symfony plugin:install sfFormExtraPlugin

<?php
class sfWidgetFormTextareaTinyMCE extends sfWidgetFormTextarea
{
  protected function configure($options = array(), $attributes = array())
  {
    $this->addOption('theme', 'advanced');
    $this->addOption('width');
    $this->addOption('height');
    $this->addOption('config', '');
  }
  public function render($name, $value = null, $attributes = array(), $errors = array())
  {
    $attributes = array_merge($this->attributes, $attributes); 
    ...

<?php
class ContenuForm extends BaseContenuForm
{
  public function configure()
  {
      $this->widgetSchema['texte'] =  new sfWidgetFormTextareaTinyMCE(
      array(
        'width'=>550,
        'height'=>350,
        'config'=>'theme_advanced_disable: "anchor,image,cleanup,help"',
        'theme'   =>  sfConfig::get('app_tinymce_theme','advanced'),
      ),
      array(
        'class'   =>  'tiny_mce'
      )
    );
    $js_path = sfConfig::get('sf_rich_text_js_dir') ? '/'.sfConfig::get('sf_rich_text_js_dir').'/tiny_mce.js' : '/sf/tinymce/js/tiny_mce.js';
    sfContext::getInstance()->getResponse()->addJavascript($js_path);
  }
}