After updating Firefox, all my bookmarks disappeared, the backup file is nearly empty, and they're not syncing from my account—is there any way to recover them?

I updated Firefox a few minutes ago and closed everything to let it finish. When I reopened it, all my bookmarks were gone. I checked the restore option in the Bookmarks menu, but only today's date was available, and clicking it did nothing. I found the bookmarkbackups folder in my profile directory, but there's only one file—859 bytes, which is basically empty. I'm signed into a Firefox account now, but my bookmarks aren't syncing from the server, which suggests they were never synced. Is there any way to recover them, or are they just gone?