Intent to de-support: traditional add-ons

Eyal Rozenberg eyalroz at
Tue Oct 1 13:45:27 UTC 2019

I don't understand what it is you're telling us. Starting with
Thunderbird 68, traditional add-ons aren't supported. Support has
already been dropped. So what exactly will be dropped in TB 72 that
hasn't been already?

As for ATN, remember that TB 60 and earlier versions will still be
running for quite a long time. It would be unfortunate if those would
lose accesss to an extensions website.


On 01/10/2019 16:02, Magnus Melin wrote:
> Since version 57, Firefox only supports add-ons through the
> WebExtensions APIs. At the time, Thunderbird decided to continue
> supporting traditional add-ons, since we hadn't yet been able to develop
> replacing APIs for add-on developers to use.
> Since then, Thunderbird has been developing WebExtensions APIs (aka
> MailExtensions), and the number of APIs available is continuously
> growing:
> Because the toolkit support for traditional add-ons has been largely
> removed, this has meant a lot of work for Thunderbird to keep things
> going for add-ons. For the server side it has also meant a lot of extra
> work ( is a fork of Add-on
> developers haven't had an easy ride either: The number of changes to
> make an add-on compatible has been significant.
> Going forwards we want to change this. Support for traditional add-ons
> is going to be dropped as soon as we're ready to do so internally. There
> are a few pieces of code that we need to convert over internally:
>   * Lightning: to be integrated into the code base
>   * Mozmill (used in our test infra): we're converting over to using
>     mochitests instead
> It's not yet clear exactly when we're ready to rip out the support for
> traditional add-ons from the code base, but it should be whitin the
> Thunderbird 72 time frame - so by end of 2019. The next major version of
> Thunderbird, version 78, will be out around June 2020. Up until then,
> code wise many things are going to change. For instance, what is left of
> XUL will be gradually going away, and documents will shifted to being
> XHTML with a less and less XUL flavor.
> Dropping support for non-MailExtension add-ons is also needed for
> Supporting old-style add-ons would require a
> significant investment in the back-end there, since the Django version
> of the back-end would reach EOL and have to go through a painful and
> expensive upgrade.
> As an author of a traditional add-on, what should you do? There are two
> routes: A) convert your add-on to a MailExtension. If the API you need
> doesn't exist yet, tell us about it
> <>.
> B) convert your add-on to a Web Extension Experiment
> <>.
> Most add-ons should be able to be converted to an experiment with a
> reasonable effort. The recommended path is forward is to convert it to
> an a MailExtension though. That will make sure the add-on works without
> significant changes over many years. If you go with option B, you'll
> have to maintain a lot of more code yourself and breakages can and will
> be bad unless you keep up really close. MailExtension Experiments should
> be seen as such, experiments with the goal of getting the API they need
> into Thunderbird core. Please work with us on getting the needed pieces
> in as a supported API. Initially we'll be allowing experiments to be
> exposed to the general public, but over time (years) Thunderbird will
> gravitate towards not having the experiments available to the general
> public, the same way it works for Firefox.
>  -Magnus
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