Firefox DevTools MCP

Name: Firefox DevTools MCP
Author: Mozilla

Mozilla's server for driving and debugging Firefox: browse, fill forms, read console, network, profiler

Official · Mozilla TypeScript Local · stdio Browser automation Developer tools

GitHub npm Website

79 popularity score ★ 553 ↓ 4.1k/wk

Connect your client

Local (npm)

Add in one click

Add to Cursor Add to VS Code Add to LM Studio Add to Goose

Opens the app, which asks before it adds the server.

Or add it by command or config

Claude CodeTerminal

claude mcp add firefox-devtools -- npx -y @mozilla/firefox-devtools-mcp@latest

Claude Desktopclaude_desktop_config.json

{
  "mcpServers": {
    "firefox-devtools": {
      "command": "npx",
      "args": [
        "-y",
        "@mozilla/firefox-devtools-mcp@latest"
      ]
    }
  }
}

Cursor~/.cursor/mcp.json

{
  "mcpServers": {
    "firefox-devtools": {
      "command": "npx",
      "args": [
        "-y",
        "@mozilla/firefox-devtools-mcp@latest"
      ]
    }
  }
}

VS Code.vscode/mcp.json

{
  "servers": {
    "firefox-devtools": {
      "type": "stdio",
      "command": "npx",
      "args": [
        "-y",
        "@mozilla/firefox-devtools-mcp@latest"
      ]
    }
  }
}

Codex~/.codex/config.toml

[mcp_servers.firefox-devtools]
command = "npx"
args = ["-y", "@mozilla/firefox-devtools-mcp@latest"]

Gemini CLITerminal

gemini mcp add --scope user firefox-devtools npx -- -y @mozilla/firefox-devtools-mcp@latest

Settings 12

Set together: connect-existing
`FIREFOX_HEADLESS`	Optional: true runs Firefox without a window (same as --headless). Default `false`.
`TOOL_PRESET`	Optional: slim, basic, developer, mozilla or all: which tool modules are on. Default `basic`.
`START_URL`	Optional: URL opened when the browser starts (same as --start-url). Default `about:blank`.
`AUTO_PROFILE`	Optional: true keeps a persistent profile under ~/.firefox-devtools-mcp, one per Firefox binary. Default `false`.
`ACCEPT_INSECURE_CERTS`	Optional: true ignores TLS certificate errors. Default `false`.
`UNRESTRICTED_SAVE_PATHS`	Optional: true lets saveTo write anywhere on disk. Default `false`. For saveTo.
`DISABLE_NETWORK_BODY_COLLECTION`	Optional: true stops capturing request and response bodies, keeping headers only. Default `false`. For get_network_request.
`CONNECT_EXISTING`	Optional: true attaches to a running Firefox instead of launching one. Default `false`.
`MARIONETTE_PORT`	Optional: Marionette port used in connect-existing mode. Default `2828`.
`IDLE_TIMEOUT`	Optional: Seconds without tool calls before a connect-existing session releases Firefox. Default `1800`.
Set together: android
`ANDROID_WIPE_APP_DATA`	Optional: true confirms the app data wipe that --android-device mode needs. Default `false`.
`ANDROID_PACKAGE`	Optional: Android app package for --android-device mode. Default `org.mozilla.firefox`.

What it does

Firefox DevTools MCP is Mozilla's server for controlling a real Firefox from an MCP client. It launches Firefox, or attaches to one already running, and talks to it over WebDriver BiDi through Selenium. You take a snapshot of the page, which gives every element a UID, and then click, hover, type, drag, fill forms or upload files by that UID. Tabs, history, dialogs, viewport size, screenshots, PDF printing and downloads have their own tools.

There are two main uses. One is plain browsing, where the assistant reads pages and works through multi-step flows on a site. The other is web development: open the page you are building, then look at its console output and network requests, put logpoints in its scripts, record a profile with the Firefox profiler or capture a screencast. Large results can go to a file through a saveTo parameter instead of filling the conversation.

Tools are grouped in modules that you choose with --tool-preset (slim, basic, developer, mozilla, all) or an explicit --tools list. The generated tool reference counts 57 tools in 19 modules. The npm build skips the launch, prefs, privileged and bidi modules, so 49 tools are reachable from it. The default basic preset turns on 35 of those, evaluate_script among them. Network, console, debugging and profiler tools need the developer preset or higher. Firefox for Android can be driven over adb too. The project is still at 0.x, so expect its interface to change.

