Browser rules reshape adtech

A browser extension is a tiny app that rides inside your browser, and Google changed the plumbing those apps use in Chrome. By July 24, 2025, Chrome 138 had disabled all old Manifest Version 2 extensions for all users, which meant some long-running tools simply stopped working unless they were rebuilt. (developer.chrome.com) The old system let extensions watch web requests as they happened, like a security guard checking every package at the door. Google’s new system, called Declarative Net Request, makes extensions hand the browser a rulebook in advance, and Chrome says that improves privacy because the extension no longer sees each request’s contents. (developer.chrome.com) Google has argued for years that this shift is about security, performance, and privacy. Its migration docs say Manifest Version 3 removes remotely hosted code, replaces long-lived background pages with service workers, and pushes request handling into browser-managed rules instead of constant extension-side interception. (developer.chrome.com 1) (developer.chrome.com 2) That sounds abstract until you hit ad blocking. The original uBlock Origin can no longer run with full support on Chrome, and its own site now lists Chrome and Chromium as supporting only uBlock Origin Lite, while Firefox and Brave still get the full version. (ublockorigin.com) Mozilla took a different path. Mozilla said in November 2023 that Firefox would support both the new Declarative Net Request system and the older blocking Web Request approach, specifically so powerful privacy and ad-blocking extensions could keep working. (blog.mozilla.org) That difference turns browser policy into market power. If one browser allows deep filtering and another limits it to predeclared rules, the same extension can be strong in Firefox, trimmed down in Chrome, and effectively split into two products with two support burdens. (blog.mozilla.org) (developer.chrome.com) The same plumbing change hits more than ad blockers. Chrome’s Manifest Version 3 also replaced persistent background pages with extension service workers that shut down when idle, which means developers have to redesign timers, state, and long-running tasks around code that can disappear and restart. (developer.chrome.com 1) (developer.chrome.com 2) That is why a free extension getting “killed” is not just a niche creator story. If your product depends on intercepting pages, rewriting requests, measuring clicks, suppressing page elements, or running always-on background logic, a browser vendor can change your economics with one platform decision and one store deadline. (developer.chrome.com 1) (developer.chrome.com 2) Chrome’s scale makes that especially sharp. When the world’s biggest browser changes extension rules, developers do not just lose a feature; they can lose distribution in the Chrome Web Store, lose compatibility on Chromium-based browsers, and get pushed into lighter versions that do less. (blog.chromium.org) (developer.chrome.com) The lesson for ad technology, measurement, and browser-based utilities is plain: browser roadmaps now function like regulation. A product manager reading a Chrome developer blog post in May 2024 was really reading an advance notice that parts of their product might be gone by July 2025. (blog.chromium.org) (developer.chrome.com)