I was wondering if WebGL is considered stable enough to be enabled by default. It makes some PDFs render much faster and it has been off by default for a while now, so we have had quite some time to test it.

If we decide to enable WebGL by default, we should not forget to update https://github.com/mozilla/pdf.js/blob/master/extensions/chromium/preferences_schema.json#L39 as well.

/cc @yurydelendik 
/cc @Snuffleupagus (because IIRC you were testing WebGL too)

const width = this.viewport.width;
    const height = this.viewport.height;
    const div = this.div;
    target.style.width = target.parentNode.style.width = div.style.width =
      Math.floor(width) + "px";
    target.style.height = target.parentNode.style.height = div.style.height =
      Math.floor(height) + "px";
    
    const relativeRotation =
      this.viewport.rotation - this.paintedViewportMap.get(target).rotation;
    const absRotation = Math.abs(relativeRotation);
    let scaleX = 1,
      scaleY = 1;
    if (absRotation === 90 || absRotation === 270) {