Don't use WP_PLUGIN_URL

Please DON’T use “WP_PLUGIN_URL.” in sharethis.php because it’s not SSL aware. When in the back-end admin panel via HTTPS (which means all the time if FORCE_SSL_ADMIN is set!), the ShareThis admin entirely fails to load.

So instead of this:
$plugin_location=WP_PLUGIN_URL.'/'.str_replace(basename( _FILE__),"",plugin_basename(__FILE__));

You’ll want this:
$plugin_location=plugins_url().'/'.str_replace(basename( __FILE__),"",plugin_basename(__FILE__));

All requests to Google-hosted libraries are like this:

src="http://ajax.googleapis.com/..."

Should be protocol-relative, like this:

src="//ajax.googleapis.com/..."

And all requests to src="http://w.sharethis.com/..." should be like this instead: src="https://ws.sharethis.com/...". You don’t need to do conditional SSL detection here, as there’s a low volume of requests for these files, and they can all just go through the ST SSL servers.

Thanks!

https://wordpress.org/plugins/share-this/