Auto Shutdown is a Firefox add-on that helps you to shut down the computer, among other tasks, when the download completes.

Besides shutting down your computer, Auto Shutdown allows you to select other commands for various operating systems. You can easily tell Auto Shutdown to power down your computer, hibernate/sleep, or even execute an external command.

Features:

• Executing user scripts after all downloads are finished or computer is idle for specific time
• Play sound after each/All downloads are finished
• Restore Firefox from last session
• Customizable shutdown/idle scripts
• Supporting DownThemAll

Download and install Auto Shutdown Firefox add-on from here.