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FF Session Importer for Firefox

A Firefox extension that imports Firefox sessionstore files (.jsonlz4, .json, .baklz4) and opens the contained tabs in Firefox windows.

Features

• Import Firefox sessions: Load Firefox sessionstore files directly into Firefox
• Multiple formats: Supports compressed (.jsonlz4, .baklz4) and uncompressed (.json) session files
• Window preservation: Each Firefox window opens in a separate Firefox window
• Simple interface: Just select a file and import

Installation

From Firefox Web Store

(Coming soon)

Manual Installation (Developer Mode)

1. Download or clone this repository
2. Open Firefox and navigate to Firefox://extensions/
3. Enable "Developer mode" (toggle in top-right corner)
4. Click "Load unpacked"
5. Select the extension directory

Usage

1. Click the extension icon in Firefox's toolbar
2. Click "Choose File" or drag & drop a Firefox sessionstore file
3. sessionstore.jsonlz4 (current session)
4. recovery.jsonlz4 (crashed session)
5. previous.jsonlz4 (previous session)
6. Any .json session backup
7. Preview the loaded tabs and windows
8. Click "Import Tabs" to open all tabs in new Firefox windows

File Locations

Firefox sessionstore files are typically located at:

• Windows: %APPDATA%\Mozilla\Firefox\Profiles\[profile]\sessionstore.jsonlz4
• macOS: ~/Library/Application Support/Firefox/Profiles/[profile]/sessionstore.jsonlz4
• Linux: ~/.mozilla/firefox/[profile]/sessionstore.jsonlz4

How It Works

1. Decompresses .jsonlz4 files using LZ4 decompression
2. Parses Firefox's sessionstore JSON format
3. Extracts URLs from tabs and windows
4. Creates new Firefox windows with the extracted tabs

Privacy

• All file processing happens locally in your browser
• No data is sent to external servers
• No tracking or analytics

Dependencies

• LZ4 decompression: Uses a modified version of lz4js by John Chadwick

Development

Building from Source

No build process required. The extension uses vanilla JavaScript.

Testing

1. Load the extension in developer mode
2. Use test sessionstore files from your Firefox profile

File Structure

firefox-session-importer/
└── Firefox/
├── lz4.js # LZ4 decompression library
├── manifest.json # Extension manifest
├── background.js # Background service worker
├── popup.html # Extension popup UI
├── popup.js # Popup functionality
├── styles.css # Popup styles
├── lib/
│ └── lz4.js # LZ4 decompression library
├── icons/ # Extension icons
├── README.md # This file
├── LICENSE # ISC License
└── CHANGELOG.md # Version history


Limitations

• No form data/cookies: Only URLs are imported, not form data, cookies, or browsing history
• Firefox-specific URLs: URLs starting with about:, Firefox:, or moz-extension: are skipped
• Large sessions: Very large sessions may take time to import

Troubleshooting

"Failed to decompress LZ4 file"

• Ensure you're using a valid Firefox sessionstore file
• Try using a different session file (recovery.jsonlz4, previous.jsonlz4)

"No valid URLs found"

• The session file may be corrupted or empty
• Try restoring from a different backup

Extension not loading

• Ensure developer mode is enabled in Firefox://extensions/
• Check Firefox console for errors (F12 → Console)

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Submit a pull request

License

ISC License - see LICENSE file for details.

Acknowledgments

• LZ4 decompression: Modified from lz4js by John Chadwick
• Firefox session format: Reverse-engineered from Firefox source code