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Firefox

How to enable Firefox’s secret ad-blocker

Posted on April 24, 2026April 26, 2026 by Martin Brinkmann

For years, I asked myself why Mozilla did not add a good content blocker to Firefox. It would be a great fit. An organization that values privacy, an open source browser that blocks most tracking out of the box.

However, for Mozilla, integrating a content blocker would also mean torpedoing its main revenue stream coming from Google.

Mozilla never made the step and others, including Brave, led by Mozilla’s ex-CEO, stepped in to fill that gap.

This changed recently

Mozilla did integrate Brave’s Rust-based adblock engine into its Firefox browser. More precisely, it is part of Firefox 149 and Mozilla describes it as a prototype rich content blocking feature.

It is not yet available as an option in the user-facing interface, let alone as something similar to the Shield feature of Brave. Still, users who run Firefox 149 can enable the content blocker and make use of it right away for testing.

Here is how that works:

  1. Load about:config in the Firefox address bar.
  2. Search for privacy.trackingprotection.content.protection.enabled
  3. Set the value to True with a click on the toggle on its right.
  4. Search for privacy.trackingprotection.content.protection.test_list_urls.
  5. Paste https://easylist.to/easylist/easylist.txt|https://easylist.to/easylist/easyprivacy.txt as the value.
  6. Restart Firefox

This enables two EasyLists, but you can add any other list that uses the same format. Separate lists with the character |.

Clearly, this is done for testing purposes. Mozilla would very likely add controls to the preferences or another user facing interface to make this easier to configure and use.

For now, it is a work in progress implementation, but one that shows that Mozilla could finally integrate what many users of its browser have wanted (or did not know they wanted) for a long time.

Tags: firefox
Category: Security & Privacy

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5 thoughts on “How to enable Firefox’s secret ad-blocker”

  1. Herman Cost says:
    April 24, 2026 at 1:17 pm

    So I went ahead and set this up just for the heck of it. But given that a great advantage of Firefox is that I can still use UBlock Origin while running it with these (and other) lists enabled, I can’t really imagine why I need the additional ‘protections’. But kudos to Mozilla for at least testing it even if they currently have it as well hidden as possible.

    Reply
  2. Tony says:
    April 24, 2026 at 2:18 pm

    This is a fairly exciting change, if they can add UI features that allow individual blocking and unblocking of elements similar to uBo. That’s the one major downside to Brave’s blocking is that the UI does not allow for easy disabling/enabling of per-domain filtering.

    Reply
  3. Tom Hawack says:
    April 24, 2026 at 2:32 pm

    Even far from, closer to uBlock Origin Lite (Manifest V3) than to uBlock Origin (Manifest V2), but interesting. If the feature happens to be opt-in (likely given the “privacy.trackingprotection.content.protection.test_list_urls” pref needs to be filled unless Mozilla plans to pre-fill it with basic filters), not sure that many will use it: IMO if you’re ad/tracking aware you search for powerful tools, not ersatz, not mild solutions. Remember the AdBlock extension (the original, very first and only at its launch) when it decided to add a “tolerance” for certain ads? The crowd yelled, anyway the crowd of true privacy aware users).

    But, but, but how is Daddy Google going to take that given, as the article reminds it, “(…) for Mozilla, integrating a content blocker would also mean torpedoing its main revenue stream coming from Google.”?. Maybe not too bad given it accepts the ‘uBlock Origin Lite’ extension on its browser (which is really very far from ‘uBlock Origin’ capacities).

    Reply
  4. Amanda says:
    April 24, 2026 at 6:12 pm

    all they had to do was ask gorhill to join the team, he was RIGHT THERE, for years, doing the work he should have been paid mountains for.

    But no, theyd rather use something attached to a shady perpetual crypto and ad machine.

    Reply
  5. VioletMoon says:
    April 25, 2026 at 2:29 pm

    140.10.0esr (64-bit)–also available on this version.

    Mozilla and its financial woes! Could create a stripped down version for elite users who are willing to pay. Could charge for that 50GB of VPN traffic. Who knows–could block the use of ad-blockers–that’s original!

    Reply

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  • April 26, 2026 by Martin Brinkmann Amazon ends sideloading on new Fire TV sticks
  • April 24, 2026 by Martin Brinkmann How to enable Firefox's secret ad-blocker
  • April 23, 2026 by Martin Brinkmann Mozilla fixed 271 vulnerabilities in Firefox 150 thanks to AI
  • April 21, 2026 by Martin Brinkmann Brave Origin is a stripped-down version of the browser that you need to buy
  • April 21, 2026 by Martin Brinkmann Microsoft confirms yet another BitLocker Recovery Screen issue in Windows 11

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