They decided recently this is a developer feature, so you have to enable the "Show Develop menu" feature (in the "Advanced" pane of Safari's preferences window).
This irritated me at first, but then I recalled the time my dad (accidentally) viewed a website's source, and how perplexing it was to him.
Okay, I feel better knowing that it's one configuration change away. The Internet had lead me to believe that I needed to download a plugin to make this work. :-/
That said, their fancy source navigation tool breaks the formatting of the ascii art. :-(
