Comment by inkyoto

Firefox has also adopted and supports Manifest v3, but Mozilla did not adopt all of Chrome/Chromium’s Manifest v3 restrictions.

In Chrome/Chromium, Manifest v3 largely replaces extension-controlled network blocking with a more restrictive «declarativeNetRequest», whereas Firefox, by contrast, has deliberately kept support for blocking «webRequest» functionality.

Importantly, the full uBlock Origin is a Manifest V2 extension. The Manifest v3-compatible version is uBlock Origin Lite, which has fewer capabilities.