From MozillaZine Knowledge Base
Mozilla Firefox’s Places system allows the use of “smart folders,” folders containing recently starred pages, recently used tags, most visited pages, and so on. In Firefox 3, a folder containing smart folders is added to the user’s bookmarks the first time their profile is used. This preference kept track of whether that folder of smart folders had been created. Its functionality was replaced by browser.places.createdSmartBookmarks, which in turn was superseded by browser.places.smartBookmarksVersion.
Possible values and their effects
A "Most Viewed" folder in the Bookmarks Toolbar Folder has been created already; do not create a new one
Create a "Most Viewed" folder in the Bookmarks Toolbar Folder, then toggle this preference to True. (Default)
First checked in
Has an effect in