Safari BabelExt.xhr is not working

[noma4i]

Example added to extension.js:

          BabelExt.xhr({
            method: "GET",
            url: 'http://www.babelext.com/',
            onload: function(response) {
              alert("YEAH!");
            }
          });

Error in safari console: DataCloneError: DOM Exception 25: An object could not be cloned.

Safari version: 8.0.2 (10600.2.5)