab(TEST_URL);
+    const { ui } = await openRDM(tab);
+
+    const { store } = ui.toolWindow;
+
+    reloadOnUAChange(true);
+
+    // Wait until the viewport has been added and the device list has been loaded
+    await waitUntilState(
+      store,
+      state =>
+        state.viewports.length == 1 &&
+        state.viewports[0].device === "Laptop with MDPI screen" &&
+        state.devices.listState == Types.loadableState.LOADED
+    );
+
+    // Select device with custom UA
+    const waitForReload = await watchForDevToolsReload(ui.getViewportBrowser());
+    await selectDevice(ui, "Fake Phone RDM Test");
+    await waitForReload();
+    await waitForViewportResizeTo(ui, testDevice.width, testDevice.height);
+    info("Should have device UA now that device is applied");
+    await testUserAgent(ui, testDevice.userAgent);
+
+    // Browser will reload to clear the UA on RDM close
+    const onReload = BrowserTestUtils.browserLoaded(ui.getViewportBrowser());
+    await closeRDM(tab);
+    await onReload;
+
+    // Ensure UA is reset to default after closing RDM
+    info("Should have default UA after closing RDM");
+    await testUserAgentFromBrowser(tab.linkedBrowser, DEFAULT_UA);
+
+    await removeTab(tab);
+
+    reloadOnUAChange(false);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_device_custom.js b/devtools/client/responsive/test/browser/browser_device_custom.js
new file mode 100644
index 0000000000..fb63719b30
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_device_custom.js
@@ -0,0 +1,237 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test adding and removing custom devices via the modal.
+
+const L10N = new LocalizationHelper(
+  "devtools/client/locales/device.properties",
+  true
+);
+
+const device = {
+  name: "Test Device",
+  width: 400,
+  height: 570,
+  pixelRatio: 1.5,
+  userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+  touch: true,
+};
+
+const unicodeDevice = {
+  name: "\u00B6\u00C7\u00DA\u00E7\u0126",
+  width: 400,
+  height: 570,
+  pixelRatio: 1.5,
+  userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+  touch: true,
+};
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { toolWindow } = ui;
+    const { document } = toolWindow;
+
+    await openDeviceModal(ui);
+
+    is(
+      getCustomHeaderEl(document),
+      null,
+      "There's no Custom header when we don't have custom devices"
+    );
+
+    info("Reveal device adder form, check that defaults match the viewport");
+    const adderShow = document.getElementById("device-add-button");
+    adderShow.click();
+    testDeviceAdder(ui, {
+      name: "Custom Device",
+      width: 320,
+      height: 480,
+      pixelRatio: window.devicePixelRatio,
+      userAgent: navigator.userAgent,
+      touch: false,
+    });
+
+    info("Fill out device adder form and save");
+    await addDeviceInModal(ui, device);
+
+    info("Verify device defaults to enabled in modal");
+    const deviceCb = [
+      ...document.querySelectorAll(".device-input-checkbox"),
+    ].find(cb => {
+      return cb.value == device.name;
+    });
+    ok(deviceCb, "Custom device checkbox added to modal");
+    ok(deviceCb.checked, "Custom device enabled");
+
+    const customHeaderEl = getCustomHeaderEl(document);
+    ok(customHeaderEl, "There's a Custom header when add a custom devices");
+    is(
+      customHeaderEl.textContent,
+      L10N.getStr(`device.custom`),
+      "The custom header has the expected text"
+    );
+
+    document.getElementById("device-close-button").click();
+
+    info("Look for custom device in device selector");
+    const deviceSelector = document.getElementById("device-selector");
+    await testMenuItems(toolWindow, deviceSelector, items => {
+      const menuItem = findMenuItem(items, device.name);
+      ok(menuItem, "Custom device menu item added to device selector");
+    });
+  },
+  { waitForDeviceList: true }
+);
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { toolWindow } = ui;
+    const { store, document } = toolWindow;
+
+    info("Select existing device from the selector");
+    await selectDevice(ui, "Test Device");
+
+    await openDeviceModal(ui);
+
+    info(
+      "Reveal device adder form, check that defaults are based on selected device"
+    );
+    const adderShow = document.getElementById("device-add-button");
+    adderShow.click();
+    testDeviceAdder(
+      ui,
+      Object.assign({}, device, {
+        name: "Test Device (Custom)",
+      })
+    );
+
+    info("Remove previously added custom device");
+    // Close the form since custom device buttons are only shown when form is not open.
+    const cancelButton = document.getElementById("device-form-cancel");
+    cancelButton.click();
+
+    const deviceRemoveButton = document.querySelector(".device-remove-button");
+    const removed = Promise.all([
+      waitUntilState(store, state => !state.devices.custom.length),
+      once(ui, "device-association-removed"),
+    ]);
+    deviceRemoveButton.click();
+    await removed;
+
+    info("Close the form before submitting.");
+    document.getElementById("device-close-button").click();
+
+    info("Ensure custom device was removed from device selector");
+    await waitUntilState(store, state => state.viewports[0].device == "");
+    const deviceSelectorTitle = document.querySelector("#device-selector");
+    is(
+      deviceSelectorTitle.textContent,
+      "Responsive",
+      "Device selector reset to no device"
+    );
+
+    info("Look for custom device in device selector");
+    const deviceSelector = document.getElementById("device-selector");
+    await testMenuItems(toolWindow, deviceSelector, menuItems => {
+      const menuItem = findMenuItem(menuItems, device.name);
+      ok(!menuItem, "Custom device option removed from device selector");
+    });
+
+    info("Ensure device properties like UA have been reset");
+    await testUserAgent(ui, navigator.userAgent);
+  },
+  { waitForDeviceList: true }
+);
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { toolWindow } = ui;
+    const { document } = toolWindow;
+
+    await openDeviceModal(ui);
+
+    info("Reveal device adder form");
+    const adderShow = document.querySelector("#device-add-button");
+    adderShow.click();
+
+    info(
+      "Fill out device adder form by setting details to unicode device and save"
+    );
+    await addDeviceInModal(ui, unicodeDevice);
+
+    info("Verify unicode device defaults to enabled in modal");
+    const deviceCb = [
+      ...document.querySelectorAll(".device-input-checkbox"),
+    ].find(cb => {
+      return cb.value == unicodeDevice.name;
+    });
+    ok(deviceCb, "Custom unicode device checkbox added to modal");
+    ok(deviceCb.checked, "Custom unicode device enabled");
+    document.getElementById("device-close-button").click();
+
+    info("Look for custom unicode device in device selector");
+    const deviceSelector = document.getElementById("device-selector");
+    await testMenuItems(toolWindow, deviceSelector, items => {
+      const menuItem = findMenuItem(items, unicodeDevice.name);
+      ok(menuItem, "Custom unicode device option added to device selector");
+    });
+  },
+  { waitForDeviceList: true }
+);
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { toolWindow } = ui;
+    const { document } = toolWindow;
+
+    // Check if the unicode custom device is present in the list of device options since
+    // we want to ensure that unicode device names are not forgotten after restarting RDM
+    // see bug 1379687
+    info("Look for custom unicode device in device selector");
+    const deviceSelector = document.getElementById("device-selector");
+    await testMenuItems(toolWindow, deviceSelector, items => {
+      const menuItem = findMenuItem(items, unicodeDevice.name);
+      ok(menuItem, "Custom unicode device option present in device selector");
+    });
+  },
+  { waitForDeviceList: true }
+);
+
+function testDeviceAdder(ui, expected) {
+  const { document } = ui.toolWindow;
+
+  const nameInput = document.querySelector("#device-form-name input");
+  const [widthInput, heightInput] = document.querySelectorAll(
+    "#device-form-size input"
+  );
+  const pixelRatioInput = document.querySelector(
+    "#device-form-pixel-ratio input"
+  );
+  const userAgentInput = document.querySelector(
+    "#device-form-user-agent input"
+  );
+  const touchInput = document.querySelector("#device-form-touch input");
+
+  is(nameInput.value, expected.name, "Device name matches");
+  is(parseInt(widthInput.value, 10), expected.width, "Width matches");
+  is(parseInt(heightInput.value, 10), expected.height, "Height matches");
+  is(
+    parseFloat(pixelRatioInput.value),
+    expected.pixelRatio,
+    "devicePixelRatio matches"
+  );
+  is(userAgentInput.value, expected.userAgent, "User agent matches");
+  is(touchInput.checked, expected.touch, "Touch matches");
+}
+
+function getCustomHeaderEl(doc) {
+  return doc.querySelector(`.device-type-custom .device-header`);
+}
diff --git a/devtools/client/responsive/test/browser/browser_device_custom_edit.js b/devtools/client/responsive/test/browser/browser_device_custom_edit.js
new file mode 100644
index 0000000000..35fee3c906
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_device_custom_edit.js
@@ -0,0 +1,117 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that adding a device, submitting it, and then editing it updates the device's
+// original values when it is saved.
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+
+const device = {
+  name: "Original Custom Device",
+  width: 320,
+  height: 480,
+  pixelRatio: 1,
+  userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+  touch: false,
+};
+
+const newDevice = {
+  name: "Edited Custom Device",
+  width: 300,
+  height: 900,
+  pixelRatio: 4,
+  userAgent: "Different User agent",
+  touch: true,
+};
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { toolWindow } = ui;
+    const { document } = toolWindow;
+
+    await openDeviceModal(ui);
+
+    info("Add device.");
+    const adderShow = document.querySelector("#device-add-button");
+    adderShow.click();
+    await addDeviceInModal(ui, device);
+
+    info("Submit the added device.");
+    let deviceSelector = document.getElementById("device-selector");
+    document.getElementById("device-close-button").click();
+
+    await testMenuItems(toolWindow, deviceSelector, menuItems => {
+      const originalDevice = findMenuItem(menuItems, device.name);
+      ok(originalDevice, "Original custom device menu item exists.");
+    });
+
+    info("Select the added device in menu.");
+    await selectDevice(ui, "Custom Device");
+    await openDeviceModal(ui);
+
+    info("Edit the device.");
+    const editorShow = document.querySelector(
+      ".device-type-custom #device-edit-button"
+    );
+    editorShow.click();
+    await editDeviceInModal(ui, device, newDevice);
+
+    info("Ensure the edited device name is updated in the custom device list.");
+    const customDevicesList = document.querySelector(".device-type-custom");
+    const editedCustomDevice = customDevicesList.querySelector(".device-name");
+    is(
+      editedCustomDevice.textContent,
+      newDevice.name,
+      `${device.name} is updated to ${newDevice.name} in the custom device list`
+    );
+
+    info("Ensure the viewport width and height are updated in the toolbar.");
+    const [width, height] = document.querySelectorAll(
+      ".text-input.viewport-dimension-input"
+    );
+    is(width.value, "300", "Viewport width is 300");
+    is(height.value, "900", "Viewport height is 900");
+
+    info("Ensure the pixel ratio is updated in the toolbar.");
+    const devicePixelRatioSpan = document.querySelector(
+      "#device-pixel-ratio-menu span"
+    );
+    is(
+      devicePixelRatioSpan.textContent,
+      "DPR: 4",
+      "Viewport pixel ratio is 4."
+    );
+
+    info("Ensure the user agent has been updated.");
+    const userAgentInput = document.querySelector("#user-agent-input");
+    is(
+      userAgentInput.value,
+      newDevice.userAgent,
+      `Viewport user agent is ${newDevice.userAgent}`
+    );
+
+    info("Ensure touch simulation has been updated");
+    const touchSimulation = document.querySelector("#touch-simulation-button");
+    ok(
+      touchSimulation.classList.contains("checked"),
+      "Viewport touch simulation is enabled."
+    );
+
+    info(
+      "Ensure the edited device is updated in the device selector when submitted"
+    );
+    document.getElementById("device-close-button").click();
+    deviceSelector = document.getElementById("device-selector");
+
+    await testMenuItems(toolWindow, deviceSelector, menuItems => {
+      const originalDevice = findMenuItem(menuItems, device.name);
+      const editedDevice = findMenuItem(menuItems, newDevice.name);
+      ok(!originalDevice, "Original custom device menu item does not exist");
+      ok(editedDevice, "Edited Custom Device menu item exists");
+    });
+  },
+  { waitForDeviceList: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_device_custom_remove.js b/devtools/client/responsive/test/browser/browser_device_custom_remove.js
new file mode 100644
index 0000000000..8d31aed6cf
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_device_custom_remove.js
@@ -0,0 +1,139 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test adding several devices and removing one to ensure the correct device is removed.
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+
+const device = {
+  width: 400,
+  height: 570,
+  pixelRatio: 1.5,
+  userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+  touch: true,
+};
+
+const device1 = Object.assign({}, device, {
+  name: "Test Device 1",
+});
+
+const device2 = Object.assign({}, device, {
+  name: "Test Device 2",
+});
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { toolWindow } = ui;
+    const { store, document } = toolWindow;
+
+    info("Verify that remove buttons affect the correct device");
+
+    const deviceSelector = document.getElementById("device-selector");
+
+    await openDeviceModal(ui);
+
+    info("Reveal device adder form");
+    let adderShow = document.querySelector("#device-add-button");
+    adderShow.click();
+
+    info("Add test device 1");
+    await addDeviceInModal(ui, device1);
+
+    info("Reveal device adder form");
+    adderShow = document.querySelector("#device-add-button");
+    adderShow.click();
+
+    info("Add test device 2");
+    await addDeviceInModal(ui, device2);
+
+    info("Verify all custom devices default to enabled in modal");
+    const deviceCbs = [
+      ...document.querySelectorAll(
+        ".device-type-custom .device-input-checkbox"
+      ),
+    ];
+    is(deviceCbs.length, 2, "Both devices have a checkbox in modal");
+    for (const cb of deviceCbs) {
+      ok(cb.checked, "Custom device enabled");
+    }
+    document.getElementById("device-close-button").click();
+
+    info("Look for device 1 and 2 in device selector");
+
+    await testMenuItems(toolWindow, deviceSelector, menuItems => {
+      const deviceItem1 = findMenuItem(menuItems, device1.name);
+      const deviceItem2 = findMenuItem(menuItems, device2.name);
+      ok(deviceItem1, "Test device 1 menu item added to device selector");
+      ok(deviceItem2, "Test device 2 menu item added to device selector");
+    });
+
+    await openDeviceModal(ui);
+
+    info("Remove device 2");
+    const deviceRemoveButtons = [
+      ...document.querySelectorAll(".device-remove-button"),
+    ];
+    is(
+      deviceRemoveButtons.length,
+      2,
+      "Both devices have a remove button in modal"
+    );
+    const removed = waitUntilState(
+      store,
+      state => state.devices.custom.length == 1
+    );
+    deviceRemoveButtons[1].click();
+    await removed;
+    document.getElementById("device-close-button").click();
+
+    info("Ensure device 2 is no longer in device selector");
+    await testMenuItems(toolWindow, deviceSelector, menuItems => {
+      const deviceItem1 = findMenuItem(menuItems, device1.name);
+      const deviceItem2 = findMenuItem(menuItems, device2.name);
+      ok(deviceItem1, "Test device 1 menu item exists");
+      ok(!deviceItem2, "Test device 2 menu item removed");
+    });
+  },
+  { waitForDeviceList: true }
+);
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { toolWindow } = ui;
+    const { document } = toolWindow;
+
+    const deviceSelector = document.getElementById("device-selector");
+
+    info("Ensure device 1 is still in device selector");
+    await testMenuItems(toolWindow, deviceSelector, menuItems => {
+      const deviceItem1 = findMenuItem(menuItems, device1.name);
+      const deviceItem2 = findMenuItem(menuItems, device2.name);
+      ok(deviceItem1, "Test device 1 menu item exists");
+      ok(!deviceItem2, "Test device 2 option removed");
+    });
+
+    await openDeviceModal(ui);
+
+    info("Ensure device 1 is still in device modal");
+    const deviceCbs = [
+      ...document.querySelectorAll(
+        ".device-type-custom .device-input-checkbox"
+      ),
+    ];
+    is(deviceCbs.length, 1, "Only 1 custom present in modal");
+    const deviceCb1 = deviceCbs.find(cb => cb.value == device1.name);
+    ok(
+      deviceCb1 && deviceCb1.checked,
+      "Test device 1 checkbox exists and enabled"
+    );
+
+    info("Ensure device 2 is no longer in device modal");
+    const deviceCb2 = deviceCbs.find(cb => cb.value == device2.name);
+    ok(!deviceCb2, "Test device 2 checkbox does not exist");
+  },
+  { waitForDeviceList: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_device_modal_exit.js b/devtools/client/responsive/test/browser/browser_device_modal_exit.js
new file mode 100644
index 0000000000..5edc78f5e3
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_device_modal_exit.js
@@ -0,0 +1,51 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test submitting display device changes on the device modal
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { document, store } = ui.toolWindow;
+
+    await openDeviceModal(ui);
+
+    const preferredDevicesBefore = _loadPreferredDevices();
+
+    info("Check the first unchecked device and exit the modal.");
+    const uncheckedCb = [
+      ...document.querySelectorAll(".device-input-checkbox"),
+    ].filter(cb => !cb.checked)[0];
+    const value = uncheckedCb.value;
+    uncheckedCb.click();
+    document.getElementById("device-close-button").click();
+
+    ok(
+      !store.getState().devices.isModalOpen,
+      "The device modal is closed on exit."
+    );
+
+    info("Check that the device list remains unchanged after exitting.");
+    const preferredDevicesAfter = _loadPreferredDevices();
+
+    is(
+      preferredDevicesAfter.added.size - preferredDevicesBefore.added.size,
+      1,
+      "Got expected number of added devices."
+    );
+    is(
+      preferredDevicesBefore.removed.size,
+      preferredDevicesAfter.removed.size,
+      "Got expected number of removed devices."
+    );
+    ok(
+      !preferredDevicesAfter.removed.has(value),
+      value + " was not added to removed device list."
+    );
+  },
+  { waitForDeviceList: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_device_modal_items.js b/devtools/client/responsive/test/browser/browser_device_modal_items.js
new file mode 100644
index 0000000000..54b6b51854
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_device_modal_items.js
@@ -0,0 +1,98 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the content of device items in the modal.
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+const {
+  parseUserAgent,
+} = require("resource://devtools/client/responsive/utils/ua.js");
+
+const L10N = new LocalizationHelper(
+  "devtools/client/locales/device.properties",
+  true
+);
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { toolWindow } = ui;
+    const { store, document } = toolWindow;
+
+    await openDeviceModal(ui);
+
+    const { devices } = store.getState();
+
+    ok(devices.types.length, "We have some device types");
+
+    for (const type of devices.types) {
+      const list = devices[type];
+
+      const header = document.querySelector(
+        `.device-type-${type} .device-header`
+      );
+
+      if (type == "custom") {
+        // we don't have custom devices, so there shouldn't be a header for it.
+        is(list.length, 0, `We don't have any custom devices`);
+        ok(!header, `There's no header for "custom"`);
+        continue;
+      }
+
+      ok(list.length, `We have ${type} devices`);
+      ok(header, `There's a header for ${type} devices`);
+
+      is(
+        header?.textContent,
+        L10N.getStr(`device.${type}`),
+        `Got expected text for ${type} header`
+      );
+
+      for (const item of list) {
+        info(`Check the element for ${item.name} on the modal`);
+
+        const targetEl = findDeviceLabel(item.name, document);
+        ok(targetEl, "The element for the device is on the modal");
+
+        const { browser, os } = parseUserAgent(item.userAgent);
+        const browserEl = targetEl.querySelector(".device-browser");
+        if (browser) {
+          ok(browserEl, "The element for the browser is in the device element");
+          const expectedClassName = browser.name.toLowerCase();
+          ok(
+            browserEl.classList.contains(expectedClassName),
+            `The browser element contains .${expectedClassName}`
+          );
+        } else {
+          ok(
+            !browserEl,
+            "The element for the browser is not in the device element"
+          );
+        }
+
+        const osEl = targetEl.querySelector(".device-os");
+        if (os) {
+          ok(osEl, "The element for the os is in the device element");
+          const expectedText = os.version
+            ? `${os.name} ${os.version}`
+            : os.name;
+          is(
+            osEl.textContent,
+            expectedText,
+            "The text in os element is correct"
+          );
+        } else {
+          ok(!osEl, "The element for the os is not in the device element");
+        }
+      }
+    }
+  },
+  { waitForDeviceList: true }
+);
+
+function findDeviceLabel(deviceName, document) {
+  const deviceNameEls = document.querySelectorAll(".device-name");
+  const targetEl = [...deviceNameEls].find(el => el.textContent === deviceName);
+  return targetEl ? targetEl.closest(".device-label") : null;
+}
diff --git a/devtools/client/responsive/test/browser/browser_device_modal_submit.js b/devtools/client/responsive/test/browser/browser_device_modal_submit.js
new file mode 100644
index 0000000000..45cf23e10e
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_device_modal_submit.js
@@ -0,0 +1,203 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test submitting display device changes on the device modal
+const { getDevices } = require("resource://devtools/client/shared/devices.js");
+
+const addedDevice = {
+  name: "Fake Phone RDM Test",
+  width: 320,
+  height: 570,
+  pixelRatio: 1.5,
+  userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+  touch: true,
+  firefoxOS: false,
+  os: "custom",
+  featured: true,
+};
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { toolWindow } = ui;
+    const { document, store } = toolWindow;
+    const deviceSelector = document.getElementById("device-selector");
+
+    await openDeviceModal(ui);
+
+    info(
+      "Checking displayed device checkboxes are checked in the device modal."
+    );
+    const checkedCbs = document.querySelectorAll(
+      ".device-input-checkbox:checked"
+    );
+    const remoteList = await getDevices();
+
+    const featuredCount = getNumberOfFeaturedDevices(remoteList);
+    is(
+      featuredCount,
+      checkedCbs.length,
+      "Got expected number of displayed devices."
+    );
+
+    for (const cb of checkedCbs) {
+      ok(
+        Object.keys(remoteList).filter(type => remoteList[type][cb.value]),
+        cb.value + " is correctly checked."
+      );
+    }
+
+    // Tests where the user adds a non-featured device
+    info("Check the first unchecked device and submit new device list.");
+    const uncheckedCb = document.querySelector(
+      ".device-input-checkbox:not(:checked)"
+    );
+    const value = uncheckedCb.value;
+    uncheckedCb.click();
+    document.getElementById("device-close-button").click();
+
+    ok(
+      !store.getState().devices.isModalOpen,
+      "The device modal is closed on submit."
+    );
+
+    info("Checking that the new device is added to the user preference list.");
+    let preferredDevices = _loadPreferredDevices();
+    ok(preferredDevices.added.has(value), value + " in user added list.");
+
+    info("Checking new device is added to the device selector.");
+    await testMenuItems(toolWindow, deviceSelector, menuItems => {
+      is(
+        menuItems.length - 1,
+        featuredCount + 1,
+        "Got expected number of devices in device selector."
+      );
+
+      const menuItem = findMenuItem(menuItems, value);
+      ok(menuItem, value + " added to the device selector.");
+    });
+
+    info("Reopen device modal and check new device is correctly checked");
+    await openDeviceModal(ui);
+
+    const previouslyClickedCb = [
+      ...document.querySelectorAll(".device-input-checkbox"),
+    ].find(cb => cb.value === value);
+    ok(previouslyClickedCb.checked, value + " is checked in the device modal.");
+
+    // Tests where the user removes a featured device
+    info("Uncheck the first checked device different than the previous one");
+    const checkboxes = [...document.querySelectorAll(".device-input-checkbox")];
+    const checkedCb = checkboxes.find(cb => {
+      if (!cb.checked || cb.value == value) {
+        return false;
+      }
+      // In the list, we have devices with similar names (e.g. "Galaxy Note 20" and "Galaxy Note 20 Ultra")
+      // Given how some test helpers are using `includes` to check device names, we might
+      // get positive result for "Galaxy Note 20" although it would actually match "Galaxy Note 20 Ultra".
+      // To prevent such issue without modifying existing helpers, we're excluding any
+      // item whose name is part of another device.
+      return !checkboxes.some(
+        innerCb =>
+          innerCb.value !== cb.value && innerCb.value.includes(cb.value)
+      );
+    });
+    const checkedVal = checkedCb.value;
+    checkedCb.click();
+    document.getElementById("device-close-button").click();
+
+    info("Checking that the device is removed from the user preference list.");
+    preferredDevices = _loadPreferredDevices();
+    ok(
+      preferredDevices.removed.has(checkedVal),
+      checkedVal + " in removed list"
+    );
+
+    info("Checking that the device is not in the device selector.");
+    await testMenuItems(toolWindow, deviceSelector, menuItems => {
+      is(
+        menuItems.length - 1,
+        featuredCount,
+        "Got expected number of devices in device selector."
+      );
+
+      const menuItem = findMenuItem(menuItems, checkedVal);
+      ok(!menuItem, checkedVal + " removed from the device selector.");
+    });
+
+    info("Reopen device modal and check device is correctly unchecked");
+    await openDeviceModal(ui);
+    ok(
+      [...document.querySelectorAll(".device-input-checkbox")].filter(
+        cb => !cb.checked && cb.value === checkedVal
+      )[0],
+      checkedVal + " is unchecked in the device modal."
+    );
+
+    // Let's add a dummy device to simulate featured flag changes for next test
+    addDeviceForTest(addedDevice);
+  },
+  { waitForDeviceList: true }
+);
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { toolWindow } = ui;
+    const { document } = toolWindow;
+
+    await openDeviceModal(ui);
+
+    const remoteList = await getDevices();
+    const featuredCount = getNumberOfFeaturedDevices(remoteList);
+    const preferredDevices = _loadPreferredDevices();
+
+    // Tests to prove that reloading the RDM didn't break our device list
+    info("Checking new featured device appears in the device selector.");
+    const deviceSelector = document.getElementById("device-selector");
+    await testMenuItems(toolWindow, deviceSelector, items => {
+      is(
+        items.length - 1,
+        featuredCount -
+          preferredDevices.removed.size +
+          preferredDevices.added.size,
+        "Got expected number of devices in device selector."
+      );
+
+      const added = findMenuItem(items, addedDevice.name);
+      ok(added, "Dummy device added to the device selector.");
+
+      for (const name of preferredDevices.added.keys()) {
+        const menuItem = findMenuItem(items, name);
+        ok(menuItem, "Device added by user still in the device selector.");
+      }
+
+      for (const name of preferredDevices.removed.keys()) {
+        const menuItem = findMenuItem(items, name);
+        ok(!menuItem, "Device removed by user not in the device selector.");
+      }
+    });
+  },
+  { waitForDeviceList: true }
+);
+
+/**
+ * Returns the number of featured devices
+ *
+ * @param {Map} devicesByType: Map of devices, keyed by type (as returned by getDevices)
+ * @returns {Integer}
+ */
+function getNumberOfFeaturedDevices(devicesByType) {
+  let count = 0;
+  const devices = [...devicesByType.values()].flat();
+  for (const device of devices) {
+    if (device.featured && device.os != "fxos") {
+      count++;
+    }
+  }
+  return count;
+}
diff --git a/devtools/client/responsive/test/browser/browser_device_pixel_ratio_change.js b/devtools/client/responsive/test/browser/browser_device_pixel_ratio_change.js
new file mode 100644
index 0000000000..c11313a188
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_device_pixel_ratio_change.js
@@ -0,0 +1,136 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests changing viewport device pixel ratio
+
+const TEST_URL = "data:text/html;charset=utf-8,DevicePixelRatio list test";
+const DEFAULT_DPPX = window.devicePixelRatio;
+const VIEWPORT_DPPX = DEFAULT_DPPX + 1;
+const Types = require("resource://devtools/client/responsive/types.js");
+
+const testDevice = {
+  name: "Fake Phone RDM Test",
+  width: 320,
+  height: 470,
+  pixelRatio: 5.5,
+  userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+  touch: true,
+  firefoxOS: true,
+  os: "custom",
+  featured: true,
+};
+
+// Add the new device to the list
+addDeviceForTest(testDevice);
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui, manager }) {
+    await waitStartup(ui);
+
+    await testDefaults(ui);
+    await testChangingDevice(ui);
+    await testResetWhenResizingViewport(ui);
+    await testChangingDevicePixelRatio(ui);
+  },
+  { waitForDeviceList: true }
+);
+
+async function waitStartup(ui) {
+  const { store } = ui.toolWindow;
+
+  // Wait until the viewport has been added and the device list has been loaded
+  await waitUntilState(
+    store,
+    state =>
+      state.viewports.length == 1 &&
+      state.devices.listState == Types.loadableState.LOADED
+  );
+}
+
+async function testDefaults(ui) {
+  info("Test Defaults");
+
+  const dppx = await getViewportDevicePixelRatio(ui);
+  is(dppx, DEFAULT_DPPX, "Content has expected devicePixelRatio");
+  testViewportDevicePixelRatioSelect(ui, {
+    value: DEFAULT_DPPX,
+    disabled: false,
+  });
+  testViewportDeviceMenuLabel(ui, "Responsive");
+}
+
+async function testChangingDevice(ui) {
+  info("Test Changing Device");
+
+  await selectDevice(ui, testDevice.name);
+  await waitForViewportResizeTo(ui, testDevice.width, testDevice.height);
+  const dppx = await waitForDevicePixelRatio(ui, testDevice.pixelRatio);
+  is(dppx, testDevice.pixelRatio, "Content has expected devicePixelRatio");
+  testViewportDevicePixelRatioSelect(ui, {
+    value: testDevice.pixelRatio,
+    disabled: true,
+  });
+  testViewportDeviceMenuLabel(ui, testDevice.name);
+}
+
+async function testResetWhenResizingViewport(ui) {
+  info("Test reset when resizing the viewport");
+
+  await testViewportResize(
+    ui,
+    ".viewport-vertical-resize-handle",
+    [-10, -10],
+    [0, -10],
+    {
+      hasDevice: true,
+    }
+  );
+
+  const dppx = await waitForDevicePixelRatio(ui, DEFAULT_DPPX);
+  is(dppx, DEFAULT_DPPX, "Content has expected devicePixelRatio");
+
+  testViewportDevicePixelRatioSelect(ui, {
+    value: DEFAULT_DPPX,
+    disabled: false,
+  });
+  testViewportDeviceMenuLabel(ui, "Responsive");
+}
+
+async function testChangingDevicePixelRatio(ui) {
+  info("Test changing device pixel ratio");
+
+  await selectDevicePixelRatio(ui, VIEWPORT_DPPX);
+  const dppx = await waitForDevicePixelRatio(ui, VIEWPORT_DPPX);
+  is(dppx, VIEWPORT_DPPX, "Content has expected devicePixelRatio");
+  testViewportDevicePixelRatioSelect(ui, {
+    value: VIEWPORT_DPPX,
+    disabled: false,
+  });
+  testViewportDeviceMenuLabel(ui, "Responsive");
+}
+
+function testViewportDevicePixelRatioSelect(ui, expected) {
+  info("Test viewport's DevicePixelRatio Select");
+
+  const button = ui.toolWindow.document.getElementById(
+    "device-pixel-ratio-menu"
+  );
+  const title = ui.toolWindow.document.querySelector(
+    "#device-pixel-ratio-menu .title"
+  );
+  is(
+    title.textContent,
+    `DPR: ${expected.value}`,
+    `DevicePixelRatio Select value should be: ${expected.value}`
+  );
+  is(
+    button.disabled,
+    expected.disabled,
+    `DevicePixelRatio Select should be ${
+      expected.disabled ? "disabled" : "enabled"
+    }.`
+  );
+}
diff --git a/devtools/client/responsive/test/browser/browser_device_selector_items.js b/devtools/client/responsive/test/browser/browser_device_selector_items.js
new file mode 100644
index 0000000000..63b8efdd50
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_device_selector_items.js
@@ -0,0 +1,79 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests the device selector button and the menu items.
+
+const MenuItem = require("resource://devtools/client/shared/components/menu/MenuItem.js");
+
+const FIREFOX_ICON =
+  'url("chrome://devtools/skin/images/browsers/firefox.svg")';
+const DUMMY_ICON = `url("${MenuItem.DUMMY_ICON}")`;
+
+const FIREFOX_DEVICE = {
+  name: "Device of Firefox user-agent",
+  userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+  width: 320,
+  height: 570,
+  pixelRatio: 5.5,
+  touch: true,
+  firefoxOS: true,
+  os: "custom",
+  featured: true,
+};
+
+const TEST_DEVICES = [
+  {
+    name: FIREFOX_DEVICE.name,
+    hasIcon: true,
+  },
+  {
+    name: "Laptop with MDPI screen",
+    hasIcon: false,
+  },
+];
+
+addDeviceForTest(FIREFOX_DEVICE);
+
+// Add the laptop to the device list
+const {
+  updatePreferredDevices,
+} = require("resource://devtools/client/responsive/actions/devices.js");
+updatePreferredDevices({
+  added: ["Laptop with MDPI screen"],
+  removed: [],
+});
+
+addRDMTask(
+  URL_ROOT,
+  async function ({ ui }) {
+    const deviceSelector =
+      ui.toolWindow.document.getElementById("device-selector");
+
+    for (const testDevice of TEST_DEVICES) {
+      info(`Check "${name}" device`);
+      await testMenuItems(ui.toolWindow, deviceSelector, menuItems => {
+        const menuItem = findMenuItem(menuItems, testDevice.name);
+        ok(menuItem, "The menu item is on the list");
+        const label = menuItem.querySelector(".iconic > .label");
+        const backgroundImage = ui.toolWindow.getComputedStyle(
+          label,
+          "::before"
+        ).backgroundImage;
+        const icon = testDevice.hasIcon ? FIREFOX_ICON : DUMMY_ICON;
+        is(backgroundImage, icon, "The icon is correct");
+      });
+
+      info("Check device selector button");
+      await selectDevice(ui, testDevice.name);
+      const backgroundImage = ui.toolWindow.getComputedStyle(
+        deviceSelector,
+        "::before"
+      ).backgroundImage;
+      const icon = testDevice.hasIcon ? FIREFOX_ICON : "none";
+      is(backgroundImage, icon, "The icon is correct");
+    }
+  },
+  { waitForDeviceList: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_device_state_restore.js b/devtools/client/responsive/test/browser/browser_device_state_restore.js
new file mode 100644
index 0000000000..f8778795c2
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_device_state_restore.js
@@ -0,0 +1,155 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that the previous selected device is restored when reopening RDM.
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+const DEFAULT_DPPX = window.devicePixelRatio;
+
+/* eslint-disable max-len */
+const TEST_DEVICE = {
+  name: "iPhone 6/7/8",
+  width: 375,
+  height: 667,
+  pixelRatio: 2,
+  userAgent:
+    "Mozilla/5.0 (iPhone; CPU iPhone OS 11_0 like Mac OS X) AppleWebKit/604.1.38 (KHTML, like Gecko) Version/11.0 Mobile/15A372 Safari/604.1",
+  touch: true,
+  firefoxOS: false,
+  os: "iOS",
+  featured: true,
+};
+/* eslint-enable max-len */
+
+// Add the device to the list
+const {
+  updatePreferredDevices,
+} = require("resource://devtools/client/responsive/actions/devices.js");
+updatePreferredDevices({
+  added: [TEST_DEVICE.name],
+  removed: [],
+});
+
+const Types = require("resource://devtools/client/responsive/types.js");
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { store } = ui.toolWindow;
+
+    reloadOnUAChange(true);
+
+    // Wait until the viewport has been added and the device list has been loaded
+    await waitUntilState(
+      store,
+      state =>
+        state.viewports.length == 1 &&
+        state.devices.listState == Types.loadableState.LOADED
+    );
+
+    info("Checking the default RDM state.");
+    testViewportDeviceMenuLabel(ui, "Responsive");
+    testViewportDimensions(ui, 320, 480);
+    await testUserAgent(ui, DEFAULT_UA);
+    await testDevicePixelRatio(ui, DEFAULT_DPPX);
+    await testTouchEventsOverride(ui, false);
+
+    info("Select a device");
+    const waitForReload = await watchForDevToolsReload(ui.getViewportBrowser());
+    await selectDevice(ui, TEST_DEVICE.name);
+    await waitForReload();
+    await waitForViewportResizeTo(ui, TEST_DEVICE.width, TEST_DEVICE.height);
+
+    info("Checking the RDM device state.");
+    testViewportDeviceMenuLabel(ui, TEST_DEVICE.name);
+    await testUserAgent(ui, TEST_DEVICE.userAgent);
+    await testDevicePixelRatio(ui, TEST_DEVICE.pixelRatio);
+    await testTouchEventsOverride(ui, TEST_DEVICE.touch);
+
+    reloadOnUAChange(false);
+  },
+  { waitForDeviceList: true }
+);
+
+addRDMTaskWithPreAndPost(
+  TEST_URL,
+  function rdmPreTask({ browser }) {
+    reloadOnUAChange(true);
+  },
+  async function ({ ui }) {
+    // Note: This code might be racy. Call watchForDevToolsReload as early as
+    // possible to catch the reload that will happen on RDM startup.
+    // We cannot easily call watchForDevToolsReload in the preTask because it
+    // needs RDM to be already started. Otherwise it will not find any devtools
+    // UI to wait for.
+    const waitForReload = await watchForDevToolsReload(ui.getViewportBrowser());
+
+    const { store } = ui.toolWindow;
+
+    info(
+      "Reopening RDM and checking that the previous device state is restored."
+    );
+
+    // Wait until the viewport has been added and the device list has been loaded
+    await waitUntilState(
+      store,
+      state =>
+        state.viewports.length == 1 &&
+        state.viewports[0].device === TEST_DEVICE.name &&
+        state.devices.listState == Types.loadableState.LOADED
+    );
+    await waitForViewportResizeTo(ui, TEST_DEVICE.width, TEST_DEVICE.height);
+    await waitForReload();
+
+    info("Checking the restored RDM state.");
+    testViewportDeviceMenuLabel(ui, TEST_DEVICE.name);
+    testViewportDimensions(ui, TEST_DEVICE.width, TEST_DEVICE.height);
+    await testUserAgent(ui, TEST_DEVICE.userAgent);
+    await testDevicePixelRatio(ui, TEST_DEVICE.pixelRatio);
+    await testTouchEventsOverride(ui, TEST_DEVICE.touch);
+
+    info("Rotating the viewport.");
+    rotateViewport(ui);
+
+    reloadOnUAChange(false);
+  },
+  function rdmPostTask({ browser }) {},
+  { waitForDeviceList: true }
+);
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { store } = ui.toolWindow;
+
+    reloadOnUAChange(true);
+
+    info(
+      "Reopening RDM and checking that the previous device state is restored."
