NoScript

A very good script blocker for Firefox. A combination of this little extension and Adblock, (which I posted about a few weeks ago), will insure that you see no unwanted pop-ups or scripted advertisements. Even more importantly, it pre-empts all malicious scripts, preventing the background installation of spyware and other 'net nasties.

Please note that this extension is a white-list application operating under a positive default: in English, that means you have to set permissions for sites you wish to allow the use of Javascript, Flash, etc., such as your banking site. Once set, however, the permissions stay that way until and unless you switch them off again. It means you'll have to take a few minutes to go through and toggle permissions for your allowed sites, but that's well worth the security of preventing any annoying or malicious scripts running on your machine.

Click here to go to the Firefox webste and install the latest version of NoScript.