I remember it using a Java applet. I think the reason none of the online test sites support it is because it’s hard to test latency & jitter in the browser as the lower layers try hard to compensate for it.
Oh. It was Flash.
Sometimes I forget that was ever a thing!
Speedtest for random server (servers listed on Ookla is quite random) is useful but ping for random server is a bit useless. Just ping for targeted server that runs service you use.