+    );
+
+    // Wait until the viewport has been added and the device list has been loaded
+    await waitUntilState(
+      store,
+      state =>
+        state.viewports.length == 1 &&
+        state.viewports[0].device === TEST_DEVICE.name &&
+        state.devices.listState == Types.loadableState.LOADED
+    );
+    await waitForViewportResizeTo(ui, TEST_DEVICE.height, TEST_DEVICE.width);
+    const waitForReload = await watchForDevToolsReload(ui.getViewportBrowser());
+    await waitForReload();
+
+    info("Checking the restored RDM state.");
+    testViewportDeviceMenuLabel(ui, TEST_DEVICE.name);
+    testViewportDimensions(ui, TEST_DEVICE.height, TEST_DEVICE.width);
+    await testUserAgent(ui, TEST_DEVICE.userAgent);
+    await testDevicePixelRatio(ui, TEST_DEVICE.pixelRatio);
+    await testTouchEventsOverride(ui, TEST_DEVICE.touch);
+
+    reloadOnUAChange(false);
+  },
+  { waitForDeviceList: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_device_width.js b/devtools/client/responsive/test/browser/browser_device_width.js
new file mode 100644
index 0000000000..11dc8fd31c
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_device_width.js
@@ -0,0 +1,168 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_URL =
+  'data:text/html;charset=utf-8,<iframe id="subframe" ' +
+  'width="200" height="200"></iframe>';
+
+addRDMTask(TEST_URL, async function ({ ui, manager }) {
+  ok(ui, "An instance of the RDM should be attached to the tab.");
+  await setViewportSizeAndAwaitReflow(ui, manager, 110, 500);
+
+  info("Checking initial width/height properties.");
+  await doInitialChecks(ui, 110);
+
+  info("Checking initial width/height with meta viewport on");
+  await setTouchAndMetaViewportSupport(ui, true);
+  await doInitialChecks(ui, 980);
+  await setTouchAndMetaViewportSupport(ui, false);
+
+  info("Changing the RDM size");
+  await setViewportSizeAndAwaitReflow(ui, manager, 90, 500);
+
+  info("Checking for screen props");
+  await checkScreenProps(ui);
+
+  info("Checking for screen props with meta viewport on");
+  await setTouchAndMetaViewportSupport(ui, true);
+  await checkScreenProps(ui);
+  await setTouchAndMetaViewportSupport(ui, false);
+
+  info("Checking for subframe props");
+  await checkSubframeProps(ui);
+
+  info("Checking for subframe props with meta viewport on");
+  await setTouchAndMetaViewportSupport(ui, true);
+  await checkSubframeProps(ui);
+  await setTouchAndMetaViewportSupport(ui, false);
+
+  info("Changing the RDM size using input keys");
+  await setViewportSizeWithInputKeys(ui);
+
+  info("Checking for screen props once again.");
+  await checkScreenProps2(ui);
+});
+
+async function setViewportSizeWithInputKeys(ui) {
+  const width = 320,
+    height = 500;
+  let resized = waitForViewportResizeTo(ui, width, height);
+  ui.setViewportSize({ width, height });
+  await resized;
+
+  const dimensions = ui.toolWindow.document.querySelectorAll(
+    ".viewport-dimension-input"
+  );
+
+  // Increase width value to 420 by using the Up arrow key
+  resized = waitForViewportResizeTo(ui, 420, height);
+  dimensions[0].focus();
+  for (let i = 1; i <= 100; i++) {
+    EventUtils.synthesizeKey("KEY_ArrowUp");
+  }
+  await resized;
+
+  // Resetting width value back to 320 using `Shift + Down` arrow
+  resized = waitForViewportResizeTo(ui, width, height);
+  dimensions[0].focus();
+  for (let i = 1; i <= 10; i++) {
+    EventUtils.synthesizeKey("KEY_ArrowDown", { shiftKey: true });
+  }
+  await resized;
+
+  // Increase height value to 600 by using `PageUp + Shift` key
+  resized = waitForViewportResizeTo(ui, width, 600);
+  dimensions[1].focus();
+  EventUtils.synthesizeKey("KEY_PageUp", { shiftKey: true });
+  await resized;
+
+  // Resetting height value back to 500 by using `PageDown + Shift` key
+  resized = waitForViewportResizeTo(ui, width, height);
+  dimensions[1].focus();
+  EventUtils.synthesizeKey("KEY_PageDown", { shiftKey: true });
+  await resized;
+}
+
+async function doInitialChecks(ui, expectedInnerWidth) {
+  const { innerWidth, matchesMedia, outerHeight, outerWidth } =
+    await grabContentInfo(ui);
+  is(innerWidth, expectedInnerWidth, "inner width should be as expected");
+  is(outerWidth, 110, "device's outerWidth should be 110px");
+  is(outerHeight, 500, "device's outerHeight should be 500px");
+  isnot(
+    window.outerHeight,
+    outerHeight,
+    "window.outerHeight should not be the size of the device's outerHeight"
+  );
+  isnot(
+    window.outerWidth,
+    outerWidth,
+    "window.outerWidth should not be the size of the device's outerWidth"
+  );
+  ok(!matchesMedia, "media query shouldn't match.");
+}
+
+async function checkScreenProps(ui) {
+  const { matchesMedia, screen } = await grabContentInfo(ui);
+  ok(matchesMedia, "media query should match");
+  isnot(
+    window.screen.width,
+    screen.width,
+    "screen.width should not be the size of the screen."
+  );
+  is(screen.width, 90, "screen.width should be the page width");
+  is(screen.height, 500, "screen.height should be the page height");
+}
+
+async function checkScreenProps2(ui) {
+  const { screen } = await grabContentInfo(ui);
+  isnot(
+    window.screen.width,
+    screen.width,
+    "screen.width should not be the size of the screen."
+  );
+}
+
+async function checkSubframeProps(ui) {
+  const { outerWidth, matchesMedia, screen } = await grabContentSubframeInfo(
+    ui
+  );
+  is(outerWidth, 90, "subframe outerWidth should be 90px");
+  ok(matchesMedia, "subframe media query should match");
+  is(screen.width, 90, "subframe screen.width should be the page width");
+  is(screen.height, 500, "subframe screen.height should be the page height");
+}
+
+function grabContentInfo(ui) {
+  return SpecialPowers.spawn(ui.getViewportBrowser(), [], async function () {
+    return {
+      screen: {
+        width: content.screen.width,
+        height: content.screen.height,
+      },
+      innerWidth: content.innerWidth,
+      matchesMedia: content.matchMedia("(max-device-width:100px)").matches,
+      outerHeight: content.outerHeight,
+      outerWidth: content.outerWidth,
+    };
+  });
+}
+
+function grabContentSubframeInfo(ui) {
+  return SpecialPowers.spawn(ui.getViewportBrowser(), [], async function () {
+    const subframe = content.document.getElementById("subframe");
+    const win = subframe.contentWindow;
+    return {
+      screen: {
+        width: win.screen.width,
+        height: win.screen.height,
+      },
+      innerWidth: win.innerWidth,
+      matchesMedia: win.matchMedia("(max-device-width:100px)").matches,
+      outerHeight: win.outerHeight,
+      outerWidth: win.outerWidth,
+    };
+  });
+}
diff --git a/devtools/client/responsive/test/browser/browser_exit_button.js b/devtools/client/responsive/test/browser/browser_exit_button.js
new file mode 100644
index 0000000000..7fbcd3cc51
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_exit_button.js
@@ -0,0 +1,81 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+
+// Test global exit button
+addRDMTask(TEST_URL, async function (...args) {
+  await testExitButton(...args);
+});
+
+// Test global exit button on detached tab.
+// See Bug 1262806
+addRDMTask(
+  null,
+  async function () {
+    let tab = await addTab(TEST_URL);
+    const { ui, manager } = await openRDM(tab);
+
+    await waitBootstrap(ui);
+
+    const waitTabIsDetached = Promise.all([
+      once(tab, "TabClose"),
+      once(tab.linkedBrowser, "SwapDocShells"),
+    ]);
+
+    // Detach the tab with RDM open.
+    const newWindow = gBrowser.replaceTabWithWindow(tab);
+
+    // Wait until the tab is detached and the new window is fully initialized.
+    await waitTabIsDetached;
+    await newWindow.delayedStartupPromise;
+
+    // Get the new tab instance.
+    tab = newWindow.gBrowser.tabs[0];
+
+    // Detaching a tab closes RDM.
+    ok(
+      !manager.isActiveForTab(tab),
+      "Responsive Design Mode is not active for the tab"
+    );
+
+    // Reopen the RDM and test the exit button again.
+    await testExitButton(await openRDM(tab));
+    await BrowserTestUtils.closeWindow(newWindow);
+  },
+  { onlyPrefAndTask: true }
+);
+
+async function waitBootstrap(ui) {
+  const { toolWindow, tab } = ui;
+  const { store } = toolWindow;
+  const url = String(tab.linkedBrowser.currentURI.spec);
+
+  // Wait until the viewport has been added.
+  await waitUntilState(store, state => state.viewports.length == 1);
+
+  // Wait until the document has been loaded.
+  await waitForFrameLoad(ui, url);
+}
+
+async function testExitButton({ ui, manager }) {
+  await waitBootstrap(ui);
+
+  const exitButton = ui.toolWindow.document.getElementById("exit-button");
+
+  ok(
+    manager.isActiveForTab(ui.tab),
+    "Responsive Design Mode active for the tab"
+  );
+
+  exitButton.click();
+
+  await once(manager, "off");
+
+  ok(
+    !manager.isActiveForTab(ui.tab),
+    "Responsive Design Mode is not active for the tab"
+  );
+}
diff --git a/devtools/client/responsive/test/browser/browser_ext_messaging.js b/devtools/client/responsive/test/browser/browser_ext_messaging.js
new file mode 100644
index 0000000000..5d1b5cf317
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_ext_messaging.js
@@ -0,0 +1,231 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/* eslint-env webextensions */
+
+"use strict";
+
+const TEST_URL = "https://example.com/";
+
+// These allowed rejections are copied from
+// browser/components/extensions/test/browser/head.js.
+const { PromiseTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/PromiseTestUtils.sys.mjs"
+);
+PromiseTestUtils.allowMatchingRejectionsGlobally(
+  /Message manager disconnected/
+);
+PromiseTestUtils.allowMatchingRejectionsGlobally(
+  /Receiving end does not exist/
+);
+
+const extension = ExtensionTestUtils.loadExtension({
+  manifest: {
+    content_scripts: [
+      {
+        matches: [TEST_URL],
+        js: ["content-script.js"],
+        run_at: "document_start",
+      },
+    ],
+  },
+  background() {
+    let currentPort;
+
+    browser.runtime.onConnect.addListener(port => {
+      currentPort = port;
+      port.onDisconnect.addListener(() =>
+        browser.test.sendMessage("port-disconnected")
+      );
+      port.onMessage.addListener(msg =>
+        browser.test.sendMessage("port-message-received", msg)
+      );
+      browser.test.sendMessage("port-connected");
+    });
+
+    browser.test.onMessage.addListener(async msg => {
+      if (msg !== "test:port-message-send") {
+        browser.test.fail(`Unexpected test message received: ${msg}`);
+      }
+
+      currentPort.postMessage("ping");
+    });
+
+    browser.test.sendMessage("background:ready");
+  },
+  files: {
+    "content-script.js": function contentScript() {
+      const port = browser.runtime.connect();
+      port.onMessage.addListener(msg => port.postMessage(`${msg}-pong`));
+    },
+  },
+});
+
+add_task(async function setup_first_test() {
+  await extension.startup();
+
+  await extension.awaitMessage("background:ready");
+});
+
+addRDMTaskWithPreAndPost(
+  TEST_URL,
+  async function pre_task() {
+    await extension.awaitMessage("port-connected");
+  },
+  async function test_port_kept_connected_on_switch_to_RDB() {
+    extension.sendMessage("test:port-message-send");
+
+    is(
+      await extension.awaitMessage("port-message-received"),
+      "ping-pong",
+      "Got the expected message back from the content script"
+    );
+  },
+  async function post_task() {
+    extension.sendMessage("test:port-message-send");
+
+    is(
+      await extension.awaitMessage("port-message-received"),
+      "ping-pong",
+      "Got the expected message back from the content script"
+    );
+  }
+);
+
+add_task(async function cleanup_first_test() {
+  await extension.awaitMessage("port-disconnected");
+
+  await extension.unload();
+});
+
+addRDMTask(TEST_URL, async function test_tab_sender() {
+  const extension2 = ExtensionTestUtils.loadExtension({
+    manifest: {
+      permissions: ["tabs"],
+
+      content_scripts: [
+        {
+          matches: [TEST_URL],
+          js: ["content-script.js"],
+          run_at: "document_start",
+        },
+      ],
+    },
+
+    async background() {
+      const TEST_URL = "https://example.com/"; // eslint-disable-line no-shadow
+
+      browser.test.log("Background script init");
+
+      let extTab;
+      const contentMessage = new Promise(resolve => {
+        browser.test.log("Listen to content");
+        const listener = async (msg, sender, respond) => {
+          browser.test.assertEq(
+            msg,
+            "hello-from-content",
+            "Background script got hello-from-content message"
+          );
+
+          const tabs = await browser.tabs.query({
+            currentWindow: true,
+            active: true,
+          });
+          browser.test.assertEq(
+            tabs.length,
+            1,
+            "One tab is active in the current window"
+          );
+          extTab = tabs[0];
+          browser.test.log(`Tab: id ${extTab.id}, url ${extTab.url}`);
+          browser.test.assertEq(extTab.url, TEST_URL, "Tab has the test URL");
+
+          browser.test.assertTrue(!!sender, "Message has a sender");
+          browser.test.assertTrue(!!sender.tab, "Message has a sender.tab");
+          browser.test.assertEq(
+            sender.tab.id,
+            extTab.id,
+            "Sender's tab ID matches the RDM tab ID"
+          );
+          browser.test.assertEq(
+            sender.tab.url,
+            extTab.url,
+            "Sender's tab URL matches the RDM tab URL"
+          );
+
+          browser.runtime.onMessage.removeListener(listener);
+          resolve();
+        };
+        browser.runtime.onMessage.addListener(listener);
+      });
+
+      // Wait for "resume" message so we know the content script is also ready.
+      await new Promise(resolve => {
+        browser.test.onMessage.addListener(resolve);
+        browser.test.sendMessage("background-script-ready");
+      });
+
+      await contentMessage;
+
+      browser.test.log("Send message from background to content");
+      const contentSender = await browser.tabs.sendMessage(
+        extTab.id,
+        "hello-from-background"
+      );
+      browser.test.assertEq(
+        contentSender.id,
+        browser.runtime.id,
+        "The sender ID in content matches this extension"
+      );
+
+      browser.test.notifyPass("rdm-messaging");
+    },
+
+    files: {
+      "content-script.js": async function () {
+        browser.test.log("Content script init");
+
+        browser.test.log("Listen to background");
+        browser.runtime.onMessage.addListener((msg, sender, respond) => {
+          browser.test.assertEq(
+            msg,
+            "hello-from-background",
+            "Content script got hello-from-background message"
+          );
+
+          browser.test.assertTrue(!!sender, "Message has a sender");
+          browser.test.assertTrue(!!sender.id, "Message has a sender.id");
+
+          const { id } = sender;
+          respond({ id });
+        });
+
+        // Wait for "resume" message so we know the background script is also ready.
+        await new Promise(resolve => {
+          browser.test.onMessage.addListener(resolve);
+          browser.test.sendMessage("content-script-ready");
+        });
+
+        browser.test.log("Send message from content to background");
+        browser.runtime.sendMessage("hello-from-content");
+      },
+    },
+  });
+
+  const contentScriptReady = extension2.awaitMessage("content-script-ready");
+  const backgroundScriptReady = extension2.awaitMessage(
+    "background-script-ready"
+  );
+  const finish = extension2.awaitFinish("rdm-messaging");
+
+  await extension2.startup();
+
+  // It appears the background script and content script can loaded in either order, so
+  // we'll wait for the both to listen before proceeding.
+  await backgroundScriptReady;
+  await contentScriptReady;
+  extension2.sendMessage("resume");
+
+  await finish;
+  await extension2.unload();
+});
diff --git a/devtools/client/responsive/test/browser/browser_in_rdm_pane.js b/devtools/client/responsive/test/browser/browser_in_rdm_pane.js
new file mode 100644
index 0000000000..546e8d5b4a
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_in_rdm_pane.js
@@ -0,0 +1,31 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Verify the inRDMPane property is set on a document when that
+// document is being viewed in Responsive Design Mode.
+
+const TEST_URL = "http://example.com/";
+
+addRDMTask(TEST_URL, async function ({ ui }) {
+  const viewportBrowser = ui.getViewportBrowser();
+
+  const contentURL = await SpecialPowers.spawn(
+    viewportBrowser,
+    [],
+    () => content.document.URL
+  );
+  info("content URL is " + contentURL);
+
+  const contentInRDMPane = await SpecialPowers.spawn(
+    viewportBrowser,
+    [],
+    () => docShell.browsingContext.inRDMPane
+  );
+
+  ok(
+    contentInRDMPane,
+    "After RDM is opened, document should have inRDMPane set to true."
+  );
+});
diff --git a/devtools/client/responsive/test/browser/browser_many_toggles.js b/devtools/client/responsive/test/browser/browser_many_toggles.js
new file mode 100644
index 0000000000..a0fe19dba4
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_many_toggles.js
@@ -0,0 +1,51 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Verify RDM can be toggled many times in a raw
+
+const TEST_URL = "https://example.com/";
+
+addRDMTask(
+  null,
+  async function () {
+    const tab = await addTab(TEST_URL);
+
+    // Record all currently active RDMs, there may not be one created on each loop
+    let opened = 0;
+    ResponsiveUIManager.on("on", () => opened++);
+    ResponsiveUIManager.on("off", () => opened--);
+
+    for (let i = 0; i < 10; i++) {
+      info(`Toggling RDM #${i + 1}`);
+      // This may throw when we were just closing is still ongoing,
+      // ignore any exception.
+      openRDM(tab).catch(e => {});
+      // Sometime pause in order to cover both full synchronous opening and close
+      // but also the same but with some pause between each operation.
+      if (i % 2 == 0) {
+        info("Wait a bit after open");
+        await wait(250);
+      }
+      closeRDM(tab);
+      if (i % 3 == 0) {
+        info("Wait a bit after close");
+        await wait(250);
+      }
+    }
+
+    // Wait a bit so that we can receive the very last ResponsiveUIManager `on` event,
+    // and properly wait for its closing.
+    await wait(1000);
+
+    // This is important to wait for all destruction as closing the tab while RDM
+    // is still closing may lead to exception because of pending cleanup RDP requests.
+    info("Wait for all opened RDM to be closed before closing the tab");
+    await waitFor(() => opened == 0);
+    info("All RDM are closed");
+
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_max_touchpoints.js b/devtools/client/responsive/test/browser/browser_max_touchpoints.js
new file mode 100644
index 0000000000..a6feb1975f
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_max_touchpoints.js
@@ -0,0 +1,103 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Verify that maxTouchPoints is updated when touch simulation is toggled.
+
+// TODO: This test should also check that maxTouchPoints is set properly on the iframe.
+// This is currently not working and should be worked on in Bug 1706066.
+
+const TEST_DOCUMENT = `doc_with_remote_iframe_and_isolated_cross_origin_capabilities.sjs`;
+const TEST_COM_URL = URL_ROOT_COM_SSL + TEST_DOCUMENT;
+
+addRDMTask(TEST_COM_URL, async function ({ ui, browser, tab }) {
+  reloadOnTouchChange(true);
+  info("Test initial value for maxTouchPoints.");
+  is(
+    await getMaxTouchPoints(browser),
+    0,
+    "navigator.maxTouchPoints is 0 when touch simulation is not enabled"
+  );
+
+  info(
+    "Test value maxTouchPoints is non-zero when touch simulation is enabled."
+  );
+  await toggleTouchSimulation(ui);
+  is(
+    await getMaxTouchPoints(browser),
+    1,
+    "navigator.maxTouchPoints should be 1 after enabling touch simulation"
+  );
+
+  info("Toggling off touch simulation.");
+  await toggleTouchSimulation(ui);
+  is(
+    await getMaxTouchPoints(browser),
+    0,
+    "navigator.maxTouchPoints should be 0 after turning off touch simulation"
+  );
+
+  info("Enabling touch simulation again");
+  await toggleTouchSimulation(ui);
+  is(
+    await getMaxTouchPoints(browser),
+    1,
+    "navigator.maxTouchPoints should be 1 after enabling touch simulation again"
+  );
+
+  info("Check maxTouchPoints override persists after reload");
+  await reloadBrowser();
+
+  is(
+    await getMaxTouchPoints(browser),
+    1,
+    "navigator.maxTouchPoints is still 1 after reloading"
+  );
+
+  info(
+    "Check that maxTouchPoints persist after navigating to a page that forces the creation of a new browsing context"
+  );
+  const previousBrowsingContextId = browser.browsingContext.id;
+
+  const waitForDevToolsReload = await watchForDevToolsReload(browser);
+  BrowserTestUtils.startLoadingURIString(
+    browser,
+    URL_ROOT_ORG_SSL + TEST_DOCUMENT + "?crossOriginIsolated=true"
+  );
+  await waitForDevToolsReload();
+
+  isnot(
+    browser.browsingContext.id,
+    previousBrowsingContextId,
+    "A new browsing context was created"
+  );
+
+  is(
+    await getMaxTouchPoints(browser),
+    1,
+    "navigator.maxTouchPoints is still 1 after navigating to a new browsing context"
+  );
+
+  info("Check that the value is reset when closing RDM");
+  // Closing RDM trigers a reload
+  const onPageReloaded = BrowserTestUtils.browserLoaded(browser, true);
+  await closeRDM(tab);
+  await onPageReloaded;
+
+  is(
+    await getMaxTouchPoints(browser),
+    0,
+    "navigator.maxTouchPoints is 0 after closing RDM"
+  );
+
+  reloadOnTouchChange(false);
+});
+
+function getMaxTouchPoints(browserOrBrowsingContext) {
+  return ContentTask.spawn(
+    browserOrBrowsingContext,
+    null,
+    () => content.navigator.maxTouchPoints
+  );
+}
diff --git a/devtools/client/responsive/test/browser/browser_menu_item_01.js b/devtools/client/responsive/test/browser/browser_menu_item_01.js
new file mode 100644
index 0000000000..72b5b835be
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_menu_item_01.js
@@ -0,0 +1,67 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test RDM menu item is checked when expected, on multiple tabs.
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+
+const {
+  startup,
+} = require("resource://devtools/client/responsive/utils/window.js");
+
+const activateTab = tab =>
+  new Promise(resolve => {
+    const { gBrowser } = tab.ownerGlobal;
+    const { tabContainer } = gBrowser;
+
+    tabContainer.addEventListener("TabSelect", function listener({ type }) {
+      tabContainer.removeEventListener(type, listener);
+      resolve();
+    });
+
+    gBrowser.selectedTab = tab;
+  });
+
+const isMenuChecked = () => {
+  const menu = document.getElementById("menu_responsiveUI");
+  return menu.getAttribute("checked") === "true";
+};
+
+add_task(async function () {
+  await startup(window);
+
+  ok(!isMenuChecked(), "RDM menu item is unchecked by default");
+});
+
+let tab2;
+
+addRDMTaskWithPreAndPost(
+  TEST_URL,
+  function pre_task() {
+    ok(!isMenuChecked(), "RDM menu item is unchecked for new tab");
+  },
+  async function task({ browser }) {
+    ok(isMenuChecked(), "RDM menu item is checked with RDM open");
+
+    tab2 = await addTab(TEST_URL);
+
+    ok(!isMenuChecked(), "RDM menu item is unchecked for new tab");
+
+    const tab = gBrowser.getTabForBrowser(browser);
+    await activateTab(tab);
+
+    ok(
+      isMenuChecked(),
+      "RDM menu item is checked for the tab where RDM is open"
+    );
+  },
+  function post_task() {
+    ok(!isMenuChecked(), "RDM menu item is unchecked after RDM is closed");
+  }
+);
+
+add_task(async function () {
+  await removeTab(tab2);
+});
diff --git a/devtools/client/responsive/test/browser/browser_menu_item_02.js b/devtools/client/responsive/test/browser/browser_menu_item_02.js
new file mode 100644
index 0000000000..d0dd755580
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_menu_item_02.js
@@ -0,0 +1,59 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test RDM menu item is checked when expected, on multiple windows.
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+
+const isMenuCheckedFor = ({ document }) => {
+  const menu = document.getElementById("menu_responsiveUI");
+  return menu.getAttribute("checked") === "true";
+};
+
+addRDMTask(
+  null,
+  async function () {
+    const window1 = await BrowserTestUtils.openNewBrowserWindow();
+    const { gBrowser } = window1;
+
+    await BrowserTestUtils.withNewTab(
+      { gBrowser, url: TEST_URL },
+      async function (browser) {
+        const tab = gBrowser.getTabForBrowser(browser);
+
+        is(
+          window1,
+          Services.wm.getMostRecentWindow("navigator:browser"),
+          "The new window is the active one"
+        );
+
+        ok(!isMenuCheckedFor(window1), "RDM menu item is unchecked by default");
+
+        const { ui } = await openRDM(tab);
+        await waitForDeviceAndViewportState(ui);
+
+        ok(isMenuCheckedFor(window1), "RDM menu item is checked with RDM open");
+
+        await closeRDM(tab);
+
+        ok(
+          !isMenuCheckedFor(window1),
+          "RDM menu item is unchecked with RDM closed"
+        );
+      }
+    );
+
+    await BrowserTestUtils.closeWindow(window1);
+
+    is(
+      window,
+      Services.wm.getMostRecentWindow("navigator:browser"),
+      "The original window is the active one"
+    );
+
+    ok(!isMenuCheckedFor(window), "RDM menu item is unchecked");
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_mouse_resize.js b/devtools/client/responsive/test/browser/browser_mouse_resize.js
new file mode 100644
index 0000000000..62aa1b1eae
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_mouse_resize.js
@@ -0,0 +1,39 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui, manager }) {
+    const store = ui.toolWindow.store;
+
+    // Wait until the viewport has been added
+    await waitUntilState(store, state => state.viewports.length == 1);
+
+    await setViewportSize(ui, manager, 300, 300);
+
+    // Do horizontal + vertical resize
+    await testViewportResize(ui, ".viewport-resize-handle", [10, 10], [10, 10]);
+
+    // Do horizontal resize
+    await testViewportResize(
+      ui,
+      ".viewport-horizontal-resize-handle",
+      [-10, 10],
+      [-10, 0]
+    );
+
+    // Do vertical resize
+    await testViewportResize(
+      ui,
+      ".viewport-vertical-resize-handle",
+      [-10, -10],
+      [0, -10],
+      ui
+    );
+  },
+  { waitForDeviceList: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_navigation.js b/devtools/client/responsive/test/browser/browser_navigation.js
new file mode 100644
index 0000000000..fbea607e6e
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_navigation.js
@@ -0,0 +1,102 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the primary browser navigation UI to verify it's connected to the viewport.
+
+const DUMMY_1_URL = "https://example.com/";
+const TEST_URL = `${URL_ROOT_SSL}doc_page_state.html`;
+const DUMMY_2_URL = "https://example.com/browser/";
+const DUMMY_3_URL = "https://example.com/browser/devtools/";
+
+addRDMTask(
+  null,
+  async function () {
+    await SpecialPowers.pushPrefEnv({
+      set: [["browser.navigation.requireUserInteraction", false]],
+    });
+
+    // Load up a sequence of pages:
+    // 0. DUMMY_1_URL
+    // 1. TEST_URL
+    // 2. DUMMY_2_URL
+    const tab = await addTab(DUMMY_1_URL);
+    const browser = tab.linkedBrowser;
+    await navigateTo(TEST_URL);
+    await navigateTo(DUMMY_2_URL);
+
+    // Check session history state
+    let history = await getSessionHistory(browser);
+    is(history.index - 1, 2, "At page 2 in history");
+    is(history.entries.length, 3, "3 pages in history");
+    is(history.entries[0].url, DUMMY_1_URL, "Page 0 URL matches");
+    is(history.entries[1].url, TEST_URL, "Page 1 URL matches");
+    is(history.entries[2].url, DUMMY_2_URL, "Page 2 URL matches");
+
+    // Go back one so we're at the test page
+    await back(browser);
+
+    // Check session history state
+    history = await getSessionHistory(browser);
+    is(history.index - 1, 1, "At page 1 in history");
+    is(history.entries.length, 3, "3 pages in history");
+    is(history.entries[0].url, DUMMY_1_URL, "Page 0 URL matches");
+    is(history.entries[1].url, TEST_URL, "Page 1 URL matches");
+    is(history.entries[2].url, DUMMY_2_URL, "Page 2 URL matches");
+
+    const { ui } = await openRDM(tab);
+    await waitForDeviceAndViewportState(ui);
+
+    ok(browser.webNavigation.canGoBack, "Going back is allowed");
+    ok(browser.webNavigation.canGoForward, "Going forward is allowed");
+    is(browser.documentURI.spec, TEST_URL, "documentURI matches page 1");
+    is(browser.contentTitle, "Page State Test", "contentTitle matches page 1");
+
+    await forward(browser);
+
+    ok(browser.webNavigation.canGoBack, "Going back is allowed");
+    ok(!browser.webNavigation.canGoForward, "Going forward is not allowed");
+    is(browser.documentURI.spec, DUMMY_2_URL, "documentURI matches page 2");
+    is(
+      browser.contentTitle,
+      "mochitest index /browser/",
+      "contentTitle matches page 2"
+    );
+
+    await back(browser);
+    await back(browser);
+
+    ok(!browser.webNavigation.canGoBack, "Going back is not allowed");
+    ok(browser.webNavigation.canGoForward, "Going forward is allowed");
+    is(browser.documentURI.spec, DUMMY_1_URL, "documentURI matches page 0");
+    is(
+      browser.contentTitle,
+      "mochitest index /",
+      "contentTitle matches page 0"
+    );
+
+    await navigateTo(DUMMY_3_URL);
+
+    ok(browser.webNavigation.canGoBack, "Going back is allowed");
+    ok(!browser.webNavigation.canGoForward, "Going forward is not allowed");
+    is(browser.documentURI.spec, DUMMY_3_URL, "documentURI matches page 3");
+    is(
+      browser.contentTitle,
+      "mochitest index /browser/devtools/",
+      "contentTitle matches page 3"
+    );
+
+    await closeRDM(tab);
+
+    // Check session history state
+    history = await getSessionHistory(browser);
+    is(history.index - 1, 1, "At page 1 in history");
+    is(history.entries.length, 2, "2 pages in history");
+    is(history.entries[0].url, DUMMY_1_URL, "Page 0 URL matches");
+    is(history.entries[1].url, DUMMY_3_URL, "Page 1 URL matches");
+
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_network_throttling.js b/devtools/client/responsive/test/browser/browser_network_throttling.js
new file mode 100644
index 0000000000..fbf97b172a
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_network_throttling.js
@@ -0,0 +1,77 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const {
+  profiles,
+} = require("resource://devtools/client/shared/components/throttling/profiles.js");
+
+// Tests changing network throttling
+const TEST_URL = "data:text/html;charset=utf-8,Network throttling test";
+
+addRDMTask(TEST_URL, async function ({ ui, manager }) {
+  // Test defaults
+  testNetworkThrottlingSelectorLabel(ui, "No Throttling", "No Throttling");
+  await testNetworkThrottlingState(ui, null);
+
+  // Test a fast profile
+  await testThrottlingProfile(
+    ui,
+    "Wi-Fi",
+    "download 30Mbps, upload 15Mbps, latency 2ms"
+  );
+
+  // Test a slower profile
+  await testThrottlingProfile(
+    ui,
+    "Regular 3G",
+    "download 750Kbps, upload 250Kbps, latency 100ms"
+  );
+
+  // Test switching back to no throttling
+  await selectNetworkThrottling(ui, "No Throttling");
+  testNetworkThrottlingSelectorLabel(ui, "No Throttling", "No Throttling");
+  await testNetworkThrottlingState(ui, null);
+});
+
+function testNetworkThrottlingSelectorLabel(
+  ui,
+  expectedLabel,
+  expectedTooltip
+) {
+  const title = ui.toolWindow.document.querySelector(
+    "#network-throttling-menu .title"
+  );
+  is(
+    title.textContent,
+    expectedLabel,
+    `Button label should be changed to ${expectedLabel}`
+  );
+  is(
+    title.parentNode.getAttribute("title"),
+    expectedTooltip,
+    `Button tooltip should be changed to ${expectedTooltip}`
+  );
+}
+
+var testNetworkThrottlingState = async function (ui, expected) {
+  const state = await ui.networkFront.getNetworkThrottling();
+  Assert.deepEqual(
+    state,
+    expected,
+    "Network throttling state should be " + JSON.stringify(expected, null, 2)
+  );
+};
+
+var testThrottlingProfile = async function (ui, profile, tooltip) {
+  await selectNetworkThrottling(ui, profile);
+  testNetworkThrottlingSelectorLabel(ui, profile, tooltip);
+  const data = profiles.find(({ id }) => id == profile);
+  const { download, upload, latency } = data;
+  await testNetworkThrottlingState(ui, {
+    downloadThroughput: download,
+    uploadThroughput: upload,
+    latency,
+  });
+};
diff --git a/devtools/client/responsive/test/browser/browser_orientationchange_event.js b/devtools/client/responsive/test/browser/browser_orientationchange_event.js
new file mode 100644
index 0000000000..21818f2d81
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_orientationchange_event.js
@@ -0,0 +1,244 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that the "orientationchange" event is fired when the "rotate button" is clicked.
+
+// TODO: This test should also check that the orientation is set properly on the iframe.
+// This is currently not working and should be worked on in Bug 1704830.
+
+const TEST_DOCUMENT = `doc_with_remote_iframe_and_isolated_cross_origin_capabilities.sjs`;
+const TEST_COM_URL = URL_ROOT_COM_SSL + TEST_DOCUMENT;
+
+const testDevice = {
+  name: "Fake Phone RDM Test",
+  width: 320,
+  height: 570,
+  pixelRatio: 5.5,
+  userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+  touch: true,
+  firefoxOS: true,
+  os: "custom",
+  featured: true,
+};
+
+// Add the new device to the list
+addDeviceForTest(testDevice);
+
+addRDMTask(TEST_COM_URL, async function ({ ui }) {
+  await pushPref("devtools.responsive.viewport.angle", 0);
+
+  info("Check the original orientation values before the orientationchange");
+  is(
+    await getScreenOrientationType(ui.getViewportBrowser()),
+    "portrait-primary",
+    "Primary orientation type is portrait-primary"
+  );
+
+  is(
+    await getScreenOrientationAngle(ui.getViewportBrowser()),
+    0,
+    "Original angle is set at 0 degrees"
+  );
+
+  info(
+    "Check that rotating the viewport does trigger an orientationchange event"
+  );
+  let waitForOrientationChangeEvent = isOrientationChangeEventEmitted(
+    ui.getViewportBrowser()
+  );
+  rotateViewport(ui);
+  is(
+    await waitForOrientationChangeEvent,
+    true,
+    "'orientationchange' event fired"
+  );
+
+  is(
+    await getScreenOrientationType(ui.getViewportBrowser()),
+    "landscape-primary",
+    "Orientation state was updated to landscape-primary"
+  );
+
+  is(
+    await getScreenOrientationAngle(ui.getViewportBrowser()),
+    90,
+    "Orientation angle was updated to 90 degrees"
+  );
+
+  info("Check that the viewport orientation values persist after reload");
+  await reloadBrowser();
+
+  is(
+    await getScreenOrientationType(ui.getViewportBrowser()),
+    "landscape-primary",
+    "Orientation is still landscape-primary"
+  );
+  is(
+    await getInitialScreenOrientationType(ui.getViewportBrowser()),
+    "landscape-primary",
+    "orientation type was set on the page very early in its lifecycle"
+  );
+  is(
+    await getScreenOrientationAngle(ui.getViewportBrowser()),
+    90,
+    "Orientation angle is still 90"
+  );
+  is(
+    await getInitialScreenOrientationAngle(ui.getViewportBrowser()),
+    90,
+    "orientation angle was set on the page early in its lifecycle"
+  );
+
+  info(
+    "Check that the viewport orientation values persist after navigating to a page that forces the creation of a new browsing context"
+  );
+  const browser = ui.getViewportBrowser();
+  const previousBrowsingContextId = browser.browsingContext.id;
+  const waitForReload = await watchForDevToolsReload(browser);
+
+  BrowserTestUtils.startLoadingURIString(
+    browser,
+    URL_ROOT_ORG_SSL + TEST_DOCUMENT + "?crossOriginIsolated=true"
+  );
+  await waitForReload();
+
+  isnot(
+    browser.browsingContext.id,
+    previousBrowsingContextId,
+    "A new browsing context was created"
+  );
+
+  is(
+    await getScreenOrientationType(ui.getViewportBrowser()),
+    "landscape-primary",
+    "Orientation is still landscape-primary after navigating to a new browsing context"
+  );
+  is(
+    await getInitialScreenOrientationType(ui.getViewportBrowser()),
+    "landscape-primary",
+    "orientation type was set on the page very early in its lifecycle"
+  );
+  is(
+    await getScreenOrientationAngle(ui.getViewportBrowser()),
+    90,
+    "Orientation angle is still 90 after navigating to a new browsing context"
+  );
+  is(
+    await getInitialScreenOrientationAngle(ui.getViewportBrowser()),
+    90,
+    "orientation angle was set on the page early in its lifecycle"
+  );
+
+  info(
+    "Check the orientationchange event is not dispatched when changing devices."
+  );
+  waitForOrientationChangeEvent = isOrientationChangeEventEmitted(
+    ui.getViewportBrowser()
+  );
+
+  await selectDevice(ui, testDevice.name);
+  is(
+    await waitForOrientationChangeEvent,
+    false,
+    "orientationchange event was not dispatched when changing devices"
+  );
+
+  info("Check the new orientation values after selecting device.");
+  is(
+    await getScreenOrientationType(ui.getViewportBrowser()),
+    "portrait-primary",
+    "New orientation type is portrait-primary"
+  );
+
+  is(
+    await getScreenOrientationAngle(ui.getViewportBrowser()),
+    0,
+    "Orientation angle is 0"
+  );
+
+  info(
+    "Check the orientationchange event is not dispatched when calling the command with the same orientation."
+  );
+  waitForOrientationChangeEvent = isOrientationChangeEventEmitted(
+    ui.getViewportBrowser()
+  );
+
+  // We're directly calling the command here as there's no way to do such action from the UI.
+  await ui.commands.targetConfigurationCommand.updateConfiguration({
+    rdmPaneOrientation: {
+      type: "portrait-primary",
+      angle: 0,
+      isViewportRotated: true,
+    },
+  });
+  is(
+    await waitForOrientationChangeEvent,
+    false,
+    "orientationchange event was not dispatched after trying to set the same orientation again"
+  );
+});
+
+function getScreenOrientationType(browserOrBrowsingContext) {
+  return SpecialPowers.spawn(browserOrBrowsingContext, [], () => {
+    return content.screen.orientation.type;
+  });
+}
+
+function getScreenOrientationAngle(browserOrBrowsingContext) {
+  return SpecialPowers.spawn(
+    browserOrBrowsingContext,
+    [],
+    () => content.screen.orientation.angle
+  );
+}
+
+function getInitialScreenOrientationType(browserOrBrowsingContext) {
+  return SpecialPowers.spawn(
+    browserOrBrowsingContext,
+    [],
+    () => content.wrappedJSObject.initialOrientationType
+  );
+}
+
+function getInitialScreenOrientationAngle(browserOrBrowsingContext) {
+  return SpecialPowers.spawn(
+    browserOrBrowsingContext,
+    [],
+    () => content.wrappedJSObject.initialOrientationAngle
+  );
+}
+
+async function isOrientationChangeEventEmitted(browserOrBrowsingContext) {
+  const onTimeout = wait(1000).then(() => "TIMEOUT");
+  const onOrientationChangeEvent = SpecialPowers.spawn(
+    browserOrBrowsingContext,
+    [],
+    () => {
+      content.eventController = new content.AbortController();
+      return new Promise(resolve => {
+        content.window.addEventListener(
+          "orientationchange",
+          () => {
+            resolve();
+          },
+          {
+            signal: content.eventController.signal,
+            once: true,
+          }
+        );
+      });
+    }
+  );
+
+  const result = await Promise.race([onTimeout, onOrientationChangeEvent]);
+
+  // Remove the event listener
+  await SpecialPowers.spawn(browserOrBrowsingContext, [], () => {
+    content.eventController.abort();
+    delete content.eventController;
+  });
+
+  return result !== "TIMEOUT";
+}
diff --git a/devtools/client/responsive/test/browser/browser_page_redirection.js b/devtools/client/responsive/test/browser/browser_page_redirection.js
new file mode 100644
index 0000000000..5a90aa1bac
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_page_redirection.js
@@ -0,0 +1,62 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test for redirection.
+
+const TEST_URL = `${URL_ROOT}sjs_redirection.sjs`;
+const CUSTOM_USER_AGENT = "Mozilla/5.0 (Test Device) Firefox/74.0";
+
+addRDMTask(
+  null,
+  async () => {
+    reloadOnUAChange(true);
+
+    registerCleanupFunction(() => {
+      reloadOnUAChange(false);
+    });
+
+    const tab = await addTab(TEST_URL);
+    const browser = tab.linkedBrowser;
+
+    const { ui } = await openRDM(tab);
+    await waitForDeviceAndViewportState(ui);
+
+    info("Change the user agent");
+    await changeUserAgentInput(ui, CUSTOM_USER_AGENT);
+    await testUserAgent(ui, CUSTOM_USER_AGENT);
+
+    info("Load a page which redirects");
+    const onRedirectedPageLoaded = BrowserTestUtils.browserLoaded(
+      browser,
+      false,
+      // wait specifically for the redirected page
+      url => url.includes(`?redirected`)
+    );
+    BrowserTestUtils.startLoadingURIString(browser, `${TEST_URL}?redirect`);
+    await onRedirectedPageLoaded;
+
+    info("Check the user agent for each requests");
+    await SpecialPowers.spawn(
+      browser,
+      [CUSTOM_USER_AGENT],
+      expectedUserAgent => {
+        is(
+          content.wrappedJSObject.redirectRequestUserAgent,
+          expectedUserAgent,
+          `Sent user agent is correct for request that caused the redirect`
+        );
+        is(
+          content.wrappedJSObject.requestUserAgent,
+          expectedUserAgent,
+          `Sent user agent is correct for the redirected page`
+        );
+      }
+    );
+
+    await closeRDM(tab);
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_page_state.js b/devtools/client/responsive/test/browser/browser_page_state.js
new file mode 100644
index 0000000000..6b01031fbb
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_page_state.js
@@ -0,0 +1,91 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test page state to ensure page is not reloaded and session history is not
+// modified.
