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 (!this.contentVisible) {
        return;
      }
      this.groupLevel--;
      const groupCtx = this.ctx;
      this.ctx = this.groupStack.pop();
      
      
      if (this.ctx.imageSmoothingEnabled !== undefined) {
        this.ctx.imageSmoothingEnabled = false;
      } else {
        this.ctx.mozImageSmoothingEnabled = false;
      }
      if (group.smask) {
        this.tempSMask = this.smaskStack.pop();
      } else {
        this.ctx.drawImage(groupCtx.canvas, 0, 0);
      }
      this.restore();
    }
    beginAnnotations() {
      this.save();
      if (this.baseTransform) {
        this.ctx.setTransform.apply(this.ctx, this.baseTransform);
      }
    }
    endAnnotations() {