This works quite well:
function DEBUGborders(){
console.log("Borders on");
var Element = document.createElement('style');
document.head.appendChild(Element);
var Sheet = Element.sheet;
Sheet.insertRule("*{outline: 1px red solid;}", 0);
} () DEBUGborders()
Copy pasting that code into the console of your browser will give you red outlines of the borders of every CSS object in your browser.
For kicks I have attached a screen shot of what happens to this page when you apply this trick:
