Which state are you a legal resident of? If you are a legal resident of any compact state, you can not apply for licensure in any of the other compact states. In your situation, if you are a legal resident of FL you have to apply for licensure in FL. When you relocate to MS you should apply for licensure by endorsement as soon as possible, and you will be allowed to work on your FL license while your MS license is being processed.
If your state if legal residence is a non-contact state then you can apply for licensure in MS.
ETA: For residency purposes, the Nurse Licensure Compact considers your state of legal residency. This might be seperate from the state that you physically live in.