Firefox DevTools MCP

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/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 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)
• --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)
• --enable-script — enable the evaluate_script tool, which executes arbitrary JavaScript in the page context (ENABLE_SCRIPT=true)
• --enable-privileged-context — enable privileged context tools: list/select privileged contexts, evaluate privileged scripts, get/set Firefox p

... View full README on GitHub