One possibility is that a couple of individual files became corrupted. This can be hard to recover from. Let's check the other possibility first: that Firefox wasn't able to use your normal profile so it created a fresh one.

Profile Manager Page

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

This page should list at least one profile and could list many. (Each profile has two folders and one or more buttons. Do not use any Remove buttons!)

The profile that Firefox is currently using will have this:

This is the profile in use and it cannot be deleted.

Do you have any other profile(s) 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, back on the about:profiles page, click the Set as default profile button for that profile so Firefox uses it automatically at the next startup.

Any progress so far?

Thanks for this feedback. I was able to sign into my user account and (eventually) I see now that most of the Settings have been restored minus the previous Tabs and Pinned Tabs, so I'm starting fresh now. :) Thanks again. . . good enough for now! Steve