Select a thumb and view it in full screen mode.
Display the navigation thumbstrip by moving the mouse to the top of the screen. Observe the sizes of the thumbs.
Return to the browser.
Use the slider to make the thumbs smaller.
Again view an image full screen and display the navigation thumbstrip. Observe the that the thumb images are the new sizes you selected in the browser (i.e., reduced) but that the thumbnails themselves remain the "old" size.
Here is an example:
