samedson/duplicate-tab

Press Alt+Shift+D to duplicate the current tab (Option+Shift+D on Mac).

JavaScript

Chrome Web Store: https://chrome.google.com/webstore/detail/duplicate-tab-shortcut/klehggjefofgiajjfpoebdidnpjmljhb

Firefox Addons: https://addons.mozilla.org/addon/duplicate-tab-shortcut/

Icon: http://findicons.com/icon/208731/copy