... is also a breed of horse.
The original Florida crackers were British settlers, and their descendants, in what is now the US state of Florida. The first of them arrived in 1763 after Spain traded Florida to Great Britain following the latter's victory over France in the Seven Years' War.
It was presumably they that bred the cattle and horses that were given the same name.
Wikipedia tells us that "The term 'cracker' was in use during the Elizabethan era to describe braggarts. The original root of this is the Middle English word crack, meaning 'entertaining conversation' (as one may be said to 'crack' a joke); this term and the Gaelicized spelling craic are still in use in Northern England.
"By the 1760s, the ruling classes, both in Britain and in the American colonies, applied the term 'cracker' to Scots–Irish and English American settlers of the remote southern back country, as noted in a letter to the Earl of Dartmouth: 'I should explain to your Lordship what is meant by Crackers; a name they have got from being great boasters; they are a lawless set of rascalls on the frontiers of Virginia, Maryland, the Carolinas, and Georgia, who often change their places of abode.' The word was later associated with the cowboys of Georgia and Florida, many of them descendants of those early frontier people who had migrated South."
© Macclesfield Quiz League 2020