LibreOffice become default since Ubuntu 11.04 Natty. As a main feature in Ubuntu Natty, Global Menu’s not supported by default in LibreOffice. However, there’s a simple extension for LibreOffice to make Global Menu back.
Open a terminal window under Applications -> Accessories menu, and run this command:
sudo apt-get install lo-menubar
Restart LibreOffice and see the global menu:
