Firefox, ie7, and ie6 are not working with this java script

Firefox, ie7, and ie6 are not working with this java script

With the java script below, firefox, ie7, and ie6 are not working properly
(ie8 worked after applied getElementsByClassName.polyfill.js.) Can anyone
find any problem on the script below for firefox, ie7, and ie6 to work?
(Chrome and safari worked fine before applied the polyfill.js .)
This java script is designed to open and close the several levels of
categories by clicking.
/*------------------------------------------
Open or close the specified node.
------------------------------------------*/
function openOrClose(tgt){
//To make the list visible when the specified node is hidden.
if(tgt.style.visibility == "hidden"){
tgt.style.display = "block";
tgt.style.visibility = "visible";
tgt.style.height = "auto";
tgt.style.paddingTop = "0.25em";
tgt.style.lineHeight = "1em";
tgt.style.opacity = 1.0;
}
//To make the list hide when the specified node is not hidden.
else{
tgt.style.display = "none";
tgt.style.visibility = "hidden";
tgt.style.height = "0px";
tgt.style.paddingTop = "0";
tgt.style.lineHeight = 0;
tgt.style.opacity = 0;
}
}
/*------------------------------------------
To open the list
------------------------------------------*/
function listopen(lv, num){
var tgt = document.getElementsByClassName("level" + lv)[num];
//To search the next level -> to open the next level list.
for(var i=0; i < document.getElementsByClassName("level" +
(lv+1)).length; i++){
var next_tgt = document.getElementsByClassName("level" + (lv+1))[i];
//li
if (next_tgt.parentNode == tgt || next_tgt.parentNode.parentNode == tgt){
openOrClose(next_tgt);
}
}
//To search the next level -> change the shape of the button that is
displayed.
for(var i=0; i < tgt.childNodes.length; i++){
var next_tgt = tgt.childNodes[i];
//ul
if(next_tgt.tagName == "UL"){
if(next_tgt.style.height == "0px"){
if(event.srcElement.parentNode.className == "category_header
plus"){
event.srcElement.innerText = '?';
event.srcElement.parentNode.className = "category_header
minus";
}
next_tgt.style.height = "auto";
}
else{
for(var i=0; i<next_tgt.parentNode.childNodes.length; i++){
if(event.srcElement.parentNode.className ==
"category_header minus"){
event.srcElement.innerText = '{';
event.srcElement.parentNode.className =
"category_header plus";
}
}
next_tgt.style.height = "0px";
}
}
}
}
/*------------------------------------------
To set up the click event
------------------------------------------*/
function setclickevent(tgt, lv, num){
//To make invisible when the level is other than 1.
if(lv!=1){
tgt.style.visibility = "hidden";
tgt.style.display = "none";
tgt.style.height = "0px";
tgt.style.lineHeight = 0;
tgt.style.paddingTop = 0;
tgt.style.paddingBottom = 0;
if(tgt.parentNode.tagName == "UL"){
tgt.parentNode.style.height = "0px";
tgt.parentNode.style.margin = "0";
tgt.parentNode.style.padding = "0";
tgt.parentNode.style.border = "none";
}
}
var hasLink_flg;
if(tgt.childNodes.length){
for (var j = 0; j < tgt.childNodes.length; j++) {
//To enlarge the scope where you can click.
if(tgt.childNodes[j].tagName == 'A'){
tgt.setAttribute('onclick', 'location.href="' +
tgt.childNodes[j].getAttribute('href') + '"');
}
//To add the event function of the accordion list
else if(tgt.childNodes[j].tagName == 'UL'){
//To display ? and add the list open function.
var linkObj = document.createElement("a");
linkObj.innerText = '{';
tgt.childNodes[0].className="category_header plus";
tgt.childNodes[0].appendChild(linkObj);
j++;
linkObj.parentNode.setAttribute('onclick', 'listopen(' + lv +
',' + num + ')');
//tgt.setAttribute('onclick', 'listopen(' + lv + ',' + num +
')');
break;
}
}
}
}
/*------------------------------------------
Initialization
------------------------------------------*/
// To search all the node that has level? class and initiali
function initCategoryList(){
var lv = 0;
//To add the click event to all the node that has level?
while(document.getElementsByClassName("level" + (++lv)).length){
for (var i = 0; i < document.getElementsByClassName("level" +
lv).length; i++) {
setclickevent(document.getElementsByClassName("level" + lv)[i],
lv, i);
}
}
}