Drupal 'Optimize CSS' performance setting breaks theme in Firefox

As a quick note today, I ran into a problem where enabling the ‘Optimize CSS’ setting on a Drupal website resulted in breaking the CSS theme on Firefox. In short, the problem was that there were some invalid things in one of the CSS files, including (a) improperly formatted comments, and (b) a few CSS coding errors. I was able to see some of those problems by using this CSS validator. Once I worked through those issues, the Drupal Optimize CSS tool was able to properly merge all of my CSS files into one file that Chrome, Firefox, IE, etc., could read. (It’s important to note that the validator did not pick up on all the comment formatting problems. I think some of the problems were related to improperly-formatted multiline comments, and Firefox in particular choked on those lines after the Drupal CSS optimizer created the single, merged file.)