uBlock Origin, one of the most widely used content-blocking extensions, no longer runs in its full form on Chrome and most Chromium-based browsers. A platform change to how extensions work is the reason, and Firefox is now the main exception.
Key takeaways
- uBlock Origin’s original design depends on browser extension capabilities that Chrome has phased out as part of its move to a new extension platform generation.
- Firefox continues to support the extension in its full form because Mozilla has kept the older, more permissive filtering interfaces available alongside newer ones.
- Most alternative browsers built on Chromium inherit Google’s extension platform decisions, so the change reaches far beyond Chrome itself.
- A reduced variant of the extension exists for the new platform, but it works differently and its maintainers describe it as less capable than the original.
- The dispute is less about advertising specifically than about how much power browsers should hand to third-party code that inspects and modifies web traffic.
What is actually happening?
Browser extensions run under a defined set of rules, published by each browser vendor, that determine what an add-on may see and do. Chrome’s rules have moved to a newer generation, commonly referred to by its manifest version number, which changes how extensions may intercept and alter network requests. Under the older approach, an extension could observe requests as the browser made them and decide, in its own code, whether to allow, block or rewrite each one. Under the newer approach, extensions largely supply declarative rule sets in advance, and the browser applies them.
uBlock Origin was built around the older model. Its filtering logic runs as the extension’s own code, which is what allows it to apply complex, conditional and cosmetic rules that depend on page context. When Chrome retired support for extensions built on the older platform, the original version of uBlock Origin stopped functioning there in its full form. Firefox, which maintains its own extension platform, has retained the older filtering interfaces even while adopting parts of the newer specification, so the extension continues to run as designed.
Why is this being discussed now?
Platform migrations of this kind do not happen on a single day. Vendors typically announce a deadline, extend it, restrict new submissions to the new format, then progressively disable older extensions for existing users. The result is a long tail of moments where individual users suddenly find a familiar add-on disabled or replaced, which repeatedly returns the subject to public attention.
The current round of attention appears to follow the point at which the practical situation became simple to state: for users who want the original extension rather than a reduced substitute, the mainstream choice has narrowed to Firefox. That framing travels well, and it is easy to verify by trying to install the extension in each browser. It also intersects with broader unease about consolidation in the browser market, since most non-Firefox browsers share the same underlying engine and extension platform.
The background a newcomer needs
Content blockers work by matching outgoing requests and page elements against long lists of rules maintained by volunteer communities. A blocker needs two things: the ability to see requests before they complete, and the ability to modify what a page looks like after it loads. Different blockers make different trade-offs, and some rely on the browser’s own built-in features rather than extension code.
The older extension interface gave add-ons broad visibility into browsing activity. That is powerful for blocking and equally powerful for surveillance if the extension is malicious or later sold to a new owner. Browser vendors have pointed to that risk, along with performance and predictability, as reasons to prefer declarative rules the browser itself evaluates. Critics respond that declarative rules constrain what sophisticated blockers can express, and that the vendor with the largest advertising business is also the one setting the constraints. Both arguments can be held at once: the security rationale is real, and so is the conflict of interest.
It is also worth being precise about scope. The new platform does not prohibit content blocking. Blockers exist and function under it. The contested question is whether they can do everything the older generation could, and in the view of uBlock Origin’s own documentation, the reduced variant cannot.
Who is affected, and how?
Ordinary users of Chromium-based browsers are affected most directly. Depending on the browser and its version, they may find the extension disabled, automatically replaced with the reduced variant, or simply unavailable to install. Many will notice only that more advertising appears, or that a site behaves differently than before. Users who rely on blocking for reasons beyond advertising — reducing data usage, limiting tracking, or making pages usable on older hardware — may notice the change more sharply.
Firefox users are, for now, unaffected in the sense that the extension continues to work. That does not make the position permanent; Mozilla has said it intends to support both approaches, but the older interfaces exist at its discretion.
Users of other Chromium-based browsers sit in a middle position. Some vendors have said they intend to keep supporting older extension capabilities in their own builds for a period, or to provide equivalent blocking through features built into the browser rather than through extensions. How long such divergence can be maintained, given that the underlying engine code comes from a shared upstream project, is genuinely uncertain, and the practical answer differs from vendor to vendor.
Filter list maintainers and extension developers face a different problem: writing and testing rules for two incompatible platforms, with different expressive limits, indefinitely.
Where informed people disagree
The clearest disagreement is over whether the platform change was motivated primarily by security or primarily by commercial interest. Neither position can be settled from the outside. The stated engineering reasons are coherent, and the commercial incentive is obvious; observers weigh them differently, often according to what they already believe about the company involved.
