Building applications with Mozilla

There’s a widespread misconception that 
 Mozilla is “just”
 a browser. Mozilla is a core platform on which XUL, JavaScript and CSS have been used
 to build a browser, a mail client, an IRC client, an HTML editor, games and much more.
 Jiří Kosek gives some background on the architecture and the applications built on the Mozilla core on his website
 in the article 
 XUL.
 If the subject interests you, follow the link to the freely available book 
 Creating Applications with Mozilla, which you can also download from the Czech site Slunečnice.
 The book is distributed under the Open Publication License. Its official site is at
 books.mozdev.org
 , where you can also read it online in HTML.