First of all, Thunderbird for whatever reason does not trust Lets Encrypt certificates. Is Thunderbird special? Next, when it asks to confirm the cert, the confirmation dialog and a message box appear, hidden under the new email window. Is there a good reason why they should not pop up, like all normal new dialogs and message boxes pop up, in millions of other softwares? Does Thunderbird have to be special and hide its dialogs? And lastly, it takes a deliberate development effort to hide new dialogs. Is there a good reason for you to do that to us, so that we have a hard time Alt-Tabbing into the confirmation dialog? What is it?