Hi

Do you have any add-ons installed in Firefox?

AdBlocker Plus & Video Download Helper

Also just checked, my PC is over 8 years old.

Cannot open AOL Mail or Facebook at times after sleeping my PC. If I revert to my Laptop or using MS Edge on my PC all is fine. I have reinstalled Firefox, but problem persists from time to time.

Try clearing Firefox cache, disable extensions, and turn off hardware acceleration, that usually fixes it after sleep issues.