canonical-link.user.js

// ==UserScript==
// @name           canonical-link
// @namespace      http://www.hatena.ne.jp/hitode909
// @include        *
// ==/UserScript==

(function() {
     if (window != window.parent) {
         return;
     }
     var link = document.querySelector('link[rel="canonical"]');
     if (link && link.href != location.href) {
         var button = document.createElement('a');
         document.querySelector('body').appendChild(button);
         button.appendChild(document.createTextNode('canonical'));
         console.log(button.style);
         with(button.style) {
             position = 'fixed';
             width = '100%';
             left = 0;
             bottom = 0;
             color = '#fff';
             background = '#000';
             fontSize = '24px';
             textAlign = 'center';
             textDecoration = 'none';
             margin = 0;
             padding = 0;
             fontWeight = 'bold';
             opacity = 0.5;
             zIndex = 9999;
         }
         button.href = link.href;
         console.log(button);
     }
})();