Sure, but how do you do that in a way that can't be circumvented? Alice creates a page with a newsletter popup, then Bob installs a plugin with a MutationObserv

Sure, but how do you do that in a way that can't be circumvented? Alice creates a page with a newsletter popup, then Bob installs a plugin with a MutationObserver [0], so Alice just adds some code to disable any such MutationObservers. Plus how do you determine when it's an unwanted modal? You don't want to block the login popup, for example. Maybe you can block all modals except for the ones generated from a "click" event, but what if the site sets a "click" listener on the <body> tag? [0] https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver https://developer.mozilla.org/en-US/docs/Web/API/MutationObs...