JavaScript - dispatchEvent isn´t a function

Question

My code:

// node = "<a href="blob:http%3A//..." download="export.csv"></a>"
var event = new MouseEvent("click");
node.dispatchEvent(event);

Console: node.dispatchEvent is not a function

The error only appears in Firefox (Chrome and IE works fine) Why isn´t the dispatchEvent firing?

Edit: fileSaver.js-Code:

Chrome: save_link=<a href="blob:http%3A//...efa07" download="export.csv"></a>

Firefox: save_link="<a href="blob:http%3A//...efa07" download="export.csv"></a>"

click(save_link); 

click = function(node) {
  var event = new MouseEvent("click");
  node.dispatchEvent(event);
}