I open a session of Firefox and it hangs and is unresponsive. I cannot close it using the exit button or the File/Exit menu, so I opened another session of Firefox. The second session works fine.

Meanwhile, the first session remains in a hung state. If I close the second session using the "X" button, the first session stays open and hung. However, when I close the second session using the "File/Exit" option from the menu, both sessions close. Without exiting through the file menu in the second session, the only way to close the hanged first session is through the Windows Task Manager.