Breaking Down onLoad
This script has a form of bookmarklet and uses Navigation Timing object to present timing of different phases of loading the page by a browser. It measures everything from triggering the action (hitting enter on url bar, refreshing page or clicking a link/button) to the moment when site is fully loaded.
It is a visual presentation of the content of
Adding it to your bookmarks allows you to analyze performance of every request you'd like to check out.
So far Navigation Timing API works in Firefox 7+, Chrome and IE 9+
Check out how it works here - http://kaaes.github.com/timing/