Accidentally screwed up Firefox's UI, how to undo the change?

[A Bad Day]

I accidentally pressed a combination of keys, which changed the UI from the default type.

Here's what my messed up UI looks like:

Here's what it used to look like (Btw, I'm using Windows 7, Classic theme. I've also disabled the Aero glass eyecandy before the UI screwup):

 

[Hawkeye22]

View->Toolbar->menu bar

remove the checkmark from menu bar.