EFF technologist Daly Barnett said that like FLoC and Privacy Sandbox before it, Manifest V3 is another example of the inherent conflict of interest that comes from Google controlling both the dominant web browser and one of the largest internet advertising networks.

It restricts the capabilities of web extensions -- especially those that are designed to monitor, modify, and compute alongside the conversation your browser has with the websites you visit. Under the new specifications, extensions like these -- like some privacy-protective tracker blockers -- will have greatly reduced capabilities.

Google's efforts to limit that access is concerning, especially considering that Google has trackers installed on 75% of the top one million websites.

It's doubtful Mv3 will do much for security. Firefox maintains the largest extension market that's not based on Chrome, and the company has said it will adopt Mv3 in the interest of cross-browser compatibility.

At the 2020 AdBlocker Dev Summit, a big cheese in the Mozilla Foundation said when a malicious extension sneaks through the security review process, it is usually interested in simply observing the conversation between your browser and whatever websites you visit.

The malicious activity happens elsewhere, after the data has already been read. A more thorough review process could improve security, but Chrome hasn't said they'll do that. Instead, their solution is to restrict capabilities for all extensions.

As for Chrome's other justification for Mv3 -- performance -- a 2020 study boffins at Princeton and the University of Chicago revealed that privacy extensions, the ones that will be hindered by Mv3, improved browser performance.