Agent Skills: browser-extension-developer

Browser Extension Developer (/ext) — Chrome/Edge Manifest V3 and Firefox WebExtensions: the service-worker lifecycle and what may not live in it, choosing between popup / options / side panel / extension page / in-page overlay / tab group, chrome.scripting injection and getting a value back out of it, tabs & tab groups, the permissions model (activeTab vs optional host permissions) and its revocation rules, long-running work that survives the popup closing, content-script security and CSP, and building/testing an extension without a browser in the loop. Use when building, reviewing, debugging or store-shipping any browser extension, or when a task involves a manifest.json with manifest_version. NOT for ordinary web-app UI (that's /fe) and NOT for browser automation with Playwright/Puppeteer (that's /e2e).