Addons » BookmarksShows an icon on the status bar when the mouse cursor is over a link to a page you bookmarked or visited before. In Firefox 3.5 and later, the extension also offers an option to disable the visited link styling to reduce the risk to privacy.

See also
Go Parent FolderAdd "Go Parent Folder" menu to context menu in The Library list view and Search result in Bookmarks Sidebar.
Bookmarks Info T!psEnhanced Information on Tooltips for your Bookmarks.
SyncPlacesSynchronizes your bookmarks, passwords and password exceptions between browsers. Uses your own (or third party) web or ftp server so you have complete control and privacy.
Netscape Link PadLink Pad is a sidebar that you can drop links onto to save for later without cluttering your bookmarks. Find a link to a YouTube video you want to watch, but don??™t have time now? Drop it into Link Pad (or even just on Link Pad??™s status bar icon), ...
Unsorted Bookmarks Folder MenuAdd Unsorted Bookmarks Folder to Bookmarks Menu