Plasmo

Plasmo is an open-source framework for building browser extensions, often described as "Next.js for browser extensions." It generates manifest.json from your file structure, gives React and TypeScript first-class support with hot module replacement, and ships built-in APIs for storage and for messaging between the popup, background worker, and content scripts. Running pnpm create plasmo gives a working extension in minutes, without the manual manifest and bundler setup extensions normally need.

Its Content Scripts UI injects React components into web pages with automatic Shadow DOM isolation, so extension styles do not clash with the host page. One codebase builds for Chrome (Manifest V3), Firefox, and Edge, and Vue and Svelte are supported with less polish than React.

Around the framework, the company behind it offers Itero: TestBed distributes beta builds to testers outside store review, and Browser Platform Publisher (also available as a free GitHub Action) automates submission to the Chrome Web Store, Firefox Add-ons, and Edge Add-ons.

The concern is maintenance. The last tagged release dates from May 2025, and the framework depends on the Parcel bundler, which creates friction with newer tooling such as Tailwind CSS v4. WXT, a Vite-based alternative, is the common choice for new projects, while Plasmo remains workable for existing React extensions that already use it. The framework is free under the MIT licence.