I have lost all of my bookmarks and the bookmark categories I made for my toolbar. When I go to "backup" they aren't there either. This happened after my laptop froze, I restarted it, and was asked to sign in to my Firefox account upon opening up the browser.
Did you check older backup in the bookmarkbackups folder as it is possible that the most recent backup(s) are already missing those bookmarks ?
The name of an automatically created JSON bookmarks backup in the bookmarkbackups folder includes a total item count (folders and separators included) and an hash value to prevent saving the same backup more than once. You also see this count in the Restore menu drop-down list. That should allow you to choose a backup that has the lost bookmarks.
- bookmarks-YYYY-MM-DD_<item count>_<hash>.jsonlz4.
You may have to check for issues with places.sqlite.
If you use Sync then best is to disconnect Sync temporarily during troubleshooting.
This can be caused by a problem with the places.sqlite and favicons.sqlite databases in the Firefox profile folder.
- use "Verify Integrity" button on the "Help -> Troubleshooting Information" (about:support) page
If errors are reported with "Verify Integrity", close and restart Firefox or reboot and retry.