This is the software publisher's description.

Showcase provides a new way to manage your Firefox tabs and windows by showing them as thumbnails in a single window, tab or sidebar. 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.

Find the Showcase menu in the 'View' menu (just under 'Sidebar'). The default shortcuts are listed there. Those may be changed using the Keyconfig extension. New buttons will be available when customizing the toolbar.

Showcase can be shown as a window, tab or sidebar. Also, it has two modes: global (which will show thumbnails for all tabs of all windows) and local (thumbnails only for the current Firefox window).

Just click the thumbnail of the browser you want, and it will be shown to you automatically. You may also right click in those thumbnails to perform the most usual operations on them. Multiple thumbnails can be selected by using left click and holding down the Control key, or using the same selection actions you would use in your system. Mouse middle button can be used to zoom a thumbnail. Use Control-F in Showcase to use the find bar.