I have all my computers set up so that the Windows taskbar is located at the bottom of the screen (as most people do). I also have the task bar set to "auto hide" which means that the task bar is hidden until the cursor is brought to the bottom of the screen. With the latest Firefox update, this function has been disabled due to the browsing window increasing in size and the only way to restore it to the earlier size is by putting the cursor at the top of the screen. Obviously you cannot have the cursor at the top and bottom of the screen at the same time. All my computers run Windows 7.