answer:It has to do with : – the the kind of graphics subsystem is on the machine, – combined with how well the operating system takes advantage of the capabilities of that graphics subsystem, – combined with how well your browser takes advantage of what your operating system has available. Some systems will have hardware acceleration for almost anything you would do with an image, and very good drivers for the operating system to hook up with, and a decent browser will make the right call to use all those. Other systems might have mediocre hardware support, with mediocre drivers, and maybe the browser you’re does not take advantage of whatever better way to move horizontally there may be.