Extracting Open Tabs from Firefox / LibreWolf

This guide explains how to extract a list of all open tabs from Firefox or LibreWolf using a small Python script. Useful for backups, migrating sessions, or just getting a quick overview of what you have open on another computer accessed over ssh.

How It Works

Firefox-based browsers store session data in a file called recovery.jsonlz4 — a JSON blob compressed with Mozilla’s variant of LZ4. The script decompresses it, walks the session structure, and prints the current URL and title for each open tab.

Prerequisites

You need the lz4 Python package:

pip install lz4

The Script

Save this as extract_tabs.py:

import json, lz4.block, sys
 
with open(sys.argv[1], "rb") as f:
    magic = f.read(8)  # skip the "mozLz40\0" header
    data = json.loads(lz4.block.decompress(f.read()))
 
for window in data.get("windows", []):
    for tab in window.get("tabs", []):
        entries = tab.get("entries", [])
        if entries:
            current = entries[tab.get("index", len(entries)) - 1]
            print(current.get("url"), "-", current.get("title", ""))

How It Works:

1. Reads the .jsonlz4 file and skips the 8-byte magic header (mozLz40\0).
2. Decompresses the LZ4 payload and parses the JSON.
3. Iterates over all windows and tabs in the session.
4. Prints the URL and title of each tab’s current history entry.

Usage

Firefox

python extract_tabs.py "$(find ~/.mozilla/firefox/ -name "recovery.jsonlz4")"

LibreWolf

python extract_tabs.py "$(find ~/.librewolf/ -name "recovery.jsonlz4")"

Tips

• The session file is only present while the browser is running (or was recently closed). If you don’t find it, look for previous.jsonlz4 as a fallback.
• Pipe through grep to filter for specific domains: python extract_tabs.py ... | grep github.com
• Redirect to a file for a quick backup: python extract_tabs.py ... > tabs.txt