SnapBack button in Safari allows to return to first page you visited from your history of current window or tab, a recent Safari 5.0.2 update removed SnapBack button feature, users started noticing that SnapBack button no longer exists in Safari, fortunately SnapBack extension brings this feature back to Safari.
SnapBack extension developer description “ SnapBack brings back the SnapBack button to the smart address field d in Safari, so you jump back to the first page in the history of the current window or tab, or to the page you marked from Contextual menu.”
You can install SnapBack Safari extension from Safari extensions gallery under productivity category. You need to restart Safari after installing SnapBack, for the extension to work.