I close FF and it shuts down on the screen. At times when I try to start FF again (either by clicking the icon or a url - FF is my default browser). I start task manager and it does not show in "APPS" nor does it show in "BACKGROUND PROCESSES" or "WINDOW PROCESSES." I then start a program called "WINPATROL" (great program) - click on a tab "ACTIVE TASKS" which list all programs running on the PC. I find Firefox currently running after I closed the program. I "kill" the process via Winpatrol which stops the process. Try again and now FF starts up with no problem. using ver 58.0.1, on a Windows 10 Home 64bit system