Do you think that Firefox is preventing the shutdown?

Perform a System File Check to fix corrupted system files Win 7, 8, 10, Vista: https://support.microsoft.com/en-us/kb/929833 Win XP: https://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/system_file_checker.mspx?mfr=true

I can't think why this would happen, and I don't see any connection with Firefox but there a couple of methods you could try(Windows10). First, as a precaution, close all open programs. As a first question are you having any other opening/closing problems? Left click on the window at the end of the taskbar at the bottom lefthand corner of the desktop. Click on the power symbol(first up on the left hand side) then try the three options - Sleep, Shutdown, Restart. 2nd method - Right click on the same window, click on the arrow at Shut down or sign out which takes you to the same three options plus Sign out. Are you able to get any action at all?

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