The offside was offside by an armpit at the most.
I saw nothing wrong with the challenge by VVD on De Gea, if it had been Mane or Shaqiri, smaller players than VVD then Firmino's goal would have stood
I agree, I think the size of VvD swayed the decision, it looked like De Gea wasn't impeded and he punched the ball badly, usually GK jump with their knee's out to block off the attacker, but he didn't, so De Gea's mistake.
Luckily we did not lose out because of it, glad we didn't hammer them by 4 or 5, don't want Ole getting sacked!