+
+const DUMMY_1_URL = "https://example.com/";
+const TEST_URL = `${URL_ROOT_SSL}doc_page_state.html`;
+const DUMMY_2_URL = "https://example.com/browser/";
+
+addRDMTask(
+  null,
+  async function () {
+    await SpecialPowers.pushPrefEnv({
+      set: [["browser.navigation.requireUserInteraction", false]],
+    });
+
+    // Load up a sequence of pages:
+    // 0. DUMMY_1_URL
+    // 1. TEST_URL
+    // 2. DUMMY_2_URL
+    const tab = await addTab(DUMMY_1_URL);
+    const browser = tab.linkedBrowser;
+    await navigateTo(TEST_URL);
+    await navigateTo(DUMMY_2_URL);
+
+    // Check session history state
+    let history = await getSessionHistory(browser);
+    is(history.index - 1, 2, "At page 2 in history");
+    is(history.entries.length, 3, "3 pages in history");
+    is(history.entries[0].url, DUMMY_1_URL, "Page 0 URL matches");
+    is(history.entries[1].url, TEST_URL, "Page 1 URL matches");
+    is(history.entries[2].url, DUMMY_2_URL, "Page 2 URL matches");
+
+    // Go back one so we're at the test page
+    await back(browser);
+
+    // Check session history state
+    history = await getSessionHistory(browser);
+    is(history.index - 1, 1, "At page 1 in history");
+    is(history.entries.length, 3, "3 pages in history");
+    is(history.entries[0].url, DUMMY_1_URL, "Page 0 URL matches");
+    is(history.entries[1].url, TEST_URL, "Page 1 URL matches");
+    is(history.entries[2].url, DUMMY_2_URL, "Page 2 URL matches");
+
+    // Click on content to set an altered state that would be lost on reload
+    await BrowserTestUtils.synthesizeMouseAtCenter("body", {}, browser);
+
+    const { ui } = await openRDM(tab);
+    await waitForDeviceAndViewportState(ui);
+
+    // Check color inside the viewport
+    let color = await spawnViewportTask(ui, {}, function () {
+      return content
+        .getComputedStyle(content.document.body)
+        .getPropertyValue("background-color");
+    });
+    is(
+      color,
+      "rgb(0, 128, 0)",
+      "Content is still modified from click in viewport"
+    );
+
+    await closeRDM(tab);
+
+    // Check color back in the browser tab
+    color = await SpecialPowers.spawn(browser, [], async function () {
+      return content
+        .getComputedStyle(content.document.body)
+        .getPropertyValue("background-color");
+    });
+    is(
+      color,
+      "rgb(0, 128, 0)",
+      "Content is still modified from click in browser tab"
+    );
+
+    // Check session history state
+    history = await getSessionHistory(browser);
+    is(history.index - 1, 1, "At page 1 in history");
+    is(history.entries.length, 3, "3 pages in history");
+    is(history.entries[0].url, DUMMY_1_URL, "Page 0 URL matches");
+    is(history.entries[1].url, TEST_URL, "Page 1 URL matches");
+    is(history.entries[2].url, DUMMY_2_URL, "Page 2 URL matches");
+
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_page_style.js b/devtools/client/responsive/test/browser/browser_page_style.js
new file mode 100644
index 0000000000..c59ba03b47
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_page_style.js
@@ -0,0 +1,70 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that the Page Style browser menu actions make it to the viewport, instead of
+// applying to the RDM UI.
+
+const TEST_URL = `${URL_ROOT}page_style.html`;
+
+addRDMTask(TEST_URL, async function ({ ui, manager }) {
+  // Store the RDM body text color for later.
+  const rdmWindow = ui.toolWindow;
+  const rdmTextColor = rdmWindow.getComputedStyle(
+    rdmWindow.document.body
+  ).color;
+
+  info(
+    "Trigger the no page style action and wait for the text color to change"
+  );
+  let onPageColorChanged = waitForContentPageTextColor(ui, "rgb(0, 0, 0)");
+  let menuItem = document.querySelector("#menu_pageStyleNoStyle");
+  menuItem.click();
+  let color = await onPageColorChanged;
+
+  is(
+    color,
+    "rgb(0, 0, 0)",
+    "The text color is black, so the style was disabled"
+  );
+
+  info("Check that the RDM page style wasn't disabled");
+  is(
+    rdmWindow.getComputedStyle(rdmWindow.document.body).color,
+    rdmTextColor,
+    "The color of the text in the RDM window is correct, so that style still applies"
+  );
+
+  info(
+    "Trigger the page style back and wait for the text color to change again"
+  );
+  onPageColorChanged = waitForContentPageTextColor(ui, "rgb(255, 0, 0)");
+  menuItem = document.querySelector("#menu_pageStylePersistentOnly");
+  menuItem.click();
+  color = await onPageColorChanged;
+
+  is(
+    color,
+    "rgb(255, 0, 0)",
+    "The text color is red, so the style was enabled"
+  );
+});
+
+function waitForContentPageTextColor(ui, expectedColor) {
+  return SpecialPowers.spawn(
+    ui.getViewportBrowser(),
+    [{ expectedColor }],
+    function (args) {
+      return new Promise(resolve => {
+        const interval = content.setInterval(() => {
+          const color = content.getComputedStyle(content.document.body).color;
+          if (color === args.expectedColor) {
+            content.clearInterval(interval);
+            resolve(color);
+          }
+        }, 200);
+      });
+    }
+  );
+}
diff --git a/devtools/client/responsive/test/browser/browser_permission_doorhanger.js b/devtools/client/responsive/test/browser/browser_permission_doorhanger.js
new file mode 100644
index 0000000000..25c10b9bf5
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_permission_doorhanger.js
@@ -0,0 +1,72 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that permission popups asking for user approval still appear in RDM
+const DUMMY_URL = "http://example.com/";
+const TEST_URL = `${URL_ROOT}geolocation.html`;
+const TEST_SURL = TEST_URL.replace("http://example.com", "https://example.com");
+
+function waitForGeolocationPrompt(win, browser) {
+  return new Promise(resolve => {
+    win.PopupNotifications.panel.addEventListener(
+      "popupshown",
+      function popupShown() {
+        const notification = win.PopupNotifications.getNotification(
+          "geolocation",
+          browser
+        );
+        if (notification) {
+          win.PopupNotifications.panel.removeEventListener(
+            "popupshown",
+            popupShown
+          );
+          resolve();
+        }
+      }
+    );
+  });
+}
+
+addRDMTask(
+  null,
+  async function () {
+    // we want to explicitly tests http and https, hence
+    // disabling https-first mode for this test.
+    await pushPref("dom.security.https_first", false);
+
+    const tab = await addTab(DUMMY_URL);
+    const browser = tab.linkedBrowser;
+    const win = browser.ownerGlobal;
+
+    let waitPromptPromise = waitForGeolocationPrompt(win, browser);
+
+    // Checks if a geolocation permission doorhanger appears when openning a page
+    // requesting geolocation
+    await navigateTo(TEST_SURL);
+    await waitPromptPromise;
+
+    ok(true, "Permission doorhanger appeared without RDM enabled");
+
+    // Lets switch back to the dummy website and enable RDM
+    await navigateTo(DUMMY_URL);
+    const { ui } = await openRDM(tab);
+    await waitForDeviceAndViewportState(ui);
+
+    const newBrowser = ui.getViewportBrowser();
+    waitPromptPromise = waitForGeolocationPrompt(win, newBrowser);
+
+    // Checks if the doorhanger appeared again when reloading the geolocation
+    // page inside RDM
+    await navigateTo(TEST_SURL);
+
+    await waitPromptPromise;
+
+    ok(true, "Permission doorhanger appeared inside RDM");
+
+    await closeRDM(tab);
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_picker_link.js b/devtools/client/responsive/test/browser/browser_picker_link.js
new file mode 100644
index 0000000000..1aedb06dd0
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_picker_link.js
@@ -0,0 +1,96 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Check that picking a link when using RDM does not trigger a navigation.
+ * See Bug 1609199.
+ */
+const TEST_URI = `${URL_ROOT}doc_picker_link.html`;
+
+addRDMTask(TEST_URI, async function ({ ui, manager }) {
+  info("Open the rule-view and select the test node before opening RDM");
+  const { inspector, toolbox } = await openRuleView();
+  await selectNode("body", inspector);
+
+  info("Open RDM");
+
+  // XXX: Using toggleTouchSimulation waits for browser loaded, which is not
+  // fired here?
+  info("Toggle Touch simulation");
+  const { document } = ui.toolWindow;
+  const touchButton = document.getElementById("touch-simulation-button");
+  const changed = once(ui, "touch-simulation-changed");
+  touchButton.click();
+  await changed;
+
+  info("Waiting for element picker to become active.");
+  await startPicker(toolbox, ui);
+
+  info("Move mouse over the pick-target");
+  await hoverElement(inspector, ui, ".picker-link", 15, 15);
+
+  // Add a listener on the "navigate" event.
+  let hasNavigated = false;
+  const { onDomCompleteResource } =
+    await waitForNextTopLevelDomCompleteResource(toolbox.commands);
+
+  onDomCompleteResource.then(() => {
+    hasNavigated = true;
+  });
+
+  info("Click and pick the link");
+  await pickElement(inspector, ui, ".picker-link");
+
+  // Wait until page to start navigation.
+  await wait(2000);
+  ok(
+    !hasNavigated,
+    "The page should not have navigated when picking the <a> element"
+  );
+});
+
+/**
+ * startPicker, hoverElement and pickElement are slightly modified copies of
+ * inspector's head.js helpers, but using spawnViewportTask to interact with the
+ * content page (as well as some other slight modifications).
+ */
+
+async function startPicker(toolbox, ui) {
+  info("Start the element picker");
+  toolbox.win.focus();
+  await toolbox.nodePicker.start();
+  // By default make sure the content window is focused since the picker may not focus
+  // the content window by default.
+  await spawnViewportTask(ui, {}, async () => {
+    content.focus();
+  });
+}
+
+async function hoverElement(inspector, ui, selector, x, y) {
+  info("Waiting for element " + selector + " to be hovered");
+  const onHovered = inspector.toolbox.nodePicker.once("picker-node-hovered");
+  await spawnViewportTask(ui, { selector, x, y }, async options => {
+    const target = content.document.querySelector(options.selector);
+    await EventUtils.synthesizeMouse(
+      target,
+      options.x,
+      options.y,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+  });
+  return onHovered;
+}
+
+async function pickElement(inspector, ui, selector) {
+  info("Waiting for element " + selector + " to be picked");
+  const onNewNodeFront = inspector.selection.once("new-node-front");
+  await spawnViewportTask(ui, { selector }, async options => {
+    const target = content.document.querySelector(options.selector);
+    EventUtils.synthesizeClick(target);
+  });
+  info("Returning on new-node-front");
+  return onNewNodeFront;
+}
diff --git a/devtools/client/responsive/test/browser/browser_preloaded_newtab.js b/devtools/client/responsive/test/browser/browser_preloaded_newtab.js
new file mode 100644
index 0000000000..bda4ada24d
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_preloaded_newtab.js
@@ -0,0 +1,34 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Verify RDM opens for a preloaded about:newtab browser.
+
+const TEST_URL = "https://example.com/";
+
+addRDMTask(
+  null,
+  async function () {
+    const preloadedBrowser = gBrowser.preloadedBrowser;
+
+    // Open a tab with about:newtab.
+    // Don't wait for load because the page is preloaded.
+    const tab = await addTab(BROWSER_NEW_TAB_URL, {
+      waitForLoad: false,
+    });
+    const browser = tab.linkedBrowser;
+    is(browser, preloadedBrowser, "Got a preloaded browser for newtab");
+
+    // Open RDM and try to navigate
+    const { ui } = await openRDM(tab);
+    await waitForDeviceAndViewportState(ui);
+
+    await navigateTo(TEST_URL);
+    ok(true, "Test URL navigated successfully");
+
+    await closeRDM(tab);
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_screenshot_button.js b/devtools/client/responsive/test/browser/browser_screenshot_button.js
new file mode 100644
index 0000000000..a5176feeca
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_screenshot_button.js
@@ -0,0 +1,44 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test global screenshot button
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+
+addRDMTask(TEST_URL, async function ({ ui }) {
+  const { toolWindow } = ui;
+  const { store, document } = toolWindow;
+
+  info("Click the screenshot button");
+  const screenshotButton = document.getElementById("screenshot-button");
+  screenshotButton.click();
+
+  const whenScreenshotSucceeded = waitUntilScreenshot();
+
+  const filePath = await whenScreenshotSucceeded;
+  const image = new Image();
+  image.src = PathUtils.toFileURI(filePath);
+
+  await once(image, "load");
+
+  // We have only one viewport at the moment
+  const viewport = store.getState().viewports[0];
+  const ratio = window.devicePixelRatio;
+
+  is(
+    image.width,
+    viewport.width * ratio,
+    "screenshot width has the expected width"
+  );
+
+  is(
+    image.height,
+    viewport.height * ratio,
+    "screenshot width has the expected height"
+  );
+
+  await IOUtils.remove(filePath);
+  await resetDownloads();
+});
diff --git a/devtools/client/responsive/test/browser/browser_screenshot_button_warning.js b/devtools/client/responsive/test/browser/browser_screenshot_button_warning.js
new file mode 100644
index 0000000000..f7940b3cbf
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_screenshot_button_warning.js
@@ -0,0 +1,59 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that warning messages emitted when taking a screenshot are displayed in the UI.
+
+const TEST_URL = `http://example.net/document-builder.sjs?html=
+  <style>
+    body {
+      margin: 0;
+      height: 10001px;
+    }
+  </style>Hello world`;
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui, browser, manager }) {
+    const { toolWindow } = ui;
+    const { document } = toolWindow;
+
+    info(
+      "Set a big viewport and high dpr so the screenshot dpr gets downsized"
+    );
+    // The viewport can't be bigger than 9999×9999
+    await setViewportSize(ui, manager, 9999, 9999);
+    const dpr = 3;
+    await selectDevicePixelRatio(ui, dpr);
+    await waitForDevicePixelRatio(ui, dpr);
+
+    info("Click the screenshot button");
+    const onScreenshotDownloaded = waitUntilScreenshot();
+    const screenshotButton = document.getElementById("screenshot-button");
+    screenshotButton.click();
+
+    const filePath = await onScreenshotDownloaded;
+    ok(filePath, "The screenshot was taken");
+
+    info(
+      "Check that a warning message was displayed to indicate the dpr was changed"
+    );
+
+    const box = gBrowser.getNotificationBox(browser);
+    await waitUntil(() => box.currentNotification);
+
+    const notificationEl = box.currentNotification;
+    ok(notificationEl, "Notification should be visible");
+    is(
+      notificationEl.messageText.textContent.trim(),
+      "The device pixel ratio was reduced to 1 as the resulting image was too large",
+      "The expected warning was displayed"
+    );
+
+    //Remove the downloaded screenshot file
+    await IOUtils.remove(filePath);
+    await resetDownloads();
+  },
+  { waitForDeviceList: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_scroll.js b/devtools/client/responsive/test/browser/browser_scroll.js
new file mode 100644
index 0000000000..5e135ca632
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_scroll.js
@@ -0,0 +1,88 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * This test is checking that keyboard scrolling of content in RDM
+ * behaves correctly, both with and without touch simulation enabled.
+ */
+
+const PAINT_LISTENER_JS_URL =
+  URL_ROOT + "../../../../../../tests/SimpleTest/paint_listener.js";
+
+const APZ_TEST_UTILS_JS_URL =
+  URL_ROOT + "../../../../../gfx/layers/apz/test/mochitest/apz_test_utils.js";
+
+const TEST_URL =
+  "data:text/html;charset=utf-8," +
+  '<head><meta name="viewport" content="width=100, height=100"/>' +
+  '<script src="' +
+  PAINT_LISTENER_JS_URL +
+  '"></script>' +
+  '<script src="' +
+  APZ_TEST_UTILS_JS_URL +
+  '"></script>' +
+  "</head>" +
+  '<div style="background:blue; width:200px; height:200px"></div>';
+
+addRDMTask(TEST_URL, async function ({ ui, manager }) {
+  await setViewportSize(ui, manager, 50, 50);
+  const browser = ui.getViewportBrowser();
+
+  for (const mv in [true, false]) {
+    await ui.updateTouchSimulation(mv);
+
+    info("Setting focus on the browser.");
+    browser.focus();
+
+    await SpecialPowers.spawn(browser, [], async () => {
+      // First of all, cancel any async scroll animation if there is. If there's
+      // an on-going async scroll animation triggered by synthesizeKey, below
+      // scrollTo call scrolls to a position nearby (0, 0) so that this test
+      // won't work as expected.
+      await content.wrappedJSObject.cancelScrollAnimation(
+        content.document.scrollingElement,
+        content
+      );
+
+      content.scrollTo(0, 0);
+    });
+
+    info("Testing scroll behavior with touch simulation " + mv + ".");
+    await testScrollingOfContent(ui);
+  }
+});
+
+async function testScrollingOfContent(ui) {
+  let scroll;
+
+  info("Checking initial scroll conditions.");
+  const viewportScroll = await getViewportScroll(ui);
+  is(viewportScroll.x, 0, "Content should load with scrollX 0.");
+  is(viewportScroll.y, 0, "Content should load with scrollY 0.");
+
+  /**
+   * Here we're going to send off some arrow key events to trigger scrolling.
+   * What we would like to be able to do is to await the scroll event and then
+   * check the scroll position to confirm the amount of scrolling that has
+   * happened. Unfortunately, APZ makes the scrolling happen asynchronously on
+   * the compositor thread, and it's very difficult to await the end state of
+   * the APZ animation -- see the tests in /gfx/layers/apz/test/mochitest for
+   * an example. For our purposes, it's sufficient to test that the scroll
+   * event is fired at all, and not worry about the amount of scrolling that
+   * has occurred at the time of the event. If the key events don't trigger
+   * scrolling, then no event will be fired and the test will time out.
+   */
+  scroll = waitForViewportScroll(ui);
+  info("Synthesizing an arrow key down.");
+  EventUtils.synthesizeKey("KEY_ArrowDown");
+  await scroll;
+  info("Scroll event was fired after arrow key down.");
+
+  scroll = waitForViewportScroll(ui);
+  info("Synthesizing an arrow key right.");
+  EventUtils.synthesizeKey("KEY_ArrowRight");
+  await scroll;
+  info("Scroll event was fired after arrow key right.");
+}
diff --git a/devtools/client/responsive/test/browser/browser_state_restore.js b/devtools/client/responsive/test/browser/browser_state_restore.js
new file mode 100644
index 0000000000..c41297cb63
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_state_restore.js
@@ -0,0 +1,90 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that the previous viewport size, user agent, dppx and touch simulation properties
+// are restored when reopening RDM.
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+const DEFAULT_DPPX = window.devicePixelRatio;
+const NEW_DPPX = DEFAULT_DPPX + 1;
+const NEW_USER_AGENT = "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0";
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui, manager }) {
+    const { store } = ui.toolWindow;
+
+    reloadOnTouchChange(true);
+    reloadOnUAChange(true);
+
+    await waitUntilState(store, state => state.viewports.length == 1);
+
+    info("Checking the default RDM state.");
+    testViewportDeviceMenuLabel(ui, "Responsive");
+    testViewportDimensions(ui, 320, 480);
+    await testUserAgent(ui, DEFAULT_UA);
+    await testDevicePixelRatio(ui, DEFAULT_DPPX);
+    await testTouchEventsOverride(ui, false);
+
+    info("Changing the RDM size, dppx, ua and toggle ON touch simulations.");
+    await setViewportSize(ui, manager, 90, 500);
+    await selectDevicePixelRatio(ui, NEW_DPPX);
+    await toggleTouchSimulation(ui);
+    await changeUserAgentInput(ui, NEW_USER_AGENT);
+
+    reloadOnTouchChange(false);
+    reloadOnUAChange(false);
+  },
+  { waitForDeviceList: true }
+);
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { store } = ui.toolWindow;
+
+    reloadOnTouchChange(true);
+    reloadOnUAChange(true);
+
+    info("Reopening RDM and checking that the previous state is restored.");
+
+    await waitUntilState(store, state => state.viewports.length == 1);
+
+    testViewportDimensions(ui, 90, 500);
+    await testUserAgent(ui, NEW_USER_AGENT);
+    await testDevicePixelRatio(ui, NEW_DPPX);
+    await testTouchEventsOverride(ui, true);
+
+    info("Rotating the viewport.");
+    rotateViewport(ui);
+
+    reloadOnTouchChange(false);
+    reloadOnUAChange(false);
+  },
+  { waitForDeviceList: true }
+);
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    const { store } = ui.toolWindow;
+
+    reloadOnTouchChange(true);
+    reloadOnUAChange(true);
+
+    info("Reopening RDM and checking that the previous state is restored.");
+
+    await waitUntilState(store, state => state.viewports.length == 1);
+
+    testViewportDimensions(ui, 500, 90);
+    await testUserAgent(ui, NEW_USER_AGENT);
+    await testDevicePixelRatio(ui, NEW_DPPX);
+    await testTouchEventsOverride(ui, true);
+
+    reloadOnTouchChange(false);
+    reloadOnUAChange(false);
+  },
+  { waitForDeviceList: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_tab_close.js b/devtools/client/responsive/test/browser/browser_tab_close.js
new file mode 100644
index 0000000000..6abe3536f9
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_tab_close.js
@@ -0,0 +1,53 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Verify RDM closes synchronously when tabs are closed.
+
+const TEST_URL = "http://example.com/";
+
+addRDMTask(
+  null,
+  async function () {
+    const tab = await addTab(TEST_URL);
+
+    const { ui } = await openRDM(tab);
+    await waitForDeviceAndViewportState(ui);
+    const clientClosed = waitForClientClose(ui);
+
+    closeRDM(tab, {
+      reason: "TabClose",
+    });
+
+    // This flag is set at the end of `ResponsiveUI.destroy`.  If it is true
+    // without waiting for `closeRDM` above, then we must have closed
+    // synchronously.
+    is(ui.destroyed, true, "RDM closed synchronously");
+
+    await clientClosed;
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
+
+addRDMTask(
+  null,
+  async function () {
+    const tab = await addTab(TEST_URL);
+
+    const { ui } = await openRDM(tab);
+    await waitForDeviceAndViewportState(ui);
+    const clientClosed = waitForClientClose(ui);
+
+    await removeTab(tab);
+
+    // This flag is set at the end of `ResponsiveUI.destroy`.  If it is true without
+    // waiting for `closeRDM` itself and only removing the tab, then we must have closed
+    // synchronously in response to tab closing.
+    is(ui.destroyed, true, "RDM closed synchronously");
+
+    await clientClosed;
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_tab_not_selected.js b/devtools/client/responsive/test/browser/browser_tab_not_selected.js
new file mode 100644
index 0000000000..ac36f788f7
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_tab_not_selected.js
@@ -0,0 +1,43 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Verify RDM opens for the correct tab, even if it is not the currently
+// selected tab.
+
+const TEST_URL = "http://example.com/";
+
+addRDMTask(
+  null,
+  async function () {
+    info("Open two tabs");
+    const tab1 = await addTab(TEST_URL);
+    const tab2 = await addTab(TEST_URL);
+
+    is(gBrowser.selectedTab, tab2, "The selected tab is tab2");
+
+    info("Open RDM for the non-selected tab");
+    const { ui } = await openRDM(tab1);
+
+    ok(!ResponsiveUIManager.isActiveForTab(tab2), "RDM is not opened on tab2");
+
+    // Not mandatory for the test to pass, but it is helpful to see the RDM tab
+    // for Try failure screenshots.
+    info("Select the first tab");
+    gBrowser.selectedTab = tab1;
+
+    info("Try to update the DPI");
+    await selectDevicePixelRatio(ui, 2);
+    const dppx = await waitForDevicePixelRatio(ui, 2, {
+      waitForTargetConfiguration: true,
+    });
+    is(dppx, 2, "Content has expected devicePixelRatio");
+
+    const clientClosed = waitForClientClose(ui);
+    await removeTab(tab2);
+    await removeTab(tab1);
+    await clientClosed;
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_tab_remoteness_change.js b/devtools/client/responsive/test/browser/browser_tab_remoteness_change.js
new file mode 100644
index 0000000000..9a445b6fd6
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_tab_remoteness_change.js
@@ -0,0 +1,45 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Verify Fission-enabled RDM remains open when tab changes remoteness.
+
+const { PromiseTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/PromiseTestUtils.sys.mjs"
+);
+PromiseTestUtils.allowMatchingRejectionsGlobally(
+  /Permission denied to access property "document" on cross-origin object/
+);
+
+const Types = require("resource://devtools/client/responsive/types.js");
+
+const TEST_URL = "http://example.com/";
+
+addRDMTask(
+  null,
+  async function () {
+    const tab = await addTab(TEST_URL);
+
+    const { ui } = await openRDM(tab);
+    const { store } = ui.toolWindow;
+    await waitUntilState(
+      store,
+      state =>
+        state.viewports.length == 1 &&
+        state.devices.listState == Types.loadableState.LOADED
+    );
+
+    // Load URL that requires the main process, forcing a remoteness flip
+    await navigateTo("about:robots");
+
+    // Bug 1625501: RDM will remain open when the embedded browser UI is enabled.
+    is(ui.destroyed, false, "RDM is still open.");
+
+    info("Close RDM");
+    await closeRDM(tab);
+
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_tab_remoteness_change_fission_switch_target.js b/devtools/client/responsive/test/browser/browser_tab_remoteness_change_fission_switch_target.js
new file mode 100644
index 0000000000..0fad9aed2d
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_tab_remoteness_change_fission_switch_target.js
@@ -0,0 +1,42 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test for target switching.
+
+const PAGE_ON_CHILD = "http://example.com/";
+const PAGE_ON_MAIN = "about:robots";
+
+const TEST_DPPX = 2;
+
+add_task(async function () {
+  // Set a pref for DPPX in order to assert whether the RDM is working correctly or not.
+  await pushPref("devtools.responsive.viewport.pixelRatio", TEST_DPPX);
+
+  info("Open a page which runs on the child process");
+  const tab = await addTab(PAGE_ON_CHILD);
+  await assertDocshell(tab, false, 0);
+
+  info("Open RDM");
+  await openRDM(tab);
+  await assertDocshell(tab, true, TEST_DPPX);
+
+  info("Load a page which runs on the main process");
+  await navigateTo(PAGE_ON_MAIN);
+  await assertDocshell(tab, true, TEST_DPPX);
+
+  info("Close RDM");
+  await closeRDM(tab);
+  await assertDocshell(tab, false, 0);
+
+  await removeTab(tab);
+});
+
+async function assertDocshell(tab, expectedRDMMode, expectedDPPX) {
+  await asyncWaitUntil(async () => {
+    const { overrideDPPX, inRDMPane } = tab.linkedBrowser.browsingContext;
+    return inRDMPane === expectedRDMMode && overrideDPPX === expectedDPPX;
+  });
+  ok(true, "The state of the docshell is correct");
+}
diff --git a/devtools/client/responsive/test/browser/browser_target_blank.js b/devtools/client/responsive/test/browser/browser_target_blank.js
new file mode 100644
index 0000000000..65dbf3386d
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_target_blank.js
@@ -0,0 +1,25 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Ensure target="_blank" link opens a new tab
+
+const TAB_URL = "http://example.com/";
+const TEST_URL =
+  `data:text/html,<a href="${TAB_URL}" target="_blank">Click me</a>`.replace(
+    / /g,
+    "%20"
+  );
+
+addRDMTask(TEST_URL, async function ({ ui }) {
+  // Click the target="_blank" link and wait for a new tab
+  await waitForFrameLoad(ui, TEST_URL);
+  const newTabPromise = BrowserTestUtils.waitForNewTab(gBrowser, TAB_URL);
+  await spawnViewportTask(ui, {}, function () {
+    content.document.querySelector("a").click(); // eslint-disable-line
+  });
+  const newTab = await newTabPromise;
+  ok(newTab, "New tab opened from link");
+  await removeTab(newTab);
+});
diff --git a/devtools/client/responsive/test/browser/browser_telemetry_activate_rdm.js b/devtools/client/responsive/test/browser/browser_telemetry_activate_rdm.js
new file mode 100644
index 0000000000..7c3927fb11
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_telemetry_activate_rdm.js
@@ -0,0 +1,116 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+const URL = "data:text/html;charset=utf8,browser_telemetry_activate_rdm.js";
+const ALL_CHANNELS = Ci.nsITelemetry.DATASET_ALL_CHANNELS;
+const DATA = [
+  {
+    timestamp: null,
+    category: "devtools.main",
+    method: "activate",
+    object: "responsive_design",
+    value: null,
+    extra: {
+      host: "none",
+      width: "1300",
+    },
+  },
+  {
+    timestamp: null,
+    category: "devtools.main",
+    method: "deactivate",
+    object: "responsive_design",
+    value: null,
+    extra: {
+      host: "none",
+      width: "1300",
+    },
+  },
+  {
+    timestamp: null,
+    category: "devtools.main",
+    method: "activate",
+    object: "responsive_design",
+    value: null,
+    extra: {
+      host: "bottom",
+      width: "1300",
+    },
+  },
+  {
+    timestamp: null,
+    category: "devtools.main",
+    method: "deactivate",
+    object: "responsive_design",
+    value: null,
+    extra: {
+      host: "bottom",
+      width: "1300",
+    },
+  },
+];
+
+addRDMTask(
+  null,
+  async function () {
+    // Let's reset the counts.
+    Services.telemetry.clearEvents();
+
+    // Ensure no events have been logged
+    const snapshot = Services.telemetry.snapshotEvents(ALL_CHANNELS, true);
+    ok(!snapshot.parent, "No events have been logged for the main process");
+
+    const tab = await addTab(URL);
+
+    await openCloseRDM(tab);
+    await gDevTools.showToolboxForTab(tab, { toolId: "inspector" });
+    await openCloseRDM(tab);
+    await checkResults();
+  },
+  { onlyPrefAndTask: true }
+);
+
+async function openCloseRDM(tab) {
+  const { ui } = await openRDM(tab);
+  await waitForDeviceAndViewportState(ui);
+
+  const clientClosed = waitForClientClose(ui);
+
+  closeRDM(tab, {
+    reason: "TabClose",
+  });
+
+  // This flag is set at the end of `ResponsiveUI.destroy`.  If it is true
+  // without waiting for `closeRDM` above, then we must have closed
+  // synchronously.
+  is(ui.destroyed, true, "RDM closed synchronously");
+
+  await clientClosed;
+}
+
+async function checkResults() {
+  const snapshot = Services.telemetry.snapshotEvents(ALL_CHANNELS, true);
+  const events = snapshot.parent.filter(
+    event =>
+      event[1] === "devtools.main" &&
+      (event[2] === "activate" || event[2] === "deactivate")
+  );
+
+  for (const i in events) {
+    const [timestamp, category, method, object, value, extra] = events[i];
+
+    const expected = DATA[i];
+
+    // ignore timestamp
+    Assert.greater(timestamp, 0, "timestamp is greater than 0");
+    is(category, expected.category, "category is correct");
+    is(method, expected.method, "method is correct");
+    is(object, expected.object, "object is correct");
+    is(value, expected.value, "value is correct");
+
+    // extras
+    is(extra.host, expected.extra.host, "host is correct");
+    ok(extra.width > 0, "width is greater than 0");
+  }
+}
diff --git a/devtools/client/responsive/test/browser/browser_toolbox_computed_view.js b/devtools/client/responsive/test/browser/browser_toolbox_computed_view.js
new file mode 100644
index 0000000000..f22ee8d246
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_toolbox_computed_view.js
@@ -0,0 +1,64 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Check that when the viewport is resized, the computed-view refreshes.
+
+const TEST_URI =
+  "data:text/html;charset=utf-8,<html><style>" +
+  "div {" +
+  "  width: 500px;" +
+  "  height: 10px;" +
+  "  background: purple;" +
+  "} " +
+  "@media screen and (max-width: 200px) {" +
+  "  div { " +
+  "    width: 100px;" +
+  "  }" +
+  "};" +
+  "</style><div></div></html>";
+
+addRDMTask(TEST_URI, async function ({ ui, manager }) {
+  info("Open the responsive design mode and set its size to 500x500 to start");
+  await setViewportSize(ui, manager, 500, 500);
+
+  info("Open the inspector, computed-view and select the test node");
+  const { inspector, view } = await openComputedView();
+  await selectNode("div", inspector);
+
+  info("Try shrinking the viewport and checking the applied styles");
+  await testShrink(view, inspector, ui, manager);
+
+  info("Try growing the viewport and checking the applied styles");
+  await testGrow(view, inspector, ui, manager);
+
+  await closeToolbox();
+});
+
+async function testShrink(computedView, inspector, ui, manager) {
+  is(computedWidth(computedView), "500px", "Should show 500px initially.");
+
+  const onRefresh = inspector.once("computed-view-refreshed");
+  await setViewportSize(ui, manager, 100, 100);
+  await onRefresh;
+
+  is(computedWidth(computedView), "100px", "Should be 100px after shrinking.");
+}
+
+async function testGrow(computedView, inspector, ui, manager) {
+  const onRefresh = inspector.once("computed-view-refreshed");
+  await setViewportSize(ui, manager, 500, 500);
+  await onRefresh;
+
+  is(computedWidth(computedView), "500px", "Should be 500px after growing.");
+}
+
+function computedWidth(computedView) {
+  for (const prop of computedView.propertyViews) {
+    if (prop.name === "width") {
+      return prop.valueNode.textContent;
+    }
+  }
+  return null;
+}
diff --git a/devtools/client/responsive/test/browser/browser_toolbox_rule_view.js b/devtools/client/responsive/test/browser/browser_toolbox_rule_view.js
new file mode 100644
index 0000000000..ff4bc4e39f
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_toolbox_rule_view.js
@@ -0,0 +1,63 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Check that when the viewport is resized, the rule-view refreshes.
+
+const TEST_URI = `${URL_ROOT}doc_toolbox_rule_view.html`;
+
+addRDMTask(TEST_URI, async function ({ ui, manager }) {
+  info("Open the responsive design mode and set its size to 500x500 to start");
+  await setViewportSize(ui, manager, 500, 500);
+
+  info("Open the inspector, rule-view and select the test node");
+  const { inspector, view } = await openRuleView();
+  await selectNode("div", inspector);
+
+  info("Try shrinking the viewport and checking the applied styles");
+  await testShrink(view, ui, manager);
+
+  info("Try growing the viewport and checking the applied styles");
+  await testGrow(view, ui, manager);
+
+  info("Check that ESC still opens the split console");
+  await testEscapeOpensSplitConsole(inspector);
+
+  await closeToolbox();
+});
+
+async function testShrink(ruleView, ui, manager) {
+  is(numberOfRules(ruleView), 2, "Should have two rules initially.");
+
+  info("Resize to 100x100 and wait for the rule-view to update");
+  const onRefresh = ruleView.once("ruleview-refreshed");
+  await setViewportSize(ui, manager, 100, 100);
+  await onRefresh;
+
+  is(numberOfRules(ruleView), 3, "Should have three rules after shrinking.");
+}
+
+async function testGrow(ruleView, ui, manager) {
+  info("Resize to 500x500 and wait for the rule-view to update");
+  const onRefresh = ruleView.once("ruleview-refreshed");
+  await setViewportSize(ui, manager, 500, 500);
+  await onRefresh;
+
+  is(numberOfRules(ruleView), 2, "Should have two rules after growing.");
+}
+
+async function testEscapeOpensSplitConsole(inspector) {
+  ok(!inspector._toolbox._splitConsole, "Console is not split.");
+
+  info("Press escape");
+  const onSplit = inspector._toolbox.once("split-console");
+  EventUtils.synthesizeKey("KEY_Escape");
+  await onSplit;
+
+  ok(inspector._toolbox._splitConsole, "Console is split after pressing ESC.");
+}
+
+function numberOfRules(ruleView) {
+  return ruleView.element.querySelectorAll(".ruleview-code").length;
+}
diff --git a/devtools/client/responsive/test/browser/browser_toolbox_rule_view_reload.js b/devtools/client/responsive/test/browser/browser_toolbox_rule_view_reload.js
new file mode 100644
index 0000000000..73aebac056
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_toolbox_rule_view_reload.js
@@ -0,0 +1,56 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Check that the ruleview is still correctly displayed after reloading the page.
+ * See Bug 1487284.
+ */
+
+// To trigger the initial issue, the stylesheet needs to be fetched from the network
+// monitor, so we can not use a data:uri with inline styles here.
+const TEST_URI = `${URL_ROOT}doc_toolbox_rule_view.html`;
+
+addRDMTaskWithPreAndPost(
+  TEST_URI,
+  async function pre_task() {
+    info("Open the rule-view and select the test node before opening RDM");
+    const ruleViewValues = await openRuleView();
+    const { inspector, view } = ruleViewValues;
+    await selectNode("div", inspector);
+
+    is(numberOfRules(view), 2, "Rule view has two rules.");
+
+    return ruleViewValues;
+  },
+  async function task({ preTaskValue }) {
+    const { inspector, view } = preTaskValue;
+
+    info("Reload the current page");
+    const onNewRoot = inspector.once("new-root");
+    const onRuleViewRefreshed = inspector.once("rule-view-refreshed");
+    await reloadBrowser();
+    await onNewRoot;
+    await inspector.markup._waitForChildren();
+    await onRuleViewRefreshed;
+
+    // Await two reflows of the Rule View window.
+    await new Promise(resolve => {
+      view.styleWindow.requestAnimationFrame(() => {
+        view.styleWindow.requestAnimationFrame(resolve);
+      });
+    });
+
+    is(
+      numberOfRules(view),
+      2,
+      "Rule view still has two rules and is not empty."
+    );
+  },
+  null
+);
+
+function numberOfRules(ruleView) {
+  return ruleView.element.querySelectorAll(".ruleview-code").length;
+}
diff --git a/devtools/client/responsive/test/browser/browser_toolbox_swap_browsers.js b/devtools/client/responsive/test/browser/browser_toolbox_swap_browsers.js
new file mode 100644
index 0000000000..61cc3cd96e
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_toolbox_swap_browsers.js
@@ -0,0 +1,175 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Verify that toolbox remains open when opening and closing RDM.
