Answer:
No, Shakespeare does not use comic relief to set an informal tone in Act 1 Scene 3 of Romeo and Juliet. In this scene, Juliet's nurse is discussing the possibility of Juliet marrying Paris with Lady Capulet. Although the nurse does use some humorous language and makes some bawdy jokes, this is not done to set an informal tone. Instead, the use of humor is intended to reveal the nurse's character and to provide some contrast with the serious and formal discussion of marriage that is taking place. Shakespeare often used humor and comic relief in his plays, but it was typically done in a strategic and intentional way, rather than simply to create an informal tone.