This identification is tentative, as bugguide itself does not seem 100% sure which Hersiilid spiders might be found in Florida. This spider is definitely from the family Hersiliidae, the longspinneret spiders, but it may be Yabisi habanensis (Florida longspinneret spider), Neotama mexicana (mexican twintailed spider), or Murricia uva (no common name). I am going with Yabisi because it is native to Florida; Neotama is native to Mexico, Texas, and other areas in the western US, and Murricia is native to Africa, although both have been imported to Florida because everything eventually comes here.
On the bright side, all three species are roughly the same, behaviorally — they use their cryptic coloration to hide against tree bark, waiting as ambush predators for prey to walk by. Prey is captured by running circles around it, weaving a circular web from the elongated spinnerets.
Those weird short third legs, by the way, are normal; the spider was hatched that way. That’s just how members of this family look.
Most longspinneret spiders (also known as tree trunk spiders) are native to Africa, China, and South America. This is another family where a lot of research remains to be done!