Back Button doesn't work When I open the page(containing back button) in the new tab/window.

I have a content type called "Materials" where users put their Material stuff which can be seen and used by anyone.
I have used a back button. At the moment I am using this code for the back button.

<p><a href="#" onclick="history.go(-1);return false;">Go Back</a></p>

The problem is, When I open any material stufff (link) on the same page, back button works as it is supposed to. But when I open the same link in the new tab/window, "Back" button doesn't work.

Here is the link, if you want to try to understand my question.
http://egitraining.esc.rl.ac.uk/online_training

I assume I need to make some changes to the code I am using, as this code looks in the history and goes to (-1) webpage.
Can anyone help me with this?

Thanks