Re: Why bother?
You can't see any benefit, at all, for providing these debugging tools directly in the applications that are used to deliver the content?
Not when it turns what should be a client application into a full-fat development environment, no.
As I said, Firebug is useful, but I wouldn't want it switched on all the time, or built into the browser without being able to disable or remove it - which is what the OP seems to be suggesting.
You wouldn't expect a desktop or mobile app to also include there own debugging environment would you? so why hinder a web browser with it?