How can I get the contents of an attachment in a Mozilla Thunderbird extension?

I'm building an extension to Mozilla Thunderbird that does some translation of messages. I'd like to add a translate attachment feature, although I'm having a bit of trouble getting to the contents of each attachment. At the moment, I'm hooking into the attachmentListContext popup, and I have some code that gathers the relevant attachment URI and URLs. How can access the binary data of each relevant atta开发者_C百科chment?

Current code to get selected attachments:

handleAttachmentTranslate : function() {
  // see code in msgHeaderViewOverlay.js in Thunderbird source
  var attachmentList = document.getElementById('attachmentList');
  var selectedAttachments = new Array();
  for (var i in attachmentList.selectedItems) {
    var attachment = attachmentList.selectedItems[i].attachment; 
    // we can now access attachment.url or attachment.uri, etc
    selectedAttachments.push(attachment.url);
    // or (ideally)
    // alert(this.translate(getData(attachment.url)))
    // but what is getData()?
  }
},

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FiltaQuilla addon does have the ability to save attachments etc. It may contain some code that's relevant.

Update Apr 25 2011: The page posted by speedball2001 has been modified between Mar 25 and Mar 31. Now it has a complete example. Check that out. It also points to a real extension that does exactly the attachment manipulation. This looks to be a promising answer.

The thought now is to hook up this new demo code to FiltaQuilla if necessary.

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Have you checked MDN? They have howtos for this kind of stuff:

http://mdn.beonex.com/en/Extensions/Thunderbird/HowTos/Common_Thunderbird_Use_Cases/View_Message.html