Probably some file permissions or anti-virus software changed and Firefox can't write the new preferences. Please see How to fix preferences that won't save.

Gryllida, thanks for the reply and for the recommendation. I checked the link you provided and none of the steps worked. I even deleted (removed) prefs.js and it only saved the settings (worked) ONCE. After changing the setting it reverted back to the initial setting. So, it appears, if I want to change the settings I must delete prefs.js every time for a ONE TIME shot for the new settings to take place.

Just peculiar

Regards,

Probably some software is locking the file. Do you have any active anti-virus software (if so, does disabling it help)? Can you try to make a new profile (see Profile Manager - Create, remove or switch Firefox profiles) and test for the issue there?

That is how it works.

Only if all settings are the default then you will see "Firefox will: (Never) Remember History".
The "Use custom settings for history" choice reverts to "(Never) Remember history" if all History and Cookies settings are the default.
If you see "Use custom settings for history" then at least one of the History / Cookie settings is not the default.

Gryllida and cor-el thanks for the information. It appears "Remember my browsing history for (number of days)" had an influence on being able to select "Remember" or NOT to remember History. It was set to a number different from 90 and by changing it to 90, the selection and setting works fine.

I thank you both for your guidance and assistance.

Regards,