How to retrieve a video on Twitter or Facebook

When you see a video on Twitter or Facebook that you like and want to either keep it on your computer or share it with someone outside the social network where you watched it, it's interesting to know how to download it.
(Please note that some protected videos will still be inaccessible by the means described below).

1. From Twitter

• Right click on the video.
• Select "Copy video address".
• Go to https://twdown.net.
• Paste the previously copied address into the input field.
• Click on "Download".
• Wait a few seconds.
• Click on the link of the desired format to download the video.

2. From Facebook

• Click on the three points of the drop-down menu at the top right of the message.
• Select "Copy Link".
• Go to https://fdown.net.
• Paste the previously copied address into the input field.
• Click on "Download".
• Wait a few seconds.
• Click on "Download video in HD quality".

This doesn't work for Facebook videos marked as private.
It seems to be a chrome extension for these videos, but I didn't test it: not sure it is secure.