Want a little more control over your browsing? RequestPolicy is an extension that improves the privacy and security of your browsing by giving you control over when cross-site requests are allowed by webpages you visit.
Here is a little more information about the add-on from the developers:
Cross-site requests are requests that your browser is told to make by a website you are visiting to a completely different website. Though usually legitimate requests, they often result in advertising companies and other websites knowing your browsing habits, including specific pages you view throughout the day. Among the attacks that cross-site requests are used in, they are particularly dangerous with Cross-Site Request Forgery (CSRF) attacks where your browser is told to make a request to another website and that other website thinks you (the person) meant to make the request.
Want to learn more? You can get more information about RequestPolicy from the Firefox Add-ons website.