Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

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

53 files changed, 8098 insertions, 0 deletions

diff --git a/browser/components/shell/HeadlessShell.sys.mjs b/browser/components/shell/HeadlessShell.sys.mjs
new file mode 100644
index 0000000000..c87a7a6d56
--- /dev/null
+++ b/browser/components/shell/HeadlessShell.sys.mjs
@@ -0,0 +1,262 @@
+/* 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/. */
+
+import { E10SUtils } from "resource://gre/modules/E10SUtils.sys.mjs";
+import { HiddenFrame } from "resource://gre/modules/HiddenFrame.sys.mjs";
+
+// Refrences to the progress listeners to keep them from being gc'ed
+// before they are called.
+const progressListeners = new Set();
+
+export class ScreenshotParent extends JSWindowActorParent {
+  getDimensions(params) {
+    return this.sendQuery("GetDimensions", params);
+  }
+}
+
+ChromeUtils.registerWindowActor("Screenshot", {
+  parent: {
+    esModuleURI: "resource:///modules/HeadlessShell.sys.mjs",
+  },
+  child: {
+    esModuleURI: "resource:///modules/ScreenshotChild.sys.mjs",
+  },
+});
+
+function loadContentWindow(browser, url) {
+  let uri;
+  try {
+    uri = Services.io.newURI(url);
+  } catch (e) {
+    let msg = `Invalid URL passed to loadContentWindow(): ${url}`;
+    console.error(msg);
+    return Promise.reject(new Error(msg));
+  }
+
+  const principal = Services.scriptSecurityManager.getSystemPrincipal();
+  return new Promise((resolve, reject) => {
+    let oa = E10SUtils.predictOriginAttributes({
+      browser,
+    });
+    let loadURIOptions = {
+      triggeringPrincipal: principal,
+      remoteType: E10SUtils.getRemoteTypeForURI(
+        url,
+        true,
+        false,
+        E10SUtils.DEFAULT_REMOTE_TYPE,
+        null,
+        oa
+      ),
+    };
+    browser.loadURI(uri, loadURIOptions);
+    let { webProgress } = browser;
+
+    let progressListener = {
+      onLocationChange(progress, request, location, flags) {
+        // Ignore inner-frame events
+        if (!progress.isTopLevel) {
+          return;
+        }
+        // Ignore events that don't change the document
+        if (flags & Ci.nsIWebProgressListener.LOCATION_CHANGE_SAME_DOCUMENT) {
+          return;
+        }
+        // Ignore the initial about:blank, unless about:blank is requested
+        if (location.spec == "about:blank" && uri.spec != "about:blank") {
+          return;
+        }
+
+        progressListeners.delete(progressListener);
+        webProgress.removeProgressListener(progressListener);
+        resolve();
+      },
+      QueryInterface: ChromeUtils.generateQI([
+        "nsIWebProgressListener",
+        "nsISupportsWeakReference",
+      ]),
+    };
+    progressListeners.add(progressListener);
+    webProgress.addProgressListener(
+      progressListener,
+      Ci.nsIWebProgress.NOTIFY_LOCATION
+    );
+  });
+}
+
+async function takeScreenshot(
+  fullWidth,
+  fullHeight,
+  contentWidth,
+  contentHeight,
+  path,
+  url
+) {
+  let frame;
+  try {
+    frame = new HiddenFrame();
+    let windowlessBrowser = await frame.get();
+
+    let doc = windowlessBrowser.document;
+    let browser = doc.createXULElement("browser");
+    browser.setAttribute("remote", "true");
+    browser.setAttribute("type", "content");
+    browser.setAttribute(
+      "style",
+      `width: ${contentWidth}px; min-width: ${contentWidth}px; height: ${contentHeight}px; min-height: ${contentHeight}px;`
+    );
+    browser.setAttribute("maychangeremoteness", "true");
+    doc.documentElement.appendChild(browser);
+
+    await loadContentWindow(browser, url);
+
+    let actor =
+      browser.browsingContext.currentWindowGlobal.getActor("Screenshot");
+    let dimensions = await actor.getDimensions();
+
+    let canvas = doc.createElementNS(
+      "http://www.w3.org/1999/xhtml",
+      "html:canvas"
+    );
+    let context = canvas.getContext("2d");
+    let width = dimensions.innerWidth;
+    let height = dimensions.innerHeight;
+    if (fullWidth) {
+      width += dimensions.scrollMaxX - dimensions.scrollMinX;
+    }
+    if (fullHeight) {
+      height += dimensions.scrollMaxY - dimensions.scrollMinY;
+    }
+    canvas.width = width;
+    canvas.height = height;
+    let rect = new DOMRect(0, 0, width, height);
+
+    let snapshot =
+      await browser.browsingContext.currentWindowGlobal.drawSnapshot(
+        rect,
+        1,
+        "rgb(255, 255, 255)"
+      );
+    context.drawImage(snapshot, 0, 0);
+
+    snapshot.close();
+
+    let blob = await new Promise(resolve => canvas.toBlob(resolve));
+
+    let reader = await new Promise(resolve => {
+      let fr = new FileReader();
+      fr.onloadend = () => resolve(fr);
+      fr.readAsArrayBuffer(blob);
+    });
+
+    await IOUtils.write(path, new Uint8Array(reader.result));
+    dump("Screenshot saved to: " + path + "\n");
+  } catch (e) {
+    dump("Failure taking screenshot: " + e + "\n");
+  } finally {
+    if (frame) {
+      frame.destroy();
+    }
+  }
+}
+
+export let HeadlessShell = {
+  async handleCmdLineArgs(cmdLine, URLlist) {
+    try {
+      // Don't quit even though we don't create a window
+      Services.startup.enterLastWindowClosingSurvivalArea();
+
+      // Default options
+      let fullWidth = true;
+      let fullHeight = true;
+      // Most common screen resolution of Firefox users
+      let contentWidth = 1366;
+      let contentHeight = 768;
+
+      // Parse `window-size`
+      try {
+        var dimensionsStr = cmdLine.handleFlagWithParam("window-size", true);
+      } catch (e) {
+        dump("expected format: --window-size width[,height]\n");
+        return;
+      }
+      if (dimensionsStr) {
+        let success;
+        let dimensions = dimensionsStr.split(",", 2);
+        if (dimensions.length == 1) {
+          success = dimensions[0] > 0;
+          if (success) {
+            fullWidth = false;
+            fullHeight = true;
+            contentWidth = dimensions[0];
+          }
+        } else {
+          success = dimensions[0] > 0 && dimensions[1] > 0;
+          if (success) {
+            fullWidth = false;
+            fullHeight = false;
+            contentWidth = dimensions[0];
+            contentHeight = dimensions[1];
+          }
+        }
+
+        if (!success) {
+          dump("expected format: --window-size width[,height]\n");
+          return;
+        }
+      }
+
+      let urlOrFileToSave = null;
+      try {
+        urlOrFileToSave = cmdLine.handleFlagWithParam("screenshot", true);
+      } catch (e) {
+        // We know that the flag exists so we only get here if there was no parameter.
+        cmdLine.handleFlag("screenshot", true); // Remove `screenshot`
+      }
+
+      // Assume that the remaining arguments that do not start
+      // with a hyphen are URLs
+      for (let i = 0; i < cmdLine.length; ++i) {
+        const argument = cmdLine.getArgument(i);
+        if (argument.startsWith("-")) {
+          dump(`Warning: unrecognized command line flag ${argument}\n`);
+          // To emulate the pre-nsICommandLine behavior, we ignore
+          // the argument after an unrecognized flag.
+          ++i;
+        } else {
+          URLlist.push(argument);
+        }
+      }
+
+      let path = null;
+      if (urlOrFileToSave && !URLlist.length) {
+        // URL was specified next to "-screenshot"
+        // Example: -screenshot https://www.example.com -attach-console
+        URLlist.push(urlOrFileToSave);
+      } else {
+        path = urlOrFileToSave;
+      }
+
+      if (!path) {
+        path = PathUtils.join(cmdLine.workingDirectory.path, "screenshot.png");
+      }
+
+      if (URLlist.length == 1) {
+        await takeScreenshot(
+          fullWidth,
+          fullHeight,
+          contentWidth,
+          contentHeight,
+          path,
+          URLlist[0]
+        );
+      } else {
+        dump("expected exactly one URL when using `screenshot`\n");
+      }
+    } finally {
+      Services.startup.exitLastWindowClosingSurvivalArea();
+      Services.startup.quit(Ci.nsIAppStartup.eForceQuit);
+    }
+  },
+};
diff --git a/browser/components/shell/ScreenshotChild.sys.mjs b/browser/components/shell/ScreenshotChild.sys.mjs
new file mode 100644
index 0000000000..994cb1a27e
--- /dev/null
+++ b/browser/components/shell/ScreenshotChild.sys.mjs
@@ -0,0 +1,31 @@
+/* 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/. */
+
+export class ScreenshotChild extends JSWindowActorChild {
+  receiveMessage(message) {
+    if (message.name == "GetDimensions") {
+      return this.getDimensions();
+    }
+    return null;
+  }
+
+  async getDimensions() {
+    if (this.document.readyState != "complete") {
+      await new Promise(resolve =>
+        this.contentWindow.addEventListener("load", resolve, { once: true })
+      );
+    }
+
+    let { contentWindow } = this;
+
+    return {
+      innerWidth: contentWindow.innerWidth,
+      innerHeight: contentWindow.innerHeight,
+      scrollMinX: contentWindow.scrollMinX,
+      scrollMaxX: contentWindow.scrollMaxX,
+      scrollMinY: contentWindow.scrollMinY,
+      scrollMaxY: contentWindow.scrollMaxY,
+    };
+  }
+}
diff --git a/browser/components/shell/ShellService.sys.mjs b/browser/components/shell/ShellService.sys.mjs
new file mode 100644
index 0000000000..b871040db1
--- /dev/null
+++ b/browser/components/shell/ShellService.sys.mjs
@@ -0,0 +1,572 @@
+/* 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/. */
+
+import { AppConstants } from "resource://gre/modules/AppConstants.sys.mjs";
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
+  Subprocess: "resource://gre/modules/Subprocess.sys.mjs",
+  WindowsRegistry: "resource://gre/modules/WindowsRegistry.sys.mjs",
+  setTimeout: "resource://gre/modules/Timer.sys.mjs",
+});
+
+XPCOMUtils.defineLazyServiceGetter(
+  lazy,
+  "XreDirProvider",
+  "@mozilla.org/xre/directory-provider;1",
+  "nsIXREDirProvider"
+);
+
+XPCOMUtils.defineLazyGetter(lazy, "log", () => {
+  let { ConsoleAPI } = ChromeUtils.importESModule(
+    "resource://gre/modules/Console.sys.mjs"
+  );
+  let consoleOptions = {
+    // tip: set maxLogLevel to "debug" and use log.debug() to create detailed
+    // messages during development. See LOG_LEVELS in Console.sys.mjs for details.
+    maxLogLevel: "error",
+    maxLogLevelPref: "browser.shell.loglevel",
+    prefix: "ShellService",
+  };
+  return new ConsoleAPI(consoleOptions);
+});
+
+/**
+ * Internal functionality to save and restore the docShell.allow* properties.
+ */
+let ShellServiceInternal = {
+  /**
+   * Used to determine whether or not to offer "Set as desktop background"
+   * functionality. Even if shell service is available it is not
+   * guaranteed that it is able to set the background for every desktop
+   * which is especially true for Linux with its many different desktop
+   * environments.
+   */
+  get canSetDesktopBackground() {
+    if (AppConstants.platform == "win" || AppConstants.platform == "macosx") {
+      return true;
+    }
+
+    if (AppConstants.platform == "linux") {
+      if (this.shellService) {
+        let linuxShellService = this.shellService.QueryInterface(
+          Ci.nsIGNOMEShellService
+        );
+        return linuxShellService.canSetDesktopBackground;
+      }
+    }
+
+    return false;
+  },
+
+  isDefaultBrowserOptOut() {
+    if (AppConstants.platform == "win") {
+      let optOutValue = lazy.WindowsRegistry.readRegKey(
+        Ci.nsIWindowsRegKey.ROOT_KEY_CURRENT_USER,
+        "Software\\Mozilla\\Firefox",
+        "DefaultBrowserOptOut"
+      );
+      lazy.WindowsRegistry.removeRegKey(
+        Ci.nsIWindowsRegKey.ROOT_KEY_CURRENT_USER,
+        "Software\\Mozilla\\Firefox",
+        "DefaultBrowserOptOut"
+      );
+      if (optOutValue == "True") {
+        Services.prefs.setBoolPref("browser.shell.checkDefaultBrowser", false);
+        return true;
+      }
+    }
+    return false;
+  },
+
+  /**
+   * Used to determine whether or not to show a "Set Default Browser"
+   * query dialog. This attribute is true if the application is starting
+   * up and "browser.shell.checkDefaultBrowser" is true, otherwise it
+   * is false.
+   */
+  _checkedThisSession: false,
+  get shouldCheckDefaultBrowser() {
+    // If we've already checked, the browser has been started and this is a
+    // new window open, and we don't want to check again.
+    if (this._checkedThisSession) {
+      return false;
+    }
+
+    if (!Services.prefs.getBoolPref("browser.shell.checkDefaultBrowser")) {
+      return false;
+    }
+
+    if (this.isDefaultBrowserOptOut()) {
+      return false;
+    }
+
+    return true;
+  },
+
+  set shouldCheckDefaultBrowser(shouldCheck) {
+    Services.prefs.setBoolPref(
+      "browser.shell.checkDefaultBrowser",
+      !!shouldCheck
+    );
+  },
+
+  isDefaultBrowser(startupCheck, forAllTypes) {
+    // If this is the first browser window, maintain internal state that we've
+    // checked this session (so that subsequent window opens don't show the
+    // default browser dialog).
+    if (startupCheck) {
+      this._checkedThisSession = true;
+    }
+    if (this.shellService) {
+      return this.shellService.isDefaultBrowser(forAllTypes);
+    }
+    return false;
+  },
+
+  /*
+   * Invoke the Windows Default Browser agent with the given options.
+   *
+   * Separated for easy stubbing in tests.
+   */
+  _callExternalDefaultBrowserAgent(options = {}) {
+    const wdba = Services.dirsvc.get("XREExeF", Ci.nsIFile);
+    wdba.leafName = "default-browser-agent.exe";
+    return lazy.Subprocess.call({
+      ...options,
+      command: options.command || wdba.path,
+    });
+  },
+
+  /*
+   * Check if UserChoice is impossible.
+   *
+   * Separated for easy stubbing in tests.
+   *
+   * @return string telemetry result like "Err*", or null if UserChoice
+   * is possible.
+   */
+  _userChoiceImpossibleTelemetryResult() {
+    if (!ShellService.checkAllProgIDsExist()) {
+      return "ErrProgID";
+    }
+    if (!ShellService.checkBrowserUserChoiceHashes()) {
+      return "ErrHash";
+    }
+    return null;
+  },
+
+  /*
+   * Accommodate `setDefaultPDFHandlerOnlyReplaceBrowsers` feature.
+   * @return true if Firefox should set itself as default PDF handler, false
+   * otherwise.
+   */
+  _shouldSetDefaultPDFHandler() {
+    if (
+      !lazy.NimbusFeatures.shellService.getVariable(
+        "setDefaultPDFHandlerOnlyReplaceBrowsers"
+      )
+    ) {
+      return true;
+    }
+
+    const handler = this.getDefaultPDFHandler();
+    if (handler === null) {
+      // We only get an exception when something went really wrong.  Fail
+      // safely: don't set Firefox as default PDF handler.
+      lazy.log.warn(
+        "Could not determine default PDF handler: not setting Firefox as " +
+          "default PDF handler!"
+      );
+      return false;
+    }
+
+    if (!handler.registered) {
+      lazy.log.debug(
+        "Current default PDF handler has no registered association; " +
+          "should set as default PDF handler."
+      );
+      return true;
+    }
+
+    if (handler.knownBrowser) {
+      lazy.log.debug(
+        "Current default PDF handler progID matches known browser; should " +
+          "set as default PDF handler."
+      );
+      return true;
+    }
+
+    lazy.log.debug(
+      "Current default PDF handler progID does not match known browser " +
+        "prefix; should not set as default PDF handler."
+    );
+    return false;
+  },
+
+  getDefaultPDFHandler() {
+    const knownBrowserPrefixes = [
+      "AppXq0fevzme2pys62n3e0fbqa7peapykr8v", // Edge before Blink, per https://stackoverflow.com/a/32724723.
+      "Brave", // For "BraveFile".
+      "Chrome", // For "ChromeHTML".
+      "Firefox", // For "FirefoxHTML-*" or "FirefoxPDF-*".  Need to take from other installations of Firefox!
+      "IE", // Best guess.
+      "MSEdge", // For "MSEdgePDF".  Edgium.
+      "Opera", // For "OperaStable", presumably varying with channel.
+      "Yandex", // For "YandexPDF.IHKFKZEIOKEMR6BGF62QXCRIKM", presumably varying with installation.
+    ];
+
+    let currentProgID = "";
+    try {
+      // Returns the empty string when no association is registered, in
+      // which case the prefix matching will fail and we'll set Firefox as
+      // the default PDF handler.
+      currentProgID = this.queryCurrentDefaultHandlerFor(".pdf");
+    } catch (e) {
+      // We only get an exception when something went really wrong.  Fail
+      // safely: don't set Firefox as default PDF handler.
+      lazy.log.warn("Failed to queryCurrentDefaultHandlerFor:");
+      return null;
+    }
+
+    if (currentProgID == "") {
+      return { registered: false, knownBrowser: false };
+    }
+
+    const knownBrowserPrefix = knownBrowserPrefixes.find(it =>
+      currentProgID.startsWith(it)
+    );
+
+    if (knownBrowserPrefix) {
+      lazy.log.debug(`Found known browser prefix: ${knownBrowserPrefix}`);
+    }
+
+    return {
+      registered: true,
+      knownBrowser: !!knownBrowserPrefix,
+    };
+  },
+
+  /*
+   * Set the default browser through the UserChoice registry keys on Windows.
+   *
+   * NOTE: This does NOT open the System Settings app for manual selection
+   * in case of failure. If that is desired, catch the exception and call
+   * setDefaultBrowser().
+   *
+   * @return Promise, resolves when successful, rejects with Error on failure.
+   */
+  async setAsDefaultUserChoice() {
+    if (AppConstants.platform != "win") {
+      throw new Error("Windows-only");
+    }
+
+    lazy.log.info("Setting Firefox as default using UserChoice");
+
+    // We launch the WDBA to handle the registry writes, see
+    // SetDefaultBrowserUserChoice() in
+    // toolkit/mozapps/defaultagent/SetDefaultBrowser.cpp.
+    // This is external in case an overzealous antimalware product decides to
+    // quarrantine any program that writes UserChoice, though this has not
+    // occurred during extensive testing.
+
+    let telemetryResult = "ErrOther";
+
+    try {
+      telemetryResult =
+        this._userChoiceImpossibleTelemetryResult() ?? "ErrOther";
+      if (telemetryResult == "ErrProgID") {
+        throw new Error("checkAllProgIDsExist() failed");
+      }
+      if (telemetryResult == "ErrHash") {
+        throw new Error("checkBrowserUserChoiceHashes() failed");
+      }
+
+      const aumi = lazy.XreDirProvider.getInstallHash();
+
+      telemetryResult = "ErrLaunchExe";
+      const exeArgs = ["set-default-browser-user-choice", aumi];
+      if (
+        lazy.NimbusFeatures.shellService.getVariable("setDefaultPDFHandler")
+      ) {
+        if (this._shouldSetDefaultPDFHandler()) {
+          lazy.log.info("Setting Firefox as default PDF handler");
+          exeArgs.push(".pdf", "FirefoxPDF");
+        } else {
+          lazy.log.info("Not setting Firefox as default PDF handler");
+        }
+      }
+      const exeProcess = await this._callExternalDefaultBrowserAgent({
+        arguments: exeArgs,
+      });
+      telemetryResult = "ErrOther";
+      await this._handleWDBAResult(exeProcess);
+      telemetryResult = "Success";
+    } catch (ex) {
+      if (ex instanceof WDBAError) {
+        telemetryResult = ex.telemetryResult;
+      }
+
+      throw ex;
+    } finally {
+      try {
+        const histogram = Services.telemetry.getHistogramById(
+          "BROWSER_SET_DEFAULT_USER_CHOICE_RESULT"
+        );
+        histogram.add(telemetryResult);
+      } catch (ex) {}
+    }
+  },
+
+  async setAsDefaultPDFHandlerUserChoice() {
+    if (AppConstants.platform != "win") {
+      throw new Error("Windows-only");
+    }
+
+    // See comment in setAsDefaultUserChoice for an explanation of why we shell
+    // out to WDBA.
+    let telemetryResult = "ErrOther";
+
+    try {
+      const aumi = lazy.XreDirProvider.getInstallHash();
+      const exeProcess = await this._callExternalDefaultBrowserAgent({
+        arguments: [
+          "set-default-extension-handlers-user-choice",
+          aumi,
+          ".pdf",
+          "FirefoxPDF",
+        ],
+      });
+      telemetryResult = "ErrOther";
+      await this._handleWDBAResult(exeProcess);
+      telemetryResult = "Success";
+    } catch (ex) {
+      if (ex instanceof WDBAError) {
+        telemetryResult = ex.telemetryResult;
+      }
+
+      throw ex;
+    } finally {
+      try {
+        const histogram = Services.telemetry.getHistogramById(
+          "BROWSER_SET_DEFAULT_PDF_HANDLER_USER_CHOICE_RESULT"
+        );
+        histogram.add(telemetryResult);
+      } catch (ex) {}
+    }
+  },
+
+  // override nsIShellService.setDefaultBrowser() on the ShellService proxy.
+  setDefaultBrowser(claimAllTypes, forAllUsers) {
+    // On Windows 10, our best chance is to set UserChoice, so try that first.
+    if (
+      AppConstants.isPlatformAndVersionAtLeast("win", "10") &&
+      lazy.NimbusFeatures.shellService.getVariable(
+        "setDefaultBrowserUserChoice"
+      )
+    ) {
+      // nsWindowsShellService::SetDefaultBrowser() kicks off several
+      // operations, but doesn't wait for their result. So we don't need to
+      // await the result of setAsDefaultUserChoice() here, either, we just need
+      // to fall back in case it fails.
+      this.setAsDefaultUserChoice().catch(err => {
+        console.error(err);
+        this.shellService.setDefaultBrowser(claimAllTypes, forAllUsers);
+      });
+      return;
+    }
+
+    this.shellService.setDefaultBrowser(claimAllTypes, forAllUsers);
+  },
+
+  setAsDefault() {
+    let claimAllTypes = true;
+    let setAsDefaultError = false;
+    if (AppConstants.platform == "win") {
+      try {
+        // In Windows 8+, the UI for selecting default protocol is much
+        // nicer than the UI for setting file type associations. So we
+        // only show the protocol association screen on Windows 8+.
+        // Windows 8 is version 6.2.
+        let version = Services.sysinfo.getProperty("version");
+        claimAllTypes = parseFloat(version) < 6.2;
+      } catch (ex) {}
+    }
+    try {
+      ShellService.setDefaultBrowser(claimAllTypes, false);
+    } catch (ex) {
+      setAsDefaultError = true;
+      console.error(ex);
+    }
+    // Here BROWSER_IS_USER_DEFAULT and BROWSER_SET_USER_DEFAULT_ERROR appear
+    // to be inverse of each other, but that is only because this function is
+    // called when the browser is set as the default. During startup we record
+    // the BROWSER_IS_USER_DEFAULT value without recording BROWSER_SET_USER_DEFAULT_ERROR.
+    Services.telemetry
+      .getHistogramById("BROWSER_IS_USER_DEFAULT")
+      .add(!setAsDefaultError);
+    Services.telemetry
+      .getHistogramById("BROWSER_SET_DEFAULT_ERROR")
+      .add(setAsDefaultError);
+  },
+
+  setAsDefaultPDFHandler(onlyIfKnownBrowser = false) {
+    if (onlyIfKnownBrowser && !this.getDefaultPDFHandler().knownBrowser) {
+      return;
+    }
+
+    if (AppConstants.isPlatformAndVersionAtLeast("win", "10")) {
+      this.setAsDefaultPDFHandlerUserChoice();
+    }
+  },
+
+  /**
+   * Determine if we're the default handler for the given file extension (like
+   * ".pdf") or protocol (like "https").  Windows-only for now.
+   *
+   * @returns {boolean} true if we are the default handler, false otherwise.
+   */
+  isDefaultHandlerFor(aFileExtensionOrProtocol) {
+    if (AppConstants.platform == "win") {
+      return this.shellService
+        .QueryInterface(Ci.nsIWindowsShellService)
+        .isDefaultHandlerFor(aFileExtensionOrProtocol);
+    }
+    return false;
+  },
+
+  /**
+   * Checks if Firefox app can and isn't pinned to OS "taskbar."
+   *
+   * @throws if not called from main process.
+   */
+  async doesAppNeedPin(privateBrowsing = false) {
+    if (
+      Services.appinfo.processType !== Services.appinfo.PROCESS_TYPE_DEFAULT
+    ) {
+      throw new Components.Exception(
+        "Can't determine pinned from child process",
+        Cr.NS_ERROR_NOT_AVAILABLE
+      );
+    }
+
+    // Pretend pinning is not needed/supported if remotely disabled.
+    if (lazy.NimbusFeatures.shellService.getVariable("disablePin")) {
+      return false;
+    }
+
+    // Currently this only works on certain Windows versions.
+    try {
+      // First check if we can even pin the app where an exception means no.
+      await this.shellService
+        .QueryInterface(Ci.nsIWindowsShellService)
+        .checkPinCurrentAppToTaskbarAsync(privateBrowsing);
+      let winTaskbar = Cc["@mozilla.org/windows-taskbar;1"].getService(
+        Ci.nsIWinTaskbar
+      );
+
+      // Then check if we're already pinned.
+      return !(await this.shellService.isCurrentAppPinnedToTaskbarAsync(
+        privateBrowsing
+          ? winTaskbar.defaultPrivateGroupId
+          : winTaskbar.defaultGroupId
+      ));
+    } catch (ex) {}
+
+    // Next check mac pinning to dock.
+    try {
+      // Accessing this.macDockSupport will ensure we're actually running
+      // on Mac (it's possible to be on Linux in this block).
+      const isInDock = this.macDockSupport.isAppInDock;
+      // We can't pin Private Browsing mode on Mac, only a shortcut to the vanilla app
+      return privateBrowsing ? false : !isInDock;
+    } catch (ex) {}
+    return false;
+  },
+
+  /**
+   * Pin Firefox app to the OS "taskbar."
+   */
+  async pinToTaskbar(privateBrowsing = false) {
+    if (await this.doesAppNeedPin(privateBrowsing)) {
+      try {
+        if (AppConstants.platform == "win") {
+          await this.shellService.pinCurrentAppToTaskbarAsync(privateBrowsing);
+        } else if (AppConstants.platform == "macosx") {
+          this.macDockSupport.ensureAppIsPinnedToDock();
+        }
+      } catch (ex) {
+        console.error(ex);
+      }
+    }
+  },
+
+  async _handleWDBAResult(exeProcess, exeWaitTimeoutMs = 2000) {
+    // Exit codes, see toolkit/mozapps/defaultagent/SetDefaultBrowser.h
+    const S_OK = 0;
+    const STILL_ACTIVE = 0x103;
+    const MOZ_E_NO_PROGID = 0xa0000001;
+    const MOZ_E_HASH_CHECK = 0xa0000002;
+    const MOZ_E_REJECTED = 0xa0000003;
+    const MOZ_E_BUILD = 0xa0000004;
+
+    const exeWaitPromise = exeProcess.wait();
+    const timeoutPromise = new Promise(function (resolve) {
+      lazy.setTimeout(
+        () => resolve({ exitCode: STILL_ACTIVE }),
+        exeWaitTimeoutMs
+      );
+    });
+
+    const { exitCode } = await Promise.race([exeWaitPromise, timeoutPromise]);
+
+    if (exitCode != S_OK) {
+      const telemetryResult =
+        new Map([
+          [STILL_ACTIVE, "ErrExeTimeout"],
+          [MOZ_E_NO_PROGID, "ErrExeProgID"],
+          [MOZ_E_HASH_CHECK, "ErrExeHash"],
+          [MOZ_E_REJECTED, "ErrExeRejected"],
+          [MOZ_E_BUILD, "ErrBuild"],
+        ]).get(exitCode) ?? "ErrExeOther";
+
+      throw new WDBAError(exitCode, telemetryResult);
+    }
+  },
+};
+
+XPCOMUtils.defineLazyServiceGetters(ShellServiceInternal, {
+  shellService: ["@mozilla.org/browser/shell-service;1", "nsIShellService"],
+  macDockSupport: ["@mozilla.org/widget/macdocksupport;1", "nsIMacDockSupport"],
+});
+
+/**
+ * The external API exported by this module.
+ */
+export var ShellService = new Proxy(ShellServiceInternal, {
+  get(target, name) {
+    if (name in target) {
+      return target[name];
+    }
+    if (target.shellService) {
+      return target.shellService[name];
+    }
+    Services.console.logStringMessage(
+      `${name} not found in ShellService: ${target.shellService}`
+    );
+    return undefined;
+  },
+});
+
+class WDBAError extends Error {
+  constructor(exitCode, telemetryResult) {
+    super(`WDBA nonzero exit code ${exitCode}: ${telemetryResult}`);
+
+    this.exitCode = exitCode;
+    this.telemetryResult = telemetryResult;
+  }
+}
diff --git a/browser/components/shell/WindowsDefaultBrowser.cpp b/browser/components/shell/WindowsDefaultBrowser.cpp
new file mode 100644
index 0000000000..34e00be89f
--- /dev/null
+++ b/browser/components/shell/WindowsDefaultBrowser.cpp
@@ -0,0 +1,162 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+/**
+ * This file exists so that LaunchModernSettingsDialogDefaultApps can be called
+ * without linking to libxul.
+ */
+#include "WindowsDefaultBrowser.h"
+
+#include "city.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/WindowsVersion.h"
+#include "mozilla/WinHeaderOnlyUtils.h"
+
+// Needed for access to IApplicationActivationManager
+// This must be before any other includes that might include shlobj.h
+#ifdef _WIN32_WINNT
+#  undef _WIN32_WINNT
+#endif
+#define _WIN32_WINNT 0x0600
+#define INITGUID
+#undef NTDDI_VERSION
+#define NTDDI_VERSION NTDDI_WIN8
+#include <shlobj.h>
+
+#include <lm.h>
+#include <shlwapi.h>
+#include <wchar.h>
+#include <windows.h>
+
+#define APP_REG_NAME_BASE L"Firefox-"
+
+static bool IsWindowsLogonConnected() {
+  WCHAR userName[UNLEN + 1];
+  DWORD size = mozilla::ArrayLength(userName);
+  if (!GetUserNameW(userName, &size)) {
+    return false;
+  }
+
+  LPUSER_INFO_24 info;
+  if (NetUserGetInfo(nullptr, userName, 24, (LPBYTE*)&info) != NERR_Success) {
+    return false;
+  }
+  bool connected = info->usri24_internet_identity;
+  NetApiBufferFree(info);
+
+  return connected;
+}
+
+static bool SettingsAppBelievesConnected() {
+  const wchar_t* keyPath = L"SOFTWARE\\Microsoft\\Windows\\Shell\\Associations";
+  const wchar_t* valueName = L"IsConnectedAtLogon";
+
+  uint32_t value = 0;
+  DWORD size = sizeof(uint32_t);
+  LSTATUS ls = RegGetValueW(HKEY_CURRENT_USER, keyPath, valueName, RRF_RT_ANY,
+                            nullptr, &value, &size);
+  if (ls != ERROR_SUCCESS) {
+    return false;
+  }
+
+  return !!value;
+}
+
+bool GetAppRegName(mozilla::UniquePtr<wchar_t[]>& aAppRegName) {
+  mozilla::UniquePtr<wchar_t[]> appDirStr;
+  bool success = GetInstallDirectory(appDirStr);
+  if (!success) {
+    return success;
+  }
+
+  uint64_t hash = CityHash64(reinterpret_cast<char*>(appDirStr.get()),
+                             wcslen(appDirStr.get()) * sizeof(wchar_t));
+
+  const wchar_t* format = L"%s%I64X";
+  int bufferSize = _scwprintf(format, APP_REG_NAME_BASE, hash);
+  ++bufferSize;  // Extra byte for terminating null
+  aAppRegName = mozilla::MakeUnique<wchar_t[]>(bufferSize);
+
+  _snwprintf_s(aAppRegName.get(), bufferSize, _TRUNCATE, format,
+               APP_REG_NAME_BASE, hash);
+
+  return success;
+}
+
+bool LaunchControlPanelDefaultPrograms() {
+  // Build the path control.exe path safely
+  WCHAR controlEXEPath[MAX_PATH + 1] = {'\0'};
+  if (!GetSystemDirectoryW(controlEXEPath, MAX_PATH)) {
+    return false;
+  }
+  LPCWSTR controlEXE = L"control.exe";
+  if (wcslen(controlEXEPath) + wcslen(controlEXE) >= MAX_PATH) {
+    return false;
+  }
+  if (!PathAppendW(controlEXEPath, controlEXE)) {
+    return false;
+  }
+
+  const wchar_t* paramFormat =
+      L"control.exe /name Microsoft.DefaultPrograms "
+      L"/page pageDefaultProgram\\pageAdvancedSettings?pszAppName=%s";
+  mozilla::UniquePtr<wchar_t[]> appRegName;
+  GetAppRegName(appRegName);
+  int bufferSize = _scwprintf(paramFormat, appRegName.get());
+  ++bufferSize;  // Extra byte for terminating null
+  mozilla::UniquePtr<wchar_t[]> params =
+      mozilla::MakeUnique<wchar_t[]>(bufferSize);
+  _snwprintf_s(params.get(), bufferSize, _TRUNCATE, paramFormat,
+               appRegName.get());
+
+  STARTUPINFOW si = {sizeof(si), 0};
+  si.dwFlags = STARTF_USESHOWWINDOW;
+  si.wShowWindow = SW_SHOWDEFAULT;
+  PROCESS_INFORMATION pi = {0};
+  if (!CreateProcessW(controlEXEPath, params.get(), nullptr, nullptr, FALSE, 0,
+                      nullptr, nullptr, &si, &pi)) {
+    return false;
+  }
+  CloseHandle(pi.hProcess);
+  CloseHandle(pi.hThread);
+
+  return true;
+}
+
+bool LaunchModernSettingsDialogDefaultApps() {
+  if (!mozilla::IsWindowsBuildOrLater(14965) && !IsWindowsLogonConnected() &&
+      SettingsAppBelievesConnected()) {
+    // Use the classic Control Panel to work around a bug of older
+    // builds of Windows 10.
+    return LaunchControlPanelDefaultPrograms();
+  }
+
+  IApplicationActivationManager* pActivator;
+  HRESULT hr = CoCreateInstance(
+      CLSID_ApplicationActivationManager, nullptr, CLSCTX_INPROC,
+      IID_IApplicationActivationManager, (void**)&pActivator);
+
+  if (SUCCEEDED(hr)) {
+    DWORD pid;
+    hr = pActivator->ActivateApplication(
+        L"windows.immersivecontrolpanel_cw5n1h2txyewy"
+        L"!microsoft.windows.immersivecontrolpanel",
+        L"page=SettingsPageAppsDefaults", AO_NONE, &pid);
+    if (SUCCEEDED(hr)) {
+      // Do not check error because we could at least open
+      // the "Default apps" setting.
+      pActivator->ActivateApplication(
+          L"windows.immersivecontrolpanel_cw5n1h2txyewy"
+          L"!microsoft.windows.immersivecontrolpanel",
+          L"page=SettingsPageAppsDefaults"
+          L"&target=SystemSettings_DefaultApps_Browser",
+          AO_NONE, &pid);
+    }
+    pActivator->Release();
+    return SUCCEEDED(hr);
+  }
+  return true;
+}
diff --git a/browser/components/shell/WindowsDefaultBrowser.h b/browser/components/shell/WindowsDefaultBrowser.h
new file mode 100644
index 0000000000..3e081aad38
--- /dev/null
+++ b/browser/components/shell/WindowsDefaultBrowser.h
@@ -0,0 +1,20 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+/**
+ * This file exists so that LaunchModernSettingsDialogDefaultApps can be called
+ * without linking to libxul.
+ */
+
+#ifndef windowsdefaultbrowser_h____
+#define windowsdefaultbrowser_h____
+
+#include "mozilla/UniquePtr.h"
+
+bool GetAppRegName(mozilla::UniquePtr<wchar_t[]>& aAppRegName);
+bool LaunchControlPanelDefaultPrograms();
+bool LaunchModernSettingsDialogDefaultApps();
+
+#endif  // windowsdefaultbrowser_h____
diff --git a/browser/components/shell/WindowsUserChoice.cpp b/browser/components/shell/WindowsUserChoice.cpp
new file mode 100644
index 0000000000..4d6f24704a
--- /dev/null
+++ b/browser/components/shell/WindowsUserChoice.cpp
@@ -0,0 +1,422 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+/*
+ * Generate and check the UserChoice Hash, which protects file and protocol
+ * associations on Windows 10.
+ *
+ * NOTE: This is also used in the WDBA, so it avoids XUL and XPCOM.
+ *
+ * References:
+ * - PS-SFTA by Danysys <https://github.com/DanysysTeam/PS-SFTA>
+ *  - based on a PureBasic version by LMongrain
+ *    <https://github.com/DanysysTeam/SFTA>
+ * - AssocHashGen by "halfmeasuresdisabled", see bug 1225660 and
+ *   <https://www.reddit.com/r/ReverseEngineering/comments/3t7q9m/assochashgen_a_reverse_engineered_version_of/>
+ * - SetUserFTA changelog
+ *   <https://kolbi.cz/blog/2017/10/25/setuserfta-userchoice-hash-defeated-set-file-type-associations-per-user/>
+ */
+
+#include <windows.h>
+#include <sddl.h>      // for ConvertSidToStringSidW
+#include <wincrypt.h>  // for CryptoAPI base64
+#include <bcrypt.h>    // for CNG MD5
+#include <winternl.h>  // for NT_SUCCESS()
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/UniquePtr.h"
+#include "nsWindowsHelpers.h"
+
+#include "WindowsUserChoice.h"
+
+using namespace mozilla;
+
+UniquePtr<wchar_t[]> GetCurrentUserStringSid() {
+  HANDLE rawProcessToken;
+  if (!::OpenProcessToken(::GetCurrentProcess(), TOKEN_QUERY,
+                          &rawProcessToken)) {
+    return nullptr;
+  }
+  nsAutoHandle processToken(rawProcessToken);
+
+  DWORD userSize = 0;
+  if (!(!::GetTokenInformation(processToken.get(), TokenUser, nullptr, 0,
+                               &userSize) &&
+        GetLastError() == ERROR_INSUFFICIENT_BUFFER)) {
+    return nullptr;
+  }
+
+  auto userBytes = MakeUnique<unsigned char[]>(userSize);
+  if (!::GetTokenInformation(processToken.get(), TokenUser, userBytes.get(),
+                             userSize, &userSize)) {
+    return nullptr;
+  }
+
+  wchar_t* rawSid = nullptr;
+  if (!::ConvertSidToStringSidW(
+          reinterpret_cast<PTOKEN_USER>(userBytes.get())->User.Sid, &rawSid)) {
+    return nullptr;
+  }
+  UniquePtr<wchar_t, LocalFreeDeleter> sid(rawSid);
+
+  // Copy instead of passing UniquePtr<wchar_t, LocalFreeDeleter> back to
+  // the caller.
