Make your firefox "turn off the light" in youtube as Google Chrome

The famous Google Chrome extension "Turn Off The Light" will offer you a shining feature when having a watch on youtube/hulu ,etc.As is below:

Yet those firefoxers need not envy this, hence we have alternatives on Firefox, though applied to youtube only. (Tested only in 3.6.3)

1.If you have not a GreaseMonkey add-on,go here to install it.

2.Install the scripts YouTube "Lights Out"

3.Now you will get a cute button when watching youtube, as is below:

 

4.Enjony it! :)