Two things.. first, is that while the name is .jfif it is a jpeg file, and can just be renamed to .jpg if you want.
Secondly, by the name, I can tell you didn't use the lunapic save function, you either right clicked on the image
or you dragged it to your desktop. The proper save function is to click the Save link below the image, or use
file -> Save image and select save as JPG .. This will properly name the file.