Adapt to Changes in Thunderbird 69-78

This document tries to cover all the internal changes that may by needed to make add-ons compatible with Thunderbird 78. If you find stuff that is no longer working but is not yet on this list, ask for help and advice in of our communication channels.

The changes are grouped by category and are listed in the order we became aware of them.

Removed XUL elements

As of Thunderbird 74, the built-in overlay loader has been removed, which means XUL overlay files are no longer supported. The preferred way to interact with Thunderbird is through WebExtension and MailExtension APIs, which only support HTML/CSS.

However, Thunderbird itself is still using XUL for its UI, and it is still possible to interact with that XUL based UI through experimental APIs. If for example you need a UI feature not yet available via MailExtension API, you can write an experimental API using a window listener and manipulate the UI as needed via JavaScript (check out the restart example). There are two ways to add XUL elements, either via pure JavaScript or via parseXULToFragment().

Since XUL is still usable, this document includes information about deprecated and removed XUL elements.

Some XUL elements have been converted to custom elements, which have an additional is="something" attribute. If such a custom element is to be created with createXULElement(), the is parameter needs to be passend in via the second argument:

let toolbar = document.createXULElement(
{ is : "customizable-toolbar" }
toolbar.setAttribute("is", "customizable-toolbar");


Removed completely in TB71. Use


All former values of the type parameter of the textbox element are supported by html:input as well. For proper styling include the following css file: chrome://messenger/skin/input-fields.css

The flex parameter is no longer supported and should be removed. Attach the input-container class to a surrounding hbox to force the input field to behave like a former flex="1" textbox.

If the input fields context menu is not working, you need to include two JavaScript files by adding:

<script src="chrome://global/content/globalOverlay.js"/>
<script src="chrome://global/content/editMenuOverlay.js.js"/>

JavaScript methods that are using element.localName == "textbox" , getElementsByTagName("textbox")or similar need to be updated as well.

Visually compare the fields before and after the conversion to be sure the UI, sizing, and spacing doesn't change.

<toolbar customizable="true">

In TB78 the XUL element toolbar with attribute customizable has been re-implemented as a custom element. It needs an additional is attribute. The following example is taken from the source of the Thunderbird calender:

<!-- Note the additional "is" attribute: -->
<toolbar is="customizable-toolbar"

Changed API


With TB69, the default namespace for createElement has switched from XUL to XHTML. So you can no longer create XUL elements with document.createElement() (but XHTML elements). To create XUL elements, use:



Bug 1558726 introduced a breaking change to the nsISocketTransportService interface:

The first parameter used to be an array and the second one its length. This length parameter has been dropped, causing all subsequent arguments to shift by one. Furthermore, to create a default socket, you now have to pass an empty array as first parameter, instead of null.

To stay backward compatible, check the argument count of "createTransport". In case it is 4 is is the new interface, in case it is 5 you got the old interface. Alternatively, you may also check if the version of Thunderbird is 69 or later.

if (transportService.createTransport.length === 4)
return transportService.createTransport(((secure) ? ["starttls"] : []), host, port, proxyInfo);
if (transportService.createTransport.length === 5) {
if (secure)
return transportService.createTransport(["starttls"], 1, host, port, proxyInfo);
return transportService.createTransport(null, 0, host, port, proxyInfo);
throw new Error("Unknown Create Transport signature");


Merged into nsICookie.


With TB70, window objects don't need to be and cannot be QI'ed to nsIDOMChromeWindow, nsIDOMWindow and nsIInterfaceRequestor. You can just remove its usage, this is backwards compatible to TB 68. See the fix applied to enigmail.

This does not apply to nsIXULWindow, which for example is used in nsIWindowMediatorListener.onOpenWindow(xulWindow).

Equally, TreeColumns and TreeContentView don't need to be and cannot be QI'ed to nsITreeView.


Renamed. Use



The 3rd parameter has been droped, which was the length of the array passed in as the 2nd parameter. See the patch applied to Thunderbird itself.


Module file extension changed in TB78 from js to jsm, now available via

const { IOUtils } = ChromeUtils.import("resource:///modules/IOUtils.jsm");


In TB78 the function AddRecipient() in the contact sidebar has been renamed to awAddRecipientsArray().


In TB71 MailServices.headerParser.parseHeadersWithArray() has been removed. Instead use:

let addresses = MailServices.headerParser.parseEncodedHeader(address);
for (let addr of addresses) {
let email =
let name =
let fullname = addr.toString();

Changes to the Address Book

Searching a nsIAbDirectory

In TB68 a nsIAbDirectory could be searched by simply attaching a search query to the URI of the directory when calling getDirectory():

let cards = MailServices.ab.getDirectory(URI + "?" + searchQuery).childCards;
while (cards.hasMoreElements()) {
let card = cards.getNext().QueryInterface(Components.interfaces.nsIAbCard);

In TB78 getDirectory() no longer accepts search queries and throws an error. Instead, use the search() method, which uses an nsIAbDirSearchListener. A simple promisified implementation could look like so:

searchDirectory: function (uri, search) {
return new Promise((resolve, reject) => {
let listener = {
cards : [],
onSearchFinished(aResult, aErrorMsg) {
onSearchFoundCard(aCard) {;
MailServices.ab.getDirectory(uri).search(search, listener);
let cards = await searchDirectory(URI, searchQuery);
for (let card of cards) {

Changes to the Preference System

Removal of onsyncfrompreference and onsynctopreference Attributes

With TB70, these two attributes have been removed from XUL elements like textbox, radio, checkbox and friends. This is no longer supported:

onsynctopreference="return onToPref();"
onsyncfrompreference="return onFromPref();"/>

Most of the XUL based preferences system has been long removed and had to be replaced by either using the preferencesBindings.js wrapper or by manually reimplementing that functionality using thensIPrefService.

The second approach is not affected by this change, as it has full control over the load and save process for all its preferences. ThepreferencesBindings.js wrapper has been updated and now supports:

function() { return onFromPref() });
function() { return onToPref() });

The nsIPrefServiceis not available via WebExtension APIs. It is therefore adviced to move away from storing addon preferences in a preference brach and instead use the local storage via the storage API. More information can be found in the update guide.