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 (
      (typeof PDFJSDev === "undefined" ||
        PDFJSDev.test("!PRODUCTION || GENERIC")) &&
      "locale" in hashParams
    ) {
      AppOptions.set("locale", hashParams.locale);
    }
    if (waitOn.length === 0) {
      return undefined;
    }
    return Promise.all(waitOn).catch(reason => {
      console.error(`_parseHashParameters: "${reason.message}".`);
    });
  },
  /**
   * @private
   */
  async _initializeL10n() {
    this.l10n = this.externalServices.createL10n(
      typeof PDFJSDev === "undefined" || PDFJSDev.test("!PRODUCTION || GENERIC")
        ? { locale: AppOptions.get("locale") }
        : null
    );
    const dir = await this.l10n.getDirection();
    document.getElementsByTagName("html")[0].dir = dir;
  },
  /**
   * @private
   */
  _forceCssTheme() {