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)

unreachable("Should not call beginImageData");
    }
    paintFormXObjectBegin(matrix, bbox) {
      if (!this.contentVisible) {
        return;
      }
      this.save();
      this.baseTransformStack.push(this.baseTransform);
      if (Array.isArray(matrix) && matrix.length === 6) {
        this.transform.apply(this, matrix);
      }
      this.baseTransform = this.ctx.mozCurrentTransform;
      if (bbox) {
        const width = bbox[2] - bbox[0];
        const height = bbox[3] - bbox[1];
        this.ctx.rect(bbox[0], bbox[1], width, height);
        this.clip();
        this.endPath();
      }
    }
    paintFormXObjectEnd() {
      if (!this.contentVisible) {
        return;
      }
      this.restore();
      this.baseTransform = this.baseTransformStack.pop();
    }
    beginGroup(group) {