If I have AddThis Share and Follow buttons integrated on my site, is there a way to tell whether the AddThis script passes any data (such as HTTP referrer) to the social networking sites upon page load? I know AddThis gets the http referrer and can drop/view their own cookies, but I'm trying to determine exactly what the AddThis script may share with the social networking sites upon my page load (and not upon any click events).
All that is passed to the social media platforms is the URL of the page being shared as a URL parameter. The social media platforms then perform a crawl of the page in question to get the details of the page to attach to the share post. Your sites cookies and referrers are not passed along as a popup window is opened which then is redirected from the addthis server to the social media providers content sharing URL's. The referrer data they see every time is just the addthis server.