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 http://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.
It must be noted that much of mozilla communication is just PR and marketing, maybe this is damage control, but somehow I think they are not well organized enough to have this kind of thing happen.
Besides how is this helping with privacy ? Trackers are still loaded and tracking.