The forum software picks up that you appear to be using Vista. That possibly suggests that you may be using rather old hardware. As everything evolves old hardware often needs to work harder to use modern software and modern websites.

You could try turning off Firefox's hardware acceleration. That may reduce the load on the hardware, but may result in reduced performance.

• Upgrade your graphics drivers to use hardware acceleration and WebGL_turning-off-hardware-acceleration

If as is more likely you are asking about problems caused by overclocking your CPU that is outside the scope of this forum but see

• https://simple.wikipedia.org/wiki/Overclocking &
  https://wikipedia.org/wiki/Overclocking

Also outside the scope of the forum but maybe check your heatsinks and fan are clean and the cpu is properly seated with fresh thermal paste.

I clicked off both Firefox and Microsoft 's hardware acceleration but to no avail. I finally got the problem solved by restoring on a back up I didn't know I saved back in 2014 !?

Thanks anyway. Perhaps I would need to replace the Vistor software as it is pretty old.

Not really on topic in this forum to discuss in any detail, but if you were to replace Windows Vista with a current Windows 10 it would cost you money, possibly more than the device was worth. You would also need to check that the device would be likely to run W10 it even if it met a minimum spec it may not work well or require an RAM upgrades. We do have a short help article

• Firefox has ended support for Windows XP and Vista

Glad you somehow fixed the issue.