In The Martian Chronicles, freedom is most interesting when it's taken away. For instance, the government passes a law (banning books), restricting the freedom of a guy like Stendahl. So he gets revenge. Or a spouse restricts a character's freedom (as Ylla's is by Yll); but she just seems to accept it. Or life on Earth is full of official and unofficial racism, so an entire group of people—African-Americans—takes off to find a new, freer world. The search for freedom has led people all over the world and, in the Chronicles, even off the world itself—even if it's not clear what freedom looks like.
Because The Martian Chronicles was written at a time when people were worried about conformity, freedom means freedom from other people's interference.
Freedom in The Martian Chronicles is a mixed concept, with both positive and negative consequences.