slayeroffice | Mouseover DOM Inspector:
This favelet allows you to view the properties of any HTML element on a page simply by mousing over the element. The element will be given a gray background, and a DIV element that trails the mouse cursor will contain the element type along with all of the specified attributes of the element. Hit the “esc” key to turn the favelet off.
Via Sam. Crazy cool and a must-have for any web designer.