In chapter 7, when the pegasi arrive at the Gildsedale Plains, Firefly asks Lightning Bolt to confirm their location. She knows the situation is slightly tense and tries to lighten the mood by goofing up.
Lightning Bolt: (checking the map) Hmmm... according to these symbols, of ancient meaning I presume, weíre somewhere... here.
Firefly: Tell me something I donít know.
Lightning Bolt: Consuming large amounts of food may lead to indigestion problems.
Moments later, Derpy drops a little gem of her own.
Lightning Bolt: Supply bunkers at 11 oíclock.
Derpy: Shoot! Itís 1057 hours! Weíve got to hurry!
(Medley and Cloud Kicker chuckle)
Firefly's facehoof when Pinkie Pie says she's throwing a party for her team just before the mission to destroy The Burning Talon in chapter 9.
Rainbow Dash asking Firefly for a permission to begin their own party in chapter 10. Complete with a proper tone and a salute.
In chapter 14, before the battle for Cloudsdale begins:
Lightning Bolt: [...] But now, letís focus on whatís ahead. RIDE OUT!
Firefly: Uh... Thunder? Whatís with that yell all of a sudden?
Lightning Bolt: I thought we need a sort of battle cry, you know, to boost our spirits! Was it bad?