That's what everyone says until they try Firebug. I'm not kidding -- I know at least three people who asked me the same question, then came back a week later and said "you're right, this is way better."

The interface is far more usable. Also, all WD can do with javascript is turn it on and off; Firebug has a full-fledged javascript debugger. (It's how I learned JS, in addition to CSS!) The DOM inspection tools are amazing.

Pretty much the only things I still use WD for are resizing the browser window and checking if I'm in quirks mode. But if breaking the page by adding a label to every div is a key feature for you, then maybe you should stick with WD. =)