Geometry task Defining reflections interactive

here is the link:
https://www.khanacademy.org/mission/geometry/task/5893250978283520

I've watched some worked examples videos and in them there is the original line or figure in blue and another one in gray. When I do my exercises I'm not able to see the one in gray.
Pls I need some feedback about
Tnx

Problem solved by updating Firefox to v. 38.0.1