Thread:Project:Support desk/RL: Eliminate render-blocking JavaScript and CSS in above-the-fold content

Pagespeed Insight returns the warning: "Eliminate render-blocking JavaScript and CSS in above-the-fold content".

This mainly affects the JS in the header from RL.

E.g. on https://www.mediawiki.org/wiki/Manual:Contents:

Why not on Wikipedia? Example: http://en.wikipedia.org/wiki/Diff

How can I fix it for my own wiki?