gecko-dev/toolkit/content/editMenuOverlay.js

// update menu items that rely on focus
function goUpdateGlobalEditMenuItems()
{
  goUpdateCommand("cmd_undo");
  goUpdateCommand("cmd_redo");
  goUpdateCommand("cmd_cut");
  goUpdateCommand("cmd_copy");
  goUpdateCommand("cmd_paste");
  goUpdateCommand("cmd_selectAll");
  goUpdateCommand("cmd_delete");
}

// update menu items that rely on the current selection
function goUpdateSelectEditMenuItems()
{
  goUpdateCommand("cmd_cut");
  goUpdateCommand("cmd_copy");
  goUpdateCommand("cmd_delete");
  goUpdateCommand("cmd_selectAll");
}

// update menu items that relate to undo/redo
function goUpdateUndoEditMenuItems()
{
  goUpdateCommand("cmd_undo");
  goUpdateCommand("cmd_redo");
}

// update menu items that depend on clipboard contents
function goUpdatePasteMenuItems()
{
  goUpdateCommand("cmd_paste");
}