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diff --git a/browser/modules/HomePage.sys.mjs b/browser/modules/HomePage.sys.mjs
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+++ b/browser/modules/HomePage.sys.mjs
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+/* 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/. */
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  CustomizableUI: "resource:///modules/CustomizableUI.sys.mjs",
+  ExtensionParent: "resource://gre/modules/ExtensionParent.sys.mjs",
+  ExtensionPreferencesManager:
+    "resource://gre/modules/ExtensionPreferencesManager.sys.mjs",
+  IgnoreLists: "resource://gre/modules/IgnoreLists.sys.mjs",
+  PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
+});
+
+const kPrefName = "browser.startup.homepage";
+const kDefaultHomePage = "about:home";
+const kExtensionControllerPref =
+  "browser.startup.homepage_override.extensionControlled";
+const kHomePageIgnoreListId = "homepage-urls";
+const kWidgetId = "home-button";
+const kWidgetRemovedPref = "browser.engagement.home-button.has-removed";
+
+function getHomepagePref(useDefault) {
+  let homePage;
+  let prefs = Services.prefs;
+  if (useDefault) {
+    prefs = prefs.getDefaultBranch(null);
+  }
+  try {
+    // Historically, this was a localizable pref, but default Firefox builds
+    // don't use this.
+    // Distributions and local customizations might still use this, so let's
+    // keep it.
+    homePage = prefs.getComplexValue(kPrefName, Ci.nsIPrefLocalizedString).data;
+  } catch (ex) {}
+
+  if (!homePage) {
+    homePage = prefs.getStringPref(kPrefName);
+  }
+
+  // Apparently at some point users ended up with blank home pages somehow.
+  // If that happens, reset the pref and read it again.
+  if (!homePage && !useDefault) {
+    Services.prefs.clearUserPref(kPrefName);
+    homePage = getHomepagePref(true);
+  }
+
+  return homePage;
+}
+
+/**
+ * HomePage provides tools to keep track of the current homepage, and the
+ * applications's default homepage. It includes tools to insure that certain
+ * urls are ignored. As a result, all set/get requests for the homepage
+ * preferences should be routed through here.
+ */
+export let HomePage = {
+  // This is an array of strings that should be matched against URLs to see
+  // if they should be ignored or not.
+  _ignoreList: [],
+
+  // A promise that is set when initialization starts and resolved when it
+  // completes.
+  _initializationPromise: null,
+
+  /**
+   * Used to initialise the ignore lists. This may be called later than
+   * the first call to get or set, which may cause a used to get an ignored
+   * homepage, but this is deemed acceptable, as we'll correct it once
+   * initialised.
+   */
+  async delayedStartup() {
+    if (this._initializationPromise) {
+      await this._initializationPromise;
+      return;
+    }
+
+    Services.telemetry.setEventRecordingEnabled("homepage", true);
+
+    // Now we have the values, listen for future updates.
+    this._ignoreListListener = this._handleIgnoreListUpdated.bind(this);
+
+    this._initializationPromise = lazy.IgnoreLists.getAndSubscribe(
+      this._ignoreListListener
+    );
+
+    this._addCustomizableUiListener();
+
+    const current = await this._initializationPromise;
+
+    await this._handleIgnoreListUpdated({ data: { current } });
+  },
+
+  /**
+   * Gets the homepage for the given window.
+   *
+   * @param {DOMWindow} [aWindow]
+   *   The window associated with the get, used to check for private browsing
+   *   mode. If not supplied, normal mode is assumed.
+   * @returns {string}
+   *   Returns the home page value, this could be a single url, or a `|`
+   *   separated list of URLs.
+   */
+  get(aWindow) {
+    let homePages = getHomepagePref();
+    if (
+      lazy.PrivateBrowsingUtils.permanentPrivateBrowsing ||
+      (aWindow && lazy.PrivateBrowsingUtils.isWindowPrivate(aWindow))
+    ) {
+      // If an extension controls the setting and does not have private
+      // browsing permission, use the default setting.
