And since you won't be able to modify web pages, it will also mean the end of customization, either for looks (ie. DarkReader, Stylus), conveniance (ie. Tampermonkey) or accessibility.
Having thought about it for a bit, it's possible for this proposal to be abused by authoritarian governments.
Suppose a government—say, Wadiya—mandated that all websites allowed on the Wadiyan Internet must ensure that visitors are using a list of verified browsers. This list is provided by the Wadiyan government, and includes: Wadiya On-Line, Wadiya Explorer, and WadiyaScape Navigator. All three of those browsers are developed in cooperation with the Wadiyan government.
Each of those browsers also happen to send a list of visited URLs to a Wadiyan government agency, and routinely scan the hard drive for material deemed "anti-social."
Because the attestations are cryptographically verified, citizens would not be able to fake the browser environment. They couldn't just download Firefox and install an extension to pretend to be Wadiya Explorer; they would actually have to install the spyware browser to be able to browse websites available on the Wadiyan Internet.
Once you get to that point it's gonna get back to dark web or some other nonstandard communication form to bypass the traditional http/https protocols for "web browsing".
🤔 People could just make a new protocol and build a separate internet from the ground up.
But they'd have to do it on free Linux computers, because the ones with Windows and Mac OSes (and the specially made chips) can be accessed directly by those companies. In principle, they can see into everyone's hard drives and add or delete shit to their whims. So a way around that would have to be found too. Scary...
Basically in those situations people find new ways to be connected. For example, while satellite dishes are banned in Iran they are pretty common in that if you don't have one you propably know someone who has. Mesh networks are currently being used in Sudan and have been in other countries where government has shut down internet. Usually shutdowns and restrictions don't happen without warning so people have usually started to smuggle in satellite internet devices. But there are two huge issues. One. you need certain level of technological literacy and there is often some financial cost applied. If you asked my mom what is dark web she would look me weirdly. Partially as her English is not great but I have never heard anyone actually using the Finnish version but mainly because she has no idea what it is. Majority of people are somewhat priced out of satellite internet globally. And no one has heard of mesh networks unless they are techies, activists or people who have experienced government severely limiting internet access.
I am always astounded about how big of procentage manage to stay connected. Need really is mother of inventions. But if you put my mom, stepdad or stepmom in these situations, they would have no idea where to start. The rest of my immediate family would figure it out as we are more or less techies.