If the black dot is “on” then the TF Visor window will stay “up” in the background when you select another app to be the foreground window. In other words, the Visor is pinned in place.
If you click the button that contains the black dot (or use your hotkey for Pin Visor, see screenshot) , the black dot will disappear and now the Visor window will automatically be dismissed when you select another app to be the foreground window.
Hope that helps!
At least it helps in my case. Thank you!