Hi There, I had this issue when I unplugged my external monitor, then I changed some settings on the laptop display, plugged the external monitor back in, changed which screen was the home screen and then changed them back - don't ask why I was doing all this nonsense, I just was :-) Anyway, I had the same problem where Firefox would open but I could not find the session on either screen. After awhile I figured it was just 'off in space' somewhere. The way I got it back was to right click on the 'phantom' window in the task bar, select 'move' and then use the left/right arrow keys until the window outline appeared on one of my screens - if you don't see an outline after holding the left arrow key for say 5 seconds, hold the right arrow key for about 10 seconds and it should come drifting back. Hope it helps.