catacaustic on "Remove third party plugin from single page"

The problem that you have is that you didn't add that snippet inside a <style> tag. What you've got now iw:

<style type="text/css" media="screen">.socialize-floating { margin-left: -105px; }</style>
.postid-966 #optin {
    display: none;
}

What it needs to be is:

<style type="text/css" media="screen">.socialize-floating { margin-left: -105px; }
.postid-966 #optin {
    display: none;
}</style>

You can either do it that way or add it to your style.css stylesheet (without the tags). Both ways will work. :)