A small utility, written in nodejs (with a little C), to unpack and display your last known Firefox tab list.

ffoxsession.js

#!/usr/bin/env nodejs

// ffoxsession is a little utility to dump the contents of your last
// known firefox session.  Works with 52 through 60 (so far).  Requires
// the lz4json utility (https://github.com/andikleen/lz4json), as
// Firefox uses some weird version of lz4 optimized for JSON data.

var fs = require("fs");
var os = require("os");

var execSync = require("child_process").execSync;
var root = require('os').homedir() + "/.mozilla/firefox/";

// I use sync'd versions a lot.  Performance is not a priority here.

var possibles = fs.readdirSync(root).filter(function(f) {
    return f.indexOf(".default") !== -1;
}).map(function(f) {
    return [root + f, fs.lstatSync(root + f)];
}).sort(function(s) {
    return [s[1].mtime];
}).map(function(s) {
    return s[0];
});

if (possibles.length === 0) {
    console.log("Could not find the user's profile");
    process.exit(1);
}

var path = possibles[0] + "/sessionstore-backups/recovery.jsonlz4";
var  input = execSync("lz4jsoncat " + path, {});
var  data = JSON.parse(input);
data.windows.forEach(function(window) {
    window.tabs.forEach(function(tab) {
        // Skip 'about' and 'file' entries:
        if (tab.entries && tab.entries[0].url.indexOf("http") === 0) {
            console.log(tab.entries[0].url);
        }
    })
});

// LICENSE: 
// https://creativecommons.org/licenses/by/4.0/
// 
// This is free software released under the CC-BY license.  Users of
// this software enjoy the following rights and responsibilities:
// 
// Share — You may copy and redistribute the material in any medium or format
//
// Adapt — You may remix, transform, and build upon the material for
// any purpose, even commercially.
// 
// Attribution — You must give appropriate credit, provide a link to
// the license, and indicate if changes were made. You may do so in any
// reasonable manner, but not in any way that suggests the licensor
// endorses you or your use.
// 
// You may not employ technological measures or legal terms that
// legally prevent others from doing anything the license permits.  THE
// SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.