The Firefox Button acts as an alternative to the regular menubar (File, Edit, View etc.), so if you can see the menu bar you're not missing any functionality.

On Windows XP the default is for the menubar to be shown instead of the Firefox button, but you can switch between the button and the menubar via the View -> Toolbars -> Menu bar option.

With the Button enabled, you can access the regular menubar by pressing the Alt key.

More details here: https://support.mozilla.com/en-US/kb/how-do-i-get-firefox-button

Windows XP does not force the Firefox button on you because XP does not have Aero. You can turn it on by unchecking menu. View ("Alt+V") -> Toolbars -> (uncheck) menu bar. It was intended to be mutually exclusive to the menu bar -- it can't be and is not if you have put other things on the menu bar. To turn it off reverse the above.

You can have all of your toolbars and toolbars you're used to as long as you include the bookmarks toolbar you would use the same vertical space with minimal styling, so I see no point to giving up toolbars on a desktop computer or laptop computer.

If you're a bit near sighted, have good hand-eye coordination you can use the styling changes, I use

• http://dmcritchie.mvps.org/firefox/firefox-problems.htm#fx4
• http://kb.mozillazine.org/User:Dmcritchie