Mozilla Labs: Prospector - LessChrome HD is a Firefox extension, can get more browsing space in Firefox, show less chrome by default unless its needed.
The core feature here is to give as much space to the page and only showing the browser interface when needed.
The default browsing behavior now is to only show tabs at the top of the window, and pointing there will reveal the rest of the browser. Moving the mouse cursor back down makes it go away.

Requirements:
* Firefox

The license of this software is Free, you can free download and free use this browser plug-ins software.