A Mozilla engineer has revealed one of the hidden techniques that Firefox 57, known as Quantum, is using to improve page load times: it delays scripts from tracking domains, such as www.google-analytics.com, in a technique dubbed “tailing.” Tailing only briefly prevents the tracking scripts loading, rather than disabling them entirely.



This has a positive effect on page load performance, as we save some of the network bandwidth, I/O, and CPU for loading and processing of images and scripts running on the site so the web page is complete and ready sooner. For sites that are either not well built or have rendering influenced by scripts from tracking domains, there can be a visible or even functional regression.

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Source: [H]ardOCP – Mozilla Reveals a Tweak That Turbo-Charged Its Browser