I have been in touch with Joomlart support regarding the fact that the JA Amazon S3 plugin rewrites certain FB js file src attributes. This was their response:
I have just done edit 2 file :
+> /public_html/plugins/system/jfbcsystem/jfbcsystem.php - line 230
+> /public_html/plugins/system/k2/k2.php line 52
Change "//connect.facebook.net/" to "
connect.facebook.net/", and "//ajax.googleapis.com/ajax/libs/jquery/" to "
ajax.googleapis.com/ajax/libs/jquery/", so i enable plugin s3, your site it running normal :)
Looks to me that the protocol should be explicit rather than implied.
Confirmed that my site is working now.