Good way to make a backup of Firefox settings?

You can sync these using Firefox's built-in Firefox Sync feature (albeit the Mozilla servers do not retain former settings, deleted bookmarks, and other old data and are not intended to serve as a "[...] true backup service [...]"):

• Bookmarks — including all tags, keywords, folders, and your custom menu order
• Passwords
• Preferences/Options of Firefox
• History of sites visited in the last 60 days
• Tabs and tab groups
• Add-ons installed on your computer or mobile device

You can set up Firefox Sync from the Sync tab of Firefox's preferences window (see support article "Share bookmarks, tabs and more with your other computers" for details).

Firefox Sync encrypts your data before sending it to Mozilla's servers, so you should keep a copy of your Recovery Key if you use the service on only a single computer and want to be able to restore your data following a hard drive failure or similar event. (However, you really should keep a full system back-up using either the utility provided with your operating system or one by a third party, which will cover more than just Firefox.)

If you want to keep old versions of the above (or anything else), you need to keep your own profile back-ups. The name of your Firefox profile folder is random, and its location varies depending on which operating system your computer runs (see support article "Back up and restore information in Firefox profiles" for details for your operating system).

Before Firefox Sync, I used MozBackup. It has a recent (beta) update after over a year. Hopefully it will be maintained.

This is what it does, according to the website:

MozBackup is a simple utility for creating backups of Mozilla Firefox, Mozilla Thunderbird, Mozilla Sunbird, Flock, SeaMonkey, Mozilla Suite, Spicebird, Songbird and Netscape profiles.

It allows you to backup and restore bookmarks, mail, contacts, history, extensions, passwords, cache etc. It's an easy way to do Firefox backup, Thunderbird backup ...

I use: Firefox Environment Backup Extension — it works great.

FEBE (Firefox Environment Backup Extension) allows you to quickly and easily backup your Firefox extensions. In fact, it goes beyond just backing up -- It will actually rebuild your extensions individually into installable .xpi files.

Here's the Mozilla Add-on page for FEBE.