In Tbird How do I return to the inbox in a single step

So thunderbird mail has this system where old emails spread horizontally across the top of the screen in small icons and if you select and open an older email from the sidebar for the inbox and then want to return to the inbox, the only way I have found to return to the inbox is to click and hold the left arrow on that horizontal bar at the top with the email icons. This is too time consuming. Is there a faster way? Also, is that bar necessary? Why not just have a system that uses the sidebar that actually identifies the individual emails.