Programmatically moving the mouse with the "xdotool"

After opening a "Mozilla Firefox" window, executing the following script will move the mouse correctly under Debian 9 but not under Debian 10. Any idea why?

Code:#!/bin/bash

winID=$(xdotool search --name "Mozilla Firefox")
echo $winID
xdotool getwindowname $winID

let x=1
let y=175
let i=1
let j=-1

for (( t=1; t<400; t++ ));
do
if [ $t -eq 100 ]; then let j=-$j; fi
if [ $t -eq 200 ]; then let i=-$i; fi
if [ $t -eq 300 ]; then let j=-$j; fi

let x=x+i
let y=y+j

xdotool mousemove --sync --window $winID $x $y
done

exit