ui.alertNotificationOrigin controls the position and direction from which popup notifications invoked by nsIAlertsService are sliding in.

Values

0
bottom right corner, vertical slide-in from the bottom
1
bottom right corner, horizontal slide-in from the right
2
bottom left corner, vertical slide-in from the bottom
3
bottom left corner, horizontal slide-in from the left
4
top right corner, vertical slide-in from the top
5
top right corner, horizontal slide-in from the right
6
top left corner, vertical slide-in from the top
7
top left corner, horizontal slide-in from the left