Something has changed in the way my Thunderbird email program operates, but I can’t figure out how it has changed. Originally when a new message arrived I would single click onto that message and it would open in the lower pane and the message would be shown as “read”. Now I have to double-click the message which then opens in a separate window. If I only single-click on the message it will not open and it remains as “unread”.
I have looked at all the tools and options to change back to the original format but cannot see where to do this. Have I missed something obvious?