Pressing f in the browser or viewer modes will display the current image in fullscreen mode. (In the browser mode, you can also double-click with the middle mouse button.)

Moving the mouse will activate a popup control panel briefly. This can be used to navigate to the next or previous image, or change zoom levels.

You can also advance to the next image by pressing PageDown or Space.

You can go back to the previous image by pressing PageUp or Backspace.

This can be used to implement a manually-controlled slideshow.

To exit the fullscreen mode, press f or Escape.