another fix for multiple windows in DMT Puntuado con 4 de 5 estrellas
I have the "All-in-One Sidebar" installed ( please see http://firefox.exxile.net/aios/index.php ),
which i really can highly recommend and:
In the Download Manager Tweak settings Datei/Fenster tab ( i'm using the german version, in english
it might be marked as File/Window or similar) i highlighted "In der Sidebar öffnen" / "Open in Sidebar".
Although this does NOT prevent from opening multiple entries in the side bar, but lets you close/erease
them with ONE MOUSE CLICK ONLY on the traffic sign "NO Entry" (round red with white bar).
So i think this would be a temporary help