发现加了句 ev.stopPropagation() 就可以了，应该是火狐的冒泡和捕获的事件触发顺序问题。

shopCar.ondrop=function(ev){
        var ev=ev||window.event;
        ev.preventDefault();
        
        ev.stopPropagation();
        
        ev.returnValue=false;
        var name=ev.dataTransfer.getData("name");
        var price=ev.dataTransfer.getData("price");
        var oP=document.createElement("p");
        oP.className="clearfix";
        var str="<span class='box box1'>1</span><span class='box box2'>"+name+"</span>"+price+"<span class='box box3'></span>";
        oP.innerHTML=str;
        this.insertBefore(oP,this.children[0]);
        allMoney.innerHTML=parseFloat(allMoney.innerHTML)+parseFloat(price)+'';
    }