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

Reliably preload across browsers with loadCSS

One issue with preloading is that it is not supported by browsers like Firefox and Internet Explorer (as of Nov 2018). As a result, these browsers will not download the CSS file and this can result into serious display issues for your web-pages. This makes it critical to include a JavaScript polyfill for preload - loadCSS.

• Download the loadCSS JavaScript file or simply copy it’s JS code from here.
• Load the loadCSS polyfill wherever CSS stylesheet preload is performed:

<style>
[Your critical CSS goes here]
</style>


<!– Reliably defer loading of non-critical CSS with loadCSS–>
<link rel=“preload” href=”[yourcssfile]” as=“style” onload=“this.onload=null; this.rel=‘stylesheet’”>
<noscript><link rel=“stylesheet” href=”[yourcssfile]” ></noscript>



<!– Inline the loadCSS preload polyfill code or load it via external JS file–>
<script src=“./cssrelpreload.js”></script>