Parse Mozilla Bookmark File

Parse Mozilla Bookmark File | Generated by AI

Home PDF

The file you’re looking at is a Firefox bookmark backup in the .jsonlz4 format. This means it’s a JSON file compressed using the LZ4 compression algorithm, and it contains your Firefox bookmarks.

📁 File Name:

bookmarks-2025-06-21_10_MU9VVxxx.jsonlz4

This is a standard naming pattern for Firefox bookmark backups.

✅ Goal: How to Parse It

You cannot directly read this file because it’s compressed with LZ4. You need to:

Decompress it (LZ4 → JSON)
Pretty-print or parse the resulting JSON

🔧 Step-by-step Instructions

Option 1: Use Python (Recommended)

Install dependencies:

pip install lz4

Then run this Python script:

import json
import lz4.block
import sys

def decompress_jsonlz4(file_path):
    with open(file_path, 'rb') as f:
        # Read the first 8 bytes - header magic
        magic = f.read(8)
        if magic != b'mozLz40\0':
            raise ValueError("Invalid file header - not a JSON-LZ4 file")

        # Read the rest of the file and decompress
        compressed_data = f.read()
        json_bytes = lz4.block.decompress(compressed_data)
        json_str = json_bytes.decode('utf-8')
        return json.loads(json_str)

# Example usage
if __name__ == "__main__":
    import sys
    file_path = sys.argv[1]
    data = decompress_jsonlz4(file_path)
    print(json.dumps(data, indent=4))

Save it as parse_bookmarks.py, then run:

python parse_bookmarks.py 'bookmarks-2025-06-21_10_MU9VV5NmyUCq9RTxuMze5iBNh7sKyRPF_ZlV5EpMqZo=.jsonlz4'

🔍 The output will be a nicely formatted JSON tree of your bookmarks.

Option 2: Use an Online Tool (Quick but Risky with Sensitive Data)

There are tools like:

https://arewecompressedyet.com/jsonlz4/
Or search for “jsonlz4 decoder”

⚠️ Warning: Do not upload sensitive files to online tools unless you’re sure they are safe and trustworthy.

Option 3: Use Node.js

If you prefer JavaScript/Node:

npm install firefox-jsonlz4

Or see this repo: https://github.com/overdodactyl/firefox-jsonlz4

📊 What’s Inside?

Once parsed, you’ll get a JSON structure like this:

{
  "title": "Bookmarks Menu",
  "children": [
    {
      "title": "Mozilla Firefox",
      "children": [
        {
          "title": "Get Help",
          "uri": "https://support.mozilla.org/products/firefox/"
        },
        ...
      ]
    }
  ]
}

You can use this data to:

Search through old bookmarks
Migrate bookmarks
Analyze your browsing/bookmarking habits

✅ Summary

Step	Action
1	Recognize that `.jsonlz4` is a compressed JSON file
2	Use Python or other tools to decompress and parse it
3	View/export the structured JSON of your Firefox bookmarks

Let me know if you want to convert this into CSV, HTML, or extract specific URLs!

Great question! Let’s break down why Mozilla uses the .jsonlz4 format for bookmarks instead of plain JSON, and address your concern about security.

🔍 Why Mozilla Uses `.jsonlz4` Instead of Plain JSON

✅ 1. Compression Efficiency

.jsonlz4 is JSON data compressed using the LZ4 algorithm.
LZ4 is fast, lightweight, and offers decent compression ratios — ideal for Firefox’s use case.
This reduces file size significantly (often by 50–70%), which:
- Saves disk space
- Speeds up backups and restores
- Reduces I/O when reading/writing bookmark files

📦 Example: A 2MB plain JSON bookmark file may compress to ~600KB–800KB with LZ4.

✅ 2. Performance

LZ4 is optimized for speed over maximum compression.
Firefox can quickly compress and decompress these files without noticeable lag.
Other algorithms like gzip or zstd are more powerful but slower or more complex.

✅ 3. Internal Format

Firefox doesn’t expose this as a user-facing format; it’s used internally for:
- Bookmarks backups (bookmarkbackups/)
- Session store (sessionstore-backups/)
It’s not meant for human editing or interoperability (like exporting for Chrome import).

For export/import, Firefox provides plain JSON via the “Import and Backup” menu.

🔒 Is `.jsonlz4` Less Secure Than JSON?

No, not inherently.

Let’s clarify:

Aspect	JSON	JSONLZ4
Data Format	Readable text	Binary-compressed
Security	None built-in	None built-in
Encryption?	No	No
Tamper Protection?	No	No

Both formats are unencrypted and unprotected by default.

So:

If someone has access to your Firefox profile, they can read either file.
Neither format protects sensitive data like URLs or titles.

💡 So Why Not Use Encrypted or Secure Formats?

Mozilla does not encrypt local profile data by default, including:

Bookmarks
History
Cookies
Passwords

Here’s Why:

User Experience: Encryption adds complexity.
Recovery: Users could lose data if they forget passwords.
Trust Assumption: Firefox assumes your system is secure.
Alternative Tools Exist: You can manually encrypt your Firefox profile directory using OS-level tools (e.g., VeraCrypt, BitLocker, etc.).

If you want encrypted profiles:

Use Firefox Lockwise for password encryption.
Use third-party tools to encrypt the entire profile folder.
Or switch to a portable Firefox on an encrypted USB drive.

🧠 Bonus Tip: How to Convert `.jsonlz4` → `.json`

You already know how from the previous answer, but here’s a quick recap using Python:

python parse_bookmarks.py bookmarks-*.jsonlz4 > bookmarks.json

Or use this one-liner if you’re comfortable in shell + Python:

cat bookmarks-*.jsonlz4 | python3 -c '
import lz4.block, sys, json
data = sys.stdin.buffer.read()[8:]
print(json.dumps(json.loads(lz4.block.decompress(data)), indent=2))' > bookmarks.json

✅ Summary

Question	Answer
Why `.jsonlz4` instead of JSON?	Compression, performance, internal use
Is `.jsonlz4` less secure than JSON?	No — both are unencrypted and readable
Can someone steal my bookmarks?	Yes, if they have access to your machine
How to make it more secure?	Encrypt your Firefox profile manually

If you’re concerned about privacy or security, the real solution is to protect access to your computer or encrypt your Firefox profile folder, not just rely on file formats.

Let me know if you’d like help writing a script to automate decryption or encrypting backups!

Back 2025.06.21 Donate