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)

constructor() {
    throw new Error("Cannot initialize DefaultExternalServices.");
  }
  static updateFindControlState(data) {}
  static updateFindMatchesCount(data) {}
  static initPassiveLoading(callbacks) {}
  static async fallback(data) {}
  static reportTelemetry(data) {}
  static createDownloadManager(options) {
    throw new Error("Not implemented: createDownloadManager");
  }
  static createPreferences() {
    throw new Error("Not implemented: createPreferences");
  }
  static createL10n(options) {