Rated 5 out of 5 stars

per Vako el nov. 10, 2018 · enllaç permanent

Add-ons not marked as compatible with Thunderbird 60 by their authors will be disabled.
This can be reverted via preference: extensions.strictCompatibility
So go to Options->Advanced tab->Config.Editor and search for "extensions.strictCompatibility" then change it from True to False by double clicking on it.