It doesn’t require an install. Simply unzip the file, plug in your HTML markup and start coding away. Your code is written to a file so you can easily export it or view it later.
I’ve been a big fan of Firebug for a really long time. It took me a while to learn how to fully utilize the console.
console.log() would dump whatever your debugging to the console. Works great with jQuery selectors to make sure they work and Json results from web services. You can also run block of code in the console, but I’m wanting to go over the log feature of it.