How to prevent a New Browser instance everytime I press my add button

I have a HTML form with a combo box and a add button
Whatever I add is displayed again in the same form
But I find that for each add I click it opens a new browser instance becoz of which when I press back I find
the number of Html forms equivalent to my number of times I press add.
Why is this happening
It does not happen in the examples I checked
How to avoid this
I am using a JSP file which repatedly calls itself using
a servlet.
Please help me