diff --git a/calendar/base/content/dialogs/calendar-event-dialog-attendees-custom-elements.js b/calendar/base/content/dialogs/calendar-event-dialog-attendees-custom-elements.js
index 53f47b6973..9e9be33375 100644
--- a/calendar/base/content/dialogs/calendar-event-dialog-attendees-custom-elements.js
+++ b/calendar/base/content/dialogs/calendar-event-dialog-attendees-custom-elements.js
@@ -9,6 +9,7 @@
 // Wrap in a block to prevent leaking to window scope.
 {
   const { MailServices } = ChromeUtils.import("resource:///modules/MailServices.jsm");
+  const { MailUtils } = ChromeUtils.import("resource:///modules/MailUtils.jsm");
 
   /**
    * MozCalendarEventFreebusyTimebar is a widget showing the time slot labels - dates and a number of
@@ -764,43 +765,7 @@
      */
     _resolveListByName(value) {
       let entries = MailServices.headerParser.makeFromDisplayAddress(value);
-      return entries.length ? this._findListInAddrBooks(entries[0].name) : null;
-    }
-
-    /**
-     * Finds list in the address books.
-     *
-     * @param {String} entryName        Value against which dirName is checked
-     * @returns {Object}                Found list or null
-     */
-    _findListInAddrBooks(entryname) {
-      let allAddressBooks = MailServices.ab.directories;
-
-      while (allAddressBooks.hasMoreElements()) {
-        let abDir = null;
-        try {
-          abDir = allAddressBooks.getNext().QueryInterface(Ci.nsIAbDirectory);
-        } catch (ex) {
-          cal.WARN("[eventDialog] Error Encountered" + ex);
-        }
-
-        if (abDir != null && abDir.supportsMailingLists) {
-          let dirs = abDir.childNodes;
-          while (dirs.hasMoreElements()) {
-            let dir = null;
-            try {
-              dir = dirs.getNext().QueryInterface(Ci.nsIAbDirectory);
-            } catch (ex) {
-              cal.WARN("[eventDialog] Error Encountered" + ex);
-            }
-
-            if (dir && dir.isMailList && dir.dirName == entryname) {
-              return dir;
-            }
-          }
-        }
-      }
-      return null;
+      return entries.length ? MailUtils.findListInAddressBooks(entries[0].name) : null;
     }
 
     /**
diff --git a/mail/base/modules/MailUtils.jsm b/mail/base/modules/MailUtils.jsm
index 66a8b613e9..4e9cc50731 100644
--- a/mail/base/modules/MailUtils.jsm
+++ b/mail/base/modules/MailUtils.jsm
@@ -533,4 +533,30 @@ var MailUtils = {
     }
     return null;
   },
+
+  /**
+   * Finds a mailing list anywhere in the address books.
+   *
+   * @param {string} entryName - Value against which dirName is checked.
+   * @returns {nsIAbDirectory|null} - Found list or null.
+   */
+  findListInAddressBooks(entryName) {
+    let allAddressBooks = MailServices.ab.directories;
+
+    while (allAddressBooks.hasMoreElements()) {
+      let abDir = allAddressBooks.getNext().QueryInterface(Ci.nsIAbDirectory);
+
+      if (abDir.supportsMailingLists) {
+        let dirs = abDir.childNodes;
+
+        while (dirs.hasMoreElements()) {
+          let dir = dirs.getNext().QueryInterface(Ci.nsIAbDirectory);
+          if (dir.isMailList && dir.dirName == entryName) {
+            return dir;
+          }
+        }
+      }
+    }
+    return null;
+  },
 };
diff --git a/mail/components/addrbook/content/addressbook.js b/mail/components/addrbook/content/addressbook.js
index d0909dad7e..ea89d4e26d 100644
--- a/mail/components/addrbook/content/addressbook.js
+++ b/mail/components/addrbook/content/addressbook.js
@@ -530,10 +530,17 @@ function SetStatusText(total) {
         ).replace("#1", total);
       }
     } else {
-      statusText = gAddressBookBundle.getFormattedString("totalContactStatus", [
-        getSelectedDirectory().dirName,
-        total,
-      ]);
+      let selectedDirectory = getSelectedDirectory();
+      // The result of getSelectedDirectory may be null, like when there's a
+      // mailing list just being created in a brand new address book.
