Presumably this occurs when the site uses a CDN for their js libraries (or even their main js). After a few days you start to spot which domains need to be enabled and which can be safely ignored.
Best i recall, even if you whitelist a CDN it only comes into action if you whitelist the root domain of the site you are visiting.
Beyond that i guess there is GRE, where you can build "firewall" rules.
For example i have Facebook blocked via it unless i visit Facebook.com directly, thus they don't see me browsing all manner of sites via their like buttons and comment boxes.
