how do I prevent drop down menus when I begin to type in a word that I don't want others to see such as a security question that was previously answered and when i type the first letter to answer the question the full answer appears in a dropdown?

When I answer a security question, there is a dropdown menu that begins immediately as I type in the first letter of the answer that has the full answer there. I want to set Firefox so that it will never drop down and remember any information that answers a question.