There are two types of thumbnail images1) within the browser (showing images in a folder as small thumbnails / tiles) there is a bigger thumbnail of currently selected image shown in the lower left (can be moved)
2) when pressing F11 in the browser, the currently selected image is shown full screen; mouve mouse to upper border of screen and an image strip (showing images in a folder as small thumbnails / tiles) is shown.
In the other full screen mode (from browser, double click one image so you land in edit / image mode, now press F11) the thumbnails in the film strip did not work but only icons were shown.