Told you so, but you wouldn't listen............should have chosen the 630 ;-p
Just kidding.
FB is not one of the fastest apps around.
But i come to understand it was a used Phone?
If so did you do a hard reset ( factory settings ).
720 Has better sunlight visibility of screen than 630. 630 doesn't have true clearblack polarizing filter, only higher brightness and laminated screen. If that's not a big deal for you, buy 630.
Sent from lumia 920