Claude for Foxfire (unofficial)

This is an unofficial community project. It is not affiliated with, endorsed by, or sponsored by Anthropic. Claude is a trademark of Anthropic.

Lets Claude Code drive your real Firefox: your own tabs, your own logins. Clicks and typing are performed with synthetic DOM events inside the page; no system-level input is ever generated. Communication is over a local unix socket only: no network port is opened.

Architecture

Claude Code ──stdio/MCP──> src/server.mjs ──unix socket (mode 600)──> src/host.mjs
                                                                          │ native messaging
                                                                          v
                                                          Firefox extension (background.js)
                                                                          │
                                                                          v
                                                          content script in the page (DOM events)

• src/server.mjs: MCP server (stdio), exposes the tools below, owns the socket ($XDG_RUNTIME_DIR/claude-in-firefox.sock, override with CLAUDE_IN_FIREFOX_SOCK).

• src/host.mjs: native messaging host launched by Firefox, bridges the socket and the extension.

• extension/: Manifest V2 extension (background page + content script, popup, options page).

Related MCP server: Kamurafox

Requirements

• Linux. The bridge socket lives in $XDG_RUNTIME_DIR and bin/install-host.mjs writes only to ~/.mozilla/native-messaging-hosts. macOS and Windows are not supported (the host manifest location differs there and is not handled).

• Firefox 128 or newer (strict_min_version in the extension manifest), installed as a regular package (deb or tarball). With Snap or Flatpak the native messaging directory is different and this setup has not been tried.

• Node.js (tested with 22). It must stay installed: the native messaging host wrapper runs it.

Install

npm install
node bin/install-host.mjs        # writes the native messaging manifest in ~/.mozilla/native-messaging-hosts/
npm run build                    # produces dist/claude-for-firefox-<version>.xpi

(node bin/install-host.mjs --uninstall removes the host manifest.) The host wrapper records the absolute path of the node that ran install-host.mjs: re-run it if you change Node version.

Load the extension, either:

• temporarily: about:debugging → This Firefox → Load Temporary Add-on… → pick extension/manifest.json (gone at the next restart); or

• permanently: Firefox release requires signed extensions. Sign it as unlisted with your own addons.mozilla.org API keys:

  export WEB_EXT_API_KEY=...      # "JWT issuer" from the AMO API keys page
  export WEB_EXT_API_SECRET=...   # "JWT secret"
  npm run sign                    # output in dist/signed/

  Each signature needs a new version in extension/manifest.json. Open the signed .xpi in Firefox to install it.

The extension id is claude-for-firefox@unofficial.extension; it must match allowed_extensions in the host manifest (done by install-host.mjs).

Register the MCP server with Claude Code:

claude mcp add claude-for-firefox -- node /path/to/src/server.mjs

Quick check

1. claude mcp list should show claude-for-firefox as connected.

2. With Firefox open and the extension loaded, ask Claude to use tabs_context: it should list your tabs.

3. Before navigate or read_page on a site, allow its domain from the extension popup (or options page); otherwise the call is refused with «dominio … non autorizzato».

Permissions

Firefox asks for these when you install the extension:

• nativeMessaging: talk to the local host (src/host.mjs), which relays to the MCP server over the unix socket

• tabs: list tabs and read their url/title, open and close the tabs Claude creates

• storage: keep your allowed domains and settings

• sessions: mark the tabs Claude created, so tabs_close only closes those

• tabGroups: put the tabs Claude opens in a «Claude» group

• <all_urls>: inject the content script into the page you allowed; it can only be injected once the domain is allowed (see below)

The manifest also declares that the extension handles browsing activity and website content, as Firefox requires. These install-time permissions are not the limit on what Claude can do: the real limit is the per-site consent below.

Per-site permissions

Claude acts only on domains you allow (and their subdomains). Manage them from the extension popup (button for the current tab's domain) or the options page. Actions on a non-allowed domain are refused. tabs_context and tabs_create are always allowed. navigate/tabs_create accept only http(s) (and about:blank for tabs_create): never file:, moz-extension:, javascript:, data:.

MCP tools

tabs_context, tabs_create (opens in background), tabs_close (only tabs created by Claude), navigate, read_page, find, click, form_input, type, press_key, scroll, screenshot, file_upload, javascript_tool (off by default, enable it in the options page), read_console_messages.

Safety guards

Typing into password fields is refused. Ideas for these guards come from nanogenomic/ClaudeCodeBrowser (MIT); the code was rewritten, not copied.

Known limits

• Synthetic events have isTrusted=false; some sites (payments, captchas, some logins) reject them.

• Screenshots of background tabs can occasionally come back blank; the extension retries and then reports an error.

• javascript_tool relies on page-level eval: a strict CSP may block it.

• Main frame only (no iframes). Several Claude Code sessions can share one Firefox: the first MCP server owns the socket, the others relay their calls through it.

Privacy

The extension sends nothing over the network by itself. Page contents it reads go only to the local Claude Code process, which in turn sends them to Anthropic like any other content of your conversation. Enable it only on sites you are comfortable sharing with the model.

Tests

node test/e2e.mjs starts a regular (non-headless) Firefox on its own Xvfb display, with a temporary profile and HOME (your real Firefox and profile are not touched; it needs Firefox at /usr/lib/firefox/firefox, xvfb, and python3). Other benches: test/guard.mjs, test/client-guard.mjs, test/multi.mjs, test/upload.mjs, test/cursor.mjs.

License

MIT, see LICENSE.