Just want chat window as a sidebar widget

I want to know too!!

Just use this code, no plugin needed:

<script>
      window.fbAsyncInit = function() {
        FB.init({
          appId      : '95100348886',
          xfbml      : true,
          version    : 'v2.6'
        });
      };

      (function(d, s, id){
        var js, fjs = d.getElementsByTagName(s)[0];
        if (d.getElementById(id)) {return;}
        js = d.createElement(s); js.id = id;
        js.src = "//connect.facebook.net/en_US/sdk.js";
        fjs.parentNode.insertBefore(js, fjs);
      }(document, 'script', 'facebook-jssdk'));
    </script>

    <div class="fb-page" 
         data-href="https://www.facebook.com/XZY/" 
         data-tabs="messages" 
         data-width="400" 
         data-height="300" 
         data-small-header="true">
      <div class="fb-xfbml-parse-ignore">
        <blockquote></blockquote>
      </div>
    </div>