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Claudezilla

Introduction

Claudezilla is a Firefox extension that gives Claude Code CLI full browser automation capabilities. It connects Claude Code to Firefox through the Model Context Protocol (MCP), letting Claude navigate pages, click elements, fill forms, take screenshots, and inspect the DOM — all without Chrome or Chromium.

Architecture

Section titled “Architecture”
┌──────────────────┐
│    Claude Code   │
│    CLI           │
└────────┬─────────┘
         │ JSON-RPC
         ▼
┌──────────────────┐
│    MCP Server    │
│    (Node.js)     │
└────────┬─────────┘
         │ Unix socket / pipe
         ▼
┌──────────────────┐
│   Native Host    │
│   (stdio)        │
└────────┬─────────┘
         │ 4-byte header + JSON
         ▼
┌──────────────────┐
│ Firefox Extension│
│ (MV2)            │
└──────────────────┘
  Content scripts
  interact with DOM

Claude Code calls MCP tools like firefox_navigate or firefox_screenshot. The MCP server translates these into commands sent over a Unix socket to the native messaging host, which forwards them to the Firefox extension via stdin/stdout with a 4-byte length-prefixed JSON protocol. The extension executes commands in the browser and returns results back through the same chain.

Key Features

Section titled “Key Features”
  • Browser control — Open windows, navigate URLs, manage tabs, close pages
  • Page interaction — Click elements, type text, press keys, scroll, wait for elements
  • Screenshots — Viewport capture with dynamic readiness detection and image compression
  • Page analysis — Structured JSON page state, accessibility snapshots, element inspection
  • JavaScript evaluation — Run expressions in page context with safety validation
  • DevTools access — Console logs and network request monitoring
  • Multi-agent coordination — Tab ownership, screenshot mutex, slot reservations, orphan cleanup
  • Focus loops — Persistent iterative development across Claude Code sessions
  • Annotated screenshots — Visual annotations overlaid on captures
  • Domain allowlist — Restrict which domains Claude can access
  • Cross-platform — macOS, Linux, and Windows 10/11 support

Next Steps

Section titled “Next Steps”