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diff --git a/remote/shared/TabManager.sys.mjs b/remote/shared/TabManager.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, {
+  AppInfo: "chrome://remote/content/shared/AppInfo.sys.mjs",
+  EventPromise: "chrome://remote/content/shared/Sync.sys.mjs",
+  generateUUID: "chrome://remote/content/shared/UUID.sys.mjs",
+  MobileTabBrowser: "chrome://remote/content/shared/MobileTabBrowser.sys.mjs",
+});
+
+// Maps browser's permanentKey to uuid: WeakMap.<Object, string>
+const browserUniqueIds = new WeakMap();
+
+export var TabManager = {
+  /**
+   * Retrieve all the browser elements from tabs as contained in open windows.
+   *
+   * @returns {Array<XULBrowser>}
+   *     All the found <xul:browser>s. Will return an empty array if
+   *     no windows and tabs can be found.
+   */
+  get browsers() {
+    const browsers = [];
+
+    for (const win of this.windows) {
+      const tabBrowser = this.getTabBrowser(win);
+
+      if (tabBrowser && tabBrowser.tabs) {
+        const contentBrowsers = tabBrowser.tabs.map(tab => {
+          return this.getBrowserForTab(tab);
+        });
+        browsers.push(...contentBrowsers);
+      }
+    }
+
+    return browsers;
+  },
+
+  get windows() {
+    return Services.wm.getEnumerator(null);
+  },
+
+  /**
+   * Array of unique browser ids (UUIDs) for all content browsers of all
+   * windows.
+   *
+   * TODO: Similarly to getBrowserById, we should improve the performance of
+   * this getter in Bug 1750065.
+   *
+   * @returns {Array<string>}
+   *     Array of UUIDs for all content browsers.
+   */
+  get allBrowserUniqueIds() {
+    const browserIds = [];
+
+    for (const win of this.windows) {
+      const tabBrowser = this.getTabBrowser(win);
+
+      // Only return handles for browser windows
+      if (tabBrowser && tabBrowser.tabs) {
+        for (const tab of tabBrowser.tabs) {
+          const contentBrowser = this.getBrowserForTab(tab);
+          const winId = this.getIdForBrowser(contentBrowser);
+          if (winId !== null) {
+            browserIds.push(winId);
+          }
+        }
+      }
+    }
+
+    return browserIds;
+  },
+
+  /**
+   * Get the <code>&lt;xul:browser&gt;</code> for the specified tab.
+   *
+   * @param {Tab} tab
+   *     The tab whose browser needs to be returned.
+   *
+   * @returns {XULBrowser}
+   *     The linked browser for the tab or null if no browser can be found.
+   */
+  getBrowserForTab(tab) {
+    if (tab && "linkedBrowser" in tab) {
+      return tab.linkedBrowser;
+    }
+
+    return null;
+  },
+
+  /**
+   * Return the tab browser for the specified chrome window.
+   *
+   * @param {ChromeWindow} win
+   *     Window whose <code>tabbrowser</code> needs to be accessed.
+   *
+   * @returns {Tab}
+   *     Tab browser or null if it's not a browser window.
+   */
+  getTabBrowser(win) {
+    if (lazy.AppInfo.isAndroid) {
+      return new lazy.MobileTabBrowser(win);
+    } else if (lazy.AppInfo.isFirefox) {
+      return win.gBrowser;
+    }
+
+    return null;
+  },
+
+  /**
+   * Create a new tab.
+   *
+   * @param {object} options
+   * @param {boolean=} options.focus
+   *     Set to true if the new tab should be focused (selected). Defaults to
+   *     false.
+   * @param {Tab=} options.referenceTab
+   *     The reference tab after which the new tab will be added. If no
+   *     reference tab is provided, the new tab will be added after all the
+   *     other tabs.
+   * @param {number} options.userContextId
+   *     The user context (container) id.
+   * @param {window=} options.window
+   *     The window where the new tab will open. Defaults to Services.wm.getMostRecentWindow
+   *     if no window is provided. Will be ignored if referenceTab is provided.
+   */
+  async addTab(options = {}) {
+    let {
+      focus = false,
+      referenceTab = null,
+      userContextId,
+      window = Services.wm.getMostRecentWindow(null),
+    } = options;
+
+    let index;
+    if (referenceTab != null) {
+      // If a reference tab was specified, the window should be the window
+      // owning the reference tab.
+      window = this._getWindowForTab(referenceTab);
+    }
+
+    const tabBrowser = this.getTabBrowser(window);
+    if (referenceTab != null) {
+      index = tabBrowser.tabs.indexOf(referenceTab) + 1;
+    }
+
+    const tab = await tabBrowser.addTab("about:blank", {
+      index,
+      triggeringPrincipal: Services.scriptSecurityManager.getSystemPrincipal(),
+      userContextId,
+    });
+
+    if (focus) {
+      await this.selectTab(tab);
+    }
+
+    return tab;
+  },
+
+  /**
+   * Retrieve the browser element corresponding to the provided unique id,
+   * previously generated via getIdForBrowser.
+   *
+   * TODO: To avoid creating strong references on browser elements and
+   * potentially leaking those elements, this method loops over all windows and
+   * all tabs. It should be replaced by a faster implementation in Bug 1750065.