+
+const TEST_URL = "http://example.com/";
+
+function getServerConnections(browser) {
+  ok(browser.isRemoteBrowser, "Content browser is remote");
+  return SpecialPowers.spawn(browser, [], async function () {
+    const { require } = ChromeUtils.importESModule(
+      "resource://devtools/shared/loader/Loader.sys.mjs"
+    );
+    const {
+      DevToolsServer,
+    } = require("resource://devtools/server/devtools-server.js");
+    if (!DevToolsServer._connections) {
+      return 0;
+    }
+    return Object.getOwnPropertyNames(DevToolsServer._connections);
+  });
+}
+
+const checkServerConnectionCount = async function (browser, expected, msg) {
+  const conns = await getServerConnections(browser);
+  is(conns.length || 0, expected, "Server connection count: " + msg);
+};
+
+const checkToolbox = function (tab, location) {
+  const toolbox = gDevTools.getToolboxForTab(tab);
+  ok(!!toolbox, `Toolbox exists ${location}`);
+};
+
+addRDMTask(
+  "",
+  async function () {
+    const tab = await addTab(TEST_URL);
+
+    const tabsInDifferentProcesses =
+      E10S_MULTI_ENABLED &&
+      gBrowser.tabs[0].linkedBrowser.frameLoader.childID !=
+        gBrowser.tabs[1].linkedBrowser.frameLoader.childID;
+
+    info("Open toolbox outside RDM");
+    {
+      // 0: No DevTools connections yet
+      await checkServerConnectionCount(
+        tab.linkedBrowser,
+        0,
+        "0: No DevTools connections yet"
+      );
+      const { toolbox } = await openInspector();
+      if (tabsInDifferentProcesses) {
+        // 1: Two tabs open, but only one per content process
+        await checkServerConnectionCount(
+          tab.linkedBrowser,
+          1,
+          "1: Two tabs open, but only one per content process"
+        );
+      } else {
+        // 2: One for each tab (starting tab plus the one we opened)
+        await checkServerConnectionCount(
+          tab.linkedBrowser,
+          2,
+          "2: One for each tab (starting tab plus the one we opened)"
+        );
+      }
+      checkToolbox(tab, "outside RDM");
+      const { ui } = await openRDM(tab);
+      if (tabsInDifferentProcesses) {
+        // 2: RDM UI adds an extra connection, 1 + 1 = 2
+        await checkServerConnectionCount(
+          ui.getViewportBrowser(),
+          2,
+          "2: RDM UI uses an extra connection"
+        );
+      } else {
+        // 3: RDM UI adds an extra connection, 2 + 1 = 3
+        await checkServerConnectionCount(
+          ui.getViewportBrowser(),
+          3,
+          "3: RDM UI uses an extra connection"
+        );
+      }
+      checkToolbox(tab, "after opening RDM");
+      await closeRDM(tab);
+      if (tabsInDifferentProcesses) {
+        // 1: RDM UI closed, return to previous connection count
+        await checkServerConnectionCount(
+          tab.linkedBrowser,
+          1,
+          "1: RDM UI closed, return to previous connection count"
+        );
+      } else {
+        // 2: RDM UI closed, return to previous connection count
+        await checkServerConnectionCount(
+          tab.linkedBrowser,
+          2,
+          "2: RDM UI closed, return to previous connection count"
+        );
+      }
+      checkToolbox(tab, tab.linkedBrowser, "after closing RDM");
+      await toolbox.destroy();
+      // 0: All DevTools usage closed
+      await checkServerConnectionCount(
+        tab.linkedBrowser,
+        0,
+        "0: All DevTools usage closed"
+      );
+    }
+
+    info("Open toolbox inside RDM");
+    {
+      // 0: No DevTools connections yet
+      await checkServerConnectionCount(
+        tab.linkedBrowser,
+        0,
+        "0: No DevTools connections yet"
+      );
+      const { ui } = await openRDM(tab);
+      // 1: RDM UI uses an extra connection
+      await checkServerConnectionCount(
+        ui.getViewportBrowser(),
+        1,
+        "1: RDM UI uses an extra connection"
+      );
+      const { toolbox } = await openInspector();
+      if (tabsInDifferentProcesses) {
+        // 2: Two tabs open, but only one per content process
+        await checkServerConnectionCount(
+          ui.getViewportBrowser(),
+          2,
+          "2: Two tabs open, but only one per content process"
+        );
+      } else {
+        // 3: One for each tab (starting tab plus the one we opened)
+        await checkServerConnectionCount(
+          ui.getViewportBrowser(),
+          3,
+          "3: One for each tab (starting tab plus the one we opened)"
+        );
+      }
+      checkToolbox(tab, ui.getViewportBrowser(), "inside RDM");
+      await closeRDM(tab);
+      if (tabsInDifferentProcesses) {
+        // 1: RDM UI closed, one less connection
+        await checkServerConnectionCount(
+          tab.linkedBrowser,
+          1,
+          "1: RDM UI closed, one less connection"
+        );
+      } else {
+        // 2: RDM UI closed, one less connection
+        await checkServerConnectionCount(
+          tab.linkedBrowser,
+          2,
+          "2: RDM UI closed, one less connection"
+        );
+      }
+      checkToolbox(tab, tab.linkedBrowser, "after closing RDM");
+      await toolbox.destroy();
+      // 0: All DevTools usage closed
+      await checkServerConnectionCount(
+        tab.linkedBrowser,
+        0,
+        "0: All DevTools usage closed"
+      );
+    }
+
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_toolbox_swap_inspector.js b/devtools/client/responsive/test/browser/browser_toolbox_swap_inspector.js
new file mode 100644
index 0000000000..a5262eeec5
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_toolbox_swap_inspector.js
@@ -0,0 +1,50 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Verify that inspector does not reboot when opening and closing RDM.
+
+const TEST_URL = "http://example.com/";
+
+const checkToolbox = async function (tab, location) {
+  const toolbox = gDevTools.getToolboxForTab(tab);
+  ok(!!toolbox, `Toolbox exists ${location}`);
+};
+
+addRDMTask(
+  "",
+  async function () {
+    const tab = await addTab(TEST_URL);
+
+    info("Open toolbox outside RDM");
+    {
+      const { toolbox, inspector } = await openInspector();
+      inspector.walker.once("new-root", () => {
+        ok(false, "Inspector saw new root, would reboot!");
+      });
+      checkToolbox(tab, "outside RDM");
+      await openRDM(tab);
+      checkToolbox(tab, "after opening RDM");
+      await closeRDM(tab);
+      checkToolbox(tab, tab.linkedBrowser, "after closing RDM");
+      await toolbox.destroy();
+    }
+
+    info("Open toolbox inside RDM");
+    {
+      const { ui } = await openRDM(tab);
+      const { toolbox, inspector } = await openInspector();
+      inspector.walker.once("new-root", () => {
+        ok(false, "Inspector saw new root, would reboot!");
+      });
+      checkToolbox(tab, ui.getViewportBrowser(), "inside RDM");
+      await closeRDM(tab);
+      checkToolbox(tab, tab.linkedBrowser, "after closing RDM");
+      await toolbox.destroy();
+    }
+
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_tooltip.js b/devtools/client/responsive/test/browser/browser_tooltip.js
new file mode 100644
index 0000000000..6721463725
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_tooltip.js
@@ -0,0 +1,129 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_CONTENT = `<h1 title="test title" style="margin: 5px">test h1</h1>`;
+const TEST_URL = `data:text/html;charset=utf-8,${TEST_CONTENT}`;
+
+// Test for the tooltip coordinate on the browsing document in RDM.
+
+addRDMTask(TEST_URL, async ({ ui }) => {
+  // Make this synthesize mouse events via the parent process because some
+  // code may cache the mouse cursor position like PresShell.  That may prevent
+  // unexpected DOM events coming from the parent process.
+  await pushPref("test.events.async.enabled", true);
+
+  info("Create a promise which waits until the tooltip will be shown");
+  const tooltip = ui.browserWindow.gBrowser.ownerDocument.getElementById(
+    "remoteBrowserTooltip"
+  );
+  const onTooltipShown = BrowserTestUtils.waitForEvent(tooltip, "popupshown");
+  const onTooltipHidden = BrowserTestUtils.waitForEvent(tooltip, "popuphidden");
+
+  info("Show a tooltip");
+  await spawnViewportTask(ui, {}, async () => {
+    const target = content.document.querySelector("h1");
+
+    // First, make sure to move mouse cursor outside the target.
+    info("Waiting for initial mousemove");
+    {
+      // FYI: Some `mousemove` events may not be sent to the content process
+      // until all preparations done in the main process and the content
+      // process. Therefore, we need to synthesize `mousemove`s until we
+      // get it in the remote process at least once.  Therefore, we cannot
+      // use a promise to wait a `mousemove` here and we need to use the while
+      // loop below.
+      let mouseMoveFired = false;
+      content.document.addEventListener(
+        "mousemove",
+        event => {
+          isnot(
+            event.target,
+            target,
+            "The first mousemove should be fired outside the target"
+          );
+          mouseMoveFired = true;
+        },
+        {
+          once: true,
+        }
+      );
+      while (!mouseMoveFired) {
+        await EventUtils.synthesizeMouse(
+          target,
+          -2,
+          -2,
+          { type: "mousemove" },
+          content
+        );
+        await EventUtils.synthesizeMouse(
+          target,
+          -1,
+          -1,
+          { type: "mousemove" },
+          content
+        );
+        // Wait for the tooltip for the target is hidden even if it was visible.
+        await new Promise(resolve =>
+          content.window.requestAnimationFrame(() =>
+            content.window.requestAnimationFrame(resolve)
+          )
+        );
+      }
+    }
+
+    const eventLogger = event =>
+      info(
+        `${event.type}: path=[${event.composedPath()}], outerHTML=${
+          event.target.outerHTML
+        }, relatedTarget=${event.relatedTarget?.outerHTML}`
+      );
+    target.addEventListener("mouseover", eventLogger);
+    target.addEventListener("mouseout", eventLogger);
+    content.document.addEventListener("mousemove", eventLogger);
+    // Then, move cursor over the target.
+    await EventUtils.synthesizeMouse(
+      target,
+      1,
+      1,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+    await EventUtils.synthesizeMouse(
+      target,
+      2,
+      1,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+    await EventUtils.synthesizeMouse(
+      target,
+      3,
+      1,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+  });
+
+  info("Wait for showing the tooltip");
+  await onTooltipShown;
+
+  info("Test the X coordinate of the tooltip");
+  isnot(tooltip.screenX, 0, "The X coordinate of tooltip should not be 0");
+
+  // Finally, clean up the tooltip if we're running in the verify mode.
+  info("Wait for hiding the tooltip");
+  await spawnViewportTask(ui, {}, async () => {
+    info("Cleaning up the tooltip with moving the cursor");
+    const target = content.document.querySelector("h1");
+    await EventUtils.synthesizeMouse(
+      target,
+      -1,
+      -1,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+  });
+  await onTooltipHidden;
+});
diff --git a/devtools/client/responsive/test/browser/browser_touch_device.js b/devtools/client/responsive/test/browser/browser_touch_device.js
new file mode 100644
index 0000000000..1c303bdd45
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_touch_device.js
@@ -0,0 +1,100 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests changing viewport touch simulation
+const TEST_URL = "data:text/html;charset=utf-8,touch simulation test";
+const Types = require("resource://devtools/client/responsive/types.js");
+
+const testDevice = {
+  name: "Fake Phone RDM Test",
+  width: 320,
+  height: 470,
+  pixelRatio: 5.5,
+  userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+  touch: true,
+  firefoxOS: true,
+  os: "custom",
+  featured: true,
+};
+
+// Add the new device to the list
+addDeviceForTest(testDevice);
+
+addRDMTask(
+  TEST_URL,
+  async function ({ ui }) {
+    reloadOnTouchChange(true);
+
+    await waitStartup(ui);
+
+    await testDefaults(ui);
+    await testChangingDevice(ui);
+    await testResizingViewport(ui, true, false);
+    await testEnableTouchSimulation(ui);
+    await testResizingViewport(ui, false, true);
+    await testDisableTouchSimulation(ui);
+
+    reloadOnTouchChange(false);
+  },
+  { waitForDeviceList: true }
+);
+
+async function waitStartup(ui) {
+  const { store } = ui.toolWindow;
+
+  // Wait until the viewport has been added and the device list has been loaded
+  await waitUntilState(
+    store,
+    state =>
+      state.viewports.length == 1 &&
+      state.devices.listState == Types.loadableState.LOADED
+  );
+}
+
+async function testDefaults(ui) {
+  info("Test Defaults");
+
+  await testTouchEventsOverride(ui, false);
+  testViewportDeviceMenuLabel(ui, "Responsive");
+}
+
+async function testChangingDevice(ui) {
+  info("Test Changing Device");
+
+  await selectDevice(ui, testDevice.name);
+  await waitForViewportResizeTo(ui, testDevice.width, testDevice.height);
+  await testTouchEventsOverride(ui, true);
+  testViewportDeviceMenuLabel(ui, testDevice.name);
+}
+
+async function testResizingViewport(ui, hasDevice, touch) {
+  info(`Test resizing the viewport, device ${hasDevice}, touch ${touch}`);
+
+  await testViewportResize(
+    ui,
+    ".viewport-vertical-resize-handle",
+    [-10, -10],
+    [0, -10],
+    {
+      hasDevice,
+    }
+  );
+  await testTouchEventsOverride(ui, touch);
+  testViewportDeviceMenuLabel(ui, "Responsive");
+}
+
+async function testEnableTouchSimulation(ui) {
+  info("Test enabling touch simulation via button");
+
+  await toggleTouchSimulation(ui);
+  await testTouchEventsOverride(ui, true);
+}
+
+async function testDisableTouchSimulation(ui) {
+  info("Test disabling touch simulation via button");
+
+  await toggleTouchSimulation(ui);
+  await testTouchEventsOverride(ui, false);
+}
diff --git a/devtools/client/responsive/test/browser/browser_touch_does_not_trigger_hover_states.js b/devtools/client/responsive/test/browser/browser_touch_does_not_trigger_hover_states.js
new file mode 100644
index 0000000000..b19e64dc2b
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_touch_does_not_trigger_hover_states.js
@@ -0,0 +1,78 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that element hover states are not triggered when touch is enabled.
+
+const TEST_URL = `${URL_ROOT}hover.html`;
+
+addRDMTask(TEST_URL, async function ({ ui }) {
+  reloadOnTouchChange(true);
+
+  await toggleTouchSimulation(ui);
+
+  info("Test element hover states when touch is enabled.");
+  await testButtonHoverState(ui, "rgb(255, 0, 0)");
+  await testDropDownHoverState(ui, "none");
+
+  await toggleTouchSimulation(ui);
+
+  info("Test element hover states when touch is disabled.");
+  await testButtonHoverState(ui, "rgb(0, 0, 0)");
+  await testDropDownHoverState(ui, "block");
+
+  reloadOnTouchChange(false);
+});
+
+async function testButtonHoverState(ui, expected) {
+  await SpecialPowers.spawn(
+    ui.getViewportBrowser(),
+    [{ expected }],
+    async function (args) {
+      let button = content.document.querySelector("button");
+      const { expected: contentExpected } = args;
+
+      info("Move mouse into the button element.");
+      await EventUtils.synthesizeMouseAtCenter(
+        button,
+        { type: "mousemove", isSynthesized: false },
+        content
+      );
+      button = content.document.querySelector("button");
+      const win = content.document.defaultView;
+
+      is(
+        win.getComputedStyle(button).getPropertyValue("background-color"),
+        contentExpected,
+        `Button background color is ${contentExpected}.`
+      );
+    }
+  );
+}
+
+async function testDropDownHoverState(ui, expected) {
+  await SpecialPowers.spawn(
+    ui.getViewportBrowser(),
+    [{ expected }],
+    async function (args) {
+      const dropDownMenu = content.document.querySelector(".drop-down-menu");
+      const { expected: contentExpected } = args;
+
+      info("Move mouse into the drop down menu.");
+      await EventUtils.synthesizeMouseAtCenter(
+        dropDownMenu,
+        { type: "mousemove", isSynthesized: false },
+        content
+      );
+      const win = content.document.defaultView;
+      const menuItems = content.document.querySelector(".menu-items-list");
+
+      is(
+        win.getComputedStyle(menuItems).getPropertyValue("display"),
+        contentExpected,
+        `Menu items is display: ${contentExpected}.`
+      );
+    }
+  );
+}
diff --git a/devtools/client/responsive/test/browser/browser_touch_event_iframes.js b/devtools/client/responsive/test/browser/browser_touch_event_iframes.js
new file mode 100644
index 0000000000..11b94d2ab1
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_touch_event_iframes.js
@@ -0,0 +1,312 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test simulated touch events can correctly target embedded iframes.
+
+// These tests put a target iframe in a small embedding area, nested
+// different ways. Then a simulated mouse click is made on top of the
+// target iframe. If everything works, the translation done in
+// touch-simulator.js should exactly match the translation done in the
+// Platform code, such that the target is hit by the synthesized tap
+// is at the expected location.
+
+info("--- Starting viewport test output ---");
+
+info(`*** WARNING *** This test will move the mouse pointer to simulate
+native mouse clicks. Do not move the mouse during this test or you may
+cause intermittent failures.`);
+
+// This test could run awhile, so request a 4x timeout duration.
+requestLongerTimeout(4);
+
+// The viewport will be square, set to VIEWPORT_DIMENSION on each axis.
+const VIEWPORT_DIMENSION = 200;
+
+const META_VIEWPORT_CONTENTS = ["width=device-width", "width=400"];
+
+const DPRS = [1, 2, 3];
+
+const URL_ROOT_2 = CHROME_URL_ROOT.replace(
+  "chrome://mochitests/content/",
+  "http://mochi.test:8888/"
+);
+const IFRAME_PATHS = [`${URL_ROOT}`, `${URL_ROOT_2}`];
+
+const TESTS = [
+  {
+    description: "untranslated iframe",
+    style: {},
+  },
+  {
+    description: "translated 50% iframe",
+    style: {
+      position: "absolute",
+      left: "50%",
+      top: "50%",
+      transform: "translate(-50%, -50%)",
+    },
+  },
+  {
+    description: "translated 100% iframe",
+    style: {
+      position: "absolute",
+      left: "100%",
+      top: "100%",
+      transform: "translate(-100%, -100%)",
+    },
+  },
+];
+
+let testID = 0;
+
+for (const mvcontent of META_VIEWPORT_CONTENTS) {
+  info(`Starting test series with meta viewport content "${mvcontent}".`);
+
+  const TEST_URL =
+    `data:text/html;charset=utf-8,` +
+    `<html><meta name="viewport" content="${mvcontent}">` +
+    `<body style="margin:0; width:100%; height:200%;">` +
+    `<iframe id="host" ` +
+    `style="margin:0; border:0; width:100%; height:100%"></iframe>` +
+    `</body></html>`;
+
+  addRDMTask(TEST_URL, async function ({ ui, manager, browser }) {
+    await setViewportSize(ui, manager, VIEWPORT_DIMENSION, VIEWPORT_DIMENSION);
+    await setTouchAndMetaViewportSupport(ui, true);
+
+    // Figure out our window origin in screen space, which we'll need as we calculate
+    // coordinates for our simulated click events. These values are in CSS units, which
+    // is weird, but we compensate for that later.
+    const screenToWindowX = window.mozInnerScreenX;
+    const screenToWindowY = window.mozInnerScreenY;
+
+    for (const dpr of DPRS) {
+      await selectDevicePixelRatio(ui, dpr);
+
+      for (const path of IFRAME_PATHS) {
+        for (const test of TESTS) {
+          const { description, style } = test;
+
+          const title = `ID ${testID} - ${description} with DPR ${dpr} and path ${path}`;
+
+          info(`Starting test ${title}.`);
+
+          await spawnViewportTask(
+            ui,
+            {
+              title,
+              style,
+              path,
+              VIEWPORT_DIMENSION,
+              screenToWindowX,
+              screenToWindowY,
+            },
+            async args => {
+              // Define a function that returns a promise for one message that
+              // contains, at least, the supplied prop, and resolves with the
+              // data from that message. If a timeout value is supplied, the
+              // promise will reject if the timeout elapses first.
+              const oneMatchingMessageWithTimeout = (win, prop, timeout) => {
+                return new Promise((resolve, reject) => {
+                  let ourTimeoutID = 0;
+
+                  const ourListener = win.addEventListener("message", e => {
+                    if (typeof e.data[prop] !== "undefined") {
+                      if (ourTimeoutID) {
+                        win.clearTimeout(ourTimeoutID);
+                      }
+                      win.removeEventListener("message", ourListener);
+                      resolve(e.data);
+                    }
+                  });
+
+                  if (timeout) {
+                    // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+                    ourTimeoutID = win.setTimeout(() => {
+                      win.removeEventListener("message", ourListener);
+                      reject(
+                        `Timeout waiting for message with prop ${prop} after ${timeout}ms.`
+                      );
+                    }, timeout);
+                  }
+                });
+              };
+
+              // Our checks are not always precise, due to rounding errors in the
+              // scaling from css to screen and back. For now we use an epsilon and
+              // a locally-defined isfuzzy to compensate. We can't use
+              // SimpleTest.isfuzzy, because it's not bridged to the ContentTask.
+              // If that is ever bridged, we can remove the isfuzzy definition here and
+              // everything should "just work".
+              function isfuzzy(actual, expected, epsilon, msg) {
+                if (
+                  actual >= expected - epsilon &&
+                  actual <= expected + epsilon
+                ) {
+                  ok(true, msg);
+                } else {
+                  // This will trigger the usual failure message for is.
+                  is(actual, expected, msg);
+                }
+              }
+
+              // This function takes screen coordinates in css pixels.
+              // TODO: This should stop using nsIDOMWindowUtils.sendNativeMouseEvent
+              //       directly, and use `EventUtils.synthesizeNativeMouseEvent` in
+              //       a message listener in the chrome.
+              function synthesizeNativeMouseClick(win, screenX, screenY) {
+                const utils = win.windowUtils;
+                const scale = win.devicePixelRatio;
+
+                return new Promise(resolve => {
+                  utils.sendNativeMouseEvent(
+                    screenX * scale,
+                    screenY * scale,
+                    utils.NATIVE_MOUSE_MESSAGE_BUTTON_DOWN,
+                    0,
+                    0,
+                    win.document.documentElement,
+                    () => {
+                      utils.sendNativeMouseEvent(
+                        screenX * scale,
+                        screenY * scale,
+                        utils.NATIVE_MOUSE_MESSAGE_BUTTON_UP,
+                        0,
+                        0,
+                        win.document.documentElement,
+                        resolve
+                      );
+                    }
+                  );
+                });
+              }
+
+              // We're done defining functions; start the actual loading of the iframe
+              // and triggering the onclick handler in its content.
+              const host = content.document.getElementById("host");
+
+              // Modify the iframe style by adding the properties in the
+              // provided style object.
+              for (const prop in args.style) {
+                info(`Setting style.${prop} to ${args.style[prop]}.`);
+                host.style[prop] = args.style[prop];
+              }
+
+              // Set the iframe source, and await the ready message.
+              const IFRAME_URL = args.path + "touch_event_target.html";
+              const READY_TIMEOUT_MS = 5000;
+              const iframeReady = oneMatchingMessageWithTimeout(
+                content,
+                "ready",
+                READY_TIMEOUT_MS
+              );
+              host.src = IFRAME_URL;
+              try {
+                await iframeReady;
+              } catch (error) {
+                ok(false, `${args.title} ${error}`);
+                return;
+              }
+
+              info(`iframe has finished loading.`);
+
+              // Await reflow of the parent window.
+              await new Promise(resolve => {
+                content.requestAnimationFrame(() => {
+                  content.requestAnimationFrame(resolve);
+                });
+              });
+
+              // Now we're going to calculate screen coordinates for the upper-left
+              // quadrant of the target area. We're going to do that by using the
+              // following sources:
+              // 1) args.screenToWindow: the window position in screen space, in CSS
+              //    pixels.
+              // 2) host.getBoxQuadsFromWindowOrigin(): the iframe position, relative
+              //    to the window origin, in CSS pixels.
+              // 3) args.VIEWPORT_DIMENSION: the viewport size, in CSS pixels.
+              // We calculate the screen position of the center of the upper-left
+              // quadrant of the iframe, then use sendNativeMouseEvent to dispatch
+              // a click at that position. It should trigger the RDM TouchSimulator
+              // and turn the mouse click into a touch event that hits the onclick
+              // handler in the iframe content. If it's done correctly, the message
+              // we get back should have x,y coordinates that match the center of the
+              // upper left quadrant of the iframe, in CSS units.
+
+              const hostBounds = host
+                .getBoxQuadsFromWindowOrigin()[0]
+                .getBounds();
+              const windowToHostX = hostBounds.left;
+              const windowToHostY = hostBounds.top;
+
+              const screenToHostX = args.screenToWindowX + windowToHostX;
+              const screenToHostY = args.screenToWindowY + windowToHostY;
+
+              const quadrantOffsetDoc = hostBounds.width * 0.25;
+              const hostUpperLeftQuadrantDocX = quadrantOffsetDoc;
+              const hostUpperLeftQuadrantDocY = quadrantOffsetDoc;
+
+              const quadrantOffsetViewport = args.VIEWPORT_DIMENSION * 0.25;
+              const hostUpperLeftQuadrantViewportX = quadrantOffsetViewport;
+              const hostUpperLeftQuadrantViewportY = quadrantOffsetViewport;
+
+              const targetX = screenToHostX + hostUpperLeftQuadrantViewportX;
+              const targetY = screenToHostY + hostUpperLeftQuadrantViewportY;
+
+              // We're going to try a few times to click on the target area. Our method
+              // for triggering a native mouse click is vulnerable to interactive mouse
+              // moves while the test is running. Letting the click timeout gives us a
+              // chance to try again.
+              const CLICK_TIMEOUT_MS = 1000;
+              const CLICK_ATTEMPTS = 3;
+              let eventWasReceived = false;
+
+              for (let attempt = 0; attempt < CLICK_ATTEMPTS; attempt++) {
+                const gotXAndY = oneMatchingMessageWithTimeout(
+                  content,
+                  "x",
+                  CLICK_TIMEOUT_MS
+                );
+                info(
+                  `Sending native mousedown and mouseup to screen position ${targetX}, ${targetY} (attempt ${attempt}).`
+                );
+                await synthesizeNativeMouseClick(content, targetX, targetY);
+                try {
+                  const { x, y, screenX, screenY } = await gotXAndY;
+                  eventWasReceived = true;
+                  isfuzzy(
+                    x,
+                    hostUpperLeftQuadrantDocX,
+                    1,
+                    `${args.title} got click at close enough X ${x}, screen is ${screenX}.`
+                  );
+                  isfuzzy(
+                    y,
+                    hostUpperLeftQuadrantDocY,
+                    1,
+                    `${args.title} got click at close enough Y ${y}, screen is ${screenY}.`
+                  );
+                  break;
+                } catch (error) {
+                  // That click didn't work. The for loop will trigger another attempt,
+                  // or give up.
+                }
+              }
+
+              if (!eventWasReceived) {
+                ok(
+                  false,
+                  `${args.title} failed to get a click after ${CLICK_ATTEMPTS} tries.`
+                );
+              }
+            }
+          );
+
+          testID++;
+        }
+      }
+    }
+  });
+}
diff --git a/devtools/client/responsive/test/browser/browser_touch_event_should_bubble.js b/devtools/client/responsive/test/browser/browser_touch_event_should_bubble.js
new file mode 100644
index 0000000000..dc9da5df74
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_touch_event_should_bubble.js
@@ -0,0 +1,51 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that simulated touch events bubble.
+
+const TEST_URL = `${URL_ROOT}touch_event_bubbles.html`;
+
+addRDMTask(TEST_URL, async function ({ ui }) {
+  info("Toggling on touch simulation.");
+  reloadOnTouchChange(true);
+  await toggleTouchSimulation(ui);
+
+  info("Test that touch event bubbles.");
+  await SpecialPowers.spawn(ui.getViewportBrowser(), [], async function () {
+    const outerDiv = content.document.getElementById("outer");
+    const span = content.document.querySelector("span");
+
+    outerDiv.addEventListener("touchstart", () => {
+      span.style["background-color"] = "green"; // rgb(0, 128, 0)
+    });
+
+    const touchStartPromise = ContentTaskUtils.waitForEvent(span, "touchstart");
+    await EventUtils.synthesizeMouseAtCenter(
+      span,
+      { type: "mousedown", isSynthesized: false },
+      content
+    );
+    await touchStartPromise;
+
+    const win = content.document.defaultView;
+    const bg = win.getComputedStyle(span).getPropertyValue("background-color");
+
+    is(
+      bg,
+      "rgb(0, 128, 0)",
+      `span's background color should be rgb(0, 128, 0): got ${bg}`
+    );
+
+    await EventUtils.synthesizeMouseAtCenter(
+      span,
+      { type: "mouseup", isSynthesized: false },
+      content
+    );
+  });
+
+  info("Toggling off touch simulation.");
+  await toggleTouchSimulation(ui);
+  reloadOnTouchChange(false);
+});
diff --git a/devtools/client/responsive/test/browser/browser_touch_pointerevents.js b/devtools/client/responsive/test/browser/browser_touch_pointerevents.js
new file mode 100644
index 0000000000..a7196fba60
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_touch_pointerevents.js
@@ -0,0 +1,77 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that simulating touch only dispatches pointer events from a touch event.
+
+const TEST_URL =
+  "data:text/html;charset=utf-8," +
+  '<div style="width:100px;height:100px;background-color:red"></div>' +
+  "</body>";
+
+addRDMTask(TEST_URL, async function ({ ui }) {
+  info("Toggling on touch simulation.");
+  reloadOnTouchChange(true);
+  await toggleTouchSimulation(ui);
+
+  await testPointerEvents(ui);
+
+  info("Toggling off touch simulation.");
+  await toggleTouchSimulation(ui);
+  reloadOnTouchChange(false);
+});
+
+async function testPointerEvents(ui) {
+  info("Test that pointer events are from touch events");
+  await SpecialPowers.spawn(ui.getViewportBrowser(), [], async function () {
+    const div = content.document.querySelector("div");
+
+    div.addEventListener("pointermove", () => {
+      div.style["background-color"] = "green"; //rgb(0,128,0)
+    });
+    div.addEventListener("pointerdown", e => {
+      Assert.strictEqual(
+        e.pointerType,
+        "touch",
+        "Got pointer event from a touch event."
+      );
+    });
+
+    info("Check that the pointerdown event is from a touch event.");
+    const pointerDownPromise = ContentTaskUtils.waitForEvent(
+      div,
+      "pointerdown"
+    );
+
+    await EventUtils.synthesizeMouseAtCenter(
+      div,
+      { type: "mousedown", isSynthesized: false },
+      content
+    );
+    await pointerDownPromise;
+    await EventUtils.synthesizeMouseAtCenter(
+      div,
+      { type: "mouseup", isSynthesized: false },
+      content
+    );
+
+    info(
+      "Check that a pointermove event was never dispatched from the mousemove event"
+    );
+    await EventUtils.synthesizeMouseAtCenter(
+      div,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+
+    const win = content.document.defaultView;
+    const bg = win.getComputedStyle(div).getPropertyValue("background-color");
+
+    is(
+      bg,
+      "rgb(255, 0, 0)",
+      `div's background color should still be red: rgb(255, 0, 0): got ${bg}`
+    );
+  });
+}
diff --git a/devtools/client/responsive/test/browser/browser_touch_simulation.js b/devtools/client/responsive/test/browser/browser_touch_simulation.js
new file mode 100644
index 0000000000..b74c9f53c4
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_touch_simulation.js
@@ -0,0 +1,341 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test global touch simulation button
+
+const TEST_URL = `${URL_ROOT_SSL}touch.html`;
+const PREF_DOM_META_VIEWPORT_ENABLED = "dom.meta-viewport.enabled";
+
+// A 300ms delay between a `touchend` and `click` event is added whenever double-tap zoom
+// is allowed.
+const DELAY_MIN = 250;
+
+addRDMTask(TEST_URL, async function ({ ui }) {
+  reloadOnTouchChange(true);
+
+  await waitBootstrap(ui);
+  await testWithNoTouch(ui);
+  await toggleTouchSimulation(ui);
+  await promiseContentReflow(ui);
+  await testWithTouch(ui);
+  await testWithMetaViewportEnabled(ui);
+  await testWithMetaViewportDisabled(ui);
+  testTouchButton(ui);
+
+  reloadOnTouchChange(false);
+});
+
+async function testWithNoTouch(ui) {
+  await SpecialPowers.spawn(ui.getViewportBrowser(), [], async function () {
+    const div = content.document.querySelector("div");
+    let x = 0,
+      y = 0;
+
+    info("testWithNoTouch: Initial test parameter and mouse mouse outside div");
+    x = -1;
+    y = -1;
+    await EventUtils.synthesizeMouse(
+      div,
+      x,
+      y,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+    div.style.transform = "none";
+    div.style.backgroundColor = "";
+
+    info("testWithNoTouch: Move mouse into the div element");
+    await EventUtils.synthesizeMouseAtCenter(
+      div,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+    is(div.style.backgroundColor, "red", "mouseenter or mouseover should work");
+
+    info("testWithNoTouch: Drag the div element");
+    await EventUtils.synthesizeMouseAtCenter(
+      div,
+      { type: "mousedown", isSynthesized: false },
+      content
+    );
+    x = 100;
+    y = 100;
+    await EventUtils.synthesizeMouse(
+      div,
+      x,
+      y,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+    is(div.style.transform, "none", "touchmove shouldn't work");
+    await EventUtils.synthesizeMouse(
+      div,
+      x,
+      y,
+      { type: "mouseup", isSynthesized: false },
+      content
+    );
+
+    info("testWithNoTouch: Move mouse out of the div element");
+    x = -1;
+    y = -1;
+    await EventUtils.synthesizeMouse(
+      div,
+      x,
+      y,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+    is(div.style.backgroundColor, "blue", "mouseout or mouseleave should work");
+
+    info("testWithNoTouch: Click the div element");
+    await EventUtils.synthesizeClick(div);
+    is(
+      div.dataset.isDelay,
+      "false",
+      "300ms delay between touch events and mouse events should not work"
+    );
+
+    // Assuming that this test runs on devices having no touch screen device.
+    ok(
+      !content.document.defaultView.matchMedia("(pointer: coarse)").matches,
+      "pointer: coarse shouldn't be matched"
+    );
+    ok(
+      !content.document.defaultView.matchMedia("(hover: none)").matches,
+      "hover: none shouldn't be matched"
+    );
+    ok(
+      !content.document.defaultView.matchMedia("(any-pointer: coarse)").matches,
+      "any-pointer: coarse shouldn't be matched"
+    );
+    ok(
+      !content.document.defaultView.matchMedia("(any-hover: none)").matches,
+      "any-hover: none shouldn't be matched"
+    );
+  });
+}
+
+async function testWithTouch(ui) {
+  await SpecialPowers.spawn(ui.getViewportBrowser(), [], async function () {
+    const div = content.document.querySelector("div");
+    let x = 0,
+      y = 0;
+
+    info("testWithTouch: Initial test parameter and mouse mouse outside div");
+    x = -1;
+    y = -1;
+    await EventUtils.synthesizeMouse(
+      div,
+      x,
+      y,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+    div.style.transform = "none";
+    div.style.backgroundColor = "";
+
+    info("testWithTouch: Move mouse into the div element");
+    await EventUtils.synthesizeMouseAtCenter(
+      div,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+    isnot(
+      div.style.backgroundColor,
+      "red",
+      "mouseenter or mouseover should not work"
+    );
+
+    info("testWithTouch: Drag the div element");
+    await EventUtils.synthesizeMouseAtCenter(
+      div,
+      { type: "mousedown", isSynthesized: false },
+      content
+    );
+    x = 100;
+    y = 100;
+    const touchMovePromise = ContentTaskUtils.waitForEvent(div, "touchmove");
+    await EventUtils.synthesizeMouse(
+      div,
+      x,
+      y,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+    await touchMovePromise;
+    isnot(div.style.transform, "none", "touchmove should work");
+    await EventUtils.synthesizeMouse(
+      div,
+      x,
+      y,
+      { type: "mouseup", isSynthesized: false },
+      content
+    );
+
+    info("testWithTouch: Move mouse out of the div element");
+    x = -1;
+    y = -1;
+    await EventUtils.synthesizeMouse(
+      div,
+      x,
+      y,
+      { type: "mousemove", isSynthesized: false },
+      content
+    );
+    isnot(
+      div.style.backgroundColor,
+      "blue",
+      "mouseout or mouseleave should not work"
+    );
+
+    ok(
+      content.document.defaultView.matchMedia("(pointer: coarse)").matches,
+      "pointer: coarse should be matched"
+    );
+    ok(
+      content.document.defaultView.matchMedia("(hover: none)").matches,
+      "hover: none should be matched"
+    );
+    ok(
+      content.document.defaultView.matchMedia("(any-pointer: coarse)").matches,
+      "any-pointer: coarse should be matched"
+    );
+    ok(
+      content.document.defaultView.matchMedia("(any-hover: none)").matches,
+      "any-hover: none should be matched"
+    );
+  });
+
+  // Capturing touch events with the content window as a registered listener causes the
+  // "changedTouches" field to be undefined when using deprecated TouchEvent APIs.
+  // See Bug 1549220 and Bug 1588438 for more information on this issue.
+  info("Test that changed touches captured on the content window are defined.");
+  await SpecialPowers.spawn(ui.getViewportBrowser(), [], async function () {
+    const div = content.document.querySelector("div");
+
+    content.addEventListener(
+      "touchstart",
+      event => {
+        const changedTouch = event.changedTouches[0];
+        ok(changedTouch, "Changed touch is defined.");
+      },
+      { once: true }
+    );
+    await EventUtils.synthesizeClick(div);
+  });
+}
+
+async function testWithMetaViewportEnabled(ui) {
+  await SpecialPowers.pushPrefEnv({
+    set: [[PREF_DOM_META_VIEWPORT_ENABLED, true]],
+  });
+
+  await SpecialPowers.spawn(
+    ui.getViewportBrowser(),
+    [{ delay_min: DELAY_MIN }],
+    async function ({ delay_min }) {
+      // A helper for testing the delay between touchend and click events.
+      async function testDelay(mvc, el) {
+        const touchendPromise = ContentTaskUtils.waitForEvent(el, "touchend");
+        const clickPromise = ContentTaskUtils.waitForEvent(el, "click");
+        await EventUtils.synthesizeClick(el);
+        const { timeStamp: touchendTimestamp } = await touchendPromise;
+        const { timeStamp: clickTimeStamp } = await clickPromise;
+        const delay = clickTimeStamp - touchendTimestamp;
+
+        const expected = delay >= delay_min;
+
+        ok(
+          expected,
+          `${mvc}: There should be greater than a ${delay_min}ms delay between touch events and mouse events. Got delay of ${delay}ms`
+        );
+      }
+
+      // A helper function for waiting for reflow to complete.
+      const promiseReflow = () => {
+        return new Promise(resolve => {
+          content.window.requestAnimationFrame(() => {
+            content.window.requestAnimationFrame(resolve);
+          });
+        });
+      };
+
+      const meta = content.document.querySelector("meta[name=viewport]");
+      const div = content.document.querySelector("div");
+
+      info(
+        "testWithMetaViewportEnabled: " +
+          "click the div element with <meta name='viewport'>"
+      );
+      meta.content = "";
+      await promiseReflow();
+      await testDelay("(empty)", div);
+    }
+  );
+
+  await SpecialPowers.popPrefEnv();
+}
+
+async function testWithMetaViewportDisabled(ui) {
+  await SpecialPowers.pushPrefEnv({
+    set: [[PREF_DOM_META_VIEWPORT_ENABLED, false]],
+  });
+
+  await SpecialPowers.spawn(
+    ui.getViewportBrowser(),
+    [{ delay_min: DELAY_MIN }],
+    async function ({ delay_min }) {
+      const meta = content.document.querySelector("meta[name=viewport]");
+      const div = content.document.querySelector("div");
+
+      info(
+        "testWithMetaViewportDisabled: click the div with <meta name='viewport'>"
+      );
+      meta.content = "";
+      const touchendPromise = ContentTaskUtils.waitForEvent(div, "touchend");
+      const clickPromise = ContentTaskUtils.waitForEvent(div, "click");
+      await EventUtils.synthesizeClick(div);
+      const { timeStamp: touchendTimestamp } = await touchendPromise;
+      const { timeStamp: clickTimeStamp } = await clickPromise;
+      const delay = clickTimeStamp - touchendTimestamp;
+
+      const expected = delay >= delay_min;
+
+      ok(
+        expected,
+        `There should be greater than a ${delay_min}ms delay between touch events and mouse events. Got delay of ${delay}ms`
+      );
+    }
+  );
+}
+
+function testTouchButton(ui) {
+  const { document } = ui.toolWindow;
+  const touchButton = document.getElementById("touch-simulation-button");
+
+  ok(
+    touchButton.classList.contains("checked"),
+    "Touch simulation is active at end of test."
+  );
+
+  touchButton.click();
+
+  ok(
+    !touchButton.classList.contains("checked"),
+    "Touch simulation is stopped on click."
+  );
+
+  touchButton.click();
+
+  ok(
+    touchButton.classList.contains("checked"),
+    "Touch simulation is started on click."
+  );
+}
+
+async function waitBootstrap(ui) {
+  await waitForFrameLoad(ui, TEST_URL);
+}
diff --git a/devtools/client/responsive/test/browser/browser_typeahead_find.js b/devtools/client/responsive/test/browser/browser_typeahead_find.js
new file mode 100644
index 0000000000..7bc22de1ef
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_typeahead_find.js
@@ -0,0 +1,70 @@
+/* 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";
+
+/**
+ * This test attempts to exercise automatic triggering of typeaheadfind
+ * within RDM content. It does this by simulating keystrokes while
+ * various elements in the RDM content are focused.
+
+ * The test currently does not work due to hitting the assert in
+ * Bug 516128.
+ */
+
+const TEST_URL =
+  "data:text/html;charset=utf-8," +
+  '<body id="body"><input id="input" type="text"/><p>text</body>';
+
+addRDMTask(TEST_URL, async function ({ ui, manager }) {
+  // Turn on the pref that allows meta viewport support.
