Questions
What is mouse polling rate?
How often the mouse sends its position to the computer. 1000 Hz means a report every millisecond, 125 Hz one every 8 ms.
Why does the test show less than my mouse's rate?
Move the mouse fast and steadily, because many mice report less often when they move slowly. Wireless power saving, USB hubs and browsers that limit events lower the number too.
Is a higher polling rate better?
Up to a point. 1000 Hz is plenty for most players; 4000 and 8000 Hz cut input delay a little more but use more CPU and battery.
Which browser gives the most accurate result?
Chrome and Edge read every mouse report directly. In other browsers the result can top out lower, sometimes at your screen's refresh rate.