Software
It's in Waterfox too, and there it does what you'd expect
Firefox 149 quietly shipped an interesting new feature buried in the code. As Mozilla bug #2013888 documents, the browser maker incorporated Brave's Rust-based adblock engine back in March - a detail surfaced in a blog post by Shivan Kaul Sahib, VP of Privacy and Security at Brave.
The important thing here is that although Firefox has picked up the core Rust code that Brave uses for its internal ad-blocker, that's not what Firefox is using it for. Right now, in fact, it's disabled by default, but as a post from the official Firefox Reddit account says:
The Firefox team is experimenting with ways to improve the built-in Enhanced Tracking Protection feature in Firefox. This is one of the libraries we're going to experiment with... Note: We are not bundling Brave's ad-blocking system, we're testing one of their open source Rust components to improve how Firefox processes tracker lists.
In other words, inclusion of the code is experimental, and it's not intended for blocking ads. That's presumably also why it didn't appear in the release notes for either the early March beta or the late March release.
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So, yes, there is code for an ad-blocker in the last two versions of Firefox, but it’s off by default, and there’s no user interface to enable it. (There are ways round this, and we'll return to that later.)
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That said, the code from Brave can do this – because as it happens, the privacy-enhanced Waterfox fork of Mozilla's browser is also experimenting with a built-in ad-blocker, and it's using the same code.
Waterfox recently celebrated its 15th birthday, and recent releases have an experimental built-in ad-blocker. At the time of writing, the latest version is 6.6.12, and that version's release notes mention the experimental ad-blocker, and link to the feature's feedback page which has more info. This says:
Waterfox recently integrated another popular add-on. The last major release, Waterfox 6.6.0 in August last year - rebased on the new Firefox 140 ESR - included a native vertical tab bar. As revealed in a 2024 blog post, this is based on an integrated version of the popular Tree Style Tab extension.
The new ad-blocker works similarly. If you enable it, on restart, Waterfox looks for other ad-blockers, such as Reg FOSS desk recommendation uBlock Origin, and offers to disable them. We tried this, and the uBO icon in the toolbar is replaced by a no-entry symbol, with a small number overlaid to show how many ads were blocked on the current page. (For instance, just two for Astronomy Picture of the Day, but 38 – and counting – for MSN.co.uk. And that's on top of network-level blocking from our Pi-hole.)
So, experimental or not, adblock-rs is in there and it does work. It is possible to enable the version embedded in the desktop version of Firefox. It's controlled by two settings in about:config. The problem is that enabling it is not as simple as installing an extension, because extensions are not allowed to change those advanced settings. There is an experimental add-on called adblock-rust Manager. The README there carefully walks you through the manual steps you need to perform to enable the engine and tell it what to block, and then the add-on can monitor it and tell you what it's doing.
We tried it, and it seems to do a perfectly acceptable job. For now, though, unless you're curious, we suggest staying with uBlock Origin, which works fine and isn't going anywhere. ®