This menu is different from all the others: It is yours. The menu is initially empty (and disabled). There are python scripting commands which will add menu elements (and submenus). Presumably this will be done from python startup scripts but it could be done at any time.
If your build did not contain python then this menu will not be present. In builds with python the menu will only exist in the font and outline glyph views.
At some point there may be some standard python scripts that ship with fontforge, and their behavior will then be documented here. Currently there are no such scripts.