preview /r/gifs on hover, displaying firefox bug

hovergifs.user.js

// ==UserScript==
// @id             www.reddit.com-0496007c-95e3-4661-b485-846f1932fbbb@scriptish
// @name           gif hover preview
// @version        0.1
// @namespace      
// @author         blendmaster
// @description    shows gifs on hover
// @match        http://www.reddit.com/r/gifs/*
// ==/UserScript==

document.addEventListener('mouseover', function (e) {
	if ( e.target.parentNode.classList.contains( 'thumbnail' ) ) {
		var img = document.createElement( 'img' ), match;
		img.src = e.target.parentNode.href;
		// quick fix to get linked imgur gifs
		if ( match = /imgur.com\/(\w+)/.exec( img.src ) ) {
			img.src = "http://imgur.com/" + match[1] + '.gif';
		}
		img.style.position = 'fixed';
		img.style.left = ( e.clientX + 10 ) + 'px';
		img.style.top = ( e.clientY + 10 ) +'px';
		img.style.opacity = 0.5;
		img.addEventListener( 'load', function () { this.style.opacity = 1; } );
		document.body.appendChild( img );
		e.target.addEventListener( 'mouseout', function remove () {
			document.body.removeChild( img );
			this.removeEventListener( 'mouseout', remove );
		});
	}
});