Content
# Firefox DevTools MCP
[](https://www.npmjs.com/package/firefox-devtools-mcp)
[](https://github.com/mozilla/firefox-devtools-mcp/actions/workflows/ci.yml)
[](https://codecov.io/gh/mozilla/firefox-devtools-mcp)
[](LICENSE-MIT) [](LICENSE-APACHE)
<a href="https://glama.ai/mcp/servers/@mozilla/firefox-devtools-mcp"><img src="https://glama.ai/mcp/servers/@mozilla/firefox-devtools-mcp/badge" height="223" alt="Glama"></a>
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.
## 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](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 firefox-devtools-mcp@latest
```
Pass options either as args or env vars. Examples:
```bash
# 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`
```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)
```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 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 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`)
> **Note on `--pref`:** 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. The `--pref` option allows overriding these defaults when needed.
### 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 firefox-devtools-mcp --android-device auto
# Target a specific device
npx firefox-devtools-mcp --android-device <serial>
# Use Firefox Nightly instead
npx firefox-devtools-mcp --android-device <serial> --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 enabled
firefox --marionette
# Run the MCP server
npx firefox-devtools-mcp --connect-existing --marionette-port 2828
```
Or set `marionette.enabled` to `true` in `about:config` (or `user.js`) to enable Marionette on every launch.
BiDi-dependent features (console events, network events) are not available in connect-existing mode; all other features work normally.
> **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
- 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](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", "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", "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](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](LICENSE-MIT) or [Apache 2.0](LICENSE-APACHE) at your option.
