Sure, speaking as a user, webkit presently owns gecko for rendering speed/compliance, I've not said otherwise. However, speaking as a developer, even chrome's excellent built-in development tools are still no match for a combo firebug/firephp/fiddler/web developer set installed on Firefox.
Well, WebKit's builtin WebInspector is rather good in my opinion (it's also very actively developed). I don't use Firebug, but from the "feature list", they both look quite similar (resource inspection with on-the fly modifications, js debugger, network analysis / performance, ...).
In OWB, I also added several features (content/ad blocker, userscript manager, stylesheet manager, url preferences, network manager...) that don't exist in a default Firefox setup and must be installed as 3rd-party extensions (which is always a hassle for the lambda user).
But of course, it's somewhat hard to compete alone against the horde of Mozilla and extensions developers.
