It would require significantly more fuel to get the stage to even the Gulf coast of Florida (much less the Atlantic coast) than it would take to return to Brownsville. Additionally, Brownsville launches will almost certainly be aimed between the southern tip of Florida and Cuba, in order to avoid traveling over any populated areas.

oh I am sure there are a few islands out there both inhabited and not so much that would present some opportunities. Much easier to deal land on something that isn't moving up and down, let alone side to side.

If launched from Texas, would they have to move side to side to land the first stage in Florida?

my apologies for not be clearer, while the movement of the Earth is a concern I was replying to the idea of trying to land on a floating platform which I do not see as feasible. Both from the standpoint of trying to find such a small location to the fact it is not going to be a stable landing area because of wave action

Would an old oil rig work?