Buttons in the navigation bar are moved around.
The Home button is to the far right of the search bar (Google..Yahoo..etc) and the Refresh button and Cancel button (X) are between the search bar and the WWW (World Wide Web) browser bar.
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You can move them to where you want, for details see the Customize Firefox controls, buttons and toolbars article. They would have been moved when you used Firefox 4 beta, if you plan to use both Firefox 3.6.13 and the Firefox 4 beta you should create a new profile (location where user data is stored) for Firefox 4 beta. Using the same profile for different versions can cause problems.
For details on doing that see these links: