# mozilla/webextension-polyfill

A lightweight polyfill library for Promise-based WebExtension APIs in Chrome

Repository: https://github.com/mozilla/webextension-polyfill
Canonical: https://ross.abutalabs.com/products/webextension-polyfill
Language: JavaScript
License: MPL-2.0
License Family: copyleft
Archived: true
Last push: 2026-07-30T12:16:33+00:00

## Health v2 (maintenance only)
Score: 10/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 95, release rhythm 8, longevity 100
- inputs: {"age_days": 3618, "days_push": 34, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: archived
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 3069, forks 238 (observed 2026-08-28T04:07:41.510103+00:00)

## What it is
A lightweight polyfill that lets browser extensions use the Promise-based `browser` API namespace in Chrome, matching Firefox's WebExtension API style. It is now a no-op on browsers with native support and the project has been retired since Chrome adopted the `browser` namespace.

## Use cases
- write chrome extensions using promise-based browser APIs
- make a webextension codebase work across chrome and firefox
- avoid callback-style chrome.* APIs in extension code
- use the same extension API namespace in chrome, edge, and opera
- write cross-browser extensions with typescript support

## When to choose
- maintaining an older extension that still targets Chrome versions before 148
- supporting legacy Chrome-based browsers (Edge <79, old Opera) that lack the browser namespace

## When to avoid
- starting a new extension targeting modern Chrome (148+) or Firefox, which support the browser namespace natively
- needing a maintained library - the project explicitly will not receive further updates
- building extensions only for Firefox or Safari, where the polyfill is a no-op

## Facets
- artifact type: library
- maturity: abandoned
- function: sdk, developer-tools
- domain: browser-extensions, web-development, developer-tools
- platform: browser, browser-extension
- tags: webextension, polyfill, promise-based-api, browser-api, chrome-extension, cross-browser, javascript

## Member repositories
- mozilla/webextension-polyfill (main) score 10

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:07:41.510103+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-29T18:46:37.999412+00:00, confidence not recorded.
  - readme: https://github.com/mozilla/webextension-polyfill (fetched 2026-08-28T04:07:41.510103+00:00, sha 8696e6b95f45)
  - registry_npm: https://registry.npmjs.org/webextension-polyfill (fetched 2026-08-29T09:43:35.392931+00:00, sha ac53393dd74e)
- Data as of 2026-08-30T08:39:29.467469+00:00.