Hi, by saying :

I followed your instructions to restore bookmarks from the saved folder Firefox created ( on the desktop )

I do not know which ones you followed. Or where you got the information f from. If the browser was closed when you were working with the files or not. More information is really good.

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

You can copy files like these with Firefox closed to the current profile folder to recover specific data.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

and

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data
• https://support.mozilla.org/en-US/kb/recover-lost-or-missing-bookmarks
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox
• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

What's What in the Profile :

• bookmarks and history: places.sqlite
• bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder
• cookies.sqlite for the Cookies
• formhistory.sqlite for saved autocomplete Form Data
• logins.json (passwords) and key4.db (58+) or key3.db (57 and older) (decryption key) for Passwords saved in the Password Manager
• if you only have key3.db then make sure to remove an existing key4.db
• cert9.db (58+) or cert8.db (57 and older) for (intermediate) certificates stored in the Certificate Manager
• if you only have cert8.db then make sure to remove an existing cert9.db
• persdict.dat for words you added to the spelling checker dictionary
• permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences)
• sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)

fyi for the future :

• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

If still need help please supply the information listed at the top and what you have done with the new information, Thank You.

The "cannot process" message could indicate a problem either with the backup file or with the database Firefox is trying restore the file to. Let's start with the backup file.

Could you open this page on my site:

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

If you position your old bookmarkbackups folder so you can see the page behind it, you can drag-and-drop a backup you want to restore onto the white box on the page.

If the file is decompressed successfully, you should see some readable text in the box. So far so good?

Next, under JSON "Backup" Format click the Check/Repair JSON button. Does it reporting finding any issues? If it found issues, save a new JSON file using the "Save JSON" button.

Try restoring that file to see whether it can be processed. As with the backups you already tried, you'll use Choose File from the Restore menu to load it: Restore bookmarks from backup or move them to another computer.

If the new JSON file cannot be processed, either, let's move on to the HTML "Export" Format section. Click the "Export HTML" button to create an HTML-format export file.

Then you can use the Import feature to bring in that file, assuming it works: Import Bookmarks from an HTML file.

Any luck?