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 (spread === null) {
          spread = document.createElement("div");
          spread.className = "spread";
          viewer.appendChild(spread);
        } else if (i % 2 === parity) {
          spread = spread.cloneNode(false);
          viewer.appendChild(spread);
        }
        spread.appendChild(pages[i].div);
      }
    }
    if (!pageNumber) {
      return;
    }
    if (this._currentScaleValue && isNaN(this._currentScaleValue)) {
      this._setScale(this._currentScaleValue, true);
    }
    this._setCurrentPageNumber(pageNumber,  true);
    this.update();
  }
  /**
   * @private
   */
  _getPageAdvance(currentPageNumber, previous = false) {
    if (this.isInPresentationMode) {
      return 1;
    }
    switch (this._scrollMode) {
      case ScrollMode.WRAPPED: {
        const { views } = this._getVisiblePages(),