Note that the version page only lists the 25 most recent versions, but the rest remain available via the API [1]. That said, this extension only has 26 versions, so it doesn't really matter for this particular case. The API also lists a creation date for the extension [2].
[1]: https://addons.mozilla.org/api/v5/addons/addon/facebook-cont...
[2]: https://addons.mozilla.org/api/v5/addons/addon/facebook-cont...