For me, I never cared about the old Firbolg, so the more Fey Firbolg is great. It's also closer, IMO, to the Irish Firbolg.
In my Eberron, Firbolgs are reclusive librarians who build their villages in secret places in the deep wilderness, and are closely related to Goliaths. I have a married pair of Firbolg Bards in my current Eberron campaign. One looks like a more jacked version of the VOlo's guide firbolg in a kilt, while the other is very short for a firbolg and looks like a cute fey goat-girl, complete with smallish curling horns. Her mom is a master artificer who is currently working in a scriptorium at the Korranberg Library, as part of a partnership with House Sivis.
The kilt-firbolg has a greatsword whose ancient magic seems to be dead, and he seeks the secrets to bring the magic back, and the pair quest to find a new home to start a new clan, as she doesn't fit in with her clan, and his clan is scattered to the winds after a somewhat violent "land acquisition" by House Vadalis of their ancient grove in the Eldeen Reaches.
As for appearance, let your imagination run wild.