We don't have synonyms for firefall yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are firefly, fireball and firecall.
(n) :
The phenomenon whereby Horsetail Fall, a seasonal waterfall in Yosemite National Park, is illuminated by the sunset so that it glows orange-red.
(n) :
(historical) A summertime event held in Yosemite National Park from 1872 to 1968, in which burning hot embers were spilled from the top of Glacier Point to the valley below, giving the appearance of a glowing waterfall.
(n) :
The phenomenon whereby Horsetail Fall, a seasonal waterfall in Yosemite National Park, is illuminated by the sunset so that it glows orange-red.
(n) :
(historical) A summertime event held in Yosemite National Park from 1872 to 1968, in which burning hot embers were spilled from the top of Glacier Point to the valley below, giving the appearance of a glowing waterfall.