Technically this extension manipulates local copy (DOM model) of the sites the user is browsing. It erases random characters from the site until you will be left with an empty browser window. While doing this it is not manipulating any files on your computer nor the files at the remote server you downloaded the website from.
Further, the scripts that the website that is being browsed are not affected. They are left as they are and they keep on running normally. The aim is to keep the site working as long as possible and also minimize the possibility that anything harmful (permanent) would happen in the process. As the extension is only manipulating DOM, refreshing the browser will start the process from beginning as it is effectively restoring the DOM to the state it was before being erased.