Kalev Lember added today a patch (#725002) in Software that includes a notification bar when a Web-App, in application details.
Internet Only Application
This application can only be used when there is an active internet connection.
After installing such an app, e.g Facebook we can launch it from Shell Applications Overview.
When we actually launch it, Web (aka Epiphany) will start with a locked address bar.
At that point Epiphany runs in application mode and we can’t navigate away from Facebook, we can’t open a new tab or anything else.
It is pretty much the same as:
$ epiphany --application-mode https://facebook.com --profile "~/.config/epiphany"
You can set whatever profile you want. A temp folder maybe.