+   *
+   * @param {string} id
+   *     A browser unique id created by getIdForBrowser.
+   * @returns {XULBrowser}
+   *     The <xul:browser> corresponding to the provided id. Will return null if
+   *     no matching browser element is found.
+   */
+  getBrowserById(id) {
+    for (const win of this.windows) {
+      const tabBrowser = this.getTabBrowser(win);
+      if (tabBrowser && tabBrowser.tabs) {
+        for (let i = 0; i < tabBrowser.tabs.length; ++i) {
+          const contentBrowser = this.getBrowserForTab(tabBrowser.tabs[i]);
+          if (this.getIdForBrowser(contentBrowser) == id) {
+            return contentBrowser;
+          }
+        }
+      }
+    }
+    return null;
+  },
+
+  /**
+   * Retrieve the browsing context corresponding to the provided unique id.
+   *
+   * @param {string} id
+   *     A browsing context unique id (created by getIdForBrowsingContext).
+   * @returns {BrowsingContext=}
+   *     The browsing context found for this id, null if none was found.
+   */
+  getBrowsingContextById(id) {
+    const browser = this.getBrowserById(id);
+    if (browser) {
+      return browser.browsingContext;
+    }
+
+    return BrowsingContext.get(id);
+  },
+
+  /**
+   * Retrieve the unique id for the given xul browser element. The id is a
+   * dynamically generated uuid associated with the permanentKey property of the
+   * given browser element. This method is preferable over getIdForBrowsingContext
+   * in case of working with browser element of a tab, since we can not guarantee
+   * that browsing context is attached to it.
+   *
+   * @param {XULBrowser} browserElement
+   *     The <xul:browser> for which we want to retrieve the id.
+   * @returns {string} The unique id for this browser.
+   */
+  getIdForBrowser(browserElement) {
+    if (browserElement === null) {
+      return null;
+    }
+
+    const key = browserElement.permanentKey;
+    if (!browserUniqueIds.has(key)) {
+      browserUniqueIds.set(key, lazy.generateUUID());
+    }
+    return browserUniqueIds.get(key);
+  },
+
+  /**
+   * Retrieve the id of a Browsing Context.
+   *
+   * For a top-level browsing context a custom unique id will be returned.
+   *
+   * @param {BrowsingContext=} browsingContext
+   *     The browsing context to get the id from.
+   *
+   * @returns {string}
+   *     The id of the browsing context.
+   */
+  getIdForBrowsingContext(browsingContext) {
+    if (!browsingContext) {
+      return null;
+    }
+
+    if (!browsingContext.parent) {
+      // Top-level browsing contexts have their own custom unique id.
+      return this.getIdForBrowser(browsingContext.embedderElement);
+    }
+
+    return browsingContext.id.toString();
+  },
+
+  getTabCount() {
+    let count = 0;
+    for (const win of this.windows) {
+      // For browser windows count the tabs. Otherwise take the window itself.
+      const tabbrowser = this.getTabBrowser(win);
+      if (tabbrowser?.tabs) {
+        count += tabbrowser.tabs.length;
+      } else {
+        count += 1;
+      }
+    }
+    return count;
+  },
+
+  /**
+   * Retrieve the tab owning a Browsing Context.
+   *
+   * @param {BrowsingContext=} browsingContext
+   *     The browsing context to get the tab from.
+   *
+   * @returns {Tab|null}
+   *     The tab owning the Browsing Context.
+   */
+  getTabForBrowsingContext(browsingContext) {
+    const browser = browsingContext?.top.embedderElement;
+    if (!browser) {
+      return null;
+    }
+
+    const tabBrowser = this.getTabBrowser(browser.ownerGlobal);
+    return tabBrowser.getTabForBrowser(browser);
+  },
+
+  /**
+   * Remove the given tab.
+   *
+   * @param {Tab} tab
+   *     Tab to remove.
+   */
+  async removeTab(tab) {
+    if (!tab) {
+      return;
+    }
+
+    const ownerWindow = this._getWindowForTab(tab);
+    const tabBrowser = this.getTabBrowser(ownerWindow);
+    await tabBrowser.removeTab(tab);
+  },
+
+  /**
+   * Select the given tab.
+   *
+   * @param {Tab} tab
+   *     Tab to select.
+   *
+   * @returns {Promise}
+   *     Promise that resolves when the given tab has been selected.
+   */
+  selectTab(tab) {
+    if (!tab) {
+      return Promise.resolve();
+    }
+
+    const ownerWindow = this._getWindowForTab(tab);
+    const tabBrowser = this.getTabBrowser(ownerWindow);
+
+    if (tab === tabBrowser.selectedTab) {
+      return Promise.resolve();
+    }
+
+    const selected = new lazy.EventPromise(ownerWindow, "TabSelect");
+    tabBrowser.selectedTab = tab;
+    return selected;
+  },
+
+  supportsTabs() {
+    return lazy.AppInfo.isAndroid || lazy.AppInfo.isFirefox;
+  },
+
+  _getWindowForTab(tab) {
+    // `.linkedBrowser.ownerGlobal` works both with Firefox Desktop and Mobile.
+    // Other accessors (eg `.ownerGlobal` or `.browser.ownerGlobal`) fail on one
+    // of the platforms.
+    return tab.linkedBrowser.ownerGlobal;
+  },
+};