In fullscreen mode you cannot launch additional windows so use this Javascript form instead.
Set browser to fullscreen (F11) before pressing start. Rendering the pieces may take some time but should be working unless a message such as "Applet crashed" comes up.
Background Color must be 6 characters giving the rgb values in hex, eg 000000=black, FFFFFF=white, FF0000=red etc.
Faded image background helps to solve the puzzle.
Ticking Rotations allows pieces to be rotated through 90° with a right-click.
Ticking Resize ensures that the image covers the given percentage of the screen no matter what its actual size is.