Over the past 18 months, Google has pushed to improve Chrome extension security—a welcome goal given the sketchy morass of extensions that have been out there for years. But one proposed change related to this effort threatens to hobble ad blocking extensions. And the pending transition has set up a showdown between Google, makers of ad blocking software, and even other browsers.

At the heart of the debate is a new application programing interface, known as the Declarative Net Request API, that Google will offer in place of an existing mechanism called the Web Request API. Ad blockers rely on that API to comb your browsing data and look for ads. Its new iteration, the company says, will better protects users' data and help ad blockers work more more efficiently. But ad blocker developers argue the new arrangement will hinder their ability to quickly and correctly identify ads, without necessarily providing the benefits touted by Google.

"This has been a controversial change since the Web Request API is used by many popular extensions, including ad blockers," Google wrote in a blog post shared with WIRED on Wednesday. "We are not preventing the development of ad blockers or stopping users from blocking ads. Instead, we want to help developers, including content blockers, write extensions in a way that protects users’ privacy."

"It becomes a bad thing when it’s the only option." Jeremy Tillman, Ghostery

Google says it has been collaborating with outside developers and incorporating their feedback since ad blocking services first got wind of the proposed changes in January. Ad blockers use the APIs Google offers to set up rules about what types of content gets blocked, and how and when it does. As a result of its discussions with developers, the company says the new Declarative Net Request API will support dynamic rules as a page is loading, not just static declarations that may lack nuance. Also the new API will limit extensions to 150,000 rules each, a big jump from the old limit of 30,000 rules per extension.

Though there may be an adjustment period for the new API, Google says the changes it has been making to Chrome extensions overall have resulted in meaningful and important improvements in user security and privacy. The company adds that the rate of malicious Chrome extension installations is down 89 percent since early 2018. And the company now blocks about 1,800 malicious uploads a month, before they are ever offered to users.

Ad blocker developers say that while they are frustrated by the extra costs to accommodate the API change, their real concern is that the changes may not serve users in the way Google says. "I think they've been trying to give the impression that they’re working with the developer community, when in fact they’re pretty entrenched in what they want to do," says Jeremy Tillman, president of the privacy and security-focused ad blocker Ghostery. "The new API is not in itself a bad thing, but it becomes a bad thing when it’s the only option because it lacks the flexibility that the Web Requests API provides."

Critics have also noted that Google's revenue is largely ad-based, giving it an inherent incentive to allow ads to run. Google has long maintained that the API changes have nothing to do with hindering ad blockers specifically, and that the company wants to work with these services to ensure a smooth transition to the new approach. Chrome also wouldn't be the first major browser to impose a rules-based system; Safari has for years, allowing 50,000 rules.

Elsewhere, the Opera, Brave, and Vivaldi browsers upped the drama this week even more by saying they would continue supporting the old Web Request API for ad blockers and other extensions, regardless of what Google has in the official Chromium code base. Google says it will only continue supporting the old API for enterprise Chrome users like businesses and schools.

Google hasn't laid out the specific timing for when the new rules, collectively called Manifest V3, will take effect. The company says it is still revising the new mechanisms and is "actively exploring other ways to expand this API." Ad blockers emphasize that they'll adapt to whatever requirements Google lays out; their survival depends on it. But it's still unclear the degree to which the changes will benefit users in the end—at least when it comes to keeping ads out of their tabs.

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