How do you secure against the system vendor (in this case the browser) limiting what the consumer/user can or can't do (alone or with the help of third parties) with the product after acquiring it though? After all security for individuals against commercial and otherwise organized interests is one of the, if not the most important security after life and health. Even if one values the market overall for financial reasons, there is a solid argument that preventing modifications (and thus also repairs) is anti-competitive. It would be damaging to society if manifestV4 is realized restricting what can run further, much like printers and operating systems where the users ability to run software they bring themselves is limited has been. Just as no one should have to go to a mechanic with a special deal with the manufacturer to get their car or tractor to work as desired, neither should users of software.