New Twiddle

components.input-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  name: 'Ben',
  result: '',
  
  didInsertElement() {
    let input = this.$('input')[0];
    this.set('result', `
			input.selectionStart: ${input.selectionStart}, 
			input.selectionEnd: ${input.selectionEnd}`
    );
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

templates.application.hbs

<span style="background-color: yellow;">In Chrome, the `input.selectionStart` and `input.selectionEnd` will have correct values of 3 after the component renders. In Firefox, they are both 0.</span>
<hr />
{{input-component}}

templates.components.input-component.hbs

input: {{input type="text" value=name}}

<hr />
<pre>{{result}}</pre>

twiddle.json

{
  "version": "0.7.2",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.4.4/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.4.3/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.4.4/ember-template-compiler.js"
  }
}