+  await pushPref("accessibility.typeaheadfind", true);
+
+  const browser = ui.getViewportBrowser();
+
+  info("--- Starting test output ---");
+
+  const expected = [
+    {
+      id: "body",
+      findTriggered: true,
+    },
+    {
+      id: "input",
+      findTriggered: false,
+    },
+  ];
+
+  for (const e of expected) {
+    await SpecialPowers.spawn(browser, [{ e }], async function (args) {
+      const { e: values } = args;
+      const element = content.document.getElementById(values.id);
+
+      // Set focus on the desired element.
+      element.focus();
+    });
+
+    // Press the 'T' key and see if find is triggered.
+    await BrowserTestUtils.synthesizeKey("t", {}, browser);
+
+    const findBar = await gBrowser.getFindBar();
+
+    const findIsTriggered = findBar._findField.value == "t";
+    is(
+      findIsTriggered,
+      e.findTriggered,
+      "Text input with focused element " +
+        e.id +
+        " should " +
+        (e.findTriggered ? "" : "not ") +
+        "trigger find."
+    );
+    findBar._findField.value = "";
+
+    await SpecialPowers.spawn(browser, [], async function () {
+      // Clear focus.
+      content.document.activeElement.blur();
+    });
+  }
+});
diff --git a/devtools/client/responsive/test/browser/browser_user_agent_input.js b/devtools/client/responsive/test/browser/browser_user_agent_input.js
new file mode 100644
index 0000000000..cd7b843790
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_user_agent_input.js
@@ -0,0 +1,24 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+const NEW_USER_AGENT = "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0";
+
+addRDMTask(TEST_URL, async function ({ ui }) {
+  reloadOnUAChange(true);
+
+  info("Check the default state of the user agent input");
+  await testUserAgent(ui, DEFAULT_UA);
+
+  info(`Change the user agent input to ${NEW_USER_AGENT}`);
+  await changeUserAgentInput(ui, NEW_USER_AGENT);
+  await testUserAgent(ui, NEW_USER_AGENT);
+
+  info("Reset the user agent input back to the default UA");
+  await changeUserAgentInput(ui, "");
+  await testUserAgent(ui, DEFAULT_UA);
+
+  reloadOnUAChange(false);
+});
diff --git a/devtools/client/responsive/test/browser/browser_viewport_basics.js b/devtools/client/responsive/test/browser/browser_viewport_basics.js
new file mode 100644
index 0000000000..b091763258
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_basics.js
@@ -0,0 +1,30 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test viewports basics after opening, like size and location
+
+const TEST_URL = "https://example.org/";
+addRDMTask(TEST_URL, async function ({ ui }) {
+  const browser = ui.getViewportBrowser();
+
+  is(
+    ui.toolWindow.getComputedStyle(browser).getPropertyValue("width"),
+    "320px",
+    "Viewport has default width"
+  );
+  is(
+    ui.toolWindow.getComputedStyle(browser).getPropertyValue("height"),
+    "480px",
+    "Viewport has default height"
+  );
+
+  // Browser's location should match original tab
+  await navigateTo(TEST_URL, { browser });
+
+  const location = await spawnViewportTask(ui, {}, function () {
+    return content.location.href; // eslint-disable-line
+  });
+  is(location, TEST_URL, "Viewport location matches");
+});
diff --git a/devtools/client/responsive/test/browser/browser_viewport_changed_meta.js b/devtools/client/responsive/test/browser/browser_viewport_changed_meta.js
new file mode 100644
index 0000000000..f0bafdd551
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_changed_meta.js
@@ -0,0 +1,124 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that resolution is as expected when the viewport tag is changed.
+// The page content is a 400 x 400 div in a 200 x 200 viewport. Initially,
+// the viewport width is set to 800 at initial-scale 1, but then the tag
+// content is changed. This triggers various rescale operations that will
+// change the resolution of the page after reflow.
+
+// Chrome handles many of these cases differently. The Chrome results are
+// included as TODOs, but labelled as "res_chrome" to indicate that the
+// goal is not necessarily to match an agreed-upon standard, but to
+// achieve web compatability through changing either Firefox or Chrome
+// behavior.
+
+info("--- Starting viewport test output ---");
+
+const WIDTH = 200;
+const HEIGHT = 200;
+const INITIAL_CONTENT = "width=800, initial-scale=1";
+const INITIAL_RES_TARGET = 1.0;
+const TESTS = [
+  // This checks that when the replaced content matches the original content,
+  // we get the same values as the original values.
+  { content: INITIAL_CONTENT, res_target: INITIAL_RES_TARGET },
+
+  // Section 1: Check the case of a viewport shrinking with the display width
+  // staying the same. In this case, the shrink will fit the max of the 400px
+  // content width and the viewport width into the 200px display area.
+  { content: "width=200", res_target: 0.5 }, // fitting 400px content
+  { content: "width=400", res_target: 0.5 }, // fitting 400px content/viewport
+  { content: "width=500", res_target: 0.4 }, // fitting 500px viewport
+
+  // Section 2: Same as Section 1, but adds user-scalable=no. The expected
+  // results are similar to Section 1, but we ignore the content size and only
+  // adjust resolution to make the viewport fit into the display area.
+  { content: "width=200, user-scalable=no", res_target: 1.0 },
+  { content: "width=400, user-scalable=no", res_target: 0.5 },
+  { content: "width=500, user-scalable=no", res_target: 0.4 },
+
+  // Section 3: Same as Section 1, but adds initial-scale=1. Initial-scale
+  // prevents content shrink in Firefox, so the viewport is scaled based on its
+  // changing size relative to the display area. In this case, the resolution
+  // is increased to maintain the proportional amount of the previously visible
+  // content. With the initial conditions, the display area was showing 1/4 of
+  // the content at 0.25x resolution. As the viewport width is shrunk, the
+  // resolution will increase to ensure that only 1/4 of the content is visible.
+  // Essentially, the new viewport width times the resolution will equal 800px,
+  // the original viewport width times resolution.
+  //
+  // Chrome treats the initial-scale=1 as inviolable and sets resolution to 1.0.
+  { content: "width=200, initial-scale=1", res_target: 4.0, res_chrome: 1.0 },
+  { content: "width=400, initial-scale=1", res_target: 2.0, res_chrome: 1.0 },
+  { content: "width=500, initial-scale=1", res_target: 1.6, res_chrome: 1.0 },
+
+  // Section 4: Same as Section 3, but adds user-scalable=no. The combination
+  // of this and initial-scale=1 prevents the scaling-up of the resolution to
+  // keep the proportional amount of the previously visible content.
+  { content: "width=200, initial-scale=1, user-scalable=no", res_target: 1.0 },
+  { content: "width=400, initial-scale=1, user-scalable=no", res_target: 1.0 },
+  { content: "width=500, initial-scale=1, user-scalable=no", res_target: 1.0 },
+];
+
+const TEST_URL = `data:text/html;charset=utf-8,
+  <html>
+    <head><meta name="viewport" content="${INITIAL_CONTENT}"></head>
+    <body style="margin:0">
+      <div id="box" style="width:400px;height:400px;background-color:green">Initial</div>
+    </body>
+  </html>`;
+
+addRDMTask(TEST_URL, async function ({ ui, manager, browser }) {
+  await setViewportSize(ui, manager, WIDTH, HEIGHT);
+  await setTouchAndMetaViewportSupport(ui, true);
+
+  // Check initial resolution value.
+  const initial_resolution = await spawnViewportTask(ui, {}, () => {
+    return content.windowUtils.getResolution();
+  });
+
+  is(
+    initial_resolution.toFixed(2),
+    INITIAL_RES_TARGET.toFixed(2),
+    `Initial resolution is as expected.`
+  );
+
+  for (const test of TESTS) {
+    const { content: content, res_target, res_chrome } = test;
+
+    await spawnViewportTask(ui, { content }, args => {
+      const box = content.document.getElementById("box");
+      box.textContent = args.content;
+
+      const meta = content.document.getElementsByTagName("meta")[0];
+      info(`Changing meta viewport content to "${args.content}".`);
+      meta.content = args.content;
+    });
+
+    await promiseContentReflow(ui);
+
+    const resolution = await spawnViewportTask(ui, {}, () => {
+      return content.windowUtils.getResolution();
+    });
+
+    is(
+      resolution.toFixed(2),
+      res_target.toFixed(2),
+      `Replaced meta viewport content "${content}" resolution is as expected.`
+    );
+
+    if (typeof res_chrome !== "undefined") {
+      todo_is(
+        resolution.toFixed(2),
+        res_chrome.toFixed(2),
+        `Replaced meta viewport content "${content}" resolution matches Chrome resolution.`
+      );
+    }
+
+    info("Reload and wait for document to be loaded to prepare for next test.");
+    await reloadBrowser();
+  }
+});
diff --git a/devtools/client/responsive/test/browser/browser_viewport_fallback_width.js b/devtools/client/responsive/test/browser/browser_viewport_fallback_width.js
new file mode 100644
index 0000000000..73ae4b211b
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_fallback_width.js
@@ -0,0 +1,53 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that the viewport's ICB width will use the simulated screen width
+// if the simulated width is larger than the desktop viewport width default
+// (980px).
+
+// The HTML below sets up the test such that the "inner" div is aligned to the end
+// (right-side) of the viewport. By doing this, it makes it easier to have our test
+// target an element whose bounds are outside of the desktop viewport width default
+// for device screens greater than 980px.
+const TEST_URL =
+  `data:text/html;charset=utf-8,` +
+  `<div id="outer" style="display: grid; justify-items: end; font-size: 64px">
+    <div id="inner">Click me!</div>
+  </div>`;
+
+addRDMTask(TEST_URL, async function ({ ui, manager }) {
+  info("Toggling on touch simulation.");
+  reloadOnTouchChange(true);
+  await toggleTouchSimulation(ui);
+  // It's important we set a viewport width larger than 980px for this test to be correct.
+  // So let's choose viewport width: 1280x600
+  await setViewportSizeAndAwaitReflow(ui, manager, 1280, 600);
+
+  await testICBWidth(ui);
+
+  info("Toggling off touch simulation.");
+  await toggleTouchSimulation(ui);
+  reloadOnTouchChange(false);
+});
+
+async function testICBWidth(ui) {
+  await SpecialPowers.spawn(ui.getViewportBrowser(), [], async function () {
+    const innerDiv = content.document.getElementById("inner");
+
+    innerDiv.addEventListener("click", () => {
+      innerDiv.style.color = "green"; //rgb(0,128,0)
+    });
+
+    info("Check that touch point (via click) registers on inner div.");
+    const mousedown = ContentTaskUtils.waitForEvent(innerDiv, "click");
+    await EventUtils.synthesizeClick(innerDiv);
+    await mousedown;
+
+    const win = content.document.defaultView;
+    const bg = win.getComputedStyle(innerDiv).getPropertyValue("color");
+
+    is(bg, "rgb(0, 128, 0)", "inner div's background color changed to green.");
+  });
+}
diff --git a/devtools/client/responsive/test/browser/browser_viewport_resizing_after_reload.js b/devtools/client/responsive/test/browser/browser_viewport_resizing_after_reload.js
new file mode 100644
index 0000000000..ad750326ae
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_resizing_after_reload.js
@@ -0,0 +1,88 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test viewport resizing, with and without meta viewport support.
+
+const TEST_URL =
+  "data:text/html;charset=utf-8," +
+  '<head><meta name="viewport" content="width=device-width"/></head>' +
+  '<body style="margin:0px;min-width:600px">' +
+  '<div style="width:100%;height:100px;background-color:black"></div>' +
+  '<div style="width:100%;height:1100px;background-color:lightblue"></div>' +
+  "</body>";
+
+addRDMTask(TEST_URL, async function ({ ui, manager }) {
+  info("--- Starting viewport test output ---");
+
+  // We're going to take a 300,600 viewport (before), reload it,
+  // then resize it to 600,300 (after) and then resize it back.
+  // At the before and after points, we'll measure zoom and the
+  // layout viewport width and height.
+  const expected = [
+    {
+      metaSupport: false,
+      before: [1.0, 300, 600],
+      after: [1.0, 600, 300],
+    },
+    {
+      metaSupport: true,
+      before: [0.5, 300, 600],
+      after: [1.0, 600, 300],
+    },
+  ];
+
+  for (const e of expected) {
+    const b = e.before;
+    const a = e.after;
+
+    const message = "Meta Viewport " + (e.metaSupport ? "ON" : "OFF");
+
+    // Ensure meta viewport is set.
+    info(message + " setting meta viewport support.");
+    await setTouchAndMetaViewportSupport(ui, e.metaSupport);
+
+    // Get to the initial size and check values.
+    await setViewportSizeAndAwaitReflow(ui, manager, 300, 600);
+    await testViewportZoomWidthAndHeight(
+      message + " before resize",
+      ui,
+      b[0],
+      b[1],
+      b[2]
+    );
+
+    // Force a reload.
+    await reloadBrowser();
+
+    // Check initial values again.
+    await testViewportZoomWidthAndHeight(
+      message + " after reload",
+      ui,
+      b[0],
+      b[1],
+      b[2]
+    );
+
+    // Move to the smaller size.
+    await setViewportSizeAndAwaitReflow(ui, manager, 600, 300);
+    await testViewportZoomWidthAndHeight(
+      message + " after resize",
+      ui,
+      a[0],
+      a[1],
+      a[2]
+    );
+
+    // Go back to the initial size and check again.
+    await setViewportSizeAndAwaitReflow(ui, manager, 300, 600);
+    await testViewportZoomWidthAndHeight(
+      message + " return to initial size",
+      ui,
+      b[0],
+      b[1],
+      b[2]
+    );
+  }
+});
diff --git a/devtools/client/responsive/test/browser/browser_viewport_resizing_fixed_width.js b/devtools/client/responsive/test/browser/browser_viewport_resizing_fixed_width.js
new file mode 100644
index 0000000000..46a2529b12
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_resizing_fixed_width.js
@@ -0,0 +1,72 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test viewport resizing, with and without meta viewport support.
+
+const TEST_URL =
+  "data:text/html;charset=utf-8," +
+  '<head><meta name="viewport" content="width=300"/></head>' +
+  "<body>meta viewport width 300</body>";
+addRDMTask(TEST_URL, async function ({ ui, manager }) {
+  info("--- Starting viewport test output ---");
+
+  // We're going to take a 600,300 viewport (before) and resize it
+  // to 50,50 (after) and then resize it back. At the before and
+  // after points, we'll measure zoom and the layout viewport width
+  // and height.
+  const expected = [
+    {
+      metaSupport: false,
+      before: [1.0, 600, 300],
+      after: [1.0, 50, 50], // Zoom is unaffected.
+    },
+    {
+      metaSupport: true,
+      before: [2.0, 300, 150],
+      after: [0.25, 300, 300], // This checks that min-zoom is active.
+    },
+  ];
+
+  for (const e of expected) {
+    const b = e.before;
+    const a = e.after;
+
+    const message = "Meta Viewport " + (e.metaSupport ? "ON" : "OFF");
+
+    // Ensure meta viewport is set.
+    info(message + " setting meta viewport support.");
+    await setTouchAndMetaViewportSupport(ui, e.metaSupport);
+
+    // Get to the initial size and check values.
+    await setViewportSizeAndAwaitReflow(ui, manager, 600, 300);
+    await testViewportZoomWidthAndHeight(
+      message + " before resize",
+      ui,
+      b[0],
+      b[1],
+      b[2]
+    );
+
+    // Move to the smaller size.
+    await setViewportSizeAndAwaitReflow(ui, manager, 50, 50);
+    await testViewportZoomWidthAndHeight(
+      message + " after resize",
+      ui,
+      a[0],
+      a[1],
+      a[2]
+    );
+
+    // Go back to the initial size and check again.
+    await setViewportSizeAndAwaitReflow(ui, manager, 600, 300);
+    await testViewportZoomWidthAndHeight(
+      message + " return to initial size",
+      ui,
+      b[0],
+      b[1],
+      b[2]
+    );
+  }
+});
diff --git a/devtools/client/responsive/test/browser/browser_viewport_resizing_fixed_width_and_zoom.js b/devtools/client/responsive/test/browser/browser_viewport_resizing_fixed_width_and_zoom.js
new file mode 100644
index 0000000000..c07bd84158
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_resizing_fixed_width_and_zoom.js
@@ -0,0 +1,89 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test viewport resizing, with and without meta viewport support.
+
+const TEST_URL =
+  "data:text/html;charset=utf-8," +
+  '<head><meta name="viewport" content="width=device-width, ' +
+  'initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0"></head>' +
+  "<body>meta viewport scaled locked at 1.0</body>";
+addRDMTask(TEST_URL, async function ({ ui, manager }) {
+  info("--- Starting viewport test output ---");
+
+  // We're going to take a 300,600 viewport (before) and resize it
+  // to 600,300 (after) and then resize it back. At the before and
+  // after points, we'll measure zoom and the layout viewport width
+  // and height.
+  const expected = [
+    {
+      metaSupport: false,
+      before: {
+        zoom: 1.0,
+        width: 300,
+        height: 600,
+      },
+      after: {
+        zoom: 1.0,
+        width: 600,
+        height: 300,
+      },
+    },
+    {
+      metaSupport: true,
+      before: {
+        zoom: 1.0,
+        width: 300,
+        height: 600,
+      },
+      after: {
+        zoom: 1.0,
+        width: 600,
+        height: 300,
+      },
+    },
+  ];
+
+  for (const e of expected) {
+    const b = e.before;
+    const a = e.after;
+
+    const message = "Meta Viewport " + (e.metaSupport ? "ON" : "OFF");
+
+    // Ensure meta viewport is set.
+    info(message + " setting meta viewport support.");
+    await setTouchAndMetaViewportSupport(ui, e.metaSupport);
+
+    // Get to the initial size and check values.
+    await setViewportSizeAndAwaitReflow(ui, manager, 300, 600);
+    await testViewportZoomWidthAndHeight(
+      message + " before resize",
+      ui,
+      b.zoom,
+      b.width,
+      b.height
+    );
+
+    // Move to the smaller size.
+    await setViewportSizeAndAwaitReflow(ui, manager, 600, 300);
+    await testViewportZoomWidthAndHeight(
+      message + " after resize",
+      ui,
+      a.zoom,
+      a.width,
+      a.height
+    );
+
+    // Go back to the initial size and check again.
+    await setViewportSizeAndAwaitReflow(ui, manager, 300, 600);
+    await testViewportZoomWidthAndHeight(
+      message + " return to initial size",
+      ui,
+      b.zoom,
+      b.width,
+      b.height
+    );
+  }
+});
diff --git a/devtools/client/responsive/test/browser/browser_viewport_resizing_minimum_scale.js b/devtools/client/responsive/test/browser/browser_viewport_resizing_minimum_scale.js
new file mode 100644
index 0000000000..b2984851d2
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_resizing_minimum_scale.js
@@ -0,0 +1,76 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test viewport resizing, with and without meta viewport support.
+
+const TEST_URL =
+  "data:text/html;charset=utf-8," +
+  '<head><meta name="viewport" content="initial-scale=1.0, ' +
+  'minimum-scale=1.0, width=device-width"></head>' +
+  '<div style="width:100%;background-color:green">test</div>' +
+  "</body>";
+addRDMTask(TEST_URL, async function ({ ui, manager }) {
+  info("--- Starting viewport test output ---");
+
+  // We're going to take a 300,600 viewport (before) and resize it
+  // to 600,300 (after) and then resize it back. At the before and
+  // after points, we'll measure zoom and the layout viewport width
+  // and height.
+  const expected = [
+    {
+      before: {
+        zoom: 1.0,
+        width: 300,
+        height: 600,
+      },
+      after: {
+        zoom: 1.0,
+        width: 600,
+        height: 300,
+      },
+    },
+  ];
+
+  for (const e of expected) {
+    const b = e.before;
+    const a = e.after;
+
+    const message = "Meta Viewport ON";
+
+    // Ensure meta viewport is set.
+    info(message + " setting meta viewport support.");
+    await setTouchAndMetaViewportSupport(ui, true);
+
+    // Get to the initial size and check values.
+    await setViewportSizeAndAwaitReflow(ui, manager, 300, 600);
+    await testViewportZoomWidthAndHeight(
+      message + " before resize",
+      ui,
+      b.zoom,
+      b.width,
+      b.height
+    );
+
+    // Move to the smaller size.
+    await setViewportSizeAndAwaitReflow(ui, manager, 600, 300);
+    await testViewportZoomWidthAndHeight(
+      message + " after resize",
+      ui,
+      a.zoom,
+      a.width,
+      a.height
+    );
+
+    // Go back to the initial size and check again.
+    await setViewportSizeAndAwaitReflow(ui, manager, 300, 600);
+    await testViewportZoomWidthAndHeight(
+      message + " return to initial size",
+      ui,
+      b.zoom,
+      b.width,
+      b.height
+    );
+  }
+});
diff --git a/devtools/client/responsive/test/browser/browser_viewport_resizing_scrollbar.js b/devtools/client/responsive/test/browser/browser_viewport_resizing_scrollbar.js
new file mode 100644
index 0000000000..ed4de1711e
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_resizing_scrollbar.js
@@ -0,0 +1,86 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test scrollbar appearance after viewport resizing, with and without
+// meta viewport support.
+
+Services.scriptloader.loadSubScript(
+  "chrome://mochikit/content/tests/SimpleTest/WindowSnapshot.js",
+  this
+);
+
+// The quest for a TEST_ROOT: we have to choose a way of addressing the RDM document
+// such that two things can happen:
+// 1) addRDMTask can load it.
+// 2) WindowSnapshot can take a picture of it.
+
+// The WindowSnapshot does not work cross-origin. We can't use a data URI, because those
+// are considered cross-origin.
+
+// let TEST_ROOT = "";
+
+// We can't use a relative URL, because addRDMTask can't load local files.
+// TEST_ROOT = "";
+
+// We can't use a mochi.test URL, because it's cross-origin.
+// TEST_ROOT =
+//   "http://mochi.test:8888/browser/devtools/client/responsive/test/browser/";
+
+// We can't use a chrome URL, because it triggers an assertion: RDM only available for
+// remote tabs.
+// TEST_ROOT =
+//   "chrome://mochitests/content/browser/devtools/client/responsive/test/browser/";
+
+// So if we had an effective TEST_ROOT, we'd use it here and run our test. But we don't.
+// The proposed "file_meta_1000_div.html" would just contain the html specified below as
+// a data URI.
+// const TEST_URL = TEST_ROOT + "file_meta_1000_div.html";
+
+// Instead we're going to mess with a security preference to allow a data URI to be
+// treated as same-origin. This doesn't work either for reasons that I don't understand.
+
+const TEST_URL =
+  "data:text/html;charset=utf-8," +
+  "<head>" +
+  '<meta name="viewport" content="width=device-width, initial-scale=1"/>' +
+  "</head>" +
+  '<body><div style="background:orange; width:1000px; height:1000px"></div></body>';
+
+addRDMTask(TEST_URL, async function ({ ui, manager }) {
+  // Turn on the prefs that force overlay scrollbars to always be visible.
+  await SpecialPowers.pushPrefEnv({
+    set: [["layout.testing.overlay-scrollbars.always-visible", true]],
+  });
+
+  info("--- Starting viewport test output ---");
+
+  const browser = ui.getViewportBrowser();
+
+  const expected = [false, true];
+  for (const e of expected) {
+    const message = "Meta Viewport " + (e ? "ON" : "OFF");
+
+    // Ensure meta viewport is set.
+    info(message + " setting meta viewport support.");
+    await setTouchAndMetaViewportSupport(ui, e.metaSupport);
+
+    // Get to the initial size and snapshot the window.
+    await setViewportSizeAndAwaitReflow(ui, manager, 300, 600);
+    const initialSnapshot = await snapshotWindow(browser);
+
+    // Move to the rotated size.
+    await setViewportSizeAndAwaitReflow(ui, manager, 600, 300);
+
+    // Reload the window.
+    await reloadBrowser();
+
+    // Go back to the initial size and take another snapshot.
+    await setViewportSizeAndAwaitReflow(ui, manager, 300, 600);
+    const finalSnapshot = await snapshotWindow(browser);
+
+    const result = compareSnapshots(initialSnapshot, finalSnapshot, true);
+    is(result[2], result[1], "Window snapshots should match.");
+  }
+});
diff --git a/devtools/client/responsive/test/browser/browser_viewport_resolution_restore.js b/devtools/client/responsive/test/browser/browser_viewport_resolution_restore.js
new file mode 100644
index 0000000000..6e5f10dff6
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_resolution_restore.js
@@ -0,0 +1,60 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that resolution is restored to its pre-RDM value after closing RDM.
+// Do this by using a chrome-only method to force resolution before opening
+// RDM, then letting RDM set its own preferred resolution due to the meta
+// viewport settings. When we close RDM and check resolution, we check for
+// something close to what we initially set, bracketed by these scaling
+// factors:
+const RESOLUTION_FACTOR_MIN = 0.96;
+const RESOLUTION_FACTOR_MAX = 1.04;
+
+info("--- Starting viewport test output ---");
+
+const WIDTH = 200;
+const HEIGHT = 200;
+const TESTS = [
+  { content: "width=600" },
+  { content: "width=600, initial-scale=1.0", res_restore: 0.782 },
+  { content: "width=device-width", res_restore: 3.4 },
+  { content: "width=device-width, initial-scale=2.0", res_restore: 1.1 },
+];
+
+for (const { content, res_restore } of TESTS) {
+  const TEST_URL =
+    `data:text/html;charset=utf-8,` +
+    `<html><head><meta name="viewport" content="${content}"></head>` +
+    `<body><div style="width:100%;background-color:green">${content}</div>` +
+    `</body></html>`;
+
+  addRDMTaskWithPreAndPost(
+    TEST_URL,
+    async function rdmPreTask({ browser }) {
+      if (res_restore) {
+        info(`Setting resolution to ${res_restore}.`);
+        browser.ownerGlobal.windowUtils.setResolutionAndScaleTo(res_restore);
+      } else {
+        info(`Not setting resolution.`);
+      }
+    },
+    async function rdmTask({ ui, manager }) {
+      info(`Resizing viewport and ensuring that meta viewport is on.`);
+      await setViewportSize(ui, manager, WIDTH, HEIGHT);
+      await setTouchAndMetaViewportSupport(ui, true);
+    },
+    async function rdmPostTask({ browser }) {
+      const resolution = browser.ownerGlobal.windowUtils.getResolution();
+      const res_target = res_restore ? res_restore : 1.0;
+
+      const res_min = res_target * RESOLUTION_FACTOR_MIN;
+      const res_max = res_target * RESOLUTION_FACTOR_MAX;
+      ok(
+        res_min <= resolution && res_max >= resolution,
+        `${content} resolution should be near ${res_target}, and we got ${resolution}.`
+      );
+    }
+  );
+}
diff --git a/devtools/client/responsive/test/browser/browser_viewport_state_after_close.js b/devtools/client/responsive/test/browser/browser_viewport_state_after_close.js
new file mode 100644
index 0000000000..3bac3b3e01
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_state_after_close.js
@@ -0,0 +1,51 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that after closing RDM the page goes back to its original state
+
+const TEST_URL =
+  "data:text/html;charset=utf-8,<style>h1 {width: 200px;} @media (hover:none) { h1 {width: 400px;background: tomato;}</style><h1>Hello</h1>";
+
+add_task(async function () {
+  const tab = await addTab(TEST_URL);
+
+  reloadOnTouchChange(false);
+  reloadOnUAChange(false);
+  await pushPref("devtools.responsive.touchSimulation.enabled", true);
+
+  is(await getH1Width(), 200, "<h1> has expected initial width");
+
+  for (let i = 0; i < 10; i++) {
+    info("Open responsive design mode");
+    await openRDM(tab);
+
+    await SpecialPowers.spawn(gBrowser.selectedBrowser, [], async function () {
+      const mql = content.matchMedia("(hover:none)");
+      if (mql.matches) {
+        return;
+      }
+      await new Promise(res =>
+        mql.addEventListener("change", res, { once: true })
+      );
+    });
+
+    is(
+      await getH1Width(),
+      400,
+      "<h1> has expected width when RDM and touch simulation are enabled"
+    );
+
+    info("Close responsive design mode");
+    await closeRDM(tab);
+
+    is(await getH1Width(), 200, "<h1> has expected width after closing RDM");
+  }
+});
+
+function getH1Width() {
+  return SpecialPowers.spawn(gBrowser.selectedBrowser, [], function () {
+    return content.document.querySelector("h1").getBoundingClientRect().width;
+  });
+}
diff --git a/devtools/client/responsive/test/browser/browser_viewport_zoom_resolution_invariant.js b/devtools/client/responsive/test/browser/browser_viewport_zoom_resolution_invariant.js
new file mode 100644
index 0000000000..69c6c0a95b
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_zoom_resolution_invariant.js
@@ -0,0 +1,60 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that resolution is as expected for different types of meta viewport
+// settings, as the RDM pane is zoomed to different values.
+
+const RESOLUTION_FACTOR_MIN = 0.96;
+const RESOLUTION_FACTOR_MAX = 1.04;
+const ZOOM_LEVELS = [
+  0.3, 0.5, 0.67, 0.8, 0.9, 1.0, 1.1, 1.2, 1.33, 1.5, 1.7, 2.0, 2.4, 3.0,
+  // TODO(emilio): These should pass.
+  // 0.3,
+  // 3.0,
+];
+
+info("--- Starting viewport test output ---");
+
+const WIDTH = 200;
+const HEIGHT = 200;
+const TESTS = [
+  { content: "width=600", res_target: 0.333 },
+  { content: "width=600, initial-scale=1.0", res_target: 1.0 },
+  { content: "width=device-width", res_target: 1.0 },
+  { content: "width=device-width, initial-scale=2.0", res_target: 2.0 },
+];
+
+for (const { content, res_target } of TESTS) {
+  const TEST_URL =
+    `data:text/html;charset=utf-8,` +
+    `<html><head><meta name="viewport" content="${content}"></head>` +
+    `<body><div style="width:100%;background-color:green">${content}</div>` +
+    `</body></html>`;
+
+  addRDMTask(TEST_URL, async function ({ ui, manager, browser }) {
+    await setViewportSize(ui, manager, WIDTH, HEIGHT);
+    await setTouchAndMetaViewportSupport(ui, true);
+
+    // Ensure we've reflowed the page at least once so that MVM has chosen
+    // the initial scale.
+    await promiseContentReflow(ui);
+
+    for (const zoom of ZOOM_LEVELS.concat([...ZOOM_LEVELS].reverse())) {
+      info(`Set zoom to ${zoom}.`);
+      await promiseRDMZoom(ui, browser, zoom);
+
+      const resolution = await spawnViewportTask(ui, {}, () => {
+        return content.windowUtils.getResolution();
+      });
+
+      const res_min = res_target * RESOLUTION_FACTOR_MIN;
+      const res_max = res_target * RESOLUTION_FACTOR_MAX;
+      ok(
+        res_min <= resolution && res_max >= resolution,
+        `${content} zoom ${zoom} resolution should be near ${res_target}, and we got ${resolution}.`
+      );
+    }
+  });
+}
diff --git a/devtools/client/responsive/test/browser/browser_viewport_zoom_toggle.js b/devtools/client/responsive/test/browser/browser_viewport_zoom_toggle.js
new file mode 100644
index 0000000000..400bfa99a9
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_viewport_zoom_toggle.js
@@ -0,0 +1,101 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Verify full zoom levels inherit RDM full zoom after exiting RDM.
+
+const TEST_URL = "https://example.com/";
+
+function getZoomForBrowser(browser) {
+  return ZoomManager.getZoomForBrowser(browser);
+}
+
+function setZoomForBrowser(browser, zoom) {
+  ZoomManager.setZoomForBrowser(browser, zoom);
+}
+
+addRDMTask(
+  null,
+  async function ({ message }) {
+    const INITIAL_ZOOM_LEVEL = 1;
+    const PRE_RDM_ZOOM_LEVEL = 1.5;
+    const MID_RDM_ZOOM_LEVEL = 2;
+
+    const tab = await addTab(TEST_URL);
+    const browser = tab.linkedBrowser;
+
+    await navigateTo(TEST_URL);
+
+    // Get the initial zoom level.
+    const initialOuterZoom = getZoomForBrowser(browser);
+    is(
+      initialOuterZoom,
+      INITIAL_ZOOM_LEVEL,
+      "Initial outer zoom should be " + INITIAL_ZOOM_LEVEL + "."
+    );
+
+    // Change the zoom level before we open RDM.
+    setZoomForBrowser(browser, PRE_RDM_ZOOM_LEVEL);
+
+    const preRDMOuterZoom = getZoomForBrowser(browser);
+    is(
+      preRDMOuterZoom,
+      PRE_RDM_ZOOM_LEVEL,
+      "Pre-RDM outer zoom should be " + PRE_RDM_ZOOM_LEVEL + "."
+    );
+
+    // Start RDM on the tab. This will fundamentally change the way that browser behaves.
+    // It will now pass all of its messages through to the RDM docshell, meaning that when
+    // we request zoom level from it now, we are getting the RDM zoom level.
+    const { ui } = await openRDM(tab);
+    await waitForDeviceAndViewportState(ui);
+
+    const uiDocShell = ui.toolWindow.docShell;
+
+    // Bug 1541692: openRDM behaves differently in the test harness than it does
+    // interactively. Interactively, many features of the container docShell -- including
+    // zoom -- are copied over to the RDM browser. In the test harness, this seems to first
+    // reset the docShell before toggling RDM, which makes checking the initial zoom of the
+    // RDM pane not useful.
+
+    const preZoomUIZoom = uiDocShell.browsingContext.fullZoom;
+    is(
+      preZoomUIZoom,
+      INITIAL_ZOOM_LEVEL,
+      "Pre-zoom UI zoom should be " + INITIAL_ZOOM_LEVEL + "."
+    );
+
+    // Set the zoom level. This should tunnel to the inner browser and leave the UI alone.
+    setZoomForBrowser(browser, MID_RDM_ZOOM_LEVEL);
+
+    // The UI zoom should be unchanged by this.
+    const postZoomUIZoom = uiDocShell.browsingContext.fullZoom;
+    is(
+      postZoomUIZoom,
+      preZoomUIZoom,
+      "UI zoom should be unchanged by RDM zoom."
+    );
+
+    // The RDM zoom should be changed.
+    const finalRDMZoom = getZoomForBrowser(browser);
+    is(
+      finalRDMZoom,
+      MID_RDM_ZOOM_LEVEL,
+      "RDM zoom should be " + MID_RDM_ZOOM_LEVEL + "."
+    );
+
+    // Leave RDM. This should cause the outer pane to take on the full zoom of the RDM pane.
+    await closeRDM(tab);
+
+    const finalOuterZoom = getZoomForBrowser(browser);
+    is(
+      finalOuterZoom,
+      finalRDMZoom,
+      "Final outer zoom should match last RDM zoom."
+    );
+
+    await removeTab(tab);
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_window_close.js b/devtools/client/responsive/test/browser/browser_window_close.js
new file mode 100644
index 0000000000..2af3d7fdd8
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_window_close.js
@@ -0,0 +1,43 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+addRDMTask(
+  null,
+  async function () {
+    const NEW_WINDOW_URL =
+      "data:text/html;charset=utf-8,New window opened via window.open";
+    const newWindowPromise = BrowserTestUtils.waitForNewWindow({
+      // Passing the url param so the Promise will resolve once DOMContentLoaded is emitted
+      // on the new window tab
+      url: NEW_WINDOW_URL,
+    });
+    window.open(NEW_WINDOW_URL, "_blank", "noopener,all");
+
+    const newWindow = await newWindowPromise;
+    ok(true, "Got new window");
+
+    info("Focus new window");
+    newWindow.focus();
+
+    info("Open RDM");
+    const tab = newWindow.gBrowser.selectedTab;
+    const { ui } = await openRDM(tab);
+    await waitForDeviceAndViewportState(ui);
+
+    ok(
+      ResponsiveUIManager.isActiveForTab(tab),
+      "ResponsiveUI should be active for tab when the window is closed"
+    );
+
+    // Close the window on a tab with an active responsive design UI and
+    // wait for the UI to gracefully shutdown.  This has leaked the window
+    // in the past.
+    info("Close the new window");
+    const offPromise = once(ResponsiveUIManager, "off");
+    await BrowserTestUtils.closeWindow(newWindow);
+    await offPromise;
+  },
+  { onlyPrefAndTask: true }
+);
diff --git a/devtools/client/responsive/test/browser/browser_window_sizing.js b/devtools/client/responsive/test/browser/browser_window_sizing.js
new file mode 100644
index 0000000000..6b8a558813
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_window_sizing.js
@@ -0,0 +1,93 @@
+/* Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that correct window sizing values are reported and unaffected by zoom. In
+// particular, we want to ensure that the values for the window's outer and screen
+// sizing values reflect the size of the viewport.
+
+const TEST_URL = "data:text/html;charset=utf-8,";
+const WIDTH = 375;
+const HEIGHT = 450;
+const ZOOM_LEVELS = [0.3, 0.5, 0.9, 1, 1.5, 2, 2.4];
+
+addRDMTask(
+  null,
+  async function () {
+    const tab = await addTab(TEST_URL);
+    const browser = tab.linkedBrowser;
+
+    const { ui, manager } = await openRDM(tab);
+    await waitForDeviceAndViewportState(ui);
+    await setViewportSize(ui, manager, WIDTH, HEIGHT);
+
+    info("Ensure outer size values are unchanged at different zoom levels.");
+    for (let i = 0; i < ZOOM_LEVELS.length; i++) {
+      info(`Setting zoom level to ${ZOOM_LEVELS[i]}`);
+      await promiseRDMZoom(ui, browser, ZOOM_LEVELS[i]);
+
+      await checkWindowOuterSize(ui, ZOOM_LEVELS[i]);
+      await checkWindowScreenSize(ui, ZOOM_LEVELS[i]);
+    }
+  },
+  { onlyPrefAndTask: true }
+);
+
+async function checkWindowOuterSize(ui, zoom_level) {
+  return SpecialPowers.spawn(
+    ui.getViewportBrowser(),
+    [{ width: WIDTH, height: HEIGHT, zoom: zoom_level }],
+    async function ({ width, height, zoom }) {
+      // Approximate the outer size value returned on the window content with the expected
+      // value. We should expect, at the very most, a 2px difference between the two due
+      // to floating point rounding errors that occur when scaling from inner size CSS
+      // integer values to outer size CSS integer values. See Part 1 of Bug 1107456.
+      // Some of the drift is also due to full zoom scaling effects; see Bug 1577775.
+      Assert.lessOrEqual(
+        Math.abs(content.outerWidth - width),
+        2,
+        `window.outerWidth zoom ${zoom} should be ${width} and we got ${content.outerWidth}.`
+      );
+      Assert.lessOrEqual(
+        Math.abs(content.outerHeight - height),
+        2,
+        `window.outerHeight zoom ${zoom} should be ${height} and we got ${content.outerHeight}.`
+      );
+    }
+  );
+}
+
+async function checkWindowScreenSize(ui, zoom_level) {
+  return SpecialPowers.spawn(
+    ui.getViewportBrowser(),
+    [{ width: WIDTH, height: HEIGHT, zoom: zoom_level }],
+    async function ({ width, height, zoom }) {
+      const { screen } = content;
+
+      Assert.lessOrEqual(
+        Math.abs(screen.availWidth - width),
+        2,
+        `screen.availWidth zoom ${zoom} should be ${width} and we got ${screen.availWidth}.`
+      );
+
+      Assert.lessOrEqual(
+        Math.abs(screen.availHeight - height),
+        2,
+        `screen.availHeight zoom ${zoom} should be ${height} and we got ${screen.availHeight}.`
+      );
+
+      Assert.lessOrEqual(
+        Math.abs(screen.width - width),
+        2,
+        `screen.width zoom " ${zoom} should be ${width} and we got ${screen.width}.`
+      );
+
+      Assert.lessOrEqual(
+        Math.abs(screen.height - height),
+        2,
+        `screen.height zoom " ${zoom} should be ${height} and we got ${screen.height}.`
+      );
+    }
+  );
+}
diff --git a/devtools/client/responsive/test/browser/browser_zoom.js b/devtools/client/responsive/test/browser/browser_zoom.js
new file mode 100644
index 0000000000..8eb0db3e18
--- /dev/null
+++ b/devtools/client/responsive/test/browser/browser_zoom.js
@@ -0,0 +1,27 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const URL = "data:text/html,foo";
+
+addRDMTaskWithPreAndPost(
+  URL,
+  async function pre({ browser }) {
+    info("Setting zoom");
+    // It's important that we do this so that we don't race with FullZoom's use
+    // of ContentSettings, which would reset the zoom.