+      if (selectedDirectory) {
+        statusText = gAddressBookBundle.getFormattedString(
+          "totalContactStatus",
+          [selectedDirectory.dirName, total]
+        );
+      } else {
+        statusText = "";
+      }
     }
 
     gStatusText.setAttribute("value", statusText);
diff --git a/mail/components/extensions/test/browser/browser_ext_menus.js b/mail/components/extensions/test/browser/browser_ext_menus.js
index 76a8744a83..19175b57a1 100644
--- a/mail/components/extensions/test/browser/browser_ext_menus.js
+++ b/mail/components/extensions/test/browser/browser_ext_menus.js
@@ -4,17 +4,11 @@
 
 let gAccount, gFolders;
 
-function treeClick(tree, row, column, event) {
-  let coords = tree.getCoordsForCellItem(row, tree.columns[column], "cell");
-  let treeChildren = tree.lastElementChild;
-  EventUtils.synthesizeMouse(
-    treeChildren,
-    coords.x + coords.width / 2,
-    coords.y + coords.height / 2,
-    event,
-    window
-  );
-}
+const { mailTestUtils } = ChromeUtils.import(
+  "resource://testing-common/mailnews/mailTestUtils.js"
+);
+
+const treeClick = mailTestUtils.treeClick.bind(null, EventUtils, window);
 
 async function checkEvent(extension, menuIds, contexts) {
   let [event, tab] = await extension.awaitMessage("onShown");
diff --git a/mailnews/addrbook/test/browser/browser.ini b/mailnews/addrbook/test/browser/browser.ini
new file mode 100644
index 0000000000..38cf578ef1
--- /dev/null
+++ b/mailnews/addrbook/test/browser/browser.ini
@@ -0,0 +1,14 @@
+[DEFAULT]
+head = head.js
+prefs =
+  ldap_2.servers.osx.description=
+  ldap_2.servers.osx.dirType=-1
+  ldap_2.servers.osx.uri=
+  mail.provider.suppress_dialog_on_startup=true
+  mail.spotlight.firstRunDone=true
+  mail.winsearch.firstRunDone=true
+  mailnews.start_page.override_url=about:blank
+  mailnews.start_page.url=about:blank
+subsuite = thunderbird
+
+[browser_mailing_lists.js]
diff --git a/mailnews/addrbook/test/browser/browser_mailing_lists.js b/mailnews/addrbook/test/browser/browser_mailing_lists.js
new file mode 100644
index 0000000000..c5b9e37aa7
--- /dev/null
+++ b/mailnews/addrbook/test/browser/browser_mailing_lists.js
@@ -0,0 +1,483 @@
+/* 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/. */
+
+/* globals DisplayNameUtils, fixIterator, MailServices, MailUtils */
+
+const { mailTestUtils } = ChromeUtils.import(
+  "resource://testing-common/mailnews/mailTestUtils.js"
+);
+
+const inputs = {
+  abName: "Mochitest Address Book",
+  mlName: "Mochitest Mailing List",
+  nickName: "Nicky",
+  description: "Just a test mailing list.",
+  addresses: [
+    "alan@example.com",
+    "betty@example.com",
+    "clyde@example.com",
+    "deb@example.com",
+  ],
+  modification: " (modified)",
+};
+
+const getDisplayedAddress = address => `${address} <${address}>`;
+
+let global = {};
+
+/**
+ * Set up: create a new address book to hold the mailing list.
+ */
+add_task(async () => {
+  let abWindow = await openAddressBookWindow();
+  let addressBook = await createNewAddressBook(abWindow, inputs.abName);
+
+  let dirTree = abWindow.document.getElementById("dirTree");
+
+  /**
+   * Click a row in the address book list (tree).
+   *
+   * @param {number} row - The tree row to click.
