It works just as its cousin on Chrome, however I had to deduct a star because it only plays the default New Leaf song. The Chrome version I had been introduced to had more options ranging from New Leaf (Rain), (Snow), as well as having KK Slider sing on Saturdays. And you were able to customize the O'Clock bell chime to your liking.
I'm sad that its not the same for this version. I hope in the future they find a way to bring those features into FireFox.