Webchunks is a Firefox3 implementation of Microsoft Webslices (feature appeared with IE8). It allows you to "follow" an area of a web page through a dedicated feed bookmarked in a new toolbar. Clicking on the toolbar entry shows the information related to your choice in a popup, without the need to open a complete web page. Should you follow information that can expire like eBay auctions, the style (bold or italic) of the toolbar's entry will reflect the status of your entry: new, expired, about to expire. With the help of an extra extension, Greasemonkey, you can insert webchunks/webslices markup into any web page so the Webchunks extension handles it. This is something the Microsoft implementation cannot do, it entirely relies on the server's markup. Please note Greasemonkey is not mandatory for Webchunks. A tutorial for Webchunks is available at http://disruptive-innovations.com/zoo/webchunks/tutorial.html
After you install the extension, check it functionality at IE8 WebSlices site.