freema/firefox-devtools-mcp

Model Context Protocol server that lets AI agents use Firefox. It has two main use cases:
- **Agentic browsing**: the agent uses the browser for regular tasks, such as reading pages, filling forms and going through multi-step flows on websites.
- **Agent-assisted web development**: the agent loads the page you are working on and inspects it with developer tools, such as the console, network requests, the debugger and the profiler.
It controls Firefox through WebDriver BiDi (via Selenium WebDriver) and works with Claude Code, Claude Desktop, Cursor, Cline and other MCP clients.
Repository: https://github.com/mozilla/firefox-devtools-mcp
> **Note**: This MCP server requires a local Firefox browser installation and cannot run on cloud hosting services like glama.ai. Use npx @mozilla/firefox-devtools-mcp@latest to run locally, or use Docker with the provided Dockerfile.
Security
Browser MCP servers carry inherent risks. A few key practices:
- **Use a dedicated Firefox profile.** Never run the server against your regular profile — the agent has access to whatever the browser can reach, including cookies and saved sessions.
- **Be cautious about which sites you visit.** Pages can return content designed to manipulate the agent (prompt injection). Stick to sites you control or trust.
- **Enable only the tool modules you need.** The default basic preset already includes evaluate_script; --tool-preset slim drops it. Higher presets such as --tool-preset developer (debugging, network, console, profiler) and --tool-preset mozilla (privileged context) expand what the agent can do further.
See SECURITY.md for a full breakdown of risks and how to report vulnerabilities.
Requirements
- Node.js ≥ 20.19.0
- Firefox 100+ installed (auto‑detected, or pass --firefox-path)
Install and use with Claude Code or Codex (npx)
Recommended: use npx so you run the latest published version from npm.
Option A — CLI
Claude Code
Codex
Option B — Edit the configuration file
Claude Code
Add to Claude Code’s mcp_settings.json:
Codex
Add to ~/.codex/config.toml:
Option C — Helper script (local dev build)
Try it with MCP Inspector
Then call tools like:
- list_pages, select_page, navigate_page
- take_snapshot then click_by_uid / fill_by_uid
- list_network_requests (always‑on capture), get_network_request
- list_downloads (always‑on capture), set_download_behavior
- screenshot_page, list_console_messages
CLI options
You can pass flags or environment variables (names on the right):
- --firefox-path — absolute path to Firefox binary
- --headless — run without UI (FIREFOX_HEADLESS=true)
- --viewport 1280x720 — initial window size
- --profile-path — use a specific Firefox profile. Firefox runs in a firefox_devtools_mcp_profile subfolder of that path, marked with a .firefox-devtools-mcp file; pointing --profile-path at a marked profile reuses it directly
- --firefox-arg — extra Firefox arguments (repeatable)
- --start-url — open this URL on start (START_URL)
- --accept-insecure-certs — ignore TLS errors (ACCEPT_INSECURE_CERTS=true)
- --connect-existing — attach to an already-running Firefox instead of launching a new one (CONNECT_EXISTING=true)
- --marionette-port — Marionette port for connect-existing mode, default 2828 (MARIONETTE_PORT)
- --pref name=value — set Firefox preference at startup via moz:firefoxOptions (repeatable)
- --tool-preset — select which tool modules to enable: slim, basic (default), developer, mozilla, or all. See Tool modules and presets. (TOOL_PRESET)
- --tools — explicit list of tool modules to enable, overriding --tool-preset entirely (e.g. --tools pages network script). See Tool modules and presets.
- --enable-script — _deprecated, use --tool-preset developer or --tools ... script debugging._ Selects the developer tool preset. (ENABLE_SCRIPT=true)
- --enable-privileged-context — _deprecated, use --tool-preset mozilla or --tools ... privileged prefs._ Selects the mozilla tool preset. Requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1 (ENABLE_PRIVILEGED_CONTEXT=true)