Thanks to the MIT Advertising Lab blog for this pointer:
“SEO for Firefox is a little plug-in for search engine optimizers (optimizators?) that ammends Google and Yahoo search results will all sorts of related trivia on sites that show up in the search results. This will give you an idea why certain site is ranked higher up than others for a particular search term. To give an example you guys can relate to: if you search for “advertising blog”, these three come up at the top: Adverblog, Adrants and Adland (I was pleasantly surprised to learn that Ad Lab is #4).”
I downloaded and enabled the plug-in and find it fairly useful. The MIT blog is a recent discovery and a good one that has gone into the blogroll.