title: selenium.common.exceptions.InvalidSelectorException with "span:contains('string')"
body: <p>I am working on selenium python in firefox. I am trying to find element by css selector</p>
  
  <pre><code>element = "span:contains('Control panel')"
  my_driver.find_element_by_css_selector(element)
  </code></pre>
  
  <p>I am getting below error</p>
  
  <pre><code> raise exception_class(message, screen, stacktrace)
  selenium.common.exceptions.InvalidSelectorException: Message: Given css selector expression "span:contains('Control panel')" is invalid: InvalidSelectorError: 'span:contains('Control panel')' is not a valid selector: "span:contains('Control panel')"
  </code></pre>
  
  <p>In selenium IDE I am successfully able to find element by this field but in Python it is not working</p>