NoScript provides essential protection for Firefox, and other Mozilla-based browsers. Most web browsers, by default, do not give you the option to customize what kind of web site content you want to be viewed in your browser. This causes major problems because sites often use 3rd party code to insert multimedia content and ads. Many of these 3rd parties can be compromised resulting in your computer becoming a victim of a security attack.
Check out this guide on how to use Noscript from ghacks.net. Also if you need a visual walk though, check out this video tutorial on how to use this plug-in.
As Noscript blocks all script related content on a web site, the site you visit may not fuction in the way you are used to until you learn how to use Noscript. Its well worth your time to understand a little bit about blocking 3rd party content on a web site you visit because you want to be in control of what content is displayed on your computer, instead of an arbitrary company being in control of your browsing experience. Many well established sites like “CNN” and even online shopping sites do not have your best interest at heart when it comes to the security of your device.
Update: 2019/12/30: A developer recently released a Noscript extension for Chrome.