Firefox is quietly experimenting with Brave’s ad-blocking engine

Mozilla has quietly begun experimenting with Brave’s Rust-based ad-blocking engine in Firefox, signaling a potential shift in how the browser handles ads and trackers.

The change was first spotted in Firefox 149 under Bugzilla entry 2013888, where Mozilla engineers introduced adblock-rust, an open-source ad-blocking engine developed by Brave Software. The finding was highlighted by Brave’s VP of Privacy and Security, Shivan Kaul, who noted that the implementation is still in an early testing phase, with no user interface, no default filter lists, and no public announcement from Mozilla.

The adblock-rust engine itself is a high-performance, Rust-based filtering system used in Brave Browser to enforce network-level blocking of ads and trackers. Waterfox also recently announced plans to integrate the engine as part of a broader shift toward built-in ad blocking, while Perplexity’s Comet browser has adopted it as well.

According to the details Kaul shared, the feature is disabled by default in Firefox and can only be enabled in the browser’s advanced configuration panel (about:config). Even after enabling it, users must manually supply filter lists such as EasyList and EasyPrivacy to achieve basic blocking functionality. The integration also exposes multiple internal preferences tied to “protection” and “annotation” modes, indicating Mozilla is experimenting with both active blocking and passive tracking classification for telemetry or UI purposes.

While Firefox already includes built-in tracking protection, it has historically lagged behind privacy-focused browsers like Brave in areas such as aggressive ad blocking and query parameter stripping. This experiment suggests Mozilla may be reevaluating its approach as competition in the privacy browser space intensifies.

Early experiment – not a feature rollout

Despite the excitement, this development does not mean Firefox users can suddenly enable Brave-like ad blocking.

What Mozilla has shipped is best understood as backend groundwork rather than a finished feature. The engine is present in the codebase, but it lacks the surrounding infrastructure needed to make it usable in a production browser.

Even when manually enabled, the current implementation provides only partial functionality. Users can achieve basic network-level blocking by supplying filter lists, but several key components are missing:

• No built-in user interface or controls
• No automatic filter list management or updates
• Unclear or incomplete support for cosmetic filtering (hiding page elements)
• No advanced protections, such as fingerprinting defenses or query parameter stripping
• Limited integration with the broader browser privacy system

Brave’s ad blocking is deeply integrated, enabled by default, and continuously maintained as part of a cohesive privacy model. In contrast, Firefox is currently testing the underlying engine in isolation, without the policy layer and user-facing features that define a full ad-blocking experience.

It remains unclear whether Mozilla plans to expand this experiment into a fully supported feature.

We contacted Mozilla to learn more about its plans for adblock-rust and whether a broader rollout is under consideration, but we have not received a response at the time of publication.