+    FullZoom.setZoom(2.0, browser);
+  },
+  async function task({ browser, ui }) {
+    is(
+      ZoomManager.getZoomForBrowser(browser),
+      2.0,
+      "Zoom shouldn't have got lost"
+    );
+
+    // wait for the list of devices to be loaded to prevent pending promises
+    await waitForDeviceAndViewportState(ui);
+  },
+  async function post() {}
+);
diff --git a/devtools/client/responsive/test/browser/contextual_identity.html b/devtools/client/responsive/test/browser/contextual_identity.html
new file mode 100644
index 0000000000..05ad403fc6
--- /dev/null
+++ b/devtools/client/responsive/test/browser/contextual_identity.html
@@ -0,0 +1,6 @@
+<html><body>
+<script>
+"use strict";
+document.title = window.location.search;
+</script>
+</body></html>
diff --git a/devtools/client/responsive/test/browser/devices.json b/devtools/client/responsive/test/browser/devices.json
new file mode 100644
index 0000000000..46e842d3ff
--- /dev/null
+++ b/devtools/client/responsive/test/browser/devices.json
@@ -0,0 +1,658 @@
+{
+  "TYPES": [
+    "phones",
+    "tablets",
+    "laptops",
+    "televisions",
+    "consoles",
+    "watches"
+  ],
+  "phones": [
+    {
+      "name": "Firefox OS Flame",
+      "width": 320,
+      "height": 570,
+      "pixelRatio": 1.5,
+      "userAgent": "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+      "touch": true,
+      "firefoxOS": true,
+      "os": "fxos"
+    },
+    {
+      "name": "Alcatel One Touch Fire",
+      "width": 320,
+      "height": 480,
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+      "firefoxOS": true,
+      "os": "fxos"
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+    {
+      "name": "Alcatel One Touch Fire C",
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+      "os": "fxos"
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+    {
+      "name": "Alcatel One Touch Fire E",
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+      "os": "fxos"
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+      "os": "blackberryos"
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+      "os": "android"
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+      "os": "android"
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+      "os": "android"
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+      "os": "android",
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+      "os": "android",
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+      "os": "fxos"
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+      "os": "fxos"
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+      "height": 450,
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+      "os": "fxos"
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+      "firefoxOS": false,
+      "os": "fireos",
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+      "os": "ios",
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+      "os": "blackberryos"
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+      "os": "nintendo"
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+      "os": "playstation"
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+      "touch": true,
+      "firefoxOS": true,
+      "os": "android"
+    },
+    {
+      "name": "Samsung Gear Live",
+      "width": 320,
+      "height": 320,
+      "pixelRatio": 1,
+      "userAgent": "",
+      "touch": true,
+      "firefoxOS": true,
+      "os": "android"
+    }
+  ]
+}
diff --git a/devtools/client/responsive/test/browser/doc_contextmenu_inspect.html b/devtools/client/responsive/test/browser/doc_contextmenu_inspect.html
new file mode 100644
index 0000000000..ee325f5ad5
--- /dev/null
+++ b/devtools/client/responsive/test/browser/doc_contextmenu_inspect.html
@@ -0,0 +1,3 @@
+<html>
+  <div style="width: 500px; height: 500px; background: red;"></div>
+</html>
diff --git a/devtools/client/responsive/test/browser/doc_page_state.html b/devtools/client/responsive/test/browser/doc_page_state.html
new file mode 100644
index 0000000000..fb4d2acf01
--- /dev/null
+++ b/devtools/client/responsive/test/browser/doc_page_state.html
@@ -0,0 +1,16 @@
+<!doctype html>
+<html>
+  <head>
+    <title>Page State Test</title>
+    <style>
+      body {
+        height: 100vh;
+        background: red;
+      }
+      body.modified {
+        background: green;
+      }
+    </style>
+  </head>
+  <body onclick="this.classList.add('modified')"/>
+</html>
diff --git a/devtools/client/responsive/test/browser/doc_picker_link.html b/devtools/client/responsive/test/browser/doc_picker_link.html
new file mode 100644
index 0000000000..fd358be443
--- /dev/null
+++ b/devtools/client/responsive/test/browser/doc_picker_link.html
@@ -0,0 +1,12 @@
+<!-- Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!doctype html>
+<html>
+  <!-- The <a> should point to a valid page to check that page navigation will
+       not happen when picking the element -->
+  <a
+    href="about:home"
+    class="picker-link"
+    style="display:block; padding: 10px; width:50px; height:50px;"
+  >Link should not open when picking</a>
+</html>
diff --git a/devtools/client/responsive/test/browser/doc_toolbox_rule_view.css b/devtools/client/responsive/test/browser/doc_toolbox_rule_view.css
new file mode 100644
index 0000000000..7ed528635b
--- /dev/null
+++ b/devtools/client/responsive/test/browser/doc_toolbox_rule_view.css
@@ -0,0 +1,10 @@
+div {
+  width: 500px;
+  height: 10px;
+  background: purple;
+}
+@media screen and (max-width: 200px) {
+  div {
+    width: 100px;
+  }
+};
diff --git a/devtools/client/responsive/test/browser/doc_toolbox_rule_view.html b/devtools/client/responsive/test/browser/doc_toolbox_rule_view.html
new file mode 100644
index 0000000000..e4a311b7ec
--- /dev/null
+++ b/devtools/client/responsive/test/browser/doc_toolbox_rule_view.html
@@ -0,0 +1,4 @@
+<html>
+  <link rel="stylesheet" charset="UTF-8" type="text/css" media="screen" href="doc_toolbox_rule_view.css"/>
+  <div></div>
+</html>
diff --git a/devtools/client/responsive/test/browser/doc_with_remote_iframe_and_isolated_cross_origin_capabilities.sjs b/devtools/client/responsive/test/browser/doc_with_remote_iframe_and_isolated_cross_origin_capabilities.sjs
new file mode 100644
index 0000000000..ba53928bed
--- /dev/null
+++ b/devtools/client/responsive/test/browser/doc_with_remote_iframe_and_isolated_cross_origin_capabilities.sjs
@@ -0,0 +1,51 @@
+"use strict";
+
+function handleRequest(request, response) {
+  response.setHeader("Content-Type", "html", false);
+
+  // Check the params and set the cross-origin-opener policy headers if needed
+  const query = new URLSearchParams(request.queryString);
+  if (query.get("crossOriginIsolated") === "true") {
+    response.setHeader("Cross-Origin-Opener-Policy", "same-origin", false);
+  }
+
+  // We always want the iframe to have a different host from the top-level document.
+  const iframeHost =
+    request.host === "example.com" ? "example.org" : "example.com";
+  const iframeOrigin = `${request.scheme}://${iframeHost}`;
+
+  const IFRAME_HTML = `
+    <!doctype html>
+  <html>
+    <head>
+      <meta charset=utf8>
+      <script>
+        globalThis.initialOrientationAngle = screen.orientation.angle;
+        globalThis.initialOrientationType = screen.orientation.type;
+      </script>
+    </head>
+    <body>
+      <h1>Iframe</h1>
+    </body>
+  </html>`;
+
+  const HTML = `
+  <!doctype html>
+  <html>
+    <head>
+      <script>
+        globalThis.initialOrientationAngle = screen.orientation.angle;
+        globalThis.initialOrientationType = screen.orientation.type;
+      </script>
+      <meta charset=utf8>
+    </head>
+    <body>
+      <h1>Top-level document</h1>
+      <iframe src='${iframeOrigin}/document-builder.sjs?html=${encodeURI(
+    IFRAME_HTML
+  )}'></iframe>
+    </body>
+  </html>`;
+
+  response.write(HTML);
+}
diff --git a/devtools/client/responsive/test/browser/favicon.html b/devtools/client/responsive/test/browser/favicon.html
new file mode 100644
index 0000000000..2a0684007c
--- /dev/null
+++ b/devtools/client/responsive/test/browser/favicon.html
@@ -0,0 +1,8 @@
+<!doctype html>
+<html>
+  <head>
+    <title>Favicon Test</title>
+    <link rel="icon" href="favicon.ico">
+  </head>
+  <body/>
+</html>
diff --git a/devtools/client/responsive/test/browser/favicon.ico b/devtools/client/responsive/test/browser/favicon.ico
new file mode 100644
index 0000000000..d44438903b
--- /dev/null
+++ b/devtools/client/responsive/test/browser/favicon.ico
diff --git a/devtools/client/responsive/test/browser/geolocation.html b/devtools/client/responsive/test/browser/geolocation.html
new file mode 100644
index 0000000000..df0014dd02
--- /dev/null
+++ b/devtools/client/responsive/test/browser/geolocation.html
@@ -0,0 +1,13 @@
+<!doctype html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>Geolocation permission test</title>
+  </head>
+  <body>
+    <script type="text/javascript">
+      "use strict";
+      navigator.geolocation.getCurrentPosition(function(pos) {});
+    </script>
+  </body>
+</html>
diff --git a/devtools/client/responsive/test/browser/head.js b/devtools/client/responsive/test/browser/head.js
new file mode 100644
index 0000000000..d2b42316a9
--- /dev/null
+++ b/devtools/client/responsive/test/browser/head.js
@@ -0,0 +1,1008 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/* eslint no-unused-vars: [2, {"vars": "local"}] */
+
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/devtools/client/shared/test/shared-head.js",
+  this
+);
+
+// Import helpers for the inspector that are also shared with others
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/devtools/client/inspector/test/shared-head.js",
+  this
+);
+
+// Load APZ test utils so we properly wait after resize
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/gfx/layers/apz/test/mochitest/apz_test_utils.js",
+  this
+);
+Services.scriptloader.loadSubScript(
+  "chrome://mochikit/content/tests/SimpleTest/paint_listener.js",
+  this
+);
+
+const {
+  _loadPreferredDevices,
+} = require("resource://devtools/client/responsive/actions/devices.js");
+const {
+  getStr,
+} = require("resource://devtools/client/responsive/utils/l10n.js");
+const {
+  getTopLevelWindow,
+} = require("resource://devtools/client/responsive/utils/window.js");
+const {
+  addDevice,
+  removeDevice,
+  removeLocalDevices,
+} = require("resource://devtools/client/shared/devices.js");
+const { KeyCodes } = require("resource://devtools/client/shared/keycodes.js");
+const asyncStorage = require("resource://devtools/shared/async-storage.js");
+const localTypes = require("resource://devtools/client/responsive/types.js");
+
+loader.lazyRequireGetter(
+  this,
+  "ResponsiveUIManager",
+  "resource://devtools/client/responsive/manager.js"
+);
+loader.lazyRequireGetter(
+  this,
+  "message",
+  "resource://devtools/client/responsive/utils/message.js"
+);
+
+const E10S_MULTI_ENABLED =
+  Services.prefs.getIntPref("dom.ipc.processCount") > 1;
+const TEST_URI_ROOT =
+  "http://example.com/browser/devtools/client/responsive/test/browser/";
+const RELOAD_CONDITION_PREF_PREFIX = "devtools.responsive.reloadConditions.";
+const DEFAULT_UA = Cc["@mozilla.org/network/protocol;1?name=http"].getService(
+  Ci.nsIHttpProtocolHandler
+).userAgent;
+
+SimpleTest.requestCompleteLog();
+SimpleTest.waitForExplicitFinish();
+
+// Toggling the RDM UI involves several docShell swap operations, which are somewhat slow
+// on debug builds. Usually we are just barely over the limit, so a blanket factor of 2
+// should be enough.
+requestLongerTimeout(2);
+
+// The appearance of this notification causes intermittent behavior in some tests that
+// send mouse events, since it causes the content to shift when it appears.
+Services.prefs.setBoolPref(
+  "devtools.responsive.reloadNotification.enabled",
+  false
+);
+// Don't show the setting onboarding tooltip in the test suites.
+Services.prefs.setBoolPref("devtools.responsive.show-setting-tooltip", false);
+
+registerCleanupFunction(async () => {
+  Services.prefs.clearUserPref(
+    "devtools.responsive.reloadNotification.enabled"
+  );
+  Services.prefs.clearUserPref("devtools.responsive.html.displayedDeviceList");
+  Services.prefs.clearUserPref(
+    "devtools.responsive.reloadConditions.touchSimulation"
+  );
+  Services.prefs.clearUserPref(
+    "devtools.responsive.reloadConditions.userAgent"
+  );
+  Services.prefs.clearUserPref("devtools.responsive.show-setting-tooltip");
+  Services.prefs.clearUserPref("devtools.responsive.showUserAgentInput");
+  Services.prefs.clearUserPref("devtools.responsive.touchSimulation.enabled");
+  Services.prefs.clearUserPref("devtools.responsive.userAgent");
+  Services.prefs.clearUserPref("devtools.responsive.viewport.height");
+  Services.prefs.clearUserPref("devtools.responsive.viewport.pixelRatio");
+  Services.prefs.clearUserPref("devtools.responsive.viewport.width");
+  await asyncStorage.removeItem("devtools.responsive.deviceState");
+  await removeLocalDevices();
+
+  delete window.waitForAllPaintsFlushed;
+  delete window.waitForAllPaints;
+  delete window.promiseAllPaintsDone;
+});
+
+/**
+ * Adds a new test task that adds a tab with the given URL, awaits the
+ * preTask (if provided), opens responsive design mode, awaits the task,
+ * closes responsive design mode, awaits the postTask (if provided), and
+ * removes the tab. The final argument is an options object, with these
+ * optional properties:
+ *
+ * onlyPrefAndTask: if truthy, only the pref will be set and the task
+ *   will be called, with none of the tab creation/teardown or open/close
+ *   of RDM (default false).
+ * waitForDeviceList: if truthy, the function will wait until the device
+ *   list is loaded before calling the task (default false).
+ *
+ * Example usage:
+ *
+ *   addRDMTaskWithPreAndPost(
+ *     TEST_URL,
+ *     async function preTask({ message, browser }) {
+ *       // Your pre-task goes here...
+ *     },
+ *     async function task({ ui, manager, message, browser, preTaskValue, tab }) {
+ *       // Your task goes here...
+ *     },
+ *     async function postTask({ message, browser, preTaskValue, taskValue }) {
+ *       // Your post-task goes here...
+ *     },
+ *     { waitForDeviceList: true }
+ *   );
+ */
+function addRDMTaskWithPreAndPost(url, preTask, task, postTask, options) {
+  let onlyPrefAndTask = false;
+  let waitForDeviceList = false;
+  if (typeof options == "object") {
+    onlyPrefAndTask = !!options.onlyPrefAndTask;
+    waitForDeviceList = !!options.waitForDeviceList;
+  }
+
+  add_task(async function () {
+    let tab;
+    let browser;
+    let preTaskValue = null;
+    let taskValue = null;
+    let ui;
+    let manager;
+
+    if (!onlyPrefAndTask) {
+      tab = await addTab(url);
+      browser = tab.linkedBrowser;
+
+      if (preTask) {
+        preTaskValue = await preTask({ message, browser });
+      }
+
+      const rdmValues = await openRDM(tab, { waitForDeviceList });
+      ui = rdmValues.ui;
+      manager = rdmValues.manager;
+    }
+
+    try {
+      taskValue = await task({
+        ui,
+        manager,
+        message,
+        browser,
+        preTaskValue,
+        tab,
+      });
+    } catch (err) {
+      ok(false, "Got an error: " + DevToolsUtils.safeErrorString(err));
+    }
+
+    if (!onlyPrefAndTask) {
+      await closeRDM(tab);
+      if (postTask) {
+        await postTask({
+          message,
+          browser,
+          preTaskValue,
+          taskValue,
+        });
+      }
+      await removeTab(tab);
+    }
+
+    // Flush prefs to not only undo our earlier change, but also undo
+    // any changes made by the tasks.
+    await SpecialPowers.flushPrefEnv();
+  });
+}
+
+/**
+ * This is a simplified version of addRDMTaskWithPreAndPost. Adds a new test
+ * task that adds a tab with the given URL, opens responsive design mode,
+ * closes responsive design mode, and removes the tab.
+ *
+ * Example usage:
+ *
+ *   addRDMTask(
+ *     TEST_URL,
+ *     async function task({ ui, manager, message, browser }) {
+ *       // Your task goes here...
+ *     },
+ *     { waitForDeviceList: true }
+ *   );
+ */
+function addRDMTask(rdmURL, rdmTask, options) {
+  addRDMTaskWithPreAndPost(rdmURL, undefined, rdmTask, undefined, options);
+}
+
+async function spawnViewportTask(ui, args, task) {
+  // Await a reflow after the task.
+  const result = await ContentTask.spawn(ui.getViewportBrowser(), args, task);
+  await promiseContentReflow(ui);
+  return result;
+}
+
+function waitForFrameLoad(ui, targetURL) {
+  return spawnViewportTask(ui, { targetURL }, async function (args) {
+    if (
+      (content.document.readyState == "complete" ||
+        content.document.readyState == "interactive") &&
+      content.location.href == args.targetURL
+    ) {
+      return;
+    }
+    await ContentTaskUtils.waitForEvent(this, "DOMContentLoaded");
+  });
+}
+
+function waitForViewportResizeTo(ui, width, height) {
+  return new Promise(function (resolve) {
+    const isSizeMatching = data => data.width == width && data.height == height;
+
+    // If the viewport has already the expected size, we resolve the promise immediately.
+    const size = ui.getViewportSize();
+    if (isSizeMatching(size)) {
+      info(`Viewport already resized to ${width} x ${height}`);
+      resolve();
+      return;
+    }
+
+    // Otherwise, we'll listen to the viewport's resize event, and the
+    // browser's load end; since a racing condition can happen, where the
+    // viewport's listener is added after the resize, because the viewport's
+    // document was reloaded; therefore the test would hang forever.
+    // See bug 1302879.
+    const browser = ui.getViewportBrowser();
+
+    const onContentResize = data => {
+      if (!isSizeMatching(data)) {
+        return;
+      }
+      ui.off("content-resize", onContentResize);
+      browser.removeEventListener("mozbrowserloadend", onBrowserLoadEnd);
+      info(`Got content-resize to ${width} x ${height}`);
+      resolve();
+    };
+
+    const onBrowserLoadEnd = async function () {
+      const data = ui.getViewportSize(ui);
+      onContentResize(data);
+    };
+
+    info(`Waiting for viewport-resize to ${width} x ${height}`);
+    // We're changing the viewport size, which may also change the content
+    // size. We wait on the viewport resize event, and check for the
+    // desired size.
+    ui.on("content-resize", onContentResize);
+    browser.addEventListener("mozbrowserloadend", onBrowserLoadEnd, {
+      once: true,
+    });
+  });
+}
+
+var setViewportSize = async function (ui, manager, width, height) {
+  const size = ui.getViewportSize();
+  info(
+    `Current size: ${size.width} x ${size.height}, ` +
+      `set to: ${width} x ${height}`
+  );
+  if (size.width != width || size.height != height) {
+    const resized = waitForViewportResizeTo(ui, width, height);
+    ui.setViewportSize({ width, height });
+    await resized;
+  }
+};
+
+// This performs the same function as setViewportSize, but additionally
+// ensures that reflow of the viewport has completed.
+var setViewportSizeAndAwaitReflow = async function (
+  ui,
+  manager,
+  width,
+  height
+) {
+  await setViewportSize(ui, manager, width, height);
+  await promiseContentReflow(ui);
+  await promiseApzFlushedRepaints();
+};
+
+function getViewportDevicePixelRatio(ui) {
+  return SpecialPowers.spawn(ui.getViewportBrowser(), [], async function () {
+    // Note that devicePixelRatio doesn't return the override to privileged
+    // code, see bug 1759962.
+    return content.browsingContext.overrideDPPX || content.devicePixelRatio;
+  });
+}
+
+function getElRect(selector, win) {
+  const el = win.document.querySelector(selector);
+  return el.getBoundingClientRect();
+}
+
+/**
+ * Drag an element identified by 'selector' by [x,y] amount. Returns
+ * the rect of the dragged element as it was before drag.
+ */
+function dragElementBy(selector, x, y, ui) {
+  const browserWindow = ui.getBrowserWindow();
+  const rect = getElRect(selector, browserWindow);
+  const startPoint = {
+    clientX: Math.floor(rect.left + rect.width / 2),
+    clientY: Math.floor(rect.top + rect.height / 2),
+  };
+  const endPoint = [startPoint.clientX + x, startPoint.clientY + y];
+
+  EventUtils.synthesizeMouseAtPoint(
+    startPoint.clientX,
+    startPoint.clientY,
+    { type: "mousedown" },
+    browserWindow
+  );
+
+  // mousemove and mouseup are regular DOM listeners
+  EventUtils.synthesizeMouseAtPoint(
+    ...endPoint,
+    { type: "mousemove" },
+    browserWindow
+  );
+  EventUtils.synthesizeMouseAtPoint(
+    ...endPoint,
+    { type: "mouseup" },
+    browserWindow
+  );
+
+  return rect;
+}
+
+/**
+ * Resize the viewport and check that the resize happened as expected.
+ *
+ * @param {ResponsiveUI} ui
+ *        The ResponsiveUI instance.
+ * @param {String} selector
+ *        The css selector of the resize handler, eg .viewport-horizontal-resize-handle.
+ * @param {Array<number>} moveBy
+ *        Array of 2 integers representing the x,y distance of the resize action.
+ * @param {Array<number>} moveBy
+ *        Array of 2 integers representing the actual resize performed.
+ * @param {Object} options
+ * @param {Boolean} options.hasDevice
+ *        Whether a device is currently set and will be overridden by the resize
+ */
+async function testViewportResize(
+  ui,
+  selector,
+  moveBy,
+  expectedHandleMove,
+  { hasDevice } = {}
+) {
+  let deviceRemoved;
+  let waitForDevToolsReload;
+  if (hasDevice) {
+    // If a device was defined, a reload will be triggered by the resize,
+    // wait for devtools to reload completely.
+    waitForDevToolsReload = await watchForDevToolsReload(
+      ui.getViewportBrowser()
+    );
+    // and wait for the device-associaton-removed event.
+    deviceRemoved = once(ui, "device-association-removed");
+  }
+
+  const resized = ui.once("viewport-resize-dragend");
+  const startRect = dragElementBy(selector, ...moveBy, ui);
+  await resized;
+
+  const endRect = getElRect(selector, ui.getBrowserWindow());
+  is(
+    endRect.left - startRect.left,
+    expectedHandleMove[0],
+    `The x move of ${selector} is as expected`
+  );
+  is(
+    endRect.top - startRect.top,
+    expectedHandleMove[1],
+    `The y move of ${selector} is as expected`
+  );
+
+  if (hasDevice) {
+    const { reloadTriggered } = await deviceRemoved;
+    if (reloadTriggered) {
+      await waitForDevToolsReload();
+    }
+  }
+}
+
+async function openDeviceModal(ui) {
+  const { document, store } = ui.toolWindow;
+
+  info("Opening device modal through device selector.");
+  const onModalOpen = waitUntilState(store, state => state.devices.isModalOpen);
+  await selectMenuItem(
+    ui,
+    "#device-selector",
+    getStr("responsive.editDeviceList2")
+  );
+  await onModalOpen;
+
+  const modal = document.getElementById("device-modal-wrapper");
+  ok(
+    modal.classList.contains("opened") && !modal.classList.contains("closed"),
+    "The device modal is displayed."
+  );
+}
+
+async function selectMenuItem({ toolWindow }, selector, value) {
+  const { document } = toolWindow;
+
+  const button = document.querySelector(selector);
+  isnot(
+    button,
+    null,
+    `Selector "${selector}" should match an existing element.`
+  );
+
+  info(`Selecting ${value} in ${selector}.`);
+
+  await testMenuItems(toolWindow, button, items => {
+    const menuItem = findMenuItem(items, value);
+    isnot(
+      menuItem,
+      undefined,
+      `Value "${value}" should match an existing menu item.`
+    );
+    menuItem.click();
+  });
+}
+
+/**
+ * Runs the menu items from the button's context menu against a test function.
+ *
+ * @param  {Window} toolWindow
+ *         A window reference.
+ * @param  {Element} button
+ *         The button that will show a context menu when clicked.
+ * @param  {Function} testFn
+ *         A test function that will be ran with the found menu item in the context menu
+ *         as an argument.
+ */
+async function testMenuItems(toolWindow, button, testFn) {
+  // The context menu appears only in the top level window, which is different from
+  // the inner toolWindow.
+  const win = getTopLevelWindow(toolWindow);
+
+  await new Promise(resolve => {
+    win.document.addEventListener(
+      "popupshown",
+      async () => {
+        if (button.id === "device-selector") {
+          const popup = toolWindow.document.querySelector(
+            "#device-selector-menu"
+          );
+          const menuItems = [...popup.querySelectorAll(".menuitem > .command")];
+
+          testFn(menuItems);
+
+          if (popup.classList.contains("tooltip-visible")) {
+            // Close the tooltip explicitly.
+            button.click();
+            await waitUntil(() => !popup.classList.contains("tooltip-visible"));
+          }
+        } else {
+          const popup = win.document.querySelector(
+            'menupopup[menu-api="true"]'
+          );
+          const menuItems = [...popup.children];
+
+          testFn(menuItems);
+
+          popup.hidePopup();
+        }
+
+        resolve();
+      },
+      { once: true }
+    );
+
+    button.click();
+  });
+}
+
+const selectDevice = async (ui, value) => {
+  const browser = ui.getViewportBrowser();
+  const waitForDevToolsReload = await watchForDevToolsReload(browser);
+
+  const onDeviceChanged = once(ui, "device-changed");
+  await selectMenuItem(ui, "#device-selector", value);
+  const { reloadTriggered } = await onDeviceChanged;
+  if (reloadTriggered) {
+    await waitForDevToolsReload();
+  }
+};
+
+const selectDevicePixelRatio = (ui, value) =>
+  selectMenuItem(ui, "#device-pixel-ratio-menu", `DPR: ${value}`);
+
+const selectNetworkThrottling = (ui, value) =>
+  Promise.all([
+    once(ui, "network-throttling-changed"),
+    selectMenuItem(ui, "#network-throttling-menu", value),
+  ]);
+
+function getSessionHistory(browser) {
+  if (Services.appinfo.sessionHistoryInParent) {
+    const browsingContext = browser.browsingContext;
+    const uri = browsingContext.currentWindowGlobal.documentURI.displaySpec;
+    const history = browsingContext.sessionHistory;
+    const body = ContentTask.spawn(
+      browser,
+      browsingContext,
+      function (
+        // eslint-disable-next-line no-shadow
+        browsingContext
+      ) {
+        const docShell = browsingContext.docShell.QueryInterface(
+          Ci.nsIWebNavigation
+        );
+        return docShell.document.body;
+      }
+    );
+    const { SessionHistory } = ChromeUtils.importESModule(
+      "resource://gre/modules/sessionstore/SessionHistory.sys.mjs"
+    );
+    return SessionHistory.collectFromParent(uri, body, history);
+  }
+  return ContentTask.spawn(browser, null, function () {
+    const { SessionHistory } = ChromeUtils.importESModule(
+      "resource://gre/modules/sessionstore/SessionHistory.sys.mjs"
+    );
+    return SessionHistory.collect(docShell);
+  });
+}
+
+function getContentSize(ui) {
+  return spawnViewportTask(ui, {}, () => ({
+    width: content.screen.width,
+    height: content.screen.height,
+  }));
+}
+
+function getViewportScroll(ui) {
+  return spawnViewportTask(ui, {}, () => ({
+    x: content.scrollX,
+    y: content.scrollY,
+  }));
+}
+
+async function waitForPageShow(browser) {
+  const tab = gBrowser.getTabForBrowser(browser);
+  const ui = ResponsiveUIManager.getResponsiveUIForTab(tab);
+  if (ui) {
+    browser = ui.getViewportBrowser();
+  }
+  info(
+    "Waiting for pageshow from " + (ui ? "responsive" : "regular") + " browser"
+  );
+  // Need to wait an extra tick after pageshow to ensure everyone is up-to-date,
+  // hence the waitForTick.
+  await BrowserTestUtils.waitForContentEvent(browser, "pageshow");
+  return waitForTick();
+}
+
+function waitForViewportScroll(ui) {
+  return BrowserTestUtils.waitForContentEvent(
+    ui.getViewportBrowser(),
+    "scroll",
+    true
+  );
+}
+
+async function back(browser) {
+  const waitForDevToolsReload = await watchForDevToolsReload(browser);
+  const onPageShow = waitForPageShow(browser);
+
+  browser.goBack();
+
+  await onPageShow;
+  await waitForDevToolsReload();
+}
+
+async function forward(browser) {
+  const waitForDevToolsReload = await watchForDevToolsReload(browser);
+  const onPageShow = waitForPageShow(browser);
+
+  browser.goForward();
+
+  await onPageShow;
+  await waitForDevToolsReload();
+}
+
+function addDeviceForTest(device) {
+  info(`Adding Test Device "${device.name}" to the list.`);
+  addDevice(device);
+
+  registerCleanupFunction(() => {
+    // Note that assertions in cleanup functions are not displayed unless they failed.
+    ok(
+      removeDevice(device),
+      `Removed Test Device "${device.name}" from the list.`
+    );
+  });
+}
+
+async function waitForClientClose(ui) {
+  info("Waiting for RDM devtools client to close");
+  await ui.commands.client.once("closed");
+  info("RDM's devtools client is now closed");
+}
+
+async function testDevicePixelRatio(ui, expected) {
+  const dppx = await getViewportDevicePixelRatio(ui);
+  is(dppx, expected, `devicePixelRatio should be set to ${expected}`);
+}
+
+async function testTouchEventsOverride(ui, expected) {
+  const { document } = ui.toolWindow;
+  const touchButton = document.getElementById("touch-simulation-button");
+
+  const flag = gBrowser.selectedBrowser.browsingContext.touchEventsOverride;
+
+  is(
+    flag === "enabled",
+    expected,
+    `Touch events override should be ${expected ? "enabled" : "disabled"}`
+  );
+  is(
+    touchButton.classList.contains("checked"),
+    expected,
+    `Touch simulation button should be ${expected ? "" : "in"}active.`
+  );
+}
+
+function testViewportDeviceMenuLabel(ui, expectedDeviceName) {
+  info("Test viewport's device select label");
+
+  const button = ui.toolWindow.document.querySelector("#device-selector");
+  ok(
+    button.textContent.includes(expectedDeviceName),
+    `Device Select value ${button.textContent} should be: ${expectedDeviceName}`
+  );
+}
+
+async function toggleTouchSimulation(ui) {
+  const { document } = ui.toolWindow;
+  const browser = ui.getViewportBrowser();
+
+  const touchButton = document.getElementById("touch-simulation-button");
+  const wasChecked = touchButton.classList.contains("checked");
+  const onTouchSimulationChanged = once(ui, "touch-simulation-changed");
+  const waitForDevToolsReload = await watchForDevToolsReload(browser);
+  const onTouchButtonStateChanged = waitFor(
+    () => touchButton.classList.contains("checked") !== wasChecked
+  );
+
+  touchButton.click();
+  await Promise.all([
+    onTouchSimulationChanged,
+    onTouchButtonStateChanged,
+    waitForDevToolsReload(),
+  ]);
+}
+
+async function testUserAgent(ui, expected) {
+  const { document } = ui.toolWindow;
+  const userAgentInput = document.getElementById("user-agent-input");
+
+  if (expected === DEFAULT_UA) {
+    is(userAgentInput.value, "", "UA input should be empty");
+  } else {
+    is(userAgentInput.value, expected, `UA input should be set to ${expected}`);
+  }
+
+  await testUserAgentFromBrowser(ui.getViewportBrowser(), expected);
+}
+
+async function testUserAgentFromBrowser(browser, expected) {
+  const ua = await SpecialPowers.spawn(browser, [], async function () {
+    return content.navigator.userAgent;
+  });
+  is(ua, expected, `UA should be set to ${expected}`);
+}
+
+function testViewportDimensions(ui, w, h) {
+  const viewport = ui.viewportElement;
+
+  is(
+    ui.toolWindow.getComputedStyle(viewport).getPropertyValue("width"),
+    `${w}px`,
+    `Viewport should have width of ${w}px`
+  );
+  is(
+    ui.toolWindow.getComputedStyle(viewport).getPropertyValue("height"),
+    `${h}px`,
+    `Viewport should have height of ${h}px`
+  );
+}
+
+async function changeUserAgentInput(ui, value) {
+  const { Simulate } = ui.toolWindow.require(
+    "resource://devtools/client/shared/vendor/react-dom-test-utils.js"
+  );
+  const { document, store } = ui.toolWindow;
+  const browser = ui.getViewportBrowser();
+
+  const userAgentInput = document.getElementById("user-agent-input");
+  userAgentInput.value = value;
+  Simulate.change(userAgentInput);
+
+  const userAgentChanged = waitUntilState(
+    store,
+    state => state.ui.userAgent === value
+  );
+  const changed = once(ui, "user-agent-changed");
+
+  const waitForDevToolsReload = await watchForDevToolsReload(browser);
+  Simulate.keyUp(userAgentInput, { keyCode: KeyCodes.DOM_VK_RETURN });
+  await Promise.all([changed, waitForDevToolsReload(), userAgentChanged]);
+}
+
+/**
+ * Assuming the device modal is open and the device adder form is shown, this helper
+ * function adds `device` via the form, saves it, and waits for it to appear in the store.
+ */
+function addDeviceInModal(ui, device) {
+  const { Simulate } = ui.toolWindow.require(
+    "resource://devtools/client/shared/vendor/react-dom-test-utils.js"
+  );
+  const { document, store } = ui.toolWindow;
+
+  const nameInput = document.querySelector("#device-form-name input");
+  const [widthInput, heightInput] = document.querySelectorAll(
+    "#device-form-size input"
+  );
+  const pixelRatioInput = document.querySelector(
+    "#device-form-pixel-ratio input"
+  );
+  const userAgentInput = document.querySelector(
+    "#device-form-user-agent input"
+  );
+  const touchInput = document.querySelector("#device-form-touch input");
+
+  nameInput.value = device.name;
+  Simulate.change(nameInput);
+  widthInput.value = device.width;
+  Simulate.change(widthInput);
+  Simulate.blur(widthInput);
+  heightInput.value = device.height;
+  Simulate.change(heightInput);
+  Simulate.blur(heightInput);
+  pixelRatioInput.value = device.pixelRatio;
+  Simulate.change(pixelRatioInput);
+  userAgentInput.value = device.userAgent;
+  Simulate.change(userAgentInput);
+  touchInput.checked = device.touch;
+  Simulate.change(touchInput);
+
+  const existingCustomDevices = store.getState().devices.custom.length;
+  const adderSave = document.querySelector("#device-form-save");
+  const saved = waitUntilState(
+    store,
+    state => state.devices.custom.length == existingCustomDevices + 1
+  );
+  Simulate.click(adderSave);
+  return saved;
+}
+
+async function editDeviceInModal(ui, device, newDevice) {
+  const { Simulate } = ui.toolWindow.require(
+    "resource://devtools/client/shared/vendor/react-dom-test-utils.js"
+  );
+  const { document, store } = ui.toolWindow;
+
+  const nameInput = document.querySelector("#device-form-name input");
+  const [widthInput, heightInput] = document.querySelectorAll(
+    "#device-form-size input"
+  );
+  const pixelRatioInput = document.querySelector(
+    "#device-form-pixel-ratio input"
+  );
+  const userAgentInput = document.querySelector(
+    "#device-form-user-agent input"
+  );
+  const touchInput = document.querySelector("#device-form-touch input");
+
+  nameInput.value = newDevice.name;
+  Simulate.change(nameInput);
+  widthInput.value = newDevice.width;
+  Simulate.change(widthInput);
+  Simulate.blur(widthInput);
+  heightInput.value = newDevice.height;
+  Simulate.change(heightInput);
+  Simulate.blur(heightInput);
+  pixelRatioInput.value = newDevice.pixelRatio;
+  Simulate.change(pixelRatioInput);
+  userAgentInput.value = newDevice.userAgent;
+  Simulate.change(userAgentInput);
+  touchInput.checked = newDevice.touch;
+  Simulate.change(touchInput);
+
+  const existingCustomDevices = store.getState().devices.custom.length;
+  const formSave = document.querySelector("#device-form-save");
+
+  const saved = waitUntilState(
+    store,
+    state =>
+      state.devices.custom.length == existingCustomDevices &&
+      state.devices.custom.find(({ name }) => name == newDevice.name) &&
+      !state.devices.custom.find(({ name }) => name == device.name)
+  );
+
+  // Editing a custom device triggers a "device-change" message.
+  // Wait for the `device-changed` event to avoid unfinished requests during the
+  // tests.
+  const onDeviceChanged = ui.once("device-changed");
+
+  Simulate.click(formSave);
+
+  await onDeviceChanged;
+  return saved;
+}
+
+function findMenuItem(menuItems, name) {
+  return menuItems.find(menuItem => menuItem.textContent.includes(name));
+}
+
+function reloadOnUAChange(enabled) {
+  const pref = RELOAD_CONDITION_PREF_PREFIX + "userAgent";
+  Services.prefs.setBoolPref(pref, enabled);
+}
+
+function reloadOnTouchChange(enabled) {
+  const pref = RELOAD_CONDITION_PREF_PREFIX + "touchSimulation";
+  Services.prefs.setBoolPref(pref, enabled);
+}
+
+function rotateViewport(ui) {
+  const { document } = ui.toolWindow;
+  const rotateButton = document.getElementById("rotate-button");
+  rotateButton.click();
+}
+
+// Call this to switch between on/off support for meta viewports.
+async function setTouchAndMetaViewportSupport(ui, value) {
+  await ui.updateTouchSimulation(value);
+  info("Reload so the new configuration applies cleanly to the page");
+  await reloadBrowser();
+
+  await promiseContentReflow(ui);
+}
+
+// This function checks that zoom, layout viewport width and height
+// are all as expected.
+async function testViewportZoomWidthAndHeight(msg, ui, zoom, width, height) {
+  if (typeof zoom !== "undefined") {
+    const resolution = await spawnViewportTask(ui, {}, function () {
+      return content.windowUtils.getResolution();
+    });
+    is(resolution, zoom, msg + " should have expected zoom.");
+  }
+
+  if (typeof width !== "undefined" || typeof height !== "undefined") {
+    const innerSize = await spawnViewportTask(ui, {}, function () {
+      return {
+        width: content.innerWidth,
+        height: content.innerHeight,
+      };
+    });
+    if (typeof width !== "undefined") {
+      is(innerSize.width, width, msg + " should have expected inner width.");
+    }
+    if (typeof height !== "undefined") {
+      is(innerSize.height, height, msg + " should have expected inner height.");
+    }
+  }
+}
+
+function promiseContentReflow(ui) {
+  return SpecialPowers.spawn(ui.getViewportBrowser(), [], async function () {
+    return new Promise(resolve => {
+      content.window.requestAnimationFrame(() => {
+        content.window.requestAnimationFrame(resolve);
+      });
+    });
+  });
+}
+
+// This function returns a promise that will be resolved when the
+// RDM zoom has been set and the content has finished rescaling
+// to the new size.
+async function promiseRDMZoom(ui, browser, zoom) {
+  const currentZoom = ZoomManager.getZoomForBrowser(browser);
+  if (currentZoom.toFixed(2) == zoom.toFixed(2)) {
+    return;
+  }
+
+  const width = browser.getBoundingClientRect().width;
+
+  ZoomManager.setZoomForBrowser(browser, zoom);
+
+  // RDM resizes the browser as a result of a zoom change, so we wait for that.
+  //
+  // This also has the side effect of updating layout which ensures that any
+  // remote frame dimension update message gets there in time.
+  await BrowserTestUtils.waitForCondition(function () {
+    return browser.getBoundingClientRect().width != width;
+  });
+}
+
+async function waitForDeviceAndViewportState(ui) {
+  const { store } = ui.toolWindow;
+
+  // Wait until the viewport has been added and the device list has been loaded
+  await waitUntilState(
+    store,
+    state =>
+      state.viewports.length == 1 &&
+      state.devices.listState == localTypes.loadableState.LOADED
+  );
+}
+
+/**
+ * Wait for the content page to be rendered with the expected pixel ratio.
+ *
+ * @param {ResponsiveUI} ui
+ *        The ResponsiveUI instance.
+ * @param {Integer} expected
+ *        The expected dpr for the content page.
+ * @param {Object} options
+ * @param {Boolean} options.waitForTargetConfiguration
+ *        If set to true, the function will wait for the targetConfigurationCommand configuration
+ *        to reflect the ratio that was set. This can be used to prevent pending requests
+ *        to the actor.
