Trying but....
Trying Ctrl-Tab....but it's indistinguishable which tab is active. At least with clicks I know from left to right I opened server1,2,3,4,5,6....20, but with Ctrl-Tab no chance to have a clue where on Earth I am.
Ctrl+Tab key, as that's much more efficient.
Alt+F4 or right click Close. With WinSCP all my day is a nightmare. Otherwise it's feature rich, just that X makes me pull out all my hair.