Google Chrome’s long-running Manifest V2 phaseout is reaching another cleanup stage, with Chromium removing one more legacy flag tied to the old extension system.
The change landed in Chromium, the open-source browser codebase behind Google Chrome. It removes the kAllowLegacyMV2Extensions feature flag, previously used for testing unpacked Manifest V2 extensions on older Chrome builds. According to the commit message, no supported Chrome version supports Manifest V2 anymore, so the leftover flag is being removed from the codebase.
To be clear, this is not a new attack on one specific extension. It is part of the wider removal of Manifest V2, the older Chrome extension platform. For most users, the most visible consequence is the classic version of the uBlock Origin extension, which depended on Manifest V2’s more powerful request-blocking capabilities.
Manifest V2 allowed extensions to use blocking WebRequest functionality, letting tools such as uBlock Origin intercept and block network requests before they loaded. Google has replaced that model with Manifest V3, a newer extension framework that changes how content blockers work and limits parts of the old blocking approach.
That is why uBlock Origin Lite exists. It is the Manifest V3-compatible version of the popular ad blocker, but it is not a direct equivalent of the classic uBlock Origin. This original extension remains strongly associated with Manifest V2 because its full filtering model depends on capabilities Chrome is removing.
A related WebExtensions discussion points to Chrome 149 as the last version with full support for Manifest V2 and blocking WebRequest in regular extension installs. Chrome 150 and 151 remove remaining switches and workarounds, further closing the door on old-style extensions in Google’s browser.
Of course, this change affects more than uBlock Origin. Any extension still depending on Manifest V2-only APIs may be affected, including older ad blockers, privacy tools, request-control extensions, and internal legacy extensions never migrated to Manifest V3. Still, uBlock Origin remains the clearest example for ordinary users.
At the same time, the situation is a bit different outside Google Chrome. Firefox continues to support the classic uBlock Origin, and some Chromium-based browsers may choose different policies around Manifest V2 or blocking WebRequest support. In regular Google Chrome, however, the direction is clear: Manifest V2 is over, and Chromium is removing what remains of its legacy support code.
