When you click on the thumbnail, the 'flipbook' will open in a 'lightbox' (not a new tab) and will look like this:
At the bottom of the screen is the control panel.
It is recommended that you use this panel for the two basic operations you require.
A: Turn the page directory on / off (A series of page thumbnails on the left of the screen)
Toggle the YELLOW icon
B: Increase / decrease image size to maximum
Toggle the RED icon.
The other controls are straightforward but using the recommended pair is simple and reliable.
AND TO READ THE PAGES: Make the image maximum size and click on a page to move left or right!
PS Pressing the Esc key returns you to the starting point.