Help needed populating form field

I’m new to Java and could use some help… Heres the situation: I have several articles that link to an email form. This form page uses the following function to get the URL of the article from which the user clicked:
function getReferrer() { document.forms[0].elements[0].value =document.referrer;
}
this populates a text field with that URL… This works fine as long as the email form opens in the same browser window. However, I would like the email form to open in a pop-up window and I can’t figure out how to get the URL of the article into the text field. Is there some way to do this? I would greatly appreciate any help. Thank you!