Rated 5 out of 5 stars

le botti56 ar Lún. 17, 2018 · buan-nasc

I have to revise my rating: give now 5 stars.
The tip from stroehli did the trick. Javasript.enabled was set to 'false' (maybe by default or by another Add-on). I set it to 'true' now everthing works fine (Thunderbird 6.0).
For German users:
Einstellungen->Erweitert->Allgemein->Konfiguration bearbeiten...