Chris May

A coworker sent me this link.  You just bookmark it, and then click the bookmark when you want to examine the layout of your page elements.

javascript:prefFile='';void(z=document.body.appendChild(document.createElement('script')));void(z.language='javascript');void(z.type='text/javascript');void(z.src='http://slayeroffice.com/tools/modi/v2.0/modi_v2.0.js');void(z.id='modi');

And it will add a little floating window in the upper left corner to show you everything you mouse over: