> For the complete documentation index, see [llms.txt](https://developer.thunderbird.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developer.thunderbird.net/add-ons/updating/tb68.md).

# Update for Thunderbird 68

{% hint style="info" %}
Technically, legacy bootstrap extensions and legacy overlay extensions need to be converted to modern WebExtensions, but by activating the **legacy mode**, their general structure does not need to be changed. Such extensions are called legacy WebExtensions.
{% endhint %}

## Required Changes

There are two types of changes which are required to make your legacy extensions compatible with Thunderbird 68:

* The legacy extension must be converted to a legacy WebExtension by replacing the old `install.rdf` by a `manifest.json`.

{% content-ref url="/pages/-Lc5vkKneusydLgduFSY" %}
[Convert legacy overlay extension to legacy WebExtension](/add-ons/updating/historical-overview/overlays.md)
{% endcontent-ref %}

{% content-ref url="/pages/-LfUZCpUvryuAmXOkWlj" %}
[Convert legacy bootstrapped extension to legacy WebExtension](/add-ons/updating/historical-overview/bootstrapped.md)
{% endcontent-ref %}

* All legacy extensions need to be updated to reflect changes in Thunderbird core, like renamed/replaced API calls, removed support for some XUL elements (need to use HTML elements now) and much more.

{% content-ref url="/pages/-Lc5wk5ug7\_NLqWCxYHg" %}
[Adapt to Changes in Thunderbird 61-68](/add-ons/updating/tb68/changes.md)
{% endcontent-ref %}

{% hint style="danger" %}
Even though it is possible to have both `install.rdf` and `manifest.json` files in your extension, so you *could* release a version compatible with Thunderbird 60 and 68, it is *not* suggested for the following reasons:

* The amount of changes is huge and some changes are incompatible with Thunderbird 60 so it will require extra steps to ensure the modified version still runs with Thunderbird 60.
* You may actually break your add-on for Thunderbird 60 users by releasing a backward compatible version for Thunderbird 68 ("Do not fix something, that is not broken").
* We think the time and resources needed to code and test backward compatible add-ons is not justified by the small amount of users running older versions of Thunderbird.
  {% endhint %}

{% hint style="success" %}
It **is** possible to maintain a legacy version **and** a WebExtension version of your add-on in parallel on ATN! You just need to use a higher major version number for the WebExtension version of your add-on and keep the old major version number when releasing a new legacy version. Basically releasing them in two different branches.
{% endhint %}