EFF Warns Chrome Users: 'Manifest V3 Is Deceitful and Threatening' (eff.org) 46
It's also 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. Yet, at the 2020 AdBlocker Dev Summit, Firefox's Add-On Operations Manager said about the extensions security review process: "For malicious add-ons, we feel that for Firefox it has been at a manageable level... since the add-ons are mostly interested in grabbing bad data, they can still do that with the current webRequest API that is not blocking." In plain English, this means that 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 (PDF) by researchers at Princeton and the University of Chicago revealed that privacy extensions, the very ones that will be hindered by Mv3, actually improve browser performance. The development specifications of web browser extensions may seem in the weeds, but the broader implications should matter to all internet citizens: it's another step towards Google defining how we get to live online. Considering that Google has been the world's largest advertising company for years now, these new limitations are paternalistic and downright creepy.