Cross-Browser Extension Development

This skill covers the full lifecycle of a browser extension built on the extension.dev platform (powered by the open-source Extension.js framework): scaffold from a template, develop with hot reload, verify against a live browser, build per browser, and publish.

Two companions do the heavy lifting. Prefer them over guessing:

• @extension.dev/mcp (MCP server): 28+ tools for scaffolding, building, live DOM inspection, log streaming, storage access, publishing, and headless release promotion. If its extension_* tools are available in the session, use them.
• extension CLI: nearly every MCP capability has a CLI equivalent (npx extension@latest <command>). Use it when the MCP server is not connected. The exceptions are extension_release_promote (also reachable as extension-mcp release promote, but not via the extension CLI) and the session tools extension_stop/extension_list_extensions.