In most of the browsers, toolbars take a lot of space on the display. You can either remove/hide the toolbars or switch to Full Screen Mode.
In the latest version of Firefox (Version 2.0) the Full Screen mode will display only the Navigation Toolbar. However you are forced to switch back to the normal view if you want to access features in other hidden toolbars.
AutoHide is a nice little Firefox Extension which gives you more control of the browser in full screen mode.
Using the extension customization dialog, you can configure “Autohide” setting for individual toolbars. The plugin is intelligent in the sense that when you install a new toolbar, it will automatically show up in the configuration dialog.
The best option I liked was the “Show Status Bar on Activity“. With this option you could make the web page occupy the entire screen(100%) and also get a feedback when there is some activity in the browser (i.e. page load/refresh etc).
One more plugin added to my favorite Firefox Extensions List