Mozilla/5.0 (Windows NT 5.1; rv:16.0) Gecko/20121026 SeaMonkey/2.13.2 On the SeaMonkey menu bar, go to [Edit > Preferences > Browser > Helper Applications]. There is no user interface to add a new entry to the list prior to actually encountering a heretofore unknown object (e.g., URI protocol, MIME type, file extension registered by the operating system). There is no user interface to delete an existing entry. Instead, users must first encounter the object and use the popup dialog to make a new entry in the list of helper applications. To delete an entry, users must edit the mimeTypes.rdf file, terminate SeaMonkey, and then relaunch SeaMonkey, which is daunting and possibly disastrous for an inexperienced user. This capability should be implemented for all three: URI protocols, MIME types, and file extensions registered by the operating system. This SeaMonkey RFE is the topic of a discussion at <news://news.mozilla.org:119/0JidnUcOYK4RHxDNnZ2dnUVZ_sWdnZ2d@mozilla.org>. See bug #708959 for a parallel Thunderbird RFE.