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.pdfDocument) {
      return false;
    }
    if (
      !(
        Number.isInteger(pageNumber) &&
        pageNumber > 0 &&
        pageNumber <= this.pagesCount
      )
    ) {
      console.error(
        `${this._name}.isPageVisible: "${pageNumber}" is not a valid page.`
      );
      return false;
    }
    return this._getVisiblePages().views.some(function (view) {
      return view.id === pageNumber;
    });
  }
  /**
   * @param {number} pageNumber
   */
  isPageCached(pageNumber) {