Prevent pop-ups from being blocked

I am using a Facebook login method in my code on page load, but when I execute this code, the pop-up blocker closes the Facebook permission window.

How can I open this window with Javascript without needing to make an exception in the pop-up blocker?

Below is my code:

FB.login(function(response)
{
    if(response.session!=null)
    {
        window.location.href='http://example.com';
    }
},
{ perms: 'email,user_birthday,publish_stream' });