Did you try the info command as suggested in the readme file on that page?

Think about using sync.

Type about:accounts<enter> in the address bar. [57+] https://accounts.firefox.com/settings

https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer Sync your bookmarks, history, passwords, add-ons and open tabs with another copy of Firefox. Learn how to set up Sync.

https://support.mozilla.org/en-US/kb/how-do-i-choose-what-types-information-sync-firefox We'll show you how to choose which types of information (bookmarks, history, add-ons, and passwords) to share across all your devices through Firefox Sync.

https://support.mozilla.org/en-US/kb/firefox-sync-troubleshooting-and-tips

https://support.mozilla.org/en-US/kb/sync-firefox-bookmarks-and-browsing-history-iOS Sync your passwords, history, tabs and other browsing information across your iOS, Android and desktop computers with Firefox Accounts.

Here's the thing, I have synced and it hasn't modified my places.sqlite file for whatever reason, at least doesn't appear to have so it feels like it doesn't become locally saved after the sync is finished. Moreover it requires that I have every version of Firefox installed that I want to sync with, rather than just using the places.sqlite files I have had backedup at various times. So I'd prefer not to go that route. I tried the info command, which returned that the places.sqlite files were incompatible as I said. I'm not sure why, but that's the issue.

It looks like every other version of Quantum changes the format of the data files, making them not backward compatible.

Sync does not care about the versions, as long as the data being synced is compatible with each member of the sync. Bookmarks, passwords, history are comparable.

As I said, sync requires that I install each version of Firefox that I have places.sqlite files for in order to load them, and then sync them. That is a terrible option.