--- slug: "firefox-devtools-mcp" source_type: "readme" source_url: "https://cdn.jsdelivr.net/gh/mozilla/firefox-devtools-mcp@main/README.md" repo: "https://github.com/mozilla/firefox-devtools-mcp" source_file: "README.md" branch: "main" --- # Firefox DevTools MCP [![npm version](https://badge.fury.io/js/@mozilla%2Ffirefox-devtools-mcp.svg)](https://www.npmjs.com/package/mozilla/firefox-devtools-mcp) [![CI](https://github.com/mozilla/firefox-devtools-mcp/workflows/CI/badge.svg)](https://github.com/mozilla/firefox-devtools-mcp/actions/workflows/ci.yml) [![codecov](https://codecov.io/gh/mozilla/firefox-devtools-mcp/branch/main/graph/badge.svg)](https://codecov.io/gh/mozilla/firefox-devtools-mcp) [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](LICENSE-MIT) [![License: Apache 2.0](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](LICENSE-APACHE) Glama 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 @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. - **Avoid enabling extra flags unless needed.** `--enable-script` and `--enable-privileged-context` significantly expand what the agent can do. See [SECURITY.md](https://github.com/mozilla/firefox-devtools-mcp/blob/HEAD/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 (npx) Recommended: use npx so you always run the latest published version from npm. Option A — Claude Code CLI ```bash claude mcp add firefox-devtools npx @mozilla/firefox-devtools-mcp@latest ``` Pass options either as args or env vars. Examples: ```bash # Headless + viewport via args claude mcp add firefox-devtools npx @mozilla/firefox-devtools-mcp@latest -- --headless --viewport 1280x720 # Or via environment variables claude mcp add firefox-devtools npx @mozilla/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` ```json { "mcpServers": { "firefox-devtools": { "command": "npx", "args": ["-y", "@mozilla/firefox-devtools-mcp@latest", "--headless", "--viewport", "1280x720"], "env": { "START_URL": "about:blank" } } } } ``` Option C — Helper script (local dev build) ```bash npm run setup # Choose Claude Code; the script saves JSON to the right path ``` ## Try it with MCP Inspector ```bash npx @modelcontextprotocol/inspector npx @mozilla/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 (executes arbitrary JavaScript in the page context) and debugging tools (list scripts, inspect source, set logpoints). Debugging tools require Firefox 153+. (`ENABLE_SCRIPT=true`) - `--enable-privileged-context` — enable privileged context tools: list/select privileged contexts, evaluate privileged scripts, get/set Firefox prefs, and list extensions. Requires `MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1` (`ENABLE_PRIVILEGED_CONTEXT=true`) - `--android-device` — enable Firefox for Android mode; value is the ADB device serial (e.g. `emulator-5554`). Run `adb devices` to list connected devices. Omit the value or use `auto` to select the single connected device automatically. - `--android-package` — Android app package name, default `org.mozilla.firefox`. Other packages: `org.mozilla.firefox_beta` for Firefox Beta, `org.mozilla.fenix` for Firefox Nightly, `org.mozilla.fenix.debug` for Firefox Nightly Debug, `org.mozilla.geckoview_example` for geckoview (`ANDROID_PACKAGE`) - `--log-file` — write MCP server logs to a file instead of stderr. Useful for debugging sessions with MCP clients that hide server output. Set `DEBUG=*` to also include verbose debug logs. Example: `--log-file /tmp/firefox-mcp.log` ### Useful preferences (`--pref`) - remote.prefs.recommended=false. When Firefox runs in automation, it applies [RecommendedPreferences](https://searchfox.org/firefox-main/source/remote/shared/RecommendedPreferences.sys.mjs) that modify browser behavior for testing. Set remote.prefs.recommended to false to skip those and have a configuration closer to a regular Firefox instance. - remote.log.level=Trace. Enable verbose WebDriver protocol logs in Firefox. The MCP server will automatically pass the matching log level to geckodriver so both sides log at the same verbosity. - app.update.disabledForTesting=false. Allow Firefox to automatically download and apply updates. Note that updates may interrupt your session. Requires also setting remote.prefs.recommended=false. ### Firefox