Working with XML in a Firefox Add-on(ex Jetpack)

I'm currently developing a Firefox add-on(using https://addons.mozilla.org/en-US/developers/docs/sdk/1.0/ ) that consumes an API where the return data is in xml.

My problem is that I need to parse the returned data, and would like to do that using a xml object.

Since the request module only supports JSON and Text ( https://addons.mozilla.org/en-US/developers/docs/sdk/1.0/packages/addon-kit/docs/request.html#Response ) I need to convert the response.text to XML. The code looks like this:

var Request = require('request').Request  
.......
var req = Request({
        url: https://to-the-api.com,
        content: {
          op: 'get-the-data-op',
          password: "super-sec",
          user: "username"
        },
        onComplete: function (response) {

         dataAsText = response.text;
         console.log("output: " + dataAsText);
        }
    });
    req.post();

I have tried to user (new DOMParser).parseFromString(response.text, 'text/xml') but unfortunately it just fails with a error like ReferenceError: DOMParser is not defined

The question is if anyone of you guys have been able to create a Xml object inside a Firefox add-on, and if so, how?

Can't you use a normal XMLHttpRequest if you want to process the response as XML?