Downloading file using javascript not working in Mozilla

Question

This how my code works. When I clicked the button, it will download the file. My code is working in Google Chrome but not working in Mozilla Firefox.

Here are my codes

HTML

<button type='Button' onClick='dlpdf("http://www.energy.umich.edu/sites/default/files/pdf-sample.pdf")'>Download</button>

JAVASCRIPT

function dlpdf(fileURL){

    if (!window.ActiveXObject) {
        var save = document.createElement('a');

        //alert(fileURL);

        save.href = fileURL;
        save.target = '_blank';
        save.download = fileURL || 'unknown';


        var event = document.createEvent('Event');
        event.initEvent('click', true, true);
        save.dispatchEvent(event);
        (window.URL || window.webkitURL).revokeObjectURL(save.href);
    }


}