This is very confusing as seen in #12974 or #12906. My suggestion would be "legacy."
BUNDLE_BUILD: versionInfo.commit,
    TESTING: defines.TESTING || process.env.TESTING === "true",
  });
  var licenseHeaderLibre = fs
    .readFileSync("./src/license_header_libre.js")
    .toString();
  var enableSourceMaps =
    !bundleDefines.MOZCENTRAL &&
    !bundleDefines.CHROME &&
    !bundleDefines.LIB &&
    !bundleDefines.TESTING &&
    !disableSourceMaps;
  var skipBabel = bundleDefines.SKIP_BABEL;
  
  
  
  
  const babelExcludes = [
    "node_modules[\\\\\\/]core-js",
    "node_modules[\\\\\\/]web-streams-polyfill",
  ];
  if (enableSourceMaps) {
    babelExcludes.push("src[\\\\\\/]core[\\\\\\/](glyphlist|unicode)");
  }
  const babelExcludeRegExp = new RegExp(`(${babelExcludes.join("|")})`);
  
  
  
  const babelPlugins = [
    "@babel/plugin-transform-modules-commonjs",