I have a dutch Thunderbird version so am guessing at item names. When I chose an already send message from the dispatched folder to edit, I can left mouse click on the text field without problem but after adding or changing text the next click in the text field anywhere among the text lines closes Thunderbird and returns me to the desktop. If I click outside the text lines it just moves the cursor to the end of line position. Starting Thunderbird again it is in the state it was when I first started it, no changes are kept like opened or closed folders. Problem exists also in protected mode.