Chrome Devevelopment Tools could be really helpful

"Your browser is one of the most and best instrumented development platforms -- you may just not realize it yet. In this episode we'll take a whirlwind tour of how to analyze network performance, rendering and layout pipeline, as well as detecting memory leaks in your Javascript code, and using audits and extensions to build faster and better apps!". A nice screencast by Ilya Grigorik. I strongly recommend the subscription to GoogleDevelopers channel.