Redbaron2: Your code is in the bottom of your pages before the </body> tag.
Yes its is. I've pasted both codes as indicated on the install instructions. This one is supposed to be pasted there on tpl_main_page.php. Perhaps you're refering to the one to be pasted on html_header.php before </head>...

The body tag on tpl_main_page.php also includes the onload code.

I don't understand why the code doesn't show on the product pages source only.

Do you know what's wrong?