http://d.hatena.ne.jp/mallowlabs/20070521/1179763506

nicovideo_thum_popup.user.js

// ==UserScript==
// @name nicovideo thumnail popup
// @author mallowlabs
// @version 0.0.2
// @namespace http://mallowlabs.s206.xrea.com/
// @updated 2008-05-19
// @published 2007-05-22
// @license public domain
// @description Show popup of thumnail in nicovideo.jp
// @include       http://www.nicovideo.jp/*
// ==/UserScript==

(function () {
	function onMouseOut(e) {
		var divPopup = document.getElementById('thum_popup')
		divPopup.innerHTML = "Could not get thumnail..."
		divPopup.style.visibility = "hidden"
	}
	
	function onMouseOver(e) {
		var divPopup = document.getElementById('thum_popup')
		var refUrl = e.target.getAttribute('href')
		if (refUrl == null) {
			// "e" may be img tag
			refUrl = e.target.parentNode.getAttribute('href')
		}
		var strs = refUrl.split("/")
		divPopup.innerHTML = "<iframe src=\"http://ext.nicovideo.jp/thumb/"
			+ strs[strs.length-1]
			+ "\" width=\"100%\" height=\"198\" scrolling=\"no\" border=\"0\" frameborder=\"0\"></iframe>"
		var st = divPopup.style
		st.left = e.pageX + 10 + "px"
		st.top = e.pageY - 150 + "px"
		st.visibility = "visible"
	}
	
	function addEvent2AllATags(){
		var aTags = document.getElementsByTagName('a')
		for (var i = 0, l = aTags.length; i < l; i++) {
			var refUrl = aTags.item(i).getAttribute('href')
			if (refUrl != null && refUrl.match(/watch\/\d*/)) {
				aTags.item(i).addEventListener('mouseover', onMouseOver, false)
				aTags.item(i).addEventListener('mouseout', onMouseOut, false)
			}
		}
	}
	
	function createPopupDiv() {
		var popup = document.createElement('div')
		var st = popup.style
		st.visibility = 'hidden'
		st.zindex = "99"
		st.border = '1px solid #CCC'
		st.position = 'absolute'
		st.width = '318' + "px"
		popup.id = "thum_popup"
		document.body.appendChild(popup)
	}
	
	createPopupDiv();
	addEvent2AllATags()
	
})();