Even the browsers own back buttons don't do what you want. When you hit the back button (browser or Zen Cart), the previous page is reloaded starting at the top with no marker as to where you where.

So I'm afraid that there is no way of returning to a specific point on a page, other than to substantially re-write the app to add lots of anchor tags and then keep track of and use them when navigating between pages - a completely disproportionate piece of work.