at the end of the address bar small button

thanks

Firefox 4 uses a combined Stop/Reload/Go button that is positioned at the right end side of the location bar.
During the page load process it shows as a Stop button and after the loading has finished the button is changed to a Reload button.
If you type in the location bar then that button becomes a Go button.

You can middle-click that Reload button to duplicate the current tab to a new tab.