Greasemonkey Image Upload

GreasemonkeyUpload.js

// ==UserScript==
// @name        test upload
// @namespace   namespace
// @description description
// @include     https://post.craigslist.org/*
// @version     1
// @grant all
// ==/UserScript==

$ = unsafeWindow.jQuery;

function getDataFromUrl(url) {
    var canvas = document.createElement('canvas'),
        ctx = canvas.getContext('2d'),
        img = new Image();
    img.src = url;
    img.onload = function() {
        canvas.setAttribute('width', img.width);
        canvas.setAttribute('height', img.height);
        ctx.drawImage(img, 0, 0);
        document.forms[0].appendChild(img);
    }
    return canvas.mozGetAsFile('image.png');
    //return canvas.toDataURL('image.png');
}

if (location.search.indexOf('editimage') > -1) {
    var url = 'http://boomtownphotos.s3.amazonaws.com/charleston/orig_boomver_1_1313035-1.jpg';
    var file = getDataFromUrl(url);
    console.log(file);
    debugger;
    var fd = new FormData(document.forms[0]);
    fd.append('file', file, 'image.png');
    //alert('submitting');
    if (confirm('submit?')) document.forms[0].submit();
}