How can tu enviar GIFs on fanpop?

That's how gif. Files work
When another user downloads it, it can mover in their desktop browsers, o phone gallery in my case

Most sites are set up that way. Otherwise, you'd be spending an hora to load one awnser on a question

If tu are trying to use a gif as an icono o in an answer it won't work. However if tu subir it to the imágenes section, it usually works.