The main branch has already moved the server's home folder from ~/.firefox-devtools-mcp to ~/.firefox-mcp and renamed the profile folder and marker file. The published package still uses the old names.

What it needs

Runtime	Node.js 20.19.0+
Runs on	macOS, Windows, Linux
Also	Firefox 100 or newer installed locally adb and a connected device for Android mode

Firefox is found automatically, or set --firefox-path. The debugger tools need Firefox 153 or newer. For --connect-existing, start Firefox yourself with --marionette --remote-debugging-port. It needs a local browser, so a cloud host without one cannot run it.

Limits

Not covered Network, console, debugging and profiler tools are off under the default basic preset: use --tool-preset developer or a --tools list
Not covered The npm build skips the launch, prefs, privileged and bidi modules even when you ask for them
Limit saveTo takes relative paths or absolute paths under ~/.firefox-devtools-mcp/output unless --unrestricted-save-paths is set
Limit Android mode wipes all data of the target app before a session and will not start without --android-wipe-app-data
Limit Leaving Marionette on in your everyday browser sets navigator.webdriver and can trip bot detection
Limit Snapshot UIDs go stale after the page navigates, so take a new snapshot
Size cap get_page_text returns 20000 characters inline by default (maxLength), more only through saveTo
Early release The ~/.firefox-mcp folder named in the main-branch README is not in the published release yet

Network, console, debugging and profiler tools are off under the default basic preset; start with --tool-preset developer or a --tools list. The prefs, privileged and launch modules are skipped by the public package even if you ask for them. Android mode wipes all data of the target app before every session, which is why it insists on --android-wipe-app-data. saveTo accepts relative paths or paths under ~/.firefox-devtools-mcp only, unless you pass --unrestricted-save-paths. Leaving Marionette enabled in your everyday browser sets navigator.webdriver and can trip bot detection. Snapshot UIDs go stale after navigation.

Who it suits

Suits web developers who test in Firefox and want an assistant to see console errors, network traffic, logpoints and profiles for a page they control, and anyone automating sites in Firefox specifically. It runs locally and can act on pages, so give it a dedicated profile and avoid --connect-existing against your daily one. For Chrome, the Chrome DevTools MCP server, which we also list, is the counterpart. For cross-browser test automation, Microsoft's Playwright MCP, also listed, is the usual pick.

Tools 49

17 only read, 32 change things. A ? marks an optional parameter.

