Claude for Mozilla

Table of Contents

• Features
• Requirements
• Installation
  • Firefox (Modern - MV3)
  • Firefox (Legacy - MV2)
  • Thunderbird
  • SeaMonkey
• Building from Source
• Usage
  • Context Menu
  • Thunderbird Features
• Configuration
• Privacy
• License
• Contributing

Claude AI assistant extension for Mozilla products - Firefox, Thunderbird, and SeaMonkey.

Features

• Sidebar Chat - Chat with Claude directly in your browser sidebar

• Context Menu - Right-click selected text to ask Claude about it

• Streaming Responses - See Claude’s responses as they’re generated

• Multiple Models - Choose between Claude Sonnet 4, Opus 4, or Haiku 3.5

• Conversation History - Your conversations are saved locally

• Thunderbird Integration - Help with email composition (Thunderbird only)

Requirements

• An Anthropic API key

• Firefox 109+ (Manifest V3) or Firefox 68+ (Manifest V2)

• Thunderbird 78+ (for email features)

• SeaMonkey 2.53+ (Manifest V2)

Installation

Firefox (Modern - MV3)

1. Download claude-mozilla-firefox-mv3.xpi from Releases

2. Go to about:debugging > This Firefox

3. Click "Load Temporary Add-on" and select the .xpi file

Firefox (Legacy - MV2)

1. Download claude-mozilla-firefox-mv2.xpi from Releases

2. Go to about:addons

3. Click the gear icon > Install Add-on From File

Thunderbird

1. Download claude-mozilla-thunderbird.xpi from Releases

2. Go to Tools > Add-ons and Themes

3. Click the gear icon > Install Add-on From File

SeaMonkey

1. Download claude-mozilla-seamonkey.xpi from Releases

2. Go to Tools > Add-ons Manager

3. Click Install from file

Building from Source

# Clone the repository
git clone https://github.com/hyperpolymath/claude-mozilla-extension.git
cd claude-mozilla-extension

# Generate icons (requires imagemagick, librsvg, or inkscape)
./scripts/generate-icons.sh

# Build all variants
./scripts/build.sh

Output files will be in dist/:

• claude-mozilla-firefox-mv3.xpi - Firefox 109+

• claude-mozilla-firefox-mv2.xpi - Firefox 68-108

• claude-mozilla-thunderbird.xpi - Thunderbird 78+

• claude-mozilla-seamonkey.xpi - SeaMonkey 2.53+

Usage

1. Click the Claude icon in your toolbar or open the sidebar

2. Enter your Anthropic API key when prompted

3. Start chatting!

Context Menu

Select any text on a webpage, right-click, and choose "Ask Claude about this" to quickly get Claude’s help with the selected content.

Thunderbird Features

In Thunderbird, Claude can help you:

• Draft email responses

• Summarize email threads

• Improve email clarity and tone

Configuration

Access settings via the gear icon in the sidebar:

• API Key - Your Anthropic API key

• System Prompt - Custom instructions for Claude

• Streaming - Enable/disable streaming responses

• Max Tokens - Maximum response length

Privacy

• Your API key is stored locally in browser storage

• Conversations are stored locally, never sent to third parties

• Only communicates with api.anthropic.com

License

AGPL-3.0-or-later

This is an independent project and is not affiliated with Anthropic. Claude is a trademark of Anthropic, PBC.

Contributing

Contributions welcome! Please ensure:

• Code follows existing style

• All files have SPDX headers

• Both MV2 and MV3 manifests are updated if needed