When Roseanne first walks into the kitchen she says, "Boy, it's just a beautiful morning today. It just makes me want to sing!" she was making a joke about her failed attempt to sing The Star Spangled Banner at a baseball game where she was booed off by the fans.
This episode is aired in real time.
The joke about her singing in the beginning is in regards to her singing the National Anthem before a San Diego Padres game which brought much criticism.