Today let’s take a look at how one goes about creating these magical extensions. The active ingredient is XUL, a markup language (the eXtensible [or “XML-Based”] User-interface Language, to be precise) that describes things like toolbars, menus, keyboard shortcuts. It’s what Firefox uses internally, in fact, to handle its own UI (what the developer types call “chrome”). XUL will provide the interface. JavaScript handles the functionality.

Your First Firefox Extension - Wired .com

I’m working on writing a Yahoo! widget for work at the moment and this shows the impact that XML is having. This might be an interesting next step. Of course, I could just use Opera to get all the bits and pieces that I want such as the RSS reader.