Sidebar auto hide isn't a standard feature in Firefox. Which extensions did you install?

Thanks for responding but I found the setting.

This is an example of a useless page on the internet. A question is posed, someone tries to answer it, then the initial poster figures it out on his/her own, providing absolutely no information for anyone else who might be having a similar issue. I created an account just to say that.

By the way, I wanted to auto-hide my vertical tab bar. The extension is 'auto-hide tabbar' and it works with both 'vert tabbar' and 'treestyle tab'--all you have to do is right-click the tabbar, and un-check auto-hide.