Meteor.user() undefined in Firefox

Meteor.user(), when logged in, does not work in Firefox 43.0.4, only works in Chrome:

Foo = React.createClass({
 getInitialState() {
  var u = Meteor.user();
  console.log(u); // undefined in Firefox but works in Chrome.
  
  return{name: ''}
 }
...
});

Server:

Meteor.publish(null, function () {
  if (this.userId) {
    return Meteor.users.find({_id: this.userId},
                             {fields: {'regtype': 1, 'profile': 1}});
  } else {
    this.ready();
  }
});

Am I doing something wrong?