It removes the ability for extensions to intercept network requests. Instead, it provides a means for extensions to block content by providing a blacklist. This is similar to how content blockers work in Safari.
It won't kill adblockers, but severely limit their functionality in the face of increasingly elaborate advertising techniques
it will work fine initially but then it will slowly get less and less effective as advertisers figuring out how to subvert declarative lists with no logic
It won't kill adblockers, but severely limit their functionality in the face of increasingly elaborate advertising techniques