[FireFox] Parent Object For Style In Setter

this is my code:

CSSStyleDeclaration.prototype.__defineSetter__('di splay',
displaySetter);

function displaySetter(value) {
var parent = findParent(document, this);
if (parent) {
if (parent.tagName == 'TD'
&& value.toLowerCase() == 'inline' ) {
value = 'table-cell'
}
}
this.setProperty('display', value , 'important');
}


function findParent(obj, style) {
var nodes = obj.childNodes;
if (obj.style == style) {
return obj;
}
for(var i = 0; i < nodes.length; i++) {
var suBsearchResult = findParent(nodes[i], style);
if (suBsearchResult) {
return suBsearchResult;
}
}
return false;
}

As you can see each time I need to scan whole document for parent which I would like to avoid. Is there any other way to get an object on which style is applied to?