這份 javascript 是在網上爬到的

function iEsc(){ return false; }

function iRec(){ return true; }

function DisableKeys() 
{
	if(event.ctrlKey || event.shiftKey || event.altKey) 
	{
		window.event.returnValue=false;
		iEsc();
	}
}
document.ondragstart=iEsc;
document.onkeydown=DisableKeys;
document.oncontextmenu=iEsc;

if (typeof document.onselectstart !="undefined")
document.onselectstart=iEsc;
else{
document.onmousedown=iEsc;
document.onmouseup=iRec;
}

function DisableRightClick(qsyzDOTnet)
{
	if (window.Event)
	{
		if (qsyzDOTnet.which == 2 || qsyzDOTnet.which == 3)
		iEsc();
	}
else
	if (event.button == 2 || event.button == 3)
	{
	event.cancelBubble = true
	event.returnValue = false;
	iEsc();
	}
}

我使用後發現我用火狐瀏覽器時

<select>標籤的下拉式選單無法點選，其他瀏覽器正常，而拿掉這份javascript 火狐就正常了

這份 javascript 該如何修改呢?

謝謝