why cant i download pictures from facebook?

[Mor]

my browser is google chrome.

the problem is : when i'm downloading pictures from facebook the file save in my computer as webp file(instead of jpg or png for example). this file type(.webp) can be open only by the browser(I get an error messge if trying to open it with the windows picture viewer).

this problem is only seen in the browser "google crhom" and only when trying to download pictures from the site "Facebook".

here is a pic so you can understand me better : http://s7.postimg.org/jwevnbtxn/image.png

p.s
even if I try to save as type (All file) in the end of the download the file still typing as webp and the windows picture viewer could not open it.