Add-ons/Thunderbird and SeaMonkey Add-ons FAQ

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Where can I find add-ons to install?

Add-ons for Firefox and Firefox for Android can be found at (also known as AMO).

Add-ons for Thunderbird and SeaMonkey can be found at

Why is there a separate site for Thunderbird and SeaMonkey add-ons?

The Firefox add-on development platform was migrated in 2017 to a new technology called WebExtensions. This makes it easy to create powerful cross-browser add-ons using web technologies. Throughout 2018, all legacy add-ons and legacy features on AMO are being phased out.

Given that Thunderbird and SeaMonkey still use legacy add-on technology, it was decided it would be easier for the add-on websites to split, so AMO can do away with legacy features and continue its development.

Who runs the Thunderbird and SeaMonkey add-ons site?

The site is managed by the Thunderbird Council and runs on Mozilla infrastructure. It runs on a forked version of the AMO code, and the Mozilla Add-ons Team are working with the Thunderbird Council to make the transition as smooth as possible.

How does this affect add-on users on Thunderbird and SeaMonkey?

This shouldn’t affect users. All AMO URLs pointing to Thunderbird or SeaMonkey add-ons should redirect to the new site. Add-on update requests should also be redirected. New versions of Thunderbird and SeaMonkey should point directly to the new site, so the redirects are eventually unnecessary.

I’m a developer. Where can I find my add-ons?

If your add-ons are compatible with Firefox or Firefox for Android, they can be found on AMO. If they are compatible with Thunderbird or SeaMonkey, they can be found on You should be able to log in using the same credentials as on AMO.

Since add-ons can support both Firefox and Thunderbird, or Firefox and SeaMonkey (or all of them), an add-on can be on both sites. The websites are independent, so changes done on one doesn’t reflect on the other.

How can I opt out of this process?

If you don’t want your add-ons on either site, you can go to your listing management page and either disable or delete your add-on. Note that if your add-on is on both sites, you might need to do this twice.

Where can I ask more questions about this?

You can post a message on our community forum or email amo-admins AT mozilla DOT com for additional information.