There are a lot of big file in online which we need to download but this kind of file take long time to complete download. So when you need to download something from online if the file is not small than you have to wait for finish download to shut down your computer. So that means you cant shut down your PC if you are not able to finish download. But what is great news to you that now from FireFox browser if you download any big file you can go away from your computer without shutdown it. After download complete your computer will automatic shutdown for you. You can sleep go for visit your Friends house what ever you want. Your computer will auto shat down after the file download complete. So now you may ask how to enable such kind of facilities in Mozilla firefox? Yes recently Mozilla FireFox has launched a new add ons for it just go here https://addons.mozilla.org/en-US/firefox/addon/5452 and install this add ons and restart FireFox .Now you can see at status bar auto shutdown icon. Just click on it and change the settings by right click on tools options.when a new file begin to download auto shut down icon will run, if you want to shat down after download finish just select it and can go for sleep, you may ask i can shutdown my pc automatically after a definite time but what i mean here you can set your auto shut down manually from your pc settings but you don’t know when your file download will be completed. So only if you do any large file download you can try this option for shut down your computer.
Update: Okay guys as far as i have seen that the owner of this add ons never update its version. So therefore if this add ons is not working , I highly recommend you to check this post if you are not able to use this add ons any more to your Browser.