title: JavaScript Error only with Chrome
body: <p>Anyone knows what is this message at Chrome?</p>
  
  <pre><code>Error in event handler for (unknown): TypeError: Cannot read property 'url' of undefined
  at chrome-extension://nfhmhhlpfleoednkpnnnkolmclajemef/content.js:4:113
  at extensions::messaging:320:11
  at Function.target.(anonymous function) (extensions::SafeBuiltins:19:14)
  at Event.dispatchToListener (extensions::event_bindings:386:22)
  at Event.dispatch_ (extensions::event_bindings:371:27)
  at Event.dispatch (extensions::event_bindings:392:17)
  at dispatchOnDisconnect (extensions::messaging:280:27) 
  </code></pre>
  
  <p>Additionaly when I go to content.js:4:113 I get</p>
  
  <pre><code>console.clear()});chrome.runtime.sendMessage({_registerTab:!0,url:window.location.href,protocol:k},function(a){a.url&amp;&amp;(window.location.href=a.url);l=a.id})};
  </code></pre>