4wd 2004 Sport Trac

Limited slip does not mean that both wheels turn. Non 4x4 front wheels both turn, and non-limited-slip 4x4 front wheels both turn. Limited slip limits the degree to which the two wheels on that end of the vehicle can differ in speed between themselves, as when you're driving on slippery surfaces. When one wheel begins to slip, the limited slip differential will use clutches to transfer torque to the other wheel (the one with good traction). This reduces torque to the spining wheel, and lets it regain traction (if traction's there to be regained).

As to whether limited slip was offered on that vehicle's front axle, I don't know.

No you don't have limited slip in the front.