Are you as obsessed with Firebug as we are? The Firefox extension helps developers and designers sort out errors in JavaScript and CSS.
You can add features to Firebug by creating a special kind of Firefox extension. Around Webmonkey we're calling them meta-extensions and we wrote about adding YSlow to Firebug recently.
Firebug contributor Jan Odvarko has written a tutorial to give you a jump start extending Firebug. Like Firefox extensions, Firebug extensions are written in XUL (an XML user interface markup language) and JavaScript. Once you've mastered Jan's hello world example, you'll want to check out all of his Firebug tutorials.
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