I don't think Moonves has the power to fire Howard. If I understand the Viacom org chart correctly, Infinity, which owns Howard's station and his syndication contract, is an entity on an equal level with, but separate from, CBS. All of the CBS
radio stations were shunted over to Infinity when Viacom ate CBS, and "CBS" the company now only controls the TV network.
So Moonie Boy could conceivably make things a little uncomfortable for Howard if he could get Redstone or Karmazin to get involved (one very big "if" considering how important Howard is financially to Infinity), but otherwise, Les can't touch Howard.