在 Thunderbird 扩展中获取邮件发件人

我正在开发一个非常简单的 Thunderbird 扩展，它应该在发送邮件时提醒发件人的姓名以及收件人的姓名。问题是下面代码片段中的 gMsgCompose.compFields.from 字段为空（.to 字段按预期工作），它处理“compose-send-message”事件。我在这里缺少什么？

function send_event_handler( evt ) {
var msgcomposeWindow = document.getElementById( "msgcomposeWindow" );
var msg_type = msgcomposeWindow.getAttribute( "msgtype" );

// do not continue unless this is an actual send event
if( !(msg_type == nsIMsgCompDeliverMode.Now || msg_type == nsIMsgCompDeliverMode.Later) )
  return;

var promptService = Components.classes["@mozilla.org/embedcomp/prompt-service;1"].getService(Components.interfaces.nsIPromptService);
promptService.alert(window, "From", gMsgCompose.compFields.from);
promptService.alert(window, "To", gMsgCompose.compFields.to);
}

window.addEventListener( "compose-send-message", send_event_handler, true );

您可以通过 msgIdentity 小部件获取发送身份：

var identityWidget = document.getElementById('msgIdentity');
var fromIdentityKey= self.identityWidget.value;

然后，使用账户管理器查找身份信息：

var acctMgr = Components.classes["@mozilla.org/messenger/account-manager;1"]
                      .getService(Components.interfaces.nsIMsgAccountManager);
var accounts = acctMgr.accounts;
for (var i = 0; i < accounts.Count(); i++) {
  var account = accounts.QueryElementAt(i, Components.interfaces.nsIMsgAccount);

  var accountIdentities = account.identities;

  for(var identCount = 0; identCount < accountIdentities.Count(); identCount++) {
    var identity = accountIdentities.QueryElementAt(identCount,
                                                 Components.interfaces.nsIMsgIdentity);

    if(identity.key == fromIdentityKey) {
       // Identity found
       alert(identity.email);
    }
  }
}