mirthfully vs happily

mirthfully and happily both are adverbs.

Word	Noun	Adjective	Verb	Adverb
mirthfully	No	No	No	Yes
happily	No	No	No	Yes

As adverbs, mirthfully and happily are synonyms defined as:

Other synonyms of mirthfully include blithely, gayly, jubilantly, merrily.

mirthfully (adverb)	happily (adverb)
in a joyous manner	in an unexpectedly lucky way
	in a joyous manner