when i click button, it is redirecting another page, but that page is opened in a same page

Generally, we have links on opportunity header to check count of line item or etc and i am trying to create Opportunity line item from opportunity header link, but it is opening opportunity line item insert page in header page itself, i mean please see my screen shot.

actually i want to show line item insert page, when user click serivce line item button on Opportunity header links

Code, I have written in Button.

{!REQUIRESCRIPT("/soap/ajax/20.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/20.0/apex.js")}

var opp = new sforce.SObject("Opportunity");
opp.Name = "{!Opportunity.Name}";

if('{! Opportunity.Count_Closure__c}' == 0)
{
window.location.href='/apex/OppClosureDeclaration?CF00Ne0000000sJl7=opp.Name&CF00Ne0000000sJl7_lkid={!Opportunity.Id}&scontrolCaching=1&retURL=%2F{!Opportunity.Id}&sfdc.override=1';
}else
alert('OPPORTUNITY CLOSURE IS ALREADY SUBMITTED');

User-added image