This extension is based on the code of a Greasemonkey script by Phillip Berndt and ported as WebExtensions with other features.
In every external link on Facebook there is link with a redirect and is very boring other than they track you.
This extension block this behaviour and is very light!
You can get this add-on from AMO: https://addons.mozilla.org/en-US/firefox/addon/facebook-direct-links/