Step 1 : Click on the video. So you can the watch video.

Step 2 : Copy the URL from the top. For example the url can be like this https://www.facebook.com/photo.php?v=740345752661940&set=vb.123701504326371&type=2&theater

Step 3 : Go to http://www.downvids.net/ here you will find a Text box where you should paste the URL of the facebook video

Step 4 : Click on download. From here you can download any of the facebook video.