+      let extensionControlled = Services.prefs.getBoolPref(
+        kExtensionControllerPref,
+        false
+      );
+      let privateAllowed = Services.prefs.getBoolPref(
+        "browser.startup.homepage_override.privateAllowed",
+        false
+      );
+      // There is a potential on upgrade that the prefs are not set yet, so we double check
+      // for moz-extension.
+      if (
+        !privateAllowed &&
+        (extensionControlled || homePages.includes("moz-extension://"))
+      ) {
+        return this.getDefault();
+      }
+    }
+
+    if (homePages == "about:blank") {
+      homePages = "chrome://browser/content/blanktab.html";
+    }
+
+    return homePages;
+  },
+
+  /**
+   * @returns {string}
+   *   Returns the application default homepage.
+   */
+  getDefault() {
+    return getHomepagePref(true);
+  },
+
+  /**
+   * @returns {string}
+   *   Returns the original application homepage URL (not from prefs).
+   */
+  getOriginalDefault() {
+    return kDefaultHomePage;
+  },
+
+  /**
+   * @returns {boolean}
+   *   Returns true if the homepage has been changed.
+   */
+  get overridden() {
+    return Services.prefs.prefHasUserValue(kPrefName);
+  },
+
+  /**
+   * @returns {boolean}
+   *   Returns true if the homepage preference is locked.
+   */
+  get locked() {
+    return Services.prefs.prefIsLocked(kPrefName);
+  },
+
+  /**
+   * @returns {boolean}
+   *   Returns true if the current homepage is the application default.
+   */
+  get isDefault() {
+    return HomePage.get() === kDefaultHomePage;
+  },
+
+  /**
+   * Sets the homepage preference to a new page.
+   *
+   * @param {string} value
+   *   The new value to set the preference to. This could be a single url, or a
+   *   `|` separated list of URLs.
+   */
+  async set(value) {
+    await this.delayedStartup();
+
+    if (await this.shouldIgnore(value)) {
+      console.error(
+        `Ignoring homepage setting for ${value} as it is on the ignore list.`
+      );
+      Services.telemetry.recordEvent(
+        "homepage",
+        "preference",
+        "ignore",
+        "set_blocked"
+      );
+      return false;
+    }
+    Services.prefs.setStringPref(kPrefName, value);
+    this._maybeAddHomeButtonToToolbar(value);
+    return true;
+  },
+
+  /**
+   * Sets the homepage preference to a new page. This is an synchronous version
+   * that should only be used when we know the source is safe as it bypasses the
+   * ignore list, e.g. when setting directly to about:blank or a value not
+   * supplied externally.
+   *
+   * @param {string} value
+   *   The new value to set the preference to. This could be a single url, or a
+   *   `|` separated list of URLs.
+   */
+  safeSet(value) {
+    Services.prefs.setStringPref(kPrefName, value);
+  },
+
+  /**
+   * Clears the homepage preference if it is not the default. Note that for
+   * policy/locking use, the default homepage might not be about:home after this.
+   */
+  clear() {
+    Services.prefs.clearUserPref(kPrefName);
+  },
+
+  /**
+   * Resets the homepage preference to be about:home.
+   */
+  reset() {
+    Services.prefs.setStringPref(kPrefName, kDefaultHomePage);
+  },
+
+  /**
+   * Determines if a url should be ignored according to the ignore list.
+   *
+   * @param {string} url
+   *   A string that is the url or urls to be ignored.
+   * @returns {boolean}
+   *   True if the url should be ignored.
+   */
+  async shouldIgnore(url) {
+    await this.delayedStartup();
+
+    const lowerURL = url.toLowerCase();
+    return this._ignoreList.some(code => lowerURL.includes(code.toLowerCase()));
+  },
+
+  /**
+   * Handles updates of the ignore list, checking the existing preference and
+   * correcting it as necessary.
