blocking="render" attribute on <link>, <script> and <style> #608

Request for Mozilla Position on an Emerging Web Specification

• Specification Title: blocking="render" attribute on <link>, <script> and <style>
• Specification or proposal URL: https://html.spec.whatwg.org/multipage/urls-and-fetching.html#blocking-attributes
  • Full proposal: https://gist.github.com/xiaochengh/9404abbecdc3b45c0e9f3d5e99fbc65d
  • WHATWG discussion: Feature proposal: blocking="render" attribute on <link>, <script> and <style> whatwg/html#7131
• Caniuse.com URL (optional):
• Bugzilla URL (optional): https://bugzilla.mozilla.org/show_bug.cgi?id=1751383
• Mozillians who can provide input (optional):

Other information

This proposal also includes the standardization of a general render-blocking mechanism, which will standardize the existing stylesheet loading behaviors and support the proposed attribute. The proposed behavior slightly differs from Firefox's current behavior: the proposal does not allow requestAnimationFrame() callbacks to fire until all render-blocking stylesheets are loaded, while Firefox currently allows it.