This is lovely!
I applied your startwindow.js file and was going to push but I had to change something and wanted to check with you first.
You have localStorage in eb$master but I don't think that works.
I suspect each window has its own local storage.
Furthermore, if one window could access the local storage of another window it is probably a security hole that some clever person could exploit for bad things.
So I put it in the standard window, including localStorage.attributes = [] which you forgot but setAttribute() needs.
If this seems right to you I'll push.

Karl Dahlke