list_pages: List the open tabs and mark the selected one
new_page changes: Open a new tab at a URLurl: stringwait?: enum
navigate_page changes: Load a URL in the selected taburl: stringwait?: enum
select_page changes: Switch which tab later tools act on, by index, URL or titlepageIdx?: numberurl?: stringtitle?: string
close_page changes: Close a tab by its indexpageIdx: number
get_page_text: Return the visible text of the page, 20000 characters inline by defaultmaxLength?: numbersaveTo?: anypreview?: number
take_snapshot: Capture the page structure with a UID for each elementmaxLines?: numberincludeAttributes?: booleanincludeText?: booleanmaxDepth?: numberincludeAll?: booleanselector?: stringsaveTo?: anypreview?: number
resolve_uid_to_selector: Turn a snapshot UID into a CSS selectoruid: string
clear_snapshot changes: Drop the stored snapshot UIDs
click_by_uid changes: Click or double-click the element with a given UIDuid: stringdblClick?: boolean
hover_by_uid changes: Move the pointer over an elementuid: string
fill_by_uid changes: Type a value into one fielduid: stringvalue: string
drag_by_uid_to_uid changes: Drag one element onto anotherfromUid: stringtoUid: string
fill_form_by_uid changes: Fill several fields in one callelements: array
upload_file_by_uid changes: Attach a local file to a file inputuid: stringfilePath: string
press_key changes: Send a key press or combinationkey: stringuid?: string
type_text changes: Type text into the focused element or a given UIDtext: stringuid?: stringsubmitKey?: string
list_network_requests: List captured network requests, with filters and sortinglimit?: numbersinceMs?: numberurlContains?: stringmethod?: stringstatus?: numberstatusMin?: numberstatusMax?: numberisXHR?: booleanresourceType?: stringsortBy?: enumdetail?: enumformat?: enumsaveTo?: anypreview?: number
get_network_request: Show the details of one captured requestid?: stringurl?: stringformat?: enumsaveTo?: anypreview?: number
set_network_cache changes: Bypass or restore the HTTP cache for a tab or globallybehavior: enumscope?: enum
list_console_messages: List console output from the page, filtered by level or textlevel?: enumlimit?: numbersinceMs?: numbertextContains?: stringsource?: stringformat?: enumsaveTo?: anypreview?: number
clear_console_messages changes: Empty the captured console log
screenshot_page: Take a screenshot of the viewport or the full pagefullPage?: booleansaveTo?: any
screenshot_by_uid: Take a screenshot of one elementuid: stringsaveTo?: any
print_page: Print the page to PDFlandscape?: booleanbackground?: booleansaveTo?: any
list_downloads: List downloads seen this sessionstatus?: enumurlContains?: stringlimit?: numberformat?: enum
clear_downloads changes: Empty the download list
set_download_behavior changes: Allow, deny or reset downloads and pick their folderbehavior: enumdownloadFolder?: string
accept_dialog changes: Accept an alert, confirm or prompt, with optional prompt textpromptText?: string
dismiss_dialog changes: Dismiss a browser dialog
navigate_history changes: Go back or forward in historydirection: enum
set_viewport_size changes: Resize the browser viewportwidth: numberheight: number
get_firefox_output: Read Firefox's own stdout and stderrlines?: numbergrep?: stringsince?: number
get_firefox_info: Report the running Firefox's version and setup
close_firefox_session changes: Shut down the browser session
install_extension changes: Install an add-on from an archive, base64 data or a foldertype: enumpath?: stringvalue?: stringpermanent?: boolean
uninstall_extension changes: Remove an installed add-on by its IDid: string
profiler_is_active: Check whether the Firefox profiler is recording
profiler_start changes: Start the profiler with a preset or custom optionspreset?: enumentries?: integerinterval?: numberfeatures?: arraythreads?: arrayactiveContext?: string
profiler_stop changes: Stop the profiler and collect or discard the profilediscard?: boolean
screencast_start changes: Start recording a video of the viewportcontext?: stringframeRate?: integerwidth?: integerheight?: integermimeType?: string
screencast_stop changes: Stop a recording and return its filescreencast?: string
evaluate_script changes: Run a JavaScript function in the page and return the resultfunction: stringargs?: arraytimeout?: numbersandbox?: stringsaveTo?: anypreview?: number
enable_debugger changes: Turn on the JS debugger for the page
list_scripts: List the scripts the page has loaded
get_script_source: Fetch the source of a loaded scriptscriptUrl: string
set_logpoint changes: Log an expression at a script line without pausingurl: stringline: numberexpression: string
remove_logpoint changes: Remove a logpointlogpoint: string
get_logpoint_results: Return the values a logpoint collectedlogpoint: string

Popularity

79 popularity score, on our list (the bar is 36)

★ 553 ↓ 4.1k/wk

GitHub stars	553	32.9 points
Stars in 30 days	+79	9.5 points
npm downloads, last week	4,137	28.9 points
Official server	Yes	8 points

Measured 2026-11-07. How the score works.

Where it is published

Code	mozilla/firefox-devtools-mcp ★ 553
npm	@mozilla/firefox-devtools-mcp 0.10.7, 2026-10-28

What it can reach

Runs	On your machine
Reaches	Drives a browser, Files on your machine, The internet
Changes things	Yes: it can write, send, create or delete
Sign-in	None
Licence	MIT OR Apache-2.0 (npm)
Last code change	2026-11-04

Runs on your machine with your user's privileges and drives a local Firefox. Whatever that browser profile holds (cookies, sessions, saved logins) is within reach, especially with --connect-existing. The default basic preset includes evaluate_script, which runs arbitrary JavaScript in any page. Its SECURITY.md flags prompt injection from page content as the main risk. Tools write files (screenshots, snapshots, screencasts, downloads) into the working directory or ~/.firefox-devtools-mcp unless --unrestricted-save-paths lifts that limit, and upload_file_by_uid sends a local file to a page. --accept-insecure-certs turns off TLS checks. No sign-in is needed.

Over time

GitHub stars 553 +79 (+17 %)

553474

9 Oct 20267 Nov 2026

npm downloads a week 4.1k +4.1k (+14675 %)

8.1k28

18 May 20267 Nov 2026

Before the site measured it, read from npm's daily download counts.

Popularity score 79 +22 (+37 %)

8258

9 Oct 20267 Nov 2026

What is rising across the directory

Sources

Page checked 2026-11-06.

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Connect your client

Add in one click

Or add it by command or config

Settings 12

What it does

What it needs

Limits

Who it suits

Tools 49

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