gfycat/imgur html5 redirect

// ==UserScript==
// @name        Gfycat/Imgur Redirect
// @namespace   asdf
// @description Changes gif links into gfy or gifv links.
// @include     *
// @version     1
// @grant       none
// @run-at      document-start
// ==/UserScript==

(function () {

    function get_html5_url(gif_url) {
        var xmlHttp = new XMLHttpRequest();
        xmlHttp.open( "GET", "http://gfycat.com/cajax/get/" + gif_url, false );
        xmlHttp.send( null );

        var gfy = JSON.parse(xmlHttp.responseText).gfyItem;

        if (gfy.webmSize < gfy.gifSize && gfy.webmSize <= gfy.mp4Size) {
            return gfy.webmUrl;
        } else if (gfy.mp4Size < gfy.gifSize && gfy.mp4Size <= gfy.webmSize) {
            return gfy.mp4Url;
        } else {
            return false;
        }
    }

    var gfy_regex = /^http:\/\/[A-Za-z]*\.gfycat\.com\/([A-Za-z]*).\gif$/;
    var imgur_regex = /^http:\/\/i\.imgur\.com\/[A-Za-z0-9]+.gif$/
    var result = gfy_regex.exec(window.location);
    var result2 = imgur_regex.exec(window.location);
    var gfy_name, html5_url


    /* if (result && result[1]) { //current url is of a gfycat gif

        gfy_name = result[1];
        html5_url = get_html5_url(gfy_name);
        if (html5_url) {
            window.location.replace(html5_url);
        }
    } else if (result2) {
        window.location.replace(window.location + "v");
    } */

    function replace_links() {
        var links = document.getElementsByTagName('a');

        for (var i = 0; i < links.length; i++) {
            var item = links[i];
            result = gfy_regex.exec(item.href);
            result2 = imgur_regex.exec(item.href);

            if (result && result[1]) {

                gfy_name = result[1];
                html5_url = get_html5_url(gfy_name);
                if (html5_url) {
                    item.href = html5_url;
                }
            } else if (result2) {
                item.href = item.href + "v";
            }
        }
    }

    window.addEventListener("DOMContentLoaded", replace_links, false);

}());