Documentation & Resources

A collection of the most important developer resources outside of

MailExtension Development

A few helpful resources relevant for developing add-ons for Thunderbird.


The official Thunderbird add-on repository.

A list of all supported values, which can be used as strict_min_version and strict_max_version values in add-on manifest files.

A guide from the extension workshop with the most recent information on debugging add-ons. It is written for Mozilla Firefox but applies for Thunderbird as well.

A guide how to use Visual Studio Code to debug Thunderbird extension.

Documentation of all Extension APIs created specifically for Thunderbird. They are called MailExtension APIs to distinguish them from the standard WebExtension APIs inherited from Firefox.

Note: Thunderbird 115 and Thunderbird Beta supports Manifest V3. The new specification is not finalized yet and will continue to change.

A collection of explanatory sample extensions.

A collection of WebExtensions. They probably won’t work directly in Thunderbird, but they may provide hints on how to use some of the WebExtension APIs that Thunderbird inherited from Firefox.

The add-on developer support repository provides useful code snippets, examples and tools in order to better "weather" the transition to the new extension structure of Thunderbird 78.

Overall add-on statistics and a very powerful search in the code of all add-ons listed on (ATN) and a few other public repositories.

Central bug tracking for Mozilla projects. Some useful pages related to Thunderbird:

The main documentation for Mozilla developers. As Thunderbird is based on the Mozilla platform, some Mozilla documentation is valid for Thunderbird as well. Useful MDN pages on WebExtension are:

Experiment Development

Useful resources for converting legacy extensions or for creating Experiments.


An online viewer to search the Firefox code base (mozilla-central) and the Thunderbird code base (comm-central).

The current Firefox code documentation, which might be needed when converting legacy extensions.

The current Thunderbird code documentation, in addition to comments in idl files on comm-central. This is still work in progress.

The archived Mozilla documentation includes information about internal components and functions used by legacy extensions. Please be aware, that those pages are not maintained and are potentially outdated. Some useful direct links:

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