A second disagreement concerns how much capability is actually lost. Some argue the reduced variant covers the great majority of everyday blocking and that the difference matters mainly at the margins. Others argue the margins are exactly where an arms race is fought, and that a blocker unable to adapt quickly loses over time. Testing this rigorously is difficult, because results depend on which sites, which filter lists and which measurement method are used.
A third concerns strategy. Some hold that browser diversity is best defended by using a browser with an independent engine. Others consider that impractical for most people and argue for pressing vendors, regulators or standards bodies instead. There is no consensus on which approach is more effective.
What this means in practice
For a reader deciding what to do, the practical position is narrow and fairly clear. Anyone who specifically wants the original extension, with its full rule syntax and behaviour, currently needs a browser that still supports the older extension interfaces — in the mainstream, that means Firefox or a browser derived from it. Anyone content with a reduced blocker has options that continue to work on the new platform.
Two cautions apply. First, checking the current state directly is more reliable than trusting any summary, including this one: browser versions and vendor policies change, and the extension’s own project pages describe what is supported at any given moment. Second, extensions claiming to restore the original behaviour under names resembling well-known blockers have historically been a vector for abuse, so installing only from a browser’s official add-on listing, and checking the publisher, matters more than usual during a transition like this one.
What to watch next
Three things are worth following. The first is whether other Chromium-based vendors maintain their exceptions or eventually align with upstream, which will show whether meaningful divergence is sustainable on a shared engine. The second is whether the reduced variant’s limits are relaxed — vendors have adjusted quotas and capabilities in the new platform before, and further adjustment is possible in either direction.
The third is regulatory. Competition authorities in several jurisdictions have examined browser and platform gatekeeping. Whether extension platform rules are treated as a competition matter, rather than a purely technical one, is unresolved, and any movement there would change the terms of the discussion considerably. None of these outcomes can be predicted from the current situation.
Frequently asked questions
Does uBlock Origin still work in Chrome?
The original version of the extension does not run in its full form on current Chrome, because Chrome has retired support for the older extension platform it was built on. A reduced variant designed for the new platform is available and does block content, but its maintainers describe it as less capable than the original. The precise behaviour depends on your Chrome version, so checking the extension’s status in your own browser is the reliable test.
Why does the extension still work in Firefox?
Firefox uses its own extension platform. While Mozilla has adopted parts of the newer extension specification for compatibility, it has kept the older request-filtering interfaces available alongside the new declarative ones. That means extensions written against the older model, including uBlock Origin in its original form, continue to run. This reflects a decision by Mozilla rather than a technical necessity, and it is not guaranteed to hold indefinitely.
What is the difference between the full extension and the reduced variant?
The full version runs its own filtering code, deciding request by request what to block and how to modify pages. The reduced variant supplies rules to the browser in advance and lets the browser apply them, which limits how conditional or context-dependent those rules can be. In everyday browsing the difference may not be obvious; it tends to appear with complex sites and with rules that need to respond quickly to changes.
Are other browsers affected as well?
Most alternative browsers are built on Chromium and inherit its extension platform, so they are affected by the same change. Some vendors have said they will keep supporting older extension capabilities in their builds for a period, or provide blocking through browser features instead of extensions. How long such differences can be sustained on a shared engine is uncertain, and the situation varies by vendor and version.
Was this change made to protect advertising revenue?
That cannot be established from the outside. The stated reasons are security, performance and predictability, and those concerns are real: the older interface gives extensions broad visibility into browsing activity, which is dangerous if an extension is malicious. It is also true that the company setting the rules operates a large advertising business. Both facts are verifiable; the motivation behind the decision is not, and informed observers weigh them differently.
Should I switch browsers because of this?
That depends on what you need. If you specifically want the original extension and its full rule syntax, a browser that supports the older extension interfaces is currently required. If a reduced blocker meets your needs, switching may not be necessary. Either way, install extensions only from official browser add-on listings, since transitions like this one attract imitations that use familiar names to gain broad permissions.
Sources and further reading
- The extension project’s own public documentation and issue tracker, which state what is and is not supported on each platform.
- Chrome’s published developer documentation on extension platform versions and the migration to declarative request rules.
- Mozilla’s developer documentation on its extension platform and its stated position on supporting both filtering approaches.
- Technology news outlets and community discussion forums, which record vendor announcements and deadline changes over time.
Surfaced from the hackernews signal “browser extension platform change”. AI-assisted draft, editorially reviewed.
