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)

if (!smask.transferMap && webGLContext.isEnabled) {
      const composed = webGLContext.composeSMask({
        layer: layerCtx.canvas,
        mask,
        properties: {
          subtype: smask.subtype,
          backdrop,
        },
      });
      ctx.setTransform(1, 0, 0, 1, 0, 0);
      ctx.drawImage(composed, smask.offsetX, smask.offsetY);
      return;
    }
    genericComposeSMask(
      maskCtx,
      layerCtx,
      mask.width,
      mask.height,
      smask.subtype,
      backdrop,
      smask.transferMap
    );
    ctx.drawImage(mask, 0, 0);
  }
  const LINE_CAP_STYLES = ["butt", "round", "square"];
  const LINE_JOIN_STYLES = ["miter", "round", "bevel"];
  const NORMAL_CLIP = {};
  const EO_CLIP = {};
  
  class CanvasGraphics {