I answered directly from Thunderbird but it seems the messages were not delivered correctly. However, I discovered that the problem was cause by some custom css I added to the theme. sorry for bothering with this.
Themes
Adaptable - Empty activity Chooser
Αυτή η συζήτηση κλειδώθηκε κι έτσι δεν μπορείτε να απαντήσετε σε αυτή.