Firebug 1.6 favorite features
Firebug 1.6, the plugin for Firefox, is newly released; for debugging or developing web apps, like Wordpress, it is simply indispensable.
A few of my favorite features:
Scrollable breadcrumbs, solves the one biggest thing that always drove me nuts, in dealing with Real World css.
Copy CSS from the inspection window by right-clicking on the declaration: