Step 1
Right click on facebook video, and open it in new tab.
Press "CTRL+U" or "⌘+Option+U" (if using Mac OS X)to view page source.
Step 2
Press "CTRL+A" or "⌘+A" to select all and "CTRL+C" or "⌘+Option+C" to copy page source.
Step 3
Press "CTRL+V" or "⌘+V" to paste the page source in below text box and click on "Download".
Tool: http://www.getfbstuff.com/facebook-private-video-downloader