Yes, extensions give additional features and functionalities to a browser, but the question is how to build an extension. If you’re really interested, here I am presenting an e-book (currently available for free) titled ‘Build Your Own Firefox Extension’ that makes you to build a custom extension for Firefox. Anyone with a minimal understanding of JavaScript and XML can build a Firefox extension. With this e-book, you can: The publisher Sitepoint giving away this e-book (normally worth $9.95) as a gift to celebrate the release of their new FREE extension called CodeBurner for Firefox.