Just last week I installed a Chrome extension called Privacy Badger. It is supposed to protect you from third party scripts included on websites that might track you. It does that by checking content loaded from other third-party domains. The side effect of this extension was that you suddenly begin to notice which sites include external scripts. I’d say I am not surprised by them on social media sites and other sites where I mostly consume the content. They are used for videos hosted on on YouTube, Facebook Like buttons, Disqus comment sections and so on.
Dear companies, please serve all scripts from servers under your control. Saving some kilobytes of data traffic is not worth the risk of exposing your users to malicious code!