These words were not synonyms to the founding Fathers. No one said, “Give me Freedom or give me death!” They were fighting for God-given rights. After the Civil War the term was changed from liberty to freedom - and that is the word we use today. But they are not interchangeable in their historic context.
That one word might be used more in the past than the other does not mean that the other word means something else. That doesn't follow. "Liberty" means liberty, not justice, or some other concept. If you have liberty you are free.
You should explain to us what exactly you think liberty means.