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)

this.externalServices.reportTelemetry({
      type: "unsupportedFeature",
      featureId,
    });
    
    
    if (this._fellback) {
      return;
    }
    this._fellback = true;
    this.externalServices
      .fallback({
        featureId,
        url: this.baseUrl,
      })
      .then(download => {
        if (!download) {
          return;
        }
        this.download({ sourceEventType: "download" });
      });
  },
  /**
   * Show the error box; used for errors affecting loading and/or parsing of
   * the entire PDF document.
   */
  _documentError(message, moreInfo = null) {