I have 5 windows open in Firefox, yet only 1 of them is visible/accessible on the Windows Taskbar. I know there are 5 windows open as Troubleshooting Information reports "Multiprocess Windows: 5/5" Sometimes when I launch Firefox, the other 4 windows will be visible, and this current one will disappear. If I go to Recently Closed Windows and open that window, it will appear, but the other 4 will be hidden again. Other times, I will launch Firefox and one window will be invisible, and it won't appear unless I close all the other windows, then it will suddenly appear out of nowhere.