Use Mouse Back Button to Go Back to Previous View

Extremely important request.

Suppose user brings up sub-folder from main window, so sub-folder is open.  Please allow the back-mouse-button to go back to the main window, as it previously appeared.

User can have many, many sub-folders.  User might like to quickly open various sub-folders, take a quick peek, then quickly go back to main window (exactly as it was a moment ago).