Comment 6 for bug 254307

Happy to say I found a page on support.mozilla.com that provided a way of restoring the buttons "properly":

http://support.mozilla.com/en-US/kb/Back+and+forward+or+other+toolbar+buttons+are+missing

So after following the instructions in the "Reset toolbars and controls" section, Firefox now has the title bar and all its buttons. Perhaps only a bug in that I didn't change the settings, they somehow got changed without my noticing - perhaps when I accepted the latest Firefox upgrade.