Preload CSS file not supported on Firefox and Mac Safari

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

   <link rel='preload' onload='this.rel="stylesheet"' as='style'
id='reworldmedia-style-css'  href='style.css' type='text/css' media='all'
/>

It works fine in Chrome but not in Safari or Firefox


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