How have you tried to shut down Firefox? Does the window close, but not the program?

Do you have the Firefox icon on your quick launch? Close Firefox. Right click on the icon and select Open New Tab. Sometimes this works. If it opens, close it by Menu > File > Exit.

Sorry, I don't understand your answer. It sounds like you might be referring to the Windows version, I'm on a Mac.

After closing everything else, hold down the power switch. This should force the power off.

None of the responses to this question offer a solution to why Firefox freezes and won't allow the computer to shutdown.

I second this problem. Some more technical details describing the issue:

• Firefox is completely invisible and unresponsive
• The Dock shows Firefox as active (dot under the icon)
• The 'Force Quit' dialog shows the Firefox process, it is however impossible to force quit Firefox. Nothing happens.
• Activity viewer or top command does not list any Firefox process. So also there is no PID to be killed.
• Unable to shutdown / restart the computer in a normal fashion. Shutdown process stalls when it comes to quitting Firefox. Only option is to force reboot using Terminal (sudo shutdown -r now) of holding down the power button.
• It looks like the 'higher layers' of the OS like Finder are unaware that Firefox process does not exist.
• Behavior occurs frequently but randomly.
• Installed and active add-ons: Ghostery, Adblock Plus and 1Password. Unclear if any of these play a role.

Today this problem occurred ones more after I closed my display, took my MBP to another place and resumed. After resuming Firefox was completely unresponsive and invisible again.