I am not going to whine about developers constantly changing the interface of the most popular browser. However, my adventures in reverting Firefox to what it used to be continue. This is version 24.1.0 and the option to hide the tab bar when only a single tab is left is gone. As usual, some googling around pointed me to a discussion that led me to this plug-in.
Installed it, restarted Firefox and it behaves as before.