You could use sync to share the data with a computer profile, and do anything you want from there.

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.

The mobile bookmarks sync with my windows 10 desktop Firefox without a problem. They appear in the desktop bookmarks menu, and I can use them just fine, but they don't show up in an HTML export. Head scratcher

You will have to do a copy and paste to get bookmarks in the mobile bookmarks folder in a real bookmarks folder and have them included in a backup.

Does the JSON file contain the mobile bookmarks? You could answer that by running the file through my converter:

https://www.jeffersonscher.com/ffu/bookbackreader.html

If you try it, please let me know.

I do see a mobile root folder in an automatically created JSON backup:

• {"guid":"mobile______","title":"mobile",....,"root":"mobileFolder" }