how to disable JavaScript in Mozilla FireFox

How do you turn on JavaScript online if you have mozilla firefox on a linux computer? My computer won't let me go on facebook and youtube because javascript is turned off. But I don't know how to turn it back on. Online it says how to turn it on if you have a windows computer but I have linux and I use mozilla firefox on there so how do I do that?

I am using Ubuntu 10 (linux) and it doesn't effect your browser. All you have to do is turn on javascript in browser. To do that,

JavaScript controls in Firefox are in the Tools / Options menu (see Tools / Options image).
Once you get the Options menu, click on the Content tab. This is the screen you’ll see.