What grip does Roger Federer use for the following shots?

[Maria]

Backhand Slice - (Backhand Modified Eastern or Continental)?
Forehand Slice - when he's in trouble and has to reach for the ball, he does an absolutely amazing slice from the forehand. Is it Continental or still Forehand Modified Eastern?
Backhand & Forehand volley - Continental?

Forehand drop shot - ????

[NotAustin]

he grips it and rips it

[Kochikame]

Roger Federer adjusts his grip depending on the nature of the surface always remember this. For example, he may use a slightly more extreme grip when playing on on clay because the ball bounces higher up than on faster surfaces.

He is using the following grips most of the time

1-Backhand slice: modified Eastern grip.
2-Forehand slice modified eastern grip, slightly between the classic old school eastern grip
3-Backhand and forehand volley continental grip