[orca-list] Different layout in the latest Thunderbird

[Hermann <meinelisten onlinehome de>]

Hi,
just updated Thunderbird, and I have to notice, that the layout of the 
program seems to have changed:
Usually there were two columns: One that shows all the folders, and one 
that shows the messages in the chosen folder.
Now I see a third column that shows me the folder name again as a tab; 
the difference is that I cannot move the folders unless I change to the 
usual folder tree by pressing tab.
So what has been changed, Orca's way to display, or - what I suspect - 
the layout in Thunderbird?
What's the sence of this?
Hermann