tecnam2003:

 

I inadvertently stopped using Firefox, which was my sole browser for the last 12 years...and bingo !!

 

That's why the speedtest website tells you to use the app instead if you test over 100, because browsers are not able to do it reliably even on a decently fast computer, and some of the poor excuses that people have still in service are no way able to get near the true speed.