When you press the Back Button in your browser the previous page is not rendered again but is fetched from the browser cache and is shown to you in the browser.
Unfortunately, this behavior cannot be modified as it is being handled by PrestaShop. The product IDs are fetched from the URL and they are shown on the product compare page. For example:
The above URL means that the products that are compared are 1,2 and 3. The parameter `compare_product_list` is used for fetching the product IDs the parameter means 1|2|3