You mean the "Clear private data" does not do the job? If you have some stuff left over in the dropdown under the address bar, there is a way to allow that to clear with history. You can add certain lines to the prefs.js file or put a user.js file with those lines in the profile.
Stop showing bookmarks in URL bar in FF3:
user_pref("browser.urlbar.matchOnlyTyped", true);
user_pref("places.frecency.bookmarkVisitBonus", 0);
user_pref("places.frecency.unvisitedBookmarkBonus", 0);
Allow typed entries in address bar to clear with history (FF3):
user_pref("places.frecency.typedVisitBonus", 0);
user_pref("places.frecency.unvisitedTypedBonus", 0);
If a bookmark does get into the dropdown list, the only good way to get it out is to copy the title and location from the organizer first, then delete the bookmark from the Bookmarks list and then clear your history. Then add in the bookmark manually to the Organizer using the saved information.
