I noticed a problem on Firefox with the placement of the zoom window (windowPosition 12).
I found out that the problem occurred because img.x on Firefox delivers different values than on Safari or Chrome. The usage of .getBoundingClientRect().left can be used on all 3 browsers with equal values. I changed img.y to .getBoundingClientRect().top for consistency.
I noticed a problem on Firefox with the placement of the zoom window (windowPosition 12). I found out that the problem occurred because img.x on Firefox delivers different values than on Safari or Chrome. The usage of .getBoundingClientRect().left can be used on all 3 browsers with equal values. I changed img.y to .getBoundingClientRect().top for consistency.