I just remembered that I haven’t blogged this yet. This might be the best handiest way to debug Javascript that I have ever used. Way better than removing lines of code until it works!

FireBug - JoeHewitt.com

FireBug is fairly simple - it adds a console to the bottom of every web page in Firefox. The console will display all Javascript errors that occurred for the page you are looking at, and objects or text that have been logged from various places

(Thanks Chris)