browsers.hbs

{{#if pendingNewBrowser}}
  {{browser-form browser=pendingNewBrowser
    save=saveNewBrowser}}
  etc.
{{else}}
  <button {{action 'createNewBrowser'}}>Add a browser</button>
{{/if}}

browsers.js

import Ember from 'ember';

export default Ember.Controller({
  //in this hypothetical example, there's no new browser until somebody
  //asks for one
  pendingNewBrowser: null,
  actions: {
    createNewBrowser() {
      this.set('pendingNewBrowser', this.store.createRecord('browser')));
    },
    
    saveNewBrowser() {
      this.get('pendingNewBrowser').save()
      .then(() => this.set('pendingNewBrowser', null));
    }
  }
});