You can select between vertical, horizontal wide, and horizontal narrow layouts of Thumbnails and Properties panels. The horizontal wide layout displays the thumbnails and the properties panels below both tree view and right (grid) view. The horizontal narrow layout displays the thumbnails and the properties panels below the right (grid) view, but the tree view remains tall.
Display thumbnail preview panel on the right or on the left. For the vertical layout, if "On the left" is selected, the thumbnail preview panel will be shown below the tree view.