Most people lock their doors and windows, use a paper shredder to protect themselves from identity theft, and install antivirus software on their computers. Yet they routinely surf the Internet without giving a second thought to whether their browser is secure and their personal information safe. Unfortunately, it's easy for someone with nefarious intentions to use a Web site to glean data from -- or introduce spyware to -- your computer. Even worse, sometimes all you have to do is randomly click on a site to have your data probed in a most unwelcome way.

Mozilla Firefox has several security settings you can adjust via the Preferences pane, but there are also more than 150 privacy and security extensions you can add as well. They are easy to install and take little time to set up; some even work automatically after you restart your browser. Let's have a look at some of the most popular and most useful.

One of the best ways to protect your computer is to prevent the browser from using JavaScript at Web sites without permission. JavaScript, though useful for developing glitzy Web sites, has gained something of a reputation as a method for doing Bad Things to unsuspecting computers. NoScript is an extension that makes every site that uses JavaScript ask your permission before running it.

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