How to close duplicated tabs in your Chrome browser

Open a New Tab
Press F12 to open Web Developer Tool
Open Console tab
Paste these code, and press ENTER to run:

chrome.tabs.query({}, function(tabs) {
    var firstSee = [];
    for (var i = 0; i < tabs.length; i++) {
        var url = tabs[i].url;
        var id = tabs[i].id;
        if (firstSee.indexOf(url) >= 0){
        } else{

Bonus: you can create a Bookmarklet to do it:

javascript:chrome.tabs.query({}, function(tabs) {var firstSee = [];for (var i = 0; i < tabs.length; i++) {var url = tabs[i].url;var id = tabs[i].id;if (firstSee.indexOf(url) >= 0){chrome.tabs.remove(id);} else{firstSee.push(url);}}})

Then open a New Tab, click that Bookmarklet. Done!