+  int sidLen = ::lstrlenW(sid.get()) + 1;
+  auto outSid = MakeUnique<wchar_t[]>(sidLen);
+  memcpy(outSid.get(), sid.get(), sidLen * sizeof(wchar_t));
+
+  return outSid;
+}
+
+/*
+ * Create the string which becomes the input to the UserChoice hash.
+ *
+ * @see GenerateUserChoiceHash() for parameters.
+ *
+ * @return The formatted string, nullptr on failure.
+ *
+ * NOTE: This uses the format as of Windows 10 20H2 (latest as of this writing),
+ * used at least since 1803.
+ * There was at least one older version, not currently supported: On Win10 RTM
+ * (build 10240, aka 1507) the hash function is the same, but the timestamp and
+ * User Experience string aren't included; instead (for protocols) the string
+ * ends with the exe path. The changelog of SetUserFTA suggests the algorithm
+ * changed in 1703, so there may be two versions: before 1703, and 1703 to now.
+ */
+static UniquePtr<wchar_t[]> FormatUserChoiceString(const wchar_t* aExt,
+                                                   const wchar_t* aUserSid,
+                                                   const wchar_t* aProgId,
+                                                   SYSTEMTIME aTimestamp) {
+  aTimestamp.wSecond = 0;
+  aTimestamp.wMilliseconds = 0;
+
+  FILETIME fileTime = {0};
+  if (!::SystemTimeToFileTime(&aTimestamp, &fileTime)) {
+    return nullptr;
+  }
+
+  // This string is built into Windows as part of the UserChoice hash algorithm.
+  // It might vary across Windows SKUs (e.g. Windows 10 vs. Windows Server), or
+  // across builds of the same SKU, but this is the only currently known
+  // version. There isn't any known way of deriving it, so we assume this
+  // constant value. If we are wrong, we will not be able to generate correct
+  // UserChoice hashes.
+  const wchar_t* userExperience =
+      L"User Choice set via Windows User Experience "
+      L"{D18B6DD5-6124-4341-9318-804003BAFA0B}";
+
+  const wchar_t* userChoiceFmt =
+      L"%s%s%s"
+      L"%08lx"
+      L"%08lx"
+      L"%s";
+  int userChoiceLen = _scwprintf(userChoiceFmt, aExt, aUserSid, aProgId,
+                                 fileTime.dwHighDateTime,
+                                 fileTime.dwLowDateTime, userExperience);
+  userChoiceLen += 1;  // _scwprintf does not include the terminator
+
+  auto userChoice = MakeUnique<wchar_t[]>(userChoiceLen);
+  _snwprintf_s(userChoice.get(), userChoiceLen, _TRUNCATE, userChoiceFmt, aExt,
+               aUserSid, aProgId, fileTime.dwHighDateTime,
+               fileTime.dwLowDateTime, userExperience);
+
+  ::CharLowerW(userChoice.get());
+
+  return userChoice;
+}
+
+// @return The MD5 hash of the input, nullptr on failure.
+static UniquePtr<DWORD[]> CNG_MD5(const unsigned char* bytes, ULONG bytesLen) {
+  constexpr ULONG MD5_BYTES = 16;
+  constexpr ULONG MD5_DWORDS = MD5_BYTES / sizeof(DWORD);
+  UniquePtr<DWORD[]> hash;
+
+  BCRYPT_ALG_HANDLE hAlg = nullptr;
+  if (NT_SUCCESS(::BCryptOpenAlgorithmProvider(&hAlg, BCRYPT_MD5_ALGORITHM,
+                                               nullptr, 0))) {
+    BCRYPT_HASH_HANDLE hHash = nullptr;
+    // As of Windows 7 the hash handle will manage its own object buffer when
+    // pbHashObject is nullptr and cbHashObject is 0.
+    if (NT_SUCCESS(
+            ::BCryptCreateHash(hAlg, &hHash, nullptr, 0, nullptr, 0, 0))) {
+      // BCryptHashData promises not to modify pbInput.
+      if (NT_SUCCESS(::BCryptHashData(hHash, const_cast<unsigned char*>(bytes),
+                                      bytesLen, 0))) {
+        hash = MakeUnique<DWORD[]>(MD5_DWORDS);
+        if (!NT_SUCCESS(::BCryptFinishHash(
+                hHash, reinterpret_cast<unsigned char*>(hash.get()),
+                MD5_DWORDS * sizeof(DWORD), 0))) {
+          hash.reset();
+        }
+      }
+      ::BCryptDestroyHash(hHash);
+    }
+    ::BCryptCloseAlgorithmProvider(hAlg, 0);
+  }
+
+  return hash;
+}
+
+// @return The input bytes encoded as base64, nullptr on failure.
+static UniquePtr<wchar_t[]> CryptoAPI_Base64Encode(const unsigned char* bytes,
+                                                   DWORD bytesLen) {
+  DWORD base64Len = 0;
+  if (!::CryptBinaryToStringW(bytes, bytesLen,
+                              CRYPT_STRING_BASE64 | CRYPT_STRING_NOCRLF,
+                              nullptr, &base64Len)) {
+    return nullptr;
+  }
+  auto base64 = MakeUnique<wchar_t[]>(base64Len);
+  if (!::CryptBinaryToStringW(bytes, bytesLen,
+                              CRYPT_STRING_BASE64 | CRYPT_STRING_NOCRLF,
+                              base64.get(), &base64Len)) {
+    return nullptr;
+  }
+
+  return base64;
+}
+
+static inline DWORD WordSwap(DWORD v) { return (v >> 16) | (v << 16); }
+
+/*
+ * Generate the UserChoice Hash.
+ *
+ * This implementation is based on the references listed above.
+ * It is organized to show the logic as clearly as possible, but at some
+ * point the reasoning is just "this is how it works".
+ *
+ * @param inputString   A null-terminated string to hash.
+ *
+ * @return The base64-encoded hash, or nullptr on failure.
+ */
+static UniquePtr<wchar_t[]> HashString(const wchar_t* inputString) {
+  auto inputBytes = reinterpret_cast<const unsigned char*>(inputString);
+  int inputByteCount = (::lstrlenW(inputString) + 1) * sizeof(wchar_t);
+
+  constexpr size_t DWORDS_PER_BLOCK = 2;
+  constexpr size_t BLOCK_SIZE = sizeof(DWORD) * DWORDS_PER_BLOCK;
+  // Incomplete blocks are ignored.
+  int blockCount = inputByteCount / BLOCK_SIZE;
+
+  if (blockCount == 0) {
+    return nullptr;
+  }
+
+  // Compute an MD5 hash. md5[0] and md5[1] will be used as constant multipliers
+  // in the scramble below.
+  auto md5 = CNG_MD5(inputBytes, inputByteCount);
+  if (!md5) {
+    return nullptr;
+  }
+
+  // The following loop effectively computes two checksums, scrambled like a
+  // hash after every DWORD is added.
+
+  // Constant multipliers for the scramble, one set for each DWORD in a block.
+  const DWORD C0s[DWORDS_PER_BLOCK][5] = {
+      {md5[0] | 1, 0xCF98B111uL, 0x87085B9FuL, 0x12CEB96DuL, 0x257E1D83uL},
+      {md5[1] | 1, 0xA27416F5uL, 0xD38396FFuL, 0x7C932B89uL, 0xBFA49F69uL}};
+  const DWORD C1s[DWORDS_PER_BLOCK][5] = {
+      {md5[0] | 1, 0xEF0569FBuL, 0x689B6B9FuL, 0x79F8A395uL, 0xC3EFEA97uL},
+      {md5[1] | 1, 0xC31713DBuL, 0xDDCD1F0FuL, 0x59C3AF2DuL, 0x35BD1EC9uL}};
+
+  // The checksums.
+  DWORD h0 = 0;
+  DWORD h1 = 0;
+  // Accumulated total of the checksum after each DWORD.
+  DWORD h0Acc = 0;
+  DWORD h1Acc = 0;
+
+  for (int i = 0; i < blockCount; ++i) {
+    for (size_t j = 0; j < DWORDS_PER_BLOCK; ++j) {
+      const DWORD* C0 = C0s[j];
+      const DWORD* C1 = C1s[j];
+
+      DWORD input;
+      memcpy(&input, &inputBytes[(i * DWORDS_PER_BLOCK + j) * sizeof(DWORD)],
+             sizeof(DWORD));
+
+      h0 += input;
+      // Scramble 0
+      h0 *= C0[0];
+      h0 = WordSwap(h0) * C0[1];
+      h0 = WordSwap(h0) * C0[2];
+      h0 = WordSwap(h0) * C0[3];
+      h0 = WordSwap(h0) * C0[4];
+      h0Acc += h0;
+
+      h1 += input;
+      // Scramble 1
+      h1 = WordSwap(h1) * C1[1] + h1 * C1[0];
+      h1 = (h1 >> 16) * C1[2] + h1 * C1[3];
+      h1 = WordSwap(h1) * C1[4] + h1;
+      h1Acc += h1;
+    }
+  }
+
+  DWORD hash[2] = {h0 ^ h1, h0Acc ^ h1Acc};
+
+  return CryptoAPI_Base64Encode(reinterpret_cast<const unsigned char*>(hash),
+                                sizeof(hash));
+}
+
+UniquePtr<wchar_t[]> GetAssociationKeyPath(const wchar_t* aExt) {
+  const wchar_t* keyPathFmt;
+  if (aExt[0] == L'.') {
+    keyPathFmt =
+        L"SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Explorer\\FileExts\\%s";
+  } else {
+    keyPathFmt =
+        L"SOFTWARE\\Microsoft\\Windows\\Shell\\Associations\\"
+        L"UrlAssociations\\%s";
+  }
+
+  int keyPathLen = _scwprintf(keyPathFmt, aExt);
+  keyPathLen += 1;  // _scwprintf does not include the terminator
+
+  auto keyPath = MakeUnique<wchar_t[]>(keyPathLen);
+  _snwprintf_s(keyPath.get(), keyPathLen, _TRUNCATE, keyPathFmt, aExt);
+
+  return keyPath;
+}
+
+UniquePtr<wchar_t[]> GenerateUserChoiceHash(const wchar_t* aExt,
+                                            const wchar_t* aUserSid,
+                                            const wchar_t* aProgId,
+                                            SYSTEMTIME aTimestamp) {
+  auto userChoice = FormatUserChoiceString(aExt, aUserSid, aProgId, aTimestamp);
+  if (!userChoice) {
+    return nullptr;
+  }
+  return HashString(userChoice.get());
+}
+
+/*
+ * NOTE: The passed-in current user SID is used here, instead of getting the SID
+ * for the owner of the key. We are assuming that this key in HKCU is owned by
+ * the current user, since we want to replace that key ourselves. If the key is
+ * owned by someone else, then this check will fail; this is ok because we would
+ * likely not want to replace that other user's key anyway.
+ */
+CheckUserChoiceHashResult CheckUserChoiceHash(const wchar_t* aExt,
+                                              const wchar_t* aUserSid) {
+  auto keyPath = GetAssociationKeyPath(aExt);
+  if (!keyPath) {
+    return CheckUserChoiceHashResult::ERR_OTHER;
+  }
+
+  HKEY rawAssocKey;
+  if (::RegOpenKeyExW(HKEY_CURRENT_USER, keyPath.get(), 0, KEY_READ,
+                      &rawAssocKey) != ERROR_SUCCESS) {
+    return CheckUserChoiceHashResult::ERR_OTHER;
+  }
+  nsAutoRegKey assocKey(rawAssocKey);
+
+  FILETIME lastWriteFileTime;
+  {
+    HKEY rawUserChoiceKey;
+    if (::RegOpenKeyExW(assocKey.get(), L"UserChoice", 0, KEY_READ,
+                        &rawUserChoiceKey) != ERROR_SUCCESS) {
+      return CheckUserChoiceHashResult::ERR_OTHER;
+    }
+    nsAutoRegKey userChoiceKey(rawUserChoiceKey);
+
+    if (::RegQueryInfoKeyW(userChoiceKey.get(), nullptr, nullptr, nullptr,
+                           nullptr, nullptr, nullptr, nullptr, nullptr, nullptr,
+                           nullptr, &lastWriteFileTime) != ERROR_SUCCESS) {
+      return CheckUserChoiceHashResult::ERR_OTHER;
+    }
+  }
+
+  SYSTEMTIME lastWriteSystemTime;
+  if (!::FileTimeToSystemTime(&lastWriteFileTime, &lastWriteSystemTime)) {
+    return CheckUserChoiceHashResult::ERR_OTHER;
+  }
+
+  // Read ProgId
+  DWORD dataSizeBytes = 0;
+  if (::RegGetValueW(assocKey.get(), L"UserChoice", L"ProgId", RRF_RT_REG_SZ,
+                     nullptr, nullptr, &dataSizeBytes) != ERROR_SUCCESS) {
+    return CheckUserChoiceHashResult::ERR_OTHER;
+  }
+  // +1 in case dataSizeBytes was odd, +1 to ensure termination
+  DWORD dataSizeChars = (dataSizeBytes / sizeof(wchar_t)) + 2;
+  UniquePtr<wchar_t[]> progId(new wchar_t[dataSizeChars]());
+  if (::RegGetValueW(assocKey.get(), L"UserChoice", L"ProgId", RRF_RT_REG_SZ,
+                     nullptr, progId.get(), &dataSizeBytes) != ERROR_SUCCESS) {
+    return CheckUserChoiceHashResult::ERR_OTHER;
+  }
+
+  // Read Hash
+  dataSizeBytes = 0;
+  if (::RegGetValueW(assocKey.get(), L"UserChoice", L"Hash", RRF_RT_REG_SZ,
+                     nullptr, nullptr, &dataSizeBytes) != ERROR_SUCCESS) {
+    return CheckUserChoiceHashResult::ERR_OTHER;
+  }
+  dataSizeChars = (dataSizeBytes / sizeof(wchar_t)) + 2;
+  UniquePtr<wchar_t[]> storedHash(new wchar_t[dataSizeChars]());
+  if (::RegGetValueW(assocKey.get(), L"UserChoice", L"Hash", RRF_RT_REG_SZ,
+                     nullptr, storedHash.get(),
+                     &dataSizeBytes) != ERROR_SUCCESS) {
+    return CheckUserChoiceHashResult::ERR_OTHER;
+  }
+
+  auto computedHash =
+      GenerateUserChoiceHash(aExt, aUserSid, progId.get(), lastWriteSystemTime);
+  if (!computedHash) {
+    return CheckUserChoiceHashResult::ERR_OTHER;
+  }
+
+  if (::CompareStringOrdinal(computedHash.get(), -1, storedHash.get(), -1,
+                             FALSE) != CSTR_EQUAL) {
+    return CheckUserChoiceHashResult::ERR_MISMATCH;
+  }
+
+  return CheckUserChoiceHashResult::OK_V1;
+}
+
+bool CheckBrowserUserChoiceHashes() {
+  auto userSid = GetCurrentUserStringSid();
+  if (!userSid) {
+    return false;
+  }
+
+  const wchar_t* exts[] = {L"https", L"http", L".html", L".htm"};
+
+  for (size_t i = 0; i < ArrayLength(exts); ++i) {
+    switch (CheckUserChoiceHash(exts[i], userSid.get())) {
+      case CheckUserChoiceHashResult::OK_V1:
+        break;
+      case CheckUserChoiceHashResult::ERR_MISMATCH:
+      case CheckUserChoiceHashResult::ERR_OTHER:
+        return false;
+    }
+  }
+
+  return true;
+}
+
+UniquePtr<wchar_t[]> FormatProgID(const wchar_t* aProgIDBase,
+                                  const wchar_t* aAumi) {
+  const wchar_t* progIDFmt = L"%s-%s";
+  int progIDLen = _scwprintf(progIDFmt, aProgIDBase, aAumi);
+  progIDLen += 1;  // _scwprintf does not include the terminator
+
+  auto progID = MakeUnique<wchar_t[]>(progIDLen);
+  _snwprintf_s(progID.get(), progIDLen, _TRUNCATE, progIDFmt, aProgIDBase,
+               aAumi);
+
+  return progID;
+}
+
+bool CheckProgIDExists(const wchar_t* aProgID) {
+  HKEY key;
+  if (::RegOpenKeyExW(HKEY_CLASSES_ROOT, aProgID, 0, KEY_READ, &key) !=
+      ERROR_SUCCESS) {
+    return false;
+  }
+  ::RegCloseKey(key);
+  return true;
+}
diff --git a/browser/components/shell/WindowsUserChoice.h b/browser/components/shell/WindowsUserChoice.h
new file mode 100644
index 0000000000..d7e887b667
--- /dev/null
+++ b/browser/components/shell/WindowsUserChoice.h
@@ -0,0 +1,103 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#ifndef SHELL_WINDOWSUSERCHOICE_H__
+#define SHELL_WINDOWSUSERCHOICE_H__
+
+#include <windows.h>
+
+#include "mozilla/UniquePtr.h"
+
+/*
+ * Check the UserChoice Hashes for https, http, .html, .htm
+ *
+ * This should be checked before attempting to set a new default browser via
+ * the UserChoice key, to confirm our understanding of the existing hash.
+ * If an incorrect hash is written, Windows will prompt the user to choose a
+ * new default (or, in recent versions, it will just reset the default to Edge).
+ *
+ * Assuming that the existing hash value is correct (since Windows is fairly
+ * diligent about replacing bad keys), if we can recompute it from scratch,
+ * then we should be able to compute a correct hash for our new UserChoice key.
+ *
+ * @return true if we matched all the hashes, false otherwise.
+ */
+bool CheckBrowserUserChoiceHashes();
+
+/*
+ * Result from CheckUserChoiceHash()
+ *
+ * NOTE: Currently the only positive result is OK_V1 , but the enum
+ * could be extended to indicate different versions of the hash.
+ */
+enum class CheckUserChoiceHashResult {
+  OK_V1,         // Matched the current version of the hash (as of Win10 20H2).
+  ERR_MISMATCH,  // The hash did not match.
+  ERR_OTHER,     // Error reading or generating the hash.
+};
+
+/*
+ * Generate a UserChoice Hash, compare it with the one that is stored.
+ *
+ * See comments on CheckBrowserUserChoiceHashes(), which calls this to check
+ * each of the browser associations.
+ *
+ * @param aExt      File extension or protocol association to check
+ * @param aUserSid  String SID of the current user
+ *
+ * @return Result of the check, see CheckUserChoiceHashResult
+ */
+CheckUserChoiceHashResult CheckUserChoiceHash(const wchar_t* aExt,
+                                              const wchar_t* aUserSid);
+
+/*
+ * Get the registry path for the given association, file extension or protocol.
+ *
+ * @return The path, or nullptr on failure.
+ */
+mozilla::UniquePtr<wchar_t[]> GetAssociationKeyPath(const wchar_t* aExt);
+
+/*
+ * Get the current user's SID
+ *
+ * @return String SID for the user of the current process, nullptr on failure.
+ */
+mozilla::UniquePtr<wchar_t[]> GetCurrentUserStringSid();
+
+/*
+ * Generate the UserChoice Hash
+ *
+ * @param aExt          file extension or protocol being registered
+ * @param aUserSid      string SID of the current user
+ * @param aProgId       ProgId to associate with aExt
+ * @param aTimestamp    approximate write time of the UserChoice key (within
+ *                      the same minute)
+ *
+ * @return UserChoice Hash, nullptr on failure.
+ */
+mozilla::UniquePtr<wchar_t[]> GenerateUserChoiceHash(const wchar_t* aExt,
+                                                     const wchar_t* aUserSid,
+                                                     const wchar_t* aProgId,
+                                                     SYSTEMTIME aTimestamp);
+
+/*
+ * Build a ProgID from a base and AUMI
+ *
+ * @param aProgIDBase   A base, such as FirefoxHTML or FirefoxURL
+ * @param aAumi         The AUMI of the installation
+ *
+ * @return Formatted ProgID.
+ */
+mozilla::UniquePtr<wchar_t[]> FormatProgID(const wchar_t* aProgIDBase,
+                                           const wchar_t* aAumi);
+
+/*
+ * Check that the given ProgID exists in HKCR
+ *
+ * @return true if it could be opened for reading, false otherwise.
+ */
+bool CheckProgIDExists(const wchar_t* aProgID);
+
+#endif  // SHELL_WINDOWSUSERCHOICE_H__
diff --git a/browser/components/shell/content/setDesktopBackground.js b/browser/components/shell/content/setDesktopBackground.js
new file mode 100644
index 0000000000..be6b108432
--- /dev/null
+++ b/browser/components/shell/content/setDesktopBackground.js
@@ -0,0 +1,252 @@
+/* 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/. */
+
+/* import-globals-from /browser/base/content/utilityOverlay.js */
+
+var gSetBackground = {
+  _position: AppConstants.platform == "macosx" ? "STRETCH" : "",
+  _backgroundColor: AppConstants.platform != "macosx" ? 0 : undefined,
+  _screenWidth: 0,
+  _screenHeight: 0,
+  _image: null,
+  _canvas: null,
+  _imageName: null,
+
+  get _shell() {
+    return Cc["@mozilla.org/browser/shell-service;1"].getService(
+      Ci.nsIShellService
+    );
+  },
+
+  load() {
+    this._canvas = document.getElementById("screen");
+    this._screenWidth = screen.width;
+    this._screenHeight = screen.height;
+    // Cap ratio to 4 so the dialog width doesn't get ridiculous. Highest
+    // regular screens seem to be 32:9 (3.56) according to Wikipedia.
+    let screenRatio = Math.min(this._screenWidth / this._screenHeight, 4);
+    this._canvas.width = this._canvas.height * screenRatio;
+    document.getElementById("preview-unavailable").style.width =
+      this._canvas.width + "px";
+
+    if (AppConstants.platform == "macosx") {
+      document
+        .getElementById("SetDesktopBackgroundDialog")
+        .getButton("accept").hidden = true;
+    } else {
+      let multiMonitors = false;
+      if (AppConstants.platform == "linux") {
+        // getMonitors only ever returns the primary monitor on Linux, so just
+        // always show the option
+        multiMonitors = true;
+      } else {
+        const gfxInfo = Cc["@mozilla.org/gfx/info;1"].getService(Ci.nsIGfxInfo);
+        const monitors = gfxInfo.getMonitors();
+        multiMonitors = monitors.length > 1;
+      }
+
+      if (
+        !multiMonitors ||
+        AppConstants.isPlatformAndVersionAtMost("win", 6.1)
+      ) {
+        // Hide span option if < Win8 since that's when it was introduced.
+        document.getElementById("spanPosition").hidden = true;
+      }
+    }
+
+    document.addEventListener("dialogaccept", function () {
+      gSetBackground.setDesktopBackground();
+    });
+    // make sure that the correct dimensions will be used
+    setTimeout(
+      function (self) {
+        self.init(window.arguments[0], window.arguments[1]);
+      },
+      0,
+      this
+    );
+  },
+
+  init(aImage, aImageName) {
+    this._image = aImage;
+    this._imageName = aImageName;
+
+    // set the size of the coordinate space
+    this._canvas.width = this._canvas.clientWidth;
+    this._canvas.height = this._canvas.clientHeight;
+
+    var ctx = this._canvas.getContext("2d");
+    ctx.scale(
+      this._canvas.clientWidth / this._screenWidth,
+      this._canvas.clientHeight / this._screenHeight
+    );
+
+    if (AppConstants.platform != "macosx") {
+      this._initColor();
+    } else {
+      // Make sure to reset the button state in case the user has already
+      // set an image as their desktop background.
+      var setDesktopBackground = document.getElementById(
+        "setDesktopBackground"
+      );
+      setDesktopBackground.hidden = false;
+      var bundle = document.getElementById("backgroundBundle");
+      setDesktopBackground.label = bundle.getString("DesktopBackgroundSet");
+      setDesktopBackground.disabled = false;
+
+      document.getElementById("showDesktopPreferences").hidden = true;
+    }
+    this.updatePosition();
+  },
+
+  setDesktopBackground() {
+    if (AppConstants.platform != "macosx") {
+      Services.xulStore.persist(
+        document.getElementById("menuPosition"),
+        "value"
+      );
+      this._shell.desktopBackgroundColor = this._hexStringToLong(
+        this._backgroundColor
+      );
+    } else {
+      Services.obs.addObserver(this, "shell:desktop-background-changed");
+
+      var bundle = document.getElementById("backgroundBundle");
+      var setDesktopBackground = document.getElementById(
+        "setDesktopBackground"
+      );
+      setDesktopBackground.disabled = true;
+      setDesktopBackground.label = bundle.getString(
+        "DesktopBackgroundDownloading"
+      );
+    }
+    this._shell.setDesktopBackground(
+      this._image,
+      Ci.nsIShellService["BACKGROUND_" + this._position],
+      this._imageName
+    );
+  },
+
+  updatePosition() {
+    var ctx = this._canvas.getContext("2d");
+    ctx.clearRect(0, 0, this._screenWidth, this._screenHeight);
+    document.getElementById("preview-unavailable").hidden = true;
+
+    if (AppConstants.platform != "macosx") {
+      this._position = document.getElementById("menuPosition").value;
+    }
+
+    switch (this._position) {
+      case "TILE":
+        ctx.save();
+        ctx.fillStyle = ctx.createPattern(this._image, "repeat");
+        ctx.fillRect(0, 0, this._screenWidth, this._screenHeight);
+        ctx.restore();
+        break;
+      case "STRETCH":
+        ctx.drawImage(this._image, 0, 0, this._screenWidth, this._screenHeight);
+        break;
+      case "CENTER": {
+        let x = (this._screenWidth - this._image.naturalWidth) / 2;
+        let y = (this._screenHeight - this._image.naturalHeight) / 2;
+        ctx.drawImage(this._image, x, y);
+        break;
+      }
+      case "FILL": {
+        // Try maxing width first, overflow height.
+        let widthRatio = this._screenWidth / this._image.naturalWidth;
+        let width = this._image.naturalWidth * widthRatio;
+        let height = this._image.naturalHeight * widthRatio;
+        if (height < this._screenHeight) {
+          // Height less than screen, max height and overflow width.
+          let heightRatio = this._screenHeight / this._image.naturalHeight;
+          width = this._image.naturalWidth * heightRatio;
+          height = this._image.naturalHeight * heightRatio;
+        }
+        let x = (this._screenWidth - width) / 2;
+        let y = (this._screenHeight - height) / 2;
+        ctx.drawImage(this._image, x, y, width, height);
+        break;
+      }
+      case "FIT": {
+        // Try maxing width first, top and bottom borders.
+        let widthRatio = this._screenWidth / this._image.naturalWidth;
+        let width = this._image.naturalWidth * widthRatio;
+        let height = this._image.naturalHeight * widthRatio;
+        let x = 0;
+        let y = (this._screenHeight - height) / 2;
+        if (height > this._screenHeight) {
+          // Height overflow, maximise height, side borders.
+          let heightRatio = this._screenHeight / this._image.naturalHeight;
+          width = this._image.naturalWidth * heightRatio;
+          height = this._image.naturalHeight * heightRatio;
+          x = (this._screenWidth - width) / 2;
+          y = 0;
+        }
+        ctx.drawImage(this._image, x, y, width, height);
+        break;
+      }
+      case "SPAN": {
+        document.getElementById("preview-unavailable").hidden = false;
+        ctx.fillStyle = "#222";
+        ctx.fillRect(0, 0, this._screenWidth, this._screenHeight);
+        ctx.stroke();
+      }
+    }
+  },
+};
+
+if (AppConstants.platform != "macosx") {
+  gSetBackground._initColor = function () {
+    var color = this._shell.desktopBackgroundColor;
+
+    const rMask = 4294901760;
+    const gMask = 65280;
+    const bMask = 255;
+    var r = (color & rMask) >> 16;
+    var g = (color & gMask) >> 8;
+    var b = color & bMask;
+    this.updateColor(this._rgbToHex(r, g, b));
+
+    var colorpicker = document.getElementById("desktopColor");
+    colorpicker.value = this._backgroundColor;
+  };
+
+  gSetBackground.updateColor = function (aColor) {
+    this._backgroundColor = aColor;
+    this._canvas.style.backgroundColor = aColor;
+  };
+
+  // Converts a color string in the format "#RRGGBB" to an integer.
+  gSetBackground._hexStringToLong = function (aString) {
+    return (
+      (parseInt(aString.substring(1, 3), 16) << 16) |
+      (parseInt(aString.substring(3, 5), 16) << 8) |
+      parseInt(aString.substring(5, 7), 16)
+    );
+  };
+
+  gSetBackground._rgbToHex = function (aR, aG, aB) {
+    return (
+      "#" +
+      [aR, aG, aB]
+        .map(aInt => aInt.toString(16).replace(/^(.)$/, "0$1"))
+        .join("")
+        .toUpperCase()
+    );
+  };
+} else {
+  gSetBackground.observe = function (aSubject, aTopic, aData) {
+    if (aTopic == "shell:desktop-background-changed") {
+      document.getElementById("setDesktopBackground").hidden = true;
+      document.getElementById("showDesktopPreferences").hidden = false;
+
+      Services.obs.removeObserver(this, "shell:desktop-background-changed");
+    }
+  };
+
+  gSetBackground.showDesktopPrefs = function () {
+    this._shell.QueryInterface(Ci.nsIMacShellService).showDesktopPreferences();
+  };
+}
diff --git a/browser/components/shell/content/setDesktopBackground.xhtml b/browser/components/shell/content/setDesktopBackground.xhtml
new file mode 100644
index 0000000000..95b05ec277
--- /dev/null
+++ b/browser/components/shell/content/setDesktopBackground.xhtml
@@ -0,0 +1,88 @@
+<?xml version="1.0"?> <!-- -*- Mode: HTML -*- -->
+
+# 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/.
+
+<?xml-stylesheet href="chrome://global/skin/global.css" type="text/css"?>
+<?xml-stylesheet href="chrome://browser/skin/setDesktopBackground.css" type="text/css"?>
+
+<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        xmlns:html="http://www.w3.org/1999/xhtml"
+        windowtype="Shell:SetDesktopBackground"
+        onload="gSetBackground.load();"
+        data-l10n-id="set-desktop-background-window"
+        style="min-width: 30em;">
+
+<linkset>
+  <html:link rel="localization" href="browser/setDesktopBackground.ftl"/>
+</linkset>
+
+<dialog id="SetDesktopBackgroundDialog"
+#ifndef XP_MACOSX
+        buttons="accept,cancel"
+#else
+        buttons="accept"
+#endif
+        buttonidaccept="set-desktop-background-accept">
+
+#ifdef XP_MACOSX
+#include ../../../base/content/macWindow.inc.xhtml
+#else
+    <script src="chrome://browser/content/utilityOverlay.js"/>
+#endif
+
+    <stringbundle id="backgroundBundle"
+                  src="chrome://browser/locale/shellservice.properties"/>
+    <script src="chrome://browser/content/setDesktopBackground.js"/>
+    <script src="chrome://global/content/contentAreaUtils.js"/>
+
+#ifndef XP_MACOSX
+    <hbox align="center">
+      <label data-l10n-id="set-background-position"/>
+      <menulist id="menuPosition"
+                oncommand="gSetBackground.updatePosition();" native="true">
+        <menupopup>
+          <menuitem data-l10n-id="set-background-center"  value="CENTER"/>
+          <menuitem data-l10n-id="set-background-tile"    value="TILE"/>
+          <menuitem data-l10n-id="set-background-stretch" value="STRETCH"/>
+          <menuitem data-l10n-id="set-background-fill"    value="FILL"/>
+          <menuitem data-l10n-id="set-background-fit"     value="FIT"/>
+          <menuitem data-l10n-id="set-background-span"    value="SPAN" id="spanPosition"/>
+        </menupopup>
+      </menulist>
+      <spacer flex="1"/>
+      <label data-l10n-id="set-background-color"/>
+      <html:input id="desktopColor"
+                  type="color"
+                  onchange="gSetBackground.updateColor(this.value);"/>
+    </hbox>
+#endif
+
+    <vbox align="center">
+      <!-- default to 16:9, will be adjusted to match user's actual screen -->
+      <stack>
+        <html:canvas id="screen" width="202" height="114" role="presentation"/>
+        <vbox pack="center">
+          <html:p id="preview-unavailable" hidden="" data-l10n-id="set-background-preview-unavailable"></html:p>
+        </vbox>
+      </stack>
+      <image id="monitor-base"/>
+    </vbox>
+
+#ifdef XP_MACOSX
+    <separator/>
+
+    <hbox pack="end">
+      <button id="setDesktopBackground"
+              data-l10n-id="set-desktop-background-accept"
+              oncommand="gSetBackground.setDesktopBackground();"/>
+      <button id="showDesktopPreferences"
+              data-l10n-id="open-desktop-prefs"
+              oncommand="gSetBackground.showDesktopPrefs();"
+              hidden="true"/>
+    </hbox>
+#endif
+
+</dialog>
+</window>
diff --git a/browser/components/shell/jar.mn b/browser/components/shell/jar.mn
new file mode 100644
index 0000000000..0816cddd68
--- /dev/null
+++ b/browser/components/shell/jar.mn
@@ -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/.
+
+browser.jar:
+*       content/browser/setDesktopBackground.xhtml            (content/setDesktopBackground.xhtml)
+        content/browser/setDesktopBackground.js               (content/setDesktopBackground.js)
diff --git a/browser/components/shell/moz.build b/browser/components/shell/moz.build
new file mode 100644
index 0000000000..eb88cb287d
--- /dev/null
+++ b/browser/components/shell/moz.build
@@ -0,0 +1,92 @@
+# -*- 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/.
+
+# For BinaryPath::GetLong for Windows
+LOCAL_INCLUDES += ["/xpcom/build"]
+
+BROWSER_CHROME_MANIFESTS += ["test/browser.ini"]
+XPCSHELL_TESTS_MANIFESTS += ["test/unit/xpcshell.ini"]
+
+JAR_MANIFESTS += ["jar.mn"]
+
+XPIDL_SOURCES += [
+    "nsIShellService.idl",
+]
+
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "cocoa":
+    XPIDL_SOURCES += [
+        "nsIMacShellService.idl",
+    ]
+
+    SOURCES += [
+        "nsMacShellService.cpp",
+    ]
+
+    LOCAL_INCLUDES += [
+        # For CocoaFileUtils
+        "/xpcom/io"
+    ]
+elif CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
+    XPIDL_SOURCES += [
+        "nsIGNOMEShellService.idl",
+    ]
+
+    SOURCES += [
+        "nsGNOMEShellService.cpp",
+    ]
+    if CONFIG["MOZ_ENABLE_DBUS"]:
+        SOURCES += [
+            "nsGNOMEShellDBusHelper.cpp",
+            "nsGNOMEShellSearchProvider.cpp",
+        ]
+        include("/ipc/chromium/chromium-config.mozbuild")
+
+elif CONFIG["OS_ARCH"] == "WINNT":
+    XPIDL_SOURCES += [
+        "nsIWindowsShellService.idl",
+    ]
+    SOURCES += [
+        "nsWindowsShellService.cpp",
+        "WindowsDefaultBrowser.cpp",
+        "WindowsUserChoice.cpp",
+    ]
+    LOCAL_INCLUDES += [
+        "../../../other-licenses/nsis/Contrib/CityHash/cityhash",
+        "/toolkit/xre",
+    ]
+    OS_LIBS += [
+        "bcrypt",
+        "crypt32",
+        "propsys",
+    ]
+
+XPIDL_MODULE = "shellservice"
+
+if SOURCES:
+    FINAL_LIBRARY = "browsercomps"
+
+EXTRA_JS_MODULES += [
+    "HeadlessShell.sys.mjs",
+    "ScreenshotChild.sys.mjs",
+    "ShellService.sys.mjs",
+]
+
+for var in (
+    "MOZ_APP_DISPLAYNAME",
+    "MOZ_APP_NAME",
+    "MOZ_APP_VERSION",
+    "MOZ_DEFAULT_BROWSER_AGENT",
+):
+    DEFINES[var] = '"%s"' % CONFIG[var]
+
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
+    CXXFLAGS += CONFIG["MOZ_GTK3_CFLAGS"]
+
+if CONFIG["MOZ_ENABLE_DBUS"]:
+    CXXFLAGS += CONFIG["MOZ_DBUS_GLIB_CFLAGS"]
+
+with Files("**"):
+    BUG_COMPONENT = ("Firefox", "Shell Integration")
diff --git a/browser/components/shell/nsGNOMEShellDBusHelper.cpp b/browser/components/shell/nsGNOMEShellDBusHelper.cpp
new file mode 100644
index 0000000000..9e1681c902
--- /dev/null
+++ b/browser/components/shell/nsGNOMEShellDBusHelper.cpp
@@ -0,0 +1,535 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:expandtab:shiftwidth=2:tabstop=2:
+ */
+/* 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/. */
+
+#include "nsGNOMEShellSearchProvider.h"
+
+#include "RemoteUtils.h"
+#include "nsIStringBundle.h"
+#include "nsServiceManagerUtils.h"
+#include "nsPrintfCString.h"
+#include "mozilla/XREAppData.h"
+#include "nsAppRunner.h"
+
+#define DBUS_BUS_NAME_TEMPLATE "org.mozilla.%s.SearchProvider"
+#define DBUS_OBJECT_PATH_TEMPLATE "/org/mozilla/%s/SearchProvider"
+
+const char* GetDBusBusName() {
+  static const char* name = []() {
+    nsAutoCString appName;
+    gAppData->GetDBusAppName(appName);
+    return ToNewCString(nsPrintfCString(DBUS_BUS_NAME_TEMPLATE,
+                                        appName.get()));  // Intentionally leak
+  }();
+  return name;
+}
+
+const char* GetDBusObjectPath() {
+  static const char* path = []() {
+    nsAutoCString appName;
+    gAppData->GetDBusAppName(appName);
+    return ToNewCString(nsPrintfCString(DBUS_OBJECT_PATH_TEMPLATE,
+                                        appName.get()));  // Intentionally leak
+  }();
+  return path;
+}
+
+static bool GetGnomeSearchTitle(const char* aSearchedTerm,
+                                nsAutoCString& aGnomeSearchTitle) {
+  static nsCOMPtr<nsIStringBundle> bundle;
+  if (!bundle) {
+    nsCOMPtr<nsIStringBundleService> sbs =
+        do_GetService(NS_STRINGBUNDLE_CONTRACTID);
+    if (NS_WARN_IF(!sbs)) {
+      return false;
+    }
+
+    sbs->CreateBundle("chrome://browser/locale/browser.properties",
+                      getter_AddRefs(bundle));
+    if (NS_WARN_IF(!bundle)) {
+      return false;
+    }
+  }
+
+  AutoTArray<nsString, 1> formatStrings;
+  CopyUTF8toUTF16(nsCString(aSearchedTerm), *formatStrings.AppendElement());
+
+  nsAutoString gnomeSearchTitle;
+  bundle->FormatStringFromName("gnomeSearchProviderSearchWeb", formatStrings,
+                               gnomeSearchTitle);
+  AppendUTF16toUTF8(gnomeSearchTitle, aGnomeSearchTitle);
+  return true;
+}
+
+static const char* introspect_template =
+    "<!DOCTYPE node PUBLIC \"-//freedesktop//DTD D-BUS Object Introspection "
+    "1.0//EN\"\n"
+    "\"http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd\">\n"
+    "<node>\n"
+    " <interface name=\"org.freedesktop.DBus.Introspectable\">\n"
+    "   <method name=\"Introspect\">\n"
+    "     <arg name=\"data\" direction=\"out\" type=\"s\"/>\n"
+    "   </method>\n"
+    " </interface>\n"
+    " <interface name=\"org.gnome.Shell.SearchProvider2\">\n"
+    "   <method name=\"GetInitialResultSet\">\n"
+    "     <arg type=\"as\" name=\"terms\" direction=\"in\" />\n"
+    "     <arg type=\"as\" name=\"results\" direction=\"out\" />\n"
+    "   </method>\n"
+    "   <method name=\"GetSubsearchResultSet\">\n"
+    "     <arg type=\"as\" name=\"previous_results\" direction=\"in\" />\n"
+    "     <arg type=\"as\" name=\"terms\" direction=\"in\" />\n"
+    "     <arg type=\"as\" name=\"results\" direction=\"out\" />\n"
+    "   </method>\n"
+    "   <method name=\"GetResultMetas\">\n"
+    "     <arg type=\"as\" name=\"identifiers\" direction=\"in\" />\n"
+    "     <arg type=\"aa{sv}\" name=\"metas\" direction=\"out\" />\n"
+    "   </method>\n"
+    "   <method name=\"ActivateResult\">\n"
+    "     <arg type=\"s\" name=\"identifier\" direction=\"in\" />\n"
+    "     <arg type=\"as\" name=\"terms\" direction=\"in\" />\n"
+    "     <arg type=\"u\" name=\"timestamp\" direction=\"in\" />\n"
+    "   </method>\n"
+    "   <method name=\"LaunchSearch\">\n"
+    "     <arg type=\"as\" name=\"terms\" direction=\"in\" />\n"
+    "     <arg type=\"u\" name=\"timestamp\" direction=\"in\" />\n"
+    "   </method>\n"
+    "</interface>\n"
+    "</node>\n";
+
+DBusHandlerResult DBusIntrospect(DBusConnection* aConnection,
+                                 DBusMessage* aMsg) {
+  DBusMessage* reply;
+
+  reply = dbus_message_new_method_return(aMsg);
+  if (!reply) {
+    return DBUS_HANDLER_RESULT_NEED_MEMORY;
+  }
+
+  dbus_message_append_args(reply, DBUS_TYPE_STRING, &introspect_template,
+                           DBUS_TYPE_INVALID);
+
+  dbus_connection_send(aConnection, reply, nullptr);
+  dbus_message_unref(reply);
+
+  return DBUS_HANDLER_RESULT_HANDLED;
+}
+
+int DBusGetIndexFromIDKey(const char* aIDKey) {
+  // ID is NN:URL where NN is index to our current history
+  // result container.
