Selecting the Thumbnail option from the control panel will pause the slideshow, open up a new window (in full screen mode) and then display thumbnails of all the images in the current folder of the slideshow.

Holding the mouse over an image will cause the filename and description (if it exists) of that picture to appear.

Clicking on any of the thumbnail images will close the window, and resume the slideshow, starting with that particular image.

To close the thumbnail window and just continue with the slideshow, click on the cross in the top right hand corner of the window.