Florida is one of 30 states to have Stand Your Ground Laws.
Under Florida law, there is no “duty to retreat” if you are attacked in any place you have a lawful right to be. Instead, you may stand your ground and meet force with force, including deadly force, if you reasonably believe it is necessary to prevent death or great bodily harm to yourself or others.
A key phrase here is “death or great bodily harm to yourself or others”. You may not use deadly force if you do not reasonably feel your life or the life of others is at risk. You are permitted to use deadly force to protect another from threat of death or bodily harm.
As long as you are legally eligible to possess a firearm you may use it to stand your ground. To do so outside your castle, you must be legally eligible for concealed carry. Basically in both cases, you must not be a convicted felon and must be over the age of 21. If you are under age you can legally protect yourself in the case of home invasion. See further posts for more details on legal firearm possession in Florida.