Your browser is the most important program on your computer and until recently there were no built-in, industrial-strength tools available for debugging web pages. As web apps become more sophisticated, so do the debugging environments. Representatives of the major browsers discuss the similarities (and differences) between the tools and we look at how they address the needs of the 2012 developer: debugging Web Workers, tweaking CSS colors to perfection, remote debugging of mobile devices and all the other functions that make in-browser development as easy as falling off a console.log().
FireFox just added the ability to have a 3D model of the DOM (it’s quite awesome!). It shows you ever element in the DOM as a layer, and you can navigate and view it by dragging around. Right now this is in the Nightly build, and isn’t in the stable release yet.