The Firebug extension is a very helpful tool for web development. But did you know that you can use its console as an output target for your Firefox extensions? It's pretty simple to do:

Firebug.Console.log("Text to log"); // Output text
Firebug.Console.log(myObj); // Output an object

Is that easy or what? Having this capability is a great way to print out JavaScript objects from your Firefox extensions, making your debugging life much easier.