+   * @param {number} clickCount - Number of clicks to synthesize.
+   */
+  let dirTreeClick = (row, clickCount) => {
+    mailTestUtils.treeClick(EventUtils, abWindow, dirTree, row, 0, {
+      clickCount,
+    });
+  };
+
+  global = {
+    abWindow,
+    addressBook,
+    dirTree,
+    dirTreeClick,
+    mailListUID: undefined,
+  };
+});
+
+/**
+ * Create a new mailing list with some addresses, in the new address book.
+ */
+add_task(async () => {
+  let mailingListWindowPromise = BrowserTestUtils.promiseAlertDialog(
+    null,
+    "chrome://messenger/content/addressbook/abMailListDialog.xul",
+    // A callback that can interact with the mailing list dialog.
+    async mlWindow => {
+      let mlDocument = mlWindow.document;
+      let mlDocElement = mlDocument.documentElement;
+
+      let listName = mlDocument.getElementById("ListName");
+      let listNameFocusEvent = await BrowserTestUtils.waitForEvent(
+        listName,
+        "focus"
+      );
+
+      let abPopup = mlDocument.getElementById("abPopup");
+      let listNickName = mlDocument.getElementById("ListNickName");
+      let listDescription = mlDocument.getElementById("ListDescription");
+      let addressInput1 = mlDocument.getElementById("addressCol1#1");
+      let addressInputsCount = mlDocument
+        .getElementById("addressingWidget")
+        .querySelectorAll("input").length;
+
+      is(
+        abPopup.label,
+        global.addressBook.dirName,
+        "the correct address book is selected in the menu"
+      );
+      is(
+        abPopup.value,
+        global.addressBook.URI,
+        "the address book selected in the menu has the correct address book URI"
+      );
+      is(listNameFocusEvent.type, "focus", "list name field is focused");
+      is(listName.value, "", "no text in the list name field");
+      is(listNickName.value, "", "no text in the list nickname field");
+      is(listDescription.value, "", "no text in the description field");
+      is(addressInput1.value, "", "no text in the addresses list");
+      is(addressInputsCount, 1, "only one address list input exists");
+
+      EventUtils.sendString(inputs.mlName, mlWindow);
+
+      // Tab to nickname input.
+      EventUtils.sendKey("TAB", mlWindow);
+      EventUtils.sendString(inputs.nickName, mlWindow);
+
+      // Tab to description input.
+      EventUtils.sendKey("TAB", mlWindow);
+      EventUtils.sendString(inputs.description, mlWindow);
+
+      // Tab to address input and add addresses zero and one by entering
+      // both of them there.
+      EventUtils.sendKey("TAB", mlWindow);
+      EventUtils.sendString(inputs.addresses.slice(0, 2).join(", "), mlWindow);
+
+      mlDocElement.getButton("accept").click();
+    }
+  );
+
+  is(
+    global.dirTree.view.getCellText(2, global.dirTree.columns[0]),
+    inputs.abName,
+    `address book ("${inputs.abName}") is displayed in the address book list`
+  );
+
+  // Select the address book.
+  global.dirTreeClick(2, 1);
+
+  // Open the new mailing list dialog, the callback above interacts with it.
+  EventUtils.synthesizeMouseAtCenter(
+    global.abWindow.document.getElementById("button-newlist"),
+    { clickCount: 1 },
+    global.abWindow
+  );
+
+  await mailingListWindowPromise;
+
+  // Confirm that the mailing list and addresses were saved in the backend.
+
+  ok(
+    DisplayNameUtils.getCardForEmail(inputs.addresses[0]).card,
+    "address zero was saved"
+  );
+  ok(
+    DisplayNameUtils.getCardForEmail(inputs.addresses[1]).card,
+    "address one was saved"
+  );
+
+  let childCards = [...global.addressBook.childCards];
+
+  ok(
+    childCards.find(card => card.primaryEmail == inputs.addresses[0]),
+    "address zero was saved in the correct address book"
+  );
+  ok(
+    childCards.find(card => card.primaryEmail == inputs.addresses[1]),
+    "address one was saved in the correct address book"
+  );
+
+  let mailList = MailUtils.findListInAddressBooks(inputs.mlName);
+
+  // Save the mailing list UID so we can confirm it is the same later.
