Chrome finishes off Manifest V2

Chrome has begun disabling remaining Manifest V2 extensions on the stable channel. Users are seeing them turned off with a notice suggesting alternatives. Enterprise policy can delay this, but only for a while.

This has been announced, delayed, re-announced and re-delayed since 2019. It is now happening.

the technical core of the fight#

MV2 gave extensions the webRequest API with blocking behavior: an extension could intercept a network request, run arbitrary JavaScript, and decide what to do. That is enormously powerful and enormously flexible.

MV3 replaces it with declarativeNetRequest: the extension registers rules ahead of time, and the browser evaluates them. The extension never sees the request.

Google's argument is performance, privacy and security: an extension that cannot see your requests cannot exfiltrate them, and rules evaluated in browser code are faster than a round trip into an extension's JavaScript context. All of that is genuinely true.

The counter-argument is capability. Content blocking that requires dynamic decisions — matching on response bodies, generating rules from observed traffic, handling sites that actively rotate their ad-serving domains — is harder or impossible under a declarative model. The rule count limits, though raised several times under pressure, are still limits.

where it actually lands#

uBlock Origin's MV3 version, uBlock Origin Lite, works well for most users and is meaningfully less capable in the tail. Its author has been consistent and unusually clear-eyed about this: Lite is not Origin, it is a different product with a different capability envelope, and calling it a drop-in replacement would be dishonest.

For most people the difference will be invisible. For the people who notice, the difference is the whole point.

the part that is actually about power#

It is possible to believe all of the following simultaneously:

• MV3's security model is a real improvement.
• The declarative approach is the right architecture for most extensions.
• A company whose revenue is advertising should not be the sole arbiter of what ad-blocking extensions can do in the browser used by most of the world.

The third one is not a technical claim and cannot be resolved with a benchmark. It is a structural conflict of interest, and it will keep producing this exact argument every time Chrome makes a platform decision, regardless of the merits of that specific decision.

what to do#

Firefox supports MV3 but kept blocking webRequest, which means full-featured content blockers still work there. Safari has its own model. If content blocking is load-bearing for you, that is now a browser choice, not an extension choice.

For extension developers: the migration is done, stop hedging, port it. The compatibility shims are worse than a real rewrite and you will maintain them forever.

For everyone else: this is a useful reminder that "the web platform" is a set of decisions made by a handful of engineering organizations, and the parts you rely on are only as durable as their continued interest in supporting them.