Quick answer

Manifest V3 (MV3) replaced Chrome's old blocking webRequest API with a new declarativeNetRequest API. This reduced the power of traditional ad/tracker blockers like uBlock Origin while giving Google more control. Most privacy extensions adapted; some (notably full uBlock Origin) cannot run in full form on MV3 Chrome. PrivacyGuard is Manifest V3 native.

The change

Under Manifest V2, extensions could use chrome.webRequest to inspect and block requests at runtime. This let filter-list engines evaluate complex rules on the fly. Under MV3, extensions must declare blocking rules up-front using declarativeNetRequest. The browser evaluates them natively.

Consequences: (a) rule-set size is capped (~30k dynamic + up to 330k static rules per extension on Chrome), (b) runtime decisions are harder, (c) event-driven background service workers replace long-lived background pages.

The controversy

The EFF and many privacy advocates argued MV3 as proposed would cripple tracker-blockers while leaving Google's own ad business unaffected. After two years of pushback Google made concessions: the rule-set limit was raised from 5k to 330k static rules per extension, and dynamic rules now allow more expressive matching.

What extensions did about it

uBlock Origin Lite — a stripped-down MV3-compatible version that uses static rule sets.
Privacy Badger — MV3-compatible after a rewrite in 2024.
PrivacyGuard — born MV3, uses declarativeNetRequest with custom rule-set generation.
Ghostery — MV3-compatible.

What you should do

In 2026 Chrome enforces MV3 for all extensions. If you have an MV2-only extension installed, it will be disabled. Switch to an MV3-native alternative — PrivacyGuard is our recommendation.

Firefox is different

Firefox's MV3 implementation kept both the declarative and blocking webRequest APIs. Full-power uBlock Origin still works on Firefox. If you need the most powerful blocking, Firefox remains the best browser.

Chrome Manifest V3: What It Means for Privacy Extensions in 2026