waiting message when FB login

Logging in should only take a few seconds, at most. If you're getting lengthy delays, it can be an indication of some server configuration issues.

To reduce the login time, I'd recommend trying to disable any socialprofile plugins you have enabled. The profile import process can take a few seconds to fetch all the data and avatars about the user. The more you have enabled, the longer it can take. Even then though, with multiple profile imports occurring into different extensions, it shouldn't take longer than 5 seconds.

When all the social profile plugins are disabled, if you still have a 'long' login process, it's likely an indicator that your server is having trouble communicating with the social network. That can be due to IPv6 configuration issues, DSN lookup problems, firewalls, or simply slow outgoing connections from your server.

With all that said, there is an option in the Configuration -> Facebook section for "Show 'Logging In' popup". Enable that and there will be a message that the login process is happening. That will help notify users, but will really just mask the underlying problem if you really are having lengthy (greater than 10 second) login times.

I hope that helps explain,
Alex