What is firefox-mcp-server CLAUDE.md?

Project instructions for a Firefox browser-control server that uses Playwright, a tool for automating browsers. It covers running the server, testing it, examples, and its browser debugging tools.

Use it to start or debug the server, run its tests and examples, automate Firefox sessions, and inspect console, network, WebSocket, or performance activity.

It gives an agent the repository-specific commands and implementation details needed to work on or use the server correctly.

How JediLuke/firefox-mcp-server configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to JediLuke/firefox-mcp-server. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/JediLuke/firefox-mcp-server/main/CLAUDE.md

Clone the repo

git clone --depth 1 https://github.com/JediLuke/firefox-mcp-server

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/jediluke/firefox-mcp-server/claude-md/github.svg)](https://agentmods.dev/instructions/jediluke/firefox-mcp-server/claude-md)

Your own site

<a href="https://agentmods.dev/instructions/jediluke/firefox-mcp-server/claude-md"><img src="https://agentmods.dev/badge/instructions/jediluke/firefox-mcp-server/claude-md/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/jediluke/firefox-mcp-server/claude-md"><img src="https://agentmods.dev/badge/instructions/jediluke/firefox-mcp-server/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 1,553 This file is loaded in full into every session.

When invoked 1,553 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.01553	$0.01553
Opus 5.5	$0.00621	$0.00621
Sonnet 5.5	$0.00311	$0.00311
Haiku 4.5	$0.00155	$0.00155

Measured 2mo ago against content hash 60f5b55ed87a, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

firefox-mcp-server CLAUDE.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

CLAUDE.md · 189 lines

How it starts

The opening of the file, as written. The whole thing — 189 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Development Commands

Running the Server

npm start - Run the MCP server
npm run dev - Run server with Node.js debugger

Testing

npm test - Run basic Firefox functionality test
npm run install-firefox - Install Firefox browser for Playwright

Example Scripts

npm run example:basic - Run basic demo script
npm run example:multiplayer - Run multiplayer testing demo

Active Implementation

The MCP server implementation is in index.js.

The server provides:

Class: FirefoxMCPServer (version 1.0.0)
29 MCP tools for browser automation and debugging
Multi-session support with complete isolation
Advanced debugging capabilities (console logs, WebSocket monitoring, network activity, performance metrics)

Architecture Overview

Core Components

MCP Server: Uses @modelcontextprotocol/sdk for stdio communication
Browser Engine: Playwright Firefox automation
Session Management: Map-based storage for browser contexts and pages
Debug Buffers: Per-tab in-memory storage for monitoring data

Key Data Structures

this.browser - Main Firefox browser instance
this.contexts - Map of contextId → BrowserContext (for session isolation)
this.pages - Map of tabId → Page (for tab management)
this.consoleLogs - Map of tabId → array of console log events
this.jsErrors - Map of tabId → array of JavaScript error events
this.networkActivity - Map of tabId → array of network events
this.wsMessages - Map of tabId → array of WebSocket messages
this.performanceMetrics - Map of tabId → performance data
this.activeTabId - Currently active tab identifier

Session Isolation Architecture

Each session gets its own browser context with:

Separate cookies and storage
Independent session data
Isolated network monitoring
Individual debug buffers

Tool Categories

Read the full file on GitHub · 189 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2mo ago First seen · 189 lines · 1,553 tokens per session scan A 60f5b55ed87a

Subscribe to this mod's changes

firefox-mcp-server CLAUDE.md is an instructions file published in the GitHub repository JediLuke/firefox-mcp-server (30 stars, last pushed 10mo ago), licensed MIT. It adds 1,553 tokens to every session, about $0.0062 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Browser automation

firefox-mcp-server CLAUDE.md next to 6 instructions from other repositories
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firefox-mcp-server: Instructions file for Claude Code