I don't think I agree, as a heavy JavaScript developer. I use FireBug specifically for JavaScript debugging, here are the reasons:
1. The console is a lot better. You aren't limited to the one line interpreter that Chrome provides.
2. Using console.log, and console.dir I get a colored DOM/JSON output. I can click the DOM element and it'll get me to the DOM/HTML tab. This is not available in Chrome. I can move the mouse over the DOM element and it'll be highlighted in the browser.
3. Add-ons: I use the jQuery and Cookies add-ons and they add a lot to the console. I can include jQuery with a click and it highlights the jQuery objects for me in the console. I can watch cookies changes from the console directly.
4. For the debugging tools, they are equal. For syntax coloring the JavaScript code, there is a Firebug add-on for that.