Firebug is a great development tool, and has a really handy logging interface that you can dump debugging info to. Just calling console.log(whatever) will dump it to the main Firebug interface as text that you can copy/paste, scroll through, etc.
If you’re developing a Firefox extension, this debugging capability is really useful. Except, calling console.log() doesn’t work, console isn’t defined for the browser, only for each window.
The trick? Call it directly from the Firebug extension object.
Be sure to capitalize both Firebug and Console, and you’ll be good to go. In addition to having great capabilities for logging, the console will prevent your debugging messages from popping up to your users, in case you leave some code where it shouldn’t be.
By the way — if you found this helpful, check back here in a few days. I’ve submitted a presentation proposal to SXSW for Firefox extension development, where I’ve got tons of info for creating extensions for web applications. They collect votes from the community, and I’d like your support. Plus, if the presentation goes through, I’ll be collecting lots of my best tips and putting them online as a resource for the attendees. That means you’ll get all of them too, and you don’t have to go anywhere!
Edit (2008-08-21: Added link for SXSW voting panel)