Do you have a menu bar at the top of the firefox window? If not, I think you hover your mouse where it should be, and right click, and a menu pops up, there should be Menu bar as one of the items, select this. The other way is Alt "M".
Or over on the right side of the window is this little gear shaped icon, it is Open Options, there the menu for options opens in a new tab.
Hope this helps, it sucks that firefox install does not have the menu bar open by default.