Both IE and netscape work fine if the popup window directly sends values to the underlying opener.
Netscape problem only arises if the new window changes...if you click a link or submit a form and repopulate the new window.
For example I had a simple pop-up color picker that always worked: pop up a pallette, pick a color, populate the opener.
For the alternate case example,the popup window was 'find or create a new customer' for an underlying opener order window.
If all that happened was to fill out the popup's initial display form, things went OK: new customer info was incorporated in the opener.
If they clicked through on the new window to find an existing customer, however, IE would populate the opener page with the found customer data, but Netscape would not.
If a user clicked through from the initial create customer to the find customer page in the new window, Netscape regarded the 'create customer' popup as the opener of the 'find customer' popup.
IE maintained that the original order page was the opener for both cases.
It pays to do some cross-browser checking...they all work differently.