gecko-dev/ipc/testshell/tests/test_ipcshell_child.js

// eslint-disable-next-line mozilla/use-services
const runtime = Cc["@mozilla.org/xre/app-info;1"].getService(Ci.nsIXULRuntime);

function run_test() {
  Assert.equal(runtime.processType, Ci.nsIXULRuntime.PROCESS_TYPE_DEFAULT);
}