GTmetrix: web-based pagespeed/yslow reports

The biggest benefit I see to this tool is that it's usable by people who don't have (or want to use) Firefox, or who don't want to install Firebug, Pagespeed, and ySlow and do all the testing themselves.

Also, since having Firebug installed actually disables the Javascript JIT in pre-3.6 Firefox (http://antennasoft.net/robcee/2009/12/15/firebug-and-the-jit...), it saves having to take that performance hit everywhere if you haven't upgraded for whatever reason.