Ahmed Shaami
Mozilla has confirmed that Firefox will continue supporting uBlock Origin, leaving it as the last major browser to do so after Google Chrome and Microsoft Edge completed their migration to the Manifest V3 extension platform. The change removes the browser API that uBlock Origin relies on to inspect and block network requests in real time, which is why the extension stops working properly on Chromium based browsers. Firefox runs on Mozilla’s own Gecko engine and still ships the webRequestBlocking API that makes the extension function.
What actually changed
Manifest V3 is Google’s rewrite of the rules that browser extensions must follow. The most consequential piece for ad blockers is the removal of blocking webRequest, the API that let an extension see a network request before it completed and decide whether to allow it. Manifest V3 replaces that with declarativeNetRequest, where the extension hands the browser a list of rules in advance and the browser does the filtering.
For most extensions this is a minor change. For content blockers it is not, because the rule based model caps how many filters can be active and removes the ability to make decisions dynamically. As PCWorld reported, that is the practical reason uBlock Origin cannot simply be ported across without losing capability.
Microsoft Edge is built on Chromium, so it inherits Google’s extension platform decisions. Once Edge finishes the transition, users there lose the full featured version of the extension too. Neowin covered Mozilla’s latest statement reaffirming Firefox’s position.
Brave is the partial exception
Brave also runs on Chromium, but the company said it will keep supporting Manifest V2 extensions by hosting them itself rather than relying on the Chrome Web Store. So “last major browser” is accurate in the sense that Firefox is the only large, independent engine still shipping the API natively, while Brave is maintaining compatibility through its own distribution. Users who want the full extension have both options for now.
Why this matters beyond ad blocking
The obvious framing is ads, but the wider point is about who controls what an extension is allowed to see. When one engine powers most browsers, a platform decision made in one place propagates to almost every user on the web. Chromium’s dominance means the extension ecosystem effectively has a single gatekeeper, and Firefox’s continued independence is one of the few practical checks on that.
There is also a security angle. Many privacy and anti tracking tools use the same APIs as content blockers. Tightening what extensions can inspect narrows the surface for badly behaved extensions, which is Google’s stated rationale, but it also narrows what defensive tools can do. Both things are true at once.
What to do if you rely on it
If uBlock Origin is part of how you work, the practical options are straightforward. Move to Firefox, move to Brave, or accept the reduced capability version of the extension on Chromium. Web developers and marketers should also note the second order effect: as blocking behaviour shifts between browsers, analytics and ad measurement will drift, and any year over year comparison that spans this transition is worth treating with some caution.
For anyone who builds websites for a living, this is a good moment to check how your pages behave with and without a content blocker active. If your site depends on scripts that a blocker removes, you may already be losing more visitors than your dashboards show.
