go to about:config, set places.frecency.unvisitedBookmarkBonus and places.frecency.unvisitedTypedBonus to 0. Then use private browsing when you visit those "secret" links.
The page on browser.urlbar.richResults says: "Has an effect in * Mozilla Firefox (nightly builds from 2007-11-29 to 2007-12-17)"
So I guess you need to do what it says under "Background" to get rid of the awesome bar: "If you’d like to disable the improved Location Bar dropdown in a version of Firefox without this preference, try the oldbar extension."