Oddly sounds exactly the same as https://support.mozilla.org/en-US/questions/1432903

Thunderbird mantains list of Oauth2 providers in following jsm module which is kind of restrictive to few well known Oauth2 providers like Google and Microsoft. https://searchfox.org/comm-central/source/mailnews/base/src/OAuth2Providers.jsm It is impossible to add my custom Oauth2 providers without modifying above jsm module. Later I found a solution to create add-on that can wrap up into experimental APIs to add my custom oauth urls, client id and secret. https://thunderbird.topicbox.com/groups/addons/Tc85dff9ce12063c6-Mb2343d4afee92f45e3868793 var scope = ChromeUtils.import("resource:///modules/OAuth2Providers.jsm", null); Unfortunately the suggestion did not work as ChromUtils.import() has dropped support for null as second argument for exporting global variables for some reason. I'd love to get this add-on working so that I can add my own custom provider that will help many customers who wanted to migrate from SASL PLAN to Oauth2 authentication mechanism. Can you share any suggestion?