+  char tmp[] = {aIDKey[0], aIDKey[1], '\0'};
+  return atoi(tmp);
+}
+
+static void ConcatArray(nsACString& aOutputStr, const char** aStringArray) {
+  for (const char** term = aStringArray; *term; term++) {
+    aOutputStr.Append(*term);
+    if (*(term + 1)) {
+      aOutputStr.Append(" ");
+    }
+  }
+}
+
+DBusHandlerResult DBusHandleInitialResultSet(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult, DBusMessage* aMsg) {
+  DBusMessage* reply;
+  char** stringArray = nullptr;
+  int elements;
+
+  if (!dbus_message_get_args(aMsg, nullptr, DBUS_TYPE_ARRAY, DBUS_TYPE_STRING,
+                             &stringArray, &elements, DBUS_TYPE_INVALID) ||
+      elements == 0) {
+    reply = dbus_message_new_error(aMsg, GetDBusBusName(), "Wrong argument");
+    dbus_connection_send(aSearchResult->GetDBusConnection(), reply, nullptr);
+    dbus_message_unref(reply);
+  } else {
+    aSearchResult->SetReply(dbus_message_new_method_return(aMsg));
+    nsAutoCString searchTerm;
+    ConcatArray(searchTerm, const_cast<const char**>(stringArray));
+    aSearchResult->SetSearchTerm(searchTerm.get());
+    GetGNOMEShellHistoryService()->QueryHistory(aSearchResult);
+    // DBus reply will be send asynchronously by
+    // nsGNOMEShellHistorySearchResult::SendDBusSearchResultReply()
+    // when GetGNOMEShellHistoryService() has the results.
+  }
+
+  if (stringArray) {
+    dbus_free_string_array(stringArray);
+  }
+
+  return DBUS_HANDLER_RESULT_HANDLED;
+}
+
+DBusHandlerResult DBusHandleSubsearchResultSet(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult, DBusMessage* aMsg) {
+  DBusMessage* reply;
+
+  char **unusedArray = nullptr, **stringArray = nullptr;
+  int unusedNum, elements;
+
+  if (!dbus_message_get_args(aMsg, nullptr, DBUS_TYPE_ARRAY, DBUS_TYPE_STRING,
+                             &unusedArray, &unusedNum, DBUS_TYPE_ARRAY,
+                             DBUS_TYPE_STRING, &stringArray, &elements,
+                             DBUS_TYPE_INVALID) ||
+      elements == 0) {
+    reply = dbus_message_new_error(aMsg, GetDBusBusName(), "Wrong argument");
+    dbus_connection_send(aSearchResult->GetDBusConnection(), reply, nullptr);
+    dbus_message_unref(reply);
+  } else {
+    aSearchResult->SetReply(dbus_message_new_method_return(aMsg));
+    nsAutoCString searchTerm;
+    ConcatArray(searchTerm, const_cast<const char**>(stringArray));
+    aSearchResult->SetSearchTerm(searchTerm.get());
+    GetGNOMEShellHistoryService()->QueryHistory(aSearchResult);
+    // DBus reply will be send asynchronously by
+    // nsGNOMEShellHistorySearchResult::SendDBusSearchResultReply()
+    // when GetGNOMEShellHistoryService() has the results.
+  }
+
+  if (unusedArray) {
+    dbus_free_string_array(unusedArray);
+  }
+  if (stringArray) {
+    dbus_free_string_array(stringArray);
+  }
+
+  return DBUS_HANDLER_RESULT_HANDLED;
+}
+
+static void appendStringDictionary(DBusMessageIter* aIter, const char* aKey,
+                                   const char* aValue) {
+  DBusMessageIter iterDict, iterVar;
+  dbus_message_iter_open_container(aIter, DBUS_TYPE_DICT_ENTRY, nullptr,
+                                   &iterDict);
+  dbus_message_iter_append_basic(&iterDict, DBUS_TYPE_STRING, &aKey);
+  dbus_message_iter_open_container(&iterDict, DBUS_TYPE_VARIANT, "s", &iterVar);
+  dbus_message_iter_append_basic(&iterVar, DBUS_TYPE_STRING, &aValue);
+  dbus_message_iter_close_container(&iterDict, &iterVar);
+  dbus_message_iter_close_container(aIter, &iterDict);
+}
+
+/*
+  "icon-data": a tuple of type (iiibiiay) describing a pixbuf with width,
+              height, rowstride, has-alpha,
+              bits-per-sample, channels,
+              image data
+*/
+static void DBusAppendIcon(GnomeHistoryIcon* aIcon, DBusMessageIter* aIter) {
+  DBusMessageIter iterDict, iterVar, iterStruct;
+  dbus_message_iter_open_container(aIter, DBUS_TYPE_DICT_ENTRY, nullptr,
+                                   &iterDict);
+  const char* key = "icon-data";
+  dbus_message_iter_append_basic(&iterDict, DBUS_TYPE_STRING, &key);
+  dbus_message_iter_open_container(&iterDict, DBUS_TYPE_VARIANT, "(iiibiiay)",
+                                   &iterVar);
+  dbus_message_iter_open_container(&iterVar, DBUS_TYPE_STRUCT, nullptr,
+                                   &iterStruct);
+
+  int width = aIcon->GetWidth();
+  int height = aIcon->GetHeight();
+  dbus_message_iter_append_basic(&iterStruct, DBUS_TYPE_INT32, &width);
+  dbus_message_iter_append_basic(&iterStruct, DBUS_TYPE_INT32, &height);
+  int rowstride = width * 4;
+  dbus_message_iter_append_basic(&iterStruct, DBUS_TYPE_INT32, &rowstride);
+  int hasAlpha = true;
+  dbus_message_iter_append_basic(&iterStruct, DBUS_TYPE_BOOLEAN, &hasAlpha);
+  int bitsPerSample = 8;
+  dbus_message_iter_append_basic(&iterStruct, DBUS_TYPE_INT32, &bitsPerSample);
+  int channels = 4;
+  dbus_message_iter_append_basic(&iterStruct, DBUS_TYPE_INT32, &channels);
+
+  DBusMessageIter iterArray;
+  dbus_message_iter_open_container(&iterStruct, DBUS_TYPE_ARRAY, "y",
+                                   &iterArray);
+  unsigned char* array = aIcon->GetData();
+  dbus_message_iter_append_fixed_array(&iterArray, DBUS_TYPE_BYTE, &array,
+                                       width * height * 4);
+  dbus_message_iter_close_container(&iterStruct, &iterArray);
+
+  dbus_message_iter_close_container(&iterVar, &iterStruct);
+  dbus_message_iter_close_container(&iterDict, &iterVar);
+  dbus_message_iter_close_container(aIter, &iterDict);
+}
+
+/* Appends history search results to the DBUS reply.
+
+  We can return those fields at GetResultMetas:
+
+  "id": the result ID
+  "name": the display name for the result
+  "icon": a serialized GIcon (see g_icon_serialize()), or alternatively,
+  "gicon": a textual representation of a GIcon (see g_icon_to_string()),
+           or alternativly,
+  "icon-data": a tuple of type (iiibiiay) describing a pixbuf with width,
+              height, rowstride, has-alpha, bits-per-sample, and image data
+  "description": an optional short description (1-2 lines)
+*/
+static void DBusAppendResultID(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult,
+    DBusMessageIter* aIter, const char* aID) {
+  nsCOMPtr<nsINavHistoryContainerResultNode> container =
+      aSearchResult->GetSearchResultContainer();
+
+  int index = DBusGetIndexFromIDKey(aID);
+  nsCOMPtr<nsINavHistoryResultNode> child;
+  container->GetChild(index, getter_AddRefs(child));
+  nsAutoCString title;
+  if (NS_FAILED(child->GetTitle(title))) {
+    return;
+  }
+
+  if (title.IsEmpty()) {
+    if (NS_FAILED(child->GetUri(title)) || title.IsEmpty()) {
+      return;
+    }
+  }
+
+  const char* titleStr = title.get();
+  appendStringDictionary(aIter, "id", aID);
+  appendStringDictionary(aIter, "name", titleStr);
+
+  GnomeHistoryIcon* icon = aSearchResult->GetHistoryIcon(index);
+  if (icon) {
+    DBusAppendIcon(icon, aIter);
+  } else {
+    appendStringDictionary(aIter, "gicon", "text-html");
+  }
+}
+
+/* Search the web for: "searchTerm" to the DBUS reply.
+ */
+static void DBusAppendSearchID(DBusMessageIter* aIter, const char* aID) {
+  /* aID contains:
+
+     KEYWORD_SEARCH_STRING:ssssss
+
+     KEYWORD_SEARCH_STRING is a 'special:search' keyword
+     ssssss is a searched term, must be at least one character long
+  */
+
+  // aID contains only 'KEYWORD_SEARCH_STRING:' so we're missing searched
+  // string.
+  if (strlen(aID) <= KEYWORD_SEARCH_STRING_LEN + 1) {
+    return;
+  }
+
+  appendStringDictionary(aIter, "id", KEYWORD_SEARCH_STRING);
+
+  // Extract ssssss part from aID
+  auto searchTerm = nsAutoCStringN<32>(aID + KEYWORD_SEARCH_STRING_LEN + 1);
+  nsAutoCString gnomeSearchTitle;
+  if (GetGnomeSearchTitle(searchTerm.get(), gnomeSearchTitle)) {
+    appendStringDictionary(aIter, "name", gnomeSearchTitle.get());
+    // TODO: When running on flatpak/snap we may need to use
+    // icon like org.mozilla.Firefox or so.
+    appendStringDictionary(aIter, "gicon", "firefox");
+  }
+}
+
+DBusHandlerResult DBusHandleResultMetas(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult, DBusMessage* aMsg) {
+  DBusMessage* reply;
+  char** stringArray;
+  int elements;
+
+  if (!dbus_message_get_args(aMsg, nullptr, DBUS_TYPE_ARRAY, DBUS_TYPE_STRING,
+                             &stringArray, &elements, DBUS_TYPE_INVALID) ||
+      elements == 0) {
+    reply = dbus_message_new_error(aMsg, GetDBusBusName(), "Wrong argument");
+  } else {
+    reply = dbus_message_new_method_return(aMsg);
+
+    DBusMessageIter iter;
+    dbus_message_iter_init_append(reply, &iter);
+    DBusMessageIter iterArray;
+    dbus_message_iter_open_container(&iter, DBUS_TYPE_ARRAY, "a{sv}",
+                                     &iterArray);
+
+    DBusMessageIter iterArray2;
+    for (int i = 0; i < elements; i++) {
+      dbus_message_iter_open_container(&iterArray, DBUS_TYPE_ARRAY, "{sv}",
+                                       &iterArray2);
+      if (strncmp(stringArray[i], KEYWORD_SEARCH_STRING,
+                  KEYWORD_SEARCH_STRING_LEN) == 0) {
+        DBusAppendSearchID(&iterArray2, stringArray[i]);
+      } else {
+        DBusAppendResultID(aSearchResult, &iterArray2, stringArray[i]);
+      }
+      dbus_message_iter_close_container(&iterArray, &iterArray2);
+    }
+
+    dbus_message_iter_close_container(&iter, &iterArray);
+    dbus_free_string_array(stringArray);
+  }
+
+  dbus_connection_send(aSearchResult->GetDBusConnection(), reply, nullptr);
+  dbus_message_unref(reply);
+
+  return DBUS_HANDLER_RESULT_HANDLED;
+}  // namespace mozilla
+
+static void ActivateResultID(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult,
+    const char* aResultID, uint32_t aTimeStamp) {
+  char* commandLine = nullptr;
+  int tmp;
+
+  if (strncmp(aResultID, KEYWORD_SEARCH_STRING, KEYWORD_SEARCH_STRING_LEN) ==
+      0) {
+    const char* urlList[3] = {"unused", "--search",
+                              aSearchResult->GetSearchTerm().get()};
+    commandLine = ConstructCommandLine(std::size(urlList), (char**)urlList,
+                                       nullptr, &tmp);
+  } else {
+    int keyIndex = atoi(aResultID);
+    nsCOMPtr<nsINavHistoryResultNode> child;
+    aSearchResult->GetSearchResultContainer()->GetChild(keyIndex,
+                                                        getter_AddRefs(child));
+    if (!child) {
+      return;
+    }
+
+    nsAutoCString uri;
+    nsresult rv = child->GetUri(uri);
+    if (NS_FAILED(rv)) {
+      return;
+    }
+
+    const char* urlList[2] = {"unused", uri.get()};
+    commandLine = ConstructCommandLine(std::size(urlList), (char**)urlList,
+                                       nullptr, &tmp);
+  }
+
+  if (commandLine) {
+    aSearchResult->HandleCommandLine(commandLine, aTimeStamp);
+    free(commandLine);
+  }
+}
+
+static void DBusLaunchWithAllResults(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult,
+    uint32_t aTimeStamp) {
+  uint32_t childCount = 0;
+  nsresult rv =
+      aSearchResult->GetSearchResultContainer()->GetChildCount(&childCount);
+  if (NS_FAILED(rv) || childCount == 0) {
+    return;
+  }
+
+  if (childCount > MAX_SEARCH_RESULTS_NUM) {
+    childCount = MAX_SEARCH_RESULTS_NUM;
+  }
+
+  // Allocate space for all found results, "unused", "--search" and
+  // potential search request.
+  char** urlList = (char**)moz_xmalloc(sizeof(char*) * (childCount + 3));
+  int urlListElements = 0;
+
+  urlList[urlListElements++] = strdup("unused");
+
+  for (uint32_t i = 0; i < childCount; i++) {
+    nsCOMPtr<nsINavHistoryResultNode> child;
+    aSearchResult->GetSearchResultContainer()->GetChild(i,
+                                                        getter_AddRefs(child));
+
+    if (!IsHistoryResultNodeURI(child)) {
+      continue;
+    }
+
+    nsAutoCString uri;
+    nsresult rv = child->GetUri(uri);
+    if (NS_FAILED(rv)) {
+      continue;
+    }
+    urlList[urlListElements++] = strdup(uri.get());
+  }
+
+  // When there isn't any uri to open pass search at least.
+  if (!childCount) {
+    urlList[urlListElements++] = strdup("--search");
+    urlList[urlListElements++] = strdup(aSearchResult->GetSearchTerm().get());
+  }
+
+  int tmp;
+  char* commandLine =
+      ConstructCommandLine(urlListElements, urlList, nullptr, &tmp);
+  if (commandLine) {
+    aSearchResult->HandleCommandLine(commandLine, aTimeStamp);
+    free(commandLine);
+  }
+
+  for (int i = 0; i < urlListElements; i++) {
+    free(urlList[i]);
+  }
+  free(urlList);
+}
+
+DBusHandlerResult DBusActivateResult(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult, DBusMessage* aMsg) {
+  DBusMessage* reply;
+  char* resultID;
+  char** stringArray;
+  int elements;
+  uint32_t timestamp;
+
+  if (!dbus_message_get_args(aMsg, nullptr, DBUS_TYPE_STRING, &resultID,
+                             DBUS_TYPE_ARRAY, DBUS_TYPE_STRING, &stringArray,
+                             &elements, DBUS_TYPE_UINT32, &timestamp,
+                             DBUS_TYPE_INVALID) ||
+      resultID == nullptr) {
+    reply = dbus_message_new_error(aMsg, GetDBusBusName(), "Wrong argument");
+  } else {
+    reply = dbus_message_new_method_return(aMsg);
+    ActivateResultID(aSearchResult, resultID, timestamp);
+    dbus_free_string_array(stringArray);
+  }
+
+  dbus_connection_send(aSearchResult->GetDBusConnection(), reply, nullptr);
+  dbus_message_unref(reply);
+
+  return DBUS_HANDLER_RESULT_HANDLED;
+}
+
+DBusHandlerResult DBusLaunchSearch(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult, DBusMessage* aMsg) {
+  DBusMessage* reply;
+  char** stringArray;
+  int elements;
+  uint32_t timestamp;
+
+  if (!dbus_message_get_args(aMsg, nullptr, DBUS_TYPE_ARRAY, DBUS_TYPE_STRING,
+                             &stringArray, &elements, DBUS_TYPE_UINT32,
+                             &timestamp, DBUS_TYPE_INVALID) ||
+      elements == 0) {
+    reply = dbus_message_new_error(aMsg, GetDBusBusName(), "Wrong argument");
+  } else {
+    reply = dbus_message_new_method_return(aMsg);
+    DBusLaunchWithAllResults(aSearchResult, timestamp);
+    dbus_free_string_array(stringArray);
+  }
+
+  dbus_connection_send(aSearchResult->GetDBusConnection(), reply, nullptr);
+  dbus_message_unref(reply);
+
+  return DBUS_HANDLER_RESULT_HANDLED;
+}
+
+bool IsHistoryResultNodeURI(nsINavHistoryResultNode* aHistoryNode) {
+  uint32_t type;
+  nsresult rv = aHistoryNode->GetType(&type);
+  if (NS_FAILED(rv) || type != nsINavHistoryResultNode::RESULT_TYPE_URI)
+    return false;
+
+  nsAutoCString title;
+  rv = aHistoryNode->GetTitle(title);
+  if (NS_SUCCEEDED(rv) && !title.IsEmpty()) {
+    return true;
+  }
+
+  rv = aHistoryNode->GetUri(title);
+  return NS_SUCCEEDED(rv) && !title.IsEmpty();
+}
diff --git a/browser/components/shell/nsGNOMEShellDBusHelper.h b/browser/components/shell/nsGNOMEShellDBusHelper.h
new file mode 100644
index 0000000000..924abf8356
--- /dev/null
+++ b/browser/components/shell/nsGNOMEShellDBusHelper.h
@@ -0,0 +1,37 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:expandtab:shiftwidth=2:tabstop=2:
+ */
+/* 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/. */
+
+#ifndef __nsGNOMEShellDBusHelper_h__
+#define __nsGNOMEShellDBusHelper_h__
+
+#include "mozilla/DBusHelpers.h"
+#include "nsINavHistoryService.h"
+
+#define MAX_SEARCH_RESULTS_NUM 9
+#define KEYWORD_SEARCH_STRING "special:search"
+#define KEYWORD_SEARCH_STRING_LEN 14
+
+class nsGNOMEShellHistorySearchResult;
+
+DBusHandlerResult DBusIntrospect(DBusConnection* aConnection,
+                                 DBusMessage* aMsg);
+DBusHandlerResult DBusHandleInitialResultSet(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult, DBusMessage* aMsg);
+DBusHandlerResult DBusHandleSubsearchResultSet(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult, DBusMessage* aMsg);
+DBusHandlerResult DBusHandleResultMetas(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult, DBusMessage* aMsg);
+DBusHandlerResult DBusActivateResult(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult, DBusMessage* aMsg);
+DBusHandlerResult DBusLaunchSearch(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult, DBusMessage* aMsg);
+bool IsHistoryResultNodeURI(nsINavHistoryResultNode* aHistoryNode);
+
+const char* GetDBusBusName();
+const char* GetDBusObjectPath();
+
+#endif  // __nsGNOMEShellDBusHelper_h__
diff --git a/browser/components/shell/nsGNOMEShellSearchProvider.cpp b/browser/components/shell/nsGNOMEShellSearchProvider.cpp
new file mode 100644
index 0000000000..b5658da034
--- /dev/null
+++ b/browser/components/shell/nsGNOMEShellSearchProvider.cpp
@@ -0,0 +1,442 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:expandtab:shiftwidth=2:tabstop=2:
+ */
+/* 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/. */
+
+#include "nsGNOMEShellSearchProvider.h"
+
+#include "nsToolkitCompsCID.h"
+#include "nsIFaviconService.h"
+#include "base/message_loop.h"  // for MessageLoop
+#include "base/task.h"          // for NewRunnableMethod, etc
+#include "mozilla/gfx/2D.h"
+#include "nsComponentManagerUtils.h"
+#include "nsIIOService.h"
+#include "nsIURI.h"
+#include "nsNetCID.h"
+#include "nsPrintfCString.h"
+#include "nsServiceManagerUtils.h"
+
+#include <dbus/dbus.h>
+#include <dbus/dbus-glib-lowlevel.h>
+
+#include "imgIContainer.h"
+#include "imgITools.h"
+
+using namespace mozilla;
+using namespace mozilla::gfx;
+
+class AsyncFaviconDataReady final : public nsIFaviconDataCallback {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIFAVICONDATACALLBACK
+
+  AsyncFaviconDataReady(RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult,
+                        int aIconIndex, int aTimeStamp)
+      : mSearchResult(aSearchResult),
+        mIconIndex(aIconIndex),
+        mTimeStamp(aTimeStamp){};
+
+ private:
+  ~AsyncFaviconDataReady() {}
+
+  RefPtr<nsGNOMEShellHistorySearchResult> mSearchResult;
+  int mIconIndex;
+  int mTimeStamp;
+};
+
+NS_IMPL_ISUPPORTS(AsyncFaviconDataReady, nsIFaviconDataCallback)
+
+// Inspired by SurfaceToPackedBGRA
+static UniquePtr<uint8_t[]> SurfaceToPackedRGBA(DataSourceSurface* aSurface) {
+  IntSize size = aSurface->GetSize();
+  CheckedInt<size_t> bufferSize =
+      CheckedInt<size_t>(size.width * 4) * CheckedInt<size_t>(size.height);
+  if (!bufferSize.isValid()) {
+    return nullptr;
+  }
+  UniquePtr<uint8_t[]> imageBuffer(new (std::nothrow)
+                                       uint8_t[bufferSize.value()]);
+  if (!imageBuffer) {
+    return nullptr;
+  }
+
+  DataSourceSurface::MappedSurface map;
+  if (!aSurface->Map(DataSourceSurface::MapType::READ, &map)) {
+    return nullptr;
+  }
+
+  // Convert BGRA to RGBA
+  uint32_t* aSrc = (uint32_t*)map.mData;
+  uint32_t* aDst = (uint32_t*)imageBuffer.get();
+  for (int i = 0; i < size.width * size.height; i++, aDst++, aSrc++) {
+    *aDst = *aSrc & 0xff00ff00;
+    *aDst |= (*aSrc & 0xff) << 16;
+    *aDst |= (*aSrc & 0xff0000) >> 16;
+  }
+
+  aSurface->Unmap();
+
+  return imageBuffer;
+}
+
+NS_IMETHODIMP
+AsyncFaviconDataReady::OnComplete(nsIURI* aFaviconURI, uint32_t aDataLen,
+                                  const uint8_t* aData,
+                                  const nsACString& aMimeType,
+                                  uint16_t aWidth) {
+  // This is a callback from some previous search so we don't want it
+  if (mTimeStamp != mSearchResult->GetTimeStamp() || !aData || !aDataLen) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Decode the image from the format it was returned to us in (probably PNG)
+  nsCOMPtr<imgIContainer> container;
+  nsCOMPtr<imgITools> imgtool = do_CreateInstance("@mozilla.org/image/tools;1");
+  nsresult rv = imgtool->DecodeImageFromBuffer(
+      reinterpret_cast<const char*>(aData), aDataLen, aMimeType,
+      getter_AddRefs(container));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  RefPtr<SourceSurface> surface = container->GetFrame(
+      imgIContainer::FRAME_FIRST,
+      imgIContainer::FLAG_SYNC_DECODE | imgIContainer::FLAG_ASYNC_NOTIFY);
+
+  if (!surface || surface->GetFormat() != SurfaceFormat::B8G8R8A8) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Allocate a new buffer that we own.
+  RefPtr<DataSourceSurface> dataSurface = surface->GetDataSurface();
+  UniquePtr<uint8_t[]> data = SurfaceToPackedRGBA(dataSurface);
+  if (!data) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  mSearchResult->SetHistoryIcon(mTimeStamp, std::move(data),
+                                surface->GetSize().width,
+                                surface->GetSize().height, mIconIndex);
+  return NS_OK;
+}
+
+DBusHandlerResult nsGNOMEShellSearchProvider::HandleSearchResultSet(
+    DBusMessage* aMsg, bool aInitialSearch) {
+  // Discard any existing search results.
+  mSearchResult = nullptr;
+
+  RefPtr<nsGNOMEShellHistorySearchResult> newSearch =
+      new nsGNOMEShellHistorySearchResult(this, mConnection,
+                                          mSearchResultTimeStamp);
+  mSearchResultTimeStamp++;
+  newSearch->SetTimeStamp(mSearchResultTimeStamp);
+
+  // Send the search request over DBus. We'll get reply over DBus it will be
+  // set to mSearchResult by nsGNOMEShellSearchProvider::SetSearchResult().
+  return aInitialSearch
+             ? DBusHandleInitialResultSet(newSearch.forget(), aMsg)
+             : DBusHandleSubsearchResultSet(newSearch.forget(), aMsg);
+}
+
+DBusHandlerResult nsGNOMEShellSearchProvider::HandleResultMetas(
+    DBusMessage* aMsg) {
+  if (!mSearchResult) {
+    NS_WARNING("Missing nsGNOMEShellHistorySearchResult.");
+    return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+  }
+  return DBusHandleResultMetas(mSearchResult, aMsg);
+}
+
+DBusHandlerResult nsGNOMEShellSearchProvider::ActivateResult(
+    DBusMessage* aMsg) {
+  if (!mSearchResult) {
+    NS_WARNING("Missing nsGNOMEShellHistorySearchResult.");
+    return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+  }
+  return DBusActivateResult(mSearchResult, aMsg);
+}
+
+DBusHandlerResult nsGNOMEShellSearchProvider::LaunchSearch(DBusMessage* aMsg) {
+  if (!mSearchResult) {
+    NS_WARNING("Missing nsGNOMEShellHistorySearchResult.");
+    return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+  }
+  return DBusLaunchSearch(mSearchResult, aMsg);
+}
+
+DBusHandlerResult nsGNOMEShellSearchProvider::HandleDBusMessage(
+    DBusConnection* aConnection, DBusMessage* aMsg) {
+  NS_ASSERTION(mConnection == aConnection, "Wrong D-Bus connection.");
+
+  const char* method = dbus_message_get_member(aMsg);
+  const char* iface = dbus_message_get_interface(aMsg);
+
+  if ((strcmp("Introspect", method) == 0) &&
+      (strcmp("org.freedesktop.DBus.Introspectable", iface) == 0)) {
+    return DBusIntrospect(mConnection, aMsg);
+  }
+
+  if (strcmp("org.gnome.Shell.SearchProvider2", iface) == 0) {
+    if (strcmp("GetInitialResultSet", method) == 0) {
+      return HandleSearchResultSet(aMsg, /* aInitialSearch */ true);
+    }
+    if (strcmp("GetSubsearchResultSet", method) == 0) {
+      return HandleSearchResultSet(aMsg, /* aInitialSearch */ false);
+    }
+    if (strcmp("GetResultMetas", method) == 0) {
+      return HandleResultMetas(aMsg);
+    }
+    if (strcmp("ActivateResult", method) == 0) {
+      return ActivateResult(aMsg);
+    }
+    if (strcmp("LaunchSearch", method) == 0) {
+      return LaunchSearch(aMsg);
+    }
+  }
+
+  return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+}
+
+void nsGNOMEShellSearchProvider::UnregisterDBusInterface(
+    DBusConnection* aConnection) {
+  NS_ASSERTION(mConnection == aConnection, "Wrong D-Bus connection.");
+  // Not implemented
+}
+
+static DBusHandlerResult message_handler(DBusConnection* conn,
+                                         DBusMessage* aMsg, void* user_data) {
+  auto interface = static_cast<nsGNOMEShellSearchProvider*>(user_data);
+  return interface->HandleDBusMessage(conn, aMsg);
+}
+
+static void unregister(DBusConnection* conn, void* user_data) {
+  auto interface = static_cast<nsGNOMEShellSearchProvider*>(user_data);
+  interface->UnregisterDBusInterface(conn);
+}
+
+static DBusObjectPathVTable remoteHandlersTable = {
+    .unregister_function = unregister,
+    .message_function = message_handler,
+};
+
+nsresult nsGNOMEShellSearchProvider::Startup() {
+  if (mConnection && dbus_connection_get_is_connected(mConnection)) {
+    // We're already connected so we don't need to reconnect
+    return NS_ERROR_ALREADY_INITIALIZED;
+  }
+
+  mConnection =
+      already_AddRefed<DBusConnection>(dbus_bus_get(DBUS_BUS_SESSION, nullptr));
+  if (!mConnection) {
+    return NS_ERROR_FAILURE;
+  }
+  dbus_connection_set_exit_on_disconnect(mConnection, false);
+  dbus_connection_setup_with_g_main(mConnection, nullptr);
+
+  DBusError err;
+  dbus_error_init(&err);
+  dbus_bus_request_name(mConnection, GetDBusBusName(),
+                        DBUS_NAME_FLAG_DO_NOT_QUEUE, &err);
+  // The interface is already owned - there is another application/profile
+  // instance already running.
+  if (dbus_error_is_set(&err)) {
+    dbus_error_free(&err);
+    mConnection = nullptr;
+    return NS_ERROR_FAILURE;
+  }
+
+  if (!dbus_connection_register_object_path(mConnection, GetDBusObjectPath(),
+                                            &remoteHandlersTable, this)) {
+    mConnection = nullptr;
+    return NS_ERROR_FAILURE;
+  }
+
+  mSearchResultTimeStamp = 0;
+  return NS_OK;
+}
+
+void nsGNOMEShellSearchProvider::Shutdown() {
+  if (!mConnection) {
+    return;
+  }
+
+  dbus_connection_unregister_object_path(mConnection, GetDBusObjectPath());
+
+  // dbus_connection_unref() will be called by RefPtr here.
+  mConnection = nullptr;
+}
+
+bool nsGNOMEShellSearchProvider::SetSearchResult(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult) {
+  MOZ_ASSERT(!mSearchResult);
+
+  if (mSearchResultTimeStamp != aSearchResult->GetTimeStamp()) {
+    NS_WARNING("Time stamp mismatch.");
+    return false;
+  }
+  mSearchResult = aSearchResult;
+  return true;
+}
+
+static void DispatchSearchResults(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult,
+    nsCOMPtr<nsINavHistoryContainerResultNode> aHistResultContainer) {
+  aSearchResult->ReceiveSearchResultContainer(aHistResultContainer);
+}
+
+nsresult nsGNOMEShellHistoryService::QueryHistory(
+    RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult) {
+  if (!mHistoryService) {
+    mHistoryService = do_GetService(NS_NAVHISTORYSERVICE_CONTRACTID);
+    if (!mHistoryService) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+
+  nsresult rv;
+  nsCOMPtr<nsINavHistoryQuery> histQuery;
+  rv = mHistoryService->GetNewQuery(getter_AddRefs(histQuery));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = histQuery->SetSearchTerms(
+      NS_ConvertUTF8toUTF16(aSearchResult->GetSearchTerm()));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsINavHistoryQueryOptions> histQueryOpts;
+  rv = mHistoryService->GetNewQueryOptions(getter_AddRefs(histQueryOpts));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = histQueryOpts->SetSortingMode(
+      nsINavHistoryQueryOptions::SORT_BY_FRECENCY_DESCENDING);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = histQueryOpts->SetMaxResults(MAX_SEARCH_RESULTS_NUM);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsINavHistoryResult> histResult;
+  rv = mHistoryService->ExecuteQuery(histQuery, histQueryOpts,
+                                     getter_AddRefs(histResult));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsINavHistoryContainerResultNode> resultContainer;
+
+  rv = histResult->GetRoot(getter_AddRefs(resultContainer));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = resultContainer->SetContainerOpen(true);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Simulate async searching by delayed reply. This search API will
+  // likely become async in the future and we want to be sure to not rely on
+  // its current synchronous behavior.
+  MOZ_ASSERT(MessageLoop::current());
+  MessageLoop::current()->PostTask(
+      NewRunnableFunction("Gnome shell search results", &DispatchSearchResults,
+                          aSearchResult, resultContainer));
+
+  return NS_OK;
+}
+
+static void DBusGetIDKeyForURI(int aIndex, nsAutoCString& aUri,
+                               nsAutoCString& aIDKey) {
+  // Compose ID as NN:URL where NN is index to our current history
+  // result container.
+  aIDKey = nsPrintfCString("%.2d:%s", aIndex, aUri.get());
+}
+
+void nsGNOMEShellHistorySearchResult::HandleSearchResultReply() {
+  MOZ_ASSERT(mReply);
+
+  uint32_t childCount = 0;
+  nsresult rv = mHistResultContainer->GetChildCount(&childCount);
+
+  DBusMessageIter iter;
+  dbus_message_iter_init_append(mReply, &iter);
+  DBusMessageIter iterArray;
+  dbus_message_iter_open_container(&iter, DBUS_TYPE_ARRAY, "s", &iterArray);
+
+  if (NS_SUCCEEDED(rv) && childCount > 0) {
+    // Obtain the favicon service and get the favicon for the specified page
+    nsCOMPtr<nsIFaviconService> favIconSvc(
+        do_GetService("@mozilla.org/browser/favicon-service;1"));
+    nsCOMPtr<nsIIOService> ios(do_GetService(NS_IOSERVICE_CONTRACTID));
+
+    if (childCount > MAX_SEARCH_RESULTS_NUM) {
+      childCount = MAX_SEARCH_RESULTS_NUM;
+    }
+
+    for (uint32_t i = 0; i < childCount; i++) {
+      nsCOMPtr<nsINavHistoryResultNode> child;
+      mHistResultContainer->GetChild(i, getter_AddRefs(child));
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        continue;
+      }
+      if (!IsHistoryResultNodeURI(child)) {
+        continue;
+      }
+
+      nsAutoCString uri;
+      child->GetUri(uri);
+
+      nsCOMPtr<nsIURI> iconIri;
+      ios->NewURI(uri, nullptr, nullptr, getter_AddRefs(iconIri));
+      nsCOMPtr<nsIFaviconDataCallback> callback =
+          new AsyncFaviconDataReady(this, i, mTimeStamp);
+      favIconSvc->GetFaviconDataForPage(iconIri, callback, 0);
+
+      nsAutoCString idKey;
+      DBusGetIDKeyForURI(i, uri, idKey);
+
+      const char* id = idKey.get();
+      dbus_message_iter_append_basic(&iterArray, DBUS_TYPE_STRING, &id);
+    }
+  }
+
+  nsPrintfCString searchString("%s:%s", KEYWORD_SEARCH_STRING,
+                               mSearchTerm.get());
+  const char* search = searchString.get();
+  dbus_message_iter_append_basic(&iterArray, DBUS_TYPE_STRING, &search);
+
+  dbus_message_iter_close_container(&iter, &iterArray);
+
+  dbus_connection_send(mConnection, mReply, nullptr);
+  dbus_message_unref(mReply);
+
+  mReply = nullptr;
+}
+
+void nsGNOMEShellHistorySearchResult::ReceiveSearchResultContainer(
+    nsCOMPtr<nsINavHistoryContainerResultNode> aHistResultContainer) {
+  // Propagate search results to nsGNOMEShellSearchProvider.
+  // SetSearchResult() checks this is up-to-date search (our time stamp matches
+  // latest requested search timestamp).
+  if (mSearchProvider->SetSearchResult(this)) {
+    mHistResultContainer = aHistResultContainer;
+    HandleSearchResultReply();
+  }
+}
+
+void nsGNOMEShellHistorySearchResult::SetHistoryIcon(int aTimeStamp,
+                                                     UniquePtr<uint8_t[]> aData,
+                                                     int aWidth, int aHeight,
+                                                     int aIconIndex) {
+  MOZ_ASSERT(mTimeStamp == aTimeStamp);
+  MOZ_RELEASE_ASSERT(aIconIndex < MAX_SEARCH_RESULTS_NUM);
+  mHistoryIcons[aIconIndex].Set(mTimeStamp, std::move(aData), aWidth, aHeight);
+}
+
+GnomeHistoryIcon* nsGNOMEShellHistorySearchResult::GetHistoryIcon(
+    int aIconIndex) {
+  MOZ_RELEASE_ASSERT(aIconIndex < MAX_SEARCH_RESULTS_NUM);
+  if (mHistoryIcons[aIconIndex].GetTimeStamp() == mTimeStamp &&
+      mHistoryIcons[aIconIndex].IsLoaded()) {
+    return mHistoryIcons + aIconIndex;
+  }
+  return nullptr;
+}
+
+nsGNOMEShellHistoryService* GetGNOMEShellHistoryService() {
+  static nsGNOMEShellHistoryService gGNOMEShellHistoryService;
+  return &gGNOMEShellHistoryService;
+}
diff --git a/browser/components/shell/nsGNOMEShellSearchProvider.h b/browser/components/shell/nsGNOMEShellSearchProvider.h
new file mode 100644
index 0000000000..f116fe5797
--- /dev/null
+++ b/browser/components/shell/nsGNOMEShellSearchProvider.h
@@ -0,0 +1,139 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:expandtab:shiftwidth=2:tabstop=2:
+ */
+/* 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/. */
+
+#ifndef __nsGNOMEShellSearchProvider_h__
+#define __nsGNOMEShellSearchProvider_h__
+
+#include "nsINavHistoryService.h"
+#include "nsUnixRemoteServer.h"
+#include "nsString.h"
+#include "nsCOMPtr.h"
+#include "mozilla/UniquePtr.h"
+#include "nsGNOMEShellDBusHelper.h"
+
+class nsGNOMEShellSearchProvider;
+
+class GnomeHistoryIcon {
+ public:
+  GnomeHistoryIcon() : mTimeStamp(-1), mWidth(0), mHeight(0){};
+
+  // From which search is this icon
+  void Set(int aTimeStamp, mozilla::UniquePtr<uint8_t[]> aData, int aWidth,
+           int aHeight) {
+    mTimeStamp = aTimeStamp;
+    mWidth = aWidth;
+    mHeight = aHeight;
+    mData = std::move(aData);
+  }
+
+  bool IsLoaded() { return mData && mWidth > 0 && mHeight > 0; }
+  int GetTimeStamp() { return mTimeStamp; }
+  uint8_t* GetData() { return mData.get(); }
+  int GetWidth() { return mWidth; }
+  int GetHeight() { return mHeight; }
+
+ private:
+  int mTimeStamp;
+  mozilla::UniquePtr<uint8_t[]> mData;
+  int mWidth;
+  int mHeight;
+};
+
+// nsGNOMEShellHistorySearchResult is a container with contains search results
+// which are files asynchronously by nsGNOMEShellHistoryService.
