How do I make all my folders open in the same window, in Nautilus?

If you want to set the file manager so that it doesn’t open a new window for each folder, you can follow these steps:

1. Double-click on the “Computer” icon on your desktop.
2. Go to the “Edit” menu and choose “Preferences.”
3. Click on the “Behavior” tab.
4. Put a check in the box marked “Always open in browser windows.”

From fedorafaq.org