Tab Preview Safari Sidebar is an extension which adds a sidebar to each Safari page you are on, previewing the current and all other open Tabs of the current window. It allows you to close Tabs, activate them directly from the Sidebar and more.... There is just one Setting: Allow Hover Previews. While moving your mouse pointer over a thumbnail or not, this will show a larger preview next to the Sidebar overlaying the current page. If you leave a thumbnail or the sidebar, the preview gets hidden as well. In the sidebar you can see a button on the very top to toggle the location of the sidebar: it can either be on the left or on the right side. It slides away by default, leaving a small part visible in the center of the screen, once you hover over it, it slides open to show its content, allowing you to access Page content below the Sidebar if there is any. Please check the developer's site for further information.