Why Vivaldi browser thinks Google’s new proposal, the Web-Environment-Integrity spec, is a major threat to the open web and should be pushed back. …

So, what is the issue?

Simply, if an entity has the power of deciding which browsers are trusted and which are not, there is no guarantee that they will trust any given browser. Any new browser would by default not be trusted until they have somehow demonstrated that they are trustworthy, to the discretion of the attesters. Also, anyone stuck running on legacy software where this spec is not supported would eventually be excluded from the web.

​To make matters worse, the primary example given of an attester is Google Play on Android. This means Google decides which browser is trustworthy on its own platform. I do not see how they can be expected to be impartial.

On Windows, they would probably defer to Microsoft via the Windows Store, and on Mac, they would defer to Apple. So, we can expect that at least Edge and Safari are going to be trusted. Any other browser will be left to the good graces of those three companies.