Facebook Messenger as a Sidebar is described as 'Allows Facebook Messenger to run as a sidebar. Talk to your friends while browsing the web. The sidebar is visible on all tabs' and is an app in the Web Browsers category. There are three alternatives to Facebook Messenger as a Sidebar for a variety of platforms, including Linux, Mac, Firefox, Windows and Google Chrome. The best alternative is Messenger & Notifier for Facebook, which is free. Other great apps like Facebook Messenger as a Sidebar are Facebook Status (Free, Open Source) and Messenger for Facebook (Free).
See your Facebook status (New Friend Requests, Messages and Notifications) on a toolbar. Perfect for those who don't want to keep Facebook open all the time. By clicking on the icon when the status change is shown, you'll be transferred directly to that status page.