Manifest V3 (MV3) is Google’s updated standard for Chrome browser extensions. It replaced the older Manifest V2 standard and fundamentally changed how extensions interact with network requests. For ad blockers, the change was significant: the API that allowed extensions to intercept and cancel outgoing requests in real time was removed.
What Is a Browser Extension Manifest?
Every Chrome extension includes a manifest.json file that declares the extension’s
name, version, permissions, and what APIs it can access. Manifest V2 and Manifest V3 are
different versions of this file format, each defining a different set of available APIs and
permission scopes.
What Changed in Manifest V3?
The most significant change for ad blockers was the removal of the webRequest blocking API.
webRequest (MV2) — What It Did
In Manifest V2, an extension could register a listener for the webRequest event.
When the browser was about to make a network request, the extension’s code would run, inspect
the URL, and decide whether to allow or block it. Ad blockers used this to cancel requests to
ad servers before any ad content was downloaded.
This approach was flexible and powerful. Extensions could apply complex, dynamically-updated rules, inspect request headers, and make blocking decisions based on context.
declarativeNetRequest (MV3) — What Replaced It
In Manifest V3, extensions must use the declarativeNetRequest API. Instead of
running extension code for each request, extensions declare a set of rules in a static JSON
format. The browser evaluates these rules internally and applies blocks without running
extension code per-request.
The advantages Google cited: better performance, reduced attack surface, and fewer opportunities for malicious extensions to spy on traffic. The disadvantage for ad blockers: the rule set is limited in size and cannot be updated dynamically at runtime the way webRequest-based blocking could be.
Which Ad Blockers Were Affected?
uBlock Origin was the most prominent casualty. Its developer assessed that the MV3 API limitations could not replicate the full capabilities of the extension. uBlock Origin was not ported to MV3 for Chrome, and Chrome Stable began disabling MV2 extensions in October 2024.
Ad blockers that already used or migrated to the declarativeNetRequest API — including ProBlocker, AdGuard, AdBlock, and Adblock Plus — were not affected.
Does MV3 Apply to Firefox?
No. Manifest V3 is a Chromium standard. Mozilla, which develops Firefox, has not adopted Google’s MV3 restrictions. Firefox continues to support the webRequest blocking API. uBlock Origin works fully on Firefox with all capabilities.
Edge, Brave, and Opera are Chromium-based and follow the MV3 standard, though enforcement timing may differ slightly from Chrome.
Is MV3 Bad for Privacy?
The removal of real-time request inspection reduces the capability of privacy-focused extensions. The counter-argument from Google is that the same API that allowed ad blockers to inspect traffic also allowed malicious extensions to do the same.
In practice, MV3-native ad blockers can still block the majority of known ad domains, trackers, and malware hosts using pre-compiled rule sets. The main loss is dynamic rule updating and complex per-site logic — capabilities that most users never configured manually.
What Should Chrome Users Do?
Install a Manifest V3-native ad blocker. ProBlocker is built from the ground up for MV3 and available on the Chrome Web Store. It blocks YouTube ads, trackers, and pop-ups without Acceptable Ads or data collection.
If you need the full capabilities of uBlock Origin (advanced cosmetic filters, dynamic rules, element picker), Firefox is the browser where those capabilities remain available.
Full Manifest V3 reference page → · Best uBlock Origin alternative for Chrome →