Firefox version 3.6.12 setInterval Random number as Param bug

if you pass a callback function that can accept parameter into setInterval. It will pass random numbers into the callback function when it wasn't suppose to.

var interval_id;
var callback_time = 5000;
var callback_fnc = function (param){
	if(typeof param == 'undefined'){
		alert("Working normally...");
	}else{
		alert("Something wrong! Variable Type: " + typeof param + " Value: " + param);
	}
}

If you pass the first param as code. It runs as usual.

function runAsCode(){
	clearInterval(interval_id);

	interval_id = setInterval(
		"callback_fnc()",
		callback_time
	);
}

However if you pass it as function. setInterval will keep passing random numbers to the callback function as param

function runAsFunction(){
	clearInterval(interval_id);

	interval_id = setInterval(
		callback_fnc,
		callback_time
	);
}