How do I turn on the left-hand column in my Facebook home page?

This is the column that had friends, groups, news feed, etc. It just disappeared and I can’t find it anywhere. I went to Facebook “help” but that was useless. I even tried google and that didn’t help.
Surely I am not the only person on the planet with this problem. Or am I?
I’m using Firefox 17 for Yahoo if that makes a difference.