+ */
+async function waitForDevicePixelRatio(
+  ui,
+  expected,
+  { waitForTargetConfiguration } = {}
+) {
+  const dpx = await SpecialPowers.spawn(
+    ui.getViewportBrowser(),
+    [{ expected }],
+    function (args) {
+      const getDpr = function () {
+        return content.browsingContext.overrideDPPX || content.devicePixelRatio;
+      };
+      const initial = getDpr();
+      info(
+        `Listening for pixel ratio change ` +
+          `(current: ${initial}, expected: ${args.expected})`
+      );
+      return new Promise(resolve => {
+        const mql = content.matchMedia(`(resolution: ${args.expected}dppx)`);
+        if (mql.matches) {
+          info(`Ratio already changed to ${args.expected}dppx`);
+          resolve(getDpr());
+          return;
+        }
+        mql.addListener(function listener() {
+          info(`Ratio changed to ${args.expected}dppx`);
+          mql.removeListener(listener);
+          resolve(getDpr());
+        });
+      });
+    }
+  );
+
+  if (waitForTargetConfiguration) {
+    // Ensure the configuration was updated so we limit the risk of the client closing before
+    // the server sent back the result of the updateConfiguration call.
+    await waitFor(() => {
+      return (
+        ui.commands.targetConfigurationCommand.configuration.overrideDPPX ===
+        expected
+      );
+    });
+  }
+
+  return dpx;
+}
diff --git a/devtools/client/responsive/test/browser/hover.html b/devtools/client/responsive/test/browser/hover.html
new file mode 100644
index 0000000000..62037dd442
--- /dev/null
+++ b/devtools/client/responsive/test/browser/hover.html
@@ -0,0 +1,37 @@
+<!doctype html>
+<meta charset="UTF-8">
+<style>
+  button {
+    background-color: rgb(255, 0, 0);
+    color: black;
+  }
+
+  button:hover {
+    background-color: rgb(0, 0, 0);
+    color: white;
+  }
+
+  .drop-down-menu {
+    height: 100px;
+    width: 100px;
+  }
+
+  .drop-down-menu .menu-items-list {
+    display: none;
+  }
+
+  .drop-down-menu:hover .menu-items-list {
+    display: block;
+  }
+</style>
+<div>
+  <button>Test Button</button>
+  <div class="drop-down-menu">
+    <div class="menu-title">Test Menu</div>
+    <ul class="menu-items-list">
+      <li class="item-one">One</li>
+      <li class="item-two">Two</li>
+      <li class="item-three">Three</li>
+    </ul>
+  </div>
+</div>
diff --git a/devtools/client/responsive/test/browser/page_style.html b/devtools/client/responsive/test/browser/page_style.html
new file mode 100644
index 0000000000..d6adad8856
--- /dev/null
+++ b/devtools/client/responsive/test/browser/page_style.html
@@ -0,0 +1,7 @@
+<style>
+body{
+  color: red;
+}
+</style>
+
+Hello RDM
diff --git a/devtools/client/responsive/test/browser/sjs_redirection.sjs b/devtools/client/responsive/test/browser/sjs_redirection.sjs
new file mode 100644
index 0000000000..9bd88a1f8e
--- /dev/null
+++ b/devtools/client/responsive/test/browser/sjs_redirection.sjs
@@ -0,0 +1,34 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+async function handleRequest(request, response) {
+  const query = new URLSearchParams(request.queryString);
+
+  const requestUserAgent = request.getHeader("user-agent");
+  const redirectRequestUserAgent = getState(
+    "redirect-request-user-agent-header"
+  );
+
+  const shouldRedirect = query.has("redirect");
+  if (shouldRedirect) {
+    response.setStatusLine(request.httpVersion, 302, "Found");
+    setState("redirect-request-user-agent-header", requestUserAgent);
+    response.setHeader(
+      "Location",
+      `http://${request.host}${request.path}?redirected`
+    );
+  } else {
+    response.setStatusLine(request.httpVersion, 200, "OK");
+    response.write(`
+      <script>
+        globalThis.requestUserAgent = ${JSON.stringify(requestUserAgent)};
+        globalThis.redirectRequestUserAgent = ${JSON.stringify(
+          redirectRequestUserAgent
+        )};
+      </script>
+      ${requestUserAgent}
+    `);
+  }
+}
diff --git a/devtools/client/responsive/test/browser/touch.html b/devtools/client/responsive/test/browser/touch.html
new file mode 100644
index 0000000000..eed55426bd
--- /dev/null
+++ b/devtools/client/responsive/test/browser/touch.html
@@ -0,0 +1,66 @@
+<!DOCTYPE html>
+
+<meta charset="utf-8" />
+<meta name="viewport" />
+<title>test</title>
+
+
+<style>
+  div {
+    border: 1px solid red;
+    width: 100px; height: 100px;
+  }
+</style>
+
+<div data-is-delay="false"></div>
+
+<script type="text/javascript">
+  "use strict";
+  const div = document.querySelector("div");
+  let initX, initY;
+
+  div.style.transform = "none";
+  div.style.backgroundColor = "";
+
+  div.addEventListener("touchstart", function (evt) {
+    const touch = evt.changedTouches[0];
+    initX = touch.pageX;
+    initY = touch.pageY;
+  }, true);
+
+  div.addEventListener("touchmove", function (evt) {
+    const touch = evt.changedTouches[0];
+    const deltaX = touch.pageX - initX;
+    const deltaY = touch.pageY - initY;
+    div.style.transform = "translate(" + deltaX + "px, " + deltaY + "px)";
+  }, true);
+
+  div.addEventListener("touchend", function (evt) {
+    if (!evt.touches.length) {
+      div.style.transform = "none";
+    }
+  }, true);
+
+  div.addEventListener("mouseenter", function (evt) {
+    div.style.backgroundColor = "red";
+  }, true);
+  div.addEventListener("mouseover", function(evt) {
+    div.style.backgroundColor = "red";
+  }, true);
+
+  div.addEventListener("mouseout", function (evt) {
+    div.style.backgroundColor = "blue";
+  }, true);
+
+  div.addEventListener("mouseleave", function (evt) {
+    div.style.backgroundColor = "blue";
+  }, true);
+
+  div.addEventListener("mousedown", null, true);
+
+  div.addEventListener("mousemove", null, true);
+
+  div.addEventListener("mouseup", null, true);
+
+  div.addEventListener("click", null, true);
+</script>
diff --git a/devtools/client/responsive/test/browser/touch_event_bubbles.html b/devtools/client/responsive/test/browser/touch_event_bubbles.html
new file mode 100644
index 0000000000..9e8decbc54
--- /dev/null
+++ b/devtools/client/responsive/test/browser/touch_event_bubbles.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+
+<meta charset="UTF-8">
+<meta name="viewport" content="width=device-width,initial-scale=1">
+<title>Simulated touch events should bubble</title>
+
+<style>
+  span {
+    background-color: red;
+    height: 100px;
+    width: 100px;
+  }
+</style>
+
+<div id="outer">
+  <div id="inner">
+    <span>Hello</span>
+  </div>
+</div>
diff --git a/devtools/client/responsive/test/browser/touch_event_target.html b/devtools/client/responsive/test/browser/touch_event_target.html
new file mode 100644
index 0000000000..bac3cfbf1e
--- /dev/null
+++ b/devtools/client/responsive/test/browser/touch_event_target.html
@@ -0,0 +1,18 @@
+<script>
+'use strict';
+
+document.documentElement.onclick = (e) => {
+  window.top.postMessage({ x: e.clientX, y: e.clientY, screenX: e.screenX, screenY: e.screenY }, "*");
+};
+
+window.onload = () => {	
+  window.top.postMessage({ ready: true }, "*");
+}
+</script>
+<style>
+body {
+	margin: 0;
+  background: green;
+}
+</style>
+<body></body>
diff --git a/devtools/client/responsive/test/xpcshell/.eslintrc.js b/devtools/client/responsive/test/xpcshell/.eslintrc.js
new file mode 100644
index 0000000000..c447323956
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for xpcshell.
+  extends: "../../../../.eslintrc.xpcshell.js",
+};
diff --git a/devtools/client/responsive/test/xpcshell/head.js b/devtools/client/responsive/test/xpcshell/head.js
new file mode 100644
index 0000000000..ee4933416c
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/head.js
@@ -0,0 +1,19 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/* eslint no-unused-vars: [2, {"vars": "local"}] */
+
+const { require } = ChromeUtils.importESModule(
+  "resource://devtools/shared/loader/Loader.sys.mjs"
+);
+
+const Store = require("resource://devtools/client/responsive/store.js");
+
+const DevToolsUtils = require("resource://devtools/shared/DevToolsUtils.js");
+
+Services.prefs.setBoolPref("devtools.testing", true);
+registerCleanupFunction(() => {
+  Services.prefs.clearUserPref("devtools.testing");
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_add_device.js b/devtools/client/responsive/test/xpcshell/test_add_device.js
new file mode 100644
index 0000000000..cea6e30989
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_add_device.js
@@ -0,0 +1,36 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test adding a new device.
+
+const {
+  addDevice,
+  addDeviceType,
+} = require("resource://devtools/client/responsive/actions/devices.js");
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  const device = {
+    name: "Firefox OS Flame",
+    width: 320,
+    height: 570,
+    pixelRatio: 1.5,
+    userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+    touch: true,
+    firefoxOS: true,
+    os: "fxos",
+  };
+
+  dispatch(addDeviceType("phones"));
+  dispatch(addDevice(device, "phones"));
+
+  equal(getState().devices.phones.length, 1, "Correct number of phones");
+  ok(
+    getState().devices.phones.includes(device),
+    "Device phone list contains Firefox OS Flame"
+  );
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_add_device_type.js b/devtools/client/responsive/test/xpcshell/test_add_device_type.js
new file mode 100644
index 0000000000..e824574380
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_add_device_type.js
@@ -0,0 +1,28 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test adding a new device type.
+
+const {
+  addDeviceType,
+} = require("resource://devtools/client/responsive/actions/devices.js");
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  dispatch(addDeviceType("phones"));
+
+  equal(getState().devices.types.length, 1, "Correct number of device types");
+  equal(
+    getState().devices.phones.length,
+    0,
+    "Defaults to an empty array of phones"
+  );
+  ok(
+    getState().devices.types.includes("phones"),
+    "Device types contain phones"
+  );
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_add_viewport.js b/devtools/client/responsive/test/xpcshell/test_add_viewport.js
new file mode 100644
index 0000000000..c9a6d9500b
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_add_viewport.js
@@ -0,0 +1,24 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test adding viewports to the page.
+
+const {
+  addViewport,
+} = require("resource://devtools/client/responsive/actions/viewports.js");
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  equal(getState().viewports.length, 0, "Defaults to no viewpots at startup");
+
+  dispatch(addViewport());
+  equal(getState().viewports.length, 1, "One viewport total");
+
+  // For the moment, there can be at most one viewport.
+  dispatch(addViewport());
+  equal(getState().viewports.length, 1, "One viewport total, again");
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_change_device.js b/devtools/client/responsive/test/xpcshell/test_change_device.js
new file mode 100644
index 0000000000..f5e3ab7f73
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_change_device.js
@@ -0,0 +1,50 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test changing the viewport device.
+
+const {
+  addDevice,
+  addDeviceType,
+} = require("resource://devtools/client/responsive/actions/devices.js");
+const {
+  addViewport,
+  changeDevice,
+} = require("resource://devtools/client/responsive/actions/viewports.js");
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  dispatch(addDeviceType("phones"));
+  dispatch(
+    addDevice(
+      {
+        name: "Firefox OS Flame",
+        width: 320,
+        height: 570,
+        pixelRatio: 1.5,
+        userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+        touch: true,
+        firefoxOS: true,
+        os: "fxos",
+      },
+      "phones"
+    )
+  );
+  dispatch(addViewport());
+
+  let viewport = getState().viewports[0];
+  equal(viewport.device, "", "Default device is unselected");
+
+  dispatch(changeDevice(0, "Firefox OS Flame", "phones"));
+
+  viewport = getState().viewports[0];
+  equal(
+    viewport.device,
+    "Firefox OS Flame",
+    "Changed to Firefox OS Flame device"
+  );
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_change_display_pixel_ratio.js b/devtools/client/responsive/test/xpcshell/test_change_display_pixel_ratio.js
new file mode 100644
index 0000000000..7cc2604b7b
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_change_display_pixel_ratio.js
@@ -0,0 +1,26 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test changing the display pixel ratio.
+
+const {
+  changeDisplayPixelRatio,
+} = require("resource://devtools/client/responsive/actions/ui.js");
+
+const NEW_PIXEL_RATIO = 5.5;
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  equal(getState().ui.displayPixelRatio, 0, "Defaults to 0 at startup");
+
+  dispatch(changeDisplayPixelRatio(NEW_PIXEL_RATIO));
+  equal(
+    getState().ui.displayPixelRatio,
+    NEW_PIXEL_RATIO,
+    `Display Pixel Ratio changed to ${NEW_PIXEL_RATIO}`
+  );
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_change_network_throttling.js b/devtools/client/responsive/test/xpcshell/test_change_network_throttling.js
new file mode 100644
index 0000000000..eb762682d8
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_change_network_throttling.js
@@ -0,0 +1,34 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test changing the network throttling state
+
+const {
+  changeNetworkThrottling,
+} = require("resource://devtools/client/shared/components/throttling/actions.js");
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  ok(
+    !getState().networkThrottling.enabled,
+    "Network throttling is disabled by default."
+  );
+  equal(
+    getState().networkThrottling.profile,
+    "",
+    "Network throttling profile is empty by default."
+  );
+
+  dispatch(changeNetworkThrottling(true, "Bob"));
+
+  ok(getState().networkThrottling.enabled, "Network throttling is enabled.");
+  equal(
+    getState().networkThrottling.profile,
+    "Bob",
+    "Network throttling profile is set."
+  );
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_change_pixel_ratio.js b/devtools/client/responsive/test/xpcshell/test_change_pixel_ratio.js
new file mode 100644
index 0000000000..d462cf39cc
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_change_pixel_ratio.js
@@ -0,0 +1,27 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test changing the viewport pixel ratio.
+
+const {
+  addViewport,
+  changePixelRatio,
+} = require("resource://devtools/client/responsive/actions/viewports.js");
+const NEW_PIXEL_RATIO = 5.5;
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  dispatch(addViewport());
+  dispatch(changePixelRatio(0, NEW_PIXEL_RATIO));
+
+  const viewport = getState().viewports[0];
+  equal(
+    viewport.pixelRatio,
+    NEW_PIXEL_RATIO,
+    `Viewport's pixel ratio changed to ${NEW_PIXEL_RATIO}`
+  );
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_change_user_agent.js b/devtools/client/responsive/test/xpcshell/test_change_user_agent.js
new file mode 100644
index 0000000000..e92d3f110f
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_change_user_agent.js
@@ -0,0 +1,28 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test changing the user agent.
+
+const {
+  changeUserAgent,
+} = require("resource://devtools/client/responsive/actions/ui.js");
+
+const NEW_USER_AGENT =
+  "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) " +
+  "AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36";
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  equal(getState().ui.userAgent, "", "User agent is empty by default.");
+
+  dispatch(changeUserAgent(NEW_USER_AGENT));
+  equal(
+    getState().ui.userAgent,
+    NEW_USER_AGENT,
+    `User Agent changed to ${NEW_USER_AGENT}`
+  );
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_resize_viewport.js b/devtools/client/responsive/test/xpcshell/test_resize_viewport.js
new file mode 100644
index 0000000000..83780ad195
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_resize_viewport.js
@@ -0,0 +1,37 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test resizing the viewport.
+
+const {
+  addViewport,
+  resizeViewport,
+} = require("resource://devtools/client/responsive/actions/viewports.js");
+const {
+  toggleTouchSimulation,
+} = require("resource://devtools/client/responsive/actions/ui.js");
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  dispatch(addViewport());
+  dispatch(resizeViewport(0, 500, 500));
+
+  let viewport = getState().viewports[0];
+  equal(viewport.width, 500, "Resized width of 500");
+  equal(viewport.height, 500, "Resized height of 500");
+
+  dispatch(toggleTouchSimulation(true));
+  dispatch(resizeViewport(0, 400, 400));
+
+  viewport = getState().viewports[0];
+  equal(viewport.width, 400, "Resized width of 400 (with touch simulation on)");
+  equal(
+    viewport.height,
+    400,
+    "Resized height of 400 (with touch simulation on)"
+  );
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_rotate_viewport.js b/devtools/client/responsive/test/xpcshell/test_rotate_viewport.js
new file mode 100644
index 0000000000..7d34daa39f
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_rotate_viewport.js
@@ -0,0 +1,27 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test rotating the viewport.
+
+const {
+  addViewport,
+  rotateViewport,
+} = require("resource://devtools/client/responsive/actions/viewports.js");
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  dispatch(addViewport());
+
+  let viewport = getState().viewports[0];
+  equal(viewport.width, 320, "Default width of 320");
+  equal(viewport.height, 480, "Default height of 480");
+
+  dispatch(rotateViewport(0));
+  viewport = getState().viewports[0];
+  equal(viewport.width, 480, "Rotated width of 480");
+  equal(viewport.height, 320, "Rotated height of 320");
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_ua_parser.js b/devtools/client/responsive/test/xpcshell/test_ua_parser.js
new file mode 100644
index 0000000000..152a504498
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_ua_parser.js
@@ -0,0 +1,129 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test for user agent parser.
+
+const {
+  parseUserAgent,
+} = require("resource://devtools/client/responsive/utils/ua.js");
+
+const TEST_DATA = [
+  {
+    userAgent:
+      "Mozilla/5.0 (Android 4.4.3; Tablet; rv:41.0) Gecko/41.0 Firefox/41.0",
+    expectedBrowser: { name: "Firefox", version: "41" },
+    expectedOS: { name: "Android", version: "4.4.3" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (Android 8.0.0; Mobile; rv:70.0) Gecko/70.0 Firefox/70.0",
+    expectedBrowser: { name: "Firefox", version: "70" },
+    expectedOS: { name: "Android", version: "8" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:54.0) Gecko/20100101 Firefox/70.1",
+    expectedBrowser: { name: "Firefox", version: "70.1" },
+    expectedOS: { name: "Windows NT", version: "6.1" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/70.0",
+    expectedBrowser: { name: "Firefox", version: "70" },
+    expectedOS: { name: "Mac OSX", version: "10.13" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (X11; Linux i586; rv:31.0) Gecko/20100101 Firefox/70.0",
+    expectedBrowser: { name: "Firefox", version: "70" },
+    expectedOS: { name: "Linux", version: null },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (iPhone; CPU iPhone OS 12_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) FxiOS/13.2b11866 Mobile/16A366 Safari/605.1.15",
+    expectedBrowser: { name: "Firefox", version: "13.2b11866" },
+    expectedOS: { name: "iOS", version: "12" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (iPhone; CPU iPhone OS 12_0 like Mac OS X) AppleWebKit/604.1.38 (KHTML, like Gecko) Version/12.0 Mobile/15A372 Safari/604.1",
+    expectedBrowser: { name: "Safari", version: "12" },
+    expectedOS: { name: "iOS", version: "12" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (iPad; CPU OS 14_7_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.1.2 Mobile/15E148 Safari/604.1",
+    expectedBrowser: { name: "Safari", version: "14.1" },
+    expectedOS: { name: "iPadOS", version: "14.7.1" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/601.7.8 (KHTML, like Gecko) Version/9.1.2 Safari/601.7.7",
+    expectedBrowser: { name: "Safari", version: "9.1" },
+    expectedOS: { name: "Mac OSX", version: "10.11.6" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (Linux; Android 8.0.0; Nexus 6P Build/OPP3.170518.006) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.87 Mobile Safari/537.36",
+    expectedBrowser: { name: "Chrome", version: "67" },
+    expectedOS: { name: "Android", version: "8" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (Linux; Android 11; SAMSUNG SM-G973U) AppleWebKit/537.36 (KHTML, like Gecko) SamsungBrowser/14.2 Chrome/87.0.4280.141 Mobile Safari/537.36",
+    expectedBrowser: { name: "Chrome", version: "87" },
+    expectedOS: { name: "Android", version: "11" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (iPhone; CPU iPhone OS 12_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) CriOS/69.0.3497.105 Mobile/15E148 Safari/605.1",
+    expectedBrowser: { name: "Chrome", version: "69" },
+    expectedOS: { name: "iOS", version: "12" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (X11; CrOS x86_64 11895.118.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.159 Safari/537.36",
+    expectedBrowser: { name: "Chrome", version: "74" },
+    expectedOS: { name: "Chrome OS", version: "11895.118" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (Windows Phone 10.0; Android 4.2.1; Microsoft; Lumia 950) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2486.0 Mobile Safari/537.36 Edge/14.14263",
+    expectedBrowser: { name: "Edge", version: "14.14263" },
+    expectedOS: { name: "Windows Phone", version: "10.0" },
+  },
+  {
+    userAgent:
+      "Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36 OPR/43.0.2442.991",
+    expectedBrowser: { name: "Opera", version: "43" },
+    expectedOS: { name: "Windows NT", version: "10.0" },
+  },
+  {
+    userAgent:
+      "Opera/9.80 (Linux armv7l) Presto/2.12.407 Version/12.51 , D50u-D1-UHD/V1.5.16-UHD (Vizio, D50u-D1, Wireless)",
+    expectedBrowser: { name: "Opera", version: "9.80" },
+    expectedOS: { name: "Linux", version: null },
+  },
+  {
+    userAgent:
+      "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)",
+    expectedBrowser: { name: "IE", version: "6" },
+    expectedOS: { name: "Windows NT", version: "5.1" },
+  },
+  {
+    userAgent: "1080p Full HD Television",
+    expectedBrowser: null,
+    expectedOS: null,
+  },
+];
+
+add_task(async function () {
+  for (const { userAgent, expectedBrowser, expectedOS } of TEST_DATA) {
+    info(`Test for ${userAgent}`);
+    const { browser, os } = parseUserAgent(userAgent);
+    deepEqual(browser, expectedBrowser, "Parsed browser is correct");
+    deepEqual(os, expectedOS, "Parsed OS is correct");
+  }
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_update_device_displayed.js b/devtools/client/responsive/test/xpcshell/test_update_device_displayed.js
new file mode 100644
index 0000000000..2d04b546ba
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_update_device_displayed.js
@@ -0,0 +1,38 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test updating the device `displayed` property
+
+const {
+  addDevice,
+  addDeviceType,
+  updateDeviceDisplayed,
+} = require("resource://devtools/client/responsive/actions/devices.js");
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  const device = {
+    name: "Firefox OS Flame",
+    width: 320,
+    height: 570,
+    pixelRatio: 1.5,
+    userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
+    touch: true,
+    firefoxOS: true,
+    os: "fxos",
+  };
+
+  dispatch(addDeviceType("phones"));
+  dispatch(addDevice(device, "phones"));
+  dispatch(updateDeviceDisplayed(device, "phones", true));
+
+  equal(getState().devices.phones.length, 1, "Correct number of phones");
+  ok(
+    getState().devices.phones[0].displayed,
+    "Device phone list contains enabled Firefox OS Flame"
+  );
+});
diff --git a/devtools/client/responsive/test/xpcshell/test_update_touch_simulation_enabled.js b/devtools/client/responsive/test/xpcshell/test_update_touch_simulation_enabled.js
new file mode 100644
index 0000000000..e96c4b3a86
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_update_touch_simulation_enabled.js
@@ -0,0 +1,24 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test updating the touch simulation `enabled` property
+
+const {
+  toggleTouchSimulation,
+} = require("resource://devtools/client/responsive/actions/ui.js");
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  ok(
+    !getState().ui.touchSimulationEnabled,
+    "Touch simulation is disabled by default."
+  );
+
+  dispatch(toggleTouchSimulation(true));
+
+  ok(getState().ui.touchSimulationEnabled, "Touch simulation is enabled.");
+});
diff --git a/devtools/client/responsive/test/xpcshell/xpcshell.toml b/devtools/client/responsive/test/xpcshell/xpcshell.toml
new file mode 100644
index 0000000000..10f33b82b7
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/xpcshell.toml
@@ -0,0 +1,30 @@
+[DEFAULT]
+tags = "devtools"
+head = "head.js"
+firefox-appdir = "browser"
+
+["test_add_device.js"]
+
+["test_add_device_type.js"]
+
+["test_add_viewport.js"]
+
+["test_change_device.js"]
+
+["test_change_display_pixel_ratio.js"]
+
+["test_change_network_throttling.js"]
+
+["test_change_pixel_ratio.js"]
+
+["test_change_user_agent.js"]
+
+["test_resize_viewport.js"]
+
+["test_rotate_viewport.js"]
+
+["test_ua_parser.js"]
+
+["test_update_device_displayed.js"]
+
+["test_update_touch_simulation_enabled.js"]
diff --git a/devtools/client/responsive/toolbar.xhtml b/devtools/client/responsive/toolbar.xhtml
new file mode 100644
index 0000000000..a977119a41
--- /dev/null
+++ b/devtools/client/responsive/toolbar.xhtml
@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- 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/. -->
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+  <head>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
+    <link
+      rel="stylesheet"
+      type="text/css"
+      href="chrome://devtools/content/responsive/index.css"
+    />
+    <script src="chrome://devtools/content/shared/theme-switching.js"></script>
+    <script src="resource://devtools/client/responsive/index.js"></script>
+  </head>
+  <body role="application">
+    <div id="root"></div>
+  </body>
+</html>
diff --git a/devtools/client/responsive/types.js b/devtools/client/responsive/types.js
new file mode 100644
index 0000000000..561f7803f6
--- /dev/null
+++ b/devtools/client/responsive/types.js
@@ -0,0 +1,139 @@
+/* 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 PropTypes = require("resource://devtools/client/shared/vendor/react-prop-types.js");
+const { createEnum } = require("resource://devtools/client/shared/enum.js");
+
+// React PropTypes are used to describe the expected "shape" of various common
+// objects that get passed down as props to components.
+
+/* ENUMS */
+
+/**
+ * An enum containing the possible states for loadable things.
+ */
+exports.loadableState = createEnum([
+  "INITIALIZED",
+  "LOADING",
+  "LOADED",
+  "ERROR",
+]);
+
+/* DEVICE */
+
+/**
+ * A single device that can be displayed in the viewport.
+ */
+const device = {
+  // The name of the device
+  name: PropTypes.string,
+
+  // The width of the device
+  width: PropTypes.number,
+
+  // The height of the device
+  height: PropTypes.number,
+
+  // The pixel ratio of the device
+  pixelRatio: PropTypes.number,
+
+  // The user agent string of the device
+  userAgent: PropTypes.string,
+
+  // Whether or not it is a touch device
+  touch: PropTypes.bool,
+
+  // The operating system of the device
+  os: PropTypes.string,
+
+  // Whether or not the device is displayed in the device selector
+  displayed: PropTypes.bool,
+};
+
+/**
+ * A list of devices and their types that can be displayed in the viewport.
+ */
+exports.devices = {
+  // An array of device types
+  types: PropTypes.arrayOf(PropTypes.string),
+
+  // An array of phone devices
+  phones: PropTypes.arrayOf(PropTypes.shape(device)),
+
+  // An array of tablet devices
+  tablets: PropTypes.arrayOf(PropTypes.shape(device)),
+
+  // An array of laptop devices
+  laptops: PropTypes.arrayOf(PropTypes.shape(device)),
+
+  // An array of television devices
+  televisions: PropTypes.arrayOf(PropTypes.shape(device)),
+
+  // An array of console devices
+  consoles: PropTypes.arrayOf(PropTypes.shape(device)),
+
+  // An array of watch devices
+  watches: PropTypes.arrayOf(PropTypes.shape(device)),
+
+  // Whether or not the device modal is open
+  isModalOpen: PropTypes.bool,
+
+  // Viewport id that triggered the modal to open
+  modalOpenedFromViewport: PropTypes.number,
+
+  // Device list state, possible values are exported above in an enum
+  listState: PropTypes.oneOf(Object.keys(exports.loadableState)),
+};
+
+/* VIEWPORT */
+
+/**
+ * Network throttling state for a given viewport.
+ */
+exports.networkThrottling = {
+  // Whether or not network throttling is enabled
+  enabled: PropTypes.bool,
+
+  // Name of the selected throttling profile
+  profile: PropTypes.string,
+};
+
+/**
+ * A single viewport displaying a document.
+ */
+exports.viewport = {
+  // The id of the viewport
+  id: PropTypes.number,
+
+  // The currently selected device applied to the viewport
+  device: PropTypes.string,
+
+  // The currently selected device type applied to the viewport
+  deviceType: PropTypes.string,
+
+  // The width of the viewport
+  width: PropTypes.number,
+
+  // The height of the viewport
+  height: PropTypes.number,
+
+  // The device pixel ratio of the viewport
+  pixelRatio: PropTypes.number,
+
+  // The user context (container) ID for the viewport
+  // Defaults to 0 meaning the default context
+  userContextId: PropTypes.number,
+};
+
+/* ACTIONS IN PROGRESS */
+
+/**
+ * The progression of the screenshot.
+ */
+exports.screenshot = {
+  // Whether screenshot capturing is in progress
+  isCapturing: PropTypes.bool,
+};
diff --git a/devtools/client/responsive/ui.js b/devtools/client/responsive/ui.js
new file mode 100644
index 0000000000..713158d654
--- /dev/null
+++ b/devtools/client/responsive/ui.js
@@ -0,0 +1,1075 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+const EventEmitter = require("resource://devtools/shared/event-emitter.js");
+const {
+  getOrientation,
+} = require("resource://devtools/client/responsive/utils/orientation.js");
+const Constants = require("resource://devtools/client/responsive/constants.js");
+const {
+  CommandsFactory,
+} = require("resource://devtools/shared/commands/commands-factory.js");
+
+loader.lazyRequireGetter(
+  this,
+  "throttlingProfiles",
+  "resource://devtools/client/shared/components/throttling/profiles.js"
+);
+loader.lazyRequireGetter(
+  this,
+  "message",
+  "resource://devtools/client/responsive/utils/message.js"
+);
+loader.lazyRequireGetter(
+  this,
+  "showNotification",
+  "resource://devtools/client/responsive/utils/notification.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "PriorityLevels",
+  "resource://devtools/client/shared/components/NotificationBox.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "l10n",
+  "resource://devtools/client/responsive/utils/l10n.js"
+);
+loader.lazyRequireGetter(
+  this,
+  "asyncStorage",
+  "resource://devtools/shared/async-storage.js"
+);
+loader.lazyRequireGetter(
+  this,
+  "captureAndSaveScreenshot",
+  "resource://devtools/client/shared/screenshot.js",
+  true
+);
+
+const RELOAD_CONDITION_PREF_PREFIX = "devtools.responsive.reloadConditions.";
+const RELOAD_NOTIFICATION_PREF =
+  "devtools.responsive.reloadNotification.enabled";
+
+function debug(msg) {
+  // console.log(`RDM manager: ${msg}`);
+}
+
+/**
+ * ResponsiveUI manages the responsive design tool for a specific tab.  The
+ * actual tool itself lives in a separate chrome:// document that is loaded into
+ * the tab upon opening responsive design.  This object acts a helper to
+ * integrate the tool into the surrounding browser UI as needed.
+ */
+class ResponsiveUI {
+  /**
+   * @param {ResponsiveUIManager} manager
+   *        The ResponsiveUIManager instance.
+   * @param {ChromeWindow} window
+   *        The main browser chrome window (that holds many tabs).
+   * @param {Tab} tab
+   *        The specific browser <tab> element this responsive instance is for.
+   */
+  constructor(manager, window, tab) {
+    this.manager = manager;
+    // The main browser chrome window (that holds many tabs).
+    this.browserWindow = window;
+    // The specific browser tab this responsive instance is for.
+    this.tab = tab;
+
+    // Flag set when destruction has begun.
+    this.destroying = false;
+    // Flag set when destruction has ended.
+    this.destroyed = false;
+    // The iframe containing the RDM UI.
+    this.rdmFrame = null;
+
+    // Bind callbacks for resizers.
+    this.onResizeDrag = this.onResizeDrag.bind(this);
+    this.onResizeStart = this.onResizeStart.bind(this);
+    this.onResizeStop = this.onResizeStop.bind(this);
+
+    this.onTargetAvailable = this.onTargetAvailable.bind(this);
+
+    this.networkFront = null;
+    // Promise resovled when the UI init has completed.
+    this.inited = this.init();
+
+    EventEmitter.decorate(this);
+  }
+
+  get toolWindow() {
+    return this.rdmFrame.contentWindow;
+  }
+
+  get docShell() {
+    return this.toolWindow.docShell;
+  }
+
+  get viewportElement() {
+    return this.browserStackEl.querySelector("browser");
+  }
+
+  get currentTarget() {
+    return this.commands.targetCommand.targetFront;
+  }
+
+  get watcherFront() {
+    return this.resourceCommand.watcherFront;
+  }
+
+  /**
+   * Open RDM while preserving the state of the page.
+   */
+  async init() {
+    debug("Init start");
+
+    this.initRDMFrame();
+
+    // Hide the browser content temporarily while things move around to avoid displaying
+    // strange intermediate states.
+    this.hideBrowserUI();
+
+    // Watch for tab close and window close so we can clean up RDM synchronously
+    this.tab.addEventListener("TabClose", this);
+    this.browserWindow.addEventListener("unload", this);
+    this.rdmFrame.contentWindow.addEventListener("message", this);
+
+    this.tab.linkedBrowser.enterResponsiveMode();
+
+    // Listen to FullZoomChange events coming from the browser window,
+    // so that we can zoom the size of the viewport by the same amount.
+    this.browserWindow.addEventListener("FullZoomChange", this);
+
+    // Get the protocol ready to speak with responsive emulation actor
+    debug("Wait until RDP server connect");
+    await this.connectToServer();
+
+    // Restore the previous UI state.
+    await this.restoreUIState();
+
+    // Show the browser UI now that its state is ready.
+    this.showBrowserUI();
+
+    // Non-blocking message to tool UI to start any delayed init activities
+    message.post(this.toolWindow, "post-init");
+
+    debug("Init done");
+  }
+
+  /**
+   * Initialize the RDM iframe inside of the browser document.
+   */
+  initRDMFrame() {
+    const { document: doc, gBrowser } = this.browserWindow;
+    const rdmFrame = doc.createElement("iframe");
+    rdmFrame.src = "chrome://devtools/content/responsive/toolbar.xhtml";
+    rdmFrame.classList.add("rdm-toolbar");
+
+    // Create resizer handlers
+    const resizeHandle = doc.createElement("div");
+    resizeHandle.classList.add(
+      "rdm-viewport-resize-handle",
+      "viewport-resize-handle"
+    );
+    const resizeHandleX = doc.createElement("div");
+    resizeHandleX.classList.add(
+      "rdm-viewport-resize-handle",
+      "viewport-horizontal-resize-handle"
+    );
+    const resizeHandleY = doc.createElement("div");
+    resizeHandleY.classList.add(
+      "rdm-viewport-resize-handle",
+      "viewport-vertical-resize-handle"
+    );
+
+    this.browserContainerEl = gBrowser.getBrowserContainer(
+      gBrowser.getBrowserForTab(this.tab)
+    );
+    this.browserStackEl =
+      this.browserContainerEl.querySelector(".browserStack");
+
+    this.browserContainerEl.classList.add("responsive-mode");
+
+    // Prepend the RDM iframe inside of the current tab's browser container.
+    this.browserContainerEl.prepend(rdmFrame);
+
+    this.browserStackEl.append(resizeHandle);
+    this.browserStackEl.append(resizeHandleX);
+    this.browserStackEl.append(resizeHandleY);
+
+    // Wait for the frame script to be loaded.
+    message.wait(rdmFrame.contentWindow, "script-init").then(async () => {
+      // Notify the frame window that the Resposnive UI manager has begun initializing.
+      // At this point, we can render our React content inside the frame.
+      message.post(rdmFrame.contentWindow, "init");
+      // Wait for the tools to be rendered above the content. The frame script will
+      // then dispatch the necessary actions to the Redux store to give the toolbar the
+      // state it needs.
+      message.wait(rdmFrame.contentWindow, "init:done").then(() => {
+        rdmFrame.contentWindow.addInitialViewport({
+          userContextId: this.tab.userContextId,
+        });
+      });
+    });
+
+    this.rdmFrame = rdmFrame;
+
+    this.resizeHandle = resizeHandle;
+    this.resizeHandle.addEventListener("mousedown", this.onResizeStart);
+
+    this.resizeHandleX = resizeHandleX;
+    this.resizeHandleX.addEventListener("mousedown", this.onResizeStart);
+
+    this.resizeHandleY = resizeHandleY;
+    this.resizeHandleY.addEventListener("mousedown", this.onResizeStart);
+
+    this.resizeToolbarObserver = new this.browserWindow.ResizeObserver(
+      entries => {
+        for (const entry of entries) {
+          // If the toolbar needs extra space for the UA input, then set a class
+          // that will accomodate its height. We should also make sure to keep
+          // the width value we're toggling against in sync with the media-query
+          // in devtools/client/responsive/index.css
+          this.rdmFrame.classList.toggle(
+            "accomodate-ua",
+            entry.contentBoxSize[0].inlineSize < 520
+          );
+        }
+      }
+    );
+
+    this.resizeToolbarObserver.observe(this.browserStackEl);
+  }
+
+  /**
+   * Close RDM and restore page content back into a regular tab.
+   *
+   * @param object
+   *        Destroy options, which currently includes a `reason` string.
+   * @return boolean
+   *         Whether this call is actually destroying.  False means destruction
+   *         was already in progress.
+   */
+  async destroy(options) {
+    if (this.destroying) {
+      return false;
+    }
+    this.destroying = true;
+
+    // If our tab is about to be closed, there's not enough time to exit
+    // gracefully, but that shouldn't be a problem since the tab will go away.
+    // So, skip any waiting when we're about to close the tab.
+    const isTabDestroyed =
+      !this.tab.linkedBrowser || this.responsiveFront?.isDestroyed();
+    const isWindowClosing = options?.reason === "unload" || isTabDestroyed;
+    const isTabContentDestroying =
+      isWindowClosing || options?.reason === "TabClose";
+
+    // Ensure init has finished before starting destroy
+    if (!isTabContentDestroying) {
+      await this.inited;
+
+      // Restore screen orientation of physical device.
+      await Promise.all([
+        this.updateScreenOrientation("landscape-primary", 0),
+        this.updateMaxTouchPointsEnabled(false),
+      ]);
+
+      // Hide browser UI to avoid displaying weird intermediate states while closing.
+      this.hideBrowserUI();
+
+      // Resseting the throtting needs to be done before the
+      // network events watching is stopped.
+      await this.updateNetworkThrottling();
+    }
+
+    this.tab.removeEventListener("TabClose", this);
+    this.browserWindow.removeEventListener("unload", this);
+    this.tab.linkedBrowser.leaveResponsiveMode();
+
+    this.browserWindow.removeEventListener("FullZoomChange", this);
+    this.rdmFrame.contentWindow.removeEventListener("message", this);
+
+    // Remove observers on the stack.
+    this.resizeToolbarObserver.unobserve(this.browserStackEl);
+
+    // Cleanup the frame content before disconnecting the frame element.
+    this.rdmFrame.contentWindow.destroy();
+
+    this.rdmFrame.remove();
+
+    // Clean up resize handlers
+    this.resizeHandle.remove();
+    this.resizeHandleX.remove();
+    this.resizeHandleY.remove();
+
+    this.browserContainerEl.classList.remove("responsive-mode");
+    this.browserStackEl.style.removeProperty("--rdm-width");
+    this.browserStackEl.style.removeProperty("--rdm-height");
+    this.browserStackEl.style.removeProperty("--rdm-zoom");
+
+    // Ensure the tab is reloaded if required when exiting RDM so that no emulated
+    // settings are left in a customized state.
+    if (!isTabContentDestroying) {
+      let reloadNeeded = false;
+      await this.updateDPPX(null);
+      reloadNeeded |=
+        (await this.updateUserAgent()) && this.reloadOnChange("userAgent");
+
+      // Don't reload on the server if we're already doing a reload on the client
+      const reloadOnTouchSimulationChange =
+        this.reloadOnChange("touchSimulation") && !reloadNeeded;
+      await this.updateTouchSimulation(null, reloadOnTouchSimulationChange);
+      if (reloadNeeded) {
+        await this.reloadBrowser();
+      }
+
+      // Unwatch targets & resources as the last step. If we are not waching for
+      // any resource & target anymore, the JSWindowActors will be unregistered
+      // which will trigger an early destruction of the RDM target, before we
+      // could finalize the cleanup.
