How do I restore my Firefox profile when I cannot even open Firefox because I receive the message "a copy of Firefox is already open?"?

I was able to use firefox, but all my bookmarks and history disappeared. Also, the forward and back arrow and refresh buttons weren't working. I followed the directions for restoring firefox profiles, and that didn't work. I wasn't able to open firefox again, and I received the message: "a copy of firefox is already open. only one copy of firefox can be open at a time." I tried closing firefox, even uninstalling it and reinstalling another file, but I still get the same message over and over again.