Please read Preferences are not saved, let me know if it helps.

Which security software (firewall, anti-virus) do you have?

Some security software has virtualization features that can cause problems by protecting and restoring files in the Firefox profile folder.

I tried to delete prefs.js, but was unable to because it was corrupted.

I have Malwarebytes' Anti-Malware. I haven't run it since the upgrade, if that matters.

You can do a disk check with the chkdsk.exe program.

If you run the chkdsk.exe program from a cmd.exe Command window then you can read the response from the chkdsk.exe program.

Open a cmd.exe window:
Start > Run: cmd.exe <press Enter>
At the command prompt (>) type or Copy&Paste: chkdsk.exe /f /r <press Enter> (put a space before /f and /r)

If you get something like: Would you like to schedule this volume to be checked the next time the system restarts? y/n then answer the question with "Y" and close all programs and reboot the computer.