Why does Firefox not remember my history settings?

I have Firefox 5.0. When I go to Tools>Options>Privacy tab, it says under History that "Firefox will: Use custom settings for history". REMEMBER SEARCH AND FORM HISTORY is checked, as well as ACCEPT COOKIES FROM SITES (Accept third party cookies is checked, Keep until I close Firefox). There is nothing in the Exceptions part. Clear history when Firefox closes is checked. Under settings, Saved Passwords is the only thing Unchecked. Now, the problem is, When I put "Firefox will: Never remember history" then click OK, when I go back, it shows "Firefox will" Use custom settings for history." How can I get it to keep on "Firefox will: Never remember history" ?