It includes a find bar that will filter the thumbnails, and the capability to select the thumbnails in the same way you would select files in your system.
Showcases can be shown as a window, tab or sidebar, you decide which one you like the most.
Just click the thumbnail of the browser you want, and it will be shown to you automatically. Of course, if you right click, you can perform more actions which can be configured in the settings menu.
Browsers that are opened or closed will be dynamically added and removed from the thumbnail list, and thumbnails will be updated if the browser they represent loads a new page.
Now you can add this feature which is probably the only one you miss when using firefox after using Internet Explorer 7.