Firefox DevTools MCP

Note: this is a (temporary) fork containing some feature on top of upstream, aimed at making the life of Firefox developers easier. The goal is to upstream what makes sense once we get a sense of the value of our features for the general public (vs. firefox development).

Model Context Protocol server for automating Firefox via WebDriver BiDi (through Selenium WebDriver). Works with Claude Code, Claude Desktop, Cursor, Cline and other MCP clients.

Repository: https://github.com/freema/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 firefox-devtools-mcp@latest to run locally, or use Docker with the provided Dockerfile.

Requirements

• Node.js ≥ 20.19.0
• Firefox 100+ installed (auto‑detected, or pass --firefox-path)

Install and use with Claude Code (npx)

Recommended: use npx so you always run the latest published version from npm.

Option A — Claude Code CLI

claude mcp add firefox-devtools npx firefox-devtools-mcp@latest

Pass options either as args or env vars. Examples:

# Headless + viewport via args
claude mcp add firefox-devtools npx firefox-devtools-mcp@latest -- --headless --viewport 1280x720

# Or via environment variables
claude mcp add firefox-devtools npx firefox-devtools-mcp@latest \
  --env START_URL=https://example.com \
  --env FIREFOX_HEADLESS=true

Option B — Edit Claude Code settings JSON

Add to your Claude Code config file:

• macOS: ~/Library/Application Support/Claude/Code/mcp_settings.json
• Linux: ~/.config/claude/code/mcp_settings.json
• Windows: %APPDATA%\Claude\Code\mcp_settings.json

{
  "mcpServers": {
    "firefox-devtools": {
      "command": "npx",
      "args": ["-y", "firefox-devtools-mcp@latest", "--headless", "--viewport", "1280x720"],
      "env": {
        "START_URL": "about:home"
      }
    }
  }
}

Option C — Helper script (local dev build)

npm run setup
# Choose Claude Code; the script saves JSON to the right path

Try it with MCP Inspector

npx @modelcontextprotocol/inspector npx firefox-devtools-mcp@latest --start-url https://example.com --headless

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
• 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-arg — extra Firefox arguments (repeatable)
• --start-url — open this URL on start (START_URL)
• --accept-insecure-certs — ignore TLS errors (ACCEPT_INSECURE_CERTS=true)
• --pref name=value — set Firefox preference at startup (repeatable, requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1)

Note on --pref: When Firefox runs in WebDriver BiDi mode, it applies RecommendedPreferences that modify browser behavior for testing. The --pref option allows overriding these defaults when needed (e.g., for Firefox development, debugging, or testing scenarios that require production-like behavior).

Example: --pref "browser.ml.enable=true" enables Firefox's ML/AI features. This is essential when using this MCP server to develop or test AI-powered features like Smart Window, since RecommendedPreferences disables it by default.

Tool overview

• Pages: list/new/navigate/select/close
• Snapshot/UID: take/resolve/clear
• Input: click/hover/fill/drag/upload/form fill
• Network: list/get (ID‑first, filters, always‑on capture)
• Console: list/clear
• Screenshot: page/by uid
• Script: evaluate_script (content), evaluate_chrome_script (privileged)
• Chrome Context: list/select chrome contexts (requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1)
• Firefox Management: get_firefox_info, get_firefox_output, restart_firefox, set_firefox_prefs, get_firefox_prefs
• Utilities: accept/dismiss dialog, history back/forward, set viewport

Local development

npm install
npm run build

# Run with Inspector against local build
npx @modelcontextprotocol/inspector node dist/index.js --headless --viewport 1280x720

# Or run in dev with hot reload
npm run inspector:dev

Troubleshooting

• Firefox not found: pass --firefox-path "/Applications/Firefox.app/Contents/MacOS/firefox" (macOS) or the correct path on your OS.
• First run is slow: Selenium sets up the BiDi session; subsequent runs are faster.
• Stale UIDs after navigation: take a fresh snapshot (take_snapshot) before using UID tools.

Versioning

• Pre‑1.0 API: versions start at 0.x. Use @latest with npx for the newest release.

CI and Release

• GitHub Actions for CI, Release, and npm publish are included. See docs/ci-and-release.md for details and required secrets.

Author

Created by Tomáš Grasl