Submit a URL to generate a node map of all of the requests on the page. Rapidly identify what third-parties are on your site, where your transmitted bytes are coming from and how slow your domains are! Read more on my blog or see an example.
Have you already run the test in WebPageTest? Use this bookmarklet to get a RequestMap of the test run: RequestMap This. Add the bookmark and click on it while you are on the WebPageTest results page (e.g. http://www.webpagetest.org/result/resultid/).