Always on top but ... not always

Hello,

Can someone help for a slight problem :

I have an html order form, from which a link opens a windows pop up to show necessary elements for the order (i.e. a choice of color for the order). This pop up is an html page with a long scrollable image inside.

The problem is :

1. If I use an "always on top" extension, the pop up blocks access to the order form.
2. If not, the pop up disappear behind the form

Well...

I thought of putting the image of the ex-pop up in a layer, make this image scroll inside the layer, and make the layer scrolling (because the informations are needed for each item bought)

Do you have something more simple ?

Thanks for any help