...
Open the browser development tools. The hotkey for most browsers is F12.
Select the console.
On the command line, enter enter:
Code Block srv.openModal(true,'<FORMKEY>')
The <FORMKEY> can be found in the URL of the preview page. See How do I open a Mopinion feedback form with my own button or link? for more details on retrieving the <FORMKEY>.
An overlay should appear on the webpage.
...