Here is a very good photo of Feather Falls from across the canyon. This is the observation deck from which the previous photo was taken. This photo was taken from just above the falls, and shows the view down the canyon.
This isn't the first time someone has gone over the falls, but I don't know how many there have been altogether. The river that feeds the falls is quite narrow, and at some places you can even jump across, but in spring it is swift and the current is strong, so anybody who slips in is very likely to be swept away, and there are many slippery spots along the banks. I'd imagine that during the gold rush era at least a few of the prospectors who vanished in the mountains probably ended up going over Feather Falls. The mountians are a perilous place.