code: protected function checkBrowserFirefox()
      {
          if (stripos($this->_agent, 'safari') === false) {
              if (preg_match("/Firefox[\/ \(]([^ ;\)]+)/i", $this->_agent, $matches)) {
                  $this->setVersion($matches[1]);
                  $this->setBrowser(self::BROWSER_FIREFOX);
                  //Firefox on Android
                  if (stripos($this->_agent, 'Android') !== false) {
                      if (stripos($this->_agent, 'Mobile') !== false) {
                          $this->setMobile(true);
                      } else {
                          $this->setTablet(true);
                      }
                  }
                  return true;
              } else if (preg_match("/Firefox$/i", $this->_agent, $matches)) {
                  $this->setVersion("");
                  $this->setBrowser(self::BROWSER_FIREFOX);
                  return true;
              }
          }
          return false;
      }
docs: Determine if the browser is Firefox or not (last updated 1.7)
  @return boolean True if the browser is Firefox otherwise false