NHGlenn said

Files all still present.

That part is very promising. Are they in a C:\Windows.old folder, or still in their original locations?

Since Firefox data is in a hidden folder, please start by setting Windows to show hidden files and folders, otherwise it's very difficult to navigate.

https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files

Then drill down through:

C:\Windows.old\Users\username\AppData\Roaming\Mozilla\Firefox\Profiles

You might only have one profile folder, or you might have several. Each profile should have a folder named bookmarkbackups containing one or more compressed backup files. These can't be easily ready except by Firefox.

Once you find a good candidate for restoration to your current Firefox, copy/paste it to your Desktop for easy access. Then try the steps in this article:

Restore bookmarks from backup or move them to another computer -- pick "Choose File" from the menu and point Firefox to your Desktop

Success?

Obviously there's more data there, but recovering it a bit trickier.

The C:\Windows.old folder may be removed within 28 days, so back up anything you feel is essential to another place.

Worked. Thanks. All bookmarks were in the back up and restored.

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