In Chrome, your browser now decides how well your ad blocker works

On 31 August 2026, Google removed the last Manifest V2 extensions from the Chrome Web Store, the final step in a migration it began years earlier, according to Chrome's own deprecation timeline. Two days later AdGuard told its users that the store had pulled the old version of its extension. For anyone who blocks ads in Chrome, the transition is now complete.

Our view is simple: in Chrome, the browser now sets the ceiling for every ad blocker, so the browser is the first decision and the extension is the second. Readers who choose a blocker by the name they remember, and ignore what the browser allows it to do and what the blocker allows by default, are choosing on the wrong evidence.

What actually changed

The change is technical, and AdGuard explained it more clearly than most: "Under MV2, an ad blocker could inspect each browser request as it happened and decide whether to allow or block it. Under MV3, the extension gives Chrome a list of blocking rules in advance, and Chrome makes most of those decisions itself." The same post says rule limits are lower than before and that "some traditional rules cannot be converted into MV3's format without losing functionality." Its conclusion was measured: "For most users, AdGuard should work much as it did before. But MV3 is still a compromise."

The limits are written down. Chrome's declarativeNetRequest documentation guarantees each extension 30,000 static rules, with anything above that drawn from a global pool shared by every extension installed in the browser. An extension can add up to 30,000 dynamic rules, of which only 5,000 may be the "unsafe" kind, and no more than 1,000 regular expression rules. Those figures are larger than the earliest proposals, and Google did listen to developers: its November 2023 announcement promised "more generous limits" for static rulesets and dynamic rules. But they are still limits, and the browser maker sets them.

The clearest illustration is uBlock Origin Lite, the MV3 successor to one of the most respected blockers. Its FAQ is candid about what it cannot do. Its filter rulesets "are updated only when the extension itself updates." Because the Chrome API cannot apply rules according to the site in the address bar, dynamic filtering "can't be supported." And by default there is "no generic cosmetic filtering," which the original did out of the box. The developer describes it as a version "suitable for those who used uBO in an install-and-forget manner," not as a like-for-like replacement.

Why the browser decision comes first

Not every browser made the same choice. Mozilla said in February 2025 that Firefox "will continue supporting both blockingWebRequest and declarativeNetRequest," which is why the full uBlock Origin still runs there. So two readers installing a blocker with the same name can end up with materially different tools depending on the browser underneath. A comparison of ad blockers that does not say which browser it assumes is answering half the question.

There is also a structural point we think buyers should keep in view. In the fourth quarter of 2025, Google advertising brought in $82.3 billion of Alphabet's $113.8 billion in total revenue, according to Alphabet's earnings release. We are not claiming that MV3 was designed to protect that income; Google's stated reasons are security and privacy, and we take them seriously below. We are saying that when the company whose main business is advertising also writes the rules for the tools that block advertising, readers are entitled to weigh that, and to prefer arrangements where those two roles are separate.

The defaults matter as much as the engine

The browser is not the only thing quietly deciding what gets through. Adblock Plus states plainly on its Acceptable Ads page that the program "is on by default," arguing that the best outcome is "a web with fewer, better ads." It also says you can switch it off in two clicks. That is a defensible position, and it is disclosed. But a reader who installs an "ad blocker" expecting it to block ads, and finds some ads permitted unless they change a setting, has been given a product that does something different from its category name. We think every blocker that allows ads by default should say so at the point of install, not only on a policy page.

The strongest case for Google's approach

The fairest counter-argument is that the old model was dangerous. An extension that can inspect and alter every request as it happens can, if it is malicious or is sold to someone who is, read and change everything a user does on the web. Google's announcement framed MV3 around "higher security and privacy guarantees," and a declarative model genuinely narrows what a rogue extension can see. Most people never change a filter setting, and AdGuard itself expects most of its users to notice little difference. On this view, a small loss of power for a few enthusiasts buys a real safety gain for everyone else.

We accept most of that. The security problem is real, and a rule list handed to the browser is easier to reason about than code watching every request. Where we part company is on who bears the cost and who decides. Privacy groups made the counter-case early: the Electronic Frontier Foundation argued in December 2021: "Advertising technology evolves rapidly, and privacy extension developers need to be able to change their approaches to it over time." A blocker whose rules refresh only when a new version passes through the store is, by design, slower to react than one that can fetch new filters itself. That is a trade-off users should be told about, not one they should discover.

What we think buyers should do

• Decide on the browser first. If the strongest content blocking matters to you, the browser's extension rules are the main constraint, and Firefox still allows the older, more flexible model.
• Read the defaults. Check whether your blocker allows any ads out of the box, and turn that off if you did not want it.
• Know what "Lite" means. An MV3 version of a familiar blocker may lack features you relied on; the developer's own FAQ is the best place to find out which.
• Judge reviews by their assumptions. A ranking of ad blockers that does not name the browser it tested on is incomplete.

The end of Manifest V2 in Chrome is not the end of ad blocking. It is the point at which the browser became the most important part of the choice. Buyers should treat it that way, and the companies selling blockers, and the one setting the rules, should be clearer about what each one now allows.