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)

return getComputedStyle(this.container).direction === "rtl";
  }
  get isInPresentationMode() {
    return this.presentationModeState === PresentationModeState.FULLSCREEN;
  }
  get isChangingPresentationMode() {
    return this.presentationModeState === PresentationModeState.CHANGING;
  }
  get isHorizontalScrollbarEnabled() {
    return this.isInPresentationMode
      ? false
      : this.container.scrollWidth > this.container.clientWidth;
  }
  get isVerticalScrollbarEnabled() {
    return this.isInPresentationMode
      ? false
      : this.container.scrollHeight > this.container.clientHeight;
  }
  /**
   * Helper method for `this._getVisiblePages`. Should only ever be used when
   * the viewer can only display a single page at a time, for example in:
   *  - `PDFSinglePageViewer`.
   *  - `PDFViewer` with Presentation Mode active.
   */
  _getCurrentVisiblePage() {