files/en-us/mozilla/firefox/releases/3/index.md
If you're a developer trying to get a handle on all the new features in Firefox 3, this is the perfect place to start. This article provides a list of the new articles covering features added to Firefox 3. While it doesn't necessarily cover every little change, it will help you learn about the major improvements.
navigator.registerProtocolHandler() method.transform() and setTransform() methods on canvases.activeElement and hasFocus attributes are supported.data: URL scheme from chrome code to embed XBL bindings directly instead of having them in separate XML files.nsIIdleService interface, which lets extensions determine how long it's been since the user last pressed a key or moved their mouse.nsIZipWriter interface lets extensions create ZIP archives.nsIThreadManager interface, along with new interfaces for threads and thread events, which provides a convenient way to create and manage threads in your code.nsIJSON interface
nsIJSON interface, which offers high-performance encoding and decoding of JSON strings.nsIParentalControlsService interface
mailto: links from other sites. Similar support is provided for other protocols as well. (Note that web applications do have to register themselves with Firefox before this will work.)gfx.color_management.enabled preference in about:config, you can ask Firefox to use the color profiles embedded in images to adjust the colors to match your computer's display.