Mozilla slipped Brave’s adblock-rust engine into Firefox 149 last month. No fanfare. No release notes mention. Just code, vendored via the browser’s Rust tooling and wired into the network stack. It’s FOSS spotted it first, thanks to a post from Shivan Kaul Sahib, Brave’s VP of Privacy and Security. The engine powers Brave Shields. Rust-built. MPL-2.0 licensed. It chews through network requests, applies cosmetic filters, handles scriptlet injections—even supports uBlock Origin’s syntax extensions. In Firefox, Mozilla engineer Benjamin VanderSloot landed it through Bugzilla 2013888 , titled “Add a prototype rich content blocking engine.” He vendored the crate, audited dependencies like flatbuffers and seahash, then integrated it via a ContentClassifierService with C++ wrappers hooked to AsyncUrlChannelClassifier. Disabled by default. No UI toggle. No bundled lists. Users hunt prefs in about:config. Flip privacy.trackingprotection.content.protection.enabled to true.…