Mechanisms. Given that 91% of pages make third-party HTTP requests, it is helpful to know what exactly is being requested. Many third-party requests lack extensions, and when viewed in a browser display only blank pages that generate HTTP requests and may also manipulate browser caches. Such requests accounted for 47% of the top 100 requests and may point toward emerging trends in the ongoing contest between user preferences and tracking techniques. The second most popular type of requested elements were JavaScript files (33%). These files are able to execute arbitrary code in a user’s browser and may be used to perform fingerprinting techniques, manipulate caches and HTML5 storage, as well as initiate additional requests. The third most popular type of content is the tried-and-true image file, which