Agreed, FedEx is the leader in in-flight fire safety and have many in-fire prevention systems. Blankets above haz can, fire extinguishers systems, etc. Even on the aircraft that do not have the new system every aircraft has a fire supression system that is connected to a haz can and is hooked up only after it is inspected by the crew.
In my mind it is related to cost and FedEx is willing to spend the bucks in the prevention of in-flight fires. Not to say there will never be one, in aviation never is a word not spoken. But FedEx does and will continue their R&D for this all important problem. And for us who do not enjoy the luxury to work for a top notch airline that can afford such an expenditure, lets hope they do have the desire to adopt the work of others.