The NoScript Firefox extension provides extra protection for Firefox, Flock, Seamonkey and other mozilla-based browsers: this free, open source add-on allows JavaScript, Java and Flash and other plugins to be executed only by trusted web sites of your choice (e.g. your online bank), and provides the most powerful Anti-XSS protection available in a browser.

NoScript's unique whitelist based pre-emptive script blocking approach prevents exploitation of security vulnerabilities (known and even not known yet!) with no loss of functionality...

You can enable JavaScript, Java and plugin execution for sites you trust with a simple left-click on the NoScript status bar icon (look at the picture), or using the contextual menu, for easier operation in popup statusbar-less windows.

Usable security
Operating NoScript is really simple.
When you install NoScript, JavaScript, Java, Flash Silverlight and possibly other executable contents are blocked by default. You will be able to allow JavaScript/Java/... execution (scripts from now on) selectively, on the sites you trust. You can allow a site to run scripts temporarily, if you're just surfing randomly, or permanently, when you visit it often and you really trust it. This means that NoScript learns from your own browser habits and tends to disappear in the background after a while, but it promptly comes back to save your day if you stumble upon a malicious web page.
When you browse a site containing blocked scripts a notification, similar to those issued by popup blocker, is shown.

Site matching
For each site you can decide to allow the exact address, or the exact domain, or a parent domain. If you enable a domain (e.g. mozilla.org), you're implicitly enabling all its subdomains (e.g. www.mozilla.org, addons.mozilla.org and so on) with every possible protocol (e.g. http and https). If you enable an address (protocol://host, e.g. http://www.mozilla.org, you're enabling its subdirectories (e.g. http://www.mozilla.org/firefox and http://www.mozilla.org/thunderbird), but not its domain ancestors nor its siblings, i.e. mozilla.org and addons.mozilla.org will not be automatically enabled.
By default only the 2nd level (base) domain is shown (e.g. mozilla.org) is shown in the menus, but you can configure appearance to show full domains and full addresses as well.

Java, Silverlight, Flash and other plugins

While its primary aim is preventing malicious JavaScript from running, NoScript can effectively block Java™, Silverlight™, Flash® and other plugins on untrusted sites. Java Applets, Flash movies/applications, Quicktime clips, PDF documents and other content won't be even downloaded from sites where you consider them annoyances or dangers, saving your bandwidth and increasing your navigation speed. While in early NoScript versions only JavaScript and Java were blocked by default, this restriction has been extended to Flash and