This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
One thing that I will tell you, so that you can look for this behavior in your tests, the browser will limit the number of simultaneous requests made to a particular server. This includes requests for things like images as well as Ajax requests.