+// The search results can be opened by Firefox then.
+class nsGNOMEShellHistorySearchResult : public nsUnixRemoteServer {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(nsGNOMEShellHistorySearchResult)
+
+  nsGNOMEShellHistorySearchResult(nsGNOMEShellSearchProvider* aSearchProvider,
+                                  DBusConnection* aConnection, int aTimeStamp)
+      : mSearchProvider(aSearchProvider),
+        mReply(nullptr),
+        mConnection(aConnection),
+        mTimeStamp(aTimeStamp){};
+
+  void SetReply(DBusMessage* aReply) { mReply = aReply; }
+  void SetSearchTerm(const char* aSearchTerm) {
+    mSearchTerm = nsAutoCString(aSearchTerm);
+  }
+  DBusConnection* GetDBusConnection() { return mConnection; }
+  void SetTimeStamp(int aTimeStamp) { mTimeStamp = aTimeStamp; }
+  int GetTimeStamp() { return mTimeStamp; }
+  nsAutoCString& GetSearchTerm() { return mSearchTerm; }
+
+  // Receive (asynchronously) history search results from history service.
+  // This is called asynchronously by nsGNOMEShellHistoryService
+  // when we have search results available.
+  void ReceiveSearchResultContainer(
+      nsCOMPtr<nsINavHistoryContainerResultNode> aHistResultContainer);
+
+  nsCOMPtr<nsINavHistoryContainerResultNode> GetSearchResultContainer() {
+    return mHistResultContainer;
+  }
+  void HandleCommandLine(const char* aBuffer, uint32_t aTimestamp) {
+    nsUnixRemoteServer::HandleCommandLine(aBuffer, aTimestamp);
+  }
+
+  void SetHistoryIcon(int aTimeStamp, mozilla::UniquePtr<uint8_t[]> aData,
+                      int aWidth, int aHeight, int aIconIndex);
+  GnomeHistoryIcon* GetHistoryIcon(int aIconIndex);
+
+ private:
+  void HandleSearchResultReply();
+
+  ~nsGNOMEShellHistorySearchResult() = default;
+
+ private:
+  nsGNOMEShellSearchProvider* mSearchProvider;
+  nsCOMPtr<nsINavHistoryContainerResultNode> mHistResultContainer;
+  nsAutoCString mSearchTerm;
+  DBusMessage* mReply;
+  DBusConnection* mConnection;
+  int mTimeStamp;
+  GnomeHistoryIcon mHistoryIcons[MAX_SEARCH_RESULTS_NUM];
+};
+
+class nsGNOMEShellHistoryService {
+ public:
+  nsresult QueryHistory(RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult);
+
+ private:
+  nsCOMPtr<nsINavHistoryService> mHistoryService;
+};
+
+class nsGNOMEShellSearchProvider {
+ public:
+  nsGNOMEShellSearchProvider()
+      : mConnection(nullptr), mSearchResultTimeStamp(0) {}
+  ~nsGNOMEShellSearchProvider() { Shutdown(); }
+
+  nsresult Startup();
+  void Shutdown();
+
+  DBusHandlerResult HandleDBusMessage(DBusConnection* aConnection,
+                                      DBusMessage* msg);
+  void UnregisterDBusInterface(DBusConnection* aConnection);
+
+  bool SetSearchResult(RefPtr<nsGNOMEShellHistorySearchResult> aSearchResult);
+
+ private:
+  DBusHandlerResult HandleSearchResultSet(DBusMessage* msg,
+                                          bool aInitialSearch);
+  DBusHandlerResult HandleResultMetas(DBusMessage* msg);
+  DBusHandlerResult ActivateResult(DBusMessage* msg);
+  DBusHandlerResult LaunchSearch(DBusMessage* msg);
+
+  // The connection is owned by DBus library
+  RefPtr<DBusConnection> mConnection;
+  RefPtr<nsGNOMEShellHistorySearchResult> mSearchResult;
+  int mSearchResultTimeStamp;
+};
+
+nsGNOMEShellHistoryService* GetGNOMEShellHistoryService();
+
+#endif  // __nsGNOMEShellSearchProvider_h__
diff --git a/browser/components/shell/nsGNOMEShellService.cpp b/browser/components/shell/nsGNOMEShellService.cpp
new file mode 100644
index 0000000000..a07d37d109
--- /dev/null
+++ b/browser/components/shell/nsGNOMEShellService.cpp
@@ -0,0 +1,506 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Preferences.h"
+
+#include "nsCOMPtr.h"
+#include "nsGNOMEShellService.h"
+#include "nsShellService.h"
+#include "nsIFile.h"
+#include "nsIProperties.h"
+#include "nsDirectoryServiceDefs.h"
+#include "prenv.h"
+#include "nsString.h"
+#include "nsIGIOService.h"
+#include "nsIGSettingsService.h"
+#include "nsIStringBundle.h"
+#include "nsServiceManagerUtils.h"
+#include "nsIImageLoadingContent.h"
+#include "imgIRequest.h"
+#include "imgIContainer.h"
+#include "mozilla/Components.h"
+#include "mozilla/GRefPtr.h"
+#include "mozilla/GUniquePtr.h"
+#include "mozilla/WidgetUtilsGtk.h"
+#include "mozilla/dom/Element.h"
+#include "nsImageToPixbuf.h"
+#include "nsXULAppAPI.h"
+#include "gfxPlatform.h"
+
+#include <glib.h>
+#include <gdk/gdk.h>
+#include <gdk-pixbuf/gdk-pixbuf.h>
+#include <stdlib.h>
+
+using namespace mozilla;
+
+struct ProtocolAssociation {
+  const char* name;
+  bool essential;
+};
+
+struct MimeTypeAssociation {
+  const char* mimeType;
+  const char* extensions;
+};
+
+static const ProtocolAssociation appProtocols[] = {
+    // clang-format off
+  { "http",   true     },
+  { "https",  true     },
+  { "chrome", false }
+    // clang-format on
+};
+
+static const MimeTypeAssociation appTypes[] = {
+    // clang-format off
+  { "text/html",             "htm html shtml" },
+  { "application/xhtml+xml", "xhtml xht"      }
+    // clang-format on
+};
+
+#define kDesktopBGSchema "org.gnome.desktop.background"_ns
+#define kDesktopColorGSKey "primary-color"_ns
+
+nsresult nsGNOMEShellService::Init() {
+  nsresult rv;
+
+  if (gfxPlatform::IsHeadless()) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  // GSettings or GIO _must_ be available, or we do not allow
+  // CreateInstance to succeed.
+
+  nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
+  nsCOMPtr<nsIGSettingsService> gsettings =
+      do_GetService(NS_GSETTINGSSERVICE_CONTRACTID);
+
+  if (!giovfs && !gsettings) return NS_ERROR_NOT_AVAILABLE;
+
+#ifdef MOZ_ENABLE_DBUS
+  if (widget::IsGnomeDesktopEnvironment() &&
+      Preferences::GetBool("browser.gnome-search-provider.enabled", false)) {
+    mSearchProvider.Startup();
+  }
+#endif
+
+  // Check G_BROKEN_FILENAMES.  If it's set, then filenames in glib use
+  // the locale encoding.  If it's not set, they use UTF-8.
+  mUseLocaleFilenames = PR_GetEnv("G_BROKEN_FILENAMES") != nullptr;
+
+  if (GetAppPathFromLauncher()) return NS_OK;
+
+  nsCOMPtr<nsIProperties> dirSvc(
+      do_GetService("@mozilla.org/file/directory_service;1"));
+  NS_ENSURE_TRUE(dirSvc, NS_ERROR_NOT_AVAILABLE);
+
+  nsCOMPtr<nsIFile> appPath;
+  rv = dirSvc->Get(XRE_EXECUTABLE_FILE, NS_GET_IID(nsIFile),
+                   getter_AddRefs(appPath));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return appPath->GetNativePath(mAppPath);
+}
+
+NS_IMPL_ISUPPORTS(nsGNOMEShellService, nsIGNOMEShellService, nsIShellService,
+                  nsIToolkitShellService)
+
+bool nsGNOMEShellService::GetAppPathFromLauncher() {
+  gchar* tmp;
+
+  const char* launcher = PR_GetEnv("MOZ_APP_LAUNCHER");
+  if (!launcher) return false;
+
+  if (g_path_is_absolute(launcher)) {
+    mAppPath = launcher;
+    tmp = g_path_get_basename(launcher);
+    gchar* fullpath = g_find_program_in_path(tmp);
+    if (fullpath && mAppPath.Equals(fullpath)) mAppIsInPath = true;
+    g_free(fullpath);
+  } else {
+    tmp = g_find_program_in_path(launcher);
+    if (!tmp) return false;
+    mAppPath = tmp;
+    mAppIsInPath = true;
+  }
+
+  g_free(tmp);
+  return true;
+}
+
+bool nsGNOMEShellService::KeyMatchesAppName(const char* aKeyValue) const {
+  gchar* commandPath;
+  if (mUseLocaleFilenames) {
+    gchar* nativePath =
+        g_filename_from_utf8(aKeyValue, -1, nullptr, nullptr, nullptr);
+    if (!nativePath) {
+      NS_ERROR("Error converting path to filesystem encoding");
+      return false;
+    }
+
+    commandPath = g_find_program_in_path(nativePath);
+    g_free(nativePath);
+  } else {
+    commandPath = g_find_program_in_path(aKeyValue);
+  }
+
+  if (!commandPath) return false;
+
+  bool matches = mAppPath.Equals(commandPath);
+  g_free(commandPath);
+  return matches;
+}
+
+bool nsGNOMEShellService::CheckHandlerMatchesAppName(
+    const nsACString& handler) const {
+  gint argc;
+  gchar** argv;
+  nsAutoCString command(handler);
+
+  // The string will be something of the form: [/path/to/]browser "%s"
+  // We want to remove all of the parameters and get just the binary name.
+
+  if (g_shell_parse_argv(command.get(), &argc, &argv, nullptr) && argc > 0) {
+    command.Assign(argv[0]);
+    g_strfreev(argv);
+  }
+
+  if (!KeyMatchesAppName(command.get()))
+    return false;  // the handler is set to another app
+
+  return true;
+}
+
+NS_IMETHODIMP
+nsGNOMEShellService::IsDefaultBrowser(bool aForAllTypes,
+                                      bool* aIsDefaultBrowser) {
+  *aIsDefaultBrowser = false;
+
+  if (widget::IsRunningUnderSnap()) {
+    const gchar* argv[] = {"xdg-settings", "check", "default-web-browser",
+                           (MOZ_APP_NAME ".desktop"), nullptr};
+    GSpawnFlags flags = static_cast<GSpawnFlags>(G_SPAWN_SEARCH_PATH |
+                                                 G_SPAWN_STDERR_TO_DEV_NULL);
+    gchar* output = nullptr;
+    gint exit_status = 0;
+    if (!g_spawn_sync(nullptr, (gchar**)argv, nullptr, flags, nullptr, nullptr,
+                      &output, nullptr, &exit_status, nullptr)) {
+      return NS_OK;
+    }
+    if (exit_status != 0) {
+      g_free(output);
+      return NS_OK;
+    }
+    if (strcmp(output, "yes\n") == 0) {
+      *aIsDefaultBrowser = true;
+    }
+    g_free(output);
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
+  nsAutoCString handler;
+  nsCOMPtr<nsIGIOMimeApp> gioApp;
+
+  for (unsigned int i = 0; i < ArrayLength(appProtocols); ++i) {
+    if (!appProtocols[i].essential) continue;
+
+    if (!IsDefaultForSchemeHelper(nsDependentCString(appProtocols[i].name),
+                                  giovfs)) {
+      return NS_OK;
+    }
+  }
+
+  *aIsDefaultBrowser = true;
+
+  return NS_OK;
+}
+
+bool nsGNOMEShellService::IsDefaultForSchemeHelper(
+    const nsACString& aScheme, nsIGIOService* giovfs) const {
+  nsCOMPtr<nsIGIOService> gioService;
+  if (!giovfs) {
+    gioService = do_GetService(NS_GIOSERVICE_CONTRACTID);
+    giovfs = gioService.get();
+  }
+
+  if (!giovfs) {
+    return false;
+  }
+
+  nsCOMPtr<nsIGIOMimeApp> gioApp;
+  nsCOMPtr<nsIHandlerApp> handlerApp;
+  giovfs->GetAppForURIScheme(aScheme, getter_AddRefs(handlerApp));
+  gioApp = do_QueryInterface(handlerApp);
+  if (!gioApp) {
+    return false;
+  }
+
+  nsAutoCString handler;
+  gioApp->GetCommand(handler);
+  return CheckHandlerMatchesAppName(handler);
+}
+
+NS_IMETHODIMP
+nsGNOMEShellService::IsDefaultForScheme(const nsACString& aScheme,
+                                        bool* aIsDefaultBrowser) {
+  *aIsDefaultBrowser = IsDefaultForSchemeHelper(aScheme, nullptr);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsGNOMEShellService::SetDefaultBrowser(bool aClaimAllTypes, bool aForAllUsers) {
+#ifdef DEBUG
+  if (aForAllUsers)
+    NS_WARNING(
+        "Setting the default browser for all users is not yet supported");
+#endif
+
+  if (widget::IsRunningUnderSnap()) {
+    const gchar* argv[] = {"xdg-settings", "set", "default-web-browser",
+                           (MOZ_APP_NAME ".desktop"), nullptr};
+    GSpawnFlags flags = static_cast<GSpawnFlags>(G_SPAWN_SEARCH_PATH |
+                                                 G_SPAWN_STDOUT_TO_DEV_NULL |
+                                                 G_SPAWN_STDERR_TO_DEV_NULL);
+    g_spawn_sync(nullptr, (gchar**)argv, nullptr, flags, nullptr, nullptr,
+                 nullptr, nullptr, nullptr, nullptr);
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
+  if (giovfs) {
+    nsresult rv;
+    nsCOMPtr<nsIStringBundleService> bundleService =
+        components::StringBundle::Service(&rv);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<nsIStringBundle> brandBundle;
+    rv = bundleService->CreateBundle(BRAND_PROPERTIES,
+                                     getter_AddRefs(brandBundle));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsAutoString brandShortName;
+    brandBundle->GetStringFromName("brandShortName", brandShortName);
+
+    // use brandShortName as the application id.
+    NS_ConvertUTF16toUTF8 id(brandShortName);
+    nsCOMPtr<nsIGIOMimeApp> appInfo;
+    rv = giovfs->FindAppFromCommand(mAppPath, getter_AddRefs(appInfo));
+    if (NS_FAILED(rv)) {
+      // Application was not found in the list of installed applications
+      // provided by OS. Fallback to create appInfo from command and name.
+      rv = giovfs->CreateAppFromCommand(mAppPath, id, getter_AddRefs(appInfo));
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+
+    // set handler for the protocols
+    for (unsigned int i = 0; i < ArrayLength(appProtocols); ++i) {
+      if (appProtocols[i].essential || aClaimAllTypes) {
+        appInfo->SetAsDefaultForURIScheme(
+            nsDependentCString(appProtocols[i].name));
+      }
+    }
+
+    // set handler for .html and xhtml files and MIME types:
+    if (aClaimAllTypes) {
+      // Add mime types for html, xhtml extension and set app to just created
+      // appinfo.
+      for (unsigned int i = 0; i < ArrayLength(appTypes); ++i) {
+        appInfo->SetAsDefaultForMimeType(
+            nsDependentCString(appTypes[i].mimeType));
+        appInfo->SetAsDefaultForFileExtensions(
+            nsDependentCString(appTypes[i].extensions));
+      }
+    }
+  }
+
+  nsCOMPtr<nsIPrefBranch> prefs(do_GetService(NS_PREFSERVICE_CONTRACTID));
+  if (prefs) {
+    (void)prefs->SetBoolPref(PREF_CHECKDEFAULTBROWSER, true);
+    // Reset the number of times the dialog should be shown
+    // before it is silenced.
+    (void)prefs->SetIntPref(PREF_DEFAULTBROWSERCHECKCOUNT, 0);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsGNOMEShellService::GetCanSetDesktopBackground(bool* aResult) {
+  // setting desktop background is currently only supported
+  // for Gnome or desktops using the same GSettings keys
+  if (widget::IsGnomeDesktopEnvironment()) {
+    *aResult = true;
+    return NS_OK;
+  }
+
+  *aResult = !!getenv("GNOME_DESKTOP_SESSION_ID");
+  return NS_OK;
+}
+
+static nsresult WriteImage(const nsCString& aPath, imgIContainer* aImage) {
+  RefPtr<GdkPixbuf> pixbuf = nsImageToPixbuf::ImageToPixbuf(aImage);
+  if (!pixbuf) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  gboolean res = gdk_pixbuf_save(pixbuf, aPath.get(), "png", nullptr, nullptr);
+  return res ? NS_OK : NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsGNOMEShellService::SetDesktopBackground(dom::Element* aElement,
+                                          int32_t aPosition,
+                                          const nsACString& aImageName) {
+  nsCOMPtr<nsIImageLoadingContent> imageContent = do_QueryInterface(aElement);
+  if (!imageContent) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // get the image container
+  nsCOMPtr<imgIRequest> request;
+  imageContent->GetRequest(nsIImageLoadingContent::CURRENT_REQUEST,
+                           getter_AddRefs(request));
+  if (!request) {
+    return NS_ERROR_FAILURE;
+  }
+  nsCOMPtr<imgIContainer> container;
+  request->GetImage(getter_AddRefs(container));
+  if (!container) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Set desktop wallpaper filling style
+  nsAutoCString options;
+  if (aPosition == BACKGROUND_TILE)
+    options.AssignLiteral("wallpaper");
+  else if (aPosition == BACKGROUND_STRETCH)
+    options.AssignLiteral("stretched");
+  else if (aPosition == BACKGROUND_FILL)
+    options.AssignLiteral("zoom");
+  else if (aPosition == BACKGROUND_FIT)
+    options.AssignLiteral("scaled");
+  else if (aPosition == BACKGROUND_SPAN)
+    options.AssignLiteral("spanned");
+  else
+    options.AssignLiteral("centered");
+
+  // Write the background file to the home directory.
+  nsAutoCString filePath(PR_GetEnv("HOME"));
+  nsAutoString brandName;
+
+  // get the product brand name from localized strings
+  if (nsCOMPtr<nsIStringBundleService> bundleService =
+          components::StringBundle::Service()) {
+    nsCOMPtr<nsIStringBundle> brandBundle;
+    bundleService->CreateBundle(BRAND_PROPERTIES, getter_AddRefs(brandBundle));
+    if (bundleService) {
+      brandBundle->GetStringFromName("brandShortName", brandName);
+    }
+  }
+
+  // build the file name
+  filePath.Append('/');
+  filePath.Append(NS_ConvertUTF16toUTF8(brandName));
+  filePath.AppendLiteral("_wallpaper.png");
+
+  // write the image to a file in the home dir
+  MOZ_TRY(WriteImage(filePath, container));
+
+  nsCOMPtr<nsIGSettingsService> gsettings =
+      do_GetService(NS_GSETTINGSSERVICE_CONTRACTID);
+  if (!gsettings) {
+    return NS_ERROR_FAILURE;
+  }
+  nsCOMPtr<nsIGSettingsCollection> backgroundSettings;
+  gsettings->GetCollectionForSchema(kDesktopBGSchema,
+                                    getter_AddRefs(backgroundSettings));
+  if (!backgroundSettings) {
+    return NS_ERROR_FAILURE;
+  }
+
+  GUniquePtr<gchar> fileURI(
+      g_filename_to_uri(filePath.get(), nullptr, nullptr));
+  if (!fileURI) {
+    return NS_ERROR_FAILURE;
+  }
+
+  backgroundSettings->SetString("picture-options"_ns, options);
+  backgroundSettings->SetString("picture-uri"_ns,
+                                nsDependentCString(fileURI.get()));
+  backgroundSettings->SetString("picture-uri-dark"_ns,
+                                nsDependentCString(fileURI.get()));
+  backgroundSettings->SetBoolean("draw-background"_ns, true);
+  return NS_OK;
+}
+
+#define COLOR_16_TO_8_BIT(_c) ((_c) >> 8)
+#define COLOR_8_TO_16_BIT(_c) ((_c) << 8 | (_c))
+
+NS_IMETHODIMP
+nsGNOMEShellService::GetDesktopBackgroundColor(uint32_t* aColor) {
+  nsCOMPtr<nsIGSettingsService> gsettings =
+      do_GetService(NS_GSETTINGSSERVICE_CONTRACTID);
+  nsCOMPtr<nsIGSettingsCollection> background_settings;
+  nsAutoCString background;
+
+  if (gsettings) {
+    gsettings->GetCollectionForSchema(kDesktopBGSchema,
+                                      getter_AddRefs(background_settings));
+    if (background_settings) {
+      background_settings->GetString(kDesktopColorGSKey, background);
+    }
+  }
+
+  if (background.IsEmpty()) {
+    *aColor = 0;
+    return NS_OK;
+  }
+
+  GdkColor color;
+  gboolean success = gdk_color_parse(background.get(), &color);
+
+  NS_ENSURE_TRUE(success, NS_ERROR_FAILURE);
+
+  *aColor = COLOR_16_TO_8_BIT(color.red) << 16 |
+            COLOR_16_TO_8_BIT(color.green) << 8 | COLOR_16_TO_8_BIT(color.blue);
+  return NS_OK;
+}
+
+static void ColorToCString(uint32_t aColor, nsCString& aResult) {
+  // The #rrrrggggbbbb format is used to match gdk_color_to_string()
+  aResult.SetLength(13);
+  char* buf = aResult.BeginWriting();
+  if (!buf) return;
+
+  uint16_t red = COLOR_8_TO_16_BIT((aColor >> 16) & 0xff);
+  uint16_t green = COLOR_8_TO_16_BIT((aColor >> 8) & 0xff);
+  uint16_t blue = COLOR_8_TO_16_BIT(aColor & 0xff);
+
+  snprintf(buf, 14, "#%04x%04x%04x", red, green, blue);
+}
+
+NS_IMETHODIMP
+nsGNOMEShellService::SetDesktopBackgroundColor(uint32_t aColor) {
+  NS_ASSERTION(aColor <= 0xffffff, "aColor has extra bits");
+  nsAutoCString colorString;
+  ColorToCString(aColor, colorString);
+
+  nsCOMPtr<nsIGSettingsService> gsettings =
+      do_GetService(NS_GSETTINGSSERVICE_CONTRACTID);
+  if (gsettings) {
+    nsCOMPtr<nsIGSettingsCollection> background_settings;
+    gsettings->GetCollectionForSchema(nsLiteralCString(kDesktopBGSchema),
+                                      getter_AddRefs(background_settings));
+    if (background_settings) {
+      background_settings->SetString(kDesktopColorGSKey, colorString);
+      return NS_OK;
+    }
+  }
+
+  return NS_ERROR_FAILURE;
+}
diff --git a/browser/components/shell/nsGNOMEShellService.h b/browser/components/shell/nsGNOMEShellService.h
new file mode 100644
index 0000000000..12190cea81
--- /dev/null
+++ b/browser/components/shell/nsGNOMEShellService.h
@@ -0,0 +1,46 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#ifndef nsgnomeshellservice_h____
+#define nsgnomeshellservice_h____
+
+#include "nsIGNOMEShellService.h"
+#include "nsToolkitShellService.h"
+#include "nsString.h"
+#ifdef MOZ_ENABLE_DBUS
+#  include "nsGNOMEShellSearchProvider.h"
+#endif
+
+class nsIGIOService;
+
+class nsGNOMEShellService final : public nsIGNOMEShellService,
+                                  public nsToolkitShellService {
+ public:
+  nsGNOMEShellService() : mAppIsInPath(false) {}
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSISHELLSERVICE
+  NS_DECL_NSIGNOMESHELLSERVICE
+
+  nsresult Init();
+
+ private:
+  ~nsGNOMEShellService() {}
+
+  bool KeyMatchesAppName(const char* aKeyValue) const;
+  bool CheckHandlerMatchesAppName(const nsACString& handler) const;
+  bool IsDefaultForSchemeHelper(const nsACString& aScheme,
+                                nsIGIOService* giovfs) const;
+
+#ifdef MOZ_ENABLE_DBUS
+  nsGNOMEShellSearchProvider mSearchProvider;
+#endif
+  bool GetAppPathFromLauncher();
+  bool mUseLocaleFilenames;
+  nsCString mAppPath;
+  bool mAppIsInPath;
+};
+
+#endif  // nsgnomeshellservice_h____
diff --git a/browser/components/shell/nsIGNOMEShellService.idl b/browser/components/shell/nsIGNOMEShellService.idl
new file mode 100644
index 0000000000..75fa5e0a30
--- /dev/null
+++ b/browser/components/shell/nsIGNOMEShellService.idl
@@ -0,0 +1,23 @@
+/* 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/. */
+
+#include "nsIShellService.idl"
+
+[scriptable, uuid(2ce5c803-edcd-443d-98eb-ceba86d02d13)]
+interface nsIGNOMEShellService : nsIShellService
+{
+  /**
+   * Used to determine whether or not to offer "Set as desktop background"
+   * functionality. Even if shell service is available it is not
+   * guaranteed that it is able to set the background for every desktop
+   * which is especially true for Linux with its many different desktop
+   * environments.
+   */
+  readonly attribute boolean canSetDesktopBackground;
+
+  /**
+   * Returns true if Firefox is set as the default handler for the scheme.
+   */
+  boolean isDefaultForScheme(in AUTF8String aScheme);
+};
diff --git a/browser/components/shell/nsIMacShellService.idl b/browser/components/shell/nsIMacShellService.idl
new file mode 100644
index 0000000000..52f97ab4a5
--- /dev/null
+++ b/browser/components/shell/nsIMacShellService.idl
@@ -0,0 +1,27 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#include "nsIShellService.idl"
+
+[scriptable, uuid(387fdc80-0077-4b60-a0d9-d9e80a83ba64)]
+interface nsIMacShellService : nsIShellService
+{
+  /**
+   * Opens the desktop preferences, e.g. for after setting the background.
+   */
+  void showDesktopPreferences();
+
+  /**
+   * @param aPaneID used by macOS to identify the pane to open.
+   *                Example arguments:
+   *                  * "" - use the default Security and Privacy pane.
+   *                  * General
+   *                  * Privacy
+   *                  * Privacy_AllFiles
+   *                  * Privacy_Camera
+   *                  * Privacy_Microphone
+   */
+  void showSecurityPreferences(in ACString aPaneID);
+};
diff --git a/browser/components/shell/nsIShellService.idl b/browser/components/shell/nsIShellService.idl
new file mode 100644
index 0000000000..4eae32c03e
--- /dev/null
+++ b/browser/components/shell/nsIShellService.idl
@@ -0,0 +1,69 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#include "nsISupports.idl"
+
+interface nsIFile;
+
+webidl Element;
+
+[scriptable, uuid(2d1a95e4-5bd8-4eeb-b0a8-c1455fd2a357)]
+interface nsIShellService : nsISupports
+{
+  /**
+   * Determines whether or not Firefox is the "Default Browser."
+   * This is simply whether or not Firefox is registered to handle
+   * http links.
+   *
+   * @param aForAllTypes  true if the check should be made for HTTP and HTML.
+   *                      false if the check should be made for HTTP only.
+   *                      This parameter may be ignored on some platforms.
+   */
+  boolean isDefaultBrowser([optional] in boolean aForAllTypes);
+
+  /**
+   * Registers Firefox as the "Default Browser."
+   *
+   * @param aClaimAllTypes Register Firefox as the handler for
+   *                       additional protocols (chrome etc)
+   *                       and web documents (.html, .xhtml etc).
+   * @param aForAllUsers   Whether or not Firefox should attempt
+   *                       to become the default browser for all
+   *                       users on a multi-user system.
+   */
+  void setDefaultBrowser(in boolean aClaimAllTypes, in boolean aForAllUsers);
+
+  /**
+   * Flags for positioning/sizing of the Desktop Background image.
+   */
+  const long BACKGROUND_TILE      = 1;
+  const long BACKGROUND_STRETCH   = 2;
+  const long BACKGROUND_CENTER    = 3;
+  const long BACKGROUND_FILL      = 4;
+  const long BACKGROUND_FIT       = 5;
+  const long BACKGROUND_SPAN      = 6;
+
+    /**
+     * Sets the desktop background image using either the HTML <IMG>
+     * element supplied or the background image of the element supplied.
+     *
+     * @param aImageElement Either a HTML <IMG> element or an element with
+     *                      a background image from which to source the
+     *                      background image.
+     * @param aPosition     How to place the image on the desktop
+     * @param aImageName    The image name. Equivalent to the leaf name of the
+     *                      location.href.
+     */
+  void setDesktopBackground(in Element aElement,
+                            in long aPosition,
+                            in ACString aImageName);
+
+  /**
+   * The desktop background color, visible when no background image is
+   * used, or if the background image is centered and does not fill the
+   * entire screen. A rgb value, where (r << 16 | g << 8 | b)
+   */
+  attribute unsigned long desktopBackgroundColor;
+};
diff --git a/browser/components/shell/nsIWindowsShellService.idl b/browser/components/shell/nsIWindowsShellService.idl
new file mode 100644
index 0000000000..26025290e9
--- /dev/null
+++ b/browser/components/shell/nsIWindowsShellService.idl
@@ -0,0 +1,187 @@
+/* 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/. */
+
+#include "nsISupports.idl"
+
+interface nsIFile;
+
+[scriptable, uuid(fb9b59db-5a91-4e67-92b6-35e7d6e6d3fd)]
+interface nsIWindowsShellService : nsISupports
+{
+  /*
+   * Creates a new shortcut (.lnk) file. This shortcut will be recorded in
+   * a new shortcuts log file located in %PROGRAMDATA%\Mozilla-1de4eec8-1241-4177-a864-e594e8d1fb38
+   * that is named after the currently running application and current user, eg:
+   * Firefox_user123_shortcuts.ini.
+   *
+   * For reasons that we haven't been able to pin down, these shortcuts get created with
+   * extra metadata on them (KnownFolderDataBlock, SpecialFolderDataBlock) that cause
+   * the Windows ShellLink classes to improperly read their target path with certain
+   * parameters. This causes any 32-bit programs that read the links (such as our
+   * installer and uninstaller) to think that 64-bit installs are located in the 32-bit
+   * Program Files directory.
+   * See https://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/6f2e7920-50a9-459d-bfdd-316e459e87c0/ishelllink-getpath-returns-wrong-folder-for-64-bit-application-when-called-from-32-bit-application
+   * for some additional discussion of this.
+   *
+   * @param aBinary Target file of the shortcut.
+   * @param aArguments Arguments to set for the shortcut. May be empty.
+   * @param aDescription The description of the shortcut. The string used here
+   *        shows up as the hover text of the shortcut in Explorer and on the
+   *        Taskbar (if the shortcut is pinned there).
+   * @param aIconFile The file containing the desired icon for the shortcut. This
+   *        can be the same file as aBinary.
+   * @param aIconIndex The index of the in aIconFile. Note that this is 0 based index
+   *        that IShellLinkW requires, _not_ a Resource ID that is sometimes used
+   *        for icons.
+   * @param aAppUserModelId The App User Model ID to set for the shortcut. This will
+   *        affect which icon on the Taskbar the application groups with when first
+   *        launched.
+   * @param aShortcutFolder The special Windows folder to create the shortcut in. One of:
+   *        CommonStartMenu, StartMenu, PublicDesktop, Desktop, or QuickLaunch.
+   * @param aShortcutName The filename of the shortcut within aShortcutFolder.
+   * @return The full native path to the created shortcut.
+   *
+   * @throws NS_ERROR_INVALID_ARG if an invalid shortcut folder is passed
+   * @throws NS_ERROR_FILE_NOT_FOUND if the shortcut file or shortcuts log cannot be
+   *         created or accessed
+   * @throws NS_ERROR_FAILURE for other types of failures
+   */
+  [implicit_jscontext]
+  Promise createShortcut(in nsIFile aBinary, in Array<AString> aArguments,
+    in AString aDescription, in nsIFile aIconFile, in unsigned short aIconIndex,
+    in AString aAppUserModelId, in AString aShortcutFolder, in AString aShortcutName);
+
+  /*
+   * Pin the current app to the taskbar. If aPrivateBrowsing is true, the
+   * Private Browsing version of the app (with a different icon and launch
+   * arguments) will be pinned instead.
+   *
+   * This MUST only be used in response to an active request from the user.
+   *
+   * If it exists, uses an existing shortcut on the Desktop or Start Menu,
+   * which would have been created by the installer (for All Users or
+   * Current User). If none can be found, one will be created with the correct
+   * AUMID for proper launching and grouping.
+   *
+   * NOTE: It is possible for the shortcut match to fail even when a
+   * shortcut refers to the current executable, if the paths differ due
+   * to e.g. symlinks. This should be rare.
+   *
+   * This is fully supported on Windows 7, 8, and 11. On Windows 10, it will
+   * definitely fail on a version prior to build 1809 (October 2018 Update).
+   *
+   * NOTE: Can only run on the main thread, but the actual work occurs on a
+   * background thread.
+   *
+   * @throws NS_ERROR_NOT_SAME_THREAD
+   *         if called off main thread.
+   * @throws NS_ERROR_NOT_AVAILABLE
+   *         if OS is not at least Windows 10 build 1809, or if creating the
+   *         Taskband Pin object fails
+   * @throws NS_ERROR_FAILURE
+   *         for unexpected errors
+   *
+   * @rejects NS_ERROR_FILE_NOT_FOUND
+   *         if a shortcut matching this app's AUMID and exe path wasn't found
+   *
+   * @returns {Promise<void>} A promise that resolves to |undefined| if
+   *                          successful or rejects with an nserror.
+   */
+  [implicit_jscontext]
+  Promise pinCurrentAppToTaskbarAsync(in bool aPrivateBrowsing);
+
+  /*
+   * Do a dry run of pinCurrentAppToTaskbar().
+   *
+   * NOTE: Can only be run on the main thread, but the actual work occurs on a
+   * background thread.
+   *
+   * This does all the same checks and setup, throws the same errors, but doesn't
+   * do the final step of creating the pin.
+   *
+   * @throws same as pinCurrentAppToTaskbarAsync()
+   * @rejects same as pinCurrentAppToTaskbarAsync()
+   * @returns same as pinCurrentAppToTaskbarAsync()
+   */
+  [implicit_jscontext]
+  Promise checkPinCurrentAppToTaskbarAsync(in bool aPrivateBrowsing);
+
+  /*
+   * Search for the current executable among taskbar pins
+   *
+   * NOTE: Can only be run on the main thread, but the actual work occurs on a
+   * background thread.
+   *
+   * NOTE: It is possible for the check to fail even when a taskbar pin refers
+   * to this executable, if the paths differ due to e.g. symlinks.
+   * It is also possible for the check to succeed with a shortcut that doesn't
+   * actually appear on the taskbar.
+   * These cases should be rare.
+   *
+   * @return Promise that always resolves, true if pinned, false otherwise
+   * @throws NS_ERROR_NOT_SAME_THREAD if not run on the main thread
+   *
+   */
+  [implicit_jscontext]
+  Promise isCurrentAppPinnedToTaskbarAsync(in AString aumid);
+
+  /*
+   * Determine where a given shortcut likely appears in the shell.
+   *
+   * Returns one of:
+   * - "StartMenu" or "StartMenuPrivate", Current User or All Users Start
+   *    Menu, including pins
+   * - "Desktop" or "DesktopPrivate", Current User or All Users Desktop
+   * - "Taskbar" or "TaskbarPrivate", Taskbar Pins
+   * - "" otherwise
+   *
+   * If a Private Browsing shortcut was used to launch, the "Private"
+   * variant of one of the above entries will be returned.
+   *
+   * NOTE: This tries to avoid I/O, so paths are compared directly as
+   * strings, which may not be accurate in all cases. It is intended
+   * for noncritical telemetry use.
+   */
+  AString classifyShortcut(in AString aPath);
+
+  [implicit_jscontext]
+  Promise hasMatchingShortcut(in AString aAUMID, in bool aPrivateBrowsing);
+
+  /*
+   * Check if setDefaultBrowserUserChoice() is expected to succeed.
+   *
+   * This checks the ProgIDs for this installation, and the hash of the existing
+   * UserChoice association.
+   *
+   * @return true if the check succeeds, false otherwise.
+   */
+  bool canSetDefaultBrowserUserChoice();
+
+  /*
+   * checkAllProgIDsExist() and checkBrowserUserChoiceHashes() are components
+   * of canSetDefaultBrowserUserChoice(), broken out for telemetry purposes.
+   *
+   * @return true if the check succeeds, false otherwise.
+   */
+  bool checkAllProgIDsExist();
+  bool checkBrowserUserChoiceHashes();
+
+  /*
+   * Determines whether or not Firefox is the "Default Handler", i.e.,
+   * is registered to handle, the given file extension (like ".pdf")
+   * or protocol (like "https").
+   */
+  boolean isDefaultHandlerFor(in AString aFileExtensionOrProtocol);
+
+
+  /*
+   * Return the Windows ProgID currently registered to handle the gven
+   * file extension (like ".pdf") or protocol (like "https").
+   *
+   * @return string ProgID, or "" when no association is registered.
+   * @throws NS_ERROR_FAILURE when the file extension or protocol
+   *         cannot be determined.
