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Gecko MCP

Automate live Firefox-family browser sessions through MCP, with tools for tabs, page reading, forms, screenshots, and input.

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Install Gecko MCP

Pick your client, then add it in one click or paste the config.

STDIONode.js
~/Library/Application Support/Claude/claude_desktop_config.json
claude_desktop_config.json
{
  "mcpServers": {
    "gecko-mcp": {
      "command": "npx",
      "args": [
        "-y",
        "gecko-mcp"
      ]
    }
  }
}

Settings → Developer → Edit Config, merge this into mcpServers, then fully quit and reopen Claude Desktop.

Automated check passed— started and listed 41 tools correctly (20d ago).

Overview

The gecko-mcp MCP server connects MCP clients to live Floorp and other Firefox-based browsers, including Firefox, LibreWolf, Waterfox, Zen, and Mullvad. It selects Floorp’s local HTTP API when available and otherwise uses Firefox Marionette, preserving access to the browser session’s tabs. Reach for it when an agent needs to inspect pages, navigate sites, complete forms, capture screenshots, or perform browser interactions. Node.js 18 or newer and browser automation enabled at launch are required.

Use cases

  • Inspect live browser tabs and page content
  • Navigate websites and complete web forms
  • Locate controls and submit browser workflows
  • Capture viewport or full-page screenshots
  • Automate rich-text editors with real keyboard input

Key features

  • Firefox-family browser automation over MCP
  • Tab management with browser IDs
  • Markdown, HTML, and structured page reads
  • CSS selector and snapshot-based element targeting
  • Form interaction and screenshots
  • Optional OS input and JavaScript evaluation

Tools41

What Gecko MCP lets your agent do. Expand a tool for its parameters.

Verified live~4.9k tokens of context

Security & health

What it can reach and how reliably it runs — from our own checks, not the maintainer’s claims.

ActiveLast checked 1d ago

Recent health check succeeded.

23/23 checks healthy over the last 91d

What it can do

From the 41 tools this server returned when we ran it; 41 declare their own safety hints.

Can delete or modify data · 6Writes files · 1Handles credentials · 2Makes network requests · 37Read-only tools · 35
Network at startup3 connections
Files written at startupNone
Install scriptsNone
npm provenanceSigned build
Package age127 days
Maintainers1

Observed 2026-10-20 in an isolated sandbox. A description of reach, not a security audit.

Supply-chain signal

No high-severity advisories surfaced by our automated scan.

Critical 0High 0Medium 0Low 0

Scanned 3d ago via OSV.dev · gecko-mcp (npm)

Adoption & maintenance

Factual signals from GitHub, npm, and our automated checks — not a rating.

GitHub stars2Stargazers on the source repository.
npm downloads225Package downloads in the last 30 days.
Last commit4mo agoMost recent push to the default branch.
Availability100%Our rolling endpoint + install checks that succeeded.
Install checkPassedOur sandbox started it and listed its tools.
Tools exposed41Callable tools this server registers over MCP.
Directory activity2 viewsConfig copies, upvotes, and views on AllMCPs.

How Gecko MCP works

What gecko-mcp MCP server does

The gecko-mcp MCP server lets an MCP client operate a live Firefox-family browser session. It can enumerate, open, navigate, and close tabs; identify the active tab; read page content as Markdown, HTML, or an accessibility tree; and capture viewport or full-page screenshots. Most operations can target the active tab or a specific browserId returned by tab tools.

Page interaction includes locating elements by visible text or tag, mapping pages to selectors and snapshot references, clicking, typing into normal or rich-text fields, filling several fields, selecting options, toggling controls, submitting forms, pressing keys, and waiting for elements. A JavaScript evaluation tool is also available, but it is locked until explicitly enabled. Sensitive value reads can retrieve the current contents of form controls, including password fields.

How it works

The gecko-mcp MCP server chooses between two browser backends. Floorp uses its built-in automation HTTP API when floorp.mcp.enabled is enabled and the local endpoint is reachable. Other Gecko browsers use Marionette, Firefox’s automation interface, with the browser started using the -marionette flag. The server communicates with MCP clients over stdio and drives the user’s existing browser session rather than providing a separate browser abstraction.

The find tool returns compact CSS selectors, while snapshot provides a structured page representation with inline fingerprints and selector mappings. This lets an agent locate controls without transferring an entire page into context. Page reads are capped at 25 KB by default.

Setup and configuration

Run npx gecko-mcp setup to register the server with supported clients, either for one project or globally. Manual MCP configuration can use npx -y gecko-mcp as the command. Node.js 18 or later is required.

For Floorp, enable floorp.mcp.enabled in about:config and restart the browser. For Firefox, LibreWolf, Waterfox, Zen, or Mullvad, start the browser with Marionette enabled; the default Marionette port is 2828. A different port can be selected with the browser profile’s marionette.port preference and the matching MARIONETTE_PORT value. GECKO_MCP_BACKEND=marionette can force the Marionette backend.

Tools and capabilities

  • Manage tabs and target them by browserId.
  • Read pages, locate elements, create snapshots, and take screenshots.
  • Click, type, fill forms, submit controls, select options, and wait for elements.
  • Use genuine Windows keyboard and mouse events through the real input tools.
  • Launch Floorp on Windows or start a Firefox-based browser with Marionette.
  • Enable or disable OS input and page JavaScript access per session.

Limitations and notes

The gecko-mcp MCP server’s OS keyboard and mouse tools are disabled by default because they can affect applications outside the browser. They must be enabled for a session or through configuration, and the real-input tools verify that Floorp is foregrounded before sending input. JavaScript evaluation has a separate lock.

On the Marionette backend, Floorp-specific snapshot fingerprints, workspace tools, and the accessibility-tree output are not supported; use find and read_page instead. Marionette must be enabled when the browser starts, so enabling it after launch does not attach to the existing session. The get_value capability can read sensitive form values, including passwords, and should be granted only in trusted workflows.

Read the full README View source on GitHub

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Frequently Asked Questions about Gecko MCP

gecko-mcp is an MCP server that connects AI clients to live Floorp and other Firefox-based browsers through Floorp’s local API or Firefox Marionette. Its main tools manage tabs, read pages, locate and interact with elements, fill forms, capture screenshots, and optionally use real OS input or page JavaScript.

Run `npx gecko-mcp setup` to register it with a supported MCP client. The wizard supports project-level or global configuration. You can also add an MCP server entry using the command `npx -y gecko-mcp`, without cloning or building the repository.

gecko-mcp works with Floorp, Firefox, LibreWolf, Waterfox, Zen, and Mullvad. Floorp uses its built-in automation API after `floorp.mcp.enabled` is enabled. Other supported browsers must be launched with the `-marionette` option.

Yes, Cursor is one of the clients supported by the setup wizard and README configuration examples. The server uses stdio, so it can also be configured manually in Cursor with the `npx -y gecko-mcp` command.

They are locked by default because genuine keyboard and mouse events can affect applications outside the browser. Enable them for a session with the corresponding tool or persistently with `GECKO_MCP_ENABLE_OS_INPUT=1`; JavaScript evaluation has a separate lock.

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