Mini-buffer is a folder navigation tool in ROX filer. It is a bar that appears at the bottom of a filer window when '/' is pressed - it allows you to jump to a different folders. Pressing 'Esc' to closes it.

Start typing the folder you require. ROX will highlight the closest match, pressing 'Enter' opens the highlighted directory.
Shortcuts-

• Pressing 'Up, Down' - highlights the previous/next matching entry
• Pressing 'Tab' will open the directory if there is only one name matching the letters typed, otherwise it will beep.

ROX filer
ROX homepage
ROX on Barry's Blog
ROX-Filer Modification
How to change sort from horizontal to vertical