old_contents: // ==UserScript==
  // @name        Smart QR
  // @namespace   http://tampermonkey.net/
  // @description Detect links to phone numbers and locations and display a QR code on mouseover.
  // @include     http://*
  // @include     https://*
  // @version     0.1
  // ==/UserScript==
  
  var i;
  
  function addQR(event) {
  	i = document.createElement("img");
  	//console.log(encodeURIComponent(event.target.smartQRvalue));
  	i.src = "https://qrcode.kaywa.com/img.php?s=6&d=" + encodeURIComponent(event.target.smartQRvalue);
  	i.style.width = "100px";
  	i.style.height = "100px";
  	i.style.position = "fixed";
  	i.style.top = "0px";
  	i.alt = "QR Code";
  	document.body.appendChild(i);
  };
  
  function removeQR() {
  	document.body.removeChild(i);
  };
  
  function addListeners(element, value) {
  	element.addEventListener('mouseover', addQR);
  	element.addEventListener('mouseout', removeQR);
  	element.smartQRvalue = value;
  }
  
  (function () {
    "use strict";
  
    //console.log(document.getElementsByName);
  	
    var links = document.getElementsByTagName('a');
  	for(var i=0, len=links.length; i < len; i++){
  		var link = links[i];
  		if (link.href) {
  			var re = new RegExp('^tel:(.*)$');
  			var matches = link.href.match(re);
  			if (matches) {
  				addListeners(link, link.href);
  			}
  		}
  		//if (link.attributes.title == "Über Hangouts anrufen") {
  		if (link.dataset) {
  			if (link.dataset.number) {
  				addListeners(link, link.dataset.number);
  			}
  		}
  	}
  }());
  
new_contents: // ==UserScript==
  // @name        Smart QR
  // @namespace   http://tampermonkey.net/
  // @description Detect links to phone numbers and locations and display a QR code on mouseover.
  // @include     http://*
  // @include     https://*
  // @version     0.1
  // ==/UserScript==
  
  var i;
  
  function addQR(event) {
  	i = document.createElement("img");
  	//console.log(encodeURIComponent(event.target.smartQRvalue));
  	i.src = "https://qrcode.kaywa.com/img.php?s=6&d=" + encodeURIComponent(event.target.smartQRvalue);
  	i.style.width = "100px";
  	i.style.height = "100px";
  	i.style.position = "fixed";
  	i.style.top = "0px";
  	i.style.zIndex = "999";
  	i.alt = "QR Code";
  	document.body.appendChild(i);
  };
  
  function removeQR() {
  	document.body.removeChild(i);
  };
  
  function addListeners(element, value) {
  	element.addEventListener('mouseover', addQR);
  	element.addEventListener('mouseout', removeQR);
  	element.smartQRvalue = value;
  }
  
  (function () {
    "use strict";
  
    //console.log(document.getElementsByName);
  	
    var links = document.getElementsByTagName('a');
  	for(var i=0, len=links.length; i < len; i++){
  		var link = links[i];
  		if (link.href) {
  			var re = new RegExp('^tel:(.*)$');
  			var matches = link.href.match(re);
  			if (matches) {
  				addListeners(link, link.href);
  			}
  		}
  		//if (link.attributes.title == "Über Hangouts anrufen") {
  		if (link.dataset) {
  			if (link.dataset.number) {
  				addListeners(link, link.dataset.number);
  			}
  		}
  	}
  }());
  
subject: Add z-index.