Fireflies by Owl City is in Ab at 90 beats per minute and runs 2:56 across 54 bars. It uses 7 chords — Bb, Eb, Ab, Bbsus, Ebsus2, Cm, F. The chord diagram changes as the song plays and the words light up as they are sung, so you can strum and sing along without reading ahead.
Want the melody line note by note? Fireflies guitar melody tab.