How is it possible to install a Popup on wordpress multi-site

Hi Guys,

First time I come on this forum and, so it seems, beautiful community, first post :slight_smile:.

I am looking to implement a newsletter subscription on a Multisite install through an overlay layer (see http://roxanajones.com).
I was therefore looking for any popup plugin that would work in that environment.

Anybody has had any good experience ?

Thanks a lot