If you want to add tracking to the login flow, you can do it when the user clicks the social login button. This will be before the authentication has fully happened, but is by far the easiest way to track (likely) logins.
To do so, edit the /components/com_jfbconnect/includes/jfbconnect.js Around line 28, you'll see:
provider: function (name)
{
Right after that curly brace, add the analytics tag you want to use. 'name' is the social network the user is trying to authenticate with.
I hope that helps answer your question. After that, there's not a good Javascript place to trigger an event.
I hope that helps explain,
Alex