Good article. Didn't think of using Firebug that way yet.
At the end of the article it's mentioned, that Firebug just works in Firefox, but please note, that there is also
Firebug Lite - a trimmed version of Firebug, which works in all browsers. Though I also have to say, that it doesn't support all features of it's big brother.
Also note, each browser is offering its own developer tools, which allow a similar approach.
Sebastian