I don't know if it is one of the worst handling cars ever, but let's face some facts, the Fox Mustang can be a handful. When we are talking about driving on the limit, the car has one of the worst sins, which is understeer up to the point of snap oversteer.
The article is correct that the suspension on the Fox is just not very good. The front suspension suffers from a combination of problems - insufficient ackermann, positive camber in compression, not enough steering angle, the list goes on and on.
The rear is an abortion all together. Poor axle control, followed by complete bind (Hello snap oversteer!) then unload and rebind again.
Due to the inherent understeer, when the thing decides to snap the front wheels are already turned into the slide and it makes it very hard to catch.
I love the Fox Mustang as much as anyone, but the suspension design leaves a lot to be desired. The aftermarket has done a great job improving on it, and with 3-5K you can get a pretty good handler. At that point the biggest problem is simply weight distribution, which is hard to fix with the engine ahead of the front tires.