The developer tools in Webkit have been really beefed up in the Nightlies for about a month now:
Surfin’ Safari - Blog Archive » Web Inspector Updates
With these changes it looks like I can abandon Firefox and my beloved Firebug extension. It looks like Glimmerblock and ClickToFlash should take care of replacing my other favorite Firefox extensions.
The beefed up web inspector has not only caught up with Firebug, but it looks like it has actually surpassed it with being able to view event listeners attached to elements within the DOM, even external listeners. The whole breakpoints thing looks pretty sweet too, as does the integrated display of session information, and the AJAX process display looks a little better than Firebug's too. Other features like console logging and the all important modification of CSS rules and selectors looks to have matched Firebug.
It will take me a while to get settled in Webkit and to get out of the habit of clicking on the Firefox icon, but from the looks of it I'm here to stay! I'll update this thread with various observations about the improved developer tools, I'd love to hear your thoughts on how you've put them to good use too!