How to prevent Forticlient popup in MacOS Guest browsers

We have several MacOS Mojave Mac Minis that are only used with a Guest account.  Each time a user opens Safari, Chrome or Firefox they get a Forticlient popoup (pic attached.)  Is there a plist or config.xml that I can preconfigure this for system use?  Each time the Guest account is logged out it resets and all users get the popup repeatedly.