The Electronic Frontier Foundation (EFF) is calling out Google’s Manifest V3 (MV3) browser extension plans, calling them “deceitful and threatening.”

MV3 represents a significant change to how Chrome browser extensions are implemented. In an effort to increase compatibility, Mozilla has already announced that Firefox will adopt MV3 too.

According to the EFF, however, MV3 represents a major threat to privacy and security, thanks to the limits it places on how extensions work.

Manifest V3, or Mv3 for short, is outright harmful to privacy efforts. It will restrict 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.

The EFF aren’t the only ones warning about MV3.

“A web browser is supposed to act on behalf of the user and respect the user’s interests,” says Jonathan Mayer, Princeton University. “Unfortunately, Chrome now has a track record as a Google agent, not a user agent. It is the only major web browser that lacks meaningful privacy protections by default, shoves users toward linking activity with a Google Account, and implements invasive new advertising capabilities. Google’s latest changes will break Chrome privacy extensions, despite academic research demonstrating that no change is necessary. These user-hostile decisions are all directly attributable to Google’s surveillance business model and enabled by its dominance of the desktop browser market.”

“Nearly all browser extensions as you know them today will be affected in some way: the more lucky ones will ‘only’ experience problems, some will get crippled, and some will literally cease to exist,” writes AdGuard’s Andrey Meshkov.

It’s unlikely Google will back down from its MV3 plans, given how much it relies on the very kinds of trackers many privacy extensions are designed to combat. Hopefully, however, Mozilla will rethink its adoption of MV3, given the company’s commitment to privacy and security.