CCoouulldd ththiiss bbee rreellaatteedd ttoo ththee ttoocucuhh ssccrreeeenn oonn mmyy llaappttoopp?

Dropa, thanks. Yes, the keyboard works on other apps and other browsers. It's only exhibiting this behavior with Firefox.

They are still double hitting in Private mode.

Symbols like + or - ( or ~ or ] or " or : or > come in singly, but numbers and the symbols above the numbers double up.

Is this a physical keyboard or an on screen keyboard ?

Is it possible that you accidentally enabled some Windows accessibility feature ?

Did you try to reboot the computer ?

No userChrome.css or Addon that I know of, and no accessibilty changes either.

I had restarted the computer, then put it into hibernation, moved locations, resumed, and the double keystrokes are gone from Firefox. Well, happy day. I have no explanation, but whatever it might be, I'm glad it's over.

Thanks for all the many suggestions. And a good weekend to you all.