+      this.commands.targetCommand.unwatchTargets({
+        types: [this.commands.targetCommand.TYPES.FRAME],
+        onAvailable: this.onTargetAvailable,
+      });
+
+      this.resourceCommand.unwatchResources(
+        [this.resourceCommand.TYPES.NETWORK_EVENT],
+        { onAvailable: this.onNetworkResourceAvailable }
+      );
+
+      this.commands.targetCommand.destroy();
+    }
+
+    // Show the browser UI now.
+    this.showBrowserUI();
+
+    // Destroy local state
+    this.browserContainerEl = null;
+    this.browserStackEl = null;
+    this.browserWindow = null;
+    this.tab = null;
+    this.inited = null;
+    this.rdmFrame = null;
+    this.resizeHandle = null;
+    this.resizeHandleX = null;
+    this.resizeHandleY = null;
+    this.resizeToolbarObserver = null;
+
+    // Destroying the commands will close the devtools client used to speak with responsive emulation actor.
+    // The actor handles clearing any overrides itself, so it's not necessary to clear
+    // anything on shutdown client side.
+    const commandsDestroyed = this.commands.destroy();
+    if (!isTabContentDestroying) {
+      await commandsDestroyed;
+    }
+    this.commands = this.responsiveFront = null;
+    this.destroyed = true;
+
+    return true;
+  }
+
+  async connectToServer() {
+    this.commands = await CommandsFactory.forTab(this.tab);
+    this.resourceCommand = this.commands.resourceCommand;
+
+    await this.commands.targetCommand.startListening();
+
+    await this.commands.targetCommand.watchTargets({
+      types: [this.commands.targetCommand.TYPES.FRAME],
+      onAvailable: this.onTargetAvailable,
+    });
+
+    // To support network throttling the resource command
+    // needs to be watching for network resources.
+    await this.resourceCommand.watchResources(
+      [this.resourceCommand.TYPES.NETWORK_EVENT],
+      { onAvailable: this.onNetworkResourceAvailable }
+    );
+
+    this.networkFront = await this.watcherFront.getNetworkParentActor();
+  }
+
+  /**
+   * Show one-time notification about reloads for responsive emulation.
+   */
+  showReloadNotification() {
+    if (Services.prefs.getBoolPref(RELOAD_NOTIFICATION_PREF, false)) {
+      showNotification(this.browserWindow, this.tab, {
+        msg: l10n.getFormatStr("responsive.reloadNotification.description2"),
+      });
+      Services.prefs.setBoolPref(RELOAD_NOTIFICATION_PREF, false);
+    }
+  }
+
+  reloadOnChange(id) {
+    this.showReloadNotification();
+    const pref = RELOAD_CONDITION_PREF_PREFIX + id;
+    return Services.prefs.getBoolPref(pref, false);
+  }
+
+  hideBrowserUI() {
+    this.tab.linkedBrowser.style.visibility = "hidden";
+    this.resizeHandle.style.visibility = "hidden";
+  }
+
+  showBrowserUI() {
+    this.tab.linkedBrowser.style.removeProperty("visibility");
+    this.resizeHandle.style.removeProperty("visibility");
+  }
+
+  handleEvent(event) {
+    const { browserWindow, tab } = this;
+
+    switch (event.type) {
+      case "message":
+        this.handleMessage(event);
+        break;
+      case "FullZoomChange":
+        // Get the current device size and update to that size, which
+        // will pick up changes to the zoom.
+        const { width, height } = this.getViewportSize();
+        this.updateViewportSize(width, height);
+        break;
+      case "TabClose":
+      case "unload":
+        this.manager.closeIfNeeded(browserWindow, tab, {
+          reason: event.type,
+        });
+        break;
+    }
+  }
+
+  handleMessage(event) {
+    if (event.origin !== "chrome://devtools") {
+      return;
+    }
+
+    switch (event.data.type) {
+      case "change-device":
+        this.onChangeDevice(event);
+        break;
+      case "change-network-throttling":
+        this.onChangeNetworkThrottling(event);
+        break;
+      case "change-pixel-ratio":
+        this.onChangePixelRatio(event);
+        break;
+      case "change-touch-simulation":
+        this.onChangeTouchSimulation(event);
+        break;
+      case "change-user-agent":
+        this.onChangeUserAgent(event);
+        break;
+      case "exit":
+        this.onExit();
+        break;
+      case "remove-device-association":
+        this.onRemoveDeviceAssociation();
+        break;
+      case "viewport-orientation-change":
+        this.onRotateViewport(event);
+        break;
+      case "viewport-resize":
+        this.onResizeViewport(event);
+        break;
+      case "screenshot":
+        this.onScreenshot();
+        break;
+      case "toggle-left-alignment":
+        this.onToggleLeftAlignment(event);
+        break;
+      case "update-device-modal":
+        this.onUpdateDeviceModal(event);
+        break;
+    }
+  }
+
+  async onChangeDevice(event) {
+    const { pixelRatio, touch, userAgent } = event.data.device;
+    let reloadNeeded = false;
+    await this.updateDPPX(pixelRatio);
+
+    // Get the orientation values of the device we are changing to and update.
+    const { device, viewport } = event.data;
+    const { type, angle } = getOrientation(device, viewport);
+    await this.updateScreenOrientation(type, angle);
+    await this.updateMaxTouchPointsEnabled(touch);
+
+    reloadNeeded |=
+      (await this.updateUserAgent(userAgent)) &&
+      this.reloadOnChange("userAgent");
+
+    // Don't reload on the server if we're already doing a reload on the client
+    const reloadOnTouchSimulationChange =
+      this.reloadOnChange("touchSimulation") && !reloadNeeded;
+    await this.updateTouchSimulation(touch, reloadOnTouchSimulationChange);
+
+    if (reloadNeeded) {
+      this.reloadBrowser();
+    }
+
+    // Used by tests
+    this.emitForTests("device-changed", {
+      reloadTriggered: reloadNeeded || reloadOnTouchSimulationChange,
+    });
+  }
+
+  async onChangeNetworkThrottling(event) {
+    const { enabled, profile } = event.data;
+    await this.updateNetworkThrottling(enabled, profile);
+    // Used by tests
+    this.emit("network-throttling-changed");
+  }
+
+  onChangePixelRatio(event) {
+    const { pixelRatio } = event.data;
+    this.updateDPPX(pixelRatio);
+  }
+
+  async onChangeTouchSimulation(event) {
+    const { enabled } = event.data;
+
+    await this.updateMaxTouchPointsEnabled(enabled);
+
+    await this.updateTouchSimulation(
+      enabled,
+      this.reloadOnChange("touchSimulation")
+    );
+
+    // Used by tests
+    this.emit("touch-simulation-changed");
+  }
+
+  async onChangeUserAgent(event) {
+    const { userAgent } = event.data;
+    const reloadNeeded =
+      (await this.updateUserAgent(userAgent)) &&
+      this.reloadOnChange("userAgent");
+    if (reloadNeeded) {
+      this.reloadBrowser();
+    }
+    this.emit("user-agent-changed");
+  }
+
+  onExit() {
+    const { browserWindow, tab } = this;
+    this.manager.closeIfNeeded(browserWindow, tab);
+  }
+
+  async onRemoveDeviceAssociation() {
+    let reloadNeeded = false;
+    await this.updateDPPX(null);
+    reloadNeeded |=
+      (await this.updateUserAgent()) && this.reloadOnChange("userAgent");
+
+    // Don't reload on the server if we're already doing a reload on the client
+    const reloadOnTouchSimulationChange =
+      this.reloadOnChange("touchSimulation") && !reloadNeeded;
+    await this.updateTouchSimulation(null, reloadOnTouchSimulationChange);
+    if (reloadNeeded) {
+      this.reloadBrowser();
+    }
+    // Used by tests
+    this.emitForTests("device-association-removed", {
+      reloadTriggered: reloadNeeded || reloadOnTouchSimulationChange,
+    });
+  }
+
+  /**
+   * Resizing the browser on mousemove
+   */
+  onResizeDrag({ screenX, screenY }) {
+    if (!this.isResizing || !this.rdmFrame.contentWindow) {
+      return;
+    }
+
+    const zoom = this.tab.linkedBrowser.fullZoom;
+
+    let deltaX = (screenX - this.lastScreenX) / zoom;
+    let deltaY = (screenY - this.lastScreenY) / zoom;
+
+    const leftAlignmentEnabled = Services.prefs.getBoolPref(
+      "devtools.responsive.leftAlignViewport.enabled",
+      false
+    );
+
+    if (!leftAlignmentEnabled) {
+      // The viewport is centered horizontally, so horizontal resize resizes
+      // by twice the distance the mouse was dragged - on left and right side.
+      deltaX = deltaX * 2;
+    }
+
+    if (this.ignoreX) {
+      deltaX = 0;
+    }
+    if (this.ignoreY) {
+      deltaY = 0;
+    }
+
+    const viewportSize = this.getViewportSize();
+
+    let width = Math.round(viewportSize.width + deltaX);
+    let height = Math.round(viewportSize.height + deltaY);
+
+    if (width < Constants.MIN_VIEWPORT_DIMENSION) {
+      width = Constants.MIN_VIEWPORT_DIMENSION;
+    } else if (width != viewportSize.width) {
+      this.lastScreenX = screenX;
+    }
+
+    if (height < Constants.MIN_VIEWPORT_DIMENSION) {
+      height = Constants.MIN_VIEWPORT_DIMENSION;
+    } else if (height != viewportSize.height) {
+      this.lastScreenY = screenY;
+    }
+
+    // Update the RDM store and viewport size with the new width and height.
+    this.rdmFrame.contentWindow.setViewportSize({ width, height });
+    this.updateViewportSize(width, height);
+
+    // Change the device selector back to an unselected device
+    if (this.rdmFrame.contentWindow.getAssociatedDevice()) {
+      this.rdmFrame.contentWindow.clearDeviceAssociation();
+    }
+  }
+
+  /**
+   * Start the process of resizing the browser.
+   */
+  onResizeStart({ target, screenX, screenY }) {
+    this.browserWindow.addEventListener("mousemove", this.onResizeDrag, true);
+    this.browserWindow.addEventListener("mouseup", this.onResizeStop, true);
+
+    this.isResizing = true;
+    this.lastScreenX = screenX;
+    this.lastScreenY = screenY;
+    this.ignoreX = target === this.resizeHandleY;
+    this.ignoreY = target === this.resizeHandleX;
+  }
+
+  /**
+   * Stop the process of resizing the browser.
+   */
+  onResizeStop() {
+    this.browserWindow.removeEventListener(
+      "mousemove",
+      this.onResizeDrag,
+      true
+    );
+    this.browserWindow.removeEventListener("mouseup", this.onResizeStop, true);
+
+    this.isResizing = false;
+    this.lastScreenX = 0;
+    this.lastScreenY = 0;
+    this.ignoreX = false;
+    this.ignoreY = false;
+
+    // Used by tests.
+    this.emit("viewport-resize-dragend");
+  }
+
+  onResizeViewport(event) {
+    const { width, height } = event.data;
+    this.updateViewportSize(width, height);
+    this.emit("viewport-resize", {
+      width,
+      height,
+    });
+  }
+
+  async onRotateViewport(event) {
+    const { orientationType: type, angle, isViewportRotated } = event.data;
+    await this.updateScreenOrientation(type, angle, isViewportRotated);
+  }
+
+  async onScreenshot() {
+    const messages = await captureAndSaveScreenshot(
+      this.currentTarget,
+      this.browserWindow
+    );
+
+    const priorityMap = {
+      error: PriorityLevels.PRIORITY_CRITICAL_HIGH,
+      warn: PriorityLevels.PRIORITY_WARNING_HIGH,
+    };
+    for (const { text, level } of messages) {
+      // captureAndSaveScreenshot returns "saved" messages, that indicate where the
+      // screenshot was saved. We don't want to display them as the download UI can be
+      // used to open the file.
+      if (level !== "warn" && level !== "error") {
+        continue;
+      }
+
+      showNotification(this.browserWindow, this.tab, {
+        msg: text,
+        priority: priorityMap[level],
+      });
+    }
+
+    message.post(this.rdmFrame.contentWindow, "screenshot-captured");
+  }
+
+  onToggleLeftAlignment(event) {
+    this.updateUIAlignment(event.data.leftAlignmentEnabled);
+  }
+
+  onUpdateDeviceModal(event) {
+    this.rdmFrame.classList.toggle("device-modal-opened", event.data.isOpen);
+  }
+
+  async hasDeviceState() {
+    const deviceState = await asyncStorage.getItem(
+      "devtools.responsive.deviceState"
+    );
+    return !!deviceState;
+  }
+
+  /**
+   * Restores the previous UI state.
+   */
+  async restoreUIState() {
+    const leftAlignmentEnabled = Services.prefs.getBoolPref(
+      "devtools.responsive.leftAlignViewport.enabled",
+      false
+    );
+
+    this.updateUIAlignment(leftAlignmentEnabled);
+
+    const height = Services.prefs.getIntPref(
+      "devtools.responsive.viewport.height",
+      0
+    );
+    const width = Services.prefs.getIntPref(
+      "devtools.responsive.viewport.width",
+      0
+    );
+    this.updateViewportSize(width, height);
+  }
+
+  /**
+   * Restores the previous actor state.
+   *
+   * @param {Boolean} isTargetSwitching
+   */
+  async restoreActorState(isTargetSwitching) {
+    // It's possible the target will switch to a page loaded in the
+    // parent-process (i.e: about:robots). When this happens, the values set
+    // on the BrowsingContext by RDM are not preserved. So we need to call
+    // enterResponsiveMode whenever there is a target switch.
+    this.tab.linkedBrowser.enterResponsiveMode();
+
+    // If the target follows the window global lifecycle, the configuration was already
+    // restored from the server during target switch, so we can stop here.
+    // This function is still called at startup to restore potential state from previous
+    // RDM session so we only stop here during target switching.
+    if (
+      isTargetSwitching &&
+      this.commands.targetCommand.targetFront.targetForm
+        .followWindowGlobalLifeCycle
+    ) {
+      return;
+    }
+
+    const hasDeviceState = await this.hasDeviceState();
+    if (hasDeviceState) {
+      // Return if there is a device state to restore, this will be done when the
+      // device list is loaded after the post-init.
+      return;
+    }
+
+    const height = Services.prefs.getIntPref(
+      "devtools.responsive.viewport.height",
+      0
+    );
+    const pixelRatio = Services.prefs.getIntPref(
+      "devtools.responsive.viewport.pixelRatio",
+      0
+    );
+    const touchSimulationEnabled = Services.prefs.getBoolPref(
+      "devtools.responsive.touchSimulation.enabled",
+      false
+    );
+    const userAgent = Services.prefs.getCharPref(
+      "devtools.responsive.userAgent",
+      ""
+    );
+    const width = Services.prefs.getIntPref(
+      "devtools.responsive.viewport.width",
+      0
+    );
+
+    // Restore the previously set orientation, or get it from the initial viewport if it
+    // wasn't set yet.
+    const { type, angle } =
+      this.commands.targetConfigurationCommand.configuration
+        .rdmPaneOrientation ||
+      this.getInitialViewportOrientation({
+        width,
+        height,
+      });
+
+    await this.updateDPPX(pixelRatio);
+    await this.updateScreenOrientation(type, angle);
+    await this.updateMaxTouchPointsEnabled(touchSimulationEnabled);
+
+    if (touchSimulationEnabled) {
+      await this.updateTouchSimulation(touchSimulationEnabled);
+    }
+
+    let reloadNeeded = false;
+    if (userAgent) {
+      reloadNeeded |=
+        (await this.updateUserAgent(userAgent)) &&
+        this.reloadOnChange("userAgent");
+    }
+    if (reloadNeeded) {
+      await this.reloadBrowser();
+    }
+  }
+
+  /**
+   * Set or clear the emulated device pixel ratio.
+   *
+   * @param {Number|null} dppx: The ratio to simulate. Set to null to disable the
+   *                      simulation and roll back to the original ratio
+   */
+  async updateDPPX(dppx = null) {
+    await this.commands.targetConfigurationCommand.updateConfiguration({
+      overrideDPPX: dppx,
+    });
+  }
+
+  /**
+   * Set or clear network throttling.
+   *
+   * @return boolean
+   *         Whether a reload is needed to apply the change.
+   *         (This is always immediate, so it's always false.)
+   */
+  async updateNetworkThrottling(enabled, profile) {
+    if (!enabled) {
+      await this.networkFront.clearNetworkThrottling();
+      return false;
+    }
+    const data = throttlingProfiles.profiles.find(({ id }) => id == profile);
+    const { download, upload, latency } = data;
+    await this.networkFront.setNetworkThrottling({
+      downloadThroughput: download,
+      uploadThroughput: upload,
+      latency,
+    });
+    return false;
+  }
+
+  /**
+   * Set or clear the emulated user agent.
+   *
+   * @param {String|null} userAgent: The user agent to set on the page. Set to null to revert
+   *                      the user agent to its original value
+   * @return {Boolean} Whether a reload is needed to apply the change.
+   */
+  async updateUserAgent(userAgent) {
+    const getConfigurationCustomUserAgent = () =>
+      this.commands.targetConfigurationCommand.configuration.customUserAgent ||
+      "";
+    const previousCustomUserAgent = getConfigurationCustomUserAgent();
+    await this.commands.targetConfigurationCommand.updateConfiguration({
+      customUserAgent: userAgent,
+    });
+
+    const updatedUserAgent = getConfigurationCustomUserAgent();
+    return previousCustomUserAgent !== updatedUserAgent;
+  }
+
+  /**
+   * Set or clear touch simulation. When setting to true, this method will
+   * additionally set meta viewport override.
+   * When setting to false, this method will clear all touch simulation and meta viewport
+   * overrides, returning to default behavior for both settings.
+   *
+   * @param {boolean} enabled
+   * @param {boolean} reloadOnTouchSimulationToggle: Set to true to trigger a page reload
+   *        if the touch simulation state changes.
+   */
+  async updateTouchSimulation(enabled, reloadOnTouchSimulationToggle) {
+    await this.commands.targetConfigurationCommand.updateConfiguration({
+      touchEventsOverride: enabled ? "enabled" : null,
+      reloadOnTouchSimulationToggle,
+    });
+  }
+
+  /**
+   * Sets the screen orientation values of the simulated device.
+   *
+   * @param {String} type
+   *        The orientation type to update the current device screen to.
+   * @param {Number} angle
+   *        The rotation angle to update the current device screen to.
+   * @param {Boolean} isViewportRotated
+   *        Whether or not the reason for updating the screen orientation is a result
+   *        of actually rotating the device via the RDM toolbar. If true, then an
+   *        "orientationchange" event is simulated. Otherwise, the screen orientation is
+   *        updated because of changing devices, opening RDM, or the page has been
+   *        reloaded/navigated to, so we should not be simulating "orientationchange".
+   */
+  async updateScreenOrientation(type, angle, isViewportRotated = false) {
+    await this.commands.targetConfigurationCommand.simulateScreenOrientationChange(
+      {
+        type,
+        angle,
+        isViewportRotated,
+      }
+    );
+  }
+
+  /**
+   * Sets whether or not maximum touch points are supported for the simulated device.
+   *
+   * @param {Boolean} touchSimulationEnabled
+   *        Whether or not touch is enabled for the simulated device.
+   */
+  async updateMaxTouchPointsEnabled(touchSimulationEnabled) {
+    return this.commands.targetConfigurationCommand.updateConfiguration({
+      rdmPaneMaxTouchPoints: touchSimulationEnabled ? 1 : 0,
+    });
+  }
+
+  /**
+   * Sets whether or not the RDM UI should be left-aligned.
+   *
+   * @param {Boolean} leftAlignmentEnabled
+   *        Whether or not the UI is left-aligned.
+   */
+  updateUIAlignment(leftAlignmentEnabled) {
+    this.browserContainerEl.classList.toggle(
+      "left-aligned",
+      leftAlignmentEnabled
+    );
+  }
+
+  /**
+   * Sets the browser element to be the given width and height.
+   *
+   * @param {Number} width
+   *        The viewport's width.
+   * @param {Number} height
+   *        The viewport's height.
+   */
+  updateViewportSize(width, height) {
+    const zoom = this.tab.linkedBrowser.fullZoom;
+
+    // Setting this with a variable on the stack instead of directly as width/height
+    // on the <browser> because we'll need to use this for the alert dialog as well.
+    this.browserStackEl.style.setProperty("--rdm-width", `${width}px`);
+    this.browserStackEl.style.setProperty("--rdm-height", `${height}px`);
+    this.browserStackEl.style.setProperty("--rdm-zoom", zoom);
+
+    // This is a bit premature, but we emit a content-resize event here. It
+    // would be preferrable to wait until the viewport is actually resized,
+    // but the "resize" event is not triggered by this style change. The
+    // content-resize message is only used by tests, and if needed those tests
+    // can use the testing function setViewportSizeAndAwaitReflow to ensure
+    // the viewport has had time to reach this size.
+    this.emit("content-resize", {
+      width,
+      height,
+    });
+  }
+
+  /**
+   * Helper for tests. Assumes a single viewport for now.
+   */
+  getViewportSize() {
+    // The getViewportSize function is loaded in index.js, and might not be
+    // available yet.
+    if (this.toolWindow.getViewportSize) {
+      return this.toolWindow.getViewportSize();
+    }
+
+    return { width: 0, height: 0 };
+  }
+
+  /**
+   * Helper for tests, etc. Assumes a single viewport for now.
+   */
+  async setViewportSize(size) {
+    await this.inited;
+
+    // Ensure that width and height are valid.
+    let { width, height } = size;
+    if (!size.width) {
+      width = this.getViewportSize().width;
+    }
+
+    if (!size.height) {
+      height = this.getViewportSize().height;
+    }
+
+    this.rdmFrame.contentWindow.setViewportSize({ width, height });
+    this.updateViewportSize(width, height);
+  }
+
+  /**
+   * Helper for tests/reloading the viewport. Assumes a single viewport for now.
+   */
+  getViewportBrowser() {
+    return this.tab.linkedBrowser;
+  }
+
+  /**
+   * Helper for contacting the viewport content. Assumes a single viewport for now.
+   */
+  getViewportMessageManager() {
+    return this.getViewportBrowser().messageManager;
+  }
+
+  /**
+   * Helper for getting the initial viewport orientation.
+   */
+  getInitialViewportOrientation(viewport) {
+    return getOrientation(viewport, viewport);
+  }
+
+  /**
+   * Helper for tests to get the browser's window.
+   */
+  getBrowserWindow() {
+    return this.browserWindow;
+  }
+
+  async onTargetAvailable({ targetFront, isTargetSwitching }) {
+    if (this.destroying) {
+      return;
+    }
+
+    if (targetFront.isTopLevel) {
+      this.responsiveFront = await targetFront.getFront("responsive");
+
+      if (this.destroying) {
+        return;
+      }
+
+      await this.restoreActorState(isTargetSwitching);
+      this.emitForTests("responsive-ui-target-switch-done");
+    }
+  }
+  // This just needed to setup watching for network resources,
+  // to support network throttling.
+  onNetworkResourceAvailable() {}
+
+  /**
+   * Reload the current tab.
+   */
+  async reloadBrowser() {
+    await this.commands.targetCommand.reloadTopLevelTarget();
+  }
+}
+
+module.exports = ResponsiveUI;
diff --git a/devtools/client/responsive/utils/e10s.js b/devtools/client/responsive/utils/e10s.js
new file mode 100644
index 0000000000..62ec6924a6
--- /dev/null
+++ b/devtools/client/responsive/utils/e10s.js
@@ -0,0 +1,99 @@
+/* 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";
+
+// The prefix used for RDM messages in content.
+// see: devtools/client/responsive/browser/content.js
+const MESSAGE_PREFIX = "ResponsiveMode:";
+const REQUEST_DONE_SUFFIX = ":Done";
+
+/**
+ * Registers a message `listener` that is called every time messages of
+ * specified `message` is emitted on the given message manager.
+ * @param {nsIMessageListenerManager} mm
+ *    The Message Manager
+ * @param {String} message
+ *    The message. It will be prefixed with the constant `MESSAGE_PREFIX`
+ * @param {Function} listener
+ *    The listener function that processes the message.
+ */
+function on(mm, message, listener) {
+  mm.addMessageListener(MESSAGE_PREFIX + message, listener);
+}
+exports.on = on;
+
+/**
+ * Removes a message `listener` for the specified `message` on the given
+ * message manager.
+ * @param {nsIMessageListenerManager} mm
+ *    The Message Manager
+ * @param {String} message
+ *    The message. It will be prefixed with the constant `MESSAGE_PREFIX`
+ * @param {Function} listener
+ *    The listener function that processes the message.
+ */
+function off(mm, message, listener) {
+  mm.removeMessageListener(MESSAGE_PREFIX + message, listener);
+}
+exports.off = off;
+
+/**
+ * Resolves a promise the next time the specified `message` is sent over the
+ * given message manager.
+ * @param {nsIMessageListenerManager} mm
+ *    The Message Manager
+ * @param {String} message
+ *    The message. It will be prefixed with the constant `MESSAGE_PREFIX`
+ * @returns {Promise}
+ *    A promise that is resolved when the given message is emitted.
+ */
+function once(mm, message) {
+  return new Promise(resolve => {
+    on(mm, message, function onMessage({ data }) {
+      off(mm, message, onMessage);
+      resolve(data);
+    });
+  });
+}
+exports.once = once;
+
+/**
+ * Asynchronously emit a `message` to the listeners of the given message
+ * manager.
+ *
+ * @param {nsIMessageListenerManager} mm
+ *    The Message Manager
+ * @param {String} message
+ *    The message. It will be prefixed with the constant `MESSAGE_PREFIX`.
+ * @param {Object} data
+ *    A JSON object containing data to be delivered to the listeners.
+ */
+function emit(mm, message, data) {
+  mm.sendAsyncMessage(MESSAGE_PREFIX + message, data);
+}
+exports.emit = emit;
+
+/**
+ * Asynchronously send a "request" over the given message manager, and returns
+ * a promise that is resolved when the request is complete.
+ *
+ * @param {nsIMessageListenerManager} mm
+ *    The Message Manager
+ * @param {String} message
+ *    The message. It will be prefixed with the constant `MESSAGE_PREFIX`, and
+ *    also suffixed with `REQUEST_DONE_SUFFIX` for the reply.
+ * @param {Object} data
+ *    A JSON object containing data to be delivered to the listeners.
+ * @returns {Promise}
+ *    A promise that is resolved when the request is done.
+ */
+function request(mm, message, data) {
+  const done = once(mm, message + REQUEST_DONE_SUFFIX);
+
+  emit(mm, message, data);
+
+  return done;
+}
+exports.request = request;
diff --git a/devtools/client/responsive/utils/key.js b/devtools/client/responsive/utils/key.js
new file mode 100644
index 0000000000..22c7278b2f
--- /dev/null
+++ b/devtools/client/responsive/utils/key.js
@@ -0,0 +1,25 @@
+/* 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 { KeyCodes } = require("resource://devtools/client/shared/keycodes.js");
+
+/**
+ * Helper to check if the provided key matches one of the expected keys.
+ * Keys will be prefixed with DOM_VK_ and should match a key in KeyCodes.
+ *
+ * @param {String} key
+ *        the key to check (can be a keyCode).
+ * @param {...String} keys
+ *        list of possible keys allowed.
+ * @return {Boolean} true if the key matches one of the keys.
+ */
+function isKeyIn(key, ...keys) {
+  return keys.some(expectedKey => {
+    return key === KeyCodes["DOM_VK_" + expectedKey];
+  });
+}
+
+exports.isKeyIn = isKeyIn;
diff --git a/devtools/client/responsive/utils/l10n.js b/devtools/client/responsive/utils/l10n.js
new file mode 100644
index 0000000000..bccea57040
--- /dev/null
+++ b/devtools/client/responsive/utils/l10n.js
@@ -0,0 +1,16 @@
+/* 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 { LocalizationHelper } = require("resource://devtools/shared/l10n.js");
+const STRINGS_URI = "devtools/client/locales/responsive.properties";
+const L10N = new LocalizationHelper(STRINGS_URI);
+
+module.exports = {
+  getStr: (...args) => L10N.getStr(...args),
+  getFormatStr: (...args) => L10N.getFormatStr(...args),
+  getFormatStrWithNumbers: (...args) => L10N.getFormatStrWithNumbers(...args),
+  numberWithDecimals: (...args) => L10N.numberWithDecimals(...args),
+};
diff --git a/devtools/client/responsive/utils/message.js b/devtools/client/responsive/utils/message.js
new file mode 100644
index 0000000000..d06f95ab27
--- /dev/null
+++ b/devtools/client/responsive/utils/message.js
@@ -0,0 +1,55 @@
+/* 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 REQUEST_DONE_SUFFIX = ":done";
+
+function wait(win, type) {
+  return new Promise(resolve => {
+    const onMessage = event => {
+      if (event.data.type !== type) {
+        return;
+      }
+      win.removeEventListener("message", onMessage);
+      resolve();
+    };
+    win.addEventListener("message", onMessage);
+  });
+}
+
+/**
+ * Post a message to some window.
+ *
+ * @param win
+ *        The window to post to.
+ * @param typeOrMessage
+ *        Either a string or and an object representing the message to send.
+ *        If this is a string, it will be expanded into an object with the string as the
+ *        `type` field.  If this is an object, it will be sent as is.
+ */
+function post(win, typeOrMessage) {
+  // When running unit tests on XPCShell, there is no window to send messages to.
+  if (!win) {
+    return;
+  }
+
+  let message = typeOrMessage;
+  if (typeof typeOrMessage == "string") {
+    message = {
+      type: typeOrMessage,
+    };
+  }
+  win.postMessage(message, "*");
+}
+
+function request(win, type) {
+  const done = wait(win, type + REQUEST_DONE_SUFFIX);
+  post(win, type);
+  return done;
+}
+
+exports.wait = wait;
+exports.post = post;
+exports.request = request;
diff --git a/devtools/client/responsive/utils/moz.build b/devtools/client/responsive/utils/moz.build
new file mode 100644
index 0000000000..503da8932a
--- /dev/null
+++ b/devtools/client/responsive/utils/moz.build
@@ -0,0 +1,16 @@
+# -*- 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(
+    "e10s.js",
+    "key.js",
+    "l10n.js",
+    "message.js",
+    "notification.js",
+    "orientation.js",
+    "ua.js",
+    "window.js",
+)
diff --git a/devtools/client/responsive/utils/notification.js b/devtools/client/responsive/utils/notification.js
new file mode 100644
index 0000000000..a261fe4252
--- /dev/null
+++ b/devtools/client/responsive/utils/notification.js
@@ -0,0 +1,60 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+loader.lazyRequireGetter(
+  this,
+  "gDevTools",
+  "resource://devtools/client/framework/devtools.js",
+  true
+);
+
+/**
+ * Displays a notification either at the browser or toolbox level, depending on whether
+ * a toolbox is currently open for this tab.
+ *
+ * @param window
+ *        The main browser chrome window.
+ * @param tab
+ *        The browser tab.
+ * @param options
+ *        Other options associated with opening.  Currently includes:
+ *        - `toolbox`: Whether initiated via toolbox button
+ *        - `msg`: String to show in the notification
+ *        - `priority`: Priority level for the notification, which affects the icon and
+ *                      overall appearance.
+ */
+async function showNotification(
+  window,
+  tab,
+  { toolboxButton, msg, priority } = {}
+) {
+  // Default to using the browser's per-tab notification box
+  let nbox = window.gBrowser.getNotificationBox(tab.linkedBrowser);
+
+  // If opening was initiated by a toolbox button, check for an open
+  // toolbox for the tab.  If one exists, use the toolbox's notification box so that the
+  // message is placed closer to the action taken by the user.
+  if (toolboxButton) {
+    const toolbox = gDevTools.getToolboxForTab(tab);
+    if (toolbox) {
+      nbox = toolbox.notificationBox;
+    }
+  }
+
+  const value = "devtools-responsive";
+  if (nbox.getNotificationWithValue(value)) {
+    // Notification already displayed
+    return;
+  }
+
+  if (!priority) {
+    priority = nbox.PRIORITY_INFO_MEDIUM;
+  }
+
+  nbox.appendNotification(value, { label: msg, priority });
+}
+
+exports.showNotification = showNotification;
diff --git a/devtools/client/responsive/utils/orientation.js b/devtools/client/responsive/utils/orientation.js
new file mode 100644
index 0000000000..500eab8faa
--- /dev/null
+++ b/devtools/client/responsive/utils/orientation.js
@@ -0,0 +1,76 @@
+/* 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 {
+  PORTRAIT_PRIMARY,
+  LANDSCAPE_PRIMARY,
+} = require("resource://devtools/client/responsive/constants.js");
+
+/**
+ * Helper that gets the screen orientation of the device displayed in the RDM viewport.
+ * This function take in both a device and viewport object and an optional rotated angle.
+ * If a rotated angle is passed, then we calculate what the orientation type of the device
+ * would be in relation to its current orientation. Otherwise, return the current
+ * orientation and angle.
+ *
+ * @param {Object} device
+ *        The device whose content is displayed in the viewport. Used to determine the
+ *        primary orientation.
+ * @param {Object} viewport
+ *        The viewport displaying device content. Used to determine the current
+ *        orientation type of the device while in RDM.
+ * @param {Number|null} angleToRotateTo
+ *        Optional. The rotated angle specifies the degree to which the device WILL be
+ *        turned to. If undefined, then only return the current orientation and angle
+ *        of the device.
+ * @return {Object} the orientation of the device.
+ */
+function getOrientation(device, viewport, angleToRotateTo = null) {
+  const { width: deviceWidth, height: deviceHeight } = device;
+  const { width: viewportWidth, height: viewportHeight } = viewport;
+
+  // Determine the primary orientation of the device screen.
+  const primaryOrientation =
+    deviceHeight >= deviceWidth ? PORTRAIT_PRIMARY : LANDSCAPE_PRIMARY;
+
+  // Determine the current orientation of the device screen.
+  const currentOrientation =
+    viewportHeight >= viewportWidth ? PORTRAIT_PRIMARY : LANDSCAPE_PRIMARY;
+
+  // Calculate the orientation angle of the device.
+  let angle;
+
+  if (typeof angleToRotateTo === "number") {
+    angle = angleToRotateTo;
+  } else if (currentOrientation !== primaryOrientation) {
+    angle = 90;
+  } else {
+    angle = 0;
+  }
+
+  // Calculate the orientation type of the device.
+  let orientationType = currentOrientation;
+
+  // If the viewport orientation is different from the primary orientation and the angle
+  // to rotate to is 0, then we are moving the device orientation back to its primary
+  // orientation.
+  if (currentOrientation !== primaryOrientation && angleToRotateTo === 0) {
+    orientationType = primaryOrientation;
+  } else if (angleToRotateTo === 90 || angleToRotateTo === 270) {
+    if (currentOrientation.includes("portrait")) {
+      orientationType = LANDSCAPE_PRIMARY;
+    } else if (currentOrientation.includes("landscape")) {
+      orientationType = PORTRAIT_PRIMARY;
+    }
+  }
+
+  return {
+    type: orientationType,
+    angle,
+  };
+}
+
+exports.getOrientation = getOrientation;
diff --git a/devtools/client/responsive/utils/ua.js b/devtools/client/responsive/utils/ua.js
new file mode 100644
index 0000000000..70c99c552d
--- /dev/null
+++ b/devtools/client/responsive/utils/ua.js
@@ -0,0 +1,129 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+const BROWSERS = [
+  {
+    name: "Firefox",
+    mustContain: new RegExp(`(?:Firefox|FxiOS)\/(${getVersionRegex(1, 1)})`),
+  },
+  {
+    name: "Opera",
+    mustContain: new RegExp(`(?:OPR|Opera)\/(${getVersionRegex(1, 1)})`),
+  },
+  {
+    name: "Safari",
+    mustContain: new RegExp(`Version\/(${getVersionRegex(1, 1)}).+Safari`),
+    mustNotContain: new RegExp("Chrome|Chromium"),
+  },
+  {
+    name: "Edge",
+    mustContain: new RegExp(`Edge\/(${getVersionRegex(0, 1)})`),
+  },
+  {
+    name: "Chrome",
+    mustContain: new RegExp(`(?:Chrome|CriOS)\/(${getVersionRegex(1, 1)})`),
+  },
+  {
+    name: "IE",
+    mustContain: new RegExp(`MSIE (${getVersionRegex(1, 1)})`),
+  },
+];
+
+const OSES = [
+  {
+    name: "iOS",
+    minMinorVersionCount: 0,
+    mustContain: new RegExp(`CPU iPhone OS (${getVersionRegex(0, 2)})`),
+  },
+  {
+    name: "iPadOS",
+    minMinorVersionCount: 0,
+    mustContain: new RegExp(`CPU OS (${getVersionRegex(0, 2)})`),
+  },
+  {
+    name: "Windows Phone",
+    minMinorVersionCount: 1,
+    mustContain: new RegExp(`Windows Phone (${getVersionRegex(1, 2)})`),
+  },
+  {
+    name: "Chrome OS",
+    minMinorVersionCount: 1,
+    mustContain: new RegExp(`CrOS .+ (${getVersionRegex(1, 2)})`),
+  },
+  {
+    name: "Android",
+    minMinorVersionCount: 0,
+    mustContain: new RegExp(`Android (${getVersionRegex(0, 2)})`),
+  },
+  {
+    name: "Windows NT",
+    minMinorVersionCount: 1,
+    mustContain: new RegExp(`Windows NT (${getVersionRegex(1, 2)})`),
+  },
+  {
+    name: "Mac OSX",
+    minMinorVersionCount: 1,
+    mustContain: new RegExp(`Intel Mac OS X (${getVersionRegex(1, 2)})`),
+  },
+  {
+    name: "Linux",
+    mustContain: new RegExp("Linux"),
+  },
+];
+
+function getVersionRegex(minMinorVersionCount, maxMinorVersionCount) {
+  return `\\d+(?:[._][0-9a-z]+){${minMinorVersionCount},${maxMinorVersionCount}}`;
+}
+
+function detect(ua, dataset) {
+  for (const {
+    name,
+    mustContain,
+    mustNotContain,
+    minMinorVersionCount,
+  } of dataset) {
+    const result = mustContain.exec(ua);
+
+    if (!result) {
+      continue;
+    }
+
+    if (mustNotContain && mustNotContain.test(ua)) {
+      continue;
+    }
+
+    let version = null;
+
+    if (result && result.length === 2) {
+      // Remove most minor version if that expresses 0.
+      let parts = result[1].match(/([0-9a-z]+)/g);
+      parts = parts.reverse();
+      const validVersionIndex = parts.findIndex(
+        part => parseInt(part, 10) !== 0
+      );
+      if (validVersionIndex !== -1) {
+        parts = parts.splice(validVersionIndex);
+        for (let i = 0; i < minMinorVersionCount + 1 - parts.length; i++) {
+          parts.unshift(0);
+        }
+      }
+      version = parts.reverse().join(".");
+    }
+
+    return { name, version };
+  }
+
+  return null;
+}
+
+function parseUserAgent(ua) {
+  return {
+    browser: detect(ua, BROWSERS),
+    os: detect(ua, OSES),
+  };
+}
+
+module.exports = { parseUserAgent };
diff --git a/devtools/client/responsive/utils/window.js b/devtools/client/responsive/utils/window.js
new file mode 100644
index 0000000000..f9bdaf0879
--- /dev/null
+++ b/devtools/client/responsive/utils/window.js
@@ -0,0 +1,43 @@
+/* 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";
+
+/**
+ * Returns the `nsIDOMWindow` toplevel window for any child/inner window
+ */
+function getTopLevelWindow(window) {
+  return window.browsingContext.topChromeWindow;
+}
+exports.getTopLevelWindow = getTopLevelWindow;
+
+function getDOMWindowUtils(window) {
+  return window.windowUtils;
+}
+exports.getDOMWindowUtils = getDOMWindowUtils;
+
+/**
+ * Check if the given browser window has finished the startup.
+ * @params {nsIDOMWindow} window
+ */
+const isStartupFinished = window => window.gBrowserInit?.delayedStartupFinished;
+
+function startup(window) {
+  return new Promise(resolve => {
+    if (isStartupFinished(window)) {
+      resolve(window);
+      return;
+    }
+    Services.obs.addObserver(function listener({ subject }) {
+      if (subject === window) {
+        Services.obs.removeObserver(
+          listener,
+          "browser-delayed-startup-finished"
+        );
+        resolve(window);
+      }
+    }, "browser-delayed-startup-finished");
+  });
+}
+exports.startup = startup;