After finding out Firefox was storing over a gigabyte of cookies, I figured it might be wise to set it up to clear them except for sites I used regularly. However, I've recently noticed that Youtube will clear regardless. I've tried entering the domain both as youtube.com as well as www.youtube.com, but my video display preferences aren't retained. This doesn't happen for other sites, like Reddit or Tumblr. What do I need to enter in the exception list to keep my settings?