Could an upcoming Google Chrome update break your ad block?

Your favorite browser extensions may soon stop working, thanks to a major change Google is making to Chrome. This can severely limit the capabilities of content blocker extensions, including ad blockers and security extensions, which prevent ads, trackers, and malware from loading in your browser.

It doesn’t just affect Google Chrome; browsers like Microsoft Edge run on Chromium, the underlying code of Google Chrome. So what does this mean?

How do ad blockers work?

Ad blockers and other content blockers work by maintaining a list of requests to block before loading. If you visit a legitimate website that is infected with malware, your content blocker can allow the legitimate website to load while blocking the connection to the infection before it can harm your device. See our guide to malicious websites and malvertising to learn how to spot them and protect yourself.

In addition, most ad blockers have a feature called cosmetic filtering. After the request to the ad server is blocked, websites still contain empty space where ads would normally be. To improve readability, cosmetic filtering removes those leftover spaces and condenses the website just before it finishes loading.

All browser extensions contain a blueprint file called Manifest to pass the most important information from the browser, such as the required permissions. Manifest itself is an API, which stands for Application Programming Interface. Learn what an API is and how they work if you are unfamiliar. Basically, it acts as an interface between the extension and the browser so that they understand how to work together.

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Support for version 1 was completely discontinued in 2014 and version 2 is planned to end in the same way. Version 3 is the version that can break through content blockers, and changes come sooner rather than later.

What will Manifest V3 change?

Since January 2022, new extensions added to the Chrome Web Store are required to use Manifest V3. In June 2023, extensions using Manifest V2 will only be accessible if you have the link to them, before being completely removed in January 2024.

(Version 3 brings a lot of changes; what we’re focusing on are the limits imposed on content blockers.)

The lists of requests to block and cosmetic filtering that we discussed earlier are also known as rules. If your adblocker has a list of malicious websites with 50,000 entries, it sets rules to block every website and checks every request to see if there is a match.

Many ad blockers and security extensions have hundreds of thousands of rules, some give you the ability to use millions. According to an blog post from AdGuarddeveloping one of the most popular ad blockers with a Manifest V3-compatible extension, the imposed limits will be 30,000 lines per extension and 330,000 lines per user.

It also explains how to disable all filters except AdGuard’s basic filter, and notifies you when this rule limit has been reached. Even the basic filter can reach over 30,000 lines, and if you have multiple content blockers, you can exceed the 330,000 limit per user. Ad flicker also occurs because cosmetic filtering doesn’t happen as quickly.

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The problem isn’t so much that ad blockers and content blockers can’t work with Manifest V3, it’s how well they will work and how much they can block.

Not everyone will be affected

As we mentioned at the beginning, this change will affect not only Google Chrome but also other Chromium browsers like Microsoft Edge. Mozilla Firefox supports Manifest V3 extensions, but does not have this problem because rules have no limits.

If you don’t use a content blocker, you probably won’t notice any difference with your existing extensions. If so, you may be limited to the number of filters you can use and therefore you can block ads.

Google claims Manifest V3 will improve security and performance in general, but some question the magnitude of these claims. Other ad blockers are likely to follow AdGuard’s release of Manifest V3 extensions, and ad blockers won’t go away overnight.

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