Preload CSS file not supported on Firefox and Safari Mac

Question

I added the attribute rel=\"preload\" to all css links like this :

Answer 1

For Firefox, it's only supported in Firefox 56 Nightly. It will ship on September 26, 2017. You can download it from here.

Update: This feature is landed on FF 56 but removed in 57. Here is the reason:

This feature was available in Firefox 56, but only for cacheable resources. It has been disabled in Firefox 57 because of various web compatibility issues (e.g. bug 1405761). An improved version that works for non-cacheable resources is expected to land in Firefox 59