+  global.mailListUID = mailList.UID;
+
+  ok(mailList, "mailing list was created");
+  ok(
+    global.addressBook.hasMailListWithName(inputs.mlName),
+    "mailing list was created in the correct address book"
+  );
+  is(mailList.dirName, inputs.mlName, "mailing list name was saved");
+  is(
+    mailList.listNickName,
+    inputs.nickName,
+    "mailing list nick name was saved"
+  );
+  is(
+    mailList.description,
+    inputs.description,
+    "mailing list description was saved"
+  );
+
+  let listCards = [...fixIterator(mailList.addressLists, Ci.nsIAbCard)];
+
+  ok(
+    listCards[0].hasEmailAddress(inputs.addresses[0]),
+    "address zero was saved in the mailing list"
+  );
+  ok(
+    listCards[1].hasEmailAddress(inputs.addresses[1]),
+    "address one was saved in the mailing list"
+  );
+  is(listCards.length, 2, "two cards exist in the mailing list");
+});
+
+/**
+ * Open the mailing list dialog and modify the mailing list.
+ */
+add_task(async () => {
+  let mailingListWindowPromise = BrowserTestUtils.promiseAlertDialog(
+    null,
+    "chrome://messenger/content/addressbook/abEditListDialog.xul",
+    // A callback that can interact with the mailing list dialog.
+    async mlWindow => {
+      let mlDocument = mlWindow.document;
+      let mlDocElement = mlDocument.documentElement;
+
+      // The address input nodes are not there yet when the dialog window is
+      // loaded, so wait until they exist.
+      await mailTestUtils.awaitElementExistence(
+        MutationObserver,
+        mlDocument,
+        "addressingWidget",
+        "addressCol1#3"
+      );
+
+      await BrowserTestUtils.waitForEvent(
+        mlDocument.getElementById("addressCol1#3"),
+        "focus"
+      );
+
+      let listName = mlDocument.getElementById("ListName");
+      let listNickName = mlDocument.getElementById("ListNickName");
+      let listDescription = mlDocument.getElementById("ListDescription");
+      let addressInput1 = mlDocument.getElementById("addressCol1#1");
+      let addressInput2 = mlDocument.getElementById("addressCol1#2");
+
+      is(listName.value, inputs.mlName, "list name is displayed correctly");
+      is(
+        listNickName.value,
+        inputs.nickName,
+        "list nickname is displayed correctly"
+      );
+      is(
+        listDescription.value,
+        inputs.description,
+        "list description is displayed correctly"
+      );
+      is(
+        addressInput1 && addressInput1.value,
+        getDisplayedAddress(inputs.addresses[0]),
+        "address zero is displayed correctly"
+      );
+      is(
+        addressInput2 && addressInput2.value,
+        getDisplayedAddress(inputs.addresses[1]),
+        "address one is displayed correctly"
+      );
+
+      let textInputs = mlDocument.querySelectorAll(".textbox-addressingWidget");
+      is(textInputs.length, 3, "no extraneous addresses are displayed");
+
+      // Add addresses two and three.
+      EventUtils.sendString(inputs.addresses.slice(2, 4).join(", "), mlWindow);
+      EventUtils.sendKey("RETURN", mlWindow);
+      await new Promise(resolve => mlWindow.setTimeout(resolve));
+
+      // Delete the address in the second row (address one).
+      EventUtils.synthesizeMouseAtCenter(
+        addressInput2,
+        { clickCount: 1 },
+        mlWindow
+      );
+      EventUtils.synthesizeKey("a", { accelKey: true }, mlWindow);
+      EventUtils.sendKey("BACK_SPACE", mlWindow);
+
+      // Modify the list's name, nick name, and description fields.
