How do I get watir-webdriver to start Firefox 4 with Firebug?

Any ideas? I've tried setting webdriver.firefox.useExisting=true as described in the link below hoping to reuse an existing window with firebug enabled, but no such luck.

http://code.google.com/p/selenium/wiki/FirefoxDriver

you have to create a specific profile where Firebug is always enabled, then launch firefox with this profile in your configuration