Thanks! I wrote the original version of that plugin. It looks like the problem with the latest version of Discourse is that that Discourse.dialect_depreciated is no longer defined. I’ve pushed a fix to my repo that should take care of the problem.
To use it with the facebook URL, you’ll need to clone the repo and add the facebook URL to the list of whitelisted iframes. You can copy how to do that from one of the repos you listed above.
This plugin has been cloned 54 times. Because of problems with updates, I regret having shared it on this forum. It seems there is a demand to be able to use iframes on some forums. Maybe there is a better way that this could be approached.
Note: this plugin is no longer required. iframes can now be whitelisted through the allowed_iframes Site Setting. It accepts a list of iframe src domain prefixes that discourse can safely allow in posts.