restore previous session

Firefox is prepared for that: https://support.mozilla.org/en-US/kb/restore-previous-session

Is your problem solved?

I had McAfee Customer Support help delete a virus. However, when he took control over the computer, he changed my Firefox settings. For example, I can no longer "Restore Previous Session", in spite of following directions in Support here. He also set it up so that I have to log back in to each site when the computer restarts. It's all very frustrating. How can I restore Firefox to "normalcy"? I didn't know he'd done all this until after we were done with the session. Please help!

Could you please try to install another Firefox? https://support.mozilla.org/en-US/kb/custom-installation-firefox-on-windows

If the new installation is ok, you can consider removing your old Firefox.