Marla Gibbs has earned her place in TV history playing Florence Johnston, the less than efficient and always wisecracking maid of George and Louise Jefferson on "The Jeffersons" (CBS, 1975-1985), and as Mary Jenkins, gossipy homemaker and general building yenta on the NBC series "227," which she also co-produced. Acting, let alone stardom, came to Marla Gibbs relatively late. A divorcee with three children, she worked as a receptionist, addressograph operator, switchboard operator, and was a reservations clerk for United Airlines before she even attempted acting professionally. In fact, she