My Question: Is using Firebug an effective approach?

Absolutely, provided you disable any plugins that mangle the tree (noscript); not important if you're using the same firefox with WWW::Mechanize::Firefox

You can use htmltreexpather.pl to generate some xpaths for you

extracting data from html using xpath

extract data from html with xpath

extract a substring between two emements, its css/xpath time again

WWW::Mechanize, WWW::Mechanize::Firefox, WWW::Scripter, HTTP::Recorder, Web::Magic, htmltreexpather.pl, getting data out of html with xpath, Re: Formating a HTML document to show certain text., Re^2: HTML::TreeBuilder:: identifing xpath-expression - first attempt, Re: Help With Online Table Scraper, Re: Formating a HTML document to show certain text.