+      let modifyField = id => {
+        EventUtils.synthesizeMouseAtCenter(id, { clickCount: 1 }, mlWindow);
+        EventUtils.sendKey("END", mlWindow);
+        EventUtils.sendString(inputs.modification, mlWindow);
+      };
+      modifyField(listName);
+      modifyField(listNickName);
+      modifyField(listDescription);
+
+      mlDocElement.getButton("accept").click();
+    }
+  );
+
+  is(
+    global.dirTree.view.getCellText(2, global.dirTree.columns[0]),
+    inputs.abName,
+    `address book ("${inputs.abName}") is displayed in the address book list`
+  );
+
+  // Double-click on the address book name to reveal the mailing list.
+  global.dirTreeClick(2, 2);
+
+  is(
+    global.dirTree.view.getCellText(3, global.dirTree.columns[0]),
+    inputs.mlName,
+    `mailing list ("${inputs.mlName}") is displayed in the address book list`
+  );
+
+  // Open the mailing list dialog, the callback above interacts with it.
+  global.dirTreeClick(3, 2);
+
+  await mailingListWindowPromise;
+
+  // Confirm that the mailing list and addresses were saved in the backend.
+
+  ok(
+    DisplayNameUtils.getCardForEmail(inputs.addresses[2]).card,
+    "address two was saved"
+  );
+  ok(
+    DisplayNameUtils.getCardForEmail(inputs.addresses[3]).card,
+    "address three was saved"
+  );
+
+  let childCards = [...global.addressBook.childCards];
+
+  ok(
+    childCards.find(card => card.primaryEmail == inputs.addresses[2]),
+    "address two was saved in the correct address book"
+  );
+  ok(
+    childCards.find(card => card.primaryEmail == inputs.addresses[3]),
+    "address three was saved in the correct address book"
+  );
+
+  let mailList = MailUtils.findListInAddressBooks(
+    inputs.mlName + inputs.modification
+  );
+
+  is(mailList && mailList.UID, global.mailListUID, "mailing list still exists");
+
+  ok(
+    global.addressBook.hasMailListWithName(inputs.mlName + inputs.modification),
+    "mailing list is still in the correct address book"
+  );
+  is(
+    mailList.dirName,
+    inputs.mlName + inputs.modification,
+    "modified mailing list name was saved"
+  );
+  is(
+    mailList.listNickName,
+    inputs.nickName + inputs.modification,
+    "modified mailing list nick name was saved"
+  );
+  is(
+    mailList.description,
+    inputs.description + inputs.modification,
+    "modified mailing list description was saved"
+  );
+
+  let listCards = [...fixIterator(mailList.addressLists, Ci.nsIAbCard)];
+
+  ok(
+    listCards[0].hasEmailAddress(inputs.addresses[0]),
+    "address zero was saved in the mailing list (is still there)"
+  );
+  ok(
+    listCards[1].hasEmailAddress(inputs.addresses[2]),
+    "address two was saved in the mailing list"
+  );
+  ok(
+    listCards[2].hasEmailAddress(inputs.addresses[3]),
+    "address three was saved in the mailing list"
+  );
+
+  let hasAddressOne = listCards.find(card =>
+    card.hasEmailAddress(inputs.addresses[1])
+  );
+
+  ok(!hasAddressOne, "address one was deleted from the mailing list");
+
+  is(listCards.length, 3, "three cards exist in the mailing list");
+});
+
+/**
+ * Open the mailing list dialog and confirm the changes are displayed.
+ */
+add_task(async () => {
+  let mailingListWindowPromise = BrowserTestUtils.promiseAlertDialog(
+    null,
+    "chrome://messenger/content/addressbook/abEditListDialog.xul",
+    // A callback that can interact with the mailing list dialog.
+    async mailingListWindow => {
+      let mlDocument = mailingListWindow.document;
+      let mlDocElement = mlDocument.documentElement;
+
+      // The address input nodes are not there yet when the dialog window is
+      // loaded, so wait until they exist.