+   */
+  AString queryCurrentDefaultHandlerFor(in AString aFileExtensionOrProtocol);
+};
diff --git a/browser/components/shell/nsMacShellService.cpp b/browser/components/shell/nsMacShellService.cpp
new file mode 100644
index 0000000000..2482032e42
--- /dev/null
+++ b/browser/components/shell/nsMacShellService.cpp
@@ -0,0 +1,281 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#include "CocoaFileUtils.h"
+#include "nsDirectoryServiceDefs.h"
+#include "nsIImageLoadingContent.h"
+#include "mozilla/dom/Document.h"
+#include "nsComponentManagerUtils.h"
+#include "nsIContent.h"
+#include "nsICookieJarSettings.h"
+#include "nsIObserverService.h"
+#include "nsIWebBrowserPersist.h"
+#include "nsMacShellService.h"
+#include "nsIProperties.h"
+#include "nsServiceManagerUtils.h"
+#include "nsShellService.h"
+#include "nsString.h"
+#include "nsIDocShell.h"
+#include "nsILoadContext.h"
+#include "nsIPrefService.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/ReferrerInfo.h"
+#include "DesktopBackgroundImage.h"
+
+#include <Carbon/Carbon.h>
+#include <CoreFoundation/CoreFoundation.h>
+#include <ApplicationServices/ApplicationServices.h>
+
+using mozilla::dom::Element;
+using mozilla::widget::SetDesktopImage;
+
+#define NETWORK_PREFPANE "/System/Library/PreferencePanes/Network.prefPane"_ns
+#define DESKTOP_PREFPANE \
+  nsLiteralCString(      \
+      "/System/Library/PreferencePanes/DesktopScreenEffectsPref.prefPane")
+
+#define SAFARI_BUNDLE_IDENTIFIER "com.apple.Safari"
+
+NS_IMPL_ISUPPORTS(nsMacShellService, nsIMacShellService, nsIShellService,
+                  nsIToolkitShellService, nsIWebProgressListener)
+
+NS_IMETHODIMP
+nsMacShellService::IsDefaultBrowser(bool aForAllTypes,
+                                    bool* aIsDefaultBrowser) {
+  *aIsDefaultBrowser = false;
+
+  CFStringRef firefoxID = ::CFBundleGetIdentifier(::CFBundleGetMainBundle());
+  if (!firefoxID) {
+    // CFBundleGetIdentifier is expected to return nullptr only if the specified
+    // bundle doesn't have a bundle identifier in its plist. In this case, that
+    // means a failure, since our bundle does have an identifier.
+    return NS_ERROR_FAILURE;
+  }
+
+  // Get the default http handler's bundle ID (or nullptr if it has not been
+  // explicitly set)
+  CFStringRef defaultBrowserID =
+      ::LSCopyDefaultHandlerForURLScheme(CFSTR("http"));
+  if (defaultBrowserID) {
+    *aIsDefaultBrowser =
+        ::CFStringCompare(firefoxID, defaultBrowserID, 0) == kCFCompareEqualTo;
+    ::CFRelease(defaultBrowserID);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMacShellService::SetDefaultBrowser(bool aClaimAllTypes, bool aForAllUsers) {
+  // Note: We don't support aForAllUsers on Mac OS X.
+
+  CFStringRef firefoxID = ::CFBundleGetIdentifier(::CFBundleGetMainBundle());
+  if (!firefoxID) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (::LSSetDefaultHandlerForURLScheme(CFSTR("http"), firefoxID) != noErr) {
+    return NS_ERROR_FAILURE;
+  }
+  if (::LSSetDefaultHandlerForURLScheme(CFSTR("https"), firefoxID) != noErr) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (aClaimAllTypes) {
+    if (::LSSetDefaultRoleHandlerForContentType(kUTTypeHTML, kLSRolesAll,
+                                                firefoxID) != noErr) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+
+  nsCOMPtr<nsIPrefBranch> prefs(do_GetService(NS_PREFSERVICE_CONTRACTID));
+  if (prefs) {
+    (void)prefs->SetBoolPref(PREF_CHECKDEFAULTBROWSER, true);
+    // Reset the number of times the dialog should be shown
+    // before it is silenced.
+    (void)prefs->SetIntPref(PREF_DEFAULTBROWSERCHECKCOUNT, 0);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMacShellService::SetDesktopBackground(Element* aElement, int32_t aPosition,
+                                        const nsACString& aImageName) {
+  // Note: We don't support aPosition on OS X.
+
+  // Get the image URI:
+  nsresult rv;
+  nsCOMPtr<nsIImageLoadingContent> imageContent =
+      do_QueryInterface(aElement, &rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+  nsCOMPtr<nsIURI> imageURI;
+  rv = imageContent->GetCurrentURI(getter_AddRefs(imageURI));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsIURI* docURI = aElement->OwnerDoc()->GetDocumentURI();
+  if (!docURI) return NS_ERROR_FAILURE;
+
+  nsCOMPtr<nsIProperties> fileLocator(
+      do_GetService("@mozilla.org/file/directory_service;1", &rv));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Get the current user's "Pictures" folder (That's ~/Pictures):
+  fileLocator->Get(NS_OSX_PICTURE_DOCUMENTS_DIR, NS_GET_IID(nsIFile),
+                   getter_AddRefs(mBackgroundFile));
+  if (!mBackgroundFile) return NS_ERROR_OUT_OF_MEMORY;
+
+  nsAutoString fileNameUnicode;
+  CopyUTF8toUTF16(aImageName, fileNameUnicode);
+
+  // and add the imgage file name itself:
+  mBackgroundFile->Append(fileNameUnicode);
+
+  // Download the image; the desktop background will be set in OnStateChange()
+  nsCOMPtr<nsIWebBrowserPersist> wbp(do_CreateInstance(
+      "@mozilla.org/embedding/browser/nsWebBrowserPersist;1", &rv));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  uint32_t flags = nsIWebBrowserPersist::PERSIST_FLAGS_NO_CONVERSION |
+                   nsIWebBrowserPersist::PERSIST_FLAGS_REPLACE_EXISTING_FILES |
+                   nsIWebBrowserPersist::PERSIST_FLAGS_FROM_CACHE;
+
+  wbp->SetPersistFlags(flags);
+  wbp->SetProgressListener(this);
+
+  nsCOMPtr<nsILoadContext> loadContext;
+  nsCOMPtr<nsISupports> container = aElement->OwnerDoc()->GetContainer();
+  nsCOMPtr<nsIDocShell> docShell = do_QueryInterface(container);
+  if (docShell) {
+    loadContext = do_QueryInterface(docShell);
+  }
+
+  auto referrerInfo =
+      mozilla::MakeRefPtr<mozilla::dom::ReferrerInfo>(*aElement);
+
+  nsCOMPtr<nsICookieJarSettings> cookieJarSettings =
+      aElement->OwnerDoc()->CookieJarSettings();
+  return wbp->SaveURI(imageURI, aElement->NodePrincipal(), 0, referrerInfo,
+                      cookieJarSettings, nullptr, nullptr, mBackgroundFile,
+                      nsIContentPolicy::TYPE_IMAGE,
+                      loadContext->UsePrivateBrowsing());
+}
+
+NS_IMETHODIMP
+nsMacShellService::OnProgressChange(nsIWebProgress* aWebProgress,
+                                    nsIRequest* aRequest,
+                                    int32_t aCurSelfProgress,
+                                    int32_t aMaxSelfProgress,
+                                    int32_t aCurTotalProgress,
+                                    int32_t aMaxTotalProgress) {
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMacShellService::OnLocationChange(nsIWebProgress* aWebProgress,
+                                    nsIRequest* aRequest, nsIURI* aLocation,
+                                    uint32_t aFlags) {
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMacShellService::OnStatusChange(nsIWebProgress* aWebProgress,
+                                  nsIRequest* aRequest, nsresult aStatus,
+                                  const char16_t* aMessage) {
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMacShellService::OnSecurityChange(nsIWebProgress* aWebProgress,
+                                    nsIRequest* aRequest, uint32_t aState) {
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMacShellService::OnContentBlockingEvent(nsIWebProgress* aWebProgress,
+                                          nsIRequest* aRequest,
+                                          uint32_t aEvent) {
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMacShellService::OnStateChange(nsIWebProgress* aWebProgress,
+                                 nsIRequest* aRequest, uint32_t aStateFlags,
+                                 nsresult aStatus) {
+  if (NS_SUCCEEDED(aStatus) && (aStateFlags & STATE_STOP) &&
+      (aRequest == nullptr)) {
+    nsCOMPtr<nsIObserverService> os(
+        do_GetService("@mozilla.org/observer-service;1"));
+    if (os)
+      os->NotifyObservers(nullptr, "shell:desktop-background-changed", nullptr);
+
+    bool exists = false;
+    nsresult rv = mBackgroundFile->Exists(&exists);
+    if (NS_FAILED(rv) || !exists) {
+      return NS_OK;
+    }
+
+    SetDesktopImage(mBackgroundFile);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMacShellService::ShowDesktopPreferences() {
+  nsCOMPtr<nsIFile> lf;
+  nsresult rv =
+      NS_NewNativeLocalFile(DESKTOP_PREFPANE, true, getter_AddRefs(lf));
+  NS_ENSURE_SUCCESS(rv, rv);
+  bool exists;
+  lf->Exists(&exists);
+  if (!exists) return NS_ERROR_FILE_NOT_FOUND;
+  return lf->Launch();
+}
+
+NS_IMETHODIMP
+nsMacShellService::GetDesktopBackgroundColor(uint32_t* aColor) {
+  // This method and |SetDesktopBackgroundColor| has no meaning on Mac OS X.
+  // The mac desktop preferences UI uses pictures for the few solid colors it
+  // supports.
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsMacShellService::SetDesktopBackgroundColor(uint32_t aColor) {
+  // This method and |GetDesktopBackgroundColor| has no meaning on Mac OS X.
+  // The mac desktop preferences UI uses pictures for the few solid colors it
+  // supports.
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsMacShellService::ShowSecurityPreferences(const nsACString& aPaneID) {
+  nsresult rv = NS_ERROR_NOT_AVAILABLE;
+
+  CFStringRef paneID = ::CFStringCreateWithBytes(
+      kCFAllocatorDefault, (const UInt8*)PromiseFlatCString(aPaneID).get(),
+      aPaneID.Length(), kCFStringEncodingUTF8, false);
+
+  if (paneID) {
+    CFStringRef format =
+        CFSTR("x-apple.systempreferences:com.apple.preference.security?%@");
+    if (format) {
+      CFStringRef urlStr =
+          CFStringCreateWithFormat(kCFAllocatorDefault, NULL, format, paneID);
+      if (urlStr) {
+        CFURLRef url = ::CFURLCreateWithString(NULL, urlStr, NULL);
+        rv = CocoaFileUtils::OpenURL(url);
+
+        ::CFRelease(urlStr);
+      }
+
+      ::CFRelease(format);
+    }
+
+    ::CFRelease(paneID);
+  }
+  return rv;
+}
diff --git a/browser/components/shell/nsMacShellService.h b/browser/components/shell/nsMacShellService.h
new file mode 100644
index 0000000000..bb08c72b4e
--- /dev/null
+++ b/browser/components/shell/nsMacShellService.h
@@ -0,0 +1,33 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#ifndef nsmacshellservice_h____
+#define nsmacshellservice_h____
+
+#include "nsToolkitShellService.h"
+#include "nsIMacShellService.h"
+#include "nsIWebProgressListener.h"
+#include "nsIFile.h"
+#include "nsCOMPtr.h"
+
+class nsMacShellService : public nsIMacShellService,
+                          public nsToolkitShellService,
+                          public nsIWebProgressListener {
+ public:
+  nsMacShellService(){};
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSISHELLSERVICE
+  NS_DECL_NSIMACSHELLSERVICE
+  NS_DECL_NSIWEBPROGRESSLISTENER
+
+ protected:
+  virtual ~nsMacShellService(){};
+
+ private:
+  nsCOMPtr<nsIFile> mBackgroundFile;
+};
+
+#endif  // nsmacshellservice_h____
diff --git a/browser/components/shell/nsShellService.h b/browser/components/shell/nsShellService.h
new file mode 100644
index 0000000000..346a16ad69
--- /dev/null
+++ b/browser/components/shell/nsShellService.h
@@ -0,0 +1,11 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#define PREF_CHECKDEFAULTBROWSER "browser.shell.checkDefaultBrowser"
+#define PREF_DEFAULTBROWSERCHECKCOUNT "browser.shell.defaultBrowserCheckCount"
+
+#define SHELLSERVICE_PROPERTIES \
+  "chrome://browser/locale/shellservice.properties"
+#define BRAND_PROPERTIES "chrome://branding/locale/brand.properties"
diff --git a/browser/components/shell/nsToolkitShellService.h b/browser/components/shell/nsToolkitShellService.h
new file mode 100644
index 0000000000..552f3cd65d
--- /dev/null
+++ b/browser/components/shell/nsToolkitShellService.h
@@ -0,0 +1,21 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#ifndef nstoolkitshellservice_h____
+#define nstoolkitshellservice_h____
+
+#include "nsIToolkitShellService.h"
+
+class nsToolkitShellService : public nsIToolkitShellService {
+ public:
+  NS_IMETHOD IsDefaultBrowser(bool aForAllTypes, bool* aIsDefaultBrowser) = 0;
+
+  NS_IMETHODIMP IsDefaultApplication(bool* aIsDefaultBrowser) {
+    // Only care about the http(s) protocol. This only matters on Windows.
+    return IsDefaultBrowser(false, aIsDefaultBrowser);
+  }
+};
+
+#endif  // nstoolkitshellservice_h____
diff --git a/browser/components/shell/nsWindowsShellService.cpp b/browser/components/shell/nsWindowsShellService.cpp
new file mode 100644
index 0000000000..6863ad300c
--- /dev/null
+++ b/browser/components/shell/nsWindowsShellService.cpp
@@ -0,0 +1,1845 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#define UNICODE
+
+#include "nsWindowsShellService.h"
+
+#include "BinaryPath.h"
+#include "imgIContainer.h"
+#include "imgIRequest.h"
+#include "mozilla/RefPtr.h"
+#include "nsComponentManagerUtils.h"
+#include "nsIContent.h"
+#include "nsIImageLoadingContent.h"
+#include "nsIOutputStream.h"
+#include "nsIPrefService.h"
+#include "nsIStringBundle.h"
+#include "nsNetUtil.h"
+#include "nsServiceManagerUtils.h"
+#include "nsShellService.h"
+#include "nsDirectoryServiceUtils.h"
+#include "nsAppDirectoryServiceDefs.h"
+#include "nsDirectoryServiceDefs.h"
+#include "nsIWindowsRegKey.h"
+#include "nsUnicharUtils.h"
+#include "nsIURLFormatter.h"
+#include "nsXULAppAPI.h"
+#include "mozilla/WindowsVersion.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/intl/Localization.h"
+#include "WindowsDefaultBrowser.h"
+#include "WindowsUserChoice.h"
+#include "nsLocalFile.h"
+#include "nsIXULAppInfo.h"
+#include "nsINIParser.h"
+#include "nsNativeAppSupportWin.h"
+#include "nsWindowsHelpers.h"
+
+#include <windows.h>
+#include <shellapi.h>
+#include <propvarutil.h>
+#include <propkey.h>
+
+#ifdef __MINGW32__
+// MinGW-w64 headers are missing PropVariantToString.
+#  include <propsys.h>
+PSSTDAPI PropVariantToString(REFPROPVARIANT propvar, PWSTR psz, UINT cch);
+#  define UNLEN 256
+#else
+#  include <Lmcons.h>  // For UNLEN
+#endif
+
+#include <comutil.h>
+#include <objbase.h>
+#include <shlobj.h>
+#include <knownfolders.h>
+#include "WinUtils.h"
+#include "mozilla/widget/WinTaskbar.h"
+
+#include <mbstring.h>
+
+#define PIN_TO_TASKBAR_SHELL_VERB 5386
+#define PRIVATE_BROWSING_BINARY L"private_browsing.exe"
+
+#undef ACCESS_READ
+
+#ifndef MAX_BUF
+#  define MAX_BUF 4096
+#endif
+
+#define REG_SUCCEEDED(val) (val == ERROR_SUCCESS)
+
+#define REG_FAILED(val) (val != ERROR_SUCCESS)
+
+#ifdef DEBUG
+#  define NS_ENSURE_HRESULT(hres, ret)                    \
+    do {                                                  \
+      HRESULT result = hres;                              \
+      if (MOZ_UNLIKELY(FAILED(result))) {                 \
+        mozilla::SmprintfPointer msg = mozilla::Smprintf( \
+            "NS_ENSURE_HRESULT(%s, %s) failed with "      \
+            "result 0x%" PRIX32,                          \
+            #hres, #ret, static_cast<uint32_t>(result));  \
+        NS_WARNING(msg.get());                            \
+        return ret;                                       \
+      }                                                   \
+    } while (false)
+#else
+#  define NS_ENSURE_HRESULT(hres, ret) \
+    if (MOZ_UNLIKELY(FAILED(hres))) return ret
+#endif
+
+using mozilla::IsWin8OrLater;
+using namespace mozilla;
+using mozilla::intl::Localization;
+
+struct SysFreeStringDeleter {
+  void operator()(BSTR aPtr) { ::SysFreeString(aPtr); }
+};
+using BStrPtr = mozilla::UniquePtr<OLECHAR, SysFreeStringDeleter>;
+
+NS_IMPL_ISUPPORTS(nsWindowsShellService, nsIToolkitShellService,
+                  nsIShellService, nsIWindowsShellService)
+
+static nsresult OpenKeyForReading(HKEY aKeyRoot, const nsAString& aKeyName,
+                                  HKEY* aKey) {
+  const nsString& flatName = PromiseFlatString(aKeyName);
+
+  DWORD res = ::RegOpenKeyExW(aKeyRoot, flatName.get(), 0, KEY_READ, aKey);
+  switch (res) {
+    case ERROR_SUCCESS:
+      break;
+    case ERROR_ACCESS_DENIED:
+      return NS_ERROR_FILE_ACCESS_DENIED;
+    case ERROR_FILE_NOT_FOUND:
+      return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  return NS_OK;
+}
+
+nsresult GetHelperPath(nsAutoString& aPath) {
+  nsresult rv;
+  nsCOMPtr<nsIProperties> directoryService =
+      do_GetService(NS_DIRECTORY_SERVICE_CONTRACTID, &rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIFile> appHelper;
+  rv = directoryService->Get(XRE_EXECUTABLE_FILE, NS_GET_IID(nsIFile),
+                             getter_AddRefs(appHelper));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = appHelper->SetNativeLeafName("uninstall"_ns);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = appHelper->AppendNative("helper.exe"_ns);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = appHelper->GetPath(aPath);
+
+  aPath.Insert(L'"', 0);
+  aPath.Append(L'"');
+  return rv;
+}
+
+nsresult LaunchHelper(nsAutoString& aPath) {
+  STARTUPINFOW si = {sizeof(si), 0};
+  PROCESS_INFORMATION pi = {0};
+
+  if (!CreateProcessW(nullptr, (LPWSTR)aPath.get(), nullptr, nullptr, FALSE, 0,
+                      nullptr, nullptr, &si, &pi)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  CloseHandle(pi.hProcess);
+  CloseHandle(pi.hThread);
+  return NS_OK;
+}
+
+static bool IsPathDefaultForClass(
+    const RefPtr<IApplicationAssociationRegistration>& pAAR, wchar_t* exePath,
+    LPCWSTR aClassName) {
+  LPWSTR registeredApp;
+  bool isProtocol = *aClassName != L'.';
+  ASSOCIATIONTYPE queryType = isProtocol ? AT_URLPROTOCOL : AT_FILEEXTENSION;
+  HRESULT hr = pAAR->QueryCurrentDefault(aClassName, queryType, AL_EFFECTIVE,
+                                         &registeredApp);
+  if (FAILED(hr)) {
+    return false;
+  }
+
+  nsAutoString regAppName(registeredApp);
+  CoTaskMemFree(registeredApp);
+
+  // Make sure the application path for this progID is this installation.
+  regAppName.AppendLiteral("\\shell\\open\\command");
+  HKEY theKey;
+  nsresult rv = OpenKeyForReading(HKEY_CLASSES_ROOT, regAppName, &theKey);
+  if (NS_FAILED(rv)) {
+    return false;
+  }
+
+  wchar_t cmdFromReg[MAX_BUF] = L"";
+  DWORD len = sizeof(cmdFromReg);
+  DWORD res = ::RegQueryValueExW(theKey, nullptr, nullptr, nullptr,
+                                 (LPBYTE)cmdFromReg, &len);
+  ::RegCloseKey(theKey);
+  if (REG_FAILED(res)) {
+    return false;
+  }
+
+  nsAutoString pathFromReg(cmdFromReg);
+  nsLocalFile::CleanupCmdHandlerPath(pathFromReg);
+
+  return _wcsicmp(exePath, pathFromReg.Data()) == 0;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::IsDefaultBrowser(bool aForAllTypes,
+                                        bool* aIsDefaultBrowser) {
+  *aIsDefaultBrowser = false;
+
+  RefPtr<IApplicationAssociationRegistration> pAAR;
+  HRESULT hr = CoCreateInstance(
+      CLSID_ApplicationAssociationRegistration, nullptr, CLSCTX_INPROC,
+      IID_IApplicationAssociationRegistration, getter_AddRefs(pAAR));
+  if (FAILED(hr)) {
+    return NS_OK;
+  }
+
+  wchar_t exePath[MAXPATHLEN] = L"";
+  nsresult rv = BinaryPath::GetLong(exePath);
+
+  if (NS_FAILED(rv)) {
+    return NS_OK;
+  }
+
+  *aIsDefaultBrowser = IsPathDefaultForClass(pAAR, exePath, L"http");
+  if (*aIsDefaultBrowser && aForAllTypes) {
+    *aIsDefaultBrowser = IsPathDefaultForClass(pAAR, exePath, L".html");
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::IsDefaultHandlerFor(
+    const nsAString& aFileExtensionOrProtocol, bool* aIsDefaultHandlerFor) {
+  *aIsDefaultHandlerFor = false;
+
+  RefPtr<IApplicationAssociationRegistration> pAAR;
+  HRESULT hr = CoCreateInstance(
+      CLSID_ApplicationAssociationRegistration, nullptr, CLSCTX_INPROC,
+      IID_IApplicationAssociationRegistration, getter_AddRefs(pAAR));
+  if (FAILED(hr)) {
+    return NS_OK;
+  }
+
+  wchar_t exePath[MAXPATHLEN] = L"";
+  nsresult rv = BinaryPath::GetLong(exePath);
+
+  if (NS_FAILED(rv)) {
+    return NS_OK;
+  }
+
+  const nsString& flatClass = PromiseFlatString(aFileExtensionOrProtocol);
+
+  *aIsDefaultHandlerFor = IsPathDefaultForClass(pAAR, exePath, flatClass.get());
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::QueryCurrentDefaultHandlerFor(
+    const nsAString& aFileExtensionOrProtocol, nsAString& aResult) {
+  aResult.Truncate();
+
+  RefPtr<IApplicationAssociationRegistration> pAAR;
+  HRESULT hr = CoCreateInstance(
+      CLSID_ApplicationAssociationRegistration, nullptr, CLSCTX_INPROC,
+      IID_IApplicationAssociationRegistration, getter_AddRefs(pAAR));
+  if (FAILED(hr)) {
+    return NS_OK;
+  }
+
+  const nsString& flatClass = PromiseFlatString(aFileExtensionOrProtocol);
+
+  LPWSTR registeredApp;
+  bool isProtocol = flatClass.First() != L'.';
+  ASSOCIATIONTYPE queryType = isProtocol ? AT_URLPROTOCOL : AT_FILEEXTENSION;
+  hr = pAAR->QueryCurrentDefault(flatClass.get(), queryType, AL_EFFECTIVE,
+                                 &registeredApp);
+  if (hr == HRESULT_FROM_WIN32(ERROR_NO_ASSOCIATION)) {
+    return NS_OK;
+  }
+  NS_ENSURE_HRESULT(hr, NS_ERROR_FAILURE);
+
+  aResult = registeredApp;
+  CoTaskMemFree(registeredApp);
+
+  return NS_OK;
+}
+
+nsresult nsWindowsShellService::LaunchControlPanelDefaultsSelectionUI() {
+  IApplicationAssociationRegistrationUI* pAARUI;
+  HRESULT hr = CoCreateInstance(
+      CLSID_ApplicationAssociationRegistrationUI, NULL, CLSCTX_INPROC,
+      IID_IApplicationAssociationRegistrationUI, (void**)&pAARUI);
+  if (SUCCEEDED(hr)) {
+    mozilla::UniquePtr<wchar_t[]> appRegName;
+    GetAppRegName(appRegName);
+    hr = pAARUI->LaunchAdvancedAssociationUI(appRegName.get());
+    pAARUI->Release();
+  }
+  return SUCCEEDED(hr) ? NS_OK : NS_ERROR_FAILURE;
+}
+
+nsresult nsWindowsShellService::LaunchControlPanelDefaultPrograms() {
+  return ::LaunchControlPanelDefaultPrograms() ? NS_OK : NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::CheckAllProgIDsExist(bool* aResult) {
+  *aResult = false;
+  nsAutoString aumid;
+  if (!mozilla::widget::WinTaskbar::GetAppUserModelID(aumid)) {
+    return NS_OK;
+  }
+  *aResult =
+      CheckProgIDExists(FormatProgID(L"FirefoxURL", aumid.get()).get()) &&
+      CheckProgIDExists(FormatProgID(L"FirefoxHTML", aumid.get()).get()) &&
+      CheckProgIDExists(FormatProgID(L"FirefoxPDF", aumid.get()).get());
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::CheckBrowserUserChoiceHashes(bool* aResult) {
+  *aResult = ::CheckBrowserUserChoiceHashes();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::CanSetDefaultBrowserUserChoice(bool* aResult) {
+  *aResult = false;
+// If the WDBA is not available, this could never succeed.
+#ifdef MOZ_DEFAULT_BROWSER_AGENT
+  bool progIDsExist = false;
+  bool hashOk = false;
+  *aResult = NS_SUCCEEDED(CheckAllProgIDsExist(&progIDsExist)) &&
+             progIDsExist &&
+             NS_SUCCEEDED(CheckBrowserUserChoiceHashes(&hashOk)) && hashOk;
+#endif
+  return NS_OK;
+}
+
+nsresult nsWindowsShellService::LaunchModernSettingsDialogDefaultApps() {
+  return ::LaunchModernSettingsDialogDefaultApps() ? NS_OK : NS_ERROR_FAILURE;
+}
+
+nsresult nsWindowsShellService::InvokeHTTPOpenAsVerb() {
+  nsCOMPtr<nsIURLFormatter> formatter(
+      do_GetService("@mozilla.org/toolkit/URLFormatterService;1"));
+  if (!formatter) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  nsString urlStr;
+  nsresult rv = formatter->FormatURLPref(u"app.support.baseURL"_ns, urlStr);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (!StringBeginsWith(urlStr, u"https://"_ns)) {
+    return NS_ERROR_FAILURE;
+  }
+  urlStr.AppendLiteral("win10-default-browser");
+
+  SHELLEXECUTEINFOW seinfo = {sizeof(SHELLEXECUTEINFOW)};
+  seinfo.lpVerb = L"openas";
+  seinfo.lpFile = urlStr.get();
+  seinfo.nShow = SW_SHOWNORMAL;
+  if (!ShellExecuteExW(&seinfo)) {
+    return NS_ERROR_FAILURE;
+  }
+  return NS_OK;
+}
+
+nsresult nsWindowsShellService::LaunchHTTPHandlerPane() {
+  OPENASINFO info;
+  info.pcszFile = L"http";
+  info.pcszClass = nullptr;
+  info.oaifInFlags =
+      OAIF_FORCE_REGISTRATION | OAIF_URL_PROTOCOL | OAIF_REGISTER_EXT;
+
+  HRESULT hr = SHOpenWithDialog(nullptr, &info);
+  if (SUCCEEDED(hr) || (hr == HRESULT_FROM_WIN32(ERROR_CANCELLED))) {
+    return NS_OK;
+  }
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::SetDefaultBrowser(bool aClaimAllTypes,
+                                         bool aForAllUsers) {
+  // If running from within a package, don't attempt to set default with
+  // the helper, as it will not work and will only confuse our package's
+  // virtualized registry.
+  nsresult rv = NS_OK;
+  if (!widget::WinUtils::HasPackageIdentity()) {
+    nsAutoString appHelperPath;
+    if (NS_FAILED(GetHelperPath(appHelperPath))) return NS_ERROR_FAILURE;
+
+    if (aForAllUsers) {
+      appHelperPath.AppendLiteral(" /SetAsDefaultAppGlobal");
+    } else {
+      appHelperPath.AppendLiteral(" /SetAsDefaultAppUser");
+    }
+
+    rv = LaunchHelper(appHelperPath);
+  }
+
+  if (NS_SUCCEEDED(rv) && IsWin8OrLater()) {
+    if (aClaimAllTypes) {
+      if (IsWin10OrLater()) {
+        rv = LaunchModernSettingsDialogDefaultApps();
+      } else {
+        rv = LaunchControlPanelDefaultsSelectionUI();
+      }
+      // The above call should never really fail, but just in case
+      // fall back to showing the HTTP association screen only.
+      if (NS_FAILED(rv)) {
+        if (IsWin10OrLater()) {
+          rv = InvokeHTTPOpenAsVerb();
+        } else {
+          rv = LaunchHTTPHandlerPane();
+        }
+      }
+    } else {
+      // Windows 10 blocks attempts to load the
+      // HTTP Handler association dialog.
+      if (IsWin10OrLater()) {
+        rv = LaunchModernSettingsDialogDefaultApps();
+      } else {
+        rv = LaunchHTTPHandlerPane();
+      }
+
+      // The above call should never really fail, but just in case
+      // fall back to showing control panel for all defaults
+      if (NS_FAILED(rv)) {
+        rv = LaunchControlPanelDefaultsSelectionUI();
+      }
+    }
+  }
+
+  nsCOMPtr<nsIPrefBranch> prefs(do_GetService(NS_PREFSERVICE_CONTRACTID));
+  if (prefs) {
+    (void)prefs->SetBoolPref(PREF_CHECKDEFAULTBROWSER, true);
+    // Reset the number of times the dialog should be shown
+    // before it is silenced.
+    (void)prefs->SetIntPref(PREF_DEFAULTBROWSERCHECKCOUNT, 0);
+  }
+
+  return rv;
+}
+
+static nsresult WriteBitmap(nsIFile* aFile, imgIContainer* aImage) {
+  nsresult rv;
+
+  RefPtr<gfx::SourceSurface> surface = aImage->GetFrame(
+      imgIContainer::FRAME_FIRST, imgIContainer::FLAG_SYNC_DECODE);
+  NS_ENSURE_TRUE(surface, NS_ERROR_FAILURE);
+
+  // For either of the following formats we want to set the biBitCount member
+  // of the BITMAPINFOHEADER struct to 32, below. For that value the bitmap
+  // format defines that the A8/X8 WORDs in the bitmap byte stream be ignored
+  // for the BI_RGB value we use for the biCompression member.
+  MOZ_ASSERT(surface->GetFormat() == gfx::SurfaceFormat::B8G8R8A8 ||
+             surface->GetFormat() == gfx::SurfaceFormat::B8G8R8X8);
+
+  RefPtr<gfx::DataSourceSurface> dataSurface = surface->GetDataSurface();
+  NS_ENSURE_TRUE(dataSurface, NS_ERROR_FAILURE);
+
+  int32_t width = dataSurface->GetSize().width;
+  int32_t height = dataSurface->GetSize().height;
+  int32_t bytesPerPixel = 4 * sizeof(uint8_t);
+  uint32_t bytesPerRow = bytesPerPixel * width;
+
+  // initialize these bitmap structs which we will later
+  // serialize directly to the head of the bitmap file
+  BITMAPINFOHEADER bmi;
+  bmi.biSize = sizeof(BITMAPINFOHEADER);
+  bmi.biWidth = width;
+  bmi.biHeight = height;
+  bmi.biPlanes = 1;
+  bmi.biBitCount = (WORD)bytesPerPixel * 8;
+  bmi.biCompression = BI_RGB;
+  bmi.biSizeImage = bytesPerRow * height;
+  bmi.biXPelsPerMeter = 0;
+  bmi.biYPelsPerMeter = 0;
+  bmi.biClrUsed = 0;
+  bmi.biClrImportant = 0;
+
+  BITMAPFILEHEADER bf;
+  bf.bfType = 0x4D42;  // 'BM'
+  bf.bfReserved1 = 0;
+  bf.bfReserved2 = 0;
+  bf.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
+  bf.bfSize = bf.bfOffBits + bmi.biSizeImage;
+
+  // get a file output stream
+  nsCOMPtr<nsIOutputStream> stream;
+  rv = NS_NewLocalFileOutputStream(getter_AddRefs(stream), aFile);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  gfx::DataSourceSurface::MappedSurface map;
+  if (!dataSurface->Map(gfx::DataSourceSurface::MapType::READ, &map)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // write the bitmap headers and rgb pixel data to the file
+  rv = NS_ERROR_FAILURE;
+  if (stream) {
+    uint32_t written;
+    stream->Write((const char*)&bf, sizeof(BITMAPFILEHEADER), &written);
+    if (written == sizeof(BITMAPFILEHEADER)) {
+      stream->Write((const char*)&bmi, sizeof(BITMAPINFOHEADER), &written);
+      if (written == sizeof(BITMAPINFOHEADER)) {
+        // write out the image data backwards because the desktop won't
+        // show bitmaps with negative heights for top-to-bottom
+        uint32_t i = map.mStride * height;
+        do {
+          i -= map.mStride;
+          stream->Write(((const char*)map.mData) + i, bytesPerRow, &written);
+          if (written == bytesPerRow) {
+            rv = NS_OK;
+          } else {
+            rv = NS_ERROR_FAILURE;
+            break;
+          }
+        } while (i != 0);
+      }
+    }
+
+    stream->Close();
+  }
+
+  dataSurface->Unmap();
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::SetDesktopBackground(dom::Element* aElement,
+                                            int32_t aPosition,
+                                            const nsACString& aImageName) {
+  if (!aElement || !aElement->IsHTMLElement(nsGkAtoms::img)) {
+    // XXX write background loading stuff!
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  nsresult rv;
+  nsCOMPtr<nsIImageLoadingContent> imageContent =
+      do_QueryInterface(aElement, &rv);
+  if (!imageContent) return rv;
+
+  // get the image container
+  nsCOMPtr<imgIRequest> request;
+  rv = imageContent->GetRequest(nsIImageLoadingContent::CURRENT_REQUEST,
+                                getter_AddRefs(request));
+  if (!request) return rv;
+
+  nsCOMPtr<imgIContainer> container;
+  rv = request->GetImage(getter_AddRefs(container));
+  if (!container) return NS_ERROR_FAILURE;
+
+  // get the file name from localized strings
+  nsCOMPtr<nsIStringBundleService> bundleService(
+      do_GetService(NS_STRINGBUNDLE_CONTRACTID, &rv));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIStringBundle> shellBundle;
+  rv = bundleService->CreateBundle(SHELLSERVICE_PROPERTIES,
+                                   getter_AddRefs(shellBundle));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // e.g. "Desktop Background.bmp"
+  nsAutoString fileLeafName;
+  rv = shellBundle->GetStringFromName("desktopBackgroundLeafNameWin",
+                                      fileLeafName);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // get the profile root directory
+  nsCOMPtr<nsIFile> file;
+  rv = NS_GetSpecialDirectory(NS_APP_APPLICATION_REGISTRY_DIR,
+                              getter_AddRefs(file));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // eventually, the path is "%APPDATA%\Mozilla\Firefox\Desktop Background.bmp"
+  rv = file->Append(fileLeafName);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsAutoString path;
+  rv = file->GetPath(path);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // write the bitmap to a file in the profile directory.
+  // We have to write old bitmap format for Windows 7 wallpapar support.
+  rv = WriteBitmap(file, container);
+
+  // if the file was written successfully, set it as the system wallpaper
+  if (NS_SUCCEEDED(rv)) {
+    nsCOMPtr<nsIWindowsRegKey> regKey =
+        do_CreateInstance("@mozilla.org/windows-registry-key;1", &rv);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = regKey->Create(nsIWindowsRegKey::ROOT_KEY_CURRENT_USER,
+                        u"Control Panel\\Desktop"_ns,
+                        nsIWindowsRegKey::ACCESS_SET_VALUE);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsAutoString tile;
+    nsAutoString style;
+    switch (aPosition) {
+      case BACKGROUND_TILE:
+        style.Assign('0');
+        tile.Assign('1');
+        break;
+      case BACKGROUND_CENTER:
+        style.Assign('0');
+        tile.Assign('0');
+        break;
+      case BACKGROUND_STRETCH:
+        style.Assign('2');
+        tile.Assign('0');
+        break;
+      case BACKGROUND_FILL:
+        style.AssignLiteral("10");
+        tile.Assign('0');
+        break;
+      case BACKGROUND_FIT:
+        style.Assign('6');
+        tile.Assign('0');
+        break;
+      case BACKGROUND_SPAN:
+        style.AssignLiteral("22");
+        tile.Assign('0');
+        break;
+    }
+
+    rv = regKey->WriteStringValue(u"TileWallpaper"_ns, tile);
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = regKey->WriteStringValue(u"WallpaperStyle"_ns, style);
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = regKey->Close();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    ::SystemParametersInfoW(SPI_SETDESKWALLPAPER, 0, (PVOID)path.get(),
+                            SPIF_UPDATEINIFILE | SPIF_SENDCHANGE);
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::GetDesktopBackgroundColor(uint32_t* aColor) {
+  uint32_t color = ::GetSysColor(COLOR_DESKTOP);
+  *aColor =
+      (GetRValue(color) << 16) | (GetGValue(color) << 8) | GetBValue(color);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::SetDesktopBackgroundColor(uint32_t aColor) {
+  int aParameters[2] = {COLOR_BACKGROUND, COLOR_DESKTOP};
+  BYTE r = (aColor >> 16);
+  BYTE g = (aColor << 16) >> 24;
+  BYTE b = (aColor << 24) >> 24;
+  COLORREF colors[2] = {RGB(r, g, b), RGB(r, g, b)};
+
+  ::SetSysColors(sizeof(aParameters) / sizeof(int), aParameters, colors);
+
+  nsresult rv;
+  nsCOMPtr<nsIWindowsRegKey> regKey =
+      do_CreateInstance("@mozilla.org/windows-registry-key;1", &rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = regKey->Create(nsIWindowsRegKey::ROOT_KEY_CURRENT_USER,
+                      u"Control Panel\\Colors"_ns,
+                      nsIWindowsRegKey::ACCESS_SET_VALUE);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  wchar_t rgb[12];
+  _snwprintf(rgb, 12, L"%u %u %u", r, g, b);
+
+  rv = regKey->WriteStringValue(u"Background"_ns, nsDependentString(rgb));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return regKey->Close();
+}
+
+/*
+ * Writes information about a shortcut to a shortcuts log in
+ * %PROGRAMDATA%\Mozilla-1de4eec8-1241-4177-a864-e594e8d1fb38.
+ * (This is the same directory used for update staging.)
+ * For more on the shortcuts log format and purpose, consult
+ * /toolkit/mozapps/installer/windows/nsis/common.nsh.
+ *
+ * The shortcuts log created or appended here is named after
+ * the currently running application and current user SID.
+ * For example: Firefox_$SID_shortcuts.ini.
+ *
+ * If it does not exist, it will be created. If it exists
+ * and a matching shortcut named already exists in the file,
+ * a new one will not be appended.
+ *
+ * In an ideal world this function would not need aShortcutsLogDir
+ * passed to it, but it is called by at least one function that runs
+ * asynchronously, and is therefore unable to use nsDirectoryService
+ * to look it up itself.
