Firefox 4 and later use a combined Stop/Reload/Go button that is positioned at the right end 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. So if Firefox is loading a site and you don't want it anymore, you can press the Stop button and then the loading should stop.

Thank you, "knorretje", for answering my question so promptly and giving me just the answer I was looking for. I had never noticed that the reload button changed function.

Thank you, again!