Re: The 'Never Remember History" does not stay checked. Is there a fix?
Do you see the "Use custom settings for history" choice?
Firefox shows the "Use custom settings for history" selection as an indication that at least one of the history and cookie settings is not the default to make you aware that changes were made.
If all History settings are default then the custom settings are hidden and you see "Firefox will: (Never) Remember History".
"Never Remember History" means that Private Browsing is active and "Always use private browsing mode" gets a check mark.