+ */
+static nsresult WriteShortcutToLog(nsIFile* aShortcutsLogDir,
+                                   KNOWNFOLDERID aFolderId,
+                                   const nsAString& aShortcutName) {
+  // the section inside the shortcuts log
+  nsAutoCString section;
+  // the shortcuts log wants "Programs" shortcuts in its "STARTMENU" section
+  if (aFolderId == FOLDERID_CommonPrograms || aFolderId == FOLDERID_Programs) {
+    section.Assign("STARTMENU");
+  } else if (aFolderId == FOLDERID_PublicDesktop ||
+             aFolderId == FOLDERID_Desktop) {
+    section.Assign("DESKTOP");
+  } else {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsCOMPtr<nsIFile> shortcutsLog;
+  nsresult rv = aShortcutsLogDir->GetParent(getter_AddRefs(shortcutsLog));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsAutoCString appName;
+  nsCOMPtr<nsIXULAppInfo> appInfo =
+      do_GetService("@mozilla.org/xre/app-info;1");
+  rv = appInfo->GetName(appName);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  auto userSid = GetCurrentUserStringSid();
+  if (!userSid) {
+    return NS_ERROR_FILE_NOT_FOUND;
+  }
+
+  nsAutoString filename;
+  filename.AppendPrintf("%s_%ls_shortcuts.ini", appName.get(), userSid.get());
+  rv = shortcutsLog->Append(filename);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsINIParser parser;
+  bool fileExists = false;
+  bool shortcutsLogEntryExists = false;
+  nsAutoCString keyName, shortcutName;
+  shortcutName = NS_ConvertUTF16toUTF8(aShortcutName);
+
+  shortcutsLog->IsFile(&fileExists);
+  // if the shortcuts log exists, find either an existing matching
+  // entry, or the next available shortcut index
+  if (fileExists) {
+    rv = parser.Init(shortcutsLog);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCString iniShortcut;
+    // surely we'll never need more than 10 shortcuts in one section...
+    for (int i = 0; i < 10; i++) {
+      keyName.AssignLiteral("Shortcut");
+      keyName.AppendInt(i);
+      rv = parser.GetString(section.get(), keyName.get(), iniShortcut);
+      if (NS_FAILED(rv)) {
+        // we found an unused index
+        break;
+      } else if (iniShortcut.Equals(shortcutName)) {
+        shortcutsLogEntryExists = true;
+      }
+    }
+    // otherwise, this is safe to use
+  } else {
+    keyName.AssignLiteral("Shortcut0");
+  }
+
+  if (!shortcutsLogEntryExists) {
+    parser.SetString(section.get(), keyName.get(), shortcutName.get());
+    // We write this ourselves instead of using parser->WriteToFile because
+    // the INI parser in our uninstaller needs to read this, and only supports
+    // UTF-16LE encoding. nsINIParser does not support UTF-16.
+    nsAutoCString formatted;
+    parser.WriteToString(formatted);
+    FILE* writeFile;
+    rv = shortcutsLog->OpenANSIFileDesc("w,ccs=UTF-16LE", &writeFile);
+    NS_ENSURE_SUCCESS(rv, rv);
+    NS_ConvertUTF8toUTF16 formattedUTF16(formatted);
+    if (fwrite(formattedUTF16.get(), sizeof(wchar_t), formattedUTF16.Length(),
+               writeFile) != formattedUTF16.Length()) {
+      fclose(writeFile);
+      return NS_ERROR_FAILURE;
+    }
+    fclose(writeFile);
+  }
+
+  return NS_OK;
+}
+
+static nsresult CreateShortcutImpl(
+    nsIFile* aBinary, const CopyableTArray<nsString>& aArguments,
+    const nsAString& aDescription, nsIFile* aIconFile, uint16_t aIconIndex,
+    const nsAString& aAppUserModelId, KNOWNFOLDERID aShortcutFolder,
+    const nsAString& aShortcutName, const nsString& aShortcutFile,
+    nsIFile* aShortcutsLogDir) {
+  NS_ENSURE_ARG(aBinary);
+  NS_ENSURE_ARG(aIconFile);
+
+  nsresult rv =
+      WriteShortcutToLog(aShortcutsLogDir, aShortcutFolder, aShortcutName);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  RefPtr<IShellLinkW> link;
+  HRESULT hr = CoCreateInstance(CLSID_ShellLink, nullptr, CLSCTX_INPROC_SERVER,
+                                IID_IShellLinkW, getter_AddRefs(link));
+  NS_ENSURE_HRESULT(hr, NS_ERROR_FAILURE);
+
+  nsString path(aBinary->NativePath());
+  link->SetPath(path.get());
+
+  wchar_t workingDir[MAX_PATH + 1];
+  wcscpy_s(workingDir, MAX_PATH + 1, aBinary->NativePath().get());
+  PathRemoveFileSpecW(workingDir);
+  link->SetWorkingDirectory(workingDir);
+
+  if (!aDescription.IsEmpty()) {
+    link->SetDescription(PromiseFlatString(aDescription).get());
+  }
+
+  // TODO: Properly escape quotes in the string, see bug 1604287.
+  nsString arguments;
+  for (auto& arg : aArguments) {
+    arguments.AppendPrintf("\"%S\" ", static_cast<const wchar_t*>(arg.get()));
+  }
+
+  link->SetArguments(arguments.get());
+
+  if (aIconFile) {
+    nsString icon(aIconFile->NativePath());
+    link->SetIconLocation(icon.get(), aIconIndex);
+  }
+
+  if (!aAppUserModelId.IsEmpty()) {
+    RefPtr<IPropertyStore> propStore;
+    hr = link->QueryInterface(IID_IPropertyStore, getter_AddRefs(propStore));
+    NS_ENSURE_HRESULT(hr, NS_ERROR_FAILURE);
+
+    PROPVARIANT pv;
+    if (FAILED(InitPropVariantFromString(
+            PromiseFlatString(aAppUserModelId).get(), &pv))) {
+      return NS_ERROR_FAILURE;
+    }
+
+    hr = propStore->SetValue(PKEY_AppUserModel_ID, pv);
+    PropVariantClear(&pv);
+    NS_ENSURE_HRESULT(hr, NS_ERROR_FAILURE);
+
+    hr = propStore->Commit();
+    NS_ENSURE_HRESULT(hr, NS_ERROR_FAILURE);
+  }
+
+  RefPtr<IPersistFile> persist;
+  hr = link->QueryInterface(IID_IPersistFile, getter_AddRefs(persist));
+  NS_ENSURE_HRESULT(hr, NS_ERROR_FAILURE);
+
+  hr = persist->Save(aShortcutFile.get(), TRUE);
+  NS_ENSURE_HRESULT(hr, NS_ERROR_FAILURE);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::CreateShortcut(
+    nsIFile* aBinary, const nsTArray<nsString>& aArguments,
+    const nsAString& aDescription, nsIFile* aIconFile, uint16_t aIconIndex,
+    const nsAString& aAppUserModelId, const nsAString& aShortcutFolder,
+    const nsAString& aShortcutName, JSContext* aCx, dom::Promise** aPromise) {
+  if (!NS_IsMainThread()) {
+    return NS_ERROR_NOT_SAME_THREAD;
+  }
+
+  ErrorResult rv;
+  RefPtr<dom::Promise> promise =
+      dom::Promise::Create(xpc::CurrentNativeGlobal(aCx), rv);
+
+  if (MOZ_UNLIKELY(rv.Failed())) {
+    return rv.StealNSResult();
+  }
+  // In an ideal world we'd probably send along nsIFile pointers
+  // here, but it's easier to determine the needed shortcuts log
+  // entry with a KNOWNFOLDERID - so we pass this along instead
+  // and let CreateShortcutImpl take care of converting it to
+  // an nsIFile.
+  KNOWNFOLDERID folderId;
+  if (aShortcutFolder.Equals(L"Programs")) {
+    folderId = FOLDERID_Programs;
+  } else if (aShortcutFolder.Equals(L"Desktop")) {
+    folderId = FOLDERID_Desktop;
+  } else {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsCOMPtr<nsIFile> updRoot, shortcutsLogDir;
+  nsresult nsrv =
+      NS_GetSpecialDirectory(XRE_UPDATE_ROOT_DIR, getter_AddRefs(updRoot));
+  NS_ENSURE_SUCCESS(nsrv, nsrv);
+  nsrv = updRoot->GetParent(getter_AddRefs(shortcutsLogDir));
+  NS_ENSURE_SUCCESS(nsrv, nsrv);
+
+  nsCOMPtr<nsIFile> shortcutFile;
+  if (folderId == FOLDERID_Programs) {
+    nsrv = NS_GetSpecialDirectory(NS_WIN_PROGRAMS_DIR,
+                                  getter_AddRefs(shortcutFile));
+  } else if (folderId == FOLDERID_Desktop) {
+    nsrv =
+        NS_GetSpecialDirectory(NS_OS_DESKTOP_DIR, getter_AddRefs(shortcutFile));
+  } else {
+    return NS_ERROR_FILE_NOT_FOUND;
+  }
+  if (NS_FAILED(nsrv)) {
+    return NS_ERROR_FILE_NOT_FOUND;
+  }
+  shortcutFile->Append(aShortcutName);
+
+  auto promiseHolder = MakeRefPtr<nsMainThreadPtrHolder<dom::Promise>>(
+      "CreateShortcut promise", promise);
+
+  nsCOMPtr<nsIFile> binary(aBinary);
+  nsCOMPtr<nsIFile> iconFile(aIconFile);
+  NS_DispatchBackgroundTask(
+      NS_NewRunnableFunction(
+          "CreateShortcut",
+          [binary, aArguments = CopyableTArray<nsString>(aArguments),
+           aDescription = nsString{aDescription}, iconFile, aIconIndex,
+           aAppUserModelId = nsString{aAppUserModelId}, folderId,
+           aShortcutFolder = nsString{aShortcutFolder},
+           aShortcutName = nsString{aShortcutName}, shortcutsLogDir,
+           shortcutFile, promiseHolder = std::move(promiseHolder)] {
+            nsresult rv = NS_ERROR_FAILURE;
+            HRESULT hr = CoInitialize(nullptr);
+
+            if (SUCCEEDED(hr)) {
+              rv = CreateShortcutImpl(
+                  binary.get(), aArguments, aDescription, iconFile.get(),
+                  aIconIndex, aAppUserModelId, folderId, aShortcutName,
+                  shortcutFile->NativePath(), shortcutsLogDir.get());
+              CoUninitialize();
+            }
+
+            NS_DispatchToMainThread(NS_NewRunnableFunction(
+                "CreateShortcut callback",
+                [rv, shortcutFile, promiseHolder = std::move(promiseHolder)] {
+                  dom::Promise* promise = promiseHolder.get()->get();
+
+                  if (NS_SUCCEEDED(rv)) {
+                    promise->MaybeResolve(shortcutFile->NativePath());
+                  } else {
+                    promise->MaybeReject(rv);
+                  }
+                }));
+          }),
+      NS_DISPATCH_EVENT_MAY_BLOCK);
+
+  promise.forget(aPromise);
+  return NS_OK;
+}
+
+// Look for any installer-created shortcuts in the given location that match
+// the given AUMID and EXE Path. If one is found, output its path.
+//
+// NOTE: DO NOT USE if a false negative (mismatch) is unacceptable.
+// aExePath is compared directly to the path retrieved from the shortcut.
+// Due to the presence of symlinks or other filesystem issues, it's possible
+// for different paths to refer to the same file, which would cause the check
+// to fail.
+// This should rarely be an issue as we are most likely to be run from a path
+// written by the installer (shortcut, association, launch from installer),
+// which also wrote the shortcuts. But it is possible.
+//
+// aCSIDL   the CSIDL of the directory to look for matching shortcuts in
+// aAUMID   the AUMID to check for
+// aExePath the target exe path to check for, should be a long path where
+//          possible
+// aShortcutSubstring a substring to limit which shortcuts in aCSIDL are
+//                    inspected for a match. Only shortcuts whose filename
+//                    contains this substring will be considered
+// aShortcutPath outparam, set to matching shortcut path if NS_OK is returned.
+//
+// Returns
+//   NS_ERROR_FAILURE on errors before any shortcuts were loaded
+//   NS_ERROR_FILE_NOT_FOUND if no shortcuts matching aShortcutSubstring exist
+//   NS_ERROR_FILE_ALREADY_EXISTS if shortcuts were found but did not match
+//                                aAUMID or aExePath
+//   NS_OK if a matching shortcut is found
+static nsresult GetMatchingShortcut(int aCSIDL, const nsAString& aAUMID,
+                                    const wchar_t aExePath[MAXPATHLEN],
+                                    const nsAString& aShortcutSubstring,
+                                    /* out */ nsAutoString& aShortcutPath) {
+  nsresult result = NS_ERROR_FAILURE;
+
+  wchar_t folderPath[MAX_PATH] = {};
+  HRESULT hr = SHGetFolderPathW(nullptr, aCSIDL, nullptr, SHGFP_TYPE_CURRENT,
+                                folderPath);
+  if (NS_WARN_IF(FAILED(hr))) {
+    return NS_ERROR_FAILURE;
+  }
+  if (wcscat_s(folderPath, MAX_PATH, L"\\") != 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Get list of shortcuts in aCSIDL
+  nsAutoString pattern(folderPath);
+  pattern.AppendLiteral("*.lnk");
+
+  WIN32_FIND_DATAW findData = {};
+  HANDLE hFindFile = FindFirstFileW(pattern.get(), &findData);
+  if (hFindFile == INVALID_HANDLE_VALUE) {
+    Unused << NS_WARN_IF(GetLastError() != ERROR_FILE_NOT_FOUND);
+    return NS_ERROR_FILE_NOT_FOUND;
+  }
+  // Past this point we don't return until the end of the function,
+  // when FindClose() is called.
+
+  // todo: improve return values here
+  do {
+    // Skip any that don't contain aShortcutSubstring
+    // This is a case sensitive comparison, but that's probably fine for
+    // the vast majority of cases -- and certainly for all the ones where
+    // a shortcut was created by the installer.
+    if (StrStrIW(findData.cFileName, aShortcutSubstring.Data()) == NULL) {
+      continue;
+    }
+
+    nsAutoString path(folderPath);
+    path.Append(findData.cFileName);
+
+    // Create a shell link object for loading the shortcut
+    RefPtr<IShellLinkW> link;
+    HRESULT hr =
+        CoCreateInstance(CLSID_ShellLink, nullptr, CLSCTX_INPROC_SERVER,
+                         IID_IShellLinkW, getter_AddRefs(link));
+    if (NS_WARN_IF(FAILED(hr))) {
+      continue;
+    }
+
+    // Load
+    RefPtr<IPersistFile> persist;
+    hr = link->QueryInterface(IID_IPersistFile, getter_AddRefs(persist));
+    if (NS_WARN_IF(FAILED(hr))) {
+      continue;
+    }
+
+    hr = persist->Load(path.get(), STGM_READ);
+    if (FAILED(hr)) {
+      if (NS_WARN_IF(hr != HRESULT_FROM_WIN32(ERROR_FILE_NOT_FOUND))) {
+        // empty branch, result unchanged but warning issued
+      } else {
+        // If we've ever gotten past this block, result will already be
+        // NS_ERROR_FILE_ALREADY_EXISTS, which is a more accurate error
+        // than NS_ERROR_FILE_NOT_FOUND.
+        if (result != NS_ERROR_FILE_ALREADY_EXISTS) {
+          result = NS_ERROR_FILE_NOT_FOUND;
+        }
+      }
+      continue;
+    }
+    result = NS_ERROR_FILE_ALREADY_EXISTS;
+
+    // Check the AUMID
+    RefPtr<IPropertyStore> propStore;
+    hr = link->QueryInterface(IID_IPropertyStore, getter_AddRefs(propStore));
+    if (NS_WARN_IF(FAILED(hr))) {
+      continue;
+    }
+
+    PROPVARIANT pv;
+    hr = propStore->GetValue(PKEY_AppUserModel_ID, &pv);
+    if (NS_WARN_IF(FAILED(hr))) {
+      continue;
+    }
+
+    wchar_t storedAUMID[MAX_PATH];
+    hr = PropVariantToString(pv, storedAUMID, MAX_PATH);
+    PropVariantClear(&pv);
+    if (NS_WARN_IF(FAILED(hr))) {
+      continue;
+    }
+
+    if (!aAUMID.Equals(storedAUMID)) {
+      continue;
+    }
+
+    // Check the exe path
+    static_assert(MAXPATHLEN == MAX_PATH);
+    wchar_t storedExePath[MAX_PATH] = {};
+    // With no flags GetPath gets a long path
+    hr = link->GetPath(storedExePath, ArrayLength(storedExePath), nullptr, 0);
+    if (FAILED(hr) || hr == S_FALSE) {
+      continue;
+    }
+    // Case insensitive path comparison
+    if (wcsnicmp(storedExePath, aExePath, MAXPATHLEN) == 0) {
+      aShortcutPath.Assign(path);
+      result = NS_OK;
+      break;
+    }
+  } while (FindNextFileW(hFindFile, &findData));
+
+  FindClose(hFindFile);
+
+  return result;
+}
+
+static nsresult FindMatchingShortcut(const nsAString& aAppUserModelId,
+                                     const nsAString& aShortcutSubstring,
+                                     const bool aPrivateBrowsing,
+                                     nsAutoString& aShortcutPath) {
+  wchar_t exePath[MAXPATHLEN] = {};
+  if (NS_WARN_IF(NS_FAILED(BinaryPath::GetLong(exePath)))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (aPrivateBrowsing) {
+    if (!PathRemoveFileSpecW(exePath)) {
+      return NS_ERROR_FAILURE;
+    }
+    if (!PathAppendW(exePath, L"private_browsing.exe")) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+
+  int shortcutCSIDLs[] = {CSIDL_COMMON_PROGRAMS, CSIDL_PROGRAMS,
+                          CSIDL_COMMON_DESKTOPDIRECTORY,
+                          CSIDL_DESKTOPDIRECTORY};
+  for (int shortcutCSIDL : shortcutCSIDLs) {
+    // GetMatchingShortcut may fail when the exe path doesn't match, even
+    // if it refers to the same file. This should be rare, and the worst
+    // outcome would be failure to pin, so the risk is acceptable.
+    nsresult rv = GetMatchingShortcut(shortcutCSIDL, aAppUserModelId, exePath,
+                                      aShortcutSubstring, aShortcutPath);
+    if (NS_SUCCEEDED(rv)) {
+      return NS_OK;
+    }
+  }
+
+  return NS_ERROR_FILE_NOT_FOUND;
+}
+
+static bool HasMatchingShortcutImpl(const nsAString& aAppUserModelId,
+                                    const bool aPrivateBrowsing,
+                                    const nsAutoString& aShortcutSubstring) {
+  // unused by us, but required
+  nsAutoString shortcutPath;
+  nsresult rv = FindMatchingShortcut(aAppUserModelId, aShortcutSubstring,
+                                     aPrivateBrowsing, shortcutPath);
+  if (SUCCEEDED(rv)) {
+    return true;
+  }
+
+  return false;
+}
+
+NS_IMETHODIMP nsWindowsShellService::HasMatchingShortcut(
+    const nsAString& aAppUserModelId, const bool aPrivateBrowsing,
+    JSContext* aCx, dom::Promise** aPromise) {
+  if (!NS_IsMainThread()) {
+    return NS_ERROR_NOT_SAME_THREAD;
+  }
+
+  ErrorResult rv;
+  RefPtr<dom::Promise> promise =
+      dom::Promise::Create(xpc::CurrentNativeGlobal(aCx), rv);
+
+  if (MOZ_UNLIKELY(rv.Failed())) {
+    return rv.StealNSResult();
+  }
+
+  auto promiseHolder = MakeRefPtr<nsMainThreadPtrHolder<dom::Promise>>(
+      "HasMatchingShortcut promise", promise);
+
+  NS_DispatchBackgroundTask(
+      NS_NewRunnableFunction(
+          "HasMatchingShortcut",
+          [aAppUserModelId = nsString{aAppUserModelId}, aPrivateBrowsing,
+           promiseHolder = std::move(promiseHolder)] {
+            bool rv = false;
+            HRESULT hr = CoInitialize(nullptr);
+
+            if (SUCCEEDED(hr)) {
+              nsAutoString shortcutSubstring;
+              shortcutSubstring.AssignLiteral(MOZ_APP_DISPLAYNAME);
+              rv = HasMatchingShortcutImpl(aAppUserModelId, aPrivateBrowsing,
+                                           shortcutSubstring);
+              CoUninitialize();
+            }
+
+            NS_DispatchToMainThread(NS_NewRunnableFunction(
+                "HasMatchingShortcut callback",
+                [rv, promiseHolder = std::move(promiseHolder)] {
+                  dom::Promise* promise = promiseHolder.get()->get();
+
+                  promise->MaybeResolve(rv);
+                }));
+          }),
+      NS_DISPATCH_EVENT_MAY_BLOCK);
+
+  promise.forget(aPromise);
+  return NS_OK;
+}
+
+static nsresult PinCurrentAppToTaskbarWin7(bool aCheckOnly,
+                                           nsAutoString aShortcutPath) {
+  nsModuleHandle shellInst(LoadLibraryW(L"shell32.dll"));
+
+  RefPtr<IShellWindows> shellWindows;
+  HRESULT hr =
+      ::CoCreateInstance(CLSID_ShellWindows, nullptr, CLSCTX_LOCAL_SERVER,
+                         IID_IShellWindows, getter_AddRefs(shellWindows));
+  if (FAILED(hr)) return NS_ERROR_FAILURE;
+
+  // 1. Find the shell view for the desktop.
+  _variant_t loc(int(CSIDL_DESKTOP));
+  _variant_t empty;
+  long hwnd;
+  RefPtr<IDispatch> dispDesktop;
+  hr = shellWindows->FindWindowSW(&loc, &empty, SWC_DESKTOP, &hwnd,
+                                  SWFO_NEEDDISPATCH,
+                                  getter_AddRefs(dispDesktop));
+  if (FAILED(hr) || hr == S_FALSE) return NS_ERROR_FAILURE;
+
+  RefPtr<IServiceProvider> servProv;
+  hr = dispDesktop->QueryInterface(IID_IServiceProvider,
+                                   getter_AddRefs(servProv));
+  if (FAILED(hr)) return NS_ERROR_FAILURE;
+
+  RefPtr<IShellBrowser> browser;
+  hr = servProv->QueryService(SID_STopLevelBrowser, IID_IShellBrowser,
+                              getter_AddRefs(browser));
+  if (FAILED(hr)) return NS_ERROR_FAILURE;
+
+  RefPtr<IShellView> activeShellView;
+  hr = browser->QueryActiveShellView(getter_AddRefs(activeShellView));
+  if (FAILED(hr)) return NS_ERROR_FAILURE;
+
+  // 2. Get the automation object for the desktop.
+  RefPtr<IDispatch> dispView;
+  hr = activeShellView->GetItemObject(SVGIO_BACKGROUND, IID_IDispatch,
+                                      getter_AddRefs(dispView));
+  if (FAILED(hr)) return NS_ERROR_FAILURE;
+
+  RefPtr<IShellFolderViewDual> folderView;
+  hr = dispView->QueryInterface(IID_IShellFolderViewDual,
+                                getter_AddRefs(folderView));
+  if (FAILED(hr)) return NS_ERROR_FAILURE;
+
+  // 3. Get the interface to IShellDispatch
+  RefPtr<IDispatch> dispShell;
+  hr = folderView->get_Application(getter_AddRefs(dispShell));
+  if (FAILED(hr)) return NS_ERROR_FAILURE;
+
+  RefPtr<IShellDispatch2> shellDisp;
+  hr =
+      dispShell->QueryInterface(IID_IShellDispatch2, getter_AddRefs(shellDisp));
+  if (FAILED(hr)) return NS_ERROR_FAILURE;
+
+  wchar_t shortcutDir[MAX_PATH + 1];
+  wcscpy_s(shortcutDir, MAX_PATH + 1, aShortcutPath.get());
+  if (!PathRemoveFileSpecW(shortcutDir)) return NS_ERROR_FAILURE;
+
+  VARIANT dir;
+  dir.vt = VT_BSTR;
+  BStrPtr bstrShortcutDir = BStrPtr(SysAllocString(shortcutDir));
+  if (bstrShortcutDir.get() == NULL) return NS_ERROR_FAILURE;
+  dir.bstrVal = bstrShortcutDir.get();
+
+  RefPtr<Folder> folder;
+  hr = shellDisp->NameSpace(dir, getter_AddRefs(folder));
+  if (FAILED(hr)) return NS_ERROR_FAILURE;
+
+  wchar_t linkName[MAX_PATH + 1];
+  wcscpy_s(linkName, MAX_PATH + 1, aShortcutPath.get());
+  PathStripPathW(linkName);
+  BStrPtr bstrLinkName = BStrPtr(SysAllocString(linkName));
+  if (bstrLinkName.get() == NULL) return NS_ERROR_FAILURE;
+
+  RefPtr<FolderItem> folderItem;
+  hr = folder->ParseName(bstrLinkName.get(), getter_AddRefs(folderItem));
+  if (FAILED(hr) || !folderItem) return NS_ERROR_FAILURE;
+
+  RefPtr<FolderItemVerbs> verbs;
+  hr = folderItem->Verbs(getter_AddRefs(verbs));
+  if (FAILED(hr)) return NS_ERROR_FAILURE;
+
+  long count;
+  hr = verbs->get_Count(&count);
+  if (FAILED(hr)) return NS_ERROR_FAILURE;
+
+  WCHAR verbName[100];
+  if (!LoadStringW(shellInst.get(), PIN_TO_TASKBAR_SHELL_VERB, verbName,
+                   ARRAYSIZE(verbName))) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+  VARIANT v;
+  v.vt = VT_I4;
+  BStrPtr name;
+  for (long i = 0; i < count; ++i) {
+    RefPtr<FolderItemVerb> fiVerb;
+    v.lVal = i;
+    hr = verbs->Item(v, getter_AddRefs(fiVerb));
+    if (FAILED(hr)) {
+      continue;
+    }
+
+    BSTR tmpName;
+    hr = fiVerb->get_Name(&tmpName);
+    if (FAILED(hr)) {
+      continue;
+    }
+    name = BStrPtr(tmpName);
+    if (!wcscmp((WCHAR*)name.get(), verbName)) {
+      if (aCheckOnly) {
+        // we've done as much as we can without actually
+        // changing anything
+        return NS_OK;
+      }
+
+      hr = fiVerb->DoIt();
+      if (SUCCEEDED(hr)) {
+        return NS_OK;
+      }
+    }
+  }
+
+  // if we didn't return in the block above, something failed
+  return NS_ERROR_FAILURE;
+}
+
+static nsresult PinCurrentAppToTaskbarWin10(bool aCheckOnly,
+                                            nsAutoString aShortcutPath) {
+  // This enum is likely only used for Windows telemetry, INT_MAX is chosen to
+  // avoid confusion with existing uses.
+  enum PINNEDLISTMODIFYCALLER { PLMC_INT_MAX = INT_MAX };
+
+  // The types below, and the idea of using IPinnedList3::Modify,
+  // are thanks to Gee Law <https://geelaw.blog/entries/msedge-pins/>
+  static constexpr GUID CLSID_TaskbandPin = {
+      0x90aa3a4e,
+      0x1cba,
+      0x4233,
+      {0xb8, 0xbb, 0x53, 0x57, 0x73, 0xd4, 0x84, 0x49}};
+
+  static constexpr GUID IID_IPinnedList3 = {
+      0x0dd79ae2,
+      0xd156,
+      0x45d4,
+      {0x9e, 0xeb, 0x3b, 0x54, 0x97, 0x69, 0xe9, 0x40}};
+
+  struct IPinnedList3Vtbl;
+  struct IPinnedList3 {
+    IPinnedList3Vtbl* vtbl;
+  };
+
+  typedef ULONG STDMETHODCALLTYPE ReleaseFunc(IPinnedList3 * that);
+  typedef HRESULT STDMETHODCALLTYPE ModifyFunc(
+      IPinnedList3 * that, PCIDLIST_ABSOLUTE unpin, PCIDLIST_ABSOLUTE pin,
+      PINNEDLISTMODIFYCALLER caller);
+
+  struct IPinnedList3Vtbl {
+    void* QueryInterface;  // 0
+    void* AddRef;          // 1
+    ReleaseFunc* Release;  // 2
+    void* Other[13];       // 3-15
+    ModifyFunc* Modify;    // 16
+  };
+
+  struct ILFreeDeleter {
+    void operator()(LPITEMIDLIST aPtr) {
+      if (aPtr) {
+        ILFree(aPtr);
+      }
+    }
+  };
+
+  mozilla::UniquePtr<__unaligned ITEMIDLIST, ILFreeDeleter> path(
+      ILCreateFromPathW(aShortcutPath.get()));
+  if (NS_WARN_IF(!path)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  IPinnedList3* pinnedList = nullptr;
+  HRESULT hr =
+      CoCreateInstance(CLSID_TaskbandPin, nullptr, CLSCTX_INPROC_SERVER,
+                       IID_IPinnedList3, (void**)&pinnedList);
+  if (FAILED(hr) || !pinnedList) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  if (!aCheckOnly) {
+    hr =
+        pinnedList->vtbl->Modify(pinnedList, nullptr, path.get(), PLMC_INT_MAX);
+  }
+
+  pinnedList->vtbl->Release(pinnedList);
+
+  if (FAILED(hr)) {
+    return NS_ERROR_FAILURE;
+  } else {
+    return NS_OK;
+  }
+}
+
+static nsresult PinCurrentAppToTaskbarImpl(
+    bool aCheckOnly, bool aPrivateBrowsing, const nsAString& aAppUserModelId,
+    const nsAString& aShortcutName, const nsAString& aShortcutSubstring,
+    nsIFile* aShortcutsLogDir, nsIFile* aGreDir, nsIFile* aProgramsDir) {
+  MOZ_DIAGNOSTIC_ASSERT(
+      !NS_IsMainThread(),
+      "PinCurrentAppToTaskbarImpl should be called off main thread only");
+
+  nsAutoString shortcutPath;
+  nsresult rv = FindMatchingShortcut(aAppUserModelId, aShortcutSubstring,
+                                     aPrivateBrowsing, shortcutPath);
+  if (NS_FAILED(rv)) {
+    shortcutPath.Truncate();
+  }
+  if (shortcutPath.IsEmpty()) {
+    if (aCheckOnly) {
+      // Later checks rely on a shortcut already existing.
+      // We don't want to create a shortcut in check only mode
+      // so the best we can do is assume those parts will work.
+      return NS_OK;
+    }
+
+    nsAutoString linkName(aShortcutName);
+
+    nsCOMPtr<nsIFile> exeFile(aGreDir);
+    if (aPrivateBrowsing) {
+      nsAutoString pbExeStr(PRIVATE_BROWSING_BINARY);
+      nsresult rv = exeFile->Append(pbExeStr);
+      if (!NS_SUCCEEDED(rv)) {
+        return NS_ERROR_FAILURE;
+      }
+    } else {
+      wchar_t exePath[MAXPATHLEN] = {};
+      if (NS_WARN_IF(NS_FAILED(BinaryPath::GetLong(exePath)))) {
+        return NS_ERROR_FAILURE;
+      }
+      nsAutoString exeStr(exePath);
+      nsresult rv = NS_NewLocalFile(exeStr, true, getter_AddRefs(exeFile));
+      if (!NS_SUCCEEDED(rv)) {
+        return NS_ERROR_FILE_NOT_FOUND;
+      }
+    }
+
+    nsCOMPtr<nsIFile> shortcutFile(aProgramsDir);
+    shortcutFile->Append(aShortcutName);
+    shortcutPath.Assign(shortcutFile->NativePath());
+
+    nsTArray<nsString> arguments;
+    rv = CreateShortcutImpl(exeFile, arguments, aShortcutName, exeFile,
+                            // Icon indexes are defined as Resource IDs, but
+                            // CreateShortcutImpl needs an index.
+                            IDI_APPICON - 1, aAppUserModelId, FOLDERID_Programs,
+                            linkName, shortcutFile->NativePath(),
+                            aShortcutsLogDir);
+    if (!NS_SUCCEEDED(rv)) {
+      return NS_ERROR_FILE_NOT_FOUND;
+    }
+  }
+
+  if (IsWin10OrLater()) {
+    return PinCurrentAppToTaskbarWin10(aCheckOnly, shortcutPath);
+  } else {
+    return PinCurrentAppToTaskbarWin7(aCheckOnly, shortcutPath);
+  }
+}
+
+static nsresult PinCurrentAppToTaskbarAsyncImpl(bool aCheckOnly,
+                                                bool aPrivateBrowsing,
+                                                JSContext* aCx,
+                                                dom::Promise** aPromise) {
+  if (!NS_IsMainThread()) {
+    return NS_ERROR_NOT_SAME_THREAD;
+  }
+
+  // First available on 1809
+  if (IsWin10OrLater() && !IsWin10Sep2018UpdateOrLater()) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  ErrorResult rv;
+  RefPtr<dom::Promise> promise =
+      dom::Promise::Create(xpc::CurrentNativeGlobal(aCx), rv);
+
+  if (MOZ_UNLIKELY(rv.Failed())) {
+    return rv.StealNSResult();
+  }
+
+  nsAutoString aumid;
+  if (NS_WARN_IF(!mozilla::widget::WinTaskbar::GenerateAppUserModelID(
+          aumid, aPrivateBrowsing))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // NOTE: In the installer, non-private shortcuts are named
+  // "${BrandShortName}.lnk". This is set from MOZ_APP_DISPLAYNAME in
+  // defines.nsi.in. (Except in dev edition where it's explicitly set to
+  // "Firefox Developer Edition" in branding.nsi, which matches
+  // MOZ_APP_DISPLAYNAME in aurora/configure.sh.)
+  //
+  // If this changes, we could expand this to check shortcuts_log.ini,
+  // which records the name of the shortcuts as created by the installer.
+  //
+  // Private shortcuts are not created by the installer (they're created
+  // upon user request, ultimately by CreateShortcutImpl, and recorded in
+  // a separate shortcuts log. As with non-private shortcuts they have a known
+  // name - so there's no need to look through logs to find them.
+  nsAutoString shortcutName;
+  if (aPrivateBrowsing) {
+    nsTArray<nsCString> resIds = {
+        "branding/brand.ftl"_ns,
+        "browser/browser.ftl"_ns,
+    };
+    RefPtr<Localization> l10n = Localization::Create(resIds, true);
+    nsAutoCString pbStr;
+    IgnoredErrorResult rv;
+    l10n->FormatValueSync("private-browsing-shortcut-text-2"_ns, {}, pbStr, rv);
+    shortcutName.Append(NS_ConvertUTF8toUTF16(pbStr));
+    shortcutName.AppendLiteral(".lnk");
+  } else {
+    shortcutName.AppendLiteral(MOZ_APP_DISPLAYNAME ".lnk");
+  }
+
+  nsCOMPtr<nsIFile> greDir, updRoot, programsDir, shortcutsLogDir;
+  nsresult nsrv = NS_GetSpecialDirectory(NS_GRE_DIR, getter_AddRefs(greDir));
+  NS_ENSURE_SUCCESS(nsrv, nsrv);
+  nsrv = NS_GetSpecialDirectory(XRE_UPDATE_ROOT_DIR, getter_AddRefs(updRoot));
+  NS_ENSURE_SUCCESS(nsrv, nsrv);
+  rv = NS_GetSpecialDirectory(NS_WIN_PROGRAMS_DIR, getter_AddRefs(programsDir));
+  NS_ENSURE_SUCCESS(nsrv, nsrv);
+  nsrv = updRoot->GetParent(getter_AddRefs(shortcutsLogDir));
+  NS_ENSURE_SUCCESS(nsrv, nsrv);
+
+  auto promiseHolder = MakeRefPtr<nsMainThreadPtrHolder<dom::Promise>>(
+      "CheckPinCurrentAppToTaskbarAsync promise", promise);
+
+  NS_DispatchBackgroundTask(
+      NS_NewRunnableFunction(
+          "CheckPinCurrentAppToTaskbarAsync",
+          [aCheckOnly, aPrivateBrowsing, shortcutName, aumid = nsString{aumid},
+           shortcutsLogDir, greDir, programsDir,
+           promiseHolder = std::move(promiseHolder)] {
+            nsresult rv = NS_ERROR_FAILURE;
+            HRESULT hr = CoInitialize(nullptr);
+
+            if (SUCCEEDED(hr)) {
+              nsAutoString shortcutSubstring;
+              shortcutSubstring.AssignLiteral(MOZ_APP_DISPLAYNAME);
+              rv = PinCurrentAppToTaskbarImpl(
+                  aCheckOnly, aPrivateBrowsing, aumid, shortcutName,
+                  shortcutSubstring, shortcutsLogDir.get(), greDir.get(),
+                  programsDir.get());
+              CoUninitialize();
+            }
+
+            NS_DispatchToMainThread(NS_NewRunnableFunction(
+                "CheckPinCurrentAppToTaskbarAsync callback",
+                [rv, promiseHolder = std::move(promiseHolder)] {
+                  dom::Promise* promise = promiseHolder.get()->get();
+
+                  if (NS_SUCCEEDED(rv)) {
+                    promise->MaybeResolveWithUndefined();
+                  } else {
+                    promise->MaybeReject(rv);
+                  }
+                }));
+          }),
+      NS_DISPATCH_EVENT_MAY_BLOCK);
+
+  promise.forget(aPromise);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::PinCurrentAppToTaskbarAsync(bool aPrivateBrowsing,
+                                                   JSContext* aCx,
+                                                   dom::Promise** aPromise) {
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=1712628 tracks implementing
+  // this for MSIX packages.
+  if (widget::WinUtils::HasPackageIdentity()) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  return PinCurrentAppToTaskbarAsyncImpl(
+      /* aCheckOnly */ false, aPrivateBrowsing, aCx, aPromise);
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::CheckPinCurrentAppToTaskbarAsync(
+    bool aPrivateBrowsing, JSContext* aCx, dom::Promise** aPromise) {
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=1712628 tracks implementing
+  // this for MSIX packages.
+  if (widget::WinUtils::HasPackageIdentity()) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  return PinCurrentAppToTaskbarAsyncImpl(
+      /* aCheckOnly = */ true, aPrivateBrowsing, aCx, aPromise);
+}
+
+static bool IsCurrentAppPinnedToTaskbarSync(const nsAutoString& aumid) {
+  // There are two shortcut targets that we created. One always matches the
+  // binary we're running as (eg: firefox.exe). The other is the wrapper
+  // for launching in Private Browsing mode. We need to inspect shortcuts
+  // that point at either of these to accurately judge whether or not
+  // the app is pinned with the given AUMID.
+  wchar_t exePath[MAXPATHLEN] = {};
+  wchar_t pbExePath[MAXPATHLEN] = {};
+
+  if (NS_WARN_IF(NS_FAILED(BinaryPath::GetLong(exePath)))) {
+    return false;
+  }
+
+  wcscpy_s(pbExePath, MAXPATHLEN, exePath);
+  if (!PathRemoveFileSpecW(pbExePath)) {
+    return false;
+  }
+  if (!PathAppendW(pbExePath, L"private_browsing.exe")) {
+    return false;
+  }
+
+  wchar_t folderChars[MAX_PATH] = {};
+  HRESULT hr = SHGetFolderPathW(nullptr, CSIDL_APPDATA, nullptr,
+                                SHGFP_TYPE_CURRENT, folderChars);
+  if (NS_WARN_IF(FAILED(hr))) {
+    return false;
+  }
+
+  nsAutoString folder;
+  folder.Assign(folderChars);
+  if (NS_WARN_IF(folder.IsEmpty())) {
+    return false;
+  }
+  if (folder[folder.Length() - 1] != '\\') {
+    folder.AppendLiteral("\\");
+  }
+  folder.AppendLiteral(
+      "Microsoft\\Internet Explorer\\Quick Launch\\User Pinned\\TaskBar");
+  nsAutoString pattern;
+  pattern.Assign(folder);
+  pattern.AppendLiteral("\\*.lnk");
+
+  WIN32_FIND_DATAW findData = {};
+  HANDLE hFindFile = FindFirstFileW(pattern.get(), &findData);
+  if (hFindFile == INVALID_HANDLE_VALUE) {
+    Unused << NS_WARN_IF(GetLastError() != ERROR_FILE_NOT_FOUND);
+    return false;
+  }
+  // Past this point we don't return until the end of the function,
+  // when FindClose() is called.
