This is a natural phenomena which occurs once a year for two weeks in February. At this time of the year, if the condition is right, the setting sun will illuminate the horsetail fall, making it glows red.
This picture is taken on Feb 17 from South Drive side. The weather condition is right but, unfortunately, the water is too low. This winter is really dry in Yosemite. Even if the condition is not perfect, the Firefall is still impressive.