Hey Bruce, did this happen after updating your Firefox? You can also check whether your data is available in a different profile:

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it. The About Profiles page will open. This page should list at least one profile and could list many.

The profile that Firefox is currently using will show:
This is the profile in use and it cannot be deleted.

Please do not delete anything here; don't use any Remove buttons.

Do you have another profile named default or default-longnumber listed on this page? If so, you can check whether it is the one you were using recently by clicking its Launch profile in new browser button.

If it isn't what you want, simply close that new window.

If it IS what you want, click the Set as default profile button for that profile on the about:profiles page. Firefox will use it automatically at the next startup.

For more information see Recover user data missing after Firefox update.

Note: If your bookmarks are not available in another Firefox profile, see Recover lost or missing Bookmarks for other solutions.

I'm having the same problem as the previous person who asked about this. I've tried doing various methods for restoring the backup file from the root directory (from bookmarkbackups folder in RD), which for me is: AppData\Roaming\Mozilla\Firefox\Profiles\s4rb8h9n.default-release

Which brings me to my other question (please see appended cap of my dual? Firefox profiles). I have no idea where "Profile:default" even originated from (or when). It has no content at all in its 'bookmarkbackups' folder. To my awareness, I've never used it. I tried restarting with it, but there isn't even any user configured settings in it- it feels like a 'dummy profile' that was never used at any point in time, and there is no one who has access to my desktop other than me. It's under lock and key 24/7 with password protect and I live alone anyway.

The profile "Profile: default-release" feels natively familiar. Recognizable and identifiable/known user configurations, passwords, bookmarks, etc- all of which are mine- no question. This profile has several bookmarkbackups JZONs in it (all of small Kb level file size). I'll include a cap of that, as well, if that helps. Again- there is no method I have found for being able to restore from any of these bookmark restore JZONs.

Thank you in advance for whatever assistance you can offer, this is quite frustrating.