+      await mailTestUtils.awaitElementExistence(
+        MutationObserver,
+        mlDocument,
+        "addressingWidget",
+        "addressCol1#4"
+      );
+
+      await BrowserTestUtils.waitForEvent(
+        mlDocument.getElementById("addressCol1#4"),
+        "focus"
+      );
+
+      let listName = mlDocument.getElementById("ListName");
+      let listNickName = mlDocument.getElementById("ListNickName");
+      let listDescription = mlDocument.getElementById("ListDescription");
+      let addressInput1 = mlDocument.getElementById("addressCol1#1");
+      let addressInput2 = mlDocument.getElementById("addressCol1#2");
+      let addressInput3 = mlDocument.getElementById("addressCol1#3");
+
+      is(
+        listName.value,
+        inputs.mlName + inputs.modification,
+        "modified list name is displayed correctly"
+      );
+      is(
+        listNickName.value,
+        inputs.nickName + inputs.modification,
+        "modified list nickname is displayed correctly"
+      );
+      is(
+        listDescription.value,
+        inputs.description + inputs.modification,
+        "modified list description is displayed correctly"
+      );
+      is(
+        addressInput1 && addressInput1.value,
+        getDisplayedAddress(inputs.addresses[0]),
+        "address zero is displayed correctly (is still there)"
+      );
+      is(
+        addressInput2 && addressInput2.value,
+        getDisplayedAddress(inputs.addresses[2]),
+        "address two is displayed correctly"
+      );
+      is(
+        addressInput3 && addressInput3.value,
+        getDisplayedAddress(inputs.addresses[3]),
+        "address three is displayed correctly"
+      );
+
+      let textInputs = mlDocument.querySelectorAll(".textbox-addressingWidget");
+      is(textInputs.length, 4, "no extraneous addresses are displayed");
+
+      mlDocElement.getButton("cancel").click();
+    }
+  );
+
+  is(
+    global.dirTree.view.getCellText(3, global.dirTree.columns[0]),
+    inputs.mlName,
+    `mailing list ("${inputs.mlName}") is displayed in the address book list`
+  );
+
+  // Open the mailing list dialog, the callback above interacts with it.
+  global.dirTreeClick(3, 2);
+
+  await mailingListWindowPromise;
+});
+
+/**
+ * Tear down: delete the address book and close the address book window.
+ */
+add_task(async () => {
+  let mailingListWindowPromise = BrowserTestUtils.promiseAlertDialog(
+    "accept",
+    "chrome://global/content/commonDialog.xul"
+  );
+
+  is(
+    global.dirTree.view.getCellText(2, global.dirTree.columns[0]),
+    inputs.abName,
+    `address book ("${inputs.abName}") is displayed in the address book list`
+  );
+
+  global.dirTreeClick(2, 1);
+  EventUtils.sendKey("DELETE", global.abWindow);
+
+  await mailingListWindowPromise;
+
+  let addressBook = [...MailServices.ab.directories].find(
+    directory => directory.dirName == inputs.abName
+  );
+
+  ok(!addressBook, "address book was deleted");
+
+  global.abWindow.close();
+});
diff --git a/mailnews/addrbook/test/browser/head.js b/mailnews/addrbook/test/browser/head.js
new file mode 100644
index 0000000000..66574fa7a9
--- /dev/null
+++ b/mailnews/addrbook/test/browser/head.js
@@ -0,0 +1,55 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* globals MailServices */
+
+async function openAddressBookWindow() {
+  let addressBookWindowPromise = BrowserTestUtils.domWindowOpened(
+    null,
+    async win => {
+      // This test function waits until the "load" event has happened.
+      await BrowserTestUtils.waitForEvent(win, "load");
+
+      return (
+        win.document.documentURI ==
+        "chrome://messenger/content/addressbook/addressbook.xul"
+      );
+    }
+  );
+
+  const addressBookButton = document.getElementById("button-address");
+  EventUtils.synthesizeMouseAtCenter(addressBookButton, { clickCount: 1 });
+
+  let abWindow = await addressBookWindowPromise;
+
+  await new Promise(resolve => abWindow.setTimeout(resolve));
+
+  ok(abWindow && abWindow instanceof Window, "address book window was opened");
+
+  return abWindow;
+}
+
+async function createNewAddressBook(abWindow, abName) {
+  let newAddressBookPromise = BrowserTestUtils.promiseAlertDialog(
+    null,
+    "chrome://messenger/content/addressbook/abAddressBookNameDialog.xul",
+    abNameDialog => {
+      EventUtils.sendString(abName, abNameDialog);
+      abNameDialog.document.documentElement.getButton("accept").click();
+    }
+  );
+
+  // Using the UI was unreliable so just call the function.
