Aardvark is a Firefox extension for interactively manipulating the content on a page. It's like a second cousin of GreaseMonkey. Once it's activated you can mouseover all the elements in a page and manipulate each one by making it wider, narrower, removing it, viewing source etc. I couldn't see a way of making these changes persistent between visits but it's a neat little tool for making adjustments to pages for readability or printing. Besides, it's just cool that you can even do this kind of thing. (via Jeff Barr)