Separate Security Issue: Update your Adobe Reader Version 2015.016.20039 Note: Other Software is offered in the download.

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

"Use custom settings for history" allows to access the current history and cookie settings for inspection and modification. Selecting "Use custom settings for history" doesn't make any changes to history and cookie settings. Firefox will keep showing "Use custom settings for history" 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: Remember History".

The "Ask me" choice for cookies has been removed in Firefox 44+ and will be treated like ACCEPT_NORMALLY (network.cookie.lifetimePolicy = 0).

• http://www.ghacks.net/2016/02/05/firefox-44ask-me-everytime-cookie-option-removed/
• http://www.ghacks.net/2016/01/18/enhance-firefox-cookie-management-with-these-add-ons/

Make sure you do not use Clear Recent History to clear the "Cookies" and the "Site Preferences".

Let the cookies expire when Firefox is closed to make them session cookies instead of using "Clear history when Firefox closes" to clear the cookies. .

• Firefox/Options/Preferences -> Privacy -> "Use custom settings for history" -> Cookies: Keep until: "I close Firefox"

You can create a cookie "Allow" exception to keep specific cookies.