This tutorial shows how to disable the global menu, so that each application having its own menu bar on Ubuntu 13.10 Saucy.
To do it, press Ctrl+Alt+T on your keyboard to open terminal. When it opens, run the commands below to disable it.
sudo apt-get remove indicator-appmenu
Restart your computer to apply the changes.
For Firefox, go to Tools –> Add-ons –> Extensions and disable ‘Global Menu Bar integration’.