IANAL, but it seems that it would be legal to open carry an "antique firearm" in Florida. However, the distinction between "firearm" and "antique firearm" in the statute is not one I would expect the average street cop to have the diligence to make. Consequently, because I do not have the time or money to defend myself in court, I wouldn't try it unless I also could take advantage of one of the exceptions in 790.25.
790.053 Open carrying of weapons.—
(1) Except as otherwise provided by law and in subsection (2), it is unlawful for any person to openly carry on or about his or her person any firearm or electric weapon or device. It is not a violation of this section for a person licensed to carry a concealed firearm as provided in s. 790.06(1), and who is lawfully carrying a firearm in a concealed manner, to briefly and openly display the firearm to the ordinary sight of another person, unless the firearm is intentionally displayed in an angry or threatening manner, not in necessary self-defense.
(2) A person may openly carry, for purposes of lawful self-defense:
(a) A self-defense chemical spray.
(b) A nonlethal stun gun or dart-firing stun gun or other nonlethal electric weapon or device that is designed solely for defensive purposes.
(3) Any person violating this section commits a misdemeanor of the second degree, punishable as provided in s. 775.082 or s. 775.083.
History.—s. 1, ch. 87-537; s. 173, ch. 91-224; s. 3, ch. 97-72; s. 1205, ch. 97-102; s. 3, ch. 2006-298; s. 1, ch. 2011-145.
90.001 Definitions.—As used in this chapter, except where the context otherwise requires:
(1) “Antique firearm” means any firearm manufactured in or before 1918 (including any matchlock, flintlock, percussion cap, or similar early type of ignition system) or replica thereof, whether actually manufactured before or after the year 1918, and also any firearm using fixed ammunition manufactured in or before 1918, for which ammunition is no longer manufactured in the United States and is not readily available in the ordinary channels of commercial trade.
. . .
(6) “Firearm” means any weapon (including a starter gun) which will, is designed to, or may readily be converted to expel a projectile by the action of an explosive; the frame or receiver of any such weapon; any firearm muffler or firearm silencer; any destructive device; or any machine gun. The term “firearm” does not include an antique firearm unless the antique firearm is used in the commission of a crime.