I love Thunderbird, but at some point a while back a message summary box between the message table and message (see image) appeared.
IMHO, it is totally unnecessary and a huge waste of screen space that I'd prefer was freed up to actually see the message. For example, as in the redacted screenshot below, very little the actual message can be seen without scrolling.
This Message Summary Box is unnecessary because all the information it provides is on the message table view. As for the buttons, they all have common shortcut keys (and/or just right click to see them in a pop up)