One security risk when browsing the internet is that many websites include scripts, small programs for particular tasks.
Scripts can range from the wholly benign, for producing rounded corners on boxes, to dangerous security risks. Noscript blocks these scripts from running in Firefox unless explicitly told otherwise.
When a script is blocked a bar with an options button appears at the bottom of the screen alerting you. This can be used to mark a website as trusted so that the restrictions are lifted. This bar can be set to disappear after a time limit if it becomes annoying. An sound can also be set to warn of blocked scripts.
Trusted websites can also be added to the whitelist in the options window.
There is a button that can be added to the toolbar with quick options for blocking or allowing scripts on a page. It helpfully changes to show whether or not the current web page has been given permission or not.
Even though Firefox is generally more secure than Internet Explorer, this is still worth installing on any computer using Firefox.