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 this._scrollMode;
  }
  /**
   * @param {number} mode - The direction in which the document pages should be
   *   laid out within the scrolling container.
   *   The constants from {ScrollMode} should be used.
   */
  set scrollMode(mode) {
    if (this._scrollMode === mode) {
      return; 
    }
    if (!isValidScrollMode(mode)) {
      throw new Error(`Invalid scroll mode: ${mode}`);
    }
    this._scrollMode = mode;
    this.eventBus.dispatch("scrollmodechanged", { source: this, mode });
    this._updateScrollMode( this._currentPageNumber);
  }
  _updateScrollMode(pageNumber = null) {