Firebug 1.0 beta

The most useful developer tool for Firefox has just hit it's first version 1.0 beta and has added some great new features. Firebug gives you all kinds of javascript and CSS debugging tools that help you track down where errors are coming from. For example, you can inspect a single HTML element and see the CSS that's being applied to it, as well as where that CSS is coming from (filename and line number). With 1.0 beta it even shows you any CSS that would have been applied, but is getting overridden by other style definitions. If you develop websites, you need this plugin.