Do a file search for bookmarks.html. That is where Firefox keeps all the favorites information. If you find the file, you can just copy it where the current file is. Make sure Firefox is not running when you do this.

I'm a bit confused what happened to cause you to lose the bookmarks. Did you also lose other settings?

Finally, I use a bookmark backup Firefox extension to keep multiple copies of the bookmark file. It just works, and I feel better knowing I have seven copies of the file handy.