1) The document discusses the history of web browsers and the "Browser Wars" between Netscape and Internet Explorer. It also discusses the rise of Firefox and how Mozilla aimed to make the Internet a better place. 2) Firefox allows extensions to extend its functionality. Extensions can range from simple single-feature extensions to more complex applications. The interface of Firefox is written in XUL, which is similar to HTML and XML. 3) Developing extensions involves setting up an environment, studying existing code, debugging through trial and error. It also requires dealing with bugs and restrictions. The process can be difficult but rewarding.