How to install a working behat (bin only) on a Symfony project

behat.yml

default:
    formatter:
        name: pretty
    paths:
        features: features
    context:
        class:  Context\FeatureContext
    extensions:
        Behat\MinkExtension\Extension:
            default_session: symfony2
            show_cmd: 'open -a Firefox.app %s'
            base_url: http://myproject.dev

        Behat\Symfony2Extension\Extension: ~

composer.json

{
    "autoload": {
        "psr-0": {
            "": "src/",
            "Context": "features/" /*don't forget this*/
        }
    },
    "require": {
        ...

        "behat/behat": "2.4.*@stable",
        "behat/mink-extension": "*",
        "behat/symfony2-extension": "*",
        "behat/mink-browserkit-driver":  "*"
    },
}

gistfile1.txt

<?php

//this file is in "features/Context/FeatureContext.php"
namespace Context;

use Behat\Behat\Exception\PendingException;
use Behat\Gherkin\Node\PyStringNode;
use Behat\Gherkin\Node\TableNode;

use Behat\MinkExtension\Context\MinkContext;
use Behat\Symfony2Extension\Context\KernelAwareInterface;

use Symfony\Component\HttpKernel\KernelInterface;

class FeatureContext extends MinkContext implements KernelAwareInterface
{
    private $kernel;

    public function __construct()
    {
      //add sub contexts here
    }

    /**
     * Sets Kernel instance.
     *
     * @param KernelInterface $kernel HttpKernel instance
     */
    public function setKernel(KernelInterface $kernel)
    {
        $this->kernel = $kernel;
    }

    /**
     * Returns Container instance.
     *
     * @return ContainerInterface
     */
    private function getContainer()
    {
        return $this->kernel->getContainer();
    }
}

homepage.feature

@homepage
Feature: Homepage working as expected (file is in features/homepage.feature)

Scenario: Homepage login
    When I go to "/"
    Then I should see "Bienvenue"