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. NoScript can render JavaScript-heavy sites unreadable, but it provides a whitelist of acceptable sites that you can easily add to in order to speed up your surfing experience.
Many people use Tor to hide their online surfing habits. FoxTor provides a way to mask and unmask your browser on the fly, without having to commit to anonymous surfing throughout an entire browsing session. It requires the use of Tor and Privoxy.
Your browser's history logs help provide a speedier surfing experience for you. Unfortunately, skilled hackers can peek at them remotely to see where you've been. Deleting log information after each browsing session would slow you down, but fortunately, there's another way. Don't delete your data -- hide it with SafeHistory.
Some of the most sensitive information sent over the Internet travels via email, so many people prefer to send their messages encrypted. The Gmail S/MIME extension encrypts Gmail messages, including attachments, automatically, as long as you have the recipient's digital certificate.
While Firefox 2 has built-in phishing protection, it never hurts to have a backup plan. The premise behind Petname is simple: leave reminder notes on your trusted Web sites and the notes will automatically appear each time you return. If you surf to what you assume is one of your whitelisted sites and no reminder note appears, you'll know something's not right. This extension is particularly useful if you're running an older version of Firefox without anti-phishing protection.
SecurePasswordGenerator is a long name for a little extension that sits in your toolbar and helps you create unique passwords. Half the battle of staying safe online is using complex and different passwords whenever you register at a Web site. Use this tool to help you create a unique password everywhere you go.
Have you ever wondered where the information you type into an online form goes once you hit "send"? With FormFox, you can find out. Once you download and enable this extension, hovering your mouse over the data field of a form or search box will reveal exactly who receives the information you enter. Use this extension to check out an unfamiliar Web site before you cough up your name, address, and credit card information while doing your online holiday shopping.
Many people use disposable or temporary email addresses around the Internet to avoid email spam. Although spam is generally considered more of a nusiance than a security issue, there are occasions when a disposable address may be a safer option than providing a real one (on message forums, for example). There are several temporary email services to choose from; the TrashMail.net Firefox extension makes that service an attractive choice.
Sometimes you need to protect your information from the prying eyes of people around you. If you're surfing at an airport or local coffee shop, people wandering past can have a look at the titles of the tabs you have open. Page Title Eraser lets you either blank out the title and icon in your browser's tabs, or replace the text with something of your choice.
When trying to protect your privacy, the last thing you want is for a Web site to collect data on what you do while you visit: where you click, how long you view a page, and so on. That's called profiling. While it's harmless if a site tracks data on how long it took you to read an article on how to install a video game, most people feel that there's no reason a Web site needs to know anything about your surfing habits, even if it's only to collect data for marketing purposes.
Most extensions and tools commonly used to prevent data profiling by search engines work by concealing information from outsiders. TrackMeNot takes the opposite approach and actually sends out a bunch of information for the search engines to process. Of course, it sends mostly false information, which means your search activities remain hidden from view and search engines won't glean any meaningful data from your visit.
These are only a few of several dozen privacy and security extensions available for Firefox; you can find a larger list at Mozilla's Web site. Tools like these can make your surfing experience safer, but remember: nothing is foolproof, and talented hackers can still find ways to pull information from your system if they try hard enough. Always be careful.