+
+  // Check all shortcuts until a match is found
+  bool isPinned = false;
+  do {
+    nsAutoString fileName;
+    fileName.Assign(folder);
+    fileName.AppendLiteral("\\");
+    fileName.Append(findData.cFileName);
+
+    // Create a shell link object for loading the shortcut
+    RefPtr<IShellLinkW> link;
+    HRESULT hr =
+        CoCreateInstance(CLSID_ShellLink, nullptr, CLSCTX_INPROC_SERVER,
+                         IID_IShellLinkW, getter_AddRefs(link));
+    if (NS_WARN_IF(FAILED(hr))) {
+      continue;
+    }
+
+    // Load
+    RefPtr<IPersistFile> persist;
+    hr = link->QueryInterface(IID_IPersistFile, getter_AddRefs(persist));
+    if (NS_WARN_IF(FAILED(hr))) {
+      continue;
+    }
+
+    hr = persist->Load(fileName.get(), STGM_READ);
+    if (NS_WARN_IF(FAILED(hr))) {
+      continue;
+    }
+
+    // Check the exe path
+    static_assert(MAXPATHLEN == MAX_PATH);
+    wchar_t storedExePath[MAX_PATH] = {};
+    // With no flags GetPath gets a long path
+    hr = link->GetPath(storedExePath, ArrayLength(storedExePath), nullptr, 0);
+    if (FAILED(hr) || hr == S_FALSE) {
+      continue;
+    }
+    // Case insensitive path comparison
+    // NOTE: Because this compares the path directly, it is possible to
+    // have a false negative mismatch.
+    if (wcsnicmp(storedExePath, exePath, MAXPATHLEN) == 0 ||
+        wcsnicmp(storedExePath, pbExePath, MAXPATHLEN) == 0) {
+      RefPtr<IPropertyStore> propStore;
+      hr = link->QueryInterface(IID_IPropertyStore, getter_AddRefs(propStore));
+      if (NS_WARN_IF(FAILED(hr))) {
+        continue;
+      }
+
+      PROPVARIANT pv;
+      hr = propStore->GetValue(PKEY_AppUserModel_ID, &pv);
+      if (NS_WARN_IF(FAILED(hr))) {
+        continue;
+      }
+
+      wchar_t storedAUMID[MAX_PATH];
+      hr = PropVariantToString(pv, storedAUMID, MAX_PATH);
+      PropVariantClear(&pv);
+      if (NS_WARN_IF(FAILED(hr))) {
+        continue;
+      }
+
+      if (aumid.Equals(storedAUMID)) {
+        isPinned = true;
+        break;
+      }
+    }
+  } while (FindNextFileW(hFindFile, &findData));
+
+  FindClose(hFindFile);
+
+  return isPinned;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::IsCurrentAppPinnedToTaskbarAsync(
+    const nsAString& aumid, JSContext* aCx, /* out */ dom::Promise** aPromise) {
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=1712628 tracks implementing
+  // this for MSIX packages.
+  if (widget::WinUtils::HasPackageIdentity()) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  if (!NS_IsMainThread()) {
+    return NS_ERROR_NOT_SAME_THREAD;
+  }
+
+  ErrorResult rv;
+  RefPtr<dom::Promise> promise =
+      dom::Promise::Create(xpc::CurrentNativeGlobal(aCx), rv);
+  if (MOZ_UNLIKELY(rv.Failed())) {
+    return rv.StealNSResult();
+  }
+
+  // A holder to pass the promise through the background task and back to
+  // the main thread when finished.
+  auto promiseHolder = MakeRefPtr<nsMainThreadPtrHolder<dom::Promise>>(
+      "IsCurrentAppPinnedToTaskbarAsync promise", promise);
+
+  // nsAString can't be captured by a lambda because it does not have a
+  // public copy constructor
+  nsAutoString capturedAumid(aumid);
+  NS_DispatchBackgroundTask(
+      NS_NewRunnableFunction(
+          "IsCurrentAppPinnedToTaskbarAsync",
+          [capturedAumid, promiseHolder = std::move(promiseHolder)] {
+            bool isPinned = false;
+
+            HRESULT hr = CoInitialize(nullptr);
+            if (SUCCEEDED(hr)) {
+              isPinned = IsCurrentAppPinnedToTaskbarSync(capturedAumid);
+              CoUninitialize();
+            }
+
+            // Dispatch back to the main thread to resolve the promise.
+            NS_DispatchToMainThread(NS_NewRunnableFunction(
+                "IsCurrentAppPinnedToTaskbarAsync callback",
+                [isPinned, promiseHolder = std::move(promiseHolder)] {
+                  promiseHolder.get()->get()->MaybeResolve(isPinned);
+                }));
+          }),
+      NS_DISPATCH_EVENT_MAY_BLOCK);
+
+  promise.forget(aPromise);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWindowsShellService::ClassifyShortcut(const nsAString& aPath,
+                                        nsAString& aResult) {
+  aResult.Truncate();
+
+  nsAutoString shortcutPath(PromiseFlatString(aPath));
+
+  // NOTE: On Windows 7, Start Menu pin shortcuts are stored under
+  // "<FOLDERID_User Pinned>\StartMenu", but on Windows 10 they are just normal
+  // Start Menu shortcuts. These both map to "StartMenu" for consistency,
+  // rather than having a separate "StartMenuPins" which would only apply on
+  // Win7.
+  struct {
+    KNOWNFOLDERID folderId;
+    const char16_t* postfix;
+    const char16_t* classification;
+  } folders[] = {{FOLDERID_CommonStartMenu, u"\\", u"StartMenu"},
+                 {FOLDERID_StartMenu, u"\\", u"StartMenu"},
+                 {FOLDERID_PublicDesktop, u"\\", u"Desktop"},
+                 {FOLDERID_Desktop, u"\\", u"Desktop"},
+                 {FOLDERID_UserPinned, u"\\TaskBar\\", u"Taskbar"},
+                 {FOLDERID_UserPinned, u"\\StartMenu\\", u"StartMenu"}};
+
+  for (size_t i = 0; i < ArrayLength(folders); ++i) {
+    nsAutoString knownPath;
+
+    // These flags are chosen to avoid I/O, see bug 1363398.
+    DWORD flags =
+        KF_FLAG_SIMPLE_IDLIST | KF_FLAG_DONT_VERIFY | KF_FLAG_NO_ALIAS;
+    PWSTR rawPath = nullptr;
+
+    if (FAILED(SHGetKnownFolderPath(folders[i].folderId, flags, nullptr,
+                                    &rawPath))) {
+      continue;
+    }
+
+    knownPath = nsDependentString(rawPath);
+    CoTaskMemFree(rawPath);
+
+    knownPath.Append(folders[i].postfix);
+    // Check if the shortcut path starts with the shell folder path.
+    if (wcsnicmp(shortcutPath.get(), knownPath.get(), knownPath.Length()) ==
+        0) {
+      aResult.Assign(folders[i].classification);
+      nsTArray<nsCString> resIds = {
+          "branding/brand.ftl"_ns,
+          "browser/browser.ftl"_ns,
+      };
+      RefPtr<Localization> l10n = Localization::Create(resIds, true);
+      nsAutoCString pbStr;
+      IgnoredErrorResult rv;
+      l10n->FormatValueSync("private-browsing-shortcut-text-2"_ns, {}, pbStr,
+                            rv);
+      NS_ConvertUTF8toUTF16 widePbStr(pbStr);
+      if (wcsstr(shortcutPath.get(), widePbStr.get())) {
+        aResult.AppendLiteral("Private");
+      }
+      return NS_OK;
+    }
+  }
+
+  // Nothing found, aResult is already "".
+  return NS_OK;
+}
+
+nsWindowsShellService::nsWindowsShellService() {}
+
+nsWindowsShellService::~nsWindowsShellService() {}
diff --git a/browser/components/shell/nsWindowsShellService.h b/browser/components/shell/nsWindowsShellService.h
new file mode 100644
index 0000000000..6127f687bd
--- /dev/null
+++ b/browser/components/shell/nsWindowsShellService.h
@@ -0,0 +1,38 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#ifndef nswindowsshellservice_h____
+#define nswindowsshellservice_h____
+
+#include "nscore.h"
+#include "nsString.h"
+#include "nsToolkitShellService.h"
+#include "nsIShellService.h"
+#include "nsIWindowsShellService.h"
+
+#include <windows.h>
+#include <ole2.h>
+
+class nsWindowsShellService : public nsIShellService,
+                              public nsToolkitShellService,
+                              public nsIWindowsShellService {
+  virtual ~nsWindowsShellService();
+
+ public:
+  nsWindowsShellService();
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSISHELLSERVICE
+  NS_DECL_NSIWINDOWSSHELLSERVICE
+
+ protected:
+  nsresult LaunchControlPanelDefaultsSelectionUI();
+  nsresult LaunchControlPanelDefaultPrograms();
+  nsresult LaunchModernSettingsDialogDefaultApps();
+  nsresult InvokeHTTPOpenAsVerb();
+  nsresult LaunchHTTPHandlerPane();
+};
+
+#endif  // nswindowsshellservice_h____
diff --git a/browser/components/shell/search-provider-files/README b/browser/components/shell/search-provider-files/README
new file mode 100644
index 0000000000..81ea16d9b6
--- /dev/null
+++ b/browser/components/shell/search-provider-files/README
@@ -0,0 +1,20 @@
+In order to get gnome shell search provider registered and active
+you need to install the firefox-search-provider.ini and firefox.desktop files system wide.
+
+The locations may be distro specific, for instance Fedora and Ubuntu expect
+the files at:
+
+/usr/share/gnome-shell/search-providers/firefox-search-provider.ini
+/usr/share/applications/firefox.desktop
+
+firefox.desktop is a system-wide Firefox launcher. It may come with your
+distribution or you can use this one. Update name of firefox desktop file at firefox-search-provider.ini
+according your actual file at /usr/share/applications.
+
+firefox-search-provider.ini registers Firefox as a search provider.
+When the file is correctly installed you can see Firefox as a searchable application
+at Settings -> Search at Gnome controll center.
+
+Gnome shell search provider is active only when Firefox is running. When it's active
+you can see it as org.mozilla.Firefox.SearchProvider D-Bus service.
+
diff --git a/browser/components/shell/search-provider-files/firefox-search-provider.ini b/browser/components/shell/search-provider-files/firefox-search-provider.ini
new file mode 100644
index 0000000000..3868e3d528
--- /dev/null
+++ b/browser/components/shell/search-provider-files/firefox-search-provider.ini
@@ -0,0 +1,5 @@
+[Shell Search Provider]
+DesktopId=firefox.desktop
+BusName=org.mozilla.Firefox.SearchProvider
+ObjectPath=/org/mozilla/Firefox/SearchProvider
+Version=2
diff --git a/browser/components/shell/search-provider-files/firefox.desktop b/browser/components/shell/search-provider-files/firefox.desktop
new file mode 100644
index 0000000000..118aae6b73
--- /dev/null
+++ b/browser/components/shell/search-provider-files/firefox.desktop
@@ -0,0 +1,273 @@
+[Desktop Entry]
+Version=1.0
+Name=Firefox
+GenericName=Web Browser
+GenericName[ca]=Navegador web
+GenericName[cs]=Webový prohlížeč
+GenericName[es]=Navegador web
+GenericName[fa]=مرورگر اینترنتی
+GenericName[fi]=WWW-selain
+GenericName[fr]=Navigateur Web
+GenericName[hu]=Webböngésző
+GenericName[it]=Browser Web
+GenericName[ja]=ウェブ・ブラウザ
+GenericName[ko]=웹 브라우저
+GenericName[nb]=Nettleser
+GenericName[nl]=Webbrowser
+GenericName[nn]=Nettlesar
+GenericName[no]=Nettleser
+GenericName[pl]=Przeglądarka WWW
+GenericName[pt]=Navegador Web
+GenericName[pt_BR]=Navegador Web
+GenericName[sk]=Internetový prehliadač
+GenericName[sv]=Webbläsare
+Comment=Browse the Web
+Comment[ca]=Navegueu per el web
+Comment[cs]=Prohlížení stránek World Wide Webu
+Comment[de]=Im Internet surfen
+Comment[es]=Navegue por la web
+Comment[fa]=صفحات شبکه جهانی اینترنت را مرور نمایید
+Comment[fi]=Selaa Internetin WWW-sivuja
+Comment[fr]=Navigue sur Internet
+Comment[hu]=A világháló böngészése
+Comment[it]=Esplora il web
+Comment[ja]=ウェブを閲覧します
+Comment[ko]=웹을 돌아 다닙니다
+Comment[nb]=Surf på nettet
+Comment[nl]=Verken het internet
+Comment[nn]=Surf på nettet
+Comment[no]=Surf på nettet
+Comment[pl]=Przeglądanie stron WWW
+Comment[pt]=Navegue na Internet
+Comment[pt_BR]=Navegue na Internet
+Comment[sk]=Prehliadanie internetu
+Comment[sv]=Surfa på webben
+Exec=firefox %u
+Icon=firefox
+Terminal=false
+Type=Application
+MimeType=text/html;text/xml;application/xhtml+xml;application/vnd.mozilla.xul+xml;text/mml;x-scheme-handler/http;x-scheme-handler/https;
+StartupNotify=true
+Categories=Network;WebBrowser;
+Keywords=web;browser;internet;
+Actions=new-window;new-private-window;
+
+X-Desktop-File-Install-Version=0.24
+
+[Desktop Action new-window]
+Name=Open a New Window
+Name[ach]=Dirica manyen
+Name[af]=Nuwe venster
+Name[an]=Nueva finestra
+Name[ar]=نافذة جديدة
+Name[as]=নতুন উইন্ডো
+Name[ast]=Ventana nueva
+Name[az]=Yeni Pəncərə
+Name[be]=Новае акно
+Name[bg]=Нов прозорец
+Name[bn_BD]=নতুন উইন্ডো (N)
+Name[bn_IN]=নতুন উইন্ডো
+Name[br]=Prenestr nevez
+Name[brx]=गोदान उइन्ड'(N)
+Name[bs]=Novi prozor
+Name[ca]=Finestra nova
+Name[cak]=K'ak'a' tzuwäch
+Name[cs]=Nové okno
+Name[cy]=Ffenestr Newydd
+Name[da]=Nyt vindue
+Name[de]=Neues Fenster
+Name[dsb]=Nowe wokno
+Name[el]=Νέο παράθυρο
+Name[en_GB]=New Window
+Name[en_US]=New Window
+Name[en_ZA]=New Window
+Name[eo]=Nova fenestro
+Name[es_AR]=Nueva ventana
+Name[es_CL]=Nueva ventana
+Name[es_ES]=Nueva ventana
+Name[es_MX]=Nueva ventana
+Name[et]=Uus aken
+Name[eu]=Leiho berria
+Name[fa]=پنجره جدید‌
+Name[ff]=Henorde Hesere
+Name[fi]=Uusi ikkuna
+Name[fr]=Nouvelle fenêtre
+Name[fy_NL]=Nij finster
+Name[ga_IE]=Fuinneog Nua
+Name[gd]=Uinneag ùr
+Name[gl]=Nova xanela
+Name[gn]=Ovetã pyahu
+Name[gu_IN]=નવી વિન્ડો
+Name[he]=חלון חדש
+Name[hi_IN]=नया विंडो
+Name[hr]=Novi prozor
+Name[hsb]=Nowe wokno
+Name[hu]=Új ablak
+Name[hy_AM]=Նոր Պատուհան
+Name[id]=Jendela Baru
+Name[is]=Nýr gluggi
+Name[it]=Nuova finestra
+Name[ja]=新しいウィンドウ
+Name[ja_JP-mac]=新規ウインドウ
+Name[ka]=ახალი ფანჯარა
+Name[kk]=Жаңа терезе
+Name[km]=បង្អួច​​​ថ្មី
+Name[kn]=ಹೊಸ ಕಿಟಕಿ
+Name[ko]=새 창
+Name[kok]=नवें जनेल
+Name[ks]=نئئ وِنڈو
+Name[lij]=Neuvo barcon
+Name[lo]=ຫນ້າຕ່າງໃຫມ່
+Name[lt]=Naujas langas
+Name[ltg]=Jauns lūgs
+Name[lv]=Jauns logs
+Name[mai]=नव विंडो
+Name[mk]=Нов прозорец
+Name[ml]=പുതിയ ജാലകം
+Name[mr]=नवीन पटल
+Name[ms]=Tetingkap Baru
+Name[my]=ဝင်းဒိုးအသစ်
+Name[nb_NO]=Nytt vindu
+Name[ne_NP]=नयाँ सञ्झ्याल
+Name[nl]=Nieuw venster
+Name[nn_NO]=Nytt vindauge
+Name[or]=ନୂତନ ୱିଣ୍ଡୋ
+Name[pa_IN]=ਨਵੀਂ ਵਿੰਡੋ
+Name[pl]=Nowe okno
+Name[pt_BR]=Nova janela
+Name[pt_PT]=Nova janela
+Name[rm]=Nova fanestra
+Name[ro]=Fereastră nouă
+Name[ru]=Новое окно
+Name[sat]=नावा विंडो (N)
+Name[si]=නව කවුළුවක්
+Name[sk]=Nové okno
+Name[sl]=Novo okno
+Name[son]=Zanfun taaga
+Name[sq]=Dritare e Re
+Name[sr]=Нови прозор
+Name[sv_SE]=Nytt fönster
+Name[ta]=புதிய சாளரம்
+Name[te]=కొత్త విండో
+Name[th]=หน้าต่างใหม่
+Name[tr]=Yeni pencere
+Name[tsz]=Eraatarakua jimpani
+Name[uk]=Нове вікно
+Name[ur]=نیا دریچہ
+Name[uz]=Yangi oyna
+Name[vi]=Cửa sổ mới
+Name[wo]=Palanteer bu bees
+Name[xh]=Ifestile entsha
+Name[zh_CN]=新建窗口
+Name[zh_TW]=開新視窗
+
+
+Exec=firefox --new-window %u
+
+[Desktop Action new-private-window]
+Name=Open a New Private Window
+Name[ach]=Dirica manyen me mung
+Name[af]=Nuwe privaatvenster
+Name[an]=Nueva finestra privada
+Name[ar]=نافذة خاصة جديدة
+Name[as]=নতুন ব্যক্তিগত উইন্ডো
+Name[ast]=Ventana privada nueva
+Name[az]=Yeni Məxfi Pəncərə
+Name[be]=Новае акно адасаблення
+Name[bg]=Нов прозорец за поверително сърфиране
+Name[bn_BD]=নতুন ব্যক্তিগত উইন্ডো
+Name[bn_IN]=নতুন ব্যক্তিগত উইন্ডো
+Name[br]=Prenestr merdeiñ prevez nevez
+Name[brx]=गोदान प्राइभेट उइन्ड'
+Name[bs]=Novi privatni prozor
+Name[ca]=Finestra privada nova
+Name[cak]=K'ak'a' ichinan tzuwäch
+Name[cs]=Nové anonymní okno
+Name[cy]=Ffenestr Breifat Newydd
+Name[da]=Nyt privat vindue
+Name[de]=Neues privates Fenster
+Name[dsb]=Nowe priwatne wokno
+Name[el]=Νέο παράθυρο ιδιωτικής περιήγησης
+Name[en_GB]=New Private Window
+Name[en_US]=New Private Window
+Name[en_ZA]=New Private Window
+Name[eo]=Nova privata fenestro
+Name[es_AR]=Nueva ventana privada
+Name[es_CL]=Nueva ventana privada
+Name[es_ES]=Nueva ventana privada
+Name[es_MX]=Nueva ventana privada
+Name[et]=Uus privaatne aken
+Name[eu]=Leiho pribatu berria
+Name[fa]=پنجره ناشناس جدید
+Name[ff]=Henorde Suturo Hesere
+Name[fi]=Uusi yksityinen ikkuna
+Name[fr]=Nouvelle fenêtre de navigation privée
+Name[fy_NL]=Nij priveefinster
+Name[ga_IE]=Fuinneog Nua Phríobháideach
+Name[gd]=Uinneag phrìobhaideach ùr
+Name[gl]=Nova xanela privada
+Name[gn]=Ovetã ñemi pyahu
+Name[gu_IN]=નવી ખાનગી વિન્ડો
+Name[he]=חלון פרטי חדש
+Name[hi_IN]=नयी निजी विंडो
+Name[hr]=Novi privatni prozor
+Name[hsb]=Nowe priwatne wokno
+Name[hu]=Új privát ablak
+Name[hy_AM]=Սկսել Գաղտնի դիտարկում
+Name[id]=Jendela Mode Pribadi Baru
+Name[is]=Nýr huliðsgluggi
+Name[it]=Nuova finestra anonima
+Name[ja]=新しいプライベートウィンドウ
+Name[ja_JP-mac]=新規プライベートウインドウ
+Name[ka]=ახალი პირადი ფანჯარა
+Name[kk]=Жаңа жекелік терезе
+Name[km]=បង្អួច​ឯកជន​ថ្មី
+Name[kn]=ಹೊಸ ಖಾಸಗಿ ಕಿಟಕಿ
+Name[ko]=새 사생활 보호 모드
+Name[kok]=नवो खाजगी विंडो
+Name[ks]=نْو پرایوٹ وینڈو&amp;
+Name[lij]=Neuvo barcon privou
+Name[lo]=ເປີດຫນ້າຕ່າງສວນຕົວຂື້ນມາໃຫມ່
+Name[lt]=Naujas privataus naršymo langas
+Name[ltg]=Jauns privatais lūgs
+Name[lv]=Jauns privātais logs
+Name[mai]=नया निज विंडो (W)
+Name[mk]=Нов приватен прозорец
+Name[ml]=പുതിയ സ്വകാര്യ ജാലകം
+Name[mr]=नवीन वैयक्तिक पटल
+Name[ms]=Tetingkap Persendirian Baharu
+Name[my]=New Private Window
+Name[nb_NO]=Nytt privat vindu
+Name[ne_NP]=नयाँ निजी सञ्झ्याल
+Name[nl]=Nieuw privévenster
+Name[nn_NO]=Nytt privat vindauge
+Name[or]=ନୂତନ ବ୍ୟକ୍ତିଗତ ୱିଣ୍ଡୋ
+Name[pa_IN]=ਨਵੀਂ ਪ੍ਰਾਈਵੇਟ ਵਿੰਡੋ
+Name[pl]=Nowe okno prywatne
+Name[pt_BR]=Nova janela privativa
+Name[pt_PT]=Nova janela privada
+Name[rm]=Nova fanestra privata
+Name[ro]=Fereastră privată nouă
+Name[ru]=Новое приватное окно
+Name[sat]=नावा निजेराक् विंडो (W )
+Name[si]=නව පුද්ගලික කවුළුව (W)
+Name[sk]=Nové okno v režime Súkromné prehliadanie
+Name[sl]=Novo zasebno okno
+Name[son]=Sutura zanfun taaga
+Name[sq]=Dritare e Re Private
+Name[sr]=Нови приватан прозор
+Name[sv_SE]=Nytt privat fönster
+Name[ta]=புதிய தனிப்பட்ட சாளரம்
+Name[te]=కొత్త ఆంతరంగిక విండో
+Name[th]=หน้าต่างส่วนตัวใหม่
+Name[tr]=Yeni gizli pencere
+Name[tsz]=Juchiiti eraatarakua jimpani
+Name[uk]=Приватне вікно
+Name[ur]=نیا نجی دریچہ
+Name[uz]=Yangi maxfiy oyna
+Name[vi]=Cửa sổ riêng tư mới
+Name[wo]=Panlanteeru biir bu bees
+Name[xh]=Ifestile yangasese entsha
+Name[zh_CN]=新建隐私浏览窗口
+Name[zh_TW]=新增隱私視窗
+Exec=firefox --private-window %u
diff --git a/browser/components/shell/test/browser.ini b/browser/components/shell/test/browser.ini
new file mode 100644
index 0000000000..ab69b0835e
--- /dev/null
+++ b/browser/components/shell/test/browser.ini
@@ -0,0 +1,69 @@
+[DEFAULT]
+
+[browser_1119088.js]
+support-files =
+  mac_desktop_image.py
+skip-if = 
+  os != "mac" 
+  verify
+[browser_420786.js]
+skip-if = os != "linux"
+[browser_633221.js]
+skip-if = os != "linux"
+[browser_doesAppNeedPin.js]
+[browser_headless_screenshot_1.js]
+support-files =
+  head.js
+  headless.html
+skip-if = 
+  os == 'win' 
+  ccov
+  tsan #Bug 1429950 , Bug 1583315, Bug 1696109, Bug 1701449
+[browser_headless_screenshot_2.js]
+support-files =
+  head.js
+  headless.html
+skip-if = 
+  os == 'win' 
+  ccov
+  tsan #Bug 1429950 , Bug 1583315, Bug 1696109, Bug 1701449
+[browser_headless_screenshot_3.js]
+support-files =
+  head.js
+  headless.html
+skip-if = 
+  os == 'win' 
+  ccov 
+  tsan #Bug 1429950 , Bug 1583315, Bug 1696109, Bug 1701449
+[browser_headless_screenshot_4.js]
+support-files =
+  head.js
+  headless.html
+skip-if = 
+  os == 'win' 
+  ccov 
+  tsan #Bug 1429950 , Bug 1583315, Bug 1696109, Bug 1701449
+[browser_headless_screenshot_cross_origin.js]
+support-files =
+  head.js
+  headless_cross_origin.html
+  headless_iframe.html
+skip-if = 
+  os == 'win' 
+  ccov
+  tsan #Bug 1429950 , Bug 1583315, Bug 1696109, Bug 1701449
+[browser_headless_screenshot_redirect.js]
+support-files =
+  head.js
+  headless.html
+  headless_redirect.html
+  headless_redirect.html^headers^
+skip-if = 
+  os == 'win' 
+  ccov
+  tsan #Bug 1429950 , Bug 1583315, Bug 1696109, Bug 1701449
+[browser_setDefaultBrowser.js]
+[browser_setDefaultPDFHandler.js]
+run-if = os == "win" && os_version != "6.1"
+reason = Test is Windows 10+.
+[browser_setDesktopBackgroundPreview.js]
diff --git a/browser/components/shell/test/browser_1119088.js b/browser/components/shell/test/browser_1119088.js
new file mode 100644
index 0000000000..bc0995fe51
--- /dev/null
+++ b/browser/components/shell/test/browser_1119088.js
@@ -0,0 +1,167 @@
+// Where we save the desktop background to (~/Pictures).
+const NS_OSX_PICTURE_DOCUMENTS_DIR = "Pct";
+
+// Paths used to run the CLI command (python script) that is used to
+// 1) check the desktop background image matches what we set it to via
+//    nsIShellService::setDesktopBackground() and
+// 2) revert the desktop background image to the OS default
+const kPythonPath = "/usr/bin/python";
+const kDesktopCheckerScriptPath =
+  "browser/browser/components/shell/test/mac_desktop_image.py";
+const kDefaultBackgroundImage_10_14 =
+  "/Library/Desktop Pictures/Solid Colors/Teal.png";
+const kDefaultBackgroundImage_10_15 =
+  "/System/Library/Desktop Pictures/Solid Colors/Teal.png";
+
+ChromeUtils.defineESModuleGetters(this, {
+  FileUtils: "resource://gre/modules/FileUtils.sys.mjs",
+});
+
+function getPythonExecutableFile() {
+  let python = Cc["@mozilla.org/file/local;1"].createInstance(Ci.nsIFile);
+  python.initWithPath(kPythonPath);
+  return python;
+}
+
+function createProcess() {
+  return Cc["@mozilla.org/process/util;1"].createInstance(Ci.nsIProcess);
+}
+
+// Use a CLI command to set the desktop background to |imagePath|. Returns the
+// exit code of the CLI command which reflects whether or not the background
+// image was successfully set. Returns 0 on success.
+function setDesktopBackgroundCLI(imagePath) {
+  let setBackgroundProcess = createProcess();
+  setBackgroundProcess.init(getPythonExecutableFile());
+  let args = [
+    kDesktopCheckerScriptPath,
+    "--verbose",
+    "--set-background-image",
+    imagePath,
+  ];
+  setBackgroundProcess.run(true, args, args.length);
+  return setBackgroundProcess.exitValue;
+}
+
+// Check the desktop background is |imagePath| using a CLI command.
+// Returns the exit code of the CLI command which reflects whether or not
+// the provided image path matches the path of the current desktop background
+// image. A return value of 0 indicates success/match.
+function checkDesktopBackgroundCLI(imagePath) {
+  let checkBackgroundProcess = createProcess();
+  checkBackgroundProcess.init(getPythonExecutableFile());
+  let args = [
+    kDesktopCheckerScriptPath,
+    "--verbose",
+    "--check-background-image",
+    imagePath,
+  ];
+  checkBackgroundProcess.run(true, args, args.length);
+  return checkBackgroundProcess.exitValue;
+}
+
+// Use the python script to set/check the desktop background is |imagePath|
+function setAndCheckDesktopBackgroundCLI(imagePath) {
+  Assert.ok(FileUtils.File(imagePath).exists(), `${imagePath} exists`);
+
+  let setExitCode = setDesktopBackgroundCLI(imagePath);
+  Assert.ok(setExitCode == 0, `Setting background via CLI to ${imagePath}`);
+
+  let checkExitCode = checkDesktopBackgroundCLI(imagePath);
+  Assert.ok(checkExitCode == 0, `Checking background via CLI is ${imagePath}`);
+}
+
+// Restore the automation default background image. i.e., the default used
+// in the automated test environment, not the OS default.
+function restoreDefaultBackground() {
+  let defaultBackgroundPath;
+  if (AppConstants.isPlatformAndVersionAtLeast("macosx", 19)) {
+    defaultBackgroundPath = kDefaultBackgroundImage_10_15;
+  } else {
+    defaultBackgroundPath = kDefaultBackgroundImage_10_14;
+  }
+  setAndCheckDesktopBackgroundCLI(defaultBackgroundPath);
+}
+
+/**
+ * Tests "Set As Desktop Background" platform implementation on macOS.
+ *
+ * Sets the desktop background image to the browser logo from the about:logo
+ * page and verifies it was set successfully. Setting the desktop background
+ * (which uses the nsIShellService::setDesktopBackground() interface method)
+ * downloads the image to ~/Pictures using a unique file name and sets the
+ * desktop background to the downloaded file leaving the download in place.
+ * After setDesktopBackground() is called, the test uses a python script to
+ * validate that the current desktop background is in fact set to the
+ * downloaded logo.
+ */
+add_task(async function () {
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: "about:logo",
+    },
+    async browser => {
+      let dirSvc = Cc["@mozilla.org/file/directory_service;1"].getService(
+        Ci.nsIDirectoryServiceProvider
+      );
+      let uuidGenerator = Services.uuid;
+      let shellSvc = Cc["@mozilla.org/browser/shell-service;1"].getService(
+        Ci.nsIShellService
+      );
+
+      // Ensure we are starting with the default background. Log a
+      // failure if we can not set the background to the default, but
+      // ignore the case where the background is not already set as that
+      // that may be due to a previous test failure.
+      restoreDefaultBackground();
+
+      // Generate a UUID (with non-alphanumberic characters removed) to build
+      // up a filename for the desktop background. Use a UUID to distinguish
+      // between runs so we won't be confused by images that were not properly
+      // cleaned up after previous runs.
+      let uuid = uuidGenerator.generateUUID().toString().replace(/\W/g, "");
+
+      // Set the background image path to be $HOME/Pictures/<UUID>.png.
+      // nsIShellService.setDesktopBackground() downloads the image to this
+      // path and then sets it as the desktop background image, leaving the
+      // image in place.
+      let backgroundImage = dirSvc.getFile(NS_OSX_PICTURE_DOCUMENTS_DIR, {});
+      backgroundImage.append(uuid + ".png");
+      if (backgroundImage.exists()) {
+        backgroundImage.remove(false);
+      }
+
+      // For simplicity, we're going to reach in and access the image on the
+      // page directly, which means the page shouldn't be running in a remote
+      // browser. Thankfully, about:logo runs in the parent process for now.
+      Assert.ok(
+        !gBrowser.selectedBrowser.isRemoteBrowser,
+        "image can be accessed synchronously from the parent process"
+      );
+      let image = gBrowser.selectedBrowser.contentDocument.images[0];
+
+      info(`Setting/saving desktop background to ${backgroundImage.path}`);
+
+      // Saves the file in ~/Pictures
+      shellSvc.setDesktopBackground(image, 0, backgroundImage.leafName);
+
+      await BrowserTestUtils.waitForCondition(() => backgroundImage.exists());
+      info(`${backgroundImage.path} downloaded`);
+      Assert.ok(
+        FileUtils.File(backgroundImage.path).exists(),
+        `${backgroundImage.path} exists`
+      );
+
+      // Check that the desktop background image is the image we set above.
+      let exitCode = checkDesktopBackgroundCLI(backgroundImage.path);
+      Assert.ok(exitCode == 0, `background should be ${backgroundImage.path}`);
+
+      // Restore the background image to the Mac default.
+      restoreDefaultBackground();
+
+      // We no longer need the downloaded image.
+      backgroundImage.remove(false);
+    }
+  );
+});
diff --git a/browser/components/shell/test/browser_420786.js b/browser/components/shell/test/browser_420786.js
new file mode 100644
index 0000000000..025cd87943
--- /dev/null
+++ b/browser/components/shell/test/browser_420786.js
@@ -0,0 +1,105 @@
+const DG_BACKGROUND = "/desktop/gnome/background";
+const DG_IMAGE_KEY = DG_BACKGROUND + "/picture_filename";
+const DG_OPTION_KEY = DG_BACKGROUND + "/picture_options";
+const DG_DRAW_BG_KEY = DG_BACKGROUND + "/draw_background";
+
+const GS_BG_SCHEMA = "org.gnome.desktop.background";
+const GS_IMAGE_KEY = "picture-uri";
+const GS_OPTION_KEY = "picture-options";
+const GS_DRAW_BG_KEY = "draw-background";
+
+add_task(async function () {
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: "about:logo",
+    },
+    browser => {
+      var brandName = Services.strings
+        .createBundle("chrome://branding/locale/brand.properties")
+        .GetStringFromName("brandShortName");
+
+      var dirSvc = Cc["@mozilla.org/file/directory_service;1"].getService(
+        Ci.nsIDirectoryServiceProvider
+      );
+      var homeDir = dirSvc.getFile("Home", {});
+
+      var wpFile = homeDir.clone();
+      wpFile.append(brandName + "_wallpaper.png");
+
+      // Backup the existing wallpaper so that this test doesn't change the user's
+      // settings.
+      var wpFileBackup = homeDir.clone();
+      wpFileBackup.append(brandName + "_wallpaper.png.backup");
+
+      if (wpFileBackup.exists()) {
+        wpFileBackup.remove(false);
+      }
+
+      if (wpFile.exists()) {
+        wpFile.copyTo(null, wpFileBackup.leafName);
+      }
+
+      var shell = Cc["@mozilla.org/browser/shell-service;1"].getService(
+        Ci.nsIShellService
+      );
+
+      // For simplicity, we're going to reach in and access the image on the
+      // page directly, which means the page shouldn't be running in a remote
+      // browser. Thankfully, about:logo runs in the parent process for now.
+      Assert.ok(
+        !gBrowser.selectedBrowser.isRemoteBrowser,
+        "image can be accessed synchronously from the parent process"
+      );
+
+      var image = content.document.images[0];
+
+      let checkWallpaper, restoreSettings;
+      try {
+        // Try via GSettings first
+        const gsettings = Cc["@mozilla.org/gsettings-service;1"]
+          .getService(Ci.nsIGSettingsService)
+          .getCollectionForSchema(GS_BG_SCHEMA);
+
+        const prevImage = gsettings.getString(GS_IMAGE_KEY);
+        const prevOption = gsettings.getString(GS_OPTION_KEY);
+        const prevDrawBG = gsettings.getBoolean(GS_DRAW_BG_KEY);
+
+        checkWallpaper = function (position, expectedGSettingsPosition) {
+          shell.setDesktopBackground(image, position, "");
+          ok(wpFile.exists(), "Wallpaper was written to disk");
+          is(
+            gsettings.getString(GS_IMAGE_KEY),
+            encodeURI("file://" + wpFile.path),
+            "Wallpaper file GSettings key is correct"
+          );
+          is(
+            gsettings.getString(GS_OPTION_KEY),
+            expectedGSettingsPosition,
+            "Wallpaper position GSettings key is correct"
+          );
+        };
+
+        restoreSettings = function () {
+          gsettings.setString(GS_IMAGE_KEY, prevImage);
+          gsettings.setString(GS_OPTION_KEY, prevOption);
+          gsettings.setBoolean(GS_DRAW_BG_KEY, prevDrawBG);
+        };
+      } catch (e) {}
+
+      checkWallpaper(Ci.nsIShellService.BACKGROUND_TILE, "wallpaper");
+      checkWallpaper(Ci.nsIShellService.BACKGROUND_STRETCH, "stretched");
+      checkWallpaper(Ci.nsIShellService.BACKGROUND_CENTER, "centered");
+      checkWallpaper(Ci.nsIShellService.BACKGROUND_FILL, "zoom");
+      checkWallpaper(Ci.nsIShellService.BACKGROUND_FIT, "scaled");
+      checkWallpaper(Ci.nsIShellService.BACKGROUND_SPAN, "spanned");
+
+      restoreSettings();
+
+      // Restore files
+      if (wpFileBackup.exists()) {
+        wpFileBackup.moveTo(null, wpFile.leafName);
+      }
+    }
+  );
+});
diff --git a/browser/components/shell/test/browser_633221.js b/browser/components/shell/test/browser_633221.js
new file mode 100644
index 0000000000..0bea31728a
--- /dev/null
+++ b/browser/components/shell/test/browser_633221.js
@@ -0,0 +1,11 @@
+function test() {
+  ShellService.setDefaultBrowser(true, false);
+  ok(
+    ShellService.isDefaultBrowser(true, false),
+    "we got here and are the default browser"
+  );
+  ok(
+    ShellService.isDefaultBrowser(true, true),
+    "we got here and are the default browser"
+  );
+}
diff --git a/browser/components/shell/test/browser_doesAppNeedPin.js b/browser/components/shell/test/browser_doesAppNeedPin.js
new file mode 100644
index 0000000000..e5dc25faf8
--- /dev/null
+++ b/browser/components/shell/test/browser_doesAppNeedPin.js
@@ -0,0 +1,54 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+ChromeUtils.defineESModuleGetters(this, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
+});
+
+registerCleanupFunction(() => {
+  ExperimentAPI._store._deleteForTests("shellService");
+});
+
+let defaultValue;
+add_task(async function default_need() {
+  defaultValue = await ShellService.doesAppNeedPin();
+
+  Assert.ok(defaultValue !== undefined, "Got a default app need pin value");
+});
+
+add_task(async function remote_disable() {
+  if (defaultValue === false) {
+    info("Default pin already false, so nothing to test");
+    return;
+  }
+
+  let doCleanup = await ExperimentFakes.enrollWithRollout({
+    featureId: NimbusFeatures.shellService.featureId,
+    value: { disablePin: true, enabled: true },
+  });
+
+  Assert.equal(
+    await ShellService.doesAppNeedPin(),
+    false,
+    "Pinning disabled via nimbus"
+  );
+
+  await doCleanup();
+});
+
+add_task(async function restore_default() {
+  if (defaultValue === undefined) {
+    info("No default pin value set, so nothing to test");
+    return;
+  }
+
+  ExperimentAPI._store._deleteForTests("shellService");
+
+  Assert.equal(
+    await ShellService.doesAppNeedPin(),
+    defaultValue,
+    "Pinning restored to original"
+  );
+});
diff --git a/browser/components/shell/test/browser_headless_screenshot_1.js b/browser/components/shell/test/browser_headless_screenshot_1.js
new file mode 100644
index 0000000000..b5f84f0f66
--- /dev/null
+++ b/browser/components/shell/test/browser_headless_screenshot_1.js
@@ -0,0 +1,74 @@
+"use strict";
+
+add_task(async function () {
+  // Test all four basic variations of the "screenshot" argument
+  // when a file path is specified.
