What is Extension.js for browser extension development?

Extension.js is an open-source CLI that provides zero-config TypeScript, React, and HMR for building Chrome, Firefox, Edge, and Safari extensions from a single codebase.

Why is browser extension development tooling so painful?

Developers must maintain separate manifest.json versions per browser, set up Webpack/esbuild manually, and have no HMR — Extension.js tries to solve all three.

What is Plasmo Framework for browser extensions?

Plasmo is the main alternative to Extension.js — a React-first extension framework, but it has a proprietary deployment layer and is less community-friendly than the MIT Extension.js.

How do you build a cross-browser extension without webpack config?

Extension.js handles manifest normalization and build output automatically. Run 'npx extension dev' to start with Chrome, Firefox, Edge support out of the box.

What framework do developers use to build Chrome extensions in 2025?

Popular options include Extension.js (zero-config), Plasmo (React-first), and WXT (TypeScript-first, HN favorite). Demand for standards-based tooling is high.

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Extension.js: Developers Want a Zero-Config CLI for Building Cross-Browser Extensions

Extension.js is an open-source CLI tool for building browser extensions with no build configuration — it handles Chrome, Firefox, Edge, and Safari in one command. HN 'Show HN' hit 381 points and 25 comments in May 2024. The problem it solves: browser extension development tooling is fragmented and painful, with Webpack/esbuild/Parcel configs, separate manifests, and no HMR. High developer demand signal for standardized extension dev tooling.

Product Idea from this Signal

A browser extension that blocks ads in Chrome under Manifest V3 using network-layer interception outside the browser's declarativeNetRequest limits

2.1k ▲

Google's Manifest V3 transition disabled uBlock Origin for around 40 million Chrome users by imposing hard rule limits on the declarativeNetRequest API that make full dynamic filtering impossible. The stranded users cannot get full ad blocking inside Chrome today. The opportunity is a browser extension that moves the filtering logic to a local proxy or native companion app running outside the browser sandbox, so Chrome rule limits are irrelevant -- the extension itself just routes traffic through a localhost interceptor that does the heavy filtering.

ad-blockingmanifest-v3chrome-extensionprivacybrowserdeveloper-toolscross-browser

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