> 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.md).

# Add-on Development

- [Introduction](https://developer.thunderbird.net/add-ons/about-add-ons.md): What you need to know about making add-ons for Thunderbird.
- [What's new?](https://developer.thunderbird.net/add-ons/whats-new.md): The latest developments for Add-On developers.
- [Manifest Version 3](https://developer.thunderbird.net/add-ons/whats-new/manifest-v3.md)
- [A "Hello World" Extension Tutorial](https://developer.thunderbird.net/add-ons/hello-world-add-on.md): All the information you need to get your first Thunderbird extension up and running.
- [Using WebExtension APIs](https://developer.thunderbird.net/add-ons/hello-world-add-on/using-webextension-apis.md): Extending the simple example extension to make use of WebExtension APIs.
- [Using a Background Page](https://developer.thunderbird.net/add-ons/hello-world-add-on/using-a-background-page.md): Extending the example extension to use a background page.
- [Using Content Scripts](https://developer.thunderbird.net/add-ons/hello-world-add-on/using-content-scripts.md): Extending the example extension to use a content script.
- [A Guide to Extensions](https://developer.thunderbird.net/add-ons/mailextensions.md): How to create extensions for Thunderbird.
- [Supported Manifest Keys](https://developer.thunderbird.net/add-ons/mailextensions/supported-manifest-keys.md): Descriptions of all manifest keys supported by Thunderbird.
- [Supported UI Elements](https://developer.thunderbird.net/add-ons/mailextensions/supported-ui-elements.md): Descriptions and examples of MailExtension APIs to interact with Thunderbird's user interface.
- [Supported WebExtension APIs](https://developer.thunderbird.net/add-ons/mailextensions/supported-webextension-api.md): Descriptions of all WebExtension API supported by Thunderbird.
- [Introducing Experiments](https://developer.thunderbird.net/add-ons/mailextensions/experiments.md)
- [A Guide to Themes](https://developer.thunderbird.net/add-ons/web-extension-themes.md): How to create themes for Thunderbird.
- [Developer Community](https://developer.thunderbird.net/add-ons/community.md): Learn how to get in touch with the Thunderbird add-on developer community.
- [Documentation & Resources](https://developer.thunderbird.net/add-ons/resources.md): A collection of the most important developer resources outside of developer.thunderbird.net.
- [Tips and Tricks](https://developer.thunderbird.net/add-ons/resources/tips-and-tricks.md): Tips and tricks for successful Thunderbird add-on development.
- [Add-on Update Guides](https://developer.thunderbird.net/add-ons/updating.md)
- [Updates for Thunderbird 140](https://developer.thunderbird.net/add-ons/updating/updates-for-thunderbird-140.md)
- [Update for Thunderbird 128](https://developer.thunderbird.net/add-ons/updating/tb128.md): Required steps to update add-ons for Thunderbird 128.
- [Update for Thunderbird 115](https://developer.thunderbird.net/add-ons/updating/tb115.md): Required steps to update add-ons for Thunderbird 115.
- [Adapt to Changes in Thunderbird 103-115](https://developer.thunderbird.net/add-ons/updating/tb115/adapt-to-changes-in-thunderbird-103-115.md)
- [Update for Thunderbird 102](https://developer.thunderbird.net/add-ons/updating/tb102.md): Required steps to update add-ons for Thunderbird 102.
- [Adapt to Changes in Thunderbird 92-102](https://developer.thunderbird.net/add-ons/updating/tb102/adapt-to-changes-in-thunderbird-92-102.md)
- [Update for Thunderbird 91](https://developer.thunderbird.net/add-ons/updating/tb91.md): Required steps to update add-ons for Thunderbird 91.
- [Adapt to Changes in Thunderbird 79-91](https://developer.thunderbird.net/add-ons/updating/tb91/changes.md)
- [Update for Thunderbird 78](https://developer.thunderbird.net/add-ons/updating/tb78.md): Required steps to update add-ons for Thunderbird 78.
- [Adapt to Changes in Thunderbird 69-78](https://developer.thunderbird.net/add-ons/updating/tb78/changes.md)
- [Update for Thunderbird 68](https://developer.thunderbird.net/add-ons/updating/tb68.md): Required steps to update add-ons for Thunderbird 68.
- [Adapt to Changes in Thunderbird 61-68](https://developer.thunderbird.net/add-ons/updating/tb68/changes.md)
- [How to convert legacy extensions?](https://developer.thunderbird.net/add-ons/updating/historical-overview.md)
- [Convert wrapped WebExtensions to modern WebExtensions](https://developer.thunderbird.net/add-ons/updating/historical-overview/wrapped-to-modern.md)
- [Convert legacy WebExtensions to modern WebExtensions](https://developer.thunderbird.net/add-ons/updating/historical-overview/legacy-to-modern.md)
- [Convert legacy overlay extension to legacy WebExtension](https://developer.thunderbird.net/add-ons/updating/historical-overview/overlays.md)
- [Convert legacy bootstrapped extension to legacy WebExtension](https://developer.thunderbird.net/add-ons/updating/historical-overview/bootstrapped.md)