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "-screenshot",
+      screenshotPath,
+    ],
+    screenshotPath
+  );
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      `-screenshot=${screenshotPath}`,
+    ],
+    screenshotPath
+  );
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "--screenshot",
+      screenshotPath,
+    ],
+    screenshotPath
+  );
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      `--screenshot=${screenshotPath}`,
+    ],
+    screenshotPath
+  );
+
+  // Test when the requested URL redirects
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless_redirect.html",
+      "-screenshot",
+      screenshotPath,
+    ],
+    screenshotPath
+  );
+
+  // Test with additional command options
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "-screenshot",
+      screenshotPath,
+      "-attach-console",
+    ],
+    screenshotPath
+  );
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "-attach-console",
+      "-screenshot",
+      screenshotPath,
+      "-headless",
+    ],
+    screenshotPath
+  );
+});
diff --git a/browser/components/shell/test/browser_headless_screenshot_2.js b/browser/components/shell/test/browser_headless_screenshot_2.js
new file mode 100644
index 0000000000..871895b45d
--- /dev/null
+++ b/browser/components/shell/test/browser_headless_screenshot_2.js
@@ -0,0 +1,48 @@
+"use strict";
+add_task(async function () {
+  const cwdScreenshotPath = PathUtils.join(
+    Services.dirsvc.get("CurWorkD", Ci.nsIFile).path,
+    "screenshot.png"
+  );
+
+  // Test variations of the "screenshot" argument when a file path
+  // isn't specified.
+  await testFileCreationPositive(
+    [
+      "-screenshot",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+    ],
+    cwdScreenshotPath
+  );
+  await testFileCreationPositive(
+    [
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "-screenshot",
+    ],
+    cwdScreenshotPath
+  );
+  await testFileCreationPositive(
+    [
+      "--screenshot",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+    ],
+    cwdScreenshotPath
+  );
+  await testFileCreationPositive(
+    [
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "--screenshot",
+    ],
+    cwdScreenshotPath
+  );
+
+  // Test with additional command options
+  await testFileCreationPositive(
+    [
+      "--screenshot",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "-attach-console",
+    ],
+    cwdScreenshotPath
+  );
+});
diff --git a/browser/components/shell/test/browser_headless_screenshot_3.js b/browser/components/shell/test/browser_headless_screenshot_3.js
new file mode 100644
index 0000000000..b55635652d
--- /dev/null
+++ b/browser/components/shell/test/browser_headless_screenshot_3.js
@@ -0,0 +1,59 @@
+"use strict";
+
+add_task(async function () {
+  const cwdScreenshotPath = PathUtils.join(
+    Services.dirsvc.get("CurWorkD", Ci.nsIFile).path,
+    "screenshot.png"
+  );
+
+  // Test invalid URL arguments (either no argument or too many arguments).
+  await testFileCreationNegative(["-screenshot"], cwdScreenshotPath);
+  await testFileCreationNegative(
+    [
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "http://mochi.test:8888/headless.html",
+      "-screenshot",
+    ],
+    cwdScreenshotPath
+  );
+
+  // Test all four basic variations of the "window-size" argument.
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "-screenshot",
+      "-window-size",
+      "800",
+    ],
+    cwdScreenshotPath
+  );
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "-screenshot",
+      "-window-size=800",
+    ],
+    cwdScreenshotPath
+  );
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "-screenshot",
+      "--window-size",
+      "800",
+    ],
+    cwdScreenshotPath
+  );
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "-screenshot",
+      "--window-size=800",
+    ],
+    cwdScreenshotPath
+  );
+});
diff --git a/browser/components/shell/test/browser_headless_screenshot_4.js b/browser/components/shell/test/browser_headless_screenshot_4.js
new file mode 100644
index 0000000000..4b93ba516e
--- /dev/null
+++ b/browser/components/shell/test/browser_headless_screenshot_4.js
@@ -0,0 +1,31 @@
+"use strict";
+
+add_task(async function () {
+  const cwdScreenshotPath = PathUtils.join(
+    Services.dirsvc.get("CurWorkD", Ci.nsIFile).path,
+    "screenshot.png"
+  );
+  // Test other variations of the "window-size" argument.
+  await testWindowSizePositive(800, 600);
+  await testWindowSizePositive(1234);
+  await testFileCreationNegative(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "-screenshot",
+      "-window-size",
+      "hello",
+    ],
+    cwdScreenshotPath
+  );
+  await testFileCreationNegative(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+      "-screenshot",
+      "-window-size",
+      "800,",
+    ],
+    cwdScreenshotPath
+  );
+});
diff --git a/browser/components/shell/test/browser_headless_screenshot_cross_origin.js b/browser/components/shell/test/browser_headless_screenshot_cross_origin.js
new file mode 100644
index 0000000000..9547773581
--- /dev/null
+++ b/browser/components/shell/test/browser_headless_screenshot_cross_origin.js
@@ -0,0 +1,9 @@
+"use strict";
+
+add_task(async function () {
+  // Test cross origin iframes work.
+  await testGreen(
+    "http://mochi.test:8888/browser/browser/components/shell/test/headless_cross_origin.html",
+    screenshotPath
+  );
+});
diff --git a/browser/components/shell/test/browser_headless_screenshot_redirect.js b/browser/components/shell/test/browser_headless_screenshot_redirect.js
new file mode 100644
index 0000000000..c50b847b62
--- /dev/null
+++ b/browser/components/shell/test/browser_headless_screenshot_redirect.js
@@ -0,0 +1,14 @@
+"use strict";
+
+add_task(async function () {
+  // Test when the requested URL redirects
+  await testFileCreationPositive(
+    [
+      "-url",
+      "http://mochi.test:8888/browser/browser/components/shell/test/headless_redirect.html",
+      "-screenshot",
+      screenshotPath,
+    ],
+    screenshotPath
+  );
+});
diff --git a/browser/components/shell/test/browser_setDefaultBrowser.js b/browser/components/shell/test/browser_setDefaultBrowser.js
new file mode 100644
index 0000000000..ecf7fcb303
--- /dev/null
+++ b/browser/components/shell/test/browser_setDefaultBrowser.js
@@ -0,0 +1,146 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+ChromeUtils.defineESModuleGetters(this, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
+  sinon: "resource://testing-common/Sinon.sys.mjs",
+});
+
+const _handleWDBAResultStub = sinon
+  .stub(ShellService, "_handleWDBAResult")
+  .callsFake(async () => {
+    throw new Error("from _handleWDBAResultStub");
+  });
+
+const _callExternalDefaultBrowserAgentStub = sinon
+  .stub(ShellService, "_callExternalDefaultBrowserAgent")
+  .callsFake(async () => ({
+    async wait() {
+      return { exitCode: 0 };
+    },
+  }));
+
+const _userChoiceImpossibleTelemetryResultStub = sinon
+  .stub(ShellService, "_userChoiceImpossibleTelemetryResult")
+  .callsFake(() => null);
+
+const userChoiceStub = sinon
+  .stub(ShellService, "setAsDefaultUserChoice")
+  .resolves();
+const setDefaultStub = sinon.stub();
+const shellStub = sinon
+  .stub(ShellService, "shellService")
+  .value({ setDefaultBrowser: setDefaultStub });
+
+registerCleanupFunction(() => {
+  _handleWDBAResultStub.restore();
+  _callExternalDefaultBrowserAgentStub.restore();
+  _userChoiceImpossibleTelemetryResultStub.restore();
+  userChoiceStub.restore();
+  shellStub.restore();
+
+  ExperimentAPI._store._deleteForTests("shellService");
+});
+
+let defaultUserChoice;
+add_task(async function need_user_choice() {
+  ShellService.setDefaultBrowser();
+  defaultUserChoice = userChoiceStub.called;
+
+  Assert.ok(
+    defaultUserChoice !== undefined,
+    "Decided which default browser method to use"
+  );
+  Assert.equal(
+    setDefaultStub.notCalled,
+    defaultUserChoice,
+    "Only one default behavior was used"
+  );
+});
+
+add_task(async function remote_disable() {
+  if (defaultUserChoice === false) {
+    info("Default behavior already not user choice, so nothing to test");
+    return;
+  }
+
+  userChoiceStub.resetHistory();
+  setDefaultStub.resetHistory();
+  let doCleanup = await ExperimentFakes.enrollWithRollout({
+    featureId: NimbusFeatures.shellService.featureId,
+    value: {
+      setDefaultBrowserUserChoice: false,
+      enabled: true,
+    },
+  });
+
+  ShellService.setDefaultBrowser();
+
+  Assert.ok(
+    userChoiceStub.notCalled,
+    "Set default with user choice disabled via nimbus"
+  );
+  Assert.ok(setDefaultStub.called, "Used plain set default insteead");
+
+  await doCleanup();
+});
+
+add_task(async function restore_default() {
+  if (defaultUserChoice === undefined) {
+    info("No default user choice behavior set, so nothing to test");
+    return;
+  }
+
+  userChoiceStub.resetHistory();
+  setDefaultStub.resetHistory();
+  ExperimentAPI._store._deleteForTests("shellService");
+
+  ShellService.setDefaultBrowser();
+
+  Assert.equal(
+    userChoiceStub.called,
+    defaultUserChoice,
+    "Set default with user choice restored to original"
+  );
+  Assert.equal(
+    setDefaultStub.notCalled,
+    defaultUserChoice,
+    "Plain set default behavior restored to original"
+  );
+});
+
+add_task(async function ensure_fallback() {
+  if (!AppConstants.isPlatformAndVersionAtLeast("win", "10")) {
+    info("Nothing to test on non-Windows");
+    return;
+  }
+
+  let userChoicePromise = Promise.resolve();
+  userChoiceStub.callsFake(function (...args) {
+    return (userChoicePromise = userChoiceStub.wrappedMethod.apply(this, args));
+  });
+  userChoiceStub.resetHistory();
+  setDefaultStub.resetHistory();
+  let doCleanup = await ExperimentFakes.enrollWithRollout({
+    featureId: NimbusFeatures.shellService.featureId,
+    value: {
+      setDefaultBrowserUserChoice: true,
+      setDefaultPDFHandler: false,
+      enabled: true,
+    },
+  });
+
+  ShellService.setDefaultBrowser();
+
+  Assert.ok(userChoiceStub.called, "Set default with user choice called");
+
+  let thrown = false;
+  await userChoicePromise.catch(() => (thrown = true));
+
+  Assert.ok(thrown, "Set default with user choice threw an error");
+  Assert.ok(setDefaultStub.called, "Fallbacked to plain set default");
+
+  await doCleanup();
+});
diff --git a/browser/components/shell/test/browser_setDefaultPDFHandler.js b/browser/components/shell/test/browser_setDefaultPDFHandler.js
new file mode 100644
index 0000000000..3314a4cf21
--- /dev/null
+++ b/browser/components/shell/test/browser_setDefaultPDFHandler.js
@@ -0,0 +1,291 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+ChromeUtils.defineESModuleGetters(this, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
+  sinon: "resource://testing-common/Sinon.sys.mjs",
+});
+
+XPCOMUtils.defineLazyServiceGetter(
+  this,
+  "XreDirProvider",
+  "@mozilla.org/xre/directory-provider;1",
+  "nsIXREDirProvider"
+);
+
+const _callExternalDefaultBrowserAgentStub = sinon
+  .stub(ShellService, "_callExternalDefaultBrowserAgent")
+  .callsFake(async () => ({
+    async wait() {
+      return { exitCode: 0 };
+    },
+  }));
+
+const _userChoiceImpossibleTelemetryResultStub = sinon
+  .stub(ShellService, "_userChoiceImpossibleTelemetryResult")
+  .callsFake(() => null);
+
+// Ensure we don't fall back to a real implementation.
+const setDefaultStub = sinon.stub();
+// We'll dynamically update this as needed during the tests.
+const queryCurrentDefaultHandlerForStub = sinon.stub();
+const shellStub = sinon.stub(ShellService, "shellService").value({
+  setDefaultBrowser: setDefaultStub,
+  queryCurrentDefaultHandlerFor: queryCurrentDefaultHandlerForStub,
+});
+
+registerCleanupFunction(() => {
+  _callExternalDefaultBrowserAgentStub.restore();
+  _userChoiceImpossibleTelemetryResultStub.restore();
+  shellStub.restore();
+
+  ExperimentAPI._store._deleteForTests("shellService");
+});
+
+add_task(async function ready() {
+  await ExperimentAPI.ready();
+});
+
+// Everything here is Windows 10+.
+Assert.ok(
+  AppConstants.isPlatformAndVersionAtLeast("win", "10"),
+  "Windows version 10+"
+);
+
+add_task(async function remoteEnableWithPDF() {
+  let doCleanup = await ExperimentFakes.enrollWithRollout({
+    featureId: NimbusFeatures.shellService.featureId,
+    value: {
+      setDefaultBrowserUserChoice: true,
+      setDefaultPDFHandlerOnlyReplaceBrowsers: false,
+      setDefaultPDFHandler: true,
+      enabled: true,
+    },
+  });
+
+  Assert.equal(
+    NimbusFeatures.shellService.getVariable("setDefaultBrowserUserChoice"),
+    true
+  );
+  Assert.equal(
+    NimbusFeatures.shellService.getVariable("setDefaultPDFHandler"),
+    true
+  );
+
+  _callExternalDefaultBrowserAgentStub.resetHistory();
+  ShellService.setDefaultBrowser();
+
+  const aumi = XreDirProvider.getInstallHash();
+  Assert.ok(_callExternalDefaultBrowserAgentStub.called);
+  Assert.deepEqual(_callExternalDefaultBrowserAgentStub.firstCall.args, [
+    {
+      arguments: [
+        "set-default-browser-user-choice",
+        aumi,
+        ".pdf",
+        "FirefoxPDF",
+      ],
+    },
+  ]);
+
+  await doCleanup();
+});
+
+add_task(async function remoteEnableWithPDF_testOnlyReplaceBrowsers() {
+  let doCleanup = await ExperimentFakes.enrollWithRollout({
+    featureId: NimbusFeatures.shellService.featureId,
+    value: {
+      setDefaultBrowserUserChoice: true,
+      setDefaultPDFHandlerOnlyReplaceBrowsers: true,
+      setDefaultPDFHandler: true,
+      enabled: true,
+    },
+  });
+
+  Assert.equal(
+    NimbusFeatures.shellService.getVariable("setDefaultBrowserUserChoice"),
+    true
+  );
+  Assert.equal(
+    NimbusFeatures.shellService.getVariable("setDefaultPDFHandler"),
+    true
+  );
+  Assert.equal(
+    NimbusFeatures.shellService.getVariable(
+      "setDefaultPDFHandlerOnlyReplaceBrowsers"
+    ),
+    true
+  );
+
+  const aumi = XreDirProvider.getInstallHash();
+
+  // We'll take the default from a missing association or a known browser.
+  for (let progId of ["", "MSEdgePDF"]) {
+    queryCurrentDefaultHandlerForStub.callsFake(() => progId);
+
+    _callExternalDefaultBrowserAgentStub.resetHistory();
+    ShellService.setDefaultBrowser();
+
+    Assert.ok(_callExternalDefaultBrowserAgentStub.called);
+    Assert.deepEqual(
+      _callExternalDefaultBrowserAgentStub.firstCall.args,
+      [
+        {
+          arguments: [
+            "set-default-browser-user-choice",
+            aumi,
+            ".pdf",
+            "FirefoxPDF",
+          ],
+        },
+      ],
+      `Will take default from missing association or known browser with ProgID '${progId}'`
+    );
+  }
+
+  // But not from a non-browser.
+  queryCurrentDefaultHandlerForStub.callsFake(() => "Acrobat.Document.DC");
+
+  _callExternalDefaultBrowserAgentStub.resetHistory();
+  ShellService.setDefaultBrowser();
+
+  Assert.ok(_callExternalDefaultBrowserAgentStub.called);
+  Assert.deepEqual(
+    _callExternalDefaultBrowserAgentStub.firstCall.args,
+    [{ arguments: ["set-default-browser-user-choice", aumi] }],
+    `Will not take default from non-browser`
+  );
+
+  await doCleanup();
+});
+
+add_task(async function remoteEnableWithoutPDF() {
+  let doCleanup = await ExperimentFakes.enrollWithRollout({
+    featureId: NimbusFeatures.shellService.featureId,
+    value: {
+      setDefaultBrowserUserChoice: true,
+      setDefaultPDFHandler: false,
+      enabled: true,
+    },
+  });
+
+  Assert.equal(
+    NimbusFeatures.shellService.getVariable("setDefaultBrowserUserChoice"),
+    true
+  );
+  Assert.equal(
+    NimbusFeatures.shellService.getVariable("setDefaultPDFHandler"),
+    false
+  );
+
+  _callExternalDefaultBrowserAgentStub.resetHistory();
+  ShellService.setDefaultBrowser();
+
+  const aumi = XreDirProvider.getInstallHash();
+  Assert.ok(_callExternalDefaultBrowserAgentStub.called);
+  Assert.deepEqual(_callExternalDefaultBrowserAgentStub.firstCall.args, [
+    { arguments: ["set-default-browser-user-choice", aumi] },
+  ]);
+
+  await doCleanup();
+});
+
+add_task(async function remoteDisable() {
+  let doCleanup = await ExperimentFakes.enrollWithRollout({
+    featureId: NimbusFeatures.shellService.featureId,
+    value: {
+      setDefaultBrowserUserChoice: false,
+      setDefaultPDFHandler: true,
+      enabled: false,
+    },
+  });
+
+  Assert.equal(
+    NimbusFeatures.shellService.getVariable("setDefaultBrowserUserChoice"),
+    false
+  );
+  Assert.equal(
+    NimbusFeatures.shellService.getVariable("setDefaultPDFHandler"),
+    true
+  );
+
+  _callExternalDefaultBrowserAgentStub.resetHistory();
+  ShellService.setDefaultBrowser();
+
+  Assert.ok(_callExternalDefaultBrowserAgentStub.notCalled);
+  Assert.ok(setDefaultStub.called);
+
+  await doCleanup();
+});
+
+add_task(async function test_setAsDefaultPDFHandler_knownBrowser() {
+  const sandbox = sinon.createSandbox();
+
+  const aumi = XreDirProvider.getInstallHash();
+  const expectedArguments = [
+    "set-default-extension-handlers-user-choice",
+    aumi,
+    ".pdf",
+    "FirefoxPDF",
+  ];
+
+  try {
+    const pdfHandlerResult = { registered: true, knownBrowser: true };
+    sandbox
+      .stub(ShellService, "getDefaultPDFHandler")
+      .returns(pdfHandlerResult);
+
+    info("Testing setAsDefaultPDFHandler(true) when knownBrowser = true");
+    ShellService.setAsDefaultPDFHandler(true);
+    Assert.ok(
+      _callExternalDefaultBrowserAgentStub.called,
+      "Called default browser agent"
+    );
+    Assert.deepEqual(
+      _callExternalDefaultBrowserAgentStub.firstCall.args,
+      [{ arguments: expectedArguments }],
+      "Called default browser agent with expected arguments"
+    );
+    _callExternalDefaultBrowserAgentStub.resetHistory();
+
+    info("Testing setAsDefaultPDFHandler(false) when knownBrowser = true");
+    ShellService.setAsDefaultPDFHandler(false);
+    Assert.ok(
+      _callExternalDefaultBrowserAgentStub.called,
+      "Called default browser agent"
+    );
+    Assert.deepEqual(
+      _callExternalDefaultBrowserAgentStub.firstCall.args,
+      [{ arguments: expectedArguments }],
+      "Called default browser agent with expected arguments"
+    );
+    _callExternalDefaultBrowserAgentStub.resetHistory();
+
+    pdfHandlerResult.knownBrowser = false;
+
+    info("Testing setAsDefaultPDFHandler(true) when knownBrowser = false");
+    ShellService.setAsDefaultPDFHandler(true);
+    Assert.ok(
+      _callExternalDefaultBrowserAgentStub.notCalled,
+      "Did not call default browser agent"
+    );
+    _callExternalDefaultBrowserAgentStub.resetHistory();
+
+    info("Testing setAsDefaultPDFHandler(false) when knownBrowser = false");
+    ShellService.setAsDefaultPDFHandler(false);
+    Assert.ok(
+      _callExternalDefaultBrowserAgentStub.called,
+      "Called default browser agent"
+    );
+    Assert.deepEqual(
+      _callExternalDefaultBrowserAgentStub.firstCall.args,
+      [{ arguments: expectedArguments }],
+      "Called default browser agent with expected arguments"
+    );
+    _callExternalDefaultBrowserAgentStub.resetHistory();
+  } finally {
+    sandbox.restore();
+  }
+});
diff --git a/browser/components/shell/test/browser_setDesktopBackgroundPreview.js b/browser/components/shell/test/browser_setDesktopBackgroundPreview.js
new file mode 100644
index 0000000000..b2dbe13db8
--- /dev/null
+++ b/browser/components/shell/test/browser_setDesktopBackgroundPreview.js
@@ -0,0 +1,87 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Check whether the preview image for setDesktopBackground is rendered
+ * correctly, without stretching
+ */
+
+add_task(async function () {
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: "about:logo",
+    },
+    async browser => {
+      const dialogLoad = BrowserTestUtils.domWindowOpened(null, async win => {
+        await BrowserTestUtils.waitForEvent(win, "load");
+        Assert.equal(
+          win.document.documentElement.getAttribute("windowtype"),
+          "Shell:SetDesktopBackground",
+          "Opened correct window"
+        );
+        return true;
+      });
+
+      const image = content.document.images[0];
+      EventUtils.synthesizeMouseAtCenter(image, { type: "contextmenu" });
+
+      const menu = document.getElementById("contentAreaContextMenu");
+      await BrowserTestUtils.waitForPopupEvent(menu, "shown");
+      const menuClosed = BrowserTestUtils.waitForPopupEvent(menu, "hidden");
+
+      const menuItem = document.getElementById("context-setDesktopBackground");
+      try {
+        menu.activateItem(menuItem);
+      } catch (ex) {
+        ok(
+          menuItem.hidden,
+          "should only fail to activate when menu item is hidden"
+        );
+        ok(
+          !ShellService.canSetDesktopBackground,
+          "Should only hide when not able to set the desktop background"
+        );
+        is(
+          AppConstants.platform,
+          "linux",
+          "Should always be able to set desktop background on non-linux platforms"
+        );
+        todo(false, "Skipping test on this configuration");
+
+        menu.hidePopup();
+        await menuClosed;
+        return;
+      }
+
+      await menuClosed;
+
+      const win = await dialogLoad;
+
+      /* setDesktopBackground.js does a setTimeout to wait for correct
+       dimensions. If we don't wait here we could read the preview dimensions
+       before they're changed to match the screen */
+      await TestUtils.waitForTick();
+
+      const canvas = win.document.getElementById("screen");
+      const screenRatio = screen.width / screen.height;
+      const previewRatio = canvas.clientWidth / canvas.clientHeight;
+
+      info(`Screen dimensions are ${screen.width}x${screen.height}`);
+      info(`Screen's raw ratio is ${screenRatio}`);
+      info(
+        `Preview dimensions are ${canvas.clientWidth}x${canvas.clientHeight}`
+      );
+      info(`Preview's raw ratio is ${previewRatio}`);
+
+      Assert.ok(
+        previewRatio < screenRatio + 0.01 && previewRatio > screenRatio - 0.01,
+        "Preview's aspect ratio is within ±.01 of screen's"
+      );
+
+      win.close();
+
+      await menuClosed;
+    }
+  );
+});
diff --git a/browser/components/shell/test/head.js b/browser/components/shell/test/head.js
new file mode 100644
index 0000000000..d2114941e4
--- /dev/null
+++ b/browser/components/shell/test/head.js
@@ -0,0 +1,159 @@
+"use strict";
+
+const { Subprocess } = ChromeUtils.importESModule(
+  "resource://gre/modules/Subprocess.sys.mjs"
+);
+
+const TEMP_DIR = Services.dirsvc.get("TmpD", Ci.nsIFile).path;
+
+const screenshotPath = PathUtils.join(TEMP_DIR, "headless_test_screenshot.png");
+
+async function runFirefox(args) {
+  const XRE_EXECUTABLE_FILE = "XREExeF";
+  const firefoxExe = Services.dirsvc.get(XRE_EXECUTABLE_FILE, Ci.nsIFile).path;
+  const NS_APP_PREFS_50_FILE = "PrefF";
+  const mochiPrefsFile = Services.dirsvc.get(NS_APP_PREFS_50_FILE, Ci.nsIFile);
+  const mochiPrefsPath = mochiPrefsFile.path;
+  const mochiPrefsName = mochiPrefsFile.leafName;
+  const profilePath = PathUtils.join(
+    TEMP_DIR,
+    "headless_test_screenshot_profile"
+  );
+  const prefsPath = PathUtils.join(profilePath, mochiPrefsName);
+  const firefoxArgs = ["-profile", profilePath, "-no-remote"];
+
+  await IOUtils.makeDirectory(profilePath);
+  await IOUtils.copy(mochiPrefsPath, prefsPath);
+  let proc = await Subprocess.call({
+    command: firefoxExe,
+    arguments: firefoxArgs.concat(args),
+    // Disable leak detection to avoid intermittent failure bug 1331152.
+    environmentAppend: true,
+    environment: {
+      ASAN_OPTIONS:
+        "detect_leaks=0:quarantine_size=50331648:malloc_context_size=5",
+      // Don't enable Marionette.
+      MOZ_MARIONETTE: null,
+    },
+  });
+  let stdout;
+  while ((stdout = await proc.stdout.readString())) {
+    dump(`>>> ${stdout}\n`);
+  }
+  let { exitCode } = await proc.wait();
+  is(exitCode, 0, "Firefox process should exit with code 0");
+  await IOUtils.remove(profilePath, { recursive: true });
+}
+
+async function testFileCreationPositive(args, path) {
+  await runFirefox(args);
+
+  let saved = IOUtils.exists(path);
+  ok(saved, "A screenshot should be saved as " + path);
+  if (!saved) {
+    return;
+  }
+
+  let info = await IOUtils.stat(path);
+  ok(info.size > 0, "Screenshot should not be an empty file");
+  await IOUtils.remove(path);
+}
+
+async function testFileCreationNegative(args, path) {
+  await runFirefox(args);
+
+  let saved = await IOUtils.exists(path);
+  ok(!saved, "A screenshot should not be saved");
+  await IOUtils.remove(path);
+}
+
+async function testWindowSizePositive(width, height) {
+  let size = String(width);
+  if (height) {
+    size += "," + height;
+  }
+
+  await runFirefox([
+    "-url",
+    "http://mochi.test:8888/browser/browser/components/shell/test/headless.html",
+    "-screenshot",
+    screenshotPath,
+    "-window-size",
+    size,
+  ]);
+
+  let saved = await IOUtils.exists(screenshotPath);
+  ok(saved, "A screenshot should be saved in the tmp directory");
+  if (!saved) {
+    return;
+  }
+
+  let data = await IOUtils.read(screenshotPath);
+  await new Promise((resolve, reject) => {
+    let blob = new Blob([data], { type: "image/png" });
+    let reader = new FileReader();
+    reader.onloadend = function () {
+      let screenshot = new Image();
+      screenshot.onload = function () {
+        is(
+          screenshot.width,
+          width,
+          "Screenshot should be " + width + " pixels wide"
+        );
+        if (height) {
+          is(
+            screenshot.height,
+            height,
+            "Screenshot should be " + height + " pixels tall"
+          );
+        }
+        resolve();
+      };
+      screenshot.src = reader.result;
+    };
+    reader.readAsDataURL(blob);
+  });
+  await IOUtils.remove(screenshotPath);
+}
+
+async function testGreen(url, path) {
+  await runFirefox(["-url", url, `--screenshot=${path}`]);
+
+  let saved = await IOUtils.exists(path);
+  ok(saved, "A screenshot should be saved in the tmp directory");
+  if (!saved) {
+    return;
+  }
+
+  let data = await IOUtils.read(path);
+  let image = await new Promise((resolve, reject) => {
+    let blob = new Blob([data], { type: "image/png" });
+    let reader = new FileReader();
+    reader.onloadend = function () {
+      let screenshot = new Image();
+      screenshot.onload = function () {
+        resolve(screenshot);
+      };
+      screenshot.src = reader.result;
+    };
+    reader.readAsDataURL(blob);
+  });
+  let canvas = document.createElement("canvas");
+  canvas.width = image.naturalWidth;
+  canvas.height = image.naturalHeight;
+  let ctx = canvas.getContext("2d");
+  ctx.drawImage(image, 0, 0);
+  let imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
+  let rgba = imageData.data;
+
+  let found = false;
+  for (let i = 0; i < rgba.length; i += 4) {
+    if (rgba[i] === 0 && rgba[i + 1] === 255 && rgba[i + 2] === 0) {
+      found = true;
+      break;
+    }
+  }
+  ok(found, "There should be a green pixel in the screenshot.");
+
+  await IOUtils.remove(path);
+}
diff --git a/browser/components/shell/test/headless.html b/browser/components/shell/test/headless.html
new file mode 100644
index 0000000000..bbde895077
--- /dev/null
+++ b/browser/components/shell/test/headless.html
@@ -0,0 +1,6 @@
+<html>
+<head><meta content="text/html; charset=utf-8" http-equiv="Content-Type"></head>
+<body style="background-color: rgb(0, 255, 0); color: rgb(0, 0, 255)">
+Hi
+</body>
+</html>
diff --git a/browser/components/shell/test/headless_cross_origin.html b/browser/components/shell/test/headless_cross_origin.html
new file mode 100644
index 0000000000..3bb09aa5d8
--- /dev/null
+++ b/browser/components/shell/test/headless_cross_origin.html
@@ -0,0 +1,7 @@
+<html>
+<head><meta content="text/html; charset=utf-8" http-equiv="Content-Type"></head>
+<body>
+<iframe width="300" height="200" src="http://example.com/browser/browser/components/shell/test/headless_iframe.html"></iframe>
+Hi
+</body>
+</html>
diff --git a/browser/components/shell/test/headless_iframe.html b/browser/components/shell/test/headless_iframe.html
new file mode 100644
index 0000000000..f318cbe0f3
--- /dev/null
+++ b/browser/components/shell/test/headless_iframe.html
@@ -0,0 +1,6 @@
+<html>
+<head><meta content="text/html; charset=utf-8" http-equiv="Content-Type"></head>
+<body style="background-color: rgb(0, 255, 0);">
+Hi
+</body>
+</html>
diff --git a/browser/components/shell/test/headless_redirect.html b/browser/components/shell/test/headless_redirect.html
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/browser/components/shell/test/headless_redirect.html
diff --git a/browser/components/shell/test/headless_redirect.html^headers^ b/browser/components/shell/test/headless_redirect.html^headers^
new file mode 100644
index 0000000000..1d7db20ea5
--- /dev/null
+++ b/browser/components/shell/test/headless_redirect.html^headers^
@@ -0,0 +1,2 @@
+HTTP 302 Moved Temporarily
+Location: headless.html
\ No newline at end of file
diff --git a/browser/components/shell/test/mac_desktop_image.py b/browser/components/shell/test/mac_desktop_image.py
new file mode 100755
index 0000000000..e3ccc77190
--- /dev/null
+++ b/browser/components/shell/test/mac_desktop_image.py
@@ -0,0 +1,168 @@
+#!/usr/bin/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/. */
+
+"""
+mac_desktop_image.py
+
+Mac-specific utility to get/set the desktop background image or check that
+the current background image path matches a provided path.
+
+Depends on Objective-C python binding imports which are in the python import
+paths by default when using macOS's /usr/bin/python.
+
+Includes generous amount of logging to aid debugging for use in automated tests.
+"""
+
+import argparse
+import logging
+import os
+import sys
+
+#
+# These Objective-C bindings imports are included in the import path by default
+# for the Mac-bundled python installed in /usr/bin/python. They're needed to
+# call the Objective-C API's to set and retrieve the current desktop background
+# image.
+#
+from AppKit import NSScreen, NSWorkspace
+from Cocoa import NSURL
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Utility to print, set, or "
+        + "check the path to image being used as "
+        + "the desktop background image. By "
+        + "default, prints the path to the "
+        + "current desktop background image."
+    )
+    parser.add_argument(
+        "-v",
+        "--verbose",
+        action="store_true",
+        help="print verbose debugging information",
+        default=False,
+    )
+    group = parser.add_mutually_exclusive_group()
+    group.add_argument(
+        "-s",
+        "--set-background-image",
+        dest="newBackgroundImagePath",
+        required=False,
+        help="path to the new background image to set. A zero "
+        + "exit code indicates no errors occurred.",
+        default=None,
+    )
+    group.add_argument(
+        "-c",
+        "--check-background-image",
+        dest="checkBackgroundImagePath",
+        required=False,
+        help="check if the provided background image path "
+        + "matches the provided path. A zero exit code "
+        + "indicates the paths match.",
+        default=None,
+    )
+    args = parser.parse_args()
+
+    # Using logging for verbose output
+    if args.verbose:
+        logging.basicConfig(level=logging.DEBUG)
+    else:
+        logging.basicConfig(level=logging.CRITICAL)
+    logger = logging.getLogger("desktopImage")
+
+    # Print what we're going to do
+    if args.checkBackgroundImagePath is not None:
+        logger.debug(
+            "checking provided desktop image %s matches current "
+            "image" % args.checkBackgroundImagePath
+        )
+    elif args.newBackgroundImagePath is not None:
+        logger.debug("setting image to %s " % args.newBackgroundImagePath)
+    else:
+        logger.debug("retrieving desktop image path")
+
+    focussedScreen = NSScreen.mainScreen()
+    if not focussedScreen:
+        raise RuntimeError("mainScreen error")
+
+    ws = NSWorkspace.sharedWorkspace()
+    if not ws:
+        raise RuntimeError("sharedWorkspace error")
+
+    # If we're just checking the image path, check it and then return.
+    # A successful exit code (0) indicates the paths match.
+    if args.checkBackgroundImagePath is not None:
+        # Get existing desktop image path and resolve it
+        existingImageURL = getCurrentDesktopImageURL(focussedScreen, ws, logger)
+        existingImagePath = existingImageURL.path()
+        existingImagePathReal = os.path.realpath(existingImagePath)
+        logger.debug("existing desktop image: %s" % existingImagePath)
+        logger.debug("existing desktop image realpath: %s" % existingImagePath)
+
+        # Resolve the path we're going to check
+        checkImagePathReal = os.path.realpath(args.checkBackgroundImagePath)
+        logger.debug("check desktop image: %s" % args.checkBackgroundImagePath)
+        logger.debug("check desktop image realpath: %s" % checkImagePathReal)
+
+        if existingImagePathReal == checkImagePathReal:
+            print("desktop image path matches provided path")
+            return True
+
+        print("desktop image path does NOT match provided path")
+        return False
+
+    # Log the current desktop image
+    if args.verbose:
+        existingImageURL = getCurrentDesktopImageURL(focussedScreen, ws, logger)
+        logger.debug("existing desktop image: %s" % existingImageURL.path())
+
+    # Set the desktop image
+    if args.newBackgroundImagePath is not None:
+        newImagePath = args.newBackgroundImagePath
+        if not os.path.exists(newImagePath):
+            logger.critical("%s does not exist" % newImagePath)
+            return False
+        if not os.access(newImagePath, os.R_OK):
+            logger.critical("%s is not readable" % newImagePath)
+            return False
+
+        logger.debug("new desktop image to set: %s" % newImagePath)
+        newImageURL = NSURL.fileURLWithPath_(newImagePath)
+        logger.debug("new desktop image URL to set: %s" % newImageURL)
+
+        status = False
+        (status, error) = ws.setDesktopImageURL_forScreen_options_error_(
+            newImageURL, focussedScreen, None, None
+        )
+        if not status:
+            raise RuntimeError("setDesktopImageURL error")
+
+    # Print the current desktop image
+    imageURL = getCurrentDesktopImageURL(focussedScreen, ws, logger)
+    imagePath = imageURL.path()
+    imagePathReal = os.path.realpath(imagePath)
+    logger.debug("updated desktop image URL: %s" % imageURL)
+    logger.debug("updated desktop image path: %s" % imagePath)
+    logger.debug("updated desktop image path (resolved): %s" % imagePathReal)
+    print(imagePathReal)
+    return True
+
+
+def getCurrentDesktopImageURL(focussedScreen, workspace, logger):
+    imageURL = workspace.desktopImageURLForScreen_(focussedScreen)
+    if not imageURL:
+        raise RuntimeError("desktopImageURLForScreen returned invalid URL")
+    if not imageURL.isFileURL():
+        logger.warning("desktop image URL is not a file URL")
+    return imageURL
+
+
+if __name__ == "__main__":
+    if not main():
+        sys.exit(1)
+    else:
+        sys.exit(0)
diff --git a/browser/components/shell/test/unit/test_macOS_showSecurityPreferences.js b/browser/components/shell/test/unit/test_macOS_showSecurityPreferences.js
new file mode 100644
index 0000000000..df3f4a5918
--- /dev/null
+++ b/browser/components/shell/test/unit/test_macOS_showSecurityPreferences.js
@@ -0,0 +1,30 @@
+/* Any copyright is dedicated to the Public Domain.
+ * https://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Test the macOS ShowSecurityPreferences shell service method.
+ */
+
+function killSystemPreferences() {
+  let killallFile = Cc["@mozilla.org/file/local;1"].createInstance(Ci.nsIFile);
+  killallFile.initWithPath("/usr/bin/killall");
+  let sysPrefsArg = ["System Preferences"];
+  let process = Cc["@mozilla.org/process/util;1"].createInstance(Ci.nsIProcess);
+  process.init(killallFile);
+  process.run(true, sysPrefsArg, 1);
+  return process.exitValue;
+}
+
+add_setup(async function () {
+  info("Ensure System Preferences isn't already running");
+  killSystemPreferences();
+});
+
+add_task(async function test_prefsOpen() {
+  let shellSvc = Cc["@mozilla.org/browser/shell-service;1"].getService(
+    Ci.nsIMacShellService
+  );
+  shellSvc.showSecurityPreferences("Privacy_AllFiles");
+
+  equal(killSystemPreferences(), 0, "Ensure System Preferences was started");
+});
diff --git a/browser/components/shell/test/unit/xpcshell.ini b/browser/components/shell/test/unit/xpcshell.ini
new file mode 100644
index 0000000000..383dcb3475
--- /dev/null
+++ b/browser/components/shell/test/unit/xpcshell.ini
@@ -0,0 +1,6 @@
+[DEFAULT]
+skip-if = toolkit == 'android' # bug 1730213
+firefox-appdir = browser
+
+[test_macOS_showSecurityPreferences.js]
+skip-if = toolkit != "cocoa"