+  abWindow.AbNewAddressBook();
+
+  await newAddressBookPromise;
+
+  let addressBook = [...MailServices.ab.directories].find(
+    directory => directory.dirName == abName
+  );
+
+  ok(addressBook, "a new address book was created");
+
+  return addressBook;
+}
diff --git a/mailnews/addrbook/test/moz.build b/mailnews/addrbook/test/moz.build
index 281cb83cd3..7189d7a51a 100644
--- a/mailnews/addrbook/test/moz.build
+++ b/mailnews/addrbook/test/moz.build
@@ -7,3 +7,7 @@ XPCSHELL_TESTS_MANIFESTS += [
     'unit/xpcshell-jsaddrbook.ini',
     'unit/xpcshell-mdbaddrbook.ini',
 ]
+
+BROWSER_CHROME_MANIFESTS += [
+    'browser/browser.ini',
+]
diff --git a/mailnews/test/resources/mailTestUtils.js b/mailnews/test/resources/mailTestUtils.js
index 92c0dbeb81..78f5a472d1 100644
--- a/mailnews/test/resources/mailTestUtils.js
+++ b/mailnews/test/resources/mailTestUtils.js
@@ -548,4 +548,61 @@ var mailTestUtils = {
     }
     return -1;
   },
+
+  /**
+   * Click on a particular cell in a tree. `window` is not defined here in this
+   * file, so we can't provide it as a default argument. Similarly, we pass in
+   * `EventUtils` as an argument because importing it here does not work
+   * because `window` is not defined.
+   *
+   * @param {Object} EventUtils - The EventUtils object.
+   * @param {Window} win - The window the tree is in.
+   * @param {Element} tree - The tree element.
+   * @param {number} row - The tree row to click on.
+   * @param {number} column - The tree column to click on.
+   * @param {Object} event - The mouse event to synthesize, e.g. `{ clickCount: 2 }`.
+   */
+  treeClick(EventUtils, win, tree, row, column, event) {
+    let coords = tree.getCoordsForCellItem(row, tree.columns[column], "cell");
+    let treeChildren = tree.lastElementChild;
+    EventUtils.synthesizeMouse(
+      treeChildren,
+      coords.x + coords.width / 2,
+      coords.y + coords.height / 2,
+      event,
+      win
+    );
+  },
+
+  /**
+   * For waiting until an element exists in a given document. Pass in the
+   * `MutationObserver` as an argument because importing it here does not work
+   * because `window` is not defined here.
+   *
+   * @param {Object} MutationObserver - The MutationObserver object.
+   * @param {Document} doc - Document that contains the elements.
+   * @param {string} observedNodeId - Id of the element to observe.
+   * @param {string} awaitedNodeId - Id of the element that will soon exist.
+   * @return {Promise.<undefined>} - A promise fulfilled when the element exists.
+   */
+  awaitElementExistence(MutationObserver, doc, observedNodeId, awaitedNodeId) {
+    return new Promise(resolve => {
+      let outerObserver = new MutationObserver((mutationsList, observer) => {
+        for (let mutation of mutationsList) {
+          if (mutation.type == "childList" && mutation.addedNodes.length) {
+            let element = doc.getElementById(awaitedNodeId);
+
+            if (element) {
+              observer.disconnect();
+              resolve();
+              return;
+            }
+          }
+        }
+      });
+
+      let nodeToObserve = doc.getElementById(observedNodeId);
+      outerObserver.observe(nodeToObserve, { childList: true });
+    });
+  },
 };