Hanuman's advice sent Ravana into a swirl of anger ,he ran towards Hanuman to kill him,but was stopped by Vibheeshana .Vibheeshana stopped Ravana ,this in no way could be considered as a favour on Hanuman .hanuman is MukhyaPrana [lord of prana] his prana could not have been saved by Vibheeshana.Vibheeshana's efforts could temporarily postpone Ravana's death. But Vibheeshana did not order Hanuman's tail to be lit by \fire . ravana inspired his rakshasas to light Hanuman's tail. Rakshasas tied cloth reams and fuel to light up fire.
Fire is a dependent of Vayu [ fire needs air to burn and not vice versa] , hence fire just could not assist in Ravana's design. However hanuman though not affected by Bramhastra , could not have been affected by mortal fire. He just acted to be under Rakshasas net and allowed them to tie cloth reams and lit fire ,only to destroy city of Lanka .
Hanuman Destroyed entire Lanka, Lanka was a fireproof city ,built by Vishwakarma. Ordinary fire could not have burnt it. Hanuman burnt Lanka with his own heat[tejas]. Hanuman is hotter than fire[agni]. Agni is no match for him. But agni knowing his capability [as against Hanuman] showed his subordination to Hanuman by being just warm rather then burning Hot towards Tail of Hanuman. This gesture from Agni was duly noted by Vayu and thus blessed by Vayu.
Lanka was a beautiful city studded with pearls and gold and jewels , this along with other Rakshasa was destroyed by Hanuman , Hanuman roared in happiness . Destruction of Evil people's wealth is also liked by God , in as much Hanuman knew he has performed a Hari seva in burning Lanka to ashes .Hanuman Roared to signify this happiness.