There isn't much art to this, just follow these steps to download Facebook videos: There are dozens of websites that claim to help download videos from Facebook, and is one of the neater options.
How to download Facebook videos on a Windows laptop or Mac, using a website
Here's how you can download Facebook videos on Windows, Mac, or Linux. If you plan to download Facebook videos regularly, a browser add-on or an external app might serve you better.
If it's a once-in-a-blue-moon thing, choose the website route. What you should choose from below depends on how frequently you think you're going to do this.