+   *
+   * @param {Object} eventData
+   *   The event data as received from RemoteSettings.
+   */
+  async _handleIgnoreListUpdated({ data: { current } }) {
+    for (const entry of current) {
+      if (entry.id == kHomePageIgnoreListId) {
+        this._ignoreList = [...entry.matches];
+      }
+    }
+
+    // Only check if we're overridden as we assume the default value is fine,
+    // or won't be changeable (e.g. enterprise policy).
+    if (this.overridden) {
+      let homePages = getHomepagePref().toLowerCase();
+      if (
+        this._ignoreList.some(code => homePages.includes(code.toLowerCase()))
+      ) {
+        if (Services.prefs.getBoolPref(kExtensionControllerPref, false)) {
+          if (Services.appinfo.inSafeMode) {
+            // Add-ons don't get started in safe mode, so just abort this.
+            // We'll get to remove them when we next start in normal mode.
+            return;
+          }
+          // getSetting does not need the module to be loaded.
+          const item = await lazy.ExtensionPreferencesManager.getSetting(
+            "homepage_override"
+          );
+          if (item && item.id) {
+            // During startup some modules may not be loaded yet, so we load
+            // the setting we need prior to removal.
+            await lazy.ExtensionParent.apiManager.asyncLoadModule(
+              "chrome_settings_overrides"
+            );
+            lazy.ExtensionPreferencesManager.removeSetting(
+              item.id,
+              "homepage_override"
+            ).catch(console.error);
+          } else {
+            // If we don't have a setting for it, we assume the pref has
+            // been incorrectly set somehow.
+            Services.prefs.clearUserPref(kExtensionControllerPref);
+            Services.prefs.clearUserPref(
+              "browser.startup.homepage_override.privateAllowed"
+            );
+          }
+        } else {
+          this.clear();
+        }
+        Services.telemetry.recordEvent(
+          "homepage",
+          "preference",
+          "ignore",
+          "saved_reset"
+        );
+      }
+    }
+  },
+
+  onWidgetRemoved(widgetId, area) {
+    if (widgetId == kWidgetId) {
+      Services.prefs.setBoolPref(kWidgetRemovedPref, true);
+      lazy.CustomizableUI.removeListener(this);
+    }
+  },
+
+  /**
+   * Add the home button to the toolbar if the user just set a custom homepage.
+   *
+   * This should only be done once, so we check HOME_BUTTON_REMOVED_PREF which
+   * gets set to true when the home button is removed from the toolbar.
+   *
+   * If the home button is already on the toolbar it won't be moved.
+   */
+  _maybeAddHomeButtonToToolbar(homePage) {
+    if (
+      homePage !== "about:home" &&
+      homePage !== "about:blank" &&
+      !Services.prefs.getBoolPref(kExtensionControllerPref, false) &&
+      !Services.prefs.getBoolPref(kWidgetRemovedPref, false) &&
+      !lazy.CustomizableUI.getWidget(kWidgetId).areaType
+    ) {
+      // Find a spot for the home button, ideally it will be in its default
+      // position beside the stop/refresh button.
+      // Work backwards from the URL bar since it can't be removed and put
+      // the button after the first non-spring we find.
+      let navbarPlacements = lazy.CustomizableUI.getWidgetIdsInArea("nav-bar");
+      let position = navbarPlacements.indexOf("urlbar-container");
+      for (let i = position - 1; i >= 0; i--) {
+        if (!navbarPlacements[i].startsWith("customizableui-special-spring")) {
+          position = i + 1;
+          break;
+        }
+      }
+      lazy.CustomizableUI.addWidgetToArea(kWidgetId, "nav-bar", position);
+    }
+  },
+
+  _addCustomizableUiListener() {
+    if (!Services.prefs.getBoolPref(kWidgetRemovedPref, false)) {
+      lazy.CustomizableUI.addListener(this);
+    }
+  },
+};