Reddit - Highlight posts

// ==UserScript==
// @name          Reddit - Highlight posts on click
// @namespace     null
// @author        gavin19
// @description   Add random background-colour to posts.
// @match         http://reddit.com/*
// @match         https://reddit.com/*
// @match         http://*.reddit.com/*
// @match         https://*.reddit.com/*
// @include        http://reddit.com/*
// @include        https://reddit.com/*
// @include        http://*.reddit.com/*
// @include        https://*.reddit.com/*
// @version       1.00
// ==/UserScript==

var loc = window.location.href;
if (loc.match(/\/comments\//i)) {
var authors = {};
var colours = [
"blue","turquoise","silver","navy","yellow","orangered"
];
var x = document.querySelectorAll('div.md');
for(var i=0,len=x.length;i<=len-1;i++){
    x[i].addEventListener('click', function(){
        var a = this.parentNode.parentNode.parentNode.querySelector('a.author').innerHTML;
        if(authors.hasOwnProperty(a)){
            for(var q=0,len=x.length;q<=len-1;q++){
                if(x[q].parentNode.parentNode.parentNode.querySelector('a.author').innerHTML === a){
                    x[q].removeAttribute("style");
                    delete authors[a];
                }
            }
        }
        else {
            authors[a] = colours[Math.floor(Math.random()*colours.length)];
            this.setAttribute('style','background-color:'+authors[a]);
            for(var d=0;d<=x.length-1;d++){
                if(x[d].parentNode.parentNode.parentNode.querySelector('a.author').innerHTML === a){
                    x[d].setAttribute('style','background-color:'+authors[a]);
                }
            }
        }

    });
}
}