Firefox keeps several bookmark backup files, maybe up to 2 weeks, but if even the oldest backup is corrupted in the same way, then you would need to look for other kinds of backups.

Windows often captures snapshots of Firefox profile folders when it installs updates. Here are the steps to investigate those:

(1) Set Windows to show hidden files and folders before diving in:

https://support.microsoft.com/en-us/windows/view-hidden-files-and-folders-in-windows-97fbc472-c603-9d90-91d0-1166d1d9f4b5

(2) Install a utility program that makes it easy to access restore points (this is much safer than using system restore). For example:

• ShadowExplorer: http://www.shadowexplorer.com/
• Shadow Copy View: https://www.nirsoft.net/utils/shadow_copy_view.html

(3) Using that program, open a restore point that is a little older than you earliest backup and explore along this path to see whether you can find a shadow copy of your profile:

\Users\your-user-name\AppData\Roaming\Mozilla\Firefox\Profiles\your.profile

Check for the bookmarkbackups folder. The files in that folder should have their creation dates coded into the file names. You can export one or more recent files to your Windows desktop (the live one, not the one in the shadow copy).

(4) Bookmark backup preview/restoration

Because bookmark backups are compressed, you could consider using my converter back to make it into an HTML "Export" format file (which can be opened as a web page). That is located here:

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

Alternately, or after you find one that has valid addresses, you can use the steps in the following article to restore it, rolling back your current set of bookmarks to the ones in the backup file:

Restore bookmarks from backup or move them to another computer

(Note: you can use "Choose File" to point Firefox to your Windows desktop where you exported the backup files.)

If you use Sync, best is to disconnect Sync temporarily during troubleshooting.

This could be a problem with the places.sqlite and favicons.sqlite files in the Firefox profile folder.

• use the "Places Database" -> "Verify Integrity" button on the "Help -> More Troubleshooting Information" (about:support) page

If errors are reported with "Verify Integrity", close and restart Firefox or reboot and retry.

If "Verify Integrity" cannot repair places.sqlite, rename/remove all places.sqlite and favicons.sqlite files in the Firefox profile folder with Firefox closed. Firefox will rebuild places.sqlite and restore the bookmarks from the most recent JSON backup in the bookmarkbackups folder.

• keep a backup copy of places.sqlite in case a new places.sqlite database has to be created
• you lose the history when a new places.sqlite is created

You may have to restore an older bookmarks backup in the bookmarkbackups folder via the Bookmarks Manager (Library).

• Bookmarks -> Manage Bookmarks -> Import & Backup -> Restore
• https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them

See also:

• https://support.mozilla.org/en-US/kb/fix-bookmarks-and-history-will-not-be-functional
• https://support.mozilla.org/en-US/kb/cant-add-change-or-save-bookmarks

You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data