By default, Firefox shows Menu Bar, Navigation Toolbar, Bookmarks Toolbar at the top. They take some space and makes the view panel smaller.
If you are using a netbook or a small display, you may want to customize the toolbar to hide the less used items. To do that, right click on the Menu Bar and select "Custmize..." from the context menu.
A Customize Toolbar dialog pops up. You can drag and drop the unwanted icons (such as the Home icon) into the dialog box to remove them. You can also drag and drop the icons or the input boxes from the Navigation Toolbar to the Menu Bar to relocate them.
I prefer to move everything I need to the Menu Bar. And then hide the Navigation Toolbar and the Bookmarks Toolbar. To hide them, click menu "View" and uncheck "Navigation Toolbar" and "Bookmarks Toolbar" from the submenu.
After doing that, you may find that the Address box and Google Search box are too small. You can then install the extension Packed Menu to hide the menus if you are not so frequently using them. After the installation of Packed Menu, only an "M" menu is shown in the toolbar, and more space is given to the Address box and Google Search box. Clicking on "M" will bring you the hidden menus.
You can also install another extension Autohide Tabbar that brings you more space and privacy.