Fox Broadcasting just released this sneak preview of Season 21, Episode 6 of “The Simpsons” starring Dan Castellaneta, Julie Kavner, Nancy Cartwright and Yeardley Smith. Series Synopsis: Originally created by cartoonist Matt Groening, “Our Favorite Family,” has graced the small screen in one form or another for over 20 years. The Simpson family first appeared on television as the subjects of interstitial “shorts” on The Tracey Ullman Show in April of 1987. The Simpsons remained a staple on The Tracey Ullman Show for three seasons until they premiered in their own half-hour series, on December 17, 1989. With the help of Jim Brooks and Sam Simon, Matt Groening’s cartoon family…