Getting tab URL in C++

Hi,

I am writing Firefox extension using C++.

I am enumerating the tabs to get their respective URLs.

Following is pseudocode:

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

nsCOMPtr<nsIWindowMediator> windowMediator =
do_GetService(NS_WINDOWMEDIATOR_CONTRACTID, &rv);
windowMediator->GetMostRecentWindow(L"navigator:browser",
getter_AddRefs(dwi));
dwi->GetDocument(getter_AddRefs(doc));
nsCOMPtr<nsIDOMDocumentXBL> xbl(do_QueryInterface(doc));
doc->GetElementById(NS_LITERAL_STRING("content"),
getter_AddRefs(domEl));
nsCOMPtr<nsIDOMElement> pAnoEl;
xbl->GetAnonymousElementByAttribute(
								domEl,
								NS_LITERAL_STRING("anonid"),
								NS_LITERAL_STRING("tabcontainer"),
								getter_AddRefs(pAnoEl)
								);
nsString retval;
PRBool bRet = 0;
nsCOMPtr<nsIDOMNodeList> nodeList;
pAnoEl->GetChildNodes(getter_AddRefs(nodeList));
nsCOMPtr<nsIDOMNode> domNode;
rv = nodeList->GetLength(&len);
for (PRUint32 i = 0; i < len; i++)
{
	nodeList->Item(i, getter_AddRefs(domNode));
	nsCOMPtr<nsIDOMXULElement> xulElement = do_QueryInterface(domNode);
	nsCOMPtr<nsIBoxObject> boxObject;
	xulElement->GetBoxObject(getter_AddRefs(boxObject));
	nsCOMPtr<nsIBrowserBoxObject> browserboxObject =
do_QueryInterface(boxObject);
}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

In the above code QueryInterface for getting nsIBrowserBoxObject fails
with error code: NS_ERROR_NO_INTERFACE.

Please suggest me the ways to get tab URL.

Help Me !!!

Thanks,
Vaibhav.