MP4 extension missing from DL files. I add it back and there's the video. Using FF58 Win 7 64

I save a video as Mp4. It goes to my desktop, but the extension is missing - the extension has been stripped away - so the file is there as a little white box icon.  I click and rename it so it has .MP4  on the extension part and everything is fine. I use VLC as my default Video app.  So the icon changes to the VLC Cone icon.  Running Win 7 64. 

Do you download via the extension SaveFrom.net Helper or the website SaveFrom.net?

Please, send me the information listed here: http://en.savefrom.net/user.php?info=1

Send a couple of links to the video that you download, for the test.