Firefox won't open

Is there a way to restore it to factory settings without losing personal data?

not doing a factory restore, it will make your computer back to how it came outr the box, BEFORE ANY DATA

have you tried uninstalling the version you are running now, downloading and installing another version and see if it loads? a few days back i faced a strange issue after applying update to version 11 after an extension update. i would double click firefox the screen would show for a second and kept going away. i uninstalled, reinstalled rebooted it wouldnt come back. opened task manager to see if its there in processes. seeing that it was not there i decided to go back to version 10.2. it ran fine, but now im on version 12 currently with no issues.