for Android Use `--android-device` to automate Firefox running on an Android device. Requires `adb` on your PATH and geckodriver, which is managed automatically. ```bash # List connected devices adb devices # Launch Firefox for Android on the single connected device npx @mozilla/firefox-devtools-mcp --android-device auto # Target a specific device npx @mozilla/firefox-devtools-mcp --android-device # Use Firefox Nightly instead npx @mozilla/firefox-devtools-mcp --android-device --android-package org.mozilla.fenix ``` Port forwarding between the host and device is handled automatically by geckodriver. ### Connect to existing Firefox Use `--connect-existing` to automate your real browsing session, with cookies, logins, and open tabs intact: ```bash # Start Firefox with Marionette and the Remote Agent (BiDi) firefox --marionette --remote-debugging-port # Run the MCP server npx @mozilla/firefox-devtools-mcp --connect-existing --marionette-port 2828 ``` Both flags are required because the MCP uses both WebDriver Classic (`--marionette`) and WebDriver BiDi (`--remote-debugging-port`). If Firefox is only started with `--marionette`, the MCP server fails to connect and asks you to restart Firefox with both flags. > **Warning:** Do not leave Marionette enabled during normal browsing. It sets > `navigator.webdriver = true` and changes other browser fingerprint signals, > which can trigger bot detection on sites protected by Cloudflare, Akamai, etc. > Only enable Marionette when you need MCP automation, then restart Firefox > normally afterward. ## 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 (with optional `saveTo` for CLI environments) - Script: evaluate_script - Privileged Context: list/select privileged ("chrome") contexts, evaluate_privileged_script (requires `MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1`) - WebExtension: install_extension, uninstall_extension, list_extensions (list requires `MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1`) - Firefox Management: get_firefox_info, get_firefox_output, restart_firefox, set_firefox_prefs, get_firefox_prefs - Profiler: profiler_is_active, profiler_start (preset or explicit config), profiler_stop (saves profile to downloads directory) - Utilities: accept/dismiss dialog, history back/forward, set viewport ### Screenshot optimization for Claude Code When using screenshots in Claude Code CLI, the base64 image data can consume significant context. Use the `saveTo` parameter to save screenshots to disk instead: ``` screenshot_page({ saveTo: "/tmp/page.png" }) screenshot_by_uid({ uid: "abc123", saveTo: "/tmp/element.png" }) ``` The file can then be viewed with Claude Code's `Read` tool without impacting context size. ## Local development ```bash 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 ``` See [CONTRIBUTING.md](https://github.com/mozilla/firefox-devtools-mcp/blob/HEAD/CONTRIBUTING.md) for more details on local development, testing, and CI. ## 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. - Windows 10: Error during discovery for MCP server 'firefox-devtools': MCP error -32000: Connection closed - **Solution 1** Wrap with `cmd /c` ([details](https://github.com/modelcontextprotocol/servers/issues/1082#issuecomment-2791786310)): ```json "mcpServers": { "firefox-devtools": { "command": "cmd", "args": ["/c", "npx", "-y", "@mozilla/firefox-devtools-mcp@latest"] } } ``` - **Solution 2** Use the absolute path to `npx` (adjust extension — `.cmd`, `.bat`, `.exe`, or `.ps1` — to match your setup): ```json "mcpServers": { "firefox-devtools": { "command": "C:\\nvm4w\\nodejs\\npx.ps1", "args": ["-y", "@mozilla/firefox-devtools-mcp@latest"] } } ``` ## Versioning - Pre‑1.0 API: versions start at `0.x`. Use `@latest` with npx for the newest release. ## Contributing See [CONTRIBUTING.md](https://github.com/mozilla/firefox-devtools-mcp/blob/HEAD/CONTRIBUTING.md) for how to file issues, run tests, and work on the project locally. ## Author Maintained by [Mozilla](https://www.mozilla.org). ## License Licensed under either of [MIT](https://github.com/mozilla/firefox-devtools-mcp/tree/HEAD/LICENSE-MIT) or [Apache 2.0](https://github.com/mozilla/firefox-devtools-mcp/tree/HEAD/LICENSE-APACHE) at your option.