My bookmarks toolbar reverted this morning to an old set of bookmarks. My firefox was also upgraded today.
Today when I started firefox, I was greeted to a version update screen. I also noticed that my bookmarks toolbar was reset to an old set of bookmarks that I previously used with the foxmarks add on. After I had removed foxmarks, I changed my bookmarks toolbar, and now it was reset to the old set of bookmarks, seemingly with the version upgrade.