I have dealt with Firefox security add-ons about a month ago and promised to write another guide this time dealing with privacy related add-ons. So what's the core difference between privacy and security anyway? I personally consider privacy to be a part of security, which explains for instance why Ghacks has only a security category, and no privacy category.
Privacy is about user information. This can be data like names, addresses, emails but also indirect data like a user's browsing habits, past purchases at an online store or a search history. Companies use the information for instance to track a user on the Internet to display targeted advertisements. But privacy can also be abused, say by malicious users who hacked into a company database to get all user names and emails, to communicate with those others afterwards (phishing comes to mind). Privacy can also be a local matter. A wife who does not want her husband to find out what she is doing on the Internet, parents who do not want their kids to see some of the sites they have been visiting.
Privacy add-ons cannot protect from all threats related to privacy. They cannot be used for example to delete your shopping history at Amazon or eBay. They can however protect you from the majority of dangers.
Firefox Privacy Preferences
Firefox has a few privacy related options that can be customized easily to improve privacy immediately. You find the settings by clicking on Tools > Options, or Firefox > Options in the menu. Switch to the privacy tab. The default setting here is to remember history. If you switch that to custom settings for history you get several new configuration options.
All of those settings are about local information, like the download or browsing history. If you do not want the browser to record the information, uncheck the box. You can also configure Firefox to clear the history on exit, which would mean that you have access to the history during sessions, but not after the browser gets closed down.
Firefox Privacy Add-ons
Firefox offers many privacy related add-ons for download. This list includes only add-ons that are working under Firefox 4. The majority will work under Firefox 3 as well, I try to mention it if an add-on does not.
Create a temporary email address for immediate use on the Internet. Handy for signing up on websites that you do not trust to keep your email address confidential, or submitting a comment on a site.
Firefox records by default what a user enters into forms on web pages. While it is possible to delete all form history at once via the clear browsing data tool, it is not comfortable to delete select form entries. You can visit the form again, enter the first characters of the text you have entered, hover over the suggestion that pops up with your mouse and press the delete key on your keyboard to delete it.
Form History Control simplifies the process. It displays all form data that is currently stored in the browser. You can use it to view, edit and delete entries easily.
Displays the form action on mouse over. The form action determines to which website or server the entered data is submitted to. This is sometimes used in malicious ways, for instance on phishing sites.
An ad blocking extension that can be extended with subscriptions to include privacy related protections to the web browser.
Protects a user's privacy by offering better Flash Cookie (LSO) handling in Firefox. Can remove Flash cookies automatically on exit, something that will be supported by Firefox soon by default.
Protects against malicious cross-domain requests, including Cross-Site Request Forgery.
CsFire protects you against malicious cross-domain requests, by rendering them harmless. This means that CsFire will remove authentication information (cookies and authentication headers), which ensures that a cross-domain request can not have harmful or undesired side-effects.
Displays information about page elements used to track website visitors. This includes tracking pixels and scripts such as Google Analytics or Facebook.
A collection of tools that improve a user's privacy on the web. This includes email and phone protection, blocking of online tracking, cookie controlling and privacy alerts that display trackers that are active on a site.
Delete cookies on-demand and based on pre-defined rules. You can use the add-on to clean up cookies from specific sites, or all cookies but those from some websites.
A similar extension is Cookie Whitelist. [Update: not available anymore, use Cookie Whitelist Buttons instead]
Block companies from tracking you through cookies and Flash cookies. Blocks more than 300 different ad companies from tracking users on the Internet.
Uses random search queries to protect against search data profiling.
Misc privacy extensions
A boss key to minimize the browser immediately.
Displays certificate updates to give the user a tool at hand to verify the legitimacy of updated certificates.
Can be used to force HTTPS connections to select websites, for instance to always connect via HTTPS to your email provider, favorite websites or financial sites.
Informs the user if an https version of the website is available. Can create rules for HTTPS Everywhere.
Turns shortened urls into their destinations so that it is possible to see the link target right on the site the short url was posted on.
Validates Firefox HTTPS security errors by querying select Network Notaries.
A web proxy add-on for Firefox. Use proxy servers to hide your real IP address or visit websites that would be blocked otherwise.
Proxilla Glype Proxy Client is an alternative, as is Phzilla and Go2 Proxy
Firefox users can improve their privacy with add-ons tremendously. The right selection depends entirely on their web use. Do you think an add-on is missing from the list? Let everyone know in the comments. Post your privacy tips there as well.