Aardvark is a great Firefox extension for web developers and designers which provides a MouseOver effect on each HTML element : a red rectangle framing each element under the cursor. You will also see a little yellow caption showing the HTML element type and its class or id if they exist.


You can then press certain keys on the keyboard to do various things, such as delete the selected element from the page, isolate the element, or move the selection rectangle outward to the containing element.