A Final Note
This article has barely scratched the surface of JavaScript debugging, but I hope it has proved useful as a starting point. The screenshots displayed here are mainly taken from Firefox/Firebug running on Ubuntu Linux, but the interfaces used by the other browsers' debugging suites are very similar.
As your JavaScript adventures continue, you may want to explore more advanced techniques such as performance profiling, call stack tracing, and examining the DOM. The resources listed in “Further Reading” should make a good place to start.
Happy debugging!