You can use Python to accomplish this task by this rather inelegant solution:
#!/usr/bin/env python3
"""
Copyright (c) 2018 Helio Machado <0x2b3bfa0>
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 3.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
"""
import json
from pathlib import Path
from lz4.block import decompress
def load_recovery(path):
"""
Loads the recovery.jsonlz4 file from the path specified and
parses the json data to a native structure. This file contains
the current tabs of the browser.
"""
with open(str(path), "rb") as recovery_file:
assert recovery_file.read(8) == b"mozLz40\0"
compressed_data = recovery_file.read()
json_data = decompress(compressed_data)
recovery = json.loads(json_data.decode())
return recovery
def recovery_path():
"""
Get the path to the recovery.jsonlz4 file.
"""
firefox_path = Path.home() / ".mozilla" / "firefox"
profile_path = list(firefox_path.glob("*.default"))[0]
session_path = profile_path / "sessionstore-backups"
return session_path / "recovery.jsonlz4"
windows = load_recovery(recovery_path())["_closedWindows"]
tabs = [tab for window in windows for tab in window["tabs"]]
urls = [tab["entries"][0]["originalURI"] for tab in tabs]
# Here you go!
print("\n".join(urls))
License: GPLv2
This should be a good start point; even if your question is not as dumb as you may suppose, I think that you should try a bit harder at finding solutions and post your research results along with the question.
I'll leave the question unmaintaned and as Community Wiki.