Chrome Ad Blocker Restrictions

For Chrome users who currently enjoy ad-free browsing, a recent announcement from Google is not likely to go down well. It has been confirmed that Google is going ahead with a controversial change to the rules which govern Chrome browser extensions. Unless you’re a paying Enterprise user, this change will mean that many content blockers, like uBlock Origin and uMatrix ad blockers, will no longer work on Chrome.

What will change

Ad blocking extensions are small software programs designed to enable users to customise their browsing experience. For extensions to work on Chrome, apps must be built and deployed in accordance with Google’s specifications. The current platform for Chrome extensions (Manifest V2) has been in place since 2012. Under Manifest V2, filtering is handled by Chrome’s webRequest API. This allows users to block certain types of content, like ads, pop-up videos and unsafe sites, before it is displayed by the browser. Last year, Google dropped hints about some of the changes in the pipeline for its upcoming revised rules for the extensions platform (Manifest V3). One change, relating to content blocking, caused particular concern among developers as Google now wants extensions to use a different API, declarativeNetRequest. Under declarativeNetRequest, Chrome will choose whether to block content based on a ruleset limited to 30,000 individual rules. The trouble is that most ad blockers filter content by relying on vast, crowdsourced blacklisting rulesets, which tend to require much more than the declarativeNetRequest 30,000 rule limit. The upshot is that the blocking capability will be dramatically reduced. Later last year there was some partial backtracking by Google. Now it seems that if you’re a paying enterprise Chrome user, you will still be able to rely on the content-blocking capabilities of webRequest. All other users will have to rely on declarativeNetRequest as the primary content blocking API.

Why have Google done this

Google strongly claims that its changes are always driven by the motivation of increasing the security, privacy and performance of Chrome extensions. The company has been especially keen to stress the likely impact of the change on browser performance. Currently, when a content filtering extension uses the webRequest API, Chrome refers the network connection request to the extension and waits for its decision on whether that connection should be allowed or blocked. With declarativeNetRequest, the extension lets the browser make the decision itself, which should results in a faster connection. However, these arguments have been greeted with some scepticism. As uBlock Origin author Raymond Hill pointed out, if users are experiencing performance lag, it’s much more likely to be down to pages bloated with trackers than the presence of content-blocking extensions. A study, published on, analysed the performance of some of the most popular ad-blocking extensions, including uBlock Origin, Adblock Plus and Ghostery. This found that median decision time per-request is actually in the sub-millisecond region: i.e. far too small to have any noticeable impact on the user experience. On the other hand, the possible business benefits to Google from this change are hard to ignore. When you’re choosing a browser to use, the ability to customise your experience with effective blocking and filtering extensions offers an attractive draw. But at the same time, Google’s primary business to focus is generating ad revenue. Over 10 years, Chrome has managed to get almost two thirds of the worldwide browser market share. With clear market dominance, it may take the view that it can afford to scale back the browser’s ad-blocking potential with a view to maximising ad revenues.

What next?

As it stands, Manifest v3 is open to public view and is still subject to change. We anticipate the proposed changes will be firmed up later this year. Developers are saying that certain ad blockers (e.g. UBlock Origin and uMatrix) will effectively no longer be able to work on the consumer version of Chrome unless they are completely redeveloped. But you will still be able to get some ad blockers that work. These will be rule-based systems similar to AdBlock Plus. There are concerns that the limit of 30,000 rules will reduce the effectiveness of these extensions. However, according to 9to5Google, these limits may not be set in stone. According to Google: “We are planning to raise these values but we won’t have updated numbers until we can run performance tests…”.

Is there a work-around?

As it stands, the only effective work around would be to change your browser to a non-chromium based one. If you are thinking of switching to a different browser, Firefox may be your best bet and has always been our recommended browser for those concerned about security and privacy. Unlike the Edge, it is not based on Chromium and the least likely to be affected by Google’s API changes.

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