I was looking at Task Manager in Windows 10, on a computer I’ve had for about two years, and noticed that Firefox was listed as being a 32-bit application. I looked in Help -> Troubleshooting Information -> Application Basics -> User Agent and, sure enough, no “x64” there. I installed/upgraded Firefox, and now I feel better.
But then I noticed Google Chrome was also 32-bit!!!! What the heck??? So I downloaded 64-bit Chrome and installed it. Of course, I see a noticeable speed difference with both and it’s only been a few minutes.