Thank you

What happened? I was browsing, then firefox locked up. I tried to switch tabs, and nothing happened. I then shut down firefox, and then restarted. It restarted in default mode with factory settings, losing all add-ons,i.e. download helper, accuweather, add blocker,etc, and all passwords. I have spent the last hour trying to reclaim everything, and firefox will not cooperate. Settings continue to revert to reset. It will not accept changing my search engine. What has happened?