HTMLViewer PopUp child windows

I’m making use of a web site in my app that wants to popup a new browser window. That seems to work OKish, thought it complains that I have a popup blocker. I respond to the NewWindow event with a window that contains a second HTML viewer and pass back the viewer from there. But, and I kind expected this and it probably explains the popup blocker complaint, there is no communication between the parent window and the child window with respect to the DOM and JavaScript. Basically the parent is popping up the child to allow for the selection of an item and then it wants to pass that back to the parent somehow, probably JS. I don’t know how it is really doing that as it is a 3rd party site completely out of my control. It works fine in a regular browser, but no so much in Xojo.

Any ideas?