I’m following the instructions here for the installation of the facebook module and the popup module, but the newsletter plugin doesn’t recognise it. There is no menu voice.
Ok, the paths are correct. Inside those folder did you see the extensions files? For example inside the facebook folder you should see the facebook.php file.
Argh!!! Newsletter Pro are not compatible with Extensions. Extensions are for Newsletter Free 3.0 and they bring to Newsletter all the features of the pro version and more.
You should install that version (there is no incompatibilities, just deactivate the pro version before).