In Firefox 3.5, all items that finish downloading are automatically removed from the Downloads window after they've successfully finished. Is there an about:config setting that tells Firefox 3.5 to let me manually clear items out instead? I've been looking for an answer for several days with no success.
Check the option
browser.download.manager.retention to ensure that it exists and is not 0. See http://developer